Bone Morphology of the Temporomandibular Joint and its Relation to Dental Occlusion

 
Mírian Aiko Nakane MATSUMOTO[1]
Ana Maria BOLOGNESE[2]
 
[1]Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Ribeirão Preto, SP, Brasil
[2]Faculdade de Odontologia, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, Brasil

Braz Dent J (1995) 6(2): 115-122 ISSN 0103-6440

| Introduction | Material/Methods | Results | Discussion | Conclusions | References |


The mandibular and temporal osseous components were analyzed in a sample of 30 dry skulls and their morphology was correlated with occlusal characteristics. In skulls with condyles of a more rounded shape, the depth of the fossa was greater. Furthermore, there was a significant correlation between greater depth of the fossa and skulls with normal overbite. However, no correlation was observed between depth of the fossa, tooth attrition and Spee curve.


Key words:temporomandibular joint, dental occlusion, bone morphology.


Introduction

The temporomandibular joint (TMJ) is a highly specialized articulation which is different from other synovial joints in that its articular surfaces are composed of dense fibrous tissue which functions like cartilage. (DuBrul, 1980).

Functionally, the temporomandibular joint is a ginglymus, where motion occurs in a rough hinge axis along a repeatable plane supported by strong lateral ligaments. It is also an arthrodial joint permitting gliding motion (Bell, 1990 and Okeson, 1989).

The osseous changes of the articular components of the TMJ related to type of occlusion have been discussed. Demirjian (1967), Seward (1976), Mongini (1975) and Gianelly et al. (1970) have reported variations in osseous components of the TMJ when correlated with occlusal disharmonies.

The objective of the present investigation was to study the osseous morphology of the TMJ in dry skulls and to correlate it with occlusal characteristics.


Material and Methods

This study was conducted on thirty dry skulls with mandibles, with maximum conservation and integrity of bone structures, condyles and temporal components, as well as complete and healthy dentition. Data referring to age, sex and skin color were obtained from records filled out at the time of death.

The dry skulls were from faioderm and melanoderm individuals, twelve females and eighteen males. Specimen age ranged from 18 to 60 years (mean = 27.7 years). Twenty-seven skulls had class I Angle (1899) malocclusion and three had class II Angle malocclusion.

A descriptive analysis of the condyle was performed based on three different aspects, according to the classification of Wedel (1978): A) anterior shape: 1, rounded or convex; 2, plane or slightly convex; 3, pointy or shaped like an inverted "V"; 4, other shapes; B) upper shape: 1, oblong; 2, rounded or oval; 3, laterally tapered, pear-shaped; 4, medially tapered, pear-shaped; 5, other shapes; C) lateral shape: 1, convex; 2, plane or slightly convex; 3, pointy or shaped like an inverted "V"; 4, other shapes.

Linear measurements of the anatomical structures that compose the temporomandibular joint were made: D) anteroposterior (a-p) condyle dimension: the distance between the most prominent points on the anterior and posterior surfaces of the condyle, perpendicular to the mediolateral axis; E) mediolateral (m-1) dimension: the distance between the most prominent medial and lateral points in relation to the mediolateral axis of the condyle; F) depth of the glenoid fossa: the distance from the deepest point of the glenoid fossa to the plane that joins the vertex of the postglenoid process to the top of the convexity of the articular tubercle.

In addition, we studied the occlusal characteristics of the sample according to the following specifications: G) amount of tooth wear or attrition: O, no wear; 1, with wear facets; 2, with cusp wear; 3, marked wear or severe abrasion; H) overbite: 1, normal, when the upper incisors covered the incisal third of the crowns of the lower incisors; 2, moderate, when the upper incisor covered the middle third of the crowns of the lower incisors; 3, deep, when the upper incisors covered the cervical third of the crowns of the lower incisors; 4, absent, when the lower and upper incisors had a top-to-top relationship; I) Spee curve: 1, normal, when the distance from the deepest point in the curvature of the lower arch to the occlusal plane, which passes through the cusps of the lower molars and the incisal borders of the lower incisors, was 2.0 mm or less; 2, moderate, when the distance from the deepest point in the curvature of the lower arch, close to the premolars, to the occlusal plane was 2.0 to 3.0 mm; 3, marked, when the distance described in 2 was more than 3.0 mm.

On the basis of the data obtained in this study, several comparisons were made between the morphological aspects of the articular components and the occlusal characteristics of the dry skulls. The following correlations were calculated: 1, between the anterior, superior and lateral condyle shapes and the depth of the glenoid fossa, Spee curve, overbite, and attrition; 2, between the depth of the glenoid fossa and overbite, Spee curve, and attrition.

Statistical analysis

Data were analyzed statistically by analysis of variance, by the Student t-test when the samples were normal, and by the Tukey test when differences were detected between samples. The linear regression equation was used in some correlations. The level of significance was set at 5% (P<0.05).


Results

Descriptive condyle analysis pointed out that in the anterior view, 58.4% of the specimens exhibited a plane or slightly convex shape, 25% a well-rounded or convex shape, 16.6% were shaped like an inverted "V", and only 3.1% were convex (Figure 1, top). In the upper view, many of the condyles (60%) had an oblong shape, 20% were pear-shaped and laterally tapered, 18.4% were pear-shaped but medially tapered, and only 1.6% had a rounded or oval shape (Figure 1, middle). Of the skulls examined in the lateral view, 55% were pointy or shaped like an inverted "V", 31.7% had a convex shape, and 13.3% were plane or slightly convex ( Figure 1, bottom).

The linear measurements of these bone structures showed that the anteroposterior dimension of the condyle ranged from 6.3 to 12.8 mm, with a mean value of 8.25 for females and 8.42 mm for males. The mediolateral dimension of the condyle ranged from 15.2 to 22.6 mm, with a mean value of 18.92 mm for females and 18.98 mm for males, with no statistically significant differences between sexes for the anteroposterior or mediolateral dimensions of the condyle. The depth of the glenoid fossa ranged from 3.75 to 7.6 mm, with a mean value of 6.02 for males and 6.11 mm for females, the differences between sexes being nonsignificant.

In the study of occlusal characteristics we observed that 36.6% of the specimens presented teeth with cusp wear, 33.4% exhibited only facets of wear, 16.7% marked wear or severe attrition, and 13.3% presented teeth with no wear (Figure 2, top). Of the skulls studied, 66.6% presented normal overbite, 23.4% had absent overbite, and 10% moderate overbite (Figure 2, middle). The Spee curve was moderate in 50% of the skulls, normal in 46.6% and marked in only 3.4% (Figure 2, bottom).

The correlations calculated between the morphologic, occlusal and dental variables were statistically significant for the anterior, upper and lateral condyle shape in relation to depth of the glenoid fossa, i.e., the depth of the glenoid fossa was greater in skulls presenting a more rounded or convex shape of this structure (Table 1). In contrast, there was no significant correlation between the anterior, upper and lateral condyle shape and occlusal characteristics such as Spee curve, overbite or tooth attrition. Another significant correlation of the present study was the greater depth of the glenoid fossa in skulls with normal overbite than in skulls with moderate or absent overbite. No such correlation was detected between depth of the glenoid fossa and Spee curve or tooth attrition (Table 1).
 
 


 
 

Figure 1 - Top, Percent distribution of the dry skull sample according to the anterior shape of the mandibular condyle: 1, rounded or convex; 2, plane or slightly convex; 3, shaped like an inverted "V". Middle, Percent distribution of the dry skull sample according to the upper shape of the mandibular condyle: 1, oblong; 2, rounded or oval; 3, laterally tapered, pear-shaped; 4, medially tapered, pear-shaped. Bottom, Percent distribution of the dry skull sample according to the lateral shape of the mandibular condyle: 1, convex; 2, plane or slightly convex; 3, pointy or shaped like an inverted "V".
 
 

Figure 2 - Top, Percent distribution of the dry skull sample according to tooth wear or attrition: 0, no wear; 1, with facets of wear; 2, with cusp wear; 3, with marked wear or severe abrasion. Middle, Percent distribu-tion of the dry skull sample according to overbite: 1, normal; 2, moderate; 3, absent. Bottom, Percent distribution of the dry skull sample according to Spee curve: 1, normal; 2, moderate; 3, marked.
 


Discussion

The skulls used in the present study were from individuals who died between 1957 and 1959. Considering that these skulls belong to contemporary human beings, a more reliable evaluation of occlusal characteristics and of morphology of the articular components would be expected. Many results of previous studies, especially with respect to the characteristics of tooth wear or attrition, are not consistent with the characteristics of human beings of our times. Angel (1948) and Wedel et al. (1978) worked with medieval material. Demirjian (1967) studied skulls from different collections. Seward (1976) studied skulls of native Australians, while Granados (1979) evaluated skulls of unknown origin, but there was evidence that many of them dated back to the 19th century. Hinton (1981b) analyzed several samples ranging from New World Aborigines to pre- and post-medieval individuals and even white North Americans who lived in the industrial era.

Analysis of the results showed no statistically significant differences between sexes for anteroposterior or mediolateral condyle dimensions or depth of the glenoid fossa. However, the values obtained by Wedel et al. (1978) and Hinton (1983) for mediolateral width were lower for women than for men. Christiansen and Thompson (1990) also reported that the transverse condylar dimension of normal adult joints was greater for men (19.6 mm) than for women (17.7 mm). With respect to depth of the glenoid fossa, the present results disagree with those reported by Demirjian (1967), who detected highly significant differences between male (8.0 mm) and female (7.4 mm) skulls. Furthermore, the dimensions detected by this investigator were greater.

Considering condyle shape, the present results were similar to those reported by Yale et al. (1966), who detected a slightly convex shape with an anterior view in 59.4% of their skulls, and different from those obtained by Öberg et al. (1971) and Wedel et al. (1978), who reported that most of the condyles (51%) presented a convex shape in an anterior view.

As to the upper aspect, most of the condyles studied here (60%) presented an oblong shape, confirming the results reported by Wedel et al. (1978). Yale et al. (1961), however, detected this oblong shape only in slightly convex condyles.

These contradictory data may be attributed to the fact that the investigators cited worked with markedly different samples. Wedel et al. (1978), for example, studied infant skulls (0 to 7 years), young skulls (7 to 14 years) and juvenile skulls (14 to 20 years), in addition to adult skulls (older than 20 years). In our investigation, we only studied skulls older than 18 years and especially in the 20-30 year range.

With respect to the occlusal characteristics, only 16.7% presented marked tooth wear or severe tooth attrition, although this percentage was higher in the samples studied by Demirjian (1967), Granados (1979) and Richards (1987), among others.

In the present study there was a difference between sexes only in the extent of tooth wear or attrition, which were greater in male specimens. Demirjian (1967) also observed this tendency, with nineteen male skulls presenting teeth with the greatest extent of attrition, whereas the female skulls presented only initial levels of wear or attrition. According to Hinton (1981a), this variation is probably the consequence of several factors, among them a more intense dental overload in males.

The present results showed no significant correlation between condyle shape and occlusal characteristics, in contrast to the results reported in most of the previous studies. Mongini (1975), for example, stated that the correlation between the morphologic appearance of the condyle and dental attrition clearly shows that these two elements depend on the functional pattern adopted by the masticatory apparatus. Granados (1979) and Richards and Brown (1981) also detected severe alterations in the condyle of skulls with teeth presenting marked wear. Richards (1987) and Wedel et al.(1978) also reported the relationship between attrition and the rates of change in condyle shape. This discordant result may possibly be attributed to the difference between the samples analyzed in the present study and those evaluated in previous studies. As mentioned earlier, these ancient collections of dry skulls are from ancestors whose alimentary habits were quite different from present ones, a fact that led to exaggerated tooth wear with an effect on the morphology of the osseous components of the temporomandibular joint. The amount of dental attrition detected in the skulls studied here was much lower than in the previous studies.

The data obtained by Demirjian (1967) disagree with those obtained here with respect to a greater depth of the glenoid fossa in skulls with a normal overbite, since this investigator did not detect a significant correlation between these variables. On the other hand, Angel (1948) observed that small overbites are related to a plane glenoid fossa. These investigators worked with specimens quite different from those used in the present study in terms of morphologic characteristics and environmental variations such as alimentation, diet and habits.

In agreement with the results reported by Demirjian (1967), we did not detect a significant correlation between depth of the glenoid fossa and extent of tooth wear or attrition. However, many investigators obtained significant results, such as Hinton (1981 a, b, 1983) who detected an abrupt reduction in the depth of the fossa in the presence of more severe levels of molar wear or attrition. Similarly, Granados (1979) reported that loss of cusp and anterior guide height occurring in the presence of marked attrition was accompanied by severe resorption of the articular eminence, which became shallower and, in some skulls, fully flattened.

The major reason for the divergences detected in the present study compared to those reported by others is the fact that the samples used in the previous studies consisted of specimens from ancestors whose alimentary habits provoked masticatory stress due to ample occlusal forces and forces of repetitive mastication, resulting in a bone morphology with its own characteristics.


Conclusions

The study of the morphology of the articular components and of the occlusal characteristics of dry skulls demonstrated a significant correlation between condyle shape and depth of the mandibular fossa, i.e., the depth of the fossa was greater in skulls with more rounded condyles. No significant correlation was observed between depth of the glenoid fossa and dental attrition or Spee curve. However, there was a significant correlation between deep glenoid fossae and skulls with normal overbite when compared to skulls with moderate or deep overbite.

References

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Wedel A, Carlsson GE, Sagne S: Temporomandibular joint morphology in a medieval skull material. Swed Dent J 2: 177-187, 1978

Yale SH: Laminagraphic cephalometry in the analysis of mandibular condyle morphology. Oral Surg Oral Med Oral Pathol 14: 793-805, 1961

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Correspondence:Profa. Dra. Mírian Aiko Nakane Matsumoto, Faculdade de Odontologia de Ribeirão Preto, USP, 14040-904 Ribeirão Preto, SP, Brasil.


Accepted August 21, 1995
Electronic publication: March, 1996


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