Original article
Cortical bone and ridge thickness of hyperdivergent and hypodivergent adults

https://doi.org/10.1016/j.ajodo.2012.03.021Get rights and content

Introduction

The purpose of this study was to assess differences in dentoalvolar cortical bone thickness between hyperdivergent and hypodivergent young adults.

Methods

Pretreatment cone-beam computed tomography images of 57 patients, including 30 hypodivergent subjects (22 women, 8 men) and 27 hyperdivergent subjects (20 women, 7 men), were analyzed. The data were imported into imaging software (version 10.5; Dolphin Imaging Systems, Chatsworth, Calif); standardized orientations were used to measure buccal and lingual cortical bone thicknesses at 16 interradicular sites of the maxilla and the mandible. Total alveolar ridge thickness and medullary space thickness were measured at the same sites.

Results

T tests showed significant (P <0.05) group differences, with hypodivergent subjects having significantly thicker buccal cortices. The lingual cortex of the maxilla was also significantly thicker in the hypodivergent than in the hyperdivergent subjects. Alveolar ridge thickness was significantly greater at all sites of the hypodivergent mandible and at the anterior 2 sites of the hypodivergent maxilla. Medullary thickness was significantly greater only in the hypodivergent mandibles between the first molars and the second premolars, and between the first and second premolars. Buccal cortical bone was significantly thicker than lingual cortical bone in the mandible; lingual bone was significantly thicker in the maxilla.

Conclusions

Cortical bone tends to be thicker in hypodivergent than in hyperdivergent subjects. This explains the concomitant differences in alveolar ridge thickness. Medullary space thickness is largely unaffected by facial divergence.

Section snippets

Material and methods

Cephalograms generated from pretreatment cone-beam computed tomography (CBCT) scans (i-CAT Classic; Imaging Sciences International, Hatfield, Pa) were evaluated to identify 57 hyperdivergent and hypodivergent white subjects (42 women and 15 men). The images were taken in a single 360° rotation at a scan time of 20 seconds, 120 kVp, and 0.4 mm voxel size. Exclusion criteria included (1) missing or unerupted permanent teeth in the quadrant measured, (2) periapical or periradicular pathologies or

Results

In general, cortical bone was thicker in the hypodivergent than in the hyperdivergent subjects (Table I; Fig 2). The only maxillary site not significantly (P <0.05) thicker in the hypodivergent subjects was the buccal site between the first molar and the second premolar. In the mandible, only the buccal sites between the molars and the premolars, and the lingual sites between the second premolar and the first molar showed statistically significant group differences.

Alveolar ridge thickness was

Discussion

Cortical bone was .08 to .64 mm thicker in the hypodivergent than in the hyperdivergent subjects; this compares closely to differences reported by Swasty et al.24 The same pattern of differences has been previously shown, but with larger differences (up to 2.5 mm) in cortical bone thickness of Japanese and Asiatic Indian dry skull mandibles.22, 23 Differences in cortical bone thickness might be explained by masticatory function; weakened masticatory muscles produce smaller bite forces, which

Conclusions

  • 1.

    Interradicular cortical bone 5 mm below the alveolar ridge is, at most sites, thicker in hypodivergent than in hyperdivergent subjects.

  • 2.

    Since medullary thickness does not differ consistently between hypodivergent and hyperdivergent subjects, differences in total alveolar ridge thickness are due primarily to differences in cortical bone thickness.

  • 3.

    Lingual cortical bone is thicker than buccal bone throughout the maxilla and the mandible, except between the mandibular first and second molars.

  • 4.

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