Effect of dentin dehydration and composite resin polymerization mode on bond strength of two self-etch adhesives.

BACKGROUND: Dual-cured composite resins are similar to self-cured composite resins in some of their clinical applications due to inadequate irradiation, lack of irradiation, or delayed irradiation. Therefore, incompatibility with self-etch adhesives (SEAs) should be taken into account with their use. On the other, the extent of dentin dehydration has a great role in the quality of adhesion of these resin materials to dentin. The aim of this study was to investigate the effect of dentin dehydration and composite resin polymerization mode on bond strength of two SEAs. MATERIALS AND METHODS: A total of 120 dentinal specimens were prepared from extracted intact third molars. Half of the samples were dehydrated in ethanol with increasing concentrations. Then Clearfil SE Bond (CSEB) and Prompt L-Pop (PLP) adhesives were applied in the two groups. Cylindrical composite resin specimens were cured using three polymerization modes: (1) Immediate light-curing, (2) delayed light-curing after 20 min, and (3) self-curing. Bond strength was measured using universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed with two-way ANOVA and Duncan post hoc tests. Statistical significance was defined at P < 0.05. RESULTS: There were no significant differences for CSEB subgroups with hydrated and dehydrated dentin samples between the three different curing modes (P > 0.05). PLP showed significant differences between subgroups with the lowest bond strength in hydrated dentin with delayed light-curing and self-cured mode of polymerization. CONCLUSION: Within the limitations of this study, a delay in composite resin light-curing or using chemically cured composite resin had a deleterious effect on dentin bond strength of single-step SEAs used in the study.

Effect of surface treatments on fracture resistance of root filled teeth with bonded fibre posts.

BACKGROUND/AIM: This study examined the effect of several dentin surface treatments on fracture resistance of root filled teeth containing bonded fibre posts. MATERIAL AND METHODS: The roots of 84 single-canal premolars were instrumented, filled with gutta-percha and randomly divided into seven groups. The coronal 9 mm of gutta-percha was removed to create a post space. In the experimental groups, canals were irrigated with distilled water, 37% phosphoric acid, 5% sodium hypochlorite, 17% EDTA, 5% sodium hypochlorite followed by 17% EDTA or 5% sodium hypochlorite followed by 10% ascorbic acid. Fibre posts were cemented using Panavia F2.0 resin cement, and the specimens were mounted in acrylic resin blocks. Following 1-week storage in an incubator, specimens were thermocycled and their fracture resistance was determined using a universal testing machine. Data were analysed using the Kruskal-Wallis test. RESULTS: Mean fracture resistance values ranged from 465.8 N in specimens treated with sodium hypochlorite and ascorbic acid to 739.1 N for those treated with sodium hypochlorite only. However, differences in fracture resistance were not statistically significant (P = 0.114). CONCLUSIONS: None of the surface treatments improved vertical fracture resistance of root filled teeth containing bonded fibre posts.

Comparison of microleakage of composite restorations using fifth and sixth generation dentin bonding agent: an in vivo study.

INTRODUCTION: The success of bonded restorations depends on effective bonding between restorative materials and tooth structure, and it prevents microleakage. New dentin bonding systems have been introduced which promotes this concept. The aim of this study was to compare the amount of microleakage between 'single bond' vs 'Prompt L-Pop' during different time periods. MATERIALS AND METHODS: In this clinical trial study, 60 nonretentive class five cavities were prepared on buccal surfaces of human premolars which were scheduled to be removed for orthodontic purposes. The cavities were restored using two different bonding agents; fifth generation (Single Bond) and sixth generation (Prompt L-Pop) and then filled with resin composite (Filtek Z-250). The samples in both groups were extracted after placing the restoration in three periods of time: Immediately, 1 week and 6 months postplacement. Specimens were sealed with two layers of nail varnish except for 1 mm around restoration and immersed in a silver nitrate solution for 24 hours. The teeth were then sectioned longitudinally and the degree of microleakage was determined by stereomicroscope based on standard usual criteria. RESULTS: Single bond showed more leakage at dentin margin than enamel margin in all three extraction periods and differences were significant among three groups (p < 0.05). In samples which were restored with Prompt L-Pop only in groups of 6 months there were significant differences between enamel and dentin margins. At enamel margin there were no significant differences between microleakage of groups according to the passage of time (p > 0.05). CONCLUSION: The results of this study using two different bonding systems, indicate that adhesion to enamel was more valuable than dentin and perhaps systems that include self-etching primers are less sensitive to remaining moisture on dentin and they are less affected during different time periods.