Presently, mandibular fractures are the most common injuries of the facial bones and range from 62.5 to 78.8% [1, 2]. Surgical patients with fractures of facial bones induce 28.3% of total patient amount in maxillofacial hospitals [2]. Mean age of patients with mandibular fractures is 29.8 years and men are more likely to be injured [3]. The issue of injury is not only medical, but also socio-economic, as it affects the majority of the able-bodied population group.
A common localization of mandibular fracture is the condylar process, inducing from 25 to 35% of all mandibular fractures [4]. The discussion around the question of the mandibular process fractures treatment remains actual. The problem of choosing a conservative or surgical treatment method, surgical access and fixing elements have not been fully resolved [5–7].
The limited surface area and volume of the bone in condylar process fractures create difficulties in choosing the size, number and shape of fixing elements [8, 9]. The new developed designs of titanium external mini-plates help to achieve the requirements of stable functional ostheosynthesis. But along with that, it can’t be the unique solution for the whole variety of clinical situations associated with an individual anatomical features and the nature of the fracture [10].
There is no detailed description of the morphological parameters for the neck of the mandible in available scientific literature. Due to this, necessity for studying the issue of the condylar process anatomical features appeared.
The aim of the study is to determine the mandible neck morphometric parameters for the rational choice of fixing elements during ostheosynthesis.
Material and methods
Current retrospective observational research was conducted on the base of the Kemerovo State Medical University, the Kuzbass Regional Clinical Hospital named after S. V. Belyaev and the group of radiation diagnostics medical centers «Diagnost» Kemerovo.
Based on the computed tomography scans of the mandible, the morphometric parameters of the neck of the mandible were studied.
This investigation method is exact and statistically there is no differences between classical examination of anatomical preparation [11, 12].
The research was conducted according to the results obtained after a cone beam computed tomography (CBCT) of the mandible and maxilla performed on a dental X-ray system KAVO ORTHOPANTOMOGRAPH OP 3D Pro («Kavo», Germany). The tomography was done per-protocol with parameters set by the manufacturer (90 kV, 3.2—12.5 mA, 8.1 s, voxel element size is 0.2 mm) according to the size of the irradiated field 130x150 mm. The software «Ez3D2009» (version 1.2.6.22) was used for the data postprocessing, the building of multiplanar reconstruction (MPR) and the 3D-reconstruction.
The inclusion criteria were:
— Men aged from 22 years, women aged from 21 years;
— The absence of bone damages, neoplasms or mandibular deformities, ankyloses of temporomandibular joint, abnormal craniofacial development, facial bone defects, rough malocclusion.
The CBCT results of 198 patients were analyzed. Research included 145 examinations corresponding to the inclusion criteria.
Patients, who performed CBCT, were divided to gender and age groups according to the age periodization of the Developmental Physiology Institute of the Russian Academy of Medical Sciences (1969): the first maturity group (22-35 years old men and 21-35 years old women), the second maturity group (36-60 years old men and 36-55 years old women), the elderly group (61-74 years old men and 56-74 years old women) and the senile group (75-90 years old). The research included 76 CBCT imagines, belonging to men (mean age is 40.5±11.7 years old) and 69 — to women (43.0±12.5 years old).
Following groups of patients have been identified depending on preservation of dentition: with intact teeth (n=54), partial secondary (n=59) and complete edentulous (n=32).
Following shapes of the mandible ramus were identified according to the results of 3D-reconstruction analysis, based on the classification of I.V. Gaivoronsky et al. (2020) [13]: platyramimandibular (n=48), orthoramimandibular (n=51), hypsiramimandibular (n=46).
The clinico-anatomical boundaries of the neck were determined using the classification of A.Neff (2014) [14].
In the program Ez3D2009 on the 3D-reconstruction image of the mandible, the lines AB and CD are marked on the right and left sides, where A is the upper point of caput mandibulae, B is gonion, line CD is the smallest length between anterior and posterior borders of the mandible ramus (Fig. 1). The results of these measures were used for the ramus latitude-altitude index calculation [13]. Further, the main line EF (base line) is marked on each side, connecting the most protruding points of the lateral pole of caput mandibulae and the posterior part of masseteric tuberosity. This line is necessary for separation the condylar process into clinico-anatomical areas (see Fig. 1).
Fig. 1. CBCT, 3D reconstruction of the mandible.
AB — height of the ramus; CD — smallest ramus width; EF — base line.
The coronal plane was passed through the middle of the caput mandibulae and the gonion to determine the upper border of the neck of the mandible in sagittal projection with MPR. Next, the layer thickness was increased until including the whole surface of caput mandibulae in the cut. In the coronal projection with MPR was built a circle with the center in the spongy substance of caput mandibulae, while the upper and lateral parts should be in contact with caput borders as much as possible. Further, the lowest auxiliary point G was marked on the circle, through which in the sagittal projection with MPR the upper border of the neck of the mandible was built, marked with the line HI, perpendicular to the base line (Fig. 2, a).
Fig. 2. CBCT of the mandibular ramus.
a — coronal projection of the MPR of the head of the mandible; b — oblique sagittal projection of the MPR of the mandibular ramus; c — axial projection of the MPR of the mandibular ramus, the cut was drawn through the lower border of the neck of the mandible. EF — base line; G — auxiliary point for determining the upper border of the neck of the mandible; JK — width of the lower border of the condylar process; NO — width of the middle of the condylar process; HI — width of the upper border of the condylar process; ML — height of the condylar process; the surface area of the neck of the mandible is marked with a red line.
Further, in the window of coronal projection with MPR the sagittal plane was built in a such way that it passed through the middle of the caput mandibulae and the mandibular angle. On the axillar projection of the MPR the sagittal plane was passed through the axis of ramus, then the layer thickness was increased until including the whole depth of the mandibular ramus in the cut. The main measurements of the neck parameters were done on the obtained image of the oblique sagittal projection with MPR of medium intensity (Fig. 2, b).
The line JK was marked on the image of sagittal projection with MPR, where J is the deepest point of mandibular incisure and K is the point on the posterior border of the mandibular ramus. The line JK is perpendicular to the base line. The marked lower and upper border allowed to measure the height of mandibular neck, indicated as the line LM, where L is the point of the lines JK and EF intersection and M is the point where the lines HI and EF are crossed. The line NO was built through the middle of the line LM, perpendicular to the base line, to measure the width of the neck in its midshaft (see Fig. 2, b).
Bone thickness was measured in the axial projection with MPR at the cuts level of lower border of the condylar process and its middle part. Two points were highlighted on each level: the first is the middle length from the posterior border of process to its center, the second is the middle length from the center of process to its anterior border. The lines were built perpendicular to the sagittal axis of mandibular ramus, through the mentioned above points and then the bone thickness was measured (Fig. 2, c).
The surface area of mandibular neck was calculated in the sagittal projection with MPR using the «measuring the area of a polygonal region» tool (Fig. 2, b).
The obtained results after the study were statistically analyzed using the SPSS program. Quantitative parameters were assessed for the normal distribution match using the Kolmogorov-Smirnov and Shapiro-Wilk criteria. Statistical parameters with a normal distribution are presented as M±SD, where M is the arithmetic mean and SD is the standard deviation. The parameters differing from normal while distribution are presented as follows: Me — median, lower and upper quartile [25th percentile; 75th percentile].
Comparison between three independent groups was done using the Kruskal-Wallis method. The level of statistical significance was taken equal to 0.05. If statistically significant differences were registered, further pairwise comparison was perfomed using the Mann–Whitney U-criterion with Bonferroni correction. The amount of paired comparisons reached 3, respectively, the level of statistical significance was taken equal to 0.017.
The comparison of two independent samples was performed using the Mann-Whitney U-criterion. When checking null hypotheses, the critical value of the statistical significant level was taken equal to 0.05.
This investigation protocol was approved by the Expert Committee of the Kemerovo State Medical University Kemerovo (Russia) on biomedical ethics (protocol No. 288 of 22.05.22).
Results and discussion
Results of measurements and comparison of mandible neck morphometric parameters, depending on gender, are showed in Tab. 1.
Table 1. Comparative characteristics of the morphometric parameters of the necks of the mandibles in men and women
|
Morphometric parameter of the neck of the mandible |
Side |
Men (n=76) |
Women (n=69) |
p-significance |
|
Width of lower border (JK line), mm |
R |
18.6±1.8 |
17.5±1.6 |
p=0.005 |
|
L |
18.4±1.7 |
17.7±1.8 |
p=0.033 |
|
|
Width of neck midshaft (NO line), mm |
R |
13.1±1.6 |
12.8±1.8 |
p>0.05 |
|
L |
13.4±1.8 |
13.1±1.7 |
p>0.05 |
|
|
Width of upper border (HI line), mm |
R |
10.4±1.6 |
10.2±1.8 |
p>0.05 |
|
L |
10.5±1.7 |
9.8 [8.9; 11.7] |
p>0.05 |
|
|
Area, mm2 |
R |
85.8±33.6 |
72.7±26.9 |
p=0.025 |
|
L |
87.2±33.5 |
76.1±28.8 |
p=0.046 |
|
|
Height (LM line), mm |
R |
6.8±2.5 |
6.0±2.1 |
p>0.05 |
|
L |
6.5±2.5 |
5.8±2.0 |
p>0.05 |
|
|
Bone thickness on JK line in the posterior part of mandibular ramus, mm |
R |
7.7 [6.9; 9.0] |
7.2±1.7 |
p=0.03 |
|
L |
8.0±1.7 |
7.1 [6.2; 8.2] |
p=0.031 |
|
|
Bone thickness on JK line in the anterior part of mandibular ramus, mm |
R |
2.9 [2.3; 3.3] |
2.4 [2.2; 2.9] |
p=0.02 |
|
L |
2.8±0.7 |
2.5±0.6 |
p=0.007 |
|
|
Bone thickness on NO line in the posterior part of mandibular ramus, mm |
R |
9.4 [8.0; 10.8] |
8.5 [7.7; 9.7] |
p=0.005 |
|
L |
9.3 [8.2; 11.0] |
8.9 [8.0; 9.6] |
p=0.032 |
|
|
Bone thickness on NO line in the anterior part of mandibular ramus, mm |
R |
4.2±1.0 |
3.7±0.9 |
p=0.005 |
|
L |
4.1±0.9 |
3.9±1.0 |
p=0.008 |
Note. R — right, L — left. Data are shown as M±SD or Me [25th percentile; 75th percentile]
It was found that dimensions of mandibular neck morphometric parameters are larger in men. Statistically significant differences were found between the sizes of mandibular neck in width of the lower border, surface area and bone thickness in men and women. The average width of the lower border on the right side for men is 18.6±1.8 mm and 17.5±1.6 mm for women. The difference between mean values is 1.1 mm. The mean bone thickness at the NO line in the anterior part of mandibular ramus on the right side for men is 4.2±1.0 mm and 3.7±0.9 mm for women.
Information about parameters of mandibular neck is limited in accessible scientific literature. Nevertheless, some authors report about the presence of gender differences in the mandibular ramus structure [15-17]. The median thickness of the mandible neck bone, which was studied through 4 measurement points, was 5.3 [3.3; 8.2] mm on the right side, 5.4 [3.2; 8.3] mm — on the left, which corresponds to the data from K. Kronseder et al. [18].
There were no statistically significant differences within each gender group between the sizes of the right and left sides (p>0.05).
The analysis of the mandible neck parameters study results, depending on the latitude-altitude index of the mandibular ramus, showed that there are statistically significant differences between hypsyramimandibular, orthoramimandibular and platyramimandibular forms in the following parameters: the width of the lower and upper borders, neck midshaft and the area. Results are shown in Tab. 2.
Table 2. Comparative characteristics of the morphometric parameters of the neck of the mandibles in groups depending on the shape of the mandibular ramus
|
Morphometric parameter of the neck of the mandible |
Side |
Hypsyramimandibular (n=46) |
Orthoramimandibular (n=51) |
Platyramimandibular (n=48) |
p-significance |
|
Width of lower border (JK line), mm |
R |
16.4±1.22, 3 |
18.0±1.31, 3 |
19 [18.6; 20.1]1, 2 |
p=0.0001 |
|
L |
16.6 [15.8; 17.7]2, 3 |
18.1±1.61, 3 |
19 [18.2; 20.8]1, 2 |
p=0.0001 |
|
|
Width of neck midshaft (NO line), mm |
R |
11.8±1.42, 3 |
12.9±1.61, 3 |
14.2±1.21, 2 |
p=0.0001 |
|
L |
12.4±1.42, 3 |
13.4 [12.2; 14.3]1, 3 |
13.8 [13.2; 15.5] 1, 2 |
p=0.0001 |
|
|
Width of upper border (HI line), mm |
R |
9.4±1.52, 3 |
10.3±1.51, 3 |
11.3±1.41, 2 |
p=0.0001 |
|
L |
9.1±1.62, 3 |
10.0±1.61, 3 |
11.4±1.21, 2 |
p=0.0001 |
|
|
Area, mm2 |
R |
67.4±23.62, 3 |
81.9±29.71 |
88.7±35.71 |
p=0.008 |
|
L |
68.9±26.32, 3 |
88.2±30.41 |
87.6±34.51 |
p=0.001 |
|
|
Height (LM line), mm |
R |
6.0±2.1 |
6.4±2.4 |
6.4±2.6 |
p>0.05 |
|
L |
5.7±2.0 |
6.6±2.3 |
6.2±2.4 |
p>0.05 |
|
|
Bone thickness on JK line in the posterior part of mandibular ramus, mm |
R |
7.7±1.6 |
7.3±2.1 |
7.8 [6.9; 8.3] |
p>0.05 |
|
L |
7.5±1.6 |
7.2±2.2 |
8.0 [6.8; 8.5] |
p>0.05 |
|
|
Bone thickness on JK line in the anterior part of mandibular ramus, mm |
R |
2.6±0.6 |
2.8 [2.2; 3.2] |
2.7±0.8 |
p>0.05 |
|
L |
2.4±0.6 |
2.7±0.6 |
2.8±0.8 |
p>0.05 |
|
|
Bone thickness on NO line in the posterior part of mandibular ramus, mm |
R |
8.8 [7.9; 10.1] |
9.2±2.3 |
9.5±1.7 |
p>0.05 |
|
L |
9.0 [7.6; 9.8] |
8.8 [8; 11.1] |
9.6±1.5 |
p>0.05 |
|
|
Bone thickness on NO line in the anterior part of mandibular ramus, mm |
R |
4.0±1.0 |
3.9±0.9 |
3.9±0.8 |
p>0.05 |
|
L |
3.7±1.0 |
4.3 [3.2; 4.8] |
4.0 [3.6; 4.7] |
p>0.05 |
Note. 1 — statistically significant differences with hypsyramimandibular (p<0.017); 2 — statistically significant differences with orthoramimandibular form (p<0.017); 3 — statistically significant differences with platyramimandibular form (p<0.017); R — right; L — left. Data are shown as M±SD or Me [25th percentile; 75th percentile].
The width of the lower borders, upper borders and neck midshaft grows with an increase of latitude-altitude index, which can be explained by an increase in the width of the mandibular ramus. But such a parameter as the height of the neck does not have statistical differences between the groups. Although the presence of correlation between an increase in the height of mandibular ramus and, accordingly, mandibular neck could be hypothesised.
I.V. Gaivoronsky et al. [13], who proposed a classification according to latitude-altitude index of the mandibular ramus, obtained statistically significant differences between the groups in most of the studied parameters, such as the height of the ramus, the smallest width of the ramus, the coronoid process base length, etc. There were no significant differences in the height and thickness of mandibular neck in this study.
Statistically significant differences within each group in the latitude-altitude index between the sizes of the right and left sides were not observed (p>0.05).
In comparison of the mandible neck morphometric parameters between the age groups statistically significant differences were not found (p>0.05). Furthermore, no differences between groups identified by the preservation of dental arch were found (p>0.05).
A.K. Jordanishvili et al. [12] report on the impact of partial secondary and complete edentulous on the mandibular ramus morphometric parameters. R. Okşayan et al. [19] found that ramus height had significant differences between patients with complete and partial edentulous. S. Fouda et al. [20] observed that the ramus height decreases with the age and tooth lose.
The results of this investigation differ from a number of foreign and domestic studies. It responds to the fact that the neck of the mandible is a limited anatomical area, less affected by the age and edentulous.
Conclusion
Morphometric parameters of the neck of the mandible have individual variability and statistically significant differences depending on gender and shape of the mandibular ramus. Planning of surgical treatment in the area of condylar process requires taking into account the CBCT data in each case.
Obtained results of the mandible neck sizes (width, thickness, bone surface area in the field of research) will help in the clinical practice for the lower jaw injuries treatment in the area of condylar process to rationally select the length, size, quantity and shape of titanium extramedullary mini-plates. These features will provide the requirements of stable-functional ostheosyntesis, depending on the gender and shape of mandibular ramus.
The authors declare no conflict of interests.