Allan Schulman

Comparison of fatigue for three prefabricated threaded post systems

Post designs may have a direct effect on fracture resistance of endodontically treated teeth. This in vitro study compared the resistance of three prefabricated threaded post systems with lateral shearing forces. After endodontics were completed, prefabricated posts were inserted according to the manufacturers instructions. A silver amalgam core was placed, and extracted human teeth were prepared to a standard size with a 1 mm gingival chamfer finished on sound dentino A cast was fabricated and cemented, and the specimens were thermocycled. The test samples were secured to an Instron testing machine and loaded until failure. Fracture patterns were recorded, fractured surface areas were measured, and compressive stresses were calculated. However, there were no statistically significant differences among threaded posts in each test group.

A compressive strength study of an all-ceramic crown

Eighteen crowns were subjected to the same occlusal loading. The porcelain-fused-to-metal crown was more than twice as resistant to the load than the Cerestore crown and almost four times stronger than the porcelain crown. These tests show that porcelain fused to metal has demonstrated its capability as a strong posterior restoration. The Cerestore crown, though superior to the porcelain crown, is significantly less resistant to fracture than the porcelain-fused-to-metal restoration.

A compressive strength study of complete ceramic crowns. Part II

The original study by this group compared the crushing strength of Cerestore crowns with porcelain-fused-to-metal crowns and porcelain jackets. Since that time, two porcelains, Dicor and Renaissance, have become available. This study compares Cerestore, Dicor, and Renaissance crowns using a porcelain-fused-to-metal crown as a standard for the type of crown with maximum strength that is currently available and an all-porcelain crown to represent the porcelain with the least strength. All of the methods used in the first study were used again. The results demonstrated that these new porcelains have strengths that make them questionable for routine use in every posterior crown situation.

Biocompatibility evaluation of casting alloys in hamsters.

A number of base metal and low gold-content alloys were evaluated in hamster cheek pouches for biocompatibility. No adverse weight changes and no abnormal behavioral patterns were noted in any of the test groups over the 14-day period of the study. Gross examination of the cheek pouches containing the alloys was no different from that of the controls. None of the alloys tested showed significant adverse histopathologic reactions. The recorded changes in incidences and degree of response were essentially no different from those of the negative control material.

In vitro tarnish of dental amalgams

1. Tuccillo-Nielsen tarnish test in an effective screening device for dental amalgams. 2. The gamma phase appears to be more tarnish prone in conventional dental amalgams than gamma 1 phase. Although gamma 2 appeared to be tarnish prone, it was difficult to discriminate this phase because of the porosity in the amalgams. 3. The copper-rich phases are the most tarnish prone in high-copper amalgams. Gross examinations of amalgam from additive systems show spotty tarnish, whereas more uniform tarnish appearance is observed in amalgams from single-composition alloys. 4. The amalgams can be graded for in vitro tarnish performance in selected groups like the additive systems and the single-composition alloys.

Flexion characteristics of fixed partial denture frameworks tested by using elapsed-time holographic interferometry

lh fl e exion of a ceramometal fixed partial denture framework under functional loading may cause fracture of the porcelain superstructure.’ The framework must be rigid without compromising biologic and esthetic acceptance. Fixed partial denture frameworks may be made as a one-piece casting (unit-cast) or as two or more units soldered together. The method to be used is usually left to the discretion of the dentist. Some design variables include the type of metal used, the geometry, and location of the solder joint. Although one-piece castings can fit more accurately* or fit as accurately as soldered individual units,) one-piece castings offer no opportunity to verify the fit of individual retainers.’ Because inaccuracy increases as casting length increases,5s6 frameworks larger than three units should be cast in two pieces and soldered.’ Previous testing of the strength of soldered joints was done under tensile loading with the assumption that there is a correlation with the compressive loads experienced in the oral cavity.‘-‘* In this study, using a compressive load, deformation was detected by elapsedtime holographic interferometry,13-‘5 an extremely sensitive tool for identifying stress-induced distortions and nondistorted displacements in the nanometer range. In addition, this method provides a permanent photographic record of the observed results. All results are based on the recorded responses of the prostheses to the same static load exceeding the calculated biting force in the human dentition in the first molar region.16 The properties of laser light allow the optical phenomenon of the interference of two beams of light to produce visible fringe patterns on objects. A hologram captures the interference patterns of two beams of light on photographic film, one beam is reflected from an object and the other functions as a steady “reference” beam coming directly from the laser. If the object is very

Tarnish of dental alloys by oral microorganisms

Five dental alloys, on exposure to blood and chocolate media with and without inoculated microorganisms, showed varying degrees of tarnish. The results indicated a composition-dependent tarnish behavior of alloys in microorganism-inoculated media, indicating a potential role for the oral microorganisms in inducing clinically observed tarnish of dental alloys. Actinomyces viscosus and periodontal pocket specimens show a similarity in their activity to induce tarnish in base metal-containing dental alloys.

Composite materials for dental implants

The requirements of endosteal dental implants are unique and stringent. The materials currently applied to implantation do not offer convincing evidence of satisfying these needs. This preliminary study reports on attempts at developing materials which would aid in obtaining a mucosal seal to maintain the integrity of the osseous, periosteal, and submucosal compartments from the oral environment and the attachment to bone as related to stress distribution. The materials that were under study were ceramic bonded to base metals and Dacron.