Evaluation of dental arches in orthodontic patients with condylar hyperplasia in a North Sumatra subpopulation: a cross-sectional study

Introduction

The unilateral non-neoplastic overgrowth of mandibular condyle that leads to occlusal interferences and joint dysfunction or pain, is identified as condylar hyperplasia (CH). The elongation of condylar head, neck, and lower arch corpus leads to the development of occlusal disharmony, dental compensation, and asymmetry due to continued abnormal growth (Bharathi et al., 2014; Wolford et al., 2014). This deformity requires assessment in condylar growth and sometimes requires high condylectomy combined with orthognathic surgery and articular disc repositioning to achieve treatment stability (Lippold et al., 2007; Wolford et al., 2009). Sequential assessments (six to twelve month intervals) of CH aim to prevent worsening functional, esthetic, skeletal, and occlusal changes during orthodontic treatment. These examinations include clinical examinations, cast analysis, and radiographic evaluations in the abnormal condylar lower arch growth. Since CH is a rare disorder, previous studies explore the multiple factors of mandibular growth asymmetry and development. The characteristics of CH are as follows: excessive or persistent growth of condyle leads to facial asymmetry with occlusal discrepancies and temporomandibular joint disorder as concurrent symptoms. It has severe asymmetry over a long-time period and can grow past the growth period gradually (Almeida et al., 2015; Goulart et al., 2018; Raijmakers et al., 2012; Wolford et al., 2014).

CH usually occurs during puberty and ceases at the same time as the completion of healthy growth (Raijmakers et al., 2012; Wolford et al., 2014). CH affects women more than men with a 3:1 ratio (Nitzan et al., 2008). It can also continue growing past the growth period (Almeida et al., 2015; Obwegeser & Makek, 1986; Pacheco et al., 2010). Finishing treatment in the soft tissues usually requires correction, especially in patients with longstanding condylar hyperplasia, and soft tissue procedures include facelifts, augmentation using medpor implants or fat grafts as alternative treatment (Alyamani & Abuzinada, 2012). The investigation of facial asymmetry with CH complexity should be integrally planned during orthodontic treatment (Olate et al., 2013).

Previous studies report that CH adversely affects morphology and size of the mandible, it also alters the occlusion development along with dental arches (Goulart et al., 2018; Mehrotra et al., 2011; Wolford et al., 2014). Genetic and environmental factors influence occlusal development and dental arch form variations. In planning orthodontics treatment, changing the dental arch form can also influence treatment stability. In patients with facial asymmetry, dental alveolar compensation is one treatment choice when treating malocclusion with dental arch asymmetry. Thus, this study aims to evaluate dental arches by analyzing the dental arch asymmetry and form in orthodontic patients with CH in a subpopulation of North Sumatra, Indonesia.

Methods

This is a retrospective study of the clinical records of suspected CH patients that sought for the initial orthodontic treatment at the Dental Hospital, Universitas Sumatra Utara between January 2015 and March 2019. The Research Ethics Committee of the Universitas Sumatera Utara Medical Faculty approved this study (378/TGL/KEPK FK USU-RSUP HAM/2019). Those patients who were treated with fixed orthodontics at the Dental Hospital, University of Sumatra have signed informed consent, which includes data collection for research purposes.

Data analysis

Evaluation of dental arch symmetry was done using plaster casts taken from the patients’ medical records.

Initial measurements. The well-trimmed plaster casts were positioned on millimeter rule paper and measurements were taken manually with a cephalometric and metal protractor. To determine the upper arch midline, a mark was located along the mid palatal suture. The symmetry axis of the upper arch midline was made by connecting the incisive papilla (As=Anterior superior) passing second palatal rugae to the most visible posterior upper arch landmark (Ps=Posterior superior) over the mid palatal suture. Once the Ps was marked, the end reference point was located on the border between the hard and soft palate. Then Ps mark of the upper arch was transferred to the lower arch (Pi=Posterior inferior) using a ruler positioned perpendicular and occluded upper and lower plaster casts. To determine the anterior lower arch point (Ai=Anterior inferior), the upper arch As was transferred to the lower arch using a ruler that occluded upper and lower plaster casts. The symmetry axis of the lower arch midline was obtained by connecting the Ai to the most visible posterior landmark (Pi) over the lingual frenulum to the posterior border of lower arch. After marking the midline symmetry axis, we can evaluate the dental arch asymmetry by measuring dental midline deviation (MD), canine tip in the dental arch (PC), distance of the upper canines from the palatal suture (DC) and inter canine distance (ICD) in the upper and lower arches (Scanavini et al., 2012).

Angular and linear measurement of the dental arch asymmetry. Angular arch asymmetry was performed by measuring the right and left canines to the upper arch symmetry axis using a cephalometric protractor in the upper arch (this is known as midline deviation (MD) (Figure 1 and Figure 2). The position of the canine (PC) is the distance from the cusp tip on each side that were projected perpendicular to the symmetry axis using a metal protractor. Distance of canines (DC) is the linear measurement from right to left canine tips (Figure 3). This angular and linear measurement of upper and lower arch dental asymmetry has predictive accuracy and is marked as negative if shifted to the left (Scanavini et al., 2012).

Figure 1. Measuring angular upper arch asymmetry.

The plaster cast model is positioned with a protractor at the cusp of the right upper arch canine (A); the protractor shows that PC of right upper arch canine is 46° (B).

Figure 2. Measuring angular lower arch asymmetry.

The plaster cast model is positioned with a protractor at the cusp of the right lower canine (A); the protractor shows that PC of right lower arch canine is 39° (B).

Figure 3. Measuring distance of the canines in upper and lower arch asymmetry.

Evaluation of dental arch form. The evaluation of dental arch form by comparing arch width and length. Dental arch dimensions were as follows: L33 (inter canine width), from right canine cusp to left canine cusp; L66 (intermolar width), from right first molar cusp to left first molar cusp; L77 (posterior intermolar width), from right second molar cusp to left second molar cusp; L31 (sagittal dental arch), from the “arrow” of the anterior curve; L61, from the incisal edge to the line joining the mesiobuccal canines of the first molar; L71, the incisal edge to the line joining the distobuccal cusps of the second molar. These six factors characterized both the arch form and the dimension that will determine the dental arch ratio: L31/L33, L61/L66, L71/L77, L33/L66, L61/L71 (Figure 4 and Figure 5). The arch is classified as narrow if three dental arch ratios (L31/L33, L61/L66, L71/L77) are positive, the arch form is classified as wide if they are negative. The arch is classified as mid if none of those dental arch ratios significantly deviates from the average. The arch form is pointed if only the L31/L33 has a noticeable intensity significantly higher value than all the comparisons (L61/L66, L71/L77, L33/L66, L61/L71). The arch is classifiedas flat only if the L31/L33 has significantly lower value than all comparisons (L61/L66, L71/L77, L33/L66, L61/L71) (Raberin et al., 1993). Those measurements were repeated in 15 days after obtaining the initial data to assess the reliability with intra-rater measurement.

Figure 4. Measurement of upper dental arch form.

The sagittal dental arch from the arrow of the anterior curve (L31) (A); from right canine cusp to left canine cusp is identified as intercanine width (L33) (B); the incisal edge to the line joining the mesiobuccal canines of the first molar (L61) (C); the dental arch dimension from right first molar cusp to the left first molar cusp is intermolar width (L66) (D); the incisal edge to the line joining the distobuccal cusp of the second molar (L71) (E); from right second molar cusp to the left second molar cusp is the posterior intermolar width (L77) (F).

Figure 5. Measurement of lower dental arch form.

The sagittal dental arch from the arrow of the anterior curve (L31) (A); from right canine cusp to left canine cusp is identified as intercanine width (L33) (B); the incisal edge to the line joining the mesiobuccal canines of the first molar (L61) (C); the dental arch dimension from right first molar cusp to the left first molar cusp is intermolar width (L66) (D); the incisal edge to the line joining the distobuccal cusp of the second molar (L71) (E); from right second molar cusp to the left second molar cusp is the posterior intermolar width (L77) (F).

Statistical analysis. Analyzing the significant difference of symmetrical angular and linear measurement of the dental arches based on gender was done using paired independent pair t-test (p<0.05). This study used the second measurement in analyzing symmetrical dental and dental arch form with chi-square and Cramer’s V correlation. SPSS version 17.0 was used for data analysis.

Results

There were total of 14 male and 20 female patients who were suspected as CH patients between 10 to 30 years old based on date of birth stated in the medical record. While there were facial asymmetry based on photography analysis, positive temporomandibular joint disorder, vertical mandibular asymmetry based on pre treatment panoramic radiographs, and posterior cross bite; there were some subjects didn’t show mid line deviation in upper and/or lower arch.

Table 1 shows the distribution of upper and lower arch dental symmetry in this study. Based on gender, there was no significant difference in upper and lower dental symmetry between male and female (Table 2). There was a significant difference (p<0.05) of upper canine distance from the palatal suture in female patients, but no significant difference in other symmetry variables between male and female (Table 3), There was also no significant difference of midline deviation between male and female in this study (Table 4). However, there was a moderate correlation (r=0.379) of midline deviation in upper and lower dental arches of this studied subjects (Table 5). In these CH patients, the dental arch form in upper and lower dental arch were mid and flat. There was also a moderate correlation (r=0.448) between upper and lower dental arch form (Table 6).

Discussion

The dental arch evaluation is an essential issue in orthodontic treatment. We performed a retrospective study of clinical records of suspected CH patients in order to evaluate dental arch symmetry. The failure in early identification of CH can lead to unfavorable esthetic and functional orthodontic treatment resulting in the development of asymmetry. Identifying the growth pattern occurring in CH and deciding the activity of condylar growth are important in treating any malocclusion with lower arch asymmetry. Wolford et al. introduced an updated classification system based on growth, clinical, histological, and imaging characteristics (Wolford et al., 2014). Progressive unilateral growth expansion of condyle, leads to facial asymmetry, malocclusion, and indirectly affects the upper arch development, also shifting off the chin towards the unaffected side (Goulart et al., 2018; Wolford et al., 2014). A study by Mehrotra et al. in 2011 on five Indian adult active CH patients reported that facial asymmetry was the most common clinical finding, followed by midline shifting, protruded chin, contralateral cross bite, and upper arch occlusal canting (Mehrotra et al., 2011). CH clinical findings show midline shifting along with chin deviation to contralateral side with related posterior cross bite (Almeida et al., 2015). Generally, patients with active CH present facial asymmetry transversally, vertically or combined (Nitzan et al., 2008). There was a significant difference in soft-tissue asymmetry between CH subjects and controls as observed in three-dimensional photographs. Therefore, this method is a valid and suitable tool for the evaluation of progressive worsening occlusion, which is a limitation of radiographs (Verhoeven et al., 2013). In some emerging countries, panoramic radiographs were suitable for screening CH, although the diagnostic gold standard was to assess condylar growth activity using bone scintigraphy (Nolte et al., 2015). Previous studies have also reported that there were no significant association between vertical mandibular asymmetry and temporomandibular disorder symptom (Mendoza-García et al., 2019; Sofyanti et al., 2018). Therefore, we used photography, positive posterior cross bite from plaster cast and positive temporomandibular disorder in a cohort of 10–30 year old patients based on their initial dental record in this study.

Table 1 shows that in our patients the midline shifted to the left on the upper and lower arch. This result might be supported by Haraguchi et al’s study that reported a higher proportion of wider left hemiface in the post pubertal stage than prepubertal stage in 1800 Japanese subjects (Haraguchi et al., 2008). However, this study result was different to a clinical study in Brazilian twin girls with CH who presented with facial asymmetry and skeletal class III whose chin and lower arch midline tend to deviate to the right side (Goulart et al., 2018).

Even though previous study reported that CH affects more women than men, with a 3:1 ratio (Nitzan et al., 2008); however, there was no significant difference of angular and linear measurement for symmetrical analysis in upper and lower dental arch based on gender in this study (Table 2). There was also no significant difference of symmetry variables in upper and lower arch dental arch of CH patients based on gender, except the upper canines distance from the palatal suture of female patients (Table 3). The outcome of this study was also suggested by Al-Zubair, which reported that the location of the central incisor and canines to each other and to other teeth is the most potent factor in determining dental arch asymmetry (Al-Zubair, 2019).

According to Scanavini et al, the differences of midline deviation in normal and class II malocclusion, is midline deviation dominant toward the left in the upper arch in each group (Scanavini et al., 2012). In this study, the different PC between the upper canines distance from the palatal suture were higher in the lower arch than the upper arch. As with the analysis of midline deviation, the lower arch showed a higher degree of asymmetry than its counterpart upper arch. In the current study, the average values of midline deviation were greater than in the previous study regardless of the type of the malocclusion. Since this study focused on CH patients, the variance of ssymmetry showed a moderate correlation in midline deviation of dental arch symmetry (Table 4) and dental arch form (Table 5). The presence of condylar hyperactivity influenced the degree of malocclusion with facial asymmetry and diversity of CH (Alyamani & Abuzinada, 2012; Pacheco et al., 2010; Pinto et al., 2016).

Prasad et al. reported that dental arch width of untreated South Indian adults which had minimal crowding and spacing, is associated with gender, race and vertical facial morphology. Then, it was important to consider the individualized arch wires (Prasad et al., 2013) In Saudi normal population, it is suggested using a nickel titanium arch wire that will produce the lowest mean absolute error, cause minimal change in the dental arch form, and less customization of stainless steel wires necessary (Al-Barakati et al., 2016). If there was a failure to preserve the arch form, it might increase the probability of relapse (Bayome et al., 2011). Relapse related to improper arch wire changes can affect periodontal breakdown, recurrence of crowding of buccal segments, or increased crowding of labial segments particularly while inter-canine width and inter-molar width have been expanded. In the present study, relatively stocky arch guide showed mid and flat arch form for both upper and lower dental arch in the studied patients. This is also similar to the lower dental arch form of a Papuan population, which showed that prevalence of mid arch form was highest whilst the pointed lower arch form was the least in lower arch analysis of 18 to 25 year old Papuan students in Manado (Saputra et al., 2016). Another Indonesian sub-population study also reported that there was only significant difference of upper dental arch for full dentition of Buginese, Makassarese, and Torajanese individuals, which was null in the lower dental arch (Rieuwpassa et al., 2012).

The variance of upper and lower dental arch relationship in each malocclusion group appeared to have a specific etiology and different treatment modality especially in adult orthodontic treatment with facial asymmetry, such as: camouflage orthodontic treatment or orthognathic surgery. In interceptive orthodontic treatment, dental arch coordination should be evaluated during occlusal changing during mandibular growth. The development asymmetry of the lower arch might be due to the condylar growth activity and joint function and it is common that a growth period elapses after the patient’s asymmetric growth is completed (Pacheco et al., 2010). The asymmetry upper dental arch showed highly significant difference between right and left posterior arch segment whilst anterior segment showed no significant difference in class I occlusion of Iraqi young adult (Allabban et al., 2017). Further study, such as genetic investigation and follow-up of the patients, may help clinicians to understand the multi-characteristics of CH based on histological findings in this North Sumatra sub-population. Genetic and environmental factors can influence the development of left-right patterning during embryogenesis and remain in the masseter muscle in adults, including the PITX2 promoter (Sofyanti et al., 2018). Ethnicity also influences the development of dental arch form related with symmetry point. In the future, evaluation of plaster casts during orthodontic treatment is a requirement especially in treating malocclusion with mandibular asymmetry in order to anticipate the biomechanics of certain arch wire type. The clinicians should be careful in using arch wire coordination to obtain optimal occlusal relationship in order to maintain treatment stability.

Conclusion

The evaluation of dental arch symmetry and arch form showed asymmetric occlusal changes of orthodontic patients with CH in this North Sumatera subpopulation. In treating these patients, plaster cast evaluation is recommended as essential and routine procedure in order to understand the complexity of occlusal characteristics due to active growth of condylar and limitations in radiography evaluation during treatment. This phenomenon is marked as one obstacle in treating growing patients if there was no early detection and proper treatment of malocclusion with facial asymmetry.

Data availability

Harvard Dataverse: Replication Data for: Angular and linear measurement of the dental arch asymmetry and dental arch form, https://doi.org/10.7910/DVN/GONORA (Sofyanti et al., 2020).

Data are available under the terms of the Creative Commons Zero "No rights reserved" data waiver (CC0 1.0 Public domain dedication).