Clinical Marginal and Internal Adaptation of Maxillary Anterior Single All-Ceramic Crowns and 2-year Randomized Controlled Clinical Trial Aslı Akın, DDS, PhD, Suna Toksavul, DDS, PhD, & Muhittin Toman, DDS, PhD Department of Prosthetic Dentistry, Faculty of Dentistry, Ege University, ˙Izmir, Turkey
Keywords All-ceramic; marginal adaptation; internal adaptation; CAD/CAM; heat-pressed. Correspondence Muhittin Toman, Department of Prosthetic Dentistry, Faculty of Dentistry, Ege University, 35100, Bornova-˙Izmir, Turkey. E-mail [email protected] Presented at the FDI 2013 Annual World Dental Conference, Istanbul, Turkey, 28–31 August 2013. The authors deny any conflicts of interest. Accepted April 22, 2014 doi: 10.1111/jopr.12217
Abstract Purpose: The aims of this randomized-controlled clinical trial were to compare marginal and internal adaptation of all-ceramic crowns fabricated with CAD/CAM and heat-pressed (HP) techniques before luting and to evaluate the clinical outcomes at baseline and at 6, 12, and 24 months after luting. Materials and Methods: Fifteen CAD/CAM (CC) and 15 HP all-ceramic crowns were placed in 15 patients. A silicone replica was obtained to measure marginal and internal adaptation of each all-ceramic crown before luting, and they were sectioned buccolingually and mesiodistally. Marginal and internal adaptations were measured using computerized light microscope at 40× magnification. Clinical evaluations took place at baseline (2 days after luting) and at 6, 12, and 24 months after luting. Replica scores were analyzed with Mann-Whitney U and Student’s t-test (α = 0.05). Survival rate of crowns was determined using Kaplan-Meier statistical analysis. Results: The median marginal gap for the CC group was 132.2 μm and was 130.2 μm for the HP group. The mean internal adaptation for the CC group was 220.3 ± 51.3 μm and 210.5 ± 31 μm for the HP group. There were no statistically significant differences with respect to marginal opening (Mann-Whitney U test; p = 0.95) and internal adaptation (Student’s t-test; p = 0.535) between the 2 groups. Based on modified Ryge criteria, 100% of the crowns were rated satisfactory during the 2-year period. Conclusion: In this in vivo study, CAD/CAM and HP all-ceramic crowns exhibited similar marginal and internal adaptations. A 100% success rate was recorded for the 15 CAD/CAM and for the 15 HP all-ceramic crowns during the 2-year period.
All-ceramic crowns have become more popular as a result of increasing demand for esthetic corrections.1,2 All-ceramic crowns can be fabricated through computer aided design/computer aided manufacturing (CAD/CAM) or can be heat-pressed (HP).1,3 The HP technique is based on the lost-wax principle. Prefabricated ceramic ingots are heated and then pressed into the lost-wax form of a crown coping. Dental CAD/CAM systems such as CEREC (Sirona Dental, Charlotte, NC, USA) use a scanning and milling process to fabricate all-ceramic copings from prefabricated ceramic blocks.4-6 Today it is accepted that all-ceramic crowns should be luted using adhesive luting techniques.7,8 Hydrofluoric acid etching followed by the application of a silane agent is a common and clinically well-proven procedure for silicate ceramics.9,10 In case of insufficient adaptation at the crown margin, cement solubility, and plaque retention may occur, which is harmful for both tooth structure and periodontal tissues.11-15 Besides adaptation of the crown at the margin, luting space dimension is also
an important aspect.16,17 The luting space needs to be uniform to facilitate placement without compromising retention and resistance. This is particularly important for all-ceramic materials, which are more fragile than cast alloys.16,18 Clinicians may be subjected to certain intraoral conditions that cannot be reproduced in laboratory settings.19 These conditions include multiple intermittent cyclic forces during chewing, grinding, and clenching, constant exposure to a moist, bacteria-rich environment, consumption of too hot or too cold liquids and acids, and traumatic or inadequate tooth brushing. In addition, specimens used for testing dental ceramics in the laboratory sometimes differ significantly in both size and structure from the restorations they represent.20 Therefore, in vivo evaluation has been the basis for establishing criteria for clinically successful and acceptable crowns.21-29 The aims of this randomized-controlled single-blinded (evaluator) clinical trial were to compare marginal and internal adaptation of two all-ceramic crowns fabricated with CAD/CAM
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Table 1 Distribution of teeth (n = 30) restored in 15 patients
Maxillary central incisor Maxillary lateral incisor Maxillary canine Total
IPS e.max CAD
IPS e.max Press
9 5 1 15
9 5 1 15
and HP techniques before luting and also to evaluate the clinical outcomes including presence of fractures, sensitivity, and secondary caries at crown margin, marginal discoloration at baseline and at 6, 12, and 24 months after luting. It was hypothesized that both marginal and internal adaptation do not vary among and there is no difference between the clinical performances of two types of all-ceramic crown-fabricating techniques.
Materials and methods This randomized-controlled, single-blinded clinical trial compared the clinical outcomes of all-ceramic crowns fabricated using lithium disilicate based glass ceramic material using CAD/CAM and HP techniques. The eligible patients were randomly assigned to one of the all-ceramic crown fabricating techniques (IPS e.max CAD and IPS e.max Press; Ivoclar Vivadent, Schaan, Liechtenstein), drawing lots after informed consents were granted. According to the power calculation, the number of crowns for each group was determined as 15 in order to detect a difference of 20 μm with a power of 80% and an error probability of 0.05. Patients with severe parafunction, periodontitis, severe gingival inflammation, and poor oral hygiene or high caries activity were excluded from the study design. Maxillary anterior teeth included in the study had adequate periodontal support for a single-unit restoration, exhibited minimal mobility, and showed adequate tooth preparation length to ensure proper retention and resistance form. The study design was approved by the Human Ethical Research Committee of the Faculty of Medicine, Ege University (09–5/4) and was conducted in accordance with the Declaration of Helsinki and Good Clinical Practice. Fifteen patients (10 women, 5 men, ages 18–64, mean age 29 years) were invited to participate in this study. All patients were informed about the characteristics of the study and granted a signed consent form. The distribution of the crowns related to all-ceramic crown fabricating technique is presented in Table 1. Thirteen crowns were placed on endodontically treated teeth, while the remaining 17 crowns were placed on vital teeth. All endodontically treated teeth were reconstructed with a glass fiber-reinforced composite post (EverStick POST; StickTech Ltd, Turku, Finland) and direct resin composite core (Tetric EvoCeram; Ivoclar Vivadent) due to severe coronal destruction. The shade was determined prior to tooth preparation for each crown. A circumferential chamfer finish line at a depth of 1 mm and 0.5 mm below the free gingival margin was
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created with rotary diamond burs during preparation. The incisal reduction was 1.5 to 2 mm, and the palatal area of the anterior teeth was reduced by 1 mm. The preparation had a divergence angle of around 6°. Finally, all sharp edges and angles were rounded. After tooth preparation, margins were finished with a fine diamond bur (856EFOl2; Komet, Lemgo, Germany). In the maxillary anterior region, the palatal concavity was accurately determined to provide proper anatomic anterior disocclusion. Gingival displacement was obtained using a retraction cord (no. 0l Ultrapack; Ultradent, South Jordan, UT) after tooth preparation. Following removal of the retraction cord, full-arch vinylpolysiloxane impressions (Virtual; Ivoclar Vivadent) of the prepared teeth were made and immediately poured with a type V dental stone (Gladstone Dental Stone; Dentsply, York, PA). Full-arch irreversible hydrocolloid impressions (CA37; Cavex, Haarlem, The Netherlands) were made of the opposing dentition and immediately poured with a type IV dental stone (GC Fujirock EP; GC Europe N.V, Leuven, Norway). The prepared teeth were temporized with autopolymerizing acrylic provisional crowns (Luxatemp; DMG, Hamburg, Germany). Provisional crowns were luted using eugenol-free temporary cement (Cavex Temporary Cement; Cavex). IPS e.max CAD (n = 15) and IPS e.max Press (n = 15) crowns were fabricated using layering technique according to the manufacturer’s instructions. At the try-in appointment, proximal contacts and occlusion were checked and corrected with fine diamond burs (46 and 25-μm grit size) under water cooling. Silicone replicas were obtained from all crowns just prior to luting procedures to evaluate marginal and internal adaptation of all-ceramic crowns. Light-viscosity silicone material (Virtual Light Body; Ivoclar Vivadent) was then mixed and poured inside the crowns. Thereafter, the crown was placed on the prepared tooth applying finger pressure for 2 minutes. Five minutes after the silicone material was mixed, the crowns were removed from the prepared tooth carefully. Medium-viscosity silicone material was also mixed to fill the inside of each crown. After setting, the crown and the two layers of silicone material were separated. No adjustments were performed for the inner surface of each crown before replication. The silicone block materials obtained from each crown were sectioned buccolingually first and then mesiodistally at the middle point of each surface with a sharp surgical blade. Transparent autopolymerized acrylic resin index was performed for the standardization of this process. Afterwards, all-ceramic crowns were luted using an adhesive luting system (Variolink II/Syntac; Ivoclar Vivadent) according to the manufacturer’s instructions.
Marginal and internal adaptation measurements
The measurement of marginal and internal adaptation of each crown was performed with a reflected light binocular stereomicroscope (Olympus SV8, Olympus; Tokyo, Japan) at 40× magnification as described by Holmes et al.30 Each point was measured three times by the same evaluator with a 24-hour interval (Fig 1). The mean of 12 marginal gap measurements
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Clinical Marginal and Internal Adaptation of All-Ceramic Crowns
test and Fisher’s Exact test (α = 0.05). Cohen’s kappa statistic was used to determine the intra-evaluator reproducibility for the marginal and internal adaptation measurements, and determining clinical evaluation scores in the calibration phase.
Results Kappa value for evaluator’s reproducibility in measurement of marginal and internal adaptation was 0.72. Similarly, kappa value for the same evaluator’s reproducibility in determining clinical evaluation scores was 0.74. Marginal opening and internal adaptation measurements
The median marginal gap for the CAD/CAM and HP groups group were 132.2 μm (Q1: 71 μm; Q3: 215.2 μm) and 130.2 μm (Q1: 88 μm; Q3: 256.5 μm), respectively. There was no statistically significant difference with respect to marginal gap according to the Mann-Whitney U test (p = 0.95). The mean internal adaptation for the CAD/CAM group was 220.3 ± 51.3 μm and 210.5 ± 31.0 μm for the HP group. Internal adaptation for the two groups was compared using Student’s t-test, and no statistically significant difference was observed (p = 0.535). Clinical evaluation Figure 1 Measurement of marginal and internal adaptation of a crown on stereomicroscope. M, margin; T, prepared tooth; CL, cement line; C, crown.
and 24 internal adaptation measurements for each crown were calculated and used for statistical analysis. Clinical evaluation
Clinical evaluation of all-ceramic crowns was performed at baseline (2 days after luting) and 6, 12, and 24 months after luting. The presence of fractures, sensitivity, and secondary caries at the crown margin, marginal adaptation, and marginal discoloration were evaluated. Modified Ryge criteria31 were used to evaluate the quality of all-ceramic crowns (Table 2). The presence of plaque was evaluated using the L¨oe & Silness plaque index and scored as 0, 1, or 2.32 Clinical examinations were performed using a mirror and sharp explorer, radiographs, and photographs. Statistical analyses
All data sets were subjected to a Kolmogorov-Smirnov test to check the normality of the distribution (α = 0.05). The distribution of marginal gap values were not normal; therefore, median value Mann-Whitney U test (α = 0.05) was used. Student’s t-test (α = 0.05) was used to identify the differences for internal adaptation values, which were normally distributed. Kaplan-Meier statistics were used to analyze the survival rates obtained for all-ceramic crowns. Porcelain fracture and partial debonding that exposed the tooth structure, secondary caries, extraction of abutment teeth, and impaired esthetic quality or function were the main criteria for irreparable failure. Modified Ryge scores were analyzed according to Pearson Chi-Square
A minor fracture was observed at the incisal edge of an allceramic crown 13 months after cementation in the HP group. Since it did not require replacement, the crown was not rated as a failure. It was repaired intraorally using a porcelain repair kit (Ultradent Porcelain Repair Kit; Ultradent). According to Kaplan-Meier survival estimation method, the estimated survival rates were 100% for both CAD/CAM and HP crowns. None of the 30 crowns exhibited caries at the cervical margin during the complete observation period. Five teeth in the CAD/CAM group showed slight sensitivity at baseline and at the first control appointment; however, no sensitivity was recorded at the following appointments. Two teeth in the HP group were recorded to have slight sensitivity at baseline. One presented with slight sensitivity at the next control appointment. There was no statistically significant difference with respect to postoperative sensitivity between two groups (p > 0.05); however, there was a statistically significant difference between two groups with respect to marginal discoloration according to chisquare test (p < 0.05). HP crowns exhibited better marginal adaptation than CAD/CAM crowns according to the chi-square test (p < 0.05). The scores for evaluated variables and their distributions are presented in Table 3. The plaque index scores are presented in Table 4.
Discussion Marginal and internal adaptation of all-ceramic crowns are two important factors for clinical longevity.2,18 The lack of adaptation due to cement solubility and plaque retention may be harmful for both tooth structure and periodontal tissues.14 In this study, marginal and internal gaps were defined according to the terminology reported by Holmes et al.30 Because the largest measurement of error would always be at the margin,
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Table 2 Criteria for the direct evaluation of the restorations Category
Score
Criteria
Fracture
Alpha Bravo Alpha Bravo Charlie Alpha Bravo Charlie Alpha Bravo Alpha Bravo
No evidence of fracture Evidence of fracture Restoration is continuous with existing anatomic form, explorer does not catch Explorer catches, no crevice is visible into which explorer will penetrate Crevice at margin, enamel exposed No discoloration Superficial staining (removable, usually localized) Deep staining (not removable, generalized) No evidence of caries contiguous with the margin of the restoration Caries is evident contiguous with the margin of the restoration No sensitivity Slight sensitivity
Marginal adaptation
Marginal discoloration
Secondary caries Postoperative sensitivity
Table 3 Clinical scores for CAD/CAM and heat-pressed all-ceramic crowns Category
Score
Fracture
Baseline
Marginal discoloration
Secondary caries Postoperative sensitivity
Baseline
6-month recall
CAD/CAM
HP
CAD/CAM
HP
CAD/CAM
HP
15
15
15
15
15
15
15
15
11 4
14 1
11 4
14 1
11 4
14 1
11 4
14 1
15
15
15
12 3
15
12 3
15
12 3
15
15
15
15
15
15
15
15
10 5
13 2
10 5
14 1
15
14 1
15
14 1
1-year recall
2 year recall
CAD/CAM HP CAD/CAM HP CAD/CAM HP CAD/CAM HP 0 1 2 3
15
11 4
7 7 1
8 4 3
12 2 1
10 2 3
13 2
11 1 3
absolute marginal discrepancy was noted as the most suitable measurement by Holmes et al30 for both overextended and underextended crown margins. Marginal and internal gaps were measured directly under a microscope after sectioning the embedded specimens; however, it is not possible to use this method in clinical conditions.5 The replica technique for measurement of marginal and internal gaps was used to overcome this limitation.2 On the other hand, the replica technique does not allow the measurement of absolute marginal discrepancy.2,18 Therefore, marginal gap 4
2 year recall
HP
Table 4 Plaque index scores for CAD/CAM and heat-pressed all-ceramic crowns Score
1-year recall
CAD/CAM Alpha Bravo Alpha Bravo Charlie Alpha Bravo Charlie Alpha Bravo Alpha Bravo
Marginal adaptation
6-month recall
was measured at the crown margin in our study. Silicone replicas were sectioned at the mid-point for both buccolingual and mesiodistal directions to standardize the measurement points. Marginal and internal gap measurement results from clinical studies are generally higher than those of in vitro studies due to several patient factors.20 It is not possible to standardize some factors such as clinical crown length, axial angle, and location of the shoulder. These may be interpreted as the limitations of this clinical study. Another limitation of this study was its sample size. Fifteen samples were calculated for each group as a result of power calculation. The sample size of this study was similar to that of a recently published randomized clinical study28 and was enough to evaluate the marginal and internal adaptation; however, this may be small to detect the difference in clinical outcome between two groups when compared to a clinical study.29 It has been reported that cement film thickness should be between 25 and 40 μm, which is a very rare situation in clinical practice.23 It has also been stated that restorations need a theoretical luting cement film thickness of 20 to 40 μm.17 For good long-term prognosis, the clinically acceptable marginal gap for a crown must be less than 120 μm according to McLean and
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von Fraunhofer,19 and 200 μm according to Bjorn et al.15 Nakamura et al6 reported that internal gap ranged from 116 to 162 μm, and marginal gap ranged from 53 to 108 μm for CEREC 3 CAD/CAM crowns. In this study the median marginal gap was measured as 132.2 and 130.2 μm for CAD/CAM and HP crowns, respectively. Median marginal gap measurements were in a clinically acceptable range. The maximum marginal gap measurements for CAD/CAM and HP groups were 215.2 and 256.5 μm, while maximum internal gap measurements for CAD/CAM and HP groups were 303.8 and 274.7 μm, respectively. In a clinical study where marginal and internal gaps for Procera all-ceramic crowns were measured using the silicone replica technique, it has been reported that the maximum marginal gap for the maxillary anterior region is 216 μm.18 In an in vivo study,27 marginal discrepancies of all-ceramic restorations were evaluated. It was reported that the median marginal opening of all-ceramic crowns was 96 μm before luting and 130 μm after luting. The results of that study were similar to the results of this study. Applying silicone material onto all-ceramic crowns before luting to obtain silicone replicas simulates luted crowns in the patient’s mouth. Since maladaptation in the axial wall area and occlusal plateau can reduce the resistance to fracture of all-ceramic restorations,8 the discrepancy is a very critical issue for the restoration survival. Nakamura et al6 examined the effect of occlusal convergence angle of abutment and the computer’s luting space setting on marginal and internal adaptation of CEREC 3 CAD/CAM allceramic crowns. They reported that the marginal gap of a crown was not affected by the luting space at the occlusal surface of an abutment when the luting space was set to 30 or 50 μm. The mean internal gap ranged between 116 and 162 μm according to their findings. The mean internal gap was measured as 146 μm when the occlusal convergence angle was set to 12° and the luting space was 50 μm.6 In our study, the luting space was set to 50 μm, and the mean internal gap was measured as 190.6 μm for CAD/CAM crowns, and as 128.3 μm for HP crowns. The highest results were found at the incisal edge for both groups (292.5 μm for CAD/CAM group, 311.6 μm for HP group). An internal cutting bur may be larger in diameter than some parts of the tooth preparation, such as the incisal edge, and this would result in a larger internal gap.4 In this study, while no statistically significant difference was observed with respect to marginal gap measurements using the replica technique at a microscope, a statistically significant difference was observed with respect to marginal adaptation in clinical evaluations according to Modified Ryge criteria. The reason for this confusion may be the overconture or underconture of all-ceramic crowns at the marginal region that cannot be evaluated using the replica technique. Both CAD/CAM and HP crowns demonstrated a survival rate of 100% over the observation period. This is compatible with the results of a recent in vivo study by Valenti and Valenti24 in which 261 IPS Empress 2 crowns were rated satisfactory over a 10-year period. In an in vivo study by Taskonak and Sertg¨oz,25 20 adhesively luted IPS Empress 2 crowns exhibited a 100% success rate after 2 years. A similar result was found in a study by Toksavul and Toman26 after a mean observation period of 58 months. All-ceramic crowns are generally used in the maxillary anterior region because of their esthetic and natural appearance.
Clinical Marginal and Internal Adaptation of All-Ceramic Crowns
In this region, the finish line of the tooth preparation at the cervical area should be approximately 0.5 mm below the free gingival crest for a successful esthetic result. Therefore, a durable dentin bonding behavior of luting composites, mediated by dentin bonding agents, is of great importance in such clinical conditions. Lack of adhesion to tooth structure causes microleakage and secondary caries at the crown margins in long-term clinical use.3 In this study, secondary caries was not detected during a clinical observation period of 2 years. Our patients are still on regular controls, and they are still being examined for the presence of fracture, marginal adaptation, marginal discoloration, secondary caries, and postoperative sensitivity and being reminded of oral hygiene procedures.
Conclusions Within the limitations of this study, there were no statistically significant differences between CAD/CAM and HP all-ceramic anterior single crowns for both marginal and internal adaptation. Mean values of marginal gap for CAD/CAM and HP all-ceramic crowns were within a clinically acceptable range. A 100% success rate was recorded for both CAD/CAM and HP all-ceramic anterior single crowns, and a satisfactory clinical performance was observed during a 2-year period.
References 1. Layton D: A critical appraisal of the survival and complication rates of tooth-supported all-ceramic and metal-ceramic fixed dental prostheses: the application of evidence-based dentistry. Int J Prosthodont 2011;24:417-427 2. Syrek A, Reich G, Ranftl D, et al: Clinical evaluation of all-ceramic crowns fabricated from intraoral digital impressions based on the principle of active wavefront sampling. J Dent 2010;38:553-559. 3. Land MF, Hopp CD: Survival rates of all-ceramic systems differ by clinical indication and fabrication method. J Evid Based Dent Pract 2010;10:37-38. 4. Giannetopoulos S, van Noort R, Tsitrou E: Evaluation of the marginal integrity of ceramic copings with different marginal angles using two different CAD/CAM systems. J Dent 2010;38:980-986. 5. Bindl A, M¨ormann WH: Marginal and internal fit of all-ceramic CAD/CAM crown-copings on chamfer preparations. J Oral Rehabil 2005;32:441-447. 6. Nakamura T, Dei N, Kojima T, et al: Marginal and Internal Fit of Cerec 3 CAD/CAM All-Ceramic Crowns. Int J Prosthodont 2003;16:244-247 7. Beier US, Kapferer I, Burtscher D, et al: Clinical performance of porcelain laminate veneers for up to 20 years. Int J Prosthodont 2012;25:79-85. 8. M¨ormann W, Wolf D, Ender A, et al: Effect of two self-adhesive cements on marginal adaptation and strength of esthetic ceramic CAD/CAM molar crowns. J Prosthodont 2009;18:403 -410. 9. Lung CY, Matinlinna JP: Aspects of silane coupling agents and surface conditioning in dentistry: an overview. Dent Mater 2012;28:467-477. 10. Cekic-Nagas I, Canay S, Sahin E: Bonding of resin core materials to lithium disilicate ceramics: the effect of resin cement film thickness. Int J Prosthodont 2010;23:469-471.
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11. Loe H: Reactions to marginal periodontal tissues to restorative procedures. Int Dent J 1968;18:759-778. 12. Silness J: Periodontal conditions in patients treated with dental bridges. J Periodontal Res 1970;5:225-229. 13. Kokubo Y, Ohkubo C, Tsumita M, et al: Clinical marginal and internal gaps of Procera AllCeram crowns. J Oral Rehabil 2005;32:526-530. 14. Sch¨atzle M, Land NP, Anerud A, et al: The influence of margins of restorations of the periodontal tissues over 26 years. J Clin Periodontol 2001;28:57-64. 15. Bjorn AL, Bjorn H, Grcovic B: Marginal fit of restorations and its relation to periodontal bone level II. Crowns. Odontol Revy 1970;21:337-346. 16. Tuntiprawon M, Wilson PR: The effect of cement thickness on the fracture strength of all-ceramic crowns. Aust Dent J 1995;40:17-21. 17. Kious AR, Roberts HW, Brackett WW: Film thicknesses of recently introduced luting cements. J Prosthet Dent 2009;101:189-192. 18. Naert I, Van der Donck A, Beckers L: Precision of fit and clinical evaluation of all-ceramic full restorations followed between 0.5 and 5 years. J Oral Rehabil 2005;32:51-57. 19. McLean JW, von Fraunhofer JA: The estimation of cement film thickness by an in vivo technique. Brit Dent J 1971;131:107-111. 20. Gemalmaz D, K¨ukrer D: In vivo and in vitro evaluation of marginal fit of class II ceromer inlays. J Oral Rehabil 2006;33:436-442. 21. Schenke F, Federlin M, Hiller KA, et al: Controlled, prospective, randomized, clinical evaluation of partial ceramic crowns inserted with RelyX Unicem with or without selective enamel
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etching. Results after 2 years. Clin Oral Investig 2012;16:451-461 22. Cehreli MC, Kokat AM, Ozpay C, et al: A randomized controlled clinical trial of feldspathic versus glass-infiltrated alumina all-ceramic crowns: a 3-year follow-up. Int J Prosthodont 2011;24:77-84. 23. Laurent M, Scheer P, Dejou J, et al: Clinical evaluation of the marginal fit of cast crowns-validation of the silicone replica method. J Oral Rehabil 2002;35:116-122. 24. Valenti M, Valenti A: Retrospective survival analysis of 261 lithium disilicate crowns in a private general practice. Quintessence Int 2009;40:573-579. 25. Taskonak B, Sertg¨oz A: Two-year clinical evaluation of lithia-disilicate-based all-ceramic crowns and fixed partial dentures. Dent Mater 2006;22:1008-1013. 26. Toksavul S, Toman M: A short-term clinical evaluation of IPS Empress 2 crowns. Int J Prosthodont 2007;20:168-172. 27. Wolfart S, Wegner SM, Al-Halabi A, et al: Clinical evaluation of marginal fit of a new experimental all-ceramic system before and after cementation. Int J Prosthodont 2003;16:587-592. 28. Esquivel-Upshaw J, Rose W, Oliveira E, et al: Randomized, controlled clinical trial of bilayer ceramic and metal-ceramic crown performance. J Prosthodont 2013;22:166-173. 29. Kern M, Sasse M, Wolfart S: Ten-year outcome of three-unit fixed dental prostheses made from monolithic lithium disilicate ceramic. J Am Dent Assoc 2012;143:234-240. 30. Holmes JR, Bayne SC, Holland GA, et al: Considerations in measurement of marginal fit. J Prosthet Dent 1989;62:405-408. 31. Ryge G: Clinical criteria. Int Dent J 1980;30:347-358. 32. L¨oe H, Silness J: Periodontal disease in pregnancy. I. Prevalence and severity. Acta Odontol Scand 1963;21:533-551.
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Keywords All-ceramic; marginal adaptation; internal adaptation; CAD/CAM; heat-pressed. Correspondence Muhittin Toman, Department of Prosthetic Dentistry, Faculty of Dentistry, Ege University, 35100, Bornova-˙Izmir, Turkey. E-mail [email protected] Presented at the FDI 2013 Annual World Dental Conference, Istanbul, Turkey, 28–31 August 2013. The authors deny any conflicts of interest. Accepted April 22, 2014 doi: 10.1111/jopr.12217
Abstract Purpose: The aims of this randomized-controlled clinical trial were to compare marginal and internal adaptation of all-ceramic crowns fabricated with CAD/CAM and heat-pressed (HP) techniques before luting and to evaluate the clinical outcomes at baseline and at 6, 12, and 24 months after luting. Materials and Methods: Fifteen CAD/CAM (CC) and 15 HP all-ceramic crowns were placed in 15 patients. A silicone replica was obtained to measure marginal and internal adaptation of each all-ceramic crown before luting, and they were sectioned buccolingually and mesiodistally. Marginal and internal adaptations were measured using computerized light microscope at 40× magnification. Clinical evaluations took place at baseline (2 days after luting) and at 6, 12, and 24 months after luting. Replica scores were analyzed with Mann-Whitney U and Student’s t-test (α = 0.05). Survival rate of crowns was determined using Kaplan-Meier statistical analysis. Results: The median marginal gap for the CC group was 132.2 μm and was 130.2 μm for the HP group. The mean internal adaptation for the CC group was 220.3 ± 51.3 μm and 210.5 ± 31 μm for the HP group. There were no statistically significant differences with respect to marginal opening (Mann-Whitney U test; p = 0.95) and internal adaptation (Student’s t-test; p = 0.535) between the 2 groups. Based on modified Ryge criteria, 100% of the crowns were rated satisfactory during the 2-year period. Conclusion: In this in vivo study, CAD/CAM and HP all-ceramic crowns exhibited similar marginal and internal adaptations. A 100% success rate was recorded for the 15 CAD/CAM and for the 15 HP all-ceramic crowns during the 2-year period.
All-ceramic crowns have become more popular as a result of increasing demand for esthetic corrections.1,2 All-ceramic crowns can be fabricated through computer aided design/computer aided manufacturing (CAD/CAM) or can be heat-pressed (HP).1,3 The HP technique is based on the lost-wax principle. Prefabricated ceramic ingots are heated and then pressed into the lost-wax form of a crown coping. Dental CAD/CAM systems such as CEREC (Sirona Dental, Charlotte, NC, USA) use a scanning and milling process to fabricate all-ceramic copings from prefabricated ceramic blocks.4-6 Today it is accepted that all-ceramic crowns should be luted using adhesive luting techniques.7,8 Hydrofluoric acid etching followed by the application of a silane agent is a common and clinically well-proven procedure for silicate ceramics.9,10 In case of insufficient adaptation at the crown margin, cement solubility, and plaque retention may occur, which is harmful for both tooth structure and periodontal tissues.11-15 Besides adaptation of the crown at the margin, luting space dimension is also
an important aspect.16,17 The luting space needs to be uniform to facilitate placement without compromising retention and resistance. This is particularly important for all-ceramic materials, which are more fragile than cast alloys.16,18 Clinicians may be subjected to certain intraoral conditions that cannot be reproduced in laboratory settings.19 These conditions include multiple intermittent cyclic forces during chewing, grinding, and clenching, constant exposure to a moist, bacteria-rich environment, consumption of too hot or too cold liquids and acids, and traumatic or inadequate tooth brushing. In addition, specimens used for testing dental ceramics in the laboratory sometimes differ significantly in both size and structure from the restorations they represent.20 Therefore, in vivo evaluation has been the basis for establishing criteria for clinically successful and acceptable crowns.21-29 The aims of this randomized-controlled single-blinded (evaluator) clinical trial were to compare marginal and internal adaptation of two all-ceramic crowns fabricated with CAD/CAM
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Table 1 Distribution of teeth (n = 30) restored in 15 patients
Maxillary central incisor Maxillary lateral incisor Maxillary canine Total
IPS e.max CAD
IPS e.max Press
9 5 1 15
9 5 1 15
and HP techniques before luting and also to evaluate the clinical outcomes including presence of fractures, sensitivity, and secondary caries at crown margin, marginal discoloration at baseline and at 6, 12, and 24 months after luting. It was hypothesized that both marginal and internal adaptation do not vary among and there is no difference between the clinical performances of two types of all-ceramic crown-fabricating techniques.
Materials and methods This randomized-controlled, single-blinded clinical trial compared the clinical outcomes of all-ceramic crowns fabricated using lithium disilicate based glass ceramic material using CAD/CAM and HP techniques. The eligible patients were randomly assigned to one of the all-ceramic crown fabricating techniques (IPS e.max CAD and IPS e.max Press; Ivoclar Vivadent, Schaan, Liechtenstein), drawing lots after informed consents were granted. According to the power calculation, the number of crowns for each group was determined as 15 in order to detect a difference of 20 μm with a power of 80% and an error probability of 0.05. Patients with severe parafunction, periodontitis, severe gingival inflammation, and poor oral hygiene or high caries activity were excluded from the study design. Maxillary anterior teeth included in the study had adequate periodontal support for a single-unit restoration, exhibited minimal mobility, and showed adequate tooth preparation length to ensure proper retention and resistance form. The study design was approved by the Human Ethical Research Committee of the Faculty of Medicine, Ege University (09–5/4) and was conducted in accordance with the Declaration of Helsinki and Good Clinical Practice. Fifteen patients (10 women, 5 men, ages 18–64, mean age 29 years) were invited to participate in this study. All patients were informed about the characteristics of the study and granted a signed consent form. The distribution of the crowns related to all-ceramic crown fabricating technique is presented in Table 1. Thirteen crowns were placed on endodontically treated teeth, while the remaining 17 crowns were placed on vital teeth. All endodontically treated teeth were reconstructed with a glass fiber-reinforced composite post (EverStick POST; StickTech Ltd, Turku, Finland) and direct resin composite core (Tetric EvoCeram; Ivoclar Vivadent) due to severe coronal destruction. The shade was determined prior to tooth preparation for each crown. A circumferential chamfer finish line at a depth of 1 mm and 0.5 mm below the free gingival margin was
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created with rotary diamond burs during preparation. The incisal reduction was 1.5 to 2 mm, and the palatal area of the anterior teeth was reduced by 1 mm. The preparation had a divergence angle of around 6°. Finally, all sharp edges and angles were rounded. After tooth preparation, margins were finished with a fine diamond bur (856EFOl2; Komet, Lemgo, Germany). In the maxillary anterior region, the palatal concavity was accurately determined to provide proper anatomic anterior disocclusion. Gingival displacement was obtained using a retraction cord (no. 0l Ultrapack; Ultradent, South Jordan, UT) after tooth preparation. Following removal of the retraction cord, full-arch vinylpolysiloxane impressions (Virtual; Ivoclar Vivadent) of the prepared teeth were made and immediately poured with a type V dental stone (Gladstone Dental Stone; Dentsply, York, PA). Full-arch irreversible hydrocolloid impressions (CA37; Cavex, Haarlem, The Netherlands) were made of the opposing dentition and immediately poured with a type IV dental stone (GC Fujirock EP; GC Europe N.V, Leuven, Norway). The prepared teeth were temporized with autopolymerizing acrylic provisional crowns (Luxatemp; DMG, Hamburg, Germany). Provisional crowns were luted using eugenol-free temporary cement (Cavex Temporary Cement; Cavex). IPS e.max CAD (n = 15) and IPS e.max Press (n = 15) crowns were fabricated using layering technique according to the manufacturer’s instructions. At the try-in appointment, proximal contacts and occlusion were checked and corrected with fine diamond burs (46 and 25-μm grit size) under water cooling. Silicone replicas were obtained from all crowns just prior to luting procedures to evaluate marginal and internal adaptation of all-ceramic crowns. Light-viscosity silicone material (Virtual Light Body; Ivoclar Vivadent) was then mixed and poured inside the crowns. Thereafter, the crown was placed on the prepared tooth applying finger pressure for 2 minutes. Five minutes after the silicone material was mixed, the crowns were removed from the prepared tooth carefully. Medium-viscosity silicone material was also mixed to fill the inside of each crown. After setting, the crown and the two layers of silicone material were separated. No adjustments were performed for the inner surface of each crown before replication. The silicone block materials obtained from each crown were sectioned buccolingually first and then mesiodistally at the middle point of each surface with a sharp surgical blade. Transparent autopolymerized acrylic resin index was performed for the standardization of this process. Afterwards, all-ceramic crowns were luted using an adhesive luting system (Variolink II/Syntac; Ivoclar Vivadent) according to the manufacturer’s instructions.
Marginal and internal adaptation measurements
The measurement of marginal and internal adaptation of each crown was performed with a reflected light binocular stereomicroscope (Olympus SV8, Olympus; Tokyo, Japan) at 40× magnification as described by Holmes et al.30 Each point was measured three times by the same evaluator with a 24-hour interval (Fig 1). The mean of 12 marginal gap measurements
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Clinical Marginal and Internal Adaptation of All-Ceramic Crowns
test and Fisher’s Exact test (α = 0.05). Cohen’s kappa statistic was used to determine the intra-evaluator reproducibility for the marginal and internal adaptation measurements, and determining clinical evaluation scores in the calibration phase.
Results Kappa value for evaluator’s reproducibility in measurement of marginal and internal adaptation was 0.72. Similarly, kappa value for the same evaluator’s reproducibility in determining clinical evaluation scores was 0.74. Marginal opening and internal adaptation measurements
The median marginal gap for the CAD/CAM and HP groups group were 132.2 μm (Q1: 71 μm; Q3: 215.2 μm) and 130.2 μm (Q1: 88 μm; Q3: 256.5 μm), respectively. There was no statistically significant difference with respect to marginal gap according to the Mann-Whitney U test (p = 0.95). The mean internal adaptation for the CAD/CAM group was 220.3 ± 51.3 μm and 210.5 ± 31.0 μm for the HP group. Internal adaptation for the two groups was compared using Student’s t-test, and no statistically significant difference was observed (p = 0.535). Clinical evaluation Figure 1 Measurement of marginal and internal adaptation of a crown on stereomicroscope. M, margin; T, prepared tooth; CL, cement line; C, crown.
and 24 internal adaptation measurements for each crown were calculated and used for statistical analysis. Clinical evaluation
Clinical evaluation of all-ceramic crowns was performed at baseline (2 days after luting) and 6, 12, and 24 months after luting. The presence of fractures, sensitivity, and secondary caries at the crown margin, marginal adaptation, and marginal discoloration were evaluated. Modified Ryge criteria31 were used to evaluate the quality of all-ceramic crowns (Table 2). The presence of plaque was evaluated using the L¨oe & Silness plaque index and scored as 0, 1, or 2.32 Clinical examinations were performed using a mirror and sharp explorer, radiographs, and photographs. Statistical analyses
All data sets were subjected to a Kolmogorov-Smirnov test to check the normality of the distribution (α = 0.05). The distribution of marginal gap values were not normal; therefore, median value Mann-Whitney U test (α = 0.05) was used. Student’s t-test (α = 0.05) was used to identify the differences for internal adaptation values, which were normally distributed. Kaplan-Meier statistics were used to analyze the survival rates obtained for all-ceramic crowns. Porcelain fracture and partial debonding that exposed the tooth structure, secondary caries, extraction of abutment teeth, and impaired esthetic quality or function were the main criteria for irreparable failure. Modified Ryge scores were analyzed according to Pearson Chi-Square
A minor fracture was observed at the incisal edge of an allceramic crown 13 months after cementation in the HP group. Since it did not require replacement, the crown was not rated as a failure. It was repaired intraorally using a porcelain repair kit (Ultradent Porcelain Repair Kit; Ultradent). According to Kaplan-Meier survival estimation method, the estimated survival rates were 100% for both CAD/CAM and HP crowns. None of the 30 crowns exhibited caries at the cervical margin during the complete observation period. Five teeth in the CAD/CAM group showed slight sensitivity at baseline and at the first control appointment; however, no sensitivity was recorded at the following appointments. Two teeth in the HP group were recorded to have slight sensitivity at baseline. One presented with slight sensitivity at the next control appointment. There was no statistically significant difference with respect to postoperative sensitivity between two groups (p > 0.05); however, there was a statistically significant difference between two groups with respect to marginal discoloration according to chisquare test (p < 0.05). HP crowns exhibited better marginal adaptation than CAD/CAM crowns according to the chi-square test (p < 0.05). The scores for evaluated variables and their distributions are presented in Table 3. The plaque index scores are presented in Table 4.
Discussion Marginal and internal adaptation of all-ceramic crowns are two important factors for clinical longevity.2,18 The lack of adaptation due to cement solubility and plaque retention may be harmful for both tooth structure and periodontal tissues.14 In this study, marginal and internal gaps were defined according to the terminology reported by Holmes et al.30 Because the largest measurement of error would always be at the margin,
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Table 2 Criteria for the direct evaluation of the restorations Category
Score
Criteria
Fracture
Alpha Bravo Alpha Bravo Charlie Alpha Bravo Charlie Alpha Bravo Alpha Bravo
No evidence of fracture Evidence of fracture Restoration is continuous with existing anatomic form, explorer does not catch Explorer catches, no crevice is visible into which explorer will penetrate Crevice at margin, enamel exposed No discoloration Superficial staining (removable, usually localized) Deep staining (not removable, generalized) No evidence of caries contiguous with the margin of the restoration Caries is evident contiguous with the margin of the restoration No sensitivity Slight sensitivity
Marginal adaptation
Marginal discoloration
Secondary caries Postoperative sensitivity
Table 3 Clinical scores for CAD/CAM and heat-pressed all-ceramic crowns Category
Score
Fracture
Baseline
Marginal discoloration
Secondary caries Postoperative sensitivity
Baseline
6-month recall
CAD/CAM
HP
CAD/CAM
HP
CAD/CAM
HP
15
15
15
15
15
15
15
15
11 4
14 1
11 4
14 1
11 4
14 1
11 4
14 1
15
15
15
12 3
15
12 3
15
12 3
15
15
15
15
15
15
15
15
10 5
13 2
10 5
14 1
15
14 1
15
14 1
1-year recall
2 year recall
CAD/CAM HP CAD/CAM HP CAD/CAM HP CAD/CAM HP 0 1 2 3
15
11 4
7 7 1
8 4 3
12 2 1
10 2 3
13 2
11 1 3
absolute marginal discrepancy was noted as the most suitable measurement by Holmes et al30 for both overextended and underextended crown margins. Marginal and internal gaps were measured directly under a microscope after sectioning the embedded specimens; however, it is not possible to use this method in clinical conditions.5 The replica technique for measurement of marginal and internal gaps was used to overcome this limitation.2 On the other hand, the replica technique does not allow the measurement of absolute marginal discrepancy.2,18 Therefore, marginal gap 4
2 year recall
HP
Table 4 Plaque index scores for CAD/CAM and heat-pressed all-ceramic crowns Score
1-year recall
CAD/CAM Alpha Bravo Alpha Bravo Charlie Alpha Bravo Charlie Alpha Bravo Alpha Bravo
Marginal adaptation
6-month recall
was measured at the crown margin in our study. Silicone replicas were sectioned at the mid-point for both buccolingual and mesiodistal directions to standardize the measurement points. Marginal and internal gap measurement results from clinical studies are generally higher than those of in vitro studies due to several patient factors.20 It is not possible to standardize some factors such as clinical crown length, axial angle, and location of the shoulder. These may be interpreted as the limitations of this clinical study. Another limitation of this study was its sample size. Fifteen samples were calculated for each group as a result of power calculation. The sample size of this study was similar to that of a recently published randomized clinical study28 and was enough to evaluate the marginal and internal adaptation; however, this may be small to detect the difference in clinical outcome between two groups when compared to a clinical study.29 It has been reported that cement film thickness should be between 25 and 40 μm, which is a very rare situation in clinical practice.23 It has also been stated that restorations need a theoretical luting cement film thickness of 20 to 40 μm.17 For good long-term prognosis, the clinically acceptable marginal gap for a crown must be less than 120 μm according to McLean and
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von Fraunhofer,19 and 200 μm according to Bjorn et al.15 Nakamura et al6 reported that internal gap ranged from 116 to 162 μm, and marginal gap ranged from 53 to 108 μm for CEREC 3 CAD/CAM crowns. In this study the median marginal gap was measured as 132.2 and 130.2 μm for CAD/CAM and HP crowns, respectively. Median marginal gap measurements were in a clinically acceptable range. The maximum marginal gap measurements for CAD/CAM and HP groups were 215.2 and 256.5 μm, while maximum internal gap measurements for CAD/CAM and HP groups were 303.8 and 274.7 μm, respectively. In a clinical study where marginal and internal gaps for Procera all-ceramic crowns were measured using the silicone replica technique, it has been reported that the maximum marginal gap for the maxillary anterior region is 216 μm.18 In an in vivo study,27 marginal discrepancies of all-ceramic restorations were evaluated. It was reported that the median marginal opening of all-ceramic crowns was 96 μm before luting and 130 μm after luting. The results of that study were similar to the results of this study. Applying silicone material onto all-ceramic crowns before luting to obtain silicone replicas simulates luted crowns in the patient’s mouth. Since maladaptation in the axial wall area and occlusal plateau can reduce the resistance to fracture of all-ceramic restorations,8 the discrepancy is a very critical issue for the restoration survival. Nakamura et al6 examined the effect of occlusal convergence angle of abutment and the computer’s luting space setting on marginal and internal adaptation of CEREC 3 CAD/CAM allceramic crowns. They reported that the marginal gap of a crown was not affected by the luting space at the occlusal surface of an abutment when the luting space was set to 30 or 50 μm. The mean internal gap ranged between 116 and 162 μm according to their findings. The mean internal gap was measured as 146 μm when the occlusal convergence angle was set to 12° and the luting space was 50 μm.6 In our study, the luting space was set to 50 μm, and the mean internal gap was measured as 190.6 μm for CAD/CAM crowns, and as 128.3 μm for HP crowns. The highest results were found at the incisal edge for both groups (292.5 μm for CAD/CAM group, 311.6 μm for HP group). An internal cutting bur may be larger in diameter than some parts of the tooth preparation, such as the incisal edge, and this would result in a larger internal gap.4 In this study, while no statistically significant difference was observed with respect to marginal gap measurements using the replica technique at a microscope, a statistically significant difference was observed with respect to marginal adaptation in clinical evaluations according to Modified Ryge criteria. The reason for this confusion may be the overconture or underconture of all-ceramic crowns at the marginal region that cannot be evaluated using the replica technique. Both CAD/CAM and HP crowns demonstrated a survival rate of 100% over the observation period. This is compatible with the results of a recent in vivo study by Valenti and Valenti24 in which 261 IPS Empress 2 crowns were rated satisfactory over a 10-year period. In an in vivo study by Taskonak and Sertg¨oz,25 20 adhesively luted IPS Empress 2 crowns exhibited a 100% success rate after 2 years. A similar result was found in a study by Toksavul and Toman26 after a mean observation period of 58 months. All-ceramic crowns are generally used in the maxillary anterior region because of their esthetic and natural appearance.
Clinical Marginal and Internal Adaptation of All-Ceramic Crowns
In this region, the finish line of the tooth preparation at the cervical area should be approximately 0.5 mm below the free gingival crest for a successful esthetic result. Therefore, a durable dentin bonding behavior of luting composites, mediated by dentin bonding agents, is of great importance in such clinical conditions. Lack of adhesion to tooth structure causes microleakage and secondary caries at the crown margins in long-term clinical use.3 In this study, secondary caries was not detected during a clinical observation period of 2 years. Our patients are still on regular controls, and they are still being examined for the presence of fracture, marginal adaptation, marginal discoloration, secondary caries, and postoperative sensitivity and being reminded of oral hygiene procedures.
Conclusions Within the limitations of this study, there were no statistically significant differences between CAD/CAM and HP all-ceramic anterior single crowns for both marginal and internal adaptation. Mean values of marginal gap for CAD/CAM and HP all-ceramic crowns were within a clinically acceptable range. A 100% success rate was recorded for both CAD/CAM and HP all-ceramic anterior single crowns, and a satisfactory clinical performance was observed during a 2-year period.
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