A modified dilatometer for determining volumetric polymerization shrinkage of dental materials

Abstract

A modified mercury dilatometer is described where any change in the volume of the sample is registered every 0.5 s as a change of the mercury height in the capillary, which is measured electronically instead of by the naked eye. The device is relatively low in cost and enables measurements to be made on samples regardless of their shape or size. Four different light-curing dental materials - Amelogen (Ultradent Dental Products, South Jordan, UT, USA), Z250 (3M/ESPE, Minneapolis, MN, USA), Permaflo (Ultradent) and Filtec flow (3M/ESPE) - were initially tested. From the results it was concluded that with this modified dilatometer reproducible measurements, with a measurement error (residual standard deviation) of less than 0.027% and an average coefficient of variation of less than 1.22%, could be obtained. Thus, the instrument is particularly suitable for the study of light-curing dental resins.

Volumetric change of flowable composite resins due to polymerization as measured with an electronic mercury dilatometer

“…The bulk fill flowable composites consisted of Smart Dentin Replacement (SDR) by Dentsply/Caulk (Milford, Germany), Venus bulk fill by Haraeus Kulzer (Hanau, Germany), Filtek bulk fill flow by 3M ESPE (Massachusetts, USA) and Xtra base bulk fill flowable by Voco (Cuxhaven, Germany). Volumetric change was measured with a specially designed electronic mercury dilatometer (Figure 1) [15] .The volumetric change due to polymerization in the dental resin material is measured as a voltage change by a pressure sensitive transducer. An analog to digital converter creates data that is transmitted from the pressure sensor to RS232 format -where the computer creates a graph of volumetric change in Microsoft Excel, From the data collected every 0.5 seconds over the 35 seconds from the curing light irradiation period the graph has time in seconds on the X-axis and the percentage of volumetric change on the Y-axis.…”

“…Various techniques are available to measure the volumetric change which occurs during irradiation with a curing light [12][13][14][15]. An electronic mercury dilatometer proved to be accurate in measuring polymerization shrinkage [1,[12][13][14][15][16][17][18]35,39].…”

“…An electronic mercury dilatometer proved to be accurate in measuring polymerization shrinkage [1,[12][13][14][15][16][17][18]35,39]. The volumetric shrinkage measured by the electronic mercury dilatometer is linear and the volumetric change is measured as the total percentage shrinkage that occurred between the preand post-gel phases.…”

“…A disadvantage with the utilization of dilatometers is that they are extremely sensitive to variations in temperature [14,19]. Oberholzer et al, [15] described a specially designed electronically controlled mercury dilatometer which measured change in volume of the sample every 0.5 seconds.…”

“…However, the moment the resin material became rigid, the internal stresses and polymerization stress started to increase [8,20]. It has been established that exposures not higher than 500 mW/cm², were able to provide a sufficient combination of irradiance and exposure time [15,21]. It was found that conversion rate resulting in carbon double bond formation can range from 55-75% under conventional irradiation conditions of 500mW/cm² [22,23].…”