Shock absorption potential of different mouth guard materials

Comparison of shock absorption capacities of three types of mouthguards: A comparative in vitro study

BACKGROUND/AIM

3D printing processes can be used to manufacture custom-made mouthguards for sports activities. Few studies have compared the impact performance of industrial-created mouthguards with that of custom-made mouthguards manufactured by thermoforming or 3D printing. The objective of this in vitro study was to compare the shock absorption capacities of custom-made mouthguards manufactured by 3D printing with industrial mouthguards and thermoformed ethylene vinyl acetate (EVA) mouthguards.

MATERIALS AND METHODS

For each type of mouthguard, eight samples were produced. 3D-printed mouthguards were manufactured using digital light processing technology. Each mouthguard was subjected to an impact performance test defined by the standard AFNOR XP S72-427, which evaluate maximum deceleration and force transmitted during impact. The thickness of each mouthguard before and after a series of five impacts was measured at the impacted inter-incisal area.

RESULTS

The mean maximum decelerations during impact ranged from 129 to 189 g for industrial mouthguards, 287 to 425 g for thermoformed EVA mouthguards, and 277 to 302 g for 3D-printed mouthguards. The mean reduction in mouthguard thickness at the impact zone after five tests was 1.2 mm for industrial mouthguards, 0.6 mm for 3D-printed mouthguards, and 2.2 mm for thermoformed EVA mouthguards.

CONCLUSIONS

Custom-made 3D printed mouthguards showed slightly better shock absorption ability than thermoformed mouthguards with respect to the indicator proposed in XP S72-427. They seemed to combine the practical advantages of thermoformed mouthguards in sports with better shock absorption capacity and lower cost. Furthermore, they had the least thickness variation during the test, and their shock absorption capacity was the least affected by repeated mechanical tests. Other types of 3D-printing resin materials that will become available must continue to be tested for shock absorption to provide the best protection to users at low cost.

Improving light-cured intermediate resin for hard and space mouthguard using a glass fiber

BACKGROUND/AIMS

A light-cured intermediate material is useful for fabricating a hard insert and a buffer space mouthguard (H&SMG). However, it requires improvement in its mechanical properties and shock-absorbing capacity. The aim of this study was to evaluate the mechanical properties of two prototype light-cured intermediate materials reinforced with glass fibers, and the impact absorption capacity and durability of H&SMGs made with the prototype intermediate materials.

MATERIALS AND METHODS

Two prototype materials containing long and microlength glass fibers in a light-cured intermediate material, Innerframe LC®, for H&SMG, were fabricated and tested. A three-point bending test was performed for evaluation of the mechanical properties. In addition, a shock absorption test was conducted using a customized pendulum impact testing machine to evaluate the H&SMGs' impact absorption capacity and durability.

RESULTS

Long and microlength glass fibers significantly improved flexural modulus and strength. H&SMGs made with these two glass fiber-containing materials had high impact absorption capacity against both low and high impact forces, while the mouthguards made with long glass fiber materials had the best results.

CONCLUSION

Long and microlength glass fibers with the prototype materials improved the mechanical properties of Innerframe LC® and the impact absorption capacity and durability of H&SMGs. H&SMGs made with the long glass fiber prototype materials had the best performance.

Effectiveness of hard inserts in sports mouthguards: a systematic review

Objectives To improve the protective capacity of conventional ethylene-vinyl acetate mouthguards, some authors have suggested reinforcement with a hard material to distribute impact energy more widely. The research question for this systematic review was: 'does the inclusion of a hard insert in mouthguards improve the protection of anterior teeth from a direct blow?'Data sources Three bibliographic databases (PubMed/Medline, Ovid/Embase and the Cochrane CENTRAL databases) were searched up to 20 February 2021. Additional searches included hand searching of key articles and journals.Data selection A systematic search of the literature included studies where the intervention was the incorporation of hard material into sports mouthguards and where the comparator was conventional mouthguard material. Eligibility required the use of anatomical specimens or anatomical analogues which included or represented anterior maxillary teeth. Twelve eligible publications were identified.Data extraction Data extraction was first carried out independently by two reviewers. Discrepancies were resolved by discussion.Data synthesis Results of individual studies were conflicting and methodological diversity created difficulty in making a synthesis of results. All studies employed low-energy impacts that did not represent the potentially high-energy impacts encountered in sport.Conclusion The efficacy of hard inserts in sports mouthguards has not been demonstrated.

Use of the fiberglass reinforcement method in thermoplastic mouthguard materials to improve flexural properties for enhancement of functionality

The purpose of this study was to evaluate the application of fiberglass reinforcement method in thermoplastic mouthguard materials to improve flexural properties and adhesive strength. Commonly used two types of commercial mouth guard materials (ethylene-vinyl acetate copolymer-based and polyolefin-based) were reinforced with glass fiber clothes by two-step hot press. Flexural strength and adhesive strength with each base material were examine via three-point bending test and delamination test, respectively. Ethylene-vinyl acetate copolymer-based fiberglass-reinforced material has significantly greater adhesive strength with base material and improvement of flexural properties compared with polyolefin-based material. These results suggest that flexural properties of both conventional commercial mouthguard materials were improved when the glass-fiber-reinforced method was applied to reinforce mouthguard materials, and more, ethylene-vinyl acetate copolymer was more desirable for the base material.

The effect of light-cured resin with a glass fiber net as an intermediate material for Hard & Space mouthguard

BACKGROUND/AIMS

Despite the use of conventional mouthguards, preventable sports-related dental injuries continue to occur. The authors have developed a two-layered ethylene polyvinyl acetate (EVA) mouthguard with a hard polyethylene terephthalate (PET) insert and a buffer space (H&SMG). However, adapting the PET onto the EVA layer requires skill. A light-cured Splint Resin (SRLC) and a glass fiber net (NET) reinforcement appear to resolve this issue. The aim of this study was to investigate whether SRLC with NET could replace PET and find a more practical application for NET.

MATERIALS AND METHODS

A pendulum impact testing machine and a dental model with strain gages were used. Six types of mouthguards were made: one with two laminated EVA blanks (LAM-MG), a three-layer type with a PET insert and an intermediate space (PET-H&SMG), a H&SMG with SRLC insert (LC-H&SMG), and three other types with differential NET-SRLC reinforcement; NET on the outer surface of SRLC, NET on the inner surface of SRLC, and NET on both the outer and inner surfaces. Five mouthguards of each type were fabricated and tested ten times with impact distances of 15 and 30 cm. Forty more impacts were applied to all H&SMGs to confirm the durability of the hard inner layer.

RESULTS

All H&SMGs showed significant strain reduction compared to the LAM-MG. PET-H&SMG and the four types of LC-H&SMG exhibited an equally slight strain (approximately 95% shock absorbing ability) in all conditions. During the test against the smaller impact, all H&SMGs showed no cracks. When tested against the stronger impact, only the LC-H&SMG with the reinforced inner surface, the double NET-reinforced LC-H&SMG, and the PET-H&SMG remained intact.

CONCLUSION

The NET-reinforced SRLC can replace PET as an intermediate mouthguard material. The NET application, at least on the internal surface, is indispensable for the LC-H&SMG reinforcement.

A Comparative Study of Shock Absorption Capacities of Custom Fabricated Mouthguards using a Triangulation Sensor

This in-vitro study compares the shock absorption qualities of five mouthguard designs measured with a triangulation laser sensor during small hard object collisions. The aim was to investigate the impact of different labial designs on mouthguard performance. Methods: Five different custom-fabricated ethylene vinyl acetate (EVA) types of mouthguards with varying thickness and different labial inserts (polyethylene terephthalate glycol-modified (PETG), nylon mesh, air space) were tested with a triangulation laser sensor during different energy blows, generated with a pendulum testing device. The pendulum hits were applied to the center of a pivoted tooth crown in a custom-built upper jaw model. Measurements were executed with the mouthguards on the model and with no mouthguard as a negative control. Results: Tooth deflection was reduced with all mouthguards in comparison to no mouthguard. Increasing mouthguard thickness improved the mouthguards’ shock absorption capacities. Also, adding labial inserts increased their preventive qualities in ascending order: Mouthguard with a soft insert (nylon mesh), a hard insert (PETG), air space plus a hard insert (PETG). Conclusion: Increasing EVA foil thickness of a mouthguard, increasing labial thickness, and adding labial inserts (soft, stiff and air space) improve mouthguard shock absorption capabilities during small hard object collisions, thereby improving dental trauma prevention.

The Role of Mouthguards in Preventing and Reducing Sports-related Trauma

a mouthguard, also known as a gumshield, mouth protector or sports guard is an appliance that covers the teeth and surrounding mucosa with the aim of preventing or reducing trauma to the teeth, gingival tissue, lips and jaws. The device is usually worn on the maxillary arch and works by separating the maxillary and mandibular dentition, protecting the teeth from the surrounding soft tissue, absorbing or redistributing shock and/or stabilising the mandible during traumatic jaw closure. They may also play a role in preventing and reducing concussion by absorbing impact forces that would otherwise be transmitted through the base of the skull to the brain, although the evidence for this is less conclusive. A mouthguard will usually fall into one of three categories: stock mouthguards (which are made ready to use and are believed to give the least protection), the mouth-formed or 'boil and bite' type (which are heated in hot water, placed in the mouth and moulded to the teeth) and custom-made mouthguards (which are usually made on a stone model of the maxillary teeth and surrounding tissue and are thought to give the most protection). These devices can be made from various materials but ethylene-vinyl acetate is by far the most popular material, probably because of the ease with which it can be used for the production of custom-made mouthguards. This paper gives a review of the role of mouthguards in preventing and reducing sports-related trauma and examines the materials that are used to fabricate them.

Crystallization and hardening of poly(ethylene-co-vinyl acetate) mouthguards during routine use

Mouthguards (MGs) made from poly(ethylene-co-vinyl acetate) (EVA) are widely used in contact sports to prevent injuries such as breaking teeth and lip lacerations and to reduce brain concussion. However, the changes in morphology and the molecular mobility of EVA, which can affect its physical properties during practical usage, have not been precisely examined. Therefore, we attempted to determine the main factors which lead to changes in MG performance after one season of practical use by high school rugby players. Solid-state nuclear magnetic resonance (NMR) and pulse NMR measurements showed the hardening of MGs, which was associated with an increased crystallinity of the EVA resulting from prolonged usage. Furthermore, our data indicated that the increase in the relative amount of the crystalline phase may be primarily attributed to temperature fluctuations and repeated changes in pressure, which could cause the hardening of EVA and eventually diminish the protective ability of MGs.

New fabrication method to maintain proper mouthguard thickness

AIM

The aim of this study was to examine the effectiveness of layering a second piece of ethylene vinyl acetate on the original sheet before fabrication to maintain the thickness of vacuum-formed mouthguards.

MATERIALS AND METHODS

Two methods were used to form mouthguards. In the first, a 3.8-mm ethylene vinyl acetate sheet was laminated after 3.0-mm ethylene vinyl acetate sheet was formed at the anterior teeth area. In the second, a second piece of 3.0-mm sheet was layered on the original 3.8-mm sheet in the region mounted on the anterior teeth. Mouthguard thickness at specific sites on the central incisors and first molars was measured. The differences in mouthguard thickness according to measurement regions and forming methods were analyzed by two-way analysis of variance and a post hoc test (Bonferroni method).

RESULTS

Mouthguard thickness differed significantly among the measurement regions (P < 0.01). Mean thickness at the central incisors was significantly greater with the sheet-layering method (5.5 mm) than with the laminate method (3.9 mm) (P < 0.01).

CONCLUSIONS

The results of this study indicate that adding a second layer of ethylene vinyl acetate to the original sheet effectively maintained the thickness of the mouthguard. This method is effective to maintain the mouthguard thickness and cost-effective method.

Effectiveness and fabrication of mouthguards

Although mouthguards have been suggested as a means for preventing dental traumatic injuries, there are still some controversies over some aspects such as effectiveness in preventing concussions, material selections, method for fabrication, design, side effects and so on. The purpose of this literature review was to clarify differences in opinions with supporting evidence on these issues and find the best guidelines for promoting usage and providing mouthguards with better protective capability and fewer side effects such as difficulty in breathing and speaking.

Soccer-related facial fractures: postoperative management with facial protective shields

Facial fractures are one of the most common orofacial injury sustained during participation in sporting events.The frequency of maxillofacial lesions varies according to the popularity that each sport has in a particular country. Soccer is the most popular sport in Italy, and it is responsible for a large number of facial traumas.Traumas and fractures in soccer mainly involve the zygomatic and nasal regions and are especially caused by direct contact that takes place mainly when the ball is played with the forehead. In particular, elbow-head and head-head impacts are the most frequent dangerous contacts.Soccer is not a violent sport, and the use of protective helmets is not allowed because it could be dangerous especially when players play the ball with the head. The use of protective facial shields are exclusively permitted to preserve players who underwent surgery for facial fractures.The use of a facial protection mask after a facial fracture treatment has already been reported. This article describes a clinical experience of management of 4 soccer-related facial fractures by means of fabrication of individual facial protective shields.

Accelerometry: a technique for quantifying movement patterns during walking

The popularity of using accelerometer-based systems to quantify human movement patterns has increased in recent years for clinicians and researchers alike. The benefits of using accelerometers compared to more traditional gait analysis instruments include low cost; testing is not restricted to a laboratory environment; accelerometers are small, therefore walking is relatively unrestricted; and direct measurement of 3D accelerations eliminate errors associated with differentiating displacement and velocity data. However, accelerometry is not without its disadvantages, an issue which is scarcely reported in gait analysis literature. This paper reviews the use of accelerometer technology to investigate gait-related movement patterns, and addresses issues of acceleration measurement important for experimental design. An overview of accelerometer mechanics is provided before illustrating specific experimental conditions necessary to ensure the accuracy of gait-related acceleration measurement. A literature review is presented on how accelerometry has been used to examine basic temporospatial gait parameters, shock attenuation, and segmental accelerations of the body during walking. The output of accelerometers attached to the upper body has provided useful insights into the motor control of normal walking, age-related differences in dynamic postural control, and gait patterns in people with movement disorders.

Mouthguards in Sport Activities

Three systematic reviews were conducted on: (i) the history of mouthguard use in sports; (ii) mouthguard material and construction; and (iii) the effectiveness of mouthguards in preventing orofacial injuries and concussions. Retrieval databases and bibliographies were explored to find studies using specific key words for each topic. The first recorded use of mouthguards was by boxers, and in the 1920s professional boxing became the first sport to require mouthguards. Advocacy by the American Dental Association led to the mandating of mouthguards for US high school football in the 1962 season. Currently, the US National Collegiate Athletic Association requires mouthguards for four sports (ice hockey, lacrosse, field hockey and football). However, the American Dental Association recommends the use of mouthguards in 29 sports/exercise activities. Mouthguard properties measured in various studies included shock-absorbing capability, hardness, stiffness (indicative of protective capability), tensile strength, tear strength (indicative of durability) and water absorption. Materials used for mouthguards included: (i) polyvinylacetate-polyethylene or ethylene vinyl acetate (EVA) copolymer; (ii) polyvinylchloride; (iii) latex rubber; (iv) acrylic resin; and (v) polyurethane. Latex rubber was a popular material used in early mouthguards but it has lower shock absorbency, lower hardness and less tear and tensile strength than EVA or polyurethane. Among the more modern materials, none seems to stand out as superior to another since the characteristics of all the modern materials can be manipulated to provide a range of favourable characteristics. Impact studies have shown that compared with no mouthguard, mouthguards composed of many types of materials reduce the number of fractured teeth and head acceleration. In mouthguard design, consideration must be given to the nature of the collision (hard or soft objects) and characteristics of the mouth (e.g. brittle incisors, more rugged occusal surfaces of molars, soft gingiva). Laminates with different shock absorbing and stress distributing (stiffness) capability may be one way to accommodate these factors.Studies comparing mouthguard users with nonusers have examined different sports, employed a variety of study designs and used widely-varying injury case definitions. Prior to the 1980s, most studies exhibited relatively low methodological quality. Despite these issues, meta-analyses indicated that the risk of an orofacial sports injury was 1.6-1.9 times higher when a mouthguard was not worn. However, the evidence that mouthguards protect against concussion was inconsistent, and no conclusion regarding the effectiveness of mouthguards in preventing concussion can be drawn at present. Mouthguards should continue to be used in sport activities where there is significant risk of orofacial injury.

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In the present investigation, an experimental dental arch model fabricated in epoxy was assayed in Kratos universal testing machine to study the mechanical behavior of ethylene and vinyl acetate copolymer (EVA) in the form of mouthguard for sports and flat plate. The following variables were considered: thickness (3 and 4-mm plates), temperature (room and mouth temperature) and presence/absence of artificial saliva. Mechanical properties of EVA were tested under compressive strength: apparent absorbed energy (J.mm-1), maximum tension (N.mm-1), maximum dislocation (mm) and maximum strength (N). Data were recorded and modeled mathematically. Regarding the absorbed energy, maximum tension and maximum force, it was verified that the higher the thickness of the mouthguards, the better the results of force dissipation and redirection to the system and to several regions of the dental arch. In the presence of saliva and close to mouth temperature, the material responded positively to these alterations, resenting increased ductibility as well as improved mechanical responses. Regarding maximum dislocation, it was observed a better accommodation of the occlusion under conditions that simulate those observed in the oral environment. In conclusion, EVA proved to be an adequate material for fabrication of mouthguards and interocclusal splints. In addition, EVA showed good results in force dissipation and demonstrated a shock-absorbing capacity and a great protection potential.

Comparison of forces transmitted through different EVA mouthguards

Athletic mouthguards have been recommended for decades with varying levels of athlete acceptance. Issues related to compliance center around the ability to breath and speak while wearing the mouthguards. Fabrication techniques have changed over time to a two-layer ethylene vinyl acetate mouthguard fabricated on a high-pressure machine. The reported ideal thickness of these mouthguards has been somewhat variable depending on the sport and anticipated level of risk. Recent research however, has identified 4 mm as the optimal thickness of EVA. In this study an acrylic dental cast was fabricated and mounted to a drop impact fixture. Mouthguards of varying ply, thickness and palatal coverage were fabricated and tested in the fixture. Strain gauges and load cells were used to evaluate the effect of ply, thickness, and palatal coverage on the ability of these mouthguards to minimize transmitted forces. The purpose of this study was to identify those variables of mouthguard construction that will minimize the overall transmitted force of impact to the anterior dentition.

Does hard insertion and space improve shock absorption ability of mouthguard?

Mouthguards are expected to reduce sports-related orofacial injuries. Numerous studies have been conduced to improve the shock absorption ability of mouthguards using air cells, sorbothane, metal wire, or hard material insertion. Most of these were shown to be effective; however, the result of each study has not been applied to clinical use. The aim of this study was to develop mouthguards that have sufficient prevention ability and ease of clinical application with focus on a hard insertion and space. Ethylene vinyl acetate (EVA) mouthguard blank used was Drufosoft and the acrylic resin was Biolon (Dreve-Dentamid GMBH, Unna, Germany). Three types of mouthguard samples tested were constructed by means of a Dreve Drufomat (Type SO, Dreve-Dentamid) air pressure machine: the first was a conventional laminated type of EVA mouthguard material; the second was a three layer type with acrylic resin inner layer (hard-insertion); the third was the same as the second but with space that does not come into contact with tooth surfaces (hard + space). As a control, without any mouthguard condition (NOMG) was measured. A pendulum type impact testing machine with interchangeable impact object (steel ball and baseball) and dental study model (D17FE-NC.7PS, Nissin, Tokyo, Japan) with the strain gages (KFG-1-120-D171-11N30C2: Kyowa, Tokyo, Japan) applied to teeth and the accelerometer to the dentition (AS-A YG-2768 100G, Kyowa) were used to measure transmitted forces. Statistical analysis (anova, P < 0.01) showed significant differences among four conditions of NOMG and three different mouthguards in both objects and sensor. About acceleration: in a steel ball which was a harder impact object, shock absorption ability of about 40% was shown with conventional EVA and hard-insertion and about 50% with hard + space. In a baseball that was softer compared with steel ball, a decrease rate is smaller, reduction (EVA = approximately 4%, hard-insertion = approximately 12%, hard + space = approximately 25%) was admitted in the similar order. A significant difference was found with all the combinations except for between EVA and hard-insertion with steel ball (Tukey test). About distortion: both buccal and lingual, distortions had become small in order of EVA, hard-insertion, and hard + space, too. The decrease rate is larger than acceleration, EVA = approximately 47%, hard-insertion = 80% or more, and hard +space = approximately 98%, in steel ball. EVA = approximately 30%, hard-insertion = approximately 75%, and hard + space = approximately 98% in baseball. And a significant difference was found with all the combinations (Tukey test). Especially, hard + space has decreased the distortion of teeth up to several percentages. Acceleration of the maxilla and distortions of the tooth became significantly smaller when wearing any type of mouthguard, in both impact objects. But the effect of mouthguard was clearer in the distortion of the tooth and with steel ball. Considering the differences of mouthguards, the hard-insertion and the hard + space had significantly greater buffer capacity than conventional EVA. Furthermore, hard + space shows quite high shock absorption ability in the tooth distortion. Namely, hard + space has decreased the distortion of teeth up to several percentages in both impact objects.

Can mouthguards prevent mandibular bone fractures and concussions? A laboratory study with an artificial skull model

Some sports' accidents are responsible for inflicting traumatic brain injuries and mandibular bone fractures when impacts occur to the chin. It is often thought that mouth guards can prevent many of these injuries. However, such assertions may be insufficient without adequate research. It is therefore necessary to establish a systematic method of investigation to solve this problem. In the present laboratory study, tests were performed using pendulum impact equipment and an artificial skull model connected to strain gages and accelerometers to simulate and measure the surface distortions related to bone deformation or fractures and the acceleration of the head related to concussions. As impacts, direct blows to the mandibular undersurface were applied. As a result, wearing a mouth guard decreased (P < 0.01) the distortion to the mandibular bone and the acceleration of the head significantly compared with not wearing a mouth guard (54.7%: to the mandible -- measured at a total of three different points, 18.5%: to the head measured at a total of three different points). Within the limits of this study, the following conclusions were drawn: The present measuring system in this study was able to evaluate the distortion to the mandibular and the acceleration of the head from the direct blow to the mandibular undersurface. Mouth guards can reduce distortion to the mandibular and the acceleration of the head from the same blow. So mouth guards might have the possibility to prevent mandibular bone fractures and concussions. However, further well-designed and exhaustive studies are vital to show that mouth guards reduce the incidence of concussions and mandibular bone fractures.

Are all mouthguards the same and safe to use? The influence of occlusal supporting mouthguards in decreasing bone distortion and fractures

The safety benefits of mouthguards have been demonstrated in many studies, with many authors and sports dentists strongly recommending the wearing of mouthguards. However, wearing a mouthguard with incorrect occlusion might cause a variety of problems. It comes as no surprise that a traumatic blow to the chin, while wearing an insufficient mouthguard lacking anterior contact, can result in severe distortions to the mandibular bone, and bone fractures. The aim of this study was to clarify how ineffective insufficient occlusal supporting mouthguards are and how dangerous they can be to use. Consequently, in this study, occlusal supportive areas were varied and accelerations of head and distortions of the mandible were measured using an artificial skull model and a pendulum impact device. As a result, the distortions of the mandible tended to increase as the supported area decreased. On the contrary, accelerations of the head decreased as the occlusion part decreased. Thus, a lot of impact energy was consumed in the distortion of the mandible; accordingly, it seemed that only a little destructive energy was transferred to the head. From this study, it would seem that wearing a mouthguard, which is insufficient in the occlusion, has the potential of causing a bone fracture of the mandible. Consequently, mouthguards should have proper occlusion.

The influence of impact object characteristics on impact force and force absorption by mouthguard material

Most impact force and impact energy absorption tests for mouthguards have used a steel ball in a drop-ball or the pendulum device. However, in reality most sports-related trauma is caused by objects other than the steel ball, e.g. various sized balls, hockey puck, or bat or stick. Also, the elasticity, the velocity and the mass of the object could change the degree and the extent of injuries. In this study, we attempted to measure the impact force from actual sports equipment in order to clarify the exact mechanism of dental-related sports injuries and the protective effects of mouthguards. The present study was conducted using the pendulum impact device and load cell. Impact objects were removable. Seven mobile impact objects were selected for testing: a steel ball, baseball, softball, field hockey ball, ice hockey puck, cricket ball, and wooden baseball bat. The mouthguard material used in this study was a 3-mm-thick Drufosoft (Dreve-Dentamid GmbH, Unna, Germany), and test samples were made of the one-layer type. The peak transmitted forces without mouthguard ranged from the smallest (ice hockey stick, 46.9 kgf) to the biggest (steel ball, 481.6 kgf). The peak transmitted forces were smaller when the mouthguard was attached than without it for all impact materials but the effect was significantly influenced by the object type. The steel ball showed the biggest (62.1%) absorption ability while the wooden bat showed the second biggest (38.3%). The other balls or the puck showed from 0.6 to 6.0% absorbency. These results show that it is important to test the effectiveness of mouthguards on specific types of sports equipment. In future, we may select different materials and mouthguard designs suitable for specific sports.

The influence of the sensor type on the measured impact absorption of mouthguard material

Mouthguards have been tested for impact energy absorption using drop-ball and/or pendulum devices. While all reports show efficiency of the mouthguard, the impact absorption abilities reported differ considerably. This difference has been attributed to differences of mouthguard material, design, and the impact force used. However, it is also possibly because of the difference in the sensors used in the experiments. The purpose of this study was to test three types of sensors and to assess which type was most appropriate for measurement of the impact absorption ability of mouthguards. A pendulum-type testing equipment and steel ball, wooden bat, baseball, field-hockey ball were used as the impact object. For all sensors or impact objects, the mouthguard decreased the impact forces. However, the absorption ability of the mouthguard varied according to the sensor or impact object. The absorbency values became smaller with the strain gauge, the accelerometer, and the load cell, respectively. With the steel ball as the impact object, 80.3% of impact absorption was measured with the strain gauge and the accelerometer but, only 62.1% with the load cell sensor. With the wooden bat, impact absorption was 76.3% with the strain gauge and 38.8% for the load cell. For the baseball ball, the absorption measurement decreased from 46.3% with the strain gauge to 4.36 with the load cell and for the field-hockey ball, the decrease in measurement values were similar (23.6% with the strain gauge and 2.43% with the load cell). It is clear that the sensor plays an important role in the measurement values reported for absorbency of mouthguard materials and a standard sensor should be used for all experiments.

The effect of mouthguard design on stresses in the tooth-bone complex

PURPOSE

Mouthguards protect the tooth-bone complex from impact loads that occur during sporting activity. The aim of this study is to investigate the effects of varying mouthguard thickness and stiffness on the magnitude of tensile stresses in the tooth-bone-complex.

METHODS

A two-dimensional, plane stress, finite element representation of a central maxillary incisor (CMI) is created. For validation purposes, displacements of the incisal edge of the unprotected tooth model are compared with in vivo displacements under similar loads. A protective mouthguard is then superimposed over the model with varied labial thickness (1-6 mm) and stiffness (9-900MPa) representing a range of designs available. A large horizontal static load of 500N is then applied to the anterior surface of the mouthguard and the resulting stresses in the tooth-bone complex are presented. It is suggested that this loading condition most accurately represent the situation occurring when a guarded tooth collides with a soft object (e.g. boxing glove).

RESULTS

It is generally found that mouthguard thickness and stiffness are both desirable in terms of reducing stresses. However, the protection offered by the low-stiffness guards, regardless of thickness, is minimal. Since this low-stiffness (9MPa) is representative of the most common choice of material in mouthguard fabrication, such findings may cast doubt on the ability of popular mouthguards to redistribute stress.

CONCLUSION

While few would disagree that these low-stiffness guards absorb shock during hard-object collisions (e.g. baseballs), they may not protect the tooth-bone during soft-object collisions (e.g. boxing gloves). In order to optimize their protective capabilities for a range of loads, the range of materials used in mouthguard construction may have to be reconsidered.