Assessing the Articular Eminence Asymmetry in Dentate, Partially Edentulous and Edentulous patients Using Cone-Beam Ct.

BACKGROUND AND OBJECTIVES: The relationship between the articular eminence (AE) inclination and masticatory system in the biomechanics of temporomandibular joint (TMJ) is defined by the degree with normal values of 30°-60° obtained between the posterior wall of the AE and a horizontal reference plane. The purpose of this study was to assess the asymmetry of the AE in dentate, partially edentulous, and edentulous patients using cone-beam computed tomography (CBCT) imaging and to compare the determined asymmetry in the dentulous with partially and completely edentulous patients.
MATERIALS AND METHODS: CBCT images of 120 TMJ joints in sixty patients were evaluated. AE inclination and height values were traced on the central sagittal slice of right and left TMJ. The patients were grouped as dentate, partially edentulous, and edentulous with an age range of 20-80 years. Statistical analysis included student's paired and independent t-test, analysis of variance, and Tukey's post hoc test, and P < 0.05 was considered statistically significant.
RESULTS: AE inclination revealed highest value in dentate patients (60.98 ± 5.42) followed by partially edentulous (53.40 ± 7.91) and lowest in the edentulous patients (51.43 ± 3.63). P < 0.001 was statistically significant between these groups.
CONCLUSION: The results obtained in the present study showed steep inclination of AE in dentate followed by partially edentulous and edentulous subjects. No significant differences among the age, gender, and sides were found. Copyright:

INTRODUCTION

Articular eminence (AE) is a part of the temporal bone which develops at about 6 years of age along with S-shaped mandibular fossa up to the second decades and varies in morphology in relation to dental status, aging, gender, and functional activities of the individuals. In the opening and closing of the mouth, the condylar process rotates and slides[12] along the AE and this would be of interest in assessing the right-left asymmetry of the eminence.[34] The relationship between the AE inclination and masticatory system (dentition) in the biomechanics of temporomandibular joint (TMJ) is defined by the degree with normal values of 30°–60°[567] obtained between the posterior wall of the AE and a horizontal reference plane.

However, variations in the right-left asymmetry of eminence >5° were also reported in the earlier studies on dry skull in comparison to clinical studies[389] and their influence on TMJ morphology.[101112]

Since the earlier methods of using conventional, panoramic, computed tomography, magnetic resonance imaging and tomography were having limitations and with variable results, cone-beam computed tomography (CBCT) has been used in this study as it is more advantageous and precise, with real three-dimensional and high spatial resolution.[1314]

The present study was done to assess the AE asymmetry in dentate, partially edentulous, and edentulous patients using CBCT imaging.

MATERIALS AND METHODS

The study was conducted on patients attending to the department of Oral Medicine and Radiology, V. S. Dental College and Hospital, Bangalore, India. The sample size of sixty patients with an age group of 20–80 years was divided into Group 1-dentate with minimum 28 teeth present, Group II-partially edentulous with posterior unilateral edentulous arch, and Group III-Completely edentulous of twenty samples each. Any craniofacial anomalies or systemic diseases (e.g., rheumatoid arthritis), pathologic lesion, or trauma in the region of TMJ were excluded from the study.

High-resolution CBCT images of sixty subjects were obtained using Kodak care stream CS9300 USA-CBCT machine, with Kvp 70–90, mA 4–10 and exposure time of 8.01s for each right and left sides of TMJ with the patient positioned vertically so that Frankfort horizontal plane was parallel to the floor. The FELDKAMP software was used for analysis.

Image observation

Primary reconstruction with 0.5 mm thick axial slices was performed initially and secondary reconstruction was done from the widest mediolateral extent of the condylar process seen from axial view. About 1.1 mm thickness of both sagittal and coronal slices were obtained perpendicular and parallel to the long axis of the condylar process, respectively.

Measurements

AE inclination is measured by BEST FIT LINE method-angle between Ebf and FH (F) plane.[161516]

The following points were used to determine the planes and angles in the study.

Po: Highest point of auditory meatus

EP: The point which the F1 line cut the eminence posterior surface

CP: Highest point of the condylar process

H: Highest point of the fossa

L: Lowest point of AE.

The following planes were constructed using the above points.

Ebf plane: The best-fit plane of the AE inclination connecting EP

FH: Frankfort horizontal passing through PO

F1: The parallel line to FH passing through point CP

F2: Parallel line to FH passing through point H.

Eminence height (Eh) is measured by the distance between the lowest point of AE (L) and the plane (F2) formed by the highest point of the fossa [H, Figure 1]. All the measurements were viewed on central sagittal slice of the condylar process [Figure 2].[17] Three experienced oral and maxillofacial radiologists evaluated the CBCT images individually.

Figure 1

Planes and angles in the study

Figure 2

Measured eminence angle and height

Statistical analysis

Statistical package for the Social Sciences (SPSS) for Windows, version 22.0 released in 2013 Armonk, NY, USA: IBM Corp; was used to perform statistical analysis. Descriptive analysis of all the explanatory parameters was done using frequency and proportions for categorical variables, whereas in mean and standard deviation (SD) for continuous variables.

Student Paired t-test was used to compare mean AE Inclination (degrees) and Height (mm) between right and left sides in different study groups. One-way analysis of variance test followed by Tukey's post hoc test was used to compare mean AE inclination (degrees) and height (mm) between different study groups. Similar age-wise comparison was also done. Gender wise comparison was performed between different study groups using independent student t-test. A P < 0.05 was considered statistically significant.

RESULTS

Table 1 shows the sample characteristics with a mean age and SD of 24.80 ± 3.85, 39.20 ± 3.94, and 61.90 ± 7.23 in Groups I, II, III, respectively, with a P < 0.001 which is statistically significant. However, there is an equal gender distribution of males and females which is nonsignificant.

Table 1

Age and gender distribution among study groups

Age	Group 1	Group 2	Group 3	P
Mean±SD	24.80±3.85	39.20±3.94	61.90±7.23	<0.001*,a
Range	20-33	35-46	50-76
Gender, n (%)
Males	10 (50.0)	10 (50.0)	10 (50.0)	1.00b
Females	10 (50.0)	10 (50.0)	10 (50.0)

aKruskal-Wallis test, bChi-square test. Group 1: Dentulous group, Group 2: Partially edentulous group, Group 3: Completely edentulous group. SD: Standard deviation

In Table 2, there is a mean difference of -0.95 in Group I and -0.10 in Group II. However, there was no statistical significance in any group. Similarly, there was no significance in the height values either.

Table 2

Comparison of mean articular eminence inclination (°) and height (mm) between right and left sides in different study groups using student paired t-test

Groups	AE angle					AE height
	Sides	n	Mean(0)±SD	Mean difference	P	Mean (mm)±SD	Mean difference	P
Group 1	Right	20	60.50±6.73	−0.95	0.55	6.31±1.85	−0.19	0.50
	Left	20	61.45±6.13			6.50±1.70
Group 2	Right	20	53.35±8.09	−0.10	0.96	6.07±1.01	0.29	0.19
	Left	20	53.45±9.49			5.78±1.38
Group 3	Right	20	55.35±6.68	2.85	0.08	6.36±1.16	−0.29	0.19
	Left	20	52.50±6.73			6.65±1.23

n: Number of joints, SD: Standard deviation, AE: Articular eminence

Table 3 shows the highest value in dentate patients (60.98 ± 5.42) followed by partially edentulous (53.40 ± 7.91) and the lowest in the edentulous patients (51.43 ± 3.63). A P < 0.001 was statistically significant between these groups. There was no statistical significance seen in the AE height values [Table 3].

Table 3

Comparison of mean articular eminence inclination (°) and height (mm) between different study groups using one-way ANOVA test

Groups	AE angle					AE height
	n	Mean(0)±SD	Minimum	Maximum	P	Mean (mm)±SD	Minimum	Maximum	P
Group 1	20	60.98±5.42	53.0	68.5	<0.001*	6.41±1.66	3.8	10.8	0.46
Group 2	20	53.40±7.91	36.0	67.5		6.21±0.77	4.8	7.4
Group 3	20	51.43±3.63	46.5	58.0		5.92±1.11	3.9	9.1

*Statistically significant. n: Number of subjects, SD: Standard deviation, AE: Articular eminence

However, the mean difference between the groups using Tukey's post hoc analysis by multiple comparisons revealed the AE angle values of 7.58 and 9.55 between Groups I and II and Groups I and III, respectively, at 95% CI which is statistically significant at P < 0.001. There was no statistical significance seen between Groups II and III [Table 4].

Table 4

Multiple comparisons of mean difference in articular eminence inclination between groups using Tukey's post hoc analysis

(I) Groups	(J) Groups	Mean difference (I-J)	95% CI for the difference		P
			Lower	Upper
Group 1	Group 2	7.58	3.07	12.08	<0.001*
	Group 3	9.55	5.05	14.06	<0.001*
Group 2	Group 3	1.98	-2.53	6.48	0.55

There were no statistical differences in relation to age and gender in the study groups with respect to AE inclination and height.

DISCUSSION

The slopes of AE are affected by masticatory forces, mechanical conditions produced by aging, environment and influenced by the loss of tooth which results in remodeling and reshaping of this osseous structure morphology with studies done in relation to this structure.

The asymmetry of AE inclination and height of both right and left sides were not significant in this study in each of the three groups, but there was significant asymmetry of AE angle between the three groups suggesting that the level of asymmetry did differ by dental status in comparison to the previous studies by Jasinevicius et al.[3] The steepness of the AE inclination was higher in dentulous patients followed by partially and completely edentulous.

The effect of occlusion on TMJ morphology[18192021] had been studied and some investigators noted that loss of posterior teeth or vertical dimension had an effect on the AE with shallower angles.[3] However, this group exhibited significantly steeper slopes along with the dentulous group. Granados et al. found that the effect on AE was higher in longer edentulous patient resulting in higher deformation rate influencing TMJ morphology.[18152223] and Sümbüllü et al. supports that AE inclination was lower in the second decade and reached the highest value in the third decade and gradually decreasing in the old age of life.[172425]

However, in this study, there was no significant difference in any age groups. Thus, this study suggests to restore the normal physiological occlusion and maintain harmonious relation in the biomechanics of the TMG.

CONCLUSION

We evaluated and compared the AE inclination and height on both right and left TMJ using CBCT and observed that the eminence inclination between the groups was statistically significant (P < 0.01) suggesting that AE slope was highest in the dentulous patients when compared to partially and completely edentulous patients. However, no statistical significance was observed in the AE inclination and height in the right and left TMJ in individual groups. Similarly, no statistical significance was observed in relation to age and gender in the study groups.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.