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

Abstract –  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.     

运动牙套的缓冲及能量吸收特性分析

目的:利用冲击试验测试不同厚度和材料的运动牙套缓冲及能量吸收特性.方法 :按照运动牙套的厚度和材料,将牙套分为5 组,每组6个试件.采用钟摆与力锤结合装置(摆锤)对牙套及牙列模型施加冲击能量,通过改变摆锤的释放高度而改变冲击能量的大小.应用力传感器与激光测振仪分别与数据采集和信号分析仪连接,获得锤头的人射速度、反弹速度...     

Comparison of forces transmitted through different EVA mouthguards

Abstract –  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.     

The effect on energy absorption of hard inserts in laminated EVA mouthguards

One of the suggestions for using laminated mouthguards is the inclusion of hard inserts to improve mouthguard performance. However, there is a paucity of published material on the use of such inserts and this study was designed to investigate this theory. Hard layers of ethylene vinyl acetate (EVA) were included in laminated mouthguard sheets which were then subject to repeated impacts with an impact rig. Hard inserts resulted in reduced energy absorption when compared with a control sheet of the same material and approximate thickness but without the hard inserts. Additionally, the further the hard inserts were located from the impact surface, the least reduction there was on energy absorption.     

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

Abstract –  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.     

Relationship between temporomandibular joint dynamics and mouthguards: feasibility of a test method

Abstract – A test system was developed establishing the feasibility of collecting biomechanical data as they relate to the use of mouthguards. Previous experimental studies have examined the physical and mechanical properties of mouthguard materials. This information has been used as a guide for establishing material standards and specifications for the fabrication of mouthguards, but it lacks the key biomechanical parameters required for a thorough mouthguard evaluation. The current study was designed to assess whether the impact force, condylar deflection, and strain superior to the temporomandibular joint region could be measured. A drop test was conducted on a cadaveric specimen to simulate loading at the chin point. To measure the force of impact, an accelerometer was attached to an impactor of known mass. High‐speed biplanar (1000 frames per second) radiographs were used to determine condylar displacement. Radio‐opaque markers were inserted into the bone at predetermined locations. Total displacement of these markers was determined in reference to anatomical landmarks. Strain gauges were attached to the mandible and skull to monitor the effects of the condyle impacting the base of the skull. Based on the data collected, forces were calculated by determining the product of the time‐based acceleration and known mass. A measurable change in force between the mouthguards and the control (no mouthguard) was demonstrated. The average condylar displacement was successfully measured and indicated as an increase in total deflection for impacts conducted with mouthguards. Quantifiable strain was measured in the region above the mandibular fossa with and without the insertion of a mouthguard at all impact conditions. However, it was determined that additional gauges would provide critical data. Key biomechanical parameters for chin‐point impacts were determined in the current study. The technique demonstrated that both displacement within the mandibular fossa and loading of the condyles occur during the impact event. Although the current study established a technique that can be used to examine the relationship between mouthguards and jaw‐joint injuries, the role, if any, mouthguards play in the reduction of injuries cannot be established until a thorough analysis is completed.     

定制牙托膜片切牙区厚度变化的影响因素

佩戴运动牙托可以缓冲外力,降低颌面部损伤的风险.运动牙托种类较多,其中个性化定制运动牙托具有较好的保护作用和较高的舒适度而备受欢迎.个性化定制运动牙托的膜片加热后可发生延展,随后发生厚度变化,尤以切牙区膜片的厚度变化更能影响其保护性能;因此,笔者就影响个性化定制运动牙托膜片切牙区的厚度变化的膜片硬度、膜片形状和膜片表面设计等膜片因素,工作模厚度和工作模摆放角度等工作模因素,加压方法,夹持托盘形状、夹持方式和夹持托盘与工作模底座的距离等夹持因素,加压时间等的研究进展作一综述.     

The ability of mouthguards to protect veneered teeth: A 3D finite element analysis

Background/Aims

Professional and amateur athletes might have veneer restorations. The aim of this study was to investigate the protective effect of mouthguards on veneered anterior restorations.

Methods

A nonlinear dynamic analysis was performed to simulate conditions during an impact with or without a custom-made mouthguard. Using a computer-aided design (CAD) software, a slice of a human maxilla was designed containing an upper right central incisor. The model was composed of mucosa, cortical bone, trabecular bone, periodontal ligament, dentin, enamel, and pulp tissue. The enamel was prepared (feather design), restored with an indirect veneer (1.0 mm thickness), and duplicated to simulate both conditions with or without a mouthguard (4 mm thickness). Both models were subdivided into finite elements using the computer-aided engineering (CAE) software. Frictionless contacts were used, and an impact was simulated in which a rigid sphere hit the model at 1 m s⁻¹. Fixation was defined at the base of the bone. The elastic modulus of the veneer was assessed by using five different restorative materials (resin composite, hybrid ceramic, zirconia-reinforced lithium silicate, lithium disilicate, and zirconia). Von Mises stress, minimal principal stress, and maximum principal stress (in MPa) were obtained and plotted for visual comparison.

Results

Von-Mises results showed higher stress concentrations in the veneer's cervical labial region for models without a mouthguard. Observing the quantitative results for each model, the highest compressive (709 MPa) and tensile (58 MPa) stresses occurred in the situation without a mouthguard with a zirconia veneer, while the lowest occurred in resin composite veneer with a mouthguard (8 and 5 MPa). The mouthguard was able to reduce the stresses in the tooth structure and it also reduced the risk of fracture in all conditions.

Conclusions

Mouthguards were beneficial in reducing the effects of dental trauma regardless of the restorative material used to manufacture the indirect veneer, since they act by dampening the generated stresses during the trauma event. Equal impact stresses on a mouthguard will lead to higher stresses in veneered teeth with more rigid restorative materials leading to a less protective effect.     

EVA mouthguards: how thick should they be?

Abstract – A major consideration in the performance of mouthguards is their ability to absorb energy and reduce transmitted forces when impacted. This is especially important to participants in contact sports such as hockey or football. The thickness of mouthguard materials is directly related to energy absorption and inversely related to transmitted forces when impacted. However, wearer comfort is also an important factor in their use. Thicker mouthguards are not user‐friendly. While thickness of material over incisal edges and cusps of teeth is critical, just how thick should a mouthguard be and especially in these two areas? Transmitted forces through different thicknesses of the most commonly used mouthguard material, ethylene vinyl acetate (EVA) (Shore A Hardness of 80) were compared when impacted with identical forces which were capable of damaging the oro‐facial complex. The constant impact force used in the tests was produced by a pendulum and had an energy of 4.4 joules and a velocity of 3 meters per second. Improvements in energy absorption and reductions in transmitted forces were observed with increasing thickness. However, these improvements lessened when the mouthguard material thickness was greater than 4 mm. The results show that the optimal thickness for EVA mouthguard material with a Shore A Hardness of 80 is around 4 mm. Increased thickness, while improving performance marginally, results in less wearer comfort and acceptance.     

Experimental comparative study of various mouthguards

Abstract— The aim of this study was to evaluate the mechanical and physical properties of several standard size commercially available mouthguards. For the purpose of objective testing, a special study model, which the various gum shield devices could be fitted onto, was developed to record tooth deflection caused by impact forces induced by a pendulum ram impact testing machine. The data measured on teeth provided with various gum shield devices were correlated with those of unprotected teeth; this enabled the individual cushioning effects of the respective devices and their specific force conduction to be evaluated. Using mouthguards considerably diminishes the deflection of the teeth subjected to stress in comparison with the row of unprotected teeth. In addition, force is transmitted to the adjacent teeth all the way to the distal regions of the row of teeth. The individual cushioning effects are directly correlated to the thickness of the material; the force distribution is determined by the rigidity of the gum shield device. The devices examined showed considerable differences with regard to force distribution and dimensioning. The study showed that this was due to the thickness of the materials, the manufacturing process and the composition of the materials of the devices examined. In comparison to laboratory-produced devices of similar material thickness, the devices that were designed to be fitted by the user achieved significantly poorer results as regards both cushioning properties and dissipation of exerted forces.     

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

Abstract – 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 = ～4%, hard‐insertion = ～12%, hard + space = ～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 = ～47%, hard‐insertion = 80% or more, and hard +space = ～98%, in steel ball. EVA = ～30%, hard‐insertion =～75%, and hard + space = ～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.     

Forces transmitted through a laminated mouthguard material with a Sorbothane insert

Abstract— Sorbothane is a visco-elastic polyurethane that has been used in sports and orthopaedic applications because of its shock-absorbing properties. The aim of this laboratory study was to evaluate the effect of an intermediate layer of Sorbothane on the peak force transmitted through two thermoplastic ethylene vinyl acetate (EVA) sheets as used in the construction of a custom-made sports mouthguard. The EVA sheets were tested at room temperature after thermal lamination under pressure, either without (control) or with a Sorbothane intermediate layer of 1.1 or 2.65 mm thickness. A piezo-electric transducer was used to measure the peak force transmitted through each sample from a free-falling steel ram. The peak force recorded was sigmficantly less for laminated EVA samples with a Sorbothane intermediate layer than for controls of comparable thickness. We conclude that a Sorbothane intermediate layer between heat-cured laminated EVA sheets, as used in the fabrication of a custom-made sports mouthguard, may dissipate significantly the force of impact resulting from a blow to the teeth and jaws.     

An improved mouthguard material

a modified mouthguard material which reduces transmitted forces is described. Tests showed that the inclusion of air cells in a 4 mm thick polyvinylacetate-polyethylene (EVA) copolymer reduced the effects of impacts of less than 10 KN when compared with a material of the same EVA composition and thickness. The EVA copolymer with air-inclusions is suitable for the construction of stock, mouth-formed and vacuum-formed mouthguards. The improved elastic properties of the modified mouthguard material properties of the modified mouthguard material reduced transmitted forces by 32 per cent when copared with traditional EVA mouthguard polymers of the same thickness.     

Rugby players'' satisfaction with custom-fitted mouthguards made with different materials

OBJECTIVES: This study compared the comfort of two bimaxillary custom-fitted mouthguards. One type was made with silicone rubber and the other with methyl-methacrylate (acrylic). METHODS: The study was a within-subject crossover clinical trial with 52 high-school rugby players who were randomly allocated to one of two groups. The first group wore a silicone mouthguard for 4 months and an acrylic one for the following 4-month period. The second group wore an acrylic mouthguard followed by a silicone one for similar periods. Comfort, bulkiness, stability, hardness, ability to talk and to breathe, oral dryness, nausea and inclination to chew were evaluated for each period using a Visual Analogue Scale questionnaire. RESULTS: There was no significant difference concerning comfort, bulkiness, ability to talk and to breathe, oral dryness and nausea between silicone and acrylic mouthguards by group and time of examination (Three-way ANOVA P>0.05). Acrylic mouthguards were more stable and harder than silicone ones (Wilcoxon's test P<0.01). Tendency to chew was greater for silicone appliances (P<0.01). For stability, hardness and inclination to chew, there was no significant difference in the response of the players based on the sequence of use of the two types of mouthguard during the survey (Mann-Whitney test P>0.05). At the end of the study, 56% of the players preferred to keep the acrylic mouthguard and 44% chose the silicone one. This choice did not vary between the groups (chi2, P>0.05). CONCLUSION: Silicone rubber mouthguards were well accepted by the players but technical improvements in silicone materials are needed to improve hardness and stability of silicone mouthguards for sport.     

Investigation of vacuum forming techniques for reduction of loss in mouthguard thickness: part 2—effects of sheet grooving and thermal shrinkage

The aim of this study was to investigate vacuum forming techniques for reduction of loss in mouthguard thickness effects of sheet grooving and thermal shrinkage of extruded sheets on molded mouthguard thickness. Mouthguards were fabricated with ethylene vinyl acetate (EVA) sheets (4.0 mm thick) using a vacuum forming machine. Sheet form was a convexing v‐shaped groove toward the back, 10–40 mm from the anterior end. The sheets were placed in the forming machine with the sheet extrusion direction either vertical or parallel to the model's centerline of right and left. Molding was performed by crimping the sheet using suction when the most descending portion of the sheet sagged downwards from the clamp, 15 mm below the basal surface. Postmolding thickness was determined using a measuring device. Measurement points were the incisal portion (incisal edge and labial surface) and molar portion (cusp and buccal surface). Differences in molded mouthguard thickness with the sheet orientation of extruded EVA sheets were analyzed by student's t‐test. The sheet in parallel axis orientation with the model's centerline yielded higher thickness than vertical orientation at the labial surface and the buccal surface. The present results suggested that addition of a groove to the sheet in conjunction with placement of the sheet with its axis of orientation parallel the centerline of the working model can effectively reduce thickness loss in the molded mouthguard with the equipment and materials used in this study.     

Pressure‐forming method using a single‐mouthguard sheet

Background/Aim

Mouthguard thickness is important for the prevention of orofacial trauma during sports. However, it is difficult to maintain the necessary thickness after forming the mouthguard. The aim of this study was to evaluate a pressure‐forming method using a single‐mouthguard sheet.

Materials and Methods

A mouthguard sheet of 3.8 mm ethylene vinyl acetate was prepared by cutting 3 mm from the anterior margin of the sheet holder with a length of 7 mm and with the width being from the buccal cusp of the upper right first premolar to the buccal cusp of the upper left first premolar and compared with the original sheet. The sheets were pressure‐formed when the sheet was heated until the centre was displaced by 15 mm from baseline. The thickness of the mouthguard was measured at the labial surface of the central incisor, and the buccal and occlusal surfaces of the first molar. The fit of the mouthguard was examined at the right central incisor and right first molar by measuring the distance between the mouthguard and the cervical margin of the working model. Differences in the thickness and the fit of the mouthguards between the sheet conditions and the measured regions were analysed by two‐way analysis of variance.

Results

Mouthguard thickness varied among the measured regions of the central incisors and first molars (P < .01). The greatest thickness was found at the labial surface of the central incisor in mouthguards fabricated using the cut sheet (P < .01). Mouthguard fit did not differ between the two sheets.

Conclusions

The results suggest that a useful mouthguard with proper thickness and fit can be produced with the pressure‐forming method using a single‐mouthguard sheet by cutting the anterior part of the sheet.     

防护牙托的性能评价

目的 研究标准型定制类牙托对于外力打击的缓冲能力。方法 利用一个特殊的工作模型。将外力打击时,单个中切牙所受的力通过舌侧金属导杆传递到压力传感器上,记录数据。比较戴防护牙托和无防护时的相对值。结果 获得了不同厚度牙托的缓冲率,各组间差异有显著性。结论 牙托的缓冲效果与材料厚度呈正相关。建议在高对抗性、高风险性的体育活动中,参加者应使用适宜的防护牙托以防止牙外伤的发生。     

The effect of wearing custom-made mouthguards on the aeroacoustic properties of Japanese sibilant /s/

Abstract – Background/Aim: There have been many reports on the discomfort of speech when wearing oral appliances. Fricatives articulated in an oral cavity can be difficult to pronounce when oral appliances are worn, because the oral cavity is partially changed by their installation. Sibilant /s/, one fricative, is especially difficult to pronounce when wearing oral appliances. This study investigates the effect of the difference in the setting positions of the palatal margin of custom-made mouthguards on the aeroacoustic characteristics of sibilant /s/.Materials and methods: Eighteen subjects (11 women and seven men) participated. The palatal margin of mouthguards was set at the gingival line for nine subjects and 4 mm from the line for another nine subjects. Acoustical analyses examined the difference of the palatal margins of the mouthguards on the autocorrelation coefficient, the zero crossing count, and the spectral peaks of sibilant /s/.Results: The results showed that the zero crossing count of the waveforms and the spectral peaks of sibilant /s/ were significantly broadened and shifted toward the low-frequency range with the mouthguard whose palatal margin extended 4 mm from the gingival line than the mouthguard whose palatal margin was set at the gingival line.Conclusion: We believe that a more appropriate palatal mouthguard design for custom-made mouthguards can be made by considering the aeroacoustical effects. Our study supported the mouthguard whose palatal margin was set at the gingival line by considering the influence on pronouncing sibilant /s/. We believe that a more appropriate palatal mouthguard design for custom-made mouthguards can be made based on the balance of aeroacoustical effects and mechanical requirements.     

Thickness and fit of mouthguards according to a vacuum‐forming process

The purpose of this study was to examine the difference in the thickness and the fit of mouthguards fabricated with a vacuum‐forming method of the mouthguard sheet material. The material used in this study was Sports Mouthguard (3.8 mm thickness). Two forming conditions were performed. In the first condition, the sheet was lowered over the working model after the vacuum was applied, and in the other trial, the sheet was lowered over the working model before the vacuum was applied. The sheets were formed using a vacuum former when the heated sheets hung 1.5 cm from the baseline. We measured the thickness and the fit of the mouthguard at the areas of the central incisor and first molar in both conditions. The difference of the thickness at the areas of the central incisor and first molar and the forming condition was analyzed by Two‐way anova . The difference of the fit according to the forming conditions was analyzed by the Mann–Whitney U test. The results showed that the thickness of the mouthguard differed at the areas of the central incisor and first molar, but the thickness of the mouthguard did not differ according to the forming conditions. The fit of the mouthguard at the central incisor and first molar was significantly different between the forming conditions (P < 0.01 and P < 0.05). These results suggested that the fit of the mouthguard was the best without any deficiency of thickness when the vacuum was applied first and then the sheet was pressed onto the working model. These results may be useful in fabricating proper mouthguards.     

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

Abstract –  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.