Fatigue test machine for denture base polymers.

A description of a single station fatigue test machine suitable for denture base polymers is given. This machine has been especially designed for dental purposes. A group of representative denture base polymers has been tested, which includes dental poly(methylmethacrylate) of the standard heat polymerized type, autopolymerizing pour type and a heat polymerized rubber graft polymer. These materials were compared and some preliminary results are given. These show that the rubber demonstrated the most satisfactory fatigue life and the pour types were least satisfactory.

Boundary lubrication and maxillofacial prosthetic polydimethylsiloxanes.

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.

Comparison of three- and four-point flexural strength testing of denture-base polymers.

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.

Intraoral strain gauge measurements on complete dentures: a methodological study.

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.

Transverse bend testing of denture base polymers.

A test rig has been designed for transverse bend testing on the Instron machine. The rig is a robust, accurately machined piece of equipment that enables this test to be carried out with accuracy and ease. A range of denture base polymers has been tested under similar conditions to the ISO standard recommendations (ISO/R 1567, 1974), and in this series all the materials except 3 satisfied the criteria laid down in the standard. The specimens were tested in water after 1 month because it has been shown previously that the materials are almost fully saturated at that time (Stafford and Huggett, 1973). Nevertheless, this immersion in water may also weaken the material and this could account for the failure of some materials to pass the standards criteria.

Augmentation of the atrophic maxillary alveolar ridge with hydroxyapatite granules in a Vicryl (polyglactin 910) knitted tube and simultaneous open vestibuloplasty.

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.

Characteristics of headgear release mechanisms: safety implications.

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.

A survey of denture hygiene in patients attending Cardiff Dental Hospital.

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.

Repair strength of denture base resins using various methods.

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.

[Mechanical properties of surface hardening polymers polymerizable by visible light]. / Látható fénnyel polimerizálható felületkeményítö polimer mechanikai tulajdonságai.

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.