John D. Walter

An investigation of debonding between heat-cured PMMA and titanium alloy (Ti-6AI-4V)

OBJECTIVES The bonding of acrylic resin to dental prostheses constructed from metal has been the subject of extensive research in recent years, much of it between base-metal alloys such as Ni-Cr alloys and dental composite. The development of techniques for the manufacture of dental appliances from titanium and titanium alloys has opened new avenues for investigation of the metal/acrylic resin bond. METHODS In this study, a bond strength comparison between two PMMA products, Trevalon and Metadent, and discs of titanium alloy, Ti-6A1-4V, was investigated using a four-point bend test configuration. Trevalon is a standard, commercially available, heat-cured acrylic resin, while Metadent is an acrylic resin incorporating a chemical bonding agent, 4-META. A comparison was made between two processes that are routinely used to enhance the bond between metal and acrylic, namely sandblasting of the metal surface and using the Silicoater system following sandblasting. Each of the samples was paired, thus allowing a further comparison to be made between samples that had undergone thermocycling in a water bath, with those that had been held at a constant temperature. RESULTS The study revealed that a superior metal/acrylic bond was achieved by the use of the silicoating system when either Trevalon or Metadent was used both before and after thermocycling. Reduced debonding loads were recorded for all samples that had undergone thermocycling. CONCLUSIONS Highest bond strengths were recorded for Trevalon or Metadent processed against a silicoated Ti-alloy surface.

Composite impression procedures

Abstract Composite impression procedures allow the dentist to vary stress on different supporting tissues in the same mouth, utilize different impression materials in the same mouth, and place sectional trays in mouths where the opening to the oral cavity prevents use of a single tray. Four types of composite impression procedures and the indications for their use were described.

Concepts of soft-palate prosthesis.

Abstract Since the initiation of soft-palate prosthesis in the eighteenth century, design has been governed by a number of theories concerning the role of the appliance. Six concepts are presented with the aim of demonstrating the evolution of the prosthesis and dispelling the belief that all the appliances of a bygone age have been based on the whimsical notions of their creators.

Palatopharyngeal activity in cleft palate subjects

A literature review of the nature of the musculature of the cleft palate and the pharynx is provided and a rationale presented for determining the anatomic level at which muscle activity occurs. Nasal endoscopy with a rigid telescope and the placement of miniaturized pressure transducers against the pharyngeal walls were the techniques used to investigate palatopharyngeal defects in cleft palate subjects. Ten basic patterns of palatopharyngeal movement are described and the likely interplay of the various muscles in producing these complex movements is discussed. Closure patterns of the palatopharyngeal isthmus varied according to whether the subjects were speaking, sucking, or swallowing. It was concluded that the presence of an obturator in the pharynx affects the pattern of activity and that the obturator should be developed to speech function rather than to swallowing.

Nasal endoscopy as a means of examining soft palate function

This paper reviews the visual methods available for the examination of the velopharyngeal portal in function. The various forms of nasal endoscope are differentiated together with the advantages and limitations of display and recording systems. Basic endoscopic technique is described.