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DENT 5302 TOPICS IN DENTAL BIOCHEMISTRY 30 March 2007 Objectives: • Role of diet in dental caries • Specific, non-specific, etiological plaque hypothesis • Metabolic activities of dental plaque related to dental caries Outline Diet and dental caries Sugars Dietary factors Caries-protecting food Specific vs Non-specific vs Etiological plaque hypothesis Acid production by dental plaque bacteria Aciduricity Production of intra- and extracellular polysaccharides Alkali production in dental plaque Methods to modify plaque acidity/cariogenicity Dietary factors Diet and dental caries Fermentable carbohydrate: Sugars and starch Downer MC. Comm Dent Health 1999;16:18-21. sucrose Positive correlation between caries experience and sucrose consumption over 50 years Currently, weaker relationship between sugar and caries? 90 nations: +ve relationship Industrialize nations: No relationship Woodward M, Walker AR. Br Dent J 1994;176:297-302. After ~ 1985, caries decreased more than sugar consumption The frequent use of fluoride Change the impact of sugars Oligosaccharides Sugar alcohols Sugars and dental caries. Touger-Decker R, van Loveren C. American J Clin Nutr 2003;78(suppl):881S-92S. Questions: Myth or Fact Honey is a natural product, you won’t get caries from it. Potatoes are non-cariogenic. Beer makes me drunk, but does not cause caries. I put Splenda in my coffee, so I am safe from both calories and caries. Cough syrup can cause tooth decay. ‘Baby bottle caries’ occurs when bedtime habits include lying with a bottle filed with milk. Dietary factors Individual factors Amount and type of carbohydrate Eating pattern Consistency Intake frequency Degree of retention ‘Caries protective' factors The Vipeholm Study Institution…..ethic x Sugar Frequently Between meals Consistency (‘Sticky’) Gustafsson BE et al. Acta Odontol Scand 1954; 11:232-264. Caries-protecting factors in food ‘Sialogogue’ Chewing gum stimulates saliva Increase the clearance of sugars and fermentable carbohydrates Buffering capacity Polyphenols Tannins (cocoa, coffee, tea) Interfere glucosyltransfersase activity of MS reduce plaque Xylitol Sugar alcohol used in chewing gum Stimulate salivary flow. Antimicrobial action ? Clinical studies: Xylitol vs Sorbitol Favoring remineralization Calcium, phosphate, protein: Cheese and dairy products Children and adolescents with low incidence of dental caries drank more milk. Eur J Epidemiol 13:659-664, 1997 Com Dent Oral Epidemiol 24:307-311, 1996 Elderly people that eat cheese several times per week had a lower incidence of root caries. Am J Clin Nutr 61:417S-422S, 1995 Remineralization of enamel was observed when cheese and milk were used as between meal snacks. Dairy products, except sweetened yogurt, generally reduced the amount of dentin demineralization. J Contemp Dent Prac 1:1-12, 2000 Cariogenic aspects of dental plaque Paradigm change Discussion: (group of 6-8) Is dental caries a transmittable, infectious disease? Yes, because………………. No, because……………….. Dental caries is a multifactorial disease resulting from an ecological shift in the tooth surface biofilm (dental plaque), leading to mineral imbalance between plaque fluid and tooth, hence net loss of tooth mineral. Fejerskov, 2004 Nonspecific Plaque Hypothesis Specific Plaque Hypothesis ? Current ? 1950 plaque = pathogenic Should be eliminated 2000 animal + S. mutans Caries Other animals more plaque more disease ?some plaque no caries? Cariogenic bacteria: mutans streptococci (MS) lactobacilli 71% of carious fissures: > 10% MS 70% of ‘caries-free’ fissures: no detectable MS Rampant caries: MS & lactobacilli Preventive & treatment: eliminate specific infection Antibiotics and immunization Bacteria & number of caries lesions ? Current ? 2000 High proportion of MS no caries / Caries developed without MS Contribution from other bacteria: S. mutans: final pH 3.95-4.1. S. mitis, S. salivarius, S. anginosus: final pH 4.05-4.5. Ecologic Plaque Hypothesis Marsh PD, 1994 • MS & other microorganisms = endogenous bacteria (resident of oral cavity) • No caries: lower level & stability in plaque composition (microbial homeostasis) • Change in local environment Frequent sugar intake Shift the balance of plaque microflora Repeated low pH Favors growth of cariogenic species Dental caries Role of cariogenic microorganisms 1. Produce acid rapidly from fermentable carbohydrate (Acidogenicity) 2. Survive and continue to produce acid at acidic pH (Aciduricity) 3. Produce extracellular polysaccharides from dietary sucrose to facilitate adherence to tooth surfaces and build-up of large bacterial deposits 4. Produce intracellular polysaccharides as storage components to prolong acid formation & acidic pH Role of cariogenic bacteria Acidogenicity Ability of bacteria to produce organic acids from fermentable carbohydrates Glycolysis (fermentation): Propionic - Anaerobic catabolism of carbohydrates Plaque Acids - Energy production Formic Glucose Acetic 2 lactic acids + 2 ATPs Homofermentative bacteria Produce > 90% lactic acid Lactic Succinic Cariogenic bacteria Heterofermentative bacteria Produce a mixture of metabolites: Organic acids - acetic, propionic, succinic, formic Ethanol Role of cariogenic bacteria Aciduricity Aciduricity = Ability of bacteria to live in a low pH environment “Dental caries is a consequence of successful adaptation by oral bacteria to survive and continue to produce acid at acidic pH” Ecologic plaque hypothesis: Beginning: - Low level of MS or lactobacilli - Other bacteria produce acid Frequent consumption of fermentable carbohydrate Best acid adaptation bacteria survive (MS & Lactobacilli) Increase level of MS & lactobacilli Maintaining intracellular pH at optimum 1. Low proton permeability of the cell membrane: cell wall thickening 2. Production of bases 3. Buffering capacity of the cytoplasm 4. Active transport of proton out of cell Proton-translocating membrane ATPase more acid production Increase energy demand increased glycolysis Zero DT. Adaptation in Dental Plaque. Cariology for the Nineties. p 333-349. Intra & extracellular polysaccharides formation Role of cariogenic bacteria Pathways of sucrose metabolism 1 3 2 Intracellular polysaccharides (IPS) Storage form of carbohydrate: glycogen-amylopectin Energy production and acids (by-product) when dietary CHO is depleted Excess nutrient: Up to 20% of sucrose converted to IPS Produced by most plaque bacteria IPS as a virulence factor: Contribute to acidogenicity Caries-prone plaque has prolong production of acid (e.g., after meal) from IPS storage Contribute to aciduricity IPS Energy for ATPase Drive protons out of cell Adapt to low pH environment Extracellular polysaccharides (EPS) Before sucrose enters the cells, <10% of sucrose glucans & fructans Diffuse into surrounding plaque Remain associated with cell glucan Glucans fructan Major component of interbacterial matrix Barrier to the outward diffusion of acids from plaque EPS may serve as carbohydrate storage: Fructans – degrade rapidly within a few hours, Glucans – longer period S. mutans Sucrose (not other CHO) disaccharide bond Fructosyltransferase Fructans energy Glucosyltransferase Glucans Glucan-binding ligands Plaque accumulation glucose sucrose (S. mutans surface ) + glucan adherence & accumulation Glucosyltransferase: Virulent factor of S.mutans Question (group of 3-4) Scanning electron micrograph of S. mutans grown in glucose broth (left), and sucrose (right). The amorphous material covering the colonies is extracellular polysaccharides. From your knowledge in the synthesis of EPS, what are the main points told by these micrographs? glucose sucrose Sucrose, not glucose, is necessary for the synthesis of EPS. EPS permit the bacteria to accumulate on the surface. Role of cariogenic bacteria Alkalinization phase Fluctuation of plaque pH Acid diffusion Buffering capacity Alkali from bacterial metabolism Alkali generation: End products are ammonia and/or CO2 Ureolysis S. salivarius, A. naeslundii, haemophili use enzyme urease to hydrolyze urea in saliva. Strickland reaction Peptostreptococci oxidize proline in amino acids and reduce protons in plaque. Arginine deiminase system (Major source of ammonia) S. gordonii, S. rattus, S. sanguis, lactobacilli, spirochetes use enzyme arginine deiminase to catabolize arginine in diet. Methods to modify plaque acidity/cariogenicity chewing gum 1. Stimulate salivary flow 2. Increasing plaque pH bicarbonate (‘baking soda’) ammonium salts 3. Disrupt plaque mechanical enzyme plant extracts 4. Antimicrobial agent chlorhexidine xylitol fluoride, stannous 5. Caries vaccine 6. Modify microflora reduce lactate producer increase lactate user (Veillonella) increase base producer Recommended references 1. Touger-Decker R, van Loveren C. Sugars and dental caries. Am J Clin Nutr 2003;78(suppl):881S-892S. 2. Zero DT. Sugars – The arch criminal? Caries Res 2004;38:277-285. 3. Marsh PD. Microbiologic Aspects of Dental Plaque and Dental Caries. Dent Clin North Am 1999;43(4):599-614. 4. Gordon Nikiforuk. Understanding Dental Caries 1. Etiology and Mechanisms, Basic and Clinical Aspects. Basel; New York: Karger 1985. Chapters 5 & 6. 5. Burne RA, Marquis RE. Alkali production by oral bacteria and protection against dental caries. FEMS Microbiology Letters 2000;193:1-6. 6. Fejerskov O. Changing paradigms in concepts of dental caries: Consequences for oral health care. Caries Res 2004;38:182-191. 7. Twetman S. Antimicrobials in future caries control? Caries Res 2004;38:223-229.