Optimization of materials for a user-formed mouthguard
A mouthguard that can be custom formed by the user at the time of need to achieve optimum fit and protection is required for sports and clinical applications. This study has evaluated two silicone-based polymer systems found sufficiently workable to be molded to the user's mouth. Compositions were optimized for setting time and mechanical properties by varying the proportions of catalyst, cross-linking agent, and filler. Mechanical tests showed the optimized silicones to have lower tensile and tear strengths and higher penetration and rebound than most present mouthguard materials. Detailed measurements of compressive stress-strain, coupled with a stress analysis of conditions in actual mouthguard use, indicate that the optimized silicone polymers possess more than adequate strength and durability for a user-formed mouthguard.
Mouthguards in Sport Activities History, Physical Properties and Injury Prevention Effectiveness
AbstractThree 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 1.61.9 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.

Growth and Development of the Middle Face
The morphologic proportions of the middle face are of particular interest to the orthodontist because they determine the upper dental arch as well as the relation between the upper and the lower jaws. Primarily there exist the influences of development within the middle face itself and second as such from the cranial base. In this case the middle face serves only as a transmitter. It is well known that this region in humans is wedged between the protruded frontal lobes and the lower face, in contrast to that of our closest related species, anthropoids. The cartilage of the nasal septum, which works as a growth center, has to resist the forces of the other expanding bodies (Stemmkirper), 2 i.e., the brain, basal cartilage, tongue, dental ridge, and mandibular joint. In accordance with the existing correlation in each individual case, those forces will either develop a normal skull with normal dental arches or mature into an anomaly. From the clinical point of view, the cause of certain malformations is supposed to be in the middle face, as, for example, in the case of progeny in Figure 1. The snub-nosed, retarded region of the middle face of this eight-year-old boy appears to be framed in profile from a steep, relatively protruded forehead and a protruded lower face. The accompanying X-ray (Fig. 2) contributes to the opinion that the mandible has overlapped the middle face. This case should be included in that group of progeny where we can look for the fault in the maxilla, according to Korkhaus and Neumann.3 On the other hand also, vertically enlarged middle faces tend toward protrusive malformation of the mandible, as we see in the twenty-year-old boy in Figure 3. With obvious general enlargement and the accentuated nasal region, he belongs to the socalled progressive type, according to von Eickstedt.4 Examination of the accompanying X-rays (Fig. 4) from the ages of fifteen and twenty-one years shows a significant descent of the nasal floor within the period of observation, a phenomenon that we can see in the length of the perpendicular from the occipital condyle to the production of the maxillary base (nasospinal-posterior nasal spina) :5 an increase from 10 to 14 mm. It is of interest that the existing protrusion developed into a bilateral open bite during the period of treatment, and we come to the conclusion from this observation that the tongue took the mandible at first in the facial direction by the descending nasal floor, but after therapeutic retardation the tongue created enough space between the dental arches. This mechanism of displacement increases to bizarre levels in cases of craniofacial dysostosis (Crouzon's disease). It occurs primarily in underdevelopment of the cranial base as well (Fig. 5). The nasal cartilage, which is suspended there and which is visibly normal-growing in quantity, as a result of this extends more to the lower than to the front. The difference between the perpendicular from the occipital condyle to