Wear, mechanical and chemical properties of castor oil toothbrush bristles

Manual toothbrushes with polyamide bristles are used for daily oral hygiene. Toothbrush bristles made from alternative raw materials like castor oil are increasingly produced but scarcely investigated. Medium hardness toothbrushes with bristles made of castor oil (AlterraBambus (ALT), Alverde (ALV), Dr. BestGreenClean (DRB), HydrophilBambus (HYD), ProkudentRecycling (PRO)) and one control toothbrush (ADAcontrol (ADA)) (n=8) were investigated for wear, dentin-surface-roughness, elastic modulus and chemical composition. Toothbrushes were subjected to 12.5k, 25k, 37.5k and 50k cycles (toothbrush-simulator) simulating 6 months of toothbrushing. Macroscopic and microscopic (50× magnification, SEM/micro-CT) images of bristle-ends, surface and overall quality were evaluated before and after mentioned intervals according to DIN_EN_ISO_20126. Data were statistically analyzed (Friedman-Test; ANOVA). No obvious wear was visible in macroscopic images. SEM-images showed acceptable bristle-ends in ADA (100%) and DRB (100%), PRO (96%), ALV (87%), ALT (82%) and HYD (73%), while bristle-surfaces were unacceptable only in HYD at 0 and 12.5k cycles. Overall evaluation was acceptable in ADA and DRB (100%), PRO (96%) ALV (84%), ALT (82%) and HYD (51%) with significant difference in ALV and HYD at different intervals. Dentin-surface-roughness ranged from 3.4-3.8μm (HYD-ALT), dentin-abrasion ranged from 60-95μm (ALV-ALT) and elastic modulus ranged from 1.14-1.81GPa (PRO-ALT) at baseline and from 0.61-1.11GPa (PRO-ADA) after 50 k cycles. Bristles had similar elemental compositions: carbon (54.6-62.7%), nitrogen (19.4-24.3%) and oxygen (16.0-21.1%), in agreement with ADA. Bristles of toothbrushes except HYD had acceptable bristle ends and surfaces. Dentin-surface-roughness, mechanical and chemical properties of castor oil bristles were similar to those of conventional polyamide bristles. • Most toothbrushes with castor oil bristles had acceptable bristle end rounding • After six months of simulated toothbrushing signs of wear were minimal • Castor oil bristles had similar behavior and properties to polyamide bristles • Dentin surface roughness did not differ between toothbrushes • DIN EN ISO 20126 for manual toothbrushes should include bristle surface texture