IM0210

implants2_2010 bone loss as Jeong, one millimeter less for flap- less approach. Alveolar bone thickness The main blood supply for buccal alveolar bone is supplied by vessels in the overlying muco periosteum34 and is greatly affected by el- evating a full thickness flap to facilitate place- ment of a dental implant. Studies suggest that if residual facial bone thickness is less than 2 mm and/or if dehiscences or fenestrations of facial bone occurred during osteotomy preparation, consideration should be given to augmenting facial bone thickness with GBR procedures.35, 36 Premature exposure of an implant cover screw through the overlying mucosa may result where mucosal tissues fail to achieve primary closure, or are too thin to avoid dehiscence, or have been traumatized with the transitional prosthesis. It was reported in the literature that patients with prematurely exposed cover screws suffered 3.9 times greater bone loss than non- exposed ones.37 Quantity of keratinized tissue Adequate keratinized tissue may be more im- portant around implants than natural teeth for several reasons: supracrestal collagen fibers are oriented in a parallel rather than in a perpendi- cular configuration adjacent to transmucosal surfaces of implants38 , providing less resistance to local trauma and microbial penetration. Peri- implant mucosa may have a reduced capacity to regenerate itself due to compromised number of cells and poor vascular suply.39 Oral hygiene, smoking, alcohol abuse Patients with poor oral hygiene and/or exist- ing periodontal disease experience greater peri- implant crestal bone loss than patient with good oral hygiene and stable periodontal status. Both current and lifetime cigarette are associated with deterioration in bone quality and impaired wound healing.40 Smoking has been shown to be one of the most significant factors predisposing to implant failure.41 Individuals who use alcohol in excess may have inadequate nutrition includ- ing vitamin deficits which may compromise ini- tial site healing.42 Diabetes It is well known that diabetic patients are at higher risk for developing periodontitis and are also more prone to infection.43 It is very likely that performance of dental implant will be af- fected as well. Poor metabolic control in dia- betic patients increases the risk of peri-implan- titis.44 Biologic width Crestal bone remodeling to establish “bio- logic width” or soft tissue seal in peri-implant mucosal tissues is considered to be an important factor contributing to early crestal bone loss with all types of endosseous dental implants (Fig. 4).45, 46 Factors known to affect this crestal bone loss include the level of micro-gap in relation to the bone crest, platform switching achieved either by implant body design and/or by using an abut- ment smaller in diameter than the implant body and tooth-implant or inter-implant horizontal distance. Another factor with deleterious effect oncrestalboneresorptionisconsideredtobethe repeated removal and replacement of abut- ments because of disruption of the soft tissue seal.47 The biologic width has changed horizontally within the platform switched implant. Level of the micro-gap The connection between implant body and prosthetic abutment is termed “micro-gap” and, in most cases, it is susceptible to microbial seed- ing and micro-movements between the parts duringclinicalfunction.Bothmicro-gapandmi- cro-movements may lead to localized inflam- mation and associated crestal bone loss if the micro-gap is within a minimum distance from the alveolar crest. Biologic width around the neck of a dental implant constitutes a mucosal seal intended to protect the underlying bone. It is formed apically to the micro-gap and requires a minimum of about 1.5 mm of fibrous connec- tive tissue between bone and epithelial attach- ment of the gingival sulcus of the implant (Fig. 5).48, 49