610 the journal of prosthetic dentistry volume 81 number 5
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Microleakage of Class V resin modified g
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- THE JOURNAL OF PROSTHETIC DENTISTRY TOLEDANO ET AL 612 VOLUME 81 NUMBER 5 Table I.
DISCUSSION
Polymerization shrinkage of resin-containing restora- tive materials may result in marginal discrepancies that lead to microleakage, marginal discoloration, and sensi- tivity. 2-4 Hygroscopic expansion can compensate, to some degree, for polymerization shrinkage. Water sorp- tion can help to reduce marginal gaps 3 ; for this reason, glass ionomer cements, which absorb the most water during the first 24 hours after placement, 6 can display less microleakage than resins. Attin et al 7 reported that Fuji II LC glass ionomer cement expanded after curing and immersion in water, whereas Dyract resin composite and Vitremer glass ionomer cement revealed a total vol- umetric loss. Thus, they concluded that water expansion is 1 factor that reduces the leakage. THE JOURNAL OF PROSTHETIC DENTISTRY TOLEDANO ET AL 612 VOLUME 81 NUMBER 5 Table I. Microleakage of the different groups Occlusal Gingival Overall Group 0 1 2 3 0 1 2 3 0 1 2 3 Fuji II LC (n = 17) 14 1 0 2 12 2 0 3 10 3 0 4 Vitremer (n = 18) 9 3 2 4 8 1 4 5 4 4 4 6 Dyract (n = 22) 7 4 6 5 6 3 0 13 5 3 1 13 Kruskal-Wallis 1-way analysis of variance indicated significant differences between all the restorative materials for both overall, occlusal, and gingival scores ( P=.03; P=.01; P=.01, respectively). Wilcoxon test (to compare occlusal, gingival, and overall scores of each material) revealed that the occlusal and gingival scores for each matched pair of restora- tive materials showed statistically significant differences between Fuji II LC and Dyract, both for the occlusal ( P=.005) and gingival (P=.005) margins and also as an overall evaluation ( P=.01) with Fuji II LC showing the least dye penetration. Although Vitremer revealed dye penetration scores between Fuji II LC and Dyract, there were no statistically significant differences between them. Also, there were no statistically significant differences between Dyract and Vitremer. Our results disagree with those of Yap et al 8 who compared the microleakage of Dyract resin composite and Fuji II LC glass ionomer cement and reported no statistically significant differences in microleakage scores. In their study, they reported a significant differ- ence between enamel and dentin; in our study, even if microleakage was less common in enamel, the differ- ence was not significantly different. These differences between the studies could be because Yap et al 8 stored their specimens in a saline solution for 1 week before testing. This storage time allows hygroscopic expansion of the material, 7 which may compensate the original polymerization shrinkage of the material, which allows less microleakage. In our study, specimens were ther- mally cycled for approximately 2 days, and the material may not have expanded completely. Yap et al 8 also sug- gested that 1 of the unique features of the resin that releases fluoride to enamel is the omission of acid etch- ing, which is a critical step in most resin composite and adhesive systems. The manufacturers have claimed that this is achieved through the use of a specially formulat- ed coupling agent with hydrophilic phosphate groups that is thought to form ionic bonds with the calcium of hydroxyapatite. Dyract resin composite also aims to be self-adhesive because of hydrophilic carboxylic groups present in its patent tetrachlorobiohenyl (TCB) resin. These questions need further investigation. No restorative material evaluated in our study com- pletely resisted microleakage at the occlusal or gingi- val walls of the tooth. Of the 3 products evaluated, Fuji II LC glass ionomer cement exhibited the least dye penetration, at both the occlusal and gingival margins, and when evaluated as overall values (enam- el and gingival scores pooled together). However, only with the overall evaluation did Fuji II LC glass ionomer cement reveal a statistically significant differ- ence with Dyract resin composite. The lack of statisti- cally significant difference in microleakage between resin-modified glass ionomers has also been previous- ly reported. 15 Uno et al 16 concluded that the superior adaptation of Fuji II LC glass ionomer cement to the cavity walls was responsible for the lower dye penetra- tion, which may be a result of the glass ionomer cement undergoing minimal setting shrinkage over a longer period and approximately one half that of resins. 17 Because the resin component is responsible for the polymerization shrinkage, and Dyract resin composite has more resin than Fuji II LC glass ionomer cement in its composition, it is possible that this is the reason for the greater microleakage scores observed with Dyract resin composite. Another reason that could explain the results is the resin component of Fuji II LC glass ionomer cement undergoing dif- ferent rates of polymerization shrinkage during light curing (as it is a dual-cure material) compared with Dyract resin composite. The microleakage scores for Vitremer glass ionomer cement fell between those recorded for Dyract resin composite and Fuji II LC glass ionomer cement, which could be due to 2 reasons. Fuji II LC is a resin-modified glass ionomer in which the HEMA content is merely blended with a polyalkenoic acid liquid, whereas Vit- remer, in addition to being a simple mixture of HEMA with polyalkenoic acid, is also modified by the attach- ment of polymerizable methacrylate side groups. 13 It is possible that Vitremer has more polymerizable resin than Fuji II LC, but less than Dyract; its microleakage values fell in between these 2 materials. The better adap- tation of Fuji II LC glass ionomer cement compared with Dyract resin composite could be also due to the 15-second dentin conditioning performed with the 10% polyacrylic acid. This dentin treatment produces a close relation between the ionomer and dentin struc- tures as it removes the smear layer, leaving the surface clean and theoretically better able to accept a glass ionomer. 18 Moreover, the Fuji II LC liquid contains approximately 40% HEMA (manufacturer’s data) and primers that contain similar hydrophilic monomers than resin-containing materials, facilitating the bonding between dentin and these type of materials. 19 Although the PAS adhesive of the Dyract resin com- posite tested had orthophosphoric acid to condition the dentin, it also contained TGDMA and elastomeric resins, which have chemical affinity with the resin con- tained in the material. When these resins shrink during polymerization, they could generate a gap where microleakage could be detected. The extent of the cur- ing shrinkage determines the formation of marginal gaps if the restorative material does not adhere enough to tooth structure or it can cause cohesive failures in the material. 23 The application of Vitremer glass ionomer cement only requires the primer application and light curing for 20 seconds. It is possible that the pH of the dentin primer could modify the smear layer sufficiently to per- mit the tooth and restorative material to come into inti- mate interfacial contact. 18 Charlton and Haveman 20 obtained higher bond strength values to dentin with Fuji II LC glass ionomer cement than with VariGlass VLC resin. Some consider this latter material a light-cured glass ionomer and not a true polyacid-modified com- posite because it does not have an acid-base cure reac- tion. 13 These differences in bond strength values could contribute, among other factors, to explain the differ- ences in the microleakage patterns recorded in our study. Polymerization shrinkage also produces material shrinkage in all directions and most often the dentin margins are unprotected to resist microleakage. 2 With restorations made with resin-reinforced glass ionomers, the adhesion is mainly due to a physicochemical reaction with dentin and enamel due to the polar nature of the polyacrylates and minerals for the dental hard tissues. Download 62.61 Kb. Do'stlaringiz bilan baham: |
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