# Precision in Prosthodontic Preparation: An In Vitro Study on the Digital Evaluation of Total Occlusal Convergence Angles Using Varying Magnification Loupes

## TL;DR

This study shows that using magnification loupes improves the precision of tooth preparation angles, with higher magnification providing better results.

## Contribution

The study demonstrates that magnification loupes, especially 6× Keplerian, improve precision in prosthodontic preparation angles.

## Key findings

- Magnification loupes significantly reduce total occlusal convergence angles compared to no magnification.
- 6× Keplerian loupes provide better precision in the mesiodistal plane than 3.2× Galilean loupes.

## Abstract

Background

Precise control of the total occlusal convergence (TOC) angle during tooth preparation is essential for the long-term success of fixed dental restorations. While magnifying loupes combined with proper illumination enhance visual acuity, their influence on the precision of the TOC angle during preparation remains insufficiently studied.

Objective

This study aimed to evaluate the impact of magnification loupes on TOC angle accuracy. Specifically, it compared mean TOC values in two planes for tooth preparations performed without magnification, with 3.2× Galilean loupes, and with 6× Keplerian loupes.

Materials and methods

Ninety right mandibular first molar typodont teeth were randomly assigned to three groups (n=30 each): control (no magnification), 3.2× Galilean, and 6× Keplerian. A single trained operator, who was a postgraduate student with formal training in tooth preparation techniques but no prior experience of using magnification loupes, performed standardized full-coverage crown preparations. Each specimen was mounted on a custom die base to ensure consistent positioning. Digital images were captured in buccolingual and mesiodistal planes, and TOC angles were measured using computer screen protractor software, referencing the gingival 2 mm of the axial wall following a study by Yoon et al. A blinded evaluator recorded all measurements. Statistical analysis was conducted using one-way analysis of variance (ANOVA) and Tukey’s post hoc test (α=0.05).

Results

Both magnification groups demonstrated significantly lower TOC angles compared to the control group in both planes (P=0.001). The 6× Keplerian group achieved significantly lower TOC angles than the 3.2× Galilean group in the mesiodistal plane, though no significant difference was observed in the buccolingual plane.

Conclusion

The use of magnification loupes enhances the precision of TOC angle assessment during tooth preparation. Higher levels of magnification, especially with 6× Keplerian loupes, provide superior control in the mesiodistal dimension, thereby contributing to improved clinical outcomes in prosthodontic procedures.