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The Effect Of Refrigerated Composite Resin Restoration On The Sealing Ability Of Class V Cavities By Dr. Wedad Y. Awliya BDS, MSc Associate professor, Department of Restorative Dental Science, College of Dentistry, King Saud University Riyadh, Saudi Arabia P.O. box 5967 Riyadh 114 E-mail [email protected] 1 Abstract Purpose: To investigate the effect of refrigerated and room temperature composite resin restorations on the sealing ability of class V cavities placed at intraoral temperature. Materials and Methods: Class V cavities were prepared in the buccal and lingual surfaces of twenty extracted human molar/premolar teeth. The prepared teeth were then divided into four groups, each group contains five teeth. Two groups were restored with refrigerated Composan and Renew composite resin (Stored at 5 oC). The other two groups were restored with Composan and Renew composite resin stored at room temperature (25 oC). Restorations of all teeth were done in a chamber adjusted at intraoral temperature (32 oC). The teeth were then prepared for the microleakage test. Specimens were immersed in 2% methylene blue dye for 24 hours, then sectioned bucco-lingually and viewed with a stereomicroscope. Results: Refrigerated Composan composite resin showed significantly less microleakage than Composan at room temperature. However, no significant difference in microleakage was found between refrigerated and room temperature Renew composite resin. Conclusion: No adverse effect on marginal seal of class V cavities was found using composite resin restorative materials directly from fridge. 2 INTRODUCTION Advances in adhesive dental technology have radically changed restorative dentistry. However, polymerization shrinkage of composite resin is still unsolved problem. The contraction stress-build up that occurs during polymerization, adversely affects the bond interface between composite resins and the hard dental tissues, leading to clinical failure of the restorations.1 Opening of the restoration margins, which may result in microleakage of fluid, discoloration near restoration margins, secondary caries, postoperative sensitivity are the most frequent consequences of the polymerization shrinkage.2,3 Although some manufacturers recommend storage of restorative and adhesive materials at room temperature, others recommend refrigerated storage to extend shelf life. In clinical situations, Materials may be taken from a refrigerator and used immediately without allowing time for equilibrium to room temperature, and this reduced temperature could have possible detrimental consequences on the efficacy of the bonding agent. Lowered temperature might increase the viscosity of the polymeric materials, which might affect penetration of the refrigerated adhesive material into dentin surface, with a resultant decrease in bond strength.4 Additionally, the degree of polymerization of the bonding resin decreases with lowered temperature,5 and this may adversely affect the physical properties of the adhesive materials.6 However, Hagge et al found that a group of refrigerated Scotchbond Muli-Purpose bonding system (at 3 oC) showed significantly higher bond strength to dentin than the group used at room temperature. 7 Therefore, the purpose of this study was to investigate the effect of using refrigerated composite resin (5 oC) and composite resin stored at room temperature (25 oC) on the sealing ability of class V cavities placed at intraoral temperature (32 oC). 3 MATERIALS AND METHODS: Twenty extracted, non-carious, human molar/premolar were used within one month after their extraction. The teeth were stored in saline until preparation. Standardized buccal and lingual class V cavities (5 mm long, 3 mm wide, and 2 mm deep) were prepared in all teeth with # 330 carbide bur (MidWest Dental Product Corp., Des Plaines IL, USA) using a high speed hand piece and air-water spray. A new bur was used for every 10 preparations. The occlusal enamel margins were beveled and the gingival walls were extended 1 mm below the cemento-enamel junction. The prepared teeth were then randomly assigned into four-experimental groups (each group contains 5 teeth, with two-cavity preparations in each tooth). The prepared teeth were stored in saline in an incubator, adjusted to simulate intraoral temperature (32 oC), 24 hours before restoration. Two types of composite resin restorative materials are used for this study (shade A3.5) following manufacture’s instructions. Renew, light cured universal hybrid composite resin (Bisco, 1100W. Irving Park Rd. Schaumburg, IL 60193, USA), and Composane light cured microhybrid composite resin, (Promdica, Domagkstr. 31, 24537 Neumunster, Germany). To prevent temperature variation in the refrigerated groups at the restoration time, 50% of the restorative materials were subdivided into equal small increments and placed at small well sealed, light blocked containers. Then these containers were stored in a refrigerator at 5 oC for 24 hours before restorations placement in the cavities. The other 50% of each material was stored at room temperature (25 oC). In the first experimental group enamel surfaces were etched with 32% phosphoric acid (Unietch, Bisco) for 30 sec, rinsed thoroughly, and excess water was removed with brief burst of air. After etching, 2 consecutive coats of Onestep light cured universal dental adhesive (Bisco, Schaumburg, IL, 60193, USA) were applied to prepared enamel and dentin structure. The adhesive was dried for 10 sec. with an air syringe, then light cured for 10 sec. Renew composite 4 resin material stored at room temperature was placed in one increment into the cavity preparations, light cured for 40 sec. with light spectrum 800 (Dentsplay, Detrey, Konstanz, Germany). In the second group, similar restorative procedures as in first group were followed using refrigerated adhesive and Renew restorative material. Cica etching gel (Promdica, Domagkstr, 31, 24537 Neumunster, Germany) was used as an etching gel for the third group for 30 sec., rinsed, then air-dried. Compobond LCM system (Promdica) was applied. Primer was rubbed into dentin for 30 sec., and then the excess primer was removed by a brush followed by careful drying of the cavities with oil–free air. The adhesive was applied evenly on all prepared dentin and enamel surfaces by using a new disposable brush, dried with faint air stream and light-cured for 20 sec. Then Composan LC restorative material which was stored at room temperature, applied to the cavities in one increment. The previous procedures, in the third group, were followed in the fourth group using refrigerated Composan LC restorative system. All the restorations were finished and polished using Soflex discs (3M Co.). All procedures were conducted by the same operator in a chamber its temperature was adjusted to simulate the intraoral temperature (32 oC). In order to prepare the restored teeth for the microleakage test, the teeth apices were sealed with a light–activated composite resin. Two coats of nail varnish were applied to the teeth except for 1 mm around the restoration margins. The restored teeth then were immersed in 2% methylene blue dye (Fisher Scientific, Fair Lawn. NJ, USA) for 24 hours, then they were washed by distilled water to remove the superficial dye. Each specimen was invested in separate clear resin block and coded before its sectioning longitudinally in a bucco-lingual direction with a low speed water-cooled diamond saw (Silverstone-Taylor Hard Tissue Microtome, Scientific Fabrication, Littleton, CO., USA). Each section was then inspected under a stereomicroscope (Wild Photomakroskop M400, Heerbrugg, 5 Switzerland) at 32x magnifications. The staining along the tooth restoration interface was recorded according to the following criteria: 0: no dye penetration 1: penetration of the dye to less than half of the cervical/occlussal wall 2: penetration of the dye further than half of the cervical/occlusal wall 3: penetration along the axial wall Data were statistically analyzed using SPSS system. Wilcoxon signed rank test, at 0.05 significance level was used to identify any difference between the different restorative techniques. Combined occlusal and cervical scores within each restoration were also compared. RESULTS Table 1 presents the microleakage data for the occlusal and gingival walls of both materials in this study. Wilcoxon signed rank test indicated that refrigerated Composan composite resin showed significantly less microleakage than Composan at room temperature (P=0.014). However, no significant difference in microleakage was found between refrigerated and room temperature Renew composite resin (P=0.489). All enamel walls of both materials (refrigerated and at room temperature) showed significantly better marginal seal than gingival walls (P< 0.05). Comparing microleakage of both Composan and Renew composite resin at room temperature no significant difference was found (P=0.511). On the other hand, refrigerated Composan composite resin showed significantly less leakage than refrigerated Renew composite resin at both margins (P=0.002). DISCUSSION The dimensional rearrangement of monomers into polymer chains during resin polymerization inevitably leads to volume shrinkage.8 In clinical situation, the curing contraction is restrained by the developing bond of the restorative 6 material to the cavity walls.9 This restriction induces polymerization contraction stress, which counteracts the developing resin-tooth bond by pulling the setting resin composite material away from the cavity walls.10,11 If the weakest link is the bonding interface with the tooth, the resin-enamel bond may survive the shrinkage, but the weaker resin-dentin interface may not.12 Although Enamel adhesion is predictable and established entity in contemporary restorative dentistry, an adequate bond to dentin is more difficult to achieve.13 This explains the better sealing ability of all composite restorations in this study at enamel walls. Using composite resin directly from the refrigerator did not adversely affect the sealing ability of the two composite resins in this study. In fact the results showed that the sealing ability of Composan composite resin was significantly improved by refrigeration. This obtained result might be due to the influence of the factors that affect polymerization shrinkage. First, thermal expansion of refrigerated composite should occur when the material reach intra oral temperature. This expansion can compensate the high contraction stresses that occur in the early stage of the setting reaction.14 Second, the curing rate and the degree of cure decrease when setting reaction occur at lower temperature.14 Thus, in case of cooled resin composite the pre-gel period could be longer and the setting stresses could be relived more easily by flow.12 Moreover, the restorative material can reach temperature higher than intra oral temperature by the thermal effect of the curing light.15 Consequently, a thermal contraction of the restorative material should be induced when it drops to intra oral temperature. This effect is reduced when cooled material are used because the overall temperature of the restoration should be lower during light curing. Therefore, the sealing ability of cooled material might be improved. The marginal seal of both composite resins used in this study at room temperature showed no significant difference. However, after refrigeration Composan significantly showed better seal. This may be attributed to effect of 7 temperature on the restorative resin as one component and the adhesive systems as another component. Composan composite resin has BisGMA and UDMA as difunctional monomers and both are extremely viscous. Although these monomers were diluted by another difunctional monomer (TEDMA), Composan viscosity seems to be higher than that of Renew, which contains Only BisGMA diluted by TEGDMA. Shrinkage stress development in the restoration can be low when shrinkage is accompanied by predominant (pre-gel) viscous flow property of the material as early mentioned.16 Temperature also, might increase the viscosity of the adhesive system. Stiffness or rigidity of a resin is quantified by Young’s modulus of elasticity, which represents the resistance of the material to elastic deformation.17 The lower Young’s modulus, the more the elastic capacity will reduce contraction stress.18 Viscous adhesive resins produce thick resin bonding layer between the stiff dentinal cavity wall and the shrinking restorative resin composite. Stretching of this intermediate layer (with a low Young’s modulus) may provide sufficient elasticity to relieve polymerization contraction stresses of the restorative resin composite.19,20,21 Composan bonding system is two-bottle adhesive (Primer and adhesive). On the other hand, the bonding system used in this study with Renew composite resin, is one-bottle adhesive. Two-bottle adhesive system may provide a thicker adhesive layer.22 However, further investigation is needed to study the effect of increased viscosity of adhesive system, because of refrigeration, on their wetting characteristics and subsequently the bond strength to tooth structure. Conclusions The results of this study indicate that marginal leakage around dentin margins is still an unsolved problem because bonding to dentin has not reached the ideal performance as bonding to enamel has. No Adverse effects on marginal seal, of class V cavities, were noted using composite resins directly from refrigerator without allowing equilibrium to 8 room temperature. In fact, Refrigeration significantly enhances the marginal seal of class V cavities restored with Composan composite resin. Since refrigeration improves significantly the sealing ability of Composan but not Renew composite resin, Further research is needed to study the effect of temperature on different adhesive systems, and on their bond strength to tooth structure. Acknowledgement The author would like to express her thanks and appreciation to Dr. Hanan Mahjoub for her help during the lab work of this study and to Dr. Nazeer Khan for his assistance in the statistic of this study. References 1. Lutz F, krejci I, Barbakow F. Quality and durability of marginal adaptation in bonded composite restoration. Dent Mater 7:107-13, 1991. 2. Swift EJ, Perdigao J, Hey Mann HO. Bonding to enamel and dentin: A brief history and state of the art. Quintessence Int 26:95-110,1995. 3. Walshaw PR, McComb D. clinical considerations for optimal dentinal bonding. Quintessence Int 27:619-625, 1996. 4. Burrow MF, Taniguchi Y, Nikaido M, et al. Influence of temperature and relative humidity on early bond strengths to dentin. J Dent 23:41-45, 1995. 5. Bausch JR, de Lange C, Davidson CL. The influence of temperature on some physical properties of dental composite. J Oral Rehabil 8:431-439, 1981. 6. Greener EH, Greener CS, Moser JB. The hardness of composites as a function of temperature. J Oral Rehabil 11:335-340, 1984. 7. Hagge MS, Lindemuth JS, Broome JC et al. Effect of refrigeration on shear bond strength of three dentine bonding systems. Am J Dent 12:131-133, 1999. 9 8. Feilzer AJ, de Gee AJ, Davidson CL. Curing contraction of composites and glass ionomer cements. J Prosthet Dent 59:297-300,1988. 9. Davidson CL. Resisting the curing contraction with adhesive composite. J Prosthet Dent 55:446-447,1986. 10. Imai Y, Kadoma Y, Kojima K, et al. importance of polymerization initiator systems and interfacial initiator of polymerization in adhesive bonding of resin to dentin. J Dent Res 70:1088-1091,1991. 11. Lutz F, Krejci I, Oldenburg TR. Elimination of polymerization contraction stresses at the margin of posterior composite resin restorations: a new restorative technique. Quintessence Int 17:659-664,1986. 12. Davidson CL, de Gee AJ. Relaxation of polymerization contraction stress by flow in dental composites. J Dent Res 63:146-148,1984. 13. Lopes GC, Andrada MC, Dental adhesion: present state of the art and future perspectives. Quintessence Int 33:213-224, 2002. 14. Bandyopadhyay S. A study of volumetric setting shrinkage of some dental materials. J Biomedical material Res 16(2):135-144, 1982. 15. Loney Rw, Price RB. Temperature transmission of high out put light-curing units through dentin. Operative Dent 26(5):516-520, 2001. 16. Davidson CL, de Gee AJ. Relaxation of polymerization stresses by flow in dental composite. J Dent Res 63:146-148, 1984. 17. Braem M, Lambrechts P, Vanherle G, and Davidson CL. Stiffness increase during the setting of dental composite resins J Dent Res 66;1713-1716, 1987. 18. Kemp-Scholte CM, Davidson CL . The marginal sealing of curing contraction gaps in class v composite resin restorations. J Dent Res 67:841-845,1988. 19. Meerbeek V. Adhesion to mineralized tissues. Operative Dent 5:101-124, 1992. 10 20. Kemp-Scholte CM, Davidson CL. Complete marginal seal of class V resin composite restoration affected by increased flexibility. J Dent Res 69:12401243, 1990. 21. Kemp-Scholte CM, Davidson CL. Marginal integrity related to bond strength and strain capacity of composite resin restoration system. J prosthet Dent 46:658-664, 1990. 22. Wilson HF, Roulet J, Fuzzi M. Advances in Operative Dentistry. Quintessence publisher, Vol I Chap 2: page 34 11 Table 1. Microleakage Scores Of The Two Composite Resin Materials (Refrigerated And At Room Temperature) At The Occlusal And Gingival Margins Material Microleakage scores at Microleakage scores at the occlusal margins the gingival margins No Score 0 Composan (Room temperature) Composan (Refrigerated) Renew (Room temperature) Renew (Refrigerated) No Score 1 2 3 0 1 2 3 20 14 4 1 1 20 2 4 10 4 20 17 2 0 1 20 0 18 1 1 20 10 8 2 0 20 0 5 13 2 20 6 9 4 1 20 0 9 9 2 12