Effect of salivary pH variations on the adhesive performance of Transbond XT and Orthocem in orthodontic bracket bonding

Objective: This in vitro study aimed to evaluate the shear bond strength of orthodontic brackets bonded to acrylic resin specimens with two adhesive systems, Transbond XT and Orthocem, under different salivary pH levels (4, 5, 6, and 7). Materials and methods: A total of 120 acrylic resin specimens (Brava Block®, FGM) were prepared and randomly assigned to three groups: control bonded with Transbond XT and Orthocem with no salivary exposure (n = 24), Transbond XT (n = 48), and Orthocem (n = 48). Each adhesive group was subdivided and immersed in artificial saliva at pH 4, 5, 6, or 7 for 30 days. Metal premolar brackets (Vector+ Roth prescription, Aditek®) were bonded following manufacturers’ protocols and subjected to shear bond strength testing using a Universal Testing Machine, following ISO 4049 standards. Data were analyzed with Analysis of Variance (ANOVA), t-test, and Tukey tests at a significance level of p < 0.05. Results: Transbond XT consistently showed higher bond strength than Orthocem across all pH levels. Maximum resistance was observed at pH 7 (21.19 ± 5.06 MPa), followed by the control group (19.64 ± 5.28 MPa). Orthocem demonstrated significantly lower values, ranging from 9.51 ± 3.87 MPa (pH 5) to 4.94 ± 2.15 MPa (pH 6). Acidic conditions reduced the bond strength of both adhesives, but Transbond XT maintained clinically reliable values, while Orthocem was more susceptible to performance decline at moderately acidic levels. Conclusions: Salivary pH directly influenced adhesive performance. Transbond XT demonstrated superior resistance under all conditions, whereas Orthocem showed lower but still clinically acceptable shear bond strength values, except at pH 6, where a marked decrease was observed.