Micromechanical versus chemical bonding between CoCr alloys and methacrylate resins.

INTRODUCTION: As adhesive systems for bonding to metals have developed in dentistry, considerable importance is attached to the preparation of the metal alloy for both mechanical and chemical bonding. Different grit sizes when sandblasting Cobalt Chromium (CoCr) will provide a different three-dimensional surface for bonding. Previous reports have shown that 4-Methacryloyloxyethyl trimellitic anhydride (4-Meta) resins offer high bond strengths to CoCr alloy, with various surface preparations providing varying bond strengths. The relevance of this to bond strength was assessed. OBJECTIVES: The aim of the study was to evaluate the importance of grit size of alumina in the preparation of CoCr alloy and to determine the effect on the tensile bond strength of four different acrylic resins to the CoCr alloy. METHODS: Ten specimens were prepared within each group of four resins. Four grit sizes were assessed, 50, 110, 250 microm, and a range from 180 to 330 microm. The specimens were tested both within one day of production after storing at 37 degrees C in phosphate-buffered saline for seven days and after thermocycling. RESULTS: Grit size resulted in a change in average contact surface area available for bonding. A significant difference (p < 0.01) existed in bond strengths between each of the materials, but no significant difference (p = 0.0673) was determined when different grit sizes were included. SIGNIFICANCE: It was concluded that grit size determined the available contact surface area of CoCr alloy for bonding but did not determine the bond strength that could be achieved between acrylic resins and CoCr alloy as a result of the poor adaptation of the resin to the complex surface topography.

Listening for rhetorical truth.

Associations are rarely as free as theory assumes; at the same time, they may tell us more than what appears on the surface. Memories, on the other hand, are rarely as reliable as they might appear. We are overtrained to listen to the unfolding story and to the narrative truth of the moment; much harder to capture is what might be called its rhetorical truth. Learning to listen for sequence, repetition, and co-occurrence tends to minimize the importance of the narrative thread and clarify instead the more suppressed meanings. In rare cases, we can even sense something of what the analysand is saying before it comes into awareness.

The virtual case report.

Reports of clinical happenings are coming under increasing suspicion because of their piecemeal nature and their problematic reliance on memory. Recent research on eyewitness testimony has raised the further concern that memory of an event can be easily and unwittingly influenced by something heard or seen after the fact. Once the psychoanalyst's memory has come under the influence of whatever theory is dominant, we can expect both an overselection of clinical happenings consistent with that theory, and an unwitting alteration of those that do not agree. Seemingly true case reports may be more virtual than veridical.