Shock absorption ability of laminate mouth guards in two different malocclusions using fiber Bragg grating (FBG) sensor.

PURPOSE: The majority of orofacial injuries affect the upper jaw, with the maxillary incisors being most prone to injury, often accounting for as many as 80% of all cases. Children with malocclusion in the anterior segment of the maxilla are more prone to traumatic injuries than those exhibiting normal occlusion, because most often the damaging force impacts directly against the maxillary anterior teeth. Hence, because of the difference of dissipation of the impact force because of the presence or absence of malocclusion, the mouthguard's shock absorption capacity would be influenced by certain factors. In the present study, a unique in vitro experiment utilizing fiber Bragg Grating (FBG) as distributed strain sensors was carried out to evaluate the shock absorption ability of laminate customized mouthguards in two different malocclusions compared with normal occlusion. MATERIAL AND METHODS: The impact was produced using a customized pendulum device with three interchangeable impact objects on typhodont models with two different malocclusions and normal occlusion from different heights. Response of gratings was monitored using an optical spectrum analyzer. Strain induced because each impact was determined from the Bragg's wavelength shifts for each grating. For every model, 12 impact strikes were measured using three different impact objects on the two specified sites by releasing the object from two different heights. RESULTS AND CONCLUSIONS: The laminated mouthguards showed significant variation in shock absorption ability when different malocclusions were compared. Hence, modifications in the original design of the laminated mouthguards should be considered for athletic competitors with malocclusion to provide adequate protection against impact. FBG sensor has shown the unique advantage of high sensitivity to strain measurement and can be used in further studies. The height of the impact is an important variable in determining the shock absorption ability of mouthguards.

Fiber Bragg grating sensor for measurement of impact absorption capability of mouthguards.

BACKGROUND: There is no standard technique to monitor impact absorption capability of mouthguards. Earlier investigations have established that strain transferred to the teeth through mouthguard is a good indication of their efficiency. In the present study, a unique experimental scheme utilizing fiber Bragg gratings (FBGs) as distributed strain sensors is proposed and investigated to estimate impact absorption capability of custom-made mouthguard. The proposed methodology is useful due to advantages such as, very small size and flexibility for ease of bonding, self-referencing, and multiplexing capability of using FBG sensors. MATERIAL AND METHODS: Finite-element analysis was performed to simulate the stress distribution due to impact on the mouthguard. The FBGs were fabricated by exposing the core of photosensitive fiber to intense Ultra-Violet light through a 'phase mask'. One FBG sensor was bonded on the jaw model and another on the mouthguard surface at similar positions, so that both gratings are simultaneously affected by impact. Two different sets of the sensors were used, one for the anterior region and another for posterior region. The impact was produced using customized pendulum device with interchangeable impact objects i.e. cricket ball, hockey ball, and steel ball. Response of gratings was monitored using optical spectrum analyzer and strain induced due to each impact was determined from the Bragg wavelength shifts for each grating. RESULTS AND CONCLUSIONS: Strain induced due to impact was calculated from the Bragg wavelength shifts. Difference in the strain values for the two gratings is interpreted as impact energy absorbed by the mouthguard. The Bragg wavelength shifts (induced strain) for FBG bonded on the jaw model was much lower than the shift for FBG bonded on the mouthguard, indicating that most of the impact energy is absorbed by the mouthguard.