40 A.Sivakumar and Ashima Valiathan

Dental Ceramics and Ormocer Technology - Navigating the Future!

A. Sivakumar and Ashima Valiathan

Department of Orthodontics.Manipal College of Dental Sciences, Manipal

The use of ceramics in dentistry is a multi-billion dollar industry, involving many different proprietary materials.Current applications of ceramics in dentistry include fillings, crowns, veneers, implants and dental brackets.Dental pins are devices which are inserted into the mandible and are used to hold prosthetic teeth in place.They are usually made from bioactive materials such as low silica glass or hydroxyl apatite. They are usedbecause of their ability to bond to biological tissues permanently. Composites such as ceramic filled polymersand short fiber reinforcements are also being used. Ormocer is one such material. Ormocer materials containinorganic-organic copolymers in addition to the inorganic silanated filler particles. It is synthesized through asolution and gelation processes (sol-gel process) from multifunctional urethane and thioether(meth)acrylatealkoxysilanes. Ormocers are described as 3-dimensionally cross-linked copolymers. Ormocer was formulatedin an attempt to overcome the problems created by the polymerization shrinkage of conventional compositesbecause the coefficient of thermal expansion is very similar to natural tooth structure.Ceramics in dentistry willbe explored and challenges facing the ceramics community will be emphasized. The key words for dentistrymay soon be "fast" and "ceramic. ... And that's where ceramics come in.

Introduction

Teeth function in one of the most inhospitableenvironments in the human body. They aresubject to larger temperature variations and pHchanges in the range 0.5 to 8. Add to this, thestresses associated with chewing may vary from20 to about 100MPa. While having to be stablein this kind of environment and able to withstandthe loads associated with chewing, dentalmaterials need to satisfy another criteria,aesthetics. With society becoming increasinglyself conscious, any dental materials that areused in visible locations must have colour andtranslucency as close to natural teeth aspossible. These requirements are almostfulfilled by ceramics, especially porcelainmaterials. Dental ceramics were first used about225 years ago. The first application wasporcelain dentures. Interestingly porcelain is stillquite widely used in dentistry. Currentapplications of ceramics in dentistry includedental restorations, crowns, veneers, implants

and orthodontic brackets. Traditionally, fillingshave been made from silver amalgams. How-ever, resin based filling materials are rapidlygaining in popularity for health and aesthetic rea-sons. These resins are usually filled with 35-85% ceramic fillers such as silicate glasses,colloidal silica or quartz. Despite the advantagesof using ceramic filled resins, these materialsmay be susceptible to wear when applied tochewing surfaces.

Porcelain fused to metal (PFM) materials con-stitute about 75% all crowns. The porcelain usedis a feldspathic porcelain. The porcelain alsocontains varying amounts of crystallized leucite.The amount of crystallized leucite influencesproperties such as strength and thermal expan-sion. Thermal expansion is critical in the manu-facture PFM implants to avoid cracking of theceramic, which could lead to failure during manu-facture or in operation. PFM materials are alsoused for veneers to cover damaged front teethand crowns, although ceramic cores are beingused in some crowns. All ceramic crowns are

Trends Biomater. Artif. Organs, Vol 20(1), pp 40-43 (2006) http://www.sbaoi.org

Dental ceramics and ormocer technology- navigating the future! 41

normally coated with porcelain so that colour andtranslucency can be matched.

Dental implants are used as an alternative tobridges where a tooth has been lost or removed.These are also made of PFM, where abiocompatible metal post made out of a materialsuch as titanium, is anchored into the jawboneand the porcelain crown is affixed to the post.The metal post may also be coated withhydroxyapatite to aid bone bonding and rapidosseointegration. Bioglass posts aresometimes used for this purpose for the samereason.

The most recent use for ceramics in dentistry isorthodontic brackets. The development anddemand for these items has been driven solelyby aesthetics. Polycrystalline alumina is thematerial of choice in this application.

Ceramics for Direct Restorations

Until the moment, all the process of conventionalcomposite resins had been carried throughexclusively in load particles (crystalline quartz,colloidal silica, barium glass) that they composethe diverse types of composite resins. Ever since,the introduction of dimethacrylates in the form ofbisphenol A glycidyl dimethacrylate (Bis GMA),there is not much change in the restorative-adhesive system. This is because the materialhas proved to be relatively reliable for bothrestorative and orthodontic purposes. On theother hand, some recent research indicated that,the bisphenol A component in the structure ofthe monomer BisGMA is suspected of havingan estrogenic effect whereas the Bis GMA itselfhas also been found to be cytotoxic in a numberof cell culture systems [1,2]. In an attempt toovercome some of the limitations and concernsassociated with the traditional composites, anew packable restorative material wasintroduced called Ormocer, which is an acronymfor organically modified ceramic technology.Ormocer materials contain inorganic-organiccopolymers in addition to the inorganic silanatedfiller particles. It is synthesized through a solutionand gelation processes (sol-gel process) frommultifunctionalurethaneandthioether(meth)acrylatealkoxysilanes. Ormocers are described as 3-dimensionally cross-linked copolymers. Theabundance of polymerization opportunities inthese materials allows Ormocers to cure without

leaving a residual monomer, thus having greaterbiocompatibility with the tissues. Ormocer was for-mulated in an attempt to overcome the problemscreated by the polymerization shrinkage of con-ventional composites because the coefficient ofthermal expansion is very similar to natural toothstructure.

ORMOCER Technology

These are organically modified nonmetallicinorganic composite materials. This newmaterial group for restorative dentistry wasdeveloped by Fraunhofer Institute for SilicateResearch, Würzburg, in cooperation withpartners from the dental industry and introducedas a dental restorative for the first time in 1998.The use of ORMOCERs is not limited to compactmaterials for dentistry. These materials havebeen successfully used for a number of yearse.g. in electronics, micro system technology,refinement of plastics, conservation andcorrosion coatings, functional coatings of glassand anti-scratch protective coatings.ORMOCERs can be classified betweeninorganic and organic polymers and have aninorganic as well as an organic network. Themonomeric molecular pre-stages arecharacterised by three structural segments. Theinorganic condensing molecule segment isused to build up the inorganic network. Aninorganic Si-O-Si network is produced throughtargeted hydrolysis and inorganicpolycondensation in a sol-gel process. Theorganically polymerizing molecular segment has(meth)acrylate groups which form an additionalhighly cross-linked network matrix after inductionof a radical-based polymerization. The inorganicpoly-condensation and the organicpolymerization result in the formation of aninorganic-organic co-polymer. The variablelinking segment can largely be modified, just asthe other structural units. The toxicological andallergological potential of this material class isconsidered lower than that of conventionalcomposite restoratives since the acrylates andmethacrylates are silane-bound and thus co-valently linked to the inorganic network. Toimprove handling, dimethacrylates are added todental ORMOCERs. The ORMOCER-basedcomposites are an innovative variation oftraditional composites with organic matrices anddo not differ from these in their practical

42 A.Sivakumar and Ashima Valiathan

application by the dentist. By incorporating fillerparticles a pasty material for dental restoration isproduced. After this production process theORMOCER-based composites have already de-veloped their inorganic network through polycon-densation. The additional organic polymeric struc-ture is established in the cavity through light-in-duced radical-based polymerization of the plasticORMOCER restorative. In order to build a bond tothe tooth, enamel and dentine are conditioned andan adhesive system is used. Effectively the newclass of material combines the surface propertiesof the silicones, the toughness of the organic poly-mers and the hardness and thermal stability ofceramics.

Nature and Characteristics

Laboratory testing of Ormocer materialssuggests a significantly lower wear ratecompared with composites [3, 4, 5]. On the otherhand, Cattani-Lorente et al [6] found that theshrinkage of Ormocer was equal to that of hybridcomposites despite having less filler content.The authors attributed their findings to thedifference in the resin matrix of Ormocer. As aresult, it was suggested that the advantages ofOrmocer include low shrinkage, high abrasionresistance, biocompatibility, and protectionagainst caries [7]. According to the manufacturer(Fraunhofer Institute), this material does notliberate any residual monomer afterpolymerization.

Applications in Dentistry

Direct restoration for all types of cavities [8, 9]Cosmetic veneers,Protective sealant for childteeth, Protective varnish as caries prophylaxisOrthodontic bonding adhesive [10]

According to a recent study, within the initial halfan hour after bonding, the new adhesive Admiracan achieve shear bond strength values that aresimilar to those obtained with Transbond XT. Onthe other hand, as currently formulated, the thickadhesive paste of Admira needed to be forciblypushed into the bracket base during the bondingprocess for it to engage the retention pad.

As a result, it is suggested that for orthodonticusage, the manufacturer should considerreformulating the composition of Admira to makeit into a relatively thinner and more flowable pastethat can readily penetrate the mesh of the bracketbase. Until the more flowable version of this neworganically modified ceramic restorative systemis developed, Ormocer should only beconsidered as potentially useful for bondingorthodontic brackets

Conclusion

With the sprouting of the ORMOCER, it hasbecome fullfilled restoration of a tooth of thedirect form, with lesser time expense and a lowcost. The technique is simple, of easy accessibleexecution and to all the professionals. It isnoticed, still, that the restoration with ORMOCERpresents excellent final burnishing [11, 12], andwith aesthetics, a privileged one in the finalresult, and still it demonstrates a minorcontraction of polymerization (1.88%) andconsequence reduction of microleakage. Having,as main advantages the reduction of thecontraction of polymerization, greater resistanceto the abrasion, better manipulation and finalburnishing, it is believed that the ORMOCERmaterial is an excellent option for posteriorrestorations.

References1. Schedle A., Franz A., Rausch-Fan X., Spittler A., Lucas T., Samorapoompichit P., Sperr W., Boltz-

Nitulescu G. Cytotoxic effect of dental composites, adhesive substances, compomers and cements.Dent Mater 14,429-440(1998).

2. Prati C., Chersoni S., Mongiorgi R., Pashley D.H. Resin-infiltrated dentin layer formation of new bondingsystems. Oper Dent 23,185-194(1998).

3. Watts D.C., Marouf A.S. Optimal specimen geometry in bonded-disk shrinkage- strain measurements onlight cured biomaterials. Dent Mater16, 447-451(2000).

4. Yap A.U., Tan C.H., Chung S.M. Wear behavior of new composite restoratives. Oper Dent 20,269-74(2004).

5. Tagtekin D.A., Yanikoglu F.C., Bozkurt F.O., Kologlu B., Sur H. Selected characteristics of an Ormocer anda conventional hybrid resin composite. Dent Mater 20, 487-97(2004)

Dental ceramics and ormocer technology- navigating the future! 43

6. Cattani-Lorente M., Bouillaguet S., Godin C.H., Meyer J.M. Polymerization shrinkage of Ormocer baseddental restorative composites. Eur Cell Mater 1, 25-26 (2001).

7. Hickel R., Dasch W., Janda R., Tyas M., Anusavice K. New direct restorative materials. Int Dent J 48,3-15 (1998).

8. Hennig A.C., Helbig EB, Haufe E, Richter G, Klimm HW.Restoration of Class V cavities with the Ormocer-based filling system Admira. Schweiz Monatsschr Zahnmed 114,104-14 (2004).

9. Rosin M., Steffen H., Konschake C., Greese U., Teichmann D., Hartmann A., Meyer G. One-year evaluationof an Ormocer restorative-a multipractice clinical trial. Clin Oral Investig 7,20-6 (2003).

10. Ajlouni R., Bishara S.E., Soliman M.M., Oonsombat C., Laffoon J.F.,Warren J. The Use of Ormocer as anAlternative Material for Bonding Orthodontic Brackets. Angle Orthod 75,106-108 (2005)

11. Baseren M. Surface roughness of nanofill and nanohybrid composite resin and ormocer-based tooth-colored restorative materials after several finishing and polishing procedures. J Biomater Appl.19, 121-34 (2004).

12. Yap A.U., Yap S.H., Teo C.K., Ng J.J. Comparison of surface finish of new aesthetic restorative materials.Oper Dent. 29(1),100-4 (2004).

CALL FOR ABSTRACTS

FOURTH INTERNATIONALCONFERENCE ON ETHICAL ISSUES

IN BIOMEDICAL ENGINEERING

APRIL 20 - 22, 2007Brooklyn, New York, USA

Subrata Saha, Ph.D. Conference ChairDepartment of Orthopaedic Surgery & Rehabilitation Medicine

SUNY Downstate Medical Center450 Clarkson Avenue - Box 30

Brooklyn, New York 11203Email - subrata.saha@downstate.edu

Office - (718)-613-8652 Fax - (718)-270-3983http://138.5.102.101/grad/bmephd/Ethics2007.pdf

Abstract submission deadline January 15, 2007