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Influence of post placement in the fracture resistance of endodontically treated incisors veneered with direct composite
Influence of post placement in the fracture resistance of endodontically treated incisors veneered with direct composite Luiz Narciso Baratieri, DDS, MS, PhD,a Mauro Amaral Caldeira de Andrada, DDS, MS, PhD,b Gilberto Müller Arcari, DDS,c and André V. Ritter, DDS, MSd Federal University of Santa Catarina Florianópolis, Brazil, and University of North Carolina at Chapel Hill, N. C. Statement of problem. Veneer preparations are considered to weaken endodontically treated maxillary incisors. Prefabricated posts have been controversially indicated to reinforce endodontically treated teeth before final restoration. Purpose. This in vitro study evaluated whether (1) veneer preparation in enamel or in enamel/dentin weakens endodontically treated maxillary incisors, (2) bonding of direct composite veneer restores the original strength of the unprepared teeth, and (3) use of prefabricated metal posts increases fracture resistance of prepared and restored teeth. Material and methods. Ninety extracted human maxillary central incisors were submitted to conventional root canal treatment. Specimens were randomly divided into 8 experimental groups (veneer preparation in enamel or dentin with/without post and with/without direct composite veneer restoration) and a control group (n = 10). Specimens were loaded to fracture, and the data were analyzed statistically. Results. Statistical analysis revealed that a conservative veneer preparation does not significantly reduce maxillary incisors’ fracture resistance. For prepared incisors, bonding of direct composite veneer restored their original strength, and the use of posts did not increase their fracture resistance. Conclusion. Conservative veneer preparations involving enamel and enamel/dentin did not significantly reduce the fracture resistance of endodontically treated maxillary incisors. In addition, restoration of the intraenamel preparations with direct composite resulted in teeth more resistant to fracture than teeth having restorations in dentin. The use of posts did not improve fracture resistance of endodontically treated maxillary incisors reduced and veneered with direct composite. (J Prosthet Dent 2000;84:180-4.)
CLINICAL IMPLICATIONS In this study, conservative preparation for direct veneers and subsequent veneering with composite did not significantly weaken endodontically treated maxillary central incisors, and the use of posts did not increase the resistance of these teeth to fracture.
D
irect composite veneers have been indicated as an esthetic and conservative treatment alternative in a variety of clinical scenarios, such as teeth with multiple restorations requiring replacement; short teeth; diastemas; and malformed, malpositioned, and/or darkened teeth.1-4 Although long-term clinical studies on direct composite veneers are scarce,5,6 the current aProfessor,
Department of Stomatology, Head of Operative Dentistry Section, University of Florianópolis, UFSC/CCS/STM, Florianópolis, SC, Brazil. bProfessor, Department of Stomatology, Operative Dentistry Section, UFSC/CCS/STM, Florianópolis, SC, Brazil. cProfessor, Department of Stomatology, Dental Materials Section, UFSC/CCS/STM, Florianópolis, SC, Brazil. dProfessor, Department of Stomatology, Operative Dentistry Section, UFSC/CCS/STM, Florianópolis, SC, Brazil; and Resident, Dental Research Center and Department of Operative Dentistry, The University of North Carolina at Chapel Hill. 180 THE JOURNAL OF PROSTHETIC DENTISTRY
generation of direct composites and adhesive systems, when properly used, allows the clinician to create direct veneers that resemble the natural elements of the tooth, namely enamel translucency, dentin hue and chroma, and adequate surface texture.7,8 In addition, the direct technique enables the clinician to exercise complete control over all the restorative phases, which is not always the case with the indirect techniques.7,8 The most conservative veneer technique is the application of the composite without tooth reduction.7-9 However, this approach is seldom applied, being feasible only when the tooth to be veneered is lingually positioned, because the application of the composite without tooth reduction leads to overcontouring. In many clinical situations, therefore, the application of direct composite veneers requires tooth reduction to compensate for the thickness of the restorative material. The amount of reduction is directly related to the esVOLUME 84 NUMBER 2
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thetic demands the case imposes. This is true mainly for darkened teeth, where greater reduction allows for greater thickness of composite and, consequently, greater potential to mask the defect.10 However, reduction might decrease the resistance of the tooth to fracture, particularly for endodontically treated teeth.11-14 In these cases, direct composite veneers are indicated only when the remaining tooth structure is relatively intact, because the endodontic access considerably weakens the tooth.15,16 Prefabricated root-canal posts have been proposed to reinforce the tooth/restoration unit in endodontically treated teeth.17,18 This is a controversial strategy, as a few studies support the strengthening effect of posts, but most studies do not.12,17,19-29 The purposes of this in vitro study were to determine whether (1) veneer preparation in enamel or in enamel/dentin weakens endodontically treated maxillary incisors, (2) bonding of direct composite veneer restores the original strength of the unprepared tooth, and (3) the use of root canal prefabricated metal posts increases the fracture resistance of the prepared tooth. The hypotheses advanced are that conservative veneer preparations do not weaken significantly maxillary incisors, and that posts are not needed for the conservative veneering of endodontically treated maxillary incisors.
MATERIAL AND METHODS Ninety human maxillary central incisors extracted because of periodontal and/or prosthetic reasons were selected, disinfected in 0.5% chloramine for 24 hours, and stored in water at 4°C. Only intact teeth were included in the study. All specimens were submitted to conventional root canal therapy, which consisted of palatal access, step-back manual instrumentation with K-files (final size No. 50), and laterally condensed manual obturation with gutta-percha and minute amounts of a zinc-oxide/eugenol sealer. Gutta-percha cones were cut by the entrance of the root canal, and the pulp chamber was mechanically cleaned with round burs and left unrestored. Methyl-alcohol 70% was scrubbed in the pulp chamber with a cotton pellet for 60 seconds to remove any residual eugenol from the sealer in the pulp chamber and thoroughly rinsed with running water. The remaining dentin structure after endodontic preparation was considered to be equivalent in all specimens. The specimens were randomly divided and distributed into 1 control and 8 experimental groups (n = 10) as follows. Figure 1 illustrates the control group (group 0) and the different preparations for each of the experimental groups.
Group 0 — Control Group 0 was the control group. The pulp chamber was restored with a light-cured hybrid composite and AUGUST 2000
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Fig. 1. Diagrammatic drawings of the procedures performed in each group. (See Material and Methods section for details). Note the matrix “shell” in groups 2, 4, 6, and 8, the post in groups 3, 4, 7, and 8, intraenamel veneer preparations in groups 1 through 4 and dentin veneer preparations in groups 5 through 8.
adhesive system, according to the manufacturer’s instructions (Sybron/Kerr, Orange, Calif.). No intermediate base was applied over the gutta-percha. After light curing the adhesive, the restorative resin was applied and light cured in 3 increments through the palatal access. Each increment of composite was cured for 40 seconds. In all groups, the pulp chambers were restored using the same method described previously. In this control group, no further treatment was performed. A XL 2000 light-curing unit (3M Dental Products, St Paul, Minn.) with a 15 mm tip was used for all polymerization procedures. Light intensity was checked every 10 curing cycles to ensure at least 450 mW/cm2 of power output. A Curing Radiometer (Demetron/ Kerr, Danbury, Conn.) was used for that purpose.
Group 1 — Veneer preparation in enamel Veneer preparations were standardized in all groups, variations being introduced only in the depth (enamel or enamel/dentin, according to the experimental group). In this experimental group, the reduction reached midenamel axially, with depth ranging from 181
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0.2 to 0.6 mm. Depth was checked with a periodontal probe. A tapered round-ended diamond (No. 2137, KGS, Sao Paulo, Brazil) was used to cut the veneer preparations. The gingival margin was maintained in enamel. There were no incisal reductions, and proximal contact areas were maintained unprepared. In group 1, the preparations were not restored.
Group 2 — Veneer preparation in enamel and direct composite veneer The reduction was as for group 1. The veneers were made according to the acrylic resin facial matrix technique, described by Baratieri et al.3 This technique is convenient when the facial surface of the tooth to be veneered maintains its form and surface details, which can be fully replicated on the veneer. Before being submitted to facial reduction, the facial aspect of the incisor is lubricated with a fine coat of petroleum jelly. Colorless acrylic resin (Duralay, Resiliance Co, DFL, Sao Paulo, Brazil) is spread over the facial surface and the proximal embrasures. The matrix should be approximately 1.5 mm thick and extend slightly beyond the margins of the future veneer preparation, so that the acrylic shell will have a “stop” during the seating of the loaded matrix. With the acrylic resin completely polymerized, the matrix is removed and its inner surface must be carefully inspected for imperfection or voids. At this stage, the matrix is stored in water until it is used (no more than 24 hours). In those groups receiving direct composite veneers (groups 2, 4, 6, and 8), the preparations were cleaned with running water followed by air-drying. The 37% phosphoric acid gel was applied on the prepared area for 15 seconds and rinsed with an air/water syringe. The etched preparation was blot-dried and the adhesive was applied and cured, as per manufacturer’s instructions. The restorative resin was applied using the acrylic matrix shell. After lubricating the inner aspect of the matrix with a thin layer of a water-soluble lubricant, the composite was layered inside the matrix. The matrix was then seated on the preparation, and the excess of uncured composite was removed with a hand instrument. The composite was initially light cured from the lingual surface, through the dental structure, for 60 seconds. Light curing was complemented from the facial aspect for an additional 60 seconds through the matrix, and then for an additional 60 seconds after the matrix was removed. The same protocol was used in all veneer restorations. If necessary, margins were finished using aluminum-oxide sequential finishing disks (Sof-Lex, 3M Dental Products, St Paul, Minn.).
Group 3 — Post and veneer preparation in enamel A standardized titanium post system was used (Unimetric T No. 1, ref. 226T/10, Maillefer, Bal182
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laigues, Switzerland) in all groups receiving root canal prefabricated posts (groups 3, 4, 7, and 8). After removal of the gutta-percha and preparation of root canal using calibrated burs, the post was cemented with zinc phosphate cement (Fleck’s zinc cement, Mizzy, Inc, Cherry Hill, N.J.). Care was taken to ensure passive fit, minimizing stresses. The “head” of the post was maintained within the pulp chamber. The veneer was prepared as described previously.
Group 4 — Post, veneer preparation in enamel and direct composite veneer After the post was seated, the pulp-chamber was restored and the enamel was prepared for veneer coverage as in group 1. Direct composite veneers were placed according to the technique described in group 2.
Group 5 — Veneer preparation in dentin Veneer preparations were made into dentin (0.5 mm beyond dentin-enamel junction axially). Gingival margins were kept in enamel. In group 5, the preparations were not restored.
Group 6 — Veneer preparation in dentin and direct composite veneer Dentin was prepared as in group 5, and direct composite veneers were placed according to the technique described for group 2.
Group 7 — Post and veneer preparation in dentin After seating of the post and pulp-chamber restoration, dentin was prepared as described previously (group 5), and the preparations were not restored.
Group 8 — Post, veneer preparation in dentin and direct composite veneer After cementation of the post, the pulp-chamber was restored and dentin was prepared for veneer coverage as in group 5. Direct composite veneers were placed. After the restorative procedures, the specimens were individually mounted in acrylic resin blocks. The clinical crowns plus 1 mm of the anatomic root surface in the center of the facial surface were left exposed. The specimens were then submitted to the fracture resistance test using a Universal testing machine (Instron Engineering Co, Canton, Mass.) at a constant speed of 2.5 mm/s. The force was applied perpendicularly to the long axis of the specimen at the center of its facial aspect, and the failure load was recorded. Data were submitted to analysis of variance at 95% confidence interval, followed by Tukey-Kramer post hoc multiple comparison test, including all possible pairwise comparisons.30 The SPSS 8.0 statistical package (SPSS Inc, Chicago, Ill.) was used to support the data analysis. VOLUME 84 NUMBER 2
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RESULTS Mean fracture resistance results, standard deviations, and statistical groupings are presented in Table I. Analysis of variance revealed significant differences among means (P=.0021). The Tukey-Kramer post hoc test (P<.05) identified the pairwise comparisons that provided statistically significant means, shown in Table I.
DISCUSSION Loss of enamel/dentin as a result of caries, fracture, erosion/abrasion, cavity preparation, or endodontic therapy may compromise the structural integrity of the tooth. Although insufficient long-term definitive evidence to support the restorability capacity of the direct adhesive restorative techniques is available, it is generally accepted that these techniques can restore the fracture resistance of endodontically treated teeth in selected cases, provided most of the crown (60%-70% of the intact tooth structure) is mantained.4,11,25 In addition, a few studies suggest that the use of posts might strengthen endodontically treated teeth.17,18 However, it is usually acknowledged that posts do not strengthen teeth and that the need for a post is determined only by substantial loss of tooth structure.11,18,26-29 In fact, studies have indicated that, in some situations, posts might be detrimental to the strength of the tooth/restoration unit.12,17,19-24 Our study evaluated in vitro the fracture resistance of endodontically treated maxillary incisors submitted to reduction and veneering with direct composite, either with or without the use of prefabricated posts. The preparation for veneers did not cause statistically significant decrease of tooth fracture resistance, as can be observed by comparison of the means obtained in the prepared and nonrestored specimens (group 1 and group 5) to the means obtained in the nonprepared control specimens (group 0). This data suggests that a conservative veneer preparation does not imply considerable loss of tooth fracture resistance, even when such preparation is extended into dentin. Veneering of intraenamel preparations (group 2) produced higher mean fracture resistance than the mean for the prepared and nonveneered specimens (group 1) and similar resistance to that obtained for the control group (group 0). This observation is in contradiction with the data obtained by Sivers and Johnson,11 Ross et al,12 Thorsteinsson et al,13 and Maltz and Tronstad,14 who attribute an increased potential for tooth fracture to any reduction of surface and loss of tooth structure. However, veneers bonded to enamel displayed significantly higher mean fracture resistance when compared with those bonded to dentin (group 2 vs 6), which may reflect a better performance of the selected restorative system in enamel when compared with dentin. AUGUST 2000
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Table I. Mean fracture resistance and standard deviations for each treatment and control group Mean fracture resistance (N) Group
2 4 3 0 7 8 1 5 6
Treatment
Preparation Preparation Preparation Control Preparation Preparation Preparation Preparation Preparation
(SD)
in enamel + veneer 407.2 (160)a in enamel + post + veneer 348.2 (91.4)a,b in enamel + post 334 (128.9)a,b,c 321.1 (130.8)a,b,c in dentin + post 314.3 (169.4)a,b,c in dentin + post + veneer 302.1 (104.9)a,b,c in enamel 260.6 (101.9)b,c in dentin 215.1 (126.7)c in dentin + veneer 171.5 (42.5)d
Pairwise comparisons indicated statistical significance at P<.05. Superscript letters indicate means that are not significantly different.
Referring to the use of posts associated with preparation and bonding of direct composite veneers on endodontically treated teeth, no statistically significant differences were observed in this study on the pairs with and without posts among the teeth prepared in enamel, prepared/restored in enamel, and prepared in dentin (group 1 vs group 3, group 2 vs group 4, and group 5 vs group 7) (P>.05). However, the specimens prepared/veneered in dentin that received a post were significantly more resistant to fracture than the ones prepared/veneered in dentin without post (group 8 vs 6). Surprisingly, the teeth prepared in dentin not veneered and not posted displayed no significantly different mean fracture resistance than those prepared in dentin, not veneered and posted (group 5 vs 7). This might indicate that the benefit of the post is unpredictable and also reflects deficiencies of the adhesive system over dentin in the groups veneered (groups 8 and 6). The results obtained in this investigation dictate important clinical guidelines regarding the use of posts in endodontically treated maxillary central incisors. The hypotheses advanced were confirmed; namely, conservative veneer preparations do not weaken significantly maxillary incisors, and the use of posts is not justified as a form of resistance for conservative veneer restorations. Their use should be restricted to retention needs in situations where the coronal portion is insufficient to receive an adequate restoration or preparation.
CONCLUSIONS On the basis of the data obtained, the following conclusions were drawn: 1. Conservative veneer preparations involving enamel and enamel/dentin did not significantly weaken endodontically treated maxillary incisors. 2. Veneering conservative enamel preparations with direct composite provided fracture resistance that was not significantly different from that of nonprepared controls. 183
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3. Teeth prepared on enamel and veneered with direct composite exhibited fracture resistance statistically superior to those teeth prepared on dentin and veneered with direct composite. 4. The use of metal prefabricated posts did not improve the fracture resistance of endodontically treated maxillary incisors prepared and restored with composite veneers. REFERENCES 1. Bello A, Jarvis RH. A review of esthetic alternatives for the restoration of anterior teeth. J Prosthet Dent 1997;78:437-40. 2. Radz GM. Creating natural vitality with direct-bonded composite veneers. Compend Contin Educ Dent 1999;20:62-70. 3. Baratieri LN, Monteiro J Jr, Andrada MA, Arcari GM. Composite veneers: a new technique. Quintessence Int 1992;23:237-43. 4. Baratieri LN, Monteiro S Jr, Andrada MAC, Vieira LC, Cardoso AC, Ritter AV. Esthetics: direct adhesive restorations on fractured anterior teeth. Chicago: Quintessence Publishing Co; 1998. p. 430. 5. Kreulen CM, Creugers NH, Meijering AC. Meta-analysis of anterior veneer restorations in clinical studies. J Dent 1998;26:345-53. 6. Welbury RR. A clinical study of a microfilled composite resin for labial veneers. Int J Paediatr Dent 1991;1:9-15. 7. Dietschi D. Free-hand composite resin restorations: a key to anterior esthetics. Pract Periodontics Aesthet Dent 1995;7:15-25. 8. Magne P, Holz J. Stratification of composite restorations: systematic and durable replication of natural esthetics. Pract Periodontics Aesthet Dent 1996;6:61-8. 9. Walls AW, Murray JJ, McCabe JF. Composite laminate veneers: a clinical study. J Oral Rehabil 1988;13:439-54. 10. Baratieri LN, Coral Neto AC, Monteiro J Jr, Andrada MA, Cardoro Vieira LC. The sandwich technique, an alternative treatment for tetracycline-stained teeth: a case report. Quintessence Int 1991;24:929-33. 11. Sivers JE, Johnson WT. Restoration of endodontically treated teeth. Dent Clin North Am 1992;36:631-50. 12. Ross RS, Nicholls JI, Harrington GW. A comparison of strains generated during placement of five endodontic posts. J Endod 1991;17:450-6. 13. Thorsteinsson TS, Yaman P, Craig RG. Stress analyses of four prefabricated posts. J Prosthet Dent 1992;67:30-3. 14. Maltz TM, Tronstad L. Fracture resistance of restored endodontically treated teeth. End Dent Traumatol 1985;1:108-11. 15. Hunter A, Flood AM. The restoration of endodontically treated teeth. Oral Health 1989;70:17-21. 16. Sato EF, Fischman DM, Santos J Jr. Who is responsible for the failure in the restoration of endodontically treated teeth? Rev Paul Odont 1987;9:12-6.
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17. Bex RT, Parker MW, Judkins JT, Pellew GB Jr. Effect of dentinal bonded resin post-core preparations on resistance to vertical root fracture. J Prosthet Dent 1992;67:768-72. 18. Marshak BL, Helft H, Filo R. Factors mitigating against the use of dowels in endodontically treated teeth. Quintessence Int 1988;19:417-21. 19. Mohey el-Din, el-Khodery A, el-Badhdady YM, Ibrahim RM. A comparative study of restorative techniques used to reinforce intact endodontically treated anterior teeth. Egypt Dent J 1990;36:193-205. 20. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effects of cement, dowel diameter and design. J Prosthet Dent 1978;39:400-5. 21. Zmener O. Comparative analysis of threaded intra-canal posts. Rev Gaœcha de Odont 1979;27:268-74. 22. Lovdahl PE, Nicholls JI. Pin-retained amalgam cores vs. cast-gold dowelcores. J Prosthet Dent 1977;38:507-514. 23. Kantor ME, Pines MS. A comparative study of restorative techniques for pulpless teeth. J Prosthet Dent 1977;38:405-12. 24. Guzy GE, Nicholls JI. In vitro comparison of intact endodontically treated teeth with without endo-post reinforcement. J Prosthet Dent 1979;42:39-44. 25. Chalifoux PR. Restoration of endodontically treated teeth: review, classification, and post design. Pract Periodontics Aesthet Dent 1998;10:247-54. 26. Assif D, Oren E, Marshak BL, Aviv I. Photoelastic analysis of stress transfer by endodontically treated teeth to the supporting structure using different restorative techniques. J Prosthet Dent 1989;61:535-43. 27. Assif D, Bitenski A, Pilo R, Oren E. Effect of post design on resistance to fracture of endodontically treated teeth with complete crowns. J Prosthet Dent 1993;69:36-40. 28. Reeh ES, Douglas WH, Messer HH. Stiffness of endodontically-treated teeth related to restoration technique. J Dent Res 1989;68:1540-4. 29. Sedgley CM, Messer HH. Are endodontically treated teeth more brittle? J Endod 1992;18:332-5. 30. Conover WJ. Practical nonparametrical statistics. New York: John Wiley; 1971. p. 464. Reprint requests to: DR ANDRÉ V. RITTER DEPARTMENT OF OPERATIVE DENTISTRY SCHOOL OF DENTISTRY THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL CB# 7450 CHAPEL HILL, NC 27599-7450 FAX: (919)966-5660 E-MAIL: [email protected] Copyright © 2000 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2000/$12.00 + 0. 10/1/108415 doi: 10.1067/mpr.2000.108415
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CLINICAL IMPLICATIONS In this study, conservative preparation for direct veneers and subsequent veneering with composite did not significantly weaken endodontically treated maxillary central incisors, and the use of posts did not increase the resistance of these teeth to fracture.
D
irect composite veneers have been indicated as an esthetic and conservative treatment alternative in a variety of clinical scenarios, such as teeth with multiple restorations requiring replacement; short teeth; diastemas; and malformed, malpositioned, and/or darkened teeth.1-4 Although long-term clinical studies on direct composite veneers are scarce,5,6 the current aProfessor,
Department of Stomatology, Head of Operative Dentistry Section, University of Florianópolis, UFSC/CCS/STM, Florianópolis, SC, Brazil. bProfessor, Department of Stomatology, Operative Dentistry Section, UFSC/CCS/STM, Florianópolis, SC, Brazil. cProfessor, Department of Stomatology, Dental Materials Section, UFSC/CCS/STM, Florianópolis, SC, Brazil. dProfessor, Department of Stomatology, Operative Dentistry Section, UFSC/CCS/STM, Florianópolis, SC, Brazil; and Resident, Dental Research Center and Department of Operative Dentistry, The University of North Carolina at Chapel Hill. 180 THE JOURNAL OF PROSTHETIC DENTISTRY
generation of direct composites and adhesive systems, when properly used, allows the clinician to create direct veneers that resemble the natural elements of the tooth, namely enamel translucency, dentin hue and chroma, and adequate surface texture.7,8 In addition, the direct technique enables the clinician to exercise complete control over all the restorative phases, which is not always the case with the indirect techniques.7,8 The most conservative veneer technique is the application of the composite without tooth reduction.7-9 However, this approach is seldom applied, being feasible only when the tooth to be veneered is lingually positioned, because the application of the composite without tooth reduction leads to overcontouring. In many clinical situations, therefore, the application of direct composite veneers requires tooth reduction to compensate for the thickness of the restorative material. The amount of reduction is directly related to the esVOLUME 84 NUMBER 2
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thetic demands the case imposes. This is true mainly for darkened teeth, where greater reduction allows for greater thickness of composite and, consequently, greater potential to mask the defect.10 However, reduction might decrease the resistance of the tooth to fracture, particularly for endodontically treated teeth.11-14 In these cases, direct composite veneers are indicated only when the remaining tooth structure is relatively intact, because the endodontic access considerably weakens the tooth.15,16 Prefabricated root-canal posts have been proposed to reinforce the tooth/restoration unit in endodontically treated teeth.17,18 This is a controversial strategy, as a few studies support the strengthening effect of posts, but most studies do not.12,17,19-29 The purposes of this in vitro study were to determine whether (1) veneer preparation in enamel or in enamel/dentin weakens endodontically treated maxillary incisors, (2) bonding of direct composite veneer restores the original strength of the unprepared tooth, and (3) the use of root canal prefabricated metal posts increases the fracture resistance of the prepared tooth. The hypotheses advanced are that conservative veneer preparations do not weaken significantly maxillary incisors, and that posts are not needed for the conservative veneering of endodontically treated maxillary incisors.
MATERIAL AND METHODS Ninety human maxillary central incisors extracted because of periodontal and/or prosthetic reasons were selected, disinfected in 0.5% chloramine for 24 hours, and stored in water at 4°C. Only intact teeth were included in the study. All specimens were submitted to conventional root canal therapy, which consisted of palatal access, step-back manual instrumentation with K-files (final size No. 50), and laterally condensed manual obturation with gutta-percha and minute amounts of a zinc-oxide/eugenol sealer. Gutta-percha cones were cut by the entrance of the root canal, and the pulp chamber was mechanically cleaned with round burs and left unrestored. Methyl-alcohol 70% was scrubbed in the pulp chamber with a cotton pellet for 60 seconds to remove any residual eugenol from the sealer in the pulp chamber and thoroughly rinsed with running water. The remaining dentin structure after endodontic preparation was considered to be equivalent in all specimens. The specimens were randomly divided and distributed into 1 control and 8 experimental groups (n = 10) as follows. Figure 1 illustrates the control group (group 0) and the different preparations for each of the experimental groups.
Group 0 — Control Group 0 was the control group. The pulp chamber was restored with a light-cured hybrid composite and AUGUST 2000
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Fig. 1. Diagrammatic drawings of the procedures performed in each group. (See Material and Methods section for details). Note the matrix “shell” in groups 2, 4, 6, and 8, the post in groups 3, 4, 7, and 8, intraenamel veneer preparations in groups 1 through 4 and dentin veneer preparations in groups 5 through 8.
adhesive system, according to the manufacturer’s instructions (Sybron/Kerr, Orange, Calif.). No intermediate base was applied over the gutta-percha. After light curing the adhesive, the restorative resin was applied and light cured in 3 increments through the palatal access. Each increment of composite was cured for 40 seconds. In all groups, the pulp chambers were restored using the same method described previously. In this control group, no further treatment was performed. A XL 2000 light-curing unit (3M Dental Products, St Paul, Minn.) with a 15 mm tip was used for all polymerization procedures. Light intensity was checked every 10 curing cycles to ensure at least 450 mW/cm2 of power output. A Curing Radiometer (Demetron/ Kerr, Danbury, Conn.) was used for that purpose.
Group 1 — Veneer preparation in enamel Veneer preparations were standardized in all groups, variations being introduced only in the depth (enamel or enamel/dentin, according to the experimental group). In this experimental group, the reduction reached midenamel axially, with depth ranging from 181
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0.2 to 0.6 mm. Depth was checked with a periodontal probe. A tapered round-ended diamond (No. 2137, KGS, Sao Paulo, Brazil) was used to cut the veneer preparations. The gingival margin was maintained in enamel. There were no incisal reductions, and proximal contact areas were maintained unprepared. In group 1, the preparations were not restored.
Group 2 — Veneer preparation in enamel and direct composite veneer The reduction was as for group 1. The veneers were made according to the acrylic resin facial matrix technique, described by Baratieri et al.3 This technique is convenient when the facial surface of the tooth to be veneered maintains its form and surface details, which can be fully replicated on the veneer. Before being submitted to facial reduction, the facial aspect of the incisor is lubricated with a fine coat of petroleum jelly. Colorless acrylic resin (Duralay, Resiliance Co, DFL, Sao Paulo, Brazil) is spread over the facial surface and the proximal embrasures. The matrix should be approximately 1.5 mm thick and extend slightly beyond the margins of the future veneer preparation, so that the acrylic shell will have a “stop” during the seating of the loaded matrix. With the acrylic resin completely polymerized, the matrix is removed and its inner surface must be carefully inspected for imperfection or voids. At this stage, the matrix is stored in water until it is used (no more than 24 hours). In those groups receiving direct composite veneers (groups 2, 4, 6, and 8), the preparations were cleaned with running water followed by air-drying. The 37% phosphoric acid gel was applied on the prepared area for 15 seconds and rinsed with an air/water syringe. The etched preparation was blot-dried and the adhesive was applied and cured, as per manufacturer’s instructions. The restorative resin was applied using the acrylic matrix shell. After lubricating the inner aspect of the matrix with a thin layer of a water-soluble lubricant, the composite was layered inside the matrix. The matrix was then seated on the preparation, and the excess of uncured composite was removed with a hand instrument. The composite was initially light cured from the lingual surface, through the dental structure, for 60 seconds. Light curing was complemented from the facial aspect for an additional 60 seconds through the matrix, and then for an additional 60 seconds after the matrix was removed. The same protocol was used in all veneer restorations. If necessary, margins were finished using aluminum-oxide sequential finishing disks (Sof-Lex, 3M Dental Products, St Paul, Minn.).
Group 3 — Post and veneer preparation in enamel A standardized titanium post system was used (Unimetric T No. 1, ref. 226T/10, Maillefer, Bal182
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laigues, Switzerland) in all groups receiving root canal prefabricated posts (groups 3, 4, 7, and 8). After removal of the gutta-percha and preparation of root canal using calibrated burs, the post was cemented with zinc phosphate cement (Fleck’s zinc cement, Mizzy, Inc, Cherry Hill, N.J.). Care was taken to ensure passive fit, minimizing stresses. The “head” of the post was maintained within the pulp chamber. The veneer was prepared as described previously.
Group 4 — Post, veneer preparation in enamel and direct composite veneer After the post was seated, the pulp-chamber was restored and the enamel was prepared for veneer coverage as in group 1. Direct composite veneers were placed according to the technique described in group 2.
Group 5 — Veneer preparation in dentin Veneer preparations were made into dentin (0.5 mm beyond dentin-enamel junction axially). Gingival margins were kept in enamel. In group 5, the preparations were not restored.
Group 6 — Veneer preparation in dentin and direct composite veneer Dentin was prepared as in group 5, and direct composite veneers were placed according to the technique described for group 2.
Group 7 — Post and veneer preparation in dentin After seating of the post and pulp-chamber restoration, dentin was prepared as described previously (group 5), and the preparations were not restored.
Group 8 — Post, veneer preparation in dentin and direct composite veneer After cementation of the post, the pulp-chamber was restored and dentin was prepared for veneer coverage as in group 5. Direct composite veneers were placed. After the restorative procedures, the specimens were individually mounted in acrylic resin blocks. The clinical crowns plus 1 mm of the anatomic root surface in the center of the facial surface were left exposed. The specimens were then submitted to the fracture resistance test using a Universal testing machine (Instron Engineering Co, Canton, Mass.) at a constant speed of 2.5 mm/s. The force was applied perpendicularly to the long axis of the specimen at the center of its facial aspect, and the failure load was recorded. Data were submitted to analysis of variance at 95% confidence interval, followed by Tukey-Kramer post hoc multiple comparison test, including all possible pairwise comparisons.30 The SPSS 8.0 statistical package (SPSS Inc, Chicago, Ill.) was used to support the data analysis. VOLUME 84 NUMBER 2
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RESULTS Mean fracture resistance results, standard deviations, and statistical groupings are presented in Table I. Analysis of variance revealed significant differences among means (P=.0021). The Tukey-Kramer post hoc test (P<.05) identified the pairwise comparisons that provided statistically significant means, shown in Table I.
DISCUSSION Loss of enamel/dentin as a result of caries, fracture, erosion/abrasion, cavity preparation, or endodontic therapy may compromise the structural integrity of the tooth. Although insufficient long-term definitive evidence to support the restorability capacity of the direct adhesive restorative techniques is available, it is generally accepted that these techniques can restore the fracture resistance of endodontically treated teeth in selected cases, provided most of the crown (60%-70% of the intact tooth structure) is mantained.4,11,25 In addition, a few studies suggest that the use of posts might strengthen endodontically treated teeth.17,18 However, it is usually acknowledged that posts do not strengthen teeth and that the need for a post is determined only by substantial loss of tooth structure.11,18,26-29 In fact, studies have indicated that, in some situations, posts might be detrimental to the strength of the tooth/restoration unit.12,17,19-24 Our study evaluated in vitro the fracture resistance of endodontically treated maxillary incisors submitted to reduction and veneering with direct composite, either with or without the use of prefabricated posts. The preparation for veneers did not cause statistically significant decrease of tooth fracture resistance, as can be observed by comparison of the means obtained in the prepared and nonrestored specimens (group 1 and group 5) to the means obtained in the nonprepared control specimens (group 0). This data suggests that a conservative veneer preparation does not imply considerable loss of tooth fracture resistance, even when such preparation is extended into dentin. Veneering of intraenamel preparations (group 2) produced higher mean fracture resistance than the mean for the prepared and nonveneered specimens (group 1) and similar resistance to that obtained for the control group (group 0). This observation is in contradiction with the data obtained by Sivers and Johnson,11 Ross et al,12 Thorsteinsson et al,13 and Maltz and Tronstad,14 who attribute an increased potential for tooth fracture to any reduction of surface and loss of tooth structure. However, veneers bonded to enamel displayed significantly higher mean fracture resistance when compared with those bonded to dentin (group 2 vs 6), which may reflect a better performance of the selected restorative system in enamel when compared with dentin. AUGUST 2000
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Table I. Mean fracture resistance and standard deviations for each treatment and control group Mean fracture resistance (N) Group
2 4 3 0 7 8 1 5 6
Treatment
Preparation Preparation Preparation Control Preparation Preparation Preparation Preparation Preparation
(SD)
in enamel + veneer 407.2 (160)a in enamel + post + veneer 348.2 (91.4)a,b in enamel + post 334 (128.9)a,b,c 321.1 (130.8)a,b,c in dentin + post 314.3 (169.4)a,b,c in dentin + post + veneer 302.1 (104.9)a,b,c in enamel 260.6 (101.9)b,c in dentin 215.1 (126.7)c in dentin + veneer 171.5 (42.5)d
Pairwise comparisons indicated statistical significance at P<.05. Superscript letters indicate means that are not significantly different.
Referring to the use of posts associated with preparation and bonding of direct composite veneers on endodontically treated teeth, no statistically significant differences were observed in this study on the pairs with and without posts among the teeth prepared in enamel, prepared/restored in enamel, and prepared in dentin (group 1 vs group 3, group 2 vs group 4, and group 5 vs group 7) (P>.05). However, the specimens prepared/veneered in dentin that received a post were significantly more resistant to fracture than the ones prepared/veneered in dentin without post (group 8 vs 6). Surprisingly, the teeth prepared in dentin not veneered and not posted displayed no significantly different mean fracture resistance than those prepared in dentin, not veneered and posted (group 5 vs 7). This might indicate that the benefit of the post is unpredictable and also reflects deficiencies of the adhesive system over dentin in the groups veneered (groups 8 and 6). The results obtained in this investigation dictate important clinical guidelines regarding the use of posts in endodontically treated maxillary central incisors. The hypotheses advanced were confirmed; namely, conservative veneer preparations do not weaken significantly maxillary incisors, and the use of posts is not justified as a form of resistance for conservative veneer restorations. Their use should be restricted to retention needs in situations where the coronal portion is insufficient to receive an adequate restoration or preparation.
CONCLUSIONS On the basis of the data obtained, the following conclusions were drawn: 1. Conservative veneer preparations involving enamel and enamel/dentin did not significantly weaken endodontically treated maxillary incisors. 2. Veneering conservative enamel preparations with direct composite provided fracture resistance that was not significantly different from that of nonprepared controls. 183
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3. Teeth prepared on enamel and veneered with direct composite exhibited fracture resistance statistically superior to those teeth prepared on dentin and veneered with direct composite. 4. The use of metal prefabricated posts did not improve the fracture resistance of endodontically treated maxillary incisors prepared and restored with composite veneers. REFERENCES 1. Bello A, Jarvis RH. A review of esthetic alternatives for the restoration of anterior teeth. J Prosthet Dent 1997;78:437-40. 2. Radz GM. Creating natural vitality with direct-bonded composite veneers. Compend Contin Educ Dent 1999;20:62-70. 3. Baratieri LN, Monteiro J Jr, Andrada MA, Arcari GM. Composite veneers: a new technique. Quintessence Int 1992;23:237-43. 4. Baratieri LN, Monteiro S Jr, Andrada MAC, Vieira LC, Cardoso AC, Ritter AV. Esthetics: direct adhesive restorations on fractured anterior teeth. Chicago: Quintessence Publishing Co; 1998. p. 430. 5. Kreulen CM, Creugers NH, Meijering AC. Meta-analysis of anterior veneer restorations in clinical studies. J Dent 1998;26:345-53. 6. Welbury RR. A clinical study of a microfilled composite resin for labial veneers. Int J Paediatr Dent 1991;1:9-15. 7. Dietschi D. Free-hand composite resin restorations: a key to anterior esthetics. Pract Periodontics Aesthet Dent 1995;7:15-25. 8. Magne P, Holz J. Stratification of composite restorations: systematic and durable replication of natural esthetics. Pract Periodontics Aesthet Dent 1996;6:61-8. 9. Walls AW, Murray JJ, McCabe JF. Composite laminate veneers: a clinical study. J Oral Rehabil 1988;13:439-54. 10. Baratieri LN, Coral Neto AC, Monteiro J Jr, Andrada MA, Cardoro Vieira LC. The sandwich technique, an alternative treatment for tetracycline-stained teeth: a case report. Quintessence Int 1991;24:929-33. 11. Sivers JE, Johnson WT. Restoration of endodontically treated teeth. Dent Clin North Am 1992;36:631-50. 12. Ross RS, Nicholls JI, Harrington GW. A comparison of strains generated during placement of five endodontic posts. J Endod 1991;17:450-6. 13. Thorsteinsson TS, Yaman P, Craig RG. Stress analyses of four prefabricated posts. J Prosthet Dent 1992;67:30-3. 14. Maltz TM, Tronstad L. Fracture resistance of restored endodontically treated teeth. End Dent Traumatol 1985;1:108-11. 15. Hunter A, Flood AM. The restoration of endodontically treated teeth. Oral Health 1989;70:17-21. 16. Sato EF, Fischman DM, Santos J Jr. Who is responsible for the failure in the restoration of endodontically treated teeth? Rev Paul Odont 1987;9:12-6.
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17. Bex RT, Parker MW, Judkins JT, Pellew GB Jr. Effect of dentinal bonded resin post-core preparations on resistance to vertical root fracture. J Prosthet Dent 1992;67:768-72. 18. Marshak BL, Helft H, Filo R. Factors mitigating against the use of dowels in endodontically treated teeth. Quintessence Int 1988;19:417-21. 19. Mohey el-Din, el-Khodery A, el-Badhdady YM, Ibrahim RM. A comparative study of restorative techniques used to reinforce intact endodontically treated anterior teeth. Egypt Dent J 1990;36:193-205. 20. Standlee JP, Caputo AA, Hanson EC. Retention of endodontic dowels: effects of cement, dowel diameter and design. J Prosthet Dent 1978;39:400-5. 21. Zmener O. Comparative analysis of threaded intra-canal posts. Rev Gaœcha de Odont 1979;27:268-74. 22. Lovdahl PE, Nicholls JI. Pin-retained amalgam cores vs. cast-gold dowelcores. J Prosthet Dent 1977;38:507-514. 23. Kantor ME, Pines MS. A comparative study of restorative techniques for pulpless teeth. J Prosthet Dent 1977;38:405-12. 24. Guzy GE, Nicholls JI. In vitro comparison of intact endodontically treated teeth with without endo-post reinforcement. J Prosthet Dent 1979;42:39-44. 25. Chalifoux PR. Restoration of endodontically treated teeth: review, classification, and post design. Pract Periodontics Aesthet Dent 1998;10:247-54. 26. Assif D, Oren E, Marshak BL, Aviv I. Photoelastic analysis of stress transfer by endodontically treated teeth to the supporting structure using different restorative techniques. J Prosthet Dent 1989;61:535-43. 27. Assif D, Bitenski A, Pilo R, Oren E. Effect of post design on resistance to fracture of endodontically treated teeth with complete crowns. J Prosthet Dent 1993;69:36-40. 28. Reeh ES, Douglas WH, Messer HH. Stiffness of endodontically-treated teeth related to restoration technique. J Dent Res 1989;68:1540-4. 29. Sedgley CM, Messer HH. Are endodontically treated teeth more brittle? J Endod 1992;18:332-5. 30. Conover WJ. Practical nonparametrical statistics. New York: John Wiley; 1971. p. 464. Reprint requests to: DR ANDRÉ V. RITTER DEPARTMENT OF OPERATIVE DENTISTRY SCHOOL OF DENTISTRY THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL CB# 7450 CHAPEL HILL, NC 27599-7450 FAX: (919)966-5660 E-MAIL: [email protected] Copyright © 2000 by The Editorial Council of The Journal of Prosthetic Dentistry. 0022-3913/2000/$12.00 + 0. 10/1/108415 doi: 10.1067/mpr.2000.108415
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