ABSTRACT
Aim : To measure the impact strength of denture base resins polymerized using short and long curing cycles by water bath, pressure cooker and microwave techniques. Materials and Methods: For impact strength testing, 60 samples were made. The sample dimensions were 60 mm × 12 mm × 3 mm, as standardized by the American Standards for Testing and Materials (ASTM). A digital caliper was used to locate the midpoint of sample. The impact strength was measured in IZOD type of impact tester using CEAST Impact tester. The pendulum struck the sample and it broke. The energy required to break the sample was measured in Joules. Data were analyzed using Student's " t" test. Results: There was statistically significant difference in the impact strength of denture base resins polymerized by long curing cycle and short curing cycle in each technique, with the long curing processing being the best. Conclusion: The polymerization technique plays an important role in the influence of impact strength in the denture base resin. This research demonstrates that the denture base resin polymerized by microwave processing technique possessed the highest impact strength.
ABSTRACT
Background : Though acrylic resins possess many desirable properties, denture fracture due to flexural fatigue or impact failure is a common problem. One major factor influencing the flexural fatigue strength of denture base resins is the processing technique used. Aim: To measure the flexural fatigue strength of denture base resins polymerized using short and long curing cycles using water bath, pressure cooker, and microwave polymerization techniques. Materials and Methods: Flexural fatigue strength of 60 samples (n=10) were measured using a cyclic 3-point loading method on a dynamic universal testing machine. Data were analyzed using a Student 't' test. Results : Comparative evaluation using Student's 't' test of mean flexural fatigue strength of samples processed by water bath processing (660.6) and the microwave technique (893.6) showed statistically significant (P <0.01) result with microwave processing being higher. Comparison of water bath (660.6) and pressure cooker (740.6) processing and microwave (893.6) and pressure cooker (740.6) processing using Student's 't' test was not statistically significant (P >0.05). In the intra-group analysis, it was found that there was statistically significant difference in samples processed using the short and long curing cycle, the latter being better in all groups, P-values being <0.05, <0.001, and <0.001 for water bath, microwave, and pressure cooker polymerization techniques, respectively. Conclusion : The polymerization procedure plays an important role in influencing the flexural fatigue strength of denture base resins, and the microwave long curing processing technique produced denture bases with highest flexural fatigue strength.
Subject(s)
Acrylic Resins/chemistry , Acrylic Resins/radiation effects , Dental Materials/chemistry , Dental Materials/radiation effects , Dental Stress Analysis/instrumentation , Denture Bases , Elastic Modulus , Humans , Materials Testing , Methylmethacrylate/chemistry , Methylmethacrylate/radiation effects , Microwaves , Pliability , Polymerization , Polymethyl Methacrylate/chemistry , Polymethyl Methacrylate/radiation effects , Pressure , Stress, Mechanical , Time Factors , Water/chemistryABSTRACT
A prospective study of 76 consecutive patients over the age of 40 years, with exudative pleural effusion, was undertaken to determine the common causes of such a clinical condition. Malignant pleural effusions were the most common in this series, found in 49 patients (64.47%), all but one being metastatic from elsewhere. Forty were secondary to a carcinoma of the bronchus, 3 from carcinoma of the breast, 1 each from carcinoma of the ovary, oesophagus, and larynx; lymphoma accounted for the remaining 2. Infective causes accounted for 24 of the effusions (31.57%). Of the infections, tuberculosis was the most common, accounting for 17 of the 24. Other infective causes included bacterial empyemas in 4, ruptured amoebic liver abscess in 2, and actinomycosis in 1. Pancreatitis, pulmonary thromboembolism, and a post-cardiotomy syndrome were diagnosed in 1 patient each, while the diagnosis remained unknown in the remaining 5 patients. In 2 patients the diagnosis was made on autopsy.