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RESTORATIVE DENTISTRY
Muhittin Toman
Clinical evaluation of 121 lithium disilicate all-ceramic crowns up to 9 years Muhittin Toman, DDS, PhD1/Suna Toksavul, DDS, PhD2 Objective: The aim of this prospective clinical study was to evaluate the clinical performance of lithium disilicate allceramic crowns for a period from 12 to 156 months. Method and Materials: One hundred and twenty five lithium disilicate all-ceramic crowns were placed in 35 patients between 2001 and 2007. One patient who received four all-ceramic crowns was excluded from the study. The remaining 34 patients received 121 all-ceramic crowns and were recalled. Ninety-eight anterior and 23 posterior crowns were inserted. All crowns were applied on vital teeth except for 11 crowns which were placed on endodontically treated teeth. Follow-up appointments were performed 6 months after insertion, then annually. Replacement of a restoration was defined as failure. Marginal integrity, marginal discoloration, secondary caries, sensitivity, color match, and ceramic surface were evaluated following modified California Dental Association/Ryge criteria. The survival rate of the crowns was determined using Kaplan-
Meier statistical analysis and log-rank test (P = .05). Results: Ten crowns were fractured. The cumulative survival rate according to Kaplan-Meier was 87.1% after mean 104.6 months (range 12 to 156 months). Location (anterior vs posterior) of all-ceramic crown did not significantly affect the survival rate according to log-rank test (P = .89). Endodontically treated teeth without post-and-core restorations exhibited a higher failure rate after all-ceramic crown application according to log-rank test (P < .001). Conclusion: In this in vivo study, lithium disilicate all-ceramic crowns exhibited a satisfactory clinical performance with an estimated survival probability of 87.1% over 104.6 months and they can be used clinically in the anterior and posterior region. Restoring endodontically treated teeth with post-and-core restorations should be considered before all-ceramic crown application. (Quintessence Int 2015;46:189–197; doi: 10.3290/j.qi.a33267)
Key words: adhesive luting, all-ceramic crowns, clinical study
All-ceramic restorations are characterized by enhanced esthetic properties, optimal integration to gingival tissues, and biocompatibility.1,2 The use of them has been steadily increasing since the introduction of highstrength core ceramics as an alternative to metal frameworks. However, ceramic material is stiff and brittle in 1
Associate Profesor, Department of Prosthodontics, Dentistry Faculty, Ege University, Bornova, Izmir, Turkey.
2
Profesor, Department of Prosthodontics, Dentistry Faculty, Ege University, Bornova, Izmir, Turkey.
Correspondence: Muhittin Toman, Department of Prosthodontics, Faculty of Dentistry, Ege University, 35100, Bornova, Izmir, Turkey. Email: [email protected]
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spite of its high strength, and tends to fracture especially when exposed to tensile forces in the mouth.3,4 Allceramic restorations can be fabricated with a variety of systems, including heat-pressed all-ceramic systems. IPS Empress 2 (Ivoclar Vivadent) is a heat-pressed, lithium disilicate all-ceramic material that offers the advantages of increased biocompatibility, natural appearance, and superior esthetics.5 A chemical and micromechanical bond between the etched porcelain and tooth structure can be accomplished with the IPS Empress 2 system.6 The adhesive luting technique, including enamel/ dentin bonding agents and dual-curing resin cement, is
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recommended for the luting of many all-ceramic systems.7 It has been reported that the adhesive luting technique improves the fracture resistance of lithium disilicate ceramic material by penetrating the flaws and irregularities of the restoration’s internal surface and inhibiting crack propagation.7 On the other hand, in a recently published clinical follow-up study it was reported that conventionally cemented three-unit fixed partial dentures made from monolithic lithium disilicate ceramic exhibited successful clinical outcomes after 10 years.8 High clinical success rates in terms of esthetics, marginal integration, and occlusion can be achieved at the luting appointment for indirect dental restorations because of technological improvements in the dental materials. However, these improvements have also made the long-term clinical success of dental restorations possible, and evaluation over a minimum of 5 years of clinical service is the gold standard for assessment of dental restorations.9-13 Certain intraoral conditions cannot be reproduced in the laboratory. These conditions include multiple intermittent cyclic forces during chewing, grinding, and clenching; constant exposure to a moist, bacteria-rich environment; ingestion of hot or cold liquids and acids; and heavy or inadequate toothbrushing. Few studies have described the survival of all-ceramic crowns and their failure rates in long-term clinical use.14-16 The aim of this clinical prospective study was to evaluate the success rate, estimated survival rate, and clinical quality of lithium disilicate all-ceramic crowns (IPS Empress 2) placed over a 6-year period from 2001 to 2007.
METHOD AND MATERIALS Seventy-nine all-ceramic crowns (IPS Empress 2) were evaluated for a mean follow-up period of 58 months and corresponding results were published in 2007.5 Forty-six all-ceramic crowns (IPS Empress 2) were further placed in 14 patients using the same all-ceramic crown system. The same clinical procedure was performed for all patients. Thus a total of 125 all-ceramic crowns were placed in 35 patients between 2001 and
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2007 at the Department of Prosthodontics, Dentistry Faculty, Ege University. Patients with severe parafunction, periodontitis, serious gingival inflammation, or poor oral hygiene or caries rates were excluded from the study. Teeth included in this 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. Four patients with 14 all-ceramic crowns in the above-mentioned study5 could not be reached after the 12-month recall appointment. Therefore, allceramic crowns in those patients were included in the statistical analysis with clinical data in the 12-month recall appointment. One patient with four all-ceramic crowns placed after 2007 could not be reached and was therefore excluded from the study. The remaining 34 patients (21 female, 13 male), who received 121 allceramic crowns, were recalled 6 months after insertion, then annually. All patients were informed of the details of the study, and their informed consents were obtained. The study design was approved by the Human Ethical Research Committee of the Faculty of Medicine (14-4.1/7). Among these, 103 crowns were placed in the maxilla and 18 were placed in the mandible. The restorations included 78 incisors, 20 canines, 14 premolars, and 9 molars. The distribution of the restorations in relation to the evaluation time is presented in Table 1. Thus, a total of 121 restorations containing 98 anterior and 23 posterior all-ceramic crowns were inserted. All crowns were applied on vital teeth except for 11 crowns that were placed on endodontically treated teeth. Six of the endodontically treated teeth received prefabricated glass fiber reinforced posts (FRC Postec, Ivoclar Vivadent) and composite cores (Tetric EvoCeram, Ivoclar Vivadent) before tooth preparation due to severe coronal destruction. Post-and-core restoration was not considered for the remaining five endodontically treated maxillary incisors due to their intact coronal structure. For 95 crowns, the opposing dentition consisted of natural teeth, whereas 26 crowns were opposed by ceramic materials.
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Table 1
Number of all-ceramic crowns according to evaluation time
Evaluation time (months)
Maxilla
Mandible Molars
Total
10
0
0
1
0
0
0
3
14
80
4
1
1
0
0
0
0
0
6
81
11
2
0
0
0
0
0
0
13
82
7
0
0
0
0
0
0
2
9
83
1
0
0
0
0
0
0
0
1
108
8
4
5
0
0
0
0
0
17
120
0
0
0
0
0
0
0
1
1
131
3
1
1
0
0
0
1
1
7
132
14
2
1
1
0
1
2
0
21
134
2
0
0
0
0
0
0
0
2
144
4
2
0
0
0
0
0
0
6
146
0
1
0
0
0
0
1
0
2
156
10
4
2
0
4
2
0
0
22
12
Incisors
Canines Premolars
Molars
Incisors
For each crown, the shade was determined prior to tooth preparation (Chromascop shade guide, Ivoclar Vivadent). For all-ceramic crown preparation design, a circumferential shoulder with rounded internal line angles with a depth of 1.0 to 1.3 mm was created with rotary diamond burs. The occlusal reduction was 2 mm for posterior and 1.5 mm for anterior crowns, and the reduction in the palatal area of anterior teeth was 0.8 mm. Finally all sharp edges and angles were rounded. After tooth preparation, margins were finished with a fine diamond bur (856EF012, Komet). The smoothness of the finish line and the ability to transfer the details to the stone die is essential for the precision and the fit of the crown. In the maxillary anterior region, the palatal concavity was accurately determined to provide proper anatomic anterior disocclusion. In the posterior region, the margins were located supra- or equigingivally to facilitate impression taking and evaluation of the marginal adaptation of the crowns. In the anterior region, the margins were located at the level of the gingival crest or slightly into the sulcus, depending on esthetic demands.17 Where needed, especially in the anterior region (equigingivally or intrasulcularly positioned margins), gingival displacement was obtained using a retraction cord (No. 1
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Canines Premolars
Ultrapack, Ultradent). Following removal of the retraction cord, full-arch vinyl-polysiloxane impressions (Affinis, Coltene Whaledent) of the prepared teeth were made and immediately poured with a type V dental stone (Glastone Dental Stone, Dentsply). Full-arch irreversible hydrocolloid impressions (CA37, Cavex) were made of the opposing dentition and immediately poured with a type IV dental stone (Silky-Rock, Whip Mix). Interocclusal registrations and facebow transfers (Quick Mount Face-Bow, Whip Mix) were obtained and the master casts were mounted in a semi-adjustable articulator (Dentatus ARH-type, Dentatus). Provisional crowns (Dentalon Plus, Kulzer) were prepared to maintain gingival health and tooth position, and provisional crowns were cemented with a eugenol-free temporary cement (Cavex Temporary Cement, Cavex). All-ceramic crowns were fabricated by the same certified dental technician using the layering technique with IPS Empress 2 layering ceramic (Ivoclar Vivadent) on lithium disilicate framework ceramic in at least 0.8 mm thickness.18 The habitual intercuspal position of the patients was maintained and the occlusion was evaluated for protrusive and lateral movements. The gingival margins surrounding the abutment teeth were completely healthy with no signs of color
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change or bleeding at the luting appointment. The operation field was isolated with cotton rolls and highvelocity evacuation during luting. Each tooth was cleaned with pumice, rinsed, and gently air-dried with an oil-free clean airflow. The internal surface of each all-ceramic crown was etched with 5% hydrofluoric acid (IPS Empress etching gel, Ivoclar Vivadent) for 60 seconds, rinsed for 30 seconds under tap water, and airdried. The internal crown surface was silanized with a silane coupling agent (Monobond S, Ivoclar Vivadent) for 60 seconds and air-dried. Enamel was etched for 30 seconds and dentin for 15 seconds with a 37% phosphoric acid (Email Preparator GS), rinsed for 30 seconds, and completely dried with oil-free air. Syntac Primer (Ivoclar Vivadent) was applied for 15 seconds and airdried. Syntac Adhesive (Ivoclar Vivadent) was applied for 10 seconds and air-dried. Subsequently, Heliobond (Ivoclar Vivadent) was brushed onto the prepared tooth surface and onto the internal surface of the all-ceramic crown. The bonding agent was air-thinned and not light polymerized. Variolink II base and the low viscosity catalyst were mixed on the mixing pad with a plastic spatula, applied to the internal surface of the crown, and the crown was seated onto the prepared tooth. Initial light polymerization was performed for 10 seconds. Excess cement was removed with a dental probe. The luting agent was polymerized from each margin using visible light with an irradiance of 480 mW/cm2 (Optilux, Kerr) for 40 seconds. The occlusion and articulation of all-ceramic crowns were controlled carefully using an 80-μm-thick articulating paper (Hanel, Coltene Whaledent) during the try-in procedure and after the crowns were luted.19 All procedural steps from preparation to luting were performed by the same clinician (MT).
Clinical evaluation Baseline data were recorded 2 days after luting. Followup appointments were performed 6 months after insertion, then annually. The clinical examination of allceramic crowns was performed by two dental clinicians after careful calibration using Cohen’s kappa statistic.
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Clinical examination included the use of a mirror, a sharp explorer, and photographs. Marginal integrity, marginal discoloration, secondary caries, sensitivity, and fracture were evaluated following modified California Dental Association (CDA)/Ryge criteria (Table 2).20 Kaplan-Meier21 analysis and log-rank test (P = .05) were used to analyze the survival rates obtained for the crowns luted on anterior or posterior teeth and on vital or endodontically treated teeth. Ceramic fracture or partial debonding that exposed the tooth structure, impaired esthetic quality or function, replacement of the crown due to extraction, or fracture of the abutment tooth were the main criteria for irreparable failure.22
RESULTS The Kappa value for evaluator’s reproducibility in determining clinical evaluation scores was 0.71. This was evaluated as substantial agreement for two evaluators. The mean observation time was 104.6 months (range, 12 to 156 months). The 12-month recall was performed for 14 all-ceramic crowns and the 156month recall for 22 all-ceramic crowns. During the evaluation period, 10 all-ceramic crowns (8 crowns for anterior region, 2 crowns for posterior region) were rated as ‘failure’. Five endodontically treated maxillary incisors received all-ceramic crowns in occlusal relation with antagonist natural dentition fractured at the cervical margin. New all-ceramic crowns were performed following restoration of endodontically treated teeth with prefabricated glass fiber reinforced post (FRC Postec) and composite core (Tetric EvoCeram). In spite of no fracturing of all-ceramic crowns they were rated as failure due to replacement. Two all-ceramic crowns on maxillary incisors and one all-ceramic crown on a maxillary canine in occlusal relation with antagonist all-ceramic crowns in the same patient fractured 120 months after luting. Layering ceramic fractured for those crowns and this caused exposure of the framework ceramic. New all-ceramic crowns were performed. An all-ceramic crown on the mandibular left first molar in occlusal relation with
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Table 2
Criteria for direct evaluation of restorations
Criterion
Anatomic form
Marginal discoloration
Marginal adaptation
Color match
Ceramic surface
Description Alpha
Restoration is continuous with tooth anatomy
Bravo
Slightly under- or overcontoured restoration; marginal ridges slightly undercontoured; contact slightly open (may be self-correcting); occlusal height reduced locally
Charlie
Restoration is undercontoured; dentin or base exposed; contact is faulty (not self-correcting); occlusal height reduced; occlusion affected
Alpha
No marginal discoloration
Bravo
Slight discoloration visible, but polishable
Charlie
Distinct discoloration visible, but not polishable
Alpha
Restoration is continuous with existing anatomic form; explorer does not catch
Bravo
Explorer catches; no crevice is visible into which explorer will penetrate
Charlie
Crevice at margin; enamel exposed
Alpha
No mismatch in color, shade, or translucency between restoration and adjacent tooth
Bravo
Mismatch between restoration and tooth structure within the normal range of tooth color, shade, or translucency
Charlie
Esthetically displeasing color, shade, or translucency
Alpha
Smooth surface (shiny after air-drying)
Bravo
Dull surface or chipping of ceramic that does not impair esthetics or function and does not expose tooth structure
Charlie
Chipping of ceramic impairing esthetics and function or exposing tooth structure; intraceramic fissures detectable with the explorer
Alpha
No evidence of caries contiguous with the margin of the restoration
Bravo
Caries is evident contiguous with the margin of the restoration
Postoperative sensitivity
Alpha
No sensitivity
Bravo
Slight sensitivity
antagonist natural dentition fractured completely in a buccolingual direction 80 months after luting and was replaced with a new crown. A maxillary right second premolar that received an all-ceramic crown in occlusal relation with antagonist natural dentition was extracted 131 months after luting due to periodontal reasons. According to the Kaplan-Meier survival estimation method, the overall survival rate of the 121 lithium disilicate all-ceramic crowns was 87.1% (Fig 1). While the survival rate in the anterior region was 87.4%, the survival rate in the posterior region was 85% according to the Kaplan-Meier analysis (Fig 2a). Applying the logrank test, it was calculated that the location of the crown (anterior vs posterior) did not significantly affect the survival rate (P = .89). The cumulative survival rates for crowns on vital teeth and on endodontically treated teeth were 91.3% and 53.0%, respectively, after 104.6 months (Fig 2b). When endodontically treated teeth
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Cumulative Survival
Caries
1.0
Survival Function
0.9
Censored
0.8
0.7
0.6 0 Fig 1
50
100 150 Time (months)
200
Survival probabilities for entire sample.
without post-and-core restorations received all-ceramic crowns, the fracture risk was higher than for vital teeth in clinical use according to the log-rank test (P < .001).
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Anterior
1.0
Posterior
0.8
0.9 Anteriorcensored
0.8 Posteriorcensored
0.7
Endodontically treated tooth Vital tooth
0.6 Endodontically treated toothcensored
0.4 0.2
Vital toothcensored
0.0
0.6 0
50 100 150 Time (months)
Table 3
0
200
Fig 2a Kaplan-Meier survival curves for lithium disilicate allceramic crowns in the anterior and posterior regions.
50 100 150 Time (months)
200
Fig 2b Kaplan-Meier survival curves for lithium disilicate allceramic crowns on endodontically treated teeth and vital teeth.
Clinical ratings [n (%)] for all-ceramic crowns
Criterion
Alpha
Anatomic form
Bravo
Charlie
106 (95.4)
5 (4.5)
0 (0.0)
Marginal discoloration
98 (88.3)
12 (10.8)
1 (0.9)
Marginal adaptation
86 (77.5)
25 (22.5)
0 (0.0)
Color match
101 (91.0)
10 (9.0)
0 (0.0)
Ceramic surface
102 (91.9)
9 (8.1)
0 (0.0)
Caries
111 (100)
0 (0.0)
0 (0.0)
Postoperative sensitivity
105 (100)
0 (0.0)
0 (0.0)
No crown on a canine tooth failed. Seven of the patients with crown fracture reported a recent history of bruxism due to various psychologic disorders. Over the whole observation period, the remaining 111 all-ceramic crowns exhibited no caries at the cervical margin, and the remaining 105 vital teeth that received all-ceramic crowns showed no postoperative sensitivity; other scores of the evaluated variables and distributions are presented in Table 3. Most of the 111 evaluated crowns were rated as excellent. The highest rating, Alpha, was awarded to 95.4% of crowns for anatomic form, 91.9% for ceramic surface, 91.0% for color match, 88.3% for marginal discoloration, 77.5% for marginal adaptation, 100% for caries, and 100% for post-operative sensitivity.
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Cumulative Survival
Cumulative Survival
1.0
In two crowns placed in the maxillary anterior region, layering ceramic chipped (Fig 3). These crowns were smoothed, finished, and not considered failed because framework ceramics were not fractured, prepared teeth surfaces were not exposed, and they were still in function. Furthermore, patients were satisfied with these crowns.
DISCUSSION This prospective clinical study evaluated the clinical performance of 121 all-ceramic crowns up to 9 years. All-ceramic crowns were fabricated using IPS Empress 2 system including lithium disilicate framework ceramic and fluorapatite veneering ceramic for optimizing
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Fig 3a Ceramic chipping at the incisal edge of the maxillary left central incisor at the 9-year control appointment.
Fig 3b Layering ceramic fracture at the buccal surface of the maxillary left lateral incisor at the 12-year control appointment.
esthetic and shape. All IPS Empress 2 crowns were cemented with a water-based, three-step etch-andrinse dentin bonding system (Syntac) and dual-cure luting composite cement (Variolink II). In the present clinical study, there were two different parts: 34 patients and 121 all-ceramic crowns. Equal numbers of all-ceramic crowns were not performed for each patient. For example, one patient received one all-ceramic crown and another one received 12 allceramic crowns. To overcome this limitation, allceramic crowns were considered to be statistically independent of one another, as in other clinical studies.5,8,14,15 Another limitation of the present study is that this study was neither a controlled nor a randomized clinical trial. All lithium disilicate all-ceramic crowns were fabricated using the IPS Empress 2 system and were luted with Variolink II. The present study would have been more valuable if it contained a control group such as porcelain-fused-to-metal crowns. On the other hand, the present clinical study has several advantages. Many all-ceramic crowns were followed up for a long period. All clinical treatment steps for fabricating lithium disilicate all-ceramic crowns were performed under standardized conditions, which are described in detail. All treatment steps were performed by the same clinician. In addition, details of the patient’s condition, tooth condition (vital or endodontically treated, with/without post-and-core restoration) before treatment, and the mode of failure of all-ceramic crowns were provided. According to these classifications, effects of location of all-ceramic crowns in the patient’s mouth and tooth condition before treatment on clinical survival rate could be evaluated.
Seventy-nine of 121 all-ceramic crowns demonstrated a survival rate of 95.24% after a mean follow-up period of 58 months.5 In the present clinical study, the IPS Empress 2 crowns demonstrated 87.1% survival rate for 104.6 months (range 12 to 156 months). It can be said that all-ceramic crowns fabricated with the IPS Empress 2 system had a survival rate of 95.24% after almost 5 years and 87.1% up to 9 years of clinical service. In a recent clinical study, a total of 104 all-ceramic crowns showed a 94.8% survival rate after an 8-year period of clinical service.14 In that study, 82 all-ceramic crowns in the anterior region and 22 all-ceramic crowns in the posterior region were evaluated and it was reported that the location of the all-ceramic crown in the patient’s mouth did not significantly affect the survival rate. In the present clinical study, 8 (8.2%) allceramic crowns of 98 all-ceramic crowns in the anterior region and 2 (8.7%) of 23 all-ceramic crowns in the posterior region failed. The location of the all-ceramic crown did not significantly affect the survival rate in the present clinical study. On the other hand, all-ceramic crowns applied to endodontically treated teeth without post-and-core restorations were prone to fracture, especially in the maxillary anterior region, despite several studies reporting that the restoration of endodontically treated teeth with posts and cores causes weakening, reducing the fracture resistance.23,24 This may be due to weakening of the endodontically treated tooth especially in the cervical region after tooth preparation for the allceramic crown, in addition to brittleness of the endodontically treated tooth.25 Teeth are weakened internally after endodontic treatment and externally after tooth preparation for all-ceramic crowns.26 There may
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also be overloading of endodontically treated teeth in the maxillary anterior region during lateral and protrusive movement of the mandible. All-ceramic crowns are generally performed in the maxillary anterior region due to esthetic reconstruction, as their appearance resembles natural teeth. In the maxillary anterior region, the finish line of tooth preparation at the cervical area is approximately 0.5 mm below the free-gingival crest due to the esthetic demands. Therefore, a durable dentin bonding behavior of luting composites mediated by dentin bonding agents is of great importance in such clinical conditions. In this respect, microleakage is an important factor for the clinical longevity of the fixed restorations.27 The reasons for all-ceramic crown failure were fracture of the ceramic and the prepared tooth in the present clinical study. None of the crowns were replaced due to biologic reasons such as secondary caries, postoperative sensitivity, or pain. In addition, when the patients in the present study were examined clinically, ceramic surfaces seem to be dull 9 years after luting. Therefore, nine all-ceramic crowns were rated as bravo for ceramic surface evaluation according to CDA criteria. This interesting finding may be related to wear of the glaze layer due to toothbrushing in long-term clinical use. This was not the reason for replacement of the all-ceramic crowns. It was reported that bulk fracture was the main reason for failure of all-ceramic crowns in clinical use.4 Bruxism accounted for the fractures in 7 out of 10 all-ceramic crowns in the present study. Three of the patients with crown fractures stated that they had no functional problems with their crowns until bruxism was reported due to psychologic discomfort. The higher occlusal forces in patients with bruxism may be the reason for fractures observed in these patients. In long-term clinical studies it was stated that failure rates were significantly associated with bruxism.15 For long-term clinical use of conventionally fabricated and conventionally luted fixed restorations, secondary caries is the most reported biologic complication according to long-term clinical evaluations.10-12 In the present clinical study, none of the teeth that received all-ceramic crowns luted with an adhesive lut-
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ing system exhibited secondary caries after 10 years. It was previously reported that improvements in adhesive luting systems did not completely prevent but significantly reduced the microleakage.27 In contrast, it was also reported that conventionally cemented allceramic fixed partial dentures exhibited clinically satisfactory outcomes after 10 years of clinical use.8 The patients included in present study are still under investigation, with the aim of collecting longer term survival data, and this continuing long-term longitudinal study will provide additional data that may support the validity of the results.
CONCLUSION Within the limitations of this prospective clinical study, 121 lithium disilicate all-ceramic crowns exhibited 87.1% cumulative survival rate up to 9 years. The location of the all-ceramic crowns (anterior vs posterior) did not significantly affect the survival rate. All-ceramic crowns fabricated for endodontically treated teeth without post-and-core restorations exhibited lower survival rates when compared with the all-ceramic crowns on vital teeth. All-ceramic crowns have a satisfactory clinical performance, and application of them seems to be a reliable treatment option.
REFERENCES 1. Prevedello GC, Vieira M, Furuse AY, Correr GM, Gonzaga CC. Esthetic rehabilitation of anterior discolored teeth with lithium disilicate all-ceramic restorations. Gen Dent 2012;60:274–278. 2. Pieger S, Salman A, Bidra AS. Clinical outcomes of lithium disilicate single crowns and partial fixed dental prostheses: A systematic review. J Prosthet Dent 2014;12:22–30. 3. Scherrer SS, Quinn JB, Quinn GD, Kelly JR. Failure analysis of ceramic clinical cases using qualitative fractography. Int J Prosthodont 2006;19:185–192. 4. Wang X, Fan D, Swain MV, Zhao K. A systematic review of all-ceramic crowns: clinical fracture rates in relation to restored tooth type. Int J Prosthodont 2012;25:441–450. 5. Toksavul S, Toman M. A short-term clinical evaluation of IPS Empress 2 crowns. Int J Prosthodont 2007;20:168–172. 6. Vargas MA, Bergeron C, Diaz-Arnold A. Cementing all-ceramic restorations: recommendations for success. J Am Dent Assoc 2011;142(Suppl 2):20S–24S. 7. Manso AP, Silva NR, Bonfante EA, Pegoraro TA, Dias RA, Carvalho RM. Cements and adhesives for all-ceramic restorations. Dent Clin North Am 2011;55:311–332. 8. 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.
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9. Haselton DR, Diaz-Arnold AM, Hillis SL. Clinical assessment of high-strength all-ceramic crowns. J Prosthet Dent 2000;83:396–401. 10. Goodacre CJ, Bernal G, Rungcharassaeng K, Kan JY. Clinical complications in fixed prosthodontics. J Prosthet Dent 2003;90:31–41. 11. Holm C, Tidehag P, Tillberg A, Molin M. Longevity and quality of FPDs: a retrospective study of restorations 30, 20, and 10 years after insertion. Int J Prosthodont 2003;16:283–289. 12. De Backer H, Van Maele G, De Moor N, Van den Berghe L, De Boever J. A 20-year retrospective survival study of fixed partial dentures. Int J Prosthodont 2006;19:143–153. 13. Schley JS, Heussen N, Reich S, Fischer J, Haselhuhn K, Wolfart S. Survival probability of zirconia-based fixed dental prostheses up to 5 years: a systematic review of the literature. Eur J Oral Sci 2010;118:443–450. 14. Gehrt M, Wolfart S, Rafai N, Reich S, Edelhoff D. Clinical results of lithium-disilicate crowns after up to 9 years of service. Clin Oral Investig 2013;17:275–284. 15. Beier US, Kapferer I, Burtscher D, Dumfahrt H. Clinical performance of porcelain laminate veneers for up to 20 years. Int J Prosthodont 2012;25:79–85. 16. Valenti M, Valenti A. Retrospective survival analysis of 261 lithium disilicate crowns in a private general practice. Quintessence Int 2009;40:573–579. 17. Padbury A Jr, Eber R, Wang HL. Interactions between the gingiva and the margin of restorations. J Clin Periodontol 2003;30:379–385. 18. Culp L. Empress 2. First year clinical results. J Dent Technol 1999;16:12–15.
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19. Shillinburg HT, Hobo S, Whitsett LD, Jacobi R, Brackett SE. Fundamentals of fixed prosthdodontics. 3rd edition. Chicago: Quintessence, 1997:451 20. Ryge G. Clinical criteria. Int Dent J 1980;30:347–358. 21. Kaplan EL, Meier P. Non parametric estimation from incomplete observations. J Am Stat Assoc 1958;53:457–465. 22. Malament K, Socransky S. Survival of Dicor glass-ceramic dental restorations over 14 years. Part II: Effect of thickness of Dicor material and design of tooth preparation. J Prosthet Dent 1999;81:662–667. 23. Heydecke G, Butz F, Strub JR. Fracture strength and survival rate of endodontically treated maxillary incisors with approximal cavities after restoration with different post and core systems: an in-vitro study. J Dent 2001;29:427–433. 24. Cheung W. A review of the management of endodontically treated teeth. J Am Dent Assoc 2005;136:611–619. 25. Carter JM, Sorensen SE, Johnson RR, Teitelbaum RL, Levine MS. Punch shear testing of extracted vital and endodontically treated teeth. J Biomech 1983;16:841–848. 26. Reeh ES, Douglas WH, Messer HH. Stiffness of endodontically treated teeth related to restoration technique. J Dent Res 1989;68:1540–1544. 27. Toman M, Toksavul S, Artunç C, Türkün M, Schmage P, Nergiz I. Influence of luting agent on the microleakage of all-ceramic crowns. J Adhes Dent 2007;9:39–47.
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RESTORATIVE DENTISTRY
Muhittin Toman
Clinical evaluation of 121 lithium disilicate all-ceramic crowns up to 9 years Muhittin Toman, DDS, PhD1/Suna Toksavul, DDS, PhD2 Objective: The aim of this prospective clinical study was to evaluate the clinical performance of lithium disilicate allceramic crowns for a period from 12 to 156 months. Method and Materials: One hundred and twenty five lithium disilicate all-ceramic crowns were placed in 35 patients between 2001 and 2007. One patient who received four all-ceramic crowns was excluded from the study. The remaining 34 patients received 121 all-ceramic crowns and were recalled. Ninety-eight anterior and 23 posterior crowns were inserted. All crowns were applied on vital teeth except for 11 crowns which were placed on endodontically treated teeth. Follow-up appointments were performed 6 months after insertion, then annually. Replacement of a restoration was defined as failure. Marginal integrity, marginal discoloration, secondary caries, sensitivity, color match, and ceramic surface were evaluated following modified California Dental Association/Ryge criteria. The survival rate of the crowns was determined using Kaplan-
Meier statistical analysis and log-rank test (P = .05). Results: Ten crowns were fractured. The cumulative survival rate according to Kaplan-Meier was 87.1% after mean 104.6 months (range 12 to 156 months). Location (anterior vs posterior) of all-ceramic crown did not significantly affect the survival rate according to log-rank test (P = .89). Endodontically treated teeth without post-and-core restorations exhibited a higher failure rate after all-ceramic crown application according to log-rank test (P < .001). Conclusion: In this in vivo study, lithium disilicate all-ceramic crowns exhibited a satisfactory clinical performance with an estimated survival probability of 87.1% over 104.6 months and they can be used clinically in the anterior and posterior region. Restoring endodontically treated teeth with post-and-core restorations should be considered before all-ceramic crown application. (Quintessence Int 2015;46:189–197; doi: 10.3290/j.qi.a33267)
Key words: adhesive luting, all-ceramic crowns, clinical study
All-ceramic restorations are characterized by enhanced esthetic properties, optimal integration to gingival tissues, and biocompatibility.1,2 The use of them has been steadily increasing since the introduction of highstrength core ceramics as an alternative to metal frameworks. However, ceramic material is stiff and brittle in 1
Associate Profesor, Department of Prosthodontics, Dentistry Faculty, Ege University, Bornova, Izmir, Turkey.
2
Profesor, Department of Prosthodontics, Dentistry Faculty, Ege University, Bornova, Izmir, Turkey.
Correspondence: Muhittin Toman, Department of Prosthodontics, Faculty of Dentistry, Ege University, 35100, Bornova, Izmir, Turkey. Email: [email protected]
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spite of its high strength, and tends to fracture especially when exposed to tensile forces in the mouth.3,4 Allceramic restorations can be fabricated with a variety of systems, including heat-pressed all-ceramic systems. IPS Empress 2 (Ivoclar Vivadent) is a heat-pressed, lithium disilicate all-ceramic material that offers the advantages of increased biocompatibility, natural appearance, and superior esthetics.5 A chemical and micromechanical bond between the etched porcelain and tooth structure can be accomplished with the IPS Empress 2 system.6 The adhesive luting technique, including enamel/ dentin bonding agents and dual-curing resin cement, is
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recommended for the luting of many all-ceramic systems.7 It has been reported that the adhesive luting technique improves the fracture resistance of lithium disilicate ceramic material by penetrating the flaws and irregularities of the restoration’s internal surface and inhibiting crack propagation.7 On the other hand, in a recently published clinical follow-up study it was reported that conventionally cemented three-unit fixed partial dentures made from monolithic lithium disilicate ceramic exhibited successful clinical outcomes after 10 years.8 High clinical success rates in terms of esthetics, marginal integration, and occlusion can be achieved at the luting appointment for indirect dental restorations because of technological improvements in the dental materials. However, these improvements have also made the long-term clinical success of dental restorations possible, and evaluation over a minimum of 5 years of clinical service is the gold standard for assessment of dental restorations.9-13 Certain intraoral conditions cannot be reproduced in the laboratory. These conditions include multiple intermittent cyclic forces during chewing, grinding, and clenching; constant exposure to a moist, bacteria-rich environment; ingestion of hot or cold liquids and acids; and heavy or inadequate toothbrushing. Few studies have described the survival of all-ceramic crowns and their failure rates in long-term clinical use.14-16 The aim of this clinical prospective study was to evaluate the success rate, estimated survival rate, and clinical quality of lithium disilicate all-ceramic crowns (IPS Empress 2) placed over a 6-year period from 2001 to 2007.
METHOD AND MATERIALS Seventy-nine all-ceramic crowns (IPS Empress 2) were evaluated for a mean follow-up period of 58 months and corresponding results were published in 2007.5 Forty-six all-ceramic crowns (IPS Empress 2) were further placed in 14 patients using the same all-ceramic crown system. The same clinical procedure was performed for all patients. Thus a total of 125 all-ceramic crowns were placed in 35 patients between 2001 and
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2007 at the Department of Prosthodontics, Dentistry Faculty, Ege University. Patients with severe parafunction, periodontitis, serious gingival inflammation, or poor oral hygiene or caries rates were excluded from the study. Teeth included in this 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. Four patients with 14 all-ceramic crowns in the above-mentioned study5 could not be reached after the 12-month recall appointment. Therefore, allceramic crowns in those patients were included in the statistical analysis with clinical data in the 12-month recall appointment. One patient with four all-ceramic crowns placed after 2007 could not be reached and was therefore excluded from the study. The remaining 34 patients (21 female, 13 male), who received 121 allceramic crowns, were recalled 6 months after insertion, then annually. All patients were informed of the details of the study, and their informed consents were obtained. The study design was approved by the Human Ethical Research Committee of the Faculty of Medicine (14-4.1/7). Among these, 103 crowns were placed in the maxilla and 18 were placed in the mandible. The restorations included 78 incisors, 20 canines, 14 premolars, and 9 molars. The distribution of the restorations in relation to the evaluation time is presented in Table 1. Thus, a total of 121 restorations containing 98 anterior and 23 posterior all-ceramic crowns were inserted. All crowns were applied on vital teeth except for 11 crowns that were placed on endodontically treated teeth. Six of the endodontically treated teeth received prefabricated glass fiber reinforced posts (FRC Postec, Ivoclar Vivadent) and composite cores (Tetric EvoCeram, Ivoclar Vivadent) before tooth preparation due to severe coronal destruction. Post-and-core restoration was not considered for the remaining five endodontically treated maxillary incisors due to their intact coronal structure. For 95 crowns, the opposing dentition consisted of natural teeth, whereas 26 crowns were opposed by ceramic materials.
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Table 1
Number of all-ceramic crowns according to evaluation time
Evaluation time (months)
Maxilla
Mandible Molars
Total
10
0
0
1
0
0
0
3
14
80
4
1
1
0
0
0
0
0
6
81
11
2
0
0
0
0
0
0
13
82
7
0
0
0
0
0
0
2
9
83
1
0
0
0
0
0
0
0
1
108
8
4
5
0
0
0
0
0
17
120
0
0
0
0
0
0
0
1
1
131
3
1
1
0
0
0
1
1
7
132
14
2
1
1
0
1
2
0
21
134
2
0
0
0
0
0
0
0
2
144
4
2
0
0
0
0
0
0
6
146
0
1
0
0
0
0
1
0
2
156
10
4
2
0
4
2
0
0
22
12
Incisors
Canines Premolars
Molars
Incisors
For each crown, the shade was determined prior to tooth preparation (Chromascop shade guide, Ivoclar Vivadent). For all-ceramic crown preparation design, a circumferential shoulder with rounded internal line angles with a depth of 1.0 to 1.3 mm was created with rotary diamond burs. The occlusal reduction was 2 mm for posterior and 1.5 mm for anterior crowns, and the reduction in the palatal area of anterior teeth was 0.8 mm. Finally all sharp edges and angles were rounded. After tooth preparation, margins were finished with a fine diamond bur (856EF012, Komet). The smoothness of the finish line and the ability to transfer the details to the stone die is essential for the precision and the fit of the crown. In the maxillary anterior region, the palatal concavity was accurately determined to provide proper anatomic anterior disocclusion. In the posterior region, the margins were located supra- or equigingivally to facilitate impression taking and evaluation of the marginal adaptation of the crowns. In the anterior region, the margins were located at the level of the gingival crest or slightly into the sulcus, depending on esthetic demands.17 Where needed, especially in the anterior region (equigingivally or intrasulcularly positioned margins), gingival displacement was obtained using a retraction cord (No. 1
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Canines Premolars
Ultrapack, Ultradent). Following removal of the retraction cord, full-arch vinyl-polysiloxane impressions (Affinis, Coltene Whaledent) of the prepared teeth were made and immediately poured with a type V dental stone (Glastone Dental Stone, Dentsply). Full-arch irreversible hydrocolloid impressions (CA37, Cavex) were made of the opposing dentition and immediately poured with a type IV dental stone (Silky-Rock, Whip Mix). Interocclusal registrations and facebow transfers (Quick Mount Face-Bow, Whip Mix) were obtained and the master casts were mounted in a semi-adjustable articulator (Dentatus ARH-type, Dentatus). Provisional crowns (Dentalon Plus, Kulzer) were prepared to maintain gingival health and tooth position, and provisional crowns were cemented with a eugenol-free temporary cement (Cavex Temporary Cement, Cavex). All-ceramic crowns were fabricated by the same certified dental technician using the layering technique with IPS Empress 2 layering ceramic (Ivoclar Vivadent) on lithium disilicate framework ceramic in at least 0.8 mm thickness.18 The habitual intercuspal position of the patients was maintained and the occlusion was evaluated for protrusive and lateral movements. The gingival margins surrounding the abutment teeth were completely healthy with no signs of color
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change or bleeding at the luting appointment. The operation field was isolated with cotton rolls and highvelocity evacuation during luting. Each tooth was cleaned with pumice, rinsed, and gently air-dried with an oil-free clean airflow. The internal surface of each all-ceramic crown was etched with 5% hydrofluoric acid (IPS Empress etching gel, Ivoclar Vivadent) for 60 seconds, rinsed for 30 seconds under tap water, and airdried. The internal crown surface was silanized with a silane coupling agent (Monobond S, Ivoclar Vivadent) for 60 seconds and air-dried. Enamel was etched for 30 seconds and dentin for 15 seconds with a 37% phosphoric acid (Email Preparator GS), rinsed for 30 seconds, and completely dried with oil-free air. Syntac Primer (Ivoclar Vivadent) was applied for 15 seconds and airdried. Syntac Adhesive (Ivoclar Vivadent) was applied for 10 seconds and air-dried. Subsequently, Heliobond (Ivoclar Vivadent) was brushed onto the prepared tooth surface and onto the internal surface of the all-ceramic crown. The bonding agent was air-thinned and not light polymerized. Variolink II base and the low viscosity catalyst were mixed on the mixing pad with a plastic spatula, applied to the internal surface of the crown, and the crown was seated onto the prepared tooth. Initial light polymerization was performed for 10 seconds. Excess cement was removed with a dental probe. The luting agent was polymerized from each margin using visible light with an irradiance of 480 mW/cm2 (Optilux, Kerr) for 40 seconds. The occlusion and articulation of all-ceramic crowns were controlled carefully using an 80-μm-thick articulating paper (Hanel, Coltene Whaledent) during the try-in procedure and after the crowns were luted.19 All procedural steps from preparation to luting were performed by the same clinician (MT).
Clinical evaluation Baseline data were recorded 2 days after luting. Followup appointments were performed 6 months after insertion, then annually. The clinical examination of allceramic crowns was performed by two dental clinicians after careful calibration using Cohen’s kappa statistic.
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Clinical examination included the use of a mirror, a sharp explorer, and photographs. Marginal integrity, marginal discoloration, secondary caries, sensitivity, and fracture were evaluated following modified California Dental Association (CDA)/Ryge criteria (Table 2).20 Kaplan-Meier21 analysis and log-rank test (P = .05) were used to analyze the survival rates obtained for the crowns luted on anterior or posterior teeth and on vital or endodontically treated teeth. Ceramic fracture or partial debonding that exposed the tooth structure, impaired esthetic quality or function, replacement of the crown due to extraction, or fracture of the abutment tooth were the main criteria for irreparable failure.22
RESULTS The Kappa value for evaluator’s reproducibility in determining clinical evaluation scores was 0.71. This was evaluated as substantial agreement for two evaluators. The mean observation time was 104.6 months (range, 12 to 156 months). The 12-month recall was performed for 14 all-ceramic crowns and the 156month recall for 22 all-ceramic crowns. During the evaluation period, 10 all-ceramic crowns (8 crowns for anterior region, 2 crowns for posterior region) were rated as ‘failure’. Five endodontically treated maxillary incisors received all-ceramic crowns in occlusal relation with antagonist natural dentition fractured at the cervical margin. New all-ceramic crowns were performed following restoration of endodontically treated teeth with prefabricated glass fiber reinforced post (FRC Postec) and composite core (Tetric EvoCeram). In spite of no fracturing of all-ceramic crowns they were rated as failure due to replacement. Two all-ceramic crowns on maxillary incisors and one all-ceramic crown on a maxillary canine in occlusal relation with antagonist all-ceramic crowns in the same patient fractured 120 months after luting. Layering ceramic fractured for those crowns and this caused exposure of the framework ceramic. New all-ceramic crowns were performed. An all-ceramic crown on the mandibular left first molar in occlusal relation with
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Table 2
Criteria for direct evaluation of restorations
Criterion
Anatomic form
Marginal discoloration
Marginal adaptation
Color match
Ceramic surface
Description Alpha
Restoration is continuous with tooth anatomy
Bravo
Slightly under- or overcontoured restoration; marginal ridges slightly undercontoured; contact slightly open (may be self-correcting); occlusal height reduced locally
Charlie
Restoration is undercontoured; dentin or base exposed; contact is faulty (not self-correcting); occlusal height reduced; occlusion affected
Alpha
No marginal discoloration
Bravo
Slight discoloration visible, but polishable
Charlie
Distinct discoloration visible, but not polishable
Alpha
Restoration is continuous with existing anatomic form; explorer does not catch
Bravo
Explorer catches; no crevice is visible into which explorer will penetrate
Charlie
Crevice at margin; enamel exposed
Alpha
No mismatch in color, shade, or translucency between restoration and adjacent tooth
Bravo
Mismatch between restoration and tooth structure within the normal range of tooth color, shade, or translucency
Charlie
Esthetically displeasing color, shade, or translucency
Alpha
Smooth surface (shiny after air-drying)
Bravo
Dull surface or chipping of ceramic that does not impair esthetics or function and does not expose tooth structure
Charlie
Chipping of ceramic impairing esthetics and function or exposing tooth structure; intraceramic fissures detectable with the explorer
Alpha
No evidence of caries contiguous with the margin of the restoration
Bravo
Caries is evident contiguous with the margin of the restoration
Postoperative sensitivity
Alpha
No sensitivity
Bravo
Slight sensitivity
antagonist natural dentition fractured completely in a buccolingual direction 80 months after luting and was replaced with a new crown. A maxillary right second premolar that received an all-ceramic crown in occlusal relation with antagonist natural dentition was extracted 131 months after luting due to periodontal reasons. According to the Kaplan-Meier survival estimation method, the overall survival rate of the 121 lithium disilicate all-ceramic crowns was 87.1% (Fig 1). While the survival rate in the anterior region was 87.4%, the survival rate in the posterior region was 85% according to the Kaplan-Meier analysis (Fig 2a). Applying the logrank test, it was calculated that the location of the crown (anterior vs posterior) did not significantly affect the survival rate (P = .89). The cumulative survival rates for crowns on vital teeth and on endodontically treated teeth were 91.3% and 53.0%, respectively, after 104.6 months (Fig 2b). When endodontically treated teeth
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Cumulative Survival
Caries
1.0
Survival Function
0.9
Censored
0.8
0.7
0.6 0 Fig 1
50
100 150 Time (months)
200
Survival probabilities for entire sample.
without post-and-core restorations received all-ceramic crowns, the fracture risk was higher than for vital teeth in clinical use according to the log-rank test (P < .001).
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Anterior
1.0
Posterior
0.8
0.9 Anteriorcensored
0.8 Posteriorcensored
0.7
Endodontically treated tooth Vital tooth
0.6 Endodontically treated toothcensored
0.4 0.2
Vital toothcensored
0.0
0.6 0
50 100 150 Time (months)
Table 3
0
200
Fig 2a Kaplan-Meier survival curves for lithium disilicate allceramic crowns in the anterior and posterior regions.
50 100 150 Time (months)
200
Fig 2b Kaplan-Meier survival curves for lithium disilicate allceramic crowns on endodontically treated teeth and vital teeth.
Clinical ratings [n (%)] for all-ceramic crowns
Criterion
Alpha
Anatomic form
Bravo
Charlie
106 (95.4)
5 (4.5)
0 (0.0)
Marginal discoloration
98 (88.3)
12 (10.8)
1 (0.9)
Marginal adaptation
86 (77.5)
25 (22.5)
0 (0.0)
Color match
101 (91.0)
10 (9.0)
0 (0.0)
Ceramic surface
102 (91.9)
9 (8.1)
0 (0.0)
Caries
111 (100)
0 (0.0)
0 (0.0)
Postoperative sensitivity
105 (100)
0 (0.0)
0 (0.0)
No crown on a canine tooth failed. Seven of the patients with crown fracture reported a recent history of bruxism due to various psychologic disorders. Over the whole observation period, the remaining 111 all-ceramic crowns exhibited no caries at the cervical margin, and the remaining 105 vital teeth that received all-ceramic crowns showed no postoperative sensitivity; other scores of the evaluated variables and distributions are presented in Table 3. Most of the 111 evaluated crowns were rated as excellent. The highest rating, Alpha, was awarded to 95.4% of crowns for anatomic form, 91.9% for ceramic surface, 91.0% for color match, 88.3% for marginal discoloration, 77.5% for marginal adaptation, 100% for caries, and 100% for post-operative sensitivity.
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Cumulative Survival
Cumulative Survival
1.0
In two crowns placed in the maxillary anterior region, layering ceramic chipped (Fig 3). These crowns were smoothed, finished, and not considered failed because framework ceramics were not fractured, prepared teeth surfaces were not exposed, and they were still in function. Furthermore, patients were satisfied with these crowns.
DISCUSSION This prospective clinical study evaluated the clinical performance of 121 all-ceramic crowns up to 9 years. All-ceramic crowns were fabricated using IPS Empress 2 system including lithium disilicate framework ceramic and fluorapatite veneering ceramic for optimizing
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Fig 3a Ceramic chipping at the incisal edge of the maxillary left central incisor at the 9-year control appointment.
Fig 3b Layering ceramic fracture at the buccal surface of the maxillary left lateral incisor at the 12-year control appointment.
esthetic and shape. All IPS Empress 2 crowns were cemented with a water-based, three-step etch-andrinse dentin bonding system (Syntac) and dual-cure luting composite cement (Variolink II). In the present clinical study, there were two different parts: 34 patients and 121 all-ceramic crowns. Equal numbers of all-ceramic crowns were not performed for each patient. For example, one patient received one all-ceramic crown and another one received 12 allceramic crowns. To overcome this limitation, allceramic crowns were considered to be statistically independent of one another, as in other clinical studies.5,8,14,15 Another limitation of the present study is that this study was neither a controlled nor a randomized clinical trial. All lithium disilicate all-ceramic crowns were fabricated using the IPS Empress 2 system and were luted with Variolink II. The present study would have been more valuable if it contained a control group such as porcelain-fused-to-metal crowns. On the other hand, the present clinical study has several advantages. Many all-ceramic crowns were followed up for a long period. All clinical treatment steps for fabricating lithium disilicate all-ceramic crowns were performed under standardized conditions, which are described in detail. All treatment steps were performed by the same clinician. In addition, details of the patient’s condition, tooth condition (vital or endodontically treated, with/without post-and-core restoration) before treatment, and the mode of failure of all-ceramic crowns were provided. According to these classifications, effects of location of all-ceramic crowns in the patient’s mouth and tooth condition before treatment on clinical survival rate could be evaluated.
Seventy-nine of 121 all-ceramic crowns demonstrated a survival rate of 95.24% after a mean follow-up period of 58 months.5 In the present clinical study, the IPS Empress 2 crowns demonstrated 87.1% survival rate for 104.6 months (range 12 to 156 months). It can be said that all-ceramic crowns fabricated with the IPS Empress 2 system had a survival rate of 95.24% after almost 5 years and 87.1% up to 9 years of clinical service. In a recent clinical study, a total of 104 all-ceramic crowns showed a 94.8% survival rate after an 8-year period of clinical service.14 In that study, 82 all-ceramic crowns in the anterior region and 22 all-ceramic crowns in the posterior region were evaluated and it was reported that the location of the all-ceramic crown in the patient’s mouth did not significantly affect the survival rate. In the present clinical study, 8 (8.2%) allceramic crowns of 98 all-ceramic crowns in the anterior region and 2 (8.7%) of 23 all-ceramic crowns in the posterior region failed. The location of the all-ceramic crown did not significantly affect the survival rate in the present clinical study. On the other hand, all-ceramic crowns applied to endodontically treated teeth without post-and-core restorations were prone to fracture, especially in the maxillary anterior region, despite several studies reporting that the restoration of endodontically treated teeth with posts and cores causes weakening, reducing the fracture resistance.23,24 This may be due to weakening of the endodontically treated tooth especially in the cervical region after tooth preparation for the allceramic crown, in addition to brittleness of the endodontically treated tooth.25 Teeth are weakened internally after endodontic treatment and externally after tooth preparation for all-ceramic crowns.26 There may
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also be overloading of endodontically treated teeth in the maxillary anterior region during lateral and protrusive movement of the mandible. All-ceramic crowns are generally performed in the maxillary anterior region due to esthetic reconstruction, as their appearance resembles natural teeth. In the maxillary anterior region, the finish line of tooth preparation at the cervical area is approximately 0.5 mm below the free-gingival crest due to the esthetic demands. Therefore, a durable dentin bonding behavior of luting composites mediated by dentin bonding agents is of great importance in such clinical conditions. In this respect, microleakage is an important factor for the clinical longevity of the fixed restorations.27 The reasons for all-ceramic crown failure were fracture of the ceramic and the prepared tooth in the present clinical study. None of the crowns were replaced due to biologic reasons such as secondary caries, postoperative sensitivity, or pain. In addition, when the patients in the present study were examined clinically, ceramic surfaces seem to be dull 9 years after luting. Therefore, nine all-ceramic crowns were rated as bravo for ceramic surface evaluation according to CDA criteria. This interesting finding may be related to wear of the glaze layer due to toothbrushing in long-term clinical use. This was not the reason for replacement of the all-ceramic crowns. It was reported that bulk fracture was the main reason for failure of all-ceramic crowns in clinical use.4 Bruxism accounted for the fractures in 7 out of 10 all-ceramic crowns in the present study. Three of the patients with crown fractures stated that they had no functional problems with their crowns until bruxism was reported due to psychologic discomfort. The higher occlusal forces in patients with bruxism may be the reason for fractures observed in these patients. In long-term clinical studies it was stated that failure rates were significantly associated with bruxism.15 For long-term clinical use of conventionally fabricated and conventionally luted fixed restorations, secondary caries is the most reported biologic complication according to long-term clinical evaluations.10-12 In the present clinical study, none of the teeth that received all-ceramic crowns luted with an adhesive lut-
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ing system exhibited secondary caries after 10 years. It was previously reported that improvements in adhesive luting systems did not completely prevent but significantly reduced the microleakage.27 In contrast, it was also reported that conventionally cemented allceramic fixed partial dentures exhibited clinically satisfactory outcomes after 10 years of clinical use.8 The patients included in present study are still under investigation, with the aim of collecting longer term survival data, and this continuing long-term longitudinal study will provide additional data that may support the validity of the results.
CONCLUSION Within the limitations of this prospective clinical study, 121 lithium disilicate all-ceramic crowns exhibited 87.1% cumulative survival rate up to 9 years. The location of the all-ceramic crowns (anterior vs posterior) did not significantly affect the survival rate. All-ceramic crowns fabricated for endodontically treated teeth without post-and-core restorations exhibited lower survival rates when compared with the all-ceramic crowns on vital teeth. All-ceramic crowns have a satisfactory clinical performance, and application of them seems to be a reliable treatment option.
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