Press-on force during polishing of resin composite restorations.

Objective: To measure the press-on force during the polishing of composite restorations carried out by 10 dentists in a clinically simulated procedure.

Methods: Composite restorations (Tetric EvoCeram Bulk Fill) were placed in standardized Class II two-surface cavities in first upper acrylic molars. The surfaces were roughened by sandblasting (50μm, 1bar). The tooth was mounted on a tailor-made device with a 3D force sensor (Kistler, Z21134-300, 10Hz). Ten dentists (7 male, 3 female) polished one Class II restoration each using the one-step polishing system OptraPol together with a dental handpiece and water spray. The dentists were allowed to use all shapes of the polishing system (small flame, large flame, cup, lens). During polishing, the press-on forces measured for up to 2 minutes. Simultaneously, the polishing procedure was recorded with a digital camera to correlate the forces with the polishing shapes and movements.

Results: In total, 17,999 force measurements were available for analysis. The mean forces of all operators varied between 0.77(±0.63) N and 2.23(±1.48) N; the difference was statistically significant (ANOVA, post-hoc Tukey B, p<0.05). All dentists exerted maximum forces higher than 3 N (between 3.3N and 18.3N). Force values exceeded 2N during 25% of the polishing time. Female dentists polished with a statistically significant lower force than male dentists (ANOVA, p<0.001). Polishing with the large flame and the cup generated significantly higher forces than polishing with the small flame and the lens (ANOVA, post hoc Tukey B, p<0.01).

Conclusions: The press-on forces applied during polishing varied significantly between dentists and within the same dentist. In about 25% of the polishing time, forces were above the 2N limit, which is recommended by some manufacturers as the maximum polishing force. Test institutes and manufacturers should evaluate the polishing performance of polishing instruments with various press-on forces.