Deformation of phosphate-bonded investment materials at elevated temperatures.
OBJECTIVE
To determine deformation in phosphate-bonded investment (PBI) materials for "in-service conditions" and to investigate the influence of air bubble pores on deformation at 900 degrees C.


METHODS
Surviving high and low strain-rate disc-rupture strength test samples were assessed for deformation. A dental centrifugal casting machine and a dental superplastic-forming machine were used to apply the loads. An indirect technique was used to measure the deformation of investment diaphragms with both a wide pore size distribution and with very low porosity for four investment materials. A total of 128 high strain-rate and 29 low strain-rate samples were investigated. A one-way analysis of variance was carried out.


RESULTS
All but one of the high strain-rate test samples showed measurable deformation. All of the low strain-rate test samples containing pores showed measurable deformation. Six out of 14 samples, in which pores had been eliminated, showed no deformation. There was no statistically significant difference in deformation between samples with no pores and those with a large pore size distribution for either the high or low strain-rate tests (P>0.05).


CONCLUSIONS
PBI must survive all forming procedures without deformation if the resultant prosthesis is to fit. One hundred micrometres is generally recognized as the acceptable tolerance of fit for removable metal-based prostheses. The vast majority of deformations measured during this investigation were considerably greater than 100 microm.
Juszczyk
Andrzej S
AS
Department of Fixed and Removable Prosthodontics, King's College London Dental Institute at Guy's, King's College and St Thomas' Hospitals, King's College London, UK. andrzej.juszczyk@kcl.ac.uk
Radford
David R
DR
Curtis
Richard V
RV
D000179:Acrylates / Q000737:chemistry; D000388:Air; D000497:Alloys; D003722:Dental Alloys / Q000737:chemistry; D003734:Dental Casting Investment / Q000737:chemistry*; D003735:Dental Casting Technique / Q000295:instrumentation; D003764:Dental Materials / Q000737:chemistry; D004548:Elasticity; D006358:Hot Temperature; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008422:Materials Testing; D045423:Microbubbles; D010710:Phosphates / Q000737:chemistry; D016062:Porosity; D013314:Stress, Mechanical; D013499:Surface Properties; D013696:Temperature; D014025:Titanium / Q000737:chemistry
D000179:Acrylates; D000497:Alloys; D003722:Dental Alloys; D003734:Dental Casting Investment; D003764:Dental Materials; D010710:Phosphates; C031462:titanium alloy (TiAl6V4); C029884:Croform; D014025:Titanium