Final Design

Final Design CAD

The MedJaw jaw therapy device went through many iterations to reach the target functional requirements. The final design consists of a block slider, attached to swappable parametric mouthpieces, driven by the users’ lever force application and restored by a sinuous spring, all of which are printed in PETG except the mouthpiece which is printed in an antibacterial PLA-Ag. The slider system’s long rails in conjunction with the spring restoration force counteract jamming caused by jaw resistance during opening and closing. Additionally, a series of ergonomic improvements to the housing and lever components were performed to ensure patient comfort during daily jaw exercise. In relation to the accessibility and foodsafe requirements of the device, the mouthpiece is both parametric and replaceable, allowing the device to be tailored to the patient, as well as thoroughly disinfected.

To learn more about each component, check out our parts page!

Cyclic Test Bench Setup

A friction test bench was devised in order to quantify the friction through finding the effort required in order to break the slider free from static friction at rest. Three separate detachable guidance rail designs were tested in conjunction with three different slider designs. Across the board, a thin “ridge” design was selected. It would later be found that although the thin “ridge” design was able to break free from static friction, the slider still jammed during the restoring stroke. Initially, the jaw was treated as a constant resistive force only on the downstroke, but after consulting Dr. Massenburg, it was realized that the jaw functions similarly to a spring, resisting all the way throughout the range of motion, roughly proportional to its angular displacement. In an attempt to understand the results from the experiment, a comprehensive static calculation was performed.

Fatigue Testing Results

The method for determining fatigue life for the PLA and PETG Housing-Spring Configurations was as follows:

Rolling Standard Deviation > Threshold * Baseline Standard Deviation

PLA and PETG spring's respective thresholds for failure were chosen as 1.6 and 2.0. (With PLA having a lower threshold due to its unpredictable behavior during cyclic testing.)

From this metric, the PLA-PLA Housing-Spring Configuration showed the worst performance, withstanding only 1900 cycles, and the PETG-PETG Housing-Spring Configuration the best with 8900 cycles. The MedJaw team recommends a full PETG print for the best fatigue performance.

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