## 4 Discussion
### Marginal Bone Loss and Success Rates of Long and Short Implants  
Both the control and the experimental groups showed minimal marginal bone loss and no statistically significant differences during the whole observation period. No correlation between the implant length and marginal bone loss was observed. Marginal bone loss is a key factor in long-term implant stability and survival rate [PERSON] and [PERSON] (2018) and authors need to pay more attention to bone loss in short implant because of its relatively higher risk as a result of less reserve in bone height for the implant to be engaged in. Several authors insisted that the first year marginal bone loss should be included in the reports on marginal bone loss, because bone resorption rate is highest during first year of loading [PERSON] and [PERSON] (2018); [PERSON] and [PERSON] (2018). Therefore, minimal marginal bone loss shown in this study during initial year after the surgery may be interpreted positively for after coming prognosis. Peri-implant soft tissue observed was also clinically healthy with negligible plaque and calculus deposits and minimal tendency to bleed (Table 4). The overall 48-week success rate in the present study was 100%, the same as the survival rate, as reviewed from the time of prosthetic delivery to the final follow-up appointment. In this study, short implants showed successful outcomes comparable to long implants in success rates, stability, and changes in marginal bone level, despite unfavorable conditions such as short length and immediate loading. These results were comparable to those of previous studies on immediately loaded single short implants [36; 51]. [PERSON] et al. [51] evaluated 6.5 mm-long flawlessly placed single implants immediately or early loaded at 6 weeks and concluded that flawlessly placed 6.5 mm-long single implants can be immediately loaded and remain successful up to 4 years after loading. Correspondingly, to the previous studies, the successful outcome of this study can mainly be explained by good bone quality and primary stability. Under strict patient selection criteria, we screened out patients with smoking habit, parafunctional habits and D4 bone density known as disadvantageous factors for implant success and tried to achieve primary stability during surgery in terms of 35-45 Ncm insertion torque with surgical procedure variations such as under-drilling. Under-preparation of implant site, not following the whole standard drilling steps, has been suggested as a means to improve primary stability [52]. The implants used in the present study, Neobiotech CMI IS-III active(r), are designed with various macrodesign features such as deep reverse buttress shaped thread, conical implant-abutment seal, micro grooves on implant collar, and self-tapping tapered apex. One of the key factors for successful stability and osseointegration is even stress distribution within peri-implant bone [53; 54]. Previous studies have reported that the aforementioned macroscopic components diminish undesirable stress and strain around the implants and improve mechanical retention during the early phase of the healing process after operation [55; 56]. For these reasons, a sharp drop of primary stability could be avoided not showing stability dip during healing period and it is concurrent with the result of our previous study using same implant system [57]. In this study, short implants with wider diameter (5.5 mm) were used comparing control group (5.0 mm) to make up for the bone-to-implant contact surface of short length implants. Wide-diameter implant has been used to improve the success rate in compromised situations such as poor bone quality and/or quantity and replacement of a failing standard implant [58; 59]. Several studies reported that failure rate was higher with standard-diameter short implants compared with wide-diameter short implants [11; 58]. Furthermore, [PERSON] and coworkers [44] concluded that primary stability was more influenced by diameter than length.