10 January 2022

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Incisor position and alveolar bone thickness

Davide Elsido

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Evaluating the position of central incisors using a lateral cephalogram is a routine part of orthodontic diagnosis. The inclination of the central incisors and their relationship to surrounding alveolar bone can be easily assessed and often govern treatment decisions involving anterior-posterior (AP) incisor movements within the jaws. The cortical surfaces of alveolar bone represent a limiting factor for orthodontic tooth movement beyond which fenestration and/or dehiscence might occur. Induced contact between incisor roots and alveolar cortical bone can also precipitate externa root resorption. Contact between maxillary incisor roots and the incisive canal has also been shown to be a risk factor for external root resorption, further limiting the range within which maxillary incisors might be safely moved in some patients.

Evaluating root positions in a sample with naturally occurring optimal occlusions could elucidate anatomic relationships between roots and alveolar bone worthy of emulation. In this study, appeared on the Angle Orthodontist December 2021 issue, the positions of maxillary and mandibular central incisors were assessed using lateral cephalograms. Their long-axis inclination as well as the AP position of the roots with respect to local alveolar bone were evaluated. Data from a sample with naturally occurring optimal occlusions were compared to a sample with naturally occurring Class II malocclusions with concurrent AP skeletal discrepancies (Cl II). 

Significant intergroup differences were found, mandibular incisor root apices were generally equidistant from the labial and lingual surfaces of the alveolus in the optimal sample but closer to the lingual surface in the Class II sample. The authors stated that in untreated individuals, maxillary central incisors tend to occupy the anterior one-third of the maxillary alveolar process, regardless of AP jaw relationships; in untreated individuals with optimal occlusions, mandibular central incisor root apices tend to be centered within the mandibular alveolar process; in untreated individuals with Class II malocclusions associated with relative mandibular retrognathia, mandibular central incisors are more positively inclined, and their root apices are more posterior than in those with untreated optimal occlusions.