# Efficiency of Orthodontic Adhesives: Influence of Saliva and Shear Direction—In Vitro Study

## TL;DR

This study found that saliva contamination reduces the bond strength of orthodontic adhesives, while applying force at a 45-degree angle improves it under dry conditions.

## Contribution

The study introduces shear force direction as a new variable in orthodontic bond-strength testing and evaluates adhesives under clinically relevant saliva contamination.

## Key findings

- Saliva contamination significantly reduces shear bond strength across all adhesive types.
- Applying shear force at 45° increases bond strength in dry conditions.
- Adhesive remnant index scores vary under contamination, indicating complex failure modes.

## Abstract

This in vitro study evaluated the shear bond strength (SBS) and adhesive remnant index (ARI) of orthodontic molar tubes bonded using conventional, hydrophilic, and self-etch adhesives under dry and saliva-contaminated conditions, while also assessing the impact of shear force direction. Extracted molars were bonded with Transbond XT™ (T), Transbond MIP™ (M), or Scotchbond Universal™ (S) under dry or saliva-contaminated conditions. Debonding was performed at 90° or 45°, introducing a clinically relevant but underexplored variable in orthodontic bond-strength testing. ARI scores were assessed via stereomicroscopy and visual inspection. Statistical tests (Kruskal–Wallis and Mann–Whitney) showed no significant SBS differences among adhesives under identical conditions (p > 0.05). However, all adhesives exhibited significantly reduced SBS under saliva contamination (p < 0.001; T: 5.4 vs. 4.1 MPa; M: 5.7 vs. 3.6 MPa; S: 5.5 vs. 4.5 MPa). In dry conditions, SBS was significantly higher with 45° debonding (p < 0.05). Under contamination, SBS varied by ARI score (p = 0.05), with ARI 0 specimens showing higher SBS than ARI 3. These findings confirm that moisture reduces bond strength across adhesive types, while 45° force application enhances SBS under dry conditions. ARI score variability under contamination may reflect complex failure modes.