Comparison of shear bond strength of orthodontic tube in glazed zirconia prostheses according to the surface treatment methods

Abstract

Current studies on zirconia bond strength mostly focus on “naked zirconia”, the inside of the zirconia crown. In the orthodontic field, tube bonding is required on the surface-“glazed” crown. In this study, shear bond strengths were measured and compared by bonding tubes not on “naked zirconia” but on “glazed zirconia” using various methods. A control group was established when bonding the tube on the glazed porcelain surface using the usual methods. After glazing one side of zirconia block and dividing the experimental groups into four random groups, the tubes were bonded by using different processing methods on each of the surfaces and using different primers.

Control group : 50-µm Al2O3 + HF + Porcelain primer Experimental group 1 : 50-µm Al2O3 + HF + Porcelain primer Experimental group 2 : 50-µm Al2O3 + Zirconia primer Experimental group 3 : 30-µm silica-coated alumina particles + Porcelain primer Experimental group 4 : 110-µm silica-coated alumina particles + Porcelain primer

Shear bond strength in each of the groups was measured by using a universal test machine. Surface characteristics were observed on the glazed surface by using SEM and a 3D optical profiler prior to applying primer, and specimens were classified according to the failure patterns. The results were as follows :

1. Shear bond strength of experimental group 2 was 10.59 MPa, which was significantly lower than all other groups (p < .05). 2. Two groups, the control group and experimental group 1 were clearly observed in the SEM images to have similar rough surfaces and cracks. However, experimental groups 2, 3 and 4 were observed as having particles attached. Experimental group 4 was observed as having bigger sized particles and more irregular rough surfaces compared to experimental groups 2 and 3. In addition, according to the results of analysis using a 3D optical profiler, the average surface roughness Sa value in experimental group 3 was significantly lower than the values for experimental groups 1, 2, 4 (p < .05). The Sa value in the control group was significantly lower than the values for experimental groups 2, 4 (p < .05). However, no significant difference was recorded among the other groups (p > .05). 3. As for the failure type of debonding surface, only adhesive failure was manifest between zirconia block surface and resin cement interface in experimental group 2. In the rest of the groups, adhesive failure between resin cement and tube base interface was mostly manifest. Therefore, this reveals a significant difference between the experimental group 2 and the rest of the groups (p < .001).

According to the results of this study, using porcelain primer after sandblasting with silica coating particles is clinically simpler, safer and more effective method in relation to glazed zirconia crown because it has a similar high shear bond strength compared to other methods without the need for hydrofluoric acid.