Anterior open-bite therapy has long been considered

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1 ONLINE ONLY Orthodontic treatment of anterior open-bite malocclusion: Stability 10 years postretention Jay P. Zuroff, a Shih-Hsuan Chen, b Peter A. Shapiro, c Robert M. Little, d Donald R. Joondeph, e and Greg J. Huang f Seattle, Wash Introduction: The postretention stability of open-bite treatment is a controversial topic in orthodontics. Methods: In this study, the lateral cephalometric radiographs of 64 patients treated with orthodontics alone were evaluated to determine the amount of postretention change. The mean postretention interval was 14 years. The sample was divided into 3 groups based on the amounts of pretreatment overbite: (1) the contact group (n 5 24), incisal overlap and incisal contact; (2) the overlap group (n 5 25), incisal overlap and no incisal contact; and (3) the open-bite group (n 5 15), no incisal overlap. The headfilms were digitized, and the values were analyzed. Results: The 3 groups reacted differently. During the postretention period, mean overbite deepened in all groups, with the contact group deepening significantly more than the open-bite group. Overjet increased significantly more in the open-bite group than in the contact group. Pretreatment overjet correlated mildly with postretention overjet relapse in the open-bite group. Conclusions: All 64 subjects had positive incisal overlap at the postretention recall. (Am J Orthod Dentofacial Orthop 2010;137:302.e1-302.e8) Anterior open-bite therapy has long been considered a challenge to orthodontists. The prevalence of anterior open bite ranges from 1.5% to 11% among various age and ethnic groups, 1 and it has been shown that approximately 17% of orthodontic patients have open bite. 2 The successful treatment of open bite with well-maintained results is difficult; the combination of anteroposterior discrepancy with skeletal open bite requires the highest degree of diagnostic and clinical skill. 3 Today, orthodontists have many treatment options. High-pull headgear, 4-8 chin cups, 8 various types of bite blocks, 9,10 functional appliances, 11 extractions, multi-loop edgewise archwires, 12 mini-implants, and orthognathic surgery are some examples of the treatment modalities for treating anterior open bite. However, the prognosis with those treatment modalities has been shown to be inconclusive. 2,12,16,19-28 a Private practice, Kennewick, Wash. b Visiting orthodontist, Department of Orthodontics, School of Dentistry, University of Washington, Seattle; private practice, Taipei, Taiwan. c Professor Emeritus, Department of Orthodontics, School of Dentistry, University of Washington, Seattle. d Professor emeritus, Department of Orthodontics, School of Dentistry, University of Washington, Seattle. e Associate professor emeritus, Department of Orthodontics, School of Dentistry, University of Washington, Seattle. f Associate professor and chairman, Department of Orthodontics, School of Dentistry, University of Washington, Seattle. The authors report no commercial, proprietary, or financial interest in the products or companies described in this article. Reprint requeststo: Shih-Hsuan (Stephanie) Chen, No.363, JingpingRd., Zhonghe City, Taipei County 235, Taiwan (R.O.C.); , shchendds@ntu.edu.tw. Submitted, April 2009; revised and accepted, June /$36.00 Copyright Ó 2010 by the American Association of Orthodontists. doi: /j.ajodo When considering the patient s investment of time, discomfort, and money, the issue of stability becomes even more important. Relapse of open bite can occur because of tongue size or posture, 29 digit-sucking habits, 30,31 respiratory problems, 32,33 condylar resorption, 34 and unfavorable growth patterns. 35 However, no known characteristics are clear predictors of relapse ,36 Despite this controversy, relatively few studies have investigated the stability of open-bite treatment. Some studies were based on the results of short posttreatment periods, 12,23 and some used different methods to measure vertical relationships. 2,24 In addition, many previous studies 2,22,24 neglected to separate the anteroposterior component from the vertical problem, as suggested by Sassouni, 37 who compared subjects with open-bite characteristics with those with deep-bite. In light of these problems, we examined open-bite subjects treated with conventional orthodontics after at least 9.5 years postretention. The purposes of the study included (1) assessment of the long-term stability of anterior open bite treated orthodontically, (2) investigation of any significant cephalometric changes during the postretention period, (3) contrast and comparison of postretention cephalometric changes in patients with various categories of vertical incisal overlap, and (4) search for significant correlations between pretreatment cephalometric values and postretention changes. MATERIAL AND METHODS All subjects from the postretention files at the University of Washington in Seattle were selected if they 302.e1

2 302.e2 Zuroff et al American Journal of Orthodontics and Dentofacial Orthopedics March 2010 Fig 1. Illustrations of pretreatment overbite in each group. met the following criteria: (1) permanent dentition at pretreatment, (2) Angle Class I or Class II malocclusion, (3) lateral cephalometric radiographs at 3 stages (T1, pretreatment; T2, posttreatment; and T3, a minimum of 9.5 years postretention, and (4) a set of dental casts available before treatment. The 64 selected subjects were divided into 3 groups based on the degree of pretreatment overbite or contact (Fig 1). The contact group included 24 patients with incisal contact as judged by the lateral cephalometric radiograph and dental casts. The overlap group contained 25 patients with overlap of the mandibular and maxillary incisal edges as projected onto the nasion-menton line but without contact of the incisors. The open-bite group comprised patients with no pretreatment overlap of incisal edges as projected onto the nasion-menton line. All patients were treated orthodontically with conventional edgewise appliances, and most overlap and openbite patients were also treated with high-pull headgear. After masking subject information with tape, the following cephalometric points were recorded directly from the films. A digitizing tablet (Scriptel, Columbus, Ohio) connected to a personal computer running Dentofacial Planner software (Dentofacial Software Inc, Toronto, Canada) was used for plotting and measurement of the following. 1. Cranial base and skull: sella and nasion. 2. Maxilla: central incisor incisal edge and first molar occlusal point (tip of the mesiobuccal cusp). 3. Mandible: first molar occlusal point, central incisor incisal edge, menton, and gonion. All digitizing was done by 1 investigator (J.P.Z.). Intraexaminer digitizing error was assessed by digitizing 10 headfilms at 2 times a week apart. The amount of error was expressed as the mean value for the absolute differences and their standard deviation, range of error, standard error of the mean, and the correlation coefficient between the 2 measurements. Seven measurements were made at each time point: T1, T2, and T3 (Fig 2). 1. Facial height: nasion to menton. 2. Maxillary incisor vertical height: nasion to the tip of the maxillary incisor. 3. Mandibular incisor vertical height: menton to the tip of the mandibular incisor. 4. Maxillary molar vertical height: length of the perpendicular line from the maxillary first molar occlusal point to the sella-nasion line. 5. Mandibular molar vertical height: length of the perpendicular line from the mandibular first molar occlusal point to the mandibular plane. 6. Overjet: distance between perpendicular lines projected onto the occlusal plane from the maxillary and mandibular incisal edges. 7. Overbite: distance between perpendicular lines projected onto the nasion-menton line from the maxillary and mandibular incisal edges. Lack of incisal overlap was recorded as a negative value.

3 American Journal of Orthodontics and Dentofacial Orthopedics Zuroff et al 302.e3 Volume 137, Number 3 Table I. Descriptives by group Variable Contact group Overlap group Open-bite group Sex 9 male 15 female 6 male 19 female 4 male 11 female Age at T1 (y) Treatment duration (y) Retention period (y) Postretention period (y) Overbite at T1 4.8 (2.1 to 9.5) 1.8 (0 to 5.9) 2.2 ( 8.9 to 0.5) (mm) Times and values represent the mean for each group. Fig 2. Cephalometric measurements: OJ, overjet; OB, overbite; FH, facial height; MxI-VH, maxillary incisor vertical height; MnI-VH, mandibular incisor vertical height; MxM-VH, maxillary molar vertical height; MnM-VH, mandibular molar vertical height. Incisal overlap was recorded as a positive value or as zero when the incisal edges were at the same level. In this study, open bite was defined as negative incisal overlap relative to the nasion-menton line (Fig 1). Statistical analysis In part I of the statistical analysis, changes from T2 to T3 in each of the 3 groups were analyzed by using the Student t test for paired data (P ). Part II of the statistical procedures consisted of analysis of the correlation between the measurements at T1 with the change in those values from T2 to T3. Correlations equal to or greater than r were considered clinically significant. Both Pearson and Spearman correlations were used. Part III of the statistical analysis sought to determine whether the changes from T2 to T3 were significantly different between groups established by their overbite at T1. Analysis of variance (ANOVA) was used to test the differences in the mean changes between groups. If changes for certain values differed between the 3 samples, the post-hoc Tukey studentized range test was used to determine which groups had significant differences. RESULTS The method error was computed for the 7 measurements, and all values were recorded in millimeters. Mean error ranged from a high of 0.71 mm for facial height, to a low of 0.29 mm for mandibular incisor vertical height. Standard deviations ranged from 0.63 to 0.11 mm. The sample characteristics were similar from group to group (Table I). The numbers of years postretention varied from 13.9 for the open-bite group to 14.5 for the overlap group, with a range of 9.5 to 33.0 years for the 64 subjects. Girls comprised 63%, 76%, and 73% of the contact, overlap, and open-bite groups, respectively. Mean age at the start of treatment was within a range of 1.2 years, at 13.1, 12.8, and 14.0 years for the contact, overlap, and open-bite groups, respectively. The contact group showed significant posttreatment changes for all 7 values investigated (Table II). These changes were also larger than the method error for each measurement. There was no significant correlation between any measurement taken at T1 and posttreatment change. When the contact group was compared with the open-bite group, there were 2 significant differences in the changes from T2 to T3 (Table III): the change in overjet for the open-bite group was significantly greater than that for the contact group at the a level, and change (deepening) in overbite was significantly larger in the contact group (a ). Overbite in the contact group deepened significantly compared with the open-bite group, and overjet in the open-bite group increased significantly compared with the contact group. At T2, all 24 subjects in the contact group had incisal contact (Fig 3). When they were reexamined at T3, only 1 subject had lost incisal contact and had the characteristics of the overlap group. In the overlap group, all measurements showed significant changes in T2 values except mandibular molar vertical height (Table II). There were no significant correlations between measurement values at T1 and posttreatment changes. There was no significant difference in posttreatment changes for the 7 variables between

4 302.e4 Zuroff et al American Journal of Orthodontics and Dentofacial Orthopedics March 2010 Table II. Posttreatment changes (T3-T2) for each group and method errors Group Contact (n 5 24) Overlap (n 5 25) Open-bite (n 5 15) Variable (mm) Mean change SD P Mean change SD P Mean change SD P Method error OJ * * * 0.30 OB NS 0.31 FH * 0.71 MxI-VH * 0.69 MnI-VH MxM-VH * 0.50 MnM-VH NS OJ, Overjet; OB, overbite; FH, facial height; MxI-VH, maxillary incisor vertical height; MnI-VH, mandibular incisor vertical height; MxM-VH, maxillary molar vertical height; MnM-VH, mandibular molar vertical height. *P 5.05; P 5.01; P 5.005; NS, not significant. Table III. Comparison of posttreatment changes (T3-T2) between groups with the Tukey studentized range test Open bite vs contact Open bite vs overlap Overlap vs contact Variable (mean change in mm) Open bite Contact Significance Open bite Overlap Significance Overlap Contact Significance OJ * NS NS OB NS NS OJ, Overjet; OB, overbite; NS, not significant. *P 5.05; P 5.01 the overlap group and the other 2 groups (Table III). After treatment, 4 subjects (16%) in this group had no incisal contact (Fig 3). At T3, 5 additional patients (20%) had lost contact for a total of 9 of 25 patients without contact. Seven (28%) of the overlap subjects had minor vertical relapses from T2 to T3. The open-bite group showed significant changes from T2 to T3 for all variables except overbite (Table II). In the correlations between variables at T1 and posttreatment change (T3-T2), a mild positive correlation (r , r s ) was found for overjet (Fig 4). The changes for overjet and overbite were statistically different when comparing the open-bite group with the contact group (Table III). At T2, 12 subjects (80%) had incisal contact, 2 subjects (13%) had incisal overlap without contact, and 1 subject (7%) had no incisal overlap (Fig 3). From T2 to T3, 6 (40%) of the incisal contact group lost incisal contact. The subject with no incisal overlap at the end of treatment deepened vertically and had positive incisal overlap at T3. Three of the 15 members (20%) of this group showed minor vertical relapse from T2 to T3, but all had postive overlap at T3. DISCUSSION Positive overbite is the outcome measurement most used to define the treatment success of open bite. However, it is possible for a patient with positive overbite to have overlap without actual incisal contact. Because of this, we separated patients with overlapping incisors from those with true contact and true open bite, and these 3 incisal relationships contact, overlap, and open bite were investigated in the long-term follow-up. The 3 groups were analyzed for significant changes across time in vertical dimensions and relationships, as well as overjet. The changes were significant for all measurements except mandibular molar vertical height in the overlap group and overbite in the open-bite group. Considering mean age at T2 (about 15) and the mean posttreatment interval (about 14 years), the vertical changes were consistent with normal growth. Mean change of overbite from T2 to T3 was positive for all 3 groups, which corresponded with the normal vertical eruption of incisors. The change was not statistically significant for the open-bite group; this might indicate a tendency in this group for less eruptive potential of the incisors. Vertical relapse occurred in only 1 of 24 contact subjects (4%), but in 7 of 25 overlap subjects (28%) and 3 of 15 open-bite subjects (20%). However, even though some subjects displayed decreased overbite from T2 to T3, none had a negative incisal overlap at T3 (Fig 3). To further understand the clinical implications of our data, the records were analyzed to determine their

5 American Journal of Orthodontics and Dentofacial Orthopedics Zuroff et al 302.e5 Volume 137, Number 3 Fig 3. Number of patients in each group at T1, T2, and T3. Fig 4. Correlation of overjet change from T2 to T3 with overjet at T1 in the open-bite group. status at T2 and T3. This information was used to determine how many changed status from T2 to T3, and what percentage of the groups had incisal contact at T3. A significant number of the overlap and open-bite groups lost contact from T2 to T3. When considering the overlap and open-bite groups together, they did not have incisal contact in 45% of the subjects at T3. Examining the groups separately at T3 showed that 4% of the contact group relapsed from contact to overlap status, 20% of the overlap group relapsed from contact to overlap status, and 40% of the open-bite group relapsed from contact to overlap status. Although no subjects in the open-bite group had a negative overbite at T3, the group demonstrated much relapse when incisal contact was the criterion used. The loss of contact was associated with a comcomitant relapse in overjet. The 3 groups were examined for correlation of values at T1 with posttreatment changes from T2 to T3. The only significant correlation was for overjet at T1 with overjet change in the open-bite group (Fig 4). However, it is reported with caution because of 2 factors: the size of the sample (n 5 15) was small, and the correlations were weak (r ). No other parameters were found to be reliable predictors of relapse; this is consistent with the findings of other studies ,36 The cohort study of Denison et al 19 on open-bite stability with orthognathic surgery used the same criteria for establishing groups based on incisal contact and overlap. They evaluated the posttreatment stability of 66 patients treated with LeFort I osteotomy to reposition the maxilla superiorly. Among these patients, 14 had pretreatment incisal contact, 24 had pretreatment incisal overlap without contact, and 28 had pretreatment open bite. The follow-up period was at least 1 year posttreatment. Overbite was defined according to the nasionmenton line, as in this study. They found that 43% of the subsample with pretreatment open bite had clinically and statistically significant increases in facial

6 302.e6 Zuroff et al American Journal of Orthodontics and Dentofacial Orthopedics March 2010 height, eruption of the maxillary molars, and decreases in overbite at posttreatment. Six patients (21%) in the open-bite group exhibited reopening of the anterior open bite during the posttreatment period. The relapse of open bite in their study was attributed to significant maxillary molar eruption without compensatory maxillary incisor eruption. In our study, no subject in the pretreatment open-bite group had a negative overbite at the last follow-up visit. However, there are several differences between the studies. First, the intervention of the 2 studies is different. Since the study of Denison et al 19 involved surgery and our study was nonsurgery, the age and severity of the open-bite patients might be different. However, the pretreatment measurements of open bite were not reported in that study. Their relapsed open-bite patients experienced posttreatment maxillary molar eruption and consequent clockwise rotation of the mandible and facial height increase; in our study of adolescents, the vertical growth of the ramus and the eruption of the incisors could have compensated for the vertical eruption of the posterior teeth, thus reducing the tendency for open-bite relapse. In addition, the length of the follow-up periods in the 2 studies was different. In this study, follow-up was at least 9.5 years after orthodontic treatment with an average of 14 years, whereas, in the study of Denison et al, follow-up was at least 1 year posttreatment with a median of 3 years. In the recently published study of Remmers et al, 25 long-term stability of orthodontically treated open bite was evaluated in a larger sample (n 5 52) at least 5 years after the end of treatment. Overbite in that study was defined similarly to our study. They found that 37 subjects (71% of the total) had a positive overbite at the end of treatment; this could be considered an indicator of successful treatment. From this successfully treated group, 10 subjects (27%) experienced relapse to a negative overlap in the posttreatment period. De Freitas et al 38 and Janson et al 36,39 evaluated the stability of orthodontic open-bite correction to compare extraction with nonextraction therapy. The extraction group (n 5 31) had follow-up records at least 5 years after treatment with a mean period of 8.35 years, and the nonextraction group (n 5 21) had follow-up records at least 3 years after treatment with a mean period of 5 years. The results of these 2 retrospective studies showed that 25.8% of the extraction patients and 38.1% of the nonextraction patients had an open-bite at the latest follow-up. Those authors further assumed that the extraction approach seemed to be more stable than nonextraction. However, the difference in the relapse rates was not significant between the groups. 39 Comparing results of our study with the nonextraction study of Janson et al, 36 in which the posttreatment overbite decrease was significant but the overjet change was not, we had better vertical stability but worse anteroposterior stability. These differences might have been due to slightly differing reference lines (Nasion-Menton vs occlusal plane perpendicular) and because the patients in that study were Class I. Kim et al 12 reported that the relapse rates of treated open bite with multi-loop edgewise archwire therapy were 6% (1 of 17) for growing subjects and 10% (2 of 27) for nongrowing subjects. The results seemed promising; however, of 55 subjects treated with multi-loop edgewise archwires, only 27 were included at the 2-year follow-up. This loss to follow-up and the potential for selection bias could have influenced the relapse rate. In addition, the follow-up period of 2 years posttreatment was relatively short. Huang et al 22 examined the effectiveness of crib therapy in the treatment of anterior open bite. A sample of 23 patients who started with negative incisal overlap all had positive incisal overlap at T3, a finding similar to ours treated with conventional orthodontics. However, the criteria for sample selection makes comparison difficult, since the sample for the crib study included patients in the mixed dentition. Lopez-Gavito et al 24 reported relapse in 35% of the open-bite patients studied. Some of those subjects were used in our investigation. However, the measurement used was the distance from the tip of the mandibular central incisor to the nearest hard tissue (tooth or palate) measured along the long axis of the tooth, and open bite was noted if this distance was 3 mm or greater. This procedure for evaluation might be sensitive to anteroposterior changes. Mini-implants, including miniscrews and miniplates, have been advocated to correct anterior open bite. 13,14 By providing skeletal anchorage for molar intrusion, counterclockwise rotation of the mandible is expected to follow and, thus, closure of the open bite. The extent of molar intrusion achieved is impressive, but most of the studies were case reports, and long-term data demonstrating stability is lacking in the literature. Studies with larger samples and long-term follow-up will be needed to further support their effectiveness. Bilateral sagittal split osteotomy has been proposed to correct anterior open bite and has the advantages of allowing anteroposterior correction and minimizing undesirable soft-tissue changes. 40 However, there are no long-term studies on stability or relapse. We compared the posttreatment stability of open bite with 2 comparison groups, incisal contact and overlap; thus, this study was unique compared with most open-bite studies. Also, we included only subjects with at least 9.5 years of follow-up. The results showed

7 American Journal of Orthodontics and Dentofacial Orthopedics Zuroff et al 302.e7 Volume 137, Number 3 a better long-term success rate than did previous studies in terms of positive overbite. However, care should be taken in interpreting these results, since the sample consisted of only 15 subjects with true open bites. We showed that all 64 subjects in the 3 groups had positive overbite at the last follow-up (minimum, 9.5 years; average, 14 years). However, 60% of our openbite subjects lacked incisal contact anteroposteriorly. More prospective studies on stability of open-bite treatment with larger samples are needed to provide a higher level of evidence. CONCLUSIONS 1. All 64 subjects, including the 15 in the open-bite group, showed positive overbite at the postretention recall. However, 60% of the open-bite group lacked incisal contact. 2. The changes in overbite and overjet from T2 to T3 were significantly different between the open-bite and the contact groups. 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