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Title: The wear of different artificial denture teeth used in implant-retained prostheses
Author: Shahdad, Shakeel
ISNI:       0000 0001 3395 997X
Awarding Body: Newcastle University
Current Institution: University of Newcastle upon Tyne
Date of Award: 2007
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Edentulous persons have been reported as 'oral invalids and very handicapped' in masticatory function. These patients are usually older people and can be successfully restored with implant-retained prostheses (IRP). However, a high rate of wear is apparent on the artificial teeth in IRP and opposing dentures necessitating prostheses to be remade partially or in total. Such maintenance has considerable clinical and laboratory cost implications, since it forms 1'. an increasing part of dentists' workload. The study investigated the wear rates among Various artificial tooth materials when subject to forces that represented those experienced in the clinical situation. The effect of abrasive slurry on the rate of wear was also investigated, as were the changes in hardness when artificial teeth were stored in food simulating solvents. A series of experiments was carried out in order to investigate these parameters on four commercially available Vivodent (VIV), Postaris (Del), Orthosit (aRT), Candulor (paR), and two experimental denture tooth materials; Experimental 1 (EXP1) and Experimental 2 (EXP2). Perspex (PER) was used as a control material. Two-body wear test A multi station wear-testing machine was constructed and used to test standardised hemispherical specimens against flat ones and measure the amount of wear using a non-contacting laser profiler to determine the depth of wear scar. Different material combinations were tested including materials worn against themselves and against hemispherical steatite abraders. Measurements were made following 2000 cycles and 10,000 cycles. Wearrates were determined as mean cross sectional area of the scar (Ilm/1 000 cycles). The results of this work revealed some interesting observations. Not all the specimens showed the classical wear pattern by creating a wear track on the flat specimen when the hemispherical abrader was sliding against it. Instead, in some material combinations there was a positive build up of material along the track and therefore a simple quantitative measurement of wear was not possible on all the specimens. The materials with a positive build up demonstrated an adhesive type of wear rather than the abrC?sive wear, which were further analysed under SEM. A technique was developed to measure wear occurring on hemispherical abraders. These were also qualitatively analysed under tool makers microscope and SEM. Abrasive and adhesive wear processes were noticed depending on the material combination tested. Three-body wear test Three-body abrasive wear tests were carried out on flat specimens using a toothbrushing machine with abrasive slurry. A laser profiler was used to measure the depth of wear scar. Measurements were made following 10,000 cycles except in porcelain specimens where measurements could only be recorded after 100,000 cycles. Wear rates were determined as mean depth mm/l 000 cycles. POR, EXPl and ORT demonstrated significantly (P<0.5) lower three-body wear rate when compared to the other materials. There was no significant difference in the wear rates between PER, VIV, DeL, and EXP2. Similarly, there was no significant difference between POR, EXPl and ORT. Effect of solvent storage on hardness The materials were tested for Martens Hardness measurements (HM) aHer storage in peppermint oil. 75% ethanol and heptane. Distilled water was used as a control storage medium. One specimen from each material group was stored in each solvent for 1 minute. 5 minutes. I hour. 24 hours. 1week and 1 month respectively. One specimen from each group was also tested dry to establish the baseline HM value. One-way ANOVA using Tukey's test on polymer based materials showed that the hardness of ORT and EXP 1 was significantly higher than the PMMA, Del and EXP2 (P
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available