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Retentive properties of five different luting cements on base and noble metal copings
Retentive properties of five different luting cements on base and noble metal copings Sule Ergin, DDS,a and Deniz Gemalmaz, DDS, PhDb Faculty of Dentistry, Marmara University, Istanbul, Turkey Statement of problem. The retention of indirectly fabricated restorations can be compromised by short or over-tapered tooth preparations. Purpose. The aim of this study was to evaluate the retentive properties of 5 different luting cements on base and noble metal copings to short and over-tapered preparations. Material and methods. Eighty extracted mandibular premolars were prepared to receive full cast copings with a flat occlusal surface, 33° taper, and 3-mm axial length. Half of the standardized metal copings were cast in an AuAgPd alloy, whereas the other half were cast in an NiCr alloy. Cementation was performed with 5 different luting cements through use of 5 kg of pressure in 90% relative humidity. Specimens were stored in distilled water at 37°C for 24 hours and thermocycled between 5°C and 55°C for 5000 cycles, with a dwell time of 30 seconds. After thermocycling, vertical tensile force was applied in a Zwick universal testing machine with a constant speed of 1 mm/min until separation was noted. A 2-factor analysis of variance was used to analyze the data, with a significance level of ␣ ⫽ .05. Results. Mean dislodgement forces for AuAgPd crowns and NiCr crowns were 120.88 N and 143.09 N, respectively, for zinc phosphate cement; 135.45 N and 150.38 N for Principle; 145.88 N and 220.71 N for Meron; 276.85 N and 225.61 N for Avanto; and 300.92 N and 381.02 N for Fuji Plus. Conclusion. Within the limitations of this study, Fuji Plus and Avanto showed significantly higher retentive strengths for AuAgPd copings in comparison to the other cements tested (P ⬍ .05). The retentive strength of Fuji Plus was significantly higher than those of the other cements tested with NiCr copings (P ⬍ .05). (J Prosthet Dent 2002;88:491-7.)
CLINICAL IMPLICATIONS In this in vitro study, given the short clinical tooth preparation with a high angle of convergence, the resin-modified glass ionomer cement Fuji Plus retained NiCr cast copings best. For AuAgPd cast copings, Avanto resin cement and Fuji Plus provided superior retention in comparison to the other luting cements tested.
D
ental luting cements are the link between indirectly fabricated restorations and the prepared tooth structure. The retention of these restorations can be compromised by short or over-tapered tooth preparations. Zinc phosphate cement has been the most popular luting material for more than 90 years. Despite its high solubility and lack of adhesion, excellent clinical performance, which can be attributed to its high fatigue strength,1 has been reported for fixed partial dentures cemented with zinc phosphate cement.2 Nevertheless, to prevent pain during cementation and to achieve better retention of cast restorations, alternative cements such as polycarboxylate and glass ionomer cements were introduced.3,4 The adhesion of polycarboxylate-based materials has been suggested to occur as a result of chemical bonding between negative a
Research Assistant, Department of Prosthodontics. Associate Professor, Department of Prosthodontics.
b
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carboxylate groups in the water-suspended polymer and positive calcium ions in the dental hard tissue.3,5 A considerable level of adhesion to both dentin and enamel has been measured in vitro for these cements,6-8 which was also partly confirmed by other clinical studies.9,10 The introduction of new adhesive techniques and materials to be used in restorative dentistry also led to the development of new dental cements with improved bond strengths. Recently introduced dental luting materials include the composites and resin-modified (hybrid) glass ionomers. The ability to adhere to multiple substrates,11,12 high strength, and insolubility in the oral environment are major advantages of the composite luting cements.13 Resin-modified glass ionomer luting cements are a combination of glass ionomer and resin chemistries set by an acid-base reaction between aluminosilicate glass powder and an aqueous solution of polyalkenoic acids modified with methacrylate groups, as well as chemically initiated free-radical polymerization of methacrylate units.14 Resin-modified glass ionomer THE JOURNAL OF PROSTHETIC DENTISTRY 491
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cements generally behave in an intermediate manner between composite and glass ionomer cements.13 The biggest advantage of these types of cements is their easy use, because multiple bonding steps are not required. For recently introduced materials, however, the number of both clinical and laboratory studies regarding performance is limited. The effect of luting agents on casting retention has been assessed in several in vitro studies.15-24 These retention tests, which typically were performed by removing a standardized casting from a stylized crown preparation with direct tensile loading, focused on the effects of the type of cement,15-23 type of metal,19 preparation taper,18,25-29 preparation height,18 surface roughness,15,20,24 and application of dentinal desensitizing agents.17,21,23 The studies related to crown retention and luting cement type reported that adhesive resins had consistently greater retention than zinc phosphate.18-21,23 Some controversial results regarding the retentive strengths of different types of luting cements also exist in the literature.19,22 Pameijer and Jefferies19 investigated retentive strengths of cast gold crowns cemented with 18 different luting agents on standardized tooth preparations with a 33° angle of convergence. They concluded that the values of retentive forces for crowns cemented with resin cements were significantly higher in comparison to those cemented with a glass ionomer cement. In a recent study, however, the retentive strengths of cast gold crowns cemented with a glass ionomer, a compomer, and a resin cement were evaluated with the use of a similar experimental design having a 10° convergence angle, and it was reported that compomer and glass ionomer cements showed significantly better retentive strengths than the resin cement.22 The authors attributed the lower retentive strength of the resin cement to the lack of an adhesive system and stated that resin cements should be used in combination with adhesive systems to achieve favorable results.22 The choice of metal may also affect retention of the cemented crown. Although many comparative studies exist showing metal bonding of various types of resin composite material used for resin-retained fixed partial dentures,30-34 limited information is available concerning the retentive strengths of base and noble metal crowns cemented with different luting cements.19 In a single study, Ernst et al22 investigated the effect of applying an additional bonding layer to the inner surface of the high gold crowns (AuAgPt) cemented with a compomer cement. They concluded that there was no significant improvement in the retentive strength related to application of an additional bonding layer on the internal surface of the crowns.22 The aim of this study was to evaluate the retentive properties of 5 different luting cements (a zinc phosphate, a glass ionomer, 2 different resin-modified glass ionomers, and a resin cement) on base (NiCr) and noble 492
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(AuAgPd) metal copings to short and over-tapered preparations.
MATERIAL AND METHODS Eighty recently extracted caries-free mandibular premolars of similar size were selected and stored in deionized water. The teeth were embedded in acrylic resin blocks to 2 mm below the cementoenamel junction. To retain the tooth in the resin, a hole was drilled, through which a stainless steel wire was placed. All standardized tooth preparations for complete metal copings were performed on a jeweler’s lathe (ZM 1500; Zime Sevindik, Adana, Turkey) with a low-speed handpiece and a diamond bur (Mani Dia-burs, 01B-2033; Mani Inc, Utsunomiya, Japan) under a copious amount of water at a preparation angle of 16.5°. Thus the final preparation had a 33° angle of convergence. The occlusal surfaces were flattened perpendicular to the long axes of the teeth. The cone-shaped preparations were at least 3-mm high, had an occlusal diameter of 3 mm, and were prepared entirely in dentin. If perforation of the pulp cavity occurred during preparation, the tooth was removed from the study. Silicone impressions (Wirosil; Bego, Bremen, Germany) of the prepared teeth were made, and casts were poured in dental stone (Fujirock EP; GC Europe, Leuven, Belgium). The stone dies were trimmed, and 2 coats of die spacer (Isocera; Bego) were applied to each master die, with time allowed for the previous layer to dry. The wax patterns were fabricated by dipping the die in a molten wax (Bredent dipping wax; Bredent, Ulm, Germany) to achieve a consistent thickness of 0.7 ⫾ 0.025 mm. The height of the wax pattern was 3 mm, which was verified with a digital micrometer with a measuring accuracy of 0.01 mm. A wax ring was attached on the occlusal surface of the wax pattern parallel to the long axis of the tooth preparation to allow tensile testing. The wax patterns were sprued and invested with phosphate-bonded investment (Bellastar; Bego). The manufacturer’s directions were followed for mixing, setting time, and wax burnout of the investment. Half of the wax patterns for each experimental group were cast in an AuAgPd alloy (AuroLloyd KF; Bego), and the other half were cast in an NiCr alloy (Wiron 99; Bego). Casting was performed according to standardized techniques in a Nautilius MP-microprocessor– controlled high-frequency vacuum-pressure casting machine (Bego). Minor adjustments necessary to seat the castings on the dies were completed with the use of a small round bur mounted in a laboratory handpiece and a microscope (MZ 12; Leitz, Wetzlar, Germany) under ⫻20 magnification. After the inferior surfaces of the copings were sandblasted with 50-m aluminum oxide particles (Korox 50; Bego), all copings were evaluated for accuracy of VOLUME 88 NUMBER 5
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Table I. Luting cements used in study Product name
Phosphate cement
Meron Principle
Producer
Heraeus Kulzer, Dormagen, Germany
Voco, Cuxhaven, Germany Dentsply L. D. Caulk Division, Del.
Batch No.
Composition
P: 0950340
P: zinc oxide, magnesium oxide
L: 1150340
L: orthophosphoric acid, water, zinc oxide, aluminum hydroxide P: fluoroaluminasilicate glass L: polyacrylic acid, water P: strontium aluminofluorosilicate glass, sodium fluoride, initiators
P: 96660 L: 96614 P: 990318
L: 990318 Fuji Plus
GC Corporation, Tokyo, Japan
P: 120491 L: 260391
Avanto
Voco Cuxhaven, Germany
C: 300391 P: 90583 L: 90582 C: 95679 P: 90617 (A) 91613 (B)
L: OEMA, PENTA, resin matrix, water, inhibitors, initiators P: aluminosilicate glass L: 2-HEMA, polyacrylic acid, proprietary resins, tartaric acid, water C: 10% citric acid, 2% ferric chloride, 88% water P: bariumborosilicate glass, silica, benzoil peroxide L: dimethacrylates UDMA, BIS-GMA vs. amines, inhibitors C: 37% phosphoric acid P: hydrophilic methacrylates, polyfunctional monomers, maleic acid, water, sodium fluoride
Type
Zinc phosphate
P/L ratio (g)
1.2/0.88
Glass ionomer
3/I
Resin-modified glass ionomer
2.5/1.2
Resin-modified glass ionomer
2/1
Resin
1.7/1
P ⫽ Powder; L ⫽ liquid; C ⫽ conditioner; P ⫽ primer.
marginal fit, to a maximum gap of 50 m, with a microscope (MZ 12; Leitz) at ⫻20 magnification. Before cementation, it was also verified that all castings were not self-retentive by ensuring that the copings separated from the tooth preparation dies without any resistance when the specimens were held upside down. Five cements were used for luting the copings: a zinc phosphate cement (Phosphate), a glass ionomer cement (Meron), a resin-modified glass ionomer cement (Principle), a resin-modified glass ionomer cement (Fuji Plus), and a resin cement (Avanto). The castings were randomly divided into 5 experimental groups, and each group consisted of 16 specimens. Sixteen specimens were cemented with 1 of the 5 luting cements, 8 for each alloy group. The same person mixed all luting agents at room temperature on a glass slab using a stainless steel spatula with a stiff blade. The powder-liquid ratios for each cement used were in accordance with the manufacturers’ recommendations and are given in Table I. For each specimen, the powder and the liquid were weighed on an electronic digital microbalance (SBA 41; Scaltec, Hamburg, Germany) that had a measuring accuracy of 0.1 mg. Because the resin-modified glass ionomer cement Fuji Plus and the resin cement Avanto should be used in combination with a conditioner and/or a dentin primer system, tooth surfaces were prepared according to the manufacturers’ instructions before the application of these cements. The dentin was etched for 15 seconds with 37% phosphoric acid for specimens cemented with Avanto, and the dentin was conditioned with a condiNOVEMBER 2002
Fig. 1. Cemented casting placed in Zwick universal testing machine.
tioner containing 10% citric acid for specimens cemented with Fuji Plus. After the preparations were rinsed for 20 seconds and moisture was removed so that the dentin remained visibly moist, copings in the Fuji Plus group were directly cemented. Primer A and B of Avanto resin cement were applied on dentinal surfaces by rubbing with a cotton pellet for 30 seconds, and cementation followed thereafter. The contents of conditioners and dentin primers used for each cement are given in Table I. 493
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Fig. 2. Graphic representation of retentive forces of luting cements in relation to alloy type. Horizontal lines connect values that are not significantly different. Table II. Mean values of separation force (in newtons)
Phosphate Principle Meron Avanto Fuji Plus
AuroLloyd KF
Wiron 99
120.88 (6) 135.45 (51) 145.88 (62) 276.85 (88) 300.92 (59)
143.09 (20) 150.38 (61) 220.71 (52) 225.61 (78) 381.02 (81)
Data are given as mean (SD). Means connected by vertical lines are not statistically different.
A static load of 5.0 kg was applied35 with a custombuilt pressure jig and maintained on the castings for 10 minutes at 90% relative humidity in a humidifier. Excess cement was removed, and specimens were then stored in distilled water at 37°C for 24 hours and thermocycled between 5°C and 55°C for 5000 cycles, with a dwell time of 30 seconds.36 A vertical uniaxial tensile load was applied to each casting with a universal testing machine (Zwick 1120; Zwick GmbH & Co KG, Ulm, Germany) with a constant speed of 1 mm/min, and separation forces were recorded (Fig. 1). The fitted surfaces of the separated castings were examined visually to determine the mode of cement failure. All specimens were fabricated and measured by the same examiner. Separation force data were analyzed statistically by use of 2-way analysis of variance (P ⬍ .05). Duncan multiple range test analysis was also used to distinguish statistically significant groups.
RESULTS Mean and SD values for each luting cement for 2 metal alloys are presented in Table II. The lowest mean 494
values were recorded for zinc phosphate cement for both the AuAgPd alloy (120.88 N) and the NiCr alloy (143.09 N). The SD values observed for zinc phosphate cement were relatively lower in comparison to those for the other luting cements tested. The highest value of mean retentive force (381.02 N) was observed for Fuji Plus for the NiCr alloy. Table III reports the probability values of the mean retentive forces as a function of luting cement and alloy type. There were significant differences in the retentive forces related to luting cement and alloy type and with interactions of the 2 variables. By Duncan multiple range test analysis, Fuji Plus and Avanto showed significantly higher retentive strengths to the AuAgPd alloy in comparison to the other cements tested. The retentive strength of Fuji Plus was significantly higher for the NiCr alloy than the retentive strengths of the other cements tested. In addition, the retentive strengths of Avanto and Meron to NiCr alloy were significantly higher than those of Principle and Phosphate cements (Table II). Analysis of variance results revealed that the differences in the retentive strengths of the luting cements recorded for the 2 alloy types were significantly different for zinc phosphate, Meron, and Fuji Plus cements (Fig. 2). Zinc phosphate, Meron, and Fuji Plus cements showed higher retentive values for the NiCr alloy than for the AuAgPd alloy. The distribution of the mode of cement failure with AuAgPd and NiCr alloys is given in Table IV. Horizontal fracture of coronal dentin occurred in 37.5% of both NiCr and AuAgPd specimens cemented with Fuji Plus (Fig. 3). VOLUME 88 NUMBER 5
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Table III. Analysis of variance results Source of variance
df
Sum of squares
Mean squares
F ratio
P value
Metal Cement Metal ⫻ cement Residual
1 4 4 70
15865.06 482462.3 45561.89 259718.1
15865.06 120615.6 11390.47 3710.258
4.28 32.51 3.07
.04 .001 .021
DISCUSSION Failure of retention of crowns occurs under a combination of masticatory forces repeated over a period of time.24 The in vitro studies that evaluated the retention of luting cements on crowns were performed mostly by direct tensile loading without considering the cyclic loading considered to simulate clinical conditions.16-23 In a single study, Gundler et al25 used an apparatus designed for applying cyclic compressive loading to crowns luted with zinc phosphate cement to investigate the retentive strength of crowns with different convergence angles. The results of this study that simulated clinical loading up to 1 million cycles were in agreement with the results of other studies that evaluated the effect of similar factors on the retentive strength of crowns by using direct tensile loading.18,26 It was recently reported that no fatigue fracture occurred in a zinc phosphate cement layer after repetitive loading of 100 N for 5.5 ⫻ 105 cycles.1 Thus the similarities between the results of the in vitro studies conducted on crowns with cyclic loading25 and direct tensile loading18,26 are thought to be the result of the high durability of the cement film layer after cyclic loading. In a recent study, Yim et al23 pointed out that inconsistent results were obtained in past research that has not controlled preparation surface area when examining the retentive strengths of cemented cast crowns. They showed that the use of standardized crown preparations in combination with a carefully designed tensile testing method produced remarkably lower variation in crown retention values. It can finally be stated that the findings of these studies, which used direct tensile loading, can be considered to relate directly to the clinical situation when standardized crown preparations and methods during specimen fabrication and testing were used. Because the adhesive and mechanical properties of luting cements were shown to be highly affected by the existence of humidity and thermal effects,11 the existence of humidity in the oral environment should also be considered in in vitro testing of luting cement retention. For this reason, all luting agents were allowed to set under humid conditions; the specimens were thermocycled before tensile testing according to the International Organization for Standardization (ISO) amendment 10477.36 The lowest mean values were recorded for zinc phosphate cement for both alloy groups. However, the mean NOVEMBER 2002
Table IV. Distribution of mode of cement failure in percentages Cement totally Cement on tooth Cement totally Dentinal on tooth and crown on casting fracture
Phosphate AuAgPd NiCr Meron AuAgPd NiCr Principle AuAgPd NiCr Fuji Plus AuAgPd NiCr Avanto AuAgPd NiCr
— —
62.5 87.5
37.5 12.5
— —
— —
50 62.5
50 37.5
— —
— —
— —
— —
62.5 62.5
— —
37.5 37.5
75 75
— 12.5
— —
25 12.5
100 100
— —
Fig. 3. Tested specimen shows retention of tooth preparation in coping.
value of retention recorded for zinc phosphate cement was not significantly different from that of the glass ionomer and the resin-modified glass ionomer cement Principle for AuAgPd copings. Fuji Plus and Avanto showed significantly higher retentive strengths to the AuAgPd alloy in comparison to other cements. To increase bond strengths of resin cements, a pretreatment 495
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of the dentin surface with dentin adhesives is commonly used. Avanto resin cement has a similar application of conditioning and priming, which supplied greater retentive force in comparison to zinc phosphate, glass ionomer, and resin-modified glass ionomer cement Principle. Resin-modified glass ionomer cement Fuji Plus, on the other hand, supplied higher retentive forces to both the NiCr and AuAgPd alloys than Avanto resin cement. Fuji Plus also has a conditioner containing 10% citric acid, 2% ferric chloride, and 88% water that dissolves the smear layer and provides an adhesive bond between prepared dentin and the luting cement. The relatively lower performance of the resin-modified glass ionomer cement Principle in comparison to both the resin cement Avanto and the resin-modified glass ionomer cement Fuji Plus can be attributed to the lack of any surfaceconditioning procedure before luting. Thus it appears that resin-based or -modified cements should be used in combination with surface-conditioning agents or adhesive to obtain the best results. The distribution of mode of cement failure revealed that fracture occurred at both the cement-metal and cement-tooth interfaces for copings luted with the zinc phosphate and glass ionomer cements. In no situation was cement observed to completely remain on the prepared tooth. However, cement was completely retained on the prepared tooth for 25% of AuAgPd copings and 12.5% of NiCr copings luted with Avanto resin cement. The adhesive bond of resin cement to tooth structure appeared to enhance superior bond of resin cement to tooth structure. On the other hand, in copings luted with the resin-modified glass ionomer cement Principle, debonded cement was observed to be retained totally on the metal surface for all specimens. This shows that the inadequate bond of Principle to the dentinal surface, most likely resulting from lack of conditioner and primer, causes the weak link of the cemented coping assembly to occur at the cement-tooth interface during tensile debonding. Cohesive dentin fracture observed for copings cemented with the resin-modified glass ionomer cement Fuji Plus was in agreement with the highest retentive values recorded for this cement. Relatively lower SD values recorded for zinc phosphate could be attributed to the assumption that handling zinc phosphate cement was less technique-sensitive. The highest SD values recorded for resin and resin-modified glass ionomer cements indicate that the luting system becomes more technique-sensitive as the adhesive bond to tooth structures is enhanced. An important factor that determines the technique sensitivity of adhesive systems is individual and locational variation in structural characteristics and mechanical properties of dentin with regard to their high impact on dentin bonding.12 It should also be noted that the lowest retentive values recorded for resin and resin-modified glass ionomer cements were 496
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still higher than the highest retentive values obtained with zinc phosphate cement. In this study, a convergence angle of 33° was selected in 3-mm high crown length to approximate the worstcase clinical scenario. By minimizing the mechanical retention from the preparation, the data emphasized the retention arising solely from the cements. It has already been proved that the angle of convergence is an important factor for retention.18,25,26 Therefore the results of this study should be considered within the experimental design of the study, and it is likely that much higher retentive forces can be achieved with ideally prepared teeth. In this study the retentive strengths of 5 different luting cements were evaluated on both base and noble copings. The study was designed to examine over-tapered mandibular premolar tooth preparations with 3-mm heights. Although resin cement and resin-modified glass ionomer cement showed higher retentive strengths, all tested cements provided retentive strengths exceeding clinically expected debonding forces of about 40 N.22 Thus it can be concluded that all 5 test cements can be used satisfactorily when they are prepared according to the manufacturers’ recommendations. The use of resin and resin-modified glass ionomer cements seems to be advantageous when extreme retention problems exist, such as short and/or over-tapered crown preparations.
CONCLUSIONS Under the conditions of this study, Fuji Plus and Avanto showed significantly higher retentive strengths for the AuAgPd alloy in comparison to the other cements tested. The retentive strength of Fuji Plus was significantly higher than the retentive strengths of the other cements tested on the NiCr alloy. In addition, cohesive dentin fracture occurred with resin-modified glass ionomer cemented copings on coping separation. Therefore all 5 test cements can be used satisfactorily when they are prepared according to the manufacturers’ recommendations. However, resin and resin-modified glass ionomer cements seem to be better choices for nonretentive coping preparations. REFERENCES 1. Yamashita J, Takakuda K, Shiozawa I, Nagasawa M, Miyairi H. Fatigue behavior of the zinc-phosphate cement layer. Int J Prosthodont 2000;13: 321-6. 2. Creugers NH, Kayser AF, van’t Hof MA. A meta-analysis of durability data on conventional fixed bridges. Community Dent Oral Epidemiol 1994;22: 448-52. 3. Smith DC. A new dental cement. Br Dent J 1968;124:381-4. 4. Wilson AD, Crisp S, Lewis BG, McLean JW. Experimental luting agents based on the glass ionomer cements. Br Dent J 1977;142:117-22. 5. Beech DR. A spectroscopic study of the interaction between human tooth enamel and polyacrylic acid (polycarboxylate cement). Arch Oral Biol 1972;17:907-11.
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6. Mizrahi E, Smith DC. The bond strength of a zinc polycarboxylate cement. Investigations into the behaviour under varying conditions. Br Dent J 1969;127:410-4. 7. Hotz P, McLean JW, Sced I, Wilson AD. The bonding of glass ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. 8. Øilo G. Bond strength of new ionomer cements to dentin. Scand J Dent Res 1981;89:344-7. 9. Brandau HE, Ziemiecki TL, Charbeneau GT. Restoration of cervical contours on nonprepared teeth using glass ionomer cement: a 4 1/2-year report. J Am Dent Assoc 1984;108:782-3. 10. Jemt T, Stålblad PA, Øilo G. Adhesion of polycarboxylate-based dental cements to enamel: an in vivo study. J Dent Res 1986;65:885-7. 11. Ishijima T, Caputo AA, Mito R. Adhesion of resin to cast alloys. J Prosthet Dent 1992;67:445-9. 12. Marshall GW Jr, Marshall SJ, Kinney JH, Balooch M. The dentin substrate: structure and properties related to bonding. J Dent 1997;25:441-58. 13. Diaz-Arnold AM, Vargas MA, Haselton DR. Current status of luting agents for fixed prosthodontics. J Prosthet Dent 1999;81:135-41. 14. Wilson AD. Resin-modified glass-ionomer cements. Int J Prosthodont 1990;3:425-9. 15. Dahl BL, Øilo G. Retentive properties of luting cements: an in vitro investigation. Dent Mater 1986;2:17-20. 16. Tjan AH, Li T. Seating and retention of complete crowns with a new adhesive resin cement. J Prosthet Dent 1992;67:478-83. 17. Mausner IK, Goldstein GR, Georgescu M. Effect of two dentinal desensitizing agents on retention of complete cast coping using four cements. J Prosthet Dent 1996;75:129-34. 18. el-Mowafy OM, Fenton AH, Forrester N, Milenkovic M. Retention of metal ceramic crowns cemented with resin cements: effects of preparation taper and height. J Prosthet Dent 1996;76:524-9. 19. Pameijer CH, Jefferies SR. Retentive properties and film thickness of 18 luting agents and systems. Gen Dent 1996;44:524-30. 20. Ayad MF, Rosenstiel SF, Salama M. Influence of tooth surface roughness and type of cement on retention of complete cast crowns. J Prosthet Dent 1997;77:116-21. 21. Johnson GH, Lepe X, Bales DJ. Crown retention with use of a 5% glutaraldehyde sealer on prepared dentin. J Prosthet Dent 1998;79:671-6. 22. Ernst CP, Wenzl N, Stender E, Willershausen B. Retentive strengths of cast gold crowns using glass ionomer, compomer, or resin cement. J Prosthet Dent 1998;79:472-6. 23. Yim NH, Rueggeberg FA, Caughman WF, Gardner FM, Pashley DH. Effect of dentin desensitizers and cementing agents on retention of full crowns using standardized crown preparations. J Prosthet Dent 2000;83:459-65. 24. Øilo G. Sealing and retentive ability of dental luting cements. Acta Odontol Scand 1978;36:317-25.
25. Gundler A, Lockowandt P, Erhardson S. Crown retention and cyclic loading (in vitro). Scand J Dent Res 1993;101:252-6. 26. Kaufman EG, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J Prosthet Dent 1961;11:487-502. 27. el-Ebrashi MK, Craig RG, Peyton FA. Experimental stress analysis of dental restorations. IV. The concept of parallelism of axial walls. J Prosthet Dent 1969;22:346-53. 28. Ohm E, Silness J. The convergence angle in teeth prepared for artificial crowns. J Oral Rehabil 1978;5:371-5. 29. Nordlander J, Weir D, Stoffer W, Ochi S. The taper of clinical preparations for fixed prosthodontics. J Prosthet Dent 1988;60:148-51. 30. Dixon DL, Breeding LC, Hughie ML, Brown JS. Comparison of shear bond strengths of two resin luting systems for a base and a high noble metal alloy bonded to enamel. J Prosthet Dent 1994;72:457-61. 31. Degrange M, Charrier JL, Attal JP, Asmussen E. Bonding of luting materials for resin-bonded bridges: clinical relevance of in vitro tests. J Dent 1994; 22:S28-32. 32. Atta MO, Smith BG, Brown D. Bond strengths of three chemical adhesive cements adhered to a nickel-chromium alloy for direct bonded retainers. J Prosthet Dent 1990;63:137-43. 33. Diaz-Arnold AM, Williams VD, Aquilino SA. Tensile strengths of three luting agents for adhesion fixed partial dentures. Int J Prosthodont 1989; 2:115-22. 34. Aboush YE, Jenkins CB. Tensile strength of enamel-resin-metal joints. J Prosthet Dent 1989;61:688-94. 35. Fransson B, Øilo G, Gjeitanger R. The fit of metal-ceramic crowns, a clinical study. Dent Mater 1985;1:197-9. 36. International Organization for Standardization Dentistry-polymer-based crown and bridge materials. Amendment ISO 10477. Geneva, Switzerland: International Organization for Standardization; 1996. Reprint requests to: DR DENIZ GEMALMAZ MARMARA UNIVERSITESI DIS HEKIMLIGI FAKULTESI 80200 NISANTASI ISTANBUL TURKEY FAX: ⫹90 212 2465247 E-MAIL: [email protected] Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 ⫹ 0 10/1/129090 doi:10.1067/mpr.2002.129090
New product news The January and July issues of the Journal carry information regarding new products of interest to prosthodontists. Product information should be sent 1 month prior to ad closing date to: Dr. Glen P. McGivney, Editor, UNC School of Dentistry, 414C Brauer Hall, CB #7450, Chapel Hill, NC 27599-7450. Product information may be accepted in whole or in part at the discretion of the Editor and is subject to editing. A black-and-white glossy photo may be submitted to accompany product information. Information and products reported are based on information provided by the manufacturer. No endorsement is intended or implied by the Editorial Council of The Journal of Prosthetic Dentistry, the editor, or the publisher.
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CLINICAL IMPLICATIONS In this in vitro study, given the short clinical tooth preparation with a high angle of convergence, the resin-modified glass ionomer cement Fuji Plus retained NiCr cast copings best. For AuAgPd cast copings, Avanto resin cement and Fuji Plus provided superior retention in comparison to the other luting cements tested.
D
ental luting cements are the link between indirectly fabricated restorations and the prepared tooth structure. The retention of these restorations can be compromised by short or over-tapered tooth preparations. Zinc phosphate cement has been the most popular luting material for more than 90 years. Despite its high solubility and lack of adhesion, excellent clinical performance, which can be attributed to its high fatigue strength,1 has been reported for fixed partial dentures cemented with zinc phosphate cement.2 Nevertheless, to prevent pain during cementation and to achieve better retention of cast restorations, alternative cements such as polycarboxylate and glass ionomer cements were introduced.3,4 The adhesion of polycarboxylate-based materials has been suggested to occur as a result of chemical bonding between negative a
Research Assistant, Department of Prosthodontics. Associate Professor, Department of Prosthodontics.
b
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carboxylate groups in the water-suspended polymer and positive calcium ions in the dental hard tissue.3,5 A considerable level of adhesion to both dentin and enamel has been measured in vitro for these cements,6-8 which was also partly confirmed by other clinical studies.9,10 The introduction of new adhesive techniques and materials to be used in restorative dentistry also led to the development of new dental cements with improved bond strengths. Recently introduced dental luting materials include the composites and resin-modified (hybrid) glass ionomers. The ability to adhere to multiple substrates,11,12 high strength, and insolubility in the oral environment are major advantages of the composite luting cements.13 Resin-modified glass ionomer luting cements are a combination of glass ionomer and resin chemistries set by an acid-base reaction between aluminosilicate glass powder and an aqueous solution of polyalkenoic acids modified with methacrylate groups, as well as chemically initiated free-radical polymerization of methacrylate units.14 Resin-modified glass ionomer THE JOURNAL OF PROSTHETIC DENTISTRY 491
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cements generally behave in an intermediate manner between composite and glass ionomer cements.13 The biggest advantage of these types of cements is their easy use, because multiple bonding steps are not required. For recently introduced materials, however, the number of both clinical and laboratory studies regarding performance is limited. The effect of luting agents on casting retention has been assessed in several in vitro studies.15-24 These retention tests, which typically were performed by removing a standardized casting from a stylized crown preparation with direct tensile loading, focused on the effects of the type of cement,15-23 type of metal,19 preparation taper,18,25-29 preparation height,18 surface roughness,15,20,24 and application of dentinal desensitizing agents.17,21,23 The studies related to crown retention and luting cement type reported that adhesive resins had consistently greater retention than zinc phosphate.18-21,23 Some controversial results regarding the retentive strengths of different types of luting cements also exist in the literature.19,22 Pameijer and Jefferies19 investigated retentive strengths of cast gold crowns cemented with 18 different luting agents on standardized tooth preparations with a 33° angle of convergence. They concluded that the values of retentive forces for crowns cemented with resin cements were significantly higher in comparison to those cemented with a glass ionomer cement. In a recent study, however, the retentive strengths of cast gold crowns cemented with a glass ionomer, a compomer, and a resin cement were evaluated with the use of a similar experimental design having a 10° convergence angle, and it was reported that compomer and glass ionomer cements showed significantly better retentive strengths than the resin cement.22 The authors attributed the lower retentive strength of the resin cement to the lack of an adhesive system and stated that resin cements should be used in combination with adhesive systems to achieve favorable results.22 The choice of metal may also affect retention of the cemented crown. Although many comparative studies exist showing metal bonding of various types of resin composite material used for resin-retained fixed partial dentures,30-34 limited information is available concerning the retentive strengths of base and noble metal crowns cemented with different luting cements.19 In a single study, Ernst et al22 investigated the effect of applying an additional bonding layer to the inner surface of the high gold crowns (AuAgPt) cemented with a compomer cement. They concluded that there was no significant improvement in the retentive strength related to application of an additional bonding layer on the internal surface of the crowns.22 The aim of this study was to evaluate the retentive properties of 5 different luting cements (a zinc phosphate, a glass ionomer, 2 different resin-modified glass ionomers, and a resin cement) on base (NiCr) and noble 492
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(AuAgPd) metal copings to short and over-tapered preparations.
MATERIAL AND METHODS Eighty recently extracted caries-free mandibular premolars of similar size were selected and stored in deionized water. The teeth were embedded in acrylic resin blocks to 2 mm below the cementoenamel junction. To retain the tooth in the resin, a hole was drilled, through which a stainless steel wire was placed. All standardized tooth preparations for complete metal copings were performed on a jeweler’s lathe (ZM 1500; Zime Sevindik, Adana, Turkey) with a low-speed handpiece and a diamond bur (Mani Dia-burs, 01B-2033; Mani Inc, Utsunomiya, Japan) under a copious amount of water at a preparation angle of 16.5°. Thus the final preparation had a 33° angle of convergence. The occlusal surfaces were flattened perpendicular to the long axes of the teeth. The cone-shaped preparations were at least 3-mm high, had an occlusal diameter of 3 mm, and were prepared entirely in dentin. If perforation of the pulp cavity occurred during preparation, the tooth was removed from the study. Silicone impressions (Wirosil; Bego, Bremen, Germany) of the prepared teeth were made, and casts were poured in dental stone (Fujirock EP; GC Europe, Leuven, Belgium). The stone dies were trimmed, and 2 coats of die spacer (Isocera; Bego) were applied to each master die, with time allowed for the previous layer to dry. The wax patterns were fabricated by dipping the die in a molten wax (Bredent dipping wax; Bredent, Ulm, Germany) to achieve a consistent thickness of 0.7 ⫾ 0.025 mm. The height of the wax pattern was 3 mm, which was verified with a digital micrometer with a measuring accuracy of 0.01 mm. A wax ring was attached on the occlusal surface of the wax pattern parallel to the long axis of the tooth preparation to allow tensile testing. The wax patterns were sprued and invested with phosphate-bonded investment (Bellastar; Bego). The manufacturer’s directions were followed for mixing, setting time, and wax burnout of the investment. Half of the wax patterns for each experimental group were cast in an AuAgPd alloy (AuroLloyd KF; Bego), and the other half were cast in an NiCr alloy (Wiron 99; Bego). Casting was performed according to standardized techniques in a Nautilius MP-microprocessor– controlled high-frequency vacuum-pressure casting machine (Bego). Minor adjustments necessary to seat the castings on the dies were completed with the use of a small round bur mounted in a laboratory handpiece and a microscope (MZ 12; Leitz, Wetzlar, Germany) under ⫻20 magnification. After the inferior surfaces of the copings were sandblasted with 50-m aluminum oxide particles (Korox 50; Bego), all copings were evaluated for accuracy of VOLUME 88 NUMBER 5
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Table I. Luting cements used in study Product name
Phosphate cement
Meron Principle
Producer
Heraeus Kulzer, Dormagen, Germany
Voco, Cuxhaven, Germany Dentsply L. D. Caulk Division, Del.
Batch No.
Composition
P: 0950340
P: zinc oxide, magnesium oxide
L: 1150340
L: orthophosphoric acid, water, zinc oxide, aluminum hydroxide P: fluoroaluminasilicate glass L: polyacrylic acid, water P: strontium aluminofluorosilicate glass, sodium fluoride, initiators
P: 96660 L: 96614 P: 990318
L: 990318 Fuji Plus
GC Corporation, Tokyo, Japan
P: 120491 L: 260391
Avanto
Voco Cuxhaven, Germany
C: 300391 P: 90583 L: 90582 C: 95679 P: 90617 (A) 91613 (B)
L: OEMA, PENTA, resin matrix, water, inhibitors, initiators P: aluminosilicate glass L: 2-HEMA, polyacrylic acid, proprietary resins, tartaric acid, water C: 10% citric acid, 2% ferric chloride, 88% water P: bariumborosilicate glass, silica, benzoil peroxide L: dimethacrylates UDMA, BIS-GMA vs. amines, inhibitors C: 37% phosphoric acid P: hydrophilic methacrylates, polyfunctional monomers, maleic acid, water, sodium fluoride
Type
Zinc phosphate
P/L ratio (g)
1.2/0.88
Glass ionomer
3/I
Resin-modified glass ionomer
2.5/1.2
Resin-modified glass ionomer
2/1
Resin
1.7/1
P ⫽ Powder; L ⫽ liquid; C ⫽ conditioner; P ⫽ primer.
marginal fit, to a maximum gap of 50 m, with a microscope (MZ 12; Leitz) at ⫻20 magnification. Before cementation, it was also verified that all castings were not self-retentive by ensuring that the copings separated from the tooth preparation dies without any resistance when the specimens were held upside down. Five cements were used for luting the copings: a zinc phosphate cement (Phosphate), a glass ionomer cement (Meron), a resin-modified glass ionomer cement (Principle), a resin-modified glass ionomer cement (Fuji Plus), and a resin cement (Avanto). The castings were randomly divided into 5 experimental groups, and each group consisted of 16 specimens. Sixteen specimens were cemented with 1 of the 5 luting cements, 8 for each alloy group. The same person mixed all luting agents at room temperature on a glass slab using a stainless steel spatula with a stiff blade. The powder-liquid ratios for each cement used were in accordance with the manufacturers’ recommendations and are given in Table I. For each specimen, the powder and the liquid were weighed on an electronic digital microbalance (SBA 41; Scaltec, Hamburg, Germany) that had a measuring accuracy of 0.1 mg. Because the resin-modified glass ionomer cement Fuji Plus and the resin cement Avanto should be used in combination with a conditioner and/or a dentin primer system, tooth surfaces were prepared according to the manufacturers’ instructions before the application of these cements. The dentin was etched for 15 seconds with 37% phosphoric acid for specimens cemented with Avanto, and the dentin was conditioned with a condiNOVEMBER 2002
Fig. 1. Cemented casting placed in Zwick universal testing machine.
tioner containing 10% citric acid for specimens cemented with Fuji Plus. After the preparations were rinsed for 20 seconds and moisture was removed so that the dentin remained visibly moist, copings in the Fuji Plus group were directly cemented. Primer A and B of Avanto resin cement were applied on dentinal surfaces by rubbing with a cotton pellet for 30 seconds, and cementation followed thereafter. The contents of conditioners and dentin primers used for each cement are given in Table I. 493
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Fig. 2. Graphic representation of retentive forces of luting cements in relation to alloy type. Horizontal lines connect values that are not significantly different. Table II. Mean values of separation force (in newtons)
Phosphate Principle Meron Avanto Fuji Plus
AuroLloyd KF
Wiron 99
120.88 (6) 135.45 (51) 145.88 (62) 276.85 (88) 300.92 (59)
143.09 (20) 150.38 (61) 220.71 (52) 225.61 (78) 381.02 (81)
Data are given as mean (SD). Means connected by vertical lines are not statistically different.
A static load of 5.0 kg was applied35 with a custombuilt pressure jig and maintained on the castings for 10 minutes at 90% relative humidity in a humidifier. Excess cement was removed, and specimens were then stored in distilled water at 37°C for 24 hours and thermocycled between 5°C and 55°C for 5000 cycles, with a dwell time of 30 seconds.36 A vertical uniaxial tensile load was applied to each casting with a universal testing machine (Zwick 1120; Zwick GmbH & Co KG, Ulm, Germany) with a constant speed of 1 mm/min, and separation forces were recorded (Fig. 1). The fitted surfaces of the separated castings were examined visually to determine the mode of cement failure. All specimens were fabricated and measured by the same examiner. Separation force data were analyzed statistically by use of 2-way analysis of variance (P ⬍ .05). Duncan multiple range test analysis was also used to distinguish statistically significant groups.
RESULTS Mean and SD values for each luting cement for 2 metal alloys are presented in Table II. The lowest mean 494
values were recorded for zinc phosphate cement for both the AuAgPd alloy (120.88 N) and the NiCr alloy (143.09 N). The SD values observed for zinc phosphate cement were relatively lower in comparison to those for the other luting cements tested. The highest value of mean retentive force (381.02 N) was observed for Fuji Plus for the NiCr alloy. Table III reports the probability values of the mean retentive forces as a function of luting cement and alloy type. There were significant differences in the retentive forces related to luting cement and alloy type and with interactions of the 2 variables. By Duncan multiple range test analysis, Fuji Plus and Avanto showed significantly higher retentive strengths to the AuAgPd alloy in comparison to the other cements tested. The retentive strength of Fuji Plus was significantly higher for the NiCr alloy than the retentive strengths of the other cements tested. In addition, the retentive strengths of Avanto and Meron to NiCr alloy were significantly higher than those of Principle and Phosphate cements (Table II). Analysis of variance results revealed that the differences in the retentive strengths of the luting cements recorded for the 2 alloy types were significantly different for zinc phosphate, Meron, and Fuji Plus cements (Fig. 2). Zinc phosphate, Meron, and Fuji Plus cements showed higher retentive values for the NiCr alloy than for the AuAgPd alloy. The distribution of the mode of cement failure with AuAgPd and NiCr alloys is given in Table IV. Horizontal fracture of coronal dentin occurred in 37.5% of both NiCr and AuAgPd specimens cemented with Fuji Plus (Fig. 3). VOLUME 88 NUMBER 5
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Table III. Analysis of variance results Source of variance
df
Sum of squares
Mean squares
F ratio
P value
Metal Cement Metal ⫻ cement Residual
1 4 4 70
15865.06 482462.3 45561.89 259718.1
15865.06 120615.6 11390.47 3710.258
4.28 32.51 3.07
.04 .001 .021
DISCUSSION Failure of retention of crowns occurs under a combination of masticatory forces repeated over a period of time.24 The in vitro studies that evaluated the retention of luting cements on crowns were performed mostly by direct tensile loading without considering the cyclic loading considered to simulate clinical conditions.16-23 In a single study, Gundler et al25 used an apparatus designed for applying cyclic compressive loading to crowns luted with zinc phosphate cement to investigate the retentive strength of crowns with different convergence angles. The results of this study that simulated clinical loading up to 1 million cycles were in agreement with the results of other studies that evaluated the effect of similar factors on the retentive strength of crowns by using direct tensile loading.18,26 It was recently reported that no fatigue fracture occurred in a zinc phosphate cement layer after repetitive loading of 100 N for 5.5 ⫻ 105 cycles.1 Thus the similarities between the results of the in vitro studies conducted on crowns with cyclic loading25 and direct tensile loading18,26 are thought to be the result of the high durability of the cement film layer after cyclic loading. In a recent study, Yim et al23 pointed out that inconsistent results were obtained in past research that has not controlled preparation surface area when examining the retentive strengths of cemented cast crowns. They showed that the use of standardized crown preparations in combination with a carefully designed tensile testing method produced remarkably lower variation in crown retention values. It can finally be stated that the findings of these studies, which used direct tensile loading, can be considered to relate directly to the clinical situation when standardized crown preparations and methods during specimen fabrication and testing were used. Because the adhesive and mechanical properties of luting cements were shown to be highly affected by the existence of humidity and thermal effects,11 the existence of humidity in the oral environment should also be considered in in vitro testing of luting cement retention. For this reason, all luting agents were allowed to set under humid conditions; the specimens were thermocycled before tensile testing according to the International Organization for Standardization (ISO) amendment 10477.36 The lowest mean values were recorded for zinc phosphate cement for both alloy groups. However, the mean NOVEMBER 2002
Table IV. Distribution of mode of cement failure in percentages Cement totally Cement on tooth Cement totally Dentinal on tooth and crown on casting fracture
Phosphate AuAgPd NiCr Meron AuAgPd NiCr Principle AuAgPd NiCr Fuji Plus AuAgPd NiCr Avanto AuAgPd NiCr
— —
62.5 87.5
37.5 12.5
— —
— —
50 62.5
50 37.5
— —
— —
— —
— —
62.5 62.5
— —
37.5 37.5
75 75
— 12.5
— —
25 12.5
100 100
— —
Fig. 3. Tested specimen shows retention of tooth preparation in coping.
value of retention recorded for zinc phosphate cement was not significantly different from that of the glass ionomer and the resin-modified glass ionomer cement Principle for AuAgPd copings. Fuji Plus and Avanto showed significantly higher retentive strengths to the AuAgPd alloy in comparison to other cements. To increase bond strengths of resin cements, a pretreatment 495
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of the dentin surface with dentin adhesives is commonly used. Avanto resin cement has a similar application of conditioning and priming, which supplied greater retentive force in comparison to zinc phosphate, glass ionomer, and resin-modified glass ionomer cement Principle. Resin-modified glass ionomer cement Fuji Plus, on the other hand, supplied higher retentive forces to both the NiCr and AuAgPd alloys than Avanto resin cement. Fuji Plus also has a conditioner containing 10% citric acid, 2% ferric chloride, and 88% water that dissolves the smear layer and provides an adhesive bond between prepared dentin and the luting cement. The relatively lower performance of the resin-modified glass ionomer cement Principle in comparison to both the resin cement Avanto and the resin-modified glass ionomer cement Fuji Plus can be attributed to the lack of any surfaceconditioning procedure before luting. Thus it appears that resin-based or -modified cements should be used in combination with surface-conditioning agents or adhesive to obtain the best results. The distribution of mode of cement failure revealed that fracture occurred at both the cement-metal and cement-tooth interfaces for copings luted with the zinc phosphate and glass ionomer cements. In no situation was cement observed to completely remain on the prepared tooth. However, cement was completely retained on the prepared tooth for 25% of AuAgPd copings and 12.5% of NiCr copings luted with Avanto resin cement. The adhesive bond of resin cement to tooth structure appeared to enhance superior bond of resin cement to tooth structure. On the other hand, in copings luted with the resin-modified glass ionomer cement Principle, debonded cement was observed to be retained totally on the metal surface for all specimens. This shows that the inadequate bond of Principle to the dentinal surface, most likely resulting from lack of conditioner and primer, causes the weak link of the cemented coping assembly to occur at the cement-tooth interface during tensile debonding. Cohesive dentin fracture observed for copings cemented with the resin-modified glass ionomer cement Fuji Plus was in agreement with the highest retentive values recorded for this cement. Relatively lower SD values recorded for zinc phosphate could be attributed to the assumption that handling zinc phosphate cement was less technique-sensitive. The highest SD values recorded for resin and resin-modified glass ionomer cements indicate that the luting system becomes more technique-sensitive as the adhesive bond to tooth structures is enhanced. An important factor that determines the technique sensitivity of adhesive systems is individual and locational variation in structural characteristics and mechanical properties of dentin with regard to their high impact on dentin bonding.12 It should also be noted that the lowest retentive values recorded for resin and resin-modified glass ionomer cements were 496
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still higher than the highest retentive values obtained with zinc phosphate cement. In this study, a convergence angle of 33° was selected in 3-mm high crown length to approximate the worstcase clinical scenario. By minimizing the mechanical retention from the preparation, the data emphasized the retention arising solely from the cements. It has already been proved that the angle of convergence is an important factor for retention.18,25,26 Therefore the results of this study should be considered within the experimental design of the study, and it is likely that much higher retentive forces can be achieved with ideally prepared teeth. In this study the retentive strengths of 5 different luting cements were evaluated on both base and noble copings. The study was designed to examine over-tapered mandibular premolar tooth preparations with 3-mm heights. Although resin cement and resin-modified glass ionomer cement showed higher retentive strengths, all tested cements provided retentive strengths exceeding clinically expected debonding forces of about 40 N.22 Thus it can be concluded that all 5 test cements can be used satisfactorily when they are prepared according to the manufacturers’ recommendations. The use of resin and resin-modified glass ionomer cements seems to be advantageous when extreme retention problems exist, such as short and/or over-tapered crown preparations.
CONCLUSIONS Under the conditions of this study, Fuji Plus and Avanto showed significantly higher retentive strengths for the AuAgPd alloy in comparison to the other cements tested. The retentive strength of Fuji Plus was significantly higher than the retentive strengths of the other cements tested on the NiCr alloy. In addition, cohesive dentin fracture occurred with resin-modified glass ionomer cemented copings on coping separation. Therefore all 5 test cements can be used satisfactorily when they are prepared according to the manufacturers’ recommendations. However, resin and resin-modified glass ionomer cements seem to be better choices for nonretentive coping preparations. REFERENCES 1. Yamashita J, Takakuda K, Shiozawa I, Nagasawa M, Miyairi H. Fatigue behavior of the zinc-phosphate cement layer. Int J Prosthodont 2000;13: 321-6. 2. Creugers NH, Kayser AF, van’t Hof MA. A meta-analysis of durability data on conventional fixed bridges. Community Dent Oral Epidemiol 1994;22: 448-52. 3. Smith DC. A new dental cement. Br Dent J 1968;124:381-4. 4. Wilson AD, Crisp S, Lewis BG, McLean JW. Experimental luting agents based on the glass ionomer cements. Br Dent J 1977;142:117-22. 5. Beech DR. A spectroscopic study of the interaction between human tooth enamel and polyacrylic acid (polycarboxylate cement). Arch Oral Biol 1972;17:907-11.
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6. Mizrahi E, Smith DC. The bond strength of a zinc polycarboxylate cement. Investigations into the behaviour under varying conditions. Br Dent J 1969;127:410-4. 7. Hotz P, McLean JW, Sced I, Wilson AD. The bonding of glass ionomer cements to metal and tooth substrates. Br Dent J 1977;142:41-7. 8. Øilo G. Bond strength of new ionomer cements to dentin. Scand J Dent Res 1981;89:344-7. 9. Brandau HE, Ziemiecki TL, Charbeneau GT. Restoration of cervical contours on nonprepared teeth using glass ionomer cement: a 4 1/2-year report. J Am Dent Assoc 1984;108:782-3. 10. Jemt T, Stålblad PA, Øilo G. Adhesion of polycarboxylate-based dental cements to enamel: an in vivo study. J Dent Res 1986;65:885-7. 11. Ishijima T, Caputo AA, Mito R. Adhesion of resin to cast alloys. J Prosthet Dent 1992;67:445-9. 12. Marshall GW Jr, Marshall SJ, Kinney JH, Balooch M. The dentin substrate: structure and properties related to bonding. J Dent 1997;25:441-58. 13. Diaz-Arnold AM, Vargas MA, Haselton DR. Current status of luting agents for fixed prosthodontics. J Prosthet Dent 1999;81:135-41. 14. Wilson AD. Resin-modified glass-ionomer cements. Int J Prosthodont 1990;3:425-9. 15. Dahl BL, Øilo G. Retentive properties of luting cements: an in vitro investigation. Dent Mater 1986;2:17-20. 16. Tjan AH, Li T. Seating and retention of complete crowns with a new adhesive resin cement. J Prosthet Dent 1992;67:478-83. 17. Mausner IK, Goldstein GR, Georgescu M. Effect of two dentinal desensitizing agents on retention of complete cast coping using four cements. J Prosthet Dent 1996;75:129-34. 18. el-Mowafy OM, Fenton AH, Forrester N, Milenkovic M. Retention of metal ceramic crowns cemented with resin cements: effects of preparation taper and height. J Prosthet Dent 1996;76:524-9. 19. Pameijer CH, Jefferies SR. Retentive properties and film thickness of 18 luting agents and systems. Gen Dent 1996;44:524-30. 20. Ayad MF, Rosenstiel SF, Salama M. Influence of tooth surface roughness and type of cement on retention of complete cast crowns. J Prosthet Dent 1997;77:116-21. 21. Johnson GH, Lepe X, Bales DJ. Crown retention with use of a 5% glutaraldehyde sealer on prepared dentin. J Prosthet Dent 1998;79:671-6. 22. Ernst CP, Wenzl N, Stender E, Willershausen B. Retentive strengths of cast gold crowns using glass ionomer, compomer, or resin cement. J Prosthet Dent 1998;79:472-6. 23. Yim NH, Rueggeberg FA, Caughman WF, Gardner FM, Pashley DH. Effect of dentin desensitizers and cementing agents on retention of full crowns using standardized crown preparations. J Prosthet Dent 2000;83:459-65. 24. Øilo G. Sealing and retentive ability of dental luting cements. Acta Odontol Scand 1978;36:317-25.
25. Gundler A, Lockowandt P, Erhardson S. Crown retention and cyclic loading (in vitro). Scand J Dent Res 1993;101:252-6. 26. Kaufman EG, Coelho DH, Colin L. Factors influencing the retention of cemented gold castings. J Prosthet Dent 1961;11:487-502. 27. el-Ebrashi MK, Craig RG, Peyton FA. Experimental stress analysis of dental restorations. IV. The concept of parallelism of axial walls. J Prosthet Dent 1969;22:346-53. 28. Ohm E, Silness J. The convergence angle in teeth prepared for artificial crowns. J Oral Rehabil 1978;5:371-5. 29. Nordlander J, Weir D, Stoffer W, Ochi S. The taper of clinical preparations for fixed prosthodontics. J Prosthet Dent 1988;60:148-51. 30. Dixon DL, Breeding LC, Hughie ML, Brown JS. Comparison of shear bond strengths of two resin luting systems for a base and a high noble metal alloy bonded to enamel. J Prosthet Dent 1994;72:457-61. 31. Degrange M, Charrier JL, Attal JP, Asmussen E. Bonding of luting materials for resin-bonded bridges: clinical relevance of in vitro tests. J Dent 1994; 22:S28-32. 32. Atta MO, Smith BG, Brown D. Bond strengths of three chemical adhesive cements adhered to a nickel-chromium alloy for direct bonded retainers. J Prosthet Dent 1990;63:137-43. 33. Diaz-Arnold AM, Williams VD, Aquilino SA. Tensile strengths of three luting agents for adhesion fixed partial dentures. Int J Prosthodont 1989; 2:115-22. 34. Aboush YE, Jenkins CB. Tensile strength of enamel-resin-metal joints. J Prosthet Dent 1989;61:688-94. 35. Fransson B, Øilo G, Gjeitanger R. The fit of metal-ceramic crowns, a clinical study. Dent Mater 1985;1:197-9. 36. International Organization for Standardization Dentistry-polymer-based crown and bridge materials. Amendment ISO 10477. Geneva, Switzerland: International Organization for Standardization; 1996. Reprint requests to: DR DENIZ GEMALMAZ MARMARA UNIVERSITESI DIS HEKIMLIGI FAKULTESI 80200 NISANTASI ISTANBUL TURKEY FAX: ⫹90 212 2465247 E-MAIL: [email protected] Copyright © 2002 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2002/$35.00 ⫹ 0 10/1/129090 doi:10.1067/mpr.2002.129090
New product news The January and July issues of the Journal carry information regarding new products of interest to prosthodontists. Product information should be sent 1 month prior to ad closing date to: Dr. Glen P. McGivney, Editor, UNC School of Dentistry, 414C Brauer Hall, CB #7450, Chapel Hill, NC 27599-7450. Product information may be accepted in whole or in part at the discretion of the Editor and is subject to editing. A black-and-white glossy photo may be submitted to accompany product information. Information and products reported are based on information provided by the manufacturer. No endorsement is intended or implied by the Editorial Council of The Journal of Prosthetic Dentistry, the editor, or the publisher.
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