Transient forces generated by projectiles on variable quality mouthguards monitored by instrumented impact testing.

OBJECTIVES: (a) To determine the force-time trace that occurs when a spring mounted simulated upper jaw is impacted; (b) to examine if mouthguards of variable quality have significant influence on such force-time traces; (c) to attempt to relate physical events to the profile of the force-time traces recorded. METHODS: A simulated jaw, consisting of ceramic teeth inserted into a hard rubber arch reinforced with a composite jawbone, was fitted with various mouthguards as part of a previous round robin study. A clinical assessment distinguished good, bad, and poor mouthguards, and these were each fitted to the jaw, which was then submitted to instrumental impact tests under conditions expected to produce tooth fractures. The force-time trace was recorded for such impact events. RESULTS: The spring mounting method caused two distinct peaks in the force-time trace. The initial one was related to inertia effects and showed an increase in magnitude with impactor velocity as expected. The second peak showed features that were related to the differences in the mouthguards selected. CONCLUSIONS: The use of a force washer within a conical ended impactor enabled force-time traces to be recorded during the impact of a spring mounted simulated jaw fitted with mouthguards of variable quality. The spring mounting system causes an initial inertial peak followed by a second peak once the spring mount has fully compressed. Good fitting guards, which keep most teeth intact, result in high stiffness targets that in turn generate high reaction forces in the impactor. If the spring mounting is omitted, the two peaks are combined to give even higher reaction forces. The force-time trace offers some potential for assessing both overall mouthguard performance and individual events during the impact sequence. Mouthguards with good retention to the jaw remained attached during the impact event and helped to preserve the structural integrity of the target. This in turn developed high forces in the second part of the force-time trace. Guards that detached during impact and allowed tooth fractures showed lower forces in the second part of the test. The force profile measured offered some quantitative support to, and agreement with, the observed clinical quality of the mouthguards.

Application of a standard test to the in vitro performance of mouthguards.

OBJECTIVE: To use a simulated upper jaw made from a rubber arch containing replaceable ceramic teeth and a renewable composite ceramic jawbone to compare the effectiveness of seven custom made mouthguard designs and a "boil and bite" mouthguard. METHODS: Following an earlier development of a standard impact test using a selection of projectile shapes and energies, the most sensitive conditions were selected. These were then applied to a series of six guards constructed in ethylene vinyl acetate and styrene butadiene. The guards were constructed to reflect possible variations in both design and materials. RESULTS: Significant differences between the mouthguard performances were observed in response to the impact conditions selected. All the custom made designs gave better performance than the "boil and bite" mouthguard. CONCLUSIONS: The differences observed indicated that the standard test should be sensitive enough to be used as an assessment procedure for the approval of the manufacture of these safety devices. A sequence of tests on eight identical mouthguards selected from a batch of 12, based on the best design, gave remarkably consistent results, indicating that both the manufacturing technique and the test method are reliable. The features of the best design should be incorporated into the current "best practice" for the construction of these devices.

Towards the development of a standard test procedure for mouthguard assessment.

A simulated upper jaw, made from a rubber arch containing replaceable ceramic teeth and a renewable composite jawbone, offers promise in assessing the performance of custom made mouthguard designs. Impact tests, involving precise assessment of jaw and tooth fractures caused by projectiles of various energies and profiles, simulate conditions that approximate to common clinical observation. Such conditions offer the most sensitive indices for assessing both improved mouthguard designs and product quality and reliability. Damage caused by the dissipation of the impact energy may be transferred within this simulated oral cavity by minor changes to the impact conditions.