In vitro comparison of two types of toothbrush bristles in penetration capacity into the peri- implant sulcus.

Aim: The aim of this preclinical study was to compare the ability of the conical and cylindrical bristles to penetrate the peri-implant sulcus. Methods: A mandibular dentition was reproduced using a plaster model. The gingival component was recreated in silicone and a glass cylinder simulating a 4mm diameter implant was positioned by replacing element # 3.6. Using an 1mm diameter optical fiber placed from the lingual side inside the cylinder, the penetration of the bristles was recorded during the brushing. The Bass Technique was performed in a humid environment from the vestibular side. This brushing motion is described as a vibratory movement of the bristles arranged at 45° respect to the long axis of the tooth into the sulcus. The protocol included 5 toothbrushes per group and 10 tests per toothbrush for a total of 50 assessments per group. Each test lasted 1 minute with controlled pressure of approximately 500gr and a stroke length of 15 mm. From the video clips acquired, 4 degrees of penetration were identified: grade 0 (<2mm), grade 1 (2-3mm), grade 2 (3-4mm), grade 3 (4-5mm) and grade 4 (5-8mm). The highest value was collected for each test. At an α level of 0.05 for a one-tailed test with a power of 80% and a margin of superiority of 40%, a sample of 10 toothbrushes was needed. Intraoperative variability was assessed with the Cohen's kappa coefficient. A generalized mixed-effect linear model (multilevel analysis) was used considering the level of bristle penetration as the primary outcome and the type of bristle as fixed effects. The level of significance α was a priori set at 0.05. The null hypothesis affirms that no difference of efficacy (level of penetration) exists between the two types of bristles. Results: Excellent agreement was obtained between the measurement performed by the examiner (K-statistics =1). The conical bristles showed 8 times greater efficacy (p = 0.001) than the cylindrical bristles; moreover, with respect to the latter, the degree of penetration of the conical bristles proved to be 2 times (p = 0.015), 20 times (p = 0.001) and 76 times (p = 0.001) higher than degrees 1, 2 and 3 respectively. The null hypothesis was therefore rejected. Conclusion: This preclinical study shows a clear and superior penetration capacity of the conical bristles compared to traditional cylindrical ones. This result suggests a greater hygienic efficacy at the peri- implant level for the newly designed bristles.