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.     

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.     

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.     

Easy fabrication of a new type of mouthguard incorporating a hard insert and space and offering improved shock absorption ability

Abstract – The positive effects of wearing a mouthguard have been indicated in various epidemiological surveys and experiments, and their usage appears to be increasing in many sports. However, many preventable sports‐related dental injuries still occur even with the use of a conventional mouthguard. We have developed a mouthguard (the Hard & Space mouthguard) with sufficient injury prevention ability (more than 95% shock absorption ability against impact with a steel ball carrying 15.2 kg m² S^?2 potential energy) and ease of clinical application. This mouthguard consists of an outer and an inner EVA layer and a middle layer of acrylic resin (hard insert), with a space to prevent contact between the inner surface of the mouthguard and the buccal surfaces of the maxillary front teeth or teeth already weakened through prior damage or treatment. The purpose of this article is to describe the method by which the Hard & Space mouthguard may easily be fabricated. We believe that this new type of mouthguard has the potential to reduce sports‐related dental injuries.     

Are all mouthguards the same and safe to use? Part 2. The influence of anterior occlusion against a direct impact on maxillary incisors

Abstract –  The purpose of this study was to clarify the influence anterior occlusion, of mouthguards, has on protecting against a direct collision to the maxillary anterior teeth. In other words, the support mandibular dentition has when wearing a mouthguard. Two types of mouthguards were used for this study, one with an appropriate anterior occlusion or a mouthguard with positive anterior occlusion (MGAO+) and another which was a single-layer mouthguard lacking the same occlusion or a mouthguard with negative anterior occlusion (MGAO−) but with the same thickness on the buccal side. The instruments used for testing were a pendulum-type impact device with two interchangeable impact objects (a steel ball and a baseball), with a plastic jaw model having artificial teeth. Four testing conditions were observed: one with the jaw open without a mouthguard (Open NoMG), the second with the jaw clenching (loaded with 30 kg weight) without a mouthguard (Clench. NoMG), the third with the jaw clenching with MGAO− (Clench. MGAO−) and the last with the jaw clenching with MGAO+ (Clench. MGAO+). The results are as follows: both types of mouthguards showed the effects in reducing the distortion of the teeth. However, the effect was significantly obvious (steel ball = about 57% shock absorption ability, baseball = about 26%) in the mouthguard with anterior occlusion or support by lower dentition through mouthguard (Clench. MGAO+) than Clench. MGAO−. Thus, the influence of anterior occlusion of mouthguards or the support of mandibular dentition through wearing a mouthguard (MGAO+) is indispensable in reducing the impact force and tooth distortion. The results of this research should further contribute to the establishment of guidelines for safer mouthguards.     

Analysis of the characteristics of mouthguards that affect isokinetic muscular ability and anaerobic power

PURPOSE

The purpose of this study was to estimate the effects of occlusal stability to identify action mechanisms of mouthguards, known to have a modulatory effect on limb muscle function.

MATERIALS AND METHODS

This study included 20 male subjects to perform the isokinetic muscle tests and the Wingate anaerobic power test on both knee joints under five closed-mouth conditions: without or with 4 types of mouthguards with thickness of 2 mm based on premolar area: (1) full-coverage, (2) anterior partial-coverage, (3) right posterior partial-coverage, and (4) left posterior partial-coverage. The obtained results were subjected to One-way ANOVA with repeated measures, followed by post hoc test of the contrast method (α=.05).

RESULTS

There was no significant difference between the closed position with and without a full-coverage mouthguard in all variables. However, significant differences were observed between with and without a partial-coverage mouthguard in muscular endurance during extension of the left knee, muscular power and endurance during flexion of the right knee. Additionally, significant differences were found between occlusal states with full- and partial-coverage mouthguards in muscular power and endurance during extension of the left knee.

CONCLUSION

These findings indicate the elevation of vertical dimension by 2 mm or the inducement of occlusal stability had little effect on isokinetic muscle strength and anaerobic performance, while uneven distribution of occlusal force might have some positive effects.     

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...     

Laboratory evaluation of mouthguard material

Abstract – The aim of this study was to evaluate, in vitro , the EVA material (polyvinylacetate-polyethylene copolymer) most commonly used in the fabrication of mouthguards and thus to help understand mouthguard performance and to improve mouthguard design. The material was tested for tensile strength, elongation, hardness and water absorption using specimens and tests described by the American Society for Testing and Materials Standards. Standard EVA sheets of 1, 2, 3 and 5 mm thickness were prepared. With increase in the thickness of the material, both the ultimate tensile strength and the elongation were decreased. The hardness and water absorption were unaffected. It was concluded that, overall, the thicker 5 mm EVA material was recommended for mouthguards as it displayed the least deformation to load and performed equally as well in the tests as other thicknesses.     

Comparing comfort and wearability between Type III single-layered and double-layered EVA mouthguards

This study compared two Type III ethylene vinyl acetate (EVA) mouthguards for wearability, comfort, fit, and patient preference. Twenty-two athletes each received two custom-fabricated athletic mouthguards, a single-layered vacuum-formed EVA mouthguard and a double-layered heat- and pressure-laminated EVA type. Athletes wore each type of mouthguard for a two-week period while playing basketball. At the end of each two-week period, the athletes completed questionnaires that evaluated 17 characteristics of each mouthguard type. Data were analyzed using the binomial test for small numbers. The double-layered heat- and pressure-laminated EVA mouthguard performed as well as or better than the single-layered vacuum-formed type in 14 of the 17 categories. There was a statistically significant patient preference for the double-layered heat- and pressure-laminated mouthguard.     

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.     

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 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.     

Forces transmitted through EVA mouthguard materials of different types and thickness

Previous studies into sporting mouthguards have been mainly attitudinal or epidemiological. The aim of the present study was to build an impact rig to measure the impact absorbed by mouthguard materials of various thicknesses. The acceleration of the pendulum of the rig was measured and used to calculate the force transmitted to the materials.
Impact tests were also performed on three commercially available mouthguard materials. Tests showed that the force transmitted through mouthguard materials was inversely related to the material thickness.
Mouthguard construction techniques with ethylene vinyl acetate (EVA) plastics should be monitored to avoid occlusal thinning especially on the incisal edges. Thinning results in reduction in the protection offered by the mouthguard.     

Fattori prognostici dell’eruzione dell’incisivo permanente incluso

Objectives

The aim of the present review was to identify factors influencing the eruption of impacted permanent incisors.

Materials and methods

Mitchell and Bennet evaluated the distance of the unerupted permanent tooth from the occlusal plane and classified it as: near (vertical displacement: crown of the impacted tooth is at the level of the coronal third of the root of the adjacent tooth; horizontal displacement: > half the width of the tooth itself); mid (vertical: the tooth is at the level of the middle third of the root of the adjacent tooth; horizontal displacement: > ½ but < 1 times the width of the tooth); far, greater displacement. Smailiene et al. analyzed the vertical position of impacted permanent incisors in relation to the contralateral erupted central incisor. They defined three positions: v1, the crown is at the level of the gingival third of the root of the adjacent permanent incisor; v2, the crown is at the level of middle third of the root; v3, the crown is at the level of apical third of the root. Bryan et al. estimated inclination of the unerupted tooth calculated as the angle between its long axis and the mid-sagittal plane.

Results and conclusions

These methods are easy to perform and effective for predicting the spontaneous eruption of malposed incisors. The vertical position of the tooth and the angle between its long axis and the mid-sagittal plane appear to be important factors for predicting eruption.     

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.     

A vacuum technique to increase anterior thickness of athletic mouthguards to achieve a full-balanced occlusion.

A full-balanced occlusion is essential for mouthguards. It has been reported that a balanced occlusion for upper and lower anterior teeth is essential for prevention of injuries occurring to the maxillary anterior teeth and alveolar bone caused by horizontal direct impact. The support of the mandibular teeth through the mouthguard is critical to prevent maxillary front tooth injury from a direct impact force. However, some vacuum mouthguard designs may not achieve a full-balanced occlusion. For example, when a player has a malocclusion, an elongated molar or premolar tooth, an open bite, a large over jet or a maxillary protrusion. An improved vacuum fabrication method is necessary to obtain full balanced occlusion in these cases as opposed to conventional vacuum type single-layer mouthguard technique.     

Oro-facial injuries and mouthguard use in elite female field hockey players

Abstract –  The objectives of this study were to assess the prevalence of oro-facial injuries, frequency of mouthguard use and players' attitudes towards the use of mouthguards among elite English female field hockey players. All 140 players of the English Hockey Association female Premiere League were asked to complete a questionnaire. Main outcome measures were prevalence of oro-facial injuries, frequency of wearing of mouthguards and attitudes to mouthguard wearing. One hundred and ten completed questionnaires were returned (79% response rate). Facial injuries were common. Nineteen percent had sustained dental injury. Five percent of the respondents had at least one tooth avulsed. Eighty-eight percent of the players said that they owned a mouthguard. Mouthguards were worn regularly during matches by 69% but were used less frequently during training. Six percent thought that mouthguards were ineffective. Eighteen percent of the subjects refused to play if they did not have their mouthguard. Sixty-nine percent of the subjects felt that the mouthguards should be worn compulsorily at all times during the game. The following were finally concluded from the study: oro-facial injuries were commonly reported; 88% of the players possessed a mouthguard; and mouthguards were worn regularly during matches by 69% but were used less frequently during training.     

Impacted Inverted Teeth with their Possible Treatment Protocols

Introduction

Inversion of the impacted tooth is a rare condition. The purpose of this article is to review this rare condition in detail on the basis of available literature. In addition, this article also explores the various multidisciplinary approaches varying from space creation to prosthodontic rehabilitation and reimplantation to endodontic treatment for inverted impacted teeth.

Discussion

A very few cases of inverted and impacted third molars have been reported in the literature. We describe few rare cases of inverted impacted teeth which presented to us in the Dept. Of Oral Surgery, K.D. Dental College and Hospital over a period of 2 years approx. we report of four cases presented to us with inverted maxillary third molars (Figs. ​(Figs.1,1, ​,2),2), inverted supernumerary tooth in anterior maxilla (Figs. ​(Figs.3,3, ​,44).Open in a separate windowFig. 1A case of inverted maxillary 3rd molar on right side showing no pathological change in dental follicle and was asymptomatic. Subsequently treated by conservative method that is tooth left in bone as suchOpen in a separate windowFig. 2OPG depicting a inverted impacted right upper third molarOpen in a separate windowFig. 3IOPA shows an inverted impacted supernumerary tooth present between the roots of central incisors, which was co-incidentally diagnosed during treatment of fractured central incisorOpen in a separate windowFig. 4IOPA showing inverted impacted supernumerary tooth, with its incisal edge encroaching into the nasal fossa

Result

The first and second case of maxillary third molar and third case, of supernumerary tooth, the patients presented were asymptomatic, hence patient opted for conservative management and continued follow up, in the fourth case, the supernumerary tooth was removed for orthodontic reasons.

Conclusion

On the basis of literature available, it has been noticed that related complications particularly depend on justification on whether the tooth follicle is with a pathology or is pathology-free. Pathology-free and asymptomatic cases can be treated in a conservative manner. Possible treatment protocol for impacted inversion is entirely dependent on patient’s needs, findings and surgeons skills.