The effect of reinforcement with woven E-glass fibers on theimpact strength of complete dentures fabricated with high-impactacrylic resin

Sung-Hun Kim, DDS, PhD,a and David C. Watts, PhD, DScb

Ewha Womans University, Seoul, Republic of Korea; University of Manchester Dental School,Universtiy of Manchester, Manchester, United Kingdom

Statement of problem. The fracture of acrylic maxillary complete dentures occurs frequently during servicethrough heavy occlusal force or accidental damage.

Purpose. The purposes of this study were to measure the impact strength of maxillary complete denturesfabricated with high-impact acrylic resin and to evaluate the effect of woven E-glass fiber-reinforcement on theimpact strength of the complete dentures.

Material and methods. Preimpregnated woven E-glass fibers (Stick Net) were used to reinforce 10 completedenture bases fabricated with a heat-polymerized high-impact acrylic resin (Lucitone 199). Ten unreinforcedcomplete dentures served as a control group. All specimens were stored in water at 378C for 2 months beforetesting. The impact strengths (J) of the dentures were measured with a falling-weight impact test. The impactstrengths of both groups were compared by a repeated measures analysis of variance (a=.05). The Weibulldistribution was also applied to calculate the cumulative fracture probability as a function of impact strength.

Results. The mean impact strength of the control dentures was 90.0 6 38.1 J at crack initiation, and95.9 6 37.7 J at complete fracture, whereas the impact strength of reinforced dentures was 201.7 6 77.9 J and277.9 6 102.5 J, respectively. Statistical analysis showed that impact strength of the high-impact acryliccomplete denture was significantly increased by the addition of woven E-glass fiber (P\.0001).

Conclusion. The impact strengths of maxillary complete dentures fabricated with high-impact acrylic resin in-creased by a factor greater than 2 when reinforced with woven E-glass fiber. (J Prosthet Dent 2004;91:274-80.)

CLINICAL IMPLICATIONS

This in vitro study showed that the addition of woven glass fibers to denture base acrylic resinsignificantly improved the impact strength. Reinforcement of denture base resin with wovenglass fibers may offer significant advantages in clinical performance of the materials, especiallyimpact strength.

Oneof the most widely used materials in prostheticdentistry is polymethyl methacrylate. Since it wasintroduced to dentistry, it has been successfully usedfor denture bases, artificial teeth, and impression trays.However, the primary problem is its poor strengthcharacteristics, including low impact strength and lowfatigue resistance.1 A study by Johnston et al2 showedthat 68% of acrylic resin dentures break within a fewyears after fabrication. This is caused primarily by impactfailure when the denture is accidentally dropped ona hard surface or by fatigue failure when the denture basedeforms repeatedly through occlusal forces.1,3

aAssistant Professor, Department of Prosthetic Dentistry, EwhaWomans University, Seoul, Republic of Korea.

bProfessor, Biomaterials Science Unit, Department of RestorativeDentistry, University of Manchester, Manchester, United King-dom.

274 THE JOURNAL OF PROSTHETIC DENTISTRY

For maxillary dentures most fractures are caused bya combination of fatigue and impact, whereas formandibular dentures, 80% of fractures are caused byimpact.4,5 In most situations, fractures occur in themidline of the denture base.6 This location of fractureoccurs more often in maxillary dentures than inmandibular dentures.7

Many attempts8-25 have been made to enhance thestrength properties of acrylic denture bases includingthe addition of metal wire.8-11 The primary problem ofusing metal wire reinforcement is poor adhesionbetween wire and acrylic resin. Although severalmethods have been used to improve the adhesionbetween these components, enhancement inmechanicalproperties, such as transverse strength and fatigueresistance, was not significant.10,12-14 Moreover,metal-reinforced denturesmay be unesthetic. Castmetalplates have been used to replace some parts of thedenture. Although metal plates increase the flexural

VOLUME 91 NUMBER 3

THE JOURNAL OF PROSTHETIC DENTISTRYKIM AND WATTS

Fig. 1. Schematic representation of fiber position in dentures. A, Occlusal view. B, Horizontal view.

strength and impact strength, they may be expensive,unesthetic, and prone to corrosion.8,9 Modifications ofchemical structure, by the addition of cross-linkingagents such as polyethyleneglycol di-methacrylate orby copolymerization with rubber, have been attem-pted15,16 and have shown no significant enhancement onstrength properties. Although the impact strength in-creases by the addition of plasticizing ingredients, otherproperties such as elastic modulus, fatigue, and transversestrength are reduced.17 Various types of fiber includingcarbon fiber,3,18-20 whisker fiber,21 aramid fiber,22 poly-ethylene fiber,23 and glass fiber24,25 have been used asa reinforcement. Reinforcement with fibers enhances themechanical strength characteristics of denture bases, suchas the transverse strength, ultimate tensile strength andimpact strength.26 In addition, fiber reinforcement hasadvantages compared with other reinforcement met-hods, including improved esthetics, enhanced bondingto the resin matrix, and ease of repair.17

Several investigators have studied the impact strengthof acrylic resin dentures reinforced with various fibers.Berrong et al22 showed that the impact strength ofpolymethyl methacrylate reinforced with Kevlar fibers wassignificantly enhanced. Braden et al27 and Gutteridge1

observed that the effect of reinforcement with ultra-highmodulus polyethylene (UHMPE) fibers on the impactstrength of acrylic denture base resin and found that thefibers increased the impact strength. Vallittu and Narva28

showed that the impact strength of autopolymerizedacrylic resin was enhanced by reinforcement with electrical(E)-glass fibers. Uzun et al26 concluded that the impactstrength of acrylic denture base resins increased withcarbon fibers, thick Kevlar fibers, polyethylene fibers, andglass fibers. Chen et al29 showed that impact strengthincreased with fiber length and concentration.

Alternatively, Vallittu et al30 found no difference inimpact strength between acrylic resin reinforced with

MARCH 2004

metal wires and resin reinforced with E-glass fibers.Carlos and Harrison31 showed that the impact strengthof the acrylic resin gradually decreased by increasing thepercentage of the untreated UHMPE beads.

Although there are many studies concerning impactstrength of acrylic resin reinforced with various kindsof fibers, all tests used specimen of rectangular acrylicresin and were carried out with the flexed-beam im-pact methods.26,28-31 Also, there are few studies regard-ing the effect of fiber reinforcement on the rubberphase-incorporated high-impact resin. Thus, the impactstrength of a fiber-reinforced high-impact acrylic com-plete denture has not been measured with a fallingweight-impact test method.32-34

The aimof this studywas to examine the effect of glassfiber-reinforcement on the impact strength of high-im-pact acrylic resin maxillary complete dentures. The nullhypothesis was that woven E-glass fiber reinforcementon the high-impact acrylic maxillary complete denturewould not enhance the impact strength of the denture.

MATERIAL AND METHODS

A maxillary cast of an edentulous patient at Man-chester Dental Hospital was selected. Twenty identicalcasts were duplicated with a silicone (Flexistone Plus;Detax, GmbH&Co, KG, Ettlingen, Germany)mold. Arecord base was fabricated with 3 sheets of softenedbaseplate wax (Truwax Baseplate Wax; Dentsply York,Pa). A wax occlusal rim was adapted on the record base,and then the cast with the record base and occlusal rimwas mounted on a semiadjustable articulator. Acrylicresin denture teeth (Anterior 5P, B2; Posterior 16, B2;Senator; Wright Health Group Ltd, Dundee, Scotland)were arranged according to the occlusal rim. Thesurfaces of the labial and buccal flanges were contouredto reproduce the appearance of natural gingiva. Next, 20

275

THE JOURNAL OF PROSTHETIC DENTISTRY KIM AND WATTS

identical wax dentures were duplicated with silicone(Flexistone Plus; Detax, GmbH & Co, KG, Ettlingen,Germany) and flasks.Half (n = 10) were used for controldentures and half were for the test dentures. Highimpact heat-polymerized polymethyl methacrylate(Lucitone 199; Dentsply) was used for the denture basematerial. The acrylic resin polymer and monomer weremixed in accordance with the manufacturer’s directions(powder/liquid ratio of 2.1 g/1 mL). Conventionalpacking and polymerizing procedureswere used. For thetest dentures, a preimpregnated E-glass fiber system(StickNet; Stick TechLtd, Turku, Finland)with a highlyporous polymer, which allowed good impregnationwithacrylic resin, was used. A sheet (60 mm 3 150 mm) ofthe fiber was cut to cover the entire palatal region of thedenture base (Fig. 1, A), and was saturated with a fluidpolymer: monomer mix (1.5:1) of Lucitone 199 acrylicresin. After being sufficiently wetted, the fiber sheet wasplaced in the palatal area during the resin dough packingstage. The precise location selected within the denturebase thickness was on the side of the intaglio surface(Fig. 1, B). The fibers were encased in resin to a depth of1 mm.

The dentures were processed for 9 hours inwater heldat a constant temperature of 73.58C and deflasked. Thethickness of the dentures was measured by a digitalvernier caliper (Mitutoyo, Kawasaki, Japan). Differencesin dimensions were carefully eliminated by trimming

Fig. 2. Schematic diagram of falling-weight impact tester.

276

the dentures to predetermined dimensions, andthen abrasive wheels (no. 00320; Buffalo DentalManufacturing Co, Syosset, NY) and silicone points(Shofu Inc, Kyoto, Japan) were used to finish thedentures. A final high polish was given all the surfaces ofthe dentures with a rag wheel and polishing material(Saphir; Renfert GmbH, Hilzingen, Germany). Thisprocedurewas repeated until 10 control dentures and 10test dentures were fabricated.

All dentures were stored in water at 378C for 2months before testing because there were few studiesabout the effect of 2 month water storage on the impactstrength of acrylic dentures. Testing was carried out at238C 6 0.58C. The impact test was performed witha specially designed apparatus consisting of a plastic tubeand an impactor (Fig. 2). The tube, which guided thedirection of the impactor, had 3 windows to minimizethe resistance between the tube and the impactor. Theimpactor was made with hard wood and had a hemi-sphere end of radius 50 mm and a mass of 0.836 kg.The testing apparatus was placed on a flat surface.The denture was placed on the small table in the tube(Fig. 3). The impactor was dropped onto the denturethrough the tube. When the impactor was released, thestarting height was recorded. If a denture was notbroken with an initial starting height of 60 cm, the testwas repeated from the same height until the denturebroke. If the denture was still unbroken after 40 suchrepetitions, the height was increased to 80 cm. Theenergy absorbed in breaking each denture was calcu-lated using the following formula35:

E ¼ mg +i¼n

i¼1

hi

Fig. 3. Schematic diagram of position of denture.

VOLUME 91 NUMBER 3

THE JOURNAL OF PROSTHETIC DENTISTRYKIM AND WATTS

where E is the Impact strength (Impact energy, J), m isthe weight of impactor (0.836 kg), g is the accelerationof gravity (9.8 m/sec2), h is the height (meters) fromwhich the impactor was dropped, and n is the number ofimpacts.

Two energies were determined for each group.One was the crack initiation energy needed to ini-tiate a crack in denture, and the other was the com-plete fracture energy needed to break the denturecompletely.

After data collection, mean values and standarddeviations were calculated and compared by a repeatedmeasures analysis of variance (a=.05). The data wereanalyzed with statistical software program (SPSSVersion 10.1; SPSS Inc, Chicago, Ill). The Weibulldistribution was also applied to calculate the cumulativefracture probability as a function of impact strength. TheWeibull equation36 used was:

FðSÞ ¼ 1� e�iðS=aÞb

where S = the impact strength at a given point, a = scaleparameter which is the impact strength level at which63.2% of test dentures that failed, and b = shapeparameter. The experimental cumulative failure proba-bility, scale parameter, shape parameter, and cumulativeWeibull probability were determined using a softwareprogram (Microsoft Excel 2000 Version 9.0; MicrosoftCo, Seattle, Wash).

RESULTS

The mean values and standard deviations of impactstrengths are seen graphically in Figure 4, and statisticalresults are shown in Tables I and II. The impact strengthof the unreinforced denture and reinforced denturewere 90.0 6 38.1 J and 201.7 6 77.9 J at crackinitiation, and 95.9 6 37.7 J and 277.9 6 102.5 J atcomplete fracture, respectively. When the denture wasreinforced with the Stick Net fiber, the impact strength

Fig. 4. Means and standard deviations of impact strength.

MARCH 2004

both at crack initiation and complete fracture signifi-cantly increased (P\.0001) and exceeded that of thecontrol by a factor greater than 2. In both groups, theimpact strength between crack initiation and completefracture were significantly different (P\.0001), butmore energy was needed for complete fracture fromcrack initiation for reinforced dentures.

Table III lists the scale parameter, shape parameter,correlation coefficient, and cumulative Weibull proba-bility. The shape parameter of all groups was greaterthan 1. This indicates wear out failures, which mean thatthe prosthesis would fail with increase of time service.When the scale parameters were compared betweengroups, it was found that the scale parameters ofreinforced dentures were greater than those of un-reinforced dentures at crack initiation and completefracture. The correlation coefficients between experi-mental cumulative probability and cumulative Weibullprobability were over 0.90. This demonstrates that theimpact strength data fit well to the Weibull distribution.

Figure 5 shows the cumulative Weibull fractureprobability plots as a function of the impact strength.

Table I. Repeated measures analysis of variance of impactstrength tests between subject factors

Source df

Type III sum

of square

Mean

square F value Sig

Reinforcement 1 1.62937545 1.62937545 29.29 \.0001

Error 18 1.00146154 0.05563675

Table II. Repeated measures analysis of variance of impactstrength tests within subject factors

Source df

Type III sum

of square

Mean

square F value Sig

Cracking period 1 0.07573670 0.07573670 48.25 \.0001

Cracking period

*reinforcement

1 0.03095115 0.03095115 19.72 0.0003

Error (cracking

period)

18 12838.00450 713.22247

Table III. Weibull analysis of results of impact strength

Unreinforced denture Reinforced denture

Crack

initiation

Complete

fracture

Crack

initiation

Complete

fracture

Scale parameter 102.6 108.8 231.8 318.3

Shape parameter 2.47 2.65 2.32 2.45

R 0.95 0.96 0.99 0.97

5% 30.82 35.49 64.32 94.66

10% 41.26 46.56 87.75 126.99

50% 88.48 94.77 197.86 273.96

90% 143.88 149.05 332.19 447.19

95% 160.06 164.61 372.14 497.90

277

THE JOURNAL OF PROSTHETIC DENTISTRY KIM AND WATTS

Fig. 5. Experimental cumulative probability versus Weibull cumulative probability of impact strength.

A significant right shift of the plots was observed. Thisindicates an improvement in the impact strength. Forunreinforced dentures, the cumulative probabilities offailure of both crack initiation and complete fracturewere very close, whereas for reinforced dentures, thecumulative probabilities were distant, indicating thatmore energywas required tocompletely fracture theden-ture when it was reinforced with the woven E-glass fiber.

DISCUSSION

Impact failure is a predominant mode of denturefailures. It is also a primary cause of fracture of maxillarydentures. A denture base material with high-impactstrength should withstand high masticatory loads orimpact caused by accidental dropping. The results in thepresent study may help clinicians to understand theimpact strength of the high-impact acrylic maxillarycomplete denture reinforced with fibers.

Degree of fiber impregnation is critical for the succesof reinforcement. Improper impregation decreases thetensile strength and elastic modulus of fiber compositebecause of the voids between fibers, increased watersorption, and decreased degree of conversion.24 Thefiber systems preimpregnated with di-methacrylatemonomers were not used in this study because the di-methacrylate polymer did not form an IPN (inter-penetrating polymer network) bond with acrylic resin.24

Thus, Stick Net fiber, a preimpregnated E-glass fibersystem with a highly porous polymer, was used in thisstudy. This fiber system was intended to allow highimpregnation of the reinforcing fibers with multiphaseand di-methacrylate–based resin matrix.

Among several different types of tests to measureimpact strength, the flexed-beam test and falling-weighttest are 2 major impact tests.32 In previous studies, most

278

impact strength tests were carried out with the flexed-beam impact methods such as the Charpy-type pendu-lum impact tester26,28,30 or the Zwick pendulum impactmachine.1,29,31 Although those tests are the mostcommonly usedmethods for measuring impact strengthin dentistry, falling-weight impact tests are an acceptablealternative.33 In the falling-weight impact test, theamount of energy required to break the material isdetermined from the weight of the object and the heightfrom which it was dropped. In this study, the falling-weight impact test was used. It was designed to simulateclinical conditions with dentures of conventional size, astest conditions that closely simulate impact conditionsin service are also important to predict failure. Thedimensions of the specimens approximated the di-mensions of actual prostheses fabricated by the conven-tional method. Therefore, the results from this test maybe more clinically relevant.

The main property of fiber is high tensile strength.25

Thus, the highest tensile strength effect can be achievedwhen the fiber is positioned as far as possible on thetension side of prosthesis rather than at the compressionside or at the center. In this study, the fiber was posi-tioned on the intaglio surface side, at a depth of 1 mmin the resin, to increase the effect of reinforcement.

Impact strength data and fracture characteristicsdepend upon many factors including material selection,geometry of the specimen, fabrication variables, stressconcentrations, position of the specimen, and temper-ature.34 Stress concentrations are the main contributorsto impact failure in dentures34 and include notches,scratches, cuts, depressions, sharp corners, holes,grooves, rough surfaces, textured surfaces, suddenchanges in thickness, foreign particles, or gas in-clusions.34 The surrounding temperature also has aneffect on the impact strength of a material.33 As the

VOLUME 91 NUMBER 3

THE JOURNAL OF PROSTHETIC DENTISTRYKIM AND WATTS

temperature increases to the glass transition temperatureor higher, the impact strength of amorphous polymersand most crystalline polymers increases because molec-ular motion in the backbone of the polymer chains isincreased enough to relieve stress concentrations.33

Thus, temperature can make a material fail in eithera brittle manner or ductile manner.34 Plasticizers canincrease the impact strength of a polymer because theylower the glass transition temperature of the polymerand increase the energy dissipation per unit volume.Plasticizers also decrease notch sensitivity and impedecrack propagation.34 Brittle polymers can be convertedinto high-impact polymer by addition of a rubber.34

This study examined the effects of fiber reinforce-ment on high-impact acrylic denture base resin,Lucitone 199. The results showed that when thedenture was reinforced with Stick Net fibers, the impactstrength increased 224% at crack initiation, and 290% atcomplete fracture. The results of this investigationindicated that the reinforcement of E-glass fiberssignificantly increase the impact strength of high-impactacrylic denture. As mentioned previously, impactstrength depends on the specimen geometry and testmethod used. Thus, it is difficult to correlate the resultsobtained from different test techniques. However, thefact that glass fiber reinforcement enhances the impactstrength of acrylic resin is in agreement with otherresearch.18,26,28-30

A limitation of this study is that only 1 denture baseresin system and 1 fiber reinforcement systemwere used.As this was a high-impact resin, similar reinforcementeffects might be expected with other high-impact resinsusing the same fiber system and for low-impact resins aswell. This follows from the fact that the high impactvalue is now dominated by the load-bearing fiberreinforcement rather than by the details of the resinmatrix structure.37

From a clinical point of view, it is preferable to selecta material with high impact strength at both oraltemperature and at room temperature. Denture basepolymers should have a high impact strength, but not atthe expense of other properties. Stress concentrators,such as a sharp surface contour, deepnotches, prominentrugae patterns, foreign particles, and surface defects,should be avoided. In addition, E-glass fiber reinforce-ment, with their improved esthetics over metal re-inforcement and improved mechanical strength, may beused.

It should be noted that impact strength of the acrylicdenture base reinforcedwith glass fibers varies accordingto the test condition, composition of resin, geometry ofdenture, fiber type, fiber form, fiber position, fiberorientation, and fiber fraction.34 These factors have animportant influence on clinical performance of thedentures. Thus these factors should be considered forfurther studies.

MARCH 2004

CONCLUSIONS

From the result of this study, the following con-clusions were drawn:

1. The impact strength of high impact, acrylicmaxillary complete denture reinforced with woven E-glass fibers was significantly higher, by a factor morethan 2, than that of the unreinforced denture both atcrack initiation and at complete fracture.2. The crack propagation energy of the high impact,

acrylic maxillary complete denture reinforced withwoven E-glass fibers was significantly higher than thatof the unreinforced denture.

REFERENCES

1. Gutteridge DL. The effect of including ultra-high modulus polyethylene

fiber on the impact strength of acrylic resin. Br Dent J 1988;164:177-80.

2. Johnston EP, Nicholls JI, Smith DE. Flexural fatigue of 10 commonly used

denture base resins. J Prosthet Dent 1981;46:478-83.

3. Manley TR, Bowman AJ, Cook M. Denture bases reinforced with carbon

fibress. Br Dent J 1979;146:25.

4. Lambrecht JR, Kydd WL. A functional stress analysis of the maxillary

complete denture base. J Prosthet Dent 1962;12:865-72.

5. Hargreaves AS. The prevalence of fractured dentures. A survey. Br Dent J

1969;126:451-5.

6. Smith DC. Acrylic denture. Mechanical evaluation; mid-line fracture. Br

Dent J 1961;110:257-67.

7. Dabbar UR, Huggett R, Harrison A. Denture fracture—survey. Br Dent J

1994;176:342-5.

8. Carroll CE, von Fraunhofer JA. Wire reinforcement of acrylic resin

prostheses. J Prosthet Dent 1984;52:639-41.

9. Ruffino AR. Effect of steel strengtheners on fracture resistance of the

acrylic resin complete denture base. J Prosthet Dent 1985;54:75-8.

10. Vallittu PK, Lassila VP. Effect of metal strengthener’s surface roughness on

fracture resistance of acrylic denture base material. J Oral Rehabil

1992;19:385-91.

11. Vallittu PK. Effect of some properties metal strengtheners on the fracture

resistance of acrylic denture base material construction. J Oral Rehabil

1993;20:241-8.

12. Hero H, Ruyter IE, Waarli ML, Hultquist G. Adhesion of resins to Ag-Pd

alloys by means of the silicoating technique. J Dent Res 1987;66:1380-5.

13. Naegeli DG, Duke ES, Schwartz R, Norling BK. Adhesive bonding of

composites to a casting alloy. J Prosthet Dent 1988;60:279-83.

14. Vallittu PK. Dimensional accuracy and stability of polymethyl methacry-

late reinforced with metal wire or with continuous glass fiber. J Prosthet

Dent 1996;75:617-21.

15. Robinson, McCabe JF. Impact strength of acrylic resin denture base

materials with surface defects. Dent Mater 1993;9:355-60.

16. Matsukawa S, Hayakawa T, Nemoto K. Development of high-toughness

resin for dental applications. Dent Mater 1994;10:343-6.

17. Jagger DC, Harrison A, Jandt KD. Review. The reinforcement of dentures.

J Oral Rehabil 1999;26:185-94.

18. Schreiber CK. Polymethyl methacrylate reinforced with carbon fibers. Br

Dent J 1971;130:29-30.

19. Bowman AJ, Manley TR. The elimination of breakages in upper dentures

by reinforcement with carbon fibres. Br Dent J 1984;156:87-9.

20. Yazdanie N, Mahood M. Carbon fiber acrylic resin composite: an

investigation of transverse strength. J Prosthet Dent 1985;54:543-7.

21. Grant AA, Greener EH. Whisker reinforcement of polymethyl methacry-

late denture base resins. Aust Dent J 1967;12:29-33.

22. Berrong JM, Weed RM, Young JM. Fracture resistance of Kevlar-reinforced

poly(methyl methacrylate) resin. a preliminary study. Int J Prosthodont

1990;3:391-5.

23. Dixon DL, Breeding LC. The transverse strengths of three denture base

resins reinforced with polyethylene fibers. J Prosthet Dent 1992;67:

417-9.

279

THE JOURNAL OF PROSTHETIC DENTISTRY KIM AND WATTS

24. Vallittu PK. Flexural properties of acrylic resin polymers reinforced

with unidirectional and woven glass fibers. J Prosthet Dent 1999;81:

318-26.

25. Vallittu PK. Some aspects of the tensile strength of unidirectional glass

fiber-polymethyl methacrylate composite used in dentures. J Oral Rehabil

1998;25:100-5.

26. Uzun G, Hersek N, Tincer T. Effect of five woven fiber reinforcements on

the impact and transverse strength of a denture base resin. J Prosthet Dent

1999;81:616-20.

27. Braden M, Davy KW, Parker S, Ladizesky NH, Ward IM. Denture base

poly(methyl methacrylate) reinforced with ultra-thin modulus polyethyl-

ene fibers. Br Dent J 1988;164:109-13.

28. Vallittu PK, Narva K. Impact strength of a modified continuous glass fiber-

polymethyl methacrylate. Int J Prosthodont 1997;10:142-8.

29. Chen SY, Liang WM, Yen PS. Reinforcement of acrylic denture base

resin by incorporation of various fibers. J Biomed Mater Res 2001;58:

203-8.

30. Vallittu PK, Vojtkova H, Lassila VP. Impact strength of denture polymethyl

methacrylate reinforced with continuous glass fibers or metal wire. Acta

Odontol Scand 1995;53:392-6.

31. Carlos NB, Harrison A. The effect of untreated UHMWPE beads on some

properties of acrylic resin denture base material. J Dent 1997;25:59-64.

32. Ward IM, Hadley DW. An introduction to the mechanical properties of

solid polymers. Indianapolis: John Wiley & Sons; 1993. p. 276-81.

33. Turner S. Mechanical testing of plastics. 2nd ed. Indianapolis: John Wiley

& Sons; 1987. p. 139-53.

280

34. Niesen LE, Landel RF. Mechanical properties of polymers and composite.

2nd ed. New York: Marcel Dekker; 1993. p. 307-17.

35. Halliday D, Resnick R, Walker J. Fundamentals of physics. 6th ed.

Indianapolis: John Wiley & Sons; 2001. p.144.

36. Dodson B. Weibull analysis. Milwaukee (WI): American Society for

Quality; 1994. p. 1-13.

37. Hull D, Clyne TW. An introduction to composite materials. 2nd ed.

Cambridge: Cambridge University Press; 1996. p. 60-77.

Reprint requests to:

DR SUNG-Hun KIM

DEPARTMENT OF PROSTHETIC DENTISTRY

MOKDONG HOSPITAL

EWHA WOMANS UNIVERSITY

911-1 MOKDONG

YANGCHEON-GU

SEOUL, REPUBLIC OF KOREA

FAX: 82(0)2 2650 5764

E-MAIL: ksh1250@ewha.ac.kr

0022-3913/$30.00

Copyright ª 2004 by the Editorial Council of The Journal of Prosthetic

Dentistry

doi:10.1016/j.prosdent.2003.12.023

VOLUME 91 NUMBER 3