The dimensional distortion of acrylic resin denture bases subjected to different dual cure materials and methods

Thokoane, Meriting Gladys
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Background: The majority of edentulous patients are unable to afford anything other than mucosa-borne complete dentures, but the conventional methods of complete denture fabrication can be lengthy and expensive. Simplified techniques have been proposed to reduce the number of clinical visits as well as the laboratory time and costs. One such technique has advocated making the final heat-cured acrylic resin denture base after the first visit, which then requires a second processing cure for the artificial teeth. This dual-cure has been reported to cause distortion of the previously cured denture base. Purpose: To measure the amount of linear and three-dimensional distortion of an acrylic resin maxillary denture base following an additional curing cycle using different processing methods. Method and Materials: A standardised method was developed for fabricating a maxillary denture base with measuring pins , as well as a standardised method for waxing an arch of teeth to the base. The pins were used to make three-dimensional measurements using a Reflex Microscope. The resins used were from the same manufacturer. Four dual cure methods of varying temperature and time were used: 1. Place flask in boiling water for 20 minutes, remove and plunge into cold water for 20 minutes; 2. Place into cold water, heat up to 70°C, leave for 1 hour, remove and bench cool; 3. Place into cold water, bring to 72°C for 8 hours and bench cool; and 4. Place in cold water, bring to the boil for 40 minutes, bench cool for 45 minutes, then plunge into cold water for 20 minutes. For each method five models were fabricated, to give a total of 20 models. Results: Although there was an overall distortion of all denture bases following a second cure, the linear and 3D differences were not statistically significant between and within the different dual cure methods tested. The mean percentage changes measured were translated into real changes in distances or angles between the pins, in order to ascertain the clinical relevance of these changes, for if they are too great, the distortion of the denture base will exceed the resilience of the mucosa as well as disrupt the peripheral seal, and the denture base will not be retentive. The largest mean change was seen in the three-dimension distance between the innermost pins in the posterior palate, but this was only 1.3mm. This also showed the worst change of all measurements, but it was still only 2.0mm. Conclusions: With the adaptive nature of the denture-supporting tissues, the changes described are unlikely to have any clinical significance. Although only one brand of denture base resin was used, it is representative of the modern rapid-cure resins, and so rapid cure methods can be advocated when a dual cure is required.
A research report submitted to the School of Oral Health Science, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Dentistry in the field of Prosthodontics. Johannesburg, 2013