ABSTRACT
This study was conducted to determine the effect of varying curing conditions on the residual monomer concentrations of heat cure acrylic denture resin
Sixty-four disc shaped acrylic resin specimens were processed at four powder-liquid ratios [2.22, 2.00, 1.80 and student-ratio] and cured in a heated water bath using 4 different curing regimes [two with a terminal boil and two without]. The residual monomer concentrations were determined at intervals of 24, 48 and 72 hours using a UV Spectrophotometer
The results indicated a decrease in residual monomer concentration with storage time. Group 4 [student-ratio] and curing by cycle 2B [placing the assembly in the water bath directly at 100°C] showed the highest overall residual monomer concentrations while group 1 [highest powder-liquid ratio] and curing by cycle 1A showed the least overall residual monomer concentrations It was concluded that students dispensing acrylic powder and liquid monomer without calculations would lead to higher residual monomers if a proper curing regime is not followed. Using a 60 minute terminal boil in the polymerization process is strongly recommended. Storing the acrylic denture bases for at least 24-48 hours in water before use will decrease residual monomers being leached into the oral environment
Subject(s)
Dental Materials , Dentures , Polymethyl Methacrylate , Self-Curing of Dental Resins , Hot TemperatureABSTRACT
Objective of the study was to determine the effect of varying powder liquid ratios and curing conditions on the residual monomer concentrations of heat cure acrylic denture resin. Sixty four disc shaped acrylic resin specimens were processed at four powder-liquid ratios [2.22, 2.00, 1.80 and student-ratio] and cured in a heated water bath using 4 different curing regimes. Curing cycles 1A and 1B initiated curing of specimens at room temperature followed by a terminal boil for 60 and 30 minutes respectively. Cycles 2A and 2B initiated curing at 70°C and 100°C respectively, without any terminal boil. The residual monomer concentrations were determined at intervals of 24, 48 and 72 hours using a UV Spectrophotometer.Regression analysis indicated a moderately strong negative correlation [-0.515] between time and residual monomer concentration which suggests residual monomer concentration decrease with storage time. Group 4 [student-ratio] and curing by cycle 2B [placing the assembly in the water bath directly at 100 degree C] showed the highest overall residual monomer concentrations while group 1 [highest powder-liquid ratio] and curing by cycle 1A showed the least overall residual monomer concentrations. Independent t tests between groups however revealed mean residual monomer concentration of samples cured by cycle 2B [0.32 +/- 0.38] to be greater than the mean [0.06 +/- 0.07] of samples cured by Cycle 1A [p value= 0.02] suggesting that cycle 1A will produce less residual monomers irrespective of the powder-liquid ratio.It was concluded that students dispensing acrylic powder and liquid monomer without calculations would lead to higher residual monomers if a proper curing regime is not followed. Using a 60 minute terminal boil in the polymerization process is strongly recommended. Storing the acrylic denture bases for at least 24-48 hours in water before use will decrease residual monomers being leached into the oral environment
ABSTRACT
The objective of this study was to investigative the influence of high insertion torques on the stress distribution around dental implants with variations in thread pitch and reductions in buccal cortical bone thickness. Two bone level dental implants [3.8mm and 5.0mm diameters and a standard length of 10mm] were modeled each having a thread pitch of 0.4mm and 0.65mm. Each implant was placed in two mandibular bone segments having buccal cortical bone thickness set at 2.0mm and 1.5mm. A total of 8 such models were created and discretized with hexahedral mesh elements with an average element size of 0.2mm. Implant-bone interface was simulated with non-linear contacts and friction. Static torque values from 50Ncm to 90Ncm were applied with an increment of 5Ncm on each fully inserted implant. Maximum von-Mises along with maximum frictional stresses were used to record stress distribution within each model. Maximum stresses seem to follow a linear relation with insertion torque showing an over-all increase in stress magnitudes with 1] a reduction in the diameter of the implants 2] decrease in thickness of the buccal cortical bone and 3] decrease in pitch of the dental implant threads from 0.65mm to 0.4mm. The maximum stress of 171.4 MPa was recorded at 90 Ncm for the 3.8mm diameter implant adjacent to a buccal bone thickness of 1mm with a thread pitch of 0.4mm. With an increase in insertion torque there is a corresponding increase in the magnitude of stress production. Maximum stresses are primarily distributed in the peri-implant region in particularly the buccal cortical bony plates. The use of profile drills to coronally flare the osteotomy especially in dense bone is highly recommended if the diameter of the final widening drills to place progressively tapered implants is narrower as compared to the diameter of the implants at the neck
ABSTRACT
Connecting implants to natural teeth as a prosthetic treatment design for the restoration of partial edentulism has been subjected to significant clinical considerations. Several studies have reported complications associated with Tooth and Implant Supported Prosthesis [TISP], while others have shown favorable outcomes. The use of TISP had been discouraged previously due to the difference in the mobility patterns of implant and teeth which can subject the prosthesis to increased stresses potentially leading to failure. However, the complications associated with TISPs seem to have been overstated. This article reviews animal studies as well as human clinical trials over the past 25 years, which have shown favorable results with TISPs. The article also discusses the questionable data which has discouraged the use of TISP. Guidelines which would aid in attaining predictable service life and fewer complications with TISPs have also been mentioned
ABSTRACT
As a consequence of dental implant treatment being considered effective, safe and predictable they are now a preferred solution for those who have lost teeth due to dental caries, periodontal disease, injuries or other reasons. The biomechanical performance of implants cannot be proven or tested in vivo due to difficulties in assessing or quantifying the level of osseointegration, the stability of the implant and various other factors. Finite element analysis [FEA] has been used extensively to examine intractable and inaccessible interfaces of the dental implant assembly and to predict biomechanical performance as well as the effect of clinical factors on implant success. Although an in depth under-standing of the theory, method, application and limitations of FEA in implant dentistry will help the clinician to interpret results of FEA studies and extrapolate these results to clinical situations, this article explains the basic practical steps involved in the utilization of FEA from a viewpoint of a researcher interested in conducting studies in dental implantology