| At present, all-ceramic restoration has become an important field of prosthodontics to repair one of the ways, because of its good biocompatibility and unique aesthetic effects by patients and doctors of all ages.There are a lot of all-ceramic crown systems for fixed restoration, but systems commonly used clinically at present are the IPS e.max, In-Ceram alumina and Kava Everest. In terms of all-ceramic restoration systems, besides beautiful outlook, clinical evaluation includes strength, marginal fit and so on. At present, as the appearance of new types of ceramic materials, the problems of strength and beautiful outlook are solved more or less, and the key point is marginal fit of the restoration. As for fixed restoration, the marginal fit is very important and the satisfactory marginal fit of a restoration is one of the essential factors for long-term success. Not only the restoration of porcelain fused to metal, but also the ceramic, there are marginal deformations during the manufacture contraction when the ceramic is cooling. In addition, there are errors of the manufacture technology. All these make a blank between the restoration and the tooth. The bad marginal fit results in the accumulation of the dental plaque, outflow of gingival crevicular fluid, microleakage following the loss of the alveolar bone, secondary caries, and periodontal disease. The marginal fit of a restoration means the degree of close together or the size of the blank between the marginal of the restoration and the tooth surface, which is an indefinite concept. There's no unified standard of measuring the marginal fit up to now. Among these, the definitive standard of measuring the marginal fit of Holmes et al is more often cited. They divide the marginal fit into internal gap or marginal gap, horizontal marginal discrepancy, vertical marginal discrepancy, absolute marginal discrepancy, etc. They think the absolute marginal discrepancy the most important, which means the length from the angle of shoulder margin of the die to the tip of margin of the crown, and it synthesizes the marginal gap of both the horizontal and the vertical marginal discrepancy.The largest marginal gap accepted clinically is controversial. ADA suggests that the thickness of cement membrane for gold alloy restoration should be lower than 40μm and Mclean et al recommend 120μm the largest gap accepted clinically. Some researchers think the amplitude of the marginal gap of 100-150μm is accepted clinically ensuring the life of the restoration. Other researchers think the marginal gap of more than 200μm is an unqualified restoration. At present, the mostly used standard in literatures is 120μm.There have been many studies domestically and abroad of marginal gaps of restorations of inlay, porcelain fused to metal, all-ceramic crown, which are of different systems or materials. Among these studies, there hasn't been any report of marginal fit of IPS e.max and Kavo Everest, which are the newest systems of Ivoclar Company. This experiment measures the sizes of the gaps between the restorations and the prepared teeth by bicolor methylsilicone rubber, then compare and evaluate the marginal fit of three commonly used all-ceramic systems (IPS e.max, In-Ceram alumina and Kavo Everest System).One extracted maxillary premolar without caries which is for orthodontic treatment is chosen in this experiment. The tooth is prepared for crown fabrication. The occlusal reduction is 2mm, the cervical reduction is 1mm, a 90°shoulder margin, and a 6°tapered angle pointing to the occlusion. After the preparation, a high polish is done using a polishing bur. A negative impression is made by double impression, and 40 dies of the same size is made by super-hard plaster. The dies are divided into 4groups randomly,Ten crowns are made for each system (porcelain fused to metal, Kavo Everest, IPS e.max, In-Ceram alumina). After the crowns take their places on the prepared tooth in vitro suitably, the measurement of the gaps is done according to the way described by Toshiyuki et al. The methyl silicone rubber of fluid type (Dimension Garant L, 3M ESPE, Seefeld, Germany) is put into the tissue surface of the crown, and then sit on the tooth. A force of 15N is pressed against the occlusion by thumb and forefinger. After the rubber is solidified, a thin rubber membrane is formed between the tooth and the restoration, which represents the gap between the restoration and the tooth and we call it gap model. Then the crown is took off the tooth, the thin rubber is stick to the tooth. Then a methyl silicone rubber of occlusion type (Detaseal bite, Detax, Ettlingen, Germany) is mixed, put into a custom-made tray and taken its place on the tooth again. After the occlusion type is solidified, the two methyl silicone rubbers combine together. Thus the occlusion type occupies the position of the abutment tooth. Then 4 cuts are made at the center margin of buccal, palate, mesial, and distal of the crown. The digital images of margins between the restoration and the shoulder are collected using anatomical microscope, filed, and measured the absolute marginal discrepancy, vertical marginal discrepancy and horizontal marginal discrepancy using an image analysis software. All the data is processed using SPSS 13.0 for statistical analysis.The result shows that the mean values for horizontal marginal discrepancy between 41.1um and 44.9um, and for vertical marginal discrepancy between 51.4um and 71.7um ,for absolute marginal discrepancy between 66.2um and 85.1um. Compared with the control group, the horizontal marginal discrepancy vertical marginal discrepancy and absolute marginal discrepancy of Kavo Everest and IPS e.max system have significant differences (P<0.01).for the In-Ceram the horizontal marginal discrepancy have significant differences(P<0.01).Compared with In-Ceram alumina, Kavo Everst and IPS e max have significant differences (P<0.05). There's no difference between In-ceram alumina and the control group (P>0.05), Kavo Everest and IPS Empress (P>0.05).The following conclusions can be drawn: 1. Compared with porcelain fused to metal, IPS e.max and Kavo Everest System demonstrate a smaller marginal discrepancies. 2. IPS e.max and Kavo Everest System demonstrate a better marginal fit compared with In-Ceram alumina. 3. Horizontal discrepancies were considerably smaller than vertical marginal discrepancies. 4.The horizontal marginal discrepancies,vertical marginal discrepancies and absolute marginal discrepancies of three all-ceramic systems were within the clinically acceptable standard of 120um. |
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