Relationship Between Biotype and Bone Morphology in the Lower Anterior Mandible: An Observational Study

Different clinical parameters have been advocated as potential predictors of alveolar and basal jawbone morphology. The aim of this study is to describe, by tomographic means, alveolar and basal osseous dimensions of the anterior mandible in healthy individuals and evaluate potential correlations with biotype, along with other clinical parameters.

One hundred consecutive healthy patients needing surgery in the posterior mandible were enrolled in this observational study (group 1 = 50 patients with thin biotype; group 2 = 50 patients with thick biotype). Data were collected for: 1) Little irregularity index for anterior crowding; 2) molar and canine class relationship; 3) previous orthodontic treatment; 4) gingival recession; and 5) band of keratinized gingiva for each of the six anterior mandibular teeth (#22 through #27). At the most mid-buccal computerized tomography slice of each tooth, other parameters were measured, including: 1) distance from the cemento-enamel junction to the bone crest; 2) tooth torque (TT); 3) labial cortical bone thickness (BT) for alveolar and basal bone; and 4) BT 5 and 10 mm apical to the tooth apex. Data were statistically analyzed, and significance was set at P ≤0.05.

Mean thickness of alveolar bone ranged from 6.66 to 4.51 mm (standard deviation [SD] = 1.46 for tooth #27; SD = 1.01 for tooth #25) whereas mean thickness of basal bone ranged from 8.9 to 8.2 mm (SD = 2.06 for tooth #22; SD = 2.06 for tooth #26). Mean thickness of bone at 5 mm from apex ranged from 11.94 to 10.47 mm (SD = 2.96 for tooth #25; SD = 2.22 for tooth #22), whereas mean thickness of bone at 10 mm from apex ranged from 13.75 to 11.08 mm (SD = 2.79 for tooth #25; SD = 2.53 for tooth #27). No statistically significant differences were detected among biotypes, whereas: 1) TT, 2) age, and 3) smoking habit were often predictors of reduction in BT in a multiple linear regression model. Male sex was often a predictor of positive changes in BT, and previous orthodontic therapy was a protective factor against developing bone loss >5 mm.

Although some differences were detected among biotypes, data indicate that biotype does not play a fundamental role in influencing alveolar BT, whereas other variables (i.e., TT, sex, age, and smoking habit) do influence alveolar BT. Further studies are needed to better understand the extent of influence of each clinical variable.