Characterising a novel alginate dental impression material with antibacterial activity

Objectives:

To develop a low-pH, antibacterial alginate dental impression material and characterise its physico-mechanical properties.

Methods:

A low-pH alginate (F1) was formulated by substituting cross-linking agent magnesium oxide (MgO) with diatomaceous earth and compared with commercial material Neocolloid (Zhermack) (CMN) for Shore A hardness, pH, tear energy and weight change in air (n=6 in all cases; all experiments carried out at room temperature, RT).   

A control material including MgO (F1c) was also included for antimicrobial experiments: materials were inoculated with approximately 1.5x10⁶ bacterial cells, incubated for 2 hours at RT and the number of surviving bacteria determined. Bacteria tested included Staphylococcus epidermidis, Escherichia coli, Streptococcus salivarius and Streptococcus mutans.

Results:

Final mean Shore A hardness was 34.1 for CMN and 31.3 for F1. An initial decrease in pH was followed by an increase to a final mean pH of 9.45 at 60 minutes for CMN compared with a decrease to 3.93 with F1. Maximum mean weight change observed in air was 4.91% for CMN and 4.51% for F1. The mean tear energy (J/m²) for CMN was 275 and 297 for F1.

Reduction in bacterial numbers (log₁₀) were : < 0.50 for S. epidermidis on control materials compared with > 3.36 on F1; 1.14-1.35 for S. salivarius on control materials compared with 2.63 on F1; < 1.00 for S. mutans on test and control materials and < 1.02 for E. coli on control materials compared with 1.69 on F1.

These preliminary data show that considerably greater antibacterial activity was achieved with F1 than with CMN and F1c under the experimental conditions.

Conclusion:

A low-pH alginate impression material exhibiting antibacterial activity has been developed with physico-mechanical properties comparable to a commercial material.

This research was funded by the Engineering and Physical Sciences Research Council (grant number EP/H020888/1).