David R. Radford, BOS, PhD, FDSRCS, MRD-

Scanning ElectronMicroscopy and Energy

Dispersive Analysis ofMachined Denture Base

Surfaces

lohn D. Waiter, BDS, DDS, FDSRCS (Ed)"

Stephen /. Chaliacombe, EDS, PhD, FDSRCStEd), FRCPath"'

UMDS, Gays Dental HospitaiUniversity of LondonLondon, United Kingdom

To relate the characteristics of rotary instruments to the surfaces theyproduce, acrylic resin, Molloplast B, and Novus were investigated withenergy dispersive analysis and scanning electron microBCOpy (secondary andbackîcatter images) before and after machining. The chemical compositionof cutting instruments, material surfaces, and residues was identified.Machined debris embedded in Molloplast B after machining with theMolloplast stone was found to contain a mean lead content of 45%. Highconcentrations of barium sulphate were discovered on the arborband-machined surface of Novus. These differences were related toclinically appropriate instrumentation, and, therefore, biocompatahilitystudies that intimately relate to the in vivo situation should be considered fornew materials. Int ¡ Prosthodont I997;W:222-23O.

The physical properties of denture base materialsincluding soft lining materials have been widely

investigated.'"^ These materials as denture bases areresponsible for retention and stability of removableprostheses in a potentially hostile environment andshould have smooth surfaces that both minimisecolonisation by dental (denture] plaque, and alloweasy cleaning. The surface ofthe material should becapable of adjustment with rotary instruments in thelaboratory and clinic. Some work has been directedto an examination of the denture base surface aftermachining."'^ FHowever, there does not appear tohave been any investigation relating the surface pro-duced to the design of the rotary instrument, nordoes there appear to have been an investigation of

'Lecturer. Department ol Prosthetic Dentistry."Reader and Heat/ of Department. Department of Prosthetic

Dentistry.'"Prolessor and Head of Department. Department of Oral

Medicine and Pathology.

Reprint requests: Dr David R. Radford, Department ofProsthetic Dentistry. Floor 21. Guys Tower. Guys DentalHospital, London Sil 9RT. United Kingdom.

the machined swarf produced or the wear debris ofthe rotary instrument. Scanning electron microscopy(SEM] and confocal microscopy in combination canprovide readily interpretable images, as well as thequantification of surface roughness. However, noidentification or quantification of the chemical con-stitutes of the adjusted surface or machining debriscan be provided by these techniques.

All methods of microscopy rely upon interpreta-tion ofthe image to yield useful information. Sincethe inception of simple single-lens microscopes inthe 15th century, numerous techniques have beendeveloped to aid in the interpretation and yield ofinformation. Despite the high resolution of theelectron microscope and the topographic widefocal field of the SFM, neither the transmissionelectron microscope or the SEM routinely usechemical information to provide additional infor-mation from the image. Energy dispersive x-rayanalysis (EDX|, which was developed in conjunc-tion with electron microscopy, can provide chemi-cal data to assist with image interpretation.

The purpose of this study was to use secondaryand backscatter SEM images and EDX to:

The Internalionaf Journiil oJ ProslhocforHii 222

1. Examine the surface features and compositionof two types of burs, an abrasive band and anabrasive stone

2. Examine the surfaces of heat-polymerisedacrylic resin after machining, with two soft lin-ing materials prior to and after polymerisationand subsequent to machining

3. Investigate the occurrence and composition ofdeposits left after machining of the denturebase materials

4. View the machined surfaces to relate them tothe cutting tools used

Materials and Methods

Denture Base Materials

Poiy(methyl methacrylate) is the most widely useddenture base material. Trevalon (Dentsply, DeTreyDivision, Weybridge, UK), a heat-polymerisedacrylic resin, was selected as a typical material.Two different types of soft lining materials werechosen because of their possible differences in sur-face quality. Molloplast B (Karl Huber, Ettlingen,Germany) is a heat-polymerised poly(dimethylsiioxane) material often considered to be the mostsatisfactory of the resilient lining materials. Theother lining material chosen was Novus (FHygenic,Akron, OH}, a heat-polymerised polyphosphazineelastomer introduced in 1990.

Rotary Instruments

The four rotary instruments used in this study were:

1. A cross-cut steel bur (Meisinger vulcanite cutterISO 310 104 155172...060, Hager and Meisin-ger, Dusseldorf, Germany)

2. A fine diamond pattern cut tungsten carbidebur (Meisinger laboratory carbide cutter ISO500 104 274140...060, Hagerand Meisinger)

3. A Molloplast stone (Bracon blue, size C, Bra-con, Hurst Green, UK)

4. A medium arbor band (13-mm diameter, sili-con carbide 80-grit, Bracon, Hurst Green, UK|

Preparation of Representative Surfaces

Samples were processed against glass, one area wasleft as a control, and two areas were machined usingdifferent rotary instruments. The surfaces were as fol-lows: ÍÍ,) Trevalon (a) as processed, (b) machinedwith a tungsten carbide bur, and (c| machined with asteel bur; (2) Molloplast B (a) as processed, (b) ma-chined with a Molloplast stone, and (c) machined

Machined Denture Base Surfaces

with an arbor band; and (3) Novus (a) as processed,(b) machined with a tungsten carbide bur, and (c)machined with an arbor band.

The choice of instrument to machine individualsurfaces was governed by normal clinical practice.Not all materials would be amenable to machin-ing by a standard set of instruments, for exampleMolloplast B is not machined effectively withcross-cut steel burs.

All materials were processed according to manu-facturers' instructions. The speed of the handpiecewas controlled at 15,000 rpm (Schick dental motorand handpiece C2, Schick Dental, Schemmerhosen,Germany), The procedure for machining the surfaceswas standardised by ensuring the rotary instrumentwas cutting only in one direction along the surface ofthe sample. Minimal pressure was applied similar tothat used in clinical practice when making fine ad-justments to the surface of a denture base. No at-tempt was made to mechanically standardise ormeasure the pressure applied by the cutting instru-ment. The time of machining could not be standard-ised because of the differing periods required for theinstruments to cut the various materials.

Preparation of the Samples for EDX Investigation

Thirty samples, 10 mm square and 2 mm thick,were produced for each material. Each sample hadthree surfaces: the control surface (as processedagainst glass) and two machined surfaces. After thestudy surfaces had been produced, specimenswere randomised by a colleague not associatedwith the study assigning a number to each sample(1 to 30). Each sample was then air dried at roomtemperature. Ten samples of each material weremounted on aluminium stubs using double-sidedmounting tape and were carbon coated (EmscopeSC 5000 sputter coater, Emitech, Ashford, UK).

Samples were viewed by SEM (Hitachi S-520,Hitachi PLC, Wokingham, UK). The EDX analysis(Kavex Delta class—^Energy dispersive spectroanalyser, Kavex Instruments, Milton Keynes, UK)was undertaken at an accelerating voltage of 13 kVunless a very heavy element was being investi-gated, when the accelerating voltage was in-creased to 25 kV. All spectra were recorded for aperiod of 100 seconds. The interpretation of thespectra was assisted by software (Micro EDS,Dapple Systems, Tumwater, WA) that allowed asemiautomatic method of quantifying individualspectra. The analysis was undertaken at a magnifi-cation of X 4,000, although the photomicrographsthat had areas of particular interest (highlightedwith delineating boxes) were photographed at a

' 10, Number 3, 1997 223 The International lournal of Prostlioiioiilics

Machined Denlurt

Fig 1 Scanning electron micrograph of the tungsten carbidebur specimen. Note the sfiarp cutting edges witb spiral rake,(Original magnification x 25; field width = 36 mm.)

Fig 2 Scanning electron micrograpb of the steel bur speci-men. Note the swarf from the cross cutting of the bur,(Original magnification x 25; field widtb 3.6 mm,¡

reduced magnification to assist in interpretation.Secondary images and backscatter images wereboth recorded to enhance data capture. Secondaryimages record topographic detail well, whereasbackscatter images allow areas containing ele-ments of high atomic number to be readily identi-fied.

Results

The results are presented as selected secondaryelectron images supported by backscatter imagesand EDX spectra where appropriate.

No statistical analysis has been undertaken asthis is not appropriate to the descriptive nature ofwork undertaken with SEM, However, all imageswere made using a standardised magnification at aset working length. The EDX analysis reduces thesubjectivity of the interpretation of the photo-micrographs.

Machining Acrylic Resin With Tungsten Carbideand Steel Burs

The SEM examination of the two burs showed con-siderable differences in their cutting edges. Theblades of ihe tungsten carbide bur were sharp andwell defined, giving the appearance of having beenlapped after sintering (Fig 1), The cutting edges ofthe steel bur appeared to have been less accuratelymachined, and adherent swarf had been left aftercross cutting and prior to hardening of the steel(Fig 2), The cutting geometry of the two types ofbur was different. The tungsten carbide bur had aspiral rake angle of 16 degrees with a negative ra-dial rake on its cutting faces. The steel bur hadstraight flutes with a positive radial rake to the cut-ting faces. Energy dispersive x-ray analysis of thetungsten carbide bur showed that it consisted oftungsten with smaller amounts of cobait and potas-sium. The steel bur was shown to consist largely of

The Iniernätional lournat of ProsthoclorKU 224 Volume 10, Number 3. IW7

Machined Demure Base Surlai

Fig 3 Scanning electron micrograph ol the acrylic resin.S = formed by the cross cut steei bur; T - formed by the tung-sten carbide bur. Note the surface fracture and smeared sur-face formed by the steei bur. An evenly textured reguiar sur-face with some smearing was formed by the tungsten carbidebur. (Original magnification x 250: fieid width = 0,36 mm,)

Fig 4 Scanning electron micrograph ol the arbor band,(Original magnification x 25: field width - 3,6 mm,)

iron with small inclusions of tungsten and potas-sium.

The tungsten carbide bur produced a consider-ably smoother surface than the steel bur whenused to machine acrylic resin. Tbe surface pro-duced by the steel bur was both fractured andgrooved; it also showed signs of smearing. Thetungsten carbide bur produced an evenly texturedsurface with slight grooving only (Fig 3), When thetungsten carbide bur was used to machine Novus italso produced a smooth surface.

Machining With the Arbor Band

Examination of the surface of the arbor bandshowed tbat if consisted of tbe abrasive with a ma-trix of cement interposed to bond the abrasive gritsto the band (Fig 4), Much surface debris of the un-used bands was observed. When Molloplast ß andNovus were machined using the arbor band, both

the resultant surfaces were rough and showed evi-dence that the surface had been torn. The cuttingsurface of the arbor band consisted of projecting,irregularly-shaped abrasive grits each measuringapproximately 0,3 mm across. A powder-like de-posit was seen on the machined Novus (Fig 5a).ßackscatter imaging showed the deposit to have ahigh contrast (Fig 5b), This differed from the non-polymerised surface of Novus, where, on backscat-ter imaging, the material had a high content of anevenly distributed material with a high atomicnumber. Energy dispersive x-ray analysis showedtbat this material was barium sulphate.

Beads of material have been previously de-scribed in polymerised Novus^; these were occa-sionally seen in this study. The bead material wasshown to contain phosphorus, barium, and smaileramounts of sulphur, calcium, chlorine, and cop-per. It was not possible to establish the presence of'inclusion material' as previously reported,*^ The

'10, Number 3, 1997 225 The International Jojrral of Proithodonlics

Machined Denture Base Surface R.iiiiord et al

Fig 5a Scanning electron micrograph ot Novus surface ma-chined by arbor band. Note the tine surtace deposit, ¡Originalmagnification x 10DO; fieid width - 90 mm,)

Fig 5b Scanning electron micrograph of the bacliscatterimage of Fig 5a. Note the high contrast ot the surface depositand the box ior analysis {Fig 5c), {Originai magnificationX 1000; fieid width ^ 90 mm.)

0.021/10/95

Fig 5c Energy dispersive x-ray anaiysis of surface depositof poiynerised Novus. Elements were identitied as phospho-rous, suipfiur, and barium.

3.02/6/95

Sk I"

Fu scale 143 12,76 KeV

Fig 5d Energy dispersive x-ray anaiysis ot the surface o(the polymerised nonmachined Novus specimen. The poly-merised Novus eiements were identified as phosphorous, sul-phur, and banum. Nole thaf the same eiements are fotjnd intfie spectra of Fjgs 5c and 5d but in different proportions.

backscafter examination of fhe surface deposiffrorn machining by fhe arbor band revealed muchmaterial of high confrasf (Fig 5b), The EDX analy.sis(Fig 5c) showed fhaf this deposit confained a highconcentrafion of barium sulphafe, far in excess offhaf found on the control surface of nonmachinedpolymerised Novus (Fig 5d).

Machining With the MoHoplasf Stone

Examination of fhis rotary instrumenf revealed anopen, parlly crystalline matrix containing abrasivegrifs of variable shape and size and with irregularcutfitig edges, Af low magnificafion the stone wasseen to have an open structure wifh large voids of

226 Volume 1U, N'jmber 3, 1997

Machined Denture aa

Fig 5 Scanning eleotron micrograph of me Molioplast stonespecimen. Note the open structure. (Ongmal magnificationX 25: tieid width - 3.6 mm.)

Fig 7 Scanning eiectron micrograpli ül liie Moliopiast atonespecimen. Note the bcx tor EDX anaiysis of the cutting edge.(Original magnification x 1000; lieid width - 90 mm.)

up to 1 mm. The matrix appeared to contain smallparticles of abrasive varying from 50 to 200 \.\m (Fig6). At higher magnification, the matrix exhibited afine crystalline structure. Sharp cutting edges wereseen on some of the larger abrasive particles in thematrix (Fig 7), and these edges were subjected toEDX analysis. Backscatter imaging of the stone athigh magnification disclosed discrete particles witha high contrast, particularly on the sharp cuttingedges. The EDX analysis of these cutting edgesshowed a spectrum consisting of silicon, aluminium,calcium, and lead. However, when the high contrastparticles were subjected to EDX analysis, it was ob-served that the major constituent was lead, withother elements, including aluminium, silicon, cal-cium, cobalt, and copper, in much smaller qualities.

Backicatter examination of the polymerised sur-face of Molloplast B after it had been machined bythe Molloplast stone showed the presence of highcontrast adherent crystalline particles. Their highcontrast indicated that they contained elementswith a high atomic number, and EDX analysis ofthese particles showed a relatively high lead con-tent averaging 45% (Fig 8). On further backscatterexamination it was observed that these high con-trast particles of up to 10 pm in size were a rela-tively common finding, although no quantificationwas attempted. The surface produced on machinedMolloplast B was even but with a pronouncedwaved pattern.

0.028/8/95

Fig 8 Energy dispersive x-ray anaiysis of tiie surface of rna-chined Moliopiast B. Elements were identitied as aiuminium,silicon, iead, potassium, calcium, cobalt.

Discussion

This study shows the wide variation in clinically ap-propriate rotary instruments used in prosthetic den-tistry, as well as the surfaces of denture base materi-als after machining. The EDX analysis combinedwith secondary electron imaging and backscatter

O, Number 3, T997 227 The Irlernalional lournai of Pro6tliodorti(

Macliined Denluri

examination proved to be a valuable investigativetool that produced interesting and unsuspected re-sults of the chemical composition of the machinedswarf of the surfaces on ihese materials.

Backscatter images are not widely reported inthe dental literature. The image is derived frombackscatter electrons that are high-energy electronsderived from the primary electron beam as it inter-acts with the nucleus of a target atom. They maybe scattered in any direction with little loss of en-ergy, and as these electrons are much more ener-getic than secondary electrons, they can escapefrom a greater depth within the sample. Therefore,compared to the image produced by secondaryelectrons, the backscafter image does not carrymuch topographic information. The higher theatomic number of an atom, the more positive thenucleus and the more likely an interaction wil loccur with the primary electron beam, resulting inthe production of backscatter electrons. In conse-quence, the backscatter image carries some addi-tional information relating to sample composition.On viewing the backscatter image, the surfacetopography is poorly resolved. However, elementswith high atomic numbers, eg, lead with an atomicnumber of 82, appear as bright areas of contrast.

The photomicrographs of the new and unusedtungsten carbide burs and steel burs showed a con-siderable contrast in the condition of their cuttingedges. The teeth of the tungsten carbide bur weresharp, well defined, and smooth, and appeared tohave been accurately ground. Because of the ex-treme hardness of tungsten carbide, its sharp cut-ting edges must be produced by grinding themusing a diamond-impregnated wheel.' The steelbur had less satisfactory cutting edges that hadbeen machined prior to hardening. The adherentswan^ left by machining the cross cuts is clearly vis-ible in Fig 2. The negative radial rake angle on thecutting faces of the tungsten carbide bur was ne-cessitated by the relative brittleness of this mater-ial. A positive radial rake angle on tungsten car-bide tools is likely to weaken the cutting edges andresult in fractures.^ This likelihood has been recog-nised in the design of tungsten carbide burs forhigh speed air rotors.' Although the extreme hard-ness of tungsten carbide results in a sharp long lifefor the bur, in these studies the materials cut werecomparatively very soft, and under such conditionsthe steel bur is likely to remain sharp for a long pe-riod. However, fillers in plastics can increase cutterwear; for example, high rates of wear occur whencutting plastic containing abrasive fillers such asfibre glass. Interestingly, Atkinson^ questionedwhether the principles used to design cutters for

engineering applications should apply i ' the de-sign of burs that are used to cut teeth, which areessenlialiy crystalline in structure, and he con-cluded that there is a complex relationship be-tween rotary instrument and cutting performance.

Over the last 10 years a greater emphasis hasbeen placed on infection conlrol, and it is wellrecognised that corrosion occurs when autoclavingsteel cutting instruments."* Corrosion is a result ofan electrochemical reaction caused by the pres-ence of oxygen and water in the autoclave formingiron hydroxide that subsequently turns to a black-ish green tarnish with incipient oxidation by air.The steel bur is likely to be attacked by corrosion,and this is seen regularly in clinical practice.Numerous Studies have shown that the joint be-tween the steel shank and tungsten carbide head ofthe bur is also attacked by corrosion during auto-claving. This is a particular problem with small di-ameter burs used in air rotors,^' although no detri-mental effects on tungsten carbide laboratorycutters have been reported in the literature.

The manufacturer of the steel bur used in this in-vestigation stated that it was made from 'selectedtungsten vanadium steel.' However, the initial EDXanalysis indicated that only iron was present. Thiswas probably because the tungsten and vanadiumcontent was too low to be detected by the EDXanalysis. Specific analysis of small inclusions in thesteel bur that the backscatter image showed to be ofhigh contrast revealed the presence of tungsten.Reference to British Standard 4659'- shows that thespecification permits some low tungsten tool steelsto contain as little as 2% tungsten and 0.1% vana-dium. Carbon was screened out of the analysis, asthis is the element used to make samples electronconductive for EDX analysis. The presence ofcobalt in the tungsten carbide bur was to be ex-pected, as cobalt is used in the multicomponentsintering process that bonds the brittle green sinterof the bur head into a hard, usable cutting tool.^

Although the tungsten carbide bur consistentlyproduced a smoother surface than the steel bur, thesurfaces generated by the steel bur may be consid-ered by some dentists to be within limits of routineclinical acceptability. Smoother finishes couldprobably have been obtained using steel burs ifthey were redesigned and more attention given tomanufacture. However, this would add to their costand may not be justified because of poor corrosionresistance during disinfection or sterilisation.

The cutting action of the arbor band was similarto that of the Molloplast stone in that both groundthe workpiece. Smoother finishes would have re-sulted if they had been manufactured using smaller

The Inlemationai Journal of Prosthodonti< 228

'.d Denture ß.isc Surfaces

abrasive grits and if the Molloplast stone had a lessopen structure. However, the rate of material re-moval would have been slower, and the cuttingsurfaces of the tools would have been more subjectto loading with swarf.

The Molloplast stone was seen to have voids aslarge as 1 mm in diameter and extending over thecutting surface as well as permeating through thestone. The voids can be introduced in the manu-facture of the stone by inclusion of material that isburned out during the manufacturing process, thuscreating an open structure. An open structure is re-quired to reduce clogging of the stone with swarffrom the cut surface, thereby reducing the need forregular cleaning during cutting. It also promoteswear of the stone which, in addition to reducingclogging, ensures that the cutting edges of thestone are renewed and remain sharp.

Wear debris from the Molloplast stone, whichwas shown to contain lead, was widely distributedand adherent to the machined surface of theMolloplast B, Although debris can be removed bypolishing, in practice a dentist is unlikely to polishthe adjustment if it is on the fit surface of a prosthe-sis. To remove the wear debris deposited by theMolloplast stone it may be necessary to clean thefit surface by ultrasonic means or rigorous wash-ing. However, this may produce other problemssuch as separation of the silicone lining from theheat-processed acrylic resin base. It is well docu-mented that separation of the lining material fromthe base is a major cause of failure of silicone soft-lining materials.'^

The other significant finding was the very highbarium sulphate content of Novus after arbor bandmachining. Although barium sulphate is used fordiagnostic purposes in radiologie medicine, its ca-sual inhalation by technician or clinician or inges-tion by the patient must be of concern. Studieshave shown that poly(methyl methacrylate) debrisimpacted in the tissues can cause inflammationleading to granuloma formation. Lazarus et a l ' "showed that the inflammatory response in the ratsubcutaneous pouch model with poly(methylmethacrylate) and 10% (wt/vol) of barium sulphatecaused a greater inflammatory response than thatcaused by poly(methyl methacrylate) debris alone.Because of these toxic reactions to barium sul-phate, it is necessary to consider carefully the im-portance of the inclusion of the substance in a softlining material. The authors are not presentlyaware of any heat-polymerised acrylic resins com-mercially available in the UK that contain barium

sulphate to make them radiopaque, Novus is nolonger commercially available. However, if bariumsulphate is to be included in soft lining materialssolely for its radiopacity, the requirement for a softlining material to be radiopaque should be recon-sidered, and its use in such volumes must be care-fully evaluated.

Conclusions

This investigation used energy dispersive x-rayanalysis to study denture base materials before andafter machining with clinically appropriate rotaryinstruments. Within the parameters of the study de-sign, the following conclusions may be made:

1, The cutting blades of the tungsten carbide burwere superior in edge sharpness and finish tothose ofthe steel bur,

2, The arbor band and Molloplast stone were rela-t ively course grinding instruments. TheMolloplast stone had an open structure to avoidclogging with swarf; the arhor band used largeabrasive grits to achieve a similar effect,

3, After machining Molloplast B with a Molloplaststone, energy dispersive x-ray analysis showedthat the wear debris had a high lead content(45%).

4, After machining with the arbor band, a pow-der-like debris was left on the Novus surface,energy dispersive x-ray analysis showed thatthis debris was barium sulphate. Barium sul-phate was found to be evenly dispersed in thenonpolymerised and the polymerised Novusprior to machining,

5, Biocompatablity studies of dental materialsshould be extended to include the biocompat-ablity of any substances produced after ma-nipulation of the material clinically or in thelaboratory,

6, The techniques of scanning electron mi-croscopy using backscatter imaging (not onlysecondary electron imaging) with energy dis-persive x-ray analysis form an additional proto-col for investigations of the surfaces of dentalmaterials.

Acknowledgments

The authors acknowledge the lechnical assistance of Mr K,Brady of the Electron Microscope Unit, Guys campus. UnitedMedical and Dental Schooli, London, and Mr |. D, Radford, for-merly the principle lecturer of the Department of MechanicaiEngineering at Brighton Poiytcrhnic, Brighton, Sussex, UK.

: 10, Number 3, 1997 229 The Irrernatioral tournai of Frosthodorlics

Machined Denluri

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Í iterature Abstract

The impact of edentulous ness on food and nutrient intake

Tooth loss is likely to reduce masticatory ability, leading to detrimental changes in foodchoices, which may in turn increase the risks of certain systemic diseases. This report com-pared 49,501 maie edentuious and dentate heaith professionals with respect to intake ofspecific nutrients and foods selected on the basis of their perceived ease of chewing andpostulated associations with systemic diseases. This report also longitudinaliy evaluated theeffect of tooth ioss on change in diet, in 1986 and 1990, dietary questionnaires were mailedto the participants who had been recruited for the Health Professionais Foilow-Up Study, intheir anaiyses, the authors compared intake of fruits, vegetables, and calo rie-adjusted nutri-ents between edentulous participants and participants having 25 or more teeth using anaiy-sis of covariance. Ali analyses were controlled for the potential confounding effects of age,heaith profession, smoking status, and exercise. Results trom the survey indicated that in-take of vegetables, dietary fiber, crude fiber, and carotene were significantiy iess among theedentulous participants, and caiorie intake, cholesteroi, and saturated fat were significantlygreater among the edentulous participants. Men who lost five or more teeth between 1966and 1990 tended to reduce truit and vegetable intake compared with men who had lost noteeth, with significantly greater reduction in consumption of appies or pears. The authorsconcluded that the differences in diet between edentulous and dentate participants couid in-crease the risks o( cancer and cardiovascuiar disease, Specificaily, they expect that the 1 gdifference in dietary fiber intake between the dentate and edentuious could lead to a 2% in-creased risk of myocardiai infarction. As the authors point out, although the increase inhealth risks resuiting from tooth ioss nay be smail, the implications could be great, as alarge segment of the population wouid be affected,

Joshlpura KJ, Wlllett WC, Douglass CW. ó Am DenMssoc 1996;127|4):459-467. References: 22.Reprints: Dr KaumudI J. Joshipura, Department of Oral Health Policy and Epidemiology, Han/ard Schoolof Dentai Medicine, IBS Longwooa Avenue, Boston, Massachusetts—R/c/iard/I, Seals. Jr, DDS, MEd,MS, Department ol Prosthoäontics. The University ol Texas Health Science Center at San Antonio

The Internarional Journal ol Prosthodontics 230 Volume to. Number 3. 1997