Dentoalveolar compensation in vertical skeletal dysplasia in an Egyptian sample

Introduction: The Dentoalveolar compensatory mechanism is the changes that occur in the dentoalveolar complex in cases of skeletal discrepancies (anteroposterior, vertical, transverse) in order to maintain functional occlusion. In a patient with a deep bite or an open bite coinciding with an extreme vertical lower face deficiency or excess, surgical approach that requires presurgical dental decompensation might be considered. Alternatively, simpler non-surgical treatment options involve dentoalveolar compensation. The determination of which option is suitable for a patient must be based on the feasibility of dentoalveolar compensation which in turn will depend on severity of skeletal discrepancy. An accurate estimation of the limits of dentoalveolar compensation is therefore a key to successful treatment. Aim of the study: To determine the extent of dentoalveolar compensation in various facial types and to investigate the influence of skeletal and dentoalveolar characteristics on overbites in long and short face individuals. Materials and methods: Lateral cephalometric X-rays from the department of Orthodontics, Alexandria University were evaluated till we got 90 lateral cephalometric X-rays of three equal groups: Long face, Average face and short face. 15 dentoalveolar measurements and 5 skeletal measurements were made on these Xrays. Comparison of linear, angular, area and ratio measurements were compared among the three study groups using ANOVA for normally distributed variables and Kruskal Wallis test for variables that were not normally distributed. Measurements that were significantly different among the three groups were further tested in comparison of pairs using Tukey post hoc test for normally distributed variables and Mann Whitney U test for variables that were not normally distributed. Comparison of overbite categories among the three groups was done using Wilcoxon signed ranks test. Non parametric correlation between study groups and categories of overbite was examined using Kendal tau b. Stepwise regression analysis was used to examine significant predictors of overbite in short, long faces separately and in the whole sample using all measured linear, area, angular and ratio measurements. Results: The results of this study showed that there were significant differences between the three groups in nine linear variables which were: ramus length, mandibular body length, anterior cranial base length, mandibular alveolar depth, mandibular and maxillary incisor alveolar and basal heights, mandibular and maxillary dentoalveolar heights and overbite. The prevalence study of different categories of overbite in the three groups showed that in the short face group about two thirds of the patients had deepbite while in the long face group only four cases had an openbite and more than half of the patients had normal or deepbite. The multiple regression analysis showed that that there were two powerful predictors of overbite in the short face group which were the ratio between the mandibular molar dentoalveolar height and mandibular incisor alveolar and basal height and the interincisal angle. In the long face group only one powerful predictor of overbite was determined which was the SN-Mandibular plane angle. Conclusions: The role of dentoalveolar compensatory mechanism in the establishment of the overbite had been shown, but still its effect is limited beyond certain limits. In the short face group the combined effect of both the mandibular molar and incisor alveolar heights play an important role in maintaining the overbite. An overbite of 3mm can be achieved if the ratio didn’t exceed 0.83.In the long face group the skeletal factors plays a more dominating role than dentoalveolar factors in controlling the overbite. Although the role of dentoalveolar compensation is more demonstrated in the long face group, its actual mechanism hadn’t been determined exactly. An overbite of 3mm can be achieved if the SN-Mandibular Plane angle didn’t exceed 39 degrees.