Cephalometric assessment of vertical control in the treatment of class II malocclusion with a combined maxillary splint

ORTHODONTICS

Cephalometric assessment of vertical control in the treatment of class II malocclusion with a combined maxillary splint

Ivana Uglik Garbui^I; Paulo Roberto Aranha Nouer^II; Darcy Flávio Nouer^III; Maria Beatriz Araújo Magnani^III; João Sarmento Pereira Neto^IV

^IAssistant Professor - São Leopoldo Mandic Dental Research Center, Campinas, SP, Brazil

^IIProfessor and Coordinator of Orthodontics - São Leopoldo Mandic Dental Research Center, Campinas, SP, Brazil

^IIIHead Professor of Orthodontics - Piracicaba Dental School, University of Campinas, Piracicaba, SP, Brazil

^IVAssistant Professor of Orthodontics - Piracicaba Dental School, University of Campinas, Piracicaba, SP, Brazil

^{Corresponding author}

ABSTRACT

Vertical control is one of the primary objectives sought by orthodontists when treating malocclusions in hyperdivergent individuals. This investigation aimed at assessing vertical control, by cephalometric measurements, during the treatment of Angle Class II Division 1 malocclusion. Thirty cases, selected from the files of the São Leopoldo Mandic Dental Research Center, Brazil, of subjects with Angle Class II Division 1 malocclusion and facial hyperdivergence, were used in this study. The patients were treated using a combined extraoral appliance during a mean treatment time of 1.1 years. Pre- and posttreatment cephalometric measurements were compared to assess vertical control. The results were submitted to ANOVA (p = 5%). The ANOVA test revealed no statistically significant difference between the pretreatment and posttreatment values of OP (Occlusal plane angle) and SN.MP. While there was a decrease in Y-axis, FMA, and PP.MP, there was an increase in SN.PP, Co-Go, AFH, PFH, and FHI. It was concluded that the divergence in the facial lower third of the patients did not increase, suggesting that the combined extraoral appliance with the line of force application directed to the resistance center of the maxilla was effective in treating Angle Class II malocclusion in hyperdivergent subjects.

Descriptors: Malocclusion, Angle Class II; Orthodontics; Extraoral Traction Appliances; Cephalometry.

Introduction

One of the primary objectives sought by orthodontists in treating hyperdivergent individuals is maintaining vertical control during the extent of the malocclusion treatment. The introduction of extraoral traction combined with removable appliances made it possible to apply a force across the entire maxillary arch, with control of both the horizontal and the vertical components.

In 1957, Gould¹ reported that changes in the inclination of the outer arm of an extraoral appliance could affect the Line of Force Application (LFA) as well as dental movement. Among the orthopedic appliances to correct Angle Class II malocclusions is the Thurow maxillary splint,² also known as combined extraoral appliance (CEA),³ which delivers force through fixed inner arms located in the palate.

The CEA is recommended especially for correcting Angle Class II malocclusions with maxillary protrusion, labially inclined upper incisors and well-positioned or retrusive mandibles. This device is effective when applied during the mixed dentition, at which time it can be used to correct malocclusions in two stages.^2,4

A good understanding of biomechanical concepts may optimize correction of Angle Class II malocclusion by using a CEA in association with a correctly directed line of force application, considering the desired movement and the center of resistance (CRe) of the molar, the maxilla and the nasomaxillary complex.^5,6

Since the extrusion of anchor molars is a common effect in using extraoral appliances that use these teeth as anchorage, the purpose of the present study was to assess vertical control in still growing hyperdivergent subjects with Angle Class II, Division 1 malocclusion, treated with an extraoral appliance combined with a palatal expander.

Material and Methods

The sample for the present study was selected from the files of scientific documentation of the São Leopoldo Mandic Dental Research Center, in compliance with Ministry of Health regulations, pursuant to Resolution n. 196/96 of the National Health Council of the Ministry of Health, dated 10/10/96, and was approved by the Research Ethics Committee, Piracicaba Dental School, University of Campinas, under protocol n. 002/2003.

Thirty cases (15 male and 15 female), selected from the files of subjects with Angle Class II, Division 1 malocclusion and facial hyperdivergence were used in this study. The patients were treated with a CEA, and the LFA was directed to the center of resistance (CRe) of the maxilla during a mean treatment time of 1.1 years. The documents included the casts and cephalometric radiographs of the subjects treated. Pre- and posttreatment cephalometric measurements were compared to assess vertical control. The following criteria of inclusion were adopted: patients with mixed and permanent dentition; with molar and canine relationships consistent with Angle Class II malocclusion; vertical growth pattern confirmed by the cephalometric values of FMA (≥ 30º), Y-axis (FHP.SGn ≥ 60º), SN.MP (≥ 35º) and ANB (≥ 4.5º).

The appliance consisted of an encapsulated (fully covered) acrylic resin plate with a 600-302 expansion screw (Dentaurum-Ispringen^®, Germany) placed between the premolars or the second deciduous molars. A telescopic tube measuring 1.2 mm in diameter (Morelli^®, Sorocaba, SP, Brazil) was inserted in the palatal region of the plate, allowing insertion and removal of a 045"/AR03X extraoral appliance (Morelli^®, Sorocaba, SP, Brazil), when necessary. The extraoral appliance was tensioned by Interlandi headgear (Morelli^®, Sorocaba, SP, Brazil). The internal arch of the extraoral appliance was inserted through the distal surface of the canines and adapted in the palate region, as near as possible to the CRe of the maxilla (according to Tanne et al.⁷, 1995, located 2 mm above the apex of the premolar roots) and to the CRe of the upper first molars (located 1-2 mm apically from the trifurcation). This arch was inserted through the anteroposterior telescopic tube ending next to the palatal root of the first molars. The anterior portion of the extraoral appliance was at a 5-6 mm distance from the labial surfaces of the upper incisors to allow breadth of movement. A 0.8 mm wire Hawley-type vestibular arch (Dentaurum-Ispringen^®, Germany) was attached to the plate when necessary, to aid in the uprighting of the upper incisors when they presented buccoversion (Figure 1).

The appliance was installed in such a way that the line of force of application was positioned over the CRe of the maxilla (Figures 2a and 2b), considering that this alignment was maintained by the traction applied by the Interlandi headgear. The force applied to each side was 250 g initially, gradually increasing up to 300 g. The patients were instructed to use the appliance 14 hours/day.

The cephalometric measurements used to assess vertical control were: Y-axis, occlusal plane angle, FMA, PP.MP, SN.MP, SN.PP, Co-Go, AFH, PFH and FHI (Figure 3). The cephalograms were traced by a single operator, and Dalhberg's error analysis was used to determine the method/operator error of the measurements (Table 1).

The errors obtained while making the measurements are summarized in Table 2. All values were within 30%, which is considered acceptable, and some were below 10%.

All the statistical calculations were performed using the Minitab software, version 14.2 (Minitab Inc., State College, PA, USA).

Results

The pre- and posttreatment mean ages of the subjects that took part in the present research are listed in Table 2.

Table 3 lists statistical analysis mean values and standard deviations of the measurements observed before and after treatment, as well as the result of the statistical significance of each measurement.

It can be observed that there was no significant difference between pre- and posttreatment measurements in either gender for the Occlusal Plane angle and for SN.MP.

On the other hand, there was a significant difference between before and after treatment values for Y-axis, FMA, PP.MP, SN.PP, AFH, PFH, Co-Go, and FHI in both genders.

Discussion

One of the fundamental goals of treating Angle Class II malocclusions with extraoral appliances at an early age, when the patient is still growing actively, is to exert vertical control during the corrective period. However, using extraoral appliances with internal arms inserted in buccal tubes in the upper molars requires double attention by the orthodontist, considering that, depending on the direction of the applied force, the direction of growth of the nasomaxillary complex may also change as a result of a clockwise vector.

Between the 50s and the 80s, the study of biomechanics of extraoral traction appliances focused solely and exclusively on assessing the angle formed between the occlusal plane and the outer arms of the appliance, and on the effects produced on the maxilla.^1,7-11 It was during this time that we gained the present knowledge that high traction forces result in better vertical control; that the resistance center of the nasomaxillary complex is located on the pterygomaxillary fissure, more specifically on its posterosuperior ridge; that the resistance center of the upper dental arch is a point resulting from the intersection of the prolongation of the dental axes; and that the combination of these factors determines the different vectors of displacement toward the maxilla and the teeth.

Thurow² also reported on the changes inflicted on the upper molars, and, in 1975, designed an appliance that delivered the force generated by extraoral traction to all the upper teeth. Later, this appliance became known as the Thurow maxillary splint. At first, it was designed with two inner arms embedded in the acrylic resin that covered the occlusal surfaces of the teeth, but changes were made through time to meet the individual needs of patients.

The present design of the appliance, as used in this study, is that of an acrylic plate that covers the palate and the occlusal and buccal surfaces of teeth, with removable inner arms inserted in the resin and extended up to the resistance center of the first molar.⁶

Analysis of the measurements for the vertical component shows that there is no statistically significant difference between the pre- and posttreatment values of the occlusal plane angle (–0.47º ± 2.45º for females and –0.73º ± 3.34º for males), suggesting that there is relative stability in the proportion of the middle third in relation to the face, since the occlusal plane maintained a constant position in relation to the Frankfort horizontal plane. In conjunction with the results for the SN.MP angle (–0.67º ± 2.48º for females and –0.60º ± 2.26º for males), it can further be suggested that there was no significant clockwise rotation of the nasomaxillary complex or the jaw, indicating that there was no increase in facial divergence.

This observation can be reinforced by the reduction in the values for Y-axis (–0.83º ± 1.38º for women and –0.47º ± 1.85º for men), PP.MP (–2.03º ± 1.89º for women and –0.60º ± 2.86º for men) and FMA (–2.46º ± 1.76º for women and –1.13º ± 2.06º for men). These values presented little variation and even a slight increase in the growth of individuals in the same age bracket,¹² showing that there was no rotation at the base of the mandible. In regard to the SN.PP angle, a statistically significant increase was observed (0.77º ± 1.02º for women and 0.23º ± 1.13º for men); nevertheless, clinically speaking, this increase may be considered small, thus propitiating closure of the anterior bite in individuals presenting it, since the face as a whole did not present clockwise growth after treatment.

The vertical control observed in the present study, considered very important in treating Class II malocclusions, has also been observed in other clinical reports^4,13-15 in which the authors directed the line of force application toward the CRe of the maxilla, as was done in the present study. Disarticulating the occlusion favors the correction of Angle Class II malocclusion and prevents the extrusion of upper molars and incisors, an effect that is unwanted in the mechanics of retraction and that influences the rotation of the mandibular plane.¹⁵

The importance of vertical control ascertained up to now gains even greater ground when analyzing the behavior of facial heights. AFH values (1.80 ± 2.14 mm for women and 2.20 ± 1.74 mm for men) and PFH values (1.60 ± 2.26 mm for women and 2.67 ± 2.61 mm for men) had statistically significant increases, denoting a vertical growth expected in the lower third of the face,^11,16 but still proportionally smaller if we consider the increase expected for these measurements in individuals in the same age bracket,¹² but remaining proportional to each other, as shown by the variation within the normal range observed for FHI values (0.010 ± 0.041 for women and 0.022 ± 0.041 for men), with no change in facial hyperdivergence. Furthermore, a greater increase in posterior facial height improves facial harmony, attenuating the dolichocephalic facial pattern.

Retention of the vertical component is not always absolute when other dentoalveolar changes are associated to Class II malocclusion, in cases where low extraoral traction is applied.^3,6,17

How the line of force application (LFA) is directed is decisive in obtaining the desired response. In the present study, the LFA was directed to the resistance center of the maxilla, in order to gain distalization and intrusion of the upper molars, resulting in good vertical control. Therefore, the combined extraoral appliance is an option to be considered in treating Class II malocclusion in hyperdivergent individuals.¹⁸

Conclusions

It was concluded that there was vertical control of cephalometric measurements, shown by the absence of significant changes in the values for the occlusal plane and for SN.MP, and by a reduction in the values of the Y-axis, FMA and PP.MP angles. The results indicated that there was no increase in facial hyperdivergence and confirmed the efficacy of the CEA in correcting the malocclusion assessed in the treatment phase.

Accepted for publication on Oct 08, 2009

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Publication Dates

• Publication in this collection
  19 Aug 2010
• Date of issue
  Mar 2010

History

• Received
  16 Apr 2009
• Accepted
  08 Oct 2009