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  1. archivesoforalbiology60(2015)385–392 Availableonlineatwww.sciencedirect.com ScienceDirect journalhomepage:http://www.elsevier.com/locate/aob Characteristicsofthesalivaflowratesofminor salivaryglandsinhealthypeople ZhenWanga,Ming-MingShenb,Xiao-JingLiua,YanSic,Guang-YanYua,* aDepartmentofOralandMaxillofacialSurgery,PekingUniversitySchoolandHospitalofStomatology,100081, Beijing,PRChina bDepartmentofOralandMaxillofacialSurgery,SchoolofStomatology,theSecondHospitalofHebeiMedical University,050000,Shijiazhuang,PRChina cDepartmentofPreventiveDentistry,PekingUniversitySchoolandHospitalofStomatology,100081,Beijing,PRChina articleinfo abstract Objectives:Toinvestigatethenormalrangeandcharacteristicsofsalivasecretioninthe minorsalivaryglands(MSGs). Design:TheflowratesofMSGsweremeasuredin4anatomicallocationsoforalmucosa,and therelationshipbetweenMSGflowratesandwholesalivaflowrateswereassessedin300 healthysubjectsstratifiedbyageandsex.Anadditional30youngfemaleswerefurther evaluatedforflowsymmetry,effectsofstimulation,circadianeffectsinMSGs,andthe relationshipwiththeflowratesofmajorsalivaryglands. Results:(1)Themeansalivaflowrateswere2.10?0.66(lowerlabialglands),2.14?0.62 (upperlabialglands),2.88?0.72(buccalglands)and2.15?0.51(palatalglands)ml/min/cm2, respectively.TheflowrateofbuccalglandswassignificantlyhigherthantheratesofSMGs inotherlocations(P<0.01).(2)5-year-oldchildrenhadthelowestMSGflowrates (P<0.0001)whilethe10–14-year-oldgrouphadthehighest(P<0.001).(3)MSGflowrates wereindependentofsex(P>0.05),rightvs.left(P>0.05),andcitricacid(2.5%)stimulation (P>0.05).(4)OnlylabialMSGdisplayedasignificantsecretorycircadianrhythmwiththe highestrateintheevening(P<0.05).(5)Aweakcorrelationwasfoundbetweentheflowrate ofpalatalglandsandthatofunstimulatedwholesaliva(r=0.195,P=0.007). Conclusions:OurfindingsprovideareferenceforfunctionalevaluationofMSGsandfor donorsiteselectionofMSGtransplantationfortreatmentofseveredryeyesyndrome. Articlehistory: Accepted23November2014 Keywords: Minorsalivarygland Saliva Salivasecretion Salivaflowrate Salivarygland #2014ElsevierLtd.Allrightsreserved. locations,theycanbedividedintolabial,buccal,palatal, lingualandretromolarglands.1Thereare600–1000MSGsin thehumanoralcavity,andtheycontributetolessthan10%of thevolumeofwholesaliva.2Despitethesmallvolumeof salivasecreted,MSGshavelongbeenconsideredtobeof significantimportancefororaltissueprotection,lubrication, maintenanceoflocalimmunityandthesenseoftaste.These 1. Introduction Thesurfaceoforaltissuesiscoveredbyathincoatofsaliva. Thisfilmismainlycomposedofsmallamountsofmucous secretionsfromtheminorsalivaryglands(MSGs).MSGsare distributedthroughouttheoralmucosa,andaccordingtotheir *Correspondingauthor.Tel.:+861082195245;fax:+861062173402. E-mailaddress:gyyu@263.net(G.-Y.Yu). Abbreviations:MSGs,Minorsalivaryglands;SM,Submandibulargland;PG,Parotidgland. http://dx.doi.org/10.1016/j.archoralbio.2014.11.016 0003–9969/#2014ElsevierLtd.Allrightsreserved.

  2. 386 archivesoforalbiology60(2015)385–392 functionsaresupportedbytheiruniqueanatomicaldistribu- tion,theirproximitytooraltissuesurfaces,andtherelatively largeamountsofmucinsandimmunoglobulinscompared withthemajorsalivaryglands.MSGsarethoughttosecrete spontaneously,whichmakesthesefunctionspossiblewhen peopleareatrest,suchasduringsleep.3However,our knowledgeaboutthesalivasecretedfromMSGsismuchless comparedtothataboutwholesalivaorsalivafrommajor salivaryglands.Furthermore,reporteddataonthesalivaflow ratesofMSGsareconflictingbecauseofvariousuncontrollable factors.3 SalivaflowratesvaryacrossMSGsindifferentlocations.It iswidelyacceptedthattheflowrateofthebuccalglandsis relativelyhigh,followedbythelowerlabialandpalatal glands.4However,thenormalvaluesofsalivaflowratesin MSGsindifferentlocations,whichisveryimportantto evaluatethesecretoryfunctionofMSGs,areofgreatvariation. Otherfactors,suchasageandsex,areknowntoinfluencethe flowrateofwholesaliva.Stimulationwithcitricacidincreases secretionofthemajorsalivaryglands.Salivasecretionfollows thecircadianrhythm,withthelowestsecretionrateduring sleepandthehighestrateinlateafternoon.5However,mostof theseflowratesweremeasuredforwholesalivaorsalivafrom majorsalivaryglands,anditisnotclearwhetherthesaliva flowrateofMSGshasthesamecharacteristicsasthatofwhole salivaorsalivafrommajorsalivaryglands.Therefore,awell- controlledsystemicstudyiscriticaltorevealthecharacter- isticsofthesalivaflowratesofMSGsinhealthypeople. SeveralfeaturesofMSGsmaycausethedifferencein secretionfrommajorsalivaryglands.Firstly,thestructureof MSGsisnotascomplexasthatofmajorsalivaryglands.MSGs consistofsmallclustersofsecretorycellswithashort excretoryductthattransportsthesalivatothesurfaceofthe mucosa.6Secondly,apartfromthelingualvonEbner’sglands, whichsecreteseroussaliva,MSGsarepredominantlymucous, withavaryingamountofsero-mucouscellsintheirstructure. Thirdly,theMSGshavelittleornosympatheticinnervations. Inadditiontootherinnervationsthatincludeneuropeptide- containing(vasoactiveintestinalpeptide,substanceP,neuro- peptideY)andnitricoxidesynthase-positivenervefibres, MSGsaremainlycontrolledviatheparasympatheticnervous systemwithcholinergictransmission.7,8Itissupportedbythe studiesthatparasympatheticagonist(carbachol)activates andantagonist(atropine)blockssecretionfromthecellsof humanlabialglands.9,10Whetherotherfactorsinfluencingthe secretionofthemajorsalivaryglandsarealsorelatedtothe secretionofMSGsremainsunclear. Theaimofthisstudywastoinvestigatethenormalrangeof salivaflowratesfromMSGsandthecharacteristicsofMSGsin differentlocationsinhealthysubjects. MSGs.Thesubjectswerefurtherdividedintofiveagegroups: 5,10–14,15–44,45–59,and60–89years,with30malesand30 femalesineachgroup.Intheothergroup,30femalesaged 21–25yearswereenrolledtoobservetheflowratesofMSGs atsymmetricsitesandafterstimulationwith2.5%citric acid,andthepossiblecircadianrhythmofsalivasecretion. Allsubjectswereingoodhealth,hadgoodoralhygiene,and werefreeofcariesandsalivaryglanddiseases.Noneofthem hadreceivedanymedicationthatcouldcausedrymouth. ThisprojectwasapprovedbytheEthicsCommitteeof thePekingUniversitySchoolofStomatology(IRB00001052- 080-48).Allsubjectssignedtheirinformedconsentfor participation. 2.2. Salivacollection Toreducepossibleinfluenceofcircadianandseasonal variationsonsalivasecretion,salivasampleswerecollected atthesametimeofday,at09:00AMand11:00AM,inanair- conditionedroom,whereroomtemperaturewaskept20–248C andhumiditywaskept40–70%.11Subjectswereaskedto refrainfromeating,drinking,smoking,andbrushingtheir teethforatleast90minbeforecollection.Salivacollectionwas performedbyanexperiencedresearcher. 2.3. Collectionofwholesaliva Beforecollection,thesubjectswereinstructedtorinsetheir mouthswithwaterandthenrestfor5minwiththeireyes openandheadtiltedslightlyforward.Byusingthespitting method,12wholesalivaatrestwascollectedfor5minintoa pre-weighedcup.After5minofrest,thestimulatedwhole salivawascollectedbysmearing2.5%citricacidsolutionon thelateralsideofthetonguewithaswabevery30sforanother 5min.Bydefiningspecificgravityofsalivaas1,flowrateswere calculatedandrecordedinml/min. 2.4. CollectionofsalivafromMSGs MSGsalivawascollectedfromthefollowingsitesoforal mucosa(Fig.1):theupperlabialmucosa(lefttothemidline, halfwaybetweenthevermilionborderandthelabial fraenum),thelowerlabialmucosa(lefttothemidline, halfwaybetweenthevermilionborderandthelabial fraenum),thebuccalmucosa(halfwaybetweenStensen’s ductandtheangleofthemouth)andthepalatalmucosa (5mmlefttothemidline,mediallyattheborderofthesoft andhardpalate).Salivafromthepalatalglandwasnot collectedin5-yeargroupand10–14-yeargroupconsidering theirinabilitytocooperate. Duringcollectionoflabialglandsaliva,thelabialmucosa wasevertedgently.Duringcollectionofbuccalorpalatal glandsaliva,thesubjectswereaskedtokeeptheirmouths wideopen.Afterthemucosawascarefullydriedwithgauze,a stripoffilterpaper(WhattmanNo.41,1?2cm2insize)was immediatelyplacedontothemucosaandthenlightpressure wasapplied.Thesalivawascollectedfor30s.Thestripof filterpaperwasremovedandplacedinanair-tightcontainer toprotectthecollectedsalivafromevaporation.The containerandthestripwereweighedbeforeandafter 2. Materialsandmethods 2.1. Subjects Threehundredandthirtysubjects(150malesand180 females;aged5–89years)wereenrolledinthisstudy.They aredividedintotwogroups.Inthefirstgroup,300subjects wereenrolledformeasurementofthesalivaflowratesfrom

  3. 387 archivesoforalbiology60(2015)385–392 Fig.1–Salivacollectingsites.(a)Upperlabialglands(b)Lowerlabialglands(c)Buccalglands(d)Palatalglands collectionusingananalyticalbalance(DenverInstrumentCo. Ltd.,Beijing;TP-114Max110gd=0.1mg).Bydefiningspecific gravityofMSGsalivaas1,flowrateswerecalculatedand recordedinml/min/cm2. 3. Results 3.1. SalivaflowratesofMSGs 2.5. theflowratesofMSGsandcollectionofmajorsalivaryglands saliva Influenceoflocation,stimulation,andbiorhythmon Inthe300healthysubjects,themeansalivaflowrateswere 2.10?0.66(lowerlabialglands),2.14?0.62(upperlabial glands),2.88?0.72(buccalglands)and2.15?0.51(palatal glands)ml/min/cm2,respectively(Table1).AmongMSGs,the buccalglandshadthehighestsecretionrate(P<0.01), followedbythepalatalglandsandlabialglands.Nosignificant differencewasfoundbetweensalivaflowratesofthepalatal, upperlabialandlowerlabialglands(P>0.05). Intheextragroupof30femalesaged21–25years,wefurther measuredtherestingflowratesofMSGsontherightside,the stimulated(with2.5%citricacid)flowratesofMSGsontheleft side,andtherestingflowratesofMSGsattwoextratime pointsonthesameday(afternoon,between15:00and17:00; evening,between19:00and21:00),followingapreviously describedprocedure.WithmodifiedLashleycupandtheWolff apparatus,12,13salivafromtheparotidgland(PG)ontheleft andthesubmandibulargland(SMG)atrestaswellasafter citricacidstimulationwascollectedfor5min. 3.2. Salivaflowratesaccordingtoageandsex ThemeanflowratesofMSGsindifferentlocationsinhealthy subjectsofdifferentageandsexareshowninTable1.No significantdifferencewasfoundaccordingtosexinthesaliva flowratesofMSGsindifferentlocations(P>0.05).A significantdifferencewasfoundbetweenthefiveagegroups (P<0.0001,Fig.2).Thehighestratewasfoundin10–14-year group(P<0.001),followedby15–44-yeargroup(P<0.001),and then45–59-yeargroupand60–89-yeargroup(P>0.05),with5- yeargrouphavingthelowestvalue. 2.6. Statisticalanalysis Theresultsofflowratewerepresentedasmean?SD.SPSS 16.0wasusedforthestatisticalanalyses.Thedifferencein salivaflowratesbetweenmaleandfemalewasanalysedby independentsamplest-test.Thevariationofsalivaflowrates atdifferentlocationsandageswereanalysedbyone-way analysisofvariance.Theeffectsofacidstimulationand symmetricallocationwereanalysedbypairedsamplet-test. ThecircadianrhythmofMSGsecretionwasanalysedby analysisofvariance.Thecorrelationofflowratesbetween MSGsandmajorsalivaryglandsorwholesalivawasanalysed bypartialcorrelation.P-valueslessthan0.05wereconsidered significant. 3.3. acidandbiorhythmonthesalivaflowrate Effectofsymmetricallocation,stimulationwithcitric Inthe30femalesubjectsaged21–25years,themeansaliva flowrateofMSGsatsymmetricalsitesisshowninTable2.No significantdifferencewasfoundbetweenMSGsatsymmetri- calsites(P>0.05),includinglowerlabial,upperlabial,and buccalglands.

  4. 388 archivesoforalbiology60(2015)385–392 Table1–FlowratesofwholesalivaandMSGsaccordingtoageandsex. Age (year) Sex N Resting wholesaliva Stimulated wholesaliva Lowerlabial glands Upperlabial glands Buccal glands Palatal glands 5 M F M F M F M F M F M+F M F 30 30 30 30 30 30 30 30 30 30 300 150 150 0.31?0.20 0.39?0.26 0.44?0.37 0.37?0.34 0.57?0.30 0.41?0.27 0.44?0.41 0.27?0.19 0.54?0.36 0.36?0.34 0.41?0.32 0.45?0.34 0.36?0.28 1.57?0.78 1.65?0.56 1.93?1.07 2.10?1.03 3.52?1.26 2.52?1.15 2.70?1.73 2.53?0.99 2.22?1.12 1.93?1.20 2.27?1.24 2.36?1.38 2.19?1.07 1.58?0.50 1.60?0.42 2.49?0.64 2.37?0.60 2.40?0.62 2.49?0.63 2.06?0.55 2.00?0.45 2.07?0.60 1.83?0.68 2.10?0.66 2.09?0.66 2.10?0.66 1.85?0.58 1.81?0.52 2.44?0.54 2.31?0.76 2.26?0.54 2.12?0.47 2.16?0.52 2.01?0.63 2.27?0.67 2.17?0.72 2.14?0.62 2.18?0.60 2.09?0.63 2.65?0.68 2.53?0.32 3.40?0.62 3.14?0.62 2.83?0.66 2.96?0.49 2.81?1.11 2.82?0.51 2.95?0.84 2.64?0.80 2.88?0.83** 2.91?0.83 2.84?0.60 10–14 15–44 2.24?0.42 2.22?0.34 2.25?0.58 1.97?0.47 2.08?0.59 2.10?0.62 2.15?0.51 2.19?0.53 2.11?0.48 45–59 60–89 Total ml/minforwholesalivaandml/min/cm2forMSGs.Valuesrepresentmean?SD. **P<0.01comparedwithlabialandpalatalglands. Afterstimulationwith2.5%citricacid,thesalivaflowrates ofMSGsdidnotshowanyobviousincrease(P>0.05), includinglowerlabial,upperlabial,andbuccalglands. ThemeansalivaflowratesofMSGsandwholesalivainthe morning(9:00–11:00),afternoon(15:00–17:00),andevening (19:00–21:00)onthesamedayareshowninTables2and3.A significantdifferenceintheflowrateofrestingwholesaliva wasfoundatdifferenttimes.Theflowratesintheafternoon (P=0.01)andintheevening(P=0.004)werehigherthaninthe morning.However,theflowratesofwholesalivastimulated with2.5%citricaciddidnotshowanytime-baseddifference (P>0.05).Thesalivaflowratesofthelowerlabialglands (P<0.05)andupperlabialglands(P<0.001)showedtime- basedvariations,whichweredifferentfromthoseobserved forrestingwholesaliva(Fig.3).Thesalivaflowrateofthe buccalglandsdidnotshowanytime-basedvariations (P=0.198). aslackofdatafor5-yeargroupand10–14-yeargroup).No correlationwasfoundbetweenflowratesofotherMSGsand majorsalivaryglandsorwholesaliva.TheflowratesofMSGs in4locationscorrelatedwitheachother(P<0.01).Detailsare showninTable4. 4. Discussion Inthisstudy,wemeasuredtheflowrateofMSGstodetermine thenormalrange;tounderstandtheinfluenceofage,sex, location,biorhythmandstimulationwith2.5%citricacid;and toelucidatetherelationshipbetweentheflowrateofMSGs andthatofmajorsalivaryglandsorwholesaliva. Therearenostandardprotocolsforthecollectionofsaliva fromMSGs.Nonetheless,variousstudieswithsubjectsof differentagesandbothsexesusingdifferentcollectingand measuringmethodshavebeencarriedout.Theresultsof thesestudiesarethereforeunderstandablyincongruous.Even so,someconcordanceshavebeenfoundamongthereported secretionrates.Themajorityofthedataindicatesthatsalivary secretionissignificantlyhigherinthebuccalglandsthanin thelabialglands,whilethepalatalflowrateisthelowest(see 3.4. andMSGs Correlationbetweentheflowratesofwholesaliva Therewasaweakcorrelationbetweentherestingflowrateof wholesalivaandthepalatalglands(r=0.195,P=0.007,n=180 Fig.2–(a)SalivaflowratesofdifferentMSGsindifferentagegroups.Errorbars:95%CI.(b)AveragesalivaflowrateofMSGs indifferentagegroups10–14-yeargrouphadthehighestflowrateandthe5-yeargrouphadthelowestflowrate.Errorbars: SD***P<0.001comparedwith5-yeargroup;**P<0.01comparedwith5-yeargroup

  5. 389 archivesoforalbiology60(2015)385–392 Table2–SalivaflowratesofMSGs30youngfemales. Flowrate(ml/min/cm2) Time n Lowerlabialglands Upperlabialglands Buccalglands Left Right Left Right Left Right 9:00–11:00 15:00–17:00 19:00–21:00 30 30 30 2.55?0.75 2.31?0.64 2.73?0.65# 2.49?0.59 2.27?0.51 2.64?0.48** 02.11?.45 2.77?0.78 2.68?0.51 2.11?0.46 2.88?0.61 2.91?0.55 Valuesrepresentmean?SD. **P<0.01comparedwith9:00–11:00;#P<0.05comparedwith15:00–17:00. Table3–Flowratesofwholesaliva,PGandSMof30youngfemales. Time Wholesaliva(ml/min) MajorSalivaryGlands(ml/min) n Resting Stimulated RestingPG StimulatedPG RestingSM StimulatedSM 9:00–11:00 15:00–17:00 19:00–21:00 30 30 30 0.33?0.21 0.43?0.25** 0.44?0.17** 2.44?1.16 2.28?1.10 2.47?0.75 0.02?0.01 0.42?0.42 0.14?0.11 0.60?0.56 Valuesrepresentmean?SD. **P<0.01comparedwith9:00–11:00. reviewbyEliassonandCarlen,2010).3Inourstudy,basedona largesampleof300healthysubjects,thebuccalglandshave thehighestflowrate,whichisconsistentwithother observations.However,theflowratesofthepalatalglands aresimilartotheratesoftheupperandlowerlabialglands, whicharedifferentfromtheresultsinpreviousreports.The factorswiththepotentialtoinfluencesalivasecretion,suchas certaindiseases,medications,smoking,drinkingalcohol, wearingdenture,stress,oranyemotionaldisturbance,were undercontrolinthepresentstudy.However,theinfluenceof theraceorethnicityofthesubjectsisworthforfurther investigation.14OursubjectsarefromanAsianpopulation, whichmightplayaroleinthedifferenceinflowratesfrom otherstudieswhosesubjectsweremainlyCaucasians. Asthesurfaceareaoftheoralcavityisabout215cm2,the numberofMSGshasbeenestimatedtobe600–1000,andthey aredistributedindifferentlocations.15Eveninthesame region,thedistributionoftheMSGsmayvaryindifferent areas.Forexample,thereisamuchsmallernumberofMSGsin themiddlethaninthelateralpartsofthelabialglands.16 Therefore,siteselectioniscriticalfortheevaluationofsaliva flowratesofMSGs.Inourstudy,wetriedtomeasuremucosa siteswherethedensityofMSGsishigher.Asaresult,wechose alateralsiteinsteadofamidlinesiteformeasuringthesaliva flowrateofboththelowerandupperlabialglands. Arecentstudy17foundthatthebuccalsalivaflowrateis higherinmorelateralsitesthaninsitesclosetotheangleof themouth.Thisresultmightbeduetothepresenceofparotid saliva.Themeasurementsinthisareaoveratimeperiodof5s variedconsiderablyandnon-systematically.3Inourstudy,we triedtominimizethevariationbymeasuringtheratefor30s. Wealsokeptoursubjectsinatiltbackwardpositionsothatthe influencefromthesalivasecretedfromparotidglandscould beruledout. Fig.3–ThepatternofbiorhythminMSGsecretion.Morning:09:00–11:00AM;Afternoon:15:00–17:00PM;Evening:19:00– 21:00PM;Errorbars:50%CI**P<0.01comparedtotheflowrateinthemorning;#P<0.05comparedtotheflowrateinthe afternoon.

  6. 390 archivesoforalbiology60(2015)385–392 Table4–CorrelationamongflowratesofMSGs,majorsalivaryglandsandwholesaliva. Stimulated whole saliva Lower labial glands Upper labial glands Buccal glands Palatal glands Resting SMG Stimulated SMG Resting PG Stimulated PG Restingwhole saliva Correlation coefficient P N Correlation coefficient P N Correlation coefficient P N Correlation coefficient P N Correlation coefficient P N Correlation coefficient P N Correlation coefficient P N Correlation coefficient P N 0.564** 0.041 ?0.026 0.057 0.195** 0.546** 0.054 0.252 -0.351 0.000 330 0.446 330 0.089 0.625 330 0.005 0.289 330 0.094 0.007 180 0.098 0.002 30 0.665** 0.776 30 0.401* 0.052 30 0.076 0.057 30 ?0.042 Stimulated wholesaliva 0.096 330 0.921 330 0.375** 0.079 330 0.357** 0.171 180 0.223** 0.000 30 ?0.333 0.028 30 ?0.165 0.104 30 0.134 0.824 30 ?0.046 Lowerlabial glands 0.000 330 0.000 330 0.318** 0.002 180 0.198** 0.073 30 0.265 0.384 30 0.191 0.354 30 0.251 0.809 30 ?0.432 Upperlabial glands 0.000 330 0.005 180 0.202** 0.157 30 ?0.285 0.311 30 ?0.252 0.435 30 ?0.731 0.217 30 0.465 Buccalglands 0.004 180 0.127 30 0.180 30 0.760** 0.710 30 0.102 0.810 30 -0.102 RestingSMG 0.000 30 0.061 30 0.329 0.590 30 0.092 Stimulated SMG 0.595 30 0.629 30 0.57* RestingPG 0.043 30 *P<0.05,**P<0.01. N:thenumberofsubjects. Highervaluesofpalatalflowratehavebeenreportedinthe posteriorandmedialsites.18Inourstudy,wemeasuredin moreposteriorsitesandfoundhigherflowrates.Thus,unlike previousstudies,nodifferencewasnoticedbetweenpalatal flowandlabialflow. Alargedegreeofsimilarityhasbeenreportedbetweenthe flowratesofbilateralparotidglandsinhealthysubjectsaswell asinpatientswithSjo ¨gren’ssyndrome.19Inourstudy,ina groupof30femalesubjectsaged21–25years,nosignificant differencewasfoundinthesalivaflowratesofMSGsat symmetricalsites.Thisresultindicatesthatitisreasonableto useunilateralMSGswhenmeasuringtheflowratesofMSGs. Itiswellknownthatwholesalivaflowratesarelowerin womenthaninmen.20However,theresultsonsex-based differencesinthesalivaflowratesofMSGsisinconsistent.A higherpalatalsecretionrateinmencomparedwithwomen wasfoundinOstlund’sstudy,21butnosimilardifferences werefoundintheseriesofstudiesreportedbyNiedermeier etal.22,23Similarly,nosex-baseddifferencewasfoundinthe labialsecretionrate,24,25whereasotherstudiesshowedlower, butnotstatisticallysignificant,secretioninthelabial,buccal, andpalatalglandsinwomen.18,26Onoetal.reportedthat significantgenderdifferencesinchewing-stimulatedwhole salivaflowratesdisappearedafterthestandardisationwith glandsizesandweight.Theyconcludedthegenderdifference ofchewing-stimulatedwholesalivaflowratesisduepartlyto differentglandsizesinhealthyyoungsubjects.27ForMSGs, situationsweresimilar.Ourresearchshowednostatistical differenceintheflowratesbetweenmaleandfemalesubjects. Asagegrows,salivasecretionfrommajorsalivaryglands decreases.20However,whetherasimilartendencyexistsin thefunctionofminorsalivaryglandsremainscontroversial. Althoughreducedfunctionofthelabialminorglandsdueto structuraldegenerativechangeshasbeenreported,28,29 measurementsoflabial,palatal,andbuccalsalivasecretion haveshownbothdecreasedandunperturbedflowrateswith increasingage.3Becksetal.observedthattheflowrateof restingwholesalivainthe5–9-yeargrouplowerthanthatof the10–14-yeargroup,whileafter14yearsuntil95,theflow rateplateaus.Althoughtheflowrateofthe50–95-yeargroupis slightlylowerthanthatofthe5–49-yeargroup,thedifference isnotsignificant.30Inourstudy,thehighestflowratewas observedinthe10–14-yeargroup,followedbythe15–44-year group,45–59-yeargroup,60–89-yeargroup,andfinally5-year group.Similartothemajorsalivaryglands,theMSGsundergo aprocessofmaturationintheirfunctionandmorphology. Thus,thelowestsalivaflowrateobservedinthe5-year-old childrenislikelyduetotheirimmatureglands,whichis

  7. 391 archivesoforalbiology60(2015)385–392 consistentwiththeresultsreportedbySonesson.31,32As childrengrow,thefunctionofMSGsincreases.Thisexplains whythe10–14-yeargrouphadahigherflowrateofMSGs. Afterwards,thoughthefunctionofmajorsalivaryglandsand MSGsplateaus,thesurfaceoftheiroralcavitymightincrease. SparseopeningsofMSGsperareamightcausedecreasedflow ratesofMSGspermucosaarea.Unlikethefindingsreported forthemajorsalivaryglands,thedecreaseinthesalivaflow rateofMSGsintheagedsubjectswasnotobviousinthis series.Thisindicatesthatthedegenerationthatoccursasa resultofagingisnotsoobviousintheMSGsasinthemajor salivaryglands. Themajorsalivaryglandshavebeenreportedtohave increasedflowratesinresponsetogustatorystimulationwith citricacid.13,33,34Ourstudyshowedsimilarresultsforthe majorsalivaryglandsandwholesaliva.However,resultson theeffectofacidstimulationontheflowrateofMSGsare controversial.Shernetal.couldnotconfirmthedifferencein flowratesafter2%citricacidstimulation.18Speirsreported thatthepercentageincreaseinflowratefromtheparotid glandwasmuchgreaterthanthatinlabialglandswithacid stimulation.35Someinvestigatorssuggestedthatstronger stimuli,suchaslemondrop,mayincreasethesecretionof MSGs.24Westudiedtheeffectofstimulationbyapplying2.5% citricacidtothesurfaceofthetongue.Ourresultsshowedthat althoughtherewasaslightincreaseafteracidstimulation,the differencewasnotsignificant(P>0.05),suggestingthatthe regulationofthesecretioninMSGsisdifferentfromthatofthe majorsalivaryglands. Biorhythmisawell-knownfactorthataffectsflowrates andthecompositionofwholesalivaandsalivaofthemajor salivaryglands.5Thisiswhyitisimportanttocollectwhole salivaandsalivasecretedfrommajorsalivaryglandsata fixedtime,usuallybetween9:00AMand11:00AMinthe morning.Inourstudy,wefurtherexploredthebiorhythm patternofthesalivasecretioninMSGs.Thesalivaflowrates ofthelowerandupperlabialglandsshowedaclearpatternof biorhythm.However,therhythmwasdifferentfromthatof restingwholesaliva.Thesalivaflowratesofthelowerand upperlabialglandsshoweddifferenceswithtime.These resultssuggestthatthecollectionofsamplesfordetermining thesalivaflowratesofMSGsshouldalsobeconductedata fixedtimeofthedayduetochangesassociatedwithits biorhythm. Thepositivecorrelationbetweenthesalivaflowratesof MSGsandwholesalivahasbeenreported.36,37However,our resultsdidnotshowacorrelationbetweentheflowratesof MSGsandwholesalivaorsalivafrommajorsalivaryglands exceptforthepalatalglandsinhealthypeople,whichis consistentwithpreviousstudies.18,22Becausetheflowrate ofthewholesalivaprimarilyreflectsthesecretionfrom majorsalivaryglandssuchassubmandibularglandsand sublingualglands,MSGsecretionmaypresentasmall portionofthewholesaliva.2ItisunderstandablethatMSG secretionmaynotbeabletochangetheflowrateofwhole saliva.OurdataalsoindicatethatMSGssecreteconstantly, whichmayhaveasignificantbiologicalimportance.Theoral mucosaneedsconstantlubrication,andMSGsmayplaya criticalroleinprovidingcontinuoussupplyofsmallamount ofsaliva. 5. Conclusion Thepresentstudydeterminedthenormalrangeofsalivaflow ratesofMSGsatdifferentorallocationsandindicatedthat fewerfactors,includinglocation,age,andbiorhythm,affect MSGsecretion.Thenormalrangemakesthisnoninvasive techniquepossibleinevaluatingdrymouthcausedby Sjo ¨gren’ssyndromeorradiationtherapyagainstheadand necktumour,oraidsinchoosingbetterdonorsitebefore transplantationofminorsalivaryglandstotreatseveredry eyesyndrome.38Consideringallinfluencingfactorsandthe relationshipbetweenMSGsandmajorsalivaryglands,a standardprotocolforcollectionofMSGsneedstobe established. Funding ThisworkwassupportedbygrantsfromtheNationalNatural ScienceFoundationofChina(No.81271161;No.81470756);the MinistryofEducation(No.20120001110045),andtheBeijing NaturalScienceFoundation(No.7132201). Conflictofinterests Thereisnoconflictofinterest. Ethicsapproval Thisstudy‘‘Characteristicsofthesalivaflowratesofminor salivaryglandsinhealthypeople’’wasconductedwiththe approvalofPekingUniversityHealthScienceCenterand BeijingBureauofHealthonJuly31,2008. Acknowledgments TheauthorsthankProfessorGuoH.ZhangatNationalCenter forResearchResourcesforrevisingthearticleandallthose whoparticipatedinthestudy. references 1.CarlsonE,OrdR.TextbookandColorAtlasofSalivaryGland Pathology:DiagnosisandManagement.JohnWiley&Sons; 2009. 2.DawesC,WoodCM.Thecontributionoforalminormucous glandsecretionstothevolumeofwholesalivainman.Arch OralBiol1973;18(3):337–42. 3.EliassonL,CarlenA.Anupdateonminorsalivarygland secretions.EurJOralSci2010;118(5):435–42. 4.SchmidegG,KivovicsP,MartonK.Flowrateofminor salivaryglandsinelderlypatientswearingcomplete dentures.FogorvSz2007;100(4):153–8. 5.DawesC.Physiologicalfactorsaffectingsalivaryflowrate, oralsugarclearance,andthesensationofdrymouthin man.JDentRes1987;66:648–53SpecNo:-L.

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