Stability of anterior open bite cases treated with upper and lower extrusion arches in adults: a follow-up study

Patients with anterior open bite (AOB) may complain of improper speech, difficulty in incising food, poor esthetics, and psychological problems.¹  The etiology of AOB could be attributed to genetic or environmental factors.¹  While genetic factors might influence the vertical growth pattern and the development of orofacial structures, environmental factors, such as thumb sucking and tongue posture,²  contribute to the development of AOB.^3,4  The presence of multiple etiologic factors for AOB makes it clinically challenging for orthodontists to treat and retain.^5,6 

AOB in adults can be well managed with surgical and nonsurgical therapies according to a comprehensive review and meta-analysis by Greenlee et al.,⁷  and stability with both treatment techniques was higher than 75%. Some patients may decline any surgical intervention due to the dangers and costs involved with such operations. Extrusive mechanics to the anterior segments, intrusive mechanics to the posterior segments, or a combination of the two are examples of nonsurgical treatment approaches used to treat AOB. The extrusion arch is one of the nonsurgical treatment approaches in the orthodontic literature that has shown promising treatment results in the closure of the AOB.^8–11 

Relapse or instability refers to the potential of an AOB to return after treatment. Treated AOB has a high rate of relapse owing to multiple etiological factors such as tongue posture, retention type, patient compliance, and genetic factors.¹²  Since one of the goals of orthodontic correction of AOB is attaining stability of the corrected bite, it is necessary to evaluate the potential for relapse of this treatment modality.

In a previous study, dental and skeletal effects of upper and lower extrusion arches implemented in the treatment of AOB in adults were reported.¹¹  No previous studies have investigated the post-treatment stability of AOB cases treated using extrusion arches. Therefore, the current study aimed to evaluate the treatment stability of AOB cases treated with the upper and lower extrusion arches in adults after at least 1 year post-orthodontic treatment. The null hypothesis was that there would be no significant change in overbite 1 year post-treatment.

This study was approved by the institutional review board at the Faculty of Dentistry, Alexandria University (IRB:00010556–IORG:0008839) as a clinical study. Informed oral and written consents were obtained from the patients before the beginning of the study.

Power analysis demonstrated that 18 patients were needed to achieve 80% power to detect a significant change in overbite of 1.6 ± 1.3 mm after orthodontic treatment at P ≤ .05.¹³  The sample size was increased to 23 patients to compensate for any potential cases lost in the follow-up. Sample size calculations were performed using MedCalc Statistical Software (MedCalc Software Ltd, Ostend, Belgium).

Adult patients (>18 years old), with full permanent dentition (except for the third molars, which were removed if erupted), mild to moderate AOB (2–5 mm), skeletal Class I or mild skeletal Class II, and crowding of no more than 5 mm, planned for nonextraction treatment were recruited. Patients with temporomandibular joint disorders, orthognathic surgical treatment needs, maxillary posterior vertical dentoalveolar excess, or increased incisal show at rest were excluded. All the cases were treated by the same orthodontist at the university hospital.

The clinical procedure was described previously.¹¹  Orthodontic correction of AOB began with leveling and alignment followed by insertion of upper and lower extrusion arches formed in 0.016 × 0.022-inch stainless-steel archwire. The anterior end of the wire was ligated to the main archwire using a steel ligature between the brackets of the lateral incisors and canines on both sides to create a one-couple force system (Figure 1).

After bite closure, extrusion arches were removed. Patients were instructed to wear 3/16-inch medium intraoral vertical box elastics with 4.5-ounce (128g) force (Ortho Technology, Tampa, Florida, USA) to help settling of teeth in the buccal region.

After debonding, bonded tongue spurs (Figure 2) were placed on the lingual surface of the lower incisors. Teeth were retained with a combination of a fixed retainer and an overlying vacuum-formed retainer (VFR) with a window to accommodate the bonded tongue spurs. Patients were asked to wear the VFR at nighttime only for at least 1 year post-treatment. Follow-up visits after debonding were scheduled every 3 months unless patients reported debonded spurs, fixed retainers, or broken VFR.

Patients were recalled 12 months after the end of the treatment completion to assess the stability of treatment using cephalometric measurements. Additionally, the Photographic Openbite Severity Index (POSI)⁵  was used to evaluate overbite clinically:

• Score (0): All incisors show positive vertical overlap (PVO).

• Score (1): One or two lateral incisors lack PVO.

• Score (2): One central incisor does not show PVO.

• Score (3): Two central incisors without PVO.

• Score (4): All incisors without PVO.

• Score (5): All anterior teeth without PVO.

• Score (6): No PVO extending posteriorly to at least one premolar tooth.

Cephalometric evaluation of the dental and skeletal changes was conducted pre-treatment, post-treatment, and at least 1 year after debonding (T₀ and T₁, and T₂, respectively). All lateral cephalograms were traced and measured on matte acetate paper by a single blinded investigator. The linear and angular measurements were recorded to the nearest 0.5 mm and 0.5°, respectively (Table 1, Figure 3).

Statistical analysis was performed using statistical software (SPSS Inc Version 22, Chicago, IL, USA). Repeated-measures analysis of variance (RM-ANOVA) was used to compare the data obtained at T₀, T_1, and T₂ after verifying normality of the data. To assess errors in landmark identification, measurements, and POSI scores, intra-examiner reliability was accomplished by remeasuring the cephalometric data and the POSI for 30% of randomly selected patients after 3 weeks from the time of initial measurement. The results were assessed by intraclass correlation coefficient.

The original sample size consisted of 23 adult females. Out of the 23 cases, 20 patients returned for recall: 20 adult female patients with a mean age of 21.6 ± 1.9 years and a mean AOB pre-treatment of 3.80 ± 1.4.

Descriptive statistics and the results of RM-ANOVA of dental and skeletal cephalometric measurements from T₀, T₁, and T₂ are summarized in Table 2. According to Mauchly’s test of sphericity, there was statistical significance (P < .01), thus sphericity was violated; Greenhouse-Geisser correction (0.68) was adopted. The main effect of time (within the groups) on dentoskeletal variables was statistically significant based on Greenhouse-Geisser correction (0.68); F = 7.4, P < .01. This effect, however, was qualified by a significant (time × dentoskeletal variables) group interaction, Greenhouse-Geisser assumed; F = 67.7, P < .01. Additionally, the mean change in dentoskeletal variables followed a quadratic trend across the 3 different timepoints and was statistically significant (F = 62.1, P < .01). The intraclass correlation coefficient showed excellent correlation between the test and retest cephalometric measurements (89%) and POSI scores (97%) with a 95% confidence interval of 87%–92%) and 96.8%–98.1%, respectively.

The mean AOB for the patients before orthodontic treatment (T₀) was −3.80 ± 1.4, which was corrected to a positive vertical incisal overlap of 1.89 ± 0.58 at T₁. The mean change in overbite was 5.69 ± 0.7 mm with an average treatment duration of 17 months ± 24 days. The positive overbite obtained was shown to be maintained at the end of orthodontic treatment: 1.40 ± 0.53 mm (T₂) (Figure 4).

Stability was evaluated quantitatively through lateral cephalometric dentoskeletal measurements (T₂, Table 2) and qualitatively by assessing the POSI. Of the 20 patients who returned for recall at a minimum of 12 months post-treatment, 85% (n = 17) showed a POSI score 0, 10% (n = 2) presented with a score of 4, and 5% (n = 1) showed a score of 1 (Figure 5). Cephalometric superimpositions of the overall dentoskeletal, maxillary, and mandibular changes are illustrated in Figure 6.

Successful orthodontic correction of AOB is not only judged by the closure of the bite at the end of orthodontic therapy, but also by the maintenance of bite closure after treatment.¹²  Therefore, it was important to evaluate stability of the treatment outcomes achieved by the extrusion arches in AOB treatment in the current study 1 year after treatment completion.

The results showed an increase in overbite at the end of orthodontic treatment (T₁) by an average of 5.9 ± 1.9 mm. The overbite decreased insignificantly by 0.49 mm at T₂, which was quite similar to a study by Kim et al.¹⁴  using the Multiloop Edgewise Archwire technique in the treatment of AOB in which the overbite decreased by 0.4 mm in the nongrowing group at the end of the 2-year follow-up period. Küçükkeles et al.¹⁵  reported 78% stability after 1 year of AOB treatment using curved archwires and anterior elastics with a decrease in the overbite by 1.25 mm due to the extrusion of first molars.

Ideally, incisor extrusion using extrusion arches is most suitable for noncompliant patients with insufficient incisor exposure at rest and smiling.¹⁶  The stability of AOB treated with incisor extrusion has been debated in the literature and was found to range from 64% to 86% depending on the treatment modality and the retention appliance employed.¹⁷  Extrusion arches work by extruding and uprighting the anterior teeth. Upper and lower incisors were extruded in the current study by an average of 2.2 and 1.98 mm, respectively. This extrusion was maintained at T₂ with a nonsignificant decrease in overbite (0.25 and 0.3 mm for the upper and lower incisors, respectively). This was consistent with the study by Küçükkeles et al.,¹⁵  which reported stability of upper and lower incisor positions 1 year after treatment. Similarly, Lo and Shapiro¹⁸  in a 5-year follow-up study of two groups of AOB patients, one with presurgical incisor extrusion and a nonextrusion group, found that extrusion of anterior teeth had no effect on AOB stability, with both groups showing equal stability (75%).

Relapse in AOB cases might occur due to intrusion of extruded incisors or extrusion of previously intruded molars. Avoiding molar extrusion is a key factor in AOB treatment to preclude any possible interference with the bite closure and a subsequent increase in anterior facial height (AFH). This is especially important in adult patients with AOB in whom molar extrusion is not compensated by mandibular ramal growth. Thus, facial esthetic goals would not be compromised particularly in patients with a hyperdivergent facial type.¹⁹  In this study, significant intrusion of the upper first molars was achieved at the end of orthodontic treatment (T₁) due to the intrusive force on the molar applied by the extrusion arch. The lower molars remained mainly stable as the lower extrusion arch prevented anticipated compensatory lower molar vertical movement in the occlusal direction. There was a nonsignificant loss at T₂ of 0.4 mm in the intrusion achieved in the maxillary first molar. The intrusion of upper molars also led to a significant decrease in the mandibular plane angle (SN-MP), AFH, and lower AFH (LAFH), which were found to be stable at T₂.

Küçükkeles¹⁵  et al. reported a reduction of 1.4 mm in overbite due to extrusion of upper and lower first molars after a 1-year follow-up in a group of patients with AOB malocclusion treated using nickel-titanium curved archwires and anterior elastics. This, in turn, lead to an increase in the mandibular plane angle and AFH. Studies using temporary anchorage devices (TAD) to treat AOB by intrusion of molars reported 78%–82% stability according to Medeiros et al.²⁰  The main cause of relapse in AOB patients treated with TADs was molar extrusion, ranging from 10% to 21.74%.²¹ 

Failure of tongue posture adaptation after orthodontic therapy has been considered a major cause of relapse of AOB. Some studies recommended tongue spurs for long-term stability of AOB treatment.²²  Tongue spurs can remind patients to maintain proper tongue rest position, therefore, decreasing the potential for relapse. In addition, maxillary and mandibular vacuum-formed retainers (VFR) were given to all patients in this study as they cover the anterior and posterior teeth and, therefore, maintain the intrusive effect on molars by covering the occlusal surfaces.²³  VFRs have been shown to have better patient compliance and are more esthetically accepted compared to other retention appliances such as Hawley appliances.²⁴ 

Cephalometric analysis of the three patients showing relapse at T₂ revealed an increase in U1-PP angle (n = 1) or extrusion of the intruded maxillary molars (n = 2). The re-extrusion of intruded molars is a common finding in relapsed AOB cases in studies implementing molar intrusion as the primary method of open bite closure.^21,25  Additionally, one case had debonded tongue spurs, resulting in improper tongue posture or activity against the incisors that resulted in AOB relapse.

One limitation of the current study could be lack of a comparative treatment group. However, this study was a follow-up of cases previously treated with extrusion arches. The last cephalometric acquisition (T₂) to assess potential relapse of AOB was 12 months after debonding. This duration was relatively short compared to other reported 3-year²⁶  and 5-year²⁷  follow-up periods in the literature. However, it has been reported that the highest tendency for AOB relapse usually occurs in the first year post-orthodontic correction.²⁶ 

• AOB cases treated with upper and lower extrusion arches showed good stability (≅85%) after at least 12 months post-treatment.