Comparison between tapered and cylindrical implants in the posterior regions of the mandible: A prospective, randomized, split-mouth clinical trial focusing on implant stability changes during early healing.

BACKGROUND: Companies affirm that tapered implants show adequate initial stability, while their installation in the lower arch is uncommon in clinical practice. PURPOSE: To compare the clinical outcomes of tapered and cylindrical implants and to study their effect on bone site characteristics and peri-implant health during healing. MATERIALS AND METHODS: The implant site dimensions were assessed by linear measurements using CBCT prior to the installation of 40 implants in the posterior mandible (20 tapered and 20 cylindrical). The bone type was registered during drilling via the surgeon's tactile perception, following the classification of Lekholm and Zarb. Primary stability (PS) was determined by the insertion torque (IT) and the implant stability quotient (ISQ). Secondary stability (SS) and the peri-implant health was monitored for 3 months through the visible plaque index (VPI), the peri-implant inflammation (PI), the probing depth index (PDI), and the gingival bleeding index (GBI). Significant differences were investigated with t-tests for independent samples, chi-square tests or Fisher's exact test. Pearson's correlation test was used to investigate the relationship between the bone site characteristics and PS (IT and ISQ), as well as the relationships between IT and ISQ for each implant type. RESULTS: Tapered and cylindrical implants showed no significant differences for any outcome variable (P > .05). A significant decrease in ISQ was observed after 7 days of healing (P = .0002), followed by a gradual increase beginning at 21 days (P = .0010) until the last follow-up time at 90 days (P = .0319). The cortical height was correlated with IT; while medullary bone dimensions were correlated with the PS as evidenced by the ISQ values. The insertion torque was significantly correlated with the PS only for the cylindrical dental implants. CONCLUSIONS: Tapered and cylindrical implants have similar biological behavior during the healing process. Bone site characteristics can influence insertion torque and implant stability.