Comparison of the accuracy of denture bases by a non-parametric method

Accuracy of adaptation of thermoformed poly(methyl methacrylate)

Thermoformed poly(methyl methacrylate) (PMMA) sheet is used to produce a number of different dental appliances such as stents, occlusal splints and baseplates for occlusal rims. The purpose of the present study was to measure the accuracy of adaptation of Perspex PMMA sheet and to determine the effect of annealing on the accuracy of the thermoformed specimens. The results of the study showed that PMMA can produce specimens that are accurately adapted to the cast. Immersion in water resulted in an increase in the space between the cast and the specimen for both thermoformed and thermoformed and annealed acrylic resin. Annealing of the thermoformed specimens had significantly less increase in space between the cast and the specimens when immersed in water over a period of 3 months.

Effects of relining on long-term marginal stability of provisional crowns

Provisional resins crowns are commonly placed to protect prepared teeth, but the marginal adaptation of interim crowns has always been a problem. These experiments examined the effects of thermocycling and occlusal loading on relined and unrelined polymethyl methacrylate resin transitional crowns. Three groups of interim crowns were made on a cast metal die tooth preparation; unrelined, relined correction, and paint-on correction. After thermocycling and occlusal loading of the specimens, the change in mean marginal gap was significantly greater for the unrelined group. Axial changes were greatest for relined group and least for the unrelined group. These results suggested that relining of polymethyl methacrylate interim crowns can be useful to prevent increases in marginal gap width during extended intraoral periods.

Measurement methods used for the determination of dimensional accuracy and stability of denture base materials

The literature relating to methods of measurement of dimensional accuracy and stability of denture base materials is reviewed. The papers are presented chronologically together with information on the measurement technique used and the reported level of accuracy. Most authors utilized optical measuring apparatus, with the use of calipers being the second most popular method.