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1.Toothdevelopment

Toothdevelopmentorodontogenesisisthecomplexprocessbywhichteethformfromembryoniccells,grow,anderupt

intothemouth.Althoughmanydiversespecieshaveteeth,non-humantoothdevelopmentislargelythesameasinhumans.Forhumanteethtohaveahealthyoralenvironment,enamel,dentin,cementum,andthe

periodontiummustalldevelopduringappropriatestagesoffetaldevelopment.Primary(baby>teethstarttoformbetweenthesixthandeighthweeks,andpermanentteethbegintoforminthetwentiethweek.Ifteethdonot

starttodevelopatornearthesetimes,theywillnotdevelopatall.

Asignificantamountofresearchhasfocusedondeterminingtheprocessesthatinitiatetoothdevelopment.Itiswidelyacceptedthatthereisafactorwithinthetissuesofthefirstbranchialarchthatisnecessaryforthedevelopmentofteeth.

Invertebratesseveralspecializationsofepithelialtissuegenerateafterthickeningspecificstructures:keratinizedstructure(hair,nails>orexoskeletonsstructure(scales,teeth>.Placoidsscalesandteethofsharksareconsideredhomologousorgans.

2.ToothStructure

Anindividualtoothconsistsofanexposed

crownanda

root

,buriedinthe

gumandjaw.Thecrownisusuallyat

leastpartlycoveredbyanouterlayerofanespecially

hardsubstancerelatedtobonecalled

enamel.Beneaththe

enamel(andsometimesexposedtothesurfaceifthe

enamelismissingorwornaway>isanintermediatelayer

ofmaterialcalled

dentine

,whichisalsosimilartobone

butisnotnearlyashardasenamel.Itsurroundsan

inner

pulpcavity

filledwith

pulp

(aliving,vascular

andwellinnervatedtissue>.Bloodvesselsandnerves

reachthepulpcavitythroughachannel,the

rootcanal,

thatpenetratestheroot.Anadditionallayerofbony

material,cementum,usuallysurroundstheroot.

Asmostteethmature,therootcanalgraduallyclosesandthepulpcavityissealedoff.Theseteetharecalled

"rooted."Incontrast,"rootless"teetharethoseinwhichtherootcanalremainsopenandthetoothcontinues

togrowindefinitely.Rodentincisorsandthemolarsofmanyarvicolinerodentsareexamplesofrootlessor

evergrowingteeth。themolarsofdogsandhumansare

rooted.

Teetharepresentinmostvertebrates(turtlesandmodernbirdsarenotableexceptions>,andinsomegroupsthediversityofteethrivalsthatseeninmammals.Asignificantdistinctionofmammals,however,isthatmammalianteetharerestrictedtojustthreebones,themaxillaryandpremaxillaryoftheupperjawandthedentaryofthelowerjaw.

Finally,anoteonorientation:mammalogistsreferto

"labial,""lingual,"and"occlusal"surfaces.Thelabial

sideofthetoothisthesideclosesttothelips。the

lingualsideliesnexttothetongue.Theocclusalsurfaceisthesurfacethatmeetsatoothorteethintheoppositejawduringchewing.

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3.Caries

Dentalcaries,alsoknownastoothdecay,isadiseasewherebacterialprocessesdamagehardtoothstructure(enamel,dentinandcementum>.Thesetissuesprogressivelybreakdown,producingdentalcavities(holesintheteeth>.Twogroupsofbacteriaareresponsibleforinitiatingcaries,StreptococcusmutansandLactobacilli.Ifleftuntreated,thediseasecanlead

topain,toothloss,infection,and,inseverecases,death.Today,cariesremainsoneofthemostcommondiseasesthroughouttheworld.Cariologyisthestudyofdentalcaries.

Thepresentationofcariesishighlyvariable,howevertheriskfactorsandstagesofdevelopmentaresimilar.Initially,itmayappearasasmallchalkyareawhichmayeventuallydevelopintoalargecavitation.Sometimescariesmaybedirectlyvisible,howeverothermethodsof

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detectionsuchasradiographsareusedforlessvisibleareasofteethandtojudgetheextentofdestruction.

Toothdecayiscausedbyspecifictypesofacid-producingbacteriawhichcausedamageinthepresenceoffermentablecarbohydratessuchassucrose,fructose,andglucose.Themineralcontentofteethissensitivetoincreasesinacidityfromtheproductionoflacticacid.Specifically,atooth(whichisprimarilymineralincontent>isinaconstantstateofback-and-forthdemineralizationandremineralizationbetweenthetoothandsurroundingsaliva.WhenthepHatthesurfaceofthetoothdropsbelow5.5,demineralizationproceedsfasterthanremineralization(i.e.thereisanetlossof

mineralstructureonthetooth'ssurface>.Thisresultsintheensuingdecay.Dependingontheextentoftoothdestruction,varioustreatmentscanbeusedtorestoreteethtoproperform,function,andaesthetics,butthereisnoknownmethodtoregeneratelargeamountsoftoothstructure.Instead,dentalhealthorganizationsadvocatepreventiveandprophylacticmeasures,suchasregularoralhygieneanddietarymodifications,toavoiddentalcaries.

Allcavitiesoccurwherecarbohydratelikesugarorstarchisinthefoodleftonteethaftereverymealorsnackandchangedtoaciddemineralisationoftoothbyplaquebacteria.

Thoughmorethan95%oftrappedfoodisleftpackedbetweenteethaftereverymealorsnack,over80%ofcavitiesdevelopinsidepitsandfissuresingroovesonchewingsurfaceswherethebrushcannotreachandthereisnoaccessforsalivaandfluoridetoneutraliseacidandremineralisedemineralisedtooth.Fewcavitiesoccurwheresalivahaseasyaccess.

Chewingfibrelikeceleryaftereatinghelpsforcesalivaintotrappedfoodtodilutecarbohydratelikesugar,neutraliseacidandremineralisedemineralisedteeth.

4.Pulpitis

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Pulpitis

ismedicalconditioninwhichthedentalpulp

becomesinflamed.

Symptoms

Increased

sensitivity

to

stimuli,

specifically

hot

and

cold,

is

acommon

symptom

of

pulpitis.

Aprolonged

throbbingpainisalsoassociatedwiththedisease.

Causes

Pulpitismaybecausedbyadentalcariesthatpenetrate

thoughtheenamelanddentintoreachthepulp,oritmay

bea

result

oftrauma,

such

as

thermal

insult

from

repeateddentalprocedures.

Inflammationassociatedwithabacterialinfection,asinthecaseofpenetratingdecay,thepulpchamberisnolongersealedofffromtheenvironmentoftheoralcavity.

Whenthepulpbecomesinflamedpressurebeginstobuildupinthepulpcavityexertingpressureonthenerveofthetoothandthesurroundingtissues.Pressurefrominflammationcancausemildtoextremepain,dependingupontheseverityoftheinflammation.Often,pulpitis

cancreatesomuchpressureonthetoothnervetheindividualwillhavetroublelocatingthesourceofthepain,confusingitwithneighbouringteeth.Inflammationinthetoothprovidesadifficultenvironmentforreducingtheinflammationinthepulpcavity.Unlikeotherpartsofthebodywherepressurecandissipatethroughthesurroundingsofttissuesandwherelymphcanreach,thepulpcavityisverydifferent.Thedentinsurroundingthepulpishardanddoesnotgiveunderthepressureoftheinflammationsothepressurehasverylittlechanceofdissipatingbeforepulpalnecrosisoccurs.Thepulpcavityinherentlyprovidesthebodywith

animmunesystemresponsechallenge,whichmakesitveryunlikelythatthebacterialinfectioncanbeeliminated.

Thepainwillusuallystoponcethepulphasdied,howevertheinfectioncanspreadtotheancillaryanatomy.

Treatment

Oncethepulphasbecomeinflamedthetoothcanbe

diagnosticallydividedintotwocategories.

reversiblepulpitis

irreversiblepulpitis

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Reversiblepulpitis

Once

the

irritant

is

removed

thepulp

remains

vital

and

isnotundulyaffectedbythechanges,andthetoothcan

berestoredvitalbyfilling.

Irreversiblepulpitis

Thepulpisirreversiblydamagedandnecrosiswillfollow.

Painmaynotsubsideafterremovaloftheirritant.Pain

may

be

sharp

or

dull

and

throbbing.

If

there

is

any

drainage,thentheseverityofpainisreduced.

Thetoothmaybeendodonticallytreatedwherebythepulpisremovedandreplacedbyguttapercha.Analternativeisextractionofthetooth.Thismayberequiredifthere

isinsufficientcoronaltissueremainingforrestorationoncetherootcanaltherapyhasbeencompleted.

5.Herpessimplex

Herpessimplexisaviraldiseasecausedbybothherpes

simplexvirus1(HSV-1>andherpessimplexvirus2(HSV-

2>.Infectionwiththeherpesvirusiscategorizedinto

oneofseveraldistinctdisordersbasedonthesiteof

infection.Oralherpes,thevisiblesymptomsofwhichare

colloquiallycalledcoldsoresorfeverblisters

thefaceandmouth.Oralherpesisthemostcommonform

ofinfection.Genitalherpes,knownsimplyas

thesecondmostcommonformofherpes.Otherdisorders

suchasherpeticwhitlow,herpesgladiatorum,ocular

herpes(keratitis>,cerebralherpesinfection

encephalitis,Mollaret'smeningitis,neonatalherpes,and

possiblyBell'spalsyareallcausedbyherpessimplex

viruses.

,infects

herpes,is

Herpesvirusescyclebetweenperiodsofactivedisease

presentingasblisterscontaininginfectiousvirus

particles—thatlast2–21days,followedbyaremission

—

period,duringwhichthesoresdisappear.Genitalherpes,however,isoftenasymptomatic,thoughviralsheddingmaystilloccur.Afterinitialinfection,thevirusesmovetosensorynerves,wheretheyresideaslife-long,latent

viruses.Causesofrecurrenceareuncertain,thoughsomepotentialtriggershavebeenidentified.Overtime,episodesofactivediseasereduceinfrequencyandseverity.

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Herpessimplexismosteasilytransmittedbydirectcontactwithalesionorthebodyfluidofaninfectedindividual.Transmissionmayalsooccurthroughskin-to-skincontactduringperiodsofasymptomaticshedding.Barrierprotectionmethodsarethemostreliablemethodofpreventingtransmissionofherpes,buttheymerelyreduceratherthaneliminaterisk.Oralherpesiseasilydiagnosedifthepatientpresentswithvisiblesoresorulcers.Earlystagesoforofacialherpesandgenital

herpesarehardertodiagnose。laboratorytestingis

usuallyrequired.TwentypercentoftheU.S.populationhasantibodiestoHSV-2,althoughnotallofthemhaveahistoryofgenitallesions.

Acureforherpeshasnotyetbeendeveloped.Onceinfected,thevirusremainsinthebodyforlife.However,afterseveralyears,somepeoplewillbecomeperpetuallyasymptomaticandwillnolongerexperienceoutbreaks,thoughtheymaystillbecontagioustoothers.Vaccinesareinclinicaltrialsbuthavenotdemonstratedeffectiveness.Treatmentscanreduceviralreproductionandshedding,preventthevirusfromenteringtheskin,andalleviatetheseverityofsymptomaticepisodes.

Herpessimplexshouldnotbeconfusedwithconditions

causedbyothervirusesintheherpesviridaefamilysuchasherpeszoster,whichisaviraldiseasecausedby

varicellazostervirus.Thereisalsoapossibilityofconfusionwithhand,footandmouthdiseaseduetoapparitionoflesionsontheskin.

6.Candidiasis

Candidiasisorthrushisafungalinfection(mycosis>of

anyoftheCandidaspecies,ofwhichCandidaalbicansis

themostcommon.Candidiasisencompassesinfectionsthatrangefromsuperficial,suchasoralthrushandvaginitis,

tosystemicandpotentiallylife-threateningdiseases.Candidainfectionsofthelattercategoryarealsoreferredtoascandidemiaandareusuallyconfinedtoseverelyimmunocompromisedpersons,suchascancer,transplant,andAIDSpatients.

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SuperficialinfectionsofskinandmucosalmembranesbyCandidacausinglocalinflammationanddiscomfortarehowevercommoninmanyhumanpopulations.Whileclearlyattributabletothepresenceoftheopportunistic

pathogensofthegenusCandida,candidiasisdescribesa

numberofdifferentdiseasesyndromesthatoftendiffer

intheircausesandoutcomes.Commonlyreferredtoasa

yeastinfection,itisalsotechnicallyknownas

candidosis,moniliasis,andoidiomycosis.

Mostcandidialinfectionsaretreatableandresultin

minimalcomplicationssuchasredness,itchingand

discomfort,thoughcomplicationmaybesevereorfatalif

leftuntreatedincertainpopulations.Inimmunocompetent

persons,candidiasisisusuallyaverylocalized

infectionoftheskinormucosalmembranes,includingthe

oralcavity(thrush>,thepharynxoresophagus,the

gastrointestinaltract,theurinarybladder,orthe

genitalia(vagina,penis>.

Candidiasisisaverycommoncauseofvaginalirritation,orvaginitis,andcanalsooccuronthemalegenitals.In

immunocompromisedpatients,Candidainfectionscanaffecttheesophaguswiththepotentialofbecomingsystemic,

causingamuchmoreseriouscondition,afungemiacalledcandidemia.

Children,mostlybetweentheagesofthreeandnineyearsofage,canbeaffectedbychronicmouthyeastinfections,normallyseenaroundthemouthaswhitepatches.However,thisisnotacommoncondition.

Symptomsofcandidiasismayvarydependingontheareaaffected.Infectionofthevaginaorvulvamaycausesevereitching,burning,soreness,irritation,andawhitishorwhitish-graycottagecheese-likedischarge,oftenwithacurd-likeappearance.Thesesymptomsarealsopresentinthemorecommonbacterialvaginosis.Ina

2002studypublishedintheJournalofObstetricsandGynecology,only33percentofwomenwhowereself-treatingforayeastinfectionactuallyhadayeast

infection,whilemosthadeitherbacterialvaginosisoramixed-typeinfection.Symptomsofinfectionofthemalegenitaliaincluderedpatchysoresneartheheadofthepenisorontheforeskin,severeitching,oraburning

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sensation.Candidiasisofthepeniscanalsohaveawhitedischarge,althoughuncommon.However,havingnosymptomsatalliscommon,andamoresevereformofthesymptomsmayemergelater.

7.Historyofanesthesia

Methodsforlesseningthesensationofpainduringsurgerydatebacktoancienttimes.Beforethediscoveryofsubstancesthatproducedgeneralanesthesia,patientsneedingsurgeryforillnessorinjuryhadtorelyonalcohol,opium(anaturalnarcoticderivedfromtheopiumpoppy>,orfumesfromananesthetic-soakedclothtodeadenthepainofthesurgeon'sknife.Oftenagroupofmenheldthepatientdownduringanoperationincasetheopiumoralcoholworeoff.Undertheseconditions,manypatientsdiedofshockfromthepainoftheoperationitself.

Nitrousoxide,ether,andchloroform.Thegasesnitrous

oxide,ether,andchloroformwerefirstusedas

anestheticsinthenineteenthcentury,usheringinthe

moderneraofanesthesia.Nitrousoxide,orlaughinggas,

wasdiscoveredasananestheticbyEnglishchemist

HumphryDavy(1791–1867>in1799.Davy'sfindingwas

ignoreduntilthenextcentury,whenConnecticutdentist

HoraceWells(1815–1848>begantoexperimentusing

nitrousoxideasananestheticduringtoothsurgery.In

1845,heattemptedtodemonstrateitspain-blocking

qualitiestoapublicaudiencebutwasunsuccessfulwhen

hebegantopullatoothbeforethepatientwasfully

anesthetized.Thepatientcriedoutinpainand,asa

result,another20yearspassedbeforenitrousoxidewas

acceptedforuseasananesthetic.

Thefirstuseofetherasananestheticduringan

operationwasclaimedbysurgeonCrawfordW.Long(1815

–

1878>ofGeorgiain1842.Theoperation,however,wasunrecorded,soofficialcreditwentinsteadto

MassachusettsdentistWilliamMorton(1819

–1868>forhis

1846publicdemonstrationofanoperationusingetherperformedinaBostonhospital.WhileMortonadministered

thegastothepatientthroughaninhalingdevice,JohnC.Warren(1778–1856>removedanecktumorwithoutthe

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patientfeelinganypain.Followingthislandmarkuseofetherasananesthetic,generalanesthesiabegantobepracticedallovertheUnitedStatesandEurope.

Chloroform

was

introduced

asa

surgical

anesthetic

by

Scottish

obstetrician

James

Young

Simpson

(1811

–1870>

in

1847.

After

first

experimenting

with

ether,

Simpson

searched

for

an

anesthetic

that

would

make

childbirth

less

painful

for

women.Although

it

easedthepain

of

labor,

chloroform

hadhigher

risks

than

those

associated

with

ether.

Neither

ether

nor

chloroform

are

used

in

surgerytoday.

8.Whatisadrysocket?

A"drysocket"occurswhenthebloodclotislostfroman

extractionsiteprematurely.Basically,thebloodclotin

thesocketservesthesametwofunctionsasa"scab"ona

skinsurfacecut.First,itassistsinthecessationof

bleedingandsecond,itprotectsunderlyingstructures

duringthehealingprocess.Likethechildwho"picksat

ascab"theareahealsintimebutispainfulforfar

longerthanifthe"scab"hadbeenleftalone.

Whenthebloodclotislostbeforetheunderlyingstructreshavehadtimetoheal,boneisexposedtotheoralenvironmentalongwithfinenerveendings.Thisisanexquisitelypainfulbutotherwiserelativelyharmlesssituation.Therearepackingmaterialswhichtheoralsurgeoncanplacetohelpeasethediscomfortbothbyphysicallyblockingthewoundandbytheactionofthechemicalsinthepackonlocalnerveendings.Generally,patientsreturntohavethepackchangedeverydayortwoandmostpatientsdonotrequiremorethan2orthreedressingchanges.Somepatientsrequirenodressingwhileothersmayrequire4or5changesofpacking.Tinctureoftimeandgoodoralhygieneusuallyresolvethesituation.

Therearesomeactivitieswhichmayincreasethepropensityfordrysocketformation...smoking,drinkingcarbonatedbeveragesinthefirst24hoursaftersurgery,spittingordrinkingthroughastrawinthatsametimeperiod...butoften"drysockets"occurfornoparticularreasonatall.

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9.Bonefracture

Abonefracture(sometimesabbreviatedFRXorFx,Fx>isa

medicalconditioninwhichthereisabreakinthe

continuityofthebone.Abonefracturecanbetheresult

ofhighforceimpactorstress,ortrivialinjuryasa

resultofcertainmedicalconditionsthatweakenthe

bones,suchasosteoporosis,bonecancer,orosteogenesis

imperfecta,wherethefractureisthentermed

pathologicalfracture.

Althoughbrokenboneandbonebreakarecommon

colloquialismsforabonefracture,breakisnotaformal

orthopedicterm.

Surgery

Surgicalmethodsoftreatingfractureshavetheirown

risksandbenefits,butusuallysurgeryisdoneonlyif

conservativetreatmenthasfailedorisverylikelyto

fail.Withsomefracturessuchashipfractures(usually

causedbyosteoporosisorosteogenesisImperfecta>,

surgeryisofferedroutinely,becausethecomplications

ofnon-operativetreatmentincludedeepveinthrombosis

(DVT>andpulmonaryembolism,whicharemoredangerous

thansurgery.Whenajointsurfaceisdamagedbya

fracture,surgeryisalsocommonlyrecommendedtomakean

accurateanatomicalreductionandrestorethesmoothness

ofthejoint.Infectionisespeciallydangerousinbones,

duetotheirlimitedbloodflow.Bonetissueispredominantlyextracellularmatrix,ratherthanlivingcells,andthefewbloodvesselsneededtosupportthislowmetabolismareonlyabletobringalimitednumberofimmunecellstoaninjurytofightinfection.Forthisreason,openfracturesandosteotomiescallforverycarefulantisepticproceduresandprophylacticantibiotics.

Occasionallybonegraftingisusedtotreatafracture.

Sometimesbonesarereinforcedwithmetal.Theseimplants

mustbedesignedandinstalledwithcare.Stress

shieldingoccurswhenplatesorscrewscarrytoolargeof

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aportionofthebone'sload,causingatrophy.Thisproblemisreduced,butnoteliminated,bytheuseoflow-modulusmaterials,includingtitaniumanditsalloys.Theheatgeneratedbythefrictionofinstallinghardwarecaneasilyaccumulateanddamagebonetissue,reducingthestrengthoftheconnections.Ifdissimilarmetalsareinstalledincontactwithoneanother(i.e.,atitaniumplatewithcobalt-chromiumalloyorstainlesssteelscrews>,galvaniccorrosionwillresult.Themetalionsproducedcandamagethebonelocallyandmaycausesystemiceffectsaswell.

Electricalbonegrowthstimulationorosteostimulationhasbeenattemptedtospeedorimprovebonehealing.Resultshoweverdonotsupportitseffectiveness.

10.Typesofdentures

Removablepartialdentures

Removablepartialdenturesareforpatientswhoare

missingsomeoftheirteethonaparticulararch.Fixed

partialdentures,betterknownas"crownandbridge",are

madefromcrownsthatarefittedontheremainingteethtoactasabutmentsandponticsmadefrommaterialstoresemblethemissingteeth.Fixedbridgesaremoreexpensivethanremovableappliancesbutaremorestable.

Completedentures

Conversely,completedenturesorfulldenturesarewornbypatientswhoaremissingalloftheteethinasinglearch(i.ethemaxillary(upper>ormandibular(lower>arc