Contributing Factors to Dental Caries Etiology Lect 2
ريا جاسم د.Dental caries is a multifactorial disease in which there is an interaction of four principle factors for the formation of the disease:
1-The host (teeth and saliva )
2- Microflora
3-Substrate (diet)
4-Time
So caries requires a susceptible host , a cariogenic oral flora and suitable diet , all theses must be present for sufficient length of time, intervention or removal of any necessary factors may prevent the disease .
Factors Related with the Tooth
Tooth CompositionTooth Morphology and Arch Form
Tooth Composition
The enamel surface is more caries resistant then the subsurface. microradiograph of initial caries lesions frequently revealed marked demineralization of the subsurface enamel beneath an outer most layer which is slightly affected .The surface enamel appears unaltered simply because it is continuously being regenerated by precipitation of solid phases (dicalcium phosphate dihydrate and fluoroapitete) .The surface enamel is harder than the underlying enamel is due to the difference between the composition of the surface enamel and that of the rest of the enamel, the surface enamel has more minerals and more organic matter but has relatively less water . In addition certain elements including fluoride , chloride , zinc , lead and iron accumulate in the enamel.
1-Changes of the enamel such as decrease in density and permeability and an increase in nitrogen and fluoride content occur with age. Theses alterations are part of the post eruptive maturation process where by teeth become more resistant to caries with time .
2-The fluoride content of the enamel surfaces and its resistance to caries attack
The conc. Of fluoride of the surface layer of enamel increases as the fluoride conc. Of the drinking water increases and such enamel is less soluble in acids.
Tooth Morphology and Arch Form
1-Pits and fissure areas of the posterior teeth are highly susceptible to caries
2-Certain surfaces of the tooth are more prone to decay , where as other surfaces rarely show decay ex. Lower first molars occlusal, buccal, mesial, distal, lingual. Where as in upper first molar the order is occlusal, mesial , palatal , buccal, and distal , also in upper lateral incisor the palatal surface is more susceptible to caries than labial surface
3-An intra oral variation exist in susceptibility to caries between different tooth types
The most susceptible teeth in permanent are the lower first molars, followed by upper first molar then U and L second molars , the second premolars, upper incisors , first premolars are the next in sequence, where as the lower incisors and canine are least likely to develop caries.
4- Irregularities in arch form
More irregularities and crowding in teeth so increased caries because there will be more plaque accumulation in these areas and more difficult to clean.Saliva
The term saliva refers to the mixture of secretions in the oral cavity ,this mixture consists of fluids derived from the major salivary glands , from minor glands of the oral mucosa and traces from the gingival exudate.
1-Saliva composition
2-Saliva flow
3-Buffer system
4-Saliva viscosity
5-PH of saliva
6-Anti Microbial agent
Salivary Composition
Saliva contain water, organic and inorganic material, epithelial cell , microorganisms and food debris , a major problem in studying saliva is that its composition varies with flow rate, nature of stimulation, duration of stimulation , plasma composition , the time of the day at which samples are collected and also saliva is mixture of secretions.A study found that the free caries people has a high amount of ammonia than in caries active person , because ammonia neutralizes acid.
Recently, no relationship has been established between ammonia, amylase, urea, calcium and phosphate and dental caries prevalence.
PH of saliva
Some researchers studied the solubility of enamel in different PH, there is dissolution of calcium and phosphate in certain PH which they called " critical PH of saliva" ,which is usually about 5.5, below the critical pH ,the inorganic material of tooth may dissolve.
Saliva flow
More salivary flow less dental caries, some people suffer from decreased or lack of salivary secretion due to pathological condition called xerostomia , these people have an increased rate of dental caries and rapid tooth destruction , xerostomia may be due to diabetes mellitus, Parkinson's, therapeutic radiation , acute viral infection , drugs (chronic administration of anticholenergic drugs or parasympathetic drugs ), surgical removal of salivary glands , congenital absence or malformation of salivary gland (rare) ,other condition as anxiety , mental stress and depression may temporarily decrease salivary flow .Physiological xerostomia occurs in all humans during sleep because the salivary glands do not secrete spontaneously.
The management of patient with xerostomia
1-Fluoride therapy.
2-Dietary control.
3-Oral hygiene measures .
4-Avoidance of xerostomic drugs.
5-Use of artificial saliva.
Saliva Viscosity
Mucin is responsible for viscosity of saliva, in the past they though that people with thick saliva develop more caries than people with watery saliva, currently no consistent relationship has been established between dental caries and viscosity .Buffer System
It is the most important factor in saliva to its relation to dental caries , a buffer is a solution which tends to maintain a constant PH to avoid any change of PH when we add acid or alkaline, in saliva, the chief buffer systems are the bicarbonate carbonic acid . The carbonic acid-bicarbonate system is the most important buffer in stimulated saliva, while in unstimulated saliva it serves as the phosphate buffer system.
Anti - Microbial Agents
These include :
SHAPE \* MERGEFORMAT
Immunoglobulins
Antibodies against specific bacteria have been reported in human saliva. Purified salivary IgA and IgG fractions have been found with agglutinating activity against oral isolates of ∂ - heamolytic streptococci.
In some studies raised salivary levels of gammaglobulines, IgA in particular have been found in association with low caries activity and such findings have been used to argue that these globulins have a protective effect , in other studies the reverse have been found.
Serum IgA levels are less difficult to measure and these have been found to be raised in those with high DMFT rates.These findings can be interpreted as showing a response to caries,rather than showing that these globulins have a protective effect.
IgA isolated from human parotid secretions specifically inhibits the adherence of certain strains of streptococci to human buccal epithelial cells ,facilitating their elimination from the oral cavity by swallowing .
It is the first line of defense of the host against pathogens which invade mucosal surfaces.
Lysozymes
This enzyme is found in saliva , nasal secretion , egg white , most tissues and body fluids .
The sublingual and submandibular saliva contain higher level of lysosymes than the parotid saliva, lysosyme alone does not lyse or prevent growth of pure culters of predominant bacteria in the oral cavity of man , in the presence of sodium lauryl sulfate , a detergent, lysozyme can lyse many cariogenic and non cariogenic streptococci , when lysozome (from egg white ) was added to cariogenic diet , no cariostatic effect could be found in experimental rats .
Lysozyme activity in whole saliva has been found to be significantly greater in a group of caries free preschool children than in a caries susceptible group.
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