J.W. Farah

Stress Analysis of a Tooth Restored with a Post and Core

An idealized axisymmetric finite element model of a second premolar restored with a post and core was used to study the distribution and magnitude of stresses as a function of the following parameters : the diameter of the post, the length and the shape of the post, and finally the interface characteristics between post and cement. Emphasis was directed toward the cement layer interposed between the post and the tooth. Bonding between the post and the cement appeared to be the most important parameter to achieve optimal mechanical behavior of the tooth-prosthesis combination.

Effects of Cement Bases on the Stresses in Amalgam Restorations

A computerized dental model was used to study the stress induced in a Class 1 amalgam restoration when supported by bases of varying materials and thicknesses. Under the same load, the maximum tensile stresses and deftections in the amalgam restoration increased at least threefold with a zinc oxideeugenol base as compared with a ZnPO 4 cement base.

Finite Element Stress Analysis of a Restored Axisymmetric First Molar

A first molar with full crown preparation and three marginal configurations-chamfer, chisel, and shoulder with a bevel-was analyzed by the finite element method. The maximum, minimum, and shear stresses were plotted as a function of the radius along various horizontal planes. The chamfer geometry exhibited the most uniform stress distribution.

Effects of Cement Bases on the Stresses and Deflections in Composite Restorations

A model was used to show that tensile and shear stresses can occur in sufficient magnitude to cause failure in a cement base supporting a composite material in a posterior Class I restoration. Highest values of stress were observed when lining materials with a low modulus were used.

Apparent Modulus of Elasticity of Dental Amalgams

The modulus of elasticity of dental amalgam has been determined by analysis of creep data (OGLESBY ET AL, J Res Natl Bur Stan 72C: 203, 1968) and by ultrasonic methods (DICKSON and OGLESBY, J Dent Res 46: 1475, 1967; HALL ET AL, J Dent Res 52: 390, 1973) to be between 63,000 and 70,000 MN/m2. These values represent the instantaneous elastic compliance term when dental amalgam is treated as a viscoelastic material. It is convenient, however, to approximate the behavior of dental amalgam as elastic in experimental stress analysis models. Thus, an apparent modulus of elasticitv (E) can be determined by measurement of the slope of a stress-strain curve in compression at a given loading rate. Values of E determined in this manner for conventional dental amalgams at the one-week period were from 9,660 to 12,400 MN/M2 within a stress range from 34.5 to 172 MN/M2 at a loading rate of 0.008 cm/min (TAYLOR ET AL, J Dent Res 28: 228, 1949). Values of El and compressive strength (S) were determined for five dental amalgams at 24-hour and one-month periods. Cylindrical specimens were prepared, using the procedure described in American Dental Association Specification no. 1 (Guide to Dental Materials and Devices, 1975),

Stress Analysis of Three Marginal Configurations of Full Posterior Crowns by Three-Dimensional Photoelasticity

A simplified method was developed by which three-dimensional composite photoelastic models were constructed. The optimum marginal configuration for the stress distribution was determined and was found to be of the chamfer type.

Reflection Photoelastic Stress Analysis of a Dental Bridge

The stress distribution on the surface of a four unit gold bridge was determined by reflection photoelasticity. The highest stress concentration was at the soldered joints. The distribution of stress was a function of the support of the abutment teeth. Good support caused the bridge to function as one that was fixed at both ends, whereas poor support caused it to function as a cantilever beam.

Effect of Cement Base Thicknesses on MOD Amalgam Restorations

The effect of five cement bases on the fracture strength of three amalgams was determined at 24 h after condensation. It was found that the type of base used was the most important factor in affecting the fracture strength of the amalgam, followed by the thickness of the base, and finally the type of amalgam that was used.

Stress Distribution in Photoelastic Models of Transverse Sections of Porcelain-Fused-to-Gold Crowns and Preparations

The stress distribution in composite photoelastic models of transverse sections of porcelain-fused-to-gold restorations and preparations was determined. The optimum design was one in which the porcelain-gold junction was on the lingual side of contact points that represented the contact of adjacent teeth.