Crestal Bone Level Alterations in Implant Therapy

Tooth restorations using implant-supported prostheses for functional and esthetic rehabilitation of patients has become an established and widely used treatment modality in modern dentistry. Preservation of peri-implant bone is one important factor for success. The quantity and quality of the bone surrounding an implant not only affect implant osseointegration, but also influence the shape and contour of the overlying soft tissues, which are important for the esthetic outcome of treatment. Therefore, assessment of periimplant marginal bone levels has become an integral part of the evaluation of the implant patient. Different evaluation protocols and success criteria based on marginal bone level changes have been described in the literature. Radiographic techniques including panoramic tomography and intra-oral radiography using long cone parallelling techniques have been widely used to monitor marginal bone levels at implants and diagnose interproximal bone loss (Kullman et al. 2007). Here the distance from a fixed reference point (e.g. implant shoulder or implant–abutment junction) to the inter-proximal bone level is recorded at baseline and monitored longitudinally. In numerous studies baseline radiographs are taken at the time of prosthesis installation, where any marginal bone level changes which occurred at the period between implant installation and prosthesis installation are not taken into account. While a panoramic tomograph allows the entire implant to be visualized limitations including image resolution and distortion are well known (Akesson et al. 1993, De Smet et al. 2002). Further limitations of conventional radiography include the inability to monitor facial and lingual/palatal bone levels, low sensitivity in the detection of early bone changes and the underestimation of bone loss (Bragger et al. 1988, De Smet et al. 2002). Recently, multi-slice computer tomography (CT) and cone beam volume imaging have been used in implant dentistry offering the advantage that osseous structures can be represented in three planes, true to scale and without overlay or distortion (Mengel et al. 2006).