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PubMed1994

Comparison of a range of addition silicone putty-wash impression materials used in the one-stage technique.

This study investigated the accuracy of one-stage polyvinylsiloxane impressions recorded in metal and plastic stock trays using regular and soft putties. Impressions were made using the one-stage technique (putty and wash simultaneously) of a full arch, copper-plated typodont with turned full crown preparations. Dies resulting from all the putty-wash impressions recorded in plastic trays had significant differential die distortion at the cervical finishing line. Although President regular putty, President soft putty, Express and Provil produced acceptable dies when used with metal trays, significant differential die distortion occurred with Extrude and Reprosil. The putty-wash/plastic tray combination is unsatisfactory. Metal trays reduce die distortion with some putty-wash systems but not with others.

Dental Impression Materials↗
PubMedDate not supplied

Master cast accuracy in single-tooth implant replacement cases: an in vitro comparison. A technical note.

PURPOSE: This in vitro study evaluated the accuracy of master casts obtained by using (1) copings modified by sandblasting and coating their roughened surfaces with impression adhesive before final impression procedures and (2) gold machined UCLA abutments as impression copings in final impression procedures for single-tooth implant replacement cases. MATERIALS AND METHODS: A polymeric resin model with a standard single implant was used to simulate a clinical situation. A group of 20 impressions were made using square impression copings sandblasted to roughen their external surfaces at a supragingival level and then coated with Impregum polyether adhesive; a second group of 20 impressions were made using gold machined UCLA abutments as impression copings. The castable part of the UCLA abutments was secured with resin to the gold machined section of the UCLA abutment to prevent movement of the castable part itself on the gold machined portion during the impression procedures; the castable portion of the UCLA was also coated with the Impregum polyether adhesive to improve the stability of the gold machined UCLA abutment inside the impression material. Master casts fabricated for both groups were analyzed to detect rotational position change of the hexagon on the implant replicas in the master casts with reference to the resin model. RESULTS: The rotational position changes of the hexagon on implant replicas were significantly less variable in the master casts obtained using gold machined UCLA abutments as impression copings than in the master casts achieved with the roughened square impression copings. DISCUSSION: Improved precision of the impression was achieved when the gold machined UCLA abutments were used as impression copings. CONCLUSION: This report suggests that using gold machined UCLA abutments as impression copings in the final impression procedures can enable the clinician to achieve a more accurate orientation of the implant replicas in the laboratory master casts for single-tooth implant replacement cases.

Air Abrasion, Dental↗
PubMedDate not supplied

A pivoting appliance for intracavitary brachytherapy in patients with reduced mouth opening.

PURPOSE: The risks of radiotherapy to normal tissues are well known. In many cases, a tumor patient suffering a relapse cannot undergo radiotherapy a second time. One exception may be the local application of brachytherapy. Afterloading devices allow the position of radiating materials near the site for treatment exactly according to three-dimensional treatment planning. This report shows the technical procedure for the fabrication of an intracavitary afterloading radiation device. MATERIALS AND METHODS: A 48-year-old woman who had received neutron radiotherapy and tumor surgery for adenoid cystic carcinoma had to be treated for relapse. The mouth opening was limited to 15 mm. The mixing tip of a silicone impression system was used as an axis for a pivoting appliance. RESULTS: Two years after reradiation, the patient was free of relapse symptoms, although an increased limitation of mouth opening was recorded. CONCLUSION: Even if the mouth opening is severely limited after tumor surgery and/or radiation, intracavitary brachytherapy still can be performed in edentulous patients using a pivoting device.

Brachytherapy↗
PubMed1998

An accuracy evaluation of four removable die systems.

STATEMENT OF PROBLEM: The advent of implant dentistry has redefined the need for accuracy of working cast models. Die stone expansion and errors introduced by removable die casts may exceed the accuracy required for the passive fit of implant prostheses. PURPOSE: Several removable die systems claim improved accuracy because of their design and/or technical advancements. This study evaluated the 3-dimensional accuracy of 4 removable die systems. All 4 systems tested use either 1 or 2 pins as the repositioning device. MATERIAL AND METHODS: Four removable die systems were evaluated (Belle de St. Claire, Pindex, DVA, and conventional brass dowel system). Master model impressions were made with polyvinyl siloxane material and were later cast with type IV die stone material. Comparative dimensional analysis between the master model and the solid and sectioned casts was made by placing the cast in a standardized position and fabricating an individual custom base for each cast. Landmarks were measured with a traveling microscope, and by mathematically rotating the casts. Discrepancies beyond that of stone expansion or residual stress release at the time of die separation were due to the inability to precisely reposition the removable die of the sectioned cast. Data were analyzed with multivariate analysis of variance and paired t tests at alpha = .05 (n = 10). RESULTS: Significant differences were found among die systems tested (P = .005). When sectioned dies were compared with the master model, the accuracy of all 4 die systems was within 0.055 mm of the master model. Once sectioned, the Pindex system had the least linear expansion in the y dimension, and the brass dowel system demonstrated the least reseating discrepancy in the z (occlusogingival) dimension. CONCLUSIONS: All 4 die systems provided a similar degree of dimensional accuracy, although Pindex showed the least horizontal movement and the brass dowel system produced the least occlusogingival reseating discrepancy.

Analysis of Variance↗
PubMed1991

Dimensional stability of a polyvinylsiloxane impression material following ethylene oxide and steam autoclave sterilization.

Polyvinlsiloxane impressions were made from a stainless steel master die machined to stimulate five full veneer crown preparations symmetrically placed in an arch form. Three groups of 10 impressions each were made. Treatment groups were sterilized using an ethylene oxide gas and a conventional steam autoclave. Casts were poured and intrapreparation, height, and diameter measurements were made using a stereomicroscope, a digital electronic caliper, and a 1-inch travel dial indicator. Analysis of dimensional changes for the two groups showed that casts made from impressions sterilized by ethylene oxide are acceptable for use in the construction of fixed or removable prostheses. Casts made from impressions sterilized in a steam autoclave can be used for the fabrication of diagnostic casts and some transitional prostheses, but not for routine construction of crowns or fixed partial dentures.

Analysis of Variance↗
PubMed1989

[Dimensional change and deformation on stone dies for full cast crowns. Differences according to impression methods using vinyl silicone impression materials].

In order to reconfirm the efficiency of an individual tooth tray, an apparatus and method were developed for measuring dimensional changes and observing over all deformation on a stone die for a full cast crown. The stone dies, which were made by combination impression methods I, II and double impression (individual tooth tray use) with vinyl silicone impression materials, were measured and compared. The results were as follows: 1. It made no difference what kind of vinyl silicone impression materials were used. 2. As to the dimensional changes: for combination impression method I, irregular results were found for the stone dies with the differences between +1 standard deviation (SD) and -1 SD being large. The variations of the other two methods were quite small, indicating that the stone dies were made accurately. 3. Observing to magnified images with the naked eye, there were no clear differences between the three methods on the marginal parts, but at the top corners of the stone dies there were good results with the double impression method. 4. It was possible to grasp easily the general aspect of dimensional changes in the stone dies using this newly developed measuring method.

Calcium Sulfate↗
PubMed1997

Comparison of occlusal contacts in maximum intercuspation for two impression techniques.

STATEMENT OF PROBLEM: At the insertion of a fixed prosthesis, occlusal interferences in maximum intercuspation are often present. PURPOSE: This study investigated and compared the accuracy of interocclusal relationships in maximum intercuspation for mounted casts obtained from a quadrant dual-arch impression technique and conventional full-arch impression techniques. MATERIAL AND METHODS: Comparisons were made between an intraoral interocclusal record and interocclusal records made on mounted casts. Irreversible hydrocolloid, reversible hydrocolloid, polysulfide, polyether, and polyvinyl siloxane were used for the full-arch impression technique. For the quadrant dual-arch impression technique, rigid polyvinyl siloxane and light-body polyvinyl siloxane injection materials were used. RESULTS: Statistical analysis revealed a statistically significant difference (p = 0.0017) in the median values among treatment groups. All pairwise multiple comparison procedures (Student-Newman-Keuls) indicated the average error of the quadrant dual-arch records was significantly different from the average error of each group of records produced with the full-arch techniques (p < 0.05). Comparison of the records of the full-arch impressions did not reveal any statistically significant differences. The average error of the full-arch records was 72 +/- 33 microns and the quadrant dual-arch average error was 5 +/- 5 microns. CONCLUSION: The quadrant dual-arch impression technique produced mounted casts with significantly more accurate maximal intercuspal relationships than mounted casts from full-arch impressions.

Alginates↗
PubMed1981

Time-dependent accuracy of elastomer impression materials. Part I: Condensation silicones.

1. Although condensation silicone elastomers can be used to produce multiple dies from a single impression, one can expect changes in dimensions of dies produced from successive pours. 2. Putty/wash systems exhibit variable behavior among different brands. Some products produce a series of dies of increasing diameter over a 4-day period, while other brands may produce a series of dies whose diameters decrease as they are successively poured. 3. Light-body wash silicone impressions made in adhesive-lined custom acrylic resin trays produce dies which increase in diameter with time. 4. Putty/wash system, in general, show a greater eccentricity of dies than is seen with custom-tray/adhesive/wash systems, but there were some significant exceptions among the brands tested. 5. There does not appear to be any difference in behavior between single-wash and double-mix techniques in the condensation-silicone systems. 6. For maximum accuracy, the condensation-silicone systems should be poured as soon as possible after making the impression.

Adhesives↗
PubMed1976

The bonding properties of elastomer tray adhesives.

1. The surface yielded by the acrylic resin formed against tinfoil provided better retention for the rubber base than any other surface tested. 2. Wax consistently gave the worst results in spite of careful boiling out. 3. The use of wax or asbestos spacers would not degrade the resin surface if tinfoil, or presumably the more easily obtainable aluminum foil, were used as a separating medium. 4. For drying times of between 15 minutes and 72 hours, no significant change was found in bond strength of elastomer to tray material. 5. Drying times of less than 15 minutes were found to be inadequate and to decrease bond strength; they are clinically inadvisable. 6. If, as a result of unavoidable delay, a tray is painted and then left for a number of days prior to making the impression, satisfactory bonding will still occur. However, if the dentist wishes to apply a second coat and dry it for 15 minutes, an increase in bond strength is likely to occur. 7. In the six systems tested, failure occurred at varied levels, from a low of 20 p.s.i. to a high of 80 p.s.i. 8. In the silicone and polyether systems, cohesive failure of the elastomer occurred before the adhesive bond between elastomer and tray failed. This finding correlates with the clinical observation that silicones and polyethers are more difficult to remove completely from acrylic resin trays when an impression has to be repeated.

Acrylic Resins↗
PubMed1999

Use of lingual frenum in determining the original vertical position of mandibular anterior teeth.

STATEMENT OF PROBLEM: There is no accurate method for determining the correct vertical dimension of occlusion in edentulous patients. Preextraction diagnostic casts may facilitate determination of vertical dimension of occlusion. In the maxilla, the incisive papilla is a stable anatomic landmark and can be used as a guide to determine the vertical relation of the edentulous patient. Unfortunately, the mandible is devoid of such a stable anatomic landmark. PURPOSE: This study evaluated the reliability of measurement of the distance between the anterior attachment of the lingual frenum and the incisal edges of the mandibular incisors, on casts, to be used as a preextraction record for determining the vertical position of the mandibular incisors in complete denture patients. MATERIAL AND METHODS: Eighteen dentate subjects (9 men, 9 women; 21-28 years; mean age 23 years) were selected. Four mandibular casts were made from irreversible hydrocolloid impression material in plastic stock trays for each subject. All subjects were instructed to elevate the tongue while the impressions were made. The vertical distance between the anterior attachment of the lingual frenum and incisal edges of mandibular central incisors was measured on the casts. Means and standard deviations of the 4 measurements were calculated and statistically analyzed. RESULTS: The mean standard deviation of the distance between the anterior attachment of the lingual frenum and incisal edges of mandibular central incisors among the subjects was 0.1326 mm (coefficient of variation 1.292%). The distance between the anterior attachment of the lingual frenum and incisal edges of mandibular incisors was relatively stable when the frenum was recorded during function. CONCLUSION: The distance between the anterior attachment of the lingual frenum and incisal edges of the mandibular central incisors can be used on preextraction diagnostic casts as a preextraction record for determining the original vertical position of the mandibular anterior teeth.

Adult↗
PubMed1986

Accuracy of addition silicones as a function of technique.

Both addition and condensation silicones produced stone dies that were larger in diameter and shorter in height than the tooth preparation. For both materials, there was little change in the distance between stone die preparations compared with the standard. The most significant difference between types of silicone was that condensation silicones produced significantly shorter dies (-0.24% to -0.37%) than addition silicones (-0.08%). Among addition silicones, Cinch produced more than twice as much vertical change (-0.16%) than the other three products (-0.06%). Since castings made from a short die will not seat completely on the prepared tooth, these results support the use of three of the four addition silicones tested. The same accuracy of impressions was achieved for all techniques (that is, putty/wash, single mix, and double mix) when addition silicones were used, whereas the putty/wash technique produced the most accurate dies for the condensation silicones. The custom tray produced dies that were much more accurate in vertical dimensions (-0.03%) than the stock trays (-0.15% to -0.21%). Thus the custom tray is the impression tray of choice, even for addition silicones, which produce relatively little polymerization shrinkage and are dimensionally stable.

Chemical Phenomena↗
PubMed1996

Irreversible hydrocolloids for crown and bridge impressions: effect of different treatments on compatibility of irreversible hydrocolloid impression material with type IV gypsums.

OBJECTIVES: The aims of this research were: 1) to determine if the compatibility between irreversible hydrocolloids (alginates) and type IV gypsums (die stones) is affected by different treatments of the impressions before pouring, and 2) to present a rating system based on Ryge's system for clinical evaluation in order to classify the quality of gypsum casts using detail reproduction and surface structure as criteria. METHODS: Impressions were taken on a Plexiglas staircase (heights of the steps 15-82 microns) with six irreversible hydrocolloids designed for crown and bridge and ten type I and II irreversible hydrocolloids. Impressions of each brand were divided into four groups. One group was treated with 2% potassium sulfate, the second with water, the third with an alginate stabilizer, Sorbanat (Guilini Chemie), and as a control, a fourth group which was not allowed to come into contact with any liquid, i.e., the impressions were poured dry. The differently treated impressions were poured with ten type IV gypsums. The quality of all gypsum casts was then judged according to the rating system. RESULTS: All the irreversible hydrocolloids, if correctly treated before pouring with a compatible gypsum, could reproduce details of 20 microns. Detail reproduction did not improve with the use of 2% potassium sulfate solution compared to water or if the impressions were poured "dry". In general, the alginate stabilizer produced casts with significantly better detail reproduction and surface structure. SIGNIFICANCE: The results show that dentists and dental technicians need to know how each specific irreversible hydrocolloid should be treated and also with which type IV gypsum it is compatible. This research also indicates that an irreversible hydrocolloid impression should not come into contact with any liquid within the first 15 min.

Alginates↗
PubMed1992

Effect of impression tray design upon the accuracy of stone casts produced from a single-phase medium-bodied polyvinyl siloxane impression material.

The study examined the accuracy of stone casts produced from impressions taken in stock polycarbonate trays, some of which had been strengthened with autopolymerizing polymethyl methacrylate resin and four designs of custom-made trays. Impressions of an acrylic master model of the mandibular arch on which two extracoronal crown preparations and one intracoronal inlay preparation had been carried out were taken using a medium-bodied polyvinyl siloxane material. Each preparation had been intended with a reference point for later measurement. Five impressions were taken for each type of tray and these were cast in die-stone after 24 h. The distances between the points were measured with a reflex microscope and the means determined for each design of tray. The mean difference between casts produced from the various tray designs and the acrylic master model were determined for each of the distances between the three measuring points. Statistical analysis showed that, with the stock trays, there were no significant differences between any of the modifications, or between them and the acrylic model, for any of the three distances (P greater than 0.1). When the results from the custom-made trays were analysed there were statistical differences between the acrylic model and the casts from the unperforated tray with no stops (P = 0.02), and between the unperforated tray with no stops and the perforated with stops for the distance A-B (P less than 0.01). There were no other significant differences.(ABSTRACT TRUNCATED AT 250 WORDS)

Dental Impression Materials↗
PubMed1999

Marginal gap of crowns made with a phosphate-bonded investment and accelerated casting method.

STATEMENT OF PROBLEM: Numerous materials and methods have been used for complete crown fabrication. Conventional investing and casting procedures for phosphate-bonded investments require a 2- to 4-hour process before completion. Accelerated laboratory techniques have been used, but may not result in castings with equal marginal accuracy. PURPOSE: This study measured the marginal gap and determined the clinical acceptability of single castings invested in a phosphate-bonded investment with the use of conventional and accelerated methods. MATERIAL AND METHODS: Forty-four individual stone casts were poured from impressions made from a master die. Conventional and accelerated methods of investing and casting were followed in the fabrication of 44 single-unit castings. Twenty-two casts were used in each of the 2 groups. Each casting and its respective stone die were examined with a microscope at 4 predetermined sites. Perpendicular and 25-degree tilted measurements of marginal gap were documented for each. Evidence of marginal gap was then evaluated by t test. RESULTS: Measurements recorded on the perpendicular and on a 25-degree tilt showed no statistically significant difference between conventional and accelerated groups. All gap measurements except one were within the range of clinical acceptability. The measurements revealed that conventional and accelerated perpendicular gap means were 13.2 and 13.6 microm, respectively, and the average tilted gap means were 31.6 and 32.2 microm, respectively. CONCLUSIONS: A phosphate-bonded investment (Ceramigold) selected for an accelerated casting technique produced single castings within 30 minutes with marginal gaps comparable to those found that used conventional methods.

Crowns↗
PubMed1998

How well are complete dentures copied?

OBJECTIVE: To assess how accurately the same set of complete dentures could be copied by 12 different laboratories. DESIGN: A prospective study. SETTINGS: Completed by commercial laboratories used by GDPs in England (1996). Results were analysed and controlled by a university department. SUBJECTS (MATERIALS) AND METHODS: The master set was constructed to include a midline diastema and a bilateral posterior crossbite. Twelve sets of silicone moulds of the master denture were prepared. GDPs selected commercial laboratories of their choice to receive the work. MAIN OUTCOME MEASURES: All stages of the work were compared with the master dentures by returning them to a specially adapted articulator. Analysis was completed using preset criteria. RESULTS: Only five of the returned copies were considered to have both good quality acrylic resin work and clear details of the teeth in wax. Only four cases reproduced the diastema. After processing, the occlusal vertical dimension had been increased in eight of the cases and the bilateral crossbite had been eliminated in all cases. CONCLUSIONS: None of the final copy dentures were considered an accurate copy of the master dentures. There is considerable scope for further training of dental technicians in this important technique.

Acrylic Resins↗
PubMed2002

Application of a 3-dimensional measurement system to complete denture impressions.

STATEMENT OF PROBLEM: Little is known about tissue displacement at the tissue/denture base interface during impression making. PURPOSE: This study used a new 3-dimensional measurement system to analyze and compare 2 complete denture reline impression techniques (1 occluding and 1 digital) to determine which resulted in less displacement of the tissue/denture base interface during impression making. MATERIAL AND METHODS: The experiment included 10 completely edentulous subjects. For each subject, 3 mandibular casts were obtained: (1) a reference cast of the existing denture base, (2) a cast made with an occluding reline impression technique, and (3) a cast made with a digital reline impression technique. With the use of an optical 3-dimensional measurement system, the corresponding casts in a common coordinate system were analyzed geometrically. For each cast, the coordinates of the barycentric point and the high point were determined. For the same subject, the differences between the coordinates of the barycentric points of the 3 casts were calculated 2-by-2. The same calculation was performed for the high points. To determine whether these differences, which represent the displacements of the barycentric points and the high points, were statistically significant, the Wilcoxon signed-rank test for paired group comparisons was applied (P<.05). Cartographic differences among the casts from the same subject also were compared. RESULTS: The uncertainty of measurement for the location of the barycentric and highest point was +/-57 microm. The uncertainty in the differences among the cartographic displays was +/-0.1 mm. Vertically, the mean distance that separated the barycentric points obtained with the 2 impression methods was 0.04 mm. Cartography data showed that the greatest dimensional differences between the 2 impression techniques (minimum 0.25 mm; maximum 1.5 mm) were located near the retromolar pad and along the lingual flange. CONCLUSION: Within the limitations of this 3-dimensional in vivo study, displacement of the tissue/denture base interface was essentially equivalent with the use of an occluding and a digital mandibular impression technique.

Aged↗
PubMed2004

Effects of relief space and escape holes on pressure characteristics of maxillary edentulous impressions.

STATEMENT OF PROBLEM: The selective pressure technique has been recommended for making impressions of maxillary edentulous residual ridges. Although various methods for making impressions have been reported, a definitive procedure has not been clearly elucidated. PURPOSE: This in vitro study evaluated changes in impression pressure produced by different types of relief space and escape holes in the impression tray for making an impression of a simulated maxillary edentulous arch. MATERIAL AND METHODS: Silicone impression material (Exadenture) and a maxillary edentulous acrylic cast were used. A miniature pressure sensor was embedded at the mid-palatal suture (point-P) and at the left first molar area on the edentulous ridge (point-R). Three types of tray relief were used: no spacer (NS), a 0.36-mm-thick sheet of wax (SS), or a 1.40-mm-thick base plate wax (BS). Four types of escape holes were made: no hole (NH), or escape holes of 0.5, 1.0, or 2.0 mm in diameter (05H, 10H, and 20H, respectively) in the area opposing point-P. Twelve trays were formed using these relief space and escape hole combinations. The cast and tray were attached to a rheometer for applying a continuous isotonic force of 5.0 kgf and compressive speed of 120 mm/min. Impressions were made and measurement of pressure (kPa) began immediately prior to compression and continued until the materials had polymerized for 2 minutes, with a sampling time of 5 Hz. Measurements were performed 5 times for each tray. The data were analyzed using 3-way analysis of variance and the Bonferroni test (alpha=.05). RESULTS: At initial pressure, the data obtained at point-P showed significantly higher values for NSNH, NS05H, SSNH, and SS05H (range: 22.29 +/- 1.58 kPa to 29.96 +/- 1.41 kPa) than those at point-R (range: 18.61 +/- 1.12 kPa to 22.71 +/- 2.11 kPa). At end pressure, the data obtained from NSNH at point P showed a significantly higher value (25.36 +/- 1.69 kPa) than that of point-R (15.36 +/- 0.99 kPa) (P<.001), whereas data from NS10H and NS20H at point-P showed a significantly lower value (6.32 +/- 0.84 kPa and 4.50 +/- 0.42 kPa) than at point-R (15.50 +/- 0.49 kPa and 14.98 +/- 0.88 kPa) (P<.001). The data obtained from SS05H, SS10H, and NS20H at point-P showed significantly lower values (range: 3.72 +/- 0.44 kPa to 9.10 +/- 0.26 kPa) than those at point-R (range: 13.40 +/- 1.31 kPa to 14.40 +/- 0.98 kPa). Moreover, the data obtained from BSNH, BS05H, BS10H, and BS20H at point-P showed significantly lower values (range: 3.24 +/- 1.96 kPa to 10.20 +/- 1.84 kPa) than those of point-R (range: 11.69 +/- 1.01 kPa to 14.04 +/- 2.08 kPa). CONCLUSION: For making impressions of an edentulous maxilla, the data suggest that a tray with an escape hole 1.0 mm or larger or a spacer thickness of base plate wax (1.40 mm) be used.

Acrylic Resins↗