Properties of encapsulated and hand-mixed zinc phosphate dental cement

Purpose: Dental cements can be supplied as loose powder and liquid or as encapsulated syringes. This study assessed the compressive strength of a recently marketed zinc phosphate encapsulated cement compared with a hand-mixed system according to the American Dental Association Specification. Materials and Methods: The mean fracture strength, standard deviations and associated Weibull Moduli (m) of the encapsulated and hand-mixed cements were determined by compressive fracturing 30 cylindrical specimens (height 6.0 +/- 0.1 mm, diameter 4.0 +/- 0.1 mm). Scanning electron microscopy was employed to assess crack growth from indentations and cement morphology. Image analysis was used to investigate the influence of mixing regime on pore distribution within the cement samples. Results: The compressive strength data showed variation in magnitude and reliability ranging from 42 8 MPa (m = 5.2 +/- 1.0) for the encapsulated cement filled directly from the capsule to 71 +/- 11 MPa (m = 6.3 +/- 1.3) for the hand-mixed cement. The encapsulated cement matrix was extensively porous, consisting of pores between 0.1-0.5 mum diameter, compared with the non-porous hand-mixed cement matrix. Larger pores (over 18 mum diameter) were related to air entrapment in the encapsulated cement on mixing while small pores (0.1-0.5 mum diameter) were indicative of vaporization porosity commonly seen with exothermic reactions.