Objectives:  Hand mixing of cements results frequently in incorrect mixing ratios. There is few knowledge how incorrect mixing ratios influence the cement properties.

Methods: The resin-modified glass ionomer cement Meron Plus (Voco, Cuxhaven, G) was mixed by hand and respectively by an automatic capsule system. The following mixing ratios were used: a) recommended powder/liquid ratio: 1:1.8, b) 1:1.6, c) 2:1. The flexural strength was determined using a three-point bending test (after 24hr), wear was evaluated with a three-body abrasion device, and the Vickers hardness was determined. Statistical analysis: Mean, std. dev., one-way ANOVA.

Results:

Automatic Mixing Capsule	Flexural strength [N/mm2]	Wear- [μm] 5*104 cycles..	Vickers hardness [HV]	Mixing per hand	Flexural strength [N/mm2]	Wear- [μm] 5*104 cycles..	Vickers hardness [HV]
2:1	57.7±2.7	155.3±13	29±.1	2:1	52.2±2.6	178.9±10	27±2
1:1.8	48.9±2.8	159.3±14	28.9±	1:1.8	47.2±1.9	164.5±12	28±0.4
1:1.6	43.4±1.7	157.5±6	29.4±1.5	1:1.6	43.0±2.1	211.8±14	23.3±0.1

The flexural strength values depend on the powder content. The more powder the higher was the flexural strength. The Vickers hardness did not vary with the chosen mixing ratios. Only wear of hand mixed specimens for the 1:1.6 ratio was significantly higher than wear of the other groups.

Conclusions: If the mixing ratios did not surpass the level of 1:1.6 up to 2:1 powder/liquid a remarkable change of the cement properties must not be expected. The hand mixed blends of this cement had a wide therapeutic range and their properties were comparable to those of the automatic mixing capsule system.

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