Stone Cast Research Articles

Record base for an edentulous maxillary arch with severe undercuts in the labial aspect of the anterior residual ridge

A procedure is described for the fabrication of a record base for an edentulous maxillary arch with severe undercuts in the labial aspect of the anterior residual ridge. The record base is fabricated from autopolymerizing resin without soft lining materials and without blockout of the labial undercut of the stone cast. (J Prosthet Dent 2002;87:99-101.)

The effect of particles size distribution of gypsum powder on cast surface roughness

The aim of this study was to determine effect of particle size distribution on surface roughness of stone cast poured from two gypsum products (ZETA and QD). Ten samples from each gypsum product were prepared, Measurements of surface roughness were carried out by profilometer. The analysis of particle size distribution of the gypsum products tested was performed with sieving machine. Analysis of variance and Duncan's multiple range test used for data analysis. The result showed that particles size distributions of the two gypsum products were significant affect the surface roughness of stone cast. It was concluded that the smoothest surface of stone cast was obtained from ZETA dental stone were attributed to the distribution of different size of stone particles

The effect of chronic renal insufficiency on orthodontic tooth movement in rats.

The purpose of this study was to determine the effects of impaired renal function on the amount of orthodontic tooth movement (OTM) in a rat model of renal insufficiency (RI). The animals were divided into three groups: a control unoperated group in which only OTM was done, a sham-operated group, and an RI group. OTM was done two weeks after performance of the sham operation or the surgery to induce RI. Renal failure was induced by electrocoagulation of one kidney cortex followed by contralateral nephrectomy. A fixed orthodontic appliance consisting of a 5 mm length of nickel-titanium closed-coil spring was ligated between the maxillary right incisor and first molar to deliver an initial mesial force of 60 g. Four weeks after RI induction, the amount of tooth movement was estimated by measuring the space created between the first and second molars on a stone cast. Bone density was measured by optical densitometry on radiographs and serum parathyroid hormone (PTH) was measured with a radioimmunoassay method. The results showed that induction of RI significantly increased both OTM (P < .05) and PTH levels (P < .01), although there was no significant difference in bone density by optical densitometry between the unoperated, sham-operated, and RI groups four weeks after RI induction. The results suggest that an increase of bone-remodeling activities, as evident from a significantly higher level of PTH, may be responsible for increase in tooth movement.

Adaptation of acrylic dentures reinforced with metal wire

The aim of this study was to reveal the effect of metal wire on the adaptation of the denture reinforced with it. Forty maxillary dentures were made with two polymerization systems (DS system and SR‐Ivocap system). The dentures were divided into two groups: (1) the unreinforced dentures (control) and (2) the dentures reinforced with metal wire 1·0 mm in diameter. Discrepancies between the denture base and the stone cast were measured at five points immediately after polymerization and after a 30‐day immersion in water. The data were analysed using a two‐way or one‐way ANOVA test. Dentures reinforced with metal wire exhibited significantly lower adaptation to the stone cast than the unreinforced ones for each polymerization system. Immersion in water did not affect the adaptation of dentures reinforced with metal wire for each polymerization. Unreinforced dentures made by the DS system had significantly smaller discrepancies compared with the dentures processed with the SR‐Ivocap system. The adaptation of the dentures reinforced with metal wire decreased in comparison with the unreinforced ones regardless of the polymerization method. This should be considered when metal wire is used clinically as reinforcement.

Complete denture mounting casts with intact anatomical landmarks

J Prosthet Dent 2001;86:444.

Effect of acrylic resin post-pressing time on dimensional change of total denture base

The dimensional alterations of denture bases were verified in function of the acrylic resin post-pressing time. Twenty stone cast/wax base sets were confected for routine flasking procedure. Thermosetting acrylic resin (Clássico) was prepared according to the instructions of the manufacturer. After final pressing, the acrylic resin was submitted to polymerization in water at 74 degrees C during 9 hours, following the immediate, 6-, 12-, and 24-hour post-pressing times. The resin bases were fixed on the casts with instantaneous adhesive and the sets were laterally sectioned in the regions corresponding to the distal aspect of canines (A), mesial aspect of first molars (B), and posterior palatal zone (C). The gap between the stone cast and the resin base was measured with a comparative microscope at five referential positions for each kind of sectioning. Data submitted to ANOVA and Tukey's test showed that there was no statistically significant difference between the immediate and the 6-hour post-pressing times as well as between the 12- and the 24-hour post-pressing times. However, there was statistically significant difference between the immediate/6-hour groups and the 12-/24-hour groups.

The Accuracy of Stone Casts and the Reproducibility of Intercuspation

The Accuracy of Stone Casts and the Reproducibility of Intercuspation

Marginal fit and short-term clinical performance of porcelain-veneered CICERO, CEREC, and Procera onlays

Statement of problem. Onlay preparations are very complex surfaces for computer surface digitization, CAD, and CAM of all-ceramic onlay cores. Purpose. This study tested the hypothesis that onlays can be fabricated with CICERO, CEREC, and Procera core technologies. Material and methods. Fifteen mandibular and 10 maxillary molars were prepared for onlays in 17 patients (11 women and 6 men). The onlay design was experimental. Molars were prepared with deep gingival chamfers in the proximal boxes and around the functional cusps. The nonfunctional cusps were prepared with broad bevels. Eight stone dies of preparations were measured with a laser beam (CICERO), 10 dies with a light beam (CEREC), and 7 dies with a contact probe (Procera). Two onlay cores were produced for the same stone die. One core was used to analyze fit on the stone die, and the other core was porcelain veneered for optimizing anatomy, esthetics, and fit of the onlay and cemented. The fit of the onlay core on the stone die and the cement width on a stone cast were measured by a microscopic digital imaging system. The onlays were evaluated for function every 6 months for 2 years. Results. Measurements of the margins by the CICERO system were (1) precise (error <4%) and (2) accurate with an SD of less than 9 μm. The proposed onlay preparation design met the requirement that all points of the surface be visible from a single point of view for optical 3-dimensional mapping by the CEREC system. For the surface measurements by the Procera contact probe, the orientation of the sapphire tip toward the preparation surface was critical, and it was necessary to apply wax to smooth internal edges. The marginal gaps of the CICERO, CEREC, and Procera cores on the stone dies were 74 μm (SD 15), 85 μm (SD 40), and 68 μm (SD 53), respectively. The cement width was 81 μm (SD 64). No fractures occurred. Conclusion. Marginal gaps for the onlay cores were no more than 85 μm. The cement width of the semicomputer-produced onlays of 81 μm was a favorable measurement value for a clinically acceptable, strong all-ceramic onlay. However, this value as well as anatomy and esthetics of the onlay depended on the craftsmanship of the porcelain veneering by the dental technician. (J Prosthet Dent 2000;84:506-13.)

Controlled polymerization system for fabricating precise dentures

Statement of Problem: Most processed resin denture bases do not fit the cast accurately because of polymerization changes in the resin. The fit is more noticeable in the palate between the denture base and the cast. Therefore, development of a polymerization system that will improve the fit of a denture base to the cast is lack of worth considering to improve the fit and retention of the denture. Purpose: A newly developed polymerization system for dentures is presented that results in excellent adaptability of the denture base to the cast when compared with 2 other polymerization systems. Material and Methods: Forty-five maxillary dentures were made with 3 resins and 3 polymerization systems (a new polymerization system, SR-Ivocap system, original microwave polymerization system). Each denture and cast was sectioned through the second molar area parallel to the posterior border. Discrepancies between denture base and stone cast were measured at several points immediately after polymerization and after 30 days of immersion in water. In addition, disks of 3 materials processed in each system were examined for absorption of water and hardness at 2 measurement stages. Data were analyzed with the split-plot or 2-way ANOVA test. Results: Dentures made with the new polymerization system had significantly smaller discrepancies, compared with dentures processed with the SR-Ivocap system and the microwave method. The amount of water absorption of the resin disks processed by the new system was less than the disks made by the other 2 systems. Dentures made with the new system exhibited significantly better adaptation to the cast than those made with the other 2 systems. Conclusion: The new polymerization system produced a more accurate method of processing dentures when fit was compared with the fit of dentures made with the other 2 denture base resins. (J Prosthet Dent 2000;83:514-20.)

Dimensional changes and pressure of dental stones set in silicone rubber impressions

Objectives: A high expansion stone has been used for improving the adaptation of dentures. Although the method is based on the idea to compensate for the processing shrinkage of the denture base resin with the high expansion stone, there are few studies on the expansion behavior of stones in an impression. The purpose of this study is to clarify the dimensional changes of stones set in silicone rubber impressions using two types of impression tray. Methods: Impressions of a master model that represents the alveolar ridge were taken using a silicone impression material and the dimensional changes in the stone casts were measured in different directions ( x, y and z-axes). Two types of impression tray were used, one with an open surface and the other with a closed surface. In order to evaluate the setting expansion of the stones and the pressure against the impression, stones were poured in other impressions that were taken from a cubic master model. The thickness of the impression was set at 2 mm. Results: A statistical analysis showed that there were significant differences in the dimensional change in the vertical direction ( z-axis) and horizontal directions ( x- and y-axes) of any stone casts set in the open tray. However, there were no significant differences in the dimensional changes in any direction of each stone cast set in the closed tray. Significance: The impression tray influences the setting expansion of stones. Stones do not uniformly expand in the open tray and the dimensional changes in the stone casts in the three-dimensions increases, when used with a high expansion stone.

Three-dimensional guidance system for implant insertion: Part II. Dual axes table--problem solving.

The three-dimensional guidance system for implant insertion is a technique for placing a radiopaque vertical orientation pin over the crest of the alveolar ridge on the stone cast during fabrication of the radiographic guide. The cross-sectional and panoramic reformatted images were reproduced on a Polaroid or 35-mm print. The true vertical orientation pin facilitates (1) identification and the exact planned location of each implant in the reformatted images of the CT scan, (2) establishment of the internal starting point for the osteotomy on a photographic print, (3) optimum implant orientation, and (4) measurement of the angulation between the true vertical orientation line and optimum implant orientation. With the aid of a newly developed dual-axes base and transfer of the internal starting point of each implant to the stone cast, the buccolingual and mesiodistal implant inclinations for each implant were transferred to a surgical guide in the form of surgical steel drill guide tubes. The resulting pilot osteotomy transfers to the alveolar bone the exact starting point and the buccolingual and mesiodistal inclination for each implant. The technique provides a three-dimensional guidance system for implant insertion that is extremely accurate and yet practical.

印象法の違いが作業模型の寸法精度に及ぼす影響について

The purpose of this study was to evaluate the impression techniques for polyvinyl siloxane impression materials in terms of the accuracy of the resultant stone casts. An acrylic resin maxillary model with nature dentition was prepared as the original model. Four impression techniques with or without undercut blockout were selected to make the impressions, using stock tray only, custom tray only, custom tray with resin copings for abutment teeth and custom tray with bridge copings. The dimensional changes of the anterior bridge area and posterior bridge area of stone casts were compared. The results obtained were as follows : 1. The effect of undercut blockout on the accuracy of stone cast was more significant in the anterior bridge area than in the posterior bridge area. 2. The dimensional changes of the anterior abutment teeth were more significantly affected by the impression techniques than those of the posterior. 3. It would appear from this study that the impressions made by custom tray with bridge coping were superior to those by the other techniques in terms of the dimensional accuracy and stability of the stone casts.

Effect of frequency and amplitude of vibration on void formation in dies poured from polyvinyl siloxane impressions

Statement of problem. Numerous factors are involved in making a void-free dental stone cast from a polyvinyl siloxane impression. Purpose. The aim of this study was to determine whether frequency and amplitude of vibration had any effect on the formation of voids on the cast surface poured from polyvinyl siloxane impression with a mechanical model vibrator. Material and methods. Impressions were poured in dental stone with a mechanical model vibrator that was set at vibration frequency 3000 cycles/min (low) and 6000 cycles/min (high) by a knob. The amplitude of vibration is provided in 5 steps and remained constant for the step set on the instrument. A total of 240 casts were prepared. The vibrator was set at low frequency and 30 impressions were poured for each of the 5 steps of amplitude. The vibrator was then set at high frequency and 30 impressions were poured for each of the 5 steps of amplitude. The resultant casts were examined for the presence of surface voids under 10× magnification. Results. Means for voids in all cast groups calculated for low and high vibration frequencies indicated that an increase in the amplitude of vibration caused an increase in the number of voids on the die surface. Conclusion. Use of high frequency of vibration 6000 cycles/min and 0.40 mm amplitude produced significantly fewer voids ( P <.0001) compared with steps 4 (0.45 mm) and 5 (0.80 mm) amplitude. (J Prosthet Dent 1998;80:490-4.)

Preliminary evaluation of an electromagnetic three-dimensional digitizer in facial anthropometry.

In this investigation, the precision of a commercial three-dimensional digitizer in the detection of facial landmarks in human adults was assessed. Fifty landmarks were identified and marked on the faces of five men, on five women, and on a stone cast of the face of one man. For each subject, the three-dimensional coordinates of the landmarks were obtained twice using an electromagnetic three-dimensional digitizer, and the duplicate digitizations were superimposed using common orientations and centers of gravity. Metric differences between homologous landmarks were assessed, and Dahlberg's error was computed. For both men and women, the error was 1.05% of the nasion-midtragion distance, while for the cast, it was 0.9%. When the duplicate digitizations were used to mathematically reconstruct the faces, and several distances, angles, volumes, and surfaces were computed, more than 80% of the measurements had coefficients of variation lower than 1%. The digitizer can assess the coordinates of facial landmarks with sufficient precision, and reliable measurements can be obtained.

Fracture strength of Type IV and Type V die stone as a function of time

Statement of problem. During the removal of casts from the impression there is the risk of stone fracture. Purpose. This study evaluated the fracture resistance of four die stone materials at different time intervals. Material and methods. Additional silicone impressions were made of a maxillary master cast. Two Type V, one Type IV die stones and one Type IV resin reinforced stone were tested. A total of 80 casts were prepared, separated, and tested on the Instron Universal Testing Machine at½, 1, 12, and 24 hours to measure resistance to fracture. Results. Significant differences to fracture resistance of the different die stone materials were observed at all time intervals except at 24 hours. The data were analyzed with ANOVA at α = 0.005 and n = 5. Conclusion. It is recommended to wait at least 12 to 24 hours when separating casts from impressions to avoid fracturing casts. Residual moisture content in a stone cast may contribute to fracture. (J Prosthet Dent 1997;78:554-9.)

Relationship between size of denture foundation area and resorption of alveolar ridge in the edentulous mandible

summary The relationship between the size of the denture foundation area and the resorption of the alveolar ridge was investigated in 55 edentulous subjects. The denture foundation area was recorded using a modelling compound impression technique with border moulding. Both sides of each edentulous mandible were examined separately, making a total of 110 experimental sides in the study. On a stone cast made from each impression, the size of the superficial denture foundation area and of the projected denture foundation area on the tentative plane of occlusion of each anatomical zone were measured. The vertical height of the alveolar ridge at the lateral incisor and first molar region was also evaluated. The size of the superficial denture foundation area in the antero‐lingual and postero‐lingual zones showed no significant correlation with the degree of alveolar ridge resorption. The size of the projected denture foundation area on the tentative plane of occlusion in the anterior section showed negative significant correlation with the degree of alveolar ridge resorption. The size of the projected denture foundation area on the tentative plane of occlusion in the posterior section showed no significant correlation with the degree of alveolar ridge resorption.

Relationship between size of denture foundation area and resorption of alveolar ridge in the edentulous mandible.

The relationship between the size of the denture foundation area and the resorption of the alveolar ridge was investigated in 55 edentulous subjects. The denture foundation area was recorded using a modelling compound impression technique with border moulding. Both sides of each edentulous mandible were examined separately, making a total of 110 experimental sides in the study. On a stone cast made from each impression, the size of of the superficial denture foundation area and of the projected denture foundation area on the tentative plane of occlusion of each anatomical zone were measured. The vertical height of the alveolar ridge at the lateral incisor and first molar region was also evaluated. The size of the superficial denture foundation area in the antero-lingual and postero-lingual zones showed no significant correlation with the degree of alveolar ridge resorption. The size of the projected denture foundation area on the tentative plane of occlusion in the anterior section showed negative significant correlation with the degree of alveolar ridge resorption. The size of the projected denture foundation area on the tentative plane of occlusion in the posterior section showed no significant correlation with the degree of alveolar ridge resorption.

A new method to simplify and increase the precision of maxillary cast mounting procedures in fully adjustable or semiadjustable articulators

This study introduces a new impression procedure that permits mounting the maxillary stone cast in an articulator for any patient treatment and is applicable to any dental arch with any impression material. A transfer tray was designed that makes it possible to transfer the patient's maxillary impression to the articulator in a one-stage procedure without the need for making record bases and occlusion rims or the need to use a face-bow bite fork. (J Prosthet Dent 1997;77:219-24.)

歯列模型のこう合器装着時におけるこう頭かん合位の再現性からみたこう合記録材の精度

歯列模型のこう合器装着時におけるこう頭かん合位の再現性からみたこう合記録材の精度

A time-saving method for indirect fabrication of cast posts and cores

Cast post obtained from wax patterns often require tedious adjustments in the mouth to seat them passively in the prepared root canals. An indirect method that uses an elastic cast for the fabrication of resin patterns has been developed. A stone cast made from a second pour of the impression of the prepared canals is then used to adjust the patterns in the dental laboratory. Posts made with the use of this indirect method routinely seat in the root canals without adjustments at the chair. The procedure is especially useful for patients who require multiple posts in the same arch.