Attempt to quantify the gap in the mandibular condyle and glenoid fossa​

Introduction

Since many patients with temporomandibular deformity have temporomandibular disorders, it is considered that the prognosis of the caseｓ is affected by changes in the temporomandibular joint load and occlusion caused by sagittal splitting of the lower jaw.​

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In order to comprehend the condition of the temporomandibular joint , the image diagnosis using Cone Beam CT (hereinafter, referred to as "CBCT") are conducted.　​

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Although it was easy to comprehend the state bone cortex using conventional tomographic images, it was difficult to comprehend the distance of the joint space and the position and shape of the mandibular condyle at each site.​

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Here we describe the quantitative evaluation of the condition of the temporomandibular joint before surgery of patients with jaw deformity with the use of CBCT and the clinical utilization of diagnostic imaging of the temporomandebular joint.

Material and method

1. Create the color mapping

DICOM data was obtained from 10 patients with jaw deformity (total of 20 joints from right and left　temporomandibular joints) with the use of CBCT (CB-MercuRay,Hitachi Medico).​

The CBCT photographing was performed at a 0.2mm voxel pitch. ​

3DCG was created by extracting the morphology of the mandibular condyle and glenoid using virtual preoperative planning software for craniofacial surgery (ProPlanCMF, Materialise Simplant O & O, Dentsply IH) from the DICOM data of the temporomandibular joint ( Fig.１)

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Next, the distance between the mandibular condyle and glenoid was color-coded, and color mapping was performed on the bone surface.​

On the color mapping, the color shade changed was set every 1.0mm within the length of 5.0mm.

2. Color mapping classification

Various shades in the color existed on the mapping of temporomandibular joints of patients with jaw deformities. Therefore, divided into four regions of front, rear, inner pole and outer pole in the color mapping, then investigated whether the region with a distance within 1.0 mm exists in an area of 5.0㎟ or more.

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Then in a case to observe such a region, the adjacent region was counted as one place and then the joints were classified according to its number (Fig. 4).

​3. Numericalization of color mapping

The color mapping of the temporomandibular joint was displayed every １.0㎟. In RGB value (A value returned by the RGB function;　specified a color as a combination of red, green ,and blue values as integers from 0 to 255.)​

Next, Distance was calculated based on the numerical values of RGB. (Fig. 2: Based on the color scale corresponding to the distance).​

The area displayed in gray was excluded, and the distance within 1 mm was shown in color green, and the percentage to the entire color scale was calculated.​

Results

The largest ratio of the region with the distance within 1,0 mm was 51.3% of Type 4 with 4　adjacent regions,　and the smallest one was 2.3 % with Type 1 with 1 adjacent region.(Table 1)

The larger the number of adjacent areas, the greater proportion of colors that are close to each other as a whole​ (Table 2). Type IV and Type Ⅲ have significantly greater proportion compared with Type I and Type Ⅱ.(Mann-Whitney U Test)

Discussion

In the occasion to plan a surgery of patients with jaw deformities, comprehending the morphology and positional relationship between the glenoid and the mandibular condyle are significant.​

 However, the morphology and positional relationship of the glenoid and mandibular condyle in patients with jaw deformities transfersin various ways.​

In this method, the relationship between the glenoid and the mandibular condyle could be quantified by quantifying the gap between the glenoid and the mandibular condyle by the color mapping.​

 As the number of adjacent regions increase, the tendency of increasing region with distance within 1.0mm was observed. However, in the further examination is necessary by increasing the number of cases.​

 In addition, to examine the number of region at the first medical examination and the stability after surgery must be performed and continued to report it.

Conclusions

It was suggested that it is useful to quantitatively measure the positional relationship between the mandibular condyle and the glenoid fossa Introduction​

Since many patients with　temporomandibular deformity have temporomandibular disorders, it is considered that the prognosis of the case s is affected by changes in the temporomandibular joint load and occlusion caused by sagittal splitting of the lower jaw.​

In order to comprehend the condition of the temporomandibular joint ,the image diagnosis using Cone Beam CT (hereinafter ,referred to as "CBCT") are conducted.​

Although it was easy to comprehend the state bone cortex using conventional tomographic images,it was difficult to comprehend the distance of the joint space and the position and shape of the mandibular condyle at each site.​

Here we describe the quantitative evaluation of the condition of the temporomandebular joint before surgery of patients with jaw deformity with the use of ​CBCTand the clinical utilization of diagnostic imaging of the temporomandebular joint.