theories of dental caries-3.pptx

Theories for the etiology of dental caries

1. OPERATIVE DENTISTRY Group 6 1

2. Classification of theories of dental caries. New theories Acidogenic theory Proteolytic theory Proteolysis chelation theory Early theories Vital theory Humoral theory Septic theory Legend of the worm theory Chemical theory Exogenous theories Acidogenic Proteolysis theory Proteolysis chelation theory Septic theory Chemical theory Endogenous theories Vital theory Humoral theory OTHER THEORIES Enzymatic theory Acid –Enzymatic theory Levine’s Ionic see saw theory Auto immune theory Sucrose chelation theory 2

3. Acidogenic Theory/Chemicoparasitic Theory • It is the most accepted theory given by WD. Miller in 1890. • Miller said, “Dental decay is a chemicoparasitic process consisting of two stages, the decalcification of enamel, which results in its total destruction, as a preliminary stage; followed by dissolution of the softened residue of the enamel and dentin. In the first stage there is a destruction which is done by the acid attack whereas the dissolution of the residue is done by the proteolytic action of the bacteria • This whole process is supported by the presence of carbohydrates, microorganisms and dental plaque. 3

4. Conts …. 4

5. Role of the factors Role of carbohydrates According to Miller’s observations, teeth decalcify when incubated in saliva and bread/sugar mixture and show no change when incubated with fat. His simple experiment demonstrated the cariogenic effects of carbohydrates. However, the cariogenic potential of dietary carbohydrates varies on their physical form, chemical composition and frequency of intake. It is a well known fact that carbohydrates which have a slow clearance rate from the oral cavity are more cariogenic than those which have a higher clearance rate. The risk of caries incidence increases greatly if the dietary sugar is sticky in nature, and when there is increased frequency of ingestion of the sugars. Polysaccharides are less easily fermented by plaque bacteria than monosaccharides and disaccharides. Glucose, sucrose and fructose which are highly fermentable have a greater role to play in the causation of dental caries. These sugars are readily broken down by the bacteria to produce acids that in turn cause the dissolution of the hydroxyapatite crystals of the enamel and dentin. 5

6. Continuation on role of carbohydrates Sucrose is readily fermented by the cariogenic bacteria (mainly  Streptococcus mutans ) to produce acids, which can demineralize the tooth.  S. mutans  use sucrose to synthesize an extracellular insoluble polysaccharide with the help of the enzyme ‘dextran’, which helps in adhering the plaque firmly on to the tooth surface. The pH of plaque falls to 4.5–5 in about 1–3 minutes of sugar intake. It is estimated that pH returns to neutral levels in approximately 30 minutes. The physical nature of the diet intake also has a bearing on the incidence of carious lesions. Coarse fibrous foods aid in greater clearance rate from the oral cavity thereby minimizing the carious incidence. However, sticky refined food and sweetened soft drinks predispose to debris accumulation and the increased likelihood of carious lesions 6

7. Role of microorganisms Lactobacillus acidophilus  along with a combination of other bacteria such as  S. mutans  and  Actinomyces  species are closely associated with the causation of dental caries. It is believed that a few types of bacteria may be intimately involved in the initiation of the carious process whereas some may be involved in the progression of the carious process. 7

8. Role of acids Miller in his observations reported that many of the microorganisms in the oral cavity were capable of producing acids and these acids were usually present in deeper carious lesions. In many of the lesions studied, lactic acid was identified in carbohydrate saliva combined mixtures. A specific microorganism,  Leptothrix buccalis , was isolated from the dentinal tubules, suggesting that the microorganisms and the acids may have a synergistic action to dissolve the organic portion of the tooth 8

9. Role of dental plaque Plaque as described by GV Black is a ‘gelatinous plaque of the caries fungus in a thin, transparent film that usually escapes observation, and which is revealed only by careful search’. It generally consists of salivary components such as mucin and desquamated epithelial cells and of microorganisms. However, long-standing plaque may accumulate to a perceptible degree in 24–48 hours. It is estimated that cariogenic plaque contains 2 × 10 8  bacteria/mg weight. The pH of plaque also varies in caries free and individuals with high caries activity. The pH is about 7.1 in caries free individuals and approximately 5.5 in individuals with high caries activity. 9

10. Sucrose Chelation Theory This theory proposes that if there is a very high concentration of sucrose in the mouth of a caries-active individual, there can be formation of complex substances like calcium saccharate and calcium complexing intermediaries by the action of phosphorylating enzymes. These complexes cause release of the calcium and phosphorus ions from the enamel and thereby resulting in tooth decay . 10

11. Autoimmune Theory According to this theory few odontoblasts, within the pulp of few certain teeth are damaged by the autoimmune mechanisms, leading to a compromised Défense mechanism and the loss of integrity of enamel or dentin. These targeted sites are potential sites for the development of carious lesions. 11

12. Proteolytic Theory • Heider, Bodecker (1878) and Abbott (1879) thrown considerable light to this theory • According to this theory, organic portion of the tooth plays an important role in the development of dental caries • It has been recognized that enamel contains 0.56 percent of organic matter out of which 0.18 percent is keratin and 0.17 percent is a soluble protein • Enamel structure which are made of the organic material such as enamel lamellae and enamel rods prove to be the pathways for the advancing microorganisms • Microorganisms invade the enamel lamellae and the acid produced by the bacteria's causes damage to the organic pathways. 12

13. Proteolysis theory (Gottlieb in 1944) Gottlieb in 1944 suggested that the initial lesion of the carious process is due to the proteolytic enzymes attacking the lamellae, rod sheaths, tufts and walls of tubules. He believed that the yellow pigmentation that is characteristic of caries was due to pigment produced by the proteolytic organisms. He also proposed that the Staphylococcus plays a vital role in initiating proteolytic activity. 13

14. Proteolytic theory ( pincus in 1949) Pincus in 1949 proposed that the proteolytic breakdown of the dental cuticle is the first step in the carious process. He proposed that the Nasmyth’s membrane and the enamel proteins are mucoproteins, which are acted upon by the sulfatase enzyme of the bacilli yielding sulfuric acid. The sulfuric acid thus produced combines with the calcium of the hydroxyapatite crystal and destroys the inorganic component of the enamel. 14

15. Conts ……. Draw back of the proteolytic theory It couldn’t provide sufficient evidences to support the claim that the initial attack on enamel is proteolytic Experimental studies have shown the occurrence of caries even in the absence of proteolytic microorganisms. However, this theory is still helpful in explaining the progression of a more advanced carious lesion 15

16. Proteolysis-Chelation Theory Some of the minor flaws of the acidogenic and the proteolytic theories were addressed in the proteolysis-chelation theory. This theory was put forward by Schatz and co-workers in 1955. Chelation is a process in which there is complexing of the metal ions to form complex substance through coordinated covalent bond which results in poorly dissociated and/or weakly ionized compound. Chelation is independent of the pH of the medium. The proteolysis-chelation theory considers dental caries to be a bacterial destruction of organic components of enamel and the breakdown products of these organic components to have chelating properties and thereby dissolve the minerals in the enamel even at the neutral/alkaline pH. Mucopolysaccharides, lipids and citrates may also act as secondary chelators. 16

17. Continuation of proteolysis chelation Schatz and co-workers observed that there is a simultaneous microbial degradation of organic component by proteolysis and the dissolution of inorganic part by the process of chelation. 17

18. “ Caries Balance Concept” (Proposed by Featherstone) • According to this theory, caries does not result from a single factor; rather, it is the outcome of the complex interaction of pathologic and protective factors • Pathological factors involved in a carious lesion are bacteria, poor dietary habits, and xerostomia. Protective factors include saliva, antimicrobial agents (chlorhexidine, xylitol), fluoride, pit and fissure sealants and an effective diet. 18

19. Conts …. 19

20. Endogenous theories Humoral theory The relative proportion of the four elemental fluids of the body determines the persons physical and mental constitution(blood, phlegm, black bile ,yellow bile) Its suggests that ‘’ An imbalance in humours of the body causes tooth decay’’ 2. Vital theory It suggests that ‘’ tooth decay originated from with in the tooth its self , like a bone gangrene’’ (gangrene is a dead part of the body tissue due to lack of blood or serious bacteria infection) 20

21. Conts …. Legend of the worm theory The theory dates back as far as 5000BC . It was believed that dental caries were caused by a tiny worm inside the tooth. And that the activity of the worm corresponded to the pain afflicted by it. The parasitic or septic theory This was the first theory that related microorganisms with caries on a causative basis. Accordingly, it was proposed that even though caries starts purely as a chemical process, but microorganisms continued the disintegration in both enamel and dentin 21

22. Conts ……. The chemical /Acid theory In the 17 -18 th century, there immerge a concept that the teeth are destroyed by acids formed in the oral cavity by fermentation of food particles around the teeth. 22

23. Current Concept of caries Introduction The current concept on caries suggests that caries have a multi-factorial synthesis. It suggests that these factors interact with each other in a specific period of time in such a way which increases demineralization of the tooth structure with resultant caries formation. There are 3 prerequisite factors for the development of dental caries i.e 1.plaque, 2. tooth 3. substrate ( keye’s triad) . Later Keye’s triad was modified to include the time factor. 23

24. Tooth The variation in tooth morphology, its composition and position contributes to caries formation Susceptible areas on tooth for caries are deep and narrow occlusal fissures, deep buccal and lingual pits, exposed root surface, margins of existing restorations. Lack of enamel maturation or presence of developmental defects increase plaque retention, bacterial colonization and make the tooth more to tooth demineralization. Tooth position also affects the initiation of dental caries, if a tooth is out of position, rotated or in any abnormal position, it becomes difficulty to clean, and hence retains more food and debris. 24

25. Substrate This refers to environmental factors with in the oral cavity that necessitate the development of caries. These include; saliva, diet Saliva; The composition, quantity, pH, viscosity and antimicrobial factors of saliva affect the development of caries Saliva contains calcium, phosphate and fluoride and normal conditions the tooth is continually in touch with saliva. These minerals help in remineralization of the early stages of carious lesions. When saliva flow is reduced or absent, there occurs the increased food retention. Since salivary buffering capacity is lost, an acid environment is encouraged which further promotes the growth of aciduric bacteria. (cause of hyposalivation; medication, dehydration, pathological conditions, mouth breathing etc). 25

26. Cont …… Diet; More refined and less fibrous foods stick stubbornly to the teeth and are not removed easily due to lack of roughages. Streptococcus mutans makes use of sucrose to produce the extracellular polysaccharide glucan. Glucan polymer help the S. Mutans to adhere to teeth. Frequency of carbohydrate intake; the greater the time lapse between acid attacks, better are the chances for repair( remineralization) to occur. 26

27. Plaque /bacteria The main etiological agent in occlusal and pit and fissure caries is the  S. mutans . Deep dentinal caries is commonly associated with lactobacilli, certain gram-positive anaerobes and filaments such as Eubacterium and Actinomyces. Root caries or cemental caries is predominantly associated with  Actinomyces viscous . However other species of Actinomyces such as  A. naeslundii  and  A. nocardia  have also been isolated. 27

28. Time/ period The time period during which all above three direct factors, i.e tooth, microorganisms and substrate are acting jointly should be adequate to produce acidic pH which is critical for dissolution of enamel to produce a carious lesion. 28

29. conclusion The current concept on caries suggests that the 4 factors mentioned above are the primary factors required for development of caries. However there are many other factors affecting the interplay between these primary factors. These include; age, sex, race, hereditary, systemic health, occupation, geographical area. 29

30. OTHER THEORIES Enzymatic Theory This theory is based on the fact that plaque bacteria produces enzymes. Enzymes involved may include phosphatase (dissolves apatite), chondroitin sulfatase (dissolves dentinal chondroitin sulphate), hyaluronidase (dissolves dentinal hyaluronic acid) and proteases (dissolve dentinal collagen). All these enzymes are produced by plaque bacteria. Acid-enzyme Theory This theory is a combination of the acidogenic and the enzyme theories. It is believed that the acids produced have a major role in enamel dissolution and the enzymes probably play a greater role in dentinal dissolution . 30

31. Levine’s Ionic See-saw Theory This theory was proposed by Levine in 1977. According to this theory, there is a chemical relationship between enamel plaque and the factors which determine the movement of minerals from saliva/plaque to enamel and vice versa, which was termed as the ionic see-saw mechanism. Levine proposed that the demineralization and remineralization of enamel is a continuous process. If in a given interval of time, more ions leave the enamel than enter it, then there is a net demineralization, which heralds the beginning of the carious process. It was proved that the ions are constantly exchanged between enamel and plaque. This theory emphasizes the importance of pH of plaque, calcium and phosphate ion concentration at the interphase and fluoride ion concentration. 31