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At least 1,117 records · Page 62Linked to original sources
PubMed2002

Abrasion resistance of a resin-impregnated type IV gypsum in comparison to conventional products.

STATEMENT OF PROBLEM: Limited abrasion resistance is one of the disadvantages of gypsum materials. One means to improve these properties may be the addition of various polymers to reinforce surface and subsurface wear resistance. PURPOSE: The purpose of this study was to evaluate the abrasion resistance of 3 types of gypsum materials with a novel abrasion wear device. MATERIAL AND METHODS: A standard test specimen (50 x 50 x 8 mm) with repeating 1 mm, 45 degrees -angle vertical ridges was used as the test surface. Three types of gypsum materials were evaluated: a type III stone, a conventional type IV stone, and a resin-impregnated type IV stone. Specimens of each material (n = 30) were poured in a vinyl polysiloxane impression of the standard test specimen with the use of an acrylic resin custom tray. Each gypsum product was mixed according to the manufacturer's instructions, poured, and separated 1 hour later. Specimens were trimmed and allowed to bench set for 24 hours (n = 15) or 7 days (n = 15). Abrasion was evaluated with the use of a reciprocal moving stage positioned below a weighted stylus. The stylus was loaded with 3 different weights (15, 50, and 75 g), and the individual gypsum specimens were moved reciprocally for 10 passes. Before and after each set of passes, the specimen was measured on an analytical balance to determine material loss. Three-way ANOVA and Scheffe's multiple comparisons test were used to analyze the data (P<.05). RESULTS: Type III gypsum at 24 hours exhibited significantly greater material loss than type IV stones at both 7 days and 24 hours (P<.001). Type III gypsum specimens exhibited significantly greater material loss at 24 hours than at 7 days (P<.001). There was no significant difference in the abrasion resistance of type IV specimens at 24 hours and 7 days. CONCLUSION: Within the limitations of this study, no significant differences in abrasion resistance were found between specimens fabricated with resin-impregnated and conventional type IV stones, although the former exhibited the least material loss.

Acrylic Resins↗
PubMed2003

The effect of tray selection, viscosity of impression material, and sequence of pour on the accuracy of dies made from dual-arch impressions.

STATEMENT OF PROBLEM: Dual-arch trays are often used to generate impressions of prepared teeth and of the opposing arch simultaneously. There is concern that accuracy of the casts generated with this technique can be affected by the type of tray, viscosity of the impression material, and sequence of pouring the cast. PURPOSE: This study compared the accuracy of working dies made from impressions with metal and plastic dual-arch trays, for 2 different viscosities of impression tray material and by altering which side of the impression was poured first. MATERIALS AND METHODS: Impressions were made of a typodont mandibular arch containing a circular stainless steel crown preparation (standard). There were 3 variables: type of dual-arch tray, impression material viscosity, and order of pour of the impressioned arches. A balanced design with independent samples was used (n=10). Two types of dual-arch trays, plastic (Triple Tray) and metal (COE Impression Tray), and 2 viscosities of addition silicone for the tray were used (Aquasil Rigid and Aquasil Monophase). Type IV gypsum (Fuji-Rock) with a ratio of 20 mL of distilled water to 100 g of powder was hand-mixed for 10 seconds then mixed under vacuum for 40 seconds and poured into the trays while being vibrated. One side of the dual-arch impression was poured with 35 g of stone and allowed to set for 1 hour before the other side was poured with 35 g of stone. The order of pour was randomized, and all casts were allowed to set for 24 hours at room temperature before removal. The dies were measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) with a measuring microscope. The gypsum working dies were placed into a custom jig fabricated to permit measurement at a fixed, reproducible position under the microscope. Each dimension of the working dies was measured 3 times, and the mean was used for the sample value. The same 3 aspects of the stainless steel standard were measured multiple times, before and then at the conclusion of measuring all working dies, to arrive at the 3 standard values to which all working die means were compared. The means for the standard used in the statistical analysis were those taken at the conclusion of the study. The intraexaminer variation for measuring the standard was 0.001 mm. A 3-factor analysis of variance was used for the statistical analysis with hypothesis testing at alpha=.05. RESULTS: Statistically significant differences were found with viscosity selection for the buccolingual and occlusogingival dimensions of the working die. The rigid material produced working dies slightly taller (1 microm) than the standard, and those from the monophase material were 4 microm shorter. Regarding tray selection, metal trays were slightly more accurate in the mesiodistal dimension, and when monophase was used in a plastic tray, gypsum dies were nearly 30 microm smaller in the mesiodistal dimension (P<.05). Differences were not detected for sequence of pouring impressions. CONCLUSION: Within the limitations of this study, the monophase material, when compared with the rigid impression material, was most accurate for the occlusogingival and mesiodistal dimensions, although not as accurate in the buccolingual. This buccolingual difference (0.002 mm-0.006 mm) would be clinically inconsequential with the application of die spacer. The rigid impression material was also unaffected by tray selection for the mesiodistal, whereas monophase was affected. When a monophase impression material was used, plastic dual-arch trays yielded gypsum dies which were significantly smaller (0.029 mm) than the ones generated from the metal trays (0.006 mm). Thus rigid impression materials can be recommended for use in dual-arch trays; however, the magnitude of the differences would generally not be clinically significant because they could be compensated for with several coats of die spacer.

Analysis of Variance↗
PubMed1983

New materials and techniques in prosthodontics.

In looking back over the past few years, dentistry has seen many changes. The newer methods and materials in complete denture prosthodontics, and the update on dental materials has been exciting. The development of many good disposable products is in keeping with other technologic advancements. Unlike aerospace and industry, dentistry has not yet entered the computer age. However, that day is not far off. With the newer materials used in the multiphases of prosthodontics, the astute practitioner can become acquainted with time-saving, clinically orientated dental materials, and new products. The clinician's appreciation of a particular product is based on individual reaction to the disposable qualities, the cost factors, the ease of handling, and the end product. The advantages of time-saving methods are crucial to office overhead today. This article has covered various phases of removable complete dentures, dental materials, and products that are appropriate to those procedures. No particular product or procedure has been specifically recommended. Instead, I have introduced products that I have used and enjoyed. Not all products can be studied and reported, so if certain materials are not mentioned, it is because not enough time was available to pursue every new product or procedure offered to the disciplines of dentistry.

Adhesives↗
PubMed1986

Visco-elastic properties of dental elastomeric impression materials.

The visco-elastic properties of a number of set elastomeric impression materials were determined using a torsional pendulum apparatus, i.e. the real (G1) and imaginary (G2) parts of the complex shear modulus and the mechanical loss tangent (Tan delta). Comparison with published data on tension and compression set for these materials showed that whilst there was no correlation between Tan delta and tension set, there was significant (greater than 99%) correlation with compression set. Treating a permanent set test as the application of a rectangular stress pulse of duration tau, and assuming (i) linear visco-elasticity theory and (ii) that G1 and G2 are independent of frequency. Fourier integral analysis predicts that Tan delta should be proportional to permanent set. Tension set does not conform to this prediction because the deformation is nonlinear. The compression set test is shown to involve shear strains and elastomers generally are Hookean in shear. Whilst the theoretical treatment applies qualitatively, there are major quantitative disparities, the reasons for which are discussed.

Dental Impression Materials↗
PubMed2006

Impression techniques for implant dentistry.

The object of making an impression in implant dentistry is to accurately relate an analogue of the implant or implant abutment to the other structures in the dental arch. This is affected by use of an impression coping which is attached to the implant or implant abutment. This impression coping is incorporated in an impression - much as a metal framework is 'picked up' in a remount impression for fixed prosthodontics. With implant copings the coping is usually attached to the implant or abutment with screws. The impression material used is usually an elastomeric impression material; the two types most widely used and shown to be the most appropriate are polyether and polyvinyl siloxane impression materials.

Dental Abutments↗
PubMed1994

Methods of measuring wound size: a comparative study.

The lack of an accepted method of accurate and objective measurement of wound dimensions is a major obstacle to the assessment of effective wound management regimes. This study compares three different wound volume measurement techniques (filling the lesion with saline, molding of a dental impression material and a computer vision method based on image processing and the Structured Light technique) in terms of accuracy, precision and practicability in a clinical environment. Three groups of hospital staff, doctors, nurses and technicians, repeatedly measured a set of 6 different models of wounds. Measuring wound volume by filling it with saline produces results with standard deviations between 9 percent and 18 percent of the actual volume. Dental impression material performs better, between 5 percent and 16 percent, but is difficult to apply and time consuming to use. Apart from the advantage of providing instant optical records of wounds, the image processing method produces more reliable volume measurements with a standard deviation of between 3 percent and 15 percent. The results demonstrate that the computer based method yields the most reproducible results with a minimum of inter-observer error but the method is not applicable for undermined, very deep and very large wounds.

Anthropometry↗
PubMed2003

Quality of materials supplied to dental laboratories for the fabrication of cobalt chromium removable partial dentures in Ireland.

The adequacy of prescription for fabrication of cobalt chromium removable partial dentures is often regarded as being less than ideal. This study examines the nature and quality of written instructions and master impression sent to dental laboratories in Ireland for fabrication of cobalt chromium removable partial denture frameworks. Questionnaires were issued to dental laboratories seeking specific information relating to the materials (impression materials and trays) and written instructions supplied, as well as the technicians' opinion regarding the suitability of these materials. One hundred completed questionnaires were returned. One-third of master impressions were made using a plastic stock tray and alginate; technicians felt that one-fifth of master impressions were unsuitable; almost three-fifths of written instructions were inadequate. The quality of clinical information examined was found to be less than adequate.

Alginates↗