- Email: [email protected]
Comparison of titanium dowel retention using four different luting agents
Comparison of titanium dowel retention using four different luting agents Ali Balbosh, DMD,a Klaus Ludwig, PhD,b and Matthias Kern, DMD, PhDc School of Dentistry, Department of Prosthodontics, Propaedeutics, and Dental Materials, Christian-Albrechts University at Kiel, Kiel, Germany Statement of problem. Luting material, surface properties, and loading conditions affect the retention of prefabricated dowels to varying degrees.
Purpose. The purpose of this study was to evaluate the effect of roughening of the dentinal walls and artificial aging on the retention of prefabricated tapered titanium dowels, using 4 different luting materials.
Material and methods. One-hundred twenty-eight single-rooted teeth were selected, the coronal aspect of each tooth was removed, and the remaining root received endodontic therapy. All specimens were divided into 4 groups (n = 32). Dowel spaces were prepared to a depth of 10 mm using ISO 90 rotary cutting instruments. Tapered titanium dowels were luted with the following luting materials: zinc-phosphate cement (Harvard cement), glass-ionomer cement (Ketac Cem EasyMix), resin composite luting agent (Panavia 21) with autopolymerizing dentin primer (ED-Primer), or a self-adhesive composite luting agent (RelyX Unicem). Both composite luting agents were used without acid etching of the canal dentin. Each luting agent was used under 2 conditions: in 1 subgroup (n = 16) the dentinal walls were not roughened, and in the other subgroup (n = 16), walls were roughened with a diamond rotary cutting instrument. Eight specimens from each subgroup were stored in water at 37°C for 3 days; the other 8 specimens were stored for 150 days and subjected to simulated aging conditions using 37,500 thermal cycles (5°C/55°C) and 300,000 mechanical loading cycles with 30 N. Dowel retention (N) was measured using a universal testing machine with a crosshead speed of 2 mm/min. Data were analyzed using 2- and 3-way ANOVAs and the Tukey HSD test (a=.05). Results. The dislodged dowels were examined microscopically to evaluate mode of failure. The nonroughened dentinal walls showed no significant differences between the different luting agents. Roughening the dentinal walls increased the retention significantly for all groups. This increase was significantly higher for the resin composite groups (P=.0001). Storage for 150 days with thermal cycling and mechanical loading caused a significant decrease in dowel retention (P=.001). The failure mode was purely adhesive at the luting material– dentin interface for all dowels cemented in nonroughened root canals. A mixed failure mode, adhesive at the luting material–dentin interface and cohesive in the luting material, was observed for dowels cemented in roughened root canals. Conclusion. Roughening the dentinal walls and the use of resin luting cements provided statistically significant increases in dowel retention values. (J Prosthet Dent 2005;94:227-33.)
CLINICAL IMPLICATIONS Based on the results of this study, roughening of dentinal walls before dowel cementation with any one of the tested luting agents is recommended for increasing dowel retention. For the best dowel retention results, resin composite luting agents should be selected.
E
ndodontic dowels are widely used for restoring endodontically treated teeth with insufficient coronal tooth structure to retain a core for a definitive restoration.1,2 Prefabricated dowel systems have recently become more popular because they provide satisfactory results, while saving chair time and reducing costs to the patient.3 However, a prefabricated dowel should adequately adapt to the prepared root canal, or a cast dowel and core should be used.4 Passive, tapered dowels have a a
Visiting Assistant Professor. Professor of Dental Materials. c Professor and Department Chairman. b
SEPTEMBER 2005
shape that is congruent with a root-canal configuration and allow for optimal preservation of tooth structure, especially in the apical region.5-7 Endodontic dowels should have good retention to provide definitive anchorage for a prosthodontic restoration. Many in vitro studies have investigated various factors and their effects on dowel retention. These factors include dowel design,3,8-11 length,3,8,9,12 diameter,3,8-10,12 luting agent,3,9,11,13-18 and preparation of the dowel space.3 Some studies have reported that tapered dowels provided lower retention when compared to parallel-sided or threaded dowels.8,9 Roughening the prepared dentin surface increases the retention of THE JOURNAL OF PROSTHETIC DENTISTRY 227
THE JOURNAL OF PROSTHETIC DENTISTRY
BALBOSH, LUDWIG, AND KERN
Table I. Luting cements and codes Group/ subgroup
Dowel space
Manufacturer
Batch No.
Zinc phosphate cement (Harvard cement, normal setting)
Hs Hr
Nonroughened Roughened
Harvard Dental, Berlin, Germany
Powder: 2112497016 Liquid: 2111099018
Glass ionomer cement (Ketac Cem EasyMix)
Ks Kr
Non-roughened Roughened
3M ESPE, Seefeld, Germany
118425
Panavia 21 EX
Ps Pr
Nonroughened Roughened
Kuraray, Osaka, Japan
41218
RelyX Unicem
Us Ur
Nonroughened Roughened
3M ESPE
136276
Cement
dowels7,19-21 or artificial crowns22-24 by increasing the surface area and enhancing the mechanical interlocking between the dentin surface and the cement. For situations in which additional dowel retention is needed, airborne-particle abrasion of the dowel surface and roughening the walls of the prepared dowel space with a diamond rotary cutting instrument may increase the retention of dowels without compromising the remaining tooth structure.7 Cements including zinc phosphate, polycarboxylate, glass ionomer, and resin composites have been used to cement endodontic dowels. The retention of a dowel varies, depending on the type of cement, its mechanical properties,11,17,25,26 and dentin structure.27,28 Most studies that tested the retention of endodontic dowels were performed shortly after cementation, without any type of simulation of oral conditions or aging.7,11,12,25 However, clinically, the dislodgement of dowel-retained restorations occurs usually after several years of function as a result of different stress factors, such as temperature change and mechanical loading.29,30 Therefore, in vitro tests evaluating dowel retention should aim to simulate clinical conditions, using artificial aging to better predict clinical behavior. The purpose of this in vitro study was to evaluate the effect of artificial aging on the retention of prefabricated tapered titanium dowels when luted with 4 different luting materials. In addition, the effect of roughening the dentinal walls was evaluated.
MATERIAL AND METHODS For this study, extracted caries-free and visually assessed fracture-free, human maxillary anterior and mandibular premolar teeth were selected, cleaned of both calculus deposits and soft tissues, and stored in 0.1% thymol solution (Caelo, Hilden, Germany). Each tooth was sectioned with a diamond rotary cutting instrument (837KR.012; Brasseler, Lemgo, Germany) under water spray, 1 mm coronal to the cemento-enamel junction. Roots with distinctly oval root canals or with a root canal diameter of more than 2 mm were excluded from the 228
study to ensure that the dowel would seat against a freshly prepared dentin surface free of undercuts or remnants of root-canal filling material. From this selection process, 128 root specimens were chosen. The coronal surface of each root specimen was flattened with a finishing diamond rotary cutting instrument (8837KR.012; Brasseler) under water spray to obtain a surface perpendicular to the long axis of the root. The pulpal tissues were removed, and the canals were instrumented up to ISO size-50 files (K-file; Dentsply De Trey, Konstanz, Germany). Sodium-hypochlorite solution (3%) (Hedinger, Stuttgart, Germany) was used to irrigate the canals throughout instrumentation. The roots were dried with paper points (Coltene/Whaledent Inc, Langenau, Germany) and obturated with an ISO size50 gutta percha master point (Kerr GmbH, Karlsruhe, Germany) and eugenol-free31,32 epoxy-amine resin sealer (AH Plus sealer; Dentsply De Trey). Lateral condensation with a finger spreader (Dentsply De Trey) and fine accessory gutta percha points (Kerr) was performed until the canals were obturated. After completion of endodontic treatment, the roots were stored in 0.1% thymol solution at room temperature for 72 hours before proceeding. For each specimen, the coronal aspect of the gutta percha was removed with a heated probe (Omnident, Rodgau Nieder-Roden, Germany), and a 10-mm-deep dowel space was prepared using an ISO-90 preparation instrument (196.204.090, Erlangen Post System; Brasseler), with a new instrument used for every 8 specimens. Throughout the preparation, the dowel space was irrigated with 3% sodium-hypochlorite solution. The prepared dowel space was dried with paper points, irrigated with 70% ethanol (Bundesmonopolverwaltung fuer Branntwein, Hamburg, Germany), and dried with paper points. The specimens were then divided into 4 groups representing each of the 4 luting agents tested. Each group was then further divided into 2 subgroups of 16 specimens each (Table I). In one subgroup, the dentinal walls were not roughened, but left in their original state after using the system’s preparation VOLUME 94 NUMBER 3
BALBOSH, LUDWIG, AND KERN
instrument, while in the other subgroup, the dentinal walls were roughened with a hand-held diamond rotary cutting instrument (196D.644.090; Erlangen Post System; Brasseler) by rotating the instrument 3 times within the canal. The prefabricated ISO size-90 titanium dowels (CP titanium ASTM grade 4, 61L16.090; Erlangen Post System; Brasseler) were provided by the manufacturer with a surface roughness value of 12 mm. Before cementation the dowels were also airborne-particle-abraded using 50-mm alumina particles (Heraeus Kulzer, Wehrheim, Germany) at 2.5-bar pressure for 15 seconds. For the zinc-phosphate cement specimens, there was no conditioning of the dentin surface. For the glass-ionomer cement specimens, the dentin surface was conditioned, according to the manufacturer’s directions, with polyacrylic acid (Ketac Conditioner) for 20 seconds. The root canal was then rinsed with distilled water and dried with paper points, and a slightly moistened paper point was left in the canal until the cement was introduced to avoid dentin dehydration. For Panavia 21 EX specimens, the dentin surface was conditioned with the system’s autopolymerizing primer (EDPrimer) for 60 seconds without previous acid etching of the canal dentin. For RelyX Unicem specimens, there was no previous acid etching or conditioning of the canal dentin. All luting materials were used according to the manufacturers’ instructions. Zinc-phosphate and glass-ionomer cements were placed into the root canal using an ISO size-40 lentulo spiral (Dentsply De Trey), whereas the resin composites were not placed into the root canal before the dowel. In all groups, the dowel was coated with the luting material and seated by finger pressure. A weight of 20 N was then applied by means of a custom-made loading apparatus for 10 minutes. During this time, oxygen-inhibiting gel (Oxyguard II; Kuraray, Osaka, Japan) was applied with a syringe to the bonding margins of Panavia 21 EX. After cementation, notches were placed in the external root surface to prevent dislodgement from an autopolymerizing acrylic resin (Technovit 4000; Heraeus Kulzer) embedding material. The roots were mounted on a custom-made Plexiglas holder (Plexiglas, Roehm, Germany), and a custom-made surveyor ensured that the holder was parallel to the long axis of the dowel. Eight specimens from each subgroup were stored in water at 37°C for 3 days. The other 8 specimens were stored for 150 days33 to evaluate the bond durability of the luting agents while simulating oral conditions. These specimens were thermal cycled (Willytec, Munich, Germany) for 37,500 cycles33 (5°-55°C) with a dwell time of 30 seconds and a transition time of 6 seconds, and subjected to 300,000 cycles of mechanical loading parallel to the long axis of the dowel, using a masticatory simulator (Willytec) with 30 N force at 1.6 Hz. The mechanical loading pattern was equivalent to 1 year of clinical function.34 The force of 30 N was SEPTEMBER 2005
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 1. Schematic diagram of tensile test apparatus. (A), Custom-made device; (B), custom-made holder; (C), resin block; (D), Plexiglas ring; (E), tooth specimen; (F), dowel.
within previously measured occlusal forces that occurred during mastication and swallowing with restored dentitions.35 For the retention test, a screw-driven universal testing machine (Zwick Z010; Zwick, Ulm, Germany) was used to apply a tensile force load parallel to the long axis of the dowels and at a crosshead speed of 2 mm/minute. The portion of the dowel that extended from the root was grasped with a custom-made device. A chain of 4 links between the device and the upper grip of the testing machine allowed for self-alignment during testing (Fig. 1). The force in N required to dislodge each dowel from the prepared dowel space was recorded. The data were analyzed using 3-way and 2-way 229
THE JOURNAL OF PROSTHETIC DENTISTRY
BALBOSH, LUDWIG, AND KERN
Fig. 2. Mean retention values and SDs for all groups after 3 daysÕ storage without thermal cycling and mechanical loading and after 150 days with thermal cycling and mechanical loading. Horizontal lines connect mean values for dowels cemented in roughened root canals that are not significantly different (P ..05). Table II. Summary of 3-way ANOVA for retention Source
Main effects Surface properties (A) Luting agents (B) Storage conditions (C) Interactions A3B A3C B3C A3B3C
Sum of squares
df
Mean square
F
P
823810.0
1
823810.0
163.97
0.0001
239966.0 57139.3
3 1
79988.5 57139.3
15.92 11.37
0.0001 0.0010
233416.0 55.7 10003.2 2328.5
3 1 3 3
77805.3 55.7 3334.4 776.2
15.49 0.01 0.66 0.15
0.0001 0.9163 0.5761 0.9266
analyses of variance (ANOVAs) and Tukey HSD tests for multiple comparisons (a=.05). The dislodged dowels were examined microscopically at 38 and 320 magnifications to evaluate the mode of failure, which was recorded.
RESULTS The mean retentive strength values and SDs are shown in Figure 2. The mean retentive values and SDs (N) for Harvard cement were 350.8 6 43.0, 300.0 6 45.6, 421.6 6 47.7, and 392.3 6 35.4 for nonroughened dentinal walls after 3 and 150 daysÕ storage and for roughened dentinal walls after 3 and 150 daysÕ storage, respectively; values for Ketac Cem were 302.5 6 56.2, 281.7 6 37.8, 371.8 6 72.9, and 362.9 6 78.1, respectively; values for Panavia 21 were 349.1 6 87.1, 309.2 6 44.7, 570.3 6 104.2, and 506.3 6 87.0, respectively; and values for RelyX Unicem were 320.7 6 230
Fig. 3. SEM photograph of roughened root canal showing microgrooves (original magnification 3150).
59.4, 257.9 6 43.4, 596.0 6 107.3, and 534.4 6 109.5, respectively. The 3-way ANOVA (Table II) revealed a significant influence of canal surface preparation (roughened versus nonroughened), luting materials, and storage conditions on dowel retention. There was a significant interaction between the surface properties of the dentin walls and the luting materials. A Tukey multiple comparison procedure was performed on the adjusted least square mean values for the surface property 3 luting material interaction. The Tukey HSD test revealed no significant differences between luting agents in nonroughened dentinal walls, but statistically significant higher retention values for the dowels luted in roughened root canals with resin composites when compared with zinc-phosphate or glass-ionomer cements (Fig. 2). VOLUME 94 NUMBER 3
BALBOSH, LUDWIG, AND KERN
The cemented aspect of all dislodged dowels was completely coated with luting agent. This result indicated that there was no adhesive failure at the luting material–dowel interface. Independent of the luting agent, the failure mode was purely adhesive at the luting material–dentin interface for all dowels cemented in nonroughened root canals. A mixed failure mode, adhesive at the luting material–dentin interface and cohesive in the luting material, was observed for dowels cemented in roughened root canals.
DISCUSSION It is known that eugenol-containing root-canal sealers inhibit the polymerization of resin luting agents.31,32 Therefore, eugenol-free epoxy-amine resin sealer was used in this study to complete the endodontic therapy. In the present study, the luting agent film thickness was not measured, because the manufacturer purports that the luting agent film thickness for the same dowel system was between 37 and 42 mm when zincphosphate cement was used. All dowels were seated into the root canal by the same investigator under finger pressure; then a weight of 20 N was applied for 10 minutes using a custom-made loading apparatus. This ensured that the luting agent film thickness was nearly constant for all dowels. The present study showed a significant increase in the retention of passive, tapered, endodontic dowels by roughening the root canal before cementation for all tested luting materials. This finding is similar to those of previous studies that reported an increased retention of dowels7,19-21 or artificial crowns22,23 by roughening the prepared dentin. The reason for this increase in the retention is a mechanical interlocking between the luting agent and the roughened dentin walls. The roughening process created circular microgrooves (Fig. 3) on the root canal surface so that the luting material could flow and anchor into these microgrooves, and dislodgement of the dowel was only possible after the cohesive fracture of the luting agent extending into these microgrooves. The retention of the dowels decreased significantly for all luting agent after 150 days of storage with thermal cycling and mechanical loading. Few in vitro studies17,34 tested the effect of thermal cycling and mechanical loading on the retention of endodontic dowels with a storage time up to 4 weeks. The results of the current study are consistent with those of previous in vitro studies,17,34 which reported that thermal cycling and mechanical loading negatively affected the retention of endodontic dowels. The fact that the retention decreases after 150 days of storage with thermal cycling and mechanical loading is also consistent with the results of clinical studies29,30 that reported loss of dowel retention after a period of 2 to 3 years of function. This SEPTEMBER 2005
THE JOURNAL OF PROSTHETIC DENTISTRY
decrease in the retention may be explained by material fatigue as result of microleakage, changes in the elastic modulus, and plastic deformation over the time under thermal cycling and mechanical loading.26 There were no significant differences between the different luting materials when the dowels were cemented in nonroughened root canals. These results are similar to those of Mendoza and Eakle15 and Hagge et al,18 who found no difference in the retention of endodontic dowels cemented in nonroughened root canals with glass-ionomer or resin composite (Panavia 21) cement. However, many studies reported a better bond strength between resin composites and dentin when compared with zinc-phosphate or glass-ionomer cement. The tested restorations were usually crowns23,24 or endodontic dowels placed after acid etching the root canal.13,14,16,25 The retention of crowns or inlays cemented with resin composite can only be compared with that of dowels to a limited extent, for 2 reasons. First, there is a difference in the preparation technique and the smear layer formation. For crown or inlay preparations, a diamond rotary cutting instrument is usually used with a horizontal movement under water spray, while for dowel preparation, a rotary cutting instrument is used with a rotational movement with or without water spray, which may lead to the formation of a thicker smear layer. Second, there is a difference in the location of the dentin being prepared. A dowel is cemented in a root canal where dentinal tubules are thicker and denser, and the bond strength of resin cemented to deep, tubule-rich dentin is generally lower than to superficial dentin.27,28 The manufacturer of Panavia 21 recommends no acid etching of the root canal, and claims that conditioning with the provided autopolymerizing primer (EDPrimer) is an effective, 1-step conditioning of cut enamel and dentin. Also, the manufacturer of RelyX Unicem recommends no acid etching of the root canal, and purports that the self-adhesive composite luting agent has an acidic milieu and is able to etch the dentin surface. The use of these 2 resin composites tested in the present study without acid etching the dentin may be the reason why the dowels luted with these resin composites in nonroughened root canals had no better retention than those luted with zinc-phosphate or glass-ionomer cement. Only after the root canals had been roughened did the resin composites exhibit significantly higher retention than the zinc-phosphate or glass-ionomer cement. However, there was no significant difference between the resin composites. These results are in agreement with another in vitro study20 in which the retention of dowels cemented with zinc-phosphate cement and a resin luting agent was tested with and without roughened canals. The reason why resin composites achieved increased retention values compared with zinc-phosphate or glass-ionomer cement 231
THE JOURNAL OF PROSTHETIC DENTISTRY
after the root canal was roughened may be the improved mechanical properties, such as flexural strength, shear strength, compressive strength, and elastic modulus of the resin composites.26 Zinc-phosphate and glassionomer cements have brittle characteristics and do not need as much load as resin composites to fail cohesively.11 In this study, the airborne-particle abrasion of titanium dowels provided a good retentive surface for the luting agents. Therefore, there was no adhesive failure at the luting material–dowel interface and the cemented dowels were coated with luting agent. The failure mode at the luting material–dentin interface did not differ among the luting materials tested. The smooth surface of prepared dentin in nonroughened root canals provided no mechanical anchorage for the luting material, and this resulted in a purely adhesive failure at the luting material–dentin interface for all dowels cemented in nonroughened root canals. Roughening the surface of prepared dentin provided a mechanical interlocking for the luting material that resulted in a mixed failure mode, adhesive at the luting material–dentin interface, and cohesive in the luting material itself, for all dowels cemented in roughened root canals. These results are in agreement with those of another study7 in which the same dowel system was used. One limitation of this study was that mechanical loading was parallel to the long axis of the dowel. Furthermore, the results of this study might differ if a less severe thermal cycling regimen (20°C-40°C) were used, since endodontic dowels are not directly exposed to the oral environment.
CONCLUSIONS Within the limitations of this study, the use of Panavia 21 or RelyX Unicem for luting prefabricated tapered titanium dowels in root canals with roughened dentinal walls significantly improved the retention compared with zinc-phosphate or glass-ionomer cement. Roughening the dentinal walls caused a cohesive failure within the luting materials and increased retention for all tested luting materials. Storage for 150 days with thermal cycling and mechanical loading caused a significant decrease in the retention for all luting agents tested.
REFERENCES 1. Assif D, Gorfil C. Biomechanical considerations in restoring endodontically treated teeth. J Prosthet Dent 1994;71:565-7. 2. Morgano SM. Restoration of pulpless teeth: application of traditional principles in present and future contexts. J Prosthet Dent 1996;75:375-80. 3. Stockton LW. Factors affecting retention of post systems: a literature review. J Prosthet Dent 1999;81:380-5. 4. Bergman B, Lundquist P, Sjogren U, Sundquist G. Restorative and endodontic results after treatment with cast posts and cores. J Prosthet Dent 1989;61:10-5. 5. Tjan AH, Whang SB. Resistance to root fracture of dowel channels with various thicknesses of buccal dentin walls. J Prosthet Dent 1985;53:496-500.
232
BALBOSH, LUDWIG, AND KERN
6. Weine FS, Wax AH, Wenckus CS. Retrospective study of tapered, smooth post systems in place for 10 years or more. J Endod 1991;17:293-7. 7. Nergiz I, Schmage P, Platzer U, McMullan-Vogel CG. Effect of different surface textures on retentive strength of tapered posts. J Prosthet Dent 1997;78:451-7. 8. Johnson JK, Sakumura JS. Dowel form and tensile force. J Prosthet Dent 1978;40:645-9. 9. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effects of cement, dowel length, diameter, and design. J Prosthet Dent 1978;39:400-5. 10. Cohen BI, Musikant BL, Deutsch AS. Comparison of retentive properties of four post systems. J Prosthet Dent 1992;68:264-8. 11. Cohen BI, Pagnillo MK, Newman I, Musikant BL, Deutsch AS. Retention of three endodontic posts cemented with five dental cements. J Prosthet Dent 1998;79:520-5. 12. Nergiz I, Schmage P, Ozcan M, Platzer U. Effect of length and diameter of tapered posts on the retention. J Oral Rehabil 2002;29:28-34. 13. Goldman M, DeVitre R, Pier M. Effect of the dentin smeared layer on tensile strength of cemented posts. J Prosthet Dent 1984;52:485-8. 14. Standlee JP, Caputo AA. Endodontic dowel retention with resinous cements. J Prosthet Dent 1992;68:913-7. 15. Mendoza DB, Eakle WS. Retention of posts cemented with various dentinal bonding cements. J Prosthet Dent 1994;72:591-4. 16. Leary JM, Holmes DC, Johnson WT. Post and core retention with different cements. Gen Dent 1995;43:416-9. 17. Rosin M, Splieth C, Wilkens M, Meyer G. Effect of cement type on retention of a tapered post with a self-cutting double thread. J Dent 2000;28:577-82. 18. Hagge MS, Wong RD, Lindemuth JS. Retention strengths of five luting cements on prefabricated dowels after root canal obturation with a zinc oxide/eugenol sealer: 1. Dowel space preparation/cementation at one week after obturation. J Prosthodont 2002;11:168-75. 19. Tjan AH, Whang SB, Miller GD. The effect of a corrugated channel on the retentive properties of an obturator-reinforced composite resin dowel-core system. J Prosthet Dent 1984;51:347-52. 20. Tjan AH, Tjan AH, Greive JH. Effects of various cementation methods on the retention of prefabricated posts. J Prosthet Dent 1987;58:309-13. 21. Cohen BI, Pagnillo MK, Newman I, Musikant BL, Deutsch AS. Retention of four endodontic posts cemented with composite resin. Gen Dent 2000; 48:320-4. 22. Oilo G, Jorgensen KD. The influence of surface roughness on the retentive ability of two dental luting cements. J Oral Rehabil 1978;5:377-89. 23. 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. 24. Tuntiprawon M. Effect of tooth surface roughness on marginal seating and retention of complete metal crowns. J Prosthet Dent 1999;81:142-7. 25. Duncan JP, Pameijer CH. Retention of parallel-sided titanium posts cemented with six luting agents: an in vitro study. J Prosthet Dent 1998; 80:423-8. 26. Li ZC, White SN. Mechanical properties of dental luting cements. J Prosthet Dent 1999;81:597-609. 27. Tagami J, Tao L, Pashley DH. Correlation among dentin depth, permeability, and bond strength of adhesive resins. Dent Mater 1990;6:45-50. 28. Pashley DH. Clinical correlations of dentin structure and function. J Prosthet Dent 1991;66:777-81. 29. Lewis R, Smith BG. A clinical survey of failed post retained crowns. Br Dent J 1988;165:95-7. 30. Mentink AG, Creugers NH, Meeuwissen R, Leempoel PJ, Kayser AF. Clinical performance of different post and core systems—results of a pilot study. J Oral Rehabil 1993;20:577-84. 31. Millstein PL, Nathanson D. Effect of eugenol and eugenol cements on cured composite resin. J Prosthet Dent 1983;50:211-5. 32. Bayindir F, Akyil MS, Bayindir YZ. Effect of eugenol and non-eugenol containing temporary cement on permanent cement retention and microhardness of cured composite resin. Dent Mater J 2003;22:592-9. 33. Kern M, Thompson VP. Durability of resin bonds to pure titanium. J Prosthodont 1995;4:16-22. 34. Stegaroiu R, Yamada H, Kusakari H, Miyakawa O. Retention and failure mode after cyclic loading in two post and core systems. J Prosthet Dent 1996;75:506-11. 35. Laurell L, Lundgren D. A standardized programme for studying the occlusal force pattern during chewing and biting in prosthetically restored dentitions. J Oral Rehabil 1984;11:39-44.
VOLUME 94 NUMBER 3
BALBOSH, LUDWIG, AND KERN
Reprint requests to: DR MATTHIAS KERN DEPARTMENT OF PROSTHODONTICS, PROPAEDEUTICS, AND DENTAL MATERIALS SCHOOL OF DENTISTRY, CHRISTIAN-ALBRECHTS UNIVERSITY AT KIEL ARNOLD-HELLER STRASSE 16 24105 KIEL, GERMANY FAX: 149 0431 597 2860 E-MAIL: [email protected]
SEPTEMBER 2005
THE JOURNAL OF PROSTHETIC DENTISTRY
0022-3913/$30.00 Copyright Ó 2005 by The Editorial Council of The Journal of Prosthetic Dentistry.
doi:10.1016/j.prosdent.2005.05.025
233
Purpose. The purpose of this study was to evaluate the effect of roughening of the dentinal walls and artificial aging on the retention of prefabricated tapered titanium dowels, using 4 different luting materials.
Material and methods. One-hundred twenty-eight single-rooted teeth were selected, the coronal aspect of each tooth was removed, and the remaining root received endodontic therapy. All specimens were divided into 4 groups (n = 32). Dowel spaces were prepared to a depth of 10 mm using ISO 90 rotary cutting instruments. Tapered titanium dowels were luted with the following luting materials: zinc-phosphate cement (Harvard cement), glass-ionomer cement (Ketac Cem EasyMix), resin composite luting agent (Panavia 21) with autopolymerizing dentin primer (ED-Primer), or a self-adhesive composite luting agent (RelyX Unicem). Both composite luting agents were used without acid etching of the canal dentin. Each luting agent was used under 2 conditions: in 1 subgroup (n = 16) the dentinal walls were not roughened, and in the other subgroup (n = 16), walls were roughened with a diamond rotary cutting instrument. Eight specimens from each subgroup were stored in water at 37°C for 3 days; the other 8 specimens were stored for 150 days and subjected to simulated aging conditions using 37,500 thermal cycles (5°C/55°C) and 300,000 mechanical loading cycles with 30 N. Dowel retention (N) was measured using a universal testing machine with a crosshead speed of 2 mm/min. Data were analyzed using 2- and 3-way ANOVAs and the Tukey HSD test (a=.05). Results. The dislodged dowels were examined microscopically to evaluate mode of failure. The nonroughened dentinal walls showed no significant differences between the different luting agents. Roughening the dentinal walls increased the retention significantly for all groups. This increase was significantly higher for the resin composite groups (P=.0001). Storage for 150 days with thermal cycling and mechanical loading caused a significant decrease in dowel retention (P=.001). The failure mode was purely adhesive at the luting material– dentin interface for all dowels cemented in nonroughened root canals. A mixed failure mode, adhesive at the luting material–dentin interface and cohesive in the luting material, was observed for dowels cemented in roughened root canals. Conclusion. Roughening the dentinal walls and the use of resin luting cements provided statistically significant increases in dowel retention values. (J Prosthet Dent 2005;94:227-33.)
CLINICAL IMPLICATIONS Based on the results of this study, roughening of dentinal walls before dowel cementation with any one of the tested luting agents is recommended for increasing dowel retention. For the best dowel retention results, resin composite luting agents should be selected.
E
ndodontic dowels are widely used for restoring endodontically treated teeth with insufficient coronal tooth structure to retain a core for a definitive restoration.1,2 Prefabricated dowel systems have recently become more popular because they provide satisfactory results, while saving chair time and reducing costs to the patient.3 However, a prefabricated dowel should adequately adapt to the prepared root canal, or a cast dowel and core should be used.4 Passive, tapered dowels have a a
Visiting Assistant Professor. Professor of Dental Materials. c Professor and Department Chairman. b
SEPTEMBER 2005
shape that is congruent with a root-canal configuration and allow for optimal preservation of tooth structure, especially in the apical region.5-7 Endodontic dowels should have good retention to provide definitive anchorage for a prosthodontic restoration. Many in vitro studies have investigated various factors and their effects on dowel retention. These factors include dowel design,3,8-11 length,3,8,9,12 diameter,3,8-10,12 luting agent,3,9,11,13-18 and preparation of the dowel space.3 Some studies have reported that tapered dowels provided lower retention when compared to parallel-sided or threaded dowels.8,9 Roughening the prepared dentin surface increases the retention of THE JOURNAL OF PROSTHETIC DENTISTRY 227
THE JOURNAL OF PROSTHETIC DENTISTRY
BALBOSH, LUDWIG, AND KERN
Table I. Luting cements and codes Group/ subgroup
Dowel space
Manufacturer
Batch No.
Zinc phosphate cement (Harvard cement, normal setting)
Hs Hr
Nonroughened Roughened
Harvard Dental, Berlin, Germany
Powder: 2112497016 Liquid: 2111099018
Glass ionomer cement (Ketac Cem EasyMix)
Ks Kr
Non-roughened Roughened
3M ESPE, Seefeld, Germany
118425
Panavia 21 EX
Ps Pr
Nonroughened Roughened
Kuraray, Osaka, Japan
41218
RelyX Unicem
Us Ur
Nonroughened Roughened
3M ESPE
136276
Cement
dowels7,19-21 or artificial crowns22-24 by increasing the surface area and enhancing the mechanical interlocking between the dentin surface and the cement. For situations in which additional dowel retention is needed, airborne-particle abrasion of the dowel surface and roughening the walls of the prepared dowel space with a diamond rotary cutting instrument may increase the retention of dowels without compromising the remaining tooth structure.7 Cements including zinc phosphate, polycarboxylate, glass ionomer, and resin composites have been used to cement endodontic dowels. The retention of a dowel varies, depending on the type of cement, its mechanical properties,11,17,25,26 and dentin structure.27,28 Most studies that tested the retention of endodontic dowels were performed shortly after cementation, without any type of simulation of oral conditions or aging.7,11,12,25 However, clinically, the dislodgement of dowel-retained restorations occurs usually after several years of function as a result of different stress factors, such as temperature change and mechanical loading.29,30 Therefore, in vitro tests evaluating dowel retention should aim to simulate clinical conditions, using artificial aging to better predict clinical behavior. The purpose of this in vitro study was to evaluate the effect of artificial aging on the retention of prefabricated tapered titanium dowels when luted with 4 different luting materials. In addition, the effect of roughening the dentinal walls was evaluated.
MATERIAL AND METHODS For this study, extracted caries-free and visually assessed fracture-free, human maxillary anterior and mandibular premolar teeth were selected, cleaned of both calculus deposits and soft tissues, and stored in 0.1% thymol solution (Caelo, Hilden, Germany). Each tooth was sectioned with a diamond rotary cutting instrument (837KR.012; Brasseler, Lemgo, Germany) under water spray, 1 mm coronal to the cemento-enamel junction. Roots with distinctly oval root canals or with a root canal diameter of more than 2 mm were excluded from the 228
study to ensure that the dowel would seat against a freshly prepared dentin surface free of undercuts or remnants of root-canal filling material. From this selection process, 128 root specimens were chosen. The coronal surface of each root specimen was flattened with a finishing diamond rotary cutting instrument (8837KR.012; Brasseler) under water spray to obtain a surface perpendicular to the long axis of the root. The pulpal tissues were removed, and the canals were instrumented up to ISO size-50 files (K-file; Dentsply De Trey, Konstanz, Germany). Sodium-hypochlorite solution (3%) (Hedinger, Stuttgart, Germany) was used to irrigate the canals throughout instrumentation. The roots were dried with paper points (Coltene/Whaledent Inc, Langenau, Germany) and obturated with an ISO size50 gutta percha master point (Kerr GmbH, Karlsruhe, Germany) and eugenol-free31,32 epoxy-amine resin sealer (AH Plus sealer; Dentsply De Trey). Lateral condensation with a finger spreader (Dentsply De Trey) and fine accessory gutta percha points (Kerr) was performed until the canals were obturated. After completion of endodontic treatment, the roots were stored in 0.1% thymol solution at room temperature for 72 hours before proceeding. For each specimen, the coronal aspect of the gutta percha was removed with a heated probe (Omnident, Rodgau Nieder-Roden, Germany), and a 10-mm-deep dowel space was prepared using an ISO-90 preparation instrument (196.204.090, Erlangen Post System; Brasseler), with a new instrument used for every 8 specimens. Throughout the preparation, the dowel space was irrigated with 3% sodium-hypochlorite solution. The prepared dowel space was dried with paper points, irrigated with 70% ethanol (Bundesmonopolverwaltung fuer Branntwein, Hamburg, Germany), and dried with paper points. The specimens were then divided into 4 groups representing each of the 4 luting agents tested. Each group was then further divided into 2 subgroups of 16 specimens each (Table I). In one subgroup, the dentinal walls were not roughened, but left in their original state after using the system’s preparation VOLUME 94 NUMBER 3
BALBOSH, LUDWIG, AND KERN
instrument, while in the other subgroup, the dentinal walls were roughened with a hand-held diamond rotary cutting instrument (196D.644.090; Erlangen Post System; Brasseler) by rotating the instrument 3 times within the canal. The prefabricated ISO size-90 titanium dowels (CP titanium ASTM grade 4, 61L16.090; Erlangen Post System; Brasseler) were provided by the manufacturer with a surface roughness value of 12 mm. Before cementation the dowels were also airborne-particle-abraded using 50-mm alumina particles (Heraeus Kulzer, Wehrheim, Germany) at 2.5-bar pressure for 15 seconds. For the zinc-phosphate cement specimens, there was no conditioning of the dentin surface. For the glass-ionomer cement specimens, the dentin surface was conditioned, according to the manufacturer’s directions, with polyacrylic acid (Ketac Conditioner) for 20 seconds. The root canal was then rinsed with distilled water and dried with paper points, and a slightly moistened paper point was left in the canal until the cement was introduced to avoid dentin dehydration. For Panavia 21 EX specimens, the dentin surface was conditioned with the system’s autopolymerizing primer (EDPrimer) for 60 seconds without previous acid etching of the canal dentin. For RelyX Unicem specimens, there was no previous acid etching or conditioning of the canal dentin. All luting materials were used according to the manufacturers’ instructions. Zinc-phosphate and glass-ionomer cements were placed into the root canal using an ISO size-40 lentulo spiral (Dentsply De Trey), whereas the resin composites were not placed into the root canal before the dowel. In all groups, the dowel was coated with the luting material and seated by finger pressure. A weight of 20 N was then applied by means of a custom-made loading apparatus for 10 minutes. During this time, oxygen-inhibiting gel (Oxyguard II; Kuraray, Osaka, Japan) was applied with a syringe to the bonding margins of Panavia 21 EX. After cementation, notches were placed in the external root surface to prevent dislodgement from an autopolymerizing acrylic resin (Technovit 4000; Heraeus Kulzer) embedding material. The roots were mounted on a custom-made Plexiglas holder (Plexiglas, Roehm, Germany), and a custom-made surveyor ensured that the holder was parallel to the long axis of the dowel. Eight specimens from each subgroup were stored in water at 37°C for 3 days. The other 8 specimens were stored for 150 days33 to evaluate the bond durability of the luting agents while simulating oral conditions. These specimens were thermal cycled (Willytec, Munich, Germany) for 37,500 cycles33 (5°-55°C) with a dwell time of 30 seconds and a transition time of 6 seconds, and subjected to 300,000 cycles of mechanical loading parallel to the long axis of the dowel, using a masticatory simulator (Willytec) with 30 N force at 1.6 Hz. The mechanical loading pattern was equivalent to 1 year of clinical function.34 The force of 30 N was SEPTEMBER 2005
THE JOURNAL OF PROSTHETIC DENTISTRY
Fig. 1. Schematic diagram of tensile test apparatus. (A), Custom-made device; (B), custom-made holder; (C), resin block; (D), Plexiglas ring; (E), tooth specimen; (F), dowel.
within previously measured occlusal forces that occurred during mastication and swallowing with restored dentitions.35 For the retention test, a screw-driven universal testing machine (Zwick Z010; Zwick, Ulm, Germany) was used to apply a tensile force load parallel to the long axis of the dowels and at a crosshead speed of 2 mm/minute. The portion of the dowel that extended from the root was grasped with a custom-made device. A chain of 4 links between the device and the upper grip of the testing machine allowed for self-alignment during testing (Fig. 1). The force in N required to dislodge each dowel from the prepared dowel space was recorded. The data were analyzed using 3-way and 2-way 229
THE JOURNAL OF PROSTHETIC DENTISTRY
BALBOSH, LUDWIG, AND KERN
Fig. 2. Mean retention values and SDs for all groups after 3 daysÕ storage without thermal cycling and mechanical loading and after 150 days with thermal cycling and mechanical loading. Horizontal lines connect mean values for dowels cemented in roughened root canals that are not significantly different (P ..05). Table II. Summary of 3-way ANOVA for retention Source
Main effects Surface properties (A) Luting agents (B) Storage conditions (C) Interactions A3B A3C B3C A3B3C
Sum of squares
df
Mean square
F
P
823810.0
1
823810.0
163.97
0.0001
239966.0 57139.3
3 1
79988.5 57139.3
15.92 11.37
0.0001 0.0010
233416.0 55.7 10003.2 2328.5
3 1 3 3
77805.3 55.7 3334.4 776.2
15.49 0.01 0.66 0.15
0.0001 0.9163 0.5761 0.9266
analyses of variance (ANOVAs) and Tukey HSD tests for multiple comparisons (a=.05). The dislodged dowels were examined microscopically at 38 and 320 magnifications to evaluate the mode of failure, which was recorded.
RESULTS The mean retentive strength values and SDs are shown in Figure 2. The mean retentive values and SDs (N) for Harvard cement were 350.8 6 43.0, 300.0 6 45.6, 421.6 6 47.7, and 392.3 6 35.4 for nonroughened dentinal walls after 3 and 150 daysÕ storage and for roughened dentinal walls after 3 and 150 daysÕ storage, respectively; values for Ketac Cem were 302.5 6 56.2, 281.7 6 37.8, 371.8 6 72.9, and 362.9 6 78.1, respectively; values for Panavia 21 were 349.1 6 87.1, 309.2 6 44.7, 570.3 6 104.2, and 506.3 6 87.0, respectively; and values for RelyX Unicem were 320.7 6 230
Fig. 3. SEM photograph of roughened root canal showing microgrooves (original magnification 3150).
59.4, 257.9 6 43.4, 596.0 6 107.3, and 534.4 6 109.5, respectively. The 3-way ANOVA (Table II) revealed a significant influence of canal surface preparation (roughened versus nonroughened), luting materials, and storage conditions on dowel retention. There was a significant interaction between the surface properties of the dentin walls and the luting materials. A Tukey multiple comparison procedure was performed on the adjusted least square mean values for the surface property 3 luting material interaction. The Tukey HSD test revealed no significant differences between luting agents in nonroughened dentinal walls, but statistically significant higher retention values for the dowels luted in roughened root canals with resin composites when compared with zinc-phosphate or glass-ionomer cements (Fig. 2). VOLUME 94 NUMBER 3
BALBOSH, LUDWIG, AND KERN
The cemented aspect of all dislodged dowels was completely coated with luting agent. This result indicated that there was no adhesive failure at the luting material–dowel interface. Independent of the luting agent, the failure mode was purely adhesive at the luting material–dentin interface for all dowels cemented in nonroughened root canals. A mixed failure mode, adhesive at the luting material–dentin interface and cohesive in the luting material, was observed for dowels cemented in roughened root canals.
DISCUSSION It is known that eugenol-containing root-canal sealers inhibit the polymerization of resin luting agents.31,32 Therefore, eugenol-free epoxy-amine resin sealer was used in this study to complete the endodontic therapy. In the present study, the luting agent film thickness was not measured, because the manufacturer purports that the luting agent film thickness for the same dowel system was between 37 and 42 mm when zincphosphate cement was used. All dowels were seated into the root canal by the same investigator under finger pressure; then a weight of 20 N was applied for 10 minutes using a custom-made loading apparatus. This ensured that the luting agent film thickness was nearly constant for all dowels. The present study showed a significant increase in the retention of passive, tapered, endodontic dowels by roughening the root canal before cementation for all tested luting materials. This finding is similar to those of previous studies that reported an increased retention of dowels7,19-21 or artificial crowns22,23 by roughening the prepared dentin. The reason for this increase in the retention is a mechanical interlocking between the luting agent and the roughened dentin walls. The roughening process created circular microgrooves (Fig. 3) on the root canal surface so that the luting material could flow and anchor into these microgrooves, and dislodgement of the dowel was only possible after the cohesive fracture of the luting agent extending into these microgrooves. The retention of the dowels decreased significantly for all luting agent after 150 days of storage with thermal cycling and mechanical loading. Few in vitro studies17,34 tested the effect of thermal cycling and mechanical loading on the retention of endodontic dowels with a storage time up to 4 weeks. The results of the current study are consistent with those of previous in vitro studies,17,34 which reported that thermal cycling and mechanical loading negatively affected the retention of endodontic dowels. The fact that the retention decreases after 150 days of storage with thermal cycling and mechanical loading is also consistent with the results of clinical studies29,30 that reported loss of dowel retention after a period of 2 to 3 years of function. This SEPTEMBER 2005
THE JOURNAL OF PROSTHETIC DENTISTRY
decrease in the retention may be explained by material fatigue as result of microleakage, changes in the elastic modulus, and plastic deformation over the time under thermal cycling and mechanical loading.26 There were no significant differences between the different luting materials when the dowels were cemented in nonroughened root canals. These results are similar to those of Mendoza and Eakle15 and Hagge et al,18 who found no difference in the retention of endodontic dowels cemented in nonroughened root canals with glass-ionomer or resin composite (Panavia 21) cement. However, many studies reported a better bond strength between resin composites and dentin when compared with zinc-phosphate or glass-ionomer cement. The tested restorations were usually crowns23,24 or endodontic dowels placed after acid etching the root canal.13,14,16,25 The retention of crowns or inlays cemented with resin composite can only be compared with that of dowels to a limited extent, for 2 reasons. First, there is a difference in the preparation technique and the smear layer formation. For crown or inlay preparations, a diamond rotary cutting instrument is usually used with a horizontal movement under water spray, while for dowel preparation, a rotary cutting instrument is used with a rotational movement with or without water spray, which may lead to the formation of a thicker smear layer. Second, there is a difference in the location of the dentin being prepared. A dowel is cemented in a root canal where dentinal tubules are thicker and denser, and the bond strength of resin cemented to deep, tubule-rich dentin is generally lower than to superficial dentin.27,28 The manufacturer of Panavia 21 recommends no acid etching of the root canal, and claims that conditioning with the provided autopolymerizing primer (EDPrimer) is an effective, 1-step conditioning of cut enamel and dentin. Also, the manufacturer of RelyX Unicem recommends no acid etching of the root canal, and purports that the self-adhesive composite luting agent has an acidic milieu and is able to etch the dentin surface. The use of these 2 resin composites tested in the present study without acid etching the dentin may be the reason why the dowels luted with these resin composites in nonroughened root canals had no better retention than those luted with zinc-phosphate or glass-ionomer cement. Only after the root canals had been roughened did the resin composites exhibit significantly higher retention than the zinc-phosphate or glass-ionomer cement. However, there was no significant difference between the resin composites. These results are in agreement with another in vitro study20 in which the retention of dowels cemented with zinc-phosphate cement and a resin luting agent was tested with and without roughened canals. The reason why resin composites achieved increased retention values compared with zinc-phosphate or glass-ionomer cement 231
THE JOURNAL OF PROSTHETIC DENTISTRY
after the root canal was roughened may be the improved mechanical properties, such as flexural strength, shear strength, compressive strength, and elastic modulus of the resin composites.26 Zinc-phosphate and glassionomer cements have brittle characteristics and do not need as much load as resin composites to fail cohesively.11 In this study, the airborne-particle abrasion of titanium dowels provided a good retentive surface for the luting agents. Therefore, there was no adhesive failure at the luting material–dowel interface and the cemented dowels were coated with luting agent. The failure mode at the luting material–dentin interface did not differ among the luting materials tested. The smooth surface of prepared dentin in nonroughened root canals provided no mechanical anchorage for the luting material, and this resulted in a purely adhesive failure at the luting material–dentin interface for all dowels cemented in nonroughened root canals. Roughening the surface of prepared dentin provided a mechanical interlocking for the luting material that resulted in a mixed failure mode, adhesive at the luting material–dentin interface, and cohesive in the luting material itself, for all dowels cemented in roughened root canals. These results are in agreement with those of another study7 in which the same dowel system was used. One limitation of this study was that mechanical loading was parallel to the long axis of the dowel. Furthermore, the results of this study might differ if a less severe thermal cycling regimen (20°C-40°C) were used, since endodontic dowels are not directly exposed to the oral environment.
CONCLUSIONS Within the limitations of this study, the use of Panavia 21 or RelyX Unicem for luting prefabricated tapered titanium dowels in root canals with roughened dentinal walls significantly improved the retention compared with zinc-phosphate or glass-ionomer cement. Roughening the dentinal walls caused a cohesive failure within the luting materials and increased retention for all tested luting materials. Storage for 150 days with thermal cycling and mechanical loading caused a significant decrease in the retention for all luting agents tested.
REFERENCES 1. Assif D, Gorfil C. Biomechanical considerations in restoring endodontically treated teeth. J Prosthet Dent 1994;71:565-7. 2. Morgano SM. Restoration of pulpless teeth: application of traditional principles in present and future contexts. J Prosthet Dent 1996;75:375-80. 3. Stockton LW. Factors affecting retention of post systems: a literature review. J Prosthet Dent 1999;81:380-5. 4. Bergman B, Lundquist P, Sjogren U, Sundquist G. Restorative and endodontic results after treatment with cast posts and cores. J Prosthet Dent 1989;61:10-5. 5. Tjan AH, Whang SB. Resistance to root fracture of dowel channels with various thicknesses of buccal dentin walls. J Prosthet Dent 1985;53:496-500.
232
BALBOSH, LUDWIG, AND KERN
6. Weine FS, Wax AH, Wenckus CS. Retrospective study of tapered, smooth post systems in place for 10 years or more. J Endod 1991;17:293-7. 7. Nergiz I, Schmage P, Platzer U, McMullan-Vogel CG. Effect of different surface textures on retentive strength of tapered posts. J Prosthet Dent 1997;78:451-7. 8. Johnson JK, Sakumura JS. Dowel form and tensile force. J Prosthet Dent 1978;40:645-9. 9. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effects of cement, dowel length, diameter, and design. J Prosthet Dent 1978;39:400-5. 10. Cohen BI, Musikant BL, Deutsch AS. Comparison of retentive properties of four post systems. J Prosthet Dent 1992;68:264-8. 11. Cohen BI, Pagnillo MK, Newman I, Musikant BL, Deutsch AS. Retention of three endodontic posts cemented with five dental cements. J Prosthet Dent 1998;79:520-5. 12. Nergiz I, Schmage P, Ozcan M, Platzer U. Effect of length and diameter of tapered posts on the retention. J Oral Rehabil 2002;29:28-34. 13. Goldman M, DeVitre R, Pier M. Effect of the dentin smeared layer on tensile strength of cemented posts. J Prosthet Dent 1984;52:485-8. 14. Standlee JP, Caputo AA. Endodontic dowel retention with resinous cements. J Prosthet Dent 1992;68:913-7. 15. Mendoza DB, Eakle WS. Retention of posts cemented with various dentinal bonding cements. J Prosthet Dent 1994;72:591-4. 16. Leary JM, Holmes DC, Johnson WT. Post and core retention with different cements. Gen Dent 1995;43:416-9. 17. Rosin M, Splieth C, Wilkens M, Meyer G. Effect of cement type on retention of a tapered post with a self-cutting double thread. J Dent 2000;28:577-82. 18. Hagge MS, Wong RD, Lindemuth JS. Retention strengths of five luting cements on prefabricated dowels after root canal obturation with a zinc oxide/eugenol sealer: 1. Dowel space preparation/cementation at one week after obturation. J Prosthodont 2002;11:168-75. 19. Tjan AH, Whang SB, Miller GD. The effect of a corrugated channel on the retentive properties of an obturator-reinforced composite resin dowel-core system. J Prosthet Dent 1984;51:347-52. 20. Tjan AH, Tjan AH, Greive JH. Effects of various cementation methods on the retention of prefabricated posts. J Prosthet Dent 1987;58:309-13. 21. Cohen BI, Pagnillo MK, Newman I, Musikant BL, Deutsch AS. Retention of four endodontic posts cemented with composite resin. Gen Dent 2000; 48:320-4. 22. Oilo G, Jorgensen KD. The influence of surface roughness on the retentive ability of two dental luting cements. J Oral Rehabil 1978;5:377-89. 23. 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. 24. Tuntiprawon M. Effect of tooth surface roughness on marginal seating and retention of complete metal crowns. J Prosthet Dent 1999;81:142-7. 25. Duncan JP, Pameijer CH. Retention of parallel-sided titanium posts cemented with six luting agents: an in vitro study. J Prosthet Dent 1998; 80:423-8. 26. Li ZC, White SN. Mechanical properties of dental luting cements. J Prosthet Dent 1999;81:597-609. 27. Tagami J, Tao L, Pashley DH. Correlation among dentin depth, permeability, and bond strength of adhesive resins. Dent Mater 1990;6:45-50. 28. Pashley DH. Clinical correlations of dentin structure and function. J Prosthet Dent 1991;66:777-81. 29. Lewis R, Smith BG. A clinical survey of failed post retained crowns. Br Dent J 1988;165:95-7. 30. Mentink AG, Creugers NH, Meeuwissen R, Leempoel PJ, Kayser AF. Clinical performance of different post and core systems—results of a pilot study. J Oral Rehabil 1993;20:577-84. 31. Millstein PL, Nathanson D. Effect of eugenol and eugenol cements on cured composite resin. J Prosthet Dent 1983;50:211-5. 32. Bayindir F, Akyil MS, Bayindir YZ. Effect of eugenol and non-eugenol containing temporary cement on permanent cement retention and microhardness of cured composite resin. Dent Mater J 2003;22:592-9. 33. Kern M, Thompson VP. Durability of resin bonds to pure titanium. J Prosthodont 1995;4:16-22. 34. Stegaroiu R, Yamada H, Kusakari H, Miyakawa O. Retention and failure mode after cyclic loading in two post and core systems. J Prosthet Dent 1996;75:506-11. 35. Laurell L, Lundgren D. A standardized programme for studying the occlusal force pattern during chewing and biting in prosthetically restored dentitions. J Oral Rehabil 1984;11:39-44.
VOLUME 94 NUMBER 3
BALBOSH, LUDWIG, AND KERN
Reprint requests to: DR MATTHIAS KERN DEPARTMENT OF PROSTHODONTICS, PROPAEDEUTICS, AND DENTAL MATERIALS SCHOOL OF DENTISTRY, CHRISTIAN-ALBRECHTS UNIVERSITY AT KIEL ARNOLD-HELLER STRASSE 16 24105 KIEL, GERMANY FAX: 149 0431 597 2860 E-MAIL: [email protected]
SEPTEMBER 2005
THE JOURNAL OF PROSTHETIC DENTISTRY
0022-3913/$30.00 Copyright Ó 2005 by The Editorial Council of The Journal of Prosthetic Dentistry.
doi:10.1016/j.prosdent.2005.05.025
233