Mandibular Condyle

Cone Beam Computerized Tomography (CBCT) data sets were acquired using ILUMA™ (IMTEC, 3 M Company, Ardmore, Oklahoma, USA), with a reconstructed layer thickness of 0.1 mm and a 512 × 512 matrix. The device was operated at 120 kVp and 3-8 mA using a high-frequency generator with a fixed anode and a 0.5-mm focal spot. A single 40-s (because the complete volume of the head was taken) high-resolution scan of each skull was made with a voxel size (mm³) set at 0.25 mm³, and a 17.0 mm diameter and 13.2 cm field of view.
All CBCT images were taken with the subjects sitting in an upright position, with their backs as nearly perpendicular to the floor as possible. The head was always stabilized with ear rods in the external auditory meatus. The subjects were instructed to look into their own eyes in a mirror 1,5 m in front of them to obtain the natural head position.
Image segmentation of the anatomic structures of interest based on 2-D Digital Imaging and Communications in Medicine (DICOM) formatted data provided different planes of view as well as three-dimensionally reconstructed volumes using Mimics™ 9.0 software (Materialise NV Technologielaan, Leuven, Belgium) (Figure 1).
The 3-D reconstruction of the condyle requires the mandibular condyle to be separated in all the three planes of space from all the other structures, mostly the soft tissues.
Each condyle was visualized in the recommended range of bone density (range of gray scale from -1350 to 1650) and segmented using an adaptive threshold, which was visually checked prior to making 3-D and volumetric measurements.
Specifically, after enlargement of the TMJ area, the remaining surrounding structures were progressively removed using various sculpting tools for the upper, lower, and side condylar contours (cortical bone), as shown in Figure 1. The segmentation was made on coronal views, and the superior, inferior, and lateral limits of the condyle were standardized (Table 1 and Figure 2a-b). On the coronal views, the superior contour of the condyle was defined where the first radiopaque point was viewed in the image depicting the synovia; the lateral contours for each section were easily identified through clear visualization of the cortical bone (Figure 2a). The inferior contour of the condyle was traced where its section passed from an "elipsoidal" shape (owing to the presence of anterior crest of the condylar head) to a more "circular" shape (suggesting that the view was at the level of the condylar neck) (Figure 2b). Accordingly, the condyle CBCT data sets were segmented with a dedicated Mimics™ tool to construct a new mask that included only the mandibular condyle (Figures 1 and 3). After the condylar segmentation, 3-D multiplanar reconstructions were produced (Figure 1), and volumetric (mm³) and surface measurements (mm²) were made for each condyle through the Mimics™ automatic function (Figure 1)

Using the AutoCAD (2010) program,¹³ a 3D solid model of the mandible with teeth was created, based on a CT image of a 20-yr-old patient¹⁴ (Fig. 2). Scan data were obtained using multi-slice CT (Brilliance 64 slice, Philips Company, Amsterdam, Holland). The CT machine was set to 120 kV, 80 mA, exposure time 30 s, and 0.5-mm nominal slice thickness. Due to modelling complications and the difficulty of mesh generation and mathematical simulation, the periodontal ligaments were omitted. A network representing the cancellous bone was also ignored. Instead, the cancellous bone was represented as a solid unit within a shell of cortical bone.¹⁵ ,¹⁶ Standard orthodontic Edgewise stainless-steel brackets with 0.022 in slots on the five mandibular teeth and bounded tube on the first molar were simulated according to the Dentarum Orthodontics Catalogue Edition 22, (Fig. 3, Fig. 4). A rectangular archwire (0.019 × 0.025 in) ligated the brackets.³ The models were uploaded to the FE program, Autodesk Inventor Professional (2020). As suggested by many studies, the mechanical characteristics of the materials are isotropic, homogenous, and linear elastic.^{15 ,16} For isotropic materials, Young's modulus and Poisson's ratio were used as elementary inputs. Young's modulus and Poisson's ratio for the cortical bone, cancellous bone, teeth, stainless steel brackets, and wires, were adopted, as shown in Table 1.¹⁷ (link)Fig. 2

CT image for 3D model creation.

Fig. 2Fig. 3

Bracket drawing within Auto CAD (2010).

Fig. 3Fig. 4

Bracket bonded on tooth surface.

Fig. 4Table 1

Mechanical properties of materials.

Table 1

Material	Young's modulus (MPaa)	Poissons Ratio
Cortical bone	13,000	0.3
Cancellous bone	1000	0.3
Teeth	20,000	0.3
Bracket	193,000	0.31
Wire	193,000	0.31

a

MPa = Mega Pascal.

In this study model for simulation, the boundary condition was the outer surface of the mandibular condyle. The mandible was reinforced by a simulated glenoid fossa, which impeded the total movement at the top of the mandibular condyle.^{16 ,17} (link) The auto-mesh order was used for mesh creation, and the accuracy of the result was affected by the number of elements elaborated in the model. The final mesh of this study model comprised 1 230 103 nodes and 803 419 elements. To simulate the PowerScope 2 appliance, a force between 150 g and 260 g were loaded mesially and vertically in relation to the distal surface of the mandibular first premolar.³

The materials consisted of the medical database of the CliniNet program (www.cgm.com, accessed on 1 October 2022) at the Department of Maxillofacial Surgery, Medical University of Lodz, Poland, and the results of computer tomography scans evaluated in RadiAnt (www.radiantviewer.com, accessed on 1 October 2022), which are available in this department. The keywords for selecting patients were mandibular fracture and mandibular condylar process fracture. The research covered the period from 1 January 2020 to 1 October 2022, which was 33 months of continuous operation of the hospital department. Patients were cared for around the clock because the hospital ward provides 24-h medical care and serves a region with a population of approximately 2.5 million. In addition, statistics on the availability of treatment should be provided. There are 39 maxillofacial surgery departments/subdepartments in Poland (38.3 million in 2020, 38.1 million in 2021, and 41.5 million residents, including 3.2 million citizens of Ukraine, in 2022 [21 ]), of which only three provide surgical treatment for mandibular head fractures. All residents of the country have the option of hospital treatment, and 35.8 million people have health insurance [22 ].
Fractures of the mandibular body, angle, and ramus, as well as fractures of the base and neck (low neck and high neck) of the mandibular condyle according to Kozakiewicz classification [14 (link)] and three types of mandibular head fractures (A, B, and C according to Neff [10 (link),11 (link)]), were counted in the archival material of the Department of Maxillofacial Surgery, Medical University of Lodz, Poland, analyzed, and subjected to radiological verification. In addition, data were collected on sex, age, place of residence, and cause of injury.
To interpret the epidemiological results, the prevalence of mandibular head fractures was additionally checked. The amount of medical-scientific research interest in the PubMed database (www.pubmed.ncbi.nlm.nih.gov/advanced/, accessed on 31 December 2022) related to the topic of this publication was checked. Studies related to mandibular head fractures (or intracapsular fractures) and studies related to the surgical treatment of such fractures were searched for. The search query was ((((((mandible head fracture)) OR ((mandible intracapsular fracture)))) AND (((((fixation)) OR ((osteosynthesis))) OR ((surg)))))) AND (1982:2022[pdat])).
Statistical analysis was performed in Statgraphics Centurion 18 (Statgraphics Technologies Inc., The Plains City, VA, USA). A p value of less than 0.05 was considered statistically significant.

The pre- and postoperative mandibles were semi-automatically segmented according to Holte et al. [20 (link)]. Subsequently, the segmentation of the mandibular condyle was refined and registration was automatically performed to align the right and left pre- and postoperative rami, separately, as proposed in the protocol validated by Verhelst et al. [23 (link)]. Surface-based registration was used for the alignment, which was shown to be more accurate and reliable than VBR for the assessment of mandibular condyle remodeling [20 (link)].
The C-plane, centered in the pre-operative mandibular notch (C-point) and parallel to the Frankfurt horizontal plane, as defined by Xi et al. [25 (link)], was used to isolate the pre- and postoperative condyles from the rami. For spatial analysis, the condylar head was spatially divided into four sub-regions: anterior/posterior-lateral and medial condylar head using two cutting planes: (1) a plane going through the lateral and medial condylar poles perpendicular to the horizontal Frankfurt plane, and (2) an orthogonal mid-plane defined by the lateral and medial condylar poles. Postoperative change of the condyle was represented by the volumetric change and by color-coded distance maps [14 (link)], quantified by the mean surface distance of the condylar head and neck, and the defined four sub-regions of the condylar head (Figure 1).