Removable Partial Dentures: Use of Rapid Prototyping Julia Magalhaes Costa Lima, MSc, DDS,1 Lilian Costa Anami, MSc, DDS,1 Rodrigo Maximo Araujo, PhD, MSc, DDS,2 & Carlos A. Pavanelli, PhD, DDS, MSc2 1
˜ Jose´ dos Campos Dental School, Post-graduate Program in Restorative Dentistry, Prosthetic Dentistry Unit, UNESP – Univ Estadual Paulista, Sao ˜ Jose´ dos Campos, Brazil Sao 2 ˜ Jose´ dos Campos Dental School, Sao ˜ Jose´ dos Campos, Department of Dental Materials and Prosthodontics, UNESP – Univ Estadual Paulista, Sao Brazil
Keywords Prototyping; CAD/CAM; dentistry. Correspondence Julia Lima, UNESP – Univ Estadual Paulista, ˜ Jose´ dos Campos Dental School, Brazil, Sao Post-graduate Program in Restorative Dentistry, Prosthetic Dentistry Unit, Av. Engenheiro Francisco Jose Longo, 777 ˜ Dimas Sao ˜ Jose´ dos Campos Sao ˜ Jardim Sao Paulo 12245–000, Brazil. E-mail: [email protected]
Abstract The CAD/CAM technology associated with rapid prototyping (RP) is already widely used in the fabrication of all-ceramic fixed prostheses and in the biomedical area; however, the use of this technology for the manufacture of metal frames for removable dentures is new. This work reports the results of a literature review conducted on the use of CAD/CAM and RP in the manufacture of removable partial dentures.
The authors deny any conflicts of interest. Accepted October 22, 2013 doi: 10.1111/jopr.12154
In recent decades, significant scientific and technological advances have led to a reduction in the human mortality rate and increased life expectancy. Thus, the world’s population is aging. The United Nations Population Division estimates that average global life expectancy will increase until 2050, resulting in 74 years as the world’s average life expectancy.1 In a survey conducted between 2002 and 2003, the Brazilian Ministry of Health noted that individuals between 65 and 74 years of age had a decayed, missing, and filled teeth (DMFT) index of 27.93, and that 92.16% of this number represented the “missing teeth” component of the index. Given these data, it was concluded that 56% of the sample evaluated in this period required prosthetic mandibular rehabilitation, and 32.4% required maxillary rehabilitation.2 In the United States 26% of people 65 years and older are edentulous, and in Canada this prevalence is 58%.3 Although prosthetic implants have become popular, patients are often unable to use this type of prosthesis, due to physiological, anatomical, and/or economic conditions, and must turn to removable partial dentures (RPDs) as an alternative treatment choice. Continuing technological advances (e.g., the use of prototyping in related areas of dentistry), have created new possibilities for the manufacture of prostheses for the field of prosthodontics.4-6 These new technologies are fundamentally 588
important for patients seeking more rapid, accurate, and functionally efficient prosthetic rehabilitation.5,7 The use of prototyping in the manufacture of dentures allows for the elimination of the waxing step, and thus reduces the potential for errors, resulting in better quality control in the dental lab.8-11 Moreover, the determination of the insertion axis is automatic, and the identification of retentive areas is rapid,12 reducing the preparation time for the removable prosthesis.7,8,13 Dentures made by prototyping present adequate adaptation, similar to that of prostheses prepared conventionally, and require fewer adjustments.10,13 This work reports the results of a literature review conducted on the use of CAD/CAM and rapid prototyping (RP) in the manufacture of RPDs.
Methods The articles used in this review were found in MEDLINEPubMed (National Library of Medicine, Washington, DC), Google Scholar, Scopus, ScienceDirect, and the Web of Science database using the keywords: 1. “rapid prototyping” and “removable partial denture” 2. “rapid prototyping,” “removable partial denture,” and “framework”
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3. “additive manufacturing” and “removable partial denture” 4. “rapid manufacturing” and “removable partial denture” 5. “dental prosthesis design,” “removable partial denture,” and “framework” Articles published in English from 2000 up to and including September 2013 were selected. All articles about RPDs fabricated by RP were included, including laboratory and clinical reports. Articles published in Chinese and regarding removable complete or fixed partial dentures were excluded. In a general review for an overview about the RP technique, only some articles were used. Articles about prototyping implants were excluded, and articles with a broader approach on the issue and on prototyping of ceramic materials were included.
Literature review Since their introduction, RPDs have been made by laboratory waxing and casting of the metal frame, with technological and scientific advances limited to this technique. Some studies7-9 reported attempts to modernize and improve the preparation of these metal frames, but few advances have been observed. New processing techniques for RP have been evaluated, such as stereolithography (SLA), selective laser sintering (SLS), selective laser melting (SLM), selective deposition modeling (SDM), 3D printing, and direct inkjet printing. These techniques have been the targets of research due to the possibility of allowing for the manufacture of complex shapes and for their potential to overcome the limitations of traditional systems in the making of fixed and/or removable dentures.12,14-17 In the case of RP, for example, a 3D design made by software (computer-aided design, CAD) generates a physical model constructed by depositing successive layers of raw material (computer-aided manufacturing, CAM).6,13 These technologies are already widely used in the fabrication of all-ceramic fixed prostheses12,14,15,18,19 and in the biomedical area.20-22 However, while RP was originally developed for metallic materials, polymers, and paper, the use of this technology for the manufacture of metal frames for dentures, for example, is new.7 Williams et al8 built a metal frame from a plastic-based epoxy resin pattern of RP and suggested a technique to facilitate the identification of the prosthetic equator and the retentive areas of the teeth involved in RPDs; however, software must be improved to facilitate more rapid manufacture of the design and to allow for the RPD metal frame to be obtained directly. Williams et al noted that the CAD/CAM techniques most commonly used in dentistry are based on the machining process of prefabricated blocks of different materials; however, this process is not the most suitable for RPD preparation, since their components present complex shapes and must be thin. Additionally, with these components, it is difficult to establish an appropriate attachment point with the milling machine, and the components can suffer deflection during the process, as reported by Smith and Dvorak.23 According to Williams et al,8 despite the potential benefits of this technique, there are some disadvantages, such as the high cost of the scanning and RP equipment. Moreover, a certain familiarity with CAD software is needed to create viable and
Rapid Prototyping and RPDs
appropriate surfaces, and this requires time and training; however, if these obstacles can be overcome, the total spent time in constructing a standard prototype in plastic with a metal frame is less than or equal to that necessary to perform waxing manually. Williams et al8 describe a relevant problem, the development of cracks in the plastic prototype, due to thermal expansion caused by the exothermic reaction of the coating material, resulting in surface defects in the final metal frame. In 2005, Eggbeer et al9 used CAD/CAM and RP technologies to manufacture metal RPD structures. The following methods were compared: SLA (3D Systems Inc., Valencia, CA), R which uses materials based on epoxy resin; ThermoJet (3D Systems Inc., Rock Hill, SC), which uses a polymeric wax; R Solidscape T66 (Solidscape Inc., Merrimack, NH), which R (Envisiontec uses a lightweight thermoplastic; and Perfactory GmbH, Marl, Germany), which uses an acrylic-based polymer. These prototypes were included in coating, and the cobalt– chromium metal alloy was melted. These four techniques, when compared with SLA, presented adequate, accurate, and rugged patterns, with a suitable surface finish, despite the need for lengthy cleaning and finishing to remove the supporting structures. The other methods produced quick and accurate prototypes, but they were noted to be extremely fragile and flexible, and susceptible to deformation when handled.12 It was observed that, in addition to the possible use of CAD/CAM technology for analysis of the adaptation, preparation, and design of the RPD metallic structure, it is also feasible to replace the wax pattern by a prototype without compromising the fit. Bibb et al24 reported a clinical case in which a metal frame was produced by CAD/CAM and RP. The die model was scanned and a 3D image was obtained, where the design of the metal frame of the mandibular partial denture was made. From this design, a prototype epoxy resin was obtained by RP. This prototype, which replaced the waxing manually done by the prosthetic technician, was included in a coating material, and the metal frame was obtained as in the conventional method. This frame provided adequate adaptation to both hard and soft tissues and was considered clinically acceptable, indicating that the resin pattern obtained by SLA had accuracy similar to that of the standard traditionally used in wax. According to the authors, the necessary adjustments required to adapt the metal frame were fewer than in the conventional technique, but the distribution and extent of these adjustments were similar between the two techniques. Recently, Wu et al25 obtained a 3D CAD framework by RP, and a sacrificial pattern was produced by RP with SLA technique. The framework was cast with Co–Cr alloy, and after suitable finishing the cast framework had a good fit on the cast. The authors believe that in the future the design of an RPD framework will become more simple and adjustable due to the existence of a database that gathers virtual components for RPD frameworks. Despite the fact that RP for the manufacture of metal frames is a reproducible and consistent technique24 that can reduce interoperator variability,25 it is still costly and error-prone, since it also depends on plaster casts obtained by the molding of elastomeric materials. Averydona6 described the procedures to obtain RPDs using the SLS technique and emphasized that an accurate dental impression is still required for this additive
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manufacturing technology, like for the traditional technique to obtain RPDs.6 For these errors to be minimized, intraoral scanners or even the reconstruction of a CT scan11 can eliminate possible distortions of plaster models. Another issue that deserves special attention is good operator training, which is also necessary to achieve successful results, especially during the scanning and design procedures in the CAD software.6 In 2005, Eggbeer et al9 predicted that in the future it would be possible to eliminate plaster models and wax/resin patterns when the metal frame could be made directly in Co–Cr by RP.9 In the following year, this became a reality. Some dental alloys that can be reliably used in the oral cavity due to their acceptable level of ion release, like Co, Cr, and Mo, are available to be used in RP.26 Williams et al,7 Bibb et al,17 and Han et al27 all reported cases of a metal frame made directly by RP. In these cases, a mold was made in a patient with partial bilateral mandibular edentulism, the plaster model was scanned, and a 3D design was obtained. An RP machine of the SLM type was used, and the metal frame was constructed by direct deposition of Co–Cr. During the construction of the metal frame, a support was formed to provide a fixed base during sintering and to conduct heat away from the material as it melted and solidified during construction of the prosthesis. After the prototyping process, the supports were removed with a reinforced cutting wheel, and the metal frame was finished and polished as in the conventional technique. The frame showed porosities in some areas, but these were not considered detrimental to normal function, since suitable adaptation was observed in the model and in the mouth. The results were satisfactory and comparable in terms of accuracy, quality of form, and function with the frames obtained by the traditional laboratory method.7,17,27 The SLS method has great potential for use in dentistry to allow for the production of complex shapes and has advantages such as the elimination of steps, including laboratory waxing and metal casting, saving time, and preventing material waste.6,7 However, the costs for constructing an RPD metal frame by this method are quite high,7,13,24 and no other studies in the literature report the use of this technique. The CAD software used for obtaining the 3D CAD model of the framework has tools to sculpt structures similar to those obtained by manual waxing. Moreover, they allow for rotation and translation of the virtual model, and the 3D CAD model virtually reproduces hand movements in all axes. Complex shapes can be designed, and sizes, shapes, and positions can be defined more quickly and easily.7 Aiming to facilitate this design process, in 2012, Jiang et al13 suggested the creation of a universal component library, from which dentists and technicians could have access to different components and simply adjust them to the required size and place. The material used in RP was the aim of Jevremovic et al’s study28 in 2012. The manufacturing of frameworks by RP is limited to Co–Cr alloys, due to their superior rigidity when compared to titanium alloys. According to the authors, this alloy presents good initial results regarding mechanical properties. In another study, Jevremovic et al29 tested the biological properties of this Co–Cr alloy and found that it had good biocompatibility, with no permanent damage to the cell function and, therefore, it was rated as a noncytotoxic alloy. In a previous 590
study they noted that some Co–Cr alloys available for SLM can contain nickel,30 a metal commonly associated with side effects, but once more they concluded that that alloy did not have a cytotoxic potential. According to them,30 this alloy used for SLM has the same characteristics of those used in the cast alloy technique. They also cited the importance of the manual finishing procedure of the metal to improve the already good condition of the surface result of the SLS procedure—homogeneous, with few pores and a fine microstructure.29 These surface roughness characteristics are directly related to the plaque retention and need to be carefully observed.
Conclusions It can be concluded that, compared with other medical areas and especially in dentistry, laboratories manufacturing RPDs still make little use of CAD/CAM and RP. Despite the high price, the use of these technologies would most benefit the manufacture of metal frames, replacing laboratory steps and thus decreasing the preparation time. Further, such technologies can achieve a better reproducibility and adaptation of prosthetic devices, besides eliminating the errors inherent in steps like waxing, casting, and coating; however, many advances in this area still need to be made so that appropriate equipment and software can be developed and the high costs of production reduced.
References 1. UNDP: World Population Prospects: The 2002 Revision. New York, United Nations, 2003, p 8 2. Ministry of Health Project SB Brazil 2003: Oral Health Status of the Population 2002–2003: Principal Results. Brasilia, Ministry of Health, 2004 3. Petersen PE: The World Oral Health Report 2003: Continuous Improvement of Oral Health in the 21st Century: The Approach of the WHO Global Oral Health Programme. New York, UN World Health Organization, 2003, p 5 4. Rekow ED: CAD/CAM in dentistry: a historical perspective and view of the future. J Can Dent Assoc 1992;58:283-288 5. Azari A, Nikzad S: The evolution of rapid prototyping in dentistry: a review. Rap Protot J 2009;15:216-225 6. Averydona M: Quality control of dental bridges and removable prostheses manufactured using Phenix Systems equipments. Proceeding of AEPR’12, 17th European Forum on Rapid Prototyping and Manufacturing. Paris, June 2012, pp. 12-14 7. Williams RJ, Bibb R, Eggbeer D, et al: Use of CAD/CAM technology to fabricate a removable partial denture framework. J Prosthet Dent 2006;96:96-99 8. Williams R, Bibb R, Rafik T: A technique for fabricating patterns for removable partial denture frameworks using digitized casts and electronic surveying. J Prosthet Dent 2004;91:85-88 9. Eggbeer D, Bibb R, Williams R: The computer-aided design and rapid prototyping fabrication of removable partial denture frameworks. Proc I Mech E Part H: J. Eng Med 2005;219:195-202 10. Chen G, Zeng X, Wang Z, et al: Fabrication of removable partial denture framework by selective laser melting. Adv Mater Res 2011;317-319:174-178 11. Budak I, Kosec B, Sokovic M: Application of contemporary engineering techniques and technologies in the field of dental prosthesis. J Achiv Mater Manufact Engineer 2012;54:233-241
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12. Melcher R, Martins S, Travitzky N, et al: Fabrication of Al2 O3 -based composites by indirect 3D-printing. Mater Lett 2006;60:572-575 13. Jiang W, Wang X, Zhao X, et al: A study on the fabrication method of removable partial denture framework by computer-aided design and rapid prototyping. Rapid Protot J 2012;18:318-323 14. Ebert J, Ozkol E, Zeichner A, et al: Direct inkjet printing of dental prostheses made of zirconia. J Dent Res 2009;88:673676 ¨ 15. Ozkol E, Ebert J, Uibel K, et al: Development of high solid content aqueous 3Y-TZP suspensions for direct inkjet printing using a thermal inkjet printer. J Eur Ceram Soc 2009;29:403409 16. Melcher R, Travitzky N, Zollfrank C, et al: 3D printing of Al2 O3 /Cu-O interpenetrating phase composite. J Mater Sci 2011;46:1203-1210 17. Bibb R, Eggbber D, Williams R: Rapid manufacture of removable partial denture frameworks. Rapid Protot J 2006;12:95-99 18. Noguera R, Lejeune M, Chartier T: 3D fine scale ceramic components formed by ink-jet prototyping process. J Eur Ceram Soc 2005;25:2055-2059 19. Zhang W, Melcher R, Travitzky N, et al: Three-dimensional printing of complex-shaped alumina/glass composites. Adv Eng Mat 2009;11:1039-1043 20. Bibb R, Brown R: The application of computer aided product development techniques in medical modeling. Biomed Sci Instr 2000;36:319-324 21. Bibb R, Bocca A, Evans P: An appropriate approach to computer aided design and manufacture of cranioplasty plates. J Maxillofacial Prosthet Technol 2002;5:28-31
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22. Hughes CW, Page K, Bibb R, et al: The custom-made titanium orbital floor prosthesis in reconstruction for orbital floor fractures. Br J Oral Maxillofacial Surg 2003;41:50-53 23. Smith S, Dvorak D: Tool path strategies for high speed milling aluminium work pieces with thin webs. Mechatronics 1998;8:291-300 24. Bibb RJ, Eggbeer D, Williams RJ, et al: Trial fitting of a removable partial denture framework made using computer-aided design and rapid prototyping techniques. Proc Inst Mech Eng H 2006;62:793-797 25. Wu F, Wang X, Zhao X, et al: A study on the fabrication method of removable partial denture framework by computer-aided design and rapid prototyping. Rapid Protot J 2012;18:318-323 26. Alifui-Segbaya F, Foley P, Williams RF: The corrosive effects of artificial saliva on cast and rapid manufacture-produced cobalt chromium alloys. Rapid Protot J 2013;19:95-99 27. Han J, Wang Y, L¨u P: A preliminary report of designing removable partial denture frameworks using a specifically developed software package. Int J Prosthodont 2010;23:370375 28. Jevremovic D, Puskar T, Kosec D, et al: The analysis of the mechanical properties of F75 Co-Cr alloy for use in selective laser melting (SLM) manufacturing of removable partial dentures (RPD). Metalurgija 2012;51:171-174 29. Jevremovic DP, Puskar TM, Budak I, et al: An RE/RM approach to the design and manufacture of removable partial dentures with a biocompatibility analysis of the F75 Co-Cr SLM alloy. Mater Techn 2012;46:123-129 30. Jevremovic D, Kojic V, Bogdanovic G, et al: A selective laser melted Co-Cr alloy used for the rapid manufacture of removable partial denture frameworks: initial screening of biocompatibility. J Serb Chem Soc 2011;76:43-52
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˜ Jose´ dos Campos Dental School, Post-graduate Program in Restorative Dentistry, Prosthetic Dentistry Unit, UNESP – Univ Estadual Paulista, Sao ˜ Jose´ dos Campos, Brazil Sao 2 ˜ Jose´ dos Campos Dental School, Sao ˜ Jose´ dos Campos, Department of Dental Materials and Prosthodontics, UNESP – Univ Estadual Paulista, Sao Brazil
Keywords Prototyping; CAD/CAM; dentistry. Correspondence Julia Lima, UNESP – Univ Estadual Paulista, ˜ Jose´ dos Campos Dental School, Brazil, Sao Post-graduate Program in Restorative Dentistry, Prosthetic Dentistry Unit, Av. Engenheiro Francisco Jose Longo, 777 ˜ Dimas Sao ˜ Jose´ dos Campos Sao ˜ Jardim Sao Paulo 12245–000, Brazil. E-mail: [email protected]
Abstract The CAD/CAM technology associated with rapid prototyping (RP) is already widely used in the fabrication of all-ceramic fixed prostheses and in the biomedical area; however, the use of this technology for the manufacture of metal frames for removable dentures is new. This work reports the results of a literature review conducted on the use of CAD/CAM and RP in the manufacture of removable partial dentures.
The authors deny any conflicts of interest. Accepted October 22, 2013 doi: 10.1111/jopr.12154
In recent decades, significant scientific and technological advances have led to a reduction in the human mortality rate and increased life expectancy. Thus, the world’s population is aging. The United Nations Population Division estimates that average global life expectancy will increase until 2050, resulting in 74 years as the world’s average life expectancy.1 In a survey conducted between 2002 and 2003, the Brazilian Ministry of Health noted that individuals between 65 and 74 years of age had a decayed, missing, and filled teeth (DMFT) index of 27.93, and that 92.16% of this number represented the “missing teeth” component of the index. Given these data, it was concluded that 56% of the sample evaluated in this period required prosthetic mandibular rehabilitation, and 32.4% required maxillary rehabilitation.2 In the United States 26% of people 65 years and older are edentulous, and in Canada this prevalence is 58%.3 Although prosthetic implants have become popular, patients are often unable to use this type of prosthesis, due to physiological, anatomical, and/or economic conditions, and must turn to removable partial dentures (RPDs) as an alternative treatment choice. Continuing technological advances (e.g., the use of prototyping in related areas of dentistry), have created new possibilities for the manufacture of prostheses for the field of prosthodontics.4-6 These new technologies are fundamentally 588
important for patients seeking more rapid, accurate, and functionally efficient prosthetic rehabilitation.5,7 The use of prototyping in the manufacture of dentures allows for the elimination of the waxing step, and thus reduces the potential for errors, resulting in better quality control in the dental lab.8-11 Moreover, the determination of the insertion axis is automatic, and the identification of retentive areas is rapid,12 reducing the preparation time for the removable prosthesis.7,8,13 Dentures made by prototyping present adequate adaptation, similar to that of prostheses prepared conventionally, and require fewer adjustments.10,13 This work reports the results of a literature review conducted on the use of CAD/CAM and rapid prototyping (RP) in the manufacture of RPDs.
Methods The articles used in this review were found in MEDLINEPubMed (National Library of Medicine, Washington, DC), Google Scholar, Scopus, ScienceDirect, and the Web of Science database using the keywords: 1. “rapid prototyping” and “removable partial denture” 2. “rapid prototyping,” “removable partial denture,” and “framework”
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 588–591
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3. “additive manufacturing” and “removable partial denture” 4. “rapid manufacturing” and “removable partial denture” 5. “dental prosthesis design,” “removable partial denture,” and “framework” Articles published in English from 2000 up to and including September 2013 were selected. All articles about RPDs fabricated by RP were included, including laboratory and clinical reports. Articles published in Chinese and regarding removable complete or fixed partial dentures were excluded. In a general review for an overview about the RP technique, only some articles were used. Articles about prototyping implants were excluded, and articles with a broader approach on the issue and on prototyping of ceramic materials were included.
Literature review Since their introduction, RPDs have been made by laboratory waxing and casting of the metal frame, with technological and scientific advances limited to this technique. Some studies7-9 reported attempts to modernize and improve the preparation of these metal frames, but few advances have been observed. New processing techniques for RP have been evaluated, such as stereolithography (SLA), selective laser sintering (SLS), selective laser melting (SLM), selective deposition modeling (SDM), 3D printing, and direct inkjet printing. These techniques have been the targets of research due to the possibility of allowing for the manufacture of complex shapes and for their potential to overcome the limitations of traditional systems in the making of fixed and/or removable dentures.12,14-17 In the case of RP, for example, a 3D design made by software (computer-aided design, CAD) generates a physical model constructed by depositing successive layers of raw material (computer-aided manufacturing, CAM).6,13 These technologies are already widely used in the fabrication of all-ceramic fixed prostheses12,14,15,18,19 and in the biomedical area.20-22 However, while RP was originally developed for metallic materials, polymers, and paper, the use of this technology for the manufacture of metal frames for dentures, for example, is new.7 Williams et al8 built a metal frame from a plastic-based epoxy resin pattern of RP and suggested a technique to facilitate the identification of the prosthetic equator and the retentive areas of the teeth involved in RPDs; however, software must be improved to facilitate more rapid manufacture of the design and to allow for the RPD metal frame to be obtained directly. Williams et al noted that the CAD/CAM techniques most commonly used in dentistry are based on the machining process of prefabricated blocks of different materials; however, this process is not the most suitable for RPD preparation, since their components present complex shapes and must be thin. Additionally, with these components, it is difficult to establish an appropriate attachment point with the milling machine, and the components can suffer deflection during the process, as reported by Smith and Dvorak.23 According to Williams et al,8 despite the potential benefits of this technique, there are some disadvantages, such as the high cost of the scanning and RP equipment. Moreover, a certain familiarity with CAD software is needed to create viable and
Rapid Prototyping and RPDs
appropriate surfaces, and this requires time and training; however, if these obstacles can be overcome, the total spent time in constructing a standard prototype in plastic with a metal frame is less than or equal to that necessary to perform waxing manually. Williams et al8 describe a relevant problem, the development of cracks in the plastic prototype, due to thermal expansion caused by the exothermic reaction of the coating material, resulting in surface defects in the final metal frame. In 2005, Eggbeer et al9 used CAD/CAM and RP technologies to manufacture metal RPD structures. The following methods were compared: SLA (3D Systems Inc., Valencia, CA), R which uses materials based on epoxy resin; ThermoJet (3D Systems Inc., Rock Hill, SC), which uses a polymeric wax; R Solidscape T66 (Solidscape Inc., Merrimack, NH), which R (Envisiontec uses a lightweight thermoplastic; and Perfactory GmbH, Marl, Germany), which uses an acrylic-based polymer. These prototypes were included in coating, and the cobalt– chromium metal alloy was melted. These four techniques, when compared with SLA, presented adequate, accurate, and rugged patterns, with a suitable surface finish, despite the need for lengthy cleaning and finishing to remove the supporting structures. The other methods produced quick and accurate prototypes, but they were noted to be extremely fragile and flexible, and susceptible to deformation when handled.12 It was observed that, in addition to the possible use of CAD/CAM technology for analysis of the adaptation, preparation, and design of the RPD metallic structure, it is also feasible to replace the wax pattern by a prototype without compromising the fit. Bibb et al24 reported a clinical case in which a metal frame was produced by CAD/CAM and RP. The die model was scanned and a 3D image was obtained, where the design of the metal frame of the mandibular partial denture was made. From this design, a prototype epoxy resin was obtained by RP. This prototype, which replaced the waxing manually done by the prosthetic technician, was included in a coating material, and the metal frame was obtained as in the conventional method. This frame provided adequate adaptation to both hard and soft tissues and was considered clinically acceptable, indicating that the resin pattern obtained by SLA had accuracy similar to that of the standard traditionally used in wax. According to the authors, the necessary adjustments required to adapt the metal frame were fewer than in the conventional technique, but the distribution and extent of these adjustments were similar between the two techniques. Recently, Wu et al25 obtained a 3D CAD framework by RP, and a sacrificial pattern was produced by RP with SLA technique. The framework was cast with Co–Cr alloy, and after suitable finishing the cast framework had a good fit on the cast. The authors believe that in the future the design of an RPD framework will become more simple and adjustable due to the existence of a database that gathers virtual components for RPD frameworks. Despite the fact that RP for the manufacture of metal frames is a reproducible and consistent technique24 that can reduce interoperator variability,25 it is still costly and error-prone, since it also depends on plaster casts obtained by the molding of elastomeric materials. Averydona6 described the procedures to obtain RPDs using the SLS technique and emphasized that an accurate dental impression is still required for this additive
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 588–591
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manufacturing technology, like for the traditional technique to obtain RPDs.6 For these errors to be minimized, intraoral scanners or even the reconstruction of a CT scan11 can eliminate possible distortions of plaster models. Another issue that deserves special attention is good operator training, which is also necessary to achieve successful results, especially during the scanning and design procedures in the CAD software.6 In 2005, Eggbeer et al9 predicted that in the future it would be possible to eliminate plaster models and wax/resin patterns when the metal frame could be made directly in Co–Cr by RP.9 In the following year, this became a reality. Some dental alloys that can be reliably used in the oral cavity due to their acceptable level of ion release, like Co, Cr, and Mo, are available to be used in RP.26 Williams et al,7 Bibb et al,17 and Han et al27 all reported cases of a metal frame made directly by RP. In these cases, a mold was made in a patient with partial bilateral mandibular edentulism, the plaster model was scanned, and a 3D design was obtained. An RP machine of the SLM type was used, and the metal frame was constructed by direct deposition of Co–Cr. During the construction of the metal frame, a support was formed to provide a fixed base during sintering and to conduct heat away from the material as it melted and solidified during construction of the prosthesis. After the prototyping process, the supports were removed with a reinforced cutting wheel, and the metal frame was finished and polished as in the conventional technique. The frame showed porosities in some areas, but these were not considered detrimental to normal function, since suitable adaptation was observed in the model and in the mouth. The results were satisfactory and comparable in terms of accuracy, quality of form, and function with the frames obtained by the traditional laboratory method.7,17,27 The SLS method has great potential for use in dentistry to allow for the production of complex shapes and has advantages such as the elimination of steps, including laboratory waxing and metal casting, saving time, and preventing material waste.6,7 However, the costs for constructing an RPD metal frame by this method are quite high,7,13,24 and no other studies in the literature report the use of this technique. The CAD software used for obtaining the 3D CAD model of the framework has tools to sculpt structures similar to those obtained by manual waxing. Moreover, they allow for rotation and translation of the virtual model, and the 3D CAD model virtually reproduces hand movements in all axes. Complex shapes can be designed, and sizes, shapes, and positions can be defined more quickly and easily.7 Aiming to facilitate this design process, in 2012, Jiang et al13 suggested the creation of a universal component library, from which dentists and technicians could have access to different components and simply adjust them to the required size and place. The material used in RP was the aim of Jevremovic et al’s study28 in 2012. The manufacturing of frameworks by RP is limited to Co–Cr alloys, due to their superior rigidity when compared to titanium alloys. According to the authors, this alloy presents good initial results regarding mechanical properties. In another study, Jevremovic et al29 tested the biological properties of this Co–Cr alloy and found that it had good biocompatibility, with no permanent damage to the cell function and, therefore, it was rated as a noncytotoxic alloy. In a previous 590
study they noted that some Co–Cr alloys available for SLM can contain nickel,30 a metal commonly associated with side effects, but once more they concluded that that alloy did not have a cytotoxic potential. According to them,30 this alloy used for SLM has the same characteristics of those used in the cast alloy technique. They also cited the importance of the manual finishing procedure of the metal to improve the already good condition of the surface result of the SLS procedure—homogeneous, with few pores and a fine microstructure.29 These surface roughness characteristics are directly related to the plaque retention and need to be carefully observed.
Conclusions It can be concluded that, compared with other medical areas and especially in dentistry, laboratories manufacturing RPDs still make little use of CAD/CAM and RP. Despite the high price, the use of these technologies would most benefit the manufacture of metal frames, replacing laboratory steps and thus decreasing the preparation time. Further, such technologies can achieve a better reproducibility and adaptation of prosthetic devices, besides eliminating the errors inherent in steps like waxing, casting, and coating; however, many advances in this area still need to be made so that appropriate equipment and software can be developed and the high costs of production reduced.
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