14 - the static strength and modulus of fiber reinforced de(1) (1)

7/30/2019 14 - The Static Strength and Modulus of Fiber Reinforced de(1) (1)

1/8

The static strength and modulus of fiber

reinforced denture base polymer

Katja K. Narva*, Lippo V. Lassila, Pekka K. Vallittu

Department of Prosthetic Dentistry and Biomaterials Research, Institute of Dentistry,

University of Turku, Lemminkaisenkatu 2, FIN-20520 Turku, Finland

Received 10 March 2004; received in revised form 28 April 2004; accepted 15 July 2004

KEYWORDSDenture base resin;Flexural properties;Fiber reinforced

composite;Glass fiber;UHMWP fiber

Summary Objectives. Partial fiber reinforcements have been employed tostrengthen dentures both during repair and in the manufacturing process. Thereinforcing fibers can be evenly distributed in the denture base polymer oralternatively fiber-rich phase in the denture base polymer can form a separatestructure. The aim of this study was to determinate static three-point flexuralstrength and modulus of denture base polymer that had been reinforced withdifferent fiber reinforcements.

Methods. The test specimens (3!5!50 mm) were made of auto-polymerizeddenture base polymer and reinforced with different fiber reinforcements. The testgroups were: (A) no fibers; (B) non-impregnated polyethylene fibers; (C) light-polymerized monomer impregnated glass fibers; (D) porous polymer preimpregnated

glass fibers and (E) light-polymerized monomerpolymer impregnated glass fibers.The fibers were oriented parallel to the long axis of the specimen and embedded intothe denture base resin on the compression side ( nZ7) or tension side (nZ7). Dryspecimens were tested with three-point static flexural strength test set-up atcrosshead speed of 5 mm/min.

Results. The statistical analysis by two-way analysis of variance showed that thebrand and the location of the fiber reinforcements significantly influenced theflexural strength (p!0.0001). However, the location of the fiber reinforcements didnot influence the flexural modulus (p!0.722).

Significance. The results suggest that impregnated and preimpregnated fibersreinforce denture base polymer more than non-impregnated fibers. Fiber reinforce-ments placed on the tensile side resulted in considerably higher flexural strength andflexural modulus values compared with same quantity of fibers placed on the

compression side.Q 2004 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Introduction

Acrylic resin, based on polymethylmethacrylate(PMMA), is one of the materials routinely used for

Dental Materials (2005) 21, 421428

www.intl.elsevierhealth.com/journals/dema

0109-5641/$ - see front matter Q 2004 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.doi:10.1016/j.dental.2004.07.007

* Corresponding author. Tel.: C358 2 333 81; fax:C358 2 3338390.

E-mail address: [email protected] (K.K. Narva).
http://www.intl.elsevierhealth.com/journals/demahttp://www.intl.elsevierhealth.com/journals/dema


2/8

the manufacture of removable dentures. Thefavorable working characteristics, ease of manipu-lation and polishability, its use in combination withinexpensive equipment, stability in the oralenvironment and the aesthetics of acrylic resinhave resulted in its extensive us as a denture basepolymer. However, the acrylic resin denture base

polymer has not fulfilled all the requirements interms of optimum mechanical properties [1] due toits brittle nature under its glass transition tempera-ture (Tg) of approximately 110 8C [2], and itssusceptibility to cyclic loading. For this reason,fatigue fracture of dentures is a common clinicalmanifestation [313]. It is unlikely that a completedenture would be broken by one heavy biting cycledue to the high volume of the denture base polymerand the geometry of the base plate [10]. However,the thin denture base plates of removable partialdentures can fracture by one loading cycle as aresult of a poorly balanced occlusion [12] and afracture of this kind could result from a static load.

Conventional methods employed to reinforcedenture base polymers generally involve the useof either metal wires or plates, however, theirinfluence is minor [36]. Fiber-reinforced compo-sites (FRC) have been introduced [1432] to over-come the problem of denture factures by improvingthe mechanical properties of the denture basepolymer. Partial fiber reinforcements, namelyaccurate placement of a relatively small quantityof fibers in the denture base polymer, have beenemployed to strengthen dentures both during repair

and in the manufacturing process [5,6].The types of fibers that have been used

to reinforce denture base polymers includearamid fibers [14,15], carbon/graphite fibers [16],

ultra-high molecular weight polyethylene (UHMWP)fibers [1720] and glass fibers [5,6,14,2132].Although UHMWP fibers have relatively good mech-anical properties, there are reports that pooradhesion of the fibers to the polymer matrix, evenwith the aid of plasma treatment, does notconsiderably increase the mechanical properties

of the denture base polymer [18]. It has beenpreviously shown that glass fibers can be adhered tothe resin by silane coupling agents and can be usedas an effective reinforcement [32]. In recent years,several brands of fiber reinforcements have becomeavailable, however, in the opinion of the authorsthere is a distinct lack of comparative informationof the reinforcing effect of the various fiberreinforcements available in the dental literature.Therefore, the aim of the current study was todetermine the static three-point flexural strengthand flexural modulus of a denture base polymer thathas been reinforced with fiber reinforcements

commonly available to dentist and dentaltechnicians.

Materials and methods

The test specimens utilized in the current study(3!5!50 mm) were manufactured from clearauto-polymerizing denture base resin (Palapress,Heraeus Kulzer GmbH & Co. KG, Wehrheim,Germany) and reinforced with four different brandsof fiber reinforcements (Table 1, Fig. 1). The

powder/liquid ratio of resin was 107 g/ml and theresin was polymerized in distilled water maintainedat 55G2 8C under air pressure of 300 kPa for 15 minsin a pneumatic curing unit (Ivomat Typ IPR, Ivoclar,

Table 1 Classification of test groups and the fiber reinforcing materials used in the current study.

Group Manufacturer Fiber type Type Preimpregnationresin

A. Control NoneB. Ribbond Ribbond Inc.,

Seattle, USAWoven ribbon poly-ethylene UHMWPa

Non-preimpregnated

C. FibreKor Jeneric/Pentron,

Wallingford, USA

Continuous uni-

directional S-glassfiber

Light-polymerizing resin

impregnated Shade Clear2K bundle, 3 mm wide

Bis-GMAb

D. Everstick StickTech Ltd,Turku, Finland

Continuous uni-directional E-glassfiber

Light-polymerizing resinimpregnated

Bis-GMA with,PMMAcbis-GMAmatrix

E. Stick StickTech Ltd,Turku, Finland

Continuous uni-directional E-glassfiber

Porous polymer preimpre-ganted fiber

PMMA

a Ultra-high molecular weight polyethylene fiber.b 2, 2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]-propane.c Polymethylmetacrylate.

K.K. Narva et al.422


3/8

Schaan, Liechtenstein). The test specimens ingroup A were manufactured without fiber reinforce-ment and were employed as the control group in thestudy. The light-polymerized resin impregnated

fiber reinforcements, namely, FibreKor and ever-Stick (group C and E, respectively,) were polymer-ized with a light-curing guide (Optilux 501, Sds Kerr,Danbury, CT). Output intensity was measured withan in-build radiometer to be 800850 mW/cm2. Thefiber reinforcements were light-polymerized byplacing the light-curing tip on the reinforcement.The 10 mm diameter of the light-curing tip wasemployed to light-polymerize over five overlappingareas for 40 s on both sides of the specimens priorto embedding the fiber reinforcements in thedenture base resin. The non-preimpregnated fiberreinforcement, namely, Ribbond (group B) andPMMA preimpregnated Stick reinforcement(group D) were wetted with a mixture of denturebase resin. All the fiber reinforcements were thenembedded in a polyvinyl siloxane Lab-putty mold(Coltene, Alstatten, Switzerland) (3.2!5.2!50.2 mm) that had been partially filled with a1 mm layer of denture base resin.

The major orientation of the fibers in groups C, Dand E (FibreKor, Stick and everStick) was parallel tothe long axis of the specimen, whereas ribbon typegroup B (Ribbond) fibers contained also fibersorientated against the long axis of the specimen.

The fibers subsequently were placed on top of thedenture base resin layer. In the case of group Dspecimens (Stick) the fibers were distributed andfilled the entire volume of the mold as the denturebase resin mixture swelled the polymer matrixpreimpregnation of the reinforcement. In groups B,C and E the fiber reinforcement was covered with afurther layer of denture base resin. Followingpolymerization, the specimens were then wetground (Stuers LabPol-21, Stuers A/S, Copenhagen,Denmark) with successively finer grades of silicon

carbide abrasive papers from P300 to P1200 (StuersA/S, Copenhagen, Denmark) to the prederminateddimensions of the specimens (3!5!50 mm) andthe test specimens were stored dry prior to testing.Static three-point-flexural strength testing wasperformed in air to determine the ultimate flexuralstrength and the associated flexural modulus at a

crosshead speed of 5 mm/min (Model LRX, LloydsInstruments Ltd, Fareham, UK). The distancebetween the supports of the test specimens was20 mm and the loaddeflection curves wererecorded with Nexygen-software (Lloyd Instru-ments Ltd, Fareham, UK). The ultimate flexuralstrength s (MPa) was determined for the specimensthat contained the main part of the fiber reinforce-ment when either placed in tension (nZ7) or incompression (nZ7) in accordance with Eq. (1),where F is the maximum load (N) applied at thehighest point of loaddeflection curve, l is thespecimen span length (mm), and b is the breath of

the specimen (mm) and h is the thickness of the testspecimen (mm). The flexural modulus E(GPa) of thespecimens was also determined when the fiberswere placed in tension (nZ7) or in compression(nZ7) in accordance with Eq. (2) where S is thestiffness (N/m) and d is the deflection (mm)corresponding to a load F (N) at a point in thelinear portion of the trace to provide the stiffnessvalue.

sZ

3Fl

2bh2(1)

EZSl3

4bh3d(2)

Following flexural strength testing, the specimenswere visually examined in an attempt to differen-tiate the origin of the fracture and the failuremode. The failure modes were classified as (1)intact test specimen; (2) the fracture path wasarrested at the fibers; (3) the fracture path passedthe fibers but did not result in complete testspecimen fracture; and (4) the test specimen wasbroken into two pieces.

The fiber content of the test specimens contain-ing glass fiber reinforcement was measured bycombustion analysis with a burnout furnace (Radi-ance Multi-stage msc, Jelrus International, Hicks-ville, NY, USA). The test specimens were dried in adesiccator for 2 days at room temperature andweighed to an accuracy of 0.001 mg prior tocombustion. In order to combust the denture basepolymer matrix, the temperature was raised 12 8Cper min until the temperature reached 700 8C. Testspecimens were maintained at 700G25 8C for 1 hand reweighed. The fiber content as a percentage

Figure 1 Fiber reinforcements used in test groups in thecurrent study. Group (B) Ribbond; Group (C) FibreKor; Group(D) Stick; and Group (E) everStick fiber reinforcement.

Flexural properties of reinforced denture polymer 423


4/8

by volume (Vf) (vol.%) was assessed in accordancewith the equation

VfZWf=Df

Wf=DfC Wp=Dp(3)

where Wf is the weight of the fiber, Df is the densityof the glass fiber (2.54 g/cm3), Wp is the weight of

the denture base resin, and Dp is the density of thedenture base resin (1.19 g/cm3).

The fiber volume of the group B (Ribbond) withthe UHMWP fibers was determined based on fibercontent as percentage by weight. The fiber contentas percentage by volume was determined inaccordance with the following equation

VfZWf=Df

Vs100% (4)

where Wf is the weight proportion of fiberreinforcement (weight of 50!4 mm Ribbond,

0.028 g), Df is density of reinforcement (polyethy-lene, 0.97 g/cm3) and Vs is the size of the specimen(3!5!50 mmZ0.75 cm3).

The flexural strength and flexural modulus of thespecimens tested with the fibers in compression ortested in tension were analyzed utilizing a two-wayanalysis of variance (ANOVA) at a 95% significance

level using a statistical software package (Statisti-cal Package for the Social Sciences for Windows,Rel. 10.0.5, Chicago, IL, USA).

Results

Testing fiber reinforcements in tension

The seven control specimens (group A) had a meanthree-point flexural strength and associated SD of128G3 MPa and three-point flexural modulus of

Figure 2 (a) Three-point flexural strength and (b) calculated three-point flexural modulus of the test specimensreinforced with various brands of fiber reinforcements and two fiber locations (compression or tension side). Verticalbars represent SD. Horizontal lines above the bars indicate groups that do not differ statistically from each other.



5/8

3.2G0.1 GPa, respectively (Fig. 2a and b). Follow-ing visual examination, it was identified that all thespecimens had fractured into two pieces (Table 2).When the light-polymerized resin impregnated glassfiber reinforced specimens (groups C and E,respectively,) were tested with the reinforcementplaced in tension, the mean three-point flexuralstrength and calculated three-point flexural moduliwere 226G16 MPa and 4.4G0.4 GPa, respectively,for group C and 266G4 MPa and 5.3G0.2 GPa,respectively, for group E specimens (Fig. 2a and b).In group C, six of the seven test specimens fracturedinto two pieces and in one of the specimens thefracture had arrested at the fibers. In group E,

fracture path passed the fibers in six specimens butdid not result in specimen fracture and theremaining test specimen was fractured brokeninto two pieces (Table 2). The non-preimpregnatedUHMWP fiber reinforcement for group B specimensresulted in a mean three-point flexural strength of151G16 MPa and a calculated three-point flexuralmodulus of 3.5G0.3 GPa (Fig. 2a and b). Thepolymer preimpregnated glass fiber reinforcedtest specimens (group D) resulted in a three-pointflexural strength of 232G26 MPa and calculatedthree-point flexural modulus of 4.8G0.7 GPa

(Fig. 2a and b). In all of the specimens in group B,the fracture path passed the fibers but did notresult in specimen fracture while in six specimens ofgroup D the fracture path was arrested at the fibersand in one specimen fracture path had passed thefibers (Table 2).

Testing with the fibers in compression

When the fiber reinforcement was located in thecompression side the light-polymerized resin

preimpregnated glass fiber reinforcements (groupsC and E) resulted in a mean three-point flexuralstrength of 174G9 MPa and a calculated three-point flexural moduli of and 4.5G0.2 GPa forgroup C, and 174G17 MPa and 5.2G0.8 GPa,respectively, for group E (Fig. 2a and b). Followingvisual examination, it was identified that four of thespecimens in group C were fractured into twopieces, in two specimens fracture had passed thefibers and in one test specimen fracture hadarrested at the fibers. In group E, all of the testspecimen fracture path had passed the fibers(Table 2). The non-preimpregnated UHMWP fiberreinforcement for group B resulted in a three-pointflexural strength of 124G7 MPa and a calculatedthree-point flexural modulus of 3.5G0.3 GPa(Fig. 2a and b). In all of the test specimen fracturehad passed the fibers (Table 2). The polymerpreimpregnated glass fiber reinforcements (groupD) had values of 197G23 MPa and 5.0G0.4 GPa,respectively, for the three-point flexural strengthand modulus (Fig. 2a and b). The test specimenswere intact in group D (Table 2).

The statistical analysis by two-way ANOVAshowed that the brand and the location of thefiber reinforcements significantly influenced the

flexural strength (p!0.0001). Utilizing a two-wayANOVA at a 95% significance level the mean three-point flexure strength values were identified to besignificantly increased for groups B, C, D and E whenthe fibers were placed in tension compared whenthe fibers were placed in compression. The two-wayANOVA showed also that only brand of the fiberreinforcement, had significant effect on flexuralmodulus (p!0.0001), the location of the fiberreinforcements did not influence the flexuralmodulus (p!0.722).

Table 2 The failure mode of the test specimens reinforced with different brands of fibre reinforcements locatedwhere the reinforcement was tested in tension or compression.

Group A,PMMA

Group B,Ribbond

Group C,FibreKor

Group D,Stick

Group E,everStick

Intact test specimen

Compression 7/7

Tension Fracture stopped at fibersCompression 1/7 Tension 1/7 6/7

Fracture passed the fibers

Compression 7/7 2/7 7/7Tension 7/7 1/7 6/7

Broken into two pieces

Compression 7/7 4/7 Tension 7/7 6/7 1/7



6/8

Combustion analysis studies highlighted that thefiber content as a percentage by weight (wt %)of thegroup B (Ribbond) specimens was 3.2 wt% whichcorresponded to 3.8 vol.%, for group C (FibreKor)2.3 wt% and 1.1 vol.%, for group D (Stick) 12 wt%and 5.8 vol.% and for the group E (everStick) testspecimens 12 wt% and 5.9 vol.%.

Discussion

Thisstudydemonstratedtheeffectoffiberreinforce-ment on the static flexural properties of a denturebase polymer. Fiber reinforcements placed on thetensile side of the test specimens under loadingresulted in considerably higher flexural strength andflexural modulus values compared with specimensthat contained the same quantity of fibers placed onthe compression side. It is suggested that this is due

to the higher tensile strength of the reinforcingfibers, which could more effectively be used if thelocation of the fibers was close to the highest tensilestress of the test specimen. As a result, in clinicalsituations the fiber reinforcements should also beplaced near the position of highest tensile stressunderfunctionalloadingofadenture.Anexampleforremovable complete denture in a maxillary jawwould be close to the oral surface of the dentureand perpendicular to the midline.

Methodologically, one limitation of the presentstudy is related to the testing of dry specimens only.

Several studies have already shown the influence ofwater saturation on the flexural properties ofreinforced denture base polymer and other dentalFRCs [25,30,31]. Because this study was aimed atthe differences between fiber reinforcements andtheir locations on the flexural properties, theresults can be interpreted accordingly. It has alsobeen reported previously that the interfacialadhesion of glass fibers to the polymer matrixthrough silane coupling agent can be deterioratedby water storage. The degree of deterioration wasrelated to the glass fiber sizing and silanation.Therefore, comparison of different brands of thefiber reinforcement can be questioned to someextend in terms of clinical significance. However, ithas also been shown that properly sized andsilanized glass fibers in denture base polymer didnot weaken in water for several years [30].

Another methodological matter is that the three-point flexural strength and modulus are used ascomparative values to evaluate differencesbetween groups. Eqs. (1) and (2) do not take intoaccount the layered structure of the test specimensinvestigated. In a homogenous polymer matrix test

specimen, the neutral axis is located in the middleof the test specimen (Fig. 3a). However, the neutralaxis is moved towards the fiber layer, when the testspecimen consists of reinforcing fibers and ahomogeneous polymer layer [33] (Fig. 3b and c).When the reinforcing fibers are positioned on thecompressive side of the test specimen, the neutralaxis is moved close to the fiber layer and highertensile stresses are exposed to the homogeneouspolymer, which causes fracture of the test speci-men at lower loads (Fig. 3c). Depending on the ratiobetween the modulus of the fiber reinforcementand the homogeneous polymer layer, the neuralaxis location even inside the fiber layer, can causethe weaker polymer layer to be exposed to highertensile stresses. This might be one explanation forthe advantageous behavior of group D (Stick),where the fibers were more evenly distributed andfilled the entire volume of the mold resulting in analmost homogenous structure.

Also the fact that the ratio of the thickness of thetest specimen versus span length is relatively highshould be taken into consideration. This has likelycontributed more shear stress in the test specimen

Figure 3 Schematic representation of highlighting theareas of tensile and compression side. If specimen ishomogenous without any reinforcement, neutral axislocated in the middle of test specimen (a), but if the fiberreinforcement is placed in tension side of the testspecimen (b), or in the compression side (c), neutralaxis is moved towards fiber reinforcement layer.



7/8

than tested previously [31] according to ISOstandard. However, the thickness of the removabledenture base at the correct location of the fiberreinforcement corresponds to the thickness of thetest specimens used in the present study.

The difference in the three-point flexuralstrength of the test specimens when the reinforce-

ment was placed in tension compared with com-pression was marked in groups C (FibreKor) and E(everStick), the light-polymerized resin impreg-nated fiber reinforced specimens. This could beattributed to having a high quantity of fibers packedefficiently such that the one side of the specimendid not contain fiber reinforcements at all. Inter-estingly, group D (Stick) specimens showed lessdifference when the reinforcement was placed intension or compression during testing. In this group,the polymer preimpregnated fiber reinforcementswelled during specimen fabrication and caused arelatively even distribution of fibers throughout the

cross section of specimen resulting in effectivecrack stopping behavior. The relatively modestreinforcing effect of the UHMWP fibers (group B),irrespective of whether the fibers were placed intension or compression suggested possibly thatthere was inadequate interfacial adhesion betweenthe denture base polymer and the fibers. It was alsopossible that the impregnation of tightly boundUHMWP fibers by the highly viscous denture baseresin was inadequate. This problem has beendiscussed previously by Vallittu [27,34]. I t i sproposed that the combination of inadequate

interfacial adhesion and the inadequate impreg-nation may hinder stress transfer from the homo-geneous polymer matrix to the fiberreinforcements, and therefore only minor differ-ence between the test specimens with fiberlocations could be found. Fiber reinforcement ingroup B (Ribbond) was not unidirectionally orientedas in the other fiber reinforcements using in thecurrent study. Group B fiber reinforcement can bedescribed as knotted as seen in Fig. 1. According tofiber geometries and Krenchels factor, uni-directional reinforcement has the most efficientreinforcing factor than any other form of reinforce-ment [35], which can be one reason for the lowerthree-point flexure strength of group B.

It is of importance to note that the flexuralmodulus of the test specimen was attributed by thebrand of the reinforcement but not by the locationof reinforcement. This can be explained by the factthat the stiffness of the fiber reinforcement layer isdominant over the homogeneous polymer layer. Asa result the three-point flexural modulus valuerecorded is indicative of the fiber reinforcementlayer, because the stiffness of a fiber reinforcement

is approximately 510 times higher than of PMMA[31]. This can be explained by the capability of thereinforcing fibers to withstand compressive stressesdue to the higher compressive moduli of reinforcingfibers compared with the homogeneous polymerPMMA.

The visual examination of the test specimens was

undertaken to differentiate the origin of thefracture and the failure mode. In the test specimensof group D (Stick) the test specimens were intact,whereas in group C (FibreKor) most of the testspecimens were fractured into two pieces and ingroup B (Ribbond) the fracture passed all the fiberreinforcements. This could be explained by therelatively even distribution of fibers throughout thetest specimens in group D. In clinical situations, adenture fracturing in two pieces is more drastic fora patient. A fracture line that has arrested at thefibers still allows the denture to function. Thecombustion analysis showed that the fiber amountin group C was significantly lower than in othergroups and this could have been one reason whymost of the test specimens were broken into twopieces.

Clinically the use of a fiber reinforcement thatswells during manufacture and enables a more evendistribution of the fibers could provide a moreeffective and less technique sensitive method toreinforce denture bases than using a high quantityof densely packed fibers that may have been placedincorrectly. Further research is needed to verify thepresent static test results with a dynamic loading

test.

Conclusion

The results suggest that impregnated and preim-pregnated fiber reinforcements reinforce denturebase polymer more than non-impregnated fiberreinforcements. Fiber reinforcements placed onthe tensile side resulted in considerably higherflexural strength and flexural modulus values

compared with same quantity of fiber reinforce-ments placed on the compression side.

References

[1] Stipho HD. Effect of a glass fiber reinforcement on somemechanical properties of autopolymerizing polymethylmetactylate. J Prosthet Dent 1998;79:5804.

[2] Ruyter IE, Svendsen SA. Flexural properties of denture basepolymers. J Prosthet Dent 1980;43:95104.



8/8

[3] Vallittu PK, Lassila VP, Lappalainen R. Evaluation of damageto removabledenturesin twocities in Finland.Acta OdontolScand1993;51:3639.

[4] Yli-Urpo A, Lappalainen R, Huuskonen O. Frequency ofdamage to and need for repairs of removable dentures. ProcFinn Dent Soc 1985;81:1515.

[5] Vallittu P. Glass fiber reinforcement in repaired acrylic resinremovable dentures: preliminary results of a clinical study.Quintessence Int 1997;28:3944.

[6] Narva KK, Vallittu PK, Helenius H, Yli-Urpo A. Clinical surveyof acrylic resin removable denture repairs with glass-fiberreinforcement. Int J Prosthodont 2001;14:21924.

[7] Hargreaves AS. The prevalence of fractured dentures. BrDent J 1969;126:4515.

[8] Darbar UR, Huggett R, Harrison A. Denture fractureasurvey. Br Dent J 1994;176:3425.

[9] Zissis AJ, Polyzois GL, Yannikakis SA. Repairs in completedentures: results of a survay. Quintessence Dent Technol1997;14955.

[10] Schneider RL. Diagnosing functional complete denturefractures. J Prosthet Dent 1985;54:80914.

[11] Smith DC. The acrylic denture. Mechanical evaluation, mid-line fracture. Br Dent J 1961;110:25767.

[12] Lassila V, Holmlund I, Koivumaa KK. Bite force and its

correlations in different denture types. Acta Odontol Scand1985;43:12732.

[13] Vallittu PK. Fracture surface characteristic of damagedacrylic-resin-based dentures as analysed by SEM-replicatechnique. J Oral Rehabil 1996;23:5249.

[14] John J, Gangadhar SA, Shah I. Flexural strength of heat-polymerized polymethyl methacrylate denture resinreinforced with glass, aramid, or nylon fibers. J ProsthetDent 2001;86:4247.

[15] Mullarky RH. Aramid fiber reinforcement of acrylic appli-ances. J Clin Orthod1985;19:6558.

[16] Ekstrand K, Ruyter IE, Wellendorf H. Carbon/graphite fiberreinforced poly (methyl methacrylate): properties underdry and wet conditions. J Biomed Mater Res 1987;21:106580.

[17] Samadzadeh A, Kugel G, Hurley E, Aboushala A. Fracturestrengths of provisional restorations reinforced withplasma-treated woven polyethylene fiber. J Prosthet Dent1997;78:44750.

[18] Tagaki K, Fujimatsu H, Usami H, Ogasawara S. Adhesionbetween high strength and high modulus polyethylene fibersby use of polyethylene gel as an adhesive. J Adhesion SciTechnol 1996;10:86982.

[19] Dixon DL, Breeding LC. The transverse strengths of threedenture base resins reinforced with polyethylene fibers.

J Prosthet Dent 1992;67:4179.

[20] Ladizesky NH, Ho CF, Chow TW. Reinforcement of complete

denture bases with continuous high performance polyethy-lene fibers. J Prosthet Dent 1992;68:9349.

[21] Kanie T, Fujii K, Arikawa H, Inoue K. Flexural propertiesand impact strength of denture base polymerreinforced with woven glass fibers. Dental Materials 2000;16:1508.

[22] Nagai E, Otani K, Satho Y, Suzuki S. J Repair of denturebase resin using woven metal and glass fiber: effect ofmethylene chloride pre-treatment. Prosthet Dent 2001;85:496500.

[23] Aydin C, Yilmaz H, Caglar A. Effect of glass fiberreinforcement on the flexural strength of different denturebase resins. Quintessence Int 2002;33:45763.

[24] Vallittu PK. A review of fiber-reinforced denture baseresins. J Prosthod1996;5:2706.

[25] Vallittu PK, Ruyter IE, Ekstrand K. Effect of water storage on

theflexural properties of E-glass andsilica fiber acrylic resincomposite. Int J Prosthodont 1998;11:34050.

[26] Vallittu PK, Narva K. Impact strength of modified continu-ous glass fiber-poly(methyl methacrylate). Int

J Prosthodont 1997;10:1428.[27] Vallittu PK. Some aspects of tensile strength of uni-

directional glass fibre-polymethyl methacrylate compositeused in dentures. J Oral Rehabil 1998;25:1005.[28] Vallittu PK. Flexural properties of acrylic polymers

reinforced with unidirectional and woven glass fibers.J Prosthet Dent 1999;81:31826.

[29] Stipho HD. Repair of acrylic resin denture base reinforcedwith glass fiber. J Prosthet Dent 1998;80:54650.

[30] Vallittu PK. Effect of 180-Week Water Storage on theFlexural Properties of E-Glass and Silica Fiber Acrylic ResinComposite. Int J Prosthodont 2000;13:3349.

[31] Lassila LVJ, Nohrstrom T, Vallittu PK. The influence ofshort-term water storage on the flexural properties ofunidirectional glass fiber-reinforced composites. Biomater

2001;23:22219.[32] Vallittu PK. Curing of a silane coupling agent and its effect

on the transverse strength of autopolymerizing polymethyl-metactylate-glass fibre composite. J Oral Rehabil 1997;24:12430.

[33] Roark RJ, Young WC, editors. Beams; flexure of straightbars. 5th ed Formulas for stress and strain, 5th ed. NewYork, USA: McGraw-Hill; 1982. p. 89127.

[34] Vallittu PK. Impregnation of glass fibers with polymethyl-metacrylate by using a powder coating method. ApplCompos Mater1995;2:518.

[35] Murphy J, editor. Design data. Reinforced plastics hand-book. Great Britain: Elsevier; 1998. p. 265.


14 - the static strength and modulus of fiber reinforced de(1) (1)

Documents