Alveolar bone loss around incisors in Class I bidentoalveolar protrusion patients: a retrospective three-dimensional cone beam CT study

Abstract

Objectives: The aim of this study was to test the null hypothesis that there is no difference in the alveolar bone thickness, bone loss or incidence of fenestrations between upper and lower incisors in skeletal Class I bidentoalveolar protrusive patients before orthodontic treatment.

Methods: Three-dimensional (3D) cone beam CT (CBCT) images were taken of 24 patients from the Republic of Korea (17 females and 7 males). Reformatted CBCT images were used to measure labial and lingual alveolar bone thickness (ABT) of the 4 upper incisors and 4 lower incisors of the 24 patients (total n = 192 incisors) at every 1/10 of root length (Level 0, cementoenamel junction (CEJ) area; Level 10, root apex area) as well as alveolar bone area (ABA) and alveolar bone loss (%BL) rate to dental root length. The numbers of fenestration teeth were also tallied.

Results: All anterior teeth were supported by <1 mm of ABT on the labial surfaces up to root length Level 8. ABA was statistically greater on the lingual aspect than the labial aspect in lower incisors. The %BL was 26.98% in the lower labial region, 19.27% in upper labial aspect and most severe on the lower lingual plate 31.25% compared with the labial plate. There were no significant differences in %BL between subgroups when categorized by sex or age. Fenestrations were 1.37 times more frequent on lower incisors (37) than upper incisors (27).

Conclusion: The null hypothesis was rejected, confirming that incisor periodontal support is poor and alveolar bone loss is severe even prior to the start of orthodontic treatment. Careful diagnosis using 3D CBCT images is needed to avoid iatrogenic degeneration of periodontal support around anterior teeth, particularly in the lower lingual bone plate region.

Figure 1

Schematic illustrations of (a) upper and (b) lower reference points, lines and measurement variables used in this study. Alveolar bone area, ABA = [(a + b)×c]/2 mm²; level 0 = line perpendicular to root axis on the cementoenamel junction area; level 10 = line perpendicular to root axis on the root apex area; F, fenestration; UABL, upper anterior bone loss; UPBL, lower posterior bone loss

Figure 2

CBCT cross-sectional slices of measurement variables on teeth studied. (a) #11, (b) #21, (c) #31, (d) #41. * on (a) denotes location of incisive canal

Figure 3

Upper alveolar bone thickness (mm) measurement at each root level position for individual incisor studied. p, posterior

Figure 4

Lower alveolar bone thickness (mm) measurement at each root level position for individual incisor studied. p, posterior

Figure 5

Comparison of alveolar bone area (ABA) (mm²) between male and female patients. MAABA, anterior alveolar bone area in male patients; FAABA, anterior alveolar bone area in female patients; MPABA, posterior alveolar bone area in male patients; FPABA, posterior alveolar bone area in female patients; *, p < 0.05

Figure 6

Comparison of alveolar bone area (ABA) (mm²) as a function of age group. YAABA, anterior alveolar bone area in young patients (aged under 20 years); OAABA, anterior alveolar bone area in older patients (aged over 20 years); YPABA, posterior alveolar bone area in young patients; OPABA, posterior alveolar bone area in older patients; Statistical significance (*) p < 0.05

Figure 7

Frequency of fenestration observed on each tooth. FN, fenestration number