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Correlation between clinical performance and degree of conversion of resin cements: a literature review

Correlation between clinical performance and degree of conversion of resin cements: a literature... www.scielo.br/jaos http://dx.doi.org/10.1590/1678-775720140524 Correlation between clinical performance and degree of conversion of resin cements: a literature review 1 2 2 3 Grace DE SOUZA , Roberto Ruggiero BRAGA , Paulo Francisco CESAR , Guilherme Carpena LOPES 1- Faculty of Dentistry, University of Toronto, Toronto, ON, Canada. 2- Department of Biomaterials and Oral Biology, Faculty of Dentistry, University of São Paulo, São Paulo, SP, Brazil. 3- Faculty of Dentistry, Federal University of Santa Catarina, Florianópolis, SC, Brazil. Corresponding address: Grace M. de Souza - 124 Edward Street, room #352 E. - Faculty of Dentistry, University of Toronto. Toronto, ON – Canada - Postal code: M5G 1G6 - Phone: 416-9794934 - Ext. 4417 - Fax: 416-9794936 - e-mail: grace.desouza@dentistry.utoronto.ca ABSTRACT esin-based cements have been frequently employed in clinical practice to lute indirect Rrestorations. However, there are numerous factors that may compromise the clinical performance of those cements. The aim of this literature review is to present and discuss some of the clinical factors that may affect the performance of current resin-based luting systems. Resin cements may have three different curing mechanisms: chemical curing, photo curing or a combination of both. Chemically cured systems are recommended to be used under opaque or thick restorations, due to the reduced access of the light. Photo- cured cements are mainly indicated for translucent veneers, due to the possibility of light transmission through the restoration. Dual-cured are more versatile systems and, theoretically, can be used in either situation, since the presence of both curing mechanisms might guarantee a high degree of conversion (DC) under every condition. However, it has been demonstrated that clinical procedures and characteristics of the materials may have many different implications in the DC of currently available resin cements, affecting their mechanical properties, bond strength to the substrate and the esthetic results of the restoration. Factors such as curing mechanism, choice of adhesive system, indirect restorative material and light-curing device may affect the degree of conversion of the cement and, therefore, have an effect on the clinical performance of resin-based cements. Keywords: Dental prosthesis retention. Dental materials. Luting agents. Biocompatible materials. (benzoyl peroxide) so as to form free radicals that INTRODUCTION will initiate the polymerization. Free radicals link to monomers by breaking carbon-carbon double Resin cements are composite resins developed bonds. The continuous addition of monomers to deliver mechanical properties and handling to a growing chain results in a polymeric chain. characteristics that are important for luting indirect In general, the maximum degree of conversion restorations. These cements contain different (DC) – the percentage of aliphatic C=C (double) monomers, which are linked together during the bonds converted into C-C (single) bonds to form polymerization reaction. Due to their application the polymeric network – reached by resin cements under an indirect restoration, in most cases the is around 60%, due to the increase of cement physical activation (photo activation) has very limited viscosity during the polymerization reaction, effect . Therefore, there is a need for chemical hindering the mobility of the reactive species . The activators. Activation of the polymerization means reaction slows down progressively up to a moment to induce the photo initiator (e.g., camphorquinone) when new bonds cannot be made . or to break the molecule of the chemical initiator J Appl Oral Sci. 358 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review Resin cements have been frequently employed maximum properties over time in areas that light for bonding indirect restorations to the teeth energy is unable to reach . The limitations of these due to their mechanical behavior – superior to systems are the reduced working time as opposed conventional cements (resin-free) –, possibility of to the extended setting time and the tendency to adhesion to the restorative material and to the tooth become “yellowish”, due to the higher concentration 7 60 29 structure with or without an adhesive system , of tertiary amines (activators) . The polymerization and superior optical properties when compared reaction in self-cured cements requires the with conventional cements. However, limitations components of the activation system – tertiary associated with the incomplete polymerization (low amine and benzoyl peroxide – to get in contact by DC) of the cement may result in higher sorption the mixing of two pastes, base and catalyst. and solubility values , causing faster degradation Dual-cure resin cements were developed 67 16,56,77 . Degradation of resin-based cements photo and chemically activated systems , reduces the bond strength between them and the obtaining optimized DC in the deepest locations substrate under a restoration, controlled working time and at the restoration margin, which may mean the short setting time. In such systems, there is a clinical loss of the restoration either by debonding, catalyst paste with a chemical initiator, usually fracture or secondary caries . Unreacted monomers benzoyl peroxide, and a base paste containing the (not bonded to the polymeric chain) may also photo-cured resin cement and the tertiary amine responsible for the activation of the self-cure 18 57 response . reaction . When both pastes are mixed together There are multiple factors that may interfere with and exposed to light, the polymerization happens the DC of resin cements and, therefore, compromise by physical (photo) and chemical (redox) activation. the longevity of indirect restorations. Some of them The appropriate working time is controlled by are the material composition (monomers and other inhibitors of the self-cure reaction or by the 56 56 components of the activation system) , possible amount of activators of the polymerization . It is inadvertent interactions between the bonding expected that in areas where there is not enough system and the cement , characteristics of the light, the interaction between the tertiary amine restoration to be cemented (optical properties and and benzoyl peroxide will be enough to ensure 14,15 4,57 thickness of the restoration) and characteristics the cement polymerization . However, when not of the photo activation step . This article aims to properly photo-activated, dual-cure resin cements 47,49,77 perform a comprehensive review of the factors may present reduced DC , which implicates 57 71 involved in the DC of the resin-based luting systems in lower hardness , higher solubility , lower 11,57 and the impact of DC on luting system properties. and compressive strengths, and lower bond strength to dentin in comparison to directly 7,77 CURING MECHANISM light-cured dual cements . For instance, a self- adhesive dual cement applied in self-curing mode As previously mentioned, photo-activated or may show DC as low as 11% after a 10-minute light-activated resin cements are indicated for setting time . Considering the clinical application situations where the light of the curing unit may of the resin-based luting systems, which are used pass through the restoration, such as translucent for the cementation of indirect restorations onto veneers and shallow inlays . These cements are tooth structure, 10 min is an undesirably long time provided in a single paste with a photoinitiator for a luting agent to obtain a great percentage system composed of a photosensitive component of the optimal setting characteristics, without (usually camphorquinone) and a tertiary amine. compromising the integrity of the margins and the 8,77 The presence of light with a wavelength of 480 cement layer under functional loading . nm (blue region of the visible spectrum) activates In general, light-cured and dual-cured cements camphorquinone , which binds to the tertiary activated by light through a restoration thinner 4,36,44,75 amine and then releases two free radicals that will than 2.0 mm have higher DC than self-cured start the monomers conversion. Photo-cured resin cements . When a dual cement is self-cured (no cements have unlimited working time, with the activation by light), mechanical properties such polymerization starting right after the exposure of the material to light . reduced by 68.9%, 59.2% and 91.1%, respectively, Chemically cured (self-cured) cements are in comparison to original values presented by dual- indicated under thick restorations, for luting cured samples . There are different factors that may intrarradicular posts and crowns made of materials affect the DC of self-cured luting systems, such as that block the light, such as metallic copings or the relatively high concentration of polymerization 42,68 highly opaque ceramics , aiming to guarantee inhibitors used to extend the material’s shelf life and J Appl Oral Sci. 359 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC to provide a clinically viable working time, ranging "# $& 27,77 from 2 to 5 minutes, which adversely inhibits in maximum degree of conversion . Therefore, polymerization during the luting procedure  when highly opaque or thicker restorations need the slow rate of polymerization activation and to be employed, a prolonged light exposure time subsequent propagation of radicals in comparison is recommended (please read “Indirect Restorative 6,49,51,61 to a directly light-activated material  Material” below), since a gradual increase in light- and the low concentration of benzoyl peroxide curing time and, therefore, in light transmission, 6,49 incorporated into those materials . Furthermore, gradually increases the Knoop hardness of resin- the hand-mixing of the two pastes incorporates based luting systems . Additionally, the use of a air bubbles that further inhibit polymerization due dual-cure system should always be considered to to the presence of oxygen and may act as stress possibly increase the DC by means of a chemical concentrators that potentially result in cracking activation of the monomeric system. throughout the cement layer . Although it has been With regard to post-activation time, the 24- demonstrated that the high incidence of air voids hour DC of light-cured and dual-cured cements reduces the stress generated by the polymerization is directly related to the DC obtained right after 4,75 shrinkage of the cement due to a change in ratio of light exposure . Even though DC is maximized 5 2,79 bonded to unbonded surfaces , '* of the inclusion of pores have not been determined. some cements present gradual increase in DC for Pores are also incorporated in dual-cured cements up to 24 hours, mainly when used in the dual- 4,10,28,31,64,79 during mixing and they may become an esthetic curing mode . However, it has been concern when cementing veneers . To minimize speculated that a delay in light activation of dual- the undesired consequences of the hand-mixing cured materials would enhance their properties procedure, some manufacturers provide cements in by allowing the self-polymerization promoters to a self-mixing apparatus (Figure 1), which eliminates react at some extent before being entrapped by the the manual mixing step, generates a homogeneous polymeric chains as soon as the photo-activation 49,74 mix and reduces the incorporation of bubbles. begins . Delaying the light activation for 2 min However, voids have been observed after automatic may, for instance, compensate for a lower dose of 56 49 mixing as well . light reaching the cement layer , but no effect is Interestingly, if light incidence on the cement observed on the bond strength of resin cements to the substrate . On the other hand, prolonged activator of dual cements improves DC when self-curing of the cement may also compromise the 1,7,15,16 49 71 compared to photo-activated-only systems overall DC and increase water sorption when light !      activation is delayed for 10 min for the same reason, 8,14,49 controversial and varies from one material indicating that an ideal balance between self-curing to another . It has been demonstrated that the and photo-activation is yet to be determined. absence of the self-curing component in light- Under ideal circumstances, light-activated resin activated systems negatively affects the DC of cements show higher DC than chemically cured 49,57 these cements when the light-curing component resin cements, irrespective of brand names . is not able to guarantee an acceptable degree of However, the DC of dual-cured cements is conversion, for example when applied underneath material-related, which means that it is more onlays of greater thickness . Considering a clinical associated with the brand name than with the application in which almost no light reaches the per se and some systems cement layer, it is desirable to use dual resin 1,10,11,15,16,31,51,73,79 cements that present a chemical curing mechanism than others . Just as an illustration, !  . However, there is the DC of a given dual-cured cement (RelyX ARC, currently no resin luting system in the market 3M Espe, St. Paul, MN, USA) may vary from 81% 2,7,45 capable of overcoming this limitation . In general, to 61% when cured under light as opposed to total the chemical activation of dual cements does not absence of light respectively, and from 56% to 26% seem enough to compensate for the absence of light when another dual-cured cement (RelyX Unicem, under thick or opaque restorations, even 24 hours 3M Espe, St. Paul, MN, USA) is cured under the same 1,15,32,61,64,65,75 43 after the beginning of the activation . conditions . This difference may be explained by the The DC of a self-adhesive dual cement may vary difference in composition between both materials. from 37% when light-cured for 20 seconds to For instance, some resin-based cements present 43 51 58% when light-cured for 40 seconds , evidencing twice as much benzoyl peroxide than others . that there is also a direct correlation between light The lower DC may affect some critical properties intensity received by a photo-activated material and of the resin-based cements . Dual cements cured 14,46,49 its DC . Laboratorial studies bring evidence that under a dual mode (photo+chemical) present the activation time generally recommended by the lower toxicity and solubility than dual cements J Appl Oral Sci. 360 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review Activation Adhesive Brand name& Commercial Recommended Characteristics (Ref #) mode strategy Manufacturer presentation ! " Biscem Bisco Self-mixing 20-30 s or 8 DC of 41.5% applicator min* Higher DC (86%) with dual-curing mode and longer measuring time interval Maxcem Elite Self-mixing 10-20 s on each Low cytotoxicity Kerr applicator surface or 4-5 DC of 26.4% min** Low bond strength (7.76 MPa) to Y-TZP High shrinkage strain at different temperatures Relatively high DC (68%) 10 min after light curing for 40 seconds RelyX Unicem Capsules or 20 s on each DC of 37.3% 3M ESPE self-mixing surface or 5-6 Mild cytotoxicity applicator min* Good bond strength (21.1 MPa) to Y-TZP Relatively high contraction stress and microhardness after light curing for 40 seconds Low shrinkage strain at different temperatures Low water solubility and high DC after 4-min curing delay SmartCem 2 Self-mixing 20-40 s on each High water solubility and reduced DC after 4-min curing delay Dentsply Caulk applicator surface or 6 Reasonable shrinkage strain at different temperatures min* SpeedCem Self-mixing 20 s on each Reasonable shrinkage strain at different temperatures IvoclarVivadent applicator surface or 160±40 s** Self-mixing 20 s or 3 min* Cement Kuraray applicator Inc. Duolink Bisco Self-mixing 40 s on each Relatively high contraction stress and microhardness after light curing for applicator or surface or 3 min 40 seconds two syringes 30 s** Multilink Automix Self-mixing 20 s on each DC of 61.4% IvoclarVivadent applicator surface or Good bond strength (31.7 MPa) to Y-TZP 180±30 s** Nexus Third Self-mixing 20 s on each Reasonable shrinkage strain at different temperatures Generation Kerr applicator surface (no info Very low bond strength to dentin under self-curing mode available on High DC (84.8%) one week after light curing for 100 seconds C self-curing) o Panavia F 2.0 Two syringes 20 s on each Inferior bond strength to resin composite (10.7 MPa) in different activation n Kuraray Inc. surface or 3 modes v min** !"$&  '+  /; <== ;> e '+/ ?? t 8.1% of secondary caries under crowns after 5 years in clinical service i J/   / >Q o strength to an indirect restoration n RelyX ARC 3M Self-mixing 40 s at the Fast curing and high DC a ESPE applicator margins or 10 Superior bond strength to resin composite (16.5 MPa) in different activation l min** modes and testing times DC of 63% when light-cured under a 2 mm thick composite resin slab at room temperature High water sorption and solubility RelyX Ultimate Self-mixing 20 s on each Very low bond strength to dentin under self-curing mode 3M ESPE applicator surface of 6 Relatively high DC (72%) one week after light curing for 100 seconds min* Variolink II Two syringes 40 s on each Relatively high cytotoxicity Ivoclar Vivadent surface (no info Reasonable bond strength (15 MPa) to Y-TZP available on DC of 56% when light-cured under a 2mm thick composite resin slab at self-curing) room temperature Low water sorption and solubility [\ C&B Cement Self-mixing 4 ~ 7 min* No measurable microhardness up to 10 min after mixing and low DC after C Bisco applicator or 7 days o two syringes n Panavia 21 Two pastes ~4 min 30 s* Low cytotoxicity v Kuraray Inc. e Superbond C&B Powder 7 min 30 s-9 3.4% of secondary caries under crowns after 5 years in clinical service n Sun Medical and liquid min 30 s** W ??    ^? t. in different dentin containers L Choice 2 Bisco One syringe 40 s over the ~59% DC 7 days after light activation I C veneer o 61 RelyX Veneer One syringe 30 s on each Reduced DC when 1.5 mm or thicker veneers are used T 3M ESPE surface - v E t. &Brand names mentioned were reproduced from the research papers included in this literature review. Therefore, there may be other brand names currently /_ </ `j  =  ///<{`W   Q and self-curing times may either consider room temperature (~23°C) or mouth temperature (~37°C). *Time after starting the mixture. **Time after placement of prostheses DC=degree of conversion; LED=light-emitting diodes; QTH=Quartz-tungsten-halogen Figure 1- Summary of some resin-based luting systems currently available and their characteristics based on the papers Q / /+Q+ +/ << / J Appl Oral Sci. 361 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC cured under the self-curing mechanism (chemical 55,65 only) . Dual curing also leads to a rapid increase thus compromising the clinical application of the 30,51 in hardness whereas chemically cured specimens material , and still may not compensate for the 22 64 30 are still soft 30 minutes or even one hour after absence of light . The clinical applicability of the mixing. Dual-curing mode also results in improved pre-heating technique is questionable, since the bond strength and mechanical properties such tooth structure could not be possibly heated up to 50°C, which would immediately result in the cement comparison to light curing or chemical curing temperature decrease. Therefore, any evaluation on 34,64 only . this topic should limit the pre-heating temperature Adhesive and self-adhesive resin to 37°C . cements have functional monomers such as 10-methacryloyloxydecyl dihidrogen phosphate (10- BONDING AND CEMENTATION MDP), 4-methacryloxyethyl trimellitate anhydride (4-META) and phosphoric esters. These resin The bonding between resin cement and the tooth cements generally have a dual-cure mechanism. structure (or the core build-up material) is generally Self-adhesive cements have acidic functionalities made possible by the use of a self-adhesive resin in order to demineralize tooth structure , and an cement or by the application of a bonding agent/ acid-base reaction between the acid groups of the system. The bonding agent/system may either be self-etch or total-etch (etch-and-rinse) . However, or the mineralized tooth surface starts immediately there are restrictions for the application of some after the mixing of the components and application +         ;! of the cement on the tooth surface . However, step total-etch (primer and adhesive in one bottle) those acidic monomers have been shown to and “all-in-one” self-etch systems and resin cements negatively affect the cement degree of conversion, with some chemical activation, either self-cured or 77 37 since they interfere with the amine initiator . This dual-cured . It has been shown that the lower interference compromises both the self-cure and the pH of the bonding agent employed, the lower the dual-cure modes . The very low polymerization the bond strength between self-cured cement and shrinkage strain of some self-adhesive cements may dentin > also be an evidence of reduced DC . Indeed, there to a self-cured cement results in 10-50% of the ;  bond strength presented when the same adhesive 31,40 63 materials and increasing the light-exposure from is bonded to a light-cured cement . 20 s to 40 s does not improve DC values after 6 The reason for those diminished bond strength hours as much as a temperature increase of the values is that when simplified-step adhesives cement improves . However, when the absence are used together with chemical-cured cements, (self-cure) and the presence (dual-cure) of photo- there is an interaction between the residual acidic activation are compared, the presence of light may monomers from the adhesive inhibition layer and result in a 10-fold increase in the material degree the binary peroxide-amine catalytic components of conversion . Although another initiator system that are commonly employed in chemically cured based on sodium aryl sulfate or aryl-borate salts has resin composites . Therefore, the tertiary amine of been proposed to compensate for the interaction the resin cement is neutralized and does not react between acidic monomers and the amine initiator with the initiator, resulting in low bond strength in self-adhesive systems, no evidence has been at the adhesive-cement interface . Besides that, !! 8,77 sodium persulfate-containing materials . & 12,13 Another way to improve the polymerization incomplete polymerization , and these are then kinetics of resin-based luting systems is to kept at the interface between the adhesive and 30,51 increase the temperature of the material . High the cement, compromising the bonding between 19,72 ;   those two substrates , which is demonstrated by 24 63 conversion than low viscosity cements , probably exclusively adhesive failure modes . To maximize due to the reduced mobility of the monomers in the performance of the resin cements, self-cured viscous materials. Increased temperature prior to or dual-cure cements are to be employed only in and during polymerization leads to higher DC, due to association either with three-step total etch systems 1,21 increased free radical and monomer mobility and or with self-etching primer systems containing collision frequency of the unreacted active groups a separate bonding agent. For all of the other resulting from the decrease in the viscosity of the adhesive systems, the resin cement employed 21,30 material . However, pre-heating (50°C) dual- should be exclusively photo-activated. cured resin cements with a higher concentration of the chemical activator (benzoyl peroxide) may J Appl Oral Sci. 362 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review When comparing the translucency of lithium- INDIRECT RESTORATIVE MATERIAL disilicate glass-ceramic and leucite-reinforced glass ceramic, Illie, et al. "Q**Y&  + When photo-activation of a resin cement is is more opaque than the latter (Figure 2). Lithium- performed, part of the visible light that reaches the disilicate glass ceramic contains a main crystalline crown is transmitted through the restoration, part is phase of “elongated crystals building a scaffold of many small interlocking needle-like crystals Consequently, the light intensity that effectively randomly oriented” , with a second crystalline reaches the cement varies according to the optical 15,62 phase consisting of lithium orthophosphate . On characteristics of the restorative material , 14,44 8,53 the other hand, leucite-reinforced glass-ceramic is such as opacity and shade 15,25,48 a less dense material, characterized by the single thickness of the restoration . The higher the 35,36 crystal formation of leucite crystals , indicating thickness and the lower the value (darkness) of the that lithium-disilicate ceramics scatter more light restoration, the lower the light intensity reaching than leucite ceramics. Light delivered to the cement the cement layer, which may compromise the DC 15,47,57,79 layer through lithium-disilicate ceramic (shade of a given cement . medium opacity 1) is reduced to 45% under 1 There are many restorative systems nowadays mm ceramic slabs, 16% under 2 mm slabs and that may be used for the manufacturing of all- approximately 8% under 3 mm slabs . Leucite- ceramic crowns (Figure 2). Each one of these reinforced glass ceramic slabs reduce the light ceramic systems has a microstructure that directly transmittance to 80%, 64% and 43% under 0.7, interferes with the amount of light that may be 14,78 1.4 and 2.0 mm thick samples, respectively . transmitted through the restoration . Considering As previously mentioned, the relationship restorations with similar shade and thickness, between restoration thickness and transmittance ceramics with a higher number of light scattering is highly dependent on the opacity of the centers (interface between different microstructural 14,51,54,80 material . However, the impact of the amount phases) are more opaque and prone to block visible 14,33,57,58 of light reaching the cement layer on its DC is light , compromising the intensity of the controversial. Dual-cure resin cements activated by physical polymerization of the resin cement . Pores, light under a 1.5 mm lithium-disilicate glass ceramic frequently found in feldspathic porcelains and glass- (Shade A2 low translucency) surface presented a DC similar to that of cements cured under direct light of these materials, act as light scattering centers exposure , whilst samples cured through 1.4 mm- as well. Light scattering occurs at interfaces of thick leucite-reinforced glass-ceramic slabs may or different phases with dissimilar refraction indexes. may not  ; A free of pores porcelain would be a material than groups activated with direct light exposure, with no light scattering interface and would thus depending on the luting system employed. In show transmittance, resulting in high DC for dual another study, samples light-cured under 1 or cements even under a 3 mm-thick layer . A multi- 2 mm thick lithium-disilicate slabs only showed phase material would scatter the light because the decreased hardness when light exposure time incident light beam will change direction from one was 20 s or less, indicating that longer exposure phase to another and the result will be a weaker times may compensate for light attenuation of incident light. A multi-phase structure within a the indirect restorative material . A randomized material also results in light scattering and low clinical split-mouth study evaluating the longevity transmittance . Thereafter, glass-infiltrated ;  ; alumina-zirconia (In-Ceram Zirconia System, Vita three different cements (two resin-based and one Zahnfabrik, Bad Säckingen, Baden-Württemberg, glass-ionomer) evidenced acceptable survival rates Germany) is the most opaque alternative among for all groups, with dual-cured cements showing current clinical options, due to the presence of four higher survival rate than glass-ionomer cement, distinct phases with different refraction indexes indicating that the opacity of the crown did not (alumina, Ceria-stabilized zirconia, lantanium glass affect the performance of the cement/restoration . & ; of only 6% in 0.5 mm-thick copings, and when transmittance values of a restoration would be even the thickness of the same material increases to more compromised considering the thickness and 1.5 mm the transmittance becomes as low as the optical characteristics of the porcelain veneer $? layer . The DC of a dual-cured cement activated spinel ceramic (In-Ceram Spinell, Vita Zahnfabrik, "$Q  & Bad Säckingen, Baden-Württemberg, Germany) with porcelain veneer layer (0.8 mm thickness) is it has only two phases (glass and spinel), with porcelain samples (2 mm thick) and to the control similar refraction indexes. J Appl Oral Sci. 363 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC Material Brand name& Sample Photo-curing Findings (Ref #) Manufacturer characteristics conditions Lithium IPS e.max Press 1.5 or 3.0 mm 20 or 40 s at 600 // +?^‚&<  / 2 50 disilicate Ivoclar Vivadent thick discs Shade mW/cm temperature glass A2 10, 20, 30, 40, Light intensity decreased ~ 62% under 1 mm, 86% under ~2 mm ceramic 1.0, 2.0 or 3.0 mm 50 or 60 s at 584 and 92% under ~3 mm thick samples. Light exposure of 30 s or thick discs Shade mW/cm longer may compensate for the 1 or 2 mm thick discs blocking the MO1 light 20 s at 1200 mW/ ƒ ' + / 1.0 mm thick discs cm ratio less affected when light-cured with 470 nm wavelength, no Shade A1 '/ 40 s at 1000 mW/ The higher the opacity of the ceramic, the lower the DC of dual- 2 13 0.5 or 0.8 mm cm cured cements; similar DC between 1.5 and 2.0 mm thick samples thick samples with veneer layer on top Shade LT, MO or HT IPS e.maxCAD 0.5, 1.0, 2.0 or 3.0 5, 10 or 15 s at Reduced hardness with 1 mm or thicker samples, irrespective of 2 35 Ivoclar Vivadent mm discs Shade 1600 mW/cm the length of light exposure MO1 or MO4 Leucite IPS Empress 1.0 mm thick 10 s at 580~1650 Light transmission reduced by ~55% through 1.0 mm thick 2 58 reinforced Ivoclar Vivadent discs Shade not mW/cm samples glass ceramic informed IPS Empress 1.0 mm thick discs 20 s at 1200 mW/ ƒ / '+/ CAD Ivoclar Shade A1 cm ratio more affected when light-cured with 470 nm wavelength, no Vivadent '/ IPS Empress 2 1.0, 1.5 or 2.0 mm 60 s at 800 mW/ No effect of ceramic thickness on bond strength between substrate 2 3 Ivoclar Vivadent thick discs Shade cm and resin cement A2 IPS Empress 0.7, 1.4 or 2 mm 40 s at 605 mW/ Light intensity decreased ~20% under 0.7 mm, 36% under ~1.4 mm Esthetic Ivoclar thick discs Shade cm  ?"&  !^ // _ << Vivadent A3 observed in DC of resin cements 1.0, 2.0 or 3.0 mm 3 cycles of 800 Negative correlation between cement hardness and ceramic GN-I GC Corp. thick discs Shade mW/cm _ </ † // _ A3 samples 0.5, 1.0, 2.0 or 3.0 5, 10 or 15 s at 15 seconds light exposure compensates for reduction in light 2 35 ProCAD Ivoclar mm discs Shade 1600 mW/cm transmittance in up to 2 mm thick samples Vivadent E100 or bleach =    In-Ceram 0.5 or 0.8 mm 40 s at 1000 mW/ ˆ   + < ="!?[&  = 2 13 alumina alumina Vita thick sample with cm (24~30%) cements and both thicknesses composite Zahnfabrick veneer layer on top Shade A2 Polycrystalline ZR Ceramill Zi 0.5 or 0.8 mm 40 s at 1000 mW/ ˆ   + < ="!^?&  = 2 13 zirconia thick sample with cm (22~24%) cements and both thicknesses veneer layer on top Shade A2 Polycrystalline Procera Nobel 0.25 or 0.6 mm 10 s at 580~1650 Both core thicknesses blocked conventional halogen light alumina Biocare core thick discs mW/cm completely; 0.25 mm core reduces Plasma Arc light by 66% and with veneering 0.6 mm by 79% material on top to equal 1.0 mm Feldspathic Ceramco 1.0 mm thick 10 s at 580~1650 Light transmission is reduced by ~63% through 1.0 mm thick 2 58 porcelain II Dentsply discs Shade not mW/cm samples Ceramco informed IPS InLine 1.5 or 2.0 mm 40 s at 1000 mW/ „ Q< / _ Ivoclar Vivadent thick discs Shade cm Vita VM7 Vita A2 20 or 40 at 900 `  _ +   < Zahnfabrick 2.0 mm thick discs mW/cm both light activation times; when darker ceramic and darker resin Shade OM1, 2M2 / > [† Q  /+ or 5M3 increase DC Micro-hybrid Sinfony 3M 1.5 mm thick discs 40 s at 800 mW/ DC of resin cements reduced from 1.5 up to 33% depending on the 2 72 indirect resin ESPE Shade D A3 cm luting system used composite Signum Heraus 2.0, 3.0 or 4.0 mm 40 s at 1200 mW/ DC decreased ~21% for samples cured under 4 mm discs when thick discs Shade cm 60 s at 800 / ^//‰ '< 2 1 A2 mW/cm 120 s at the curing protocol on the DC 400 mW/cm &Brand names mentioned were reproduced from the research papers included in this literature review. Therefore, there may be other brand names currently in the market that would represent the categories of materials described in this Figure. DC=degree of conversion Figure 2- Correlation between indirect restorative materials and the curing properties of the resin cement underneath J Appl Oral Sci. 364 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review 14 1 group, activated under direct light exposure . measured under 2 mm thick onlays . With regard to When the impact of the shade of the ceramic the effect of shade on indirect composite resin light system is evaluated, it can be observed that if transmittance, Arrais, et al. (2008) demonstrated shades with higher chroma are used, less energy that only 11% of light reaches the cement layer reaches the cement layer, since dark pigments when cured through a 2 mm microhybrid composite , negatively A2 shade as opposed to 8% when A4 shade was employed, but no effect on DC was observed for Dual-cured cements light-activated under 2 mm- dual-cured resin cements with higher concentration thick samples of darker dentin shade of feldspathic of benzoyl peroxide. The authors pointed out that porcelain present significantly lower DC than the adhesive component also presented a chemical cements light-activated under lighter shades . activator of the polymerization and could, therefore, When yellow and translucent shades of a resin compensate for the absence of light . cement were light-activated under the darker porcelain, only prolonged light-exposure time LIGHT CURING DEVICE (40 seconds) was capable of increasing the DC of the cement yellow shade , indicating that the It has been demonstrated that the hardness combination of darker shades in both the cement of dual-cured cements is dependent on the level and the indirect restorative material compromise of exposure to the curing light . As previously the overall DC of the cement layer. mentioned, the component responsible for With regard to laminate veneers, some studies the chemical activation of the material cannot 3,32 show that although the bond strength between compensate for the total absence of light . veneers and tooth structure is not affected by The higher the light intensity and the longer the shade or opacity of the ceramic system, the DC of exposure time of the resin cement, the higher the cement may be diminished by either thicker, the Knoop hardness of the dual-cured materials . darker or more opaque restorations , frequently However, even when under direct light exposure, used to mask severely darkened teeth, and a there is a limit above which the DC of a photo or lower DC of the cement layer may compromise the dual-cure cement cannot be increased . esthetic result due to the continuous discoloration Quartz-tungsten-halogen (QTH) light curing of the material . The analysis of the DC of a light- units (LCU) deliver light irradiance varying between 2 17,50,64 cured resin cement after the superimposition of 400 and 1360 mW/cm . When exposure time different veneer materials with different thicknesses (40 s, 60 s or 120 s) and intensity (1200, 800 or 400 indicated that the effect of light attenuation on mW/cm ) of light exposure on DC of dual cements was evaluated, different materials showed different 62 1 ceramic thicknesses of 1.0 mm or less . results , although all the associations resulted in the Considering the optical properties of the indirect same amount of energy (48 J). Activation of dual restorative composites, there are different factors cements under 2 mm resin composite onlays using playing a role in light transmittance, such as particle low light intensity for prolonged time presented a size distribution, thickness of the restoration trend towards higher DC, probably due to the slow and shade. The smaller the particles, the more increase in the material viscosity, allowing more interfaces will be present acting as light scattering monomers mobility . centers , consequently increasing the opacity of Light-emitting diodes (LED)-based units were the material employed, which indicates that larger introduced in the market in 2001 and are another particles allow for deeper activation of the cement option to activate photo-cured resin cements. 4,57,58 layer by light . Interestingly, the hardness of These units generate light under a narrower dual resin-based cements is less affected when spectrum (between 450 and 490 nm) with the photo-activation is performed through an indirect peak around 468 nm, the ideal wavelength for restorative composite – either microfilled or resin-based materials using camphorquinone as micro-hybrid – than when it is performed through the photoinitiator . When the photo-activation of a an all-ceramic system – lithium disilicate and cement is performed through a ceramic system, light 57 57 glass ceramic . When the effect of thickness is transmittance increases for higher wavelengths . evaluated, there is indeed an inverse correlation The higher mean wavelength of LED lights improves between thickness of an indirect composite resin the capacity of the equipment to activate resin 36,76 restoration and Knoop hardness of the resin based cements under indirect restorations . However, luting system . Dual resin cements cured under 2 light-intensity is also critical, since LED with mm-thick micro-hybrid composite samples show relatively low light intensity (320 mW/cm ) results in decreased Knoop hardness at the bottom of dual- 30 53 ideal conditions , and the DC of dual cements is cured cement samples . 12% lower under 4 mm onlays in comparison to that The effect of QTH (905 mW/cm ) and LED (1585 J Appl Oral Sci. 365 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC mW/cm ) curing units on Knoop hardness of resin- of the resin cements is again more related to based cements indicated that there was no effect the commercial brand and, consequently, to the of LCU on the hardness of dual-cure cements . material composition than to the curing device itself, Samples cured under 1.4 and 2.0 mm ceramic slabs with LED and argon ion laser devices resulting in (leucite glass ceramic, shade A3) showed lower lower DC for one of the materials in the photo-cured hardness values than samples cured under direct mode . Although the short range of the spectra light exposure and under 0.7 mm slabs . Authors peak for LED devices may be advantageous when observed that hardness on dual-cured luting agents curing under ceramic systems, a wider range may may not be dependent on the light source, as long be clinically interesting to photo-activate alternative as the irradiance level for the effective wavelength photoinitiators, promoting a higher DC for QTH region to activate the photo-initiator is similar . lights even in the presence of lower light intensity. With the application of high-power curing units In addition to the factors presented above, in dentistry, LED-based equipment with high light there are other variables playing a role in the DC intensity (1000-1600 mW/cm ) are being advertised of light-activated resin-based cements, such as the as an alternative to reduce the curing time of distance between the tip of the curing device and 4,52,75 resin-based materials. However, the minimum time the cement layer and other indirect factors 38,50,52,59 required to properly cure a dual-cured luting system reducing the light intensity being delivered . is 15 s under ideal conditions, so that maximized Based on the results presented and the number of mechanical properties can be obtained . Therefore, studies indicating that prolonged light-activation it is not recommended to reduce the light exposure !   ! 43,53,80 time to less than 15 seconds on each side of a cured cements , increasing the light exposure restoration, irrespective of light intensity . Indeed, time, even though this would mean a couple more it has been demonstrated that light-curing a dual- minutes of clinical procedure, would be certainly cure cement for 9 s with a LED device (1100 mW/ cm & restoration. conversion . The authors observed that exposing dual-cure material to high intensity light may CONCLUSION increase its viscosity more rapidly, hindering the migration of active radical components responsible The clinical success of an indirect restoration is for further polymerization . Similar results were not only attributed to the DC of the resin cement or obtained when LED device (1100 mW/cm ) with to its mechanical properties, since there are other different activation modes and QTH (600 mW/ aspects that determine the clinical performance of cm ) were used to photoactivate resin cements dental prostheses. Nonetheless, ensuring a high DC between ceramic samples (lithium disilicate) and is paramount to obtain the best out of the chemical human dentin, and the authors found out that and physical properties of the resin cement, groups photo-activated for 10 s presented inferior besides being a critical factor for biocompatibility. bond strength . Higher bond strength results were When performing a luting procedure, one should obtained when LED devices under exponential mode pay attention to the characteristics of the indirect and QTH were used, and since the exponential restorative material to be employed, and make mode was applied for twice as much time as the a conscious decision of using a cement system other LED groups, the overall energy delivered was that would be more indicated to the clinical case increased, which may have enhanced the DC . necessities. Curing modes and the best light-curing Authors also observed that higher light intensity technique are examples of information that is to produces higher contraction strains during resin be available. It is crucial for clinicians to know and polymerization, which may promote debonding understand the cement systems they are working at the adhesive interface . Therefore, prolonged with. exposure times are desirable not only to increase the energy delivered to the luting material, in an REFERENCES attempt to compensate for the attenuation of the 1- Acquaviva PA, Cerutti F, Adami G, Gagliani M, Ferrari M, light promoted by the indirect restorative material, Gherlone E, et al. 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Curing potential of dual-polymerizable resin cements in simulated clinical situations. Q**YQ`|*Y!$` ~Š  Q**$Y|$*$! 37- Inoue S, Vargas MA, Abe Y, Yoshida Y, Lambrechts P, Vanherle 17- Cekic I, Ergun G, Lassila LV, Vallittu PK. Ceramic-dentin G, et al. Microtensile bond strength of eleven contemporary bonding: effect of adhesive systems and light-curing units. J Adhes + ~‡ Q**$'|Q'€!`‚ Q**€|$€!Q' 38- Jung H, Friedl KH, Hiller KA, Haller A, Schmalz G. Curing 18- Chang HH, Chang MC, Wang HH, Huang GF, Lee YL, Wang YL,       ƒ et al. Urethane dimethacrylate induces cytotoxicity and regulates [+ Q**$‚|$‚!$ cyclooxygenase-2, hemeoxygenase and carboxylesterase 39- Kitasako Y, Burrow MF, Katahira N, Nikaido T, Tagami J. Shear Q*$`$*|€QQ! bond strengths of three resin cements to dentine over 3 years in 31. vitro~Q**$Q|$'!`` 19- Cheong C, King NM, Pashley DH, Ferrari M, Toledano M, Tay 40- Kitzmüller K, Graf A, Watts D, Schedle A. Setting kinetics and FR. Incompatibility of self-etch adhesives with chemical/dual- shrinkage of self-adhesive resin cements depend on cure-mode cured composites: two-step vs one-step systems. Oper Dent. Q*$$Q€|‚``!‚$ Q**'QY|€`€!‚‚ 41- Komori PC, Paula AB, Martin AA, Tango RN, Sinhoreti MA, 20- D'Arcangelo C, Zarow M, De Angelis F, Vadini M, Paolantonio Correr-Sobrinho L. Effect of light energy density on conversion M, Giannoni M, et al. Five-year retrospective clinical study of degree and hardness of dual-cured resin cement. Oper Dent. indirect composite restorations luted with a light-cured composite Q*$*'‚|$Q*!` [+ Q*$`$Y|$‚!Q` 42- Krämer N, Lohbauer U, Frankenberger R. Adhesive luting of 21- Daronch M, Rueggeberg FA, De Goes MF, Giudici R. ‡ ~Q***$'|*!€ Polymerization kinetics of pre-heated composite. J Dent Res. 43- Kumbuloglu O, Lassila LV, User A, Vallittu PK. A study of the Q**Y‚|'Y!`' physical and chemical properties of four resin composite luting 22- Darr AH, Jacobsen PH. Conversion of dual cure luting cements.   [~Š  Q**`$€|'‚€!' ~† $‚QQ|`'!€ J Appl Oral Sci. 367 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC 44- Linden JJ, Swift EJ Jr, Boyer DB, Davis BK. Photo-activation 64- Santos GC Jr, El-Mowafy O, Rubo JH, Santos MJ. Hardening of of resin cements through porcelain veneers. J Dent Res. dual-cure resin cements and a resin composite restorative cured $$€*|$‚`!€ ;–>‰ ]^   ~ ‡ Q**`€*|'Q'!Y 45- Lührs AK, De Munck J, Geurtsen W, Van Meerbeek B. Composite 65- Schmid-Schwap M, Franz A, König F, Bristela M, Lucas T, ! „ Q*$`'*|QQ!'*$ Piehslinger E, et al. Cytotoxicity of four categories of dental 46- Lührs AK, Pongprueksa P, De Munck J, Geurtsen W, Van Q**Q‚|'*!Y Meerbeek B. Curing mode affects bond strength of adhesively 66- Selz CF, Strub JR, Vach K, Guess PC. Long-term performance of luted composite CAD/CAM restorations to dentin. Dent Mater. posterior InCeram Alumina crowns cemented with different luting Q*$`'*|QY$!$ agents: a prospective, randomized clinical split-mouth study over `€!„“Œ ”‡ „[ [+ Q*$`$Y|$‚!€*' on mechanical properties and polymer structure of dual-cured 67- Silva EM, Noronha-Filho JD, Amaral CM, Poskus LT, Guimarães Q**YQ`|‚`! JG. Long-term degradation of resin-based cements in substances 48- Moraes RR, Brandt WC, Naves LZ, Correr-Sobrinho L, Piva +  | E. Light- and time-dependent polymerization of dual-cured resin ‡† Q*$'Q$|Q€$!€ Q**Y|Q‚€! 68- Sjögren G, Molin M, van Dijken JW. A 10-year prospective evaluation of CAD/CAM-manufactured (Cerec) ceramic inlays 49- Moraes RR, Faria-e-Silva AL, Ogliari FA, Correr-Sobrinho cemented with a chemically cured or dual-cured resin composite. L, Demarco FF, Piva E. Impact of immediate and delayed light [~Š  Q**`$€|Q`$! activation on self-polymerization of dual-cured dental resin luting 69- Souza-Junior EJ, Prieto LT, Soares GP, Dias CT, Aguiar FH, Q**‚|Q*‚!$** Paulillo LA. The effect of curing light and chemical catalyst on 50- Nalcaci A, Kucukesmen C, Uludag B. Effect of high-powered the degree of conversion of two dual cured resin luting cements. LED polymerization on the shear bond strength of a light- „Q*$QQ€|$`‚!‚$ polymerized resin luting agent to ceramic and dentin. J Prosthet 70- Suh BI, Feng L, Pashley DH, Tay FR. Factors contributing to the Q**‚`|$`*!‚ ;  ! 51- Oliveira M, Cesar PF, Giannini M, Rueggeberg FA, Rodrigues J, cured or dual-cured composites. Part III. Effect of acidic resin Arrais CA. Effect of temperature on the degree of conversion and ~‡ Q**'‚|Q€!YQ working time of dual-cured resin cements exposed to different 71- Svizero NR, Silva MS, Alonso RC, Rodrigues FP, Hipólito VD, † Q*$Q'€|'€*! }„ ‚Q!†ƒ ‡@’ ƒ‡@  ƒˆ> ~Q*$''Q|'Q!`$ light sources to polymerize composite beneath a simulated ceramic 72- Tay FR, Pashley DH, Garcia-Godoy F, Yiu CK. Single-step, ~Š  Q**`$|$‚$!€ self-etch adhesives behave as permeable membranes after 53- Passos SP, Kimpara ET, Bottino MA, Santos GC Jr, Rizkalla AS. polymerization. Part II. Silver tracer penetration evidence. Am J Effect of ceramic shade on the degree of conversion of a dual-cure Q**`$€|'$‚!QQ ƒ#>[}„ Q*$'Q|'$€!Q' 73- Tezvergil-Mutluay A, Lassila LV, Vallittu PK. Degree of 54- Pazin MC, Moraes RR, Goncalves LS, Borges GA, Sinhoreti conversion of dual-cure luting resins light-polymerized through MA, Correr-Sobrinho L. Effects of ceramic thickness and curing + Q**€‚|Q*$!‚ unit on light transmission through leucite-reinforced material €`! >  !ˆ       ! and polymerization of dual-cured luting agent. J Oral Sci. Biebuyck JJ, Mestdagh M, Larbanois P, et al. A physico-chemical Q**Y‚*|$'$! explanation of the post-polymerization shrinkage in dental resins. 55- Pearson GJ, Longman CM. Water sorption and solubility of „ Q**QQ|`*‚!$Q resin-based materials following inadequate polymerization by a 75- Uctasli S, Hasanreisoglu U, Wilson HJ. The attenuation of + !    ~† $Y$|‚€!$ radiation by porcelain and its effect on polymerization of resin 56- Pegoraro TA, Silva NR, Carvalho RM. Cements for use in   ~† $`Q$|‚‚!€‚ • ‡ Q**€‚$|`‚'!€$ €!’‡„ „ }j~ ”> 57- Pick B, Gonzaga CC, Junior WS, Kawano Y, Braga RR, Cardoso and indenter load on the Knoop hardness of dental composites Š^ [ polymerized with LED and halogen technologies. Dent Mater. indirect restorative materials on resin cement polymerization. Eur Q**`Q*|Q$!Y ~Q*$*`|'$`!Q' €€!— ‡^ @‰;^j ”> 58- Pilo R, Cardash HS. Post-irradiation polymerization of different of four self-etching, self-adhesive resin cements. Dent Mater. anterior and posterior visible light-activated resin composites. Q**Q‚|$$*`!Y $QY"‚&|Q!'*` 78- Watts DC, Cash AJ. Analysis of optical transmission by 400- 59- Rasetto FH, Driscoll CF, Prestipino V, Masri R, von Fraunhofer 500 nm visible light into aesthetic dental biomaterials. J Dent. JA. Light transmission through all-ceramic dental materials: a pilot $`QQ|$$Q!€ ~Š  Q**`$|``$! 79- Yan YL, Kim YK, Kim KH, Kwon TY. Changes in degree of 60- Rodrigues RF, Ramos CM, Francisconi PA, Borges AF. The conversion and microhardness of dental resin cements. Oper shear bond strength of self-adhesive resin cements to dentin Q*$*'‚|Q*'!$* and enamel: an in vitro  ~Š  Q*$‚$$'|QQ*!€ 80- Zhang X, Wang F. Hardness of resin cement cured under 61- Rueggeberg FA, Caughman WF. The influence of light different thickness of lithium disilicate-based ceramic. Chin Med exposure on polymerization of dual-cure resin cements. Oper ~"^&Q*$$$Q`|'€Q!€ $'$Y|`Y!‚‚ 62- Runnacles P, Correr GM, Baratto Filho F, Gonzaga CC, Furuse AY. Degree of conversion of a resin cement light-cured through ceramic veneers of different thicknesses and types. Braz Dent J. Q*$`Q‚|'Y!`Q 63- Sanares AM, Itthagarun A, King NM, Tay FR, Pashley DH. Adverse surface interactions between one-bottle light- cured adhesives and chemical-cured composites. Dent Mater. Q*$$$€|‚`Q!‚ J Appl Oral Sci. 368 2015;23(4):358-68 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Oral Science Pubmed Central

Correlation between clinical performance and degree of conversion of resin cements: a literature review

Journal of Applied Oral Science , Volume 23 (4) – Aug 1, 2015

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Pubmed Central
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1678-7757
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1678-7765
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10.1590/1678-775720140524
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Abstract

www.scielo.br/jaos http://dx.doi.org/10.1590/1678-775720140524 Correlation between clinical performance and degree of conversion of resin cements: a literature review 1 2 2 3 Grace DE SOUZA , Roberto Ruggiero BRAGA , Paulo Francisco CESAR , Guilherme Carpena LOPES 1- Faculty of Dentistry, University of Toronto, Toronto, ON, Canada. 2- Department of Biomaterials and Oral Biology, Faculty of Dentistry, University of São Paulo, São Paulo, SP, Brazil. 3- Faculty of Dentistry, Federal University of Santa Catarina, Florianópolis, SC, Brazil. Corresponding address: Grace M. de Souza - 124 Edward Street, room #352 E. - Faculty of Dentistry, University of Toronto. Toronto, ON – Canada - Postal code: M5G 1G6 - Phone: 416-9794934 - Ext. 4417 - Fax: 416-9794936 - e-mail: grace.desouza@dentistry.utoronto.ca ABSTRACT esin-based cements have been frequently employed in clinical practice to lute indirect Rrestorations. However, there are numerous factors that may compromise the clinical performance of those cements. The aim of this literature review is to present and discuss some of the clinical factors that may affect the performance of current resin-based luting systems. Resin cements may have three different curing mechanisms: chemical curing, photo curing or a combination of both. Chemically cured systems are recommended to be used under opaque or thick restorations, due to the reduced access of the light. Photo- cured cements are mainly indicated for translucent veneers, due to the possibility of light transmission through the restoration. Dual-cured are more versatile systems and, theoretically, can be used in either situation, since the presence of both curing mechanisms might guarantee a high degree of conversion (DC) under every condition. However, it has been demonstrated that clinical procedures and characteristics of the materials may have many different implications in the DC of currently available resin cements, affecting their mechanical properties, bond strength to the substrate and the esthetic results of the restoration. Factors such as curing mechanism, choice of adhesive system, indirect restorative material and light-curing device may affect the degree of conversion of the cement and, therefore, have an effect on the clinical performance of resin-based cements. Keywords: Dental prosthesis retention. Dental materials. Luting agents. Biocompatible materials. (benzoyl peroxide) so as to form free radicals that INTRODUCTION will initiate the polymerization. Free radicals link to monomers by breaking carbon-carbon double Resin cements are composite resins developed bonds. The continuous addition of monomers to deliver mechanical properties and handling to a growing chain results in a polymeric chain. characteristics that are important for luting indirect In general, the maximum degree of conversion restorations. These cements contain different (DC) – the percentage of aliphatic C=C (double) monomers, which are linked together during the bonds converted into C-C (single) bonds to form polymerization reaction. Due to their application the polymeric network – reached by resin cements under an indirect restoration, in most cases the is around 60%, due to the increase of cement physical activation (photo activation) has very limited viscosity during the polymerization reaction, effect . Therefore, there is a need for chemical hindering the mobility of the reactive species . The activators. Activation of the polymerization means reaction slows down progressively up to a moment to induce the photo initiator (e.g., camphorquinone) when new bonds cannot be made . or to break the molecule of the chemical initiator J Appl Oral Sci. 358 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review Resin cements have been frequently employed maximum properties over time in areas that light for bonding indirect restorations to the teeth energy is unable to reach . The limitations of these due to their mechanical behavior – superior to systems are the reduced working time as opposed conventional cements (resin-free) –, possibility of to the extended setting time and the tendency to adhesion to the restorative material and to the tooth become “yellowish”, due to the higher concentration 7 60 29 structure with or without an adhesive system , of tertiary amines (activators) . The polymerization and superior optical properties when compared reaction in self-cured cements requires the with conventional cements. However, limitations components of the activation system – tertiary associated with the incomplete polymerization (low amine and benzoyl peroxide – to get in contact by DC) of the cement may result in higher sorption the mixing of two pastes, base and catalyst. and solubility values , causing faster degradation Dual-cure resin cements were developed 67 16,56,77 . Degradation of resin-based cements photo and chemically activated systems , reduces the bond strength between them and the obtaining optimized DC in the deepest locations substrate under a restoration, controlled working time and at the restoration margin, which may mean the short setting time. In such systems, there is a clinical loss of the restoration either by debonding, catalyst paste with a chemical initiator, usually fracture or secondary caries . Unreacted monomers benzoyl peroxide, and a base paste containing the (not bonded to the polymeric chain) may also photo-cured resin cement and the tertiary amine responsible for the activation of the self-cure 18 57 response . reaction . When both pastes are mixed together There are multiple factors that may interfere with and exposed to light, the polymerization happens the DC of resin cements and, therefore, compromise by physical (photo) and chemical (redox) activation. the longevity of indirect restorations. Some of them The appropriate working time is controlled by are the material composition (monomers and other inhibitors of the self-cure reaction or by the 56 56 components of the activation system) , possible amount of activators of the polymerization . It is inadvertent interactions between the bonding expected that in areas where there is not enough system and the cement , characteristics of the light, the interaction between the tertiary amine restoration to be cemented (optical properties and and benzoyl peroxide will be enough to ensure 14,15 4,57 thickness of the restoration) and characteristics the cement polymerization . However, when not of the photo activation step . This article aims to properly photo-activated, dual-cure resin cements 47,49,77 perform a comprehensive review of the factors may present reduced DC , which implicates 57 71 involved in the DC of the resin-based luting systems in lower hardness , higher solubility , lower 11,57 and the impact of DC on luting system properties. and compressive strengths, and lower bond strength to dentin in comparison to directly 7,77 CURING MECHANISM light-cured dual cements . For instance, a self- adhesive dual cement applied in self-curing mode As previously mentioned, photo-activated or may show DC as low as 11% after a 10-minute light-activated resin cements are indicated for setting time . Considering the clinical application situations where the light of the curing unit may of the resin-based luting systems, which are used pass through the restoration, such as translucent for the cementation of indirect restorations onto veneers and shallow inlays . These cements are tooth structure, 10 min is an undesirably long time provided in a single paste with a photoinitiator for a luting agent to obtain a great percentage system composed of a photosensitive component of the optimal setting characteristics, without (usually camphorquinone) and a tertiary amine. compromising the integrity of the margins and the 8,77 The presence of light with a wavelength of 480 cement layer under functional loading . nm (blue region of the visible spectrum) activates In general, light-cured and dual-cured cements camphorquinone , which binds to the tertiary activated by light through a restoration thinner 4,36,44,75 amine and then releases two free radicals that will than 2.0 mm have higher DC than self-cured start the monomers conversion. Photo-cured resin cements . When a dual cement is self-cured (no cements have unlimited working time, with the activation by light), mechanical properties such polymerization starting right after the exposure of the material to light . reduced by 68.9%, 59.2% and 91.1%, respectively, Chemically cured (self-cured) cements are in comparison to original values presented by dual- indicated under thick restorations, for luting cured samples . There are different factors that may intrarradicular posts and crowns made of materials affect the DC of self-cured luting systems, such as that block the light, such as metallic copings or the relatively high concentration of polymerization 42,68 highly opaque ceramics , aiming to guarantee inhibitors used to extend the material’s shelf life and J Appl Oral Sci. 359 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC to provide a clinically viable working time, ranging "# $& 27,77 from 2 to 5 minutes, which adversely inhibits in maximum degree of conversion . Therefore, polymerization during the luting procedure  when highly opaque or thicker restorations need the slow rate of polymerization activation and to be employed, a prolonged light exposure time subsequent propagation of radicals in comparison is recommended (please read “Indirect Restorative 6,49,51,61 to a directly light-activated material  Material” below), since a gradual increase in light- and the low concentration of benzoyl peroxide curing time and, therefore, in light transmission, 6,49 incorporated into those materials . Furthermore, gradually increases the Knoop hardness of resin- the hand-mixing of the two pastes incorporates based luting systems . Additionally, the use of a air bubbles that further inhibit polymerization due dual-cure system should always be considered to to the presence of oxygen and may act as stress possibly increase the DC by means of a chemical concentrators that potentially result in cracking activation of the monomeric system. throughout the cement layer . Although it has been With regard to post-activation time, the 24- demonstrated that the high incidence of air voids hour DC of light-cured and dual-cured cements reduces the stress generated by the polymerization is directly related to the DC obtained right after 4,75 shrinkage of the cement due to a change in ratio of light exposure . Even though DC is maximized 5 2,79 bonded to unbonded surfaces , '* of the inclusion of pores have not been determined. some cements present gradual increase in DC for Pores are also incorporated in dual-cured cements up to 24 hours, mainly when used in the dual- 4,10,28,31,64,79 during mixing and they may become an esthetic curing mode . However, it has been concern when cementing veneers . To minimize speculated that a delay in light activation of dual- the undesired consequences of the hand-mixing cured materials would enhance their properties procedure, some manufacturers provide cements in by allowing the self-polymerization promoters to a self-mixing apparatus (Figure 1), which eliminates react at some extent before being entrapped by the the manual mixing step, generates a homogeneous polymeric chains as soon as the photo-activation 49,74 mix and reduces the incorporation of bubbles. begins . Delaying the light activation for 2 min However, voids have been observed after automatic may, for instance, compensate for a lower dose of 56 49 mixing as well . light reaching the cement layer , but no effect is Interestingly, if light incidence on the cement observed on the bond strength of resin cements to the substrate . On the other hand, prolonged activator of dual cements improves DC when self-curing of the cement may also compromise the 1,7,15,16 49 71 compared to photo-activated-only systems overall DC and increase water sorption when light !      activation is delayed for 10 min for the same reason, 8,14,49 controversial and varies from one material indicating that an ideal balance between self-curing to another . It has been demonstrated that the and photo-activation is yet to be determined. absence of the self-curing component in light- Under ideal circumstances, light-activated resin activated systems negatively affects the DC of cements show higher DC than chemically cured 49,57 these cements when the light-curing component resin cements, irrespective of brand names . is not able to guarantee an acceptable degree of However, the DC of dual-cured cements is conversion, for example when applied underneath material-related, which means that it is more onlays of greater thickness . Considering a clinical associated with the brand name than with the application in which almost no light reaches the per se and some systems cement layer, it is desirable to use dual resin 1,10,11,15,16,31,51,73,79 cements that present a chemical curing mechanism than others . Just as an illustration, !  . However, there is the DC of a given dual-cured cement (RelyX ARC, currently no resin luting system in the market 3M Espe, St. Paul, MN, USA) may vary from 81% 2,7,45 capable of overcoming this limitation . In general, to 61% when cured under light as opposed to total the chemical activation of dual cements does not absence of light respectively, and from 56% to 26% seem enough to compensate for the absence of light when another dual-cured cement (RelyX Unicem, under thick or opaque restorations, even 24 hours 3M Espe, St. Paul, MN, USA) is cured under the same 1,15,32,61,64,65,75 43 after the beginning of the activation . conditions . This difference may be explained by the The DC of a self-adhesive dual cement may vary difference in composition between both materials. from 37% when light-cured for 20 seconds to For instance, some resin-based cements present 43 51 58% when light-cured for 40 seconds , evidencing twice as much benzoyl peroxide than others . that there is also a direct correlation between light The lower DC may affect some critical properties intensity received by a photo-activated material and of the resin-based cements . Dual cements cured 14,46,49 its DC . Laboratorial studies bring evidence that under a dual mode (photo+chemical) present the activation time generally recommended by the lower toxicity and solubility than dual cements J Appl Oral Sci. 360 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review Activation Adhesive Brand name& Commercial Recommended Characteristics (Ref #) mode strategy Manufacturer presentation ! " Biscem Bisco Self-mixing 20-30 s or 8 DC of 41.5% applicator min* Higher DC (86%) with dual-curing mode and longer measuring time interval Maxcem Elite Self-mixing 10-20 s on each Low cytotoxicity Kerr applicator surface or 4-5 DC of 26.4% min** Low bond strength (7.76 MPa) to Y-TZP High shrinkage strain at different temperatures Relatively high DC (68%) 10 min after light curing for 40 seconds RelyX Unicem Capsules or 20 s on each DC of 37.3% 3M ESPE self-mixing surface or 5-6 Mild cytotoxicity applicator min* Good bond strength (21.1 MPa) to Y-TZP Relatively high contraction stress and microhardness after light curing for 40 seconds Low shrinkage strain at different temperatures Low water solubility and high DC after 4-min curing delay SmartCem 2 Self-mixing 20-40 s on each High water solubility and reduced DC after 4-min curing delay Dentsply Caulk applicator surface or 6 Reasonable shrinkage strain at different temperatures min* SpeedCem Self-mixing 20 s on each Reasonable shrinkage strain at different temperatures IvoclarVivadent applicator surface or 160±40 s** Self-mixing 20 s or 3 min* Cement Kuraray applicator Inc. Duolink Bisco Self-mixing 40 s on each Relatively high contraction stress and microhardness after light curing for applicator or surface or 3 min 40 seconds two syringes 30 s** Multilink Automix Self-mixing 20 s on each DC of 61.4% IvoclarVivadent applicator surface or Good bond strength (31.7 MPa) to Y-TZP 180±30 s** Nexus Third Self-mixing 20 s on each Reasonable shrinkage strain at different temperatures Generation Kerr applicator surface (no info Very low bond strength to dentin under self-curing mode available on High DC (84.8%) one week after light curing for 100 seconds C self-curing) o Panavia F 2.0 Two syringes 20 s on each Inferior bond strength to resin composite (10.7 MPa) in different activation n Kuraray Inc. surface or 3 modes v min** !"$&  '+  /; <== ;> e '+/ ?? t 8.1% of secondary caries under crowns after 5 years in clinical service i J/   / >Q o strength to an indirect restoration n RelyX ARC 3M Self-mixing 40 s at the Fast curing and high DC a ESPE applicator margins or 10 Superior bond strength to resin composite (16.5 MPa) in different activation l min** modes and testing times DC of 63% when light-cured under a 2 mm thick composite resin slab at room temperature High water sorption and solubility RelyX Ultimate Self-mixing 20 s on each Very low bond strength to dentin under self-curing mode 3M ESPE applicator surface of 6 Relatively high DC (72%) one week after light curing for 100 seconds min* Variolink II Two syringes 40 s on each Relatively high cytotoxicity Ivoclar Vivadent surface (no info Reasonable bond strength (15 MPa) to Y-TZP available on DC of 56% when light-cured under a 2mm thick composite resin slab at self-curing) room temperature Low water sorption and solubility [\ C&B Cement Self-mixing 4 ~ 7 min* No measurable microhardness up to 10 min after mixing and low DC after C Bisco applicator or 7 days o two syringes n Panavia 21 Two pastes ~4 min 30 s* Low cytotoxicity v Kuraray Inc. e Superbond C&B Powder 7 min 30 s-9 3.4% of secondary caries under crowns after 5 years in clinical service n Sun Medical and liquid min 30 s** W ??    ^? t. in different dentin containers L Choice 2 Bisco One syringe 40 s over the ~59% DC 7 days after light activation I C veneer o 61 RelyX Veneer One syringe 30 s on each Reduced DC when 1.5 mm or thicker veneers are used T 3M ESPE surface - v E t. &Brand names mentioned were reproduced from the research papers included in this literature review. Therefore, there may be other brand names currently /_ </ `j  =  ///<{`W   Q and self-curing times may either consider room temperature (~23°C) or mouth temperature (~37°C). *Time after starting the mixture. **Time after placement of prostheses DC=degree of conversion; LED=light-emitting diodes; QTH=Quartz-tungsten-halogen Figure 1- Summary of some resin-based luting systems currently available and their characteristics based on the papers Q / /+Q+ +/ << / J Appl Oral Sci. 361 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC cured under the self-curing mechanism (chemical 55,65 only) . Dual curing also leads to a rapid increase thus compromising the clinical application of the 30,51 in hardness whereas chemically cured specimens material , and still may not compensate for the 22 64 30 are still soft 30 minutes or even one hour after absence of light . The clinical applicability of the mixing. Dual-curing mode also results in improved pre-heating technique is questionable, since the bond strength and mechanical properties such tooth structure could not be possibly heated up to 50°C, which would immediately result in the cement comparison to light curing or chemical curing temperature decrease. Therefore, any evaluation on 34,64 only . this topic should limit the pre-heating temperature Adhesive and self-adhesive resin to 37°C . cements have functional monomers such as 10-methacryloyloxydecyl dihidrogen phosphate (10- BONDING AND CEMENTATION MDP), 4-methacryloxyethyl trimellitate anhydride (4-META) and phosphoric esters. These resin The bonding between resin cement and the tooth cements generally have a dual-cure mechanism. structure (or the core build-up material) is generally Self-adhesive cements have acidic functionalities made possible by the use of a self-adhesive resin in order to demineralize tooth structure , and an cement or by the application of a bonding agent/ acid-base reaction between the acid groups of the system. The bonding agent/system may either be self-etch or total-etch (etch-and-rinse) . However, or the mineralized tooth surface starts immediately there are restrictions for the application of some after the mixing of the components and application +         ;! of the cement on the tooth surface . However, step total-etch (primer and adhesive in one bottle) those acidic monomers have been shown to and “all-in-one” self-etch systems and resin cements negatively affect the cement degree of conversion, with some chemical activation, either self-cured or 77 37 since they interfere with the amine initiator . This dual-cured . It has been shown that the lower interference compromises both the self-cure and the pH of the bonding agent employed, the lower the dual-cure modes . The very low polymerization the bond strength between self-cured cement and shrinkage strain of some self-adhesive cements may dentin > also be an evidence of reduced DC . Indeed, there to a self-cured cement results in 10-50% of the ;  bond strength presented when the same adhesive 31,40 63 materials and increasing the light-exposure from is bonded to a light-cured cement . 20 s to 40 s does not improve DC values after 6 The reason for those diminished bond strength hours as much as a temperature increase of the values is that when simplified-step adhesives cement improves . However, when the absence are used together with chemical-cured cements, (self-cure) and the presence (dual-cure) of photo- there is an interaction between the residual acidic activation are compared, the presence of light may monomers from the adhesive inhibition layer and result in a 10-fold increase in the material degree the binary peroxide-amine catalytic components of conversion . Although another initiator system that are commonly employed in chemically cured based on sodium aryl sulfate or aryl-borate salts has resin composites . Therefore, the tertiary amine of been proposed to compensate for the interaction the resin cement is neutralized and does not react between acidic monomers and the amine initiator with the initiator, resulting in low bond strength in self-adhesive systems, no evidence has been at the adhesive-cement interface . Besides that, !! 8,77 sodium persulfate-containing materials . & 12,13 Another way to improve the polymerization incomplete polymerization , and these are then kinetics of resin-based luting systems is to kept at the interface between the adhesive and 30,51 increase the temperature of the material . High the cement, compromising the bonding between 19,72 ;   those two substrates , which is demonstrated by 24 63 conversion than low viscosity cements , probably exclusively adhesive failure modes . To maximize due to the reduced mobility of the monomers in the performance of the resin cements, self-cured viscous materials. Increased temperature prior to or dual-cure cements are to be employed only in and during polymerization leads to higher DC, due to association either with three-step total etch systems 1,21 increased free radical and monomer mobility and or with self-etching primer systems containing collision frequency of the unreacted active groups a separate bonding agent. For all of the other resulting from the decrease in the viscosity of the adhesive systems, the resin cement employed 21,30 material . However, pre-heating (50°C) dual- should be exclusively photo-activated. cured resin cements with a higher concentration of the chemical activator (benzoyl peroxide) may J Appl Oral Sci. 362 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review When comparing the translucency of lithium- INDIRECT RESTORATIVE MATERIAL disilicate glass-ceramic and leucite-reinforced glass ceramic, Illie, et al. "Q**Y&  + When photo-activation of a resin cement is is more opaque than the latter (Figure 2). Lithium- performed, part of the visible light that reaches the disilicate glass ceramic contains a main crystalline crown is transmitted through the restoration, part is phase of “elongated crystals building a scaffold of many small interlocking needle-like crystals Consequently, the light intensity that effectively randomly oriented” , with a second crystalline reaches the cement varies according to the optical 15,62 phase consisting of lithium orthophosphate . On characteristics of the restorative material , 14,44 8,53 the other hand, leucite-reinforced glass-ceramic is such as opacity and shade 15,25,48 a less dense material, characterized by the single thickness of the restoration . The higher the 35,36 crystal formation of leucite crystals , indicating thickness and the lower the value (darkness) of the that lithium-disilicate ceramics scatter more light restoration, the lower the light intensity reaching than leucite ceramics. Light delivered to the cement the cement layer, which may compromise the DC 15,47,57,79 layer through lithium-disilicate ceramic (shade of a given cement . medium opacity 1) is reduced to 45% under 1 There are many restorative systems nowadays mm ceramic slabs, 16% under 2 mm slabs and that may be used for the manufacturing of all- approximately 8% under 3 mm slabs . Leucite- ceramic crowns (Figure 2). Each one of these reinforced glass ceramic slabs reduce the light ceramic systems has a microstructure that directly transmittance to 80%, 64% and 43% under 0.7, interferes with the amount of light that may be 14,78 1.4 and 2.0 mm thick samples, respectively . transmitted through the restoration . Considering As previously mentioned, the relationship restorations with similar shade and thickness, between restoration thickness and transmittance ceramics with a higher number of light scattering is highly dependent on the opacity of the centers (interface between different microstructural 14,51,54,80 material . However, the impact of the amount phases) are more opaque and prone to block visible 14,33,57,58 of light reaching the cement layer on its DC is light , compromising the intensity of the controversial. Dual-cure resin cements activated by physical polymerization of the resin cement . Pores, light under a 1.5 mm lithium-disilicate glass ceramic frequently found in feldspathic porcelains and glass- (Shade A2 low translucency) surface presented a DC similar to that of cements cured under direct light of these materials, act as light scattering centers exposure , whilst samples cured through 1.4 mm- as well. Light scattering occurs at interfaces of thick leucite-reinforced glass-ceramic slabs may or different phases with dissimilar refraction indexes. may not  ; A free of pores porcelain would be a material than groups activated with direct light exposure, with no light scattering interface and would thus depending on the luting system employed. In show transmittance, resulting in high DC for dual another study, samples light-cured under 1 or cements even under a 3 mm-thick layer . A multi- 2 mm thick lithium-disilicate slabs only showed phase material would scatter the light because the decreased hardness when light exposure time incident light beam will change direction from one was 20 s or less, indicating that longer exposure phase to another and the result will be a weaker times may compensate for light attenuation of incident light. A multi-phase structure within a the indirect restorative material . A randomized material also results in light scattering and low clinical split-mouth study evaluating the longevity transmittance . Thereafter, glass-infiltrated ;  ; alumina-zirconia (In-Ceram Zirconia System, Vita three different cements (two resin-based and one Zahnfabrik, Bad Säckingen, Baden-Württemberg, glass-ionomer) evidenced acceptable survival rates Germany) is the most opaque alternative among for all groups, with dual-cured cements showing current clinical options, due to the presence of four higher survival rate than glass-ionomer cement, distinct phases with different refraction indexes indicating that the opacity of the crown did not (alumina, Ceria-stabilized zirconia, lantanium glass affect the performance of the cement/restoration . & ; of only 6% in 0.5 mm-thick copings, and when transmittance values of a restoration would be even the thickness of the same material increases to more compromised considering the thickness and 1.5 mm the transmittance becomes as low as the optical characteristics of the porcelain veneer $? layer . The DC of a dual-cured cement activated spinel ceramic (In-Ceram Spinell, Vita Zahnfabrik, "$Q  & Bad Säckingen, Baden-Württemberg, Germany) with porcelain veneer layer (0.8 mm thickness) is it has only two phases (glass and spinel), with porcelain samples (2 mm thick) and to the control similar refraction indexes. J Appl Oral Sci. 363 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC Material Brand name& Sample Photo-curing Findings (Ref #) Manufacturer characteristics conditions Lithium IPS e.max Press 1.5 or 3.0 mm 20 or 40 s at 600 // +?^‚&<  / 2 50 disilicate Ivoclar Vivadent thick discs Shade mW/cm temperature glass A2 10, 20, 30, 40, Light intensity decreased ~ 62% under 1 mm, 86% under ~2 mm ceramic 1.0, 2.0 or 3.0 mm 50 or 60 s at 584 and 92% under ~3 mm thick samples. Light exposure of 30 s or thick discs Shade mW/cm longer may compensate for the 1 or 2 mm thick discs blocking the MO1 light 20 s at 1200 mW/ ƒ ' + / 1.0 mm thick discs cm ratio less affected when light-cured with 470 nm wavelength, no Shade A1 '/ 40 s at 1000 mW/ The higher the opacity of the ceramic, the lower the DC of dual- 2 13 0.5 or 0.8 mm cm cured cements; similar DC between 1.5 and 2.0 mm thick samples thick samples with veneer layer on top Shade LT, MO or HT IPS e.maxCAD 0.5, 1.0, 2.0 or 3.0 5, 10 or 15 s at Reduced hardness with 1 mm or thicker samples, irrespective of 2 35 Ivoclar Vivadent mm discs Shade 1600 mW/cm the length of light exposure MO1 or MO4 Leucite IPS Empress 1.0 mm thick 10 s at 580~1650 Light transmission reduced by ~55% through 1.0 mm thick 2 58 reinforced Ivoclar Vivadent discs Shade not mW/cm samples glass ceramic informed IPS Empress 1.0 mm thick discs 20 s at 1200 mW/ ƒ / '+/ CAD Ivoclar Shade A1 cm ratio more affected when light-cured with 470 nm wavelength, no Vivadent '/ IPS Empress 2 1.0, 1.5 or 2.0 mm 60 s at 800 mW/ No effect of ceramic thickness on bond strength between substrate 2 3 Ivoclar Vivadent thick discs Shade cm and resin cement A2 IPS Empress 0.7, 1.4 or 2 mm 40 s at 605 mW/ Light intensity decreased ~20% under 0.7 mm, 36% under ~1.4 mm Esthetic Ivoclar thick discs Shade cm  ?"&  !^ // _ << Vivadent A3 observed in DC of resin cements 1.0, 2.0 or 3.0 mm 3 cycles of 800 Negative correlation between cement hardness and ceramic GN-I GC Corp. thick discs Shade mW/cm _ </ † // _ A3 samples 0.5, 1.0, 2.0 or 3.0 5, 10 or 15 s at 15 seconds light exposure compensates for reduction in light 2 35 ProCAD Ivoclar mm discs Shade 1600 mW/cm transmittance in up to 2 mm thick samples Vivadent E100 or bleach =    In-Ceram 0.5 or 0.8 mm 40 s at 1000 mW/ ˆ   + < ="!?[&  = 2 13 alumina alumina Vita thick sample with cm (24~30%) cements and both thicknesses composite Zahnfabrick veneer layer on top Shade A2 Polycrystalline ZR Ceramill Zi 0.5 or 0.8 mm 40 s at 1000 mW/ ˆ   + < ="!^?&  = 2 13 zirconia thick sample with cm (22~24%) cements and both thicknesses veneer layer on top Shade A2 Polycrystalline Procera Nobel 0.25 or 0.6 mm 10 s at 580~1650 Both core thicknesses blocked conventional halogen light alumina Biocare core thick discs mW/cm completely; 0.25 mm core reduces Plasma Arc light by 66% and with veneering 0.6 mm by 79% material on top to equal 1.0 mm Feldspathic Ceramco 1.0 mm thick 10 s at 580~1650 Light transmission is reduced by ~63% through 1.0 mm thick 2 58 porcelain II Dentsply discs Shade not mW/cm samples Ceramco informed IPS InLine 1.5 or 2.0 mm 40 s at 1000 mW/ „ Q< / _ Ivoclar Vivadent thick discs Shade cm Vita VM7 Vita A2 20 or 40 at 900 `  _ +   < Zahnfabrick 2.0 mm thick discs mW/cm both light activation times; when darker ceramic and darker resin Shade OM1, 2M2 / > [† Q  /+ or 5M3 increase DC Micro-hybrid Sinfony 3M 1.5 mm thick discs 40 s at 800 mW/ DC of resin cements reduced from 1.5 up to 33% depending on the 2 72 indirect resin ESPE Shade D A3 cm luting system used composite Signum Heraus 2.0, 3.0 or 4.0 mm 40 s at 1200 mW/ DC decreased ~21% for samples cured under 4 mm discs when thick discs Shade cm 60 s at 800 / ^//‰ '< 2 1 A2 mW/cm 120 s at the curing protocol on the DC 400 mW/cm &Brand names mentioned were reproduced from the research papers included in this literature review. Therefore, there may be other brand names currently in the market that would represent the categories of materials described in this Figure. DC=degree of conversion Figure 2- Correlation between indirect restorative materials and the curing properties of the resin cement underneath J Appl Oral Sci. 364 2015;23(4):358-68 Correlation between clinical performance and degree of conversion of resin cements: a literature review 14 1 group, activated under direct light exposure . measured under 2 mm thick onlays . With regard to When the impact of the shade of the ceramic the effect of shade on indirect composite resin light system is evaluated, it can be observed that if transmittance, Arrais, et al. (2008) demonstrated shades with higher chroma are used, less energy that only 11% of light reaches the cement layer reaches the cement layer, since dark pigments when cured through a 2 mm microhybrid composite , negatively A2 shade as opposed to 8% when A4 shade was employed, but no effect on DC was observed for Dual-cured cements light-activated under 2 mm- dual-cured resin cements with higher concentration thick samples of darker dentin shade of feldspathic of benzoyl peroxide. The authors pointed out that porcelain present significantly lower DC than the adhesive component also presented a chemical cements light-activated under lighter shades . activator of the polymerization and could, therefore, When yellow and translucent shades of a resin compensate for the absence of light . cement were light-activated under the darker porcelain, only prolonged light-exposure time LIGHT CURING DEVICE (40 seconds) was capable of increasing the DC of the cement yellow shade , indicating that the It has been demonstrated that the hardness combination of darker shades in both the cement of dual-cured cements is dependent on the level and the indirect restorative material compromise of exposure to the curing light . As previously the overall DC of the cement layer. mentioned, the component responsible for With regard to laminate veneers, some studies the chemical activation of the material cannot 3,32 show that although the bond strength between compensate for the total absence of light . veneers and tooth structure is not affected by The higher the light intensity and the longer the shade or opacity of the ceramic system, the DC of exposure time of the resin cement, the higher the cement may be diminished by either thicker, the Knoop hardness of the dual-cured materials . darker or more opaque restorations , frequently However, even when under direct light exposure, used to mask severely darkened teeth, and a there is a limit above which the DC of a photo or lower DC of the cement layer may compromise the dual-cure cement cannot be increased . esthetic result due to the continuous discoloration Quartz-tungsten-halogen (QTH) light curing of the material . The analysis of the DC of a light- units (LCU) deliver light irradiance varying between 2 17,50,64 cured resin cement after the superimposition of 400 and 1360 mW/cm . When exposure time different veneer materials with different thicknesses (40 s, 60 s or 120 s) and intensity (1200, 800 or 400 indicated that the effect of light attenuation on mW/cm ) of light exposure on DC of dual cements was evaluated, different materials showed different 62 1 ceramic thicknesses of 1.0 mm or less . results , although all the associations resulted in the Considering the optical properties of the indirect same amount of energy (48 J). Activation of dual restorative composites, there are different factors cements under 2 mm resin composite onlays using playing a role in light transmittance, such as particle low light intensity for prolonged time presented a size distribution, thickness of the restoration trend towards higher DC, probably due to the slow and shade. The smaller the particles, the more increase in the material viscosity, allowing more interfaces will be present acting as light scattering monomers mobility . centers , consequently increasing the opacity of Light-emitting diodes (LED)-based units were the material employed, which indicates that larger introduced in the market in 2001 and are another particles allow for deeper activation of the cement option to activate photo-cured resin cements. 4,57,58 layer by light . Interestingly, the hardness of These units generate light under a narrower dual resin-based cements is less affected when spectrum (between 450 and 490 nm) with the photo-activation is performed through an indirect peak around 468 nm, the ideal wavelength for restorative composite – either microfilled or resin-based materials using camphorquinone as micro-hybrid – than when it is performed through the photoinitiator . When the photo-activation of a an all-ceramic system – lithium disilicate and cement is performed through a ceramic system, light 57 57 glass ceramic . When the effect of thickness is transmittance increases for higher wavelengths . evaluated, there is indeed an inverse correlation The higher mean wavelength of LED lights improves between thickness of an indirect composite resin the capacity of the equipment to activate resin 36,76 restoration and Knoop hardness of the resin based cements under indirect restorations . However, luting system . Dual resin cements cured under 2 light-intensity is also critical, since LED with mm-thick micro-hybrid composite samples show relatively low light intensity (320 mW/cm ) results in decreased Knoop hardness at the bottom of dual- 30 53 ideal conditions , and the DC of dual cements is cured cement samples . 12% lower under 4 mm onlays in comparison to that The effect of QTH (905 mW/cm ) and LED (1585 J Appl Oral Sci. 365 2015;23(4):358-68 DE SOUZA G, BRAGA RR, CESAR PF, LOPES GC mW/cm ) curing units on Knoop hardness of resin- of the resin cements is again more related to based cements indicated that there was no effect the commercial brand and, consequently, to the of LCU on the hardness of dual-cure cements . material composition than to the curing device itself, Samples cured under 1.4 and 2.0 mm ceramic slabs with LED and argon ion laser devices resulting in (leucite glass ceramic, shade A3) showed lower lower DC for one of the materials in the photo-cured hardness values than samples cured under direct mode . Although the short range of the spectra light exposure and under 0.7 mm slabs . Authors peak for LED devices may be advantageous when observed that hardness on dual-cured luting agents curing under ceramic systems, a wider range may may not be dependent on the light source, as long be clinically interesting to photo-activate alternative as the irradiance level for the effective wavelength photoinitiators, promoting a higher DC for QTH region to activate the photo-initiator is similar . lights even in the presence of lower light intensity. With the application of high-power curing units In addition to the factors presented above, in dentistry, LED-based equipment with high light there are other variables playing a role in the DC intensity (1000-1600 mW/cm ) are being advertised of light-activated resin-based cements, such as the as an alternative to reduce the curing time of distance between the tip of the curing device and 4,52,75 resin-based materials. However, the minimum time the cement layer and other indirect factors 38,50,52,59 required to properly cure a dual-cured luting system reducing the light intensity being delivered . is 15 s under ideal conditions, so that maximized Based on the results presented and the number of mechanical properties can be obtained . Therefore, studies indicating that prolonged light-activation it is not recommended to reduce the light exposure !   ! 43,53,80 time to less than 15 seconds on each side of a cured cements , increasing the light exposure restoration, irrespective of light intensity . Indeed, time, even though this would mean a couple more it has been demonstrated that light-curing a dual- minutes of clinical procedure, would be certainly cure cement for 9 s with a LED device (1100 mW/ cm & restoration. conversion . The authors observed that exposing dual-cure material to high intensity light may CONCLUSION increase its viscosity more rapidly, hindering the migration of active radical components responsible The clinical success of an indirect restoration is for further polymerization . Similar results were not only attributed to the DC of the resin cement or obtained when LED device (1100 mW/cm ) with to its mechanical properties, since there are other different activation modes and QTH (600 mW/ aspects that determine the clinical performance of cm ) were used to photoactivate resin cements dental prostheses. Nonetheless, ensuring a high DC between ceramic samples (lithium disilicate) and is paramount to obtain the best out of the chemical human dentin, and the authors found out that and physical properties of the resin cement, groups photo-activated for 10 s presented inferior besides being a critical factor for biocompatibility. bond strength . Higher bond strength results were When performing a luting procedure, one should obtained when LED devices under exponential mode pay attention to the characteristics of the indirect and QTH were used, and since the exponential restorative material to be employed, and make mode was applied for twice as much time as the a conscious decision of using a cement system other LED groups, the overall energy delivered was that would be more indicated to the clinical case increased, which may have enhanced the DC . necessities. Curing modes and the best light-curing Authors also observed that higher light intensity technique are examples of information that is to produces higher contraction strains during resin be available. It is crucial for clinicians to know and polymerization, which may promote debonding understand the cement systems they are working at the adhesive interface . 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Journal

Journal of Applied Oral SciencePubmed Central

Published: Aug 1, 2015

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