A patient that presents with an edentulous site planned for implant therapy needs a thorough clinical and radiographic evaluation to determine adequacy of bone in 3 dimensions to facilitate placement of an implant in a prosthetically driven position, to provide predictable osseointegration and long-term successful outcomes. Visual examination, intraoral palpation of the edentulous site, measurement of the inter arch restorative space, two dimensional radiographs and CBCT scan analysis are all tools that will help assess the bone volume.
The amount of bone required in mesio-distal, bucco-lingual and apico-coronal dimension varies depending on the tooth type, number of missing teeth and the prosthetic plan. General guidelines for required bone quantity in an edentulous site are as follows:
- Mesiodistal dimension – A strong correlation exists between bone loss at adjacent teeth and the teeth – implant horizontal distance. With decreasing distance, bone loss increases. A safe distance of about 1.5 mm is, hence, recommended between implant and adjacent teeth.18 However, this lateral spacing is recommended to be at least 3 mm when an implant is placed in the esthetic zone to create harmonious emergence profile and soft tissue fill in the papillary areas.19 When two adjacent implants are placed, an inter-implant distance of at least 3 mm is critical to maintain crestal bone levels.20
- Bucco-lingual – The adequacy of bone in the bucco-lingual dimension will determine implant selection and need for bone grafting. Though bone volume in this dimension can be gauged clinically, for definitive assessment a 3-dimensional cone beam scan is recommended. A buccal wall thickness of 2 mm facial to the implant is necessary to prevent bone loss, gingival recession and help with long-term stability.21
- Apico-coronal – The vertical bone height available for implant placement can be restricted by anatomic structures such as nasal floor, maxillary sinus, mental foramen and inferior alveolar nerve. Radiographic assessment using either a 2-dimensional or 3-dimensional radiograph will be required to determine length of implant, need for sinus augmentation and vertical ridge augmentation. A safe distance from vital structures such as mental foramen and the inferior alveolar nerve canal is paramount to prevent damage to these vital structures and sensory dysfunction.22