Abstract
ABSTRACTObjective:This study evaluated the hardness and modulus of elasticityof the dentin bond interface using total-etch (Single Bond /SB) and self-etch (Clearfil SE Bond/CSEB) adhesives associated with Nd:YAG Laser irradiation through the unpolymerized adhesives.Material and Methods: The occlusal surfaces of 12 human third molars were ground until superficial dentin was exposed. A standardized circular cavity was performed on the occlusal surface. Specimens were sectioned in the mesio-distal direction, and the 24 hemi-crowns were divided into four groups: Group SB/Control - SB + polymerization; Group SB/Laser - SB + Nd:YAG laser (174.16J/cm2/60s/non-contact) + polymerization; Group CSEB/Control – CSEB + polymerization; Group CSEB/Laser - CSEB + Nd:YAG laser (174.16J/cm2/cm2/60s/non-contact) + polymerization. Composite were placed in the cavities and polymerized. The specimens were immersed in distilled water and stored in an oven at 37ºC for 24h and then submitted to nanoindentation in a Nano Indenter® XP appliance. Results: The results were submitted to ANOVA, Tukey’s test and Student's-t test (p < 0.05). Conclusão: It was concluded that the application of the Nd:YAG laser in both adhesive systems did not changed the hybrid layer hardness; however, it increases the modulus of elasticity in the hybrid layer for both adhesives tested and it maybe preserves the integrity of the adhesive interface and its durability. Clinical relevance: The application of Nd:YAG laser prior to photopolymerization of adhesive systems can increase the modulus of elasticity in the hybrid layer and may contribute to stress distribution in the adhesive interface during the polymerization preserving the integrity of the adhesive interface and its durability.
Highlights
S ince the introduction of the acid etching technique by Buonocore et al [1] in 1955, dental materials and restorative techniques have being modified to improve longevity and durability of restorations
The hypotheses tested were: a) Nd:YAG laser does not interfere in the nanohardness of the hybrid layer; b) Nd:YAG laser does not interfere in the modulus of elasticity of the hybrid layer; c) The hybrid layer does not show differences in the hardness and modulus of elasticity when compared to the adhesive layer, with or without laser irradiation
In order to obtain the values of the modulus of elasticity, the effect of the indenters that are not perfectly rigid; that is to say, the deformations they undergo are taken into consideration with the introduction of the socalled reduced elastic modulus Er, defined by the equation: The specimens were individually tested, and the nanohardness and modulus of elasticity (GPa) values were submitted to ANOVA and Tukey tests, at a level of significance of 5% (p < 0.05)
Summary
S ince the introduction of the acid etching technique by Buonocore et al [1] in 1955, dental materials and restorative techniques have being modified to improve longevity and durability of restorations. The results obtained in that study showed a significant increase in bond strength and proved the recrystallization of dentin8 This methodology was later studied by other authors, who found a positive influence on bond strength [9,10,11,12] and reduction in nanoleakage [13] with the use of this dentin treatment. From the conventional microhardness tests, a great deal of quantitative information is obtained from the load-displacement data, as opposed to only visual observations of the indentation in the sample [14,15,16] This in vitro study uses the nanoindentation technique to evaluate the mechanical properties (nanohardness and modulus of elasticity) of the bond interface between human dentin and a conventional (Single Bond) or self-etching (Clearfil SE Bond) adhesive system, with or without Nd:YAG laser treatment before light polymerization. The hypotheses tested were: a) Nd:YAG laser does not interfere in the nanohardness of the hybrid layer; b) Nd:YAG laser does not interfere in the modulus of elasticity of the hybrid layer; c) The hybrid layer does not show differences in the hardness and modulus of elasticity when compared to the adhesive layer, with or without laser irradiation
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