Evaluation of labio-lingual bony support of lower incisors in orthodontically untreated adults with the help of computed tomography.

The aim of the present study was to assess bone volume and bone density in orthodontically untreated adults using a CT analyzing method, with reference data in the clinically essential area of the lower incisors being obtained. For quantitative and qualitative assessment of the labial and lingual bony support of the lower incisors, existing CT-images of 20 adult men with a near-to-normal occlusion and a clinically healthy periodontal situation were evaluated. With the help of a special program (SIM/Plant) and on the basis of axial scans, sagittal scans were constructed, permitting the individual imaging of the lower incisors and their alveolar process. The bony support of each tooth was registered labially and lingually perpendicular to the tooth axis at intervals corresponding to 10% of the root length. At the various root levels, especially at the upper parts of the roots, only small amounts of bony support, if any, were frequently observed. Labially, bony fenestrations and dehiscences were frequently seen, but lingually mostly dehiscences. No clinically relevant association was found between labial bony support and cephalometrically registered inclination of the lower incisors. Bone density, which was registered in Hounsfield units at the gingival, middle and apical thirds of the root levels, increased from the gingival to the apical thirds of the roots, generally with lower lingual than labial values. Before initiating orthodontic treatment a thorough clinical assessment of the anatomical situation in the lower incisor segment should be carried out. At present bone volume in this area can be reliably assessed only with computed tomography; however, this has to be weighed up against increased radiation risks. Therefore, the form of the symphysis should initially be roughly assessed by means of conventional cephalometry, with additional CT-based analysis of individual teeth being confined to special indications.