Sports mouthguards and orthodontic treatment

Characteristics of MGs

1. Stock MGs

Stock MGs are bought ‘over the counter’ and have no capability to adjust to an individual's dental morphological characteristics and are consequently worn without modification.² They come in different sizes and are mostly made from polyurethane, or a co-polymer of vinyl acetate or ethylene. Although inexpensive, stock MGs are thought to be the least favourable as they fit poorly, are difficult to wear and offer minimum protection. Their poor fit may cause dislodgement during use with the consequent risk of airway obstruction (Figure 1).³⁴

2. Mouth formed/‘boil and bite’ MGs

‘Boil and bite’ MGs are widely available at pharmacies and sport stores. They appear to be the most commonly used MG type.^7,35 They are made of a thermoplastic material which is heated in hot water and the athlete moulds the MG to his/her mouth by biting, sucking and using finger pressure. Some require constant biting to hold them in place which can affect speech and breathing.¹² Owing to their low temperature of formation, they continue to deform so that retention and occlusal thickness reduces. The protection offered, therefore, may be limited (Figures 2 and 3).^2,34

3. Custom-made MGs

These are specially made from a cast of a dental impression of a jaw taken by an oral health professional and are generally more expensive than stock and ‘boil and bite’ MGs.⁷ They are considered to be more effective in preventing and reducing the severity of dental trauma, more retentive and offer a better fit compared with other MG types.^13,21,25 In addition, patient acceptability appears to be greater.²¹

Fabrication

Ethylene vinyl acetate (EVA) has been the predominant material of choice for custom-made MG fabrication due to its availability, formability and ease of manipulation, though it may have limitations in terms of shock absorption capability and rigidity.²⁸

Fabrication involves a thermoforming process which involves heating an EVA ‘blank’ in a pressure or vacuum-thermoforming machine above the cast (Figures 4, 5). When the ‘blank’ is soft enough, air pressure or a vacuum is applied which closely moulds the soft material to the cast.³⁶

The thermoplastic material ‘thins’ during the fabrication process and this may influence the effectiveness of MGs, particularly when it occurs in the area where the external impact is generally exerted, usually the upper anterior region.^24,28 Studies have shown that, during fabrication, thicknesses decreased from 25% to 50% for the custom-made MGs and 70–99% for mouth-formed/’boil and bite’ MGs. This suggests greater effectiveness with custom-made MGs.³⁷ Thickness and impact performance, however, may not be sufficient criteria to characterize efficiency performance of MGs.³⁸ Interestingly, incorporation of colour pigments into the thermoplastic material may provide superior adaptation and more firmly fitting MGs than clear material.³⁹

Pre-fabrication EVA ‘blank’ (Figure 6) thicknesses of 3–6 mm have been recommended as a balance between sufficient energy absorption and minimal deformation, and wearer comfort and acceptance.^25,28,40

Table 2 outlines the general design features of MGs.^{1,12,14,30,34} Careful attention to the thermoforming process may ensure superior fit and minimal thinning of the thermoplastic material. Recent in vitro evidence suggests that the ‘thoroughly dried’ working model should be positioned 15 mm posteriorly from the centre of the pressure former during pressure forming and the model should be inclined to where the labial surface of anterior teeth can make a ‘sharp angle’ to the sheet surface.^41,42 During vacuum-forming, heating of the thermoplastic sheet to 120°C and a ‘sagging distance’ of 15 mm may provide the most suitable forming process.^43,44

Table 2. General design features of MGs.

The approximate material thickness should be 2–3 mm on the labial aspect, 3 mm on the occlusal aspect and 2 mm on the palatal aspect The labial flange should extend to within 2 mm of the vestibular reflection The palatal flange should extend about 10 mm above the gingival margin The edge of the labial flange should be rounded in cross-section The edge of the palatal flange should be tapered in cross-section All teeth to the distal of the maxillary second molars should be incorporated In the mixed dentition, the MG should extend to the distal surface of the maxillary first molars On closing the mouth, there should be even contact between the MG's occlusal surface and the lower teeth

The thermoforming process facilitates ‘lamination’. This is the fabrication of ‘multiple layered’ MGs since heated EVA sheets can be fused to each other firmly and allow better thickness control. Consequently, logos and different colour combinations can be incorporated.² ‘Laminated’ MGs may also be more dimensionally stable than other custommade MG types.⁴⁵

There appears to be little robust evidence to indicate which thermoforming process is more effective, although it is suggested that ‘pressure-formed laminated’ MGs may be superior.^8,13,46 A recent in vitro study has shown that the vacuum-forming method maintained the MG thickness while the pressure-forming method obtained better fit.³⁶ Further research, however, is required to establish whether this has clinical significance. Another study reported that patient acceptability for the double-layered, heat- and pressure-laminated MG was greater compared to the single-layered, vacuum-thermoformed EVA MG.^36,47

Current research appears to indicate that fitted, custom-made mouthguards result in fewer problems, such as difficulty in breathing and speaking.^13,25 In addition, MGs do not appear to impact on physiological measurements relevant to athletic performance.⁴⁸

Orthodontic considerations

Most orthodontic treatment is carried out before or during adolescent years. It is during this time when there is a reported peak in the incidence of dental injury while participating in contact sports.⁴⁹ Many patients undergoing orthodontic treatment do not wear MGs while participating in contact sports.⁵⁰ Orthodontic patients wearing removable appliances are advised to remove their appliances and use MGs for contact sports.¹⁴

Fixed orthodontic appliances are an additional risk factor for traumatic injuries in the maxillofacial region during sports events.⁵¹ A potential orofacial injury may occur more easily because of increased tooth mobility and the presence of orthodontic appliances.⁸ This may result in additional damage to soft tissues, loosening of brackets and bending of archwires.^2,12,52

Additional MG considerations for orthodontic patients wearing fixed orthodontic appliances include:

Non-customized MGs (such as Orthoguard™), which incorporate a channel to accommodate fixed orthodontic appliances (such as orthodontic brackets, tubes, molar bands and archwires) and planned orthodontic movement of teeth have been described (Figures 1, 7–9).^12,13-14 Although less expensive, they may be poorly retentive, offer less protection against dental injury and require more frequent replacement.

Custom-made MGs (modified to facilitate the presence of fixed orthodontic appliances, prospective tooth movement and passive/active eruption of teeth) are considered, therefore, to offer superior protection from dental injury, greater fit and patient comfort.^{2,12,22,50,51-52}

Fabrication of a MG for a patient wearing fixed appliances

Figures 10–13 outline the steps involved in the fabrication of a MG for a 13-year-old patient wearing fixed orthodontic appliances. This is a variation of previous descriptions of modified custom-made MGs fabricated by the vacuum-thermoforming technique.^22,50,51 This simple method uses dental plaster for ‘blocking out’ on the cast and fabrication is via the pressure-forming technique.

This method can be modified further to facilitate patients in the transitional/mixed dentition and for patients wearing fixed slow and rapid maxillary expansion appliances.⁵³

Discussion

The risk of dental injury appears to be greater in those who participate in sporting activity and do not wear a MG compared with those who participate in sporting activity and wear a MG. The risk may be even greater in those with an increased overjet. In addition to superior protection, fitted custom-made MGs appear to result in fewer breathing and speaking problems during wear and do not seem to impact on physiological measurements relevant to athletic performance.⁴⁸ Further research, however, is still required to establish the optimal design, material and mode of fabrication of MGs.

Additional MG considerations for orthodontic patients include minimal bulk, maximum retention and space requirements for planned tooth movements. To achieve these considerations, a method of fabrication using dental plaster, which is a comparatively inexpensive, readily available and a dimensionally stable material, as the ‘block-out material’ for maintaining the space for fixed orthodontic appliances and planned tooth movements has been described in the article presented here. To decrease bulk and increase MG rigidity, a lamination technique was applied. A pressure-forming technique was employed which may provide superior protection from dental injury, greater fit and patient comfort. The described method may be modified for those in the transitional/mixed dentition and for patients wearing fixed slow and rapid maxillary expansion appliances.

Conclusions