Does the universal adhesive's film thickness affect dentin-bonding effectiveness?

OBJECTIVES: To investigate the influence of adhesive resin application modalities on the film thickness of the adhesive resin and the effectiveness of a two-step universal adhesive (UA) bonded in self-etch (SE) bonding mode to high C-factor class-I cavity-bottom dentin. MATERIALS AND METHODS: After application of the primer of G2-Bond Universal (G2B, GC), the adhesive resin was applied into standard class-I cavities (human molars) following four application modalities: (1) one layer, strongly air-blown; (2) one layer, gently air-blown; (3) two layers, each gently air-blown; (4) one layer, not air-blown. After being restored with composite, each tooth was sectioned to obtain one micro-specimen (n = 10), of which the adhesive resin film thickness was measured using optical microscopy. The micro-tensile bond strength (µTBS) was tested immediately or upon 100,000 thermocycles. Statistical analyses involved Kruskal-Wallis and Mann-Whitney U testing (p < 0.05). RESULTS: G2B's µTBS was significantly affected by the adhesive resin application modality and aging. Gently air-blowing the adhesive resin resulted in significantly higher immediate µTBS than strong air-blowing or no air-blowing. No significant difference in µTBS was found between single or double gently air-blown adhesive resin applications. The adhesive resin film thickness significantly varied with the application modalities. CONCLUSIONS: A too thin or too thick adhesive resin film thickness adversely affected bond strength of the two-step UA applied in SE mode and high C-factor condition. CLINICAL RELEVANCE: The adhesive resin layer thickness can affect the bonding performance of two-step UAs in high C-factor cavities. Dental clinicians remain advised to avoid improper air-blowing of UAs and strictly follow the application instructions.

Multi-Parameter Characterization of HEMA/BPA-free 1- and 2-step Universal Adhesives Bonded to Dentin.

PURPOSE: This study aimed to investigate the bonding effectiveness of two HEMA/BPA-free universal adhesives (UAs) to flat dentin, to characterize their adhesive-dentin interfacial ultrastructure, and to measure their water sorption (Wsp), water solubility (Wsl), and hydrophobicity. MATERIALS AND METHODS: The immediate and aged (50,000 thermocycles) microtensile bond strength (µTBS) to flat dentin of the HEMA/BPA-free UAs Healbond Max (HbMax; Elsodent) and Healbond MP (HbMP; Elsodent) as well as the reference adhesives OptiBond FL (Opti-FL; Kerr), Clearfil SE Bond 2 (C-SE2; Kuraray Noritake), and Scotchbond Universal (SBU; 3M Oral Care) was measured. The adhesive-dentin interfaces of HbMax and HbMP were characterized by TEM. Wsp and Wsl of all adhesive resins and of the primer/adhesive resin mixtures of HbMax, Opti-FL, and C-SE2 were measured. Hydrophobicity was determined by measuring the contact angle of water dropped on adhesive-treated dentin. RESULTS: In terms of µTBS, HbMax and HbMP performed statistically similarly to Opti-FL and C-SE2, but outperformed SBU. Aging only significantly reduced the µTBS of SBU when applied in E&R bonding mode. TEM revealed typical E&R and SE hybrid-layer ultrastructures at dentin, while electron-lucent globules of unknown origin, differing in size and shape, were observed within the adhesive resin of HbMP and even more frequently in that of HbMax. Higher Wsp was measured for the primer/adhesive resin mixtures than for the adhesive resins. Opti-FL was more hydrophobic than all other adhesives tested. CONCLUSION: The HEMA/BPA-free UAs bonded durably to flat dentin with bond strengths comparable to those of the gold-standard E&R/SE adhesives and superior to that of the HEMA/BPA-containing 1-step UA.

Bonding of Composite Cements Containing 10-MDP to Zirconia Ceramics Without Dedicated Ceramic Primer.

PURPOSE: To measure zirconia-to-zirconia microtensile bond strength (µTBS) using composite cements with and without primer. MATERIALS AND METHODS: Two Initial Zirconia UHT (GC) sticks (1.8x1.8x5.0 mm) were bonded using four cements with and without their respective manufacturer's primer/adhesive (G-CEM ONE [GOne] and G-Multi Primer, GC; Panavia V5 [Pv5]), and Panavia SA Cement Universal [PSAu], and Clearfil Ceramic Plus, Kuraray Noritake; RelyX Universal (RXu) and Scotchbond Universal Plus [SBUp], 3M Oral Care). Specimens were trimmed to an hour-glass shaped specimen whose isthmus is circular in cross-section. After 1-week water storage, the specimens were either tested immediately (1-week µTBS) or first subjected to 50,000 thermocycles (50kTC-aged µTBS). The fracture mode was categorized as either adhesive interfacial failure, cohesive failure in composite cement, or mixed failure, followed by SEM fracture analysis of selected specimens. Data were analyzed using linear mixed-effects statistics (α = 0.05; variables: composite cement, primer/adhesive application, aging). RESULTS: The statistical analysis revealed no significant differences with aging (p = 0.3662). No significant difference in µTBS with/without primer and aging was recorded for GOne and PSAu. A significantly higher µTBS was recorded for Pv5 and RXu when applied with their respective primer/adhesive. Comparing the four composite cements when they were applied in the manner that resulted in their best performance, a significant difference in 50kTC-aged µTBS was found for PSAu compared to Pv5 and RXu. A significant decrease in µTBS upon 50kTC aging was only recorded for RXu in combination with SBUp. CONCLUSION: Adequate bonding to zirconia requires the functional monomer 10-MDP either contained in the composite cement, in which case a separate 10-MDP primer is no longer needed, or in the separately applied primer/adhesive.