Correlation Between Mandibular Cortical Index and Primary Implant Stability

Introduction Adequate initial stability during implant placement is essential for successful implant therapy. Although elderly patients require special care for bone metabolic disorders, the prognosis of implant treatment in patients with osteoporosis remains unknown. This study aimed to statistically evaluate the mandibular cortical index (MCI) and implant stability quotient (ISQ). Methods This study included patients who visited the Nihon University School of Dentistry Dental Hospital, Japan, between 2012 and June 2025. The following information was extracted from the medical records: sex, age at implant placement, systemic diseases, implant size, and implant stability quotient (ISQ) data measured using a resonance frequency analyzer. The mandibular cortical index (MCI) classification of digital panoramic radiography (DPR) images taken after implant placement was evaluated in this study. The ISQ values and MCI data obtained were statistically analyzed at the implant level. Results The study included 79 patients (34 men and 45 women with a mean age of 60.3 ± 10.3 years at the time of implant placement) and 190 implants. The mean ISQ value was 71.6 ± 10.8 mm. The MCI classification at the implant level was as follows: Class I, 43 implants (72.8 ± 10.4); Class II, 100 implants (73.2 ± 10.4); and Class III, 47 implants (67.2 ± 11.2). Spearman's rank correlation coefficient revealed a weak negative correlation with ISQ values in MCI cases (-0.216, p < 0.01). However, no significant correlation was observed between the age at implant placement and ISQ values (-0.057, p > 0.05). A one-way analysis of variance with the ISQ value as the dependent variable revealed that the mean ISQ value for Class III was significantly lower (P < 0.01). Conclusion Class III in the MCI classification reflects bone demineralization. In this study, a significant decrease in the ISQ values was observed in the Class III group. Therefore, it was predicted that stability during implant placement would be reduced in cases involving porous mandibles. When assessing the prognosis of implant treatment, the morphology of the mandibular cortical bone should be carefully observed. For elderly patients and those at risk for osteoporosis, in particular, preoperative diagnosis of MCI is expected to be useful in predicting deterioration of bone quality at the implant site. This information can be used to adjust implant diameter and insertion torque and to determine the necessity of bone grafting procedures.