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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 8  |  Issue : 4  |  Page : 255-262

Relationship between dentofacial morphology and mandibular movement from rest position to maximum intercuspation in Class II division 1 malocclusion patients


Department of Preventive Dentistry, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla, Thailand

Date of Submission11-Apr-2019
Date of Acceptance11-Sep-2019
Date of Web Publication15-Oct-2019

Correspondence Address:
Dr. Chairat Charoemratrote
Department of Preventive Dentistry, Faculty of Dentistry, Prince of Songkla University, Hat Yai, Songkhla 90110
Thailand
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ijhas.IJHAS_21_19

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  Abstract 


BACKGROUND: The objective of this study was to determine the relationship between dentofacial morphology and mandibular movement from rest position to maximum intercuspation in Class II division 1 malocclusion patients.
MATERIALS AND METHODS: The sample comprised of 45 patients who were 10–14 years old and had Class II division 1 malocclusions. Eighteen cephalometric variables were evaluated to determine the dentofacial morphology using lateral cephalograms. Mandibular movements were recorded from mandibular rest position to maximum intercuspation using mandibular kinesiography. Spearman's correlation coefficient was used to analyze the relationships between mandibular movement and other dentofacial variables.
RESULTS: Mandibular movement in the anteroposterior dimension was significantly negatively correlated with the curve of Spee (COS) (r = −0.45) and freeway space (r = −0.44) and positively correlated with the sella-nasion-mandibular plane (SN-MP) angle (r = 0.47) and the Frankfort-mandibular plane angle (FMA) angle (r = 0.44). Two types of mandibular movement in the anteroposterior dimension were observed. Twenty-six of 45 patients (57.8%) exhibited posterior mandibular movement from rest position to maximum intercuspation (backward group) and 19 subjects (42.2%) presented anterior movement (forward group). COS and freeway space were greater in the backward group. The SN-MP and FMA angles were higher in the forward group.
CONCLUSIONS: COS, freeway space, and mandibular plane angle may relate to mandibular movement from rest position to maximum intercuspation in Class II division 1 malocclusion. Patients with deep COS combined with a large freeway space and smaller mandibular plane angle tend to present posterior mandibular movement from rest position to maximum intercuspation.

Keywords: Class II division 1 malocclusion, dentofacial morphology, mandibular movement


How to cite this article:
Jariyavithayakul P, Charoemratrote C. Relationship between dentofacial morphology and mandibular movement from rest position to maximum intercuspation in Class II division 1 malocclusion patients. Int J Health Allied Sci 2019;8:255-62

How to cite this URL:
Jariyavithayakul P, Charoemratrote C. Relationship between dentofacial morphology and mandibular movement from rest position to maximum intercuspation in Class II division 1 malocclusion patients. Int J Health Allied Sci [serial online] 2019 [cited 2019 Nov 11];8:255-62. Available from: http://www.ijhas.in/text.asp?2019/8/4/255/269245




  Introduction Top


The relationship between dentofacial morphology and oral function is complex and not clearly understood. Many approaches are used to explore this relationship. They include an assessment of electromyographic activity and jaw movement parameters to define function and cephalometric and anatomic parameters to define morphology.[1],[2],[3],[4] Although many studies have reported correlations between dentofacial morphology and mandibular function, most investigations have focused on mandibular border movements or oral activities.

While mandibular border movements have been extensively investigated, normal mandibular function seldom reaches this border. Therefore, the first few millimeters of motion from rest position to maximum intercuspation may be of particular interest. Normally, the movements undergo both translation and rotation even in the small range of mandibular movements.[5] The condyles rotate and move anteriorly and inferiorly along the articular eminence during initiation of jaw opening, in which the mandible should move downward and forward from full occlusion to the physiological rest position, but the translation of the mandible forward is countered by rotation of the condyle. However, differences of anteroposterior changes of the mandible were detected in patients with different types of malocclusion.[6]

Some researchers reported that the mandible might be displaced posteriorly from the rest position in some patients with Class II malocclusion, leading to the appearance of a more severe skeletal discrepancy when the teeth are occluded than the true discrepancy.[6],[7] It has been postulated that the dentofacial morphology may affect mandibular movements. Several studies have demonstrated a significant correlation between mandibular movement and craniofacial morphology.[8],[9] They concluded that the variations in the range of mandibular movement were due to differences in craniofacial morphology. However, previous studies focused on jaw movement without dentofacial morphology investigations[6],[7] or jaw movement related to craniofacial morphology without a dentofacial morphology evaluation.[8],[9]

Since mandibular movements are associated with dental factors,[10] determining the influence of both dental and skeletal morphologies on mandibular movement can provide helpful information to further understand the development and etiology of malocclusions that can lead to the appropriate treatment plan. Therefore, the present study aimed to determine the relationship between the dentofacial morphology and mandibular movement in Class II division 1 malocclusion patients.


  Methods Top


Sample

This study was approved by the Ethics Committee on Human Research at the Faculty of Dentistry, Prince of Songkla University. All participants and their parents provided informed consent prior to participating in this study.

The sample size was calculated using G*power software (version 3.1.9.2) (Franz Faul, University of Kiel, Kiel, Germany). Based on the correlation between mandibular movement and dentofacial variables (r = 0.45) reported in a previous study[11] with a significance level of 0.05 and power of 80%, a minimum of 36 samples was required. However, it was recommended to increase this by 20% to improve the representation. Therefore, the sample size should be at least 45 samples.

Forty-five healthy patients (25 males and 20 females) between 10 and 14 years (mean ± standard deviation [SD], 11.80 ± 1.51 years) were recruited from the orthodontic clinic at Prince of Songkla University. In selecting the sample, the inclusion criteria were skeletal Class II relationship measured in cephalometric radiograph (ANB >5°) and Class II division 1 with a molar relationship more than half-cusp on both sides and an overjet >4 mm. The exclusion criteria were a previous history of orthodontic treatment or undergoing orthodontic treatment, any dysfunctional disorders of the masticatory system or temporomandibular joint, and any abnormal oral habits.

Cephalometric analysis

Lateral cephalograms were taken using a Gendex GXDP-700™ series (Gendex Dental System, Hatfield, PA, USA). Tracing, registration of the landmarks, and measurements were performed by one investigator using Dolphin Imaging® software (version 11.7.05.66) (Dolphin Imaging, Chatsworth, CA, USA). All cephalograms were standardized and all measurements were adjusted for magnification. Reference points and linear and angular measurements are illustrated in [Figure 1]a, b and [Table 1].
Figure 1: (a) Cephalometric landmarks and reference planes. (b) Dental height measurements

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Table 1: Linear and angular measurements used to assess dentofacial variables

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Mandibular movement recording and analysis

A JT-3D™ Magnetic Jaw Tracker (BioResearch Assoc. Inc., Milwaukee, WI, USA) was used to evaluate mandibular movement. The kinesiograph system consisted of a senor array head frame and a magnet (6 × mm 10 mm × 3 mm) connected to a BioPak system (BioResearch Assoc. Inc., Milwaukee, WI, USA).

The recordings were taken in the morning to avoid any possible muscle fatigue effects on the physiologic rest position.[12] Patients were asked to sit upright in a chair and look straight into a mirror in order to establish a visual reference to maintain a natural head position. The magnet was attached to the labial surface of the mandibular incisors below the occlusion. The headframe was adjusted for each patient and calibrated using the internal rezeroing mechanism so that the magnet was located in the middle of the recording region of the sensors. Before recording, the patients received preliminary training of how to maintain a habitual rest position. Patients were asked to moisten their lips, swallow saliva, and breathe deeply. The patients were then instructed to open and close their jaws from maximum intercuspation to the rest position in a habitual manner. During the recording, no conversation or instructions other than those above were given in order to avoid bias or disturb the movements. Movements were assessed in the anteroposterior and vertical dimensions. Measurements were recorded three times and the mean value was calculated. A negative value was taken to indicate backward movement from the rest position, while a positive value indicated forward movement.

Statistical analysis

All statistical analyses were performed using SPSS 17.0 for Windows (SPSS Inc., Chicago, IL, USA). Statistical significance was defined as P < 0.05 for all tests. Descriptive parameters are reported as mean and SD values for each variable. The Shapiro–Wilk test was used to determine the normality of the distributions. Independent t-tests were used to examine differences between sexes. The Mann–Whitney U-test was used to compare nonnormally distributed variables. The relationship between mandibular movements and dentofacial morphologies was evaluated using the Spearman correlation coefficient. In addition, based on the different patterns of mandibular movement in the anteroposterior dimension, the Mann–Whitney U-test was used to compare variables between the forward and backward groups.

Method error

Method error in locating radiographic landmarks and the measuring procedure was calculated using the Dahlberg formula. All measurements were repeated for ten randomly selected radiographs at an interval of 1 month. Linear and angular measurements did not exceed 0.5 units for any variables investigated. Paired t-tests did not detect a significant difference between the two series of replicate measurements (P > 0.05).

Reproducibility of kinesiograph records

To evaluate the reproducibility of the kinesiograph recordings, the recordings of two consecutive measurements of incisor movement of ten randomly selected patients were compared with the paired t-test. Two trials were performed at a 1-month interval. Differences between the first and second recordings of mandibular movements were not statistically significant [Table 2].
Table 2: Comparison of the mandibular movement recordings taken two consecutive times

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  Results Top


The demographic features of the patients are shown in [Table 3]. No statistically significant differences were observed between the male and female patients. Since most variables were not significantly different, the data for both sexes were pooled for subsequent analysis.
Table 3: Comparison of age, mandibular movements and dentofacial variables in male and female patients with Class II division 1 malocclusion

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[Figure 2]a, [Figure 2]b, [Figure 2]c, [Figure 2]d present examples of mandibular movement from rest position to maximum intercuspation in the backward and forward groups. [Table 4] summarizes the correlations between mandibular movement and dentofacial variables. Mandibular movement in the anteroposterior dimension was significantly negatively correlated with the curve of Spee (COS) and freeway space, and positively correlated with the sella-nasion-mandibular plane (SN-MP) and Frankfort-mandibular plane (FMA) angles. As the depth of the COS and freeway space increased, the mandible moved more posteriorly from rest to maximum intercuspation. On the other hand, as the SN-MP and FMA angles became greater, the mandible moved more anteriorly from rest to maximum intercuspation. No statistical significance was found between the mandibular movement in the vertical dimension and any of the dentofacial variables.
Figure 2: Examples of mandibular movements from rest position to maximum intercuspation in the backward group (a: sagittal, b: frontal) and the forward group (c: sagittal, d: frontal) (grid size = 2 mm)

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Table 4: Relationships between mandibular movements and dentofacial variables in Class II division 1 malocclusion

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In this study, two types of mandibular movement in the anteroposterior dimension were observed. Twenty-six of 45 patients (57.8%) exhibited posterior mandibular movement from rest position to maximum intercuspation (backward group) (−1.51 ± 0.74 mm) and 19 of 45 patients (42.2%) presented with anterior movement (forward group) (1.27 ± 0.44 mm). The dentofacial variables of these two groups are compared in [Table 5]. Statistically significant differences were found in the COS, freeway space, and SN-MP and FMA angles. The COS and freeway space were statistically significantly greater (P < 0.05) in the backward group. However, the SN-MP and FMA angles were statistically significantly greater (P < 0.05) in the forward group.
Table 5: Comparison of age, dentofacial morphologies, and mandibular movements in Class II division 1 malocclusion for patients in the backward and forward groups

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  Discussion Top


The objective of this study was to explore the relationship between the dentofacial morphology and mandibular movement. In general, the shift of the mandible in malocclusion is compensated by adaptation within the neuromuscular system but may also indicate permanent displacement of the mandible and develop into musculoskeletal problems with age.[13] Thus, it is essential to determine mandibular movement and function during the growth period in individuals in whom adaptive and degenerative changes are not affected by malocclusion.[14]

We used a simple, noninvasive magnetic kinesiograph system to measure mandibular movement. The magnet attached to the teeth was small and lightweight; therefore, any interference with jaw movement was minimal. The accuracy of this system has also been proven with a high degree of linearity over the normal range of human mandibular motion.[15] Therefore, the measurements obtained in this study reveal habitual physiological patterns of mandibular movements.[16]

The rest position of the mandible needs to be considered. Since the mandible is suspended in space and controlled by muscles and gravity, it was suggested that the postural position of the mandible could be affected by temporomandibular dysfunction, emotional stress, aging, breathing pattern, and head position.[17],[18],[19] Several studies stated head posture could alter the mandibular position. A headrest may also affect muscle relaxation.[19] Therefore, a restrictive headrest was not used in this study in order to obtain natural head position. In addition, the activity of the masticatory muscles also has an influence on the postural position of the mandible. When muscle fatigue occurred after chewing, the freeway space significantly increased.[12] Therefore, the recordings were set in the morning to avoid any influence of muscle activity and fatigue inherent in the physiologic rest position.

A correlation analysis revealed that the amount and direction of movement in the anteroposterior dimension correlated negatively with the depth of the COS. As the depth of the COS increases, the mandible moves more posteriorly from rest position to maximum intercuspation. Graber proposed that a deep COS with overextruded incisors can lead to initial contact at the anterior teeth, forcing the mandible into a retruded position.[20] This finding corresponded to previous studies that reported that the COS was influenced by the anteroposterior mandibular position. When the mandible was positioned more posteriorly, the increase of the COS was greater.[21] Moreover, the COS was significantly deeper in Class II malocclusion than other malocclusions.[22] However, it is difficult to compare our data with previous studies because they evaluated mandibular position based on lateral cephalograms and did not evaluate the mandibular movements.

With respect to the COS, lower dental heights, which are the causative factors for the depth of the COS, need to be evaluated. Unfortunately, we observed no correlation between the COS and either the lower anterior or posterior dental heights. This may be contributed to the use of the mandibular plane as the reference plane.[23] A flat mandibular plane may present a less lower anterior dental height (LADH) but more lower posterior dental height (LPDH). On the other hand, in the case of a steep mandibular plane, the LADH is more, while the LPDH is less.

The vertical dimension of the mandibular rest position, known as the freeway space, showed a negative correlation with mandibular movement in the anteroposterior dimension. This means that patients with a larger freeway space tend to present with posterior mandibular movement from the rest position. This was in agreement with previous studies.[20],[24] It has been postulated that the disharmony between the occlusal vertical dimension and postural vertical dimension, which indicates a large freeway space, the posterior temporalis fibers, as well as the posterior masseter fibers become dominant in the closing maneuver. This leads to overclosure and promotes a Class II tendency.[20] A larger freeway space in Class II malocclusion could lead the mandible to move upward and backward when the teeth are occluded.

In our study, the freeway space was 3.31 ± 0.95 mm. This was slightly smaller than the value reported by Ricketts[7] (3.6 ± 1.5 mm) but higher than the valued reported by Brown[11] (2.90 mm). These values were twice compared to patients with Class I malocclusion in those studies. These findings may possibly be explained by the decreased airway volume and lower muscle activity in the masticatory muscles.[25],[26],[27] First, it was reported that patients with a retruded mandible had a posterior tongue position[25] and smaller airway space.[26] This could be an adaptive compensatory feature of the mandible to prevent respiratory impairment. In addition, the elevator muscles, especially the masseter muscle, maintain mandibular position exhibited in lower muscle activity in patients with Class II malocclusion compared to patients with Class I group malocclusion.[27]

The anteroposterior pattern of mandibular movement is a particularly interesting finding of this study. Two types of movement were observed. Posterior mandibular movement from rest position to maximum intercuspation was exhibited in 57.8% of individuals, while the remainder exhibited anterior movement. Therefore, the patients were categorized by the direction of mandibular movement into the backward and forward groups. A difference in the vertical pattern was detected between the backward and forward groups. The forward group had a significantly steeper mandibular plane than the backward group. The possible reason may be explained by muscle orientation, which presented with an inclination of the masseter muscle that was more acute in relation to the Frankfort horizontal plane in the high mandibular plane angle group than the low-angle group.[28] The forward inclination of the masseter muscle may pull the mandible anteriorly.

When assessing the freeway space between the groups, the backward group exhibited a larger freeway space than the forward group. This was consistent with a previous study which showed that the low Frankfort horizontal-mandibular plane group had significantly greater vertical opening than the high-angle group.[29] These results were consistent with Yemm's equilibration theory of clinical rest position in which the mandibular posture may be determined by the need to maintain an airway.[30] However, other factors which may affect the mandibular movement such as muscle activity, joint laxity, and the steepness of the articular eminence could be investigated in further studies.

Overall, mandibular movements represent interplay between the dentofacial morphology and neuromuscular function and emphasize the existence of a close link between form and function. This study found that the patients who presented with a deeper COS combined with a large freeway space and low mandibular plane angle exhibited more backward mandibular movement. This posterior displacement may worsen Class II tendency into more severe Class II relationship. Since normal function can promote normal growth and development, it would be of interest to conduct a clinical study to determine whether leveling of the COS could induce anterior displacement and facilitate the craniofacial growth. Later on, this forward movement of the mandible would improve the Class II relationship.


  Conclusions Top


Dentofacial morphologies are associated with mandibular movements. The COS, freeway space, and mandibular plane angle may be related to mandibular movement from rest position to maximum intercuspation in patients with Class II division 1 malocclusion. Patients with a deep COS combined with a large freeway space and smaller mandibular plane angle tend to present with posterior mandibular movement from rest position to maximum intercuspation.

Acknowledgments

We greatly appreciate the Graduate School of Prince of Songkla University and the Faculty of Dentistry at Prince of Songkla University for grant support.

Financial support and sponsorship

The study was financially supported by the Graduate School of Prince of Songkla University and the Faculty of Dentistry at Prince of Songkla University.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]



 

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