| Porcelain crown and castable ceramic crown have been applied widely on prosthodontic clinic because of its good esthetics, wear resistance and biocompatibility. But it is suseptible to failure from peri-odontitis, root surface caries, and secondary tooth cracks when subjected to marginal gap. Some patients with full ceramic crown have suffered from the defect and the phenomenon is a focus among dentists. Porcelain technologys and materials have made quickly development in recent years, and the adaptation of full ceramic crown has improved on prosthodontic clinic. But a test on its adaptation is needed. There are many techniques that evaluate the adaptation of all ceramic crowns at present. Our study used ultra low viscosity silicone, color image scanner and computer Photoshop5.0 software to measure the adaptation of porcelain crown and castableceramic crown.SubjectiveStudy the adaptation of porcelain crown and castable ceramic crown, and discuss its clinical feasibility to help us select a better full ceramic crown.Material and methodThe stone die which originated from the castable ceramic crown (Ivoclar Vivadent Int ) of first maxillary premolar was selected for the study. The cavosurface margin was a 90 degree shoulder 1 mm in width for the die. The high silicone impression of the stone die was made and poured with wax . 38 identical wax dies were constructed one by one. Next, 38 plastic dies were replicated from 38 wax dies by means of molding plastic technique . 38 identical plastic dies were separated randomly from two groups. There are 19 plastic dies in each group.A group was selected randomly for castable ceramic crown. Firstly , two coats of die spacer were placed to within 1 mm of the margins on all dies. 19 wax molds of castable ceramic crown were composed on 19 plastic dies to ensure that all wax patterns were accurate. Secondly , these wax patterns were invested in Empress castable ceramic investment. Each wax pattern was burned out in a two step procedure . The first step involved heating to 2501 with a hold time of 30 minutes . The second step involved heating to 950^ for castable ceramic crowns, with a hold time of 60 minutes. The glass was cast at 1360T1 using a casting machine and then bench cooled. The castings were sandblasted with 50fxm aluminum oxide particles, cleaned in an ultrasonic cleaner in distilled water for 15 minutes. Any modules on the inside of the casting were removed with an abrasive stone. Spacer of plastic die was removed with MM A. 19 plastic dies and 19 castable ceramic crowns were marked in the same number.Porcelain crowns were composed with another group . Firstly , 19refractory dies were replicated from the 19 plastic dies, and marked according to the number of plastic die. Secondly, Excelco veneer porcelain was piled up on the processed refractory dies, and burned in vaccum pocelain machine. Lastly, 19 porcelain crowns were removed, cleaned and marked according to its plastic die. The number of them is same.Adaptation testing:38 ceramic crowns were seated separately in their plastic dies with light blue, ultra low viscosity silicone. The silicon was mixed automatically in mixed gun, which stiffed completely two minutes later. The silicone film was drawn from crown and scanned by scanner. The date were analyzed by computer photoshopS. 0 softwear. An F - test was used to compare the variability of two full ceramic crowns.ResultsA statistically significant difference in film thickness was found between porcelain crowns and castable ceramic crowns (p <0. 01). The porcelain crown had significantly better adaptation than castable ceramic crown ( p <0. 01) . The mean film thickness on axis , mesial surface of porcelain crowns were drawn respectively:48. 16um ( s =6. 19um) ; 50.68um (s =5.05Um). And the mean film thickness on axis, mesial surface of castable ceramic crowns were drawn respectively: 70.74um ( s = 8. 43um) ; 101. 37um (s =7. 97um). Q - test was further done to compare each other . No statistically significant difference was fou...
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