野村義明　花田信弘　劉艷飛

摘要：光催化劑有兩個(gè)主要作用：有機(jī)化合物的降解和超親水性，這些作用使其具有抗菌和自清潔的效果。目前，光催化劑已經(jīng)被應(yīng)用于醫(yī)學(xué)臨床實(shí)踐。兩種主要的口腔疾病（齲齒和牙周?。┯绊懼驇资畠|人，而治療口腔疾病則可以直接接觸到口腔內(nèi)的病灶。牙科領(lǐng)域會(huì)使用到各種先進(jìn)的牙科材料。因此，光催化劑可以成為牙科臨床實(shí)踐的有用工具。本文綜述了光催化劑在牙科研究中的應(yīng)用研究，并展望了光催化劑在牙科研究中的未來前景。關(guān)鍵詞：光催化劑；牙科臨床實(shí)踐；牙科研究；牙科材料

中圖分類號(hào)：O 644文獻(xiàn)標(biāo)志碼：A

Recent advances of application of photocatalyst for dental research

NOMURA Yoshiaki ， HANADA Nobuhiro， LIU Yanfei

（Institute of Photochemistry and Photocatalyst， University of Shanghai for Science and Technology， Shanghai 200093， China）

Abstract： Photocatalysthastwomajoreffects：degradationoforganiccompoundsandsuperhydrophilicity. These effects lead to the antimicrobial and self-cleaning effects. Photocatalyst hasbeenappliedformedicalclinicalpractices.Twomajororaldiseases（dentalcariesandperiodontaldisease） globally influence on several billons of people. Treatment of oral diseases allows direct accesstolesionsintheoralcavity.Andtherearevariousadvanceddentalmaterialsindentistry.Therefore，photocatalystcanbeusefultoolfordentalclinicalpractice.Theaimthisreportistosummarizetheresearchofapplicationofphotocatalystfordentalresearchandtofindoutthefutureprospectiveforphotocatalyst to dentistry.

Keywords： photocatalyst; dental clinical practice; dental research; dental materials

Dr.Fujishima，presidentofInstituteofPhotochemistryandPhotocatalystofUniversityofShanghaiforScienceandTechnology，foundoutthephotocatalyticreactionmechanism [1].Thisphenomenonhastwomajoreffects：degradationoforganic compounds and superhydrophilicity.

Photocatalystisknowntodecomposevariousorganiccompoundsunderilluminationbygeneratingvariousradicals.Organiccompoundsadsorbedonthesurface can be self-cleaned by the photodecomposition.In addition， super hydrophilic effect makes the organiccompoundshardtoattachthesurface.Photocatalystshave multiple applications in air purifiers， paints， and self-cleaningcoatingsformedicaldevicessuchas catheters，aswellasintheeliminationof microbes. Photocatalystisalsoappliedtodentalresearchand clinical dental practice.

Dentalcariesandperiodontaldiseasesaretwo majororaldiseases. Globally，itisestimatedthat 2 billion people suffer from dental caries of permanent teethand 514 millionchildrensufferfromcariesof primaryteeth. Prevalenceof themainoraldiseases continuestoincreasegloballywithgrowing urbanizationandchangesinlivingconditions. Periodontaldiseaseaffectsthetissuesthatboth surroundandsupporttheteeth. Thediseaseis characterized by bleeding orswollen gums， pain and sometimes bad breath. Severe periodontal diseases are estimatedtoaffectaround 19% of theglobaladult population，representingmorethan 1 billioncases worldwide[2].

These two major oral diseases are affected by oral pathogenicbacteria. Inhumanbody，therearetwo major bacterial flora： intestinal bacterial flora and oral bacterialflora. Anoral microbiomeconsistsof more than 700 speciesofbacteria [3-9]. Tocontroloral bacterial flora lead to the prevention of oral diseases， treatmentoforaldiseasesallowsdirectaccessto lesionsintheoralcavity，andtherearevarious advanceddentalmaterialsindentistry. Therefore， photocatalyst can be useful tool to control oral bacterial flora. Finally， photocatalyst can be useful tool for the prevention of oral diseases.

The aim of this report is to summarize the research of application of photocatalyst for dental research and to find out the future prospective for photocatalyst to dentistry.

1 Martials and Methods

1.1 Search Strategy

Electronicdatabase，PubMedwassearchedfor eligible studies. Abstracts were reviewed， and full-text articleswereinspectedforinclusioncriteria. The referencelistsfromreviewedstudieswerealso examined to seek additional sources.

Keywordsearchtermsusingmedicalsubjectheadings and text words included. Search details were asfollows：（“photocatalyst ”[MeSHterms] or “photocatalyst ”[all fields]） and （（“dental ”[MeSH Terms] or “dental ”[all fields]） or （“oral ”[MeSH terms] or “oral ”[all fields]））（“photocatalyst ”[all Fields]） and （（“dental ”[all fields]） or “oral ”[allfields]））. Studies were included if they were written in English.

1.2 Study Selection

An initial search for studies using saliva for the evaluation of periodontitis generated 46 articles. During thepreliminaryanalysis， 14 studieswereexcluded because they were not concerned with dental research. After reviewed thearticles， two reviewarticles were removed. Finally， 29 articleswereindependently reviewed and summarized by two authors （Nomura Y. and Hanada N.）.

1.3 Classification

According to the review of the abstracts full-text articles，articleswereclassifiedbasedonthe applicationofphotocatalystfordentalmaterials， clinical dental practice or dental research into 3 major categories： antibacterialeffectonnoveldental materials， dental materials （implant， resin， others and dentalpractice （toothwhitening/bleaching）. After classification， the articles were summarized.

2 Results

Atotalof 46 articleswerehitonthePubMed database， 29 were included for the review. According totheclassificationsdescribedinmaterialsand methods， 6 articleswereclassifiedintoantibacterial effect of novel dental materials， 9 were implant， 4 were resin， 3 were other dental materials and 5 were tooth whitening/bleaching.

2.1 Antibacterial effect of novel dental materials Sevenarticlesweremettherequirementfor antibacterial effect of novel dental materials. Without one article[10]， photocatalysis activity leaded resulted in anti-microbial activity （Tab.1）. One article investigated thechangesof bacterialinnercellmoleculeswhich leaded the mechanism of the antimicrobial activity of photocatalyst[11]. Onearticlehadshownthatcombinationofhydroxyapatite，whichisthemajor componentoftoothenamel，andTiO2 actedforremineralizationfor surface[12]（Tab.1）.

2.2 Applicationofphotocatalystfordental materials

2.2.1 Dental implant

Dental implants involve the insertion of synthetic roots into the jawbone where teeth have been lost and thefabricationof artificialteeththereon. Themajor materials used for the dental implant is now titanium. At initialstage， antibacterial activity of photocatalyst coating or surface treatment of titanium were confirm- ed [16-19]. Otherthanantimicrobialactivity，effectof photocatalysis on bone formation was also investigat- ed [20-24]（Tab.2）.

2.2.2 Resin

Poly methyl methacrylate is often used in clinical dentalpractice. Itusedasdenturebase，provisional restoration，artificialteethondenturebaseetc. Two studiesinvestigatedtheantimicrobialeffectof photocatalyst on resin [25-28]. One article investigated the effectofphotocatalystonthecuringreaction [26]（Tab.3）.

2.2.3 Other dental materials

By the tooth extraction， wearing ill fit denture， or inflamed gum disease， the gum attached to the denturesurfacebecomessensitive. Tissueconditioneris temporally used on the mucosal surface of the denture until the inflammation of gum is healing. Two articles investigatedtheantimicrobialeffectof photocatalyst applyingtissueconditioners[29-30]. Onearticle investigated the effect of the photocatalyst containing toothpaste[31]（Tab.4）.

2.3 Dental clinical procedures

Fordentalclinicalprocedures， 6 articleswere applied photocatalyst for whitening/bleaching （Tab.5）. Teeth whitening involves bleaching teeth to make them lighter. Itcan't make teeth brilliant white， butitcan lighten the existing color by several shades. At initial stage，threearticlesinvestigatedthedegradationof pigments by photocatalyst[32-34]. Then materials used for the teeth bleaching were modified[35-36].

3 Discussion

Inthisarticle，wesystematicallyreviewedthe articleconcerned with photocatalystapplyingfor the dental research and clinical practice.

In the treatment of oral diseases， lesions in oralcavity? can? be? directly? accessible.? Complex? drugdelivery? systems? are? not? necessary.? In? addition，dentistry? has? various? advanced? dental? materials.Restorative? and? prosthetic? treatments? are? major? dentalpractice.? Fine? dental? materials? are? indispensable? forthese? treatments.? These? two? major? characteristics? ofdentistry? make? the? application? of? novel? materials? forthe dental treatment easy. All of the articles reviewed inthis? study? are? concerned? with? the? dental? materials.Among the 29 articles reviewed in this report， 10 wereconcerned with dental implant.

Dental? implant，? which? is? an? artificial? root? of? theteeth，? consisted? of? titanium.? Therefore，? applicationphotocatalyst? for? the? surface? of? the? implant? istechnically easy. Biocompatibility and antimicrobe areimportant? factors? for? the? prognosis? of? dental? implant.The prognosis of dental implant mainly depends on theinfection? in? the? gap? between? dental? implant? andsupportive? tissue[37].? It? is? called? as? peri-implantitis? orperi-implant? disease.? Peri-implantitis? has? become? aglobal burden[38-39]. Prevalence of peri-implantitis were1%? to? 47% [40] ， 29.48%[41]or? 80%[42].? Eight? articlesout? of? ten? concerned? with? dental? implant? wereinvestigated? antimicrobial? effect? of? the? photocatalyst.Photocatalyst? effectively? reduced? bacterial? adhesion[17-19，21，24]，? biofilm? formation[16].? After? insertion? ofdental? implant? into? the? jaw? bone，? irradiation? to? obtainthe? photocatalystic? effect? is? impossible.? However，complete sterilization is indispensable during the dentalimplant surgery. Bacterial contamination largely effectson? the? prognosis? of? dental? implant[43].? Even? the? sorttime? periods，? contentious? antimicrobial? effect? ofphotocatalyst? may? effectively? work? for? the? preventionof contamination during the surgery.

Four? articles? reported? the? application? ofphotocatalyst? for? resin.? In? dental? practice，? PMMA? isfrequently used. One of the characteristics of PMMA is hydrophilia. Absorbency of complex oral fluid makes theprothesisandprovisionalrestorationsfilthy. In addition， microbes colonize on the surface of PMMA. Coating photocatalyst on the surface of resin effectively works for the sanitization of the dental materials [27-28]. Inaddition，itpromotesthecuringreactionsof PMMA[26].

Thereweretwoarticlesconcernedwithtissue conditioner [29-30]. Tissue conditioner is a denture lining material for inflated gum that support the denture. The majorcomponentof tissueconditionerisageltype PMMA. Even through application of tissue conditioner is temporal， it is easy to be staining， coloration， stinking andmoulding. Includingphotocatalystintissue conditionerhasantifungaleffect. Untilthe inflammationofgumheeling，patientsvisitdental clinic. Irradiation can be applicable during the patient visitdentalclinics. Effectofphotocatalystmaybe desirable to keep tissue conditioner clean.

Whitening/bleaching the discolored teeth improve the quality of life of the patients[44]. Hydrogen peroxide isthemajorreagentforwhitening/bleaching. Photocatalystenhancestheremovalof thestainon toothsurface[32-34]. Itisalsoeffectivefordiscolored teethbytetracycline[35]. Takingtetracyclineduring fetusorinfantagepigmentssedimentinnerteeth[7]. Photocatalyst containing whitening/bleaching materials are already packaged and commercially available. As UV irradiation is incapable for human oral cavity， the research concerning whitening/bleaching were focused on the safety and effectiveness of the light source[32-34].

Several articles with application of photocatalystfordentalresearchanddentalclinicalpractice. However， information is not enough. Photocatalyst is a usefultoolfordentalclinicalpractice. Forthe application of photocatalyst for dental clinical practice， accumulationof evidencesandcommercializationof dental materials are necessary.

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（編輯：董偉）