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PubMed1989

[Mechanical analysis of the denture bases, using the photoelastic-coating method. 1. Influence of the coating on mechanical properties of the test denture].

The anterior palatal area may be related with the flexural rigidity and bending strength of the upper complete dentures. Therefore, the deformation of this area should be measured widely and continuously when new materials were applied to the dentures. The influence of the photoelastic coating on the mechanical properties of the upper complete dentures was investigated, prior to the measurement of surface strains on the denture bases by the photoelastic coatings. In this experiment, the uniform-moment bending method was employed simulating the occlusal situation. The flexural rigidity of the denture bases depended on the palatal materials in spite of the presence of the coating. The strains concentrated on the anterior palatal area were slightly decreased when the coating was bonded to the polished surface of the palate. The reinforcing effect was significant when the resin dentures of low elastic modulus were coated. The photoelastic-coating method was suitable for the qualitative analysis of the strain distribution of the denture base and selecting the test points to make strain measurement accurate.

Dental Stress Analysis↗
PubMed1979

[Studies on the thinning of the upper acrylic resin complete denture with the reinforced palate. (Part 1). Thinning of the resin denture base with the standard shape (author's transl)].

The acrylic denture bases are most commonly used as compared with metallic denture bases at present. For this reason, it is due to many excellent properties, for example, simple processing, easy repair, cheapness and so on. But an inherent disadvantage is liability of an acrylic denture base to make thick so as to maintain stiffness and strength and it makes patients uncomfortable. Therefore, the purpose of this paper is to make the palatal region of the upper complete denture thin with about 0.7 mm in thickness, and to keep the same mechanical properties as the normal resin dentures using the composites materials with carbon cloth. Tensils test of the plate test-piece and uniform bending test of the upper complete denture with steel wings were respectively performed. The results obtained in this investigation are as follows: 1) The acrylic composites reinforced with carbon cloth have shown the superior mechanical properties to be compared with the acrylic resin to be generally used. 2) The thickness of the reinforced thin denture is decreased to 0.7 mm (its thickness is 60% of the normal thickness of the one), nevertheless, the stiffness and strength are increased with the using of the composite materials. 3) The region of highest surface tensile stress in the denture was on the polished surface of the palatal aspect of the denture in the area immediately behind the anteriors, but at this region, the strain of the reinforced thin denture base decreased its strain 10% in comparison with the non-reinforced normal thick one.

Acrylic Resins↗
PubMed1996

Fracture surface characteristics of damaged acrylic-resin-based dentures as analysed by SEM-replica technique.

The aim of this study was to determine some characteristics of the fracture surface of an acrylic resin denture. For this purpose, five complete upper dentures and two complete lower dentures that had fractured into two pieces were collected, the fracture surfaces were duplicated with the SEM-replica technique and duplicated surfaces were investigated with a scanning electron microscope. The reproducibility of the SEM-replica technique was tested by comparing one original sample surface and its replica surface of the same area. The SEM-photomicrographs revealed a series of fine striations in the fracture surfaces of both the upper and lower dentures perpendicularly orientated to the direction of the fracture propagation. A smooth area on the fracture surface was assumed to indicate a slow fatigue fracture process, and a rougher area fracturing with increased velocity.

Dental Restoration Failure↗
PubMed1980

[Studies on the thinning of the upper acrylic resin complete denture with the reinforced palate. (Part 2) Influence of the different palate forms on the thin plate dentures (author's transl)].

In this paper, succeeding the study of the part 1 on the thinning of the upper acrylic resin complete denture with the reinforced palate, it was investigated to keep the same stiffness and strength as the normal resin dentures, and to make the patient comfortable. Besides, many different palate forms exist in the patient's mouth in clinical cases, and so, influence of these forms on the thin plate dentures comes into question. Therefore, 3 types of the palate forms (the standard shape, the extremely large torus and the generally shallow shape) were established, and then the flexural stiffness and strength, and the deformation of the denture bases were scrutinized in this paper. The results obtained in this investigation are as follows: 1) The maxillary torus with sheer bulk had little influence on the flexural stiffness and strength. But, about the generally shallow-shaped denture bases, the mechanical properties dropped a little as compared the normal resin denture bases. The reinforced thin denture bases of which thickness was 60% of the normal one, showed the excellent mechanical properties in spite of the difference of the palate forms. 2) In the upper complete denture base, in spite of the palate forms, anteriority and posteriority of the one were deformed against the load direction around the frontal section through the bilateral canines, and the bilateral ridges of the one were deformed to the load direction around the midline of the denture base. The deformation was extremely decreased by not only the palate but also the whole of the denture base as the reinforced one.

Acrylic Resins↗
PubMed1990

[Studies on canine guidance in complete dentures].

The effect of canine guidance with guiding angles of 70, 55 and 30 degrees in relation to the median sagittal plane and balanced occlusion on the kinetics of upper complete dentures was investigated both in an in-vitro-experiment and in patients. It appeared that canine-guided dentures led to considerable dislocations during tooth-guided lateral movements, whereas balanced occlusion caused only minor movements, which were always directed toward the alveolar ridge.

Cuspid↗
PubMed1976

[Studies on the stability of total prostheses].

1. The load capacity of complete upper dentures objectively proved greater than that of lower dentures. 2. The load capacity and, consequently, the stability of position of the lateral area of upper dentures objectively diminished with advancing time of wearing, but increased in the lower jaw. 3. The stability of complete dentures is not determined exclusively by the quality of the denture bearing tissue. 4. The measured stability of position of complete dentures did not correspond with the subjective impression of full function; in general, this was stated to be as good as ever by all patients.

Adult↗
PubMed1990

[Stress distribution of supporting tissues under denture. Application of visco-elastic analysis in prosthetic field].

Viscoelastic finite element method was attempted to apply to the removable prosthodontic field. To examine the accuracy of this analysis, the results obtained from creep test of soft lining materials were compared with the calculated results by using this analysis. Stress relaxation in the supporting tissue under the upper complete denture was simulated by using viscoelastic analysis. The results were as follows; 1. The calculated results were in approximate agreement with experiment. 2. When the occlusal table of the denture was move 0.3 mm to the vertical direction, the calculated results indicated the soft tissue acted as a part of the stress relaxation in the supporting structures. 3. By using viscoelastic analysis, the time dependent deformation of the denture base and stress distributions in the supporting structures could be simulated.

Alveolar Process↗
PubMed1990

[A basic study on pressure distribution of supporting structures under complete denture. 1. Application of pressure dispersion analyzing system by using impedance grid sensor to measure the pressure of supporting structures under complete denture].

In order to measure the pressure distribution on supporting structures under complete denture, we used impedance grid pressure sensor and examined its accuracy and availability. The results were as follows: 1. The sensitivity of this sensor was high when the distance between electrodes was short. 2. This sensor showed large change in output voltage and high sensitivity in the case of soft elastic materials. 3. This sensor showed the high linearlity between output voltage and applied load. 4. This sensor showed hysteresis loop under cycle load. 5. Base line of this sensor that has the urethane rubber as elastic material was changed when the load was applied intermittently. We measured the pressure distribution over supporting bones under upper complete denture by using simulator of maxillary edentulous with this impedance grid pressure sensor. We could observe the pressure distribution and pressure region in detail and visually when the load was applied to the both occlusal tables evenly.

Alveolar Process↗
PubMed1995

Oral health status of a population of community-dwelling older Canadians.

A sample of 170 responsive residents of seniors housing centres in Winnipeg, Canada, were studied, (>65 years, mean 82 years), with the objectives of relating their dental state to their perception of need and uptake of service. Only 6% rated their oral health as poor, 46% reported a dental visit within the previous year and 68% felt they needed dental treatment. A lack of perceived need (88%) was the primary reason why dental care was not sought more frequently. Hygiene practices revealed that only 7% brushed < 1 time/day, 60% never flossed, 14% cleaned their dentures <1 time/day, and 42% slept with their dentures. Dental histories showed that examination (94%), prosthodontic treatment (76%), and restorative services (65%) were the most commonly sought treatments. Perceived dental needs included prosthodontic treatment (39%), periodontal/prophylactic treatment (10%), restorative treatment (9%) and pain relief (9%). Study subjects had 2.8 decayed teeth, a DMFT of 25.1, and a Root Caries Index of 38%. CPITN scores of 3 or 4 in at least one sextant were found in 80% of subjects. Of the 41% edentulous, all wore complete dentures but 15% of complete upper dentures and 51% of complete lower dentures fitted poorly. Of the partial dentures, 20% fitted poorly. Soft tissue anomalies were seen in 67% of subjects and 47% had TMJ anomalies. Overall, 77% of edentulous subjects and all dentate subjects required some dental treatment even though 46% had seen a dentist within the preceding year. It is concluded that appropriate management of such people needs further attention.

Aged↗
PubMed1994

[Posterior palatal sealing in Hungarian dental practice].

The purpose of the survey was to receive data about the methods, materials and instruments used in the development of the border seal at pharyngeal region. The problem concerned how the theoretical principles are realised in the everyday practice. A questionnaire consisting of 10 questions was given out to 35 dental laboratories in 31 towns of the country. 33 completed forms were returned. On the basis of the survey's results the authors conclude that in everyday practice practically nothing realizes from the recommendations of dental literature. The shape of the upper complete dentures' palatal seal is made by dental technicians, regretfully without the cooperation of dentists and what is more disappointing without their instructions. Dental technicians are left to their own resources to form the pharyngeal seal by mechanical engraving of the casts.

Dental Prosthesis Design↗
PubMed1990

[Influence on the movement of a complete denture caused by differences in artificial tooth materials].

An experiment using modal analysis was used to ascertain the activity of complete dentures and artificial teeth. Three types of artificial teeth were used: a porcelain tooth, a resin tooth and a hard resin tooth. Animation and displacement values were used as criteria in determining the influence that differences in tooth materials had on the activity of the complete denture. The experiment was conducted to act as an aid in denture design and the following results were obtained: 1. The resonance frequency for the different test materials ranged from mode 4 to mode 7. 2. Regarding displacement value, a value of 1 micron or more was obtained in the 1 octave bandwidth for the 250 Hz band, 500 Hz band and the 1 kHz band. Among these, maximum displacement for the upper complete denture was as follows: When a porcelain tooth was used and a vibration of 1 for mode 1 (197 Hz) was applied, the value for the 3 cusp tip was 39.48 microns and that for the labial denture border side was 43.35 microns. As for the lower complete denture, when a porcelain tooth was used and 5 oscillation was applied for mode 1 (309 Hz), the value for the 3 cusp tip was 68.38 microns and that for the rear part of the denture border was 139.2 microns. 3. Regarding the activity of the complete denture in the 250 Hz and 1 kHz bands, when a porcelain tooth was used, a curve mode was observed for the upper complete denture in the labiolingual direction with the cervical line as the border. When the resin tooth and hard resin tooth were used, it was difficult to recognize any change with the cervical line as the border. It was also difficult to recognize a change at the cervical section for the lower complete denture. 4. As for the 500 Hz band, when a porcelain tooth and a resin tooth were used, there were frequencies (300 Hz-400 Hz) at which twisting in a labiolingual direction at the cervical section was recognized for the upper complete denture as well as frequencies (400 Hz-600 Hz) where this was not recognized. A rigid body mode was recognized when the hard resin tooth was used. In addition, differences in the location for applying for vibration had an influence on the activity of the lower complete denture.

Acrylic Resins↗
PubMed1989

[Three dimensional study of facial height].

There is no know scientifically accurate method of determining the correct vertical dimension. By the vertical dimension we mean the distance between the subnasale & the bottom of chin when patients were radiograped in the physiologic rest positions with & without prostheses. The author measured seven selected points in a midsagittal profile plane of 50 patients (26 complete upper & lower denture, 24 complete upper & removable lower partial denture) by the cephalometric methods. The following conclusions were obtained from this study. 1. Vertical dimension was measured 70.03 mm during removal of upper & lower dentures in mouth, 70.18 mm during insertion of upper denture only, 70.83 mm during insertion of lower denture only & 70.88 mm during insertion of upper & lower dentures, therefore mandibular denture alone in mouth has a slightly significant effects. 2. Vertical dimension between male & female from partially/fully edentulous patients was proved 72.15 mm in male & 68.81 mm in female. 3. Anterior-posterior displacement is largely associated with upper lip movement & superior-inferior displacement is generally associated with a function of lower lip & mandibular structure movements. 4. The magnitude of horizontal displacement for all points ranged from 0 to 8.4 mm & vertical displacement for all points ranged from 0 to 12 mm displacement. The maximum horizontal displacement in point II & maximum vertical displacement in point III was measured. 5. Increase in height may be associated with contraction of dental arches; or conversely, reduction of vertical height may be associated with expansion of the dental arches due to muscle tonicity & lip contours.

Cephalometry↗
PubMed1987

Cantilever bridges or removable partial dentures in geriatric patients: a two-year study.

The purpose of this study was to compare prosthetic, functional and occlusal conditions in twenty-seven patients treated with distally extending cantilever bridges and twenty-six patients treated with removable partial dentures (RPD) in the mandible. All patients had a complete upper denture. Mean age of the patients in both groups was about 69 years. The patients were under a supervised oral hygiene care throughout the 2-year study period. There were 6.9 +/- 1.7 mandibular teeth left in the bridge group and 7.5 +/- 1.7 in the RPD group and the mean number of posterior teeth (natural teeth/denture teeth/pontics) in occlusion was 4.1 +/- 1.1 and 7.3 +/- 1.4, respectively. During the study period signs and symptoms of mandibular dysfunction became significantly aggravated in the RPD group, P less than 0.05. A balanced occlusion in the muscular contact position was observed in 90% of the patients in the bridge group and in 76% of the RPD wearers. During the study period the need for dental or prosthetic treatment was negligible in the patients treated with bridges. In the RPD group, twenty-two teeth were restored with fillings due to caries and in eight patients major adjustments of the sublingual bar were necessary due to irritation of the oral mucosa. This study has shown that treatment with distally extending cantilever bridges in the mandible is a favourable alternative to treatment with removable partial dentures in elderly patients with a reduced dentition.

Aged↗