This benchtop test provides empirical evidence for the fatigue properties of nucleus devices. Fatigue cyclic loading is applied to simulate the functional loading of a nucleus device under moderate to high loads representative of those experienced in vivo, including worst-case conditions. The test is then accelerated to obtain results in less time than physiological rates would allow.
Testing objective is determining the fatigue properties of nucleus devices per ASTM 2789-10 (2015) “Standard Guide for Mechanical and Functional Characterization of Nucleus Devices” and ASTM 2346-05 (2011) “Standard Test Methods for Static and Dynamic Characterization of Spinal Artificial Discs”. Tests are typically performed at 2Hz for 10 million cycles or until functional failure occurs. Fatigue tests are conducted in a 0.9% saline environmental bath at 37°C at a rate of 2Hz or less, although alternative fluids and frequencies can be used as long as they are justified. Devices are typically loaded at loads experienced during common activities, with a worst-case load of 3,500N of compressive force without failure. Loads on the discs of healthy adults in various positions and activities have been studied and are presented in table 1.
A device failure is defined by the device manufacturer and can be any material yielding, permanent deformation, loosening of the implant assembly or fracture of any component during or at the end of test. The device manufacturer will also examine the devices post-testing against the acceptance and/or failure criteria.
The test system utilizes a test fixture designed by MDT (see picture) that is integrated with an MTS Servohydraulic Tester. The tester is capable of determining static failure loads and applying fatigue cyclic loading to the dental implants.
MDT tests are conducted in accordance with ANSI/ISO/IEC 17025-2005. Testing schedules and resource needs are determined during project kickoff meetings with MDT engineers and the customer. Services are performed in accordance with standard operating procedures and test protocols specific to the project. Standard tests do not begin without a protocol signed by both the customer and an MDT representative. For feasibility or non-standard tests, MDT will develop a method and protocol with customer input and will review the final process with the customer prior to initiation of the test.
The test equipment software monitors the cycle count and displacement throughout the duration of the test. MDT engineers monitor the test daily and record the temperature and pressure for the system, as well as the outside radial strain at predetermined positions for each device being tested. MDT sends weekly updates to ensure customers are apprised of the status of their test. Updates include raw data collected throughout the week for the customer's analysis.
Inspection Services Offered:
MDT offers several inspection and monitoring methods including:
• High speed video inspection of devices or fixture validation
• Visual Inspections
Tests are conducted in accordance with ANSI/ISO/IEC 17025-2005. In compliance with this standard, MDT test reports include comprehensive documentation and summary of the test protocol and results. Any test method deviations, additions, or exclusions are documented and reviewed with the customer prior to beginning the test. Information within the report includes the specific test conditions, statements of compliance with test protocol, and the estimated measurement uncertainty. The reported results only relate to the items tested. Any opinions and interpretations provided by MDT are clearly marked as such. Any additional information required by customer-specific methods will also be noted. At the conclusion of the test, MDT provides the customer with a Microsoft Windows formatted CD containing copies of all raw data, inspection results, and other information collected during the test (see example test reports).
Please take a few moments to tell us more about your device and test requirements in our short questionnaire, and we will be happy to provide you with a quote.