READERS' FORUM
Letters to the editor* Asymmetries evaluated with cone-beam computed tomography
Am J Orthod Dentofacial Orthop 2014;145:2 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.11.008
W
REFERENCES
ith great interest and respect, I read the research reported by Minich et al (Minich CM, Ara ujo EA, Behrents RG, Buschang PH, Tanaka OM, Kim KB. Evaluation of skeletal and dental asymmetries in Angle Class II subdivision malocclusions with cone-beam computed tomography. Am J Orthod Dentofacial Orthop 2013;144:57-66). First and foremost, I want to express appreciation to the authors for their efforts and contributions in investigating the etiologic factors of Class II subdivision malocclusions. They found significant skeletal and dental differences between the Class I and Class II sides by measuring with cone-beam computed tomography and stated that dental asymmetries account for about two thirds of the total asymmetry. Nevertheless, I have 2 concerns and 2 questions regarding this article. My first concern is about the subjects, who were divided into 2 groups, an uncrowded group and a crowded group. There was no control group, and the ages of the patients in each group were not clarified. However, it was reported that even people with normal occlusion might have craniofacial asymmetry,1 and a study has shown that mandibular asymmetry can change with age.2 Therefore, the differences found between the Class I and Class II sides might have been enlarged or reduced because there was no control group with normal occlusion. In addition, I question the accuracy of the results because the subjects' ages were not clarified. My second concern is about 1 landmark. The authors concluded that a significant mandibular asymmetry was identified, so I wondered whether it was contradictory that they chose the genial tubercles to represent the middle of the mandible, which might create confounding factors. In addition to the concerns above, I have 2 more questions. First, since the tooth-size discrepancy (Bolton index) of the patients was not mentioned, is it necessary to exclude subjects with an obvious tooth-size discrepancy? Second, the authors used the mesiobuccal cusp of the first molar to represent its position. What if the first molars are rotated? Will this affect the result? Or is there a better landmark to represent the molars? Jingyu Li Chengdu, Sichuan, China *The viewpoints expressed are solely those of the author(s) and do not reflect those of the editor(s), publisher(s), or Association.
2
1. Shah SM, Joshi MR. An assessment of asymmetry in the normal craniofacial complex. Angle Orthod 1978;48:141-8. 2. Melnik AK. A cephalometric study of mandibular asymmetry in a longitudinally followed sample of growing children. Am J Orthod Dentofacial Orthop 1992;101:355-66.
Authors' response
W
e want to thank Jingyu Li et al for the feedback on our study evaluating asymmetries in Class II subdivision malocclusions using cone-beam computed tomography (CBCT). Dr Li brought up a few concerns regarding our subjects. The first concern was that we divided our study sample into 2 groups, a crowded group and an uncrowded group, but we did not have a control group of normal Class I patients. We were focusing on Class II subdivision malocclusions and wanted to know the difference between the Class I and the Class II sides. We were not initially interested in comparing these groups with a Class I control group. However, after completing our research, we think it would be a great continuation of the study to test this method and technique on a normal Class I control sample to investigate with CBCT whether similar asymmetries can be found in Class I occlusion groups. A second question from Dr Li was that we did not define a specific age group. We decided to use the permanent dentition as a criterion instead of a specific age (patients had to have all permanent teeth present from first molar to first molar). Dental age and chronologic age can vary quite a bit, so we decided to use dentition as the selection criterion. Also, Class II subdivision malocclusions are difficult to find; if we had limited our sample to a specific age group—eg, age 18 and older to represent nongrowing patients—we would have had a difficult time finding enough patients to study. In addition, orthodontists usually begin treating patients based on when the permanent teeth have erupted, so this selection criterion better represents real clinical situations. Another question was in regard to the landmark we chose to represent the middle of the mandible. Dr Li felt that our results might be contradictory because we
Letters to the editor* Asymmetries evaluated with cone-beam computed tomography
Am J Orthod Dentofacial Orthop 2014;145:2 0889-5406/$36.00 Copyright Ó 2014 by the American Association of Orthodontists. http://dx.doi.org/10.1016/j.ajodo.2013.11.008
W
REFERENCES
ith great interest and respect, I read the research reported by Minich et al (Minich CM, Ara ujo EA, Behrents RG, Buschang PH, Tanaka OM, Kim KB. Evaluation of skeletal and dental asymmetries in Angle Class II subdivision malocclusions with cone-beam computed tomography. Am J Orthod Dentofacial Orthop 2013;144:57-66). First and foremost, I want to express appreciation to the authors for their efforts and contributions in investigating the etiologic factors of Class II subdivision malocclusions. They found significant skeletal and dental differences between the Class I and Class II sides by measuring with cone-beam computed tomography and stated that dental asymmetries account for about two thirds of the total asymmetry. Nevertheless, I have 2 concerns and 2 questions regarding this article. My first concern is about the subjects, who were divided into 2 groups, an uncrowded group and a crowded group. There was no control group, and the ages of the patients in each group were not clarified. However, it was reported that even people with normal occlusion might have craniofacial asymmetry,1 and a study has shown that mandibular asymmetry can change with age.2 Therefore, the differences found between the Class I and Class II sides might have been enlarged or reduced because there was no control group with normal occlusion. In addition, I question the accuracy of the results because the subjects' ages were not clarified. My second concern is about 1 landmark. The authors concluded that a significant mandibular asymmetry was identified, so I wondered whether it was contradictory that they chose the genial tubercles to represent the middle of the mandible, which might create confounding factors. In addition to the concerns above, I have 2 more questions. First, since the tooth-size discrepancy (Bolton index) of the patients was not mentioned, is it necessary to exclude subjects with an obvious tooth-size discrepancy? Second, the authors used the mesiobuccal cusp of the first molar to represent its position. What if the first molars are rotated? Will this affect the result? Or is there a better landmark to represent the molars? Jingyu Li Chengdu, Sichuan, China *The viewpoints expressed are solely those of the author(s) and do not reflect those of the editor(s), publisher(s), or Association.
2
1. Shah SM, Joshi MR. An assessment of asymmetry in the normal craniofacial complex. Angle Orthod 1978;48:141-8. 2. Melnik AK. A cephalometric study of mandibular asymmetry in a longitudinally followed sample of growing children. Am J Orthod Dentofacial Orthop 1992;101:355-66.
Authors' response
W
e want to thank Jingyu Li et al for the feedback on our study evaluating asymmetries in Class II subdivision malocclusions using cone-beam computed tomography (CBCT). Dr Li brought up a few concerns regarding our subjects. The first concern was that we divided our study sample into 2 groups, a crowded group and an uncrowded group, but we did not have a control group of normal Class I patients. We were focusing on Class II subdivision malocclusions and wanted to know the difference between the Class I and the Class II sides. We were not initially interested in comparing these groups with a Class I control group. However, after completing our research, we think it would be a great continuation of the study to test this method and technique on a normal Class I control sample to investigate with CBCT whether similar asymmetries can be found in Class I occlusion groups. A second question from Dr Li was that we did not define a specific age group. We decided to use the permanent dentition as a criterion instead of a specific age (patients had to have all permanent teeth present from first molar to first molar). Dental age and chronologic age can vary quite a bit, so we decided to use dentition as the selection criterion. Also, Class II subdivision malocclusions are difficult to find; if we had limited our sample to a specific age group—eg, age 18 and older to represent nongrowing patients—we would have had a difficult time finding enough patients to study. In addition, orthodontists usually begin treating patients based on when the permanent teeth have erupted, so this selection criterion better represents real clinical situations. Another question was in regard to the landmark we chose to represent the middle of the mandible. Dr Li felt that our results might be contradictory because we
