Periodontology د.سهى محمد سامي حسن Lec. 5 ماجستير- – جراحة الفم والوجه والفكين Dental calculus : 1. Definition 2. Types of calculus 3. Sub gingival calculus 4. Supra gingival calculus 5. Theories of calculus formation 6. Mode of attachment of calculus

calculus formation . Calculus formation is preceded by the plaque formation , the plaque formation serve as an organic matrix for the subsequent mineralization of the deposit . Initially some crystals are seen in the inter microbial matrix frequently in close apposition to the external aspect of bacteria , gradually the matrix between the microorganism becomes entirely calcified and eventually the bacteria also become mineralized . while the deposition of crystals within preformed plaque is the usual mode of calculus formation , minerals may also be deposited at the surface of supra gingival plaque accumulation , in such foci the crystals are rod shaped and these crystal are calcium phosphate precipitated as Brushite .

The time required for supra gingival calculus formation is about two weeks , the first evidence of calcification may occur after few days however the development of a deposit with crystal composition characteristic of old calculus requires months or years .

Attachment of calculus to the teeth . Calculus often adhere firmly to teeth and sub gingival calculus may be difficult to remove ,one reason for its firm attachment to the tooth may be that the pellicle beneath the plaque also calcifies so that calculus crystals come into intimate contact with the enamel , cementum or dentin crystals . also calculus may be introduced inside the surface irregularity ,so that calculus is virtually locked to the tooth .

In case of periodontal disease small pieces of cementum may be lost as a result of wear when the periodontal ligament was still attached ,under such conditions it becomes impossible to remove all calculus without the loss of some of the tissues of the teeth .

Theories of calculus formation: Calculus has puzzled , there are two important aspects must be explain it : A. The nucleation of the crystallite . B. Their growth .

1.Mineralization theory . The saliva is super saturated with respect to the salts and thus it is able to support crystal growth , but that spontaneous precipitation does not occur unless the solution is seeded crystals for this nucleation process are present in the tooth surface but since they are covered by a pellicle they can not be used for this function .

2. Carbon dioxide theory . It claims that freshly secreted saliva leaving the opening of the salivary ducts has a CO2 tension of about of 60 mm Hg , expired air is lower than that it is about 29 mm Hg , the atmosphere is 0.3 mm Hg , this discrepancy will result in the escape of CO2 from saliva , the PH will rise , when the PH of saliva increase , less Ca and phosphorous can be accommodated in the ionized form and consequently spontaneous precipitation may occur , once crystallites are present the physiological super saturation accounts for this growth. This theory explain the formation of calculus near the orifice of the major salivary gland in copious amount. it can not explain the formation of sub gingival calculus , which may be formed from the salts in the gingival exudates .

3. Ammonia theory . Ammonia is a break down product from urea and might result in a local PH increase in plaque , the PH of plaque is actually frequently above that of saliva , this is attributed to proteolytic activity which may result in the formation of amines , urea and ammonia . proteolytic enzymes are present in plaque , and a positive correlation has been found between their proteolytic activity and calculus formation .

It is thought that the organic matrix of plaque could act as a seeding agent , when crystallization is nucleated by a compound of different chemical composition the phenomenon is termed epitaxis .Although epitaxis has been claimed for the last 25 years to occur in biological mineralization including calculus , the compound responsible has still not been identified .

It is reasonable to assign bacteria a key role in a possible mechanism for the mineralization process . this does not mean that they a lone are responsible for producing nucleating compounds .

Effect of calculus on periodontal tissues : Calculus by itself is harmless to the periodontal tissues except probably the mechanical irritation of its structure to the periodontal tissues. Also the presence of dental plaque always on the porous surface of dental calculus make the calculus very harmful to the periodontal tissues because here it will affect the periodontal tissues both mechanically and chemically and can produce inflammatory changes ,also calculus may interfere with the proper brushing techniques . so from those reasons calculus should be removed to prevent the inflammation of the periodontal tissues . Calculus should be removed also to keep the mechanical method s of teeth brush more easy , since Calculus is considered to be one of the major factors for plaque retention .

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