Material and methods

The subjects included 40 men and 40 women with Class III malocclusions, whose mean age before treatment was 23 years (range, 18-34 years). The criteria for inclusion in the study were a Class III molar relationship, a negative overjet, an ANB angle less than 0°, and a Wits appraisal less than –1 mm. Consecutive patients were selected and divided into 2 groups, each with 20 men and 20 women. Those who had received orthodontic therapy alone made up the nonsurgical group; those who had required orthognathic surgery of mandibular setback combined with orthodontic treatment comprised the surgical group. Some patients were excluded from the study because complete records were lacking. We also excluded subjects with craniofacial syndromes, cleft lip or palate, and trauma history.

The goals of orthodontic treatment, with or without orthognathic surgery, are to achieve harmonious facial esthetics and a functional occlusion, but soft-tissue changes also play an important role in evaluating treatment effects. The Taiwan Board of Orthodontics introduced an objective grading system for assessing posttreatment dental casts and panoramic radiographs similar to that of the American Board of Orthodontics and supplemented by lateral cephalographs. The Taiwan Board of Orthodontics objective grading system evaluates 20 criteria. In this retrospective study with this grading system, we evaluated orthodontic and orthognathic surgical patients who were consecutively completed in 2006 to 2009. The mean scores for orthodontic patients were 78%. There were 1 patient in the “slightly improved” category and no patients in the “worse” or “no improvement” categories. The mean scores for orthognathic surgical patients were 74%. There were no patients in the “worse,” “no improvement,” or “slightly improved” categories. A mean score of more than 70% represents a high standard of treatment in the “greatly improved” category. The mean scores of this study indicate excellent-to-good treatment results for both groups.

In this study, we used lateral cephalometric radiographs obtained before treatment. A correction of 10% was made for the magnification of the linear measurements from each cephalogram. Thirty cephalometric landmarks on the craniofacial complex were identified and digitized ( Fig 1 ). A computerized cephalometric system, Winceph (version 8.0, Rise, Sendai, Japan), was used to obtain 25 cephalometric measurements, including 12 angular, 9 linear, and 4 ratio variables ( Table I ). Descriptive statistics, including means, standard deviations, and Student t tests results, were computed for each measurement ( Table II ). We selected 25 cephalometric measurements that were used in previous studies. The Bonferroni adjustment with an alpha level of 0.002 (0.05/25) was applied as a multiple-comparison correction when several statistical tests were performed simultaneously. The most suitable measurements were statistically validated and clinically relevant. Measurements that were statistically different between the 2 groups with the 2-sample t test and the Bonferroni adjustment were further analyzed by the ROC curve analysis.

Cephalometric landmarks: 1 , N, nasion; 2 , S, sella; 3 , Po, porion; 4 , Or, orbitale; 5 , ANS, anterior nasal spine; 6 , PNS, posterior nasal spine; 7 , A, Point A; 8 , U1E, maxillary central incisor edge; 9 , U1A, maxillary central incisor apex; 10 , B, Point B; 11 , Pg, pogonion; 12 , Gn, gnathion; 13 , Me, menton; 14 , Cd, condylion; 15 , Go, gonion; 16 , GoI, gonial intersection; 17 , L1E, mandibular incisor edge; 18 , L1A, mandibular incisor apex; 19 , BL, lingual Point B; 20 , G, glabella; 21 , N’, soft-tissue nasion; 22 , Sn, subnasale; 23 , Pg’, soft-tissue pogonion; 24 , Ls, labrale superius; 25 , Li, labrale inferius; 26 , Stoms, stomion superius; 27 , Stomi, stomion inferius; 28 , Si, mentolabial sulcus; 29 , Gn’, soft-tissue gnathion; 30 , Me’, soft-tissue menton.

Systematic measurement errors were estimated by means of paired Student t tests, and the random method error ( ME ) was quantified with Dahlberg’s formula, ME = √Σd2/2n, where d is the difference between duplicate measurements and n is the number of double measurements.

We study used the ROC analysis and the area under the curve (AUC) to determine the set of cephalometric measurements for the best discrimination between orthodontic therapy and orthognathic surgery. The ROC curve is a plot of sensitivity (true positive rate) on the y-axis and 1–specificity (false positive rate) on the x-axis. The different points on the curve correspond to different cutoff points used to designate the surgery group. The AUC is generally considered a reasonable summary of the overall diagnostic accuracy of the continuous variables. In general, for 2 variables, the variable with higher AUC is considered a better indicator for the surgery group. For each ROC curve, a cutoff point that yields the best combination of sensitivity and specificity can be identified to provide a recommendation for surgery. All data analyses were performed by using SAS software (version 9, SAS Institute, Cary, NC).

Results

To assess errors in the cephalometric digitizing, 1 investigator (C.Y.L.) digitized 20 randomly selected lateral cephalographs. The same investigator redigitized the same cephalographs after an interval of 2 weeks. The method errors between the double measurements were analyzed. No significant differences appeared between the 2 sets of repeated measurements. The method errors were between 0.16 and 0.29 mm for linear measurements, between 0.26° and 0.60° for angular measurements, and between 0.14% and 0.30% for ratios. The intraclass correlation coefficients were from 0.973 to 0.990. The reliability was high for all values. Table II shows the means and standard deviations of the 25 cephalometric measurements of both groups. Of these, 14 measurements were significantly different between the surgical and nonsurgical groups (overjet, Wits appraisal, L1-MP, Mx/Mn ratio (Cd-A/Cd-Gn), gonial angle, overbite, Si-(Li-Pg’), PP-MP, G-Sn/Sn-Me’, symphysis width, H-angle, PFH/AFH, SN-MP, Pg-Nv) ( P <0.002 [0.05/25]), based on the Bonferroni multiple-comparisons procedure. Table III shows the results of further computing the AUCs based on these 14 original measurements (range, 0.694-0.908). Their corresponding cutoff points, which yielded the highest values of sensitivity + specificity, were determined. The 14 cephalometric measurements were dichotomized into 2 parts based on the cutoff points. Depending on the clinical criteria, the part with a tendency to surgery was given a score of 1 and the other was given a score of 0. For example, in the overjet measurement, participants with a measure of less than or equal to –4.73 mm were considered to have a tendency for surgery and were given a score of 1. Hence, each of the 14 measurements was transferred into a new score of 1 and 0. The next step was to determine the optimal number of dichotomized measurements for inclusion in the final scoring system. The 14 dichotomized measurements were added 1 by 1 from the measurements with highest to lowest AUC values. Table IV shows the score systems with measurements 2 through 14 with their corresponding AUC values. Although higher AUCs would have better diagnostic accuracy, the AUCs after 6 dichotomized measurements were not greatly changed (0.96 to 0.97). Hence, a scoring system based on 6 dichotomized measurements (overjet, Wits appraisal, L1-MP, Mx/Mn ratio, overbite, and gonial angle) provided an acceptable AUC (0.96) and a feasible number (6) of measurements for the scoring system. For the scoring system of 6 dichotomized measurements, the possible scores of 0 to 6 corresponded to 0 to 6 measurements with values within the part of score 1 (tendency for surgery) in Table III .

Using the cutoff points in Table III to dichotomize each of the 14 cephalometric measurements, the optimal combination of sensitivities and specificities is shown in Table III . Since no single measurement can have satisfactory classification performance, a scoring system that combined cephalometric measurements was then compared and analyzed ( Table IV and Fig 2 ). Table V shows the sensitivity and specificity of scores 0 to 6. A score of 4 with the highest value of sensitivity + specificity appeared to be the cutoff point, indicating the best combination of sensitivity (88%) and specificity (90%), of the requirement for surgical treatment ( Fig 2 ).

The ROC curve of the final 6-measurement scoring system with the best cutoff point.

Table V

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