Considerations for Altering Preparation Designs of Porcelain Inlay/Onlay Restorations for Nonvital Teeth Foudda Homsy, DCD, DES Fixed Prosth, Rita Eid, DCD, DU Fixed Prosth, Wiam El Ghoul, DCD, DU Fixed Prosth, & Jose Johann Chidiac, DChD, MSc, Ass Etr Fac Med, Cert TMD/OFP Department of Prosthodontics, Lebanese University, Baabda, Lebanon
Keywords Cavity design; ceramic; inlay; onlay; vital; nonvital. Correspondence Jose Johann Chidiac, Lebanese University School of Dentistry, Department of Prosthodontics, PO Box 40105, Baabda Baabda n.a, Lebanon. E-mail: [email protected] The authors deny any conflicts of interest. Accepted October 23, 2014 doi: 10.1111/jopr.12279
Abstract Purpose: The aim of this study was to compare all ceramic inlay/onlay survival rates in vital and nonvital teeth having the same cavity design. Filling the pulp chamber with ceramic materials or not was also discussed. Materials and Methods: Ceramic class II inlays/onlays were made on 11 premolars and 30 molars: 14 vital, 27 endodontically treated. The same tooth preparation design was performed on vital and nonvital teeth: In nonvital teeth the pulp chambers were covered by a glass ionomer cement until the pulpal floor depths were between 2 and 2.5 mm, more likely similar to the vital teeth preparations. In vital teeth, glass ionomer was used as a liner to achieve pulpal floor depths between 2 and 2.5 mm when needed. The restorations were assessed (at baseline, 6 months, 1 and 2 years) according to three criteria: marginal discoloration, marginal integrity, and fracture of teeth/restorations, consistent with United States Public Health Service (USPHS) criteria. Results: Eight teeth (19%) showed minor marginal discolorations, while three molars (7%) had loss of marginal integrity. These margins were adjusted using rubber polishing cups and were then judged clinically acceptable. From these three molars, one was vital and two were endodontically treated. No fracture of teeth or restorations was observed. Chi square and exact probability tests were used. There was no statistical difference between vital and nonvital teeth (p = 0.719 chi-squared and Fisher) or between premolars and molars (p = 0.564 chi-squared; 1.000, Fisher). Conclusion: Within the limitations of this study there was no difference for the same inlay/onlay cavity design between vital and nonvital teeth. In nonvital teeth, it seems that filling the pulp chamber with a ceramic core material is not important. Long-term observation periods are needed to reinforce the clinical behavior outcome.
Restoring posterior teeth with direct composite resin, indirect composite resin, or a ceramic inlay/onlay restoration seems to give an equally acceptable treatment modality regarding marginal adaptation.1-5 However, all-ceramic inlays and onlays seem to transfer less stress than composite resin restorations to tooth structure.6 Because most clinical studies have been conducted on vital teeth,7-17 little information is currently available relative to nonvital teeth.8-20 According to Yamanel et al,6 the ceramic inlay/onlay restorations seem to give equally good results in nonvital teeth. Endodontically treated teeth have been treated with composite resin or ceramic inlays/onlays with satisfactory long-term results ranging from 2 to 10 years.21,22 Primary causes of restorative failure have been cohesive bulk fracture and marginal deficiencies.19,23 Marginal adaptation seems to play a significant role in long-term clinical performance of the restorations.1 Several studies have shown that if occlusal marginal gaps are greater than 100 µm, excessive wear of resin cement occurs. If the gaps are in the proximal
surfaces of the teeth near the gingival third, the risk of gingival inflammation and periodontal disease increases.1 In addition, because of bacterial growth and adhesion on resin cement, secondary caries and marginal discoloration might occur.1 Chipping of restoration margins or changes in the color of surrounding tissues have been observed clinically.24 Another failure of ceramic restorations has been reported to occur as bulk fractures.24 Factors associated with clinical success of ceramic inlay/onlay restorations appear to be related to cavity preparation,25-28 cementing agents,29 insufficient thickness,30 and internal defects in ceramics.31 Ceramic materials with more favorable mechanical properties have the potential to function effectively as inlays/onlays.19,32 IPS e.max Press (Ivoclar Vivadent AG, Schaan, Liechtenstein), which is a multiphase glass-ceramic with a high degree of crystallinity and favorable mechanical properties (flexural strength 400 MPa)18,19 demonstrated strength against fracture and tensile forces.19
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In nonvital teeth, there seems to be a positive relationship between the amount of tooth structure remaining and fracture resistance.20,25-27,33,34 To improve longevity of ceramic restorations, a change in concept and design for all-ceramic restorations has been proposed for nonvital teeth. It consists of widening the pulp chambers and introducing ceramic inside the pulp chambers to form what is called an “endo crown.”35 There are no evidence-based criteria concerning the cavity design differences between vital and nonvital teeth, particularly when introducing the ceramic inside the pulp chamber. The aim of this pilot study was to compare all-ceramic inlay survival rates regarding marginal integrity and fracture resistance in vital and nonvital teeth having similar cavity designs. The importance of filling the pulp chambers with ceramic materials was also discussed.
Table 1 Distribution of 41 inlays and onlays Type of tooth Premolar Molar
Number of prepared teeth
Vital teeth
Nonvital teeth
11 30
3 (27%) 11 (37%)
8 (73%) 19 (63%)
Materials and methods Twenty-six patients, 14 women and 12 men, with a mean age of 45 years (range: 18-78), requiring inlays or onlays were selected. Inclusion criteria were: (1) Failing restorations due to caries on posterior mandibular and maxillary teeth (2) No history of pain in the teeth to be restored (3) High level of oral hygiene (full-mouth plaque scores FMPS < 20%)36 (4) Absence of active periodontal (full-mouth bleeding scores FMBS < 20%)37 and pulpal diseases (absence of clinical and radiographic signs of pulpal inflammation or necrosis) (5) Absence of caries and active lesions38 (6) Absence of bruxism (attrition score 1 or 2 described by Yadav)39 The study was conducted at the Department of Fixed Prosthodontics, School of Dentistry, Lebanese University. Three clinicians experienced in placing ceramic inlays and onlays treated all patients. A fourth did the recall visits every 6 months. The three dentists used the same protocol and calibrated their technique: they examined preparation designs and agreed on the use and set-up criteria following the modified United States Public Health Service (USPHS) guidelines.40 When no agreement was found between examiners, the lower level of criteria was chosen. Patients were informed about the study, signed a written informed consent, and agreed to attend regular recall visits every 6 months for a period of 24 months. The Scientific and Ethical Committee of the School of Dentistry, Lebanese University, approved the protocol. Ceramic class II inlays/onlays were placed on four mandibular premolars, seven maxillary premolars, 14 mandibular molars, and 16 maxillary molars. Fourteen were vital teeth; 27 were endodontically treated (Table 1). Fourteen teeth were restored with class II inlays (Fig 1); 27 were restored with class II onlays (Fig 2). The same tooth preparation was performed for vital and nonvital teeth: The pulp chambers of nonvital teeth were covered with glass ionomer cement (GIC; Ketac Cem; 3M ESPE, St Paul, MN) until the pulpal floors became similar to the vital teeth configurations. Once the pulpal chambers were 2
Figure 1 Ceramic inlay preparation design for posterior endodontically treated teeth.
Figure 2 Ceramic onlay preparation design for posterior endodontically treated teeth.
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Figure 3 (A) Horizontal width of proximal boxes corresponding to intercuspal distance. (B) Width of occlusal isthmus ranged between 1/3 to 1/2 of intercuspal distance. (C) Width of gingival floor of proximal boxes: 1 mm.
sealed with GIC, both vital and nonvital tooth preparations were performed to similar dimensions using slightly conical diamonds burs (#4137 [ISO #025] and #4138 [ISO#018]; KG Sorensen Ind Com Ltda, Sa˜o Paulo, Brazil). A taper of approximately 8° to 10° was prepared without beveling the margins. All preparations were completed along the longitudinal axis of the teeth. The pulpal floor depths were prepared to depths of 2 to 2.5 mm from the occlusal cavosurface margin of the preparations (from the deepest pit of the fossae). Depth determination was measured using a scaled periodontal probe (23/UNC15; Hu Friedy, Chicago, IL). Measurements were rounded to the nearest ± 0.5 mm. The probe was fitted with a tight rubber stopper and inserted vertically within the cavity along the buccal and lingual (or palatal) walls until contact of the stopper was achieved. If a cusp was fractured or undermined, it was prepared for an onlay preparation. A reduction of 2 mm on the functional cusps and 1 mm on the nonfunctional cusps was established. The widths of the gingival floor preparations were 1 mm. The widths of occlusal isthmuses ranged from 1/3 (moderate cavities) to 1/2 the width of the intercuspal width (for extended cavities; Fig 3). The proximal portions of the preparations were finished 1 mm occlusal to the cemento-enamel junctions. Proximal boxes of the preparations were extended to the intercuspal distance. Internal line angles were rounded to smooth the preparations. In vital teeth, GIC (Ketac Cem) was used as a liner when the restorations were too deep to achieve depths between 2 and 2.5 mm. The enamel margins were then finished with hand instrumentation. Full-arch impressions were made with poly(vinyl siloxane) impression material (Express, putty and light; 3M ESPE). The interim prostheses were fabricated using self-curing acrylic resin (Alike powder & liquid; GC America, Alsip, IL) and cemented with eugenol-free cement (TempBond NE; Kerr, Rastatt, Germany).
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Within a week of the impressions, the same dental technician fabricated all inlays and onlays with IPS e.max Press. Restorations were heat-pressed following the lost-wax IPS-Empress method. The intraoral fits were evaluated under rubber dam (Dental Dam 5*5 medium green package; SS White Dental, Lakewood, NJ) using a control paste (Fit Checker Black; GC, Tokyo, Japan). Pressure spots were removed from the internal surface of the restoration using a red ring diamond ball bur (FG 314; Intensive SA, Montagola, Switzerland). This procedure was repeated until the pressure spots disappeared. Intraoral adjustments were performed with finishing diamond burs (FG 3526 Cerinlay Set; Intensive SA). Interproximal contacts were assessed with waxed dental floss (Oral B Essential floss; Procter & Gamble, Cincinnati, OH). Prior to insertion, the thicknesses of the inlays and onlays were checked using a pair of tactile compasses with an accuracy of 0.01 mm (Caliper Iwanson spring metal Ea; Hu-Friedy). The restorations were luted under rubber dam (Dental Dam 5*5 medium green package) using the total-etch technique. The prepared teeth were cleaned with pumice slurry (Glitter; Premier Dental Products, Plymouth Meeting, PA) and etched with 37% phosphoric acid gel (Scotchbond Etchant; 3M, ESPE) for 15 seconds; afterwards adhesive (Prime & Bond NT dual-cure dental adhesive; Dentsply, York, PA) was applied. The internal surfaces of the restorations were etched with 9.5% hydrofluoric acid (Bisco Inc, Schaumburg, IL) for 20 seconds and rinsed. Then a silane agent (Calibra silane coupling agent; Dentsply Caulk, Milford, DE) was applied and dried. The cavity preparations and internal surfaces of the restorations were covered with dual-cure resin cement (Calibra; Dentsply Caulk) according to the manufacturer’s instructions. Polymerization of the luting agent was performed by light curing of 120 seconds from different positions (40 seconds for each direction; Paradigm LED Curing Light; 3M ESPE). The rubber dam was removed and centric and eccentric occlusal contacts were adjusted following the habitual occlusion of the patient in intercuspal contact position using diamond finishing burs (FG 3525 Cerinlay Set) under water cooling followed by rubber cups and Sof-Lex discs (3M ESPE). Restoration margins were polished with silicone polishers (#9418.204.030; Komet Dental, Lemgo, Germany) and interproximally with polishing strips (Sof-Lex). In all, 41 restorations were cemented. The restorations were assessed according to three criteria: marginal discoloration, marginal integrity, and fracture of restoration/tooth chosen from the modified USPHS criteria (Ryge criteria)40 by a fourth independent investigator using mirrors, probes, and 2.5× magnification dental loupes (Keeler Ltd; Windsor, UK). For the criteria of marginal discoloration, “Alpha” indicated no discoloration, “Bravo” indicated a discoloration that could be removed by polishing, and “Charlie” indicated a permanent discoloration. For the marginal integrity criteria, “Alpha” indicated no probe catch and no crevice visible, “Bravo” indicated probe catch but no visible evidence of a crevice into which the probe could penetrate, and “Charlie” indicated that the probe penetrated into a crevice of a depth that exposed dentine. Fractures were determined by visual (cracks) and clinical inspection (pain during biting): “Alpha” indicated no evidence of fracture, while “Bravo” indicated evidence of fracture.
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Table 2 Distribution of the “Bravo” value according to the vitality of teeth Criteria Marginal discoloration Marginal integrity
Alpha
Bravo
Vital
Nonvital
33 38
8 3
5 1
3 2
Table 3 Distribution of the “Bravo” value according to the type of teeth Criteria Marginal discoloration Marginal integrity
Bravo
Premolar
Molar
8 3
2 (25%) 0 (0%)
6 (75%) 3 (100%)
Descriptive statistics were used to describe the frequency distribution of evaluated criteria. Chi-square and Fisher’s exact test were performed to determine the differences in the clinical behavior between vital and nonvital teeth for molars and premolars. Level of significance was set at p ࣘ 0.05 (1 degree of freedom).
Results The results of four recall visits during a period of 24 months for the 41 restored teeth were as follows: Marginal discoloration was noted “Alpha” on 33 teeth; 8 teeth had “Bravo” values (six molars and two premolars). From these eight teeth, five were vital, and three were endodontically treated. Marginal integrity was scored “Alpha” on 38 teeth; three had “Bravo” values. All three were molars. From these three molars, one was vital and two were endodontically treated. From all 14 vital teeth, one molar lost its vitality although it was noted an “Alpha” value for both criteria. No fracture of teeth or restorations was observed. No “Charlie” values were noted (Tables 2 and 3). One patient had pulpitis after 6 months. Endodontic treatment was done followed by a conventional post and crown. There was no statistical difference between vital and nonvital teeth (chi squared value p = 0.719 and Fischer’s exact test p = 0.719). There was no statistical difference between premolars and molars (chi squared value p = 0.564 and Fischer’s exact test p = 1.000).
Discussion The present study investigated a total of 41 ceramic inlays/onlays placed in vital and nonvital teeth and followed up for a period of 24 months. In the literature, some clinical studies had almost the same amount of time, while others showed longer observation periods.2,3,7,20,29 In the current study, a time limit of 24 months was due to the difficulty with recall visit compliance. All restorations were examined according to the modified Ryge criteria or USPHS40 by one operator trained to use this system. To reduce experimental bias, this operator did not participate in the clinical steps; he was recruited for the followup evaluations. Ryge criteria are useful in the evaluation of longevity of composite and ceramic inlay restorations and have 4
been widely used in the literature. Their use in this study was therefore useful to compare the current results with other studies. Results showed that the majority of restorations in this study had an “Alpha” rating for all the characteristics studied: 76% for marginal discoloration and 92% for marginal integrity. The small values of the “Bravo” results could not be considered an important value because there was no statistical difference between the two ratings (p = 0.194). In this study, marginal discoloration had Bravo ratings for 24% and marginal integrity for 8% regardless of whether teeth were vital. These findings were in accordance with previous studies that reported an increased baseline score for marginal discoloration (from 2.86% to 14.29% at Bravo level) at the 1- and 2-year recalls.8,18 Fradeani et al reported that marginal discoloration and marginal integrity were interrelated, and both would deteriorate with time.9 This fact can be attributed to the wear of resin luting cement, which was considered to be one critical aspect of adhesively luted ceramic restorations.31 This was found in some prospective studies, in which the marginal adaptation was the criterion with the lowest Alpha ratings9-11,31 and may also have affected the results of this study, provided the timeframe for follow-up was longer. No recurrent caries, no debonding, no tooth fracture, and no inlay/onlay fractures were observed in this study. This finding might be the result of short recall visits when compared to 5-year observation periods. Many studies have proven that ceramic material was an alternative to other materials such as composite resin, even for extensive defects.6 Beside the esthetic advantages, these restorations present fluorescence, resistance to compression and wear, a thermal expansion coefficient similar to the structure, and biocompatibility.15,20,32 Other advantages of the inlay/onlay ceramic technique are a reduced volume of composite resin shrinkage limited to the resin luting layer4 in comparison to resin composite restoration20 and a thermal expansion coefficient of ceramic similar to that of the tooth substance, both of which are known to have positive effects on marginal adaptation.4 Studies have reported that ceramics exhibit exceptional bond strength to tooth structure when bonded adhesively.25 Despite their many advantages, ceramics are fragile under tensile strain, making them susceptible to fracture during the luting procedure and under occlusal force.26 This is due to ceramic rigidity; it cannot effectively redistribute stresses into the cavity, resulting in an increase in the amount of stress on the tooth.23 According to Dalpino et al and other authors, indirect manufactured ceramic restorations in larger cavities have a greater ability to withstand fractures than directly manufactured composites do.2,34 Dalpino et al34 revealed that ceramic inlays in extensive MOD (mesial, occlusal, distal) cavities showed significantly fewer marginal gaps after thermal aging and mechanical loading than composite resin restorations. These findings were also confirmed by Hitz et al.5 The current study had no fracture of the ceramic inlay/onlay restorations. This result was consistent with the findings of Tagtekin et al.19 The fracture of ceramic inlays depends on a number of factors, of which the ceramic system is one of significant interest.19 The strength of IPS e.max Press might be the reason for these improved results over a period of
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2 years even for nonvital teeth. All restorations opposed natural teeth. In the present study, GIC was used as a base to block out undercuts, helping to standardize the depth of the pulpal floor and reducing the loss of tooth substance during cavity preparation.31 GIC bases may reduce the risk of cusp fracture during the time between cavity preparation and the insertion of adhesive inlays.23 It seems that depth of the preparation and the remaining inter-axial thickness were among the most critical factors that reduced the fracture resistance of teeth.27 In the current study, a ceramic inlay/onlay with an average depth of 2 to 2.5 mm and a width of 50% of the intercuspal distance might explain the nonsignificant differences between vital and nonvital teeth or between premolars and molars in regard to fracture resistance. There are few in vivo studies in this regard, but regarding cavity design, several designs have been proposed.25,33 Wide preparations in molars should be restored with ceramic onlays, not inlays, because of the lower inverse of the Tsai-Wu strength ratio index and a favorable distribution of contact stresses between the cement and enamel during mastication.24 In the current study, it was decided that a conservative preparation with a butt joint margin was the best path to follow, especially in places exposed to significant loads.24 Knife-edge preparations may result in marginal fracture of the restorations.24 Beveled inlays were excluded because, according to the Tsai-Wu Criterion,24 the sharp edge of the ceramics and the tooth around it may chip during mastication. The thickness of the ceramic is an important factor to prevent its fracture. The recommended minimum thickness of 1.5 mm should be observed from the bottom apical area of the cavity to the central fossae to improve strength.12 According to van Dijken et al, a cuspal overlay should ideally permit a material thickness of 2 mm.30 In the current study, onlays had rounded margins and a material thickness of 2 mm on the functional cusp, because it demonstrated the lowest values of the inverse of the Tsai-Wu strength ratio. According to this criterion, if the inverse of the Tsai-Wu strength ratio index in the tested material is lower than 1, the material will not fracture; however, if this value is over 1, then damage to the material might occur.24
Conclusion Within the limitations of this study (41 restorations over 2 years), there was no difference for similar inlay/onlay cavity designs between vital and nonvital teeth. Marginal adaptation and marginal discoloration were the same for both types of teeth in molars and in premolars. In nonvital teeth, it seems that there was no need to fill the pulp chamber with a ceramic core, provided adequate tooth structure remained.
References 1. Zarrati S, Mahboub F: Marginal adaptation of indirect composite, glass-ceramic inlays and direct composite: an in vitro evaluation. J Dent 2010;7:77-83 2. Lange RT, Pfeiffer P: Clinical evaluation of ceramic inlays compared to composite restorations. Oper Dent 2009;34:263-272
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3. Blatz MB: Long-term clinical success of all-ceramic posterior restorations. Quintessence Int 2004;33:415-426 4. Uludag B, Ozturk O, Ozturk AN: Microleakage of ceramic inlays luted with different resin cements and dentin adhesives. J Prosthet Dent 2009;102:235-241 5. Hitz T, Ozcan M, G¨ohring TN: Marginal adaptation and fracture resistance of root-canal treated mandibular molars with intracoronal restorations: effect of thermocycling and mechanical loading. J Adhes Dent 2010;12:279-286 6. Yamanel K, Caglar A, G¨ulsahi K, et al: Effects of different ceramic and composite materials on stress distribution in inlay and onlay cavities: 3-D finite element analysis. Dent Mater J 2009;28:661-670 7. Otto T, Schneider D: Long-term clinical results of chairside Cerec CAD/CAM inlays and onlays: a case series. Int J Prosthodont 2008;21:53-59 8. Guess PC, Strub JR, Steinhart N, et al: All-ceramic partial coverage restorations-Midterm results of a 5-year prospective clinical splitmouth study. J Dent 2009;37:627-637 9. Fradeani M, Aquilano A, Bassein L: Longitudinal study of pressed glass ceramic inlays for four and half years. J Prosthet Dent 1997;78:346-356 10. Manhart J, Scheibenbogen-Fuchsbrunner A, Chen HY, et al: A 2-year clinical study of composite and ceramic inlays. Clin Oral Invest 2000;4:192-198 11. Galiatsatos AA, Berqou D: Six-year clinical evaluation of ceramic inlays and onlays. Quintessence Int 2008;39:407-412 12. Santos MJ, Mondelli RF, Navarro MF, et al: Clinical evaluation of ceramic inlays and onlays fabricated with two systems: five-year follow-up. Oper Dent 2013;38:3-11 13. Santos MJM, Mondelli RFL: Clinical evaluation of ceramic inlays and onlays fabricated with two systems: two year follow-up. Oper Dent 2004;29:123-130 14. Tashner M, Frankerberger R, Garcia-Godoy F, et al: IPS Empress inlays luted with a self-adhesive resin cement after 1 year. Am J Dent 2009;22:55-59 15. Murgueitio R, Bernal G: Three-year clinical follow-up of posterior teeth restored with leucite-reinforced IPS Empress onlays and partial veneer crowns. J Prosthodont 2012;21:340-345 16. Silva R, Ribeiro A, Catirze A, et al: Clinical performance of indirect esthetic inlays and onlays for posterior teeth after 40 months. Braz J Oral Sci 2009;8:153-158 17. Kr¨amer N, Frankerberger R: Clinical performance of bonded leucite-reinforced glass ceramic inlays and onlays after eight years. Dent Mater 2005;21:262-271 18. Ozyoney G, Yan Ko˘glu F, Ta˘gtekin D, et al: The efficacy of glassceramic onlays in the restoration of morphologically compromised and endodontically treated molars. Int J Prosthodont 2013;26:230-234 19. Tagtekin DA, Ozyoney G, Yanikoglu F: Two-year clinical evaluation of IPS Empress II ceramic onlays/inlays. Oper Dent 2009;34:369-378 20. Cubas G, Habekost L, Camacho GB, et al: Fracture resistance of premolars restored with inlay and onlay ceramic restorations and luted with two different agents. J Prosthodont Res 2011;55:53-59 21. Lin CL, Chang YH, Pai CA: Evaluation of failure risks in ceramic restorations for endodontically treated premolar with MOD preparation. Dent Mater 2011;27:431-438 22. Lin CL, Chang YH, Pa CA: Estimation of the risk of failure for an endodontically treated maxillary premolar with MODP preparation and CAD/CAM ceramic restorations. J Endod 2009;35:1391-1395 23. Jiang W, Bo H, Yongchun G, et al: Stress distribution in molars restored with inlays or onlays with or without endodontic
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treatment: a three dimensional finite element analysis. J Prosthet Dent 2010;103:6-12 Dejak B, Mlotkowski A, Romanowicz M: Strength estimation of different designs of ceramic inlays and onlays in molars based on the Tsai-wu failure criterion. J Prosthet Dent 2007;98: 89-100 Thompson MC, Thompson KM, Swain M: The all-ceramic, inlay supported fixed partial denture. Part 1. Ceramic inlay preparation design: a literature review. Aust Dent J 2010;55:120127 Soares CJ, Martins LR, Fonseca RB, et al: Influence of cavity design on fracture resistance of posterior leucite-reinforced ceramic restorations. J Prosthet Dent 2006;95:421-429 Hannig C, Westphal C, Becker K, et al: Fracture resistance of endodontically treated maxillary premolars restored with CAD/CAM ceramic inlays. J Prosthet Dent 2005;94: 342-349 Hopp C, Land M: Considerations for ceramic inlays in posterior teeth: a review. Clin Cosmet Investig Dent 2013;5:21-32 Kr¨amer N, Frankenberger R, Pelka M, et al: IPS Empress inlays and onlays after four-years: a clinical study. J Dent 1999;27:325-331 van Dijken JW, Hasselrot L, Ormin A, et al: Restorations with extensive dentin/enamel bonded ceramic coverage. A 5-year follow-up. Eur J Oral Sci 2001;109:222-229 Santos MJ, Francischone CE, Santos J´unior GC, et al: Clinical evaluation of two types of ceramic inlays and onlays after 6 months. J Appl Oral Sci 2004;12:213-218
32. Vohra F, Rashid H, Ab Ghani S: Modern adhesive ceramic onlays, a predictable replacement of full veneer crowns: a report of three cases. J Dow Uni Health Sci 2014;8:35-40 33. Seow LL, Toh CG, Wilson NH: Remaining tooth structure associated with various preparation designs for the endodontically treated maxillary second premolar. Eur J Prosthodont Restor Dent 2005;13:57-64 34. Dalpino PH, Franciscone CE, Ishikiriama A, et al: Fracture resistance of teeth directly and indirectly restored with composite resin and indirectly restored with ceramic materials. Am J Dent 2002;15:389-396 35. Fages M, Bennasar B: The Endocrown: a different type of all-ceramic reconstruction for molars. J Can Dent Assoc 2013;79:d140 36. O’Leary TJ, Drake RB, Naylor JE: The plaque control record. J Periodontol 1972;43:38 37. Cortellini P, Pini Prato G, Tonetti MS: Periodontal regeneration of human infrabony defects. I. Clinical measures. J Periodontol 1993;64:254-260. 38. Braga MM, Mendes FM, Ekstrand KR: Detection activity assessment and diagnosis of dental caries lesions. Dent Clin North Am 2010;54:479-493. 39. Yadav S. A Study on Prevalence of dental attrition and its relation to factors of age, gender and to the sign of TMJ dysfunction. J Indian Prosthodont Soc 2011;11:98-105. 40. Taschnera M, Kr¨amerb N, Lohbauera U, et al: Leucite-reinforced glass ceramic inlays luted with self-adhesive resin cement: A 2-year in vivo study. Dent Mat 2012;28:535-540
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Keywords Cavity design; ceramic; inlay; onlay; vital; nonvital. Correspondence Jose Johann Chidiac, Lebanese University School of Dentistry, Department of Prosthodontics, PO Box 40105, Baabda Baabda n.a, Lebanon. E-mail: [email protected] The authors deny any conflicts of interest. Accepted October 23, 2014 doi: 10.1111/jopr.12279
Abstract Purpose: The aim of this study was to compare all ceramic inlay/onlay survival rates in vital and nonvital teeth having the same cavity design. Filling the pulp chamber with ceramic materials or not was also discussed. Materials and Methods: Ceramic class II inlays/onlays were made on 11 premolars and 30 molars: 14 vital, 27 endodontically treated. The same tooth preparation design was performed on vital and nonvital teeth: In nonvital teeth the pulp chambers were covered by a glass ionomer cement until the pulpal floor depths were between 2 and 2.5 mm, more likely similar to the vital teeth preparations. In vital teeth, glass ionomer was used as a liner to achieve pulpal floor depths between 2 and 2.5 mm when needed. The restorations were assessed (at baseline, 6 months, 1 and 2 years) according to three criteria: marginal discoloration, marginal integrity, and fracture of teeth/restorations, consistent with United States Public Health Service (USPHS) criteria. Results: Eight teeth (19%) showed minor marginal discolorations, while three molars (7%) had loss of marginal integrity. These margins were adjusted using rubber polishing cups and were then judged clinically acceptable. From these three molars, one was vital and two were endodontically treated. No fracture of teeth or restorations was observed. Chi square and exact probability tests were used. There was no statistical difference between vital and nonvital teeth (p = 0.719 chi-squared and Fisher) or between premolars and molars (p = 0.564 chi-squared; 1.000, Fisher). Conclusion: Within the limitations of this study there was no difference for the same inlay/onlay cavity design between vital and nonvital teeth. In nonvital teeth, it seems that filling the pulp chamber with a ceramic core material is not important. Long-term observation periods are needed to reinforce the clinical behavior outcome.
Restoring posterior teeth with direct composite resin, indirect composite resin, or a ceramic inlay/onlay restoration seems to give an equally acceptable treatment modality regarding marginal adaptation.1-5 However, all-ceramic inlays and onlays seem to transfer less stress than composite resin restorations to tooth structure.6 Because most clinical studies have been conducted on vital teeth,7-17 little information is currently available relative to nonvital teeth.8-20 According to Yamanel et al,6 the ceramic inlay/onlay restorations seem to give equally good results in nonvital teeth. Endodontically treated teeth have been treated with composite resin or ceramic inlays/onlays with satisfactory long-term results ranging from 2 to 10 years.21,22 Primary causes of restorative failure have been cohesive bulk fracture and marginal deficiencies.19,23 Marginal adaptation seems to play a significant role in long-term clinical performance of the restorations.1 Several studies have shown that if occlusal marginal gaps are greater than 100 µm, excessive wear of resin cement occurs. If the gaps are in the proximal
surfaces of the teeth near the gingival third, the risk of gingival inflammation and periodontal disease increases.1 In addition, because of bacterial growth and adhesion on resin cement, secondary caries and marginal discoloration might occur.1 Chipping of restoration margins or changes in the color of surrounding tissues have been observed clinically.24 Another failure of ceramic restorations has been reported to occur as bulk fractures.24 Factors associated with clinical success of ceramic inlay/onlay restorations appear to be related to cavity preparation,25-28 cementing agents,29 insufficient thickness,30 and internal defects in ceramics.31 Ceramic materials with more favorable mechanical properties have the potential to function effectively as inlays/onlays.19,32 IPS e.max Press (Ivoclar Vivadent AG, Schaan, Liechtenstein), which is a multiphase glass-ceramic with a high degree of crystallinity and favorable mechanical properties (flexural strength 400 MPa)18,19 demonstrated strength against fracture and tensile forces.19
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In nonvital teeth, there seems to be a positive relationship between the amount of tooth structure remaining and fracture resistance.20,25-27,33,34 To improve longevity of ceramic restorations, a change in concept and design for all-ceramic restorations has been proposed for nonvital teeth. It consists of widening the pulp chambers and introducing ceramic inside the pulp chambers to form what is called an “endo crown.”35 There are no evidence-based criteria concerning the cavity design differences between vital and nonvital teeth, particularly when introducing the ceramic inside the pulp chamber. The aim of this pilot study was to compare all-ceramic inlay survival rates regarding marginal integrity and fracture resistance in vital and nonvital teeth having similar cavity designs. The importance of filling the pulp chambers with ceramic materials was also discussed.
Table 1 Distribution of 41 inlays and onlays Type of tooth Premolar Molar
Number of prepared teeth
Vital teeth
Nonvital teeth
11 30
3 (27%) 11 (37%)
8 (73%) 19 (63%)
Materials and methods Twenty-six patients, 14 women and 12 men, with a mean age of 45 years (range: 18-78), requiring inlays or onlays were selected. Inclusion criteria were: (1) Failing restorations due to caries on posterior mandibular and maxillary teeth (2) No history of pain in the teeth to be restored (3) High level of oral hygiene (full-mouth plaque scores FMPS < 20%)36 (4) Absence of active periodontal (full-mouth bleeding scores FMBS < 20%)37 and pulpal diseases (absence of clinical and radiographic signs of pulpal inflammation or necrosis) (5) Absence of caries and active lesions38 (6) Absence of bruxism (attrition score 1 or 2 described by Yadav)39 The study was conducted at the Department of Fixed Prosthodontics, School of Dentistry, Lebanese University. Three clinicians experienced in placing ceramic inlays and onlays treated all patients. A fourth did the recall visits every 6 months. The three dentists used the same protocol and calibrated their technique: they examined preparation designs and agreed on the use and set-up criteria following the modified United States Public Health Service (USPHS) guidelines.40 When no agreement was found between examiners, the lower level of criteria was chosen. Patients were informed about the study, signed a written informed consent, and agreed to attend regular recall visits every 6 months for a period of 24 months. The Scientific and Ethical Committee of the School of Dentistry, Lebanese University, approved the protocol. Ceramic class II inlays/onlays were placed on four mandibular premolars, seven maxillary premolars, 14 mandibular molars, and 16 maxillary molars. Fourteen were vital teeth; 27 were endodontically treated (Table 1). Fourteen teeth were restored with class II inlays (Fig 1); 27 were restored with class II onlays (Fig 2). The same tooth preparation was performed for vital and nonvital teeth: The pulp chambers of nonvital teeth were covered with glass ionomer cement (GIC; Ketac Cem; 3M ESPE, St Paul, MN) until the pulpal floors became similar to the vital teeth configurations. Once the pulpal chambers were 2
Figure 1 Ceramic inlay preparation design for posterior endodontically treated teeth.
Figure 2 Ceramic onlay preparation design for posterior endodontically treated teeth.
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Figure 3 (A) Horizontal width of proximal boxes corresponding to intercuspal distance. (B) Width of occlusal isthmus ranged between 1/3 to 1/2 of intercuspal distance. (C) Width of gingival floor of proximal boxes: 1 mm.
sealed with GIC, both vital and nonvital tooth preparations were performed to similar dimensions using slightly conical diamonds burs (#4137 [ISO #025] and #4138 [ISO#018]; KG Sorensen Ind Com Ltda, Sa˜o Paulo, Brazil). A taper of approximately 8° to 10° was prepared without beveling the margins. All preparations were completed along the longitudinal axis of the teeth. The pulpal floor depths were prepared to depths of 2 to 2.5 mm from the occlusal cavosurface margin of the preparations (from the deepest pit of the fossae). Depth determination was measured using a scaled periodontal probe (23/UNC15; Hu Friedy, Chicago, IL). Measurements were rounded to the nearest ± 0.5 mm. The probe was fitted with a tight rubber stopper and inserted vertically within the cavity along the buccal and lingual (or palatal) walls until contact of the stopper was achieved. If a cusp was fractured or undermined, it was prepared for an onlay preparation. A reduction of 2 mm on the functional cusps and 1 mm on the nonfunctional cusps was established. The widths of the gingival floor preparations were 1 mm. The widths of occlusal isthmuses ranged from 1/3 (moderate cavities) to 1/2 the width of the intercuspal width (for extended cavities; Fig 3). The proximal portions of the preparations were finished 1 mm occlusal to the cemento-enamel junctions. Proximal boxes of the preparations were extended to the intercuspal distance. Internal line angles were rounded to smooth the preparations. In vital teeth, GIC (Ketac Cem) was used as a liner when the restorations were too deep to achieve depths between 2 and 2.5 mm. The enamel margins were then finished with hand instrumentation. Full-arch impressions were made with poly(vinyl siloxane) impression material (Express, putty and light; 3M ESPE). The interim prostheses were fabricated using self-curing acrylic resin (Alike powder & liquid; GC America, Alsip, IL) and cemented with eugenol-free cement (TempBond NE; Kerr, Rastatt, Germany).
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Within a week of the impressions, the same dental technician fabricated all inlays and onlays with IPS e.max Press. Restorations were heat-pressed following the lost-wax IPS-Empress method. The intraoral fits were evaluated under rubber dam (Dental Dam 5*5 medium green package; SS White Dental, Lakewood, NJ) using a control paste (Fit Checker Black; GC, Tokyo, Japan). Pressure spots were removed from the internal surface of the restoration using a red ring diamond ball bur (FG 314; Intensive SA, Montagola, Switzerland). This procedure was repeated until the pressure spots disappeared. Intraoral adjustments were performed with finishing diamond burs (FG 3526 Cerinlay Set; Intensive SA). Interproximal contacts were assessed with waxed dental floss (Oral B Essential floss; Procter & Gamble, Cincinnati, OH). Prior to insertion, the thicknesses of the inlays and onlays were checked using a pair of tactile compasses with an accuracy of 0.01 mm (Caliper Iwanson spring metal Ea; Hu-Friedy). The restorations were luted under rubber dam (Dental Dam 5*5 medium green package) using the total-etch technique. The prepared teeth were cleaned with pumice slurry (Glitter; Premier Dental Products, Plymouth Meeting, PA) and etched with 37% phosphoric acid gel (Scotchbond Etchant; 3M, ESPE) for 15 seconds; afterwards adhesive (Prime & Bond NT dual-cure dental adhesive; Dentsply, York, PA) was applied. The internal surfaces of the restorations were etched with 9.5% hydrofluoric acid (Bisco Inc, Schaumburg, IL) for 20 seconds and rinsed. Then a silane agent (Calibra silane coupling agent; Dentsply Caulk, Milford, DE) was applied and dried. The cavity preparations and internal surfaces of the restorations were covered with dual-cure resin cement (Calibra; Dentsply Caulk) according to the manufacturer’s instructions. Polymerization of the luting agent was performed by light curing of 120 seconds from different positions (40 seconds for each direction; Paradigm LED Curing Light; 3M ESPE). The rubber dam was removed and centric and eccentric occlusal contacts were adjusted following the habitual occlusion of the patient in intercuspal contact position using diamond finishing burs (FG 3525 Cerinlay Set) under water cooling followed by rubber cups and Sof-Lex discs (3M ESPE). Restoration margins were polished with silicone polishers (#9418.204.030; Komet Dental, Lemgo, Germany) and interproximally with polishing strips (Sof-Lex). In all, 41 restorations were cemented. The restorations were assessed according to three criteria: marginal discoloration, marginal integrity, and fracture of restoration/tooth chosen from the modified USPHS criteria (Ryge criteria)40 by a fourth independent investigator using mirrors, probes, and 2.5× magnification dental loupes (Keeler Ltd; Windsor, UK). For the criteria of marginal discoloration, “Alpha” indicated no discoloration, “Bravo” indicated a discoloration that could be removed by polishing, and “Charlie” indicated a permanent discoloration. For the marginal integrity criteria, “Alpha” indicated no probe catch and no crevice visible, “Bravo” indicated probe catch but no visible evidence of a crevice into which the probe could penetrate, and “Charlie” indicated that the probe penetrated into a crevice of a depth that exposed dentine. Fractures were determined by visual (cracks) and clinical inspection (pain during biting): “Alpha” indicated no evidence of fracture, while “Bravo” indicated evidence of fracture.
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Table 2 Distribution of the “Bravo” value according to the vitality of teeth Criteria Marginal discoloration Marginal integrity
Alpha
Bravo
Vital
Nonvital
33 38
8 3
5 1
3 2
Table 3 Distribution of the “Bravo” value according to the type of teeth Criteria Marginal discoloration Marginal integrity
Bravo
Premolar
Molar
8 3
2 (25%) 0 (0%)
6 (75%) 3 (100%)
Descriptive statistics were used to describe the frequency distribution of evaluated criteria. Chi-square and Fisher’s exact test were performed to determine the differences in the clinical behavior between vital and nonvital teeth for molars and premolars. Level of significance was set at p ࣘ 0.05 (1 degree of freedom).
Results The results of four recall visits during a period of 24 months for the 41 restored teeth were as follows: Marginal discoloration was noted “Alpha” on 33 teeth; 8 teeth had “Bravo” values (six molars and two premolars). From these eight teeth, five were vital, and three were endodontically treated. Marginal integrity was scored “Alpha” on 38 teeth; three had “Bravo” values. All three were molars. From these three molars, one was vital and two were endodontically treated. From all 14 vital teeth, one molar lost its vitality although it was noted an “Alpha” value for both criteria. No fracture of teeth or restorations was observed. No “Charlie” values were noted (Tables 2 and 3). One patient had pulpitis after 6 months. Endodontic treatment was done followed by a conventional post and crown. There was no statistical difference between vital and nonvital teeth (chi squared value p = 0.719 and Fischer’s exact test p = 0.719). There was no statistical difference between premolars and molars (chi squared value p = 0.564 and Fischer’s exact test p = 1.000).
Discussion The present study investigated a total of 41 ceramic inlays/onlays placed in vital and nonvital teeth and followed up for a period of 24 months. In the literature, some clinical studies had almost the same amount of time, while others showed longer observation periods.2,3,7,20,29 In the current study, a time limit of 24 months was due to the difficulty with recall visit compliance. All restorations were examined according to the modified Ryge criteria or USPHS40 by one operator trained to use this system. To reduce experimental bias, this operator did not participate in the clinical steps; he was recruited for the followup evaluations. Ryge criteria are useful in the evaluation of longevity of composite and ceramic inlay restorations and have 4
been widely used in the literature. Their use in this study was therefore useful to compare the current results with other studies. Results showed that the majority of restorations in this study had an “Alpha” rating for all the characteristics studied: 76% for marginal discoloration and 92% for marginal integrity. The small values of the “Bravo” results could not be considered an important value because there was no statistical difference between the two ratings (p = 0.194). In this study, marginal discoloration had Bravo ratings for 24% and marginal integrity for 8% regardless of whether teeth were vital. These findings were in accordance with previous studies that reported an increased baseline score for marginal discoloration (from 2.86% to 14.29% at Bravo level) at the 1- and 2-year recalls.8,18 Fradeani et al reported that marginal discoloration and marginal integrity were interrelated, and both would deteriorate with time.9 This fact can be attributed to the wear of resin luting cement, which was considered to be one critical aspect of adhesively luted ceramic restorations.31 This was found in some prospective studies, in which the marginal adaptation was the criterion with the lowest Alpha ratings9-11,31 and may also have affected the results of this study, provided the timeframe for follow-up was longer. No recurrent caries, no debonding, no tooth fracture, and no inlay/onlay fractures were observed in this study. This finding might be the result of short recall visits when compared to 5-year observation periods. Many studies have proven that ceramic material was an alternative to other materials such as composite resin, even for extensive defects.6 Beside the esthetic advantages, these restorations present fluorescence, resistance to compression and wear, a thermal expansion coefficient similar to the structure, and biocompatibility.15,20,32 Other advantages of the inlay/onlay ceramic technique are a reduced volume of composite resin shrinkage limited to the resin luting layer4 in comparison to resin composite restoration20 and a thermal expansion coefficient of ceramic similar to that of the tooth substance, both of which are known to have positive effects on marginal adaptation.4 Studies have reported that ceramics exhibit exceptional bond strength to tooth structure when bonded adhesively.25 Despite their many advantages, ceramics are fragile under tensile strain, making them susceptible to fracture during the luting procedure and under occlusal force.26 This is due to ceramic rigidity; it cannot effectively redistribute stresses into the cavity, resulting in an increase in the amount of stress on the tooth.23 According to Dalpino et al and other authors, indirect manufactured ceramic restorations in larger cavities have a greater ability to withstand fractures than directly manufactured composites do.2,34 Dalpino et al34 revealed that ceramic inlays in extensive MOD (mesial, occlusal, distal) cavities showed significantly fewer marginal gaps after thermal aging and mechanical loading than composite resin restorations. These findings were also confirmed by Hitz et al.5 The current study had no fracture of the ceramic inlay/onlay restorations. This result was consistent with the findings of Tagtekin et al.19 The fracture of ceramic inlays depends on a number of factors, of which the ceramic system is one of significant interest.19 The strength of IPS e.max Press might be the reason for these improved results over a period of
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2 years even for nonvital teeth. All restorations opposed natural teeth. In the present study, GIC was used as a base to block out undercuts, helping to standardize the depth of the pulpal floor and reducing the loss of tooth substance during cavity preparation.31 GIC bases may reduce the risk of cusp fracture during the time between cavity preparation and the insertion of adhesive inlays.23 It seems that depth of the preparation and the remaining inter-axial thickness were among the most critical factors that reduced the fracture resistance of teeth.27 In the current study, a ceramic inlay/onlay with an average depth of 2 to 2.5 mm and a width of 50% of the intercuspal distance might explain the nonsignificant differences between vital and nonvital teeth or between premolars and molars in regard to fracture resistance. There are few in vivo studies in this regard, but regarding cavity design, several designs have been proposed.25,33 Wide preparations in molars should be restored with ceramic onlays, not inlays, because of the lower inverse of the Tsai-Wu strength ratio index and a favorable distribution of contact stresses between the cement and enamel during mastication.24 In the current study, it was decided that a conservative preparation with a butt joint margin was the best path to follow, especially in places exposed to significant loads.24 Knife-edge preparations may result in marginal fracture of the restorations.24 Beveled inlays were excluded because, according to the Tsai-Wu Criterion,24 the sharp edge of the ceramics and the tooth around it may chip during mastication. The thickness of the ceramic is an important factor to prevent its fracture. The recommended minimum thickness of 1.5 mm should be observed from the bottom apical area of the cavity to the central fossae to improve strength.12 According to van Dijken et al, a cuspal overlay should ideally permit a material thickness of 2 mm.30 In the current study, onlays had rounded margins and a material thickness of 2 mm on the functional cusp, because it demonstrated the lowest values of the inverse of the Tsai-Wu strength ratio. According to this criterion, if the inverse of the Tsai-Wu strength ratio index in the tested material is lower than 1, the material will not fracture; however, if this value is over 1, then damage to the material might occur.24
Conclusion Within the limitations of this study (41 restorations over 2 years), there was no difference for similar inlay/onlay cavity designs between vital and nonvital teeth. Marginal adaptation and marginal discoloration were the same for both types of teeth in molars and in premolars. In nonvital teeth, it seems that there was no need to fill the pulp chamber with a ceramic core, provided adequate tooth structure remained.
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32. Vohra F, Rashid H, Ab Ghani S: Modern adhesive ceramic onlays, a predictable replacement of full veneer crowns: a report of three cases. J Dow Uni Health Sci 2014;8:35-40 33. Seow LL, Toh CG, Wilson NH: Remaining tooth structure associated with various preparation designs for the endodontically treated maxillary second premolar. Eur J Prosthodont Restor Dent 2005;13:57-64 34. Dalpino PH, Franciscone CE, Ishikiriama A, et al: Fracture resistance of teeth directly and indirectly restored with composite resin and indirectly restored with ceramic materials. Am J Dent 2002;15:389-396 35. Fages M, Bennasar B: The Endocrown: a different type of all-ceramic reconstruction for molars. J Can Dent Assoc 2013;79:d140 36. O’Leary TJ, Drake RB, Naylor JE: The plaque control record. J Periodontol 1972;43:38 37. Cortellini P, Pini Prato G, Tonetti MS: Periodontal regeneration of human infrabony defects. I. Clinical measures. J Periodontol 1993;64:254-260. 38. Braga MM, Mendes FM, Ekstrand KR: Detection activity assessment and diagnosis of dental caries lesions. Dent Clin North Am 2010;54:479-493. 39. Yadav S. A Study on Prevalence of dental attrition and its relation to factors of age, gender and to the sign of TMJ dysfunction. J Indian Prosthodont Soc 2011;11:98-105. 40. Taschnera M, Kr¨amerb N, Lohbauera U, et al: Leucite-reinforced glass ceramic inlays luted with self-adhesive resin cement: A 2-year in vivo study. Dent Mat 2012;28:535-540
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