Bonding durability of custom-made mouthpiece for scuba diving after water storage under pressure

Effect of surface treatment of ethylene vinyl acetate on the delamination of custom-fitted mouthguards

BACKGROUND/AIM

Contamination of ethylene vinyl acetate (EVA) during mouthguard fabrication can cause delamination. The study evaluated the effects of different EVA surface treatments on the contact angle, laminate bond strength, and elongation capacity.

MATERIALS AND METHODS

Specimens of two bonded EVA plates were prepared (n = 30). The Shore A hardness of standardized EVA plate specimens was measured before and after thermo-plasticization. The EVA plates were randomly allocated to one of five different surface treatment groups: no treatment (control); isopropyl alcohol, 100%; chloroform, 99.8%; self-cure acrylic resin monomer (methacrylate, ethylene glycol dimethacrylate, and chemical initiator-amine type); and ethyl alcohol, 70%. The maximum breaking force and elongation at the site of fracture were recorded using a universal testing machine. The contact angle surface was measured using ImageJ software. Scanning electron microscopy of the EVA surface was performed. The laminate bond strength was obtained by dividing the maximum breaking force by the bonding area between the two EVA plates. The laminate bond strength and maximum elongation data were analyzed by one-way ANOVA, followed by the Tukey's and the Dunnet test. The failure mode data was analyzed using the chi-square test (α = .05).

RESULTS

EVA surface treatment significantly influenced the laminate bond strength and maximum elongation (p < .001). The control group had a higher contact angle and significantly lower laminate bond strength and maximum elongation than the other groups (p < .001). The acrylic resin monomer and chloroform-treated specimens had similar laminate bond strength and maximum elongation. The acrylic resin monomer group had a significantly lower contact angle (p < .001).

CONCLUSIONS

All treatments had a significantly higher laminate bond strength and maximum elongation than the control group. The acrylic resin monomer and chloroform groups had a significantly higher laminate bond strength and maximum elongation and the acrylic resin monomer group had a lower contact angle than the other groups. The chloroform should be avoided due its hazardous effects.

Shock Absorption Behavior of Elastic Polymers for Sports Mouthguards: An In Vitro Comparison of Thermoplastic Forming and Additive Manufacturing

Background. There are several in vitro testing options to investigate the efficacy of sports mouthguards. None of these represent everyday situations, but the effects of simple laws of physics can be observed. This enables the comparison of conventional materials for mouthguards towards fabrications from additive manufacturing. Methods. A ball-drop experiment measured the maximum force and temporospatial distribution of a vertical impact on six material groups and a reference group (No-MG). Three conventional materials (ethylenvinylacetate) with 1, 2, and 3 layers were compared with additively manufactured (AM) specimens of comparable layering with a respective thickness of 4 mm, 5 mm, and 6.8 mm. Results. A maximum force of 8982.35 N ± 305.18 (No-MG) was maximum damped to 2470.60 N ± 87.00 (conventional 6.8 mm) compared with 5585.09 N ± 203.99 (AM 6.8 mm) Thereby, the ratio between shock absorption per millimeter was best for 4 mm thickness with means of 1722 N (conventional) and 624 N (AM). Conclusions. Polymer layers demonstrated a force reduction up to 71.68%. For now, additively processed resins of comparable hardness and layering are inferior to conventional fabrications.

Appropriate fabrication method for pressure-formed mouthguards using polyolefin sheets

BACKGROUND/AIM

Polyolefin sheet mouthguards are usually formed in the same manner as ethylene-vinyl acetate sheet mouthguards. However, the heating condition of the polyolefin sheet for the pressure-forming process has not been determined. The aim of this study was to examine the appropriate heating condition for polyolefin sheet mouthguards when fabricated with the pressure-formed technique.

MATERIALS AND METHODS

Mouthguard sheets of 3.0 mm polyolefin were pressure formed on working models at three heating temperatures: 90°C, 105°C, and 120°C. 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 central incisor and the first molar by measuring the distance between the mouthguard and the cervical margin of the working model. Differences in the thickness and fit of the mouthguards according to the heating conditions and the measured regions were analyzed using 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 with the heating temperature of 90°C (p < .01). The greatest thickness was found in mouthguards fabricated with the heating temperature of 105°C at the buccal surface of the first molar (p < .01), and 105°C or 120°C at the occlusal surface of the first molar (p < .01). The fit was not significantly different among the three heating conditions both at the central incisor and the first molar.

CONCLUSIONS

The appropriate heating condition for pressure-formed mouthguards using polyolefin sheets was 90°C to maintain the mouthguard thickness at the anterior teeth area with proper fit.

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.

Present Status in Polymeric Mouthguards. A Future Area for Additive Manufacturing?

Athletes from contact sports are more prone to orofacial injuries because of the exposure to possible shocks and collisions derived from physical proximity. The use of protector polymeric mouthguards proved to be useful in the prevention of the described injuries. There are different types of mouthguards with varying ranges of protection and prices, but they are all made from polymers and share the same propose: to absorb and dissipate the impact energy resulting from the shocks. As they are used inside the mouth, they should not impair breathing and speaking nor compromise the comfort of the athlete. However, the ideal mouthguard is yet to be created. The choice of the most appropriate polymeric material and the standard required properties have not yet been reported. Regardless of the numerous studies in this field, normalized control parameters for both material characterization and mouthguard fabrication are absent. This paper aims to present a review of the current types of available mouthguards and their properties/characteristics. Moreover, a detailed description of the most common polymers for the fabrication of mouthguards, together with the manufacturing techniques, are discussed.

The influence of temperature on sheet lamination process when fabricating mouthguard on dental thermoforming machine

Laminated custom-made mouthguards tend to delaminate with use; this is a problem in clinical use. Insufficient bonding strength causes delamination, and bonding strength is strongly affected by heating temperature during lamination. The present study aimed to evaluate the influence of heating temperature on the sheet lamination process. Seven mouthguard sheet products were laminated together at different heating temperatures. To evaluate the bonding strength, a delamination test (n = 6) was performed, and the fracture patterns were inspected visually. To evaluate the shock absorption capability, a falling impact test (n = 5) was performed, and the specimen thicknesses were measured. All recorded values were analyzed using two-way analysis of variance and Tukey's Honest Significant Difference Test (P < 0.05). The present study confirmed that bonding strength was dependent on heating temperature: In ethylene-vinyl acetate copolymer products, the bonding strength was almost constant at 130°C and above, and it was constant at 110°C and above in polyolefin products. The thickness of every specimen decreased and, in some specimens, the shock absorption capability decreased with increasing heating temperature. The present study concludes that the heating temperature during the sheet lamination process when laminated custom-made mouthguards are fabricated may not be less than 120°C in ethylene-vinyl acetate copolymer products and 110°C in polyolefin products.

Influence of wearing a scuba diving mouthpiece on the stomatognathic system - considerations for mouthpiece design

Although diver's mouth syndrome (DMS) has long been recognized by scuba divers, little attention has been paid to the influence of wearing a scuba diving mouthpiece on the stomatognathic system. In this review, DMS-related stomatognathic events (DMS-SE) while wearing a mouthpiece, the relationship between components of the mouthpiece and those events, and design considerations to reduce the risk of those events are discussed based on evidence from 32 articles concerning scuba diving mouthpieces. Forward movement of the mandible, loss of molar occlusal support, and continuous jaw clenching while wearing a mouthpiece are considered to be pathogenic for DMS-SE. Several experimental studies have suggested a relationship between incidence of those events and the design of mouthpiece components such as the connector, labial flange, platform, and occlusal rug, and the possibility of reducing risk of those events through design customization of these components. Improvement of the shape of commercially available mouthpieces and creation of custom-made mouthpieces may thus contribute to the prevention and treatment of DMS-SE and the provision of a comfortable diving environment.

Combined analysis of shock absorption capability and force dispersion effect of mouthguard materials with different impact objects

The aims of the present study were to investigate the shock absorption capability and force dispersion effect of mouthguard (MG) materials using load cell and film sensors. Two kinds of MG materials, ethylene vinyl acetate and polyolefin, were chosen for this study. When impact forces of approximately 5,000 N were applied on the MG materials using a round flat-nosed rod and a bluntly pointed rod, peak intensities were measured using the load cell sensor while peak stresses and impressed stress distribution areas were measured using the film sensor. Combined analysis using both load cell and film sensors clearly showed the shock absorption properties and force dispersion effects of different MG materials with different impact object shapes. Therefore, impact analysis involving a combined use of these sensor systems was useful and reliable in assessing the shock absorption capability and force dispersion effect of MG materials.