Margareta Ringqvist

Isometric bite force and its relation to dimensions of the facial skeleton.

Maximum voluntary isometric bite force was recorded at the incisors and at the molars in 29 healthy females aged 19–23 years. The relationships between the variations in bite force and dimensions of the facial skeleton were studied by means of linear simple and multiple regression analyses.There was a high correlation between incisor and molar bite force. Bite force was mainly associated with a long mandible and a small gonion angle. 49% of the variation in incisor bite force could be explained by variations in the length of the mandible, the gonion angle and the length of the anterior cranial base. 56% of the variation in molar bite force could be explained by variations in the length of the mandible, the gonion angle and a long maxilla.

A prospective randomized study of a dental appliance compared with uvulopalatopharyngoplasty in the treatment of obstructive sleep apnoea.

The enthusiasm for uvulopalatopharyngoplasty (UPPP) in the treatment of obstructive sleep apnoea (OSA) has declined in recent years, partly because of a lower success rate over time and partly because of adverse effects. Reports on the beneficial effects of dental appliances exist, but only one prospective randomized study has been published comparing dental appliances with nasal continuous positive airway pressure (CPAP) treatment. No study has been published comparing dental appliance treatment with UPPP. Ninety-five male patients with confirmed OSA, subjective daytime sleepiness and an apnoea index (AI) > 5 were randomized for subsequent treatment with either a dental appliance or UPPP. There were 49 patients in the dental appliance group and 46 in the UPPP group. Thirty-seven patients in the dental appliance group and 43 in the UPPP group completed the 12-month follow-up. The success rate (rate of patients with at least a 50% reduction in AI) for the dental appliance group was 95%, which was significantly higher (p < 0.01) than the 70% success rate for the UPPP group. According to the criteria for OSA (apnoea index > or = 5 or apnoea/hypopnoea index > or = 10), 78% of the dental appliance group and 51% of the UPPP group were normalized after 12 months. The difference between the groups was significant (p < 0.05). These findings suggest that the dental appliance technique is useful in the treatment of mild to moderate OSA.

The reliability of histochemical fibre typing of human necropsy muscles

SummaryThe reliability of muscle fibre typing of post mortem specimens was investigated with special reference to the influence of time and temperature. In specimens stored at +4° C, muscle fibre typing could be reliably performed up to at least ten and fifteen days post mortem for the masseter and biceps brachii muscles respectively. The corresponding figures for storage at room temperature were three and six days. The difference in the preservation of enzyme activity between masticatory and limb muscles might be related to the demonstrated difference in the fibre type composition and thus the enzyme content and energy sources.

Histochemical enzyme profiles of fibres in human masseter muscles with special regard to fibres with intermediate myofibrillar ATPase reaction

Abstract Histochemical staining methods were applied to biopsy material from the masseter muscles of 17 subjects who were being operated upon for mandibular prognathism. Comparisons were made with biopsy specimens from 8 biceps brachii muscles. In biceps brachii only fibres of type I (weakly stained) and fibres of type II (strongly stained) were demonstrated with the myofibrillar ATPase reaction at pH 9.4, whereas in the masseter, fibres with an intermediate intensity of staining were distinguished along with type I and type II fibres in 36 of 38 specimens. Like type I fibres these fibres exhibited a strong or moderate NADH 2 tetrazolium reductase reaction, a strong ATPase reaction after acid preincubation, and a weak ATPase reaction after alkali preincubation; however, like type II fibres they showed a strong phosphorylase reaction. Further studies are required to determine whether this pattern is part of the normal anatomy or reflects alterations in muscle function.

Development of fiber types in human fetal muscle: An immunocytochemical study

Human fetal muscles have been studied using immunocytochemical methods with antibodies directed against different myosin isoforms. We show that fiber type differences can be detected as early as 15-16 weeks of gestation. At this time it would appear that both the heavy and light chains characteristic of slow myosin are found in some myotubes.

Fibre sizes of human masseter muscle in relation to bite force

Abstract The diameters and the percentage distribution of type I, type II and intermediate fibres in the masseter muscles (fibre typing based on ATPase staining at pH 9.4) were correlated with maximum voluntary isometric bite force in 10 subjects with mandibular prognathism. The bite force was recorded at the molars on both sides. There was a positive significant correlation between the size of type II fibres and bite force, but not between the size of type I or intermediate fibres and bite force. This suggests that primarily type II fibres are designed for powerful biting efforts. The percentage distribution of the different fibre types was not significantly correlated with bite force.

Special histochemical muscle-fibre characteristics of the human lateral pterygoid muscle

Abstract The histochemical fibre-type profile was analyzed in 10 human lateral pterygoid muscles from young adults with complete dentitions and normal intermaxillary relations. The distributions of various types of fibre in the lateral pterygoid differed from those of normal human limb and trunk muscles as well as from those of human masseter and temporal muscles. There was a marked predominance of type I fibres, a high frequency of adenosine triphosphatase (ATPase) intermediate fibres and type IIC fibres and lack of type IIA ones. The muscle fibres, especially the type II fibres, were smaller than those in limb and trunk muscles. There was marked intra-muscular variability in both the proportion and diameter of the types. Type I fibres were larger in diameter than the others and occupied, on average, 81 per cent of the overall fibre crass-sectional area. Type II and the ATPase intermediate fibres were larger in males than in females. There was no difference in type I fibre diameter or fibre-type proportion between females and males. No difference in fibre diameter was observed between the two heads of the muscle, but the proportions of fibre types differed significantly in four muscles. The fibre-type composition in the adult lateral pterygoid muscle indicates a capacity for endurance during continuous work at relatively low forces and accords with the stabilizing effect on the mandibular joint attributed to this muscle.

Histochemical fibre composition of the human digastric muscle

The histochemical muscle-fibre composition of the anterior and posterior belly of the human digastric muscle was analysed in young male adults. Both bellies, of differing embryological origin and supplied by different cranial nerves, showed a fibre composition similar to that of normal limb and trunk muscles. Type I, type IIA and type IIB fibres each occupied about one-third of the total fibre population and were evenly distributed in a mosaic pattern. About 1 per cent of fibres were type IIC and ATPase (pH 9.4) intermediate fibres. Thus, there were major differences between the anterior belly of digastric and the likewise trigeminal nerve innervated masticatory muscles with respect to both histochemical profile and size and distribution of various types of fibre. The observations suggest that the fibre pattern of the digastric is not primarily related to its specific nervous supply but its special functional demands. The predominance of type II fibres indicates a capacity for fast acceleration and speed in mandibular movements. The disparity in fibre-type profile between the digastric and the jaw elevator muscles might be related to changing demands during evolution. Civilized diets need no heavy mastication and, while the requirements upon the jaw elevators have thus changed, the functional demands on the jaw openers would have remained unchanged.

Histochemical fibre-type profile in the human masseter muscle☆

A histochemical characterization of the masseter muscle was performed on biopsy samples of dentate subjects with normal occlusion. There was a continuum of ranges of oxidative and glycolytic capacities of the masseter muscle fibres. Besides the lightly-stained type I and the darkly-stained type II fibres, fibres with intermediate staining reactions for standard ATPase at pH 9.4, IM fibres, were seen in all biopsy samples. IM fibres had some staining characteristics in common with type I, i.e. the reaction for NADH-TR and for ATPase after preincubation at pH 4.6 and 4.2. Like type II fibres they showed strong reaction for menadione-linked alpha-glycerophosphate dehydrogenase and for phosphorylase. The ATPase reaction after preincubation at pH 4.6 did not generally reveal subtypes of type II. It is concluded that the masseter muscle in normal human subjects has a very special fibre composition, with ATPase-IM fibres being a part of the normal fibre population.

Heterogeneous distribution of myosin in human masticatory muscle fibres as shown by immunocytochemistry

On the basis of enzymic properties, different fibre types can be distinguished in human skeletal muscle (type I fibres and type II fibres with subtypes) and there is a correlation between fibre types and the occurrence of slow and fast myosin. In human masticatory muscles, fibres with ATPase activity at pH 9.4, intermediate between that of type I (low activity) and type II (high activity), are frequent. On cryostat-sectioned material, highly specific antibodies against fast myosin, slow myosin and slow light chains were applied. The myosin composition of human masticatory muscles was very heterogeneous, in contrast to that in limb muscles, with various proportions of slow and fast myosins, heavy as well as light chains. Type I fibres contained slow myosin only and type II mainly fast myosin, ATPase IM and type IIC fibres contained a mixture of slow and fast myosins in variable amounts. The findings conform with physiological evidence of a continuum of contraction times for motor units in the human masticatory muscles and suggests that these muscles are highly adapted to the special and complicated functions of the stomatognathic system.