ORIGINAL ARTICLE Buccal cortical bone thickness for mini-implant placement Sebastian Baumgaertel a and Mark G. Hans b Cleveland, Ohio Introduction: The thickness of cortical bone is an important factor in mini-implant stability. In this study, we investigated the buccal cortical bone thickness of every interdental area as an aid in planning mini-implant placement. Methods: From the cone-beam computed tomography scans of 30 dry skulls, 2-dimensional sli- ces through every interdental area were generated. On these, cortical bone thickness was measured at 2, 4, and 6 mm from the alveolar crest. Intraclass correlation was used to determine intrarater reliability, and anal- ysis of variance (ANOVA) was used to test for differences in cortical bone thickness. Results: Buccal cortical bone thickness was greater in the mandible than in the maxilla. Whereas this thickness increased with increas- ing distance from the alveolar crest in the mandible and in the maxillary anterior sextant, it behaved differently in the maxillary buccal sextants; it was thinnest at the 4-mm level. Conclusions: Interdental buccal cortical bone thicknes varies in the jaws. There appears to be a distinct pattern. Knowledge of this pattern and the mean values for thickness can aid in mini-implant site selection and preparation. (Am J Orthod Dentofacial Orthop 2009;136:230-5) A bsolute anchorage has been a long sought after, but rarely achieved, treatment ideal. Therefore, orthodontic mini-implants, which can provide this desired form of anchorage, are more popular than ever. This is also reflected in the increasing number of studies in the orthodontic literature. However, despite the recent surge in scientific articles, plenty is still un- known about this topic. 1 The literature is rich in case reports illustrating the successful use of mini-implants for various indications. Mini-implants are placed in many anatomic sites, depending on the indication and the biomechanics used. 2-5 Popular implant sites appear to be the palate, the lingual aspect of the maxillary alveolar process, the retromolar area in the mandible, and the buccal cor- tical plate in the maxilla and the mandible. 2-7 The latter has proven to be a versatile placement site and has thus been the subject of several investigations. 8-10 Many local anatomic factors must be considered; no single factor can be isolated to mark the ideal placement site. Among the more important factors for placement in the buccal cortex are soft-tissue anatomy, interradicular distance, sinus morphology, nerve location, and buccolin- gual bone depth. 11,12 More recently, an interest in cortical bone thickness and quality has developed in conjunction with orthodon- tic skeletal anchorage systems. 9,13-15 The influence of bone quality on the long-term success of oral implants is undisputed and has been known for over a decade. 16 Bone quality can be expressed as the ratio of cortical to trabecular bone. In 1985, Lekholm and Zarb 17 sug- gested a classification system to categorize bone into 4 classes of bone quality. This ultimately became the stan- dard classification in implant dentistry: (1) almost the entire jaw is homogenous compact bone, (2) a thick layer of compact bone surrounds a core of dense trabecular bone, (3) a thin layer of cortical bone surrounds a core of dense trabecular bone, and (4) a thin layer of cortical bone surrounds a core of low-density trabecular bone. However, further investigations showed that it is not primarily the ratio of cortical bone to trabecular bone that influences implant stability as much as the absolute amount of dense cortical bone. Cortical bone has a higher modulus of elasticity than trabecular bone, is stronger and more resistant to deformation, and will bear more load in clinical situations than trabecular bone. 18 What applies to traditional dental implants also applies to orthodontic mini-implants: thicker corti- cal bone provides greater primary stability. 19-21 Knowledge of the buccal cortical bone thickness in various areas can guide clinicians in selecting the From the Department of Orthodontics, School of Dental Medicine, Case Western Reserve University, Cleveland, Ohio. a Assistant clinical professor. b Professor and chairman. The authors report no commercial, proprietary, or financial interest in the prod- ucts or companies described in this article. Reprint requests to: Sebastian Baumgaertel, Case Western Reserve University, School of Dental Medicine, Department of Orthodontics, 10900 Euclid Ave, Cleveland, OH 44106; e-mail, sxb155@case.edu. Submitted, June 2007; revised and accepted, October 2007. 0889-5406/$36.00 Copyright Ó 2009 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2007.10.045 230