Evaluation of Glenoid Fossa Morphology in Different Facial Growth Patterns: A Cone Beam Computed Tomography Study

PURPOSE: The aim of current study was to assess the glenoid fossa morphology among diﬀerent ver&cal skeletal pa=erns using cone beam computed tomography (CBCT). MATERIALS AND METHODS : The CBCT images of 63 pa&ents with Class I sagi=al skeletal pa=ern were classiﬁed into three groups based on posterior facial height (PFH)/anterior facial height (AFH) ra&o. Each group divided in to normal, horizontal, and ver&cal growth pa=ern groups. Depth, width, and inclina&on of glenoid fossa were measured and assessed on CBCT images. One-way analysis of variance (ANOVA) and Tukey post-hoc test were used to compare mean values of measured variables among the groups. RESULTS: The width (28.76 ± 0.79) and depth (14.61 ± 0.514) of glenoid fossa were lower in horizontal in comparison to ver&cal and normal growth pa=erns (P-value < 0.05). Although steepness of glenoid fossa was higher in normal growth pa=ern (123.8 ± 16.68), no sta&s&cally signiﬁcant diﬀerences were seen (P-value = 0.819). CONCLUSION: The width and depth of glenoid fossa were signiﬁcantly lower in horizontal growth pa=ern.


Introduction
Temporomandibular joint (TMJ) is one of the most complex joints due to its anatomical, histological, and biomechanical characteristics [1]. TMJ is the joint between the mandible and the temporal bone of the skull that consists of mandibular condyle, glenoid fossa and articular eminence of the temporal bone [2]. Some previous studies showed association between the joint morphology and different facial patterns. Therefore, knowing about the articular eminence inclination could help clinician in the diagnosis, establishing more biological treatment modalities and treatment response between different facial types [3,4].
Several recent studies have investigated the association between joint morphology and sagittal craniofacial patterns [5][6][7][8][9][10][11][12][13]. Little is known about the association between the growth pattern and glenoid fossa morphology. To the best of our knowledge, there were only two studies that evaluated the association between the glenoid fossa morphology and vertical craniofacial morphology [14,15]. The study conducted by Lin et al. evaluated articular eminence angle h#p://den*stry3000.pi#.edu using lateral cephalometry [14]. The other study assessed the position and morphology of the temporomandibular joint in skeletal Class II females using CBCT [15].
CBCT is a choice to evaluate TMJ structures because of several advantages including high-resolution images, short scanning times, reduced radiation dose and no magnification or distortion for accurate measurement of joint structure dimensions [16,17]. Therefore, the aim of present study was to assess the glenoid fossa morphology among different vertical skeletal patterns using CBCT.

Material and Methods
This cross-sectional study protocol was approved by institutional Research Ethics Committee of Shiraz University of Medical Sciences (SUMS) (IR.SUMS.DENTAL.REC.1399.005). Diagnostic CBCT images of 63 adult patients (17 verticals, 29 horizontals and 17 normal) who referred to Radiology Department of Dental School of SUMS for dental services such as impacted teeth, PNS, maxillofacial CBCT and etc. entered this study. The inclusion criterion follows: sufficient image sharpness and contrast to visualize the structure to be evaluated (glenoid fossa , articular eminence, sella turcica, mandible and nasion), and patients with skeletal Class I relationships on the basis of ANB angle, 0 to 4 degrees [18]. The exclusion criteria were symptoms of temporomandibular disorders, history of TMJ surgery and/or TMJ trauma, or fracture in the TMJ region, any congenital abnormalities or systemic diseases potentially affecting joint morphology. CBCT of patients presenting evidence of degenerative joint disease in the images were excluded from the study. All CBCT scans were taken by the same clinician using New Tom VGi. The exposure factors set at 120 kVp, 4.6 mA, exposure time of 20 s, and a field of view of 15 × 15 cm. The CBCT images were taken with the participants biting in maximum dental intercuspation and their heads positioned so that the Frankfort plane was parallel to the floor. The images divided into three groups according to growth pattern based on posterior facial height (PFH)/anterior facial height (AFH) ratio (Table 1).
On the axial view, the section of the condylar process that had the widest mediolateral diameter on the left and right sides was chosen as the reference view for reconstruction of the sagittal slices. In this section, a line parallel to the long axis of the condylar process was drawn and sagittal images were reconstructed as 0.5 mm slice interval/thickness. The measurements were establishing on the central sagittal section of the condyle. The glenoid fossa depth was established by measuring the perpendicular distance between the highest point of fossa and the line passing through the most inferior point on the articular eminence and the posterior glenoid process ( Figure  1.b). The glenoid fossa width defined as the distance between the most inferior point on the articular eminence and the posterior glenoid process (Figure 1.b). The articular eminence inclination was measured by top-roof line method, i.e., the angle between Frankfort plane and the plane passing through the highest point in the roof of glenoid fossa and the lowest point at the crest of the articular eminence (Figure 1.c).

Variables
Growth

Statistical analysis
Data were analyzed using SPSS software package V.18 (version 18, SPSS Inc, Chicago, IL, USA). All CBCT images were re-measured by the same examiner after a 2-week interval to confirm intra-observer reliability. Intra-Class correlation coefficient was used to assess the reliability of the measurements. Oneway analysis of variance (ANOVA) and Tukey post-hoc test were used to evaluate the association between different growth patterns and glenoid fossa morphology. P-value less than 0.05 was considered significant.

Results
A total of 63 adult patients were included in this study. Distribution of glenoid fossa morphology based on the width, depth and inclination is shown in

Discussion
Sagittal and vertical facial disharmonies can affect the relationship of the mandible to the cranial base. Therefore, glenoid fossa position is likely to play an important role in the establishment of different craniofacial patterns and orthopedic/orthodontic therapies [19][20][21]. In current study we determined the association between glenoid fossa morphology and different growth patterns using CBCT images.
The variability and complexity of the TMJ make it difficult for accurate radiographic examination and clinical diagnosis [22]. Different radiographic methods have been used in previous studies to examine the TMJ morphology, such as computed tomography [23], magnetic resonance imaging [24], conventional tomography [25], and CBCT [26][27][28]. Standard 2D radiographs of the TMJ have several limitations including superimposition of overlying structures, magnification and distortion that limit the ability to evaluate TMJ [29,30]. CBCT, a recently developed imaging technology, has been used for 3D imaging of the TMJ and has been shown to delineate the joint   [34].
There were different concepts about the depth and width of the glenoid fossa. Our results showed that the depth and width of glenoid fossa in horizontal growth pattern was significantly smaller than other groups in skeletal Cl I. Lower depth seems to be in accordance with clockwise rotation of anterior and posterior cranial bases [36]. Lin et al. [15] and Katsavrias et al. [37] expressed that the depth of the glenoid fossa in high-angle was significantly smaller than control and the low-angle groups but there were no statistical differences between three groups in regard to width of glenoid fossa. The differences might be due to different case selections; skeletal Cl I in current study vs skeletal class II female cases and different sagittal skeletal patterns in Lin's and Katsavrias' respectively.
The inclination of the glenoid fossa was lower although not statistically significant in the horizontal compared with vertical and normal growth pattern groups. On the other hand, Lin et al. [15] and Widman et al. [14] demonstrated that inclination of articular eminence and mandibular plane angle were inversely related. The variation in the results from these studies might be due to different radiographic methods and the index for growth pattern classification with varying accuracy. Current study analyzed CBCT images of Class I adult patients and adopted Jaraback's as a reliable index to represent the growth pattern.
Widman et al. [14] and Lin et al. [15] examined the angle of articular eminence with lateral cephalometry and adopted mandibular plane angle to classify patients. We assumed that unlike SN-MP and FMA, representing the relation of the mandibular base to cranial base, Jaraback's is a special index to classify patients according to their growth patterns.

Conclusion
Due to the importance of muscular function on the TMJ it is recommended further studies focusing on the relationship of muscle function and glenoid fossa morphology.
The width and depth of glenoid fossa were significantly lower in horizontal growth pattern. No statistically significant differences were found between inclinations of glenoid fossa among three groups.