Effect of incorporation of silane in the bonding agent on the repair potential of machinable esthetic blocks

Abstract

Objective: To investigate the repair potential of CAD/CAM (computer-aided design/computer-aided manufacturing) ceramic and composite blocks using a silane-containing bonding agent with different repair protocols.

Materials and methods: Twenty-four discs were constructed from CAD/CAM ceramic and composite blocks. The discs were divided into six groups according to surface pre-treatment employed; GI: Diamond stone roughening (SR), GII: SR+ silanization (SR+S), GIII: Hydrofluoric acid etching (HF), GIV: HF+ silanization (HF+S), GV: Silica coating (SC), GVI: SC+ silanization (SC+S). Silane-containing bonding agent (Single Bond Universal adhesive, 3M ESPE) was applied to the pre-treated discs. Prior to light curing, irises were cut from tygon tubes (internal diameter = 0.8 mm and height = 0.5 mm) and mounted on each treated surface. Nanofilled resin composite (Filtek Z350(XT), 3M ESPE) was packed into the cylinder lumen and light-cured (n = 10). The specimens were subjected to microshear bond strength testing (μ-SBS) using universal testing machine. Failure modes of the fractured specimens were analyzed using field emission scanning electron microscope (FESEM). Eight representative discs were prepared to analyze the effect of surface treatments on surface topography using FESEM. μ-SBS results were analyzed using ANOVA and Tukeys post-hoc test.

Results: Three-way ANOVA results showed that the materials, surface pre-treatment protocols, and silanization step had a statistically significant effect on the mean μ-SBS values at P ≤ 0.001. For ceramic discs, the groups were ranked; GIV (24.45 ± 7.35)> GVI ((20.18 ± 2.84)> GV (7.14 ± 14)= GII (6.72 ± 1.91)=GI (6.34 ± 2.21)=GIII (5.72 ± 2.18). For composite discs, groups were ranked; GI (24.98 ± 7.69)=GVI (24.84 ± 7.00) >GII (15.85 ± 5.29) =GV (14.65 ± 4.5)= GIV (14.24 ± 2.95)≥ GIII ((9.37 ± 2.78).

Conclusion: The additional silanization step cannot be omitted if the repair protocol comprises of either hydrofluoric acid etching or silica coating for both CAD/CAM esthetic restorative materials. However, this step can be suppressed by using silane-containing adhesive with diamond stone roughened repair protocol.

Keywords: Computer-aided design/computer-aided manufacturing esthetic blocks; microshear bond strength; repair; scanning electron microscopy; silane.

Figure 1

Bar chart representing the μ-SBS mean values of all tested groups

Figure 2

SEM photos of representative specimens from ceramic. (a) adhesive failure in HF group, (b) cohesive failure in HF+S group, (c) mixed failure in HF+S group, (d) mixed failure in SC+S group

Figure 3

SEM photos of representative specimens from indirect resin composite. (a) adhesive failure in HF group, (b) mixed failure in SR group, (c and d) mixed failure in SC+S group

Figure 4

SEM photos representing the surface topography of ceramic blocks (a) Control, (b) Diamond stone roughening, (c) Hydrofluoric acid etching, (d) Silica Coating. SR revealed uneven surfaces with pits and porosities [Figure 4b]. HF etching revealed micro-involutions and recess areas created by etching the glass ceramic [Figure 4c]. In SC group, micromechanical retentive features were evident (4D) with the presence of attached silica/alumina particles

Figure 5

SEM photos representing the surface topography of composite blocks. (a) Control, (b) Diamond stone roughening, (c) Hydrofluoric acid etching, (d) Silica Coating. SR revealed uneven surfaces with pits and porosities with the existence of the grinding marks from diamond stone [Figure 5b]. HF etching was associated with partial degradation of the resin matrix and little evidence of microprosities and undercuts [Figure 5c]. In SC group, micromechanical retentive features were evident with the presence of attached silica/alumina particles [Figure 5d]