Berit Lindqvist

Bruxism in twins

A twin investigation was carried out to elucidate the influence of heredity in the development of bruxism. The material consisted of 117 pairs of twins of four age classes, average age 12.1 years, in the county of Vasterbotten. Zygosity was determined using blood group serological methods. Bruxism was diagnosed by recording bruxo facets. Occlusal interferences and palpation tenderness in certain masticatory muscles were also recorded.The results show that monozygotic twins have a statistically significant higher frequency of the same facet pattern than do dizygotic twins. It was not established that heredity influences the occurrence of occlusal interferences or muscle tenderness. The study supports the hypothesis that hereditary factors are important to the genesis and pattern of bruxism.

Isometric Bite Force in Children and its Relation to Body Build and General Muscle Force

Bite force, muscle strength in various muscle groups and body build (skeletal dimensions) were examined in 12 year old children, 37 boys and 42 girls. There were no statistically significant differences in bite force between boys and girls, and only small differences between the children and adults (20-30 years of age) who had been examined earlier with the same technique. In the children, maximum bite force covariated slightly with muscular force and skeletal dimension (r = 0.24 – 0.28, P<0.05), while no statistically significant correlation was found in similarly examined adults. It is suggested that masticatory training is important for bite force while factors relating to body build seem less important.

Bruxism in children with brain damage

Ninety-one children with brain damage were examined with regard to the degree of dental wear in relation to the degree and symptom of brain damage. Abnormal wear was found in a statistically established greater frequency in the group of children most severely mentally retarded, while it was not found in children of normal intelligence. Of the children with most severe mental retardation, 8 were at a 6-month level of development and all of these had abnormal wear. The others had reached the one-year-old stage, at which it is likely that normal protective reflexes or the ability to sense pain in the parodontium begin to develop. Of 7 children with severe cerebral palsy, 4 showed abnormal wear and also belonged to the most severely mentally retarded group. The investigation shows that abnormal dental wear is more closely related to a low level of mental development than to the degree of severity of cerebral palsy. The absence of proprioception in the parodontium is discussed as a possible cause of bruxism.

Extraction of the deciduous second molar in hypodontia

Summary. The germ of the second premolar is absent in 3.3% of the Swedish population. When the deciduous second molar exfoliates excessive space results and space closure can be achieved by using appliances. If, however, the deciduous molar is extracted during bite development, growth factors may be helpful in closing the extraction space. This hypothesis was investigated in 101 children aged 5–12 years. Planned extraction of the deciduous second molar was carried out after cast and profile registration. Cast registration was made annually and oblique lateral radiography and registration of mandibular dysfunction were recorded after the second molars had come into occlusion. Four years after extraction the residual space in the lower jaw was on average 2 mm, and in the upper jaw <1mm. The rate of space closure is not affected by the age at extraction. Extraction after root development of the neighbouring teeth was complete often led to closure of the extraction space by tipping of these teeth. Correct prediction of the space closure following extraction of the deciduous second molar is obtained in 84% of cases if the initial values for the angle ss-n-sm, the interincisive angle and the overbite and overjet are known. The results indicate that in cases of hypodontia of the second premolar extraction of the corresponding deciduous molar should be seriously considered as a treatment alternative.

Bite force in children with bruxism.

The bite force of 51 twelve-year-old bruxists was compared with that of a control group of the same age, in order to establish whether bruxism affects bite force and whether there is any connection between the degree of tooth abrasion and bite force. Criteria for bruxism were bruxo facets in the bite and, in the same children, teeth-grinding at the time of examination. No differences in bite force values for bruxists and non-bruxists were found for either very light bite or maximum bite. One group with dentine facets had a higher bite force value for very light bite than the children with enamel facets. Otherwise there was no difference between the various facet groups regarding the bite force produced.

A three-dimensional photographic method for documentation and measurement of dental conditions

SummaryA 3-D photographic technique was developed for the registration of bite conditions. This technique may replace plaster models for archiving purposes. To achieve this, photographic equipment and computer programs should be user friendly, not too expensive, and allow measurements that satisfy scientific demands. This purpose was fulfilled by combining the following elements: a photographic unit with standardized conditions for 3-D photography and a reference object with known coordinates where bite impressions or models are placed during photography. To reconstruct 3-D coordinates from photographs these are placed on a digitizer connected to a computer programmed for reconstructing 3-D coordinates from the digitized 2-D data. The accuracy of the 3-D reconstruction of coordinates, x, y, z, was tested by means of 3-D photographs of a test object with reference points having a precision of ±0.5 μm. The mean error for distances of 5 mm and 15 mm varied between −0.17 mm and +0.15 mm. Measurements of 45° and 90° angles had an accuracy that varied from −0.5° to +0.9° and from −1.2° to +1.5° respectively. An angle between lines and a plane of 54.7° displayed a mean error of ±1.6°. The test of the accuracy of the 3-D photographic technique for calculating distances and angles demonstrated that it fulfills demands for scientific applications on clinical material.ZusammenfassungEine dreidimensionale fotografische Technik für die Registrierung von Bißverhältnissen wurde entwickelt. Diese Technik sollte in einem gewissen Ausmaß Gipsmodelle für Archivierungszwecke erssetzen. Die fotografische Ausrüstung sollte benutzerfreundlich und nicht zu teuer sein und Messungen erlauben, die wissenschaftliche Ansprüche zufriedenstellt. Dieser Zweck wurde erfüllt, indem folgende Bestandteile kombiniert wurden: eine fotografische Einheit mit standardisierten Verhältnissen für das 3D-Fotografieren und ein Referenzobjekt mit bekannten Koordinaten, auf dem während des Fotografiervorgang ein Abdruck oder das Modell eines Bisses plaziert wurde. Um 3D-Koordinaten von Fotografien zu rekonstruieren, wurden diese auf einen Digitalisierer gelegt, der an einen Computer mit einem Program für die Rekonstruktion von 3D-Koordinaten aus digitalisierten zweidimensionalen Daten angeschlossen war. Die Genauigkeit der x-, y- und z-Koordinaten aus der 3D-Rekonstruktion wurde mit Hilfe von 3D-Fotografien eines Testobjektes mit Referenzspunkten getestet, die eine Genauigkeit von ±0.5 μm besaßen. Die mittlere Fehlerquote für Abstände von 5 bis 15 mm variierte zwischen −0,17 mm und +0,15 mm. Messungen von 45°-und 90°-Winkeln hatten eine Genauigkeit, die zwischen −0.5° und +0,9°, bzw. −1,2° und +1,5° variierte. Ein Winkel zwischen einer Linie und einer Ebene von 54,7° wies eine mittlere Fehlerquote von ±1,6° auf. Ein Genauigkeitstest der dreidimensionalen Technik für die Abstands- und Winkelberechnung zeigte, daß sie den Anforderungen an die wissenschaftliche Verwendung klinischen Materials genügte.