of new adhesive
Shane N. White, MA, BDentSc, University of Southern of Stomatology, Beijing
MS,a and Zhaokun of Dentistry, Beijing,
This study determined and compared the film thicknesses of new adhesive luting agents. The method was in compliance with American National Standards Institution/American Dental Association (ADA) Specification No. 8 for zinc phosphate cement. Each of the 20 materials tested was manipulated exactly as described in the manufacturers’ instructions. An electronic gauge with an accuracy of 0.6 pm was recalibrated after each recording, and each luting agent was measured 10 times. The mean film thickness and standard deviation were calculated for each luting agent; an analysis of variance and a multiple comparison test were also performed. Nine materials satisfied the ADA type I specification for film thicknesses less than 25 pm, and these included a hydroxyapatite cement, glass ionomer cements, zinc phosphate cements, and polycarboxylate cements. Five other materials met the ADA type II specification for film thicknesses of less than 40 pm, and these included a glass ionomer cement, a resinous cement, a zinc phosphate cement, and glass ionomer-resinous hybrids. Six resinous cements recorded film thicknesses greater than 40 pm, and suggestions were made regarding future development and research.(J PROSTHET D~~~1992;67:782-5.)
mc phosphate cement has been the principal luting agent of choice for the cementation of castings.’ Several new classesof adhesive luting agents (ALA) have recently been introduced.2-7 Most of these materials were initially developed as restorative materials or as liners and bases, but were then reformulated as luting agents. They include glass ionomer cements, polycarboxylate cements, various types of resin that are mainly Bis-glycidylmethacrylate (Bis-GMA) derivatives with some inorganic filler, glass ionomerlresinous hybrid cements, and hydroxyapatite cements. Some of the new ALAS have demonstrated substantial reduction of microleakage and improved retention.8, g The physical properties of most of these ALAS have also been shown to be comparable to, or better than those of zinc phosphate.5, 6,lo-l3 Different components, particle sizes,viscosities, fillers, and setting reactions substantially influence the film thickness of various classesof ALAS. Few ALAS have had their film thicknesses reported in the literature, and comprehensive comparative analyses have not been reported. The purpose of this study was to determine and compare the film thicknesses of different classesof new adhesive luting agent. MATERIAL
The method used was in broad compliance with American National Standards Institute/American Dental Association Specification No. 8 for zinc phosphate cement, secaResearch Dentistry, bAssociate Institute
Assistant and Professor, Department of Restorative USC School of Dentistry. Professor, Department of Dental Materials, Research of Stomatology, Beijing Medical University.
tion 126.96.36.199 Tests were conducted at a room temperature of 23’ C, with a relative humidity of 67%. All materials were manipulated according to manufacturers’ instructions. All dual-cure resins were cured with a fiberoptic visible light-curing unit (Marathon 2, Den-Mat, Santa Maria, Calif.). The encapsulated glass ionomer cements were mixed in an amalgam triturator (Capmix, ESPE, Seefeld/ Oberbay, Germany). Before testing, two experienced investigators calibrated their techniques until uniformity was established. One researcher then made all the test specimens. A portion of the standard mix of cement was positioned between two flat round glass plates of uniform thickness, with a surface area of 2 cm2. The identical plates were used in the same orientation for each measurement. Before making each specimen, the plates were cleaned with water, then with acetone, and were left to volatilize. After each manufacturer’s recommended mixing time had elapsed, a load of 15 kg was applied vertically to the plates. An electronic gauge (Minicon Electronic Gage, Seimitsu, Tokyo, Japan), with an accuracy of 0.5 pm and a scale range of 300 pm, was selected. Measurements were made to the nearest micron, and all measurements were recorded 10 minutes after mixing began. The instrument was recalibrated at a 15 kg load on the cleaned glass plates before each measurement; each ALA was measured 10 times. The names, formulations, and manufacturers of each material tested are listed in Table I. The mean film thickness and its standard deviation were calculated for each ALA. The analysis of variance (ANOVA) was performed to determine statistically significant differences between the ALA groups, and Tukey’s multiple comparisons test were computed to determine which ALAS were statistically similar.
I. Luting agent names, formulations, and manufacturers
Modern Tenacin ZP, P-L Shofu Hybond zinc phosphate ZP, P-L Fleck’szinc phosphate ZP, P-L Ketac-Cem GI, P-L
Caulk/Dentsply, York, Pa. Shofu, Kyoto, Japan Keystone, Cherry Hill, N.J. ESPE, Seefeld/Oberbay,
Germany Ketac-Cem caplet GI, CAP GC Fuji I GI, P-L GC Fuji I capsule GI, CAP Shofu glass ionomer GI, P-L HA Bioment HA, P-L Durelon PC, P-L Shofu Hybond
polycarboxylate PC, P-L C + B Metabond R, P-L Thin Film Cement R, P-P Tenure R t DBA
Panavia Ex R, P-L Ultrahond R, P-P, DC All-Bond R, P-L
Marathon R, P-P, DC Infinity
Geristore R/GI, P-P, DC
Germany GC, Tokyo, Japan
GC, Tokyo, Japan Shofu, Kyoto, Japan Yamahachi, Gamagori,Japan ESPE, Seefeld/Oberbay, Germany Shofu, Kyoto, Japan Sun Medical, Kyoto, Japan
Den-Mat, Santa Maria, Calif. Den-Mat, Santa Maria, Calif. Kuraray, Okayama Japan Den-Mat, Santa Maria, Calif. Bisco,Downers Grove, Ill. Den-Mat, Santa Maria, Calif. Den-Mat, Santa Maria, Calif. Den-Mat, Santa Maria, Calif.
ZP, Zinc phosphate; GI, glass ionomer; HA, hydroxyapatite PC, polycarboxylate; R, resin; RIGI, resin-glass ionomer hybrid; P-L, powder-liquid; P-P, paste-paste; CAP, capsule; DBA, dentin bonding agent; DC, dual-cure.
RESULTS The ANOVA demonstrated statistically significant differences between the various adhesive luting agents at the p < 0.0001 level. The Tukey multiple comparisons test at (Y= 0.05 verified statistically similar ALA groups that were different from other groups (Table II). Mean film thicknesses and standard deviations for each ALA group are displayed in Table III and Fig. 1. DISCUSSION The material with the lowest film thickness, a hydroxyapatite cement, had a significantly lower film thickness than the other cements but some of its other physical properties are inferior.7 The next eight ranked materials were all statistically similar to one another, and all recorded mean film thicknesses less than 25 pm; they therefore can be classified as American Dental Association (ADA) type I materials.14 According to ADA Specification No. 8, type I materials are “designed for the accurate seating of precision appliances and for other uses.” The following classes of materials were represented in this group: hydroxyapa-
Tukey multiple comparison test
HA Bioment Ketac Cem Ketac Cem caplet Tenacin Shofu Hybond zinc phosphate Durelon GC Fuji I GC Fuji I capsule Shofu Hybond polycarboxylate Shofu glass ionomer C t B Metabond Fleck’s zinc phosphate Geristore Infinity Den-Mat thin film cement + TE Den-Mat thin film cement Panavia Ex Ultrabond All-Bond Marathon Z’E, Tenure, Den-Mat. Statistically similar groups, linked by vertical lines.
tite, glass ionomer, zinc phosphate, and polycarboxylate cements. ADA type II materials can have a maximal film thickness of 40 pm. ADA type II materials are “recommended for all uses except the cementing of precision appliances.“14 Classesof material represented in this group, but not in the ADA type I group, included resins and glass ionomer-resinous hybrids. Luting agents are selected on the basis of established criteria for specific clinical situations. When the class of luting agent has been chosen, any member of a specific class that is not inferior to other members of that class can be used (Table II). Two glassionomermaterials (Ketac Cem, ESPE, Seefeld/ Oberbay, Germany; and GC Fuji I, GC, Tokyo, Japan) were tested in conventional powder-liquid form and in a prepackaged capsule form triturated on an amalgamator. No significant difference was recorded between either form, but one glass ionomer cement (GC Fuji I) was more sensitive to triturator energy settings and times, and tended to set rapidly. It was discovered that the glass ionomer test cement between the glass plates required longer to set than the extruded excess,or the excessremaining on the mixing pad. A similar phenomenon has also been noted clinically. One resinous cement (Panavia Ex, Kuraray, Okayama, Japan), known for rapid anaerobic setting, displayed an inordinately high standard deviation (Table III). Despite careful handling of this material according to the manufacturer’s directions, it appeared to begin to set before the glass disks were seated. Dentists are advised to manipulate this material rapidly, and to always maintain a thin film
1. Film thickness means and standard deviations in microns. 1,
ation. III. Film thickness means and standard deviations* in microns
HA Bioment Ketac Cem Ketac Cem caplet Tenacin Shofu Hybond zinc phosphate Durelon GC Fuji I GC Fuji I capsule Shofu Hybond polycarboxylate Shofu glass ionomer C + B Metabond Fleck’s zinc phosphate Geristore Infinity Den-Mat thin film cement + Tenure Den-Mat thin film cement Panavia Ex Ultrabond All-Bond Marathon *Values
9.7 19.5 19.6 20.1 20.5 22.5 22.5 23.0 23.9 25.4 26.3 28.1 29.5 30.7 41.7 43.2 44.7 77.6 89.0 106.7
(1.2) (1.6) (0.7) (0.7)
0.1) (2.0) 0.6) (1.6) 0.1) (0.5)
(2.3) (2.6) (3.4)
(2.7) (11.8) (4.3)
over a broad area for maximal exposure to air, because the cement should never be allowed to pool. A resinous cement (Den-Mat Thin Film Cement, DenMat, Santa Maria, Calif.) was tested both with and without a dentin bonding agent (Tenure, Den-Mat). Surprisingly, the standard deviation with the dentin bonding agent was much less than without the agent. The film thickness with the dentin bonding agent was slightly lower but not statistically different than without the dentin bonding agent. Possibly the dentin bonding agent exerted
some local control on the polymerization of the resinous film.lE’ Type II resin-based materials, and some cements with even greater film thicknesses, are currently used routinely for cementation of fixed partial dentures (FPDs). Some of these materials do not meet ADA type I specifications or do not possess other beneficial properties, such as increased tensile and compressive strength, the ability to bond strongly to casting alloys or to tooth structure, and the ability to decrease marginal microleakage.6, I1 Laboratory procedures must be controlled to compensate for luting agent.s with high film thicknesses; one approach would be to lower the expansion ratios of intracoronal casting investments. Greater thickness of die relief could also be used for the fabrication of extracoronal castings.16,l7 The generally high film thickness of the resins is not as critical in the seating of porcelain inlays, onlays, veneers, and indirectly fabricated composite resin restorations. These restorations typically shrink during fabrication and have poorly adapted margins. The high strength of the resins, their ability to bond strongly to tooth structure, their acceptable wear characteristics, insolubility, and tooth-like optical properties make them ideal for this purpose. Two resins specifically marketed for this purpose (Ultrabond, Den-Mat; and Marathon, Den-Mat) were included as negative controls for the resins marketed for cementation of conventional FPDs (C+B Metabond, Sun Medical, Kyoto, Japan; Den-Mat Thin Film Cement; Panavia; and All-Bond, Bisco, Downer’s Grove, Ill.). Several factors influence the film thickness of a luting material. These include the substrate that the material is tested against, the size or shape of filler particles, the viscosity of the unset material, and its rate of set. The high viscosity resin-based materials set rapidly before they can
flow sufficiently to achieve their theoretical minimal film thicknesses. A resin with a high filler content will possess improved physical properties and decreased shrinkage on polymerization, but a higher filler content concomitantly elevates viscosity and diminishes flow. The rate of set is also dependent on resin polymer size; smaller polymers generally set faster. The relative amounts of initiator and inhibitor are commonly chosen to accomplish maximal polymerization. Generally a greater effectiveness and concentration of initiator will increase the rate of reaction and the number of new bonds formed, but will reduce the time for flow before set. Therefore there is a balance between achieving optimal physical properties and minimal film thickness with a resinous cement. The manufacturers should carefully consider these factors and develope new resinous cements, rather than simply modify existing systems. The results of this study are in agreement with those of numerous other studies.‘0-13p17*ls However, one study,lg using a similar methodology, reported considerably lower values for the film thickness of zinc phosphate cement. The authors noted their unusual results, but offered no explanation.lg Jorgensen20 demonstrated that the film thickness of zinc phosphate cement is related to, but not the same as, marginal seating of cast restorations. Both marginal seating and film thickness are related to the magnitude and duration of the applied load, the viscosity of the luting agent, and the ambient temperature.20 These factors were all carefully controlled in ADA Specification No. 8, and in this study. Jorgensen20 also demonstrated the importance of the hydraulic environment on the behavior of zinc phosphate cement, related to preparation taper, casting relief, cement escape grooves, vents, and surface roughness. Many ALAS interact chemically or mechanically with dentin, so the testing of film thickness on dentinal surfaces should be examined, as should the effect of ALAS on the seating of standardized conventional castings. SUMMARY The film thicknesses of certain new adhesive luting agents were unacceptably high according to ADA Specification No. 8. Suggestions have been made with respect to further development and research.
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DR. SHANE N. WHITE DIRECTOR OF RESTORATIVE RESEARCH DEPARTMENT OF RESTORATIVE DENTISTRY USC SCHOOL OF DENTISTRY 925 WEST 34~~ STREET, No. 4367 Los ANGELES, CA 90089-0641