Fracture resistance of implant-supported screw- versus cement-retained porcelain fused to metal single crowns: SEM fractographic analysis.
OBJECTIVE
The present in vitro study aimed at evaluating the fracture resistance of both implant-supported screw- and cement-retained porcelain fused to metal (PFM) single crowns. A scanning electron microscope (SEM) evaluation of the mode of failure of the specimens was also performed.


METHODS
Forty PFM premolar-shaped identical single crowns were realized. The restorations were divided into two groups: cement-retained (group 1) and screw-retained (group 2) prostheses. Compressive loading tests and SEM fractographic analyses were performed. The data were statistically analysed by means of the Student's t-test, with a confidence interval of 95%.


RESULTS
The mean fracture load value was 1657 (+/-725) N in group 1 and 1281 (+/-747) N in group 2; the statistical analysis pointed out no significant differences between the two groups (p=0.115). The mean work at maximum load value was 0.775 (+/-0.619) J in group 1 and 0.605 (+/-0.526) J in group 2; the statistical analysis pointed out no significant differences between the two groups (p=0.355). All the samples were affected by cohesive fractures of the porcelain. Screw-retained crowns showed microcracks at the level of the occlusal access to the screw and extensive fractures in the whole thickness of the ceramics. On the contrary, cement-retained restorations were affected by less wide paramarginal fractures of the porcelain.


CONCLUSIONS
A stronger implant-prosthetic connection was noticed in cemented restorations group than in screw-retained single crowns. Even though negatively influenced by the presence of the occlusal access to the screw, the metal-ceramics bond can be considered predictable in both the implant-prosthetic connection systems analysed.
Zarone
Fernando
F
Department of Fixed Prosthodontics, School of Dentistry, University Federico II, Naples, Italy. zarone@unina.it
Sorrentino
Roberto
R
Traini
Tonino
T
Di lorio
Donato
D
Caputi
Sergio
S
D002484:Cementation; D019245:Compressive Strength; D003442:Crowns; D019250:Dental Implants, Single-Tooth; D017268:Dental Prosthesis Retention / Q000295:instrumentation / Q000379:methods*; D019094:Dental Prosthesis, Implant-Supported; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D016876:Metal Ceramic Alloys; D008855:Microscopy, Electron, Scanning
D016876:Metal Ceramic Alloys