This study aims to explore the height and thickness of the anterior alveolar bone of hyperdivergent skeletal ClassⅡ malocclusion between different ages and calculate the incidence rates of fenestration and dehiscence using cone-beam computed tomography (CBCT) .

The sample consisted of 46 persons of hyperdivergent skeletal ClassⅡ malocclusion who met the inclusion criteria. They were divided into two groups, teenager group (26 cases, age: 12.9 ± 1.2 years) and adult group (20 cases, age: 22.3 ± 3.2 years) . The CBCT images were collected to measure the height and thickness of the anterior alveolar bone of the upper right side and calculate the incidence rates of fenestration and dehiscence. Independent t-test (normal distribution) or Mann-Whitney U-test (skewed distribution) were used for the measurement of the height and thickness of the anterior alveolar bone. Chi-square test was used to compare the incidence rates of fenestration and dehiscence between the two groups.

For the hyperdivergent skeletal ClassⅡ malocclusion, the alveolar bone attachment of the incisors of both jaws in the adult group were lower than those in the teenager group (P<0.05) ; The alveolar bone thickness at 2 mm level from cemeto-enamel junction and the apical level of the incisors of both jaws in the adult group were lower than those in the teenager group (P<0.05) ; The alveolar bone area of the incisors of both jaws in the adult group were smaller than those in the teenager group (P<0.05) . In the adult group of the hyperdivergent skeletal Class Ⅱ malocclusion, the incidence rates of fenestration and dehiscence were 10.00% and 32.50% respectively and in the teenager group were 3.37% and 14.90% respectively before orthodontic treatment. Compared with teenagers, the incidence rates of fenestration and dehiscence were much higher in adults (χ^{2Fenestration}= 6.794, P_Fenestration= 0.009; χ^2Dehiscence= 16.030, P_Dehiscence<0.001) .

For the hyperdivergent skeletal ClassⅡ malocclusion, the quantity of anterior alveolar bone in the adult group was less than that of the teenager group. Compared with the teenagers, the incidence rates of fenestration and dehiscence were much higher in adults.