# Evaluation of Shear Bond Strength and Surface Morphology (via SEM) of Different Provisional Crowns and Surface Treatments to PMMA

## TL;DR

This study compares how well different temporary crown materials stick to PMMA after various surface treatments, finding that autopolymerizing PMMA performed best.

## Contribution

The study introduces a novel comparison of shear bond strength across multiple provisional crown materials and surface treatments using PMMA relining.

## Key findings

- PMAC (autopolymerizing PMMA) showed the highest shear bond strength (26.85 MPa) compared to other materials.
- Surface treatments with methylene chloride or acetone on PLAD did not significantly improve bond strength.
- PLAD and PLAI materials exhibited 100% adhesive failure, while PMAC, PMAM, and PMAD showed mixed failure modes.

## Abstract

To compare the shear bond strengths (SBSs) of different provisional crown materials with various surface treatments when relined with autopolymerizing polymethyl methacrylate (PMMA).

Part 1: Seventy‐five specimens were divided into five groups: PMAC (autopolymerizing PMMA), PMAM (CAD/CAM system PMMA), PMAD (3D‐printed PMMA), PLAI (injectable polylactic acid [PLA]), and PLAD (3D‐printed PLA). All specimens were surface‐treated by sandblasting followed by 180 s of MMA application, then relined with autopolymerizing PMMA. Part 2: Forty‐five PLAD specimens were divided into three groups: PLAD (control), PLAD MC (methylene chloride treatment), and PLAD AT (acetone treatment), then relined with autopolymerizing PMMA. All samples underwent thermocycling before being evaluated for SBS with a universal testing machine (Shimadzu, Japan). Statistical analysis was performed using one‐way ANOVA and Tukey’s HSD at a significance level of p ≤ 0.05. Failure modes were examined using a stereomicroscope, and surface morphology was evaluated by scanning electron microscopy (SEM).

In Part 1, the mean SBS values in MPa were: PMAC (26.85 ± 1.31), PMAM (22.92 ± 1.20), PMAD (13.98 ± 1.20), PLAI (10.19 ± 1.59), and PLAD (8.44 ± 1.14). Significant differences were found between all groups (p ≤ 0.05). In Part 2, the mean SBS values in MPa were: PLAD (8.44 ± 1.14), PLAD MC (8.35 ± 0.84), and PLAD AT (7.83 ± 1.13). No significant differences were found between the three groups (p  > 0.05). PMAC, PMAM, and PMAD exhibited mixed failure modes in 87.5%, 80%, and 73.3% at the fractured surfaces of the specimens, respectively. In contrast, PLAD and PLAI displayed 100% adhesive failure. PLAD, PLAD MC, and PLAD AT also showed 100% adhesive failure at fractured surfaces.

The PMAC group achieved the highest SBS among all tested materials. Surface treatment of PLAD with methylene chloride or acetone did not significantly improve SBS compared to the untreated control.