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Plaque Fluid and the Caries Process

DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY 2 April 2007. Plaque Fluid and the Caries Process. Objectives:. Effect of bacterial acids and plaque fluid on the mineral phase of enamel The concept of critical pH Enamel-plaque fluid interaction. Outline. Plaque fluid composition.

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Plaque Fluid and the Caries Process

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  1. DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY 2 April 2007 Plaque Fluid and the Caries Process Objectives: • Effect of bacterial acids and plaque fluid on the mineral phase of enamel • The concept of critical pH • Enamel-plaque fluid interaction

  2. Outline • Plaque fluid composition • Stephan curve • Enamel substrate • Enamel – plaque fluid interaction • The concept of critical pH • Erosion • Ultrastructure of enamel caries lesion

  3. Plaque Composition 80% water 20% solid • Bacterial and salivary protein – 50% • Carbohydrates and lipids – 20-30% Extra and intracellular polysaccharides - Synthesized by bacteria - Bacterial attachment and cohesion - Reservoir of fermentable substrates • Inorganic components – 25% Ca, P: several times higher than in saliva Most Ca is non-ionic. becomes ionized as pH drops Determine rates of enamel dissolution and remineralization Other ions: K, Na, Mg, and F. Critical point: Dental plaque is responsible for the majority of chemical activities on the tooth surface.

  4. Plaque Fluid • Plaque fluid = extracellular aqueous phase of dental plaque • Provide aqueous medium for diffusion and exchange of substances between saliva and tooth surface • Separated from plaque by centrifugation • 500 mg wet weight plaque sample 150 nL plaque fluid • Changes in ionic composition of plaque fluid cariogenic conditions Rested plaque fluid: one to several hours after eating Starved plaque fluid: following overnight fasting Total organic acids (mmol/L) 56.3 - 102.1 31.9 - 61.5 pH 5.69 - 6.54 6.78 - 7.08 Rested plaque Starved plaque

  5. Lactic acid: the main acid involved in caries formation Lactic acid concentrations in plaque fluid following a 2-min 10% sucrose rinse Time (min) Acid (mmol/L) 0 17.5 7 37.5 15 33.4 23 18.6 Lactic Margolis HC, Moreno EC. Composition and cariogenic potential of dental plaque fluid. Crit Rev Oral Biol Med 1994;5:1-25

  6. ? ? ? Stephan curve Stephan RM. JADA 1940;27:718-723 Changes in hydrogen-ion concentration on tooth surfaces and in carious lesion. Stephan RM. JADA 1944; 23:257-266 Intra-oral hydrogen-ion concentrations associated with dental caries activity.

  7. What contributes to the extent of pH drop after glucose challenge? • Type and amount of CHO available • Bacteria present • Salivary composition and flow • Other food ingested • Thickness and age of dental plaque

  8. Resting plaque pH: • Constant within each individual, but differences among groups. • Caries-inactive – resting pH ~ 6.5 - 7 • Caries-prone– lower resting pH What contributes to the differences in resting plaque? • Bacterial composition affects metabolic properties of plaque • Storage form of CHO energy source when diet is depleted When the host does not ‘eat’, cariogenic bacteria still produce acids form storage carbohydrates

  9. What are the differences in plaque fluid between ‘caries-free’ and caries-positive individuals? ‘caries-free’ caries-positive Composition Na+ Mg2+ K+ Calcium P 14.2 + 3.5 2.0 + 0.4 59.9 + 4.9 16.2 + 5.2 13.9 + 1.9 16.5 + 5.4 2.6 + 0.4 71.4 + 11.3 6.9 + 0.4 15.6 + 3.6 * pH 7.02 + 0.05 6.79 + 0.12 * Acid Lactic Acetic Propionic 1.8 + 0.7 19.9 + 3.5 5.8 + 1.5 2.6 + 1.2 20.3 + 4.6 5.8 + 1.5 * DS (enamel) 7.11 + 0.66 5.42 + 0.68 Margolis HC. Enamel-plaque fluid interaction. Cariology for the Nineties, 1993

  10. Enamel substrate • Enamel: 96% by weight or 87% by volume mineral • 13 vol % interprismatic space is diffusion channel • Major mineral component (teeth and bone): • Calcium phosphate crystals ~ Hydroxyapatite Ca10(PO4)6(OH)2 Hydroxyapatite lattice structure Hydroxyl ions form columns of parallelogram Calcium ions form triangle around hydroxyl ion Phosphates fill space Nikiforuk G. Understanding Dental Caries. Karger 1985

  11. ≠ Ca10(PO4)6(OH)2 • Biological mineral is ‘nonstoichiometric’ • Concentration of the chemical components is different from pure HAP • Substitution of three primary constituents with - carbonate - other trace elements (impurities): F, Na, Cl, Mg, K, Zn, Si, Sr Current concept: Dental mineral is carbonated HAP • Carbonate (CO3)2- substitute (PO4)3- or 2 (OH)- • Carbonate ions disturb the regular array of ions in the crystal lattice • More soluble in acid than pure HAP

  12. Discussion (group of 5-6) When a tooth is just erupted into the oral cavity, it is more susceptible to demineralization. Why?

  13. Post-eruptive Maturation Newly erupted teeth have relatively greater caries susceptibility During demineralization, carbonate is lost and excluded after remin Decrease carbonate & increase fluoride in enamel surface Less susceptible to demineralization = post-eruptive maturation Simplified formula of tooth mineral (Ca)10-x(Na)x(PO4)6-y(CO3)z(OH)2-u(F)u

  14. When do teeth dissolve? Teeth dissolve when pH is lower than a critical pH Solubility product (Ksp) Ksp is the ionic activity products of substance at saturation Ksp = Concentrations of the component ions to the power in saturated solution e.g., HAP Ca5(PO4)3OH ; Ksp(HAP) = [Ca2+]5[PO43-]3[OH-] = 7.36 x 10-60 Ksp(enamel) = 5.5 x 10-55 Ksp(carbonated-HAP) = 4.57 x 10-49 Ksp is a constant value Acidic solution: H+ remove PO43- & OH- Decrease [PO4] & [OH] in solution Apatite mineral dissolves [PO4] & [OH] rise to maintain the saturation level

  15. 1/9 IAP (ionic activity products in solution) DS = Ksp (ionic activity products at saturation) DS = 1 : Saturation condition DS < 1 : Solution undersaturated WRT mineral Demineralization DS > 1 : Solution supersaturated WRT mineral Remineralization Ionic Activity Product (IAP) Determined the same way as Ksp, but use the ion concentrations in the solution. Degree of saturation (DS) Ratio of the ionic product of a substance in the solution (IAP) to its ionic product at saturation (Ksp ) e.g., for hydroxyapatite (Ca5(PO4)3OH) Margolis HC, Moreno EC Crit Rev Oral Biol Med 1994;5:1-25 (WRT = with respect to)

  16. pH of saliva & plaque fluid > critical pH • Saliva & plaque fluid contain Ca, P, OH IAP > Ksptooth enamel The concept of critical pH = pH at which a solution is just saturated WRT a particular mineral If the solutionpH > critical pH supersaturated mineral precipitate If the solutionpH < critical pHundersaturated mineral dissolve Normal condition: Our teeth do not dissolve in saliva or plaque fluid Saliva and plaque fluid aresupersaturated WRT tooth enamel The tooth will dissolve when the pH of fluid phase is less than critical pH. Critical pH of carious formation in enamel ~ 4.5-5.5 • Coincide with pH when plaque bacteria ferment carbohydrates • HAP is undersaturated & FAP is supersaturated

  17. demineralization pH6.5 6.05.5 5.0 4.54.0 3.5 3.0 FAP HAP deposit caries erosion pH6.5 6.05.5 5.0 4.54.0 3.5 3.0 remineralization Critical pH Carious lesion forms at pH 4.5 - 5.5 Erosion lesion forms when pH < 4.5

  18. 'Erosion' ‘acid corrosion' Loss of dental hard tissue through chemical etching and dissolution by acids of non-bacterial origin • Endogenous acid: gastric acid, gingival crevicular fluid • Exogenous acid:diet, medicine, industry Gastroesophageal reflux disease, vomiting Frequent and prolonged ingestion of acidic fruits, fruit juices and acidic beverages • 3/4 of a bottle of white wine • Every evening for 34 years • Sipping over a 3 hours after dinner • Wine pH ranges about 3-4. Dental consumption due to wine consumption. Mandel L. JADA 2005;136:71-75

  19. Can acidic food and drinks soften enamel surface? Enamel samples alternately immersed, 5 sec each, in food or drink and in artificial saliva for 10 cycles. * * * pH 2.74 3.78 3.75 3.83 4.20 S. Wongkhantee et al., J Dent 2006;34:214-220. Effect of acidic food and drinks on surface hardness of enamel, dentine, and tooth-coloured filling materials.

  20. Critical pH is not a fixed value Solubility isotherm 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 pH 100 10 1 0.1 0.01 0.001 0.0001 HAP calcium (mol/l) FAP oral fluid Current concepts on the theories of the mechanism of action of fluoride. ten Cate JM. Acta Odontol Scand 1999;57:325-9.

  21. Ultrastructure of enamel caries lesion Crystal damage from acid: - Surface etching - Central defect or hairpin • Crystal core has more dislocations or lattice defects • Higher carbonate content • Dissolving crystals are smaller • Increased intercrystalline space Larger crystal at prism periphery from remineralization

  22. 1. Surface zone 2. Body of lesion 3. Dark zone 4. Translucent zone Sound enamel 3 2 4 1 1 2 3 4 Larger crystals in surface zone and dark zone Indication of remineralization Range of crystal size in each zone of early enamel lesion

  23. Recommended references 1. Zero DT. Dental Caries Process. Dent Clin North Am 1999;43(4):635-664. 2. Featherstone JD. The science and practice of caries prevention. J Am Dent Assoc 2000;131:887-899. 3. Gordon Nikiforuk. Understanding Dental Caries 1. Etiology and Mechanisms, Basic and Clinical Aspects. Basel; New York: Karger 1985. Chapters 4 &10. 4. Margolis HC, Moreno EC. Composition and cariogenic potential of dental plaque fluid. Crit Rev Oral Biol Med 1994;5:1-25. 5. Margolis HC. Enamel – plaque fluid interactions. In WH Bowen and LA Tabak (Eds) Cariology for the nineties. University of Rochester Press 1993:173-186.

  24. Diagram showing effect of increase Ca on degree of saturation of plaque fluid with respect to enamel Question: Which line represent individuals with higher tendency for caries formation?

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