Compressive and Diametral Tensile Strength of TitaniumReinforced Composites Brett I . Cohen, Ph.D.,* Allan S. Deutsch, D.M.D.,' Spyridon Condos, D.D.S.,' Barry Lee Musikant, D.M.D.: and Warren Scherer, D.D.S.§
This article determines the compressive and diametral tensile strength of two titanium-reinforced composites (Bis-GMA-based),Ti-Core and Flexi-Flow cem with titanium and compares their strengths to dentin and commercially available core materials and cements. In addition scanning electron microscope (SEMI photographs were taken of Ti-Core and Flexi-Flow cem with titanium. Compressive and tensile loading was performed on a modifled universal testing apparatus. Ti-Core and Flexi-Flow cem with titanium were measured to have compressive strengths of 41,132 and 41,876 psi and tensile strengths of 5219 and 4930 psi, respectively. Statistically (ANOVA,one-way analysis of variance), these titanium-reinforced composites are stronger in compressive and tensile strength than Ketac-Silver, Flecks zinc cement, Durelon, Ketac-Cem, and GC Miracle Mix. Both titaniumreinforced composite materials approach the compressive and diametral tensile strengths of dentin (43,100 and 6000 psi). SEMs revealed that the titanium was uniformly and homogeneously interspersed within the resin matrix of the material.
he use of a composite resin restorative system to restore teeth due to caries and/or fracture before placement of a crown restoration is well documented in dental literature.'-" Since the development of the dental restorative composite resin system (Bis-GMA-based)by Bowen, researchers have been trying to improve existing composite resin systems and alter their characteristics for improved clinical applications. Studies of fatigue associated with composite resins have shown that there is a strong correlation between fatigue and the compressive and diametral tensile strength of dental compositeresin materials. 12.13 The relationship between fatigue and compressive and tensile strength seems to indicate that composite resins with higher compressive and tensile strength will withstand fatigue better and longer.I2Therefore, a possible way for reducing failure associated with dental composite resins due to age and function is to improve the existing compressive and tensile strengths for these dental restorative materials. Many researchers have found that addition of fillers to resin systems can result in enhanced characteristics
Vice-President of Dental Research; tCo-director of Dental Research: EssentialDental Laboratories. S. Hackensack. New Jersey. $PracticingDentist/Cllnical Instructor. New York University College of Dentistry:*Assistant Professor and Director of the Advanced Education Program in General Dentistry. New York Unlversi@ College of Dentistry. New York. New York Address reprint requests to Brett I. Cohen. Ph.D.. Essential Dental Laboratories, 89 Leuntng Street. S . Hackensack. NJ 07606 8 1992 Decker Periodicals Inc.
such as increases in compressive and tensile strength.1e1e For example, fillers such as quartz glass, barium glass, zirconia-silica, amorphous silica, micas, glass powders, alumino silicates, silicon dioxide, and many others have all been used to enhance the physical characteristics of a given dental resin. One of the aims of this experiment was to see if the addition of titanium with conventional fillers to a BisGMA-based dental resin resulted in significantincreases in the compressiveand tensile strength. Titanium is well known in dental literature as a chemically inert metal with excellent biocompatibility and anticorrosive Addition of titanium with conventional flllers was performed on two different viscosity consistencies that included a low viscosity post cement (FlexiFlow cem with titanium, Essential Dental Systems, S. Hackensack, NJ) and a higher viscosity core build-up paste (Ti-Core, Essential Dental Systems). This study determined the compressive and diametral tensile strength of two titanium-reinforced composite systems and compared their strengths to commercially available core materials, cements and dentin. Also included in this study are the scanning electron microscope photographs (SEM) of the titanium-reinforced post cement, Flexi-Flow cem with titanium and the titanium-reinforced core material, '&Core.
MATERIALS AND METHODS The experiment was divided into two parts. In part one, compressive strengths were tested for each group
and in part two, diametral tensile strengths were tested for each group. The nine separate groups included group 1-Ti-Core, group 2-Flexi-Flow cem with titanium, group 3-Flexi-Flow cem (without titanium), group 4Den-Mat Core Paste (Den-MatCorporation,SantaMaria, CA), group 5-Ketac-Silver (ESPE-Premier, Norristown, PA), group 6-Durelon liquid and powder (ESPE-Premier), group 7-Flecks zinc cement (Mizzy, Inc. Clifton Forge, VA), group 8-Ketac-Cem (ESPE-Premier), and group 9-GC Miracle Mix (GC International Corporation, Tokyo, Japan) (Table 1).Each group comprised a minimum of 10 samples. All samples were prepared according to the manufacturer's directions. Samples for diametral tensile strength were prepared according to ADA Specification number 27 (Resin-Based Filling Materials). Cylindrical samples for diametral tensile and compressive strength were made with the use of templates. Each cylinder sample was allowed to cure for 1 hour and then placed at 100%humidity for 24 hours (before testing. After this 24-hour period, the samples were allowed to air dry before compressive and tensile loading was performed with the exception of the glass-ionomer samples (KetacSilver, GC Miracle Mix, and Ketac-Cem), which were tested while the samples were wet. The compressive strength was calculated from the following equation:
cross-head speed of 0.25 inches per minute (0.635 cm/ min) resulted in samples that were crushed. The load in
pounds applied to each test specimen was read off a digital display that recorded the highest value obtained. The compressive or diametral tensile strength was then calculated and expressed in pounds per square inch (psi).
STATISTICAL METHODS The data on diametral tensile and compressive strength were each separately analyzed using one-way analysis of variance (ANOVA). The ANOVA factor was "group." There were nine groups, numbered 1 to 9, respectively, as follows: Ti-Core, Fled-Flow cem with titanium, Flexi-Flow cem (without titanium), Den-Mat Core Paste, Ketac-Silver, Durelon, Flecks zinc cement, Ketac-Cem, and GC Miracle Mix. When ANOVA showed a significant difference between groups, Duncan's multiple range test was used to determine, specifically, which groups differed from one another.26
SCANNING ELECTRON MICROSCOPE (SEM) METHODS Samples were fabricated by mixing Ti-Core and Flexi-Flow cem with titanium base and catalyst into thin sections. These specimens were desiccated and coated with a thinfilm of gold-palladium alloy within a vacuum coating unit. The specimens were then examined in a scanning electron microscope, Super I11A (International Scientific Instruments, Avon, CT), at an accelerated voltage of 10 kV. For each specimen, representative electron micrographs werf:taken. Electron micrographs were taken of Ti-Core at 700 X, 1200 X, and 3000 x magnification.Electron micrographs were taken of FlexiFlow cem with titanium at 500 x, 700 x, and 3500 x magnification.Images were recorded using Polaroid type 55 (positive/negative)film, and the negatives were fixed with a sodium sulflte solution.
P Compressive Strength = n.I-2 where parameters p and r are, p = pounds of force at fracture (load) and r = radius of the sample. The diametral tensile strength was calculated from the following equation: 2.P Diametral Tensile Strength = n*d*1 where parameters p, d, and 1 are: p = pounds of force at fracture (load), d = diameter of sample, and 1 = length of sample. A force applied with a modiffed universal testing machine (Comten Industries, St. Petersburg, FL) at a
Table 1. Manufacturer, Product, and Batch Numbers Used in This Study GroupProduct 1-TI-Core 2-Flexl-Flow cem/wlth Titanium 3-Flexl-Flow cem 4-Den-Mat Paste 5-Ketac-Silver &Flecks zlnc cement Liquid Powder 7-Durelon liquid and powder Llquld Powder bKetac-Cem 9-GC Miracle MIX
Essential Dental Systems Essential Dental Systems Essential Dental Systems Den-Mat Corporation ESPE-Premler
110790 092890 110990 600172 MD 050790
Miny Inc. Mlny Inc.
ESPE-Premier ESPE-Premier ESPE-Premier GC Internatlonal
MD031089 MD011190 MD022290 270801
JOURNAL OF ESTHETIC DENTISTRY VOLUME 4,SUPPLEMENT 1992
Table 3. Means and Standard Deviation in Decreasing Order for the Diametral Tensile Strength (psi) for Groups 1 to 9 and Dentin
RESULTS Compressive Strength Table 2 summarizes the means and standard deviations in order of decreasing compressive strength for each group studied. ANOVA revealed a highly significant difference (p < .0001) between groups. Duncan’s multiple range test shows that there are six distinct groupings (i.e., products are in the same groupings if their compressivestrength means are not significantly different from each other): 2 and 1 versus 4 versus 3 versus 5 versus 9 and 7 versus 6 and 8. In other words, products 1 and 2 are not different from one another, but they each have higher means than 4; 4 has a higher mean than 3; 3 has a higher mean than 5; 5 has a higher mean than 9 and 7; 9 and 7 are not different from each other, and they each have higher means than 6 and 8; and 6 and 8 are not different from each other.
1-Ti-Core 2-Flexi-Flow/Titanium 4-Den-Mat 3-Flexi-Flow 5-Ketac-Silver 9-GC Miracle Mix bDurelon 8-Ketac-Cem 7-Flecks zinc cement
5219 4930 4694 4268 1814 1408 1285 996 90 1
The results indicated that the titanium in both T’iCore and Flexi-Flow cem with titanium appeared to be uniformly interspersed within the composite matrix (Figs. 1to 4)(lowm a w c a t i o n of: 700 x for Ti-Core and 500 x and 700 x for Flexi-Flow cem with titanium). Higher magnification (1200 x, 3000 x for Ti-Core and 3500 x for Flexi-Flowcem with titanium) (see Figs. 2 and 4) revealed that the composite materials are highly fiLled with diffused titanium particles. These titanium particles appear to be embedded within the composite matrix and not just applied to the surface.
Table 3 summarizes the means and standard deviations in order of decreasing diametral tensile strength for each group studied. ANOVA revealed a highly significant difference (p < .0001) between groups. Duncan’s multiple range test shows that there are four distinct groupings (i.e., products are in the same groupings if their diametral tensile strength means are not sign& cantly different from each other): 1, 2, and 4 versus 3 versus 5 versus 9 and 6 and 8 and 7. There is some evidence that 9 and 6 may be different from 8 and 7; however, one of the shortcomings of any multiple comparisons test is that it may not have the power to discriminate between certain groupings that appear to be different. In otherwords, products 1,2, and 4 are not different fi-om one another, but they each have higher means than 3:3 has a higher mean than 5; 5 has a higher mean than each of 9,6,8. and 7 (which are not different from each other).
DISCUSSl0N Addition of titanium to both the post cement, FlexiFlow cem with titanium and core build-up paste, TiCore, resulted in significant increases in compressive and diametral tensile strength as compared to the other dental materials studied. Flexi-Flow cem with titanium measured a compressive and diametral tensile strength
Table 2. Means and Standard Deviation in Decreaslng Order for the Compressive Strength (psi) for Groups 1 to 9 and Dentin Mean
2-Flexi-Flow/Tltanlum 1-Ti-Core 4-Den-Mot 3-Flexi-Flow 5-Ketac-Silver 9-GC Miracle Mix 7-Flecks zinc cement 6-Durelon 8-Ketac-Cem
41876 41 131 32741 29534 16697 14197 12198 9152 9142
f 3273 f 3662 f 2690 It 4352 f 2318 f 2653 f 1150 iz 886 f 1448
f 529 f 328 k 703 f 297 k 322 f 450 f 214 f 235 f 145
Scanning Electron Microscope
Figure 1. SEM of Ti-Coreat 700 x magnification.
Figure 2. SEM of Ti-Core at 1200 x (leg?) /3000 x (right) magnification.
Figure4. SEMofFleld-Flowcemwithtitaniumat700X [k$)/ 3500 x (right)magniflcation.
........................................................................................................................ 45000 40000
5CD L 0)
Flex)-Flow TI Flexi-Flow Dennal Ketac-Silver Durelon Fleck's (ZnPl Ketac-Cem GC t l i r a c l e n i x
n 15000 0
10000 5000 0
Figure 3. SEM of Flexi-Flow cem with titanium at 500 x magnification.
Figure 5. Compressive strength of groups 1to 9 and dentin.
of 41,876 and 4930 psi respectively, while Ti-Core measured a compressive and tensile strength of 41,131 and 5219 psi. These values are now approaching the compressive and diametral tensile strength of dentin, which was measured to be 43,100and 6000 In all groups studied, the composite, Den-Mat Core Paste, the glass ionomer cements, Ketac-Silver, KetacCem, and GC Miracle Mix, the zinc phosphate cement (Flecks), and the polycarboxylate cement (Durelon) measured compressive and diametral tensile strengths consistently lower than that of the titanium-reinforced composites (Figs. 5 and 6). Both Ketac-Silver and Ketac-Cem are reported to have a compressive and diametral tensile strength of 27,550,17,400psi and 2030,1305 psi, respectively.28 Here, we report a compressive and diametral tensile
strength of 16.697,9142 psi and 1814,996 psi. The values for the compressive and tensile strength in this study seem to be consistently lower than that found in the literature by Wilson and M~Lean.~" Both Flecks zinc cement (zinc phosphate cement) and Durelon (polycarboxylate cement) are reported to have compressive and diametral tensile strengths of 17,000,10,200psi and 1200. 1830 psi, re~pectively.~~ Here, we report a compressive and diametral tensile strength of 12,198,9152 psi and 901. 1285 psi. T h e values for the compressive and tensile strength in this study seem to be consistently lower than that found in the literature by O B ~ i e n . ~ ~ It is interesting to note that upon mMng of the titanium-reinforced composites a definite exothermic reaction was noted. The material was felt to become
JOURNAL OF ESTHETIC DENTISTRY VOLUME 4,SUPPLEMENT 1992
2. Diametral tensile strength of the titanium-reinforced composite resins was statistically greater than any other group tested except for Den-Mat Core Paste. Their strengths were also very close to the strength of dentin. 3. SEM revealed that the titanium was homogeneously incorporated within the resin matrix of the composite resin.
Diametral Tensile Strength
De"lin TI-COle Flex,-Flaw TI Flex>-Flow Denflsl
Kela~-Sllver D"d0" Fleck6 C n P I
GC Miracle flb
1. Brady WF. Reisback MH. A restorative resin foundation material. J Prosthet Dent 1982;48:676-679. 2. Spalten RG. Compositeresins to restore mutilated teeth. J Prosthet Dent 1971;25:323. 3. Johnson JK,Schwartz NL, Blackwell RJ.Evaluation and restoration of endodonticallytreated posterior teeth. J Am Dent Assoc 1976;93:579. 4. Rose LA. Composite build-up technique to restore a molar crown. Dent Surv 1973;49:36. 5. Janis J M . Lugassy AA. Pin-retained compositeresin buildup for extensively broken-down vital teeth. J Am Dent Assoc 1972;85:346. 6. Baraban DJ. Immediate restoration of pulpless teeth. J Prosthet Dent 1972;40:607. 7. Landwerlen JR, Berry HH. The composite resin post and core. J Prosthet Dent 1972;28:500. 8. Hormati AA. Denehy GE. Retention of cast crowns cemented to amalgam and composite resin cores. J Prosthet Dent 1981;45:525. 9. Stahl GJ,ONeal Rl3. The composite resin dowel and core. J Prosthet Dent 1975;33:642. 10. Feller RP,Ricks CL, MatthewsTG,Santucci EA. Three-year clinical evaluation of composite formulations for posterior teeth. J Prosthet Dent 1987;57:544. 11. de Lange C,Bausch JR, Davidson CL. The influenceof shelf life and storage conditionson some propertiesof composite resins. J Prosthet Dent 1983;49:349. 12. Soderholm KJ. Relationship between compressive yield strength and filler fractions of PMMA composites. Acta Odontol Scand 1982;40:145. 13. Mjor IA.Revision av fyllningar.Tandlakartidningen 1980;
Figure 6. Diametral tensile strength of groups 1 to 9 and dentin.
quite warm upon setting. We can only hypothesize that the titanium in the compositemay be acting as some sort of catalyst in converting double bonds to single bonds and thereby increasing the percentage cure of the material. This may be one explanation for the increase in physical properties. Another explanation for the increase in strength may come if the titanium is actually crosslinking to the polymers themselves. This may give an overall more rigid and stronger structure. We feel it is important that the core build-up material have a strength similar to that of dentin, especially in restorations where the core is composed of both dentin and core material. Similar strength will prevent uneven flexure of the core material under function and hence premature fatigue failure of the core and the restoration. Similar compressive and diametral tensile strengths will also help lessen ditching when going from dentin to composite during preparation of the core with the dental handpiece. Similarly, an ideal post cement should be strong in compressive and diametral tensile strength and have strengths that approach dentin in order to hold a post more securely in the canal. Dental composite resin cements bonded to the dentin seem not to be failing at the cement dentin or post cement interphase, but rather the failure seems to come cohesively within the cement itself.
72:375. 14. von Fraunhofer JA, Curtis P. The physical and mechanical properties of anterior and posterior composite restorative materials. Dent Mater 1989;5:365-368. 15. Craig RG. Chemistry, composition, and properties of composite resins. Dent Clin North Am 1981;25:219-239. 16. Dennison JB. Craig RG. Physical properties and finished surface texture of composite restorative resins. J Am Dent Assoc 1972;85:lOl. 17. Draughn RA, Harrison A. Relationship between abrasive wear and micro-structure of composite resins. J Prosthet Dent 1978;40:220. 18. Fan PL. Dennison JB, Powers J M . Properties of conventional and micro-filled composites. J Mich Dent Assoc 1980:62:455. 19. AkagawaY. Hashimoto M. Kondo N,YamasakiA, Tsuru H. Tissue reaction to implanted biomaterials. J Prosthet Dent 1985;53:681. 20. Keller JC, Young FA, Hansel B. Systemic effects of porous Ti dental implants. Dent Mater 1985;1:41-42. 21. Kasemo B.Biocompatibilily of titanium implants: surface science aspects. J Prosthet Dent 1983;492332.
CONCLUSIONS A new class of titanium-reinforced composite resin
was examined.A cement and a core material were tested for compressive and diametral tensile strength. SEM examination of the materials was also performed. 1. Compressive strength for the titanium-reinforced composite resins was statistically greater than any other group tested and very close to the strength of dentin.
Noncarious Cervical Lesions
22. Miyakawa 0 ,Watanabe K. Okawa S, Nakano S. Kobayashi M, ShiokawaN. Layered structure of cast titanium surface. Dent Mater 1989: 8:175-185. 23. Smith DC, Williams DF. Biocompatibilityof dental materials. Vol4. Boca Raton, FL: CRC Press, 1982. 24. Toth RW. Parr GR, Gardner LK. Soft tissue response to endosseous titanium oral implants. J Prosthet Dent 1985; 54:564.
25. Underwood E J . Trace element in human and animal nutrition. 4th. Ed. New York Academic Press, 1977. 26. Zar JH. Biostatistical analysis. Englewood Cliffs, N J : F'rentice-Hall, 1974. 27. OBrien WJ. Dental materials: properties and selection. Chicago: Quintessence Publishing, 1989:538-543. 28. Wilson AD. McLean JW.Glass-ionomer cement. Chicago: Quintessence Publishing, 1988:6&68.
Noncarious Cervical Lesions: The Decision To Ignore or Restore John 0. Grippo, D.D.S.*
Avariety of unusual noncarious cervical lesions (NCL)are depicted that appear to negate W.D. Miller's toothbrush/dentifrice abrasion theory and demonstrate that other factors may be involved in their etiology. Confusion exists in the designation of NCL ever since G.V. Black stated in 1908 that toothbrush/dentifrice abrasion is an erosive effect. Since abrasion and erosion are two distinct activities, it is suggested that dentistry adopt the same terminology as chemical engineering in order to foster improved communication between the sciences. The term "abfraction" has been used to supplant erosion because it seems more appropriate when describing the loss of tooth substance attributable to effects of occlusal loading forces as well as the physiochemical breaking that occurs during stress corrosion. Numerous reasons, based on accepted engineering principles, indicate that NCL should be restored. It is incumbent on dentists to become cognizant of these reasons, since this would help them inform patients of the benefits to be gained by restoring such deficient areas.
The fist 11 reasons (listed below) are based on established engineering principles, while the remaining reasons are additional benefits the patient derives from having these areas restored. Their etiology, although a dilemma somewhat shrouded in mystery, is becoming more clear because of advances in modem biodental engineering technology. These regressive cervical alterations of teeth, which have been observed for hundreds of years, have been called notchings, grooves, "keilformigeDefekte" (German, meaning wedge-shaped defects),' wastings,l abrasions, erosions, explosion^,^ ablation^,^ or abfraction~.~ Most dentists, when asked the reason for gingival recession and tooth substance loss appearing at the gingival margin, ascribe these occurrences to overzealous tooth brushing with a hard brush. This concept is readily accepted by the patient; however, there are a variety of lesions, found in unusual locations, that make this simplistic explanation unacceptable.
ncreased longevity and the subsequent increased number of dentate humans are established and readily accepted facts. Dentistry, through improved personal oral hygiene, fluoridation, diet modiflcation. and advanced restorative procedures, has contributed to this longevity of teeth. These preventive measures have resulted in a reduction of caries, thus enabling other areas of dentistry to gain more attention (e.g., caries-free cervical hard tissue lesions) (Figs. 1 and 2). This article attempts to clarify the classification of noncarious cervical lesions (NCL) and presents sound reasons for their restoration, whether they be abrasive, erosive, corrosive, abfractive, or combined in nature.
*SeniorLecturer.SchoolofEngineerhg.BioengineerlngPrOgram.Western New England College, Springfield. Massachusetts Address reprint requests to John 0. Grlppo, D.D.S.. 123 Dwlght Road, Longmeadow, MA 0 1101 0 1992 Decker Periodicals Inc.