Effects of remaining dentin thickness on the bond strength of bleached dentin

Abstract

Background: The bond strength of resin composites to dentin was reported to be related to either the remaining dentin thickness (RDT) or bleaching treatment. However, information is limited regarding the effects of RDT on the bond strength of bleached dentin. The present study aimed to investigate the effects of RDT on the microshear bond strength (μSBS) of resin cement to bleached dentin. Methods: A total of 120 dentin specimens were prepared and randomly divided into 2 groups: a bleaching group (group B) and a control group (group C). Hydrogen peroxide with a concentration of 35% (Ultradent, USA) was applied on the dentin surface for 2 × 1 d for group B, while no bleaching treatment was performed for group C. After the treatment, the specimens were finished and polished to obtain different RDTs (2, 1, and 0.5 mm) and divided into 3 groups of 20 specimens each. The bonding procedure was performed using Panavia V5 (Kuraray, Japan) with a bonding area of 0.785 mm 2. For each group, half of the specimens were subjected to 5000 thermal cycles (subgroup T), while the other half did not receive thermocycling (subgroup N) (n = 10). The specimens were then subjected to the μSBS test using a universal testing machine. Data were analyzed by a three-way analysis of variance (α = 0.05). The fracture modes of the specimens were confirmed with a measuring microscope. Representative specimens with different fracture modes were observed with scanning electron microscopy (SEM). Results: The μSBS values were significantly affected by bleaching treatment (p < 0.001), whereas no significant effect was observed for thermocycling (p = 0.293). In terms of RDT, a significantly different μSBS value was found among the subgroups with different RDTs in group C (p = 0.003). However, the RDT did not significantly affect the μSBS values of bleached dentin in group B (p = 0.779). The μSBS values were significantly lower in group B than in group C (p < 0.001). A higher percentage of adhesive failure was observed in group B than in group C. Conclusion: Based on the present findings, it can be concluded that the RDT did not affect the bond strength of resin cement to bleached dentin. Clinical significance: Since RDT did not affect the bond strength of resin cement to bleached dentin, bonding procedures should not be performed immediately after intracoronal bleaching, even if the dentin is planned to be removed due to a tooth preparation process.

Does the application of whitening dentifrices during at-home bleaching affect the bond strength of resin composite to dentin?

“…A predominance of adhesive fracture at the enamel-composite interface was observed in all groups except group 4 (control), whereas the least frequently identified fracture was the cohesive failure in most of the study groups. Previous studies also demonstrated a higher percentage of adhesive failure in the samples submitted to whitening treatments [ 11 , 12 , 39 ]. There was no significant difference in the distribution of failure mode among the study groups.…”

“…The findings of this study also imply that extending the polymerization time of adhesive systems would have no beneficial effect on adhesion to a whitened dentin surface. Therefore, clinicians should focus on other approaches to increase bond strength after tooth whitenings such as the extended waiting time before a restorative procedure or the application of an antioxidant on the bleached substrate [ 12 , 13 ].…”

“…It appears that other factors are involved in jeopardizing the bond strength after the application of bleaching agents such as decreased mineral content and increased roughness and porosity of the enamel/dentin surface [ 11 , 14 ]. Another factor that may contribute to the reduction in bond strength is the collapse or degradation of the dentin collagenous network as a result of dehydration or activation of metalloproteinase enzymes [ 12 , 13 ]. The presence of residual oxygen inside the dental structure can also damage the bonding materials [ 38 ] or interfere with the formation of resin tags and the hybrid layer [ 21 ], and in this way, account for the decrease in bond strength values.…”

“…Furthermore, the effect of aging protocols was not considered in the present study. However, some studies reported that exposure to long-term water storage or thermocycling did not significantly impair the bond strength to enamel/dentin [ 12 , 14 , 46 ]. Another limitation of this study was that the specimens were kept in normal saline solution between the whitening treatments instead of artificial saliva and this may differ from the clinical conditions where the remineralizing potential of saliva may repair the effects of whitening agents on tooth structure.…”

Effect of Antioxidant and Buffering Agent Mixture on Dentin Shear Bond Strengths of Laminate Veneer and pH Change of External Medium After Intracoronal Bleaching

“…6 Another common side effect is the decreased bond strength. 7,8 The presence of residual oxygen and peroxide from the bleaching agent may provoke the decrement of the bonding strength in bleached teeth according to some bleaching studies.…”