Wax Pattern Research Articles

A Study on the Dewaxing Behavior of Carbon-Black-Modified LDPE–Paraffin Wax Composites for Investment Casting Applications

Dewaxing is an intermediate step in investment casting which can determine the properties of final metallic product and is strongly dependent on the properties of pattern wax. Processing of pattern wax composites with the conventionally available heating processes is energy intensive and requires high processing time, thus resulting in the lower processing rate at larger scale. Use of microwave technology for the dewaxing study is highly attractive alternative owing to the advantage of energy-efficient processing. The processing time of pattern wax composite of paraffin wax, bitumen, polyethylene and EVA in microwaves oven as a function of susceptor has been investigated. Carbon black was used as microwave susceptor in wax composites at several weight percentages. The efficient processing and melting behavior of pattern wax composite utilizing microwave dewaxing, thanks to the creation of heat sensitive sites within the pattern wax composite by the susceptor material, were analyzed in this study. FTIR-ATR, rheometer, TGA, DSC, UTM, SEM and OM were used to study the behavior of the wax composite. With the increase in the susceptor (CB) loading from 0.15 to 0.75%, an increase in the thermal stability of 6.86% was observed as depicted by the increase in the on-set temperature of the specimens. 71.9% decrease in the melt flow time of pattern wax composite was observed with the incorporation of 1.5% of CB as compared to reference specimen which manifested an inverse relationship between susceptor loading and processing time in the presence of microwave.

Design of occlusal wear facets of fixed dental prostheses driven by personalized mandibular movement

Statement of problemExisting virtual articulators simulate mandibular movement by using various parameters and are used to design restorations. However, they are not able to reproduce actual patient movements, and the designs of occlusal wear facets by them and by personalized mandibular movement have not been compared. PurposeThe purpose of this clinical study was to establish a clinical application protocol for a virtual articulator based on previous research and to evaluate the accuracy of the occlusal wear facets designed by it. Material and methodsThe gypsum casts of 12 participants were scanned with a cast scanner as the original data. A single crown, 3-unit splinted crowns, a 5-unit fixed partial denture, and a fixed complete denture were virtually prepared on the digital mandibular casts by using the Geomagic Studio 2013 software program. High points were created at the wear facets, and corresponding digital wax patterns with occlusal interferences were generated. The exocad software program was used to design corresponding restorations with the copy method. Static (STA restoration) and dynamic (DYN restoration) occlusal adjustments were carried out with the built-in virtual articulator. The mandibular movements of participants were recorded by the novel virtual articulator system, and the occlusal surfaces of the digital wax patterns were adjusted (FUN restoration). The restorations adjusted with the 3 methods were compared with the original data. The mean value and root mean square (RMS) of 3D deviation and positive volumes (V+) in the occlusal direction were measured. Depending on the normality, 1-way ANOVA and the Kruskal-Wallis test were used to analyze the influence of occlusal surface design methods on the morphology of occlusal wear facets (α=.05). ResultsThe mean deviation of the 4 kinds of STA restorations ranged from 0.19 mm to 0.22 mm, the DYN restorations from 0.13 mm to 0.17 mm, and the FUN restorations from 0.03 mm to 0.09 mm. A significant difference was found between the STA and FUN restorations of the 3-unit splinted crowns and 5-unit fixed partial dentures (Ρ=.013, Ρ=.021). The mean values of 3D deviation and V+ decreased from the STA group to the DYN group and then to the FUN group. The RMS and V+ were statistically similar (Ρ>.05). ConclusionsThe preliminary results of the study indicate that the FUN 3-unit splinted crowns and 5-unit fixed partial dentures designed with the self-developed virtual articulator were better than the STA restorations. The FUN restorations were more coincident with the morphology of the wear facets on the original teeth.

An approach to eliminate shell cracking problem in fused deposition modeling pattern based investment casting process

Fused deposition modeling process can be used to make complex plastic parts directly from the three dimensional CAD drawings without any requirement of tooling. For low volume production, these plastic parts can be used instead of wax patterns in investment casting process to reduce high cost of tooling required for making wax patterns. But with plastic patterns there is a problem of ceramic shell cracking during the pattern burnout process. This shell cracking is mainly due to thermal expansion of the plastic sprue and plastic patterns. In this paper, a method has been proposed to eliminate the problem of shell cracking by using a wax sprue instead of plastic sprue. A joint has been designed to attach plastic patterns with wax sprue. It has been found that the proposed method is successful in eliminated the shell cracking problem. In addition to this, the proposed method is expected to reduce the process cycle time and cost.

Classification for mandibular deviation and facial asymmetry and its clinical significance

Judged from the clinical manifestations, etiological mechanisms and jaw morphological structures, malocclusions with mandibular deviation and facial asymmetry are classified into three main categories, i.e., those with mandibular positioning factors, those with mandibular condyle defects, and those with jaw congenital deformities. In the first category, three subtypes, including mandibular rotation caused by dentitional irregularities, by dental compensation and by habitual posturing, are further defined. In the second category, mandibular deviation caused by condylar asymmetrical resorption or hyperplasia are defined as the two subtypes. The third category is further divided into two subtypes, i.e., jaw and facial asymmetry resulting from maxillary or mandibular structural deformities. The prime goal of orthodontic therapy is to displace and restore the deviated mandible to its right position, followed by correction of occlusal intercuspation. As an important procedure of the whole treatment protocol, It is critical to detect and localize the correct mandibular position by manipulation and then register it by wax pattern and articulator transferring. For the cases with mandibular functional elements and condylar asymmetrical length, the treatment modalities include orthopedic repositioning of the mandible by using occlusal and bite plane, SGTB and SGHB therapies; for cases with growth and developmental anomalies, orthognathic intervention should be an optimal solution.

Influence of Conventional Versus Digital Workflow on Marginal Fit and Fracture Resistance of Different Pressable Occlusal Veneers After Thermomechanical Fatigue Loading

Objectives: The aim of the study was to evaluate the marginal fit and fracture resistance after thermomechanical fatigue of two types of glass ceramic occlusal veneers constructed using two techniques for wax pattern. Methods: Thirty-two non-carious maxillary molars were used in this study. Teeth were prepared to receive all ceramic occlusal veneers. Prepared teeth were randomly divided into two equal groups according to the fabrication material of the occlusal veneer: Group I (e-max): pressable lithium disilicate glass ceramics. Group II (Celtra): pressable zirconia-reinforced lithium silicate glass ceramics. Each group was further subdivided into two equal subgroups according to the technique of construction of the wax pattern: Subgroup A (CAD/CAM): CAD/CAM technique. Subgroup B (Conventional): Conventional technique. Wax patterns were sprued, invested and heat pressed to produce the two types of ceramic occlusal veneers. All occlusal veneers were cemented to their corresponding teeth using adhesive resin cement. Thermomechanical aging was performed on all the samples. Vertical marginal gap distance measurement and fracture resistance testing were done. Results: The results of this study revealed that e.max (Conventional) recorded the highest vertical marginal gap mean values followed by Celtra (Conventional) then Celtra (CAD/CAM) while e.max (CAD/CAM) recorded the lowest mean values. It was found that e.max (conventional) recorded the highest fracture resistance mean values followed by Celtra (conventional) then e.max processed by (CAD/CAM) while Celtra processed by (CAD/CAM) recorded the lowest mean values. Conclusions: CAD/CAM constructed wax pattern presents a viable alternative option to conventional wax pattern. Celtra Press material revealed promising results.

Evaluation of accuracy of fit in cast metal post fabricated with direct and indirect techniques using micro-CT - An in vitro study.

Accuracy of fit of cast metal posts fabricated with direct and indirect techniques. To evaluate the accuracy of fit of cast metal posts fabricated with direct and indirect techniques using micro-CT. Sixty extracted human maxillary central incisors were used. The teeth were decoronated leaving 2 mm at the cementoenamel junction. Four patterns for each tooth were made including one direct and indirect wax pattern and one direct and indirect resin pattern. In total, 240 patterns and castings were made. Each tooth was scanned using microcomputed tomography (μCT) system with a resolution of 14.5 μm. μCT analyzer Sky scanner software was used to calculate the volume of space between the post and the canals. Statistical analysis used: The student paired t-test and unpaired t-test were used to determine the significant differences between groups. The overall space between the canal walls and posts made with the direct wax and resin technique had an average mean value of 1.10 mm3, whereas with the indirect technique resin and wax pattern, the average mean was 1.30 mm3 which was significant. Within the limitations of the study, it was found that the accuracy of fit is better in direct technique using wax pattern.

Evaluation and comparison of the porosities in the acrylic mandibular denture bases processed by two different curing cycles, using two different brands of commercially available denture base resins – An in vitro study

Purpose: This study evaluated and compared the amount of porosities in two different acrylic materials processed by two different curing cycles.Materials and Methods: A total of 200 mandibular edentulous master casts were fabricated by using a standard silicone mold. These casts were divided into two groups with 100 samples for each group and each group was divided into two subgroups with 50 samples depending on the curing cycles. On the master cast, a wax pattern was fabricated with 2 mm of thickness and processed by conventional flasking method to obtain the mandibular master specimen. This master specimen along with the master cast was flasked and mold space was created for the placement of test specimens. All these samples were subjected to curing cycles along with the test specimens followed by porosity analysis of the specimens.Results: ANOVA analysis inferred that there is a statistically significant difference between the mean porosity values between the groups.Conclusion: Analysis of mean porosity of all groups reveals that heat-polymerized specimens of Dental Products of India (DPI) processed with a long curing cycle have lesser mean percent porosity values.

A method of hollowing the obturator prosthesis and an overview on the pros and cons of the various materials used for hollowing.

Prosthetic rehabilitation of a partial or total maxillectomy with an obturator is the most acceptable treatment option. The hollowing of the obturator prosthesis is beneficial as it reduces the stresses over the underlying and surrounding tissues. A simple technique of fabricating a hollow bulb obturator has been discussed in this article. At the step of the packing of a denture, the hollow wax pattern of the defect area is formed with modeling wax. This hollow wax pattern is filled with water and is allowed to freeze to form an ice block. This ice block is removed from the wax pattern and is interposed between two layers for heat-cured acrylic resin and is then cured. After processing the denture, the water is retrieved by making a small hole in denture base, which is packed after hollowing with a cold cure acrylic resin. A lightweight prosthesis with a uniform thickness was achieved with a readily available and easily retrievable material, i.e., ice.

Binary Gaussian Process classification of quality in the production of aluminum alloys foams with regular open cells

Aluminum alloys foams with homogeneous and regular open cells have been frequently proposed and used as support structures for catalytic applications. In this kind of application, the quality of produced metal foam assumes primary importance. This paper presents an application of a classifier algorithm to predict quality in the manufacturing process of aluminum alloy foams with homogeneous and regular open cells. A data analysis methodology of experimental data, which is based on Binary Gaussian Process Classification, is presented. The proposed method is a Bayesian classification method, which gets away from any assumptions about the relationship between process inputs (the geometric design parameters of the regular unit cells) and process output (probability to obtain defective foam). We demonstrate that the proposed methodology can provide an effective tool to derive a model for the prediction of quality. An investment casting process, via 3D printing of wax patterns, is considered throughout the paper. Despite this specific case study, the methodology can be exploited in different processes in which the assumptions of traditional statistical approaches could not be easily verified, e.g., additive manufacturing.

Effect of the Use of Die Lubricant on the Marginal Fit of Wax Patterns.

The aim of this study was to evaluate the effect of die lubricant on the fit of wax patterns. An ivorine tooth was prepared to receive full-coverage metal-ceramic restoration with 360° shoulder finish line. The tooth was duplicated 40 times using additional silicone. The impression was poured with Type IV dental stone. These 40 dies were divided into 2 groups 20 each. Group A: The patterns were fabricated with the use of die lubricant. Group B: The patterns were fabricated without the use of die lubricant. Later, these patterns were sequentially checked for the marginal fit on the stereomicroscope. The readings from the stereomicroscope were tabulated; independent Student's t-test was used to compare the marginal fit between Group A and Group B. The mean gap on all four tooth surfaces in Group A (with use of die lubricant) was more compared to Group B (without use of die lubricant).Conclusion:Die lubricant definitely has their effect on fit of the wax pattern which later might be duplicated in the casting.

Asante Indigenous Lost Wax Cast Evolution for Profitable Economic Growth

Globalization and competition with modern industrial products is the basic and fundamental setback for the viability, sustainability and preservation of local cultural heritage of traditional arts in most part of the world. This has been the case of Casting done at Krofofrom in the Asante Kingdom of Ghana. Castings done at Krofofrom can be improved to compete with the global market for profitable economic growth. This study examined the adaptation strategies in the preservation and sustainability of the Krofofrom village traditional brass casting technology. The composition of casting mould cores used by Krofofrom artisans comprises charcoal, cow dung and clay. Although this composition results in a very stable core that disintegrates easily after casting, defects in the form of pin holes are a common occurrence on the inner walls of the cast artefacts, thereby ruining the finish. In many instances these pinholes are difficult if not impossible to remove or seal. To improve the performance of the existing core, experiments were carried out to determine suitable materials and the proportions required to reformulate and enhance the core composition. The addition of Plaster of Paris (P.O.P) to the composition prevented shrinkage and fracture while the presence of saw dust provided microscopic holes in the core structure to facilitate easy core disintegration after casting. High content aluminous clay component served to improve the refractory properties of the core. The new core composition comprising charcoal, P.O.P, saw dust and aluminous clay showed an improvement over the existing Krofofrom core composition. The improved composition yielded efficient cores that disintegrated easily after casting and impart smoother inner wall surface devoid of pinholes. Piercing and carving useful for wax pattern production is achievable when the appropriate wax formulation developed in this study is adhered to.

The Effect of Residual Dentition on the Dynamic Adjustment of Wear Facet Morphology on a Mandibular First Molar Crown

To evaluate the effect of different residual dentitions on the dynamic adjustment of wear facet morphology on a single mandibular first molar crown with a virtual articulator. Gypsum casts (N = 12) of natural full dentitions were mounted on an articulator and scanned. The mandibular right first molar (#46) was prepared and a copy of the tooth before it was prepared and used to design the crown. The wear facets on the original #46 were selected and elevated by 0.3 mm in the occlusal direction to generate high points. The #46 with high points was segmented to create a digital wax pattern. Then different teeth were virtually removed to generate 4 types of residual dentitions: Type I (no teeth), Type II (adjacent teeth), Type III (ipsilateral posterior teeth and canine), and Type IV (all teeth). The crowns were adjusted dynamically with different residual teeth to guide mandibular movement of the virtual articulator. Three-dimensional deviations, negative and positive volumes between crowns and wear facets on the original #46 were analyzed. The Kruskal-Wallis test was used to analyze the results. The mean deviation values and positive volumes decreased with the decrease in residual teeth, and the negative volumes showed an opposite trend. The mean deviation values, root mean square, and positive volumes were not significantly different. The negative volume of the crowns of Type I was different from that of Type IV (p = 0.031). Residual dentition affects the dynamic adjustment of wear facet morphology. When there are insufficient residual teeth, mandibular movements should be accurately measured.

Development of hybrid pattern material for investment casting process: an experimental investigation on improvement in pattern characteristics

ABSTRACT In this work, a hybrid pattern material is introduced for investment casting process to enhance the properties/characteristics of the pattern. The hybrid pattern material is prepared by mixing coconut oil into conventional wax pattern material’s ingredients and named as coconut oil-based hybrid (COBH) pattern material. A comprehensive experimentation was performed to examine the influence of injection parameters viz. injection temperature (IT), injection flow rate (IFR), and die temperature (DT) on COBH pattern characteristics such as surface roughness (SR), average shrinkage (AS), and needle penetration (NP). Regression models were developed and statistically analyzed. Additionally, multi-response optimization (MRO) was carried out using the desirability technique for minimum SR, AS, and NP. The ANOVA results revealed that all input variables significantly influenced the characteristics of the COBH pattern. The optimal parametric settings of IT = 65°C, IFR = 3.5 lpm and DT = 35°C obtained by MRO provided the desired responses (i.e., minimum SR, AS, and NP). The developed COBH pattern ban be utilized for the development of good quality castings.

Effect of reinforcing heat cured acrylic resin denture base with silanated and non-silanated glass fiber on some of its mechanical properties.

The aim of this study was to evaluate the effect of reinforcing heat cured acrylic resin denture base with silanated and non-silanated glass fiber on some of its mechanical properties (impact strength and flexural strength). Material and Methods: A total number of 140 specimens were used in this study. The specimens were divided into three groups, heat cured acrylic resin (HCAR) 20 specimens (control group), HCAR reinforced with glass fiber (60 specimens’ group I), and HCAR reinforced with silanated glass fiber (60 specimens’ group II). Then group I and group II was divided into three sub-groups according to the percentage of glass fiber incorporation {(5% by weight, 10% by weight and 15% by weight. Each sub group consists of 10 specimens for each test. Following A.D.A. specification No 12 for denture base polymers. wax patterns of specimens were prepared with different dimensions for every test Impact strength was tested by Charpy’s impact testing machine, while Flexural Strength Test was performed using Nexygen from Lloyd Instruments.Results: reinforcing heat cured acrylic resin denture base with 5% glass fiber with and without silane coupling agent will increase impact and flexural strength mean values significantly.Conclusion: reinforcing heat cured acrylic resin denture base with glass Fiber within limit with or without saline coupling agent will improve its impact and flexural strength values.

Fabrication of titanium restoration by means of calcium aluminate-bonded magnesia investment material and one-chamber arc casting apparatus.

Cast titanium restoration for molars has high biocompatibility and is covered by the Japanese national health insurance. Titanium casting requires specific investment material and casting apparatus. A cast restoration for the mandibular left second molar was fabricated using titanium in this study. A wax pattern fabricated on a definitive cast was invested in calcium aluminate-bonded magnesia investment material. Titanium was cast using an argon gas pressure one-chamber casting apparatus. No defects were observed on the surface and the hole was clearly reproduced. A smooth surface on the restoration was obtained by polishing at low speed. Reproductivity and polishing properties of the titanium restoration fabricated in this study were comparable to those of conventional dental metal restorations.

Chemical bonding of polycaprolactone on the surface of hydroxyapatite via silanization and ring opening polymerization

In this study, surface modification of hydroxyapatite (HAp) by grafting polycaprolactone (PCL) is described. This method is carried out into two steps: (1) A treatment of HAp powder with a mixture of tetraorthosilicate (TEOS) and 3-aminopropyl-etriethoxysilane (APTES) to introduce amine groups and enhance nucleophilicity of surface functionalities; (2) Initiation of the Ring Opening Polymerization (ROP) of the ε-caprolactone (CL) in the presence of the silanized HAp. Moreover, the impact of the reaction time (24, 48 and 72 h) on the grafting amount of PCL is performed. The results of FTIR analysis confirmed the presence of carbonyl groups on the silanized HAp, providing evidence of grafting of PCL on the HAp surface. WAXS pattern showed no formation of a secondary phase after surface modification and the crystallinity is preserved. SEM/TEM analysis revealed a homogenous surface powder composed of irregular nanoscale crystals. TGA analysis indicated the dependence of PCL graft amount on the reaction time. Finally, the effect of surface modification on HAp/PCL nanocomposites morphology was investigated.

Effect of varying levels of expertise on the reliability and reproducibility of the digital waxing of single crowns: A preliminary in vitro study

Statement of problemThe digital waxing of single crowns can be affected by the quality of intraoral scans and use of computer-aided design (CAD) software programs. However, clinical outcomes of the resulting crowns are also affected by computer-aided manufacturing (CAM) methodologies. Studies on the effect of different levels of expertise on digital waxing are lacking. PurposeThe purpose of this in vitro study was to assess the impact of different levels of expertise on the reliability and reproducibility of margin outlining during digital waxing. Material and methodsThirty analogs of implant stock abutments (Ø4.8×4 mm) were embedded into resin blocks. To simulate different clinical situations, abutments were divided into 3 groups: 10 abutments (group GOS) received artificial gingiva and were scanned with an open system intraoral scanner, while 10 abutments with (group GIS) and 10 abutments without artificial gingiva (group IS) were scanned with an intraoral scanner within an integrated CAD-CAM system. All resulting standard tessellation language (STL) files were used by 2 different observers (an experienced CAD professional and a clinician with basic CAD knowledge) to digitally design a left mandibular central incisor in the same software program. All resulting digital crown designs were exported to STL files to assess crown margin accuracy at the coupling interface by superimposition with the control STL file of the scan body designed for the same abutment by the manufacturer. For this purpose, a CAD software program was used to automatically calculate median, minimum, and maximum deviations of margins in millimeters. Statistically significant pairwise differences among groups and between observers were assessed with the Wilcoxon signed-rank test (α=.05). ResultsFor the CAD professional, median deviations between designed crown STL files and the control STL of the scan body were 0.08 mm (range: 0.04 to 0.15) for group GOS; 0.10 mm (range: 0.06 to 0.18) for group GIS; and 0.05 mm (range: 0.03 to 0.08) for group IS. For the clinician, median deviations were 0.08 mm (range: 0.04 to 0.12) for group GOS; 0.11 mm (range: 0.07 to 0.17) for group GIS; and 0.05 mm (range: 0.04 to 0.11) for group IS. There were no significant differences between observers (P>.05). However, statistically significant differences were found between group IS and the other 2 groups (P=.001) but not between groups GOS and GIS (P>.05). ConclusionsThe present findings suggest that a digital wax pattern made with a dental CAD software program is not affected by varying levels of expertise but might be affected by subgingival margins.

Development and application of intelligent monitoring system for rapid tooling applied in low-pressure injection molding

Investment casting is widely used to manufacture a variety of metal components through wax patterns fabricated by low-pressure injection molding of wax. With the high labor cost in the precision casting industry, ensuring the quality of wax patterns during the production process is crucial to manufacturers. Accordingly, an intelligent monitoring system was developed for silicone rubber mold applied in injection molding of wax patterns. The cooling time of the injection molded part obtained by the intelligent monitoring system is very close to that obtained by the on-site data acquisition system. The relationship between the temperature of the injection molded part and the cooling time after the injection molding of wax can be monitored remotely. The developed intelligent monitoring system has the functions of identifying six process parameters, including injection temperature, coolant inlet temperature, coolant inlet coolant flow rate, injection pressure, injection time, and mold temperature. The developed intelligent monitoring system is very practical and provides good application prospects in the batch production process of wax patterns.

Additive Manufacturing in Dentistry: Current Technologies, Clinical Applications, and Limitations

Purpose of ReviewThis review aimed to illustrate the utility of additive manufacturing technologies for the fabrication of polymer, metal, and ceramic components within the confines of their current and potential clinical applications in dentistry.Recent FindingsThe literature reviewed on five additive manufacturing technologies, namely, vat-polymerization, material jetting, material extrusion, powder-based fusion, and binder jetting, have been investigated in relevance to their dental applications. These technologies have the following existing or potential clinical applications: diagnostic and definitive casts, custom trays, positioning guides for custom abutments, tooth preparation guides, interim dental restorations, all-ceramic crowns, metal crowns and copings, silicone indices, occlusal devices, complete dentures, wax patterns for intra- and extra-coronal restorations, surgical guides, removable partial dentures, and tooth- or implant-supported frameworks.SummaryVat-polymerization, material jetting, and powder-based fusion technologies have existing clinical applications utilizing mainly polymers and metals. Additive manufacturing technologies need further development to be used with ceramic materials for dental applications.

Application of Stereolithography Based 3D Printing Technology in Investment Casting.

Advanced methods for manufacturing high quality parts should be used to ensure the production of competitive products for the world market. Investment casting (IC) is a process where a wax pattern is used as a sacrificial pattern to manufacture high precision casting of solid metal parts. Rapid casting is in turn, a technique that eases the IC process by combining additive manufacturing (AM) technologies with IC. The use of AM technologies to create patterns for new industrial products is a unique opportunity to develop cost-effective methods for producing investment casting parts in a timely manner. Particularly, stereolithography (SLA) based AM is of interest due to its high dimensional accuracy and the smooth surface quality of the printed parts. From the first appearance of commercially available SLA printers in the market, it took a few decades until desktop SLA printers became available to consumers at a reasonable price. Therefore, the aim of this review paper is to analyze the state-of-the-art and applicability of SLA based 3D printing technology in IC manufacturing, as SLA based AM technologies have been gaining enormous popularity in recent times. Other AM techniques in IC are also reviewed for comparison. Moreover, the SLA process parameters, material properties, and current issues are discussed.