The transverse strengths of three denture reinforced with polyethylene fibers
Donna L. Dixon, DMD,a and Larry C. Breeding, DMD, MSEdb University of Iowa, College of Dentistry, Iowa City, Iowa, and University of Kentucky, College of Dentistry, Lexington,Ky. This investigation compared the transverse strengths of three denture base resins with and without polyethylene reinforcement fibers. These fibers were incorporated in 10 specimens each of a high-impact strength resin, a rapid heat-polymerized resin, and a light-activated resin. Each specimen was broken on an Instron universal testing machine using a three-point load after processing and air drying. The values obtained were then compared with values previously recorded for the same type of specimens without incorporated fibers. Only the light-activated denture base resin specimens exhibited a significantly higher mean transverse strength after polyethylene fiber reinforcement. (J PROSTHET DENT 1992;67:417-9.)
ecently, much attention hasbeendirected toward the addition of various types of fibers to acrylic resinsto enhancetheir physical and mechanicalproperties. For instance,it hasbeenreported that carbon fibers improve the fatigue and tensile strengths,’ transverse deflection,2 and modulusof elasticity3 of poly(methylmethacrylate) resins. The unesthetic dark color of these fibers, however, may prohibit their use in someintraoral locations. Kevlar fibers (Fibreflex, Biomedical Composites,Menomonee Falls, Wise.) have been shown to significantly increasethe impact strength of poly(methylmethacrylate) resin4 Still, with these fibers, the color is unesthetic, and their useis limited to certain intraoral applications. Polyethylene fibers have also been observedto increase the impact strength,5v6 Young’s modulus, and flexural strength6 of poly(methylmethacrylate) resins.Unlike carbon and Kevlar fibers, however, polyethylene fibers are almost invisible in characterized resin denture bases.5 This investigation measuredthe transverse strengths of a high-impact strength denture baseresin, a rapid heatpolymerized denture baseresin, and a light-activated denture baseresin, all reinforced with polyethylene fibers. It comparedthese measurementswith values obtained from a previous study7 in which these materials were tested without reinforcement fibers. MATERIAL
Three denture baseresinswere selectedfor use in this investigation: (1) Lucitone 199 long-cured (Dentsply, International, York, Pa.), a high-impact strength resin; (2) Accelar 20 (ColumbusDental Co., St. Louis, MO.), a rapid
heat-polymerized resin; and (3) Triad (Dentsply, International), a light-activated resin.Usingstonemoldsdescribed by Dixon et al.,710specimens(65 X 10 X 3 mm) were made from each resin. A multifibered strand of polyethylene reinforcement fibers (DVA Reinforcement Fibers, Dental Ventures of America, Inc., Anaheim Hills, Calif.) was removed from the packageand cut into pieces 65 mm in length. After mixing either Lucitone 199or Accelar 20 resin according to manufacturers’ instructions, each compartment in the stone mold was half-filled with the mixture. Two precut multifibered strands werethen evenly distributed, longitudinally, acrossthe half-filled mold. The monomer correspondingto each resin was placed on the fibers prior to adding the final resin mixture and packing. The Triad resin specimenswere prepared in a stainlesssteel mold,7and the DVA fibers were incorporated using a procedure similar to that described above. With the Triad resin specimens, however, Triad VLC bonding agent (Dentsply, International) was used to saturate the fibers instead of monomer. Following processingor light-activation for the sameperiods of time usedin the investigation by Dixon et a1.,7each resinspecimenwasdeflaskedor removedfrom the stainless steelmold, all flash waseliminated, and all specimenswere allowed to remain at room temperature for 24 hours. The specimenswere then broken using an Instron Universal testing machine (Instron Corp., Canton, Mass.) and a transverse testing rig.7 A 50 kg load cell with a crosshead speedof 0.5 cm/min wasused. The transverse strength of eachresin specimenwascalculated usingthe following formulas: 3Pl S=morS=
aAssistant Professor, Department of Prosthodontics, University of Iowa, College of Dentistry. bAssociate Professor, Department of Oral Health Practice, University of Kentucky, College of Dentistry. 10/l/31366
3 X load X length 2 X width X thickness?
Following data collection, statistical analyseswere conducted to compare the transverse strengths of the DVAreinforced specimengroups with each other and with the transverse strengths of specimenswithout fiber reinforcement.7 417
I. Calculated Resin
10 9 10 10 10 10
Lucitone 199 (no fibers) Lucitone 199 (fibers) Accelar 20 (no fibers) Accelar 20 (fibers) Triad (no fibers) Triad (fibers)
data for each resin group
96.260 93.620 81.979 83.667 49.961 73.869
5.756 8.000 10.895 11.762 6.975 14.177
1.820 2.667 3.445 3.719 2.206 4.483
33.127 63.992 118.704 138.343 48.654 200.999
5.979 8.545 13.290 13.698 13.961 19.193
CV, Coefficient of variation.
Model 5 53 Error Corr. total 58
comparison of mean transverse the resin groups
14,095.7026 5,370.3812 19,466.0838
Cow, Corrected; ANOVA, analysis of variance. *Significant at p < 0.05. Table
Duncan’s multiple strengths between
Lucitone 199 (no fibers) Lucitone 199 (fibers) Accelar 20 (fibers) Accelar 20 (no fibers) Triad (fibers) Triad (no fibers)
range test of mean resin groups No.
10 9 10 10 10 10
96.260 93.620 85.867 ‘I 81.979 I 73.869 I 49.961
Lines join groups that are not significantly different at p < 0.05.
RESULTS The calculated mean transverse strength values for each material, with and without reinforcement fibers,7 are summarized in Table I. Only 9 of 10 fiber-reinforced Lucitone 199 resin specimens fractured during three-point load testing. The unbroken specimen reached the maximum deflection possible in the testing rig. The results of a oneway analysis of variance (p < 0.05) are presented in Table II. Duncan’s multiple range test was then performed, and the results are displayed in Table III. The inclusion of fibers did not significantly increase the mean transverse strengths of either Lucitone 199 or Accelar 20 resins. However, there was a significant increase for the Triad resinreinforced specimens when compared with the nonreinforced specimens. The reinforced Triad resin specimens were similar in strength to nonreinforced Accelar 20 resin specimens, and the reinforced Accelar 20 and Lucitone 199 resins were similar in strength.
DISCUSSION To date, no studies have examined the effects of incorporating reinforcement fibers in a high-impact denture 418
base resin such as Lucitone 199. The results of this investigation indicated that the inclusion of multifibered polyethylene strands decreases the mean transverse strengths of these specimens, but not significantly. The incorporation of the fibers in Accelar 20 resin resulted in no significant, increase in mean transverse strength when compared with the strengths of the nonreinforced specimens. The effect of reinforcement fibers on the transverse strengths of light-activated denture base resins has not appeared in the literature. This study showed that the mean transverse strength of Triad denture base resin significantly increases with polyethylene fiber reinforcement.. With fiber incorporation, the mean transverse strength of Triad was similar to that of Accelar 20 without fibers. According to Yazdanie and Mahood, placement of reinforcement fibers in acrylic resin during packing may be difficult, as was found to be true during our investigation. Because DeBoer et al.* noted that carbon fiber reinforcement is optimized when the fibers are parallel to the denture base surface, we attempted to place the DVA fibers parallel to the test surface of the specimens. This placement proved to be very difficult because during packing the fibers often protruded outside the mold compartment. Even distribution in a single direction of the polyethylene fibers was virtually impossible to ensure. Although an attempt was made to keep all fibers within the specimens, some were expelled into the resin flash and were lost during finishing. Any effect on the resin transverse strengths as a result of this variation in exact number of fibers per specimen would be most noticeable where a significant increase in transverse strength was exhibited, and would be expressed in the standard deviation for the significantly affected groups. This effect becomes apparent when comparing the standard deviation for the fiber reinforced Triad resin specimens with that of the Triad resin control specimens.
According to this investigation, if Triad denture base resin is used to fabricate removable prostheses, it would be beneficial to incorporate esthetic polyethylene fibers into the resin during packing. However, because of the tendency for these fibers to be expressed toward the edges of the mold during packing, problems following prosthesis insertion may become evident. Fibers protruding from the proMARCH
4. 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. 5. Braden M, Davy KWM, Parker S, Ladizesky NH, Ward IM. Denture base poly (methyl methacrylate) reinforced with ultra-high modulus polyethylene fibres. Br Dent J 1988,164:109-13. 6. Gutteridge DL. The effect of including ultra-high modulus polyethylene fibre on the impact strength of acrylic resin. Br Dent J 1988;164:17780. 7. Dixon DL, Ekstrand KG, Breeding LC. The transverse strengths of three denture base resins. J PROSTHET DENT 1991;66:510-3. 8. DeBoer J, Vermilyea SG, Brady RE. The effect of carbon fiber orientation on the fatigue resistance and bending properties of two denture resins. J PROSTHET DENT 1984;51:119-21.
cessed resin may not always be smoothly finished, which may result in intraoral irritations.*
CONCLUSION The incorporation of polyethylene fibers does not significantly increase the mean transverse strengths of either Lucitone 199 or Accelar 20 denture base resins. The mean transverse strength of Triad denture base resin, however, is significantly increased by fiber incorporation. REFERENCES
1. Manley TR, Bowman AJ, Cook M. Denture bases reinforced with carbon fibres. Br Dent J 1979;146:25. 2. Schreiber CK. Polymethylmethacrylate reinforced with carbon fibres. Br Dent J 1971;130:29-30. 3. Yazdanie N, Mahood M. Carbon fiber acrylic resin composite: an investigation of transverse strength. J PROSTHET DENT 1985;54:543-7.
DR. DONNA L. DIXON COLLEGE OF DENTISTRY UNIVEFSITY OF IOWA IOWA CITY, IA 52242
Shear strength of laboratory-processed composite bonded to a silane-coated nickel-chromium-beryllium Harold
Schoolof Dentistry, Jackson,Miss.
The shear bond strengths of three commercial laboratory curing composite resin veneers bonded to a nickel-chromium-beryllium alloy treated with the Silicoater system were evaluated. Two light-cured resins and one heat- and pressure-cured resin were evaluated. No statistically significant difference in bond strengths among the three resins was found. Microscopic analysis of the fracture surfaces indicated that all failures were complex and cohesive in nature within the resin and composite. On the basis of the shear bond strengths measured, any of the composite resin veneers tested appear to be clinically acceptable. (J PROSTHET DENT 1992;67:419-22.)
aboratory-cured resin veneers have been introducedasan alternative veneeringmaterial to porcelain and acrylic resin. They are microfilled compositeresinsbased on the BisGMA and urethane dimethacrylate resin systems. A number of these materials have becomecommercially availab1e.lThesematerialsvary in their composition2 and physical properties.3 Principle variations in chemical composition are monomer composition and concentration of filler particles. Physical properties of a particular resin are generally not superior in all characteristics and may vary according to the specific physical property tested.4 Advantages of resin veneersinclude favorable esthetics,
*Assistant Professor, Department bThird year dental student.
abrasionsimilar to natural tooth substance,and the ability to be repaired. Polymerization is initiated by light curing or heat and pressurepolymerization. Applications of theseprosthetic veneering resinsinclude pontics for resinbonded fixed partial dentures, overlay removable partial dentures, veneered crowns, and fixed partial dentures. Bonding of laboratory polymerized composite resin to metal has traditionally been provided by mechanical retention such as beads, mesh, and loops. The chemicalbonding resin veneerseliminate the need for these bulkier macroretentive features and the pooling of opaquing material around retention beadsis eliminated. Several methods have been introduced to enhancethe bonding of resinveneersto castalloys. One method is based on the Silicoating system (Kulzer Inc., Irvine, Calif.). The Silicoating system provides a pyrolytically applied silica surface (SiO,-C) to which composite resin will bond by 419