ABSTRACT
Objective: To assess the color stability and translucency of full cubic stabilized zirconia (FSZ) following orthodontic bonding with different surface treatments and coffee thermocycling (CTC). Methods: This in vitro study was conducted on 120 disc-shaped specimens of FSZ. Thirty specimens were selected as the control group and remained intact. The remaining specimens were randomly divided into three groups based on the type of surface treatment (n = 30): airborne particle abrasion (APA), silica-coating (CoJet), and carbon dioxide (CO2) laser. After metal bracket bonding in the test groups, debonding and polishing were performed. Subsequently, all specimens underwent CTC (10,000 cycles). Color parameters, color difference (ΔE00), and translucency parameter (TP) were measured three times at baseline (t0), after debonding and polishing (t1), and after CTC (t2). Data were statistically analyzed (α = 0.05). Results: Significant difference existed among the groups regarding ΔE00t0t2 (p < 0.001). The APA group showed minimum (ΔE00 = 1.15 ± 0.53) and the control group showed maximum (ΔE00 = 0.19 ± 0.02) color stability, with no significant difference between the laser and CoJet groups (p = 0.511). The four groups were significantly different regarding ΔTPt0t2 (p < 0.001). Maximal increases in TP were noted in the CoJet (1.00 ± 0.18) and APA (1.04 ± 0.38) groups while minimal increase was recorded in the control group (0.1 ± 0.02). Conclusions: Orthodontic treatment makes zirconia restorations susceptible to discoloration and increased translucency. Nonetheless, the recorded ΔE00 and ΔTP did not exceed the acceptability threshold.
ABSTRACT
OBJECTIVES: Information regarding the effects of orthodontic bracket debonding on zirconia restorations, and the preferred method for residual adhesive removal from the zirconia restoration surface is lacking. Thus, this study aimed to assess the effects of different methods of residual adhesive removal after orthodontic bracket debonding on flexural strength, surface roughness, and phase transformation of high-translucent (HT) zirconia. MATERIALS AND METHODS: This in vitro study evaluated 72 bar-shaped HT zirconia specimens; 18 specimens were assigned to the control group. Metal brackets were bonded to the remaining specimens by resin cement. After bracket debonding, the residual adhesive on the surface of specimens was removed by three methods (n=18): a 30-flute tungsten-carbide (TC) bur at low speed, an ultrafine diamond bur at high speed, and Er:YAG laser irradiation. The surface roughness (Ra and Rz) was measured. X-ray diffraction (XRD) analysis was carried out, and the flexural strength was measured as well. Data were statistically analyzed (α=0.05). RESULTS: Before polishing, all methods increased the Ra and Rz values (P<0.05) except for the diamond bur yielding a Rz value comparable to that of the control group. The Ra values of the test groups were comparable after polishing, and still higher than that of the control group (P<0.05). The flexural strength of all three test groups was comparable (P>0.05), and significantly lower than that of the control group (P<0.001). The monoclinic phase was not observed in any group. CONCLUSIONS: Orthodontic bracket debonding adversely affects the surface roughness and flexural strength of zirconia despite polishing.
