The Food and Drug Administration (FDA or the Agency), the US regulating authority in the sphere of medical devices and other healthcare products, has published a guidance document dedicated to denture base resins. In particular, the document addresses the aspects related to the performance criteria for the safety and performance-based pathway. The present draft guidance describes the regulatory approach suggested by the FDA. The authority encourages medical device manufacturers and other parties involved to provide their feedback and suggestions on the matters outlined therein. These comments will be considered by the FDA when developing a final version of the guidance.
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The authority additionally mentions that guidance documents are not intended to introduce new rules and requirements themselves but to provide additional clarifications regarding the way the regulatory requirements set forth by current legislation should be interpreted and applied, suggesting the approach to be followed by the parties involved. However, an alternative approach could be applied, provided such an approach complies with the respective regulatory requirements and has been agreed with the authority in advance.
Regulatory Background
The present document addresses the aspects related to the performance criteria for denture base resins intended to be placed on the market under the Safety and Performance Based Pathway. According to the guidance, interested parties are allowed to follow the approach outlined in the document when submitting a 510(k) application instead of a comparison of the device in question to a similar medical device already placed on the market as prescribed under the general rule.
The guidance also contains references to the FDA-recognised voluntary consensus standards the medical device manufacturers may use when demonstrating conformity with the applicable regulatory requirements. In particular, the FDA refers to the international standard ISO 20795-1 Dentistry – Base polymers – Part 1: Denture base polymers.
As mentioned before, FDA guidance documents are non-binding in their nature, and provisions thereof should be construed only as recommendations to be followed.
Specific Aspects
Denture base resins covered by the scope of the present FDA guidance are Class II medical devices subject to regulation under 21 CFR 872.3760 with the product code EBI. These devices are intended to reline a denture surface that contacts tissue, repair a fractured denture, or form a new denture base. The regulating authority additionally emphasizes that such medical devices are not allowed for over-the-counter (OTC) use. Hence, the scope of the guidance does not cover resins for OTC relining or repairing denture bases, preformed denture teeth, or partially fabricated denture kits. The authority pays special attention to the materials used to manufacture denture base resins described in the guidance. In particular, there are 5 types of materials that are applicable:
- Type 1: Heat-polymerizable materials;
- Type 2: Autopolymerizable materials;
- Type 3: Thermoplastic blank or powder;
- Type 4: Light-activated materials;
- Type 5: Microwave cured materials.
It is also important to mention that in the case of denture base resins manufactured by the device of additive manufacturing technologies (3D printing), special requirements would be applicable. According to the guidance, in such cases, additional information should be provided by the manufacturer, namely:
- Description of all procedures and mechanisms used in the course of the manufacturing process;
- Printing parameters;
- Information about build volume parameters, including such details as print directions or number of medical devices manufactured simultaneously in the context of consistency of the manufacturing process;
- Information about the way leftover material should be reused (e.g. mixture of virgin and leftover material in the appropriate proportion);
- Detailed instructions for end-users;
- A verification and validation report of dimensional measurements demonstrating that the physical output of the system for fabricating the device meets design input specifications for critical dimensions within pre-specified tolerances for the device type and intended use to demonstrate consistency and reproducibility between build cycles made on samples from multiple build cycles; and
- Information about performance testing.
The authority is also entitled to request additional information and documentation, should it be reasonably necessary to perform the assessment of a medical device subject to review. If the manufacturer finds it necessary to perform additional testing beyond the scope of that described in the present FDA guidance, the Agency recommends filing a Pre-Submission in order to discuss important aspects in advance (before submitting the main application).
Testing Performance Criteria
The guidance further describes the particular performance criteria to be applied in the context of denture base resins. As mentioned, if the medical device in question is eligible for the Safety and Performance Based Pathway, and the manufacturer decides to follow such an approach, a standard side-by-side comparison to a similar medical device already placed on the market is not required. Instead, the manufacturer shall submit an application accompanied by a results summary for all tests performed. According to the guidance, this could include results summary, test protocols, or complete test reports. In this regard, the FDA also refers to the appropriate guidance on Recommended Content and Format of Non-Clinical Bench Performance Testing Information in Premarket Submissions.
According to the present draft guidance on denture base resins, the scope of mechanical bench testing these devices should be subject to prior to submitting the application shall cover the following types of testing:
- Ultimate flexural strength;
- Flexural modulus;
- Stress intensity factor;
- Fracture work;
- Residual monomer;
- Water sorption;
- Water solubility.
Additive Manufacturing Testing Considerations
As mentioned, if additive manufacturing technologies are used to produce denture base resins, the scope of assessment should cover such aspects as:
- Ultimate flexural strength;
- Flexural modulus;
- Stress intensity factor; and
- Fracture work.
According to the guidance, when analyzing the safety and performance of denture base resins manufactured by the process of additive manufacturing technologies, the manufacturer should take into consideration specific aspects associated with the use of such technologies, including the layer-by-layer manufacturing process that could significantly impact the properties of a final product. In particular, this could impact the way the device will perform under load. Other aspects to be considered include the use of leftover material and the impact it causes on the safety and performance of the device. Additionally, the manufacturer shall take into consideration the applicable printing directions and other printing parameters. The testing to be performed should be sufficient to assess potential worst-case scenarios and provide accurate and reliable information about the safety and performance of the device. At the same time, specifics of the additive manufacturing process are less likely to impact the performance of the device in such tests as a residual monomer, water sorption, and water solubility.
In summary, the present FDA draft guidance describes the approach to be applied when assessing the safety and performance of denture base resins. The document pays special attention to specific aspects associated with the devices manufactured with the use of additive manufacturing technologies and the way this impacts testing results.
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