Thermal expansion coefficient of dental composites measured with strain gauges

Objectives. A simple test method was developed to determine the coefficient of thermal expansion of prevailing restorative resin composites and to study the transient behavior as a function of temperature and repeated thermocycles.Methods. Strain gauges were used to determine the thermal expansion for seven commonly used restorative resin composites by measuring the instantaneous strain along with temperature change. The temperature was measured by means of a thermocouple, the tip of which was embedded in the composite. The differences among the test groups were analyzed using ANOVA, followed by Scheffé's multiple comparisons test.Results. The coefficient of thermal expansion determined for the composites tested was: 22.5 ± 1.4 × 10⁻⁶/°C (Z-100), 23.5 ± 1.4 × 10⁻⁶/°C (P-50), 32.6 ± 1.6 × 10⁻⁶/°C (Herculite XR), 34.1 ± 1.8 × 10⁻⁶/°C (APH), 35.4 ± 1.4 × 10⁻⁶/°C (Conquest), 41.6 ± 1.5 × 10⁻⁶/°C (Silux Plus), 44.7 ± 1.2 × 10⁻⁶/°C (Heliomolar). The coefficient was almost linear in the considered temperature range (26–75°C) for all composites (r > 0.99) and decreased with each consecutive thermocycle (p < 0.1).Significance. Thermally induced loads, introduced into restored teeth by the mismatch of the coefficient of thermal expansion of the tooth and the restorative material, may be related to microleakage and wear problems. A highly filled hybrid composite such as Z-100 had a coefficient of thermal expansion closest to that of the tooth crown, confirming other studies which demonstrated the benefits of high filler loading in matching the properties of the dental hard tissues.     

Patients’ attitude towards residents’ participation during gynaecological surgery

Objective

To evaluate patients’ attitude towards participation of residents in training in gynaecological surgery and patients understanding of resident position.

Study design

An observational survey study was performed between July and February 2007-2008 in an outpatient clinic of a department of obstetrics and gynaecology of a teaching hospital. Patients planned for gynaecological surgery were concerned eligible. 247 questionnaires were handed out of which 204 were returned (response rate 82.6%). Primary outcome measure was level of confidence in a resident performing hysterectomy in various operative settings. Secondary, patients’ understanding of the medical education system was tested.

Results

There was no difference between confidence in a specialist performing a hysterectomy compared to an experienced resident considered competent and under supervision of a specialist. Respondents have significantly less confidence in less experienced residents operating under supervision and in all residents operating without supervision (P < 0.001). From the respondents, 85.6% believes a resident in training has received less education than a resident not in training. 38.6% believes a resident received less training than a medical student. Statistical analysis was done in SPSS 16.0 (SSPS Inc., Chicago, IL, USA) using a Wilcoxon signed-rank test.

Conclusions

Respondents have confidence in a resident in training performing an operation under supervision when it concerns an experienced resident that is considered competent. A majority of respondents does not understand the position of a resident in training. Patient education on resident participation should be improved and the certainty that an operating resident is competent should be emphasized.     

Diffusion‐prepared stimulated‐echo turbo spin echo (DPsti‐TSE): An eddy current‐insensitive sequence for three‐dimensional high‐resolution and undistorted diffusion‐weighted imaging

In this study, we present a new three‐dimensional (3D), diffusion‐prepared turbo spin echo sequence based on a stimulated‐echo read‐out (DPsti‐TSE) enabling high‐resolution and undistorted diffusion‐weighted imaging (DWI). A dephasing gradient in the diffusion preparation module and rephasing gradients in the turbo spin echo module create stimulated echoes, which prevent signal loss caused by eddy currents. Near to perfect agreement of apparent diffusion coefficient (ADC) values between DPsti‐TSE and diffusion‐weighted echo planar imaging (DW‐EPI) was demonstrated in both phantom transient signal experiments and phantom imaging experiments. High‐resolution and undistorted DPsti‐TSE was demonstrated in vivo in prostate and carotid vessel wall. 3D whole‐prostate DWI was achieved with four b values in only 6 min. Undistorted ADC maps of the prostate peripheral zone were obtained at low and high imaging resolutions with no change in mean ADC values [(1.60 ± 0.10) × 10^?3 versus (1.60 ± 0.02) × 10^?3 mm²/s]. High‐resolution 3D DWI of the carotid vessel wall was achieved in 12 min, with consistent ADC values [(1.40 ± 0.23) × 10^?3 mm²/s] across different subjects, as well as slice locations through the imaging volume. This study shows that DPsti‐TSE can serve as a robust 3D diffusion‐weighted sequence and is an attractive alternative to the traditional two‐dimensional DW‐EPI approaches.     

Monodisperse Versus Polydisperse Ultrasound Contrast Agents: Non-Linear Response,Sensitivity, and Deep Tissue Imaging Potential

It has been proposed that monodisperse microbubble ultrasound contrast agents further increase the signal-to-noise ratio of contrast-enhanced ultrasound imaging. Here, the sensitivity of a polydisperse pre-clinical agent was compared experimentally with that of its size- and acoustically sorted derivatives by using narrowband pressure- and frequency-dependent scattering and attenuation measurements. The sorted monodisperse agents had up to a two-orders-of-magnitude increase in sensitivity, that is, in the average scattering cross section per bubble. Moreover, we found, for the first time, that the highly non-linear response of acoustically sorted microbubbles can be exploited to confine scattering and attenuation to the focal region of ultrasound fields used in clinical imaging. This property is a result of minimal pre-focal scattering and attenuation and can be used to minimize shadowing effects in deep tissue imaging. Moreover, it potentially allows for more localized therapy using microbubbles through the spatial control of resonant microbubble oscillations.