Production Of Dental Prostheses Research Articles

Investigation and optimization of hot pressed porcelain dental prostheses production by MSLA application

PurposeDifferent technologies may currently be used to produce dental prostheses, such as additive manufacturing and traditional milling. This study aims to evaluate and improve the fabrication process for hot-pressed porcelain dental prostheses and compare the use of masked stereolithography apparatus (MSLA) casting to computer-aided design/computer-aided manufacturing (CAD/CAM) casting. The cost-benefit analysis of producing dental prostheses through various technologies, including additive manufacturing and traditional milling, has not been fully explored. The cost of materials and processes used to produce prostheses varies based on complexity of design and materials used, and long-term effects, such as durability and wear and tear, must be taken into account.Design/methodology/approachUsing key elements of part costs and estimation cost models, a multivariable approach was used to evaluate the practicality of the recommended strategy and process improvement.FindingsThe research found that MSLA casting provides a higher return on investment than CAD/CAM casting, and the optimized production process could be more suitable for the size and annual demand for prostheses.Originality/valueOverall, this study highlights the need for a more comprehensive understanding of the cost-benefit analysis of different dental prosthesis production methods and emphasises the importance of evaluating long-term effects on the cost-benefit analysis.

Mechanical and Surface Characteristics of Selective Laser Melting-Manufactured Dental Prostheses in Different Processing Stages.

Due to the expansion of the use of powder bed fusion metal additive technologies in the medical field, especially for the realization of dental prostheses, in this paper, the authors propose a comparative experimental study of the mechanical characteristics and the state of their microscale surfaces. The comparison was made from material considerations starting from two dental alloys commonly used to realize dental prostheses: Ni-Cr and Co-Cr, but also technologies for obtaining selective laser melting (SLM) and conventional casting. In addition, to compare the performances with the classical casting technology, for the dental prostheses obtained through SLM, the post-processing stage in which they are in a preliminary finishing and polished state was considered. Therefore, for the determination of important mechanical characteristics and the comparative study of dental prostheses, the indentation test was used, after which the hardness, penetration depths (maximum, permanent, and contact depth), contact stiffness, and contact surface were established, and for the determination of the microtopography of the surfaces, atomic force microscopy (AFM) was used, obtaining the local areal roughness parameters at the miniaturized scale-surface average roughness, root-mean-square roughness (RMS), and peak-to-peak values. Following the research carried out, several interesting conclusions were drawn, and the superiority of the SLM technology over the classic casting method for the production of dental prostheses in terms of some mechanical properties was highlighted. At the same time, the degree of finishing of dental prostheses made by SLM has a significant impact on the mechanical characteristics and especially the local roughness parameters on a miniaturized scale, and if we consider the same degree of finishing, no major differences are observed in the roughness parameters of the surfaces of the prostheses produced by different technologies.

Effect of Different Filler Contents and Printing Directions on the Mechanical Properties for Photopolymer Resins.

Photopolymer resins are widely used in the production of dental prostheses, but their mechanical properties require improvement. We evaluated the effects of different zirconia filler contents and printing directions on the mechanical properties of photopolymer resin. Three-dimensional (3D) printing was used to fabricate specimens using composite photopolymers with 0 (control), 3, 5, and 10 wt.% zirconia filler. Two printing directions for fabricating rectangular specimens (25 mm × 2 mm × 2 mm) and disk-shaped specimens (φ10 mm × 2 mm) were used, 0° and 90°. Three-point bending tests were performed to determine the flexural strengths and moduli of the specimens. The Vickers hardness test was performed to determine the hardness of the specimens. Tukey’s multiple comparison tests were performed on the average values of the flexural strengths, elastic moduli, and Vickers hardness after one-way ANOVA (α = 0.05). The flexural strengths and elastic moduli at 0° from high to low were in the order of 0, 3, 10, and 5 wt.%, and those at 90° were in the order of 3, 0, 10, and 5 wt.% (p < 0.05). For 5 and 10 wt.%, no significant differences were observed in mechanical properties at 0° and 90° (p < 0.05). The Vickers hardness values at 0° and 90° from low to high were in the order of 0, 3, 5, and 10 wt.% (p < 0.05). Within the limits of this study, the optimal zirconia filler content in the photopolymer resin for 3D printing was 0 wt.% at 0° and 3 wt.% at 90°.

3D Printing in Digital Prosthetic Dentistry: An Overview of Recent Developments in Additive Manufacturing.

Popular media now often present 3D printing as a widely employed technology for the production of dental prostheses. This article aims to show, based on factual information, to what extent 3D printing can be used in dental laboratories and dental practices at present. It attempts to present a rational evaluation of todays´ applications of 3D printing technology in the context of dental restorations. In addition, the article discusses future perspectives and examines the ongoing viability of traditional dental laboratory services and manufacturing processes. It also shows which expertise is needed for the digital additive manufacturing of dental restorations.

3D-Printing of zirconia dental prostheses

Introduction Yittria-stabilised-zirconia is a biomaterial widely employed in the production of dental prostheses through several traditional manufacturing and shaping processes (such as machining and surface grinding of a green or sintered block, gel-casting and injection moulding) which carry relatively high labour, tooling, moulding and waste material costs. Additive manufacturing 3D-printing processes, such as robocasting, enable the quick production of customised and intricate parts without the need for costly milling tools and moulds [1,2]. In this work, the robocasting process was employed in the production of zirconia parts using a layer-by-layer deposition strategy of a dispersed ceramic powder slurry through a numerically controlled extruder and nozzle. The highest possible solid content allowing for proper extrusion through a fine nozzle was determined for a plain, inexpensive water-based slurry of zirconia powders and dispersing agent. Materials and methods A commercial open-source 3D printer was modified to use a standard micrometric syringe and needle as an extruder Figure 1. An initial batch of 80 wt.% solid zirconia powder slurry was produced using a predetermined optimal CE64 dispersant ratio and equal portions were subsequently condensed through air-drying at 50 °C until an 82, 84, 86, 88 or 90 wt.% solid content ratio was reached. Each slurry was then used for the robocasting of zirconia cuboid samples, which were air-dried for 48 h at 50 °C and sintered at 1500 °C for 2 h. Sintered sample densities were measured using the Archimedes method and the polished base sample surfaces were characterised through microscopy analysis, hardness and toughness tests. The slurry yielding the best results was, thus selected for the production of a sintered tooth prototype using the same sample extrusion speeds, nozzle travel speeds and diameter (0.45 mm). Figure 1. Visual comparison of green samples robocasted from printable pastes. Results The best sample print quality was attained using 88 wt.% solid content slurries, which resulted in minimal microscopic sintering defects and no extrusion faults due to transient clogging of the extrusion nozzle, thus reaching a sintered density 97% that of theoretical. A full-size tooth prototype was successfully fabricated using the 88 wt.% solid content slurries Figure 2. Discussion and conclusions: The 88 wt.% solid content slurry showed increased viscosity, consistently raising extrusion pressure and shear stresses which likely broke-up any soft agglomerates, thus avoiding temporary nozzle clogging and the formation of agglomerate-related sintering defects. The 90 wt.% slurry showed near-dilatant behaviour, possibly possessing harder agglomerates. Thus, sintered sample parts with 97% theoretical density were realised from an 88 wt.% plain water-based slurry with no binders or plasticisers that would otherwise require an additional pre-sintering burnout stage and likely generate sintering defects. Figure 2. Post-sintering public domain molar tooth prototype printed using the using the 88 wt.% solid slurry next to an unrelated extracted tooth for comparison. The sliced 3D prototype tooth model used is shown in the rightmost picture.

Mechanical properties of new denture base material modified with gold nanoparticles.

Poly(methyl methacrylate) (PMMA) is the most commonly used material in the production of dental prostheses, and its application is often accompanied by the formation of biofilm. The aim of this work was the preparation of a PMMA/gold nanoparticles (AuNps) composite to improve the antimicrobial properties of heat-polymerised PMMA. The AuNPs were synthesised from gold (III) acetate by Ultrasonic Spray Pyrolysis (USP).In the present study, flexural strength and elastic modulus were investigated, as well as thermal conductivity, density and hardness of the PMMA/AuNps` nanocomposite, with different concentrations of AuNps. Flexural strength and elastic modulus were measured using a three-point bending test, and surface hardness was evaluated using the Vickers hardness test. The thermal conductivity of the samples was measured using the Transient Plane Source (TPS) technique. Density was determined by the pycnometry procedure. Statistical analysis was conducted on the data obtained from the experiments. The flexural strength and elastic modulus of AuNps/PMMA nanocomposites decreased for all groups containing AuNps. Thermal conductivity and density increased in all groups containing AuNps compared to the control group, but it was not significant in all groups. Vickers hardness values increased significantly with an increase in AuNps` content, with the highest value 21.45 HV obtained at 0.74 wt% of AuNps. Statistical analysis was performed by means of the SPSS 19 software package. Incorporation of AuNps into heat-polymerised PMMA resin led to decrease of the flexural strength and elastic modulus. At the same time, the density, thermal conductivity and hardness increased.

Occupational exposure of dental technicians to methyl methacrylate: Genotoxicity assessment

Dental technicians may be chronically exposed to methyl methacrylate (MMA), used in the production of dental prostheses. We have studied whether occupational exposure to MMA affects genotoxicity biomarkers such as 8-OHdG formation, comet assay, and buccal micronucleus frequency. MMA exposure was assessed via ambient air analysis. Although no significant differences between exposed and non-exposed individuals were seen with respect to blood genotoxicity measurements, we found a higher level of buccal-cell anomalies in the exposed group.

Svojstva i primena dentalnih poliamida

Introduction: By examining numerous thermoplastic and flexible materials that would aesthetically and functionally surpass acrylates used for the production of dental prostheses, polyamides were discovered as materials with great potential application in prosthodontics. The aim of this study was to describe polyamide materials used for the production of partial dentures. Material and methods: The main methodological approach of this study was a systematic search of the literature in two electronic databases: Google Scholar and PubMed using predefined keyword combinations. Results: The advantage of polyamide dentures is the comfort and ease of accommodation of the patient, with preserved optimal mechanical and physical properties. The dentures are flexible but rigid enough to be resistant to shock and fractures. Due to their low specific weight, polyamide dentures are light, extremely thin and do not interrupt patient speech. Excellent aesthetics are provided by a high choice of working colors and high translucency of the material, which ensures that the soft tissue that's covered by the denture base or clasp is seen through the prosthesis and gives it a more natural appearance in the patient's mouth. Conslusion: Polyamides, unlike acrylates, do not contain residual monomers, so they have an greater degree of biocompatibility. They can be used for the production of both complete and partial dentures, in combination with a Cr-Co skeleton, or crowns and bridges.

ИССЛЕДОВАНИЕ ПРОЧНОСТНЫХ И УСТАЛОСТНЫХ ХАРАКТЕРИСТИК АРМИРОВАННОГО ЧАСТИЦАМИ ДИОКСИДА ТИТАНА ПОЛИМЕРНОГО КОМПОЗИЦИОННОГО МАТЕРИАЛА ДЛЯ БАЗИСОВ СЪЕМНЫХ ЗУБНЫХ ПРОТЕЗОВ

Background. Removable designs are used in orthopedic dentistry for prosthetics of patients. The most used materials for the manufacture of bases of removable dental prosthesis currently are acrylate-based plastics. More than 90 % of removable dental prosthesis designs are produced with using of this material. The affordable cost of acrylate-based plastics prosthesis makes this material attractive for different groups of population. But this material has a number of well-known disadvantages: at first, the high concentration of residual monomer, which has a toxic effect, may cause allergic reaction and impossibility of using prosthesis; secondly, the porous structure of material contributes to the microbial seeding of the prosthesis; also, material shrinkage is up to 8 %. In connection with above, the certified in Russia Vertex ThermoSens (Vertex-Dental B.V., the Netherlands; ISO-Certificate 9001:2008) polyamide construction material deserves attention. This material has no residual monomer in its composition; the prostheses has an ability to be corrected in laboratory; shrinkage in the process of manufacturing designs is minimal. It is important to note such advantages as the high density of thermoplastics in combination with low specific weight and minimal porosity, which significantly reduces the formation of a microbial film on prostheses. Objectives. The aim of the research is to enhance the strength and fatigue characteristics of material based on Vertex ThermoSens, reinforced with titanium dioxide particles, for prosthetics of patients with complex clinical situations. Methods. In this work, the mechanical characteristics of reinforced with titanium dioxide powder (5 and 10 % by weight) polyamide material have been investigated. Tests on a static three-point bend at room temperature and temperature of 40 ºC and tests on fatigue of samples of this material were performed. Results. The analysis of changes of characteristics of material at different mass fractions of filler was carried out. Higher mechanical characteristics of the material with 10 % filling were noted, in particular, greater resistance to elevated temperatures and greater fatigue life. Conclusions. On the basis of research results it is possible to make a conclusion that using 1st group material is more effective for dental prosthesis production than using 2nd group material. The research results will be relevant for working out of dentures for patients with various clinical situation.

New perspectives for recycling dental zirconia waste resulting from CAD/CAM manufacturing process

On modern prosthodontics, CAD/CAM technology is the main manufacturing technique to produce the all-ceramic restorations. Zirconia stabilized with 3%mol of yttria (3Y-TSZ) is the most used material in the production of dental prostheses (e.g. crowns), due to its high biocompatibility, high mechanical strength, oxidation and abrasion resistance, high hardness and fracture toughness. The machining of crowns can produce a waste of approximately 30% of the initial blank, generating a significant economic loss (∼US$ 1087/kg) for the prosthetic laboratories.This work describes the beneficiation of zirconia powder resultant from CAD/CAM milling process, and suggests different applications based on the new properties. Is proposed a recycling solution by mixing the residues with commercial powder with 5, 10 and 50 vol% of residues and prepared by dry mixing, then pressed at 100 MPa and sintered at 1500 °C for 2 h. The quality control of the residues included the particle size distribution, the crystalline phases and chemical composition. For the recycled mixtures it was analyzed the color difference, the microstructure and mechanical properties, as Young and Weibull modulus, and flexural strength, to evaluate the potential uses of this new material.These residues can be used without any additional treatment on applications such as zirconia sand blasting for prosthodontics and as raw material for jewelry, pigment and refractory industries. In the case of the recycled mixtures is suggested the use in jewelry applications, taking advantage of their uniform color and mechanical properties which are similar to hardened noble metals alloys.

Evaluation of internal fit of interim crown fabricated with CAD/CAM milling and 3D printing system.

PURPOSEThis study is to evaluate the internal fit of the crown manufactured by CAD/CAM milling method and 3D printing method.MATERIALS AND METHODSThe master model was fabricated with stainless steel by using CNC machine and the work model was created from the vinyl-polysiloxane impression. After scanning the working model, the design software is used to design the crown. The saved STL file is used on the CAD/CAM milling method and two types of 3D printing method to produce 10 interim crowns per group. Internal discrepancy measurement uses the silicon replica method and the measured data are analyzed with One-way ANOVA to verify the statistic significance.RESULTSThe discrepancy means (standard deviation) of the 3 groups are 171.6 (97.4) µm for the crown manufactured by the milling system and 149.1 (65.9) and 91.1 (36.4) µm, respectively, for the crowns manufactured with the two types of 3D printing system. There was a statistically significant difference and the 3D printing system group showed more outstanding value than the milling system group.CONCLUSIONThe marginal and internal fit of the interim restoration has more outstanding 3D printing method than the CAD/CAM milling method. Therefore, the 3D printing method is considered as applicable for not only the interim restoration production, but also in the dental prosthesis production with a higher level of completion.

Virtual prouction of dental prostheses using a dental virtual articulator

Dental virtual articulators constitute a great improvement in the design of dental prostheses. The use of computer aided design (CAD) systems and Reverse engineering tools permits the introduction of kinematic analysis in virtual design processes. This paper presents a research project aiming at designing a dental virtual articulator in order to simulate and analyse the mandibular movements. After a virtual construction of the articulator, plaster models of the jaw must be scanned. Apart from this, by means of a face bow, the relative location of the occlusal surface referred to the intercondilar axis must be registered. Afterwards, with the help of the CAD system, the dental prosthesis is finally developed as mandibular movements are simulated. The main value of this paper is its contribution to the methodology for the implementation of virtual design in the production of dental prostheses.

Impression Materials and Storage Time Influence on Cast Models Accuracy

ABSTRACT Background There are a great amount of materials and techniques to use during dental prosthesis production that may confuse the dentist at the time of choice. Material's choice should be done considering ideal chemicophysical and biological properties and high detail reproduction. Aims The present study aimed to test the influence of differents impression materials and storage times on the dimensional accuracy of casting models. Materials and methods Four elastomeric materials– polysulfide, polyether, condensation silicone and addition silicone–were used to reproduce a master model of human teeth which were prepared for metaloceramic fixed prosthodontics. Six reference points were established on each tooth in order to determine four intervals: MD–mesial-distal, BL–buccal-lingual and CO–cervical-occlusal distance from premolar, and INT– interpillar distance–from the distal surface of the premolar to the mesial surface of the molar. The impressions were stored for half, 2 and 12 hours and pondered with a type IV gypsum. Results Cast measurements data were subjected to ANOVA (4 × 3), Tukey's – α = 0.05, Kruskal-Wallis and Dunn's tests – α = 0.05. The interaction between materials and storage time presented statistically significant for VP and CO intervals. For each storage time, materials presented dimensional alteration statistically significant. Conclusion Impression materials accuracy was affected by the storage time. All materials presented different dimensional accuracy when evaluated in a same period of time. Polysulfide was the only material that presented stable behavior over the time. How to cite this article Gonçalves FS, de Freitas Oliveira W, Soares LA, Carlo HL, da Mota AS, Popoff DAV, Soares CJ. Impression Materials and Storage Time Influence on Cast Models Accuracy. Int J Experiment Dent Sci 2013;2(1):18-23.

The Application of Rapid Prototyping in Prosthodontics

Dentists have used rapid prototyping (RP) techniques in the fields of oral maxillofacial surgery simulation and implantology. With new research emerging for molding materials and the forming process of RP techniques, this method is becoming more attractive in dental prosthesis fabrication; however, few researchers have published material on the RP technology of prosthesis pattern fabrication. This article reviews and discusses the application of RP techniques for prosthodontics including: (1) fabrication of wax pattern for the dental prosthesis, (2) dental (facial) prosthesis mold (shell) fabrication, (3) dental metal prosthesis fabrication, and (4) zirconia prosthesis fabrication. Many people could benefit from this new technology through various forms of dental prosthesis production. Traditional prosthodontic practices could also be changed by RP techniques in the near future.

The Effect of Adding a Stone Base on the Accuracy of Working Casts Using Different Types of Dental Stone

Gypsum products are used for the preparation of stone casts of oral and maxillofacial structures and as important adjuncts to dental laboratory operations involved in the production of dental prostheses. The aim of this study was to determine the effect on the dimensional accuracy of a working cast of adding a stone base using different stone products. A total of forty impressions of a mandibular dentoform were made. The impressions were dried with compressed air and stored at room temperature for 24 hours before pouring stone casts. The forty impressions were randomly divided into four groups of ten each. All forty impressions were poured once using one pre-weighed 140 Gm package of Silky Rock (SR) Type IV improved stone (Whip Mix Corporation, Louisville, KY, USA ) per impression. All working casts and the die setups were prepared according to the manufacturer's recommendations for pin placement (M.R. Dual pin and sleeve). Four different types of dental stone (II, III, and IV) and Flow Stone (FS) were used as bases for the working models. They were mixed according to the manufacturer's recommendations. The lower posterior teeth were flattened on the dentoform prior to taking the impressions. All were indexed using a mounted abrasive disc. Four teeth were selected as follows: 21, 28, 30, and 18. These represented A, B, C, and D landmarks, respectively. All measurements (five times for each specimen) were made with a Universal measuring microscope (Unitron Instruments, Inc., Bohemia, NY, USA). After the pre-sectioned measurements were recorded, the stone base was poured. A manual hand saw was used to section and fabricate removable dies for the mandibular landmarks A, B, C, and D. The dies were later seated and removed ten times to simulate the average amount of handling during laboratory procedures. Each die was carefully seated and measurements were made using the same technique as for the master model and unsectioned casts. Multivariate repeated measures analysis of variance (MANOVA) was used to test the difference in three different landmark distances (AB, AC, and AD) among the master model before and after sectioning of the working dies and among the four different base materials. Univariate analysis of variance (ANOVA) was conducted for each measurement, AB, AC, and AD to test the difference in landmark distances on the master model at pre sectioning and then at post sectioning using four different base materials. When there was a significant main effect (p < .05), the Student-Newman-Keul's (SNK) were used to test for pair wise comparison of means (P<0.05). The results of the MANOVA indicated there was a significant difference in three landmark measurements on the master model before and after sectioning of the working dies for the four different base materials (F = 6.60, p = 0.0001). In addition there was a significant difference in three landmark measurements on the master model at: (1) pre sectioning (p = 0.0001), (2) between the master model and SR material (p = 0.0002), (3) between the master model and Laboratory Plaster (LP) material (p = 0.0001), (4) between the master model and Quick Stone (QS) material (p = 0.0001), and (5) between the master model and FS material (p = 0.0001).

Cobalt exposure evaluation in dental prostheses production

Dental laboratory technicians may be exposed to a number of toxic materials including metal alloys that have been identified as potential health hazards. Particularly, alloys, such as vitallium, wisil, duralium and vironite which in dentistry are used in the production of crowns, bridges and dental prostheses. The most common constituents of these prosthese are cobalt (45–70%), chromium (25–30%), molybdenum, silica, nickle, tantalum and other metals in different amounts. The objectives of this paper are to describe the technology related to the production of dental prostheses, evaluating the most hazardous working jobs and reporting results concerning the monitoring of cobalt and chromium in the urine of 31 people employed in five laboratories of Bergamo, Italy, where workplace air monitoring has also been undertaken.

Laboratory techniques for the construction of intranasal prostheses

T his article describes the laboratory stages in the construction of two types of intranasal prostheses: the alar splint and the septal obturator. Although it does not fall within the dental field, the provision of these prostheses is a service that dental surgeons and technicians may be asked by otorhinologists to provide. The construction requires a knowledge of the materials and techniques used in the production of dental prostheses.