Stability of open-bite malocclusion correction in

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1 ORIGINAL ARTICLE Stability of anterior open-bite extraction and nonextraction treatment in the permanent dentition Guilherme Janson, a Fabrício inelli Valarelli, b Rejane Targino Soares Beltrão, b Marcos Roberto de Freitas, c and José Fernando Castanha Henriques c Bauru, São aulo, Brazil Introduction: Although stability of anterior open-bite extraction and nonextraction treatment has been investigated, results suggesting that extraction treatment is more stable have not been confronted. Therefore, the purpose of this cephalometric study was to compare the long-term stability of anterior open-bite extraction and nonextraction treatment in the permanent dentition. Methods: consisted of 21 patients treated without extractions, and group 2 included 31 patients treated with extractions who had orthodontic treatment with fixed appliances. Cephalometric headplates were obtained at pretreatment, posttreatment, and postretention. The groups were compared at these 3 times and during the treatment and posttreatment periods with independent t tests. The number of patients with a clinically significant relapse of the open bite was compared between the groups with chi-square tests. Results: During treatment, the maxillary incisors had greater retraction amounts, and the mandibular incisors had greater retraction and lingual tipping, and less extrusion in the extraction group. In the posttreatment period, the extraction group demonstrated statistically greater stability of the overbite. However, there was no statistically significant difference in the percentages of patients with clinically significant relapse of the open bite between the groups. Conclusion: Open-bite extraction treatment has greater stability of the overbite than open-bite nonextraction treatment. (Am J Orthod Dentofacial Orthop 2006;129:768-74) Stability of open-bite malocclusion correction in the permanent dentition is the major concern in 1-8 the orthodontic treatment of this problem. Several authors investigated the stability of open-bite malocclusion correction without differentiating between 1,2,9 extraction and nonextraction treatment approaches. More recently, we conducted 2 studies that separately investigated the stability of nonextraction 10 and extraction 11 treatment, and the results pointed toward greater stability of extraction treatment. However, these results have not been directly confronted to elucidate whether the stability of extraction treatment is significantly greater than that of the nonextraction approach. Therefore, our objective was to test the following null hypothesis: stability of anterior open-bite treatment in From the Department of Orthodontics, Bauru Dental School, University of São aulo, Bauru, São aulo, Brazil. a Associate professor. b Graduate student. c rofessor. Supported by FAES (processes 00/ and 00/ ). Reprint requests to: Dr Guilherme Janson, Department of Orthodontics, Bauru Dental School, University of São aulo, Alameda Octávio inheiro Brisolla 9-75, Bauru, S, , Brazil; , jansong@travelnet.com.br. Submitted, July 2004; revised and accepted, November /$32.00 Copyright 2006 by the American Association of Orthodontists. doi: /j.ajodo the permanent dentition with and without extractions is similar in the long term. MATERIAL AND METHODS The sample comprised 2 patient groups of both sexes from the orthodontic department at Bauru Dental School, University of São aulo. consisted of 21 subjects (16 female, 5 male) with Class I malocclusions and a mean age of 12.4 years (range, years) at pretreatment (T1) treated without extractions. Thirteen patients underwent maxillary expansion with either hyrax or Haas appliances to correct posterior crossbites or to provide space in the maxillary arch. The mean treatment time was 2.4 years (range, years) between T1 and posttreatment (T2). The mean posttreatment period for this group was 5.22 years (range, years). consisted of 31 patients (23 female, 8 male) with a mean age of years at T1 treated with extractions. The mean treatment time was 2.46 years (range, years) between T1 and T2. The mean posttreatment period for this group was 8.35 years (range, years). Sixteen patients had Angle Class I malocclusions, and 15 had Class II malocclusions. Twenty-four were treated with 4 first premolar extractions, 2 were treated with 4 second premolar extractions, 1 was treated with 768

2 American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 6 Janson et al second maxillary premolar and 2 first mandibular premolar extractions, and 4 were treated with 2 maxillary premolar extractions. Seven underwent maxillary expansion with either hyrax or Haas appliances to correct posterior crossbites or to provide space in the maxillary arch. The primary selection criterion for both groups was an initial anterior open bite of at least 1 mm. Additional criteria included all maxillary and mandibular teeth up to the second molars, and treatment with edgewise appliances, associated with anterior vertical elastics. Treatment was conducted with the standard edgewise technique, which is characterized by the use of x in conventional brackets. For leveling and alignment, the usual wire sequence begins with in twist-flex or in nitinol wire, followed by , , and in stainless steel round wires. In group 2, anterior retraction was accomplished by x in or x in rectangular wires, and extraoral headgear and lip bumper to reinforce anchorage for the maxillary and mandibular teeth, respectively, when necessary. Extraoral headgear was used either to help in correcting the Class II relationship or to reinforce anchorage. Nineteen patients used highpull, 10 used cervical-pull, and 2 did not use headgear. In both groups, detailing of tooth positioning and finishing procedures were accomplished by x in or x in rectangular wires and in round wires, respectively. Intermaxillary elastics (3/16 inch) were also used to help close the anterior open bite. No additional auxiliaries were used to control the vertical dimension. After the active treatment period, a Hawley retainer was used in the maxillary arch and a bonded 3x3retainer in the mandibular arch. Myofunctional therapy was recommended to the patients to correct tongue posture and function. Lateral cephalograms of both groups were obtained from each subject at 3 stages: T1, T2, and after mean follow-up periods of 5.22 years for group 1 and 8.35 years for group 2 (T3). Because of the long time span between the evaluation stages, the lateral headfilms were obtained with various x-ray machines, which produced different magnification factors of the images between 6% and 10.94%. The cephalometric tracings and landmark identification were performed on acetate paper by a different investigator (F..V. and R.T.S.B.) for each group and then digitized with a DT-11 digitizer (Houston Instruments, Austin, Tex) and a Numonics AccuGrid XNT (model A30TLF digitizer, Numonics, Montgomeryville, a) for groups 1 and 2, respectively (Figs 1 and Fig 1. Dental cephalometric variables. Maxillary: 1, Mx1.: maxillary incisor long axis to palatal plane angle; 2, Mx1.NA: maxillary incisor long axis to NA angle; 3, Mx1-NA: distance between most anterior point of crown of maxillary incisor and NA line; 4, Mx1-: perpendicular distance between incisal edge of maxillary central incisor and palatal plane (maxillary incisor dentoalveolar height); 5, Mx6-: perpendicular distance between mesial cusp of maxillary first molar and palatal plane. Mandibular: 6, Md1.NB: mandibular incisor long axis to NB line angle; 7, Md1-NB: distance between most anterior point of crown of mandibular incisor and NB line; 8, IMA: incisor mandibular plane angle; 9, Md1-M: perpendicular distance between incisal edge of mandibular incisor and mandibular plane (mandibular incisor dentoalveolar height); 10, Md6-M: perpendicular distance between mesial cusp of mandibular first molar and mandibular plane. Maxillomandibular: 11, Overbite: distance between incisal edges of maxillary and mandibular central incisors, perpendicular to functional occlusal plane (also magnified in Fig 2). lanner Software, Toronto, Ontario, Canada), which corrected the image magnification factors of the groups. Because mandibular crowding is an important factor in the extraction decision, it was calculated in both groups to help in understanding the 2 treatment plans. Mandibular crowding of the initial dental study models was calculated as the difference between arch length (circumference, from left to right first molars) and the sum of tooth widths from first molar to first molar in millimeters. In a well-aligned arch, arch length is equal 2, Table I). These data were stored on a computer andto the sum of the tooth widths. Negative values indicated crowding. analyzed with Dentofacial lanner 7.02 (Dentofacial

3 770 Janson et al American Journal of Orthodontics and Dentofacial Orthopedics June 2006 software (Statistica for Windows 6.0, Statsoft, Tulsa, Okla). A clinically significant relapse of anterior open bite was defined as a negative overbite between the maxillary and mandibular incisors at T3. Therefore, to establish a clinical parameter for the probability of open-bite correction stability, the percentages of patients with and without clinically significant relapses were calculated from the total patients in each group. The percentages of patients with clinically significant relapses in each group were compared with the chisquare test. Fig 2. Overbite measurement (magnified). Overbite: distance between incisal edges of maxillary and mandibular central incisors, perpendicular to functional occlusal plane. Table I. Skeletal cephalometric variables Maxillary 1. SNA: SN to NA angle Mandibular 2. SNB: SN to NB angle Maxillomandibular 3. ANB: NA to NB angle 4. FMA: Frankfurt mandibular plane angle 5. SN.GoGn: SN to GoGn angle 6. LAFH: Lower anterior face height 7. SN.: SN to palatal plane angle 8. SN.O: SN to occlusal plane angle Because the groups were traced and digitized by different examiners, an interexaminer error study had to made. Therefore, 15 randomly selected radiographs were retraced, redigitized, and remeasured by the 2 examiners. The interexaminer casual error was calculated according to Dahlberg s formula (Se d 2 /2n), 13 where Se 2 2 is the error variance and d is the difference between the 2 determinations of the same variable. The systematic error was evaluated with dependent t test, at 05. Statistical analyses To apply the t test, normal distribution of the samples was verified with the Kolmogorov-Smirnov test. The results showed that all variables were normally distributed in both groups. Therefore, independent t tests were used for comparison of the groups at T1, T2, and T3, and between the changes during treatment (T2-T1) and posttreatment (T3-T2) of the groups. The results were regarded as significant at.05. These analyses were performed with Statistica RESULTS The casual errors were between 0.27 (Mx6-) and 1.65 (SN.O), with only 2 variables above 1. Of the 19 variables, only the following 4 had interexaminer systematic errors: SNB angle, FMA, SN-GoGn, and Mx1-. Therefore, the results for these variables should be interpreted with caution. had less crowding, posttreament time, and open bite than group 2 at T1. At this stage, group 2 had a slightly more accentuated vertical pattern and more procumbent maxillary and mandibular incisors (Table II). During the treatment period, the maxillary incisors had greater retraction, and the mandibular incisors had greater retraction and lingual tipping in group 2 than in group 1. In the same period, the mandibular incisors had greater extrusion in group 1 than in group 2 (Table III). In the posttreatment stage, the slightly more vertical pattern of group 2 manifested again, and the mandibular incisors ended more upright in this group (Table IV). During the posttreatment period, group 1 showed greater maxillary and mandibular anterior development, and greater overbite decrease than group 2 (Table V). In the postretention stage, the mandible was shorter in group 2, which again continued to exhibit a slightly more vertical pattern. The mandibular incisors remained more upright, and the amount of overbite was also greater in group 2. There was no statistically significant difference in the percentages of patients with clinically significant relapse between the groups (Table VI). DISCUSSION The sample sizes of 21 and 31 patients in groups 1 and 2, respectively, can be considered satisfactory because of the rigid criteria of long-term posttreatment time for sample selection. They were selected from the files of the orthodontic department, which had more than 2000 treated and documented patients, as pointed out previously. 11 There might be some concern about group compatibility because group 2 included 15 Angle

4 American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 6 Janson et al 771 Table II. Results of compatibility tests between groups 1 and 2 at T1 for cephalometric variables Table III. Comparison of treatment changes between groups (t tests) Initial crowding (mm) * Initial age (y) Treatment time (y) osttreatment age (y) osttreatment time (y) * SNA angle ( ) SNB angle ( ) ANB angle ( ) FMA ( ) SN. ( ) SN.O ( ) * SN.GoGn ( ) LAFH (mm) Mx1.NA ( ) Mx1-NA (mm) * Mx1. ( ) Mx1- (mm) Mx6- (mm) Md1.NB ( ) Md1-NB (mm) * IMA ( ) Md1-M (mm) Md6-M (mm) Overbite (mm) * Class II malocclusions, whereas group 1 had only Class I patients. However, behavior of the overbite is similar in both malocclusions with time. In addition, there is no evidence that stability of open-bite correction in Class I malocclusions is different than in Class II malocclusions; previous studies have not differentiated 1-3,17 these 2 malocclusion types in their samples. The subjects in group 2 had significantly greater crowding, more accentuated vertical pattern (SN.O), more protruded maxillary and mandibular incisors, and greater amounts of open bite than those in group 1 (Table II). These factors contributed to performing extraction treatment in this group, as would be expected. 1,9,18-21 The posttreatment time of group 2 was also longer than group 1. Therefore, it could be criticized that these groups could not be compared. 22,23 However, a more accentuated vertical pattern and especially the greater amount of open bite and longer SNA angle ( ) SNB angle ( ) ANB angle ( ) FMA ( ) SN. ( ) SN.O ( ) SN.GoGn ( ) LAFH (mm) Mx1.NA ( ) Mx1-NA (mm) * Mx1. ( ) Mx1- (mm) Mx6- (mm) Md1.NB ( ) * Md1-NB (mm) * IMA ( ) * Md1-M (mm) * Md6-M (mm) Overbite (mm) posttreatment time of group 2 would tend to accentuate 2,22-25 the open-bite relapse of this group. Consequently, because the results showed otherwise, as will be further discussed, these dissimilarities provide additional support for our results. It is exactly because group 2, which had the greatest tendency for greater relapse of the open bite, had a smaller relapse than group 1 that this comparison can be sustained. If the opposite had occurred ie, group 1 had a smaller relapse than group 2 the results could be questioned. It is obvious that whenever 2 groups are being compared, they must be ideally similar for every characteristic. However, in this comparison, group 2 had all the expected factors that could contribute to a greater open-bite relapse tendency. Nevertheless, the results were contrary to these expectations, which mean that open-bite extraction treatment provides greater stability of the open-bite correction. Still, one could argue that the longer posttreatment time of group 2 included a 3.13-year postgrowth period that could favor its greater stability of open-bite correction. However, because the groups had similar initial ages and were treated for similar time

5 772 Janson et al American Journal of Orthodontics and Dentofacial Orthopedics June 2006 Table IV. Comparison of groups at T2 (t tests) SNA angle ( ) SNB angle ( ) ANB angle ( ) FMA ( ) SN. ( ) SN.O ( ) * SN.GoGn ( ) * LAFH (mm) Mx1.NA ( ) Mx1-NA (mm) Mx1. ( ) Mx1- (mm) Mx6- (mm) Md1.NB ( ) * Md1-NB (mm) IMA ( ) * Md1-M (mm) Md6-M (mm) Overbite (mm) periods, group 2 was observed during a similar year growth period as group 1 and during an additional 3.13-year nongrowing period. It is known that, generally, the greater the posttreatment time, the greater the tendency for relapse of orthodontic corrections and especially the greater the tendency for open-bite relapse. 2,22-25 Through this rationale, the longer posttreat - ment time of group 2 would tend to cause greater open-bite relapse; this is contrary to our findings and therefore provides additional support for them. Crowding was not evaluated and compared between the groups at T2 and T3 because it is not correlated to open-bite relapse. 1,12,22 To minimize open-bite relapse, myofunctional therapy is usually recommended after orthodontic treatment The treatment protocol of the groups included myofunctional therapy after treatment. However, because this was a retrospective study, it could not be ascertained from the clinical charts that all patients in both groups followed the recommendations and underwent such therapy. Because the probability of patients who had myofunctional therapy was the same in both groups, they can be regarded as Table V. Comparison of posttreatment changes (T3-T2, t tests) SNA angle ( ) * SNB angle ( ) * ANB angle ( ) FMA ( ) SN. ( ) SN.O ( ) SN.GoGn ( ) LAFH (mm) Mx1.NA ( ) Mx1-NA (mm) Mx1. ( ) Mx1- (mm) Mx6- (mm) Md1.NB ( ) Md1-NB (mm) IMA ( ) Md1-M (mm) Md6-M (mm) Overbite (mm) * compatible in this respect. It is difficult to assess this factor in retrospective studies as evidenced in the literature. 1,9,17 Because the primary objective of this study was to directly compare these 2 groups, no control group was used. Behavior of the posttreatment overbite of these groups was compared with a normal occlusion control 10,11 group in our previous studies. Since at the end of treatment an artificial normal occlusion is obtained, it is expected to behave as such. Therefore, the groups were compared with a normal occlusion control group and not to an open-bite control group, in those previous studies, 10,11 because for ethical reasons it would be difficult to follow open-bite subjects for such a long time without providing treatment, and because behavior of the overbite is similar in open-bite malocclusions and normal occlusions with time. Treatment and posttreatment The overbite changes were analyzed primarily during the posttreatment period, comparatively between the groups, which is the main focus of this investigation

6 American Journal of Orthodontics and Dentofacial Orthopedics Volume 129, Number 6 Janson et al 773 Table VI. Comparison of groups at T3 (t tests) and percentages of patients with clinically significant relapse between groups (chi-square test) SNA angle ( ) SNB angle ( ) * ANB angle ( ) FMA ( ) SN. ( ) SN.O ( ) SN.GoGn ( ) * LAFH (mm) Mx1.NA ( ) Mx1-NA (mm) Mx1. ( ) Mx1- (mm) Mx6- (mm) Md1.NB ( ) * Md1-NB (mm) IMA ( ) * Md1-M (mm) Md6-M (mm) Overbite (mm) * Clinically significant relapse (chi-square test) ercentage of patients (%) Stability 61.9 Relapse 38.1 Stability 74.2 (Table V). Subsequently, changes in overbite and other variables during treatment and posttreatment between the groups were analyzed to elucidate whether they could explain overbite behavior during the posttreatment period. had a statistically greater overbite decrease than did group 2, confirming previous speculation that nonextraction open-bite treatment is less 14,34-36 How- 17 stable than extraction treatment (Table V). During treatment, changes in maxillary, mandibular, maxillomandibular relationships, growth pattern, and overbite do not seem to explain this different behavior because they were similar between the groups (Table III). The differences in the maxillary and mandibular component forward-displacement changes in the posttreatment period might have occurred because group 2 had slightly more vertical growth than group 1. Vertical growers usually have less apical base anteroposterior displacement than normal or horizontal growers. ever, it is unlikely that these changes contributed to the Relapse differences in overbite behavior between the groups. During treatment, there were only significant differences in the maxillary and mandibular dentoalveolar components between the groups (Table III). The maxillary incisors had greater retraction, and the mandibular incisors had greater retraction and lingual tipping, and less extrusion in the extraction group (Tables III and IV). It can be speculated that these factors, especially the smaller mandibular incisor extrusion of the extraction group, could explain the different behavior of the posttreatment overbite between the groups. Greater retraction and lingual tipping of the incisors, through the drawbridge principle, would provide greater bite closure with less extrusion of the incisors. If the incisors are less extruded, they would tend to 1,9,18 have better posttreatment stability. This was observed with the mandibular incisors that had comparatively greater extrusion during treatment in the nonextraction group (Md1-M). The posttreatment changes of the vertical development of the maxillary and mandibular incisors showed only a tendency of greater development in group 2, without statistical significance. erhaps the cumulative effects of these nonsignificant changes in the maxillary and mandibular incisors vertical development also contributed to the greater stability of the overbite (Table V). The overbite decrease in group 1 was greater than in group 2, despite the nonsignificant greater amount of overbite at T2 in group 1 in relation to group 2 (Table IV). As a result of the smaller relapse of group 2 in relation to group 1, overbite at T3 was also greater in group 2 (Table VI). As mentioned before, the longer posttreatment time of group 2 in relation to group 1 would tend to cause 2,22-25 greater relapse for that group (Table II). Never - theless, group 2 had greater stability of the open-bite correction. Therefore, the longer posttreatment time of this group supported even more consistently the results obtained. Direct comparison of these results with others in the literature was not possible because of the lack of similar studies. Despite the statistically significant difference in overbite relapse between the groups, there were no significant differences in the percentages of patients 10,11 with clinically significant relapses. This might have occurred because of the relatively small number of patients in the groups for the nonparametric statistical test used, which is usually less precise than a parametric test and requires more patients to show subtle differences. Future studies with more patients in the groups are necessary to confirm these speculations.

7 774 Janson et al American Journal of Orthodontics and Dentofacial Orthopedics June 2006 Clinical implications One should not take these results as a reason for extracting to correct open bites in the permanent dentition. The extraction group had several other factors that required extractions to be performed, as previously mentioned. These results should, rather, be used to help in decision making in open-bite borderline patients, but all other characteristics should be considered. CONCLUSIONS The null hypothesis was rejected because open-bite extraction treatment provides greater stability of the overbite correction than nonextraction treatment. However, there was no statistically significant difference between the percentages of patients with clinically significant relapse between the groups. REFERENCES 1. Lopez-Gavito G, Wallen TR, Little RM, Joondeph DR. Anterior open-bite malocclusion: a longitudinal 10-year postretention evaluation of orthodontically treated patients. 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