JPOR-288; No. of Pages 3 journal of prosthodontic research xxx (2015) xxx–xxx
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/jpor
Editorial
Dental materials used for metal-free restorations: Recent advances and future challenges
As one of the Associate Editors for the Journal of Prosthodontic Research (JPR), I have been pleasantly surprised that numerous papers regarding dental materials and technologies have recently been submitted to JPR from all over the world, given that the main dental society in which I am active is the Japanese Society for Dental Materials and Devices. As all our readers can see in the Instructions for Authors for our journal, ‘‘adhesive dentistry; dental materials; and aesthetic dentistry’’ is defined as one of the targeted topics for JPR. In addition, ‘‘digital dentistry’’ has seen marked developments through computer-aided design and computer-aided dental manufacturing (CAD/CAM) technology, and has therefore been added as another targeted topic for JPR, as these developments have been rapidly adopted and applied to clinical dentistry. Incidentally, this has previously been discussed at length by the Editor-in-Chief of JPR, Professor Kazuyoshi Baba [1], and hence further discussion concerning digital dentistry will be omitted here. Needless to say, from the distant past through to the present day, dentistry has been continuously invigorated by the development of both dental materials and technologies. In other words, one could suggest that there is no progress in dentistry without the development of dental materials and technologies. Generally, in the prosthodontic treatment of
missing or decayed teeth, artificial materials see use as dental materials to restore oral function. With the improving awareness of patients regarding oral health-related quality of life and the advances in dentistry, the demands (not only from patients, but also from dentists) for such dental materials have diversified. What do you think is the most important property for such dental materials: durability, suitability, biocompatibility, esthetics, or cost performance? I think it is important for dentists and patients to understand both the advantages and limitations of dental materials, to allow the selection of the best materials, because although the advantages of new dental materials and technologies are emphasized, the limitations are often less obvious. In this editorial, I would like to briefly discuss the current status and future needs of dental materials for metal-free restorations in prosthodontics.
1. Classification of dental materials and development of zirconia restorations As is well-known, dental materials are generally classified into four types: metals; ceramics; polymers; and composites. Which materials are best for each dental prosthesis? That is, dentists and patients need to make choices between these alternatives. As you know, all these dental materials have both advantages and disadvantages. Historically, metal alloys such as gold alloy, silver alloy, and cobalt–chromium–nickel alloy are the oldest of the four major classes of raw materials that have been widely used in dental prostheses such as crowns, fixed partial dentures (FPDs), and removable partial dentures (RPDs) in prosthodontics. Such metal alloys are strong and durable, and have a long history of use in dentistry, but are not esthetically pleasing because of their metallic color, and carry a risk of causing allergic or toxic reactions within the soft or hard tissues of the oral cavity. On the other hand, new dental ceramics such as castable ceramics and CAD/CAM ceramics have been introduced to dentistry since the 1980s, and have shown considerable potential for esthetic restorations. To
Please cite this article in press as: Tanimoto Y. Dental materials used for metal-free restorations: Recent advances and future challenges. J Prosthodont Res (2015), http://dx.doi.org/10.1016/j.jpor.2015.07.003
JPOR-288; No. of Pages 3
2
journal of prosthodontic research xxx (2015) xxx–xxx
achieve completely metal-free restoration, polycrystalline zirconia-based ceramics with high mechanical properties such as yttrium partially stabilized tetragonal zirconia polycrystalline (Y-TZP) and ceria-stabilized tetragonal zirconia polycrystalline and alumina nanocomposites (Ce-TZP/ Al2O3) have been successfully introduced to clinical dentistry during the past decade, along with dental CAD/CAM systems [2]. Surprisingly, Ce-TZP/Al2O3 shows a high fracture toughness of 19 MPa m1/2 and resistance to low-temperature degradation, although Y-TZP suffers from low-temperature degradation. Of course, zirconia-based ceramics such as CeTZP/Al2O3 and Y-TZP are not ductile in the manner of metal alloys, but are now clinically available as FPDs. Furthermore, the possibility of metal-free restorations made from zirconiabased ceramics for prosthodontic treatments is greatly increasing. For example, zirconia implants that are manufactured in 1- or 2-piece designs, especially zirconia abutments, have been introduced for esthetic restorations, low plaque retention, and good stabilization for soft tissues. In current implantology, numerous reports have described surface modifications to implants using titanium and its alloys, such as plasma spraying, blasting, acid-etching, and their combinations, to provide roughened surfaces facilitating bone fixation [3]. On the other hand, surface modification techniques for such zirconia implants are not well-established due to the low electroconductivity of zirconia and the difficulty in processing. In addition, the ability of zirconia implants to achieve osseointegration is still unclear; further long-term follow-up of zirconia implants is thus needed. Likewise, the application of zirconia-based ceramics such as Ce-TZP/Al2O3 to RPDs has recently been attempted, but remains in the experimental stage [4]. As a final topic concerning zirconia restorations, bonding systems for zirconia have recently gained wider interest, because it is also important to improve the bonding of zirconia with veneering or resin-based luting agents. The mechanisms needed to obtain adequate bonding between zirconia and veneering are still unclear, and the high incidence of veneer chipping on zirconia cores has been reported as a critical problem. Meanwhile, surface treatment with 10-methacryloyloxydecyl dihydrogen phosphate, after sandblasting with airborne particles, has been reported as one of the most reliable resinto-zirconia adhesive systems [2]. However, further work using different approaches for bonding systems involving zirconia is clearly necessary.
2.
Application of fiber-reinforced composites
In terms of metal-free restorations other than zirconia restorations, I am eagerly expecting the application of fiberreinforced composites (FRCs) comprising fiber-reinforcement and resin composites to dental prostheses [5]. FRCs have been used to fabricate dental appliances such as crowns, FPDs, and RPDs in both basic research and clinical experiments. Dental prostheses made from FRCs are often much more esthetically pleasing than those made from metal alloys. In current prosthodontics, FRCs have seen particular use as fiber dowels (posts), because they have an elastic modulus similar to that of dentin, resulting in less damage to the remaining tooth
structure. In the near future, FRCs will be applied to a wide range of esthetic restorations as tailored materials, because the properties of FRCs can be tuned by changing the parameters of the fiber (e.g., fiber type, volume fraction, and diameter).
3. Non-metal clasp dentures using thermoplastic resins Finally, another topic that I want to mention here is the fact that, RPDs made from thermoplastic resins such as polyamide, polyester, and polycarbonate have seen increasing use in recent times. In a position paper by the Japan Prosthodontic Society (JPS) [6], RPDs using the ‘‘resin clasp’’ retentive part were defined as ‘‘non-metal clasp dentures’’ (NMCDs). Such NMCDs made using thermoplastic resins are often much more esthetically pleasing than conventional RPDs with metal clasps. However, the use of such NMCDs without metal frameworks may seriously affect remaining tissues because of their low rigidity, and such NMCDs do not conform to the standard principles for RPD design. Accordingly, the formulation of evidence-based guidelines for the clinical application of NMCDs in the near future is anticipated, particularly by the members of JPS.
4.
Summary
This editorial discusses relatively new dental materials centered upon metal-free restoration in prosthodontics. However, if a potential manuscript offers high-quality, interesting information for JPR readers, we will of course keep the door open for publication in JPR; not only for such new dental materials, but also for conventional dental materials needing additional research. This is because new materials and technologies will continue to progress through advances in knowledge of and experience with traditional materials and technologies.
references
[1] Baba K. Editorial: Paradigm shifts in prosthodontics. J Prosthodont Res 2014;58:1–2. [2] Miyazaki T, Nakamura T, Matsumura H, Ban S, Kobayashi T. Current status of zirconia restoration. J Prosthodont Res 2013;57:236–61. [3] Shibata Y, Tanimoto Y. A review of improved fixation methods for dental implants. Part I: Surface optimization for rapid osseointegration. J Prosthodont Res 2015;59: 20–33. [4] Urano S, Hotta Y, Miyazaki T, Baba K. Bending properties of Ce-TZP/A nanocomposite clasps for removable partial dentures. Int J Prosthodont 2015;28:191–7. [5] Vallittu PK. High-aspect ratio fillers: fiber-reinforced composites and their anisotropic properties. Dental Mater 2015;31:1–7. [6] Fueki K, Ohkubo C, Yatabe M, Arakawa I, Arita M, Ino S, et al. Clinical application of removable partial dentures using thermoplastic resin. Part I: Definition and indication of non-metal clasp dentures. J Prosthodont Res 2014;58:3–10.
Please cite this article in press as: Tanimoto Y. Dental materials used for metal-free restorations: Recent advances and future challenges. J Prosthodont Res (2015), http://dx.doi.org/10.1016/j.jpor.2015.07.003
JPOR-288; No. of Pages 3
3
journal of prosthodontic research xxx (2015) xxx–xxx
Yasuhiro Tanimoto PhD Department of Dental Biomaterials, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan E-mail address: [email protected] (Y. Tanimoto)
Received 14 July 2015 http://dx.doi.org/10.1016/j.jpor.2015.07.003 1883-1958/# 2015 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
Please cite this article in press as: Tanimoto Y. Dental materials used for metal-free restorations: Recent advances and future challenges. J Prosthodont Res (2015), http://dx.doi.org/10.1016/j.jpor.2015.07.003
Available online at www.sciencedirect.com
ScienceDirect journal homepage: www.elsevier.com/locate/jpor
Editorial
Dental materials used for metal-free restorations: Recent advances and future challenges
As one of the Associate Editors for the Journal of Prosthodontic Research (JPR), I have been pleasantly surprised that numerous papers regarding dental materials and technologies have recently been submitted to JPR from all over the world, given that the main dental society in which I am active is the Japanese Society for Dental Materials and Devices. As all our readers can see in the Instructions for Authors for our journal, ‘‘adhesive dentistry; dental materials; and aesthetic dentistry’’ is defined as one of the targeted topics for JPR. In addition, ‘‘digital dentistry’’ has seen marked developments through computer-aided design and computer-aided dental manufacturing (CAD/CAM) technology, and has therefore been added as another targeted topic for JPR, as these developments have been rapidly adopted and applied to clinical dentistry. Incidentally, this has previously been discussed at length by the Editor-in-Chief of JPR, Professor Kazuyoshi Baba [1], and hence further discussion concerning digital dentistry will be omitted here. Needless to say, from the distant past through to the present day, dentistry has been continuously invigorated by the development of both dental materials and technologies. In other words, one could suggest that there is no progress in dentistry without the development of dental materials and technologies. Generally, in the prosthodontic treatment of
missing or decayed teeth, artificial materials see use as dental materials to restore oral function. With the improving awareness of patients regarding oral health-related quality of life and the advances in dentistry, the demands (not only from patients, but also from dentists) for such dental materials have diversified. What do you think is the most important property for such dental materials: durability, suitability, biocompatibility, esthetics, or cost performance? I think it is important for dentists and patients to understand both the advantages and limitations of dental materials, to allow the selection of the best materials, because although the advantages of new dental materials and technologies are emphasized, the limitations are often less obvious. In this editorial, I would like to briefly discuss the current status and future needs of dental materials for metal-free restorations in prosthodontics.
1. Classification of dental materials and development of zirconia restorations As is well-known, dental materials are generally classified into four types: metals; ceramics; polymers; and composites. Which materials are best for each dental prosthesis? That is, dentists and patients need to make choices between these alternatives. As you know, all these dental materials have both advantages and disadvantages. Historically, metal alloys such as gold alloy, silver alloy, and cobalt–chromium–nickel alloy are the oldest of the four major classes of raw materials that have been widely used in dental prostheses such as crowns, fixed partial dentures (FPDs), and removable partial dentures (RPDs) in prosthodontics. Such metal alloys are strong and durable, and have a long history of use in dentistry, but are not esthetically pleasing because of their metallic color, and carry a risk of causing allergic or toxic reactions within the soft or hard tissues of the oral cavity. On the other hand, new dental ceramics such as castable ceramics and CAD/CAM ceramics have been introduced to dentistry since the 1980s, and have shown considerable potential for esthetic restorations. To
Please cite this article in press as: Tanimoto Y. Dental materials used for metal-free restorations: Recent advances and future challenges. J Prosthodont Res (2015), http://dx.doi.org/10.1016/j.jpor.2015.07.003
JPOR-288; No. of Pages 3
2
journal of prosthodontic research xxx (2015) xxx–xxx
achieve completely metal-free restoration, polycrystalline zirconia-based ceramics with high mechanical properties such as yttrium partially stabilized tetragonal zirconia polycrystalline (Y-TZP) and ceria-stabilized tetragonal zirconia polycrystalline and alumina nanocomposites (Ce-TZP/ Al2O3) have been successfully introduced to clinical dentistry during the past decade, along with dental CAD/CAM systems [2]. Surprisingly, Ce-TZP/Al2O3 shows a high fracture toughness of 19 MPa m1/2 and resistance to low-temperature degradation, although Y-TZP suffers from low-temperature degradation. Of course, zirconia-based ceramics such as CeTZP/Al2O3 and Y-TZP are not ductile in the manner of metal alloys, but are now clinically available as FPDs. Furthermore, the possibility of metal-free restorations made from zirconiabased ceramics for prosthodontic treatments is greatly increasing. For example, zirconia implants that are manufactured in 1- or 2-piece designs, especially zirconia abutments, have been introduced for esthetic restorations, low plaque retention, and good stabilization for soft tissues. In current implantology, numerous reports have described surface modifications to implants using titanium and its alloys, such as plasma spraying, blasting, acid-etching, and their combinations, to provide roughened surfaces facilitating bone fixation [3]. On the other hand, surface modification techniques for such zirconia implants are not well-established due to the low electroconductivity of zirconia and the difficulty in processing. In addition, the ability of zirconia implants to achieve osseointegration is still unclear; further long-term follow-up of zirconia implants is thus needed. Likewise, the application of zirconia-based ceramics such as Ce-TZP/Al2O3 to RPDs has recently been attempted, but remains in the experimental stage [4]. As a final topic concerning zirconia restorations, bonding systems for zirconia have recently gained wider interest, because it is also important to improve the bonding of zirconia with veneering or resin-based luting agents. The mechanisms needed to obtain adequate bonding between zirconia and veneering are still unclear, and the high incidence of veneer chipping on zirconia cores has been reported as a critical problem. Meanwhile, surface treatment with 10-methacryloyloxydecyl dihydrogen phosphate, after sandblasting with airborne particles, has been reported as one of the most reliable resinto-zirconia adhesive systems [2]. However, further work using different approaches for bonding systems involving zirconia is clearly necessary.
2.
Application of fiber-reinforced composites
In terms of metal-free restorations other than zirconia restorations, I am eagerly expecting the application of fiberreinforced composites (FRCs) comprising fiber-reinforcement and resin composites to dental prostheses [5]. FRCs have been used to fabricate dental appliances such as crowns, FPDs, and RPDs in both basic research and clinical experiments. Dental prostheses made from FRCs are often much more esthetically pleasing than those made from metal alloys. In current prosthodontics, FRCs have seen particular use as fiber dowels (posts), because they have an elastic modulus similar to that of dentin, resulting in less damage to the remaining tooth
structure. In the near future, FRCs will be applied to a wide range of esthetic restorations as tailored materials, because the properties of FRCs can be tuned by changing the parameters of the fiber (e.g., fiber type, volume fraction, and diameter).
3. Non-metal clasp dentures using thermoplastic resins Finally, another topic that I want to mention here is the fact that, RPDs made from thermoplastic resins such as polyamide, polyester, and polycarbonate have seen increasing use in recent times. In a position paper by the Japan Prosthodontic Society (JPS) [6], RPDs using the ‘‘resin clasp’’ retentive part were defined as ‘‘non-metal clasp dentures’’ (NMCDs). Such NMCDs made using thermoplastic resins are often much more esthetically pleasing than conventional RPDs with metal clasps. However, the use of such NMCDs without metal frameworks may seriously affect remaining tissues because of their low rigidity, and such NMCDs do not conform to the standard principles for RPD design. Accordingly, the formulation of evidence-based guidelines for the clinical application of NMCDs in the near future is anticipated, particularly by the members of JPS.
4.
Summary
This editorial discusses relatively new dental materials centered upon metal-free restoration in prosthodontics. However, if a potential manuscript offers high-quality, interesting information for JPR readers, we will of course keep the door open for publication in JPR; not only for such new dental materials, but also for conventional dental materials needing additional research. This is because new materials and technologies will continue to progress through advances in knowledge of and experience with traditional materials and technologies.
references
[1] Baba K. Editorial: Paradigm shifts in prosthodontics. J Prosthodont Res 2014;58:1–2. [2] Miyazaki T, Nakamura T, Matsumura H, Ban S, Kobayashi T. Current status of zirconia restoration. J Prosthodont Res 2013;57:236–61. [3] Shibata Y, Tanimoto Y. A review of improved fixation methods for dental implants. Part I: Surface optimization for rapid osseointegration. J Prosthodont Res 2015;59: 20–33. [4] Urano S, Hotta Y, Miyazaki T, Baba K. Bending properties of Ce-TZP/A nanocomposite clasps for removable partial dentures. Int J Prosthodont 2015;28:191–7. [5] Vallittu PK. High-aspect ratio fillers: fiber-reinforced composites and their anisotropic properties. Dental Mater 2015;31:1–7. [6] Fueki K, Ohkubo C, Yatabe M, Arakawa I, Arita M, Ino S, et al. Clinical application of removable partial dentures using thermoplastic resin. Part I: Definition and indication of non-metal clasp dentures. J Prosthodont Res 2014;58:3–10.
Please cite this article in press as: Tanimoto Y. Dental materials used for metal-free restorations: Recent advances and future challenges. J Prosthodont Res (2015), http://dx.doi.org/10.1016/j.jpor.2015.07.003
JPOR-288; No. of Pages 3
3
journal of prosthodontic research xxx (2015) xxx–xxx
Yasuhiro Tanimoto PhD Department of Dental Biomaterials, Nihon University School of Dentistry at Matsudo, Matsudo, Chiba 271-8587, Japan E-mail address: [email protected] (Y. Tanimoto)
Received 14 July 2015 http://dx.doi.org/10.1016/j.jpor.2015.07.003 1883-1958/# 2015 Japan Prosthodontic Society. Published by Elsevier Ireland. All rights reserved.
Please cite this article in press as: Tanimoto Y. Dental materials used for metal-free restorations: Recent advances and future challenges. J Prosthodont Res (2015), http://dx.doi.org/10.1016/j.jpor.2015.07.003
