Objective: The retentive strength of four chemically activated resin cements used for post placement were measured along with their hardness and diametral strength to determine their relationship. A correlation could aid selection and development. Three dual-cure resin cements (not VLC) plus one chemical cured only control cement were used to cement preformed titanium parallel-sided posts.

Material and methods: Sixty human recently extracted premolar teeth were endodontically treated, prepared with a 9 mm deep post-space and randomly divided into 4 test groups (n=15). Parapost XP posts(size5) were cemented using Panavia21(control), PanaviaF, RelyX Unicem and Linkmax resin cements. Dual-cured cement posts were test with no light, 100% humidity, 37^oC (one week) in Instron(.05in./min.). Samples(N=140) were molded for diametral strength and Knoop hardness measurement.

Results: ANOVA and Tukey-Kramer statistical analysis revealed significant differences among the cements. Relyx Unicem(7.6MPa), the most retentive, was not different than Linkmax(6.8MPa)). PanaviaF(4.5MPa) and Panivia21(3.0MPa) had significantly lower retention but were not different. Scatter-plots suggested no correlation.

Conclusions: The dual-curable cements used in the chemical mode had similar or significantly better retention compared to the chemical activated only control resin cement. The data scatter made correlation ineffective. Examination of the post failure surfaces and canals with 40x light microscopy suggested that low retention values for a cement was associated with contamination of canal with gutta percha, larger voids and lack of canal undercut, medium retention was associated with smaller voids and some canal undercut, and higher retentive strength was associated with minimal voids and major coronal canal undercuts as indicated by areas with cement fractured from the post retained in canal undercuts. The increased retention from natural undercuts formed by variation in the lateral width of the canal suggests that prepared undercuts could increase post retention where needed. (Supported by an Alexander Fellowship)

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