Cephalometric evaluation of deep overbite correction using anterior bite turbos
ABSTRACT
Objectives
To evaluate the outcome of treating deep overbite (OB) using anterior bite elevators concurrently with a pre-adjusted edgewise appliance.
Materials and Methods
The Case Western Reserve University (CWRU) cephalometric analysis was used to isolate tipping movement of upper (TUI) and lower incisors (TLI), bodily tooth movement of upper (BUI), and lower incisors (BLI), as well as vertical skeletal changes in the anterior region of the maxilla (MXSK) and mandible (MNSK). Thirty treated subjects were examined at pretreatment (T1) and posttreatment (T2) and compared to an untreated control group matched on age, sex, and Angle malocclusion from the Bolton Brush Growth Study Collection (CWRU, Cleveland, Ohio).
Results
Overbite (OB) in the treated group was decreased significantly (P < .001) (−5.6 mm) compared to controls. Statistically significant (P < .001) changes were found for BUI (−0.7 mm), TUI (0.9 mm), TLI (−1.4 mm), BLI (−1.1 mm), and MNSK (−1.6 mm). Most of the overbite correction was in the lower arch and included tipping and intrusion of the lower incisors along with an increase in lower vertical facial height.
Conclusions
Deep OB correction was achieved efficiently using anterior bite elevators with pre-adjusted edgewise appliance. Correction using bite turbos would be a treatment option for individuals presenting with decreased lower facial height and deep bite.
INTRODUCTION
Deep overbite (OB) correction has always been considered a challenging objective of comprehensive orthodontic treatment. The etiology of deep OB is believed to develop from multiple factors, hence, the various methods and differing appliances designed to “open the bite.” Ultimately, the vertical discrepancy in both jaws is controlled by molar drift toward the occlusal plane along with incisor bodily movement and/or tipping, and vertical skeletal growth of the maxilla and the mandible.1,2
Since the introduction of the orthodontic biteplate, it has been used as an adjunct in treatment of deep OB. A two-phase treatment protocol using removable biteplates on deep bite patients demonstrated the improvement of OB was a result of upper and lower incisor proclination.3 More recently, a similar study conducted on prepubertal vs pubertal patients revealed that treatment in the permanent dentition leads to a more favorable outcome through dentoalveolar changes with no significant skeletal modification.4 Most authors agree that removable biteplates allow the posterior teeth to erupt into occlusion without intrusion of the lower incisors, thus, increasing lower vertical facial height.5–11
In the last 10 years there has been an increase in the use of anterior bite elevators, also known as “turbos,” in deep bite cases. Considering their small size, ease of fabrication, and ease of use, turbos present a convenient alternative to conventional removable biteplates. Because turbos are attached to the lingual surface of the upper incisors, patient compliance is not a concern.
The purpose of this study was to determine the effects of anterior bite turbos in combination with pretorqued pre-angulated orthodontic brackets in growing patients. The Case Western Reserve University (CWRU) vertical pitchfork cephalometric analysis was used to isolate tipping and bodily tooth movements of the maxillary and mandibular incisors as well as the vertical skeletal changes.
MATERIALS AND METHODS
Subjects
The Institutional Review Board of Case Western Reserve University (IRB #2017-2179) approved this study, which retrospectively examined the cephalometric records of 57 patients treated by a single orthodontist in private practice (Marissa Keesler, Neenah, WI). Each patient was treated with anterior bite elevators, 3 or 5 mm in size, fixed on the lingual surfaces of the maxillary central incisors, and 0.022 × 0.028-inch self-ligating brackets. A combination of round, square, and rectangular archwires was used for each patient. Wires included (012, 014, 016, 018) nickel titanium, (18 × 18, 18 × 25, 20 × 20, 21 × 28, 21 × 25) BF, (16 × 22, 19 × 25, 21 × 25) stainless steel, and (19 × 25) titanium-molybdenum alloy. Short double elastics were only used to correct Class II molar discrepancy.
Thirty sets of lateral cephalograms met the inclusion criteria: (1) pretreatment (T1) and posttreatment (T2) cephalograms of diagnostic quality, (2) orthodontic treatment using anterior bite elevators, (3) OB at T1 ≥5 mm, (4) 10–14 years of age at T1, (5) Angle Class I or II malocclusion, and (6) positive anterior/posterior overjet. The excluded subjects had at least one of the following criteria: (1) inadequate diagnostic quality of radiographs, (2) not in the range of 10–14 years of age, (3) use of any functional orthopedic appliances, (4) extractions or missing teeth (excluding third molars), (5) use of intrusion arch mechanics or reverse curve of Spee (RCS) wires or temporary anchorage devices, (6) craniofacial disorders, Angle Class III, or orthognathic surgery. Thirty untreated controls, matched for age, sex, and Angle malocclusion were selected from the Bolton Brush Growth Study collection (Cleveland, Ohio).12
Image Collection
All treatment radiographs were taken on a single machine (CS 8100SC, Carestream Dental LLC, Atlanta, Ga) with patients in natural head position and maximum intercuspation. The magnification of the lateral cephalograms was consistent at 8% and all images were de-identified prior to digitization by the investigator (SE). Control group lateral cephalograms were retrieved from the digital library of the Bolton Brush legacy collection after being scanned via film digitizer (VIDAR DosimetryPRO Advantage, Vidar Systems Corp., Herndon, Va). All orientations and measurements were performed by the same investigator.
Technical Details
All images were digitally traced by one investigator (SE) using commercially available imaging software (Dolphin version 11.95, Patterson Dental Supply INC., St. Paul, Minn). Six linear landmarks were identified on each cephalogram (anterior nasal spine [ANS], center of rotation of the maxillary, and mandibular central incisors [CRU1 and CRL1], incisal edges of the maxillary and mandibular central incisors [IEU1 and IEL1], and Menton [Me]). The images at T1 and T2 were digitally superimposed for the best fit of the greater wing of the sphenoid, planum sphenoidale, and the anterior wall of Sella. This method of superimposition is a digitally modified version of a cephalometric analysis that has been used in previous studies13–15 and is considered highly accurate because, after 7 years of age, the registered landmarks are extremely stable.16 The software created a Cartesian coordinate system and the superimposition of the two tracings resulted in the 0,0 point in both tracings to be coincident. This is a modification of the use of a fiducial line employed in traditional lightbox acetate tracings in previously published studies that used the CWRU analysis.11,13–15
The CWRU analysis results in six linear and two angular variables. Figure 1 shows a schematic diagram of the skeletal, dental, and angular variables. Maxillary skeletal change (MXSK) is the vertical change of ANS from T1 to T2. Bodily movement of the maxillary incisor (BUI) is the distance between ANS and the center of rotation of the upper incisor (CRU1). Tipping movement of the maxillary incisor (TUI) is the distance between CRU1 and the incisal edge of the upper central incisor (IEU1). Tipping movement of the mandibular incisor (TLI) is the difference between center of rotation of the lower central incisor (CRL1) and the incisal edge of the lower central incisor (IEL1). Bodily movement of the mandibular incisor (BLI) is the distance between the CRL1 and Menton. Mandibular skeletal change (MNSK) is the vertical distance between ANS and Menton. Gonial angle (Ga) is the angle between the inferior border of the mandible and the posterior border of the ramus. Mandibular plane angle was measured between the Sella-Nasion plane and the mandibular plane (SN-MPA).
Citation: The Angle Orthodontist 93, 5; 10.2319/061622-432.1
Convention of Signs
A negative sign (−) was assigned to dental and skeletal movements that reduced the vertical overbite, whereas movements that increased the vertical overbite were assigned a positive sign (+). For example, bodily movement of the maxillary incisor (BUI) away from the occlusal plane (ie, intrusion) would receive a negative sign. The net changes in the linear variables were used to calculate the change in overbite using the following equation where Δ stands for the net change: Δ Overbite (OB) = Δ MXSK + Δ MNSK + Δ BUI + Δ TUI + Δ BLI + Δ TUI.
Statistical Analysis
All data were analyzed with the Statistical Package for the Social Sciences personal computer version (SPSS, Chicago, Ill). Shapiro-Wilks test was used to test for normal distribution of each parameter. Descriptive statistics (means, standard deviations, and ranges) were calculated to assess the effects of sex, race, and age matching as well as to determine the presence of any dentoalveolar changes between the treated and control individuals. Two-tailed paired t-tests were used to evaluate the statistical significance between means of both groups. Alpha was ≤0.05 and Beta ≤0.2 for all tests.
To assess investigator tracing and measurement error, 10 random subjects at T1 and T2 (five treated and five control) were retraced and the six linear and the two angular variables were remeasured. The second set of tracings and measurements were compared with the first set by using intraclass correlation coefficients.
RESULTS
Thirty treated subjects, 15 male and 15 female Caucasians, met the inclusion criteria. The mean age at T1 was 12.9 years of age and 14.8 years at T2. The average treatment time was 22.8 months, and the mean duration of anterior bite elevator placement was 12.2 months. Nineteen patients were Angle Class II, and 11 were Class I. The control group was selected from the Bolton Brush Growth Study Collection and matched on age, gender, and Angle class with the treated group (Table 1).
At T1, only one variable, TUI, showed a statistically significant difference between the groups (P ≤ .001). TUI was greater in the treated group (22.8 mm) compared to the control (21.3 mm), indicating that the incisors were more upright in the treatment group. Apart from that, there were no other significant differences between the groups (Table 2).
Assessment of the post-treatment skeletal and dental changes showed that six variables (MXSK, BUI, TUI, TLI, MNSK, and MPA) met the parametric assumptions based on the Shapiro-Wilk test. Therefore, two-tailed paired t-tests were used to detect significant differences between those variables. A Mann-Whitney test was used for the remaining three variables (BLI, OB, and GA), which were not normally distributed according to the normality test. Results are shown in Table 3.
In summary, in the treated subjects, all variables except MXSK and GA contributed to a reduction in overbite. The net OB change was a net change of −5.6 mm due to a significant −5.2 mm decrease in overbite in the treated group compared to a slight increase (0.4 mm) in overbite in the control group. The mean intraclass correlation coefficients of the repeated measurements were between 0.908 and 0.958.
DISCUSSION
This study evaluated the relative contributions to deep overbite correction of skeletal and dental components of growing adolescents treated with anterior bite turbos and a pre-adjusted edgewise appliance. As observed in previous studies, an increase in lower vertical facial height (MNSK) during orthodontic treatment of growing patients was a major factor in decreasing OB.11,13 The CWRU analysis allows practitioners an easy way to compare the effects of different treatment strategies for the correction of deep overbite. This allows the clinician to create a decision matrix based on the pretreatment characteristics of the patient and the documented effects of various biomechanical systems to choose a treatment option that will achieve the most beneficial facial and dental changes for that patient.
Previously, the effects of cervical headgear and tandem mechanics, removable appliance therapy (bionator), nonextraction treatment with preadjusted edgewise appliances and continuous arch mechanics, extraction of first premolars with preadjusted edgewise appliances and continuous arch mechanics, and extraction of first premolars using Tweed mechanics were reported.11,13,14 In addition, this analysis has been used to study open bite correction with extraction of first molars15 and the effects of the active vertical corrector. All of these studies isolated the changes in the same six variables that contributed to the final orthodontic result. The results of the present study were most similar to those seen with nonextraction continuous arch mechanics using an edgewise appliance system. In both strategies, the majority of correction was due to increased vertical mandibular growth. However, there was less lower incisor proclination using the bite turbos, and small, but significant, relative intrusion of the upper and lower incisors. The only appliance system studied to date that did not achieve overbite correction by increasing vertical mandibular growth was the Tweed system in which overbite was corrected primarily by intrusion of the upper and lower incisors.
It has been widely believed that facial types have a strong relationship with dental overbite and, hence, require different treatment approaches.17–19 Using a digitized method of the described technique to analyze the cephalograms, only one of the variables showed significant differences at T1, TUI. The treated sample was categorized to have an average lower facial height of 62 mm that coincided with the norms (64 mm ±4) and a SN-mandibular plane angle average recorded at 32.9°. Both values suggested that the treated group as well as the matched control were normodivergent with normal facial growth patterns. This suggested that, in cases of extreme hypodivergence, the effects of the bite turbos may be different.
As might be expected, the effect of the bite turbos on vertical downward growth of MXSK was negligible. The maxillary incisors, on the other hand, had 0.6-mm relative intrusion compared to controls, and labial tipping resulting in an additional 0.9 mm of overbite correction caused by forward movement of the upper incisors. These findings were different when compared to Forsberg et al., who concluded that the anterior fixed bite plane resulted in anterior rotation of the maxilla and reduction in vertical development of the upper face height.10 The lower incisors also showed significant changes over the course of the treatment period compared to the control subjects. There was relative intrusion of the lower incisors and additional overbite correction due to labial tipping.
The treated subjects obtained a net 5.6 mm of OB correction, which was predominantly achieved by increasing lower anterior facial height (MNSK) via extrusion of the posterior teeth (Figure 2). This was similar to the effect of a removable bite plane as described by Bahador et al., who also found an increase in vertical facial height.5 Thus, the advantages of the bite turbos were ease of use and elimination of patient compliance issues sometimes found with a removable appliance.
Citation: The Angle Orthodontist 93, 5; 10.2319/061622-432.1
Limitations
A limitation of this study design was that the increase in lower facial height could have been the result of maxillary or mandibular molar eruption or a combination of both.
CONCLUSIONS
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Anterior bite turbo mechanics should be considered in patients with deep anterior overbite, especially individuals with decreased lower facial height.
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Significant bodily and tipping movements of maxillary and mandibular incisors contributed to overall overbite reduction (Figure 3).
Citation: The Angle Orthodontist 93, 5; 10.2319/061622-432.1
Schematic diagram of the skeletal, dental, and angular variables.
Schematic diagram illustrating the net difference between both groups (treated minus control).
Percentage contribution of change in variables to overbite correction.
Contributor Notes