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1、Cariology Cariology and and EndodonticsEndodonticsA discipline to study the etiology, pathogenic mechanism, pathology, pathology-physiology,clinical expression,treatment and favorable turn etc. of the disease on dental hard tissue and pulp tissue. The content of the textbookCariology Non-cariogenic
2、disease of dental hard tissue EndodonticsOperative dentistryHistoryIn 50s yearsOral medicineCariologyOperative dentistryEndodonticsNon-cariogenic disease of dental hard tissueDisease of Oral mucosaPreventive dentistryPeriodontologyPaediatrics for dentistryStomatology in ancient timesBefore Christ (B
3、.C.)There were some record about cariesImage liking character (script) worm + toothThe chinese were known to have treated dental ills with knife, cautery, and acupuncture, a technique whereby they punctured different areas of the body with a needle.In Dynasty Han (A.D.215282)There are some record ab
4、out periodontologyAnno DominiPulpitisIn Han, Mr. Zhang Zhong Jing was a very famous writings in which there was a record about arsenicArsenic is a toxicant medicine which has been generally used for killing pulp In Dynasty Tang (A.D.710 era)the people use silver paste to fill tooth decay In Tang, to
5、oth brush with willow twig a toothbrush with hair planted was invented in A.D.911 century from a tomb of an emperors son-in-law of Liao from Chi Fong city3 events above describedreflected ancient civilization of our countryDentistry development in West countryThe first known dentist was an Egyptian
6、named Hesi-re (3000 B. C.). He was chief toothist to the pharaohs, he was also a physician, indicating an association between medicine and dentistry.The GreeksHippocrates (500 B. C.) appreciated the importance of teeth. He accurately described the technique for reducing a fracture of the jaw and als
7、o replacing a dislocated mandible. He was familiar with extraction forceps for this is mentioned in one of his writings.Aristotle (384 B.C.) also stated figs and soft sweets produce decay.Galen (200A. D. Romans)was first to recognize that toothache could be:Pulpitis or pericementitisHe also classifi
8、ed teeth into centrals,cuspids and molars.B. Leonardo da Vinci (end of 15th Century) - he described the anatomy of the jaws, teeth and maxillary sinus. These drawings are the first to accurately describe the maxillary sinus. However, credit has been given to Dr. Nathaniel Highmore of England (1650).
9、D. Leeuwenhoek (17th Century) - invented the microscope. He described the dental tubuli and was the first to see organisms of the mouth Anton van leeuwenhoekK. John Greenwood (1789) - dentures for George Washington were made by him.a red laser scansGeorge Washingtons false teeth not woodenLaser scan
10、s find gold, ivory, lead, human and animal teeth L. Pierre Fauchard (18th Century - 1728) - Father of Scientific Dentistry. Wrote a great text Surgeon Dentist. He also wrote a complete work on Odontology in two volumes, 843 pages. He recognized the intimate relationship between oral conditions and g
11、eneral health. He advocated the use of lead to fill cavities. He removed all decay and if the pulp was exposed, he used the cautery. Musee dArt Dentaire Pierre Fauchardat the Academie Nationale de Chirurgie Dentaire22 Rue Emile Menier, 75116, Paris FranceHe prescribed oil of cloves and cinnamon for
12、pulpitis. He described partial dentures and full dentures in his text. He constructed dentures with springs and used human teeth. Gold dowels were used in root canals filled with lead. He was also known as Father of Orthodontics. Fauchard died in 1768 at the age of 83. 1763 A.DJohn Baker, M.D. Surge
13、on Dentist. The earliest qualified dentist to practice in Boston and in America. 1836 A.D.Arsenic introduced for the killing of pulps, by Spooner.1840 A.D.The American Society of Dental Surgeons, first national dental organization. The Baltimore College of Dental Surgery, the first school in the wor
14、ld for the training of dentists was founded by Harris and Harden.Founded by Harris and Harden1859 A.D.Organization of American Dental Association on a representative basis.1890 W.D. Miller propose a chemical-bacteria Paraorganism theory to explain the mechanism of caries1891 A.D.Extension for preven
15、tion and scientific cavity preparation promulgated by G.V. Black. 1892 A.D. The establishment of a three-year course in dental colleges.1906 A.D.Einhorn recommends novacaine and adrenalin combination for local anesthesia.1915 A.D.McKay and Black publish results of investigation of fluoride in drinki
16、ng water.1956 A.D.Air-rotor drill, 250,000 RPM Dr. Robert Borden.Stomatology in China before 1949 West China University (1910) Shanghai Second University(1920) 4th Military Medical University(1935) University(1943)Shanghai Second UniversityWest China University 1918(School 1910)The first dental scho
17、ol in China was founded in West ChinaMedical University in 1917. A.W. LindsayA. W. Lindsay was teachingAfter 1949Hubei Medical College 1960 Founder Prof. Xia Liang Cai In recent 20 years, the science and techniques got great progressThere are 12 faculties or dental schools in each province Caries re
18、searchCaries VaccineEtiology & prevention Pulp diseaseModern root canal traitment Pulp biologyStem cell final targetAchievementsCraniofacial-oral-dental research in the century21stThe leadership team of NIDR initiated a strategic planning process in 1999 to identifyWhere we are (strengths, weaknesse
19、s, opportunities and threats)Where we want to go (e.g., mission and vision)How we plan to get there (strategic plan)Several scientific areas will be concerned in century 21stFrom molecular biology to clinical investigations; etiology, pathogenesis, epidemiology, prevention, diagnosis and treatment o
20、f inherited craniofacial-oral-dental diseases and disorders. e.g., ectodermic, dysplasia, cleft lip and palate, amelogenesis imperfect, dentin genesis imperfect, osteogenesis imperfect, and other inherited diseases.Inherited disease and disordersHereditary hypoplasiaHereditary aplasia of the enamel
21、dental caries Periodontitis Oral candidiasis Herpes Hepatitis,HIV/AIDSInfections diseasesViral, bacterial, fungal and parasitic such asDiseased PeriodontiumPrimary herpetic stomatitisCandidal stomatitisNeoplastic diseaseSupports basic, patient oriented, and community-based research on the etiology,
22、pathogenesis and metastasis, epidemiology, prevention, diagnosis, treatment of oral and pharyngeal neoplastic diseases Chronic disabling diseasesThe full range of research involving chronic disabling disease associated with the craniofacial-oral-dental complexThis includes osteoporosis, osteoarthrit
23、is and related bone disorders, temporo-mandible joint diseases and disorders, neuropathies and neuro-degenerative diseases including those involving oral sensory and motor functions and autoimmune diseases such as sjgrens syndrome. Chronic diseases of cran-oral-dental complex and other systemic dise
24、ases (e.g., diabetes)Biomaterials, biomimetics and tissue engineering Biomaterials used for the repair, regeneration, restoration and reconstruction of craniofacial-oral-dental molecules,cells, tissues and organs The study of computer aid design (CAD) computer aid manufacture (CAM) for dentureBehavi
25、or, health promotion and environment aimed at assessing the interactive roles of sociological, behavior, economic, environmental, genetic, and biomedical factors in craniofacial-oral-dental diseases and disorders 1996 Diet and Oral HealthCariology is a discipline within Stomatology which deals with
26、the complex interplaying between the oral fluids and the microbial deposits in relation to subsequent changes in the dental hard tissues. Several index have been used in dental caries Prevalence= No of the patients with caries No of the specific population in an area at risk of getting caries at tha
27、t time Prevalence of caries: the total caries experience of a population in existence at a certain time in a designated area.Caries incidence is usually expressed as the number of new decayed teeth or surfaces per-a period in a individual,group, or population. Incidence of cariesDMF=Decayed teeth+Mi
28、ssing teeth+Filled teeth/Number of subjects examined DMFTvIf surface have been counted, then we refer to the score as DMF-SvIf the teeth have been counted, then it is refer to as DMF-TvThe DMF-S or DMF-T are often referred to as an “indexThe distribution of dental caries in oral cavityReducing tende
29、ncy in developed country The DMFT prevalence of 12-year-old children in the Nordic countries in the period 1974-91.Denmark,Finland ,Norway and Sweden seem to follow the same downward trend, whereas Iceland has started a more rapid decline somewhat later. Increasing tendency in developing country9584
30、98959892959813Romania China Fuji Tonga Jordanian45627883858662DMFTs for 12 Years-old in Part of developing countryThe caries prevalence of China Time Population people with caries prevalence Before 1949 32469 19258 59.3019501959 219312 106781 48.7019601969 544708 217774 40.0019701979 3766290 6362 36
31、.00 131340 40.54 permanent teethCities 25080Countryside 20636 29.70 Cities 19683 79.55Countryside 16253 58.48Deciduous teethThe DMFT prevalence of 12-year-old children in 11 provinces of China 1.41 0.98Shanghai 1.17 0.95Tianjing 1.41 1.02Gansu 0.36 0.8Shandong 0.69 0.59Yunnan 0.46 0.88Liaoning 0.76
32、1.29Zhejiang 1.22 1.46Hubei 0.98 0.51Guangdong 0.91 1.65Sichuan 0.57 0.37Account 0.67 0.88 Province DMFT(1983) DMFT(1995) Age DMFT 12 1.03 15 1.42 18 1.60 3544 2.11 6574 2.49 (DFT) The DMFT prevalence in 1995Current concept of caries etiologyDental caries is a multifactorial disease in which there i
33、s an interplay of three principal factors: the host (primarily the saliva and teeth), the microflora, and the substrate, or diet. A fourth factor time must be considered in any discussion of the etiology of caries. Diagrammatically,these factors can be portrayed as four overlapping circles. Micro-or
34、ganismshost & toothSub-strateThe four circles diagrammatically represent the factors involved in the carious process.all four factors must act concurrently (overlapping of the circles)for caries to occurtimeno cariesno cariesno cariesno cariescariesCaries requires a susceptible host, a cariogenic or
35、al flora and a suitable substrate that must be present for a sufficient length of timeSalivathe term saliva refers to the mixture of secretions in the oral carityvSaliva is produced day and night and it is constantly swallowed vSaliva is present as a proteinaceous film covering all surfaces of oral
36、cavityThis mixture consists of fluids derived from the major salivary glands minor glands of oral mucose traces from gingival exudateEffect of desalivation on incidence and extent caries in animals Effect of desalivation on caries in hamstersGruopNo. hamstersAvg. no. carious teethAvg. caries scoreIn
37、tact Salivary glands202.34.0Desalivated*1010.539.0*Parotid, submandibular, and sublingual glands.Decreased salivary flow and caries in humansvSarcoidosisvSjogrens syndromevTharapeutic radiationHydrogen ionBuffering abilityCalciumInorganic phosphateFluoricle Inorganic componentsOrganic componentsmuci
38、nsGlycoproteinsStatherin and acidic proline-rich proteinsamylaseAntrmicrobial proteinsSaliva and dental cariesthe quantity of saliva associated with caries experienceRelationship between salivary characteristics and caries prevalencePropertyRelationshipPropertyRelationshipFlow ratepHCa-Buffer capaci
39、ty+PO4NH3AmylaseViscosityUrea-Salivary composition and cariesAntibacterial factors of glandular origin could protect oral mucosal and hard surfaces by helping to regulate the quantity and species distribution of oral microbesOral Microorganisms and dental plaqueIn contrast to mucosal surfaces, the s
40、urfaces of teeth are not constantly renewed by shedding of colonized epithelial cells. Surfaces of teethSome special sites occlusal fissues Approximal surfaceDental depositsBiofilms on dental surface-matrix-embedded microbial population, adherent to each other and/or to surface or interfacesAcquired
41、 pellicleAcellular, homogeneous organic film that forms on enamel and other hard surface by selective adsorption of salivary proteins. adsorption of salivary proteins or glycoproteinsOrigin Immediately after cleaning and polishing, salivary secrete deposit in the defects of enamel.v Surface pellicle
42、v Subsurface pellicleHistological appearanceThe surface pellicle appears acellular and faintly granular under TEM Surface PelliclePellicles of unknown age may vary in thickness from 501000nm.globular fibrillar granular Different morphological typesA subsurface pellicleconsisting of dendritic process
43、es that spread into the intercrystalline spaces and extend to 3m into the enamel.90% water 10% solid material compositionAccording to chemical analysesamino acids account for 45% to 50% carbohydrates amount 10% to 15% of the dry weight lipidFunctionvhealing, repairing, or protecting the enamel surfa
44、cevimparting selective permeability to the enamelvinfluencing the adherence of specific oral microorganisms to the tooth surfacevserving as a substrate or nutrient for the organismssummaryvOrganic depositvNaturally forms by selective adsorptionvOrigin of protein from salivavAfter polishing, reforms
45、rapidlyvBacteria settle on the pellicle as soon as it forms vformation of dental plaqueDental Plaque In the fourth century B. C. Aristotle related soft, adhere food deposits to tooth decay, but it was not until the advent of the microscope in the seventeenth century that “animalcules (microorganism)
46、 were seen in these dental deposits.Anton van leeuwenhoek, a draper and sheriffs chamberlain in Delft recognized the limitation of mechanical oral hygiene in removing these deposits. Anton Van leeuwenhoek saw large numbers of living cells in scrapings from teeth:I judge from myself that all the peop
47、le living in our united Netherlands are not as many as the living animalcules that I carry in my own mouth this very day.Terminology1847 Ficinus a slime coating denticulate Williams demonstrated the presence of a mass of microorganisms 1895 G.V. Black gelatinous microbial plaqueDental plaque Most fi
48、gurative description: a bacterial aspic with millions of organisms standing shoulder to shoulder More formal definition by Le: plaque is the soft, non-mineralized, bacterial deposit which forms on teeth and dental prosthesis that are not adequately cleanedMorphology of dental plaque A white or off-w
49、hite accumulation Variable thicknessThree main typies of organisms coccoid rod-shaped filamentous classificationvSupragingival plaque vSubgingival plaque vDental calculus (calcified plaque)Supragingival plaquevSmooth surface plaque vFissure plaque Supragingival smooth surface plaqueDivided into 4 ar
50、eas: plaque/tooth interfacecondensed microbial layerbody of the plaque plaque surfaceplaque/tooth interfaceIn some locations no pelicleHigher magnification of plaque-enamel border. Microorganisms that divide in horizontal planes are in direct contact with enamel (1 30,000). Condensed microbial layer
51、 a layer of very densely packed coccoid organisms, from 320 cells thickPart of a 7-day-old interdental plaque grown on enamel. The enamel matrix (bottom), appearing as a fine meshwork, is covered by a thin electron-dense and discontinuous pellicle. Immediately above this is the condensed microbial l
52、ayer which is covered by a layer of coccoid and filamentous micro-organisms and probably Neisseria. The intermicrobial space is electron-lucent and reveals cell remnants ( 1 6,500).vBody of the plaquev this occupies by far the largest portion of the plaque Thin section of plaque made of different ba
53、cterial species-predominantly coccoidal.Dense aggregation of microorganisms at the enamel surface (lower left)vPlaque surfacev loosely arrangement vGreat variety: coccoid, rod like, “corncobIn the surface layer of plaque some microorganisms co-aggregate with other species, as visualized by the prese
54、nce of so-called corn cob structuresMagnified view of “corncobFree surface of plaque composed of unidentified organismsFree surface of plaque composed of coccoid gram-positive (heavily stained cell walls ) and unidentified gram-negative microorganismsFissure plaque Gram-positive cocci and short rods
55、 predominate in a homogeneous,matrix, with occasional yeast cells Palisade and branching filaments are absent within the fissuresA: survey of dental plaque situated within a deep, narrow fissure of a premolarB: the upper half of the fissure is filled with dark material, the lower half is les dense C
56、: Higher magnification reveals a plaque consisting of mostly ghostlike membrane and cell wall structures Subgingival plaque The matrix is sparse Organisms:filamentous organisms, bacilli, cocci, spirochetes Gram negative bacteriaThe filamentous nature of plaque associated with gingivitis. Note attach
57、ment of smaller bacteria to filamentsCalcified plaqueSupragingival calcucus white chalky yellowSub gingival calculus greenish blackDental calculus is plaque in which mineralization has involved both the plaque matrix and the microorganisms.Formation and development of dental plaques vUneven tooth su
58、rface vCarious lesions vill-filling margins of restorationsvIrregularities in positioning of the teeth the location favoring plaque formation:vPellicle formationvMicrobial colonization Process of formationPlaque formation can be considered as three phasesvInitial colonizationvRapid bacterial growthv
59、Remodeling Bacteria are thought to be unspecifically associated with the tooth surface under the influence of Van der walls attractive forces as well as repulsive negative electrostatic forcesInitial microbial colonizationVan der walls forcesThere is a weakness forces between the molecules to be equ
60、al to 1/101/100 energe of chemical bondDepend on the cause and character of producing the forces:vOrientation forcevInduction force vDispersion forceOrientation forceInduction forceDispersion forceA firm attachment may subsequently be achieved by specific mechanismsLigands theoryRecognized system “a
61、dhesions receptorsSimplified explanation of the principle of selective adherence of bacteria to enamel. Successful attachment is achieved when the surface characteristics of a bacterium fit with a component in the pellicle (P)Two-reaction process for S.mutans initial weak attachment occurs between b
62、acterial cell proteins and salivary glycoproteins of the acquired pellicle and is followed by cellular accumulation mediated by sucrose-dependent glucans and cell surface receptor ligands.The adherence of selected oral bacteria initially involves non specific, low-affinity, very rapid binding reacti
63、ons followed by specific, high-affinity, slower, but stronger attachment to the acquired pellicle Microbial succession Receptors (oligossacharides) S.Oralis has a glactose-hinding adhesinActiuomyces viscosus proline rich proteinStatherin s.sangnis sialic acid Pioneer bacteria create an environment w
64、hich is either more attractive for secondary invaders or increase unfavorable condition to themselves. In this way the resident microbial community is gradually replaced by other species In mature dental plaque there may be a subtle balance(homeostasis) that tends to eject invading species not previ
65、ously present. Structural features of microbial colonization Initial microbial deposition after a cleaned tooth surface has been exposed for 4h to the oral environment, surprisingly few bacteria are found (one of reports)After 4 hours exposure the enamel is covered by pellicle which is a granular de
66、posit, primarily located in Tomes processes pits (TP) and in perikymatal grooves (P)The first bacteria to colonize the tooth surface are of the cocco-bacillary type (B ).note that the granular deposit does not cover the tooth surface in a uniform layer (PE) At this early stage bacteria are of the co
67、ccid or cocco-bacillary type and always reside in shallow depressions on the surface After 8h only a few smaller groups of microorganisms have settled on the surface sheltered by the perikymata Numerous bacteria spread across the surface as a monolayer In 12-h-old bacterial deposits the microorganis
68、ms spread in monolayer along the perikymata (P )In same areas multiplying microorganisms form multiplayer, individual organisms are embedded in an inter-microbial matrix. The monolayer of bacteria (upper part) is gradually replaced by a multiplayer (lower part )which is embedded in an intermicrobial
69、 matrix (X)vWithin 1 day the tooth surface is almost completely covered by blanket of microorganisms vmonolayer are intermitted with multilayers. After 1 day the surface of the micro-biota is mainly made up of coccoid bacteria, with a few filamentsDuring the course of the 2nd day the bacterial depos
70、its are colonized by multiple filamentous organisms with a perpendicular orientation to the surfaceDistinct morphological changes may be recorded on the surface of the microbiota when comparing the bacterial deposits after 24 (Fig. 5-12) and 48 h(Fig.5-13). Whereas the 24-h-old bacterial deposit com
71、prises a mass of coccoid bacteria from which a few filaments extend, the 48-h-old microbiota is almost entirely dominated by filamentous organisms28Initial colonization of root cementum occurs in principle as outline for enamel surface, but process more rapidly Because of the irregular surface to to
72、pography of root surfaces, colonization does not take place according to a particular pattern 48-h-old bacterial deposits on root cementum and enamel surfaces from the same individual. Note that the microbial deposits are thicker and more densely packed on root cementummature dental plaque During th
73、e early days, plaque growth occurs mainly as a result of cell division, but continuous adsorption of single microorganisms from saliva also contributes to the expansion of the bacterial deposit The corn cob are composed of a central filament coated with spherical organisms, and appear to have a dire
74、ct interspecies relationship machinated by surface fibrilsAs the microbiota grows older, characteristic structural changes are noted deep to the surface. The most striking change is the formation of an inner layer of densely packed gram-positive pleomorphic bacteria next to the tooth surface Ultrast
75、ructure of 2 week-old dental plaque from 3 individuals with different colonization patterns. Note that , in addition to differences in thickness, the outer parts of the deposits vary in composition and structure. Relative proportions of selected organisms in developing supragingival plaque on the la
76、bial surface of incisors. Plaque samples were obtained 1,3,5,7, and 9 days after thorough prophylaxis.Chemical composition of plaque plaque contain about 80% water 20% solids protein 40% to 50% carbohydrates account for 13% to 18% lipids account for 10% to 14% otherDirect smearsCount of 2 1011 micro
77、organisms/gIn centrifuge31011 organisms/g2/3 of plaque must consist of bacteria that means 70% the area is composed of microorganisms and 30% of intercellular material (matrix)Carbohydrates of plaque Glucose is the main carbohydrate found in hydrolyzed extracts of plaque arabinoseribose galactosefuc
78、ose Much of the carbohydrate exists in the form of extracellular polymers vglucans (homopolymers of glucose)vfructans (homopolymers of fructose )vHeteropolysaccharides Plaque microorganisms forming extracellular polysaccharides Glucans Fructans HeteropolysaccharidesStreptococcus sanguis Actinomyces
79、viscosus Actinomyces viscosusStreptococcus mutans Streptococcus mutans Lactobacillus buclneri Streptococcus salivarius Streptococcus salivarius lactobacillus cellobiosusStreptococcus mitior Lactobacillus caseiLactobacillus caseiLactobacillus acidophilusNeisseria sp. Cariogenic bacteriavRats raised u
80、nder bacteria-free conditions did not develop cariesvIn 1960 Keyes performed a series of experiments that established dental caries as infectious disease Diagram of caries formation due to passage of bacteria from rat dams to their pups, elimination of the disease by treatment of animals with antibi
81、otics, and the occurrence of caries following various types of inoculations. The infection was reintroduced by contact with infected animals, inoculation with isolated strains of “caries-inducingstreptococci, and transfer of bacterial plaque or feces. DR. ROBERT KOCHThe agent must be present in ever
82、y case of the disease; The agent must be isolated from the host and grown in a lab dish; The disease must be reproduced when a pure culture of the agent is inoculated into a healthy susceptible host; The same agent must be recovered again from the experimentally infected hostKochs postulatesSpecific
83、 bacteria and cariesLactobacilli these bacteria were thought to play an important role in caries etiology when it was first found that early carious plaque contained elevated levels of lactobacilli compared with plaque from non-carious surfaces LactobacillCaries free group: 100/mlCaries active group
84、: 100000/mlIn a group of caries-free children the mean number of lactobacilli per 1ml of saliva was in the hundreds, while in caries active children the mean number per1ml was in the range of 100,000.The early observation on changes in lactobacillus levels in the oral cavity led many dental scientis
85、ts to consider these bacteria as the specific microbial etiological factor in human caries For a number of reasons, the lactobacilli failed to qualify as an exclusive etiological agent in human caries formation:The affinity of lactobacilli for tooth surface is low, 0.01%High levels of lactobacilli t
86、end to exist after caries has developed, caries can frequently be initiated in the absence of detectable lactobacilli. The lactobacilli are secondary invaders, they may contribute to the progression of decay due to their acidogenic and aciduric properties ConclusionStreptococci In vitro studies with
87、 the oral streptococci have demonstrated many features that support their role as cariogenic agents vRelatively rapid generation vTo produce large quantities of acid vAciduric vTo utilize a wide range of fermentable carbohydrates vTo produce extracellular polysaccharidesvTo store intracellular carbo
88、hydratevTo form plaque matrixStreptococcus mutansIn the early 1920s, Clark attempted to evaluate the etiology of caries by analyzing the microbial content of plaque from human carious lesionsA streptococcal bacterium was consistently isolated from the samples and its pleomorphic nature (range from c
89、occi to rods, depending on the culture conditions) caused it to be named Streptococcus mutansOrland etc. demonstrated that microorganisms were required for imitation of dental caries in rats In 1960s at the NIDR got a series of successKeyes and Fitzgerald showed that in rats, caries is an infectious
90、 and transmissible disease, and that specific streptococci from carious lesion in animals could induce extensive decay in hamsters. S.mutans and Human cariesS.mutans represents less than 1% the flora in pooled plaque from caries-inactive individualsS.mutans normally makes up 5% to 10% of the total b
91、acteria present in pooled plaque samples obtained from caries-active subjectsHigh concentrations of S. mutans is found mainly at retentive sites such as caries lesions, occlusal surface, pits and fissures, and approximal areas A series studies indicate that S.mutans is significant involved in occlus
92、al fissure decayS.mutans and sucroseOne of the more unique features of S.mutans is the ability to utilize dietary sucrose to enhance colonization of the oral cavityS. mutans has the ability to metabolize the disaccharide sucrose by several pathways Two extracellular sucrose-dependent polysaccharide-
93、forming enzymes are constitutively produced and excreted from the cell by S.mutansDextransucrase or glucosyltransferase(GTF) is the enzyme responsible for glucan production. When glucan is formed by GTF, the products contain varying proportions of (16) and (1 3) linkage The (1 3) linkage are critica
94、lly important in that as their proportion increases the glucan becomes less soluble in waterClassification of mutans streptococci Other cariogenic bacteriaBacteria capable of producing carious lesions at different sites in the dentition of germ-free rats siteBacterium Smooth occlusal RootSurfaces Fi
95、ssures Surfaces Lactobacillus acidophlilus - + -Lactobacillus casei - + -Streptococcus mutans+ + + Streptococcus sanguis - + - Streptococcus salivarius+ + -Streptococcus mitior - + -Streptococcus milleri+ + -Streptococcus faecalis - + -Actinomyces viscosus - + -Actinomyces naeslundii - + +Actinomyce
96、s israelii - + +Rothia sp. - - +The Actinomyces species and other gram positive rods may be involved in the initiation of lesions on root surfaces of human teethMembers of the genus veillonella are obligate anaerobes and are found in significant numbers in dental plaque and salivaWithin plaque these
97、 bacteria have the capacity to utilize lactic acid and convert it to less harmful productsThe progress on bioflms researchOur understanding of biofilms has been advanced over last decade by the application of novel techniques.These include non-invasive and non-destructive microscopic techniques (e.g
98、. scanning confocal laser microscopy)That biofilms are usually lightly structured with channels traversing the depth of biofilm, creating primitive circulatory system.What is the significance of biofilmsGene expression can alter markedly when cell form a biofilm, resulting in many organisms having a
99、 radically different phenotype following attachment to a surface.DNA microarrays have show that 73 genes and 50% of the detectable proteome were differentially regulated in biofilms of P.aeruginosa when compared with conventional liquid grown (planktonic) cell.Cell-cell communicationGram-positive ba
100、cteria generally communicate via small diffusible peptidesGram-negative bacteria secrete acyl homoserine lactones (AHLS)The MIC of an organism growing on a surface can range from two-to 1000-fold greater than the same cells grown planktonically What is the significance of microbial communities The c
101、omponent organisms are not merely passive neighbors but rather that they are involved in wide range of physical, metabolic and molecular interactions.This community life-style provides enormous potential benefits to the participating organismsvA broader habitat range for growthvAn increased metaboli
102、c deversity and efficiencyvAn enhanced resistanc to environmental stressHorizontal gene transfer is also more feasible in multi-species biofilmsPlaque structureConfocal laser scanning microscopy has revealed that supergingival plaque can have a structured architecture.Polymer-containing channels or
103、pores have been observed that link the plaque/oral environment interface.Typical vertical (xz) section through a four-day human plaque sample taken in reflected-light mode. Images were taken at 0.6-umintervals from the top of the biofilm to the enamel surface underlying it. The image clearly demonst
104、rates the bacterial aggregates (grey-white) separated by areas of low reflectance (arrowed) presumed to be channels. Inverted biomass (M) and associated narrow attachment points (A) can also be observed. Scale bar = 25 umThat bacterial vitality varies throughout the biofilm, with the most viable bac
105、teria present in the central part of plaque and lining the voids and channels.Two-color xy section of a fluorescein-stained biofilm showing reflected light (red) and fluorescence (green) at a depth of 20um below the plaque surface.Optical sections (1 um each) of biofilm 2, vital fluorescence visuali
106、zation. First layer starting adjacent to enamel (bottom, left), 13th layer 25 um apart from bottom (top, left).Considerable heterogeneity in pH over relatively short distances in model mixed culture oral biofilms.Such environmental heterogeneity will allow fastidious bacteria to survive in plaque, a
107、nd enable microorganisms to co-exist.This explains how organisms with apparently contradictory metabolic and growth requirements are able to persist at the same site.Bacterial composition of dental plaque biofilmsNew techniquesv16s rRNA amplificationvFISHvCheckboard DNA hybridizationvDNA microarrayT
108、hat approximately 50% cells in plaque cannot as yet be cultured in the lab.Around 40% of amplified clones represent novel phynotypes.These culture-independent studies are changing our views on the role of bacteria in disease.That poorly classified organisms that are currently difficult or impossible
109、 to grow in the lab can predominate in deep pockets.Biofilm regulation of gene experessionDuring the initial stages of biofilm formation by S.mutans (first 2h following attachment), 33 proteins were differentially expressed (25 proteins were up-regulated, 8 proteins down-regulated)To communicate wit
110、h one another in a cell density-dependant manner via small diffusible molecules.Lysed cells in biofilms could act as donors of chromosomal DNA, thereby increasing the opportunity for horizontal gene transfer in dental plaque.That oral bacteria do not exist as independent entities but rather function as a co-ordinated, spetially organized and metabolically integrated microbial community.Thanks
