Material and methods

Fifty-nine patients (26 men, 33 women) with skeletal Class III malocclusion and an anterior crossbite who had facemask treatment during the growth period were included in this study. Initially, 73 patients were selected from the archives of the Department of Orthodontics, Yonsei University Dental Hospital, in Seoul, Korea, on the basis of inclusion and exclusion criteria. The inclusion criteria were correction of Class III problems after facemask treatment, initiation of orthopedic treatment at a skeletal maturity index of less than 4, and availability of pretreatment (T0), posttreatment (T1), and postretention (T2) records. T1 referred to the end of facemask protraction, whereas T2 referred to growth completion confirmed by fusion of the epiphysis and metaphysis of the distal radius on a hand-wrist radiograph. The exclusion criteria were second phase treatment with a fixed appliance, centric relation-centric occlusion discrepancy, congenital missing teeth, facial asymmetry with menton deviation greater than 2 mm at T0, systemic disease, craniofacial syndrome, and previous orthodontic treatment. Using facial photographs and dental casts obtained at T2, 3 orthodontists (Y.J.C., J.E.C., K.H.K) with more than 10 years of experience independently classified the patients into successful (n = 37; 14 men, 23 women) and unsuccessful (n = 22; 12 men, 10 women) groups according to our criteria for success: overjet and overbite greater than 1 mm and an acceptable facial profile. Fourteen patients were additionally excluded because the 3 experts did not agree with regard to the facial profile, although these patients showed an overjet and an overbite greater than 1 mm. Eventually, 59 patients were included. The mean age at T0 was 9.18 years, and the mean facemask treatment duration was approximately 1 year ( Table I ). The maxilla was protracted using approximately 350 to 450 g of force per side, directed slightly downward on the basis of the conventional protocol. All patients wore a facemask for at least 12 hours per day until a positive overjet was achieved. Then, they wore a Class III activator as a retainer at night for approximately 2 to 3 years. The mean overjets were –2.2, 3.7, and 2.8 mm at T0, T1, and T2, respectively, in the successful group, and –1.4, 3.2, and –0.6 mm at the same time points in the unsuccessful group. This study was approved by the institutional review board of Yonsei University Hospital (3-2014-0097). Because of the retrospective nature of the study, the institutional review board waived the requirement for written informed consent from the patients.

Cephalometric analysis was performed using lateral cephalograms obtained at T0. For linear measurements, a horizontal reference plane (HRP) was drawn 7° downward from the sella-nasion line at sella, and a vertical reference plane (VRP) was drawn perpendicular to the HRP at sella. To indicate the maxillary and mandibular positions, we measured perpendicular distances between the following 6 landmarks and HRP and VRP, respectively: ANS, PNS, A-point, B-point, pogonion, and articulare. Other linear and angular measurements are shown in Figures 1 and 2 , respectively. Vceph software (version 6.0; Cybermed, Seoul, Korea) was used for the cephalometric analyses, and each lateral cephalogram was calibrated to scale by using a ruler attached to a head holder before the measurements. Using variables with statistically significant differences between the successful and unsuccessful groups, we formulated an equation to predict the long-term success of treatment.

Linear cephalometric measurements used to assess the long-term outcomes of orthopedic treatment for skeletal Class III malocclusion in this study. HRP and VRP indicate the horizontal and vertical reference planes, respectively. HRP is drawn 7° downward from the sella-nasion line at sella, and VRP is drawn perpendicular to HRP at sella. Perpendicular distances between 6 landmarks (ANS, PNS, A-point, B-point, pogonion, and articulare) and VRP and HRP, respectively, were measured. The following additional measurements were obtained: ANS-PNS, Ar-A point, Ar-Pog, Ar-Go, Go-Me, Wits appraisal, N-ANS, ANS-Me, N-Me (anterior facial height), S-Go (posterior facial height), and posterior/anterior facial height ratio.

Angular cephalometric measurements used to assess the long-term outcomes of orthopedic treatment for skeletal Class III malocclusion in this study. The abbreviations are the same as used in Figure 1 . The dotted lines are parallel to the mandibular plane. SNA, SNB, and ANB were measured, and the following values obtained: PP-MP (palatal plane angle), SN-MP (mandibular plane angle), N-S-Ar (saddle angle), S-Ar-Go (articular angle), Ar-Go-Me (gonial angle), N-A-Pog (facial convexity angle), AB-NPog (AB plane angle), and AB-MP.

We selected 4 previously published studies that had investigated cephalometric predictors of the long-term success of Class III orthopedic treatment during the growth period and had proposed prediction models. The success criteria and success rates in these studies are summarized in Table II . Three studies divided their patients into successful and unsuccessful groups, and the remaining study proposed 3 categories: good, fair, and poor. For conciseness and convenience, we categorized the good and fair groups as successful and the poor group as unsuccessful in our study.

We investigated the effects of different patient characteristics and success criteria on the success rates and the effects of different patient characteristics and prediction models on the accuracy of prediction (predictability). First, to investigate the effects of patient characteristics, we classified our patients using the T2 records into successful and unsuccessful groups on the basis of the success criteria in each study, and we calculated each success rate. The success rate derived from our patients was compared with the previously reported success rate in the corresponding study. Second, to investigate the effects of success criteria, we compared the 5 success rates derived from our patients on the basis of the success criteria in the 4 studies and our study.

Third, to investigate the effects of different patient characteristics on the predictability of the prediction models, we applied our patient records to the prediction models and success criteria in the previous studies and derived the prediction outcomes and treatment outcomes, respectively. Using the T0 records of our patients, we divided them into favorable and unfavorable (prognosis) groups by the prediction model proposed in each study. Similarly, we divided our patients into successful and unsuccessful (treatment) groups on the basis of the success criteria in each study using the T2 records of our patients. Next, per each study, we classified our patients into 4 subgroups: favorable-successful, favorable-unsuccessful, unfavorable-successful, and unfavorable-unsuccessful. The favorable-successful and unfavorable-unsuccessful groups represented accurate predictions, whereas the other 2 groups represented inaccurate predictions. Afterward, the accuracy of prediction for our patients was calculated using each previous model and compared with the previous results.

Finally, the predictabilities of the 5 prediction models for our patient sample were compared. We applied the T0 records of our patients to each prediction model to obtain the prediction outcome, and we applied the T2 records to the success criteria in our study to obtain the treatment outcome. The accuracy of prediction was then calculated for each model.

Results

The treatment success rate in this study was 62.7% when calculated using our success criteria. The success rates in the 4 previous studies ranged from 40.7% to 67.8%, depending on the success criteria used. The success rates were relatively high (66.1%-67.8%) when judged by the criteria of 2 studies, but relatively low when judged by those of the remaining 2 studies ( Table II ).

Tables III and IV show comparisons of cephalometric measurements before and after treatment between the successful and unsuccessful groups in this study. The successful group had shorter distances between ANS, A-point, B-point, and pogonion from HRP, a higher Wits appraisal value, shorter distances of N-ANS and N-Me, a larger articular angle, and a larger AB to mandibular plane angle compared with the unsuccessful group at T0 ( P <0.05). After treatment, most of the variables were not significantly different ( P >0.05).

Nine variables—HRP-ANS, HRP–A-point, HRP–B-point, HRP-Pog, Wits appraisal, N-ANS, N-Me, articular angle, and AB-MP angle—were used for discriminant analysis. In a stepwise manner, 3 variables—AB-MP angle, Wits appraisal, and articular angle—were selected to distinguish the 2 groups. The discriminant formula was as follows.

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