The cancellous bone density in the abnormal BTM group was significantly lower than that in the normal BTM group. This suggests that cancellous bone with a high BTM was likely to actually be poor medullary bone. There were three patterns of low BMD: high values of bone formation markers only, high values of both bone formation and bone resorption markers, and high values of bone resorption markers only. In this study, the BMDs were low even in patients who only had abnormal bone formation marker values. The BTM reflects bone turnover, and we considered that the BMD decreased because of the increased bone turnover. Given that bone is repeatedly forming and resorbing, we suggest that there were aspects of bone formation that were detected with an inclination towards bone resorption in this case. Therefore, we believe that attention should still be paid to any decline in bone quality even when it is solely the bone formation marker that is high. Biochemical BTMs provide information on bone resorption and formation, correlate with the rate of bone loss, and predict the likelihood of hip fracture; however, we only assessed BTMs at baseline in this study. Therefore, we need to remeasure these levels when following up on these patients because accelerated bone turnover, indicated by high BTM levels, implies bone loss.

In the abnormal group, the cancellous bone density showed no significant difference between SLA (internal connection system) and MK-III (external connection system) at baseline. Meanwhile, MBL was significantly larger in MK-III implants than in the SLA implants during the follow-up period. Norton reported that the incorporation of an internal conical interface could dramatically enhance the ability of a dental implant unit to resist bending forces. Asvanund et al. reported that there were more stresses generated at the implant-abutment connection level by external implant abutment connections than by internal implant abutment connections. The load is concentrated mainly on the implant abutment interface, thus reducing the stress concentration of the internal connection implants that use the platform switching concept in the peri-implant bone region. Therefore, the present study findings agree with those of the previous studies. We suggest that the MBL of external connection system implants in patients with reduced bone quality was increased by stressing the bone, even though it seems that there is no difference in BMD on the radiographic assessment.