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The risk of serious eye injury caused by a headgear appliance is a significant concern. Various safety release mechanisms have been developed in order to help prevent this type of injury, but little testing has been done. The purpose of this study was to test 18 headgear release mechanisms. Four characteristics were evaluated: force at release, extension at release, consistency of release, and performance at different rates of pull. At the point of release, mean force values ranged from 5.33 pounds to 32.83 pounds, and mean extension values ranged from 0.84 inches to 2.93 inches. Consistency was based on the percent standard deviation, and the appliances were ranked relative to each other. Nine of the 18 appliances had statistically significant differences in the two pull rates for either variable or both, but the clinical significance is uncertain. The results show a wide range of performance among the 18 appliances tested and indicate that some perform better than others.

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The object of this study was to measure the repair strength of denture base resins repaired using, (a) standard heat activated polymerising resin, (b) a denture base resin especially formulated for microwave-activated polymerisation, and (c) an autopolymerising resin. Comparisons were made between conventional water bath and microwave curing and autopolymerised resin repairs, using transverse bend and impact tests. Repairs with the two heat-activated denture base resins were carried out using conventional dental flasking procedures, whereas autopolymerised resin repairs were carried out in open gypsum moulds. The results indicate that the transverse strength, and impact resistance of the resin specimens repaired with microwave irradiation were generally superior to specimens repaired by using a water bath curing cycle or the use of an autopolymerising resin.

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A modified technique for augmentation of the severely atrophic edentulous maxillary alveolar ridge is described. The augmentation was carried out using a knitted polyglactin 910 mesh tube filled with porous hydroxyapatite granules, the tube being inserted through the access achieved by an open vestibuloplasty. The results of an in-vivo animal study showed that the absorption of the mesh was complete between 49 and 70 days. The clinical study included 11 patients in all of whom there was severe maxillary ridge atrophy and major prosthetic problems; follow-up was for a mean of 25 months. The procedure was without significant complication and produced a mean immediate absolute augmentation of 5.5 mm and substantially increased vestibular depth. A gradual reduction of ridge height was found over time. Nevertheless all patients showed significantly increased ability to wear their dentures. The technique is presented as a safe and predictable alternative to the use of bone grafts and titanium implants in these severely atrophic cases.

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Patients attending the Cardiff Dental Hospital were interviewed by staff and students in the Department of Prosthetic Dentistry and a multidisciplinary teaching clinic. Information on denture hygiene was collected using a questionnaire. This questionnaire consisted of nineteen questions on the methods and materials used for denture hygiene, along with details pertinent to the patients and their dentures. One thousand patients were interviewed. The results showed that patients were less critical of standards of denture hygiene than clinicians. Only 46% of patients believed their dentures stained. This suggests high patient apathy regarding denture hygiene, that should be addressed in health education programs.

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Strain gauges were used to record in vivo and in vitro functional deformations in a fixed prosthetic appliance supported and retained by osseointegrated titanium implants. Four linear gauges were attached to each of totally 5 implant abutment cylinders and gauge signals were transferred into a computer via a digital converter. A computer program (ASYST) was used for collection, calibration and analysis of data obtained. Based on the results of a series of explorative in vitro tests, in vivo experiments were performed at maximum biting as well as during chewing on certain normally available food items. The results show fundamental differences between in vitro and in vivo testing conditions. Unexpectedly high bending of the implants was recorded in many of the in vivo loading situations.

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The construction of facial prostheses simulating the missing tissues as closely as possible is an imperative and demanding task. Such prostheses will be comprised of parts presenting different mechanical properties attempting to simulate facial tissues. In this study the mechanical properties of a room temperature vulcanized (RTV) silicone facial elastomer were modified, altering the molecular architecture by controlling the amount of cross-linking. A wide range of compliance was achieved which enables more lifelike facial prostheses to be made in clinical practice.

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This paper discusses the advantages and the limitations of strain gauge clinical research in prosthodontics. It also demonstrates the possibility of long term studies by explaining a methodological study that was undertaken on a group of 19 patients on two occasions a year apart. Of this group six were supplied with maxillary and mandibular complete dentures, five had maxillary complete dentures and mandibular osseointegrated fixed 10-12 unit bridges, and eight had maxillary and mandibular complete dentures at the first experimental session and osseointegrated fixed 10-12 unit bridges in the mandible at the second. It was found that during maximum biting the direction of functional strain was comparatively stable at a given point of a denture. It was evident that in experiments 12 months apart no major changes had taken place in the experimental dentures nor the denture bearing tissues. The accuracy of the strain gauges used was maintained and there were no failures due to loss of retention of the gauges. Loss of insulation and short circuiting was an occasional problem but instantly recognized if it occurred.

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Polydimethylsiloxanes exhibit hydrophobic behaviour and poor wettability. These features impose some problems with the clinical performance of the material when used for the construction of intraoral and extraoral facial prostheses. Surface active agents were added to modify the surface energy of the polydimethylsiloxane and contact angle measurements were carried out to observe wetting characteristics. Five siloxane-alkene oxide block copolymers, one organosilicon quaternary ammonium chloride and an epoxyalkyl silane ester were used as surfactants. The best surfactant in terms of permanency and contact angle lowering achieved a value of 24 degrees when added at 10% level compared with 57 degrees for the unmodified silicone. The fairly high viscosity, combined with a comb-like structure, together with the high hydroxyl number of 75 provided the correct balance of permanence and wetting characteristics.

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A plastic layer polymerized on the surface of denture base material in a thickness of, in average, 40 microns by means of visible light was significantly harder with respect to industrial acrylic surfaces. At an irradiation time of 90s according to factory prescription no harder surface appeared even in case of multiple covering. The surface became significantly harder with an irradiation of 150s. Of the denture base material products the Trevalon and the QC-20 products showed the forming of significantly harder surface.

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A new denture base system, Provac, has been developed for complete and partial dentures, and for relining. The Provac material is methyl methacrylate, which cures with the aid of barbituric acid. In this study the physical and mechanical properties of the new resin were investigated and compared with those of a conventional autopolymerizing material (Croform) and a conventional heat polymerizing material (Trevalon). It was found that the dimensional accuracy of Provac was better than that of the conventional heat-curing material, Trevalon, and the denture was finished more easily and quickly. The physical and mechanical properties of Provac resin were found to be similar to those of the other two materials, and conformed to the International Specifications for denture base materials. The residual monomer levels in Provac material were always higher than the minimal obtainable values associated with conventional heat-cured materials when these were polymerized with a terminal boil during the curing cycle.

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Flexural failure of denture-base materials is considered the primary mode of clinical failure. However, there are several methods of conducting flexural tests, and none has been demonstrated to be the most appropriate. Three- and four-point bend-testing were compared, with four different dental polymers used. The values for modulus of elasticity determined by the two tests were not statistically different. However, the values for flexural strength from the three-point bend test were always greater, suggesting that that parameter is dependent on the testing procedure. Modifications to the existing denture-base material specification are suggested.

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Variations in the polymer/monomer mixing ratios from 1.5:1 to 4.5:1 vol/vol have been evaluated to determine the effect on dimensional accuracy and impact resistance of a PMMA homopolymer. Two polymerisation cycles were used. It was shown that a wide variation in mixing ratios (1.5:1 to 4:1) had no effect on dimensional accuracy or impact resistance and that a polymerisation cycle that includes a final boiling period is preferred. It was further found that notched impact resistance was almost an order of magnitude below unnotched impact resistance, emphasising the weakening effect of sharp contours on the impact resistance of denture resins.

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The applicability of an electronic thermometer CRAFTEMP in taking intraoral temperatures was determined. Sublingal temperatures in ten young subjects with complete natural dentitions, and the temperatures at the denture base-mucosa interface and on the polished surface of both maxillary and mandibular complete dentures in ten elderly patients were measured. The results showed that there was a temperature difference between the polished surface of the maxillary denture and the denture base-mucosa interface. This was statistically significant in the female but not in the male subjects. No temperature difference could be demonstrated with any of the mandibular dentures. The CRAFTEMP was found to be a convenient and reliable method for intraoral temperature measurement.

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