Stability of overbite correction
Danz JC, Greuter C, Sifakakis I, Fayed M, Pandis N, Katsaros C. Stability and relapse after orthodontic treatment of deep bite cases—a long-term follow-up study. Eur J Orthod 2014;36:522-30
A deepbite is defined as the vertical overlap of the maxillary incisors, when measured (either in millimeters or as a percentage) perpendicular to the occlusal plane. A deepbite can have skeletal or dental origins that will dictate the treatment approach. Therapeutic objectives for a deepbite are mainly to prevent tissue trauma from tooth contact. This retrospective study was conducted both to determine the risk factors for a deepbite, and also to evaluate the relapse tendency posttreatment. Sixty-one previously treated patients with an overbite exceeding 50% participated in the study. Patient records consisted of 3 sets of dental casts: pretreatment, posttreatment, and end of follow-up. Two lateral cephalograms taken at pretreatment and posttreatment were evaluated. Measurements on the pretreatment to the end of follow-up plaster models were done by 1 investigator. The median follow-up period was 11.9 years. The patients were treated by various treatment modalities; most received at least a mandibular fixed retainer and a maxillary removable biteplate during retention. Relapse was defined as an increase in incisor overlap from below 50% after treatment to equal to or more than 50% at the long-term follow-up. Ten percent of the patients showed relapse equal to or greater than 50% incisor overlap, and their amounts of overbite increase were low. The partial-treatment group had a significantly increased prevalence of gingival contact at the end of the follow-up compared with the complete-treatment group. It was not possible to identify important factors to predict relapse of deepbite malocclusion, since the prevalences and amounts of relapse were too low because of the sample size, outcome, and retention procedures.
Reviewed by Yasir Kachroo
Monocortical and bicortical mini-implant stability
Holberg C, Winterhalder P, Rudzki-Janson I, Wichelhaus A. Finite element analysis of mono- and bicortical mini-implant stability. Eur J Orthod 2014;36:550-6
Many factors affect the success rate of mini-implants, and longer mini-implants are believed to have an enhanced primary stability than shorter ones. The authors of this study aimed to determine the biomechanical difference between monocortical and bicortical anchorage types and their effects on primary stability. They used a computed tomography image of a mandibular segment with a missing tooth and orthodontic elements generated with computer-aided design to construct a model. Three anchorage types were simulated: 2 lengths of monocortical anchorage (5 and 7 mm) and 1 bicortical anchorage (10 mm), all with the same diameter of 1.6 mm. Finally, using the finite element method, the effective stress was calculated within a localized area when 1.5 N of force was applied. The results showed that the short monocortical mini-implant had the greatest effective stress, whereas the long variant of the monocortical mini-implant showed somewhat lower stress values. The bicortical mini-implant had the lowest level of effective stress. When nonparametric tests were performed using the Kruskal-Wallis and Mann-Whitney U tests, highly significant differences were indicated. Rank correlation according to the Spearman test showed that the peri-implant stress values were lower when the mini-implant was longer and inserted deeper into the alveolar bone. Based on the findings, the authors concluded that the reduction of stress induced in the cortical bone indicates that bicortical anchorage seems to be superior in primary stability. However, even in monocortical anchorage, a longer length seemed to reduce the leverage effect and provide better stability.
Reviewed by Jay Sung
Monocortical and bicortical mini-implant stability
Holberg C, Winterhalder P, Rudzki-Janson I, Wichelhaus A. Finite element analysis of mono- and bicortical mini-implant stability. Eur J Orthod 2014;36:550-6
Many factors affect the success rate of mini-implants, and longer mini-implants are believed to have an enhanced primary stability than shorter ones. The authors of this study aimed to determine the biomechanical difference between monocortical and bicortical anchorage types and their effects on primary stability. They used a computed tomography image of a mandibular segment with a missing tooth and orthodontic elements generated with computer-aided design to construct a model. Three anchorage types were simulated: 2 lengths of monocortical anchorage (5 and 7 mm) and 1 bicortical anchorage (10 mm), all with the same diameter of 1.6 mm. Finally, using the finite element method, the effective stress was calculated within a localized area when 1.5 N of force was applied. The results showed that the short monocortical mini-implant had the greatest effective stress, whereas the long variant of the monocortical mini-implant showed somewhat lower stress values. The bicortical mini-implant had the lowest level of effective stress. When nonparametric tests were performed using the Kruskal-Wallis and Mann-Whitney U tests, highly significant differences were indicated. Rank correlation according to the Spearman test showed that the peri-implant stress values were lower when the mini-implant was longer and inserted deeper into the alveolar bone. Based on the findings, the authors concluded that the reduction of stress induced in the cortical bone indicates that bicortical anchorage seems to be superior in primary stability. However, even in monocortical anchorage, a longer length seemed to reduce the leverage effect and provide better stability.
Reviewed by Jay Sung
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