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Journal of the Anatomical Society of India

Effect Of Dietary Consistency On The Growth Of The Condylar Cartilage Of The Mandible In Rats

Author(s): Vaid, L.K., Pradhan, P,. *Chakrabarti, S.

Vol. 51, No. 2 (2002-07 - 2002-12)

Department of Anatomy, R.G. Kar Medical College, and *Department of Pathology, N.R.S. Medical College, Kolkata, W.B. INDIA.

Abstract

The temporomandibular joint, which is the joint for mastication, is covered by fibrocartilage. A group of young albino rats (n=15) was fed with normal hard diet, whereas another group having the equal number was fed with water-soft diet. It was found morphologically that there was significantly reduced growth pattern of the condylar cartilage of mandible if the animals were fed with soft diet, in comparison to that of the other group, fed with hard diet. Histological study of the mandible of rats, fed with soft diet also showed that the thickness of all the layers of the condylar cartilage were much less than the other group. So, we concluded that the growth of the mandibular cartilage must be dependent on some mechanical forces, exerted during mastication.

Key words: temporomandibular joint, condylar cartilage, dietary consistency.

Introduction:

The temporomandibular joint is a joint for mastication and it has got a variety of movements, like elevation, depression, protrusion and retraction. In adults the articular surface of the condylar (ellipsoid) joint is covered with white fibrocartilage, composed predominantly of collagen fibres and few cartilage cells. The joint space is completely divided into upper and lower parts by an articular disc (Soames, 1995). The mandible as well as the temporomandibular joint changes with age.

In man, the proximal zone of the conical condylar cartilage persists as an epiphyseal plate, which proliferates to cause vertical increase in the ramus of mandible during first to third postnatal years. The condylar cartilage is covered on its articular aspect by self-perpetuating fibrous tissue. Beneath this lies the proliferating intermediate zone, which is responsible for ramal growth as well as general mandibular growth. Again deep to that hypertrophic chondrocytes and then bone are present. The remodelling is continuous until the adult size is reached, but the adult range of mandibular movement is reached between 10 to 15 years (Wright and Moffett, 1974). Morphologically, the condylar cartilage is a growth cartilage during growing period. It begins to differentiate into articular cartilage from the central area of condyles of 16-week old rat and becomes mature articular cartilage at 32-weeks of age (Takahash et al, 1996).

In experimental models, the normal growth pattern of the cartilage is found, if the young animals are fed with normal diet, whereas the condylar cartilage of rat shows least growth potential in comparison to some primary cartilages during organ culture (Copray et al, 1986). Again the bone mass is found to be reduced mainly due to thinner cortical bone rather than lower cortical bone density, if the new born rat is fed with soft diet instead of normal hard diet (Bersin et al, 1999). The water content as well as both the wet and dry weights of the condylar cartilage is also greatly reduced in those rats, fed with soft diet though there was no significant differences in the body weight gain between the two groups (Bouvier and Hylander, 1984; Hinton, 1993).

In our study, we examined gross morphological and histological changes of the condylar cartilage of the mandible under different local mechanical factors, by giving the newborn rats the food of varied consistency. The aim of the study was to observe whether the growth of the mandibular cartilage is dependent on the mechanical forces, exerted during eating of hard foods or not.

Materials and Methods:

Thirty albino rats (15 males and 15 females), each 2 weeks of age, were used in our experiment. The rats were weighed and housed 2 per cage and after 2 weeks these were changed to 1 per cage to ensure that all the rats had adequate food intake all the time (Bouvier and Hylander, 1984). The total experimental period was 8 weeks.

The experimental models were randomly divided into two groups, with 15 rats in each group, ignoring their sex (Bouvier and Zimny, 1987)

Group-I fed on hard diet consisting of roasted pea, gram or dried pieces of bread for 8 weeks.

Group-II fed on soft diet consisting of powder of pea and gram or bread - mixed with water to liquefy for 8 weeks.

All the rats were weighed initially (at 2 weeks) and then after 8 weeks. After 8 weeks, all the rats were sacrificed under ether anaesthesia. The mandible of each rat was studied histologically after morphological analysis.

Gross morphological study- After dissection, different dimensions of the mandibular condyle were measured with calipers (Bouvier, 1988) (Fig. - 1).

  1. maximum antero-posterior condylar length
  2. maximum medio-lateral condylar width
  3. maximum depth of condylar cartilage on its lateral surface.

Histological study - Each mandibular condyle was fixed with 10% formalin and decalcified with 10% ethyl-diamine-tetra-acetic acid (EDTA) for 5 days. After decalcification, all the condyles were processed manually. Paraffin blocks were made, 6 micron thick sections were cut, stained with Haematoxylin & Eosin (H & E) and examined under light microscope.

Results:

The weight data collected after eight weeks of the experiment showed that the weight gain in case of rats fed with hard diet (Group-I) was slightly more than in case of rats fed with soft diet (Group-II). However, the slight difference in weight is not statistically significant (Table-1).

Table-1 : Weight gain of two groups of rats, fed with hard diet and soft diet respectively:

Body weight
of rats
(in grams) ± S.D.
In hard
diet groups (n=15)
In soft
diet groups (n=15)
Initial weight (at 2 weeks of age) 94 ± 4 93 ± 5
Weight after sacrifice (at 8 weeks of age) 265 ± 24 260 ± 21

REMARKS: Body weight differences are not statistically significant (by standard error of differences).

In contrast, the morphological appearances of the mandicular condyles in the soft diet group differed significantly from those in the hard diet group (Table 2).

Table-2 : Statistical analysis of different condylar dimensions:

Different
measurements
of condylar
cartilage
In hard
diet groups
(mean ± SD)
In soft
diet groups
(mean ± SD)
t-value*
Length 4.12 + 0.46 3.48 + 0.44 3.895
Width 1.96 + 0.32 1.43 + 0.29 4.759
Depth 1.62 + 0.24 1.18 + 0.25 4.918

*all are significant at 0.5% level

The histological study showed that the total thickness of the condylar cartilage was much less in the rats of Group-II than that in the rats of Group-I. The comparative pictures clearly showed that all the layers of the condylar cartilage i.e. articular layer, and proliferative as well as maturing hypertrophic zone of subarticular layer, were increased in thickness in Group-I (Fig.-2 and 3).

Discussion:

Relevant anatomy of mandibular condyle of albino rat (Soames, 1995; Wright and Moffett, 1974). The tissue of the mandibular condyle in rats can be divided into 2 general layers

1. Articular tissue layer-it consists of dense fibro-cartilage whose collagen fibres are oriented parallel to articular surface. It is continuous with the fibrous periosteum along the neck of the condyle.

2. Sub-articular tissue layer

(a) Proliferating zone- It lies just deep to articular tissue layer. Outer part of this zone is composed of undifferentiated mesenchymal cells within the basophilic ground substance. In the inner part it is the principal site of cell proliferation. Chondrocytes are present within the intercellular matrix.

(b) Hypertrophic zone- the deepest zone contains larger, spherical, maturing chondrocytes arranged in apparently random fashion. Each cell is surrounded by a basophilic halo. The intercellular matrix begins to mineralise within the inner most hypertrophying cells and is subsequently eroded by chondroblastic activity.

Osteogenesis takes place at the junction of the hypertrophic zone and the endosteal surface, either by endochondral ossification or by special type of intramembranous bone formation.

It is very vital to note that all the experimental animals must be provided with identical conditions of caging and adequate amount of food, while using water-softened diet as well as hard diet (Bouvier and Hylander, 1984). Like other workers, we also found no marked differences in respect of weight gain.

Weijs and Dantuma (1975) performed electromyographic study of the muscles of mastication in rats. According to them, the joint is loaded under compression during incising (gnawing) and unloaded during mastication (chewing at the molars). This means that under normal condition a greater resultant compressive force exists on the condyle during incising than during mastication. Again, Simon (1977) studied the effect of compressive forces on the mandibular joint during incising, in a different way. All the incisor teeth of rats were removed at 10 days of age. He observed that there is reduction in the thickness of the condylar cartilage in those experimental animals. Thus, the presence of incisors might be an important factor in normal mandibular joint development. Hinton (1991) also observed that there was significant decrease in the mitotic activity of the cartilage after myotomy of the lateral pterygoid muscles in rats.

Similarly, Bouvier and Hylander (1984), Bouvier and Zimny (1987) described that smallar condyles with thinner layer of condylar cartilage were found in rats with soft diet in comparison to those of rats, which were fed on hard diet. Condyle revealed a smooth non-porous articular surface in the soft diet groups. In hard diet groups, condyles had a rougher, more porous non-articular surface. According to them, sex and time of the diets did not significantly effect the results.

In our study, the length, width and depth of the condylar cartilage were significantly decreased in rats of Group-II, fed with soft diet, in comparison to those measurements in other group of rats, fed with hard diet. Again in the histological study, all the layers of the condylar cartilage were also decreased in Group-II.

According to the studies by the previous workers and ours, it has been observed that the growth of the condylar cartilage was suppressed in vitro, in absence of incisor teeth and also in animals, fed with soft diet. The function of the incisors was less in rats with soft diet, as there was less compressive force on the temporomandibular joint, whereas the normal growth pattern is found in vivo, when the animals have all the incisors and they were fed with hard diet. Thus we can conclude that the local mechanical factors exert an important influence on the postnatal growth and development of condylar cartilage of the mandible.

References:

  1. Bouvier, M. (1988): Effects of age on the ability of the rat temporomandibular joint to respond to changing functional demands. Journal of Dental Research; 67(9): 1206-1212.
  2. Bouvier, M; Hylander, W.L. (1984) : The effect of dietary consistency on gross and histological morphology in the cranio-facial region of young rats. American Journal of Anatomy. 170(1): 117-126.
  3. Bouvier, M. Zimny, M.L. (1987): Effects of mechanical loads on surface morphology of the condylar cartilage of the mandible in rats. Acta Anatomica (Basel). 129(4): 293-300.
  4. Bersin, A; Kiliaridis. S; Strid, K.G. (1999) : Effects of masticatory function on the internal bone structure in the mandible of the growing rat. European Journal of Oral Sciences. 107(1): 35-44.
  5. Copray, J.C; Jansen, H.W; Duterloo, H.S. (1986): Growth and growth pressure of mandibular condylar and some primary cartilages of the rat in vitro. American Journal of Orthodontics and Dentofacial Orthopedics. 90(1): 19-28.
  6. Hinton, R.J. (1991): Jaw protruder muscles and condylar cartilage growth in the rat. American Journal of Orthodontics and Dentofacial Orthopedics. 100(5): 436-442.
  7. Hinton, R.J. (1993): Effect of dietary consistency on the matrix synthesis and composition in the rat condylar cartilage. Acta Anatomica (Basel). 147(2): 97-104.
  8. Simon, M.R. (1977): The role of compressive forces in the normal maturation of the condylar cartilage in the rat. Acta Anatomica (Basel). 97: 351-360.
  9. Soames, R.W.: Gray's anatomy, In: Skeletal system Edited by Williams, P.L; 38th edition (ELBS), Churchill Livingstone, pp 577-581. (1995)
  10. Takahashi, I; Mizogushi, I; Sasano, Y; Saitoh, S; Ishida, M; Kagayama, M; Mitani, H. (1996): Age-related changes in the localisation of glycosaminoglycans in condylar cartilage of the mandible in rats. Anatomy and Embryology (Berl), 194(5): 489-500.
  11. Weijs, W.A; Dantuma, R. (1975): Electromyography and mechanics of mastication in the albino rat. Journal of Morphology. 146: 1-33.
  12. Wright, D.M. and Moffett, B.C. Jr. (1974): The postnatal development of the human temporomandibular joint. American Journal of Anatomy. 141: 235-249.

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Fig. 1 : Diagram of one half of mandible (rat) showing different measurements of the condyle. (1-maximum length; 2-maximum width; 3-maximum depth) [A- incosor tooth, B-coronoid process, C- condyle, D-angle of mandible]

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Fig. 2 : Photomicrograph of sagittal section of mandibular joint, showing increase in thickness of different layers as well as increase in total thickness of condylar cartilage in rat, fed with hard diet. (H&E stain, x100 magnification under light microscope).

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[A : articular layer; P : proliferating zone; H : hypertrophic zone] Fig. 3- Photomicrograph of sagittal section of mandibular joint, showing thinner condylar cartilage in rat, fed with soft die. (H & E stain, x100 magnification under light microscope). [A : articular layer; P : proliferating zone; H : hypertrophic zone]

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