INTRODUCTION
The masticatory apparatus comprises of teeth, periodontal tissues, oral mucosa, salivary glands, neuromuscular system, jawbones, tongue and temporomandibular joints. The gradual transition from dentulous to edentulous state has important implications in prosthodontic treatment, which includes the treatment choice, clinical procedures and the prognosis. Some of the age-related changes that affect the orofacial structures might be physiologically normal, however treatment should be rendered to the elderly people with an awareness of biologic factors since the adaptive mechanism and tissue regenerative potentials are usually significantly lowered. Hence, they require a different approach, modified treatment planning and knowledge of how the tissue changes associated with senescence affect oral health.
DENTAL TISSUE
As age advances, the wear of enamel accentuates giving the occlusal surfaces of a flat appearance. The gradual change in the quantity and quality of dentine due to formation of secondary dentine result in teeth that are more yellow and with decreased translucency. There is a significant increase in the thickness of cementum on the root. In addition, gingival recession as age advances, contributes to the discoloration and root caries. Teeth also show signs of root resorption, which may be a result of local injuries and mechanical stresses. With increasing age the volume of pulp decreases as a result of continuous apposition of dentin. This is associated with fibrosis of the pulp tissue and reduced vascularization. Tooth wear is a major problem in the older patients. The causes are attrition, abrasion and erosion. Attrition is the gradual loss of tooth substance due to mechanical action on the tooth as in para functional habits like bruxism/increased occlusal forces. Abrasion is usually caused by friction from a foreign body, independent of occlusion between teeth. Erosion is defined as the loss of hard tooth substance due to chemical process not involving bacteria, for example, the intake of acidic beverages.
Generally restorative and prosthetic treatment of worn dentitions is difficult to create sufficient retention for the partial prosthesis due to decrease in the size of the teeth and continued ill effects on the prosthesis. It may also be difficult to completely eliminate the factors causing wear of teeth.
PERIODONTAL TISSUES
The periodontium consists of the supporting tissues of the tooth, comprising the gingiva, periodontal attachment, alveolar bone and cementum. The structure of the periodontium becomes more irregular with age and deposition of cementum, which continues throughout life. One of the main reasons for complete edentulism is periodontal disease. Periodontitis is a slow progressive disease, which results in pocket formation due to loss of periodontal attachments, gingival recession and exposure of the root surface, increased tooth mobility and ultimate loss of the affected teeth. This sequence is not a result of age but of chronic disease state within the supporting structure of the tooth. Early sequential loss of teeth because of periodontal disease may, however, cause irregular resorption of bony ridge, which may compromise the stability of denture.
ORAL MUCOSA
The oral mucosa comprises three broad categories: (1) Masticatory mucosa, which is keratinized or para keratinized and covers the palatal vault and the attached gingiva. (2) Lining mucosa, which is nonkeratinized and comprises the mobile lining tissues within the mouth, including the cheeks, the floor of the mouth, ventral surface of the tongue and the soft palate.(3) Specialized mucosa which covers the lips and dorsum of the tongue.
The oral tissues like other tissues in the body change as an individual grows older. The oral mucosa of the aged is friable and easily injured. The mucosa in the elderly person is generally thin and tightly stretched and it blanches easily. Aging produces changes in the blood vessels, particularly atherosclerotic changes. Oral varicosities are often noted on the undersurface of the 3tongue and in the floor of the mouth. The incidence of oral cancer is associated with aging patients, which accounts for approximately 4 percent of all cancers. Here the mucosa should be carefully examined and critically evaluated. When the mucosa lacks adequate keratinization, the protective capacity provided by the keratinized layer is reduced and the patient is prone to suffer from chemical, bacterial and mechanical irritations. The capacity of the prosthesis to initiate mechanical irritations in these patients is, therefore, a significant problem in patient management. The mucosa presenting heavy layers of thick keratin should be closely and continuously examined. The level of pain threshold of soft tissue changes markedly after the menopausal period and male climacteric. Hence, denture tolerance as a consequence, is markedly reduced.
SALIVARY GLANDS
Sufficient amount of saliva is necessary for the maintenance of oral health and comfort. In this respect, saliva is particularly important in wearers of removable dentures to protect the oral mucosa from mechanical irritation and infections and to achieve retention in complete dentures. The normal unstimulated salivary flow rate is 0.38±0.21 ml/min. Impaired salivary secretion or xerostomia is likely, if the unstimulated flow rate is less than 0.12 ml/min. Of the whole unstimulated saliva, 40 percent is derived from the submandibular glands and 8 percent from mucosal glands. The normal stimulated salivary flow rate is less than 0.60 ml/min of the whole stimulated saliva and 50 to 65 percent is derived from the parotid glands.
In major salivary glands of humans, fat accumulation occurs predominantly as progressive infiltration, which increases with age. These adipose cells may gradually encroach on the parenchyma extending inwards from the periphery of the lobules replacing the entire lobule with adipose tissue. There is an age-related increase in the amount and density of the fibrous skeletal component both around the ducts and in the septa which thus, appears widened intralobularly so that the acini becomes more widely spaced. The masticatory function stimulates salivary flow. Hence, decreased masticatory function will cause oral dryness and reduced salivary flow because of atrophy of salivary glands and reduced synthesis and secretion of saliva. Thus, appropriate masticatory function is important for proper maintenance of the salivary flow and overall quality of life for the elderly. The diminished function of the glands also results in physiochemical changes in the saliva, which shows a decrease in ptyalin content and an increase in mucous content.
Reduced salivary flow contributes to dry and inelastic oral mucosa, cracked lips, fissuring of tongue and oral mucosa, sore spots under the denture, poor retention of denture and difficulty in swallowing. Due to lowered ptyalin content of saliva, digestion of cooked starch is remarkably reduced. Xerostomia also affects oral hygiene and adherence of food particles to tissues predisposing it to infection.
NEUROMUSCULAR SYSTEM
As age advances there is a decrease in the speed with which muscle tension can be developed and released and in the muscle power by which work can be performed. There is reduction in the fiber muscle mass. Furthermore a slowly progressive degeneration of the muscles is a feature of the aging process consistent with long contraction of tissues and slowly contracting muscles.
JAW BONES
In elderly subjects, the bone formation activity is decreased in relation to bone resorption activity in the jawbones. The cortical porosity of the mandible also increases. Changes are characterized by altered anatomy with a shift in the origin of mentalis, buccinator, mylohyoid and genioglossus muscles that assume superior position along with mental foramen in the mandible. The degenerative changes in the blood vessels cause decreased blood supply to the bones. The mandibular blood supply becomes merely extra-osseous via the plexus of vessel formed by the facial, buccal and lingual arteries.
TEMPOROMANDIBULAR JOINTS
With advancing age the joint tends to lose its ability to withstand degenerative changes and shows progressive change comparable to those seen in osteoarthritis. These changes vary from slight fraying of the articular surfaces to cleft formation between the bundles of fibrous tissue of which the articular surfaces and the disc are composed. The severities of changes are related to advancing age and are more intense. When there is loss of posterior part of the dentition, mandibular condyle itself undergoes gradual reduction in size and the articular surface becomes flattened with advancing age. Temporomandibular disorders include a number of clinical problems that involves the masticatory musculature, temporomandibular joints and associated structures. Temporomandibular disorders indicate a deviation from normal function that may be the cause or the consequence of changes or disorders of one or more components of the masticatory apparatus.
TONGUE
Taste buds, which are responsible for taste perception, reside predominantly in the papillae of the tongue, although smaller populations are also present in the epithelia of the soft palate and the larynx. There is a tendency for the taste buds to diminish in number in old age. “Bald tongue”, one in which the filiform papillae are atrophic is a common finding in elderly people. “Caviare tongue” is the term applicant to the nodular enlargement of the large veins underneath the surface of the tongue. This is very common in patients over 60 years of age.
The main risk factors are irreversibility of caries and periodontal diseases which, if not controlled, lead to tooth loss, resorption of the residual ridge, destabilized occlusal conditions and impaired masticatory ability. Following prosthetic treatment acceptable function of the masticatory apparatus can often be maintained.
SELF-HELP QUESTIONS
- Define attrition, abrasion and erosion of teeth.
- What are the features of periodontitis?
- What are the ill effects of reduction in keratinized layer of oral mucosa?
- What is the normal unstimulated salivary flow rate?
- What is xerostomia?
- What are the consequences of xerostomia?
- What is bald tongue?
- What is caviare tongue?
- What is macroglossia?
- Mention the causes of xerostomia.
BIBLIOGRAPHY
- Nagle RJ, Sears VH, Silverman SI. Dental Prosthetics—Complete Dentures. St. Louis: C.V. Mosby Company 1958; 73–110.