Per Rygh

Activation of the vascular system: A main mediator of periodontal fiber remodeling in orthodontic tooth movement☆

The behavior and role of blood vessels and blood-borne cells in the process of the remodeling of the periodontal ligament (PDL) incident to experimental tooth movement was studied in rats. Particular interest was focused on areas of tension and of pressure with frontal bone resorption but without overt hyalinization. An increase of vascular activity occurred in the above mentioned situations. Extensive breakdown of collagen was observed in pressure areas with frontal resorption and in areas of tension concomitant with vascular invasion. Two patterns of fiber and bone remodeling were seen in areas of tension: intense vascular activity within the periodontal membrane and intense vascular activity inside the alveolar bone. Macrophages occurred consistently near blood vessels both in areas of tension and in areas of resorption. These are multipotent cells that obviously influence the remodeling process.

Ultrastructural changes in tension zones of rat molar periodontium incident to orthodontic tooth movement

The purpose of this study was, by introducing transmission electron microscopy, to clarify fine details of tissue reactions in the periodontal ligament on the tension side. A preliminary investigation was undertaken on nine rats in which experimental tooth movement lasted 2 days, 14 days, and 28 days. It was hoped that these new observations might help in the planning and directing of further studies. A marked increase of interstitial spaces between the formed ligament structures of the periodontal ligament was characteristic of the initial phases of tension. The cells and the endoplasmic reticulum within the cells were spindle shaped and oriented in the direction of strain. Occasionally, collagen fibrils were observed within the cytoplasm of fibroblasts. During experimental tension a higher prevalence of elastic fibers was observed and new details of the reaction of collagen fibrils were obtained. The new cementum and bone deposited during the experiment were studied. The preliminary study indicated that electron microscopy may become a valuable tool for the study of the tension side.

Ultrastructural changes in pressure zones of human periodontium incident to orthodontic tooth movement

In order to characterize the ultrastructural alterations of cells, vasculature and fibrils that occur on the pressure side of the periodontal ligament when teeth are subjected to orthodontic forces of a magnitude generally used in clinical practice, eleven premolar teeth were moved buccally by means of a fixed appliance. The experimental periods were 2, 21 and 50 days. Previous light microscopic observations of cellular and vascular disturbances in compressed zones of the periodontal ligament were verified. In addition, ultrastructural details of the process of degeneration and necrosis of cells and vascular elements were obtained. It was demonstrated that cells and blood vessels in the hyalinized zones are damaged to an extent where restitution to normal function is inconceivable. Although collagen fibrils disintegrated by longitudinal splitting into filaments without periodicity, the majority of fibrils retained the cross striations. Apart from differences related to the time factor, there was close agr...

Ultrastructural Cellular Reactions in Pressure Zones of Rat Molar Periodontium Incident to Orthodontic Tooth Movement

Changes in the cells of the periodontal ligament of teeth subjected to orthodontic forces have been described. the purpose of the present study was to characterize these changes at the ultrastructural level. In 67 rats, maxillary first molars were moved buccally by means of fixed appliances rxerting forces of 5–25 g. Animals were sacrificed after periods of 30 min to 28 days. the experimental teeth with surrounding periodontal tissues were removed and processed for electron microscopy. Cellular changes not involving the nucleus, such as dilation of the endoplasmic reticulum and moderate swelling of mitochondria occurred within 30 min of force application. After 2 hrs, this cellular swelling was marked. Large vacuoles had formed in the cytoplasm, and the mitochondria frequently revealed considerable enlargement. More advanced degradation of cellular components was observed after experimental periods of 2 hrs or more. Rupture of the cell membrane had frequently occurred leaving isolated nuclei in various st...

Orthopedic protraction of the upper jaw in cleft lip and palate patients during the deciduous and mixed dentition periods in comparison with normal growth and development.

Cleft lip and palate (CLP) patients often develop maxillary retrusion after cleft repair. Since 1977, a group of 98 cases with negative overjet (anterior crossbite) during the period of deciduous dentition has been treated by the Bergen CLP team. The purpose of treatment has been to achieve favorable occlusion with positive overjet and overbite by means of anterior orthopedic traction (protraction). The average age at start of treatment was 6 years 11 months, and mean treatment duration was 13 months. The protraction force was 700 g. The serial lateral cephalograms of the treated CLP group were compared with those of a noncleft group with normal growth. Normalization of the sagittal maxillomandibular relationship (ANB angle) was achieved. Significant changes were a more anterior position of the upper jaw, and a more posterior position of the lower jaw, due to mandibular clockwise rotation. The variation was considerable. This paper reports the overall changes in the whole CLP group (ALL-C group).

The effect of maxillary protraction on front occlusion and facial morphology

The intention of this work was to study the dentoalveolar and basal jaw changes in a group of children (aged 5-10 years) with nonforced anterior crossbite treated with maxillary protraction from a face mask and to compare the changes with those found in a control group with normal dentoalveolar and basal maxillomandibular relationship. The data were obtained from lateral cephalograms of 22 children taken before treatment, after a treatment period of 3-12 months, and after an observation period of 6-48 months. A group of children (n = 40) with normal maxillomandibular relationship served as controls. During treatment the mandibular prognathism was reduced, and a positive overjet was established in 18 children. The changes during the observation period were generally comparable to those found in the control group, and thus indicated a very small relapse tendency. The posttreatment comparison of the groups showed fewer significant differences than before treatment, indicating that the treatment had a normalizing effect not only on the negative overjet but also on the general face morphology.

Intercanine widening and sagittal effect of maxillary transverse expansion in patients with cleft lip and palate during the deciduous and mixed dentitions

Since 1977 cleft lip and palate (CLP) patients with maxillary deficiency have received an interceptive orthopedic treatment consisting of (a) transverse expansion, (b) protraction, and (c) fixed retention. Ideally the treatment should be completed early enough to permit spontaneous eruption of the maxillary permanent incisors into normal occlusion without orthodontic intervention. The early transverse expansion considerably increases space so that unerupted malpositioned incisors spread out spontaneously, creating optimal conditions for eruption and root formation. Dental diagnosis in the cleft areas is made easier. Posterior crossbites in 112 CLP patients were expanded with a modified quad-helix appliance cemented with four bands in the deciduous or mixed dentition. Intercanine widening was about 3 mm per month regardless of cleft type. Several authors have claimed that transverse expansion of the upper jaw will increase sagittal overjet. Other authors have not found such an effect. The sagittal effect on the maxilla was studied in 68 CLP patients who had received transverse expansion. Analysis of the lateral cephalograms revealed no significant sagittal dentofacial maxillary treatment effects involving forward movement of maxilla, but a downward clockwise rotation of the mandible was found.

Soft-tissue profile changes during widening and protraction of the maxilla in patients with cleft lip and palate compared with normal growth and development

During the last 15 years, cleft lip and palate (CLP) patients with maxillary deficiency in the care of the Bergen CLP team have undergone an interceptive orthopedic treatment phase during the deciduous and mixed dentition period. The present study includes 68 patients who received maxillary transverse expansion by use of a modified quad-helix appliance and 98 cases given maxillary protraction by a facial mask. All cases were treated until an acceptable normal occlusion was attained. Lateral cephalograms were taken immediately before and after the active treatment periods. Sagittal changes of the soft-tissue profile during transverse expansion and protraction were analyzed separately for unilateral complete cleft lip and palate (UCLP) patients and bilateral complete cleft lip and palate (BCLP) patients. The soft-tissue profiles of the groups were compared to growth changes of noncleft age-matched children (NORM group). During the short period of maxillary transverse expansion (mean period, 3.5 months) no significant change of the soft-tissue profile was found, except in the protrusion of the lower lip in the BCLP group. During the period of maxillary protraction (mean periods, 12 months in the UCLP group and 15 months in the BCLP group) the soft-tissue profile improved significantly by reducing the characteristic tendency towards a concave profile in CLP patients with maxillary deficiency. Significant increases of the sagittal maxillomandibular lip relation (angle SS-N-SM: mean increase, 2.5 degrees) and the Holdaway-angle (H-angle: mean increase, 3.0 degrees) were found to be similar in the UCLP and BCLP groups. However, the use of different reference lines for evaluation of treatment effects upon the soft-tissue profile resulted in conflicting findings suggesting that anteriorly situated reference lines are more suitable for the evaluation of CLP patients. Thus, the esthetic line (E.line) indicated a favorable position of the lips after treatment; the subspinale-pogonion line (ss.pg) revealed an improved soft-tissue profile; the soft-tissue-facial line (N.PG) showed a retruded nose and upper lip; whereas basal references such as the nasionsella line (NSL) and the occlusal-line perpendicular (OLP) mainly showed major differences between the CLP groups and the NORM groups.

Severe overjet and overbite reduced alveolar bone height in 19-year-old men

Few investigations have reported convincing evidence of an association between malocclusion and loss of periodontal tooth support. The contradictory findings may in part be explained by the selection of material and by method differences. In many studies not-very-severe malocclusion was compared with not-very-correct occlusion. Only recently have measuring methods been developed that calculate the distance between the cementoenamel junction (CEJ) and the interproximal alveolar bone crest (AC) to the nearest 0.01 mm with acceptable accuracy. The association between overjet > or = 8 mm and the reduction of the bone support as expressed by the distance between CEJ and AC in 21 military recruits was compared with a peer group of 50 recruits with nearly ideal occlusion. The results showed a significant reduction of bone height (mean = 0.96 mm) of the four upper front teeth and of the four lower incisors (mean = 0.35 mm) in the malocclusion group. Similarly, a group of 31 army recruits with overbite > or = 6 mm revealed a significant reduction of bone height of 0.71 mm of the upper front teeth and 0.49 mm of the lower front teeth. Overjet and overbite did not appear in combination in this material. In conclusion, alveolar bone height was reduced in regions with severe malocclusion when compared with corresponding regions in healthy men with near ideal occlusion. The material was military recruits (age 19 years).

Tissue response to space closure in monkeys: a comparison of orthodontic magnets and superelastic coil springs

Interest in using magnets for generating orthodontic forces started with the widespread availability of rare earth magnetic alloys. In vivo studies have indicated that a static magnetic field and/or corrosion products from the magnetic materials may induce biological effects when in close contact with cells or tissues. In the clinical situation, orthodontic magnets are often situated some distance away from the gingiva and bone. Consequently, the previously observed biological effects may not be found in an experimental situation mimicking the clinical setting. Thus, the present experimental study was undertaken to test this hypothesis using commercially available cobalt-samarium magnets for orthodontic treatment in comparison to treatment with Sentalloy closed coil springs with respect to possible side effects on alveolar bone growth, gingival epithelial thickness as well as rate of space closure. Corrosion of the uncovered areas of the magnets was already evident after 6 weeks. No statistical differences were found between the magnet and coil spring specimens with respect to rate of space closure, bone formation or epithelial thickness. The only two variables that differed significantly between magnet and coil spring specimens was that there were more resorption and more tetracycline labelled osteocyte lacunae under the magnets. In conclusion, although some marginal statistical differences were found between the magnet and coil spring specimens with respect to cell and tissue reactions, the near lack of cell and tissue effects of the magnets in the present clinical experimental situation compared to previous studies in which the magnets were positioned in close contact with the tissue under study, indicate limited adverse clinical effects.