Effect of Varying Working Distances between Sandblasting Device and Composite Substrate Surface on the Repair Bond Strength

Abstract

This study investigates the effect of defined working distances between the tip of a sandblasting device and a resin composite surface on the composite-composite repair bond strength. Resin composite specimens (Ceram.x Spectra ST (HV); Dentsply Sirona, Konstanz, Germany) were aged by thermal cycling (5000 cycles, 5-55 °C) and one week of water storage. Mechanical surface conditioning of the substrate surfaces was performed by sandblasting with aluminum oxide particles (50 µm, 3 bar, 10 s) from varying working distances of 1, 5, 10, and 15 mm. Specimens were then silanized and restored by application of an adhesive system and repair composite material (Ceram.x Spectra ST (HV)). In the negative control group, no mechanical surface pretreatment or silanization was performed. Directly applied inherent increments served as the positive control group (n = 8). After thermal cycling of all groups, microtensile repair bond strength was assessed, and surfaces were additionally characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The negative control group reached the significantly lowest microtensile bond strength of all groups. No significant differences in repair bond strength were observed within the groups with varying sandblasting distances. Composite surfaces sandblasted from a distance of 1 mm or 5 mm showed no difference in repair bond strength compared to the positive control group, whereas distances of 10 or 15 mm revealed significantly higher repair bond strengths than the inherent incremental bond strength (positive control group). In conclusion, all sandblasted test groups achieved similar or higher repair bond strength than the inherent incremental bond strength, indicating that irrespective of the employed working distance between the sandblasting device and the composite substrate surface, repair restorations can be successfully performed.

Keywords: aluminum oxide sandblasting; composite repair; microtensile bond strength; working distance.

Figure 1

Experimental design.

Figure 2

Microtensile repair bond strengths (MPa) of composite surfaces after sandblasting from varying working distances. Significant differences between groups are indicated by different letters (p < 0.05). Within each boxplot, the median is represented by a horizontal bold black line. The 25% and 75% data quartiles are shown as boxes, and the whiskers mark the 1.5 × interquartile range (IQR) at the 25th and 75th percentile of each group. The outliers of groups 2 and 4 are shown as circles.

Figure 3

Percentage (%) of failure mode distribution per group.

Figure 4

Scanning electron microscopy (SEM) images (5000× magnification) of the composite surfaces of all groups. G1: positive control group; G2: negative control group; G3–G6: composite substrate surfaces sandblasted from working distances of 1 mm (G3), 5 mm (G4), 10 mm (G5), and 15 mm (G6).