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PubMedDate not supplied

The dimensional accuracy of 12 impression material and die stone combinations.

This study determined the dimensional accuracy of dies made using a combination of four impression materials and three Type IV die stones. A metal die was prepared for a molar complete cast crown, and 10 stone replicas were made using 12 different combinations of impression materials and die stones. The distances between reference points on the metal and stone dies were measured in three directions with a traveling microscope. Analysis of variance and Duncan's MR comparisons (P less than or equal to .05) showed that all of the stone dies were larger than the metal die. Although there were significant differences between some of the impression material/die stone combinations, all of the stone dies were measured to be within 9 microns of each other. No one impression material/die stone combination consistently produced the smallest or largest die in the three measured directions.

Analysis of Variance↗
PubMedDate not supplied

[Evaluation of cervical discrepancy of gold crowns in stone dies from various impression materials].

A stainless steel master die simulating a dental preparation for crown was used to make 3 gold castings from wax patterns obtained in 3 different ways: a) directly from the naked master die; b) from the same master die with a copper coping 30 microns thick; and c) with a similar copper coping, but 40 microns thick. The discrepancies of fit of the 3 master gold crowns were evaluated in 99 stones dies (33 for each casting) obtained from 11 different elastomeric impression materials (3 replicae of each). The results showed that: 1) stone dies with no coping presented a medium discrepancy of 284 microns, inadequate for clinical use; 2) the 30 microns and 40 microns copings presented medium discrepancies of 18 and 9 microns respectively, both suitable for clinical use. Thus, the use of copings tend to equalize the cervical discrepancy of fit of gold crowns, whatever be the elastomeric impression material used.

Crowns↗
PubMed1990

[The neuromuscular effect of anterior guidance on the protrusive movement pattern of the mandible. Observations in the horizontal plane].

The influence of a temporarily altered anterior guidance on mandibular movement patterns of tooth-guided and non-guided protrusion was examined in a clinical study on 20 patients, all with complete sets of teeth. Registration and recordings of movements were done with the computer-aided ultrasonic measuring system MT 1602. Based on an average measuring time of 40 min for each patient the main results were as follows: 1. The shape of the anterior guidance strongly influences the horizontal tracings of tooth-guided and non-guided protrusion. In most cases these tracings show a deviation from the mid-sagittal path due to neuromuscular coordination. 2. Insertion of an idealized, symmetrical anterior guidance or a horizontal plateau lessens the mandibular deviation and harmonizes the tooth-guided and non-guided paths. However, the old neuromuscular engrams are not completely erased. 3. Newly formed engrams can be erased much easier than old ones.

Adult↗
PubMed1990

Avoidance of cast breakage during removal from the impression.

Breakage of a dental cast during its removal from the impression may result in inaccuracies in the finished appliance. The origin and prevention of the factors that can lead to cast breakage are found in the diagnostic phase. Casts of isolated teeth that are long, have marked gingival recession, and have a narrow clinical neck are prone to fracture. If casts of these types of teeth cannot be avoided, measures can be taken to prevent fracture. Wax can be used to thicken teeth with narrow clinical necks or to block out interproximal spaces in adjacent teeth without proximal contacts. The materials used to make the impressions and casts should also be chosen carefully. Methods of removing the cast to avoid fracture include the use of a soldering iron to cut the tray. Once the tray is sectioned, the impression material is free to elongate, and the cast can be removed easily.

Dental Casting Technique↗
PubMed1990

The transfer effect of leadup activities.

Previous literature shows that operative laboratory performance can be significantly improved through leadup training where students complete simulated preparations in plastic blocks. Since the task requirements of most fixed prosthodontic preparations seem similar to those of operative dentistry, it may be hypothesized that leadup training utilizing operative-like preparations would facilitate performance in the projects of both courses. The objective of this study was to test that hypothesis. The performance of students who had completed the leadup training nine months earlier was compared with that of randomly selected control groups, with replacement, in a subsequent operative and fixed prosthodontics course. Calibrated raters were unaware of group affiliation of products. Analyses of variance showed that students in the experimental group statistically significantly outperformed those in the control group on the two operative preparations which were most like products completed during the leadup training. There was no such difference for any of the three fixed prosthodontics products. It is concluded that transfer of training is highly specific and that leadup training must simulate the criterion in both its cognitive and motor components, if it is to have a facilitating effect.

Analysis of Variance↗
PubMed1990

Optimal placement of osseointegrated implants.

In summary, there is no substitute for thorough diagnosis, treatment planning, and meticulous surgical and prosthetic treatment. Proper utilization of surgical and radiographic correction-stents is one of the important aspects of the presurgical phase. The stents facilitate the accurate placement of implants in optimal positions where sufficient bone is present. In cases with insufficient bone, the stents may help in making a strategic alteration of the chosen implant site.

Acrylic Resins↗
PubMed1989

[Observation with SEM on the displacement of mucosal surface in process of denture fabrication].

The process of denture fabrication entails a series of steps that begin with impression-taking. Dimensional accuracy and displacement of surface repeatability affect results in these individual steps. Although changes in individual materials have already been measured in the past, there has been almost no measurement up to now of denture fabrication up to the denture base, using the mucous membrane as the standard and then measuring changes in the displacement of surface repeatability for each step. Noticing this lack, the authors used a Scanning Electron Microscope (SEM), presently the only non-contact measuring instrument that can be used, and measured changes at the different stages including the mucous membrane, the impression materials, the plaster and the resin. A drying process is required for the mucous membrane, and such a process can cause changes in the mucous membrane which is the basis of measurement. For this reason, the authors used Araldite, a product from Ciba-Geigy AG, as a replica material and made replicas for all the test materials, using the replicas for measurement. Results were as follows: 1. Araldite was used as the replica material, thus making it possible with the SEM to observe changes in the displacement of surface repeatability at the individual stages. 2. Major changes in the accuracy of surface were observed during impression-taking and in the period of moving from the impression material to the plaster. 3. During high-power observation with the SEM, the fine bumps on the surface of the plaster and resin disappeared and the surfaces became smooth. This is believed to be the result of the separating agent and heat.

Dental Impression Materials↗
PubMed1989

[Study on the disinfection of alginate impressions. 2. Dimensional stability and surface roughness after immersing or spraying treatment with povidone-iodine solution].

The dimensional changes of four alginate impression materials and the surface roughness of stone casts following the treatment with 0.07% Povidone-Iodine solution were evaluated. The impressions were treated by either immersing or spraying. The dimensional change was measured by an electronic micrometer with a non-pressure direct method for 60 minutes. The surface roughness of stone casts obtained from the impressions following optimal treatment was also measured. Two products were dimensionally stable for 60 minutes after spraying with the solution, while the other two were stable for 30 minutes in the solution. No effect of the treatment was observed on the surface roughness of stone casts.

Alginates↗
PubMed1989

[Dima: a solution for many implant problems].

The Authors point out the importance of a preliminary detailed examination on cases where an intrabone implanthology operation is necessary. The patient is examined from a neuromuscolar point of view, then a stereognatograph is used to check his chewing function. The subject is carefully examined under the profile of his individual characteristics by means of a print which reveals the drawing of the bone's profile under the area of the tooth and the perforation of the cutting edges exactly at the right point and in the direction desired by the dentist.

Adult↗