The effect of preparation height and luting agent on the resistance form of cemented cast crowns under load fatigue.
BACKGROUND
The minimum amount of resistance form required for the success of a clinical crown is unknown.There is little information on the fatigue performance of complete coverage restorations on natural tooth preparations cemented with different luting cements.


OBJECTIVE
The purpose of this study was to evaluate the effect of tooth preparation height and luting agent on resistance form using unidirectional load fatigue testing. For a given tooth preparation with a clinically relevant total occlusal convergence (TOC), the adequacy of resistance form was investigated.


METHODS
Sixty-four human maxillary premolars were prepared with occlusal-cervical dimensions of 2, 3,4, or 5 mm and a TOC of 20 degrees. Complete metal crowns were cemented using either zinc phosphate cement (HY Bond;ZP groups) or resin cement (Panavia F; PF groups). Cyclic load fatigue testing was done with an applied load of 6.0 kg at 2.6 Hz. Load cycles to preliminary failure were detected with a strain gauge at the palatal crown-tooth interface. Results were subjected to the Kruskal-Wallis test and the Wilcoxon post-hoc rank sum test (alpha=.05).


RESULTS
Groups ZP4, ZP5, PF2, PF3, PF4, and PF5 had the highest mean number of cycles to preliminary failure,while group ZP2 had the lowest mean number of cycles to failure. Group ZP2 was significantly different (P<.001) from all other test groups for the number of cycles to failure.


CONCLUSIONS
For the 2- and 3-mm preparation height groups, zinc phosphate cement exhibited a poorer fatigue performance compared to Panavia F. There was no significant difference in the number of cycles to failure for groups ZP4,ZP5, PF2, PF3, PF4, and PF5. For both cements, the number of cycles to failure increased with increasing resistance length. (J Prosthet Dent 2009;102:155-164)
Leong
Elvin W J
EW
Faculty of Dentistry, National University of Singapore, Singapore. drleong@specialistdentalgroup.com
Choon Tan
Keson Beng
KB
Nicholls
Jack Ivan
JI
Chua
Ee Kiam
EK
Wong
Keng Mun
KM
Neo
Jennifer Chiew Lian
JC
D001641:Bicuspid; D003442:Crowns; D001840:Dental Bonding / Q000379:methods*; D003738:Dental Cements / Q000737:chemistry*; D017005:Dental Debonding; D017268:Dental Prosthesis Retention / Q000379:methods*; D019232:Dental Restoration Failure; D003799:Dental Stress Analysis; D006801:Humans; D018709:Statistics, Nonparametric; D019228:Tooth Crown / Q000033:anatomy & histology; D019231:Tooth Preparation, Prosthodontic / Q000379:methods*; D016474:Weight-Bearing
D003738:Dental Cements