Influence of external and internal surface roughness modifications on ceramic flexural strength

Ceramic materials are widely used in dental restorations due to their aesthetic and mechanical properties. Surface smoothness is known to influence ceramic durability. Prior research has shown that polishing can reduce surface defects, which may improve mechanical performance. However, the effect of polishing after external or internal adjustments remains unclear. No prior work had resolved how internal modifications interact with external polishing. This gap motivated an investigation into how different adjustment and polishing protocols affect ceramic surface roughness and flexural strength. Existing studies often focus on single adjustment types, but dual adjustments are common in clinical settings. The need for clarity on combined effects is evident. This study aims to address that uncertainty by comparing multiple adjustment and polishing combinations.

The aim of this study was to evaluate how external and internal adjustments, with or without polishing, affect ceramic surface roughness and flexural strength. Adjustments are routine in dental restorations but may introduce surface defects. The researchers propose that polishing could mitigate these effects. No prior work had resolved whether polishing after internal adjustments influences mechanical properties. The study tested six different adjustment and polishing protocols. The goal was to determine if polishing reduces roughness without compromising strength. This approach allows for a direct comparison of various clinical scenarios. The findings may inform best practices for ceramic restoration finishing.

Sixty bar-shaped ceramic specimens were fabricated from lithium disilicate and assigned to six groups. Each group underwent a specific adjustment and polishing protocol. Surface roughness was measured using Ra values. A 3-point bend test was used to assess flexural strength. Scanning electron microscopy (SEM) provided surface morphology data. The external and internal surfaces were ground with a diamond rotary instrument. Adjustments were made perpendicularly to the specimen’s long axis. Statistical analysis included 1-way ANOVA and post-hoc tests. The study design allowed for a controlled comparison of surface modifications and their mechanical outcomes.

Group EAP showed significantly lower surface roughness than G, EA, IA, and EIA (P<.001). EAP was similar to EPIA in roughness. No significant differences in flexural strength were found across all six groups (P=.081). SEM confirmed surface morphology changes after polishing. External adjustments without polishing did not alter roughness. Internal adjustments alone had no effect on strength. Polishing after external adjustments reduced roughness but not strength. The combination of external and internal adjustments with polishing did not improve mechanical performance.

The authors propose that polishing after external adjustments reduces surface roughness without affecting flexural strength. Internal adjustments alone do not alter mechanical properties. The combination of external and internal adjustments with polishing does not enhance strength. These findings suggest that polishing is beneficial for surface smoothness but not for mechanical performance. No significant differences in strength were observed across all groups. The study supports the use of polishing to improve aesthetics without compromising durability. The results align with the hypothesis that surface roughness and strength are not directly correlated. The authors did not propose future directions or new clinical guidelines.