Shear bond strength of metallic orthodontic brackets to zirconium crowns treated by sandblasting compared to enamel using a universal adhesive: An in vitro study.

OBJECTIVES: Orthodontic brackets are increasingly bonded to the surface of zirconium crowns due to the growing aesthetic demands in adults' restorations. Therefore, providing a reliable bond between these substrates is of great importance. This study aimed at investigating the shear bond strength (SBS) of orthodontic metal brackets bonded to zirconium treated by sandblasting. In addition, the value was compared with SBS between metal brackets and enamel. MATERIALS AND METHODS: Samples were divided into three groups including first premolar enamel specimens (n=20), untreated zirconium blocks (n=20) and sandblasted zirconium blocks (n=20). Enamel specimens underwent etching and bonding procedures using 37% phosphoric acid and 3M™ Scotchbond™ Universal adhesive. Zirconium blocks were randomly allocated to two groups. The first group was prepared by sandblasting with 50µm aluminium oxide particles (Al2O3) under 4 bars pressure followed by bonding brackets with 3M™ Scotchbond™ Universal adhesive. Metal brackets were also bonded to the untreated zirconium group using the same adhesive. All samples underwent thermocycling, and SBS was calculated using a universal testing machine with a crosshead speed of 1mm/min. Data were analysed using One-way Anova and Tukey's tests. RESULTS: The highest SBS was recorded in sandblasted zirconium group (26.17±8.22MPa) followed by enamel group (23.667±7.00MPa) and untreated zirconium group (11.49±7.00MPa). There was a significant difference between the SBS of untreated zirconium and that of two other groups. CONCLUSION: Perfect SBS was achieved by sandblasting pre-treatment, comparable to that of enamel. Therefore, sandblasting of zirconium crowns is recommended prior to bonding orthodontic brackets.

Effect of Bleaching Mouthwash on Force Decay of Orthodontic Elastomeric Chains.

INTRODUCTION: Force decay elastomeric chains are significant, and it is a clinical problem. AIM: The aim of this study was to evaluate the effects of bleaching agent in the mouthwash on the force decay of orthodontic chains. MATERIALS AND METHODS: In this experimental study, 160 gray closed elastomeric chains were randomly divided into three groups (one control and two test groups). Four loops of chains were stretched for 25 mm on custom-made jig. Control group specimens were immersed in artificial saliva during the test period. Test group specimens were immersed twice a day for 30 seconds in the whitening (LISTERINE® HEALTHY WHITE™) and daily sodium fluoride (LISTERINE® TOTAL CARE ZERO) mouthwashes. All specimens were immersed in artificial saliva at 37°C. Force was measured at different time points (initial, 1, 7, 14, 21, 28 days). Statistical analysis was performed by two-way analysis of variance (ANOVA) and Bonferroni methods (a = 0.05). RESULTS: Force of elastomeric chains was decreased dramatically in all groups during the experiment. After 24 hours, force was decreased by 42.18, 48.34, and 53.38% in control group, daily, and bleaching mouthwash groups respectively. The corresponding numbers after 4 weeks were 66.30, 76.73, and 86.48. The difference between three groups at days 1 and 28 was statistically significant (p < 0.05). CONCLUSION: Within the limitations of the current in vitro study, bleaching and sodium fluoride mouthwashes could cause force decay of orthodontic elastomeric chains. Whitening mouthwash is more weakening for elastomeric chains. CLINICAL SIGNIFICANCE: Use of whitening mouthwash by orthodontic patients could decrease the force of elastomeric chains, so it could be recommended to use them for a short time.

The effect of toothpastes with bleaching agents on the force decay of elastomeric orthodontic chains.

OBJECTIVE: The aim of this study was to evaluate the effect of agents available in whitening toothpastes (Crest® and Sensodyne®) in vitro on the force decay of elastomeric chains used in orthodontics. MATERIALS AND METHODS: A total of 300 specimens of elastomeric chains were divided into five groups (n = 60) and were evaluated. These groups included (1) the regular Crest® toothpaste and distilled water solution, (2) whitening Crest® toothpaste and distilled water solution, (3) regular Sensodyne® toothpaste and distilled water solution, (4) whitening Sensodyne® toothpaste and distilled water solution, and (5) distilled water as a control group. The samples' force was measured using Instron at intervals of 0, 1, 7, 14, 21, and 28 days. Data were analyzed by SPSS software. RESULTS: At the initial time point, the difference in the force values of elastomeric chain between any of the groups was not significant (P > 0.05). On the 1st day, there was a significant difference (P < 0.05) between all groups except the groups of whitening Crest®, regular, and whitening Sensodyne® (P > 0.05). On days 7, 14, and 28, the rate of decline for all groups was statistically significant (P < 0.05). CONCLUSIONS: According to the results obtained in the present study, it seems that toothpastes without whitening agents have less effect on force decay of elastomeric chain over time.