Mandibular growth direction prediction using symphysis morphology

Introduction

Growth and development are integral processes, which define the existence of life. Growth of an organism is the interplay between its genetic constitution and the environment in which it thrives. At the macroscopic or clinical level, growth is exemplified by an increase in height and weight, while at the microscopic level, it is accompanied by an increase in the number of cells and their size.1, 2

The mandible develops from the mandibular process of the first branchial arch. Mandibular growth occurs as a result of the combined processes of proliferation and ossification of secondary cartilage at the condyle, as well as differential formation and remodeling of bone along the entire surface of the mandible.

It is important to predict the magnitude and direction of mandibular growth in any case of orthodontic treatment. Mandibular growth is very critical in the development of balanced dentofacial structures and hence, influence the therapeutic result of orthodontic treatment. With the knowledge of mandibular growth, better therapeutic decisions can be made regarding timing and duration of the treatment, extraction pattern and possible need for surgery.

Prediction of mandibular growth pattern has been done by various parameters like condylar morphology,3 shape of lower border of mandible, 4 anterior facial height,5 cervical vertebrae,6 craniocervicalangle, 7 frontal sinus8 with varying degree of success.

Some authors found a significant association between mandibular morphology and growth direction3, 5, 9, 10, 11 whereas others have annulled any correlation between the two.12

Among the mandibular structures the mandibular symphyseal morphology serves as a reference anatomical landmark for esthetics and beauty of the face in general and of the lower part in particular. 13, 14 Functional environment can affect the shape and size of mandibular symphysis demonstrating an adaptive morphological response to the biomechanical loads experienced at various points in the masticatory cycle.15, 16 ^15,16 Studies conducted so far to find the correlation between symphysis morphology orantegonial notch and mandibular growth direction have got varied conclusions with some of studies concluding the relationship of symphysis morphology or antegonial notch with mandibular growth direction while some of the studies concluding that there is no relationship between the two. Most of these studies have been done on American and Caucasians population. Only few studies have been conducted on Asian population and hence the present study is undertaken to assess the reliability of symphyseal morphology as a predictor of direction of mandibular growth in Indian population.

Aims and Objectives

Materials and Methods

Pretreatment lateral cephalograms of 30 adult patients (15 males and 15 females) aged 18 years and above reporting to the Department of Orthodontics and Dentofacial Orthopaedics at Inderprashta Dental College and Hospital, Ghaziabad requiring orthodontic treatment were randomly selected.

Materials: (Figure 1)

Lateral cephalograms, tracing sheet (Company- Gateway; Thickness- 90 Micron), 0.3mm lead pencil, metallic scale and set squares.

Figure 1

Armamentarium

Cephalometric evaluation of symphysis

1. Calculation of Symphysis Dimensions- A line tangent to point B was taken as the long axis of the symphysis. A grid was placed with lines of grid parallel and perpendicular to constructed tangent line. Superior limit of symphysis was taken at point B with inferior, anterior and posterior limits taken at most inferior, anterior and posterior borders of symphyseal outline respectively. (Figure 2).

   1. Symphysis Height- Distance from superior to inferior limit on grid.

   2. Symphysis Depth- Distance from anterior to posterior limit on grid.

   3. Symphysis Ratio- Divide symphysis height by symphysis depth.

   4. Symphysis Angle-Postero superior angle formed by line through menton and point B and mandibular plane.

Figure 2

Measurement of symphyseal parameters

Results

Lateral Cephalograms of 30 adult patients (15 males and 15 females) reporting to the Department of Orthodontics and Dentofacial Orthopaedics, Inderprastha Dental College and Hospital, Sahibabad, Ghaziabad (U.P) aged 18 years and above were randomly selected and traced. Four symphyseal parameters (Height of Symphysis, Depth of Symphysis, and Symphysis Ratio, Symphysis Angle) and seven cephalometric parameters (S.N to Y-axis angle, SN-Mandibular Plane Angle, Palatal Plane- Mandibular Plane Angle, Gonial Angle, Bjork Sum, Percentage of Lower Facial Height to Total Facial Height, Posterior Facial Height to Anterior Facial Height) were measured.

The data was subjected to Pearson’s Correlation test to find any correlation between symphysis morphology and cephalometric parameters.

Table 1, Table 2, Table 3 shows the correlation between symphysis height and cephalometric parameters. In the overall sample (Table 1), there was a significant negative relationship between symphysis height and Bjork sum with p-value 0.016. There was no significant relationship between symphysis height and other cephalometric parameters. In the male group (Table 2) posterior facial height / anterior facial height ratio and symphysis height parameter showed a significant positive relationship with p-value 0.040 while all other values showed no significant relationship. In female group (Table 3), there was no significant relationship between height of symphysis and cephalometric parameters.

Table 4, Table 5, Table 6 shows correlation between symphysis depth and cephalometric parameters. In the over-all sample (Table 4), it was found that there is significant positive relationship between depth of symphysis and posterior facial height/ anterior facial height ratio with p-value 0.033. In the male and female groups (Table 5, Table 6), there was no significant correlation between depth of symphysis and cephalometric parameters.

Table 7, Table 8, Table 9 shows correlation between symphysis ratio and cephalometric parameters. In the overall group (Table 7), there was not a significant relationship between symphysis ratio and cephalometric parameters. In the male group (Table 8), it was found that there was a significant positive relationship between symphysis ratio and posterior facial height to anterior facial height with p-value 0.022 while all other values showed no significant relationship. In the female group (Table 9), there was not a significant relationship between symphysis ratio and cephalometric parameters.

Discussion

The present study was undertaken to find the correlation if any between symphyseal morphological parameters or antegonial notch depth and mandibular growth direction.

Symphyseal parameters (height, depth, ratio and angle), antegonial notch depth and seven cephalometric parameters (S.N to Y-axis angle, SN-Mandibular plane angle, Palatal plane- Mandibular plane angle, Gonial angle, Bjork sum, Percentage of lower facial height to total facial height, Percentage of posterior facial height to anterior facial height) predicting growth directions were measured for 30 patients (15 Males, 15 Females).

Pearson correlation test was done to find any correlation between symphysis morphology and cephalometric parameters among overall group and separately for male and female group.

Pearson correlation test indicated that in overall group, there was a significant negative relationship between symphysis height and Bjork sum. This further indicates that the decrease in symphyseal height is associated with vertical growth pattern. Also it was found that in overall group, there is a positive correlation between depth of symphysis and posterior facial height / anterior facial height ratio. This indicates that increase in depth of symphysis is associated with horizontal growth pattern.

In male group, Pearson correlation test indicated that there is significant positive correlation between symphysis height and posterior facial height / anterior facial height ratio. It denotes that increase in symphyseal height is associated with increase in Posterior Facial Height/ Anterior Facial Height ratio i.e. horizontal growth pattern.

Symphysis ratio and Posterior Facial Height/Anterior Facial Height was found to be having significant positive correlation in male sample which further indicates that increase in symphyseal ratio is associated with increase in Posterior Facial Height/ Anterior Facial Height i.e. horizontal growth pattern.

Thus, the present study results indicate that increase in height and depth of symphysis are associated with horizontal growth pattern in overall sample. In males increase in height and symphysis ratio is associated with horizontal growth pattern.

The results of this study are similar to the study done by Aki et al (1994)5 in context to depth of symphysis where increase in depth was associated with horizontal growth pattern.

Conclusion

The conclusion of the present study-

Source of Funding

None.

Conflicts of Interest

None.