In the present study, MBB cases constituted 34% of 389 patients and 1224 cases in total and 61% of all bone graft cases performed by the same surgeon in the past 5 years from January 2010 to December 2014. More complicated implant restoration cases have been executed along with bone graft at Pusan National University Dental Hospital. This may be due to the limitations of local clinics, such as a deficient amount of bone graft materials.
Various methods have been introduced in order to evaluate initial implant stability. Recently, resonance frequency analysis (RFA), non-invasive method developed by the study of Meredith, has been the most accepted technique. In his in vivo study, Meredith connected a convertor onto implant to measure resonance frequency (RF) and ultimately to examine peri-implant bone [9, 10]. A number of studies employed RFA to investigate initial stability of implants, verifying the efficacy of the method [11,12,13,14,15,16]. Therefore, such non-invasive method of RFA can be qualified as an objective index to assess initial implant stability in the present study.
Mandibular body bone graft, which was used for MBB grafting in this study, and ramal bone graft share comparable properties except their harvest sites. In general, due to excellent accessibility and remote distance from inferior alveolar nerve, ramal bone graft has been chosen widely. However, body bone graft was adopted to contour more fittingly in the present study. Despite of numerous advantages of MBB graft as mentioned earlier, MBB graft faces disadvantages including potential damage on inferior alveolar nerve, insufficient available amount of harvest, and poor revascularization since it is mostly occupied with cortical bone [5, 17, 18]. On purpose of overcoming such weaknesses, CT analysis was performed to prevent nerve injury, and some cases with severe bone defect were excluded through judicious case selection [17]. Moreover, decortication was carried out in order to promote revascularization at recipient site [5].
In this study, implant stability of the MBB group was not significantly different from that of the group which did not receive bone graft. Furthermore, as comparing to the bovine bone group, the MBB group demonstrated greater implant stability. In general, implant placement was not challenging when performing GBR with bovine bone, and autogenous bone graft cases manifested less favorable environment for installing implants. The present study showed that satisfactory implant stability was achieved through autogenous bone graft even under unfavorable condition for implantation due to its outstanding bone formation and retention abilities.
Based on assessment of the MBB cases, the factors affecting implant stability included gender, implant placement site, and implant diameter. On the other hand, age and implant height demonstrated no significant influence on implant stability.
The influence of gender on implant stability has been controversial, but the present study showed better implant stability in females than in males. This may due to different habits and tendencies of each sex. In particular, smoking tendency, which is one of the major contributors of implant failure, is generally higher in males, and Sverzut et al. reported that male smokers tend to display higher implant failure [19].
Many studies have verified the effect of age on implant stability [20, 21], but a few studies have assessed a relationship between age and implant stability in autogenously grafted area. In the present study, there was no significant association between age and implant study in the MBB cases. Therefore, further studies are necessary to investigate with more specimens and cases.
Among the various implant placement sites adopted in this study, mandibular posterior regions showed the highest implant stability and maxillary posterior regions displayed the lowest. Esposito et al. reported a higher implant failure in maxilla than in mandible [22]. Furthermore, Steenberghe et al. revealed that the posterior region in maxilla particularly manifested more failures [23]. The present study also observed similar results that may be due to differences in bone quality and quantity between maxilla and mandible. However, further studies are required to study a relationship between implant site and implant stability after grafting autogenously, MBB graft in particular.
In many cases, larger implant diameter achieves greater implant stability [24]. Smaller implant diameter tends to risk successful implant restoration for retaining less support against occlusal load. However, when implant diameter exceeds the standard size, implant stability declines [25]. Implants of more than 5 mm in diameter are commonly chosen on purpose of rescuing implants of 4 mm when poor bone quality seems to be responsible for implant failure. Nevertheless, smaller implant diameters exhibited lower ISQ values in this study. Although a research has shown that narrow implants can achieve acceptable stability in edentulous posterior area [26], the present study demonstrated lower ISQ values for narrower implants. This may be since MBB graft allowed sufficient bone quality and quantity in most of the cases.
In addition, longer implant height provides satisfactory implant stability while shorter implant height generally increases implant failure rate [24]. Some studies have reported that sufficient stability can be achieved with a length of 8 mm or more [27]. However, the present study showed no significant correlation between implant height and ISQ value. Furthermore, implants less than 8 mm in height were barely used in this study. Through MBB graft, adequate bone height was achieved successfully, requiring no excessively short implants.
