Risk Assessment Before Extraction for Immediate Implant Placement in the Posterior Mandible: a Computerized Tomographic Scan Study

Background: Controversy exists in treatment planning relative to the attempt of saving a tooth with unfavorable prognosis or extracting it and placing an immediate or delayed implant. Preextraction radiographic assessments of teeth are traditionally performed using two-dimensional periapical and panoramic radiographs. These can reveal bone loss around a tooth, but have limited use in assessing implant risk before tooth extraction. Three-dimensional radiographs or cone-beam (CB) or computerized tomographic (CT) scans are often taken after tooth extraction and socket healing to assess the healed ridge as a potential implant site. However, when treatment planning for an immediate implant in the posterior mandible, a CT scan taken before tooth extraction can be of value in assessing the available bone and anatomy of the area. This allows the clinician and patient to consider alternative options, such as treating and maintaining the tooth or using a delayed implant protocol, when the site presents a high risk for immediate implant placement (IIP). The purpose of the present study is to assess the prevalence of sites associated with the mandibular second premolar, mandibular first molar, and mandibular second molar teeth that present high risk for IIP using a preextraction CT scan to assess the available apical bone and the anatomy of the posterior mandible in the area of the anticipated extraction site.

Methods: One hundred consecutive CT scans were obtained and screened from the New York University College of Dentistry, Office of Quality Assurance-Approved Implant Dentistry Database. Forty-one of these CT scans were further assessed because they included the presence of ≥2 of the following tooth types: mandibular second premolars, mandibular first molars, and mandibular second molars. Measurements were obtained on the axial sections of the selected teeth to evaluate the amount of bone available apical to the root apices to determine the frequency of sites where an IIP protocol presented a high risk for inferior alveolar nerve injury or lingual plate perforation.

Results: Of the 135 teeth assessed from 41 CT scans, 65% of the mandibular second premolars, 53% of the mandibular first molars, and 73% of mandibular second molars had <6 mm of bone available for IIP, presenting high risk for inferior alveolar nerve injury. Of the sites in which the inferior alveolar canal did not limit available bone for IIP, 7% of the second premolars, 9% of the first molars, and 31% of the second molars presented high risk for lingual plate perforation.

Conclusions: Preextraction CT scans may present a useful diagnostic aid to assess the risk of inferior alveolar nerve injury and lingual plate perforation for IIP in the posterior mandible. This information may be used for assessing risk when deciding whether to retain a questionable tooth or replace it with an implant with either an IIP or delayed protocol.