Dental Agents PDF

Inorganic Pharmaceutical Chemistry: Dental Agents A wide variety of inorganic compounds used in dentistry are of interest to pharmacists. These include polishing, cleaning, and anticaries agents. This chapter will be limited to those agents used in the prevention of caries (dentifrices and fluoride...

Inorganic Pharmaceutical Chemistry: Dental Agents A wide variety of inorganic compounds used in dentistry are of interest to pharmacists. These include polishing, cleaning, and anticaries agents. This chapter will be limited to those agents used in the prevention of caries (dentifrices and fluoride salts), polishing agents, and desensitizing agents. Anticaries Agents Today, when considering caries (tooth decay) prevention, one usually thinks of fluorides, since fluoridated water, fluoride drops, topical fluoride application to teeth, fluoride-containing vitamins, and fluoride dentifrices are now commonplace. The exact cause and mechanism of caries have still not been completely elucidated. It is probably associated with diet in that people consuming a diet high in fermentable carbohydrates have a higher incidence of dental caries than those on low carbohydrate diets. The formation of caries is attributed to the action of acids, mostly lactic, obtained from oral bacterial metabolism of dietary carbohydrate. The buildup of plaque on the tooth surface usually aids the decay process by forming pockets or crevices on the tooth surface in which food particles can lodge and be degraded by the bacteria of the mouth. Currently accepted and documented approaches to caries prevention include flossing and brushing accompanied by fluoride, administered either internally or topically to the teeth. When taken internally, fluoride in solution or in rapidly soluble salts is absorbed almost completely from the gastrointestinal tract. Deposition of fluoride in the bones and teeth is currently believed to occur by fluoride replacing the hydroxyl and possibly carbonate anions of hydroxyapatite (a mixed calcium salt of carbonate, phosphate, and hydroxide). Ca10(PO4)6(OH)2 + 2F− → Ca10(PO4)6F2 + 2OH− 1 Inorganic Pharmaceutical Chemistry: Dental Agents Fig. 1 Hydroxyapatite Structure (Hap) is a mineral composed mainly of phosphorus and calcium, naturally occurring in human bones and teeth. The compound is one of the apatites. Its general chemical formula is Ca10(PO4)6(OH)2 Careful analysis of teeth has shown that the concentration of fluoride is greater in the surface layer of enamel in both erupted and unerupted teeth. This is explained by the fact that the enamel loses contact with the tissue fluids after calcification is completed. Thus, fluoride uptake from tissue fluids is limited to the external surface. The outer surface will continue to pick up fluoride. Demineralization is the process by which minerals, primarily calcium and phosphate, are lost from the tooth enamel. This occurs when acids produced by bacteria in the mouth (often because of metabolizing dietary sugars) lower the pH in the oral environment, making it acidic. Under acidic conditions, the enamel, composed mainly of hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂), starts to dissolve, releasing calcium and phosphate ions into the saliva. The mechanism by which fluoride inhibits caries formation is still to be completely elucidated. There are two current hypotheses: (1) decreased acid solubility of enamel (2) bacterial inhibition. 2 Inorganic Pharmaceutical Chemistry: Dental Agents Fluoride reduces the solubility of tooth enamel in acidic environments, thereby providing significant protection against dental caries. This effect is particularly pronounced in enamel that has already been compromised by carious lesions, as the increased permeability of the damaged enamel facilitates greater fluoride uptake. When absorbed, fluoride interacts with hydroxyapatite converting it to fluorapatite, which is less soluble and more resistant to acid attack. Despite this known effect, the precise mechanism by which fluoride reduces enamel solubility remains unclear. While the formation of fluorapatite is a documented process, the extent of conversion where only a small fraction of hydroxyl groups is replaced by fluoride appears insufficient to account for the substantial decrease in acid solubility observed. Alternative hypotheses include fluoride’s role in reducing defects within enamel crystals or its competition with carbonate during the formation of apatite, potentially resulting in a more stable, acid-resistant structure. The bacterial inhibition hypothesis suggests that fluoride inhibits bacterial enzymes, thereby reducing acid production in dental plaque. Despite fluoride being bound within plaque, it still appears effective in reducing acid production. In contrast, the effect of topically applied sodium fluoride diminishes within a week, suggesting that fluoride's caries-preventive action may involve another mechanism. Although fluoridated plaque might seem beneficial, it can also cause gum inflammation, which indicates the need for plaque removal. Fluoride is administered by two routes, orally and topically. Both are effective, but the oral route places fluoride into systemic circulation, allowing the fluoride to be laid down in unerupted teeth as they are formed. The most convenient dosage form is fluoridation of the public water supply. This is usually done by adding sodium fluoride or a fluorosilicate, yielding a fluoride concentration of 0.7 to 1 ppm. This is 3 Inorganic Pharmaceutical Chemistry: Dental Agents equivalent to an average daily intake of 2.2 mg of sodium fluoride based on a person drinking six 6-oz glasses of water. 1- Sodium Fluoride (NaF) Mol. Wt. 41.99 Sodium fluoride is an inorganic chemical which is widely used for fluoride ion in dental products preparations. It protects the teeth from acid demineralization during bacterial growth. It provides strength for tooth enamel and prevents tooth decay. Minor quantity of sodium fluoride is used in drinking water. It may be prepared by neutralization of hydrofluoric acid (HF) with sodium carbonate (Na2CO3). 2HF + Na2CO3 → 2NaF + H2O + CO2 (gas) Another method is prepared by double decomposition of calcium fluoride with sodium carbonate. CaF2 + Na2CO3 → 2NaF + CaCO3 It is a white powder, colorless and odorless. It is soluble in water and insoluble in alcohol. Upon acidification, hydrofluoric acid is produced:- NaF + HCl → HF + NaCl Used to prevent dental caries with a usual dose of 2.2 mg (equivalent to 1 mg of fluoride ion). Applied as 1.5-3.0 ppm (equivalent to 0.7-1.3 ppm of fluoride ion) in drinking water; topically, as 2% solution to the teeth. It’s formulated as sodium fluoride solution, tablet, oral gel for systemic use or as mouth wash for local use. 2- Stannous fluoride (SnF2) Mol. Wt. 156.7 Stannous fluoride solutions are extensively used for topical fluoride applications. A simple application of a freshly prepared 8% solution at 6- to 12-month intervals is 4 Inorganic Pharmaceutical Chemistry: Dental Agents used. Stannous fluoride solution deteriorates on standing with oxidation of the stannous cation (Sn⁺²) to the stannic cation (Sn⁺⁴), resulting in a precipitate that makes the solution ineffective. Thus, the stannous fluoride solution must be freshly made. A detailed study of the stability of stannous fluoride solutions shows that: (1) Stability is increased with increasing stannous fluoride concentration. (2) The rate of turbidity formation is temperature dependent. (3) The loss of stannous cation is both pH-dependent and dependent upon the buffer or complexing agent used. The reason for concern over loss of stannous ion activity is because of reports that the stannous cation is itself anticariogenic. Stannous fluoride occurs as a white, crystalline powder and has a bitter, salty taste. It melts at about 213° C. Stannous fluoride is freely soluble in water and is practically insoluble in alcohol, ether, and chloroform. It is for topical use only. Cleaning agents / Dentifrices A dentifrice is a substance used with a toothbrush for the purpose of cleaning the surface of teeth. Dentifrices contain agents for cleaning tooth surfaces and providing polishing effect on the cleaned teeth. These agents are abrasive in nature. They are responsible for physically removing plaque and debris. The overall effect provides whiteness to the teeth. Dentifrices are applied as powders or pastes. Examples include: dicalcium phosphate, sodium metaphosphate, calcium pyrophosphate, calcium carbonate and calcium monohydrate phosphate. Creating a fluoride-containing toothpaste is challenging due to chemical incompatibilities between fluoride and traditional polishing agents like calcium 5 Inorganic Pharmaceutical Chemistry: Dental Agents salts. When calcium carbonate or calcium monohydrate phosphate is used, they react with fluoride, forming insoluble compounds like calcium fluoride (CaF₂), which reduces the available fluoride for tooth protection. To overcome this, calcium pyrophosphate (Ca₂P₂O₇) is used as it is water-insoluble enough to maintain effective fluoride levels while preventing unwanted reactions. Additionally, sodium polyphosphate ([NaPO₃]ₙ) with reduced solubility is another viable option. Currently, crest® is an example of a toothpaste using stannous fluoride and calcium pyrophosphate that meets these criteria. CaCO3 + 2F− → CaF2 + CO32− Ca(H2PO4)2 + 2F− → CaF2 + 2H2PO4− 1- Calcium carbonate (CaCO3) It is the most abundant and widely distributed calcium salt. It occurs as colorless crystalline powder, it is odorless with salty taste and readily soluble in water but insoluble in alcohol. It is prepared by precipitation by mixing the boiling solutions of calcium chloride and sodium carbonate and allowing the precipitation to cool. CaCl2 + Na2CO3 → 2NaCl + CaCO3 ↓ Calcium carbonate is prepared by the reaction of calcium oxide with water and carbon dioxide. Initially water is added to calcium oxide then it forms calcium hydroxide. Carbon dioxide is passed through this solution to precipitate the desired calcium carbonate. CaO (calcium oxide) + H2O → Ca(OH)2 (calcium hydroxide) Ca(OH)2 + CO2 → CaCO3↓ + H2O 6 Inorganic Pharmaceutical Chemistry: Dental Agents It is used as dentifrice, both powders and pastes. 2- Pumice Pumice is a substance of volcanic origin, consisting chiefly of complex silicates of aluminum, potassium, and sodium. It occurs as very light, hard, rough, porous, grayish masses, or as a gritty, grayish powder. Pumice is odorless and tasteless, stable in air, practically insoluble in water, and is not attacked by acids. It is used in a slurry form to assist dental technicians to obtain a smooth surface. It is also used as a mild abrasive in oral hygiene pastes, polishing compounds and in the polishing of natural teeth during prophylaxis. The gritty texture of pumice makes it ideal for polishing smooth surfaces. The effectiveness of pumice as a polishing agent depends on the fineness of the particles. Finer particles are used for polishing because they are less aggressive, providing a smooth finish without scratching the enamel surface. Desensitizing Agents Desensitizing agents are used in dental preparations to reduce teeth sensitivity to heat and cold. They act as local anesthetic. Examples include strontium chloride and zinc chloride. 1- Strontium chloride SrCl2 Mol. Wt. 158.53 It is prepared by adding strontium carbonate to hydrochloric acid until effervescence gets ceased. The solution is filtered, concentrated and allowed to crystallize. SrCO3 + 2HCl → SrCl2 + H2O + CO2 It acts as a desensitizing agent in dental remedy. 7 Inorganic Pharmaceutical Chemistry: Dental Agents 2- Zinc Chloride ZnCl₂ Mol. Wt. 136.28 Zinc Chloride occurs as a white or practically white, odorless, crystalline powder or white or practically white crystalline granules. Zinc Chloride is very deliquescent. A 1 in 10 solution is acid to litmus. Zinc chloride is very soluble in water and freely soluble in alcohol and glycerin. Its solution in water or in alcohol is usually slightly turbid, but the turbidity disappears when a small quantity of hydrochloric acid is added. Used as an astringent and dentin desensitizer. Dental Cements and Fillers Dental cements are used to temporarily cover protect areas that have undergo operation as in dental surgery. The cementing material is applied as a paste which gets hardened in a short while and it can be removed by the dentist. Temporary cement is also medicated usually with eugenol which is an antiseptic and local anesthetic. Example, Zinc oxide eugenol. 1- Zinc-Eugenol Cement Zinc-Eugenol Cement consists of two parts: (1) the powder and (2) the liquid. Their respective formulas are: The powder Zinc acetate: 0.5 g Zinc stearate: 1 g Zinc oxide: 70 g Rosin: 28.5 g The liquid Eugenol: 85 ml 8 Inorganic Pharmaceutical Chemistry: Dental Agents Cottonseed oil: 15 ml To prepare the cement, mix ten parts of the powder with one part of the liquid to form a thick paste immediately before use. The mixture will set into a hardened mass consisting of zinc oxide embedded in a matrix of long, sheath like crystals of zinc eugenolate ([C₁₀H₁₁O₂]₂Zn). Zinc oxide-eugenol preparations are widely used by dentists for their sedative effect on pulpal pain, particularly when restoring teeth with deep carious lesions. Best of Luck… Assist. Teacher Yousef Sabah Ali 9