## 5 Discussion  
In the present study we found a 100% cumulative survival rate and an approximately 90% success rate for the immediate restoration procedure in a cohort of 39 patients (118 implants) followed-up for a mean of 32.3 months. We detected a relatively low mean marginal bone loss per implant (1.19 \(\pm\) 0.63 mm) 12-84 months after implant placement. These figures are comparable to the mean marginal bone loss observed in delayed as well as immediately loaded implants [15; 44; 45; 46; 47]. This outcome is probably the result of bone substitute grafting, which enhances bone fill and augments the buccal bony plate [43; 48], as well as to the good compliance of the patients. The present encouraging data on marginal bone loss of combined GBR and multiple implant placements are comparable to those recently reported for single tooth replacement using a similar GBR protocol [49; 50]. The survival rate of the current study patients, in whom the extractions were mainly due to periodontal reasons, reflects that of [PERSON] and colleagues [51], who reported a 98.8% survival rate at 12 months after implant placement rehabilitated with a full-arch prosthesis supported by six implants. Our results are also comparable with [PERSON] and colleagues' report [52] of a mean 1.2 \(\pm\) 0.9 mm bone loss one year after implant placement in periodontally compromised sites. Similar to their study findings, most of the socket walls in the current study participants were compromised in vertical and/or horizontal dimensions, mainly due to previous periodontal disease. Slightly over one-half (51%) of the teeth in the present study were extracted due to advanced periodontal disease. The remaining teeth were extracted due to caries including deep horizontal \begin{table}
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Table 4: Treatment outcomes per implant level. A comparison according to the reason for extractions between 61 implants in patients with periodontitis and 55 implants in patients with a caries etiology. fractures of the crown and external resorption, Primary stability of the implant is a key factor for success in the immediate loading approach [10; 11; 12; 13; 14]. In the present study, all the implants replaced teeth in regions that are prone--at least theoretically (type 2, 3) [14]--to immediate loading procedures (excluding second and third molar areas) [14]. The threshold value of primary stability was achieved even in those placed in the first molar region due to the palatal bone engagement of the implants that favors osseointegration. This can be achieved by using implants with appropriate macro geometry in combination with an under-preparation of the implant site that takes into consideration the local bone quality [10; 11; 12]. Solidarization of the implants with the prosthesis may also contribute to increased stability [10; 11; 12]. In the present study, an attempt had been made to minimize the potential collapse of buccal bone by using slow resorbable allograft mineralized material in the space that was created by the dimensional discrepancy between the bony walls of the extraction socket and the body of the implant, commonly described as the \"gap\". A collagen membrane was used to enhance bone regeneration and reduce the risk of membrane infection in the event of any soft-tissue dehiscence occurring postoperatively [53; 54]. A recent study [55] demonstrated that facial soft-tissue thickness (labio-palatal) was greater at sites that received bone grafts and provisional restorations compared to sites without either grafts or restorations. Moreover, current thinking in this area of research is that increasing peri-implant soft-tissue thickness increases the color-masking ability and bone stability [56; 57]. A possible explanation for the soft-tissue enhancement achieved by using bone grafts may be that particulate graft materials could be incorporated and encapsulated into the peri-implant mucosal soft tissues [58].