Class I and II CAD-CAM ceramic restorations can be considered durable alternatives to direct and laboratory-fabricated restorations.

This clinical retrospective study assessed the longevity of CAD-CAM ceramic restorations (Cerec) inserted into the cavities of 95 patients in a private practice in Berlin, Germany.

Three hundred and eight ceramic restorations were inserted into cavities in the posterior teeth of 95 patients between 1992 and 1994. One operator placed all restorations in a single sitting. Seventy-four patients, including 226 restorations, returned to the practice for a final examination at the end of 10 years. Reasons for non-attendance include relocation (15), death (2) and personal reasons (4). Again, all examinations were performed by a single examiner, however, not the same dentist who initially treated the patients. Out of the 226 restorations, 39 had been inserted in Class I cavities and 187 in Class II cavities (84 two-surfaces, 103 three or more surfaces). In the latter group, one cusp was replaced in 20 cases and two cusps in three cases. All the restorations were fabricated using Cerec 1 (46 Dicor, 180 Vita Mark II) and cemented adhesively with Vita Cerec Duo Cement in combination with Syntac Classic under a rubber dam. Kaplan-Meier survival analysis was calculated under the following failure-criteria: 1) secondary decay, 2) any kind of loss of the restoration, 3) fracture of the restoration, 4) tooth fracture and 5) marginal gap reaching dentin or base material. For statistical analysis, SPSS 12.0 was used. The survival rate was 94.7% (12 failures) after five years and 85.7% (23 failures) after 10 years.

The results of the current study show that the survival rate of Cerec 1 restorations, as applied in this study, are comparable with the survival rates of cast gold restorations.

In 1985, the first ceramic restoration produced with the Cerec system was inserted at the University of Zurich Dental School, Zurich, Switzerland, by WH Mörmann.1 The primary advantages of this system are: a) the use of prefabricated high performance ceramic blocks2 and b) ceramic restorations can be delivered to patients in one sitting.3 However, a criticism was that this CAD/CAM system was unable to fulfill clinical demands, because the precision of Cerec 1 restorations was not as high as that of the laboratory manufactured ones. In an in vitro study by Hahn, an insufficient dimensional fit (average marginal gap 125 μm) and inconsistent reproductional characteristics (straight lines were reproduced as concave or convex) for Cerec 1 inlays was found when compared to laboratory fabricated ceramic restorations.4 In their clinical study, Siervo and others found marginal gaps ranging from 170 to 280 microns for Cerec 1, whereas only 80 to 100 microns were found for the laboratory produced ceramic inlays.5 However, the clinical relevance of these marginal gaps is questionable, since ceramic restorations are luted with composite material, which may permanently seal the gap. Therefore, it was the aim of the current clinical retrospective study to assess the longevity of CAD/CAM ceramic restorations (Cerec) that were inserted in patients in a private practice in Berlin, Germany.

A total of 95 patients were treated with Cerec-1 restorations (Sirona, Bensheim, Germany) in a private practice in Berlin between 1992 and 1994. Overall, 308 restorations were cemented adhesively (Syntac Classic, Vivadent, Schaan, Liechtenstein; Vita Cerec Duo Cement, Vita Zahnfabrik, Bad Säckingen, Germany) in cavities of posterior teeth by one operator in a single sitting. In all cases, a rubber dam was applied. The restorations were fabricated out of feldspathic ceramic (Vita Mark II, Vita Zahnfabrik) or glass ceramic blocks (Dicor, Corning Dentsply, Konstanz, Germany). All patients who had received at least one such Cerecrestoration were asked by letter to take part in a follow-up examination. Seventy-four patients, including 226 Cerec restorations, participated in the follow-up examination. Reasons for non-participation were relocation (15), death (2) and personal reasons (4). All examinations were performed by a single operator, despite that dentist not being the same one who had inserted the restorations. In addition to personal data, the following parameters were recorded: number of tooth-surfaces restored, number of replaced cusps, cervical margin in dentin/enamel, prior root canal treatment and the presence of bruxism.

Out of the 226 restorations, 39 were inserted in Class I cavities and 187 in Class II cavities (84 two-surfaces, 103 three or more surfaces). Within the three or more surfaces group, one cusp was replaced in 20 cases and two cusps in three cases.

Patients routinely appeared for follow-up every three-to-six months. If a failure was detected at a routine check-up or at the final examination, the day after the preceding examination was noted as the day of failure. For statistical analysis, the Kaplan-Meier survival rate was calculated. Cox regression served to identify parameters influencing the failure rate. For all statistical analysis, SPSS 12.0 (SPSS Inc, Chicago, IL, USA) was used.

Out of the 74 patients who returned for examination, 34 were female (46%) and 40 were male (54%). The mean age was 43.6 years (SD 10.4; minimum 22 years, maximum 65 years).

Figure 1 shows the Kaplan-Meier survival rate.

Figure 1

Kaplan-Meier survival analysis.

Figure 1

Kaplan-Meier survival analysis.

Close modal

A restoration was defined as a failure when any one of the following criteria was fulfilled: 1) secondary decay, 2) any kind of loss of the restoration, 3) fracture of the restoration, 4) tooth fracture and 5) marginal gap reaching dentin or base material. According to these criteria, the survival rate was 94.7% after five years and 85.7% after 10 years. Accordingly, an annual failure rate of 1.1% after five years and 1.4% after 10 years could be calculated. The reasons for failure are shown in Table 1.

Table 1

Reasons for Restoration Failure

Reasons for Restoration Failure
Reasons for Restoration Failure

In two of the cases, two failures were found in the same patient after 10 years. The remaining 19 failures occurred in 19 patients. One of the two cases of tooth fracture occurred in a tooth with prior root canal treatment. For premolars, the Kaplan-Meier analysis showed survival rates of 95.9% after five years (four failures) and 88.5% after 10 years (nine failures). The respective values for molars were 93.7% (eight failures) and 84% (14 failures). Cox regression showed no influence in the failure rate (p<0.05) for the following parameters: number of restored tooth surfaces (0–4), number of replaced cusps (0–2), cervical margin in enamel (yes/no), prior root canal treatment (yes/no), type of ceramic (Dicor, Vita mark II) and the presence of bruxism (yes/no, as determined by the presence of wear facets).

In the current study, the annual failure rate for Cerec 1 restorations ranged from 1.1% after five years to 1.4% after 10 years. This result is in accordance with other studies. In a recent study by Sjögren and others, the survival rate was 89% and the average annual loss was 1.1% after 10 years.6 In a review, Manhart and others reported annual failure rates between 0 and 5.6% for CAD/CAM ceramic restorations.7 In a systematic review including 15 clinical studies, Martin and Jedynakiewicz found a survival rate of 97.4% after 4.2 years for intra-coronal restorations fabricated with Cerec 1 and 2.2 This resulted in an annual failure rate of 0.6%, which is lower than the current study. An explanation for this finding could be the shorter observation period. In the current study, an increasing annual failure rate was found over time. Moreover, the inclusion of restorations fabricated with Cerec 2 in the review by Martin and Jedynakiewicz may have had a positive impact on the results. Mörman and others found that the grinding precision of Cerec 2 was 2.4 times higher than that of Cerec 1, resulting in average marginal gaps of 56 (SD 27) microns.8 Posselt and Kerschbaum carried out a study in which 2,328 restorations were placed in 794 patients.9 The survival rate was 95.5% after nine years and the annual failure rate 0.5%. Reiss and Walter found a survival rate of 90% after 10 years and 84.9% after 11.8 years in a study that included 1,010 Cerec restorations in 299 patients.10 The average annual loss was 1.0% and 1.3%.

Overall, it can be stated that the data found in the current study are in accordance with the current literature. Slight discrepancies in survival rates and average annual loss may be attributed to variations in indication (for example, cavity size and marginal bounds), clinical procedures (preparation and luting techniques), study samples and the examination procedure. In order to eliminate bias, the final examination in the current study was performed by a dentist who had not treated the patients. In case of failure, a worst-case scenario was taken as a basis to calculate the failure date. Since patients participated in checkups every three-to-six months, the exact date of failure within these time periods could not be determined. Therefore, the day after the last visit with the intact restoration was chosen as the date of failure for the restoration. This might have resulted in some underestimation of the longevity of the restorations.

The most common reasons for failure in the current study were loss of the restoration, secondary decay and fracture of the restoration (Table 1). The term “any kind of loss of the restoration” was chosen if the restoration was not in situ at the time of final examination and if the reason for loss could not be determined. Since ceramic fracture is deemed to be the most common reason for restoration failure,2,6,10–11 it may be speculated that most of the losses occurred due to fracture of the restoration.

Speculation can also be made as to why the size of the restorations, the cervical margin in dentin and bruxism did not influence the failure rate. One reason may be that the presence of the above findings were too rare or, in the case of restoration size and bruxism, that the preparation type and extension, which could not be exactly determined retrospectively, superimposed these parameters.

As Cerec restorations can be delivered to patients within a single sitting, a comparison with direct restorations seems appropriate. Downer and others included studies with simple Class I and II amalgam, composite, glass ionomer and cast gold restorations in their review. The authors reported survival rates of 50% between 10 and 20 years. However, substantial variability, such as restoration type, materials, the patient, the operator, the practice environment and the type of care system influenced the longevity of the restorations.12 Bearing in mind these restrictions, with an average annual loss of 2.5% to 5.0%, these restorations did not reach the longevity of the Cerec restorations from the current study. During observation periods ranging from 2 to 20 years, Manhart and others reported annual failure rates between 0 and 7.4% for amalgam. For direct composite restorations, values from 0 to 9% were reported. These observation periods ranged from 1 to 11 years.7 In both cases, the failure rates of 0%/year were reported for short-term studies and/or studies that included very few restorations. Therefore, they do not seem to be representative. In conclusion, when compared with the current literature, the Cerec restorations from the current study performed better than direct restorations.

Nonetheless, cast gold restorations may still be seen as the “gold standard.” For Class I and II cast gold restorations, Erpenstein and others reported annual failure rates between 0.6% (>3 surfaces) and 1.9% (Class I) in a retrospective study. After an observation period of 25 years, 2,071 restorations were included in the analysis.13 In a two-year prospective study, Federlin and others found no difference in failure rate between partial gold crowns and partial ceramic crowns.14 

Stoll and others examined 3,518 cast gold restorations that were placed by students and postgraduate dentists at a dental school. The 10-year survival rate for Class I inlays was 76.1%, 88.3% (mo) and 83.4% (do) for Class II inlays with two surfaces and 87.5% for mod inlays. The value for partial crowns was 86.1% and 85.7% for all restorations.15 The latter value is exactly the same as that of the current study after 10 years.

Based on the current study, it can be concluded that ceramic Class I and II restorations fabricated with Cerec 1 in the setting of a private practice can be considered to be durable alternatives to direct and laboratory fabricated restorations.

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Author notes

Stefan Zimmer, DDS, MPHD, PhD, professor and chairman, University Witten/Herdecke, Dept of Operative and Preventive Dentistry, Witten, Germany

Oliver Göhlich, DDS, private practice, Berlin, Germany

Stefan Rüttermann, DDS, associate professor, Heinrich-Heine-University, Dept of Operative and Preventive Dentistry and Endodontics, Düsseldorf, Germany

Hermann Lang, DDS, PhD, professor, Heinrich-Heine-University, Dept of Operative and Preventive Dentistry and Endodontics, Düsseldorf, Germany

Wolfgang H-M Raab, DDS, PhD, professor and chairman, Heinrich-Heine-University, Dept of Operative and Preventive Dentistry and Endodontics, Düsseldorf, Germany

Claudia R Barthel, DDS, PhD, professor, Heinrich-Heine-University, Dept of Operative and Preventive Dentistry and Endodontics, Düsseldorf, Germany