We read with great interest the article that documents cortical bone and ridge thickness (Horner KA, Behrents RG, Kim KB, Buschang PH. Cortical bone and ridge thickness of hyperdivergent and hypodivergent adults. Am J Orthod Dentofacial Orthop 2012;142:170-8). Cortical bone and ridge thickness help to determine the stability of temporary skeletal anchorage devices, as well as implant diameter, length, and the presence of inflammation. Miniscrew implants are widely used to provide anchorage in orthodontics because they are easy to insert and remove. We congratulate the authors for their efforts. However, we have questions about the article.
The authors reached a conclusion that maxillary lingual and mandibular buccal cortical bone thicknesses increase from posterior to anterior. However, this is not consistent with the statistics in Table III and the results on page 174; the posterior buccal sites tended to have thicker cortical bone than did the anterior sites, but only the differences in the mandible were statistically significant.
As mentioned in the Discussion section, since strains from musculature primarily affect the cortical bone, the medullary thickness shows no significant difference between hypodivergent and hyperdivergent subjects. However, occlusal forces not only affect cortical bone, but also influence cancellous bone. Although medullary thickness doesn’t show any significant differences, is the density of the cancellous bone also not affected by the facial divergence?
Another consideration is that only hypodivergent and hyperdivergent subjects were studied in the article. What about patients with average angles? Because the stability of temporary skeletal anchorage devices is a concern, we had hoped that the article could be of some help in our clinic.