光催化剂在牙科研究中的应用进展

野村义明　花田信弘　刘艳飞

摘要：光催化劑有两个主要作用：有机化合物的降解和超亲水性，这些作用使其具有抗菌和自清洁的效果。目前，光催化剂已经被应用于医学临床实践。两种主要的口腔疾病（龋齿和牙周病）影响着全球几十亿人，而治疗口腔疾病则可以直接接触到口腔内的病灶。牙科领域会使用到各种先进的牙科材料。因此，光催化剂可以成为牙科临床实践的有用工具。本文综述了光催化剂在牙科研究中的应用研究，并展望了光催化剂在牙科研究中的未来前景。关键词：光催化剂；牙科临床实践；牙科研究；牙科材料

中图分类号：O 644文献标志码：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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（編辑：董伟）