Comparison Between Antegonial Notch Depth, Symphysis Morphology and Ramus Morphology Among Different Growth Patterns In Skeletal Class I And Class Ii Subjects

Keywords

Antegonial Notch Depth; Ramus Height; Symphysis Morphology; Growth Patterns.

Introduction

Skeletal Malocclusions are a part of frequently seen dentoskeletal disharmony that occur due to a wide variety of etiology that includes genetics, environmental factors etc. Skeletal growth of the mandible varies widely in both the sagittal as well as vertical dimensions. Sagittally, the skeletal growth is classified in to Class I, Class II and Class III while vertically the growth pattern is divided into horizontal growth pattern, average growth pattern and vertical growth patterns. Knowledge of dental and skeletal characteristics together with different growth patterns is a necessity in determining treatment plans for successful treatment outcomes [19]. The success of the treatment of malocclusions may be improved or impaired depending on the variations in the direction, timing, and duration of the development in the facial areas[30, 4].

Prediction of the growth pattern of the mandible plays an important role in diagnosis and treatment planning [27]. Backward and downward rotation of mandibles occur during growth due to apposition beneath the gonial angle with excessive resorption under the symphysis. This results in upward curving of the inferior border of the mandible anterior to the angle of mandible is known as antegonial notching[6, 41, 43]. In adolescents with Deep antegonial notches, the mandible showed some characteristics such as retrusive mandible, short corpus length and ramus height and greater gonial angle when compared with shallow mandibular antegonial notches [40].

The mandibular symphysis also considered as one of the predictors for the direction of mandibular growth rotation and as the primary reference for esthetic considerations in lower one-third of the face [1]. Morphology and dimension of the symphysis may be indirectly affected by lower incisor inclination and dentoalveolar compensation occurred as a result of anteroposterior jaw discrepancy [3]. Thick symphysis is noted in horizontal growth patterns [34, 37]. Extraction and non extraction treatment plan depends on the symphysis morphology and movement of incisors in alveolar bone such as non extraction treatment plan is acceptable in thick symphysis and extraction treatment plan is indicated in small chin [28]. Mandibular ramus morphology is an important indicator for mandibular growth and mandibular ramus height is deficient in vertical growth pattern compared to horizontal growth pattern [29].

Very few studies have been reported about mandibular morphology in different growth patterns, thus the purpose of this study was to evaluate the mandibular morphology in different growth patterns of skeletal class I and class II subjects.

Materials and Methods

The sample size for this retrospective cross sectional study consists of 60 pretreatment lateral cephalograms of individuals. They were divided in to two groups consisting of 30 skeletal class I and 30 Class II cases which were further grouped based on the growth pattern as described below. Simple random sampling methods have been used to avoid sampling bias.

Inclusion Criteria:

Patients with skeletal class I and class II malocclusion.

High quality radiographs with adequate sharpness were taken by using standard techniques and exposure conditions in natural head position.

Patients with full permanent dentition.

Patients with the age group of 18 to 30 years.

Skeletal class I and class II subjects were selected based on ANB angle between (0-4 degrees) and ANB angle of more than 4 degrees respectively.

Exclusion Criteria:

Patients with previous history of orthodontic treatment and other mandibular surgery.

Patients with any other congenital anomalies or syndromes and hypodontia.

Patients with facial asymmetry and congenital malformations.

All cephalograms were traced digitally by using FACAD software. Based on Jarabak’s ratio sample was divided into average, horizontal, and vertical growth patterns in both control group and case group.

Group 1: skeletal class I
Average growth pattern - 10
Horizontal growth pattern - 10
Vertical growth pattern - 10

Group 2: skeletal class II
Average growth pattern - 10
Horizontal growth pattern - 10
Vertical growth pattern - 10

Cephalometric linear and angular measurements as follows,

Anterior facial height - the linear distance measured between Nasion and Menton.

Posterior facial height - the linear distance measured between Sella and Gonion.

Jarabak’s ratio - posterior facial height divided by Anterior facial height.

Antegonial notch depth - the linear distance measured along a perpendicular drawn from deepest part of convexity to a tangent through two points on either side of the notch on the lower border of the mandible [28].(figure 1).

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Figure 1:

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Figure 1. Measurements of Antegonial notch.

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Symphysis angle - the posterior-superior angle formed by the line through Menton and point B and the mandibular plane [1](figure 2).

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Figure 2:

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Figure 2. Measurements of symphysis angle.

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Symphysis width: The perpendicular distance from the pogonion to the most convex point of the lingual curvature of the symphysis.( figure 3).

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Figure 3:

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Figure 3. Measurements of symphysis width.

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Ramus height - the linear distance between Articulare and Gonion [28].(figure 4).

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Figure 4:

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Figure 4. Measurements of ramus height.

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Statistical Analysis:

An analysis of variance (ANOVA) test was performed to determine the comparison between groups for all these variables in both skeletal class I and class II. Independent t test was done to determine the comparison between skeletal class I and class II subjects for all variables. Mean and SD values for all variables were determined for all the groups.

Results and Discussion

For skeletal class II, as can be seen from Tables 1&2, the antegonial notch depth was found to be greater in vertical growth pattern than horizontal and average growth pattern( p<0.05). Large symphysis width and symphysis angle is noted in horizontal growth patterns compared to vertical and average growth patterns( p<0.05). Ramus height is significantly increased in horizontal and average groups compared to vertical growth patterns( p<0.05). While Table 3 &4 show that in skeletal class I, antegonial notch depth was found to be greater in vertical growth pattern than horizontal and average growth pattern( p<0.05). Large symphysis width and symphysis angle is noted in horizontal growth patterns compared to vertical and average growth patterns( p<0.05). Ramus height is significantly increased in horizontal and average groups compared to vertical growth patterns( p<0.05). Table 5 showed that there was no significant difference between skeletal class I and class II malocclusion for all parameters( p>0.05). Figures 4&5 show the mean plots of skeletal class I and class II for all the variables respectively.

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Table 1:

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Table 1. One way ANOVA test with descriptives was done to determine the values of the mean and standard deviation in skeletal class II.

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Table 2:

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Table 2. One way ANOVA Post Hoc test was done to determine the significant difference among different growth pattern in skeletal class II.

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Table 3:

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Table 3. One way ANOVA test with descriptives was done to determine the values of the mean and standard deviation in skeletal class I.

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Table 4:

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Table 4. One way ANOVA Post Hoc test was done to determine the significant difference among different growth patterns in skeletal class I.

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Table 5:

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Table 5. Independent t test was done to determine the comparison between skeletal class I and class II subjects for all variables and showed that there was no significant difference between skeletal class I and class II malocclusion for all parameters( p>0.05).

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Figure 5:

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Figure 5. Mean plots of skeletal class I for all variables.

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Figure 6:

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Figure 6. Mean plots of skeletal class II for all variables.

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Previously our team had conducted numerous clinical trials[12, 21, 25, 37, 42, 45, 46, 42] lab animal studies [14, 15, 20, 32, 33, 36] and in vitro studies [13, 9] over the past 5 years. Now this research study focused on prediction of growth pattern of mandible by analyzing the different anatomical structures of mandible.

Depth Of Antegonial Notch:

Depth of antegonial notch was found to be greater in vertical growth pattern compared to horizontal and average growth pattern. Similar findings have been reported by Singer et al [40], Bjork and Skieller [8] and Bjork [7, 9] in their implant studies. Lambrechts et al stated that the deep antegonial notch group found more in vertical mandibular growth patterns that result in a increase in the anterior facial height than the shallow notch group, hence antegonial notch depth may be considered as possible predictor for the direction of facial growth (Lambrechts et al., 1996) [26]. Kolodziej et al [24]. suggested that a statistically significant negative relationship was found between mandibular antegonial notch depth and horizontal growth pattern and (Kolodziej et al., 2002)[24]. Condylar bone change is not only related to retrognathic mandible but also to antegonial notch depth and ramus notch depth [2].

For Bone-formation mechanism of the antegonial notch, Enlow demonstrated that the size of the antegonial notch is determined mainly by ramus-corpus angle and extent of bone deposition on the inferior margin of the corpus on either side of the notch and concluded that less prominent antegonial notch is noted if ramuscorpus angle is closed and a much more prominent antegonial notch is observed if it becomes opened [10]. Hovell showed that, the antegonial notch is produced by role of muscles such as masseter and the medial pterygoid especially when condylar growth fails to contribute to the lowering of the mandible [18]. Becker demonstrated that impaired mandibular growth and muscular imbalance will occur if the condylar area, an important growth site injured by inflammatory reactions, results in growth changes that produce antegonial notching [5]. On the contrary no reports have been found against a positive relationship between vertical growth pattern and antegonial notch depth. Overall consensus of previous studies are favourable to our present study as the present study is in agreement with the findings of previous studies.

Symphysis Width and Symphysis Angle:

The anatomy of the mandibular symphysis is an important consideration in evaluating patients seeking orthodontic treatment [7, 1]. According to the size and shape of the symphysis many clinicians classify the growth pattern of the mandible anteriorly or posteriorly [23].

In our study large symphysis width and symphysis angle is noted in horizontal growth patterns compared to vertical and average growth patterns. Similar findings have been reported in some literature such as aki et al, mangla et al, gupta et al attributed that large symphyseal angle, symphysis width and small symphysis ratio was observed in horizontal growth patterns compared to vertical growth patterns [1, 17, 28]. Roy et al also found in his study that external symphysis increases its size from vertical to horizontal growth pattern [35]. Thick symphysis is noted in horizontal growth pattern [34]. Gracco et al showed that symphysis thickness was greater in short-faced subjects than in long-faced subjects [16]. In patients with horizontal growth pattern,short symphysis height, large symphyseal depth, and small symphyseal ratio is noted as compared with the hyperdivergent group the results were statistically significant but larger symphysis angle showed not statistically significant difference compared to hyperdivergent group [22]. Sassouni and Nanda and Bjork have found pronounced apposition beneath the symphysis with concavity in the inferior border of mandible associated with the tendency toward backward jaw rotation of mandible [7, 38]. Symphysis width was wider in the hypodivergent Class II group but symphysis height was similar among all the groups [11]. No findings have been found against the positive relationship between horizontal growth pattern and symphysis morphology, hence overall consensus is in agreement with the findings of the study.

Ramus Height:

Ramus height is significantly increased in horizontal and average groups compared to vertical growth patterns. Similar findings have been reported in some literature such as muller et al, schudy et al, sassouni et al, Nanda who all reported a considerable deficiency in vertical growth patterns [17, 29, 31, 38, 39]. Ramus height is significantly smaller in vertical growth patterns and larger in hypodivergent groups [28]. No a findings have been found against a positive relationship between horizontal growth pattern and ramus height, hence overall consensus is in agreement with the findings of this study.

There was no significant difference between skeletal class I and class II malocclusion for all parameters ( p>0.05), hence concluded that sagittal relationship does not alter the vertical measured variables between skeletal class I and class II malocclusion.

Future Scope:

From clinical perspective, in an individual-seeking orthodontic treatment, the decision to extract, anchorage preparation and biomechanics and period of retention are dependent on different growth patterns which is greatly influenced by anatomy of mandible, hence thorough knowledge about various growth patterns should be considered as important because it will greatly helpful in diagnosis and treatment planning.

Conclusion

Depth of antegonial notch was found to be greater in vertical growth pattern compared to horizontal and average growth pattern.

Large symphysis width and symphysis angle was noted in horizontal growth patterns compared to vertical and average growth patterns.

Ramus height was significantly increased in horizontal and average groups compared to vertical growth patterns in both skeletal class I and class II malocclusion.

The study shows that the vertical pattern of growth is independent of the type of sagittal pattern of growth.

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