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- Quality in metal AM
In the dental industry, the only required certification for metal AM is for materials, which is elaborated on extensively in this chapter. Relevant quality aspects for design, machine, process, post-processing, metrology and maintenance are discussed.
Keywords: AM in the dental industry, regulations, material certification
- Additive manufacturing applications in the dental industry
- Requirements of dental products
- Machine / process
- Post processing
- Metrology & maintenance
1. Additive manufacturing applications in the dental industry
For the application of additive manufacturing in the dental industry we address the following articles:
- Indian Dental Academic presentation on the use of titanium and titanium alloys in the dental industry (2013)
- 3D printing technologies for dental applications (3dprinting.com, 2012)
Metal AM applications are crowns, bridges, frames and bars on implants. Resin applications al large range of products manufactured by dental laboratories, including models and splints.
2. Requirements of a dental products
The follow requirements are relevant for intra oral dental applications.
- Mechanical behaviour
The material need the required biocompatibility and properties (see regulations for standards).
For metal AM fabricated parts, 20 microns accuracy is sufficient, other (resin) applications can have a lower accuracy.
The required coating depends on the applications. quality issues with coating concern surface quality and aesthetics.
For generic AM standards we refer you to chapter 'application: regulations and requirements'.
For a service provider to be certified to produce dental prosthetics, the only required certification is for materials, as the material supplier is responsible for the end product.
The following materials are used for AM in the dental industry:
- Cobalt chrome
- Resin materials
For resins, the following ISO standards are applicable:
- ISO 20795-1:2013classifies denture base polymers and copolymers and specifies their requirements.
- ISO 20795-2:2013is applicable to orthodontic base polymers and copolymers used in the construction .of both active and passive orthodontic appliances and specifies their requirements.
- ISO 10477:2004classifies polymer-based dental crown and bridge materials and specifies their requirements.
- ISO 527-1:2012specifies the general principles for determining the tensile properties of plastics and plastic composites under defined conditions.
- ISO 868:2003specifies a method for the determination of the indentation hardness of plastics and ebonite.
- ISO 179-1:2010specifies a method for determining the Charpy impact strength of plastics under defined conditions.
For cobalt chrome metals, the following standards are applicable:
- ISO 22674:2006classifies metallic materials that are suitable for the fabrication of dental appliances and restorations.
- ISO 9693-1:2012specifies test methods for determining the compatibility of metallic and ceramic materials used for dental restorations by testing the composite structure
For titanium metals, the following standards are applicable:
- ASTM F2924is the first AM specific standard that has been given for Ti6Al4V alloys
- ASTM F136, F1472and ISO 5832-3:1996 describe the use of Ti6Al4V alloys for surgical implant applications in terms of material requirements and the manufacturing process
As every part designed for AM is unique, quality issues can best be described per case, such as the dental bridge. Generic quality issues for design can be studied in chapter 'design'.
5. Machine/ process
Available metal AM systems for dental applications are listed in the ManSYS exploitable result 'a guidance document for a dental platform'. General quality issues for process and machine can be found in the corresponding chapters. Metal AM dental applications are manufactured with SLM technology.
6. Post processing
7. Metrology and maintenance
Test methods for dental applications;
- Check the scanned file and design by designer
- Manual checking dimensions by using a model
- Visual colour check against colour standard.
- Visual inspection by operator
Maintenance of intra oral dental applications require regular check ups with a dentist to inspect quality and maintenance of the application.