In Vitro Evaluation of Manual, Electric, and Sonic Toothbrushing on Composite Restoration Surface Properties and Retention in Primary Teeth

Background: The longevity of composite restorations in primary teeth depends on the preservation of both mechanical performance and surface integrity under daily oral hygiene procedures. While powered toothbrushes have been widely investigated for plaque control, their potential effects on restorative materials in the primary dentition remain insufficiently characterized. This preliminary in vitro study evaluated the influence of manual, oscillating-rotating electric, and sonic toothbrushing on the surface microhardness, surface roughness, and shear resistance of resin composite restorations in primary teeth. Methods: Thirty extracted non-carious primary teeth were standardized, cavity-prepared, and restored using a self-etch adhesive system and a resin composite material. Specimens were randomly assigned to three groups (n = 10) according to brushing modality: manual, electric, or sonic. After a standardized 60 min brushing simulation under controlled conditions, surface microhardness was measured using a Vickers microhardness tester, surface roughness was assessed with contact profilometry, and restoration retention was evaluated as maximum load at failure under shear-type mechanical loading. Surface morphology was further analyzed by scanning electron microscopy. Results: No statistically significant differences were observed among groups in surface microhardness (p = 0.606) or maximum dislodgement load (p = 0.806). In contrast, surface roughness differed significantly according to toothbrush type (p < 0.001), with the highest Ra values recorded in the sonic group. Scanning electron microscopy corroborated these findings, showing progressively greater surface irregularities, porosities, and microdefects from manual to sonic brushing. Under the present in vitro conditions, the sonic toothbrush group showed the highest final surface roughness values, whereas no significant differences were observed in microhardness or restoration retention. Conclusions: Under the present short-term in vitro conditions, the sonic toothbrush group showed higher final surface roughness values than the manual and electric groups, while no significant differences were observed in microhardness or restoration retention. These results are limited to the specific toothbrush systems tested and these findings should be interpreted as preliminary in vitro results from an exploratory sample with limited statistical power.