Outcome assessment of lingual and labial appliances compared with cephalometric analysis, peer assessment rating, and objective grading system in Angle Class II extraction cases
To validate our hypothesis that there would be significant differences in treatment outcomes, including cephalometric values, degree of root resorption, occlusal indices, and functional aspect, between cases treated with labial and lingual appliances. Twenty-four consecutively treated Class II cases with extractions and lingual appliance were compared with 25 matched cases treated with extraction and labial appliance. Orthodontic treatment outcomes were evaluated by cephalometric analysis, peer assessment rating, and an objective grading system (OGS). Additionally, functional analysis was also performed in both groups after orthodontic treatment. Statistical comparison was performed using the Wilcoxon signed rank test within the groups, and the Mann-Whitney U-test was used to compare between the labial and lingual groups. The only significant difference between the groups was that the interincisal angle was larger in the lingual group than in the labial group. OGS evaluation showed that control over root angulation was significantly worse in the lingual group than in the labial group. There was no significant difference between groups in the amount of root resorption or in functional evaluation. Generally, lingual appliances offer comparable treatment results to those obtained with labial appliances. However, care should be taken with lingual appliances because they are more prone to produce uprighted incisors and root angulation.ABSTRACT
Objective:
Materials and Methods:
Results:
Conclusions:
INTRODUCTION
In some Asian countries, many patients refuse orthodontic treatment because of concerns related to the esthetics of labial appliances. The use of lingual appliances is a commonly used alternative, but compared to labial appliances, these are thought to result in different clinical outcomes, such as “bite opening,”1 decreased axial inclination of the maxillary incisors,2 and reduced torque control.3 The short interbracket distance in lingual appliances is also problematic, especially during detailing,4 and the delivery of uncontrolled forces and moments may put the teeth at risk of root resorption.5
Past studies1,6 have mainly used cephalometric analysis to evaluate the clinical outcome of lingual appliances, but occlusal indices are rarely included. However, cephalometric analysis is not the only way to monitor changes in premolar and molar overjet (OJ) and problems with torque. Several studies have evaluated the severity of malocclusion using the discrepancy index (DI),7 whereas clinical orthodontic outcomes can be tested using occlusal indices, such as peer assessment rating (PAR) and the objective grading system (OGS).8,9 There have been several biomechanical and laboratory studies2,10,11 and case reports12 related to lingual appliances, but only a few clinical studies1,6 have compared their clinical outcome with that of labial appliances. Furthermore, these clinical studies are rather outdated and therefore have limited relevance to modern lingual appliances, which have undergone significant improvements in terms of bracket design, methods of setup, and indirect bonding techniques.
In the present study, we hypothesized that there could be significant differences between lingual and labial appliances in terms of the clinical outcomes (including cephalometric values, the degree of root resorption, PAR, OGS, and functional evaluation13) when treating Class II cases with premolar extraction.
MATERIALS AND METHODS
The study protocol was reviewed and approved by the Institutional Board of Okayama University.
This retrospective study used data from the first 24 consecutive cases that met the inclusion criteria for the lingual cases and compared these cases with 25 matched labial cases. The main variables within these groups were age, sex, and severity of the malocclusion. All eligible patients (ie, those who met the Okayama University Hospital criteria and provided informed consent for their participation) were included in the analysis. The criteria for case selection were as follows:
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No previous phase 1 treatment or surgical treatment;
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An age of at least 18 years at the start of treatment;
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Maxillary and mandibular first premolars extracted;
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Angle Class II malocclusion;
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Mandibular plane angle >30°; and
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No temporomandibular joint dysfunction (TMD) symptoms.
The labial group comprised five men and 20 women with an average (± standard deviation [SD]) age of 24.2 ± 4.1 years. The lingual group consisted of four men and 20 women with an average age of 26.4 ± 4.7 years.
The same clinician (Dr Takano-Yamamoto) diagnosed and reviewed all patients at 6-month intervals to assess their responses to a standardized and common treatment sequence. All patients were treated with 0.018-inch slot brackets. Lingual cases were treated with STb lingual brackets (Ormco, Orange, Calif).14 The wire sequence in all labial cases was 0.014- or 0.016-inch nickel-titanium (Ni-Ti), 0.016 × 0.022-inch Ni-Ti, 0.016 × 0.022-inch stainless steel (SS), and 0.017 × 0.022-inch SS. The wire sequence in all lingual cases was 0.014- or 0.016-inch Ni-Ti, 0.018-inch titanium-molybdenum alloy (TMA) or 0.016-inch SS, 0.017 × 0.022-inch copper (Co)-Ni-Ti, 0.0175 × 0.0175-inch TMA or 0.016 × 0.016-inch SS, 0.016 × 0.022-inch SS or 0.017 × 0.022-inch SS. Anterior retraction was by en mass retraction in all cases. A transpalatal arch or Nance appliance was required in both groups.
Evaluation by Occlusal Indices
DI (Table 1) and PAR (Table 2) were used to analyze the severity of each case. PAR and OGS were used for posttreatment evaluation to analyze the quality of the finished cases in both groups.
Radiographic Evaluation
Eight angular parameters (Figure 1) and 11 linear parameters (Figure 2) were analyzed. Root resorption was quantitatively estimated from periapical radiographic films.15
Citation: The Angle Orthodontist 85, 3; 10.2319/031014-173.1
Citation: The Angle Orthodontist 85, 3; 10.2319/031014-173.1
Functional Evaluation
Functional evaluation was performed pre- and posttreatment using a 6–degrees of freedom jaw-movement recording system (Gnathohexagraph system, version 1.31; Ono Sokki, Kanagawa, Japan), the operation of which has been described elsewhere.13 Each subject was required to demonstrate maximal voluntary jaw opening and dynamic protrusive and lateral excursive movements with the teeth in contact.
Method Error
All cephalometric tracings and occlusal cast measurements were performed by the same examiner. All cephalometric (Table 3), OGS (Table 4), and root resorption measurements were repeated after 4 weeks, and the method error was calculated using the following equation:
where Sx is the measurement error, D is the difference between duplicate measurements, and N is the number of duplicate measurements.16
Statistics
The Wilcoxon signed rank test was used to examine the difference between pre- and posttreatment cephalometric analysis in each group. Because the sample size was small and the data were paired and nonparametric, we used the Mann-Whitney U-test to compare the cephalometric analyses and OGS scores between the two groups. P > .05 was considered insignificant. Statistical analyses were performed using Statview software (SPSS, Chicago, Ill).
RESULTS
Measurement errors were 0.16 mm, 0.26°, 3.2 points, and 0.11 mm for linear cephalometric, angular cephalometric, OGS, and root resorption measurements, respectively. A high intraclass correlation coefficient of reliability (γ) was observed between the two scoring sessions in both cephalometric (γ = 0.95) and OGS (γ = 0.92) analyses.
Pretreatment
Variables for the DI analysis are presented in Table 1. The average DI scores (±SD) were 21.3 ± 11.1 inches in the labial group and 22.1 ± 11.6 inches in the lingual group. There was no significant difference between the two groups in any of the analyzed variables before treatment. The total unweighted pretreatment PAR scores (mean ± SD) were not significantly different, at 25.0 ± 9.6 and 28.0 ± 7.2, for labial and lingual treatments, respectively (Table 2). Thus, the two groups had comparable occlusal features and severity of malocclusion. The cephalometric characteristics are presented in Table 3. There were no significant differences between the groups in any of the analyzed cephalometric measurements.
Posttreatment
The average treatment times were 29.4 ± 5.6 months and 32.5 ± 6.7 months in the labial and lingual groups, respectively. This difference was not significant. There were significant differences in both groups between the pre- and posttreatment PAR scores for most variables (Table 2), but not between the two groups in terms of posttreatment PAR scores. In both labial and lingual groups, a significant difference was observed between pre- and posttreatment cephalometric values of SN-U1, IIA, OJ, and PTM-U6/PP (Table 3). The only significant posttreatment difference observed between the two groups was for IIA. Significantly more retraction of both maxillary and mandibular incisors was observed in the lingual group. OGS evaluation was 24.5 ± 7.9 and 25.3 ± 6.7 in the labial and lingual groups, respectively, and the only significant difference between groups was in the root angulation parameter (Table 4). Root resorption was not significantly different between the labial (1.1 ± 0.5 mm) and the lingual (1.3 ± 0.6 mm) group. Jaw movements (maximum opening, maximum protrusion, and maximum lateral excursion) increased in both labial and lingual groups (Table 5). Indeed, the increase in lateral excursion on the working side was statistically significant in both groups.
DISCUSSION
Our study used subjects being treated for Angle Class II malocclusion (ie, ANB of approximately 5° with average to high angle mandibular plane angle of >30° in all cases, with an average of approximately 40°). Furthermore, the average of DI was approximately 28 points in both groups, indicating that the cases analyzed perhaps had more severe malocclusions and were more difficult to treat than were those in previous studies.1,6 Considerable attention was therefore required to maintain vertical control as well as posterior-anterior (anchorage) control. The absence of any significant difference between the two groups in terms of DI, PAR, and skeletal characteristics suggested that they had a similar severity of malocclusion at the start of treatment.
Vertical Control of Mandibular Plane Angle “Bite-Opening Effect”
Lingual appliances are purported to cause intrusion of incisors and extrusion of molars, resulting in clockwise mandibular rotation.1 Indeed, some types of lingual bracket create a “bite plane” effect, with the lower incisors biting on the upper bracket, resulting in an opening of the bite. We used small-sized STb brackets that caused no bite plane effect. Cephalometric analysis confirmed that there was minimal change in the mandibular plane angle in the lingual group, although there was a slight tendency for the maxillary molars to extrude. However, overall there is no significant increase in the vertical dimension when using lingual appliances and, therefore, no apparent “bite-opening effect” compared with cases involving labial appliances.
Vertical Control of Incisors
In Class II high angle cases, one of the keys for successful treatment is to achieve proper incisor control during retraction. Generally, tipping with extrusion of incisors is not desirable during anterior retraction. However, in this study, the maxillary incisors did tend to extrude. We hypothesize that especially in lingual cases, the en mass nature of incisor retraction makes intrusion difficult and, therefore, makes extrusion more likely. Thus, in lingual cases, the use of miniscrews with a hook near the center of resistance may help with intruding the incisors during anterior retraction. In contrast, mandibular incisors were intruded in both labial and lingual cases, a phenomenon that has been reported in previous studies of Class II correction.1,6 The addition of a reverse curve of Spee in the lower archwire (to compensate for the extrusion of the maxillary incisors) may explain this mandibular incisor intrusion. Therefore, Class II high angle cases treated with labial appliances should ideally include a component of maxillary incisor intrusion, which may require additional appliances, such as miniscrews and J-hook headgear, for optimum results.
Incisor Torque Control
We believe that adequate incisor torque control was achieved in both groups because our values of posttreatment incisor angulation were similar to those from a previous study17 that analyzed such changes in bialveolar cases. Maxillary and mandibular incisor retraction (reflected in the IIA value) were greatest when using the lingual appliance, despite incisor torque control being apparently more difficult with lingual than with labial appliances.18 A recent finite element analysis19 reported that lingual crown tipping was more exaggerated with lingual appliances than with labial appliances. Thus, our data confirm the tendency for lingual appliances to tip incisors by exerting lingual crown torque to a greater extent than do labial appliances. Therefore, to produce bodily retraction of the incisors, the addition of labial crown torque in the anterior segment or the placement of “V” bends during anterior retraction is recommended.
Anchorage Control
There was an approximately 2.5 mm of anchorage loss in the maxillary molars in both groups. This is consistent with the results in patients treated by premolar extraction and traditional mechanics where the maxillary molars were mesialized by approximately 30% of the extraction space.20 There was no significant difference in the anchorage value between the two groups. Additionally, there was approximately 1.3 to 1.5 mm of mesial movement of the mandibular molars in both groups, suggesting no significant difference in the anchor value in between the lingual and the labial appliances.
OGS and PAR Evaluation
The posttreatment PAR analysis resulted in no significant difference between the groups. Although the unweighted scores were slightly higher in the lingual group, the analysis gave lower scores when it was weighted either by US or UK standards. This is because the OJ scored fewer points in the lingual group than in the labial group, and it is this parameter that most significantly affects the weighted scores (×4.5 in US weighting and ×6.0 in UK weighting). Thus, there may be a tendency for lingual treatment to result in less OJ than is associated with labial appliances at the end of the treatment.
There was no significant difference in the total OGS score between the two groups, with both scoring approximately 25 points, which is considered to be the “average” quality of finished cases.21 Only root angulation was significantly different between groups, with patients treated with a lingual appliance having higher (worse) OGS scores than labial cases, particularly in the incisor region. We suggest that the short interbracket distance in lingual appliance, especially in the incisor region, makes it difficult to place bends in the archwire between the incisors, precluding ideal root paralleling. To regain some control over root paralleling, it may be necessary to step down the wire size during the finishing stage.
Root Resorption
The pattern of the incisor retraction with the labial appliance is a known factor in root resorption in these cases.22 Indeed, a previous study23 indicated that there is a direct relationship between the amount of retraction and the severity of root resorption with labial appliance. The total amount of posttreatment root resorption (1.1 mm in labial treatment, 1.3 mm in lingual treatment) after orthodontic treatment in this study was similar to that seen in previous reports investigating labial24 and lingual5 appliances. Despite greater incisor retraction in the lingual group, there was no significant difference in the amount of root resorption, so we conclude that the lingual brackets used here have no negative effect on root resorption. This is in contrast to previous evidence25 indicating that lingual root torque (but not the labial root torque) was a predictor of root resorption.
Functional Analysis
A major concern with lingual appliances is the lingual tipping of the maxillary incisors,2,3 which is thought to be a causative factor in TMD.26 Inadequate incisor angulation can limit mandibular movement during lateral and antero-posterior jaw movements. Thus, we felt that evaluation of jaw movement was important to reveal any functional problems related to TMD that may arise from our treatments.
The results from our 6–degrees of freedom jaw movement recording system revealed significant improvement on the working side during lateral excursion posttreatment by analysis in lingual cases. We conclude that by establishing a Class I relationship between the canine and molar and by achieving an appropriate OJ and overbite, increased lateral jaw movement is facilitated.27 Furthermore, there was no significant difference between the lingual and labial groups in terms of their effects on any of the jaw movements, suggesting that lingual appliances do not cause any functional problems.
CONCLUSIONS
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Exaggerated uprighting of the maxillary and mandibular incisors following treatment of Class II extraction cases with lingual appliances indicates the need for increased lingual root torque in these cases to regain control of incisor movement during retraction.
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Lingual appliances do not cause any more root resorption than do labial appliances.
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Preserving root paralleling is challenging when using lingual appliances, especially in the incisor region, so additional archwire bending may be necessary during detailing.
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Lingual appliances do not cause significant limitation of dynamic jaw movement and are thus no more likely than labial appliances to contribute to TMD.
Angular measurements. 1. SNA angle (SNA); 2. SNB angle (SNB); 3. ANB angle (ANB); 4. SN to mandibular plane (Mp-SN); 5. SN to occlusal plane (Occl Pl); 6. SN to maxillary incisal (SN-U1); 7. mandibular plane to mandibular incisor (L1-Mp); and 8. interincisal angle (IIA).
Linear measurements. 1. Anterior cranial base (S-N); 2. Anterior facial height (N-Me); 3. Lower anterior facial height (Me/PP); 4. Horizontal distance between the maxillary and mandibular incisal edges (OJ); 5. Vertical distance between the maxillary and mandibular incisal edges (OB); 6. Maxillary incisal edge to palatal plane (PP-U1); 7. Maxillary molar cusp to palatal plane (PP-U6); 8. Horizontal distance between pterygomaxillary fissure and maxillary molar cusp vertical on palatal plane (PTM-U6/PP); 9. Mandibular incisal edge to mandibular plane (Mp-L1); 10. Mandibular molar cusp to mandibular plane (Mp-L6); and 11. horizontal distance between point B and mandibular molar cusp vertical on mandibular plane (L6-B/Mp).
Contributor Notes