Comparison of Thermal Conductivity, Flexural Strength, and Surface Hardness of Alumina Incorporated and Conventional Heat-Activated Denture Base Resins

Introduction: Commonly used polymethyl methacrylate (PMMA) denture base material cannot be considered as ideal due toinferior thermal and mechanical properties.Aim: The aim of the study was to evaluate and compare the thermal conductivity, flexural strength, and surface hardness ofheat cure acrylic resin incorporated with 10 wt.% and 15 wt.% alumina and conventional denture base resin.Materials and Methods: A total of 108 specimens were prepared. Specimens were divided into three main groups. Group Aspecimens were disk shaped (50 mm × 5 mm) and used for measuring thermal conductivity. Groups B and C specimens wererectangular shaped (65 mm × 10 mm × 3 mm) and were used for measuring flexural strength and surface hardness, respectively.Each group was further divided into three subgroups (1, 2, and 3) depending on the concentration, namely, PMMA without filler(control), PMMA + 10 wt.% of Al2O3, and PMMA + 15 wt.% of Al2O3 containing 12 samples each. Thermal conductivity wasmeasured using a modified guarded hot plate apparatus. Flexural strength was assessed with a three-point bending test usinga universal testing machine. Hardness testing was conducted using a Vickers Hardness Tester. The results were analyzedusing one-way ANOVA followed by post hoc comparison by Tukey’s method.Results: Mean values of thermal conductivity were (in W/mK) 0.190, 0.231, and 0.275 for subgroups A1, A2, and A3, respectively.The mean flexural strength values were (in MPa) 56.62, 66.73, and 74.24 for subgroups B1, B2, and B3, respectively. Meanvalues of surface hardness was calculated to be (in HV) 15.17, 16.51, and 17.91 for subgroup C1, C2, and C3, respectively.There was statistically significant improvement in thermal conductivity, flexural strength, and surface hardness after incorporationof alumina and the increase was in proportion to the weight percentage of alumina filler.Conclusion: Incorporation of alumina into heat cure denture base resin significantly improved the thermal conductivity, flexuralstrength, and surface hardness.

An analysis of personnel dose reports in medical radiation occupational workers from an oncology center

Background: To evaluate the risk involved, there is need to know the quantum of personnel exposures in whole service. Dose reports from an Oncology Centre over 7 block periods, 5 years each from 1979 till 2013 are analyzed. Materials and Methods: Personnel monitoring [PM] reports till 1990s with film badges and later thermoluminescent [TL] badges [CaSo4.Dy] were evaluated. 35 years total service was taken to represent total professional service of staff superannuating at age 60 years. Results: Mean personnel equivalent dose for 5 year block period is 3.30+/-0.43 mSv [n=7 blocks]. Maximum dose in any block period was 30-60 mSv. Equivalent doses 22% were zero, 64.3% within 5 mSv. 2.1% were above 30 mSv in 5 year periods. Doses were decreasing order 11.8 mSv [radiopharmaceutical preparation], 4.3 mSv [nuclear medicine], 4.1 mSv [medical physics], 2.2 mSv[brachytherapy]; 1.2 mSv [radiodiagnosis], 1.1 mSv [external beam radiotherapy] and 0.73 mSv [radiation sterilization plant]. Conclusion: The whole body personnel dose in are much lower than recommended annual dose equivalent limits of 100 mSv/ 5 years. The magnitude of recorded doses to staff show that the risk is negligible and the principle of ALARA is being practiced in the work areas

dosimetric study of deep skin electron therapy with overlapping stationary radiation fields - a case report

For radiotherapy of total skin including sub-cutaneous tissue up to a depth of 3 cm on the entire left leg of an adult [Angiosarcoma skin], a complex treatment with multiple stationary electron fields was planned at our clinic. The details of dosimetry, clinical dose measurements are presented. The treatment planned with 6 overlapping 9 MeV electron fields in Clinac 2300CD linac. With 25x25 cm cone, a cut-out insert provided 56 × 30 cm field at FSD 213 cm, while patient lying on the floor. Dose distributions were checked using Kodak V densitometric film in cylindrical plastic can phantom. The calibration was carried out using solid water phantom, water equivalent IMRT phantom and water can leg phantom. A dose of 45 Gy in 23 fractions at 5 fractions/week was prescribed. 6 field overlapping field factor was measured by the method described for total body electron irradiation [AAPM]. Skin doses were estimated at random selected points using TLD chips and semiconductor diodes. Measured absorbed doses by three methods were 0.174 cGy/MU, 0.166 cGy/MU and 0.162 cGy/MU agreed well with the calculated value 0.163 cGy/MU. 6 field overlap factor was 2.315. Clinical dose estimates of mean skin dose was 246.0 + 14 cGy [n=18], delivering higher dose by 23%. The gonad dose estimate under shield was <5%. The excess dose to skin delivered in first 14 fractions was adjusted in following 9 fractions. It appears that the excess dose in real situation may be due to either floor backscatter or non uniform overlap of dose from adjacent fields