Abstract
Objective: This study evaluated the durability of bond strength to dentin using total-etch (Single Bond /SB) and self-etch (Clearfil SE Bond/CSEB) adhesives associated with Nd:YAG Laser irradiation through the unpolymerized adhesives. Also, this study evaluated micromorfological chances in hybryd layer after 12 months wter storage.Material and Methods: Bovine incisors were worn to expose a dentin area and were divided into 4 groups (n = 15):Group 1 (Control) – SB + photopolymerization; Group 2 (Control) – CSEB + photopolymerization; Group 3 (Experimental/Laser) - SB + Nd:YAG laser (149.28 J/cm2) + photopolymerization; Group 4 (Experimental/Laser) – CSEB + Nd:YAG (149.28 J/cm2) + photopolymerization.Composite blocks were fabricated; intact teeth were stored for 24 h or 12 months (12 m), sectioned into beams and submitted to microtensile bond strength tests.Two teeth from each group (n = 2) were prepared for SEM analysis. Results: Results were analyzed by three-way ANOVA (adhesive, Technique and storage time) and Tukey tests (0.05). Results: For interaction Adhesive X Technique X Storage time the mean values (MPa) were:SB/Control/24h = 34.05(±6.14)a; CSEB /Control/24h = 32.12(±5.26)a; SB/Laser/24h = 30.54(±5.94)a; CSEB/Laser/24h = 29.45(±5.11)a; SB/Control/12m = 29.36(±5.57)a; CSEB/Control/12m = 29.09(±8.84)a; SB/Laser/12m = 22.06(±3.77)b; CSEB/Laser/12m = 13.35(± 3.35)c. Conclusion: SEM showed evident areas of micromorphological alterations on lased samples after 12 months water storage with accelerated degradation of the hybrid layer.Bond strength decreased when dentin irradiated with the Nd:YAG laser through unpolymerized adhesives was stored in water for 12 months.Laser irradiation of dentin through unpolymerized self-etch adhesive significantly reduced bond strength when compare with total-etch adhesive after 12 months water storage. Keywords:Dental adhesives; Dentin bonding; Nd yag; Tensile strength.
Highlights
After nearly 4 decades of research, composite restorations continues to have higher failure rates [1,2]
This study evaluated the durability of bond strength to dentin using total-etch (Single Bond /SB) and self-etch (Clearfil SE Bond/CSEB) adhesives associated with Nd:YAG laser irradiation through the unpolymerized adhesives
SB total-etch adhesive presented higher bon strength values compared with CESB selfetch adhesive (p = 0.0049), the unlased surface treatment presented higher bond strength values compared with lased surface treatment (p = 0.0000) and storage in water for 24 h presented higher bond strength values compared with storage in water for 12 months (p = 0.0001)
Summary
After nearly 4 decades of research, composite restorations continues to have higher failure rates [1,2] These failures have been observed mainly at the gingival margins of preparations for adhesive restorations, where the substrate is the dentin/cement junction [1]. The total-etch technique can result in an excessive etching and formation of a deep zone of demineralized dentin; the adhesive may not infiltrate throughout the entire decalcified area, originating a hybrid layer with regions of exposed collagen fibers more susceptible to hydrolysis (weak zone) [3]. Self-etching adhesives are composed of acidic resin monomers that simultaneously promote superficial dentin demineralization and resin adhesive infiltration into the dentin tissue [5] These adhesive reduce the possibility of weak zone formation, the clinical steps, and the technique sensitivity as regards maintenance of dentin humidity [6]. The longevity of hybrid layer has been still widely questioned as a consequence of hydrolysis of the adhesive interface over time
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