Encapsulated verses hand-mixed zinc phosphate dental cement

Zinc phosphate cements are commonly supplied as two components, powder and liquid, and the proportions of the constituents are determined by operator experience. A capsulated system which is mechanically mixed has been market ed and this study investigated the performance of the encapsulated cement s ystem. The mean fracture strength, standard deviation and associated Weibul l Moduli (m) of encapsulated cements were determined by compressive fractur ing 20 cement specimens filled directly from the mixing syringe or from nar rower cement tubes. Pore distribution within the cylindrical specimens was determined using image analysis to assess the influence of the method of mo uld filling with the cement. The strength data showed variation in magnitud e and consistency ranging from 44.6 +/- 13.7 MPa (m = 3.18 +/- 0.71) for ce ments filled directly from the syringe to 61.0 +/- 7.8 MPa (m = 8.35 +/- 1. 87) for cements filled from cement tubes. Larger pores were found in specim ens consolidated directly from the cement syringe. Mechanical mixing of the encapsulated cement resulted in air entrapment in the cement mix which man ifested itself as large pores (over 200 mu m diameter) within the cylindric al specimens. The smaller orifice of the cement tube compared with the syri nge was considered to be responsible for eliminating the majority of the ai r entrapped in the cement mass during mixing. Whilst mechanical mixing of e ncapsulated cements is quicker and more convenient, the encapsulated specim ens consolidated according to the manufacturers instructions from the syrin ge offered no significant advantage in terms of reliability or strength ove r hand-mixed cements in this investigation. (C) 1999 Elsevier Science Ltd. All rights reserved.