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.

Improvement in Ti-porcelain bonding by SiO(2) modification of titanium surface through cast method.

This study aimed to improve Ti-porcelain bonding strength through SiO2 modifications. Wax patterns were coated with SiO2 mixed with tetraethoxy silane (group C), patterns without coating were used as controls and subdivided into sandblasting group (group S) and polishing group (group P). Castingsurfaces were analyzed with XRD, while Ti-ceramic interfaces were characterized using SEM/EDS. Metal-ceramic specimens were tested in three point bending, and characterizations were also analyzed with SEM/EDS of porcelain debonding surfaces. In group C, SiO2 and Ti5Si3 phases were observed; SEM micrograph showed that Ti-porcelain had a compacted interface, and EDS maps of the interface illustrated the diffusion of Si, Al, and Sn to Ti, and cohesive fracture within the bonding agent. The bond strength of group C was 39.04±5.0 MPa, which was 15% higher than that of group S and 32% higher than that of group P. SiO2 coating could improve Ti-porcelain bond strength.

A comparison of the accuracy of patterns processed from an inlay casting wax, an auto-polymerized resin and a light-cured resin pattern material.

BACKGROUND: Traditionally, inlay casting waxes have been used to fabricate patterns for castings. Newer resin pattern materials offer greater rigidity and strength, allowing easier laboratory and intraoral adjustment without the fear of pattern damage. They also claim to possess a greater dimensional stability when compared to inlay wax. AIMS: This study attempted to determine and compare the marginal accuracy of patterns fabricated from an inlay casting wax, an autopolymerized pattern resin and a light polymerized pattern resin on storage off the die for varying time intervals. MATERIALS AND METHODS: Ten patterns each were fabricated from an inlay casting wax (GC Corp., Tokyo, Japan), an autopolymerized resin pattern material (Pattern resin, GC Corp, Tokyo, Japan) and a light-cured resin pattern material (Palavit GLC, Hereaus Kulzer GmbH, Germany). The completed patterns were stored off the die at room temperature. Marginal gaps were evaluated by reseating the patterns on their respective dies and observing it under a stereomicroscope at 1, 12, and 24 h intervals after pattern fabrication. RESULTS: The results revealed that the inlay wax showed a significantly greater marginal discrepancy at the 12 and 24 h intervals. The autopolymerized resin showed an initial (at 1 h) marginal discrepancy slightly greater than inlay wax, but showed a significantly less marginal gap (as compared to inlay wax) at the other two time intervals. The light-cured resin proved to be significantly more dimensionally stable, and showed minimal change during the storage period. CONCLUSION: The resin pattern materials studied, undergo a significantly less dimensional change than the inlay waxes on prolonged storage. They would possibly be a better alternative to inlay wax in situations requiring high precision or when delayed investment (more than 1 h) of patterns can be expected.

Clinical evaluation of interocclusal recording materials in bilateral free end cases

Cinco combinações de materiais comumente utilizados para registros intermaxilares em casos de extremidades livres bilaterais foram avaliados: base de resina acrílica + cera; base de resina acrílica + pasta zincoenólica; base de resina acrílica + cera + resina Duralay; silicona de condensação; e placa de resina acrílica + hidrocolóide irreversível. Foi realizada a medida da distância vertical entre pontos referenciais em 6 regiões nas bases dos modelos articulados. As medidas obtidas com a articulação manual dos modelos foram tomadas como padrão de comparação para as medidas obtidas com os materiais testados. Os resultados foram submetidos à análise estatística por meio de análise de variância e teste de Tukey. Houve diferença estatisticamente significante (p<0.05) entre a silicona de condensação e a combinação da base de resina acrílica + cera, porém entre os demais materiais não houve diferença estatisticamente significante. A silicona de condensação apresentou as maiores diferenças em relação às medidas obtidas pela articulação manual dos modelos e a combinação da base de resina acrílica + cera apresentou as menores diferenças. Com base nos achados deste estudo, a seguinte escala de reprodutibilidade pode ser estabelecida, do melhor para o pior: base de resina acrílica + cera; placa de resina acrílica + hidrocolóide irreversível; base de resina acrílica + cera + pasta zincoenólica; base de resina acrílica + cera + resina Duralay; e silicona de condensação.

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.

[Effects of investment materials on cast shrinkage of base metal alloys].

OBJECTIVE: To compare the influence of different investment materials, methods and crown height on the cast shrinkage of full crowns made of dental base metal alloy. METHODS: All of the 288 wax patterns were made and divided into three groups according to their crown height. In every group, wax patterns were invested in metal rings and paper rings with three types investment material and cast with base metal alloys. Then the inside diameters of castings were measured and analyzed by statistical package SPSS. RESULTS: Differences between groups invested with the three types of material were significant(P < 0.01). There were significant difference between the groups investing with metal rings and paper rings(P < 0.01). CONCLUSION: The component of investment material and invested ring can affect the cast shrinkage of dental base metal alloy apparently.

Effect of wax melting range and investment liquid concentration on the accuracy of a three-quarter crown casting.

STATEMENT OF PROBLEM: Dental casting accuracy is influenced by the setting expansion of investment materials. Although setting expansion can help compensate for casting shrinkage, it cannot be fully realized under a confined wax pattern. Exactly how soft a wax pattern should be to ensure optimum setting expansion has not been determined. PURPOSE: In this study, the relationship between wax characteristics and the casting accuracy of a three-quarter crown was investigated. MATERIAL AND METHODS: Four different wax materials were used: paraffin 135 with a softening temperature of 37.5 degrees C (P38), paraffin 1080 with a softening temperature of 63.5 degrees C, Shofu Red with a softening temperature of 41.5 degrees C, and Shofu Hard with a softening temperature of 51 degrees C. Two mixtures of phosphate-bonded investment were prepared: one with 100% special liquid and another with 75% special liquid plus 25% distilled water. For both, the liquid/powder ratio was 16:100. A type IV gold alloy was cast into a three-quarter crown mold. The discrepancy at 6 locations (1 lingual, 1 mesial, 1 distal, and 3 facial) was measured with a traveling microscope. Five readings were collected. Means and standard deviations were calculated for all data. A 2-way analysis of variance followed by the Student-Newman-Keuls test for multiple comparisons was used to identify significant differences between groups at the 95% confidence level. RESULTS: For the gingival measurement sites (lingual, mesial, and distal), there was no significant difference in cast adaptation when Shofu Hard and paraffin 1080 waxes were used. However, the results with these 2 waxes were different than with Shofu Red and P38. For the 3 facial measurement sites, significantly different measurements were found for each wax; P38 demonstrated the best results. Casting shrinkage was smaller with the use of 100% special liquid. CONCLUSION: Within the limitations of this study, casting shrinkage was affected by the type of wax used and was sensitive to the site at which dimensional measurements were performed. The higher the softening temperature, the larger the casting shrinkage.

A review of 243 errors possible during the fabrication of a removable partial denture: part II.

In Part II of this series, possible errors 72 through 168, all of which may be committed during the fabrication of a removable partial denture, are presented. Suggestions for avoiding the problems and solutions for correcting them are described.

A review of 243 errors possible during the fabrication of a removable partial denture: part III.

In Part III of this series, possible errors 169 through 243, all of which may be committed during the fabrication of a removable partial denture, are presented. Suggestions for avoiding the problems and solutions for correcting them are described.

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.

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.

The effect of potential investment expansion and hot strength on the fit of full crown castings made with phosphate-bonded investment.

In an earlier investigation, it was shown that when full crowns are cast in gypsum-bonded investments, their relative inaccuracy is affected by both the investment's potential expansion and its hot strength. This study repeated the earlier one, but used a high-melting gold alloy and two phosphate-bonded investments. The investments were used under conditions which gave a range of potential expansions and hot strengths. Casting inaccuracies were determined both diametrally and axially. All castings showed distortion, which varied under the different conditions. All were oversized axially, by amounts varying from + 0.8% to +2.3%. Diametral inaccuracies ranged from -0.2% to +0.7%. Investment expansion had a strong effect on axial inaccuracy, but a negligible effect on diametral inaccuracy. Conversely, hot strength had a strong effect on diametral inaccuracy, but only a very weak effect on axial inaccuracy. With phosphate-bonded investments, both potential expansion and hot strength are important parameters of relative casting inaccuracy. In combination, these properties showed very strong correlations with both diametral and axial inaccuracies. The observed distortions were the result of anisotropic mould expansion and anisotropic alloy shrinkage. The best fit, and least distortion, occurred with an investment setting under dry conditions.

Stabilization investment template for direct casting connection of implant framework segments.

This article presents a procedure whereby a template made of casting investment is used to stabilize a sectioned implant framework that has been adapted in a passive relationship to the implant analogs in a corrected master cast. The joints in the sectioned framework are filled with wax, sprues attached, and the template and sectioned framework are invested in a casting ring. When the casting procedure is completed, the framework will be reconnected by direct metal casting.

Pattern waxes and inaccuracies in fixed and removable partial denture castings.

It is the desire of every dentist and dental technician to produce a restoration that will fit the patient with a minimum of adjustments and certainly one that does not require remaking. Yet many abuse the materials with which they work, either through improper manipulation, lack of familiarity with their properties, or by attempting to reduce laboratory time by taking short cuts. Wax is one of the materials that requires more knowledge and skill to manipulate accurately because it has a considerably higher coefficient of thermal expansion (and contraction) than any other dental material. It often contributes considerably to the inaccuracies of cast dental restorations. This article provides a review of dental waxes used to make prosthodontic castings and points out some of the properties of waxes that must be controlled to make accurate restorations.

The effect of storage time of removable partial denture wax pattern on the accuracy of fit of the cast framework.

STATEMENT OF PROBLEM: Situations may arise in dental laboratories that could result in a time lapse between preparing the wax pattern of the removable partial denture framework and its casting into the cobalt-chromium alloy. PURPOSE: This study investigated the effect of storage time of the wax pattern before casting and the influence of the palatal major connector design on the accuracy of its fit on the master casts. MATERIAL AND METHODS: Forty-two frameworks were prepared with two designs of major connectors, which were divided into three subgroups according to the storage time of the wax patterns: 24 hours, 1 week, and 1 month. Discrepancies in the fit of the connectors to their respective casts were measured at specific locations for both connector designs. RESULTS: In both framework design groups, there was a significant deterioration in fit (p < 0.0005) of the major connectors with the increase in storage time of their wax patterns on their respective refractory casts. Gap discrepancies were more pronounced towards the center of the palate. CONCLUSIONS: The greatest discrepancies appeared at the middle sections of the connectors more than at the lateral section (p < 0.0005). Furthermore, frameworks with modified palatal plate major connectors exhibited greater inaccuracies in their fit than those with the anterior posterior palatal strap design, as evidenced by the increase in mean gap discrepancies under the palatal plate design (p < 0.0005).

Effect of selected physical properties of waxes on investments and casting shrinkage.

This study evaluated the relationship between flow characteristics, bending strength, and softening temperature of paraffin and dental inlay waxes to casting shrinkage when patterns were invested with a phosphate-bonded investment. This study found that the casting shrinkage decreased as the flow of the wax pattern increased. If a low flow wax is used or if there is a need for a thick pattern, the size of the casting ring should be increased. When wax patterns are formed for cast restorations, it is important to select the type of wax with the most desirable properties for the margin and the occlusal portions. Moreover, to accurately fabricate castings, it is necessary to understand the physical properties of the chosen waxes.

Waxes for functional impressions.

The aim of this study was to develop a wax suitable to serve as a functional impression material. Several binary mixtures of paraffin, beeswax and rosin were prepared. They were characterized by differential thermal analysis (DTA), and tested for plastic deformation, thermal expansion, detail reproduction and mechanical properties. It was found that the combinations of paraffin with rosin can function well as impression materials, as they combine a high value of plastic deformation at 37 degrees C with relatively low values at room temperature. Concentrations of rosin as small as 1% or 2% are adequate to produce this result. The flow of paraffin was significantly reduced by the addition of beeswax. A linear relationship was found between the 37 degrees C flow values of paraffin-beeswax mixtures and the proportions of the ingredients.

Stability of dental waxes following repeated heatings.

The flow and strength properties of dental waxes were examined following excessive and repeated heatings of the materials. For one product, the flow at 40 +/- 0.5 degrees C was reduced by 25.3% following heating above 200 degrees C. A decrease of the elastic modulus at 20 +/- 1 degree C by approximately 66% was observed in some cases after the heating temperature had been increased to 300 degrees C. Property variations were related to compositional changes, which were investigated by infrared spectoscopy and thermal analysis. Exposure of dental waxes to temperatures higher than 200 degrees C, particularly if it is repeated, may affect the composition and properties, resulting in inferior materials.

Crown pattern waxes: a study of their behavior on heating and cooling.

The values of the critical physical properties, flow and linear thermal expansion, of crown pattern waxes were determined and compared with those reported by previous investigators. The method is one proposed by the American Dental Association, and measurements were conducted in the temperature range of 27 to 52 degrees C. At temperatures higher than 37 degrees C most of the materials tested exhibited flow values that although rather low seem to be suitable for laboratory use. As expected, the linear thermal expansion was considerable, ranging from 1% to 1.5% or more as the temperature was increased from 27 degrees to 47 degrees C. The arrest points of the cooling curves, which are indicative of the composition of the materials, were recorded and studied. The possibility of correlating the arrest points with the transition points observed on the flow and expansion curves was investigated. Although attempts have been made to improve them, the commonly used dental waxes are not yet entirely free of their known drawback of large and perhaps uncontrollable thermal expansion.