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Posteruptive tooth migration between 6 and 14 years involves both total arch displacement and intra-alveolar tooth movement. Central incisors, canines, and permanent first molars all drift forward within the alveolar bone. The molars, and to a lesser extent the incisors, drift occlusally. With respect to lingual arch contour, lateral movement of molars and canines is negligible.
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The migration of the germ of the 2nd lower molars after the extraction of all adjacent teeth in comparison to the health side was investigated in Vietnamese hanging belly pigs. The animals were killed in seven age groups so that the results could be evaluated in dependence upon the time. The biometric results reveal migratory phenomena similar to those described for humans after tooth extraction.
Changes of the dental arch dimensions after surgical correction of mandibular prognathism are very limited. Except for a decrease of the mandibular intercanine width, an increase of the mandibular intermolar width, and a decrease of the maxillary dental arch length, the dentition remains remarkably stable. It thus seems that the changed function postoperatively does not result in great changes in the position of the teeth within the jaws.
Up to now, the early detection and the discriminating evaluation of periodontal insufficiency are not feasible due to the variety of conditions provoking a pathological response of the tissues. In general, the defence may be regarded as sufficient. Exceptions to this rule are periodontal changes existent already in adolescence and therapy-resistant gingivitides in which endogenous causal factors obviously predominate. A disproportion of tooth mobility to bone reduction and a tendency to abscess-formation, tooth migrations and recurrences after periodontal therapy are indicative of insufficiency. The development of a progressive course is to be compared with the breakdown of the barrier of defence. The reduction or elimination of provoking and conditioning factors prior to prosthetic therapy is considered to be the way to maintain the "stability" of the periodontal tissues.
Our findings indicate a cellular basis for the connective tissue remodeling which takes place during physiologic tooth movement. This cell is the fibroblast which is capable of synthesizing and degrading collagen simultaneously and, utilizing this ability, the orderly control of collagen remodeling within the periodontal ligament is possible. It is suggested that this cellular basis of connective remodeling will have a direct significance for orthodontic tooth movement once control mechanisms have been established.
Transseptal fibers are a part of the gingival group of fibers of the periodontal membrane, and they are very tough and resistant. They form a chain from tooth to tooth which, provided that it remains intact and is sufficiently strong to resist displacing muscular pressures, will preserve the contacts between the teeth throughout the arch. If the continuity of the chain is interrupted, the balance of the forces acting upon the teeth on either side of the break is upset and considerable displacements can occur. Maxillary median diastemas are classified as "simple" or "persistent" according to their etiology, and an operation to clear the upper midline suture of transeptal fibers is described as an essential part of the treatment of persistent upper median diastema.
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Traumatic events at an early age may lead to developmental dental anomalies and ectopic tooth eruption. A case is reported in which a traumatic injury at two months of age resulted in the development of supernumerary teeth in the upper right premaxillary region. The maxillary canine ectopically erupted or transposed into the space left by the missing central incisor and eliminated the need for a prosthesis in this region.
Denture reduction in formal orthodontic treatment does not appear to prevent the impaction of lower third molars. The extraction of premolar teeth is best carried out as close as possible to the eruption time of the cuspids. The posterior part of the mandibular arch should be evaluated by the study of lateral oblique roentgenograms and one of several options regarding treatment should then be adopted.
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The results of this study show that positional changes occur in the mandibular third molar at least until 20 years of age. A significant number of mandibular third molars in young adults in positions of mesio-angular impaction attain an upright position in a year. A significant relationship exists between the initial age of the patient and the amount of change in the inclination of the third molar. Initial inclination is closely related to the change in inclination in mandibular third molars.
The laser reflexion method, a direct contactless measuring technique with a high accuracy, has been applied for clinical purposes. A prototype has been tested using a laser beam to illuminate a patient's tooth fixed to the equipment by an impression plate. The reflected patterns were thrown onto a screen with a coordinate system and photographically recorded, and the movement of the tooth has been geometrically calculated. The relapse tendency after orthodontic treatment of a patient with periodontal disease and parafunctions was studied by repeated measurements of the left medial upper incisor. By use of the method, it was possible to observe that the velocity of the studied tooth was highest during the 1st day and, besides the horizontal movement, a rotation of the tooth began at the end of the measuring period.