Properties of Various Mixing Ratios of Carboxylate Cements

Properties of various mixing ratios of carboxylate cements

Objectives:  Hand mixing of luting agents may result in incorrect mixing ratios. The knowledge is poor how carboxylate cements react if mixed with aberrant mixing ratios.

Methods: Basing on the recommended powder/liquid ratio, mixings with 25% and 50% too much and too few powder/liquid ratio were carried out. Vickers hardness (VH) (after 24hr) and three-body abrasion were evaluated. Scanning difference calorimetry showed the enthalpy changes of the set cements depending on the mixing ratio. Statistics: Mean, std. dev., ANOVA.

Results:

powder / liquid	Aqua-lox	VH	wear [µm]	Car- boco	VH	wear [ym]	Durelon	VH	wear [ym]
50% less	2.7:1	7.7 ±1.0	220.7±50	1.5:1	10.9±2.5	184.1 ±36	1:1	12.5 ±2.6	112.8±23
25% less	4.1:1	15.2±1.8	134.8±29	2.25:1	18.1±2.8	162.7 ±28	1.5:1	15.9 ±2.5	99.7 ±17
correct	5.5:1	26.8±3.7	88.5 ±24	3:1	24.1±6.2	139.1 ±40	2:1	19.6 ±2.0	76.8 ±11
25% more	6.9:1	37.9±4.6	78.7 ±10	3.75:1	27.1±5.6	154.1 ±26	2.5:1	26.2 ±2.1	66.6 ±14
50% more	8.3:1	41.4±3.3	62.6 ±15	4.5:1	29.8±6.2	143.4 ±33	3:1	29.2 ±2.7	57.4 ±11

A twenty five or fifty percent higher liquid content resulted in a significant lower Vickers hardness of all carboxylate cements. Increasing powder content seemed to shift to a saturation concentration, where the hardness could not be increased. This effect was particulary shown for Carboco. Durelon show a linear relationship between wear and powder/liquid ratio, while Carboco and particularly Aqualox had an exponentional increase of wear with increasing liquid content.

Conclusions: The mechanical properties of carboxylate cements seemed to be more influenced by too high liquid than by too high powder content. A mixing ratio error of 25 percent and more can significantly influence the mechanical properties.