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Orthodontic camouflage versus orthognathic surgery for class III deformity: comparative cephalometric analysis

Orthodontic camouflage versus orthognathic surgery for class III deformity: comparative cephalometric analysis



International Journal of Oral & Maxillofacial Surgery, 2017-04-01, Volume 46, Issue 4, Pages 490-495, Copyright © 2016 International Association of Oral and Maxillofacial Surgeons


Abstract

The objective of this study was to compare different cephalometric variables in adult patients with class III malocclusions before and after treatment, in order to determine which variables are indicative of orthodontic camouflage or orthognathic surgery. The cases of 156 adult patients were assessed: 77 treated with orthodontic camouflage and 79 treated with orthodontics and orthognathic surgery. The following cephalometric variables were measured on pre-treatment (T1) and post-treatment (T2) lateral cephalograms: sella–nasion–A-point (SNA), sella–nasion–B-point (SNB), and A-point–nasion–B-point (ANB) angles, Wits appraisal, facial axis angle, mandibular plane angle, upper and lower incisor inclination, and inter-incisal angle. There were statistically significant differences in cephalometric variables before and after treatment between the two groups. The percentage of normal pre-treatment measurements in the camouflage orthodontics group was 30.7%, which worsened slightly to 28.4% post-treatment. However in the group receiving surgery, this was 24.5% pre-treatment, improving to 33.5% after surgery. SNA, SNB, Wits appraisal, lower incisor inclination, and inter-incisal angle showed differences between the two groups before and after treatment. Wits appraisal, lower incisor inclination, and inter-incisal angle were indicative of one or other treatment. Upper and lower incisor decompensation in both groups did not reach ideal values, which impeded complete skeletal correction in 52% of surgical cases.

The prevalence of class III malocclusion varies considerably between Asians (12%), Europeans (1.5–5.3%), and Caucasians (1–4%). The A-point–nasion–B-point (ANB) angle is one of the most widely used variables for determining skeletal class, although some authors consider that Wits appraisal is the most useful parameter for identifying patients who can then be treated by orthodontic treatment alone or in combination with orthognathic surgery. Wits is the distance in millimetres from A point to B point projected and measured on the occlusal plane.

Dentoalveolar compensation before treatment varies depending on the skeletal discrepancies. Correct positioning of the lower incisors has been considered an important treatment objective before orthognathic surgery. Some authors have stated that certain skeletal class III patients treated with orthognathic surgery showed more severe skeletal discrepancies and greater compensation in incisor inclination before surgery than others.

Non-growing patients with moderate class III skeletal malocclusion and acceptable facial aesthetics can benefit from camouflage orthodontic treatment, while patients with severe class III skeletal malocclusion can benefit from orthognathic surgery. When surgical treatment is planned, an optimal result will depend on incisor decompensation. Some of these patients fail to achieve an ideal ANB angle or an optimal result due to incomplete decompensation of the upper and lower incisors resulting from a lack of vestibular bone support or excessive retroclination of the lower incisors before treatment.

Studies comparing class III patients treated by orthodontics alone or by orthognathic surgery are scarce. The aims of this study were (1) to compare different cephalometric variables in adult patients with class III malocclusion between a group treated with camouflage orthodontics and another treated with orthodontics and orthognathic surgery, in order to determine which variables are indicative of one or other treatment, and (2) to evaluate the repercussions of incisor decompensation on the skeletal correction of surgical cases.

Materials and methods

The protocol for this cross-sectional observational human study was approved by the Ethics Committee on Human Research of the University of Valencia, Spain. Rights were protected by the Institutional Review Board. This study followed criteria established in the Declaration of Helsinki for research involving human subjects, and also conformed to STROBE guidelines.

Power analysis showed that a sample size of at least 60 patients would provide an 80% probability of detecting a medium effect ( f = 0.2) associated with an interaction term, using an analysis of variance (ANOVA) model at a confidence level of 95% and assuming a correlation of 0.45 among repeated measurements.

Three hundred and forty patients who underwent treatment in the Orthodontic Department of the Faculty of Medicine and Dentistry, University of Valencia, Spain, between January 2005 and April 2015 were selected to take part in the study. A number of additional patients were recruited to compensate for possible dropouts.

Inclusion criteria established prior to commencement were the following: age over 20 years at the beginning of treatment, Wits appraisal ≤3 mm, good quality initial and final lateral radiographs, patients who had not undergone any extractions, and patients without any congenital deformity, syndrome, or cleft palate.

Following the application of the inclusion criteria, a sample of 156 patients was selected (mean age 23.2 ± 2.6 years, range 20.5–31.1 years). Seventy-seven had received camouflage orthodontic treatment (group C; 36 female, 41 male), while 79 patients had undergone surgery and formed the surgery group (group S; 30 female, 49 male). Of these latter patients, 30 underwent maxillary advancement, 16 underwent mandibular setback, and 33 underwent bimaxillary surgery.

Initial (T1) and final (T2) lateral cephalograms were selected for the cephalometric study. Fourteen cephalometric hard tissue landmarks per radiograph were digitized and nine measurements were obtained. These measurements were based on the cephalometric analyses of Steiner and Tweed ( Fig. 1 and Table 1 ). The cephalometric analysis software used was NemoCeph 11.3.1 (Nemotec, Madrid, Spain).

Cephalometric measurements.
Fig. 1
Cephalometric measurements.

Table 1
Cephalometric measurements, definitions, and mean values.
Measurement Definition Mean value ± SD
SNA (°) Angle between S–N and N–A planes 82 ± 2
SNB (°) Angle between S–N and N–B planes 80 ± 2
ANB (°) Angle between N–A and N–B planes 2 ± 2
Wits (mm) Distance in millimetres from AO to BO on the occlusal plane 1 ± 2 male
0 ± 2 female
Facial axis, FA (°) Angle between S–N and S–Gn planes 66 ± 2
Mandibular plane angle, MPA (°) Angle between S–N and the mandibular plane (Ag–Me) 32 ± 2
Upper incisor inclination, UII (°) Angle between the axis of the upper incisor (UIA–UIT) and palatal plane (PNS–ANS) 110 ± 2
Lower incisor inclination, LII (°) Angle between the mandibular plane (Ag–Me) and the axis of the lower incisor (LIA–LIT) 90 ± 2
Inter-incisal angle, IA (°) Angle between the upper incisal axis and the lower incisal axis 132 ± 6
SD, standard deviation; S, sella; N, nasion; A, A-point; B, B-point; O, occlusal plane; Gn, gnathion; Ag, antigonion; Me, menton; UIA, upper incisor apex; UIT, upper incisor tip; PNS, posterior nasal spine; ANS, anterior nasal spine; LIA, lower incisor apex; LIT, lower incisor tip.

To characterize the reproducibility of measurements, intra-observer and inter-observer coefficients of variation (CV) were calculated. To quantify the intra-observer CV, all lateral cephalometric radiographs were traced and measured 1 week after the main data collection. All lateral cephalometric radiographs were traced and measured again by a second observer. An intra-class correlation coefficient (ICC) was calculated to assess the reliability of intra- and inter-observer measurements.

A parametric model was chosen when checking the normality of the distribution of variables using the Kolmogorov–Smirnov test. Comparisons between groups were performed with the Student t -test and ANOVA. Factor comparison was performed using the χ 2 test and linear correlations with Pearson's r correlation coefficient and R 2 estimation. All measurements were analyzed using the statistics program SPSS v. 15.0 for Windows (SPSS Inc., Chicago, IL, USA). The statistician was blinded to group assignment.

Results

Measurement reproducibility results showed an intra-observer CV lower than the inter-observer CV (1.5% and 2.3%, respectively). The ICC was 0.981 for intra-observer measurements and 0.92 for inter-observer measurements.

Table 2 shows the mean and standard deviation (SD) values for the cephalometric variables before (T1) and after treatment (T2) and the changes produced as a result of treatment (difference between T1 and T2) for the two study groups: orthodontic camouflage and orthognathic surgery. Statistically significant differences were found between the two groups for Wits appraisal, lower incisor inclination, and inter-incisal angle ( P < 0.05), due to greater skeletal discrepancy in the surgery group. Wits appraisal was identified as being an ideal parameter for determining surgical treatment. The sella–nasion–B-point (SNB) angle was higher in the surgery group than in the camouflage group, with a clinically significant difference, but not a statistically significant difference ( P = 0.054). There was no statistically significant difference in facial axis or mandibular plane angle between the groups ( P > 0.05). These measurements were not found to be relevant in the decision to perform surgery, as they were identified as normal and remained unchanged in the post-treatment group. Table 2 also shows that there was a strong correlation between the values in both groups before and after treatment. Positive and statistically significant Pearson's correlation was obtained between ANB and the inclination of the lower incisor in the surgical group at T1 and in both groups at T2.

Table 2
Measurement values (mean ± SD) obtained before treatment (T1) and after treatment (T2), and the change during treatment (T2 − T1).
Measurement Group a Ideal value T1 T2 T2 − T1
Sig. b Sig. b Sig. b Pearson's r c Sig. (bilateral)
SNA (°) C 82 ± 2 80 ± 4.2 0.438 80.3 ± 4.4 0.002* 0.29 ± 2.1 0.003* 0.883 0.000
S 80.9 ± 4 84.1 ± 4.2 3.20 ± 4.3 0.446 0.015
SNB (°) C 80 ± 2 82 ± 4 0.054 81.2 ± 4.2 0.036* −0.77 ± 1.7 0.984 0.910 0.000
S 84.1 ± 4.2 83.3 ± 3.3 −0.79 ± 3.7 0.555 0.002
ANB (°) C 2 ± 2 −1.9 ± 2.3 0.083 −1 ± 2.8 0.015* 0.92 ± 1.9 0.000* 0.736* 0.000
S −3.2 ± 3.1 0.8 ± 2.5 4.03 ± 3.3 0.350 0.062
Wits (mm) C 1 ± 2 (M) −7 ± 1.9 <0.0001* −4.7 ± 2.7 0.859 2.28 ± 2.9 0.000* 0.663* 0.000
S 0 ± 2 (F) −11.2 ± 3.2 −4.6 ± 2 6.62 ± 4.2 0.225 0.241
FA (°) C 66 ± 2 66.7 ± 3.9 0.749 67.4 ± 4.5 0.132 0.66 ± 1.7 0.226 0.926* 0.000
S 66.4 ± 4.4 65.4 ± 5.3 −1 ± 6.9 0.802* 0.000
MPA (°) C 32 ± 2 33.4 ± 5.9 0.426 34.4 ± 6.2 0.384 0.96 ± 1.6 0.616 0.966* 0.000
S 34.8 ± 6.6 37 ± 13.9 2.17 ± 12.3 0.749* 0.000
UII (°) C 110 ± 2 114 ± 5.5 0.388 116.7 ± 9.3 0.933 2.74 ± 9.8 0.514 0.133 0.509
S 112.7 ± 5.5 116.9 ± 7.6 4.20 ± 6.7 0.491 0.007
LII (°) C 90 ± 2 86.2 ± 6 <0.0001* 79.6 ± 8.1 0.035* −6.55 ± 7.4 0.000* 0.490 0.010
S 77.5 ± 8.7 85.4 ± 11.6 7.93 ± 12.3 0.470 0.010
IA (°) C 132 ± 6 133.3 ± 7.7 0.008* 136.1 ± 12 0.042* 2.85 ± 13.4 0.003* 0.137 0.496
S 140 ± 10.4 124.9 ± 25.4 −15.07 ± 26.9 0.185 0.338
SD, standard deviation; SNA, sella–nasion–A-point angle; SNB, sella–nasion–B-point angle; ANB, A-point–nasion–B-point angle; M, male; F, female; FA, facial axis angle; MPA, mandibular plane angle; UII, upper incisor inclination; LII, lower incisor inclination; IA, inter-incisal angle.

a S, surgery group ( n = 79); C, camouflage group ( n = 77).

b Asterisk (*) denotes a statistically significant difference, P < 0.05.

c Asterisk (*) denotes a statistically significant difference, r > 0.6.

Table 3 shows an overall assessment of the numbers of individual patients whose cephalometric variables could be classified as below the norm, at the norm, and above the norm before and after treatment, thus evaluating the extent of norm fulfilment. For patients treated by camouflage orthodontics, 30.7% of the measurements showed normal values at T1, while at T2 this value dropped to 28.4%. For patients treated by orthognathic surgery, 24.5% of the measurements showed normal values at T1, while at T2 normal values rose to 33.5%.

Table 3
Patient distribution in the below norm (below), norm, and above norm (above) value categories. .
T1 (before treatment), % ( n ) T2 (after treatment), % ( n )
Camouflage group ( n = 77) Surgery group ( n = 79) Camouflage group ( n = 77) Surgery group ( n = 79)
Below Norm Above Below Norm Above Below Norm Above Below Norm Above
SNA (°) 48.1 (37) 40.2 (31) 11.7 (9) 50.6 (40) 36.7 (29) 12.7 (10) 48.1 (37) 33.7 (26) 18.2 (14) 13.9 (11) 38.0 (30) 48.1 (38)
SNB (°) 18.2 (14) 29.9 (23) 51.9 (40) 3.8 (3) 30.4 (24) 65.8 (52) 22.1 (17) 40.2 (31) 37.7 (29) 13.9 (11) 20.3 (16) 65.8 (52)
ANB (°) 88.3 (68) 10.4 (8) 1.3 (1) 92.4 (73) 7.6 (6) 0 (0) 74.0 (57) 22.1 (17) 3.9 (3) 51.9 (41) 36.7 (29) 11.4 (9)
Wits (mm) 100 (77) 0 (0) 0 (0) 100 (79) 0 (0) 0 (0) 80.5 (62) 19.5 (15) 0 (0) 88.6 (70) 11.4 (9) 0 (0)
FA (°) 32.4 (25) 29.9 (23) 37.7 (29) 38.0 (30) 38.0 (30) 24.0 (19) 32.5 (25) 26.0 (20) 41.5 (32) 27.9 (22) 54.4 (43) 17.7 (14)
MPA (°) 15.6 (12) 55.8 (43) 28.6 (22) 16.4 (13) 41.8 (33) 41.8 (33) 14.3 (11) 48.0 (37) 37.7 (29) 3.8 (3) 54.4 (43) 41.8 (33)
UII (°) 14.3 (11) 22.1 (17) 63.6 (49) 20.2 (16) 30.4 (24) 49.4 (39) 18.2 (14) 14.3 (11) 67.5 (52) 7.6 (6) 12.7 (10) 79.7 (63)
LII (°) 54.5 (42) 33.8 (26) 11.7 (9) 88.6 (70) 0 (0) 11.4 (9) 84.4 (65) 7.8 (6) 7.8 (6) 58.2 (46) 24.1 (19) 17.7 (14)
IA (°) 18.2 (14) 54.5 (42) 27.3 (21) 13.9 (11) 35.5 (28) 50.6 (40) 18.2 (14) 44.1 (34) 37.7 (29) 36.7 (29) 49.4 (39) 13.9 (11)
SNA, sella–nasion–A-point angle; SNB, sella–nasion–B-point angle; ANB, A-point–nasion–B-point angle; FA, facial axis angle; MPA, mandibular plane angle; UII, upper incisor inclination; LII, lower incisor inclination; IA, inter-incisal angle.

Discussion

Differences between cephalometric measurements

Comparing cephalometric measurements between the groups before treatment (T1), surgery patients showed a more negative Wits appraisal, greater lower incisor lingual inclination, and a greater inter-incisal angle, due to greater skeletal discrepancy. These results are in agreement with those of various studies by other authors. The results also confirm the claims of many researchers that Wits appraisal is an ideal parameter for differentiating between class III patients suited to treatment by orthognathic surgery and those suited to treatment by orthodontics alone.

Analyzing differences in values before and after treatment, statistically significant differences were identified for sella–nasion–A-point (SNA), ANB, lower incisor inclination, inter-incisal angle, and Wits appraisal. ANB increased in the surgery group as a result of an increase in SNA, a finding that contradicts the results of Troy et al. Pre-treatment values for facial axis angle and mandibular plane angle were classified as normal in the surgery group, and so correction was not a surgical objective and these values remained unchanged.

For patients who underwent orthognathic surgery, incomplete decompensation impeded complete surgical correction of the jaws, a result similar to those reported in several other studies.

A strong correlation was found between initial and final values, indicating that the effect of treatment behaved in a very similar way for all patients. For variables corresponding to anteroposterior skeletal analysis, the correlation was much greater in cases treated by camouflage orthodontics. Surgery produced changes in values that were more dependent on treatment than on the pre-treatment value.

Correlation between ANB angle and incisor inclination

The relationship between incisor decompensation and surgical success in class II surgical-orthodontic cases has been documented in the literature, while there have been only two studies describing the relationship between ANB angle and incisor inclination before treatment in class III. The present results indicated no significant correlation between ANB angle and upper incisor inclination in both groups. This finding differs from that of Kim et al. However, the present study did identify a correlation between ANB angle and lower incisor inclination before treatment, but only in orthognathic surgery cases, a finding that is in agreement with those of Kim et al. and Ishikawa et al.

Patient distribution as below the norm, at the norm, or above the norm before treatment (T1)

The SNA angle was below the norm in 48.1% of patients treated by orthodontic camouflage before treatment, indicating that the SNA value might have little relevance when it comes to deciding the treatment plan. This is in agreement with Guyer et al. However, the SNB angle showed values above the norm in both groups. SNB did have some relevance for deciding whether to treat with or without surgery. This finding is in agreement with Guyer et al. and Bettina and Kiliaridis. Wits appraisal was below the norm in all patients. This confirms the findings of other authors who have stated that Wits appraisal is the most decisive parameter.

Most patients presented increased upper incisor inclinations, which were more frequent in the orthodontic camouflage group. This differed from lower incisor inclination, which was more frequent in the surgery group. This confirms the findings of the present study detailed above and those of Ishikawa et al. and Kim et al., who also reported that the more negative the ANB angle, the more negative the lower incisor angle.

Patient distribution as below the norm, at the norm, or above the norm after treatment (T2)

SNA showed similar values in the two groups and only a third of the sample presented ideal values. Those with SNB angles at the norm who underwent orthognathic surgery showed little change as a result of treatment; this is similar to the finding of Johnston et al. In the present study, only 36.7% of patients treated with orthognathic surgery presented ideal ANB angle values, a percentage similar to that reported by Johnston et al., but lower than the percentage (65%) obtained by Troy et al.

Upper incisor inclination was the same and increased in both groups. These results are similar to those of Troy et al. and Pereira-Stabile et al. The incomplete pre-surgical decompensation of the upper incisors places limitations on maxillary correction by surgery. This in turn influences both Wits appraisal values and SNA, SNB, and ANB angles, which failed to undergo complete correction.

Lower incisor inclination presented the opposite situation, as treatment by orthognathic surgery produced vestibular inclination, although the decompensation remained incomplete in 24.1% of cases, with 58.2% remaining lingually inclined; these results are very similar to those of Pereira-Stabile et al., but are slightly higher than those of Johnston et al. Upper and lower incisor decompensation in both groups did not reach ideal values, which impeded complete skeletal correction in 51.9% of surgical cases.

In conclusion, SNA and SNB angles, Wits appraisal, lower incisor inclination, and inter-incisal angle showed differences between the two groups before or after treatment. Wits appraisal, lower incisor inclination, and inter-incisal angle were indicative of orthodontic camouflage or orthognathic surgery. A correlation between the ANB angle and lower incisor inclination before treatment was found, but only in the cases treated by orthognathic surgery. Upper and lower incisor decompensation in both groups did not reach ideal values, which impeded complete skeletal correction in half of the surgical cases.

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