COMPARATIVE ANALYSIS OF SHEAR BOND STRENGTH IN ORTHODONTIC BRACKETS: SELF-ETCH PRIMERS VERSUS CONVENTIONAL ACID ETCHING – AN IN VITRO STUDY

Abstract

This in vitro study aimed to compare the shear bond strength (SBS) and failure modes of orthodontic brackets bonded with a self-etch primer (SEP) system versus conventional acid etching. Fifty non-carious human premolars were randomly divided into two groups: Group A (conventional acid etching with 37% phosphoric acid) and Group B (SEP: Fusion Bond 7). Brackets were bonded using a light-cure adhesive, and SBS was tested after 24 hours using a universal testing machine. The Adhesive Remnant Index (ARI) was assessed to evaluate failure modes. Results revealed a statistically significant difference in SBS, with Group A exhibiting higher mean bond strength (64.84 ± 55.43 MPa) compared to Group B (49.16 ± 26.79 MPa; *p* = 0.008). Despite lower SBS, the SEP group demonstrated clinically acceptable bond strength (6–8 MPa). ARI scores indicated distinct failure patterns: cohesive failures dominated in Group A (60% score 2, 28% Score 3), while Group B showed adhesive failures at the enamel interface (52% score 1, 36% Score 0), leaving minimal residual adhesive. The conventional method’s higher variability (SD = 55.43 MPa) highlighted its technique sensitivity, whereas SEPs simplified bonding by eliminating rinsing and drying steps, reducing chairside time and contamination risks. These findings underscore the trade-off between bond strength and procedural efficiency. While conventional acid etching remains optimal for high-stress scenarios (ceramic brackets), SEPs offer a minimally invasive alternative, prioritizing enamel preservation and ease of use in moisture-sensitive environments. However, the study’s in vitro design limits clinical extrapolation, warranting further research with thermal cycling and long-term clinical trials. Orthodontists should select bonding protocols based on clinical demands, balancing strength, efficiency, and enamel integrity.