Introduction
The mandible is the most durable and only movable bone that constitutes the lower one-third of the face.1 It exhibits a higher degree of sexual dimorphism.2 It has a curved body that is connected to the ramus on either side by a mandibular angle.3 The mandibular condyle and coronoid processes are two anatomical structures located in the superior portion of the ramus of the mandible. Both of these structures are separated by a groove called a mandibular notch.4, 5, 6, 7
The anterior portion of the ramus is formed by the triangular eminence known as the coronoid process. It serves as the point of attachment for the temporalis muscle, which elevates the jaw.7 The condyle is a broad and wide projection forming the posterior limit of the ramus. It articulates with the glenoid fossa of the temporal bone to form the temporomandibular joint (TMJ).8
The bone morphology of these structures is predominantly influenced by muscle attachments and their functions.9 The other factors that also have an impact on the morphology are growth, dietary habits, hormones, genetic constitution, etc.10 Morphometric understanding of these structures is key to the diagnosis of various disorders associated with the temporomandibular region. It also aids in devising a plan for the management of such disorders. In recent times, the coronoid process has been utilized as an autogenous free graft for TMJ reconstruction.11 In 2014, Tapas reported that the coronoid process is a suitable donor site for autologous bone grafting due to its biocompatibility and shorter operating time for harvesting.12
Numerous research has been documented in the literature that utilized dry mandibular skulls to study the dimensions and morphology of the coronoid and condyle processes.3, 13, 14 This assisted in identifying an individual's age, sex, and gender as well as aid in anthropological identification.15 Over the past decades, various studies have been conducted using orthopantomography (OPG) and computed tomography (CT) to analyze the morphometry and corelation between these two structures.1, 10, 16 In 2013, Stopa reported the condylar coronoid index to assess coronoid hyperplasia using CT images.17 However, there is no study in the literature that can determine the linear measurements and angulation of these structures to the mandibular notch.
The purpose of this study is to evaluate the anatomical corelation between the condyle and coronoid of the mandible. The secondary objective is to provide linear measurement and angulation of the coronoid and condylar processes to those of the sigmoid notch.
Materials and Methods
100 high-resolution computed tomography (HRCT) DICOM (Digital Imaging and Communication in Medicine) images were obtained from department archived data in order to conduct this retrospective analysis. The study had been approved by the institutional ethical committee (IEC No. 3054/IEC/2021). The data were obtained by reviewing clinical case record sheets and imaging records between 2018 and 2024 in department of Oral and Maxillofacial surgery, SRM Kattankulathur Dental College and Hospital. Demographic information such as age, gender, and high-resolution computed tomography (HRCT) images were included. Clinical records lacking HRCT imaging or HRCT of any anomalies related to the mandible, as well as records from patients who were older than 80 years or younger than 18 years, had been excluded in the study.
All the HRCT scans were taken in a G-optima 128-slice machine by a single radiologist specializing in oral and maxillofacial radiology. During acquisition, the patient was in a natural head position and gently biting into a centric relation, with the lips in a relaxed position. All the images were obtained in 1mm-thick DICOM (Digital Imaging and Communications in Medicine) format.
After acquisition, these images were incorporated into the MIMICS Materialize software. The mandibular portion in each segment was masked in order to generate virtual stereolithography (STL) models. These STL models were incorporated into 3-Matic software for volumetric measurement. Two separate oral and maxillofacial surgeons with extensive training in software programming performed all of the morphometric analysis.
For all the mandible STL models, four reliable points were marked. This includes the tip of the coronoid process, the tip of the condylar process, the deepest point of the sigmoid notch, and gonion. After marking reliable points, the mandibular plane along the lower border of the mandible, the anterior ramus, and the posterior ramus plane of the mandible were drawn. A sigmoid plane was established by drawing a line perpendicular to the anterior and posterior ramus planes, crossing the deepest point in the sigmoid notch as described in Figure 1. The parameters evaluated were
Length of coronoid process = line X (from tip of coronoid to sigmoid plane)
Length of condylar process = line Y (from tip of condyle to sigmoid plane)
Angulation of coronoid = α (line X to sigmoid plane)
Angulation of condyle = β (line Y to sigmoid plane)
Statistical analysis
The statistical analysis was performed with SPSS version 20.0. The means of condylar length and angle were compared to the coronoid length and angle for the left and right sides, respectively, using the Wilcoxon signed rank test. The means of coronoid length, coronoid angle, condylar length, and coronoid angle were compared with the gender on the left and right sides, respectively, using the Mann Whitney U test. The means of coronoid length, coronoid angle, condylar length, and coronoid angle were compared with the age groups on the left and right sides, respectively, using the Kruskal-Walli’s test. The use of kappa analysis helped to prevent disputes or conflicts amongst examiners. On a nominal scale, the grades of agreement between two raters were evaluated using Cohen's kappa coefficient. In order to minimize interobserver error, interrater and inter-rater reliability were evaluated.
Results
Out of 100 HRCT data obtained, 87 were male and 13 were female, with a mean age of 49 years. On both the left and right sides, there is a statistically significant difference (p < 0.005) between the length of the coronoid and the length of the condyle. On the right side, the average length of the condyle was 17.57 ± 5.22 mm, and on the left side, it was 17.81 ± 6.09 mm. The mean coronoid length observed on the right side was 15.53 ± 8.07 mm, while the average length observed on the left side was 14.61 ± 5.48 mm.
There is a statistically significant difference between condyle angle and coronoid angle on both the left and right sides, with a p value ≤ 0.005. It was found that the condyle's angulation to the sigmoid line was 79.75 ± 16.61º on the left side and 78.76 ± 16.15º on the right. Comparably, the coronoid's angulation to the sigmoid line was 64.25 ± 15.70 º on the left side and 63.90 ± 16.97 º on the right.
There is no statistically significant difference present in the condyle length, coronoid length, condyle angle, or coronoid angle on both sides with respect to age and gender, respectively. The condyle length for males was 4 ± 5.5 mm higher than the condyle length of females on both sides. However, the coronoid length of males and females varies in a range of 0.5-2mm on both sides of the mandible.
After evaluation, the intrarater and interrater reliability values were determined to be 0.86 and 0.82, respectively. The two examiners showed a high degree of agreement, based on the kappa analysis rating.
Table 1
Comparison between the means of condylar length and angle with the coronoid length and angle on both sides
Table 2
Comparison between the means of right-side condylar length, condylar angle, coronoid length & coronoid angle with the gender
Table 3
Comparison between the means of left-side condylar length, condylar angle, coronoid length & coronoid angle with the gender
Table 4
Comparison between the means of left-side condylar length, condylar angle, coronoid length & coronoid angle with the age groups
Table 5
Comparison between the means of left-side condylar length, condylar angle, coronoid length & coronoid angle with the age groups
Discussion
Remodelling is a term used to describe a physiological process that adapts and modifies the structure.18, 19 The morphological variety of the anatomic structure is influenced by various factors such as developmental discrepancies, genetic determinants, and functional variation arising during the growth process.10, 13 Remodelling of the mandible frequently occurs in tandem with changes in the distribution and direction of stress.18, 19
Based on our study, males have longer condyles than females. However, the coronoid's length does not alter significantly. This is in line with the results published in 2023 by Yamashita et al.1 Hormonal fluctuations together with hereditary factors are the basis of this sexual dimorphism. The female hormone oestrogen has been documented in literature to be a major factor in bone remodelling. Similarly, testosterone also affects the remodelling of the bones.2, 20
In relation to the age factor, our findings have also shown several intriguing remodelling processes. As one gets older, the condylar process gets shorter and less angular. On the other hand, as people age, their coronoid process's length and angulation increases. There have been various theories that explain the elongation of the coronoid process, which includes temporalis hyperactivity, dysfunction of the temporomandibular joint caused by chronic disc displacement, dental causes like the guidance of occlusion, variation in condylar inclination, and other factors like hormonal stimulus, nutrition, and genetic inheritance.10, 13 In 2021, Jiang et al. conducted a retrospective cohort study to assess the regrowth of the coronoid process following coronoidectomies in 57 cases. In a total of 96 coronoidectomies, he found 74 coronoid processes (77.1%) showed complete (n = 44, 45.8%), non-union (n = 19, 19.8%), or partial (n = 11, 11.5%) regrowth, whereas no evidence of regeneration was found in 22 sites.21 The most frequent cause of condylar remodelling is stress and functional over load generated by the masticatory muscles.22 Milam et al. (1998) postulated that condylar resorption is caused by free radicals produced in the TMJ.23
In forensic medicine and anthropology, the mandible is one of the bones that is used to determine the age and gender of an individual, as well as racial determination.5, 9, 15 Our study inference will contribute to determining the gender and age of the individual by analyzing the length and angulation of the condyle and coronoid processes.
Understanding the complex morphology of the TMJ region is essential in the field of oral and maxillofacial surgery. This aids surgeons in the proper planning and management of TMJ abnormalities. It also aids in customizing prostheses for individuals who require total joint replacement. Currently, the coronoid process is utilized as a free graft for all types of reconstructive maxillofacial surgical procedures, such as orbital floor reconstruction, paranasal augmentation, TMJ ankylosis, trauma, tumors, facial paralysis, alveolar defects, non-union fracture of the mandible, and osseous defect reconstruction.11 In 2008, Zhu et al. reported a study in which they utilized the coronoid process as a free bone graft following gap arthroplasty in a TMJ ankylosis patient.24 Similarly, in 2017, Yang et al. conducted the study to assess any disturbance in the mandibular growth of the children with TMJ ankylosis who had undergone reconstruction of the condyle with an autologous coronoid graft. He reported that the rate of growth of the mandible was not affected.25 The limitations of our study are a smaller sample size and a lack of a diverse population.
Conclusion
To conclude, understanding the morphological variation of the mandibular ramus region, especially condylar and coronoid processes, aids in various fields of medicine like forensics and anthropology, reconstructive maxillofacial surgery, etc. In recent times, with advanced imaging technology and the advent of various simulation software, harvesting coronoid grafts for various maxillofacial defects has become much easier. Furthermore, our study inference will aid surgeons in planning coronoid grafts for condylar reconstruction as well as other maxillofacial reconstructions. Additionally, it helps in forensic odontology to determine a person's age and gender.
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