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Fig. 1: 88.7 per cent survival rate (Kaplan-Meier) of CEREC inlays and onlays, after an observation period of up to 17 years.
Wilhelm Schneider, Germany

By Wilhelm Schneider, Germany

Fri. 20. February 2009

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CAD/CAM restorations made chairside with CEREC are among the most intensively studied restorations in dentistry. Numerous studies show that the clinical results of restorations made with the CEREC method are, at the very least, on par with those of cast gold. Because durability is one of the most important criteria for ceramic use, Dr Tobias Otto (Aarau, Switzerland) recently published evaluation of longterm data collected over a period of 17 years is highly pertinent.1

As one of the first in Switzerland to use CEREC in private practice, Otto has—since 1989—documented 200 inlays and onlays that were manufactured with CEREC 1 and feldspathic ceramic (VITA Mark I), and inserted in 108 patients at his office from 1989 to 1991. He assessed the results using the modified USPHS criteria, and summarised them after ten and also 17 years of clinical observation. Of the 200 CEREC inlays and onlays (largely 3- and 4-surface) originally inserted, it was possible to examine 187 restorations for their clinical quality after an average of ten years; the other cases were not available due to recall-patient dropout. Upon insertion, all cavities were coated with bonding agent and the restorations adhesively luted with a composite cement using rubber-dam.

Of the 187 restorations, 95 per cent were still clinically intact according to technical criteria. USPHS scores of Charlie or Delta were given to 15 restorations, which were thus classified as failures. Failures occurred after six to nine years of function, and most frequently involved 3-surface restorations. Reasons for failure were ceramic fractures (eight cases), fractures of tooth cusps (three cases), and caries (three cases). Within the first two years, two teeth required endodontic treatment, but the inlays remained in situ. A survival rate of 90.4 per cent after ten years was calculated (Kaplan-Meier method), after evaluating all failures due to technical and anatomical conditions. Restorations in premolars performed somewhat better than those in molars. That fractures in this study usually occurred at the thinnest part of the inlay (isthmus fracture) indicates that the minimum ceramic thickness of 1.5 mm must be maintained.

The adhesive technique, consistently used here, proved to be sufficient, given a CEREC 1 adhesive joint of 150 μm. Twenty seven per cent of the patients reported post-insertion discomfort (pressure pain), but this soon disappeared. With the introduction of functional dentin adhesives, which were not available at the beginning of the study, bite-down oversensitivity ceased to occur. After ten years of service, it was already possible to show that CEREC restorations had at least met the survival probability of cast fillings, and were thus comparable to the ‘gold standard’.


Figs. 2 & 3: Survival rates of 1- to 4-surface restorations, after an observation period of up to 17 years, showing no significant differences between them (Fig. 2). Survival rates in molars and premolars, with CEREC restorations in premolars exhibiting a higher success rate (Fig. 3).

Otto’s longitudinal study with an up to 17-year observation period demonstrates a survival rate of 88.7 per cent for the 187 restorations, after an average of 15 years service time—i.e., the annual loss rate was 0.75 per cent. Failures with Charlie and Delta scores (USPHS), most of which were due to ceramic fractures, arose between the 6thand 13th years of service. This markedly exceeds the survival probability of laboratory-made ceramic inlays, and is on about the same level as alternative long-term restorations, such as cast gold inlays, which showed a survival rate of 87 per cent and an annual loss rate of 0.7 per cent after 20 years.2

A comparison of the 166 clinically-intact CEREC inlays in Otto’s study with the baseline 200 restorations in 1991, shows a success rate of 83 per cent after an average of 15 years of service. This survival rate exceeds that quoted by Smales for cast inlays after 15 years by a 1.5 per cent loss per year3 and a 1.3 per cent annual failure rate for all-ceramic inlays not produced using CAD/CAM methods.4

Twenty-one restorations in 17 patients were no longer clinically intact. The reasons were ceramic fractures (62 per cent) and tooth fractures (14 per cent). The remaining failures were based on recurrent caries (19 per cent) and endodontic events (5 per cent). Restorations in premolars exhibited a slighter risk of loss than those in molars.

These results are partly attributable to the fact that the ceramic inlays were manufactured chairside, without temporary restorations, and inserted in one session. With conventional laboratory-made restorations, however, a temporary is unavoidable. The temporary, non-adhesively luted restoration lies in the cavity like a wedge, and transfers the unbuffered masticatory forces directly to the weakened remaining tooth structure. Without intimate contact between the temporary and the hard dental tissues, the cavity walls lack stabilisation for several days. Through the chewing pressure, the temporary restoration is subject to torsion, due to the low E-module of the composite. The result is an uneven distribution of stress with peaks at the tooth-temporary restoration interface.

The introduced force also deforms poorly protected cusp walls and can initiate partial fractures and enamel margin cracks. In contrast, the immediate insertion of a CEREC inlay provides a contamination free, adhesive bond to the hard dental tissue, and stabilises weakened cusps. The stabilising effect on the remaining tooth and the attainable adhesive bond apparently offset the consequences of wider adhesive joints, as shown by long-term clinical results.5

Another long-term study on the longevity of CEREC restorations was published by Reiss in 2006. In private practice, 299 patients received 1,010 CEREC inlays and onlays chairside. After 15 to 18 years of service, 84.4 per cent of the restorations were still clinically perfect. By the end of the study period, at 18.3 years, no further events had been observed. When the study began, dentin adhesives were not yet available. If the patients in the study are separated into those treated with and without dentin adhesives, the influence of these materials becomes apparent. Without dentin adhesives, the survival rate after 16 years dropped to 80 per cent; when dentin adhesives were used, the survival rate rose to 90 per cent.6

Similar results were reported by Arnetzl. Between 1988 and 1990, he adhesively inserted 358 2- and 3-surface inlays made of Dicor, Optec, Hi-Ceram, Duceram, and CEREC 1 (Mark I). The control group consisted of cemented gold inlays. After 15 years, CEREC and gold achieved a survival rate of 93 per cent, which differed significantly from the laboratory-made, sintered ceramic inlays with a failure rate of 32 per cent.7,8

In a review of the literature from the past ten years, Hickel and Manhardt calculated the annual loss rate of restorative materials for Class I and II cavities. Their results showed that, compared to cast gold fillings, CEREC restorations had up to 25 per cent fewer failures.9

Posselt and Kerschbaum published an interesting study from private practice10, in which 2,328 CEREC restorations in 794 patients were examined. The survival rate after nine years was 95.5 per cent. Restoration size, tooth vitality, CP treatment, tooth type, and filling location (maxilla vs. mandible) all had no significant influence on the prognosis of success. The most frequent reasons for failure were tooth loss via extraction (22.9 per cent) and fractures (17.1 per cent).

In a meta-analysis, the clinical survival probability of high-quality, conservative types of restorations was examined as well as the costs for their manufacture. The highest success rates were achieved by gold inlays and CEREC inlays. A comparison of economic efficiency and longevity demonstrated the superior performance of CEREC restorations; the higher cost price of gold inlays places the cast restorations second.11

In the past, numerous CEREC studies have repeatedly shown that ceramic inlays and onlays manufactured chairside at least match the clinical survival rate of cast gold restorations. Now, the most recent clinical long-term results prove that CEREC restorations are in the forefront.

Editorial note: A complete list of references is available from the publisher. This article was originally published in Cosmetic Dentistry Vol. 2, Issue 4, 2008.

Contact info

Dr Wilhelm Schneider
Bachwiesenstrasse 2
60599 Frankfurt/Main
Germany

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