Internal fit of three-unit fixed dental prostheses produced by computer-aided design/computer-aided manufacturing and the lost-wax metal casting technique assessed using the triple-scan protocol.

Suboptimal adaptation of fixed dental prostheses (FDPs) can lead to technical and biological complications. It is unclear if the computer-aided design/computer-aided manufacturing (CAD/CAM) technique improves adaptation of FDPs compared with FDPs made using the lost-wax and metal casting technique. Three-unit FDPs were manufactured by CAD/CAM based on digital impression of a typodont model. The FDPs were made from one of five materials: pre-sintered zirconium dioxide; hot isostatic pressed zirconium dioxide; lithium disilicate glass-ceramic; milled cobalt-chromium; and laser-sintered cobalt-chromium. The FDPs made using the lost-wax and metal casting technique were used as reference. The fit of the FDPs was analysed using the triple-scan method. The fit was evaluated for both single abutments and three-unit FDPs. The average cement space varied between 50 µm and 300 µm. Insignificant differences in internal fit were observed between the CAD/CAM-manufactured FDPs, and none of the FPDs had cement spaces that were statistically significantly different from those of the reference FDP. For all FDPs, the cement space at a marginal band 0.5-1.0 mm from the preparation margin was less than 100 µm. The milled cobalt-chromium FDP had the closest fit. The cement space of FDPs produced using the CAD/CAM technique was similar to that of FDPs produced using the conventional lost-wax and metal casting technique.

Marginal and internal fit of metal copings fabricated with rapid prototyping and conventional waxing.

STATEMENT OF PROBLEM: Given the limitations of conventional waxing, computer-aided design and computer-aided manufacturing (CAD-CAM) technologies have been developed as alternative methods of making patterns. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fit of metal copings derived from wax patterns fabricated by rapid prototyping (RP) to those created by the conventional handmade technique. MATERIAL AND METHODS: Twenty-four standardized brass dies were milled and divided into 2 groups (n=12) according to the wax pattern fabrication method. The CAD-RP group was assigned to the experimental group, and the conventional group to the control group. The cross-sectional technique was used to assess the marginal and internal discrepancies at 15 points on the master die by using a digital microscope. An independent t test was used for statistical analysis (α=.01). RESULTS: The CAD-RP group had a total mean (±SD) for absolute marginal discrepancy of 117.1 (±11.5) µm and a mean marginal discrepancy of 89.8 (±8.3) µm. The conventional group had an absolute marginal discrepancy 88.1 (±10.7) µm and a mean marginal discrepancy of 69.5 (±15.6) µm. The overall mean (±SD) of the total internal discrepancy, separately calculated as the axial internal discrepancy and occlusal internal discrepancy, was 95.9 (±8.0) µm for the CAD-RP group and 76.9 (±10.2) µm for the conventional group. The independent t test results showed significant differences between the 2 groups. The CAD-RP group had larger discrepancies at all measured areas than the conventional group, which was statistically significant (P<.01). CONCLUSIONS: Within the limitations of this in vitro study, the conventional method of wax pattern fabrication produced copings with better marginal and internal fit than the CAD-RP method. However, the marginal and internal fit for both groups were within clinically acceptable ranges.

Marginal and internal fit of pressed ceramic crowns made from conventional and computer-aided design and computer-aided manufacturing wax patterns: An in vitro comparison.

STATEMENT OF PROBLEM: To our knowledge, no studies have evaluated the influence of the wax fabrication technique on the internal adaptation and marginal accuracy of pressed ceramic single crowns. PURPOSE: The purpose of this in vitro study was to compare the marginal and internal fit of a lithium disilicate crown fabricated either from conventional waxing or from a subtractive milled wax pattern. MATERIAL AND METHODS: Ten silicone impressions were made for a maxillary canine prepared to receive a complete crown. Two pressed lithium disilicate glass ceramic copings were made on the die poured from each impression. The first was from a conventional wax pattern and the second from milled wax blocks. The replica technique was used to measure the fit by scanning electron microscope at ×80 magnification. Collected data were analyzed with the paired Student t test for the marginal and wall fit. For the occlusal fit, the difference in scores did not follow a normal distribution, and the Wilcoxon signed ranks test was used (α=.05). RESULTS: The mean values +SD were 170.3 ±50.7 µm for the marginal fit and 130.3 ±21.6 µm for the internal fit with the conventional technique. For the computer-aided design and computer-aided manufacturing (CAD-CAM) technique, they were 105.1 ±39.6 µm and 98.1 ±26.1 µm. Statistical significance was found for the marginal and internal fit (P<.05). The occlusal fit median and interval interquartile scores were 305.0 µm (269.9 to 334.4) for conventional fabrication and 199.0 µm (141.5 to 269.9) for subtractive manufacturing. The differences were not statistically significant (P>.05). CONCLUSIONS: The subtractive CAD-CAM waxing technique resulted in the improved fit of a pressed lithium disilicate crown by decreasing the marginal discrepancies and internal adaptation.

Marginal adaptation of four inlay casting waxes on stone, titanium, and zirconia dies.

STATEMENT OF PROBLEM: Different inlay casting waxes do not produce copings with satisfactory marginal accuracy when used on different die materials. PURPOSE: The purpose of this study was to evaluate the marginal accuracy of 4 inlay casting waxes on stone dies and titanium and zirconia abutments and to correlate the findings with the degree of wetting between the die specimens and the inlay casting waxes. MATERIAL AND METHODS: The inlay casting waxes tested were Starwax (Dentaurum), Unterziehwachs (Bredent), SU Esthetic wax (Schuler), and Sculpturing wax (Renfert). The marginal opening of the waxes was measured with a stereomicroscope on high-strength stone dies and on titanium and zirconia abutments. Photographic images were obtained, and the mean marginal opening for each specimen was calculated. A total of 1440 measurements were made. Wetting between die materials and waxes was determined after fabricating stone, titanium, and zirconia rectangular specimens. A calibrated pipette was used to place a drop of molten wax onto each specimen. The contact angle was calculated with software after an image of each specimen had been made with a digital camera. Collected data were subjected to a 2-way analysis of variance (α=.05). Any association between marginal accuracy and wetting of different materials was found by using the Pearson correlation. RESULTS: The wax factor had a statistically significant effect both on the marginal discrepancy (F=158.31, P<.001) and contact angle values (F=68.09, P<.001). A statistically significant effect of the die material factor both on the marginal adaptation (F=503.47, P<.001) and contact angle values (F=585.02, P<.001) was detected. A significant correlation between the marginal accuracy and the contact angle values (Pearson=0.881, P=.01) was also found. CONCLUSIONS: Stone dies provided wax copings with the best marginal integrity, followed by titanium and zirconia abutments. Unterziehwachs (Bredent), wax produced the best marginal adaptation on different die materials. A significant correlation was found between the marginal accuracy and the contact angle values. As the contact angle value became smaller, the marginal accuracy improved. All combinations of waxes and stone and titanium dies presented a high wettability.

A simple method to fabricate stabilized record bases: a modified approach using casting wax for the borders.

Retention and stability of a record base is often compromised in the mouth because of blockout procedures performed before adapting a record base material on a definitive cast. This article presents a technique of fabricating a stable and retentive record base, in which a definitive cast does not receive a blockout procedure so that the record base engages the facial undercuts in the cast by means of a green coloured inlay casting wax.

Simplified technique for orbital prosthesis fabrication: a clinical report.

Loss of orbital content can cause functional impairment, disfigurement of the face, and psychological distress. Rehabilitation of an orbital defect is a complex task, and if reconstruction by plastic surgery is not possible or not desired by the patient, the defect can be rehabilitated by an orbital prosthesis. The prosthetic rehabilitation in such cases depends on the precisely retained, user-friendly removable maxillofacial prosthesis. Many times, making an impression of the orbital area with an accurate record of surface details can be a difficult procedure. The critical areas are making a facial moulage, mold preparation, and attaching the retention device, particularly when eyeglass frames are used. This case focuses on these hindrance factors. A simple basket was used for the impression tray to obtain the facial moulage. A putty mold was used, and attachment of the prosthesis to a retention device was accomplished with positional distance. This method proves to be an economical and simple way of making an orbital prosthesis.

An alternative approach in fabrication of fixed complete dentures using a duplicate denture.

The traditional prosthetic steps in the fabrication of a fixed complete denture after implant osseointegration include final impression, verification of implant positioning in the working cast, mounting of the working cast, and mock denture wax trial insertion prior to the laboratory fabrication of the metal substructure; however, in patient scenarios of immediate loading of implants, the interim conversion prosthesis can be used to advance from the final impression to the milling of the underlying framework in one appointment. Consistency in the initial wax trial insertion, radiographic guide, and intraoral positioning of the conversion prosthesis can result in a well-designed definitive prosthesis in less time with the use of the existing duplicate complete denture.

Reproduction of intra-radicular surface anatomy of extracted human teeth: comparison of three different materials using injection technique.

This in vitro study compared the reproduction of intra-radicular surface anatomy of extracted human teeth taken by silicon, inlay casting wax and acrylic resin using an injection technique to determine which material produced fewer voids. Twenty impressions/patterns using this technique were made for each material and compared with each other on the basis of number, location and size of voids. Length of each dowel impression/ pattern was also compared. The percentage of void free surfaces using silicon, inlay casting wax and acrylic resin were 90%, 100% and 85% respectively. Most of the voids were less than 1mm in size and situated in the middle third of the impression/pattern. There was no significant difference in the length of the impression/ pattern taken by the three materials. Using the injection technique to reproduce the intra-radicular anatomy of the dowel space, all three materials will show predictably good results.

A modification of a direct technique for the fabrication of posts and using wax pattern.

This new direct technique for the fabrication of posts and cores using a wax pattern is easy to manipulate. It requires no special armamentarium and is appropriate for various situations. It provides the advantage of a direct technique and ensures the post pattern's precise fit. It also avoids the disadvantage of other direct techniques, the limitation of the direction of the cores by the placement of the broaches, the pins, or the prefabricated dowels.

Novel method for titanium crown casting using a combination of wax patterns fabricated by a CAD/CAM system and a non-expanded investment.

OBJECTIVES: For titanium casting, most commercial investments for titanium recommend casting at a low mold temperature to reduce oxidation. However, the thermal expansion values of the molds at low casting temperatures may be insufficient. The purpose of the current study was to investigate the possibility of obtaining accurate titanium crown casts using wax pattern fabricated by a CAD/CAM system with a non-expanded mold. METHODS: Three types of experimental magnesia-based investments (A, B and C) were made and their properties were evaluated for dental use. Two kinds of wax patterns for full-coverage coping crowns (S-0: cement space of 0 microm; S-20: cement space of 20 microm) were fabricated using a commercial CAD/CAM system. A traditional method (TM) using inlay wax was performed for comparison. The investment for titanium casting was decided from the fundamental data of experimental investments. Titanium crowns were replaced on the stone die and the thickness of the cement layer was evaluated. RESULTS: There were no significant differences for the setting time and setting expansion among the experimental investments, but the aluminous cement content played a role in hardening and contracting the mold. The fit of the titanium crowns differed significantly between the TM and the CAD/CAM system. The ranges of thickness obtained from the TM, S-0 and S-20 were 20.78-357.88 microm, 25.12-107.46 microm and 17.84-58.92 microm, respectively. SIGNIFICANCE: High quality titanium crown casting was obtained using a combination of wax patterns fabricated by a CAD/CAM system and a non-expanded MgO-based investment.

Clinical evaluation of interocclusal recording materials in bilateral free end cases.

Five combinations of materials commonly used for intermaxillary records in cases of bilateral free end saddle were evaluated: acrylic resin base + wax; acrylic resin base + wax + ZOE paste; acrylic resin base + wax + Duralay resin; condensation silicone; and acrylic resin plate + irreversible hydrocolloid. The materials were evaluated by measuring the vertical distance between pairs of reference points located on the bases of the upper and lower articulated casts. The measurements obtained by manual articulation of the casts were used as the standards to which the measurements obtained with the recording materials were compared. ANOVA revealed significant differences among the materials and the Tukey's test showed that condensation silicone differed significantly (p<0.05) from the acrylic resin + wax combination, while no significant differences (p>0.05) were observed among the remaining materials. The condensation silicone presented the greatest differences from the measurements obtained by manual articulation of the casts whereas the acrylic resin base + wax combination presented the least differences. Based on the findings of this study, the following scale of fidelity can be settled from best to worst: acrylic resin base + wax; acrylic resin plate + alginate; acrylic resin base + wax + ZOE; acrylic resin base + wax + Duralay; and condensation silicone.

Fixation of cadaver eyes for surgical practice.

Cadaver eyes for surgical practice may be prepared by melting No. 7 dental wax in a 1-ounce medicine glass and fixing the globe with melted dental wax. The preparation is then placed in a styrofoam wig stand with openings prepared for the medicine glass.

Wetting effects of surface treatments on inlay wax-investment combinations.

Gypsum-bonded and phosphate-bonded investments were applied to wax surfaces which were untreated, treated by buffing with cotton moistened with a die lubricant containing organic solvent, or treatment with a wax pattern cleaner. Contact angles between the investment material and wax surfaces were measured and compared. The treatment of a wax pattern with a surface tension reducing agent significantly increases the degree of wetting by both gypsum- and phosphate-bonded investments.

Effect of investment mass on distortion of MOD wax patterns.

Flaring of proximal walls of years, but not examined. In this experiment, the mass of investment peripheral to the wax patterns was varied by use of casting rings of the same lengths but of different diameters. Thirty castings were made individually, ten from each ring of 28 mm, 48 mm, and 60 mm diameter. The castings were cemented to their parent dies, sectioned mesiodistally, and the cement spaces at specific sites measured. Flaring angles were calculated for the proximal walls and were found to be inversely proportional to the diameters of the casting rings, and, thus, to the peripheral mass of investment. Further studies to detail the fluid mechanics of investments and to predict wax pattern behavior are warranted.

Void formation by axial expansion of a gypsum-bonded investment.

The lengths of castings have been found to be dependent, in part, on the length of the ring lining material relative to the length of the casting ring. Five MOD inlay wax patterns were invested individually in open metal, in closed metal, and in plastic casting rings 35 mm or 42 mm long and 28 mm in diameter. The gingival walls of the wax patterns were placed either 8 mm or 15 mm from the uppermost ends of the rings. Specimens were broken in a mesiodistal direction, and the voids at the gingival walls were measured. The largest voids (139 microns) occurred in 42-mm-long plastic rings with the gingival walls 8 mm from the uppermost ends of the rings. The smallest voids (20 microns) occurred in the 35-mm-long closed metal rings. The boundaries between the investment and the voids were curved rather than accurately reflecting the straight gingival walls of the wax patterns.

Rheology of dental waxes.

OBJECTIVES: The rheological properties of waxes are of considerable interest in dentistry, yet the only adopted method of characterizing them in this respect is arbitrary and uninterpretable. The intention was to identify a means of doing so in an objective fashion and to apply it to a variety of products to establish the scope of behavior. METHOD: The modified Stokes' falling ball method was used to determine the apparent viscosity of 11 waxes over 25-45 degrees C under a wide range of loads and, therefore, strain rates. RESULTS: The falling ball method was demonstrated to be applicable over at least 7 orders of magnitude in viscosity, 7 in terminal velocity, and 3 in load. Waxes were shown to be pseudoplastic, lacking any identifiable yield point and having marked departures from Newtonian behavior. The pseudoplasticity followed a power law, the exponent of which (the pseudoplasticity parameter) was temperature dependent in a complex manner, but which showed a definite relationship to the reduced temperature, referred to the liquidus temperature. A master curve could not be constructed because of this variation, but also because of discontinuities in the isothermal contours attributed to stress-melting of components of the wax mixture. Stress-melting may in part account for the pseudoplasticity. SIGNIFICANCE: A standardized viscosity number has been defined at 30 degrees C and under 10 N load as the common logarithm of the falling ball apparent viscosity in order to characterize the flow behavior of dental waxes with a single convenient number. The shear thinning exponent, the reciprocal of the pseudoplasticity parameter, provides a similarly convenient measure of the stress-sensitivity of the wax. Direct objective comparison of the rheology of dental waxes may now be made, facilitating selection by the user through appropriate labeling.

Clinical and laboratory steps for the fabrication of a fixed, cement-retained, implant-supported, complete-arch maxillary prosthesis.

The fabrication of a complete-arch maxillary prosthesis has been associated with several prosthetic complications and difficulties. Although it has been reported that phonetics, esthetics, and proper lip support are difficult to achieve, there is a scarcity of literature on the clinical and laboratory procedures necessary to minimize these complications. The current article provides clinical and laboratory steps that may enable the clinician to achieve more predictable restorative results when fabricating a cement-retained, implant-supported, complete-arch maxillary prosthesis.

A laboratory evaluation of the construction of resin-bonded cast restorations.

OBJECTIVE: To compare the effect of two construction techniques and two pattern materials on the fit of resin-bonded cast restorations. DESIGN: In-vitro study carried out by one operator. SETTING: Postgraduate university hospital. SUBJECTS AND METHODS: 65 nickel-chrome castings were constructed using refractory die and lift-off techniques with wax and acrylic resin pattern material. They were cemented onto master silver dies, embedded in self-curing acrylic resin and sectioned along their long axes. Interfacial distance between the master silver die and casting was measured. RESULTS: A significant different between the range of figures in each group (Mann-Whitney Test, P < 0.01) was found. Construction techniques can be ranked in order of fit of castings: 1. Refractory die, wax patterns: 42.6 microns (SD 12.03). 2. Refractory die, acrylic resin patterns: 53.7 microns (SD.16.06).3. Conventional technique, acrylic resin patterns: 85.5 microns (SD 31.62). 4. Lift-off technique, wax patterns: 139 microns (SD 53.15).5. Lift-off technique, acrylic patterns: 172.8 microns (SD 74.04). CONCLUSIONS: Castings constructed using refractory die technique and subsequently cemented resulted in a more accurate and less variable fit than those produced with the lift-off technique. Wax patterns lead to more accurate castings than acrylic resin and locating indentations may interfere with the cementation of castings when lift-off techniques are used.

Dimensional accuracy of small gold alloy castings. Part 1. A brief history and the behaviour of inlay waxes.

Part 1 reviews published studies which relate to materials and techniques contributing to the dimensional accuracy of small dental castings. A brief history of the cire perdue or lost-wax method of casting alloys and the development of modern dental casting materials and techniques are presented. Data on the behaviour of inlay wax, in particular its contraction and distortion, are reviewed as is the extensive literature about the casting shrinkage of gold alloys (Part 2) and the setting and thermal expansion of investments under both laboratory and practical conditions (Part 3). Part 4 discusses the role of the casting ring and its asbestos liner. Asbestos as a liner has now largely been replaced by two alternative materials, one based on cellulose and the other on ceramic fibres. The limited literature on the effect of these newer materials on casting accuracy is also reviewed, as their introduction may require significant changes in the traditional technology of dental casting.

Dimensional changes of ring-shaped pattern.

Ring shaped wax patterns, having the same outside diameter and different inside diameters, were invested with a gypsum-bonded cristobalite investment. The wax pattern was eliminated in an electric furnace at 120 degrees C. A fusible alloy with a melting point of 47 degrees C was cast at room temperature. The dimensional deviations between the fusible alloy casting and the wax pattern were calculated using the inside diameter, ring width and outside diameter. On the other series, a gold alloy casting of the same size was fabricated in the usual manner of the dental precise casting procedure, and the dimension was compared with that of the wax pattern. In the comparison of 2 types of patterns, dimensional change by setting expansion was different. Dimensional change of the small inside diameter specimen differed at 3 portions measured, but that of the large inside diameter specimen was comparable at 3 portions. Concerning the resultant gold alloy casting, dimensional change at the outside diameter differed from each other, but those at ring width and inside diameter were comparable to each other. The difference in the inside diameter influenced dimensional change by setting expansion as well as that of the resultant casting.