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Biomedical subjects

P Rygh

Publications and source records attributed to P Rygh.

At least 19 recordsLinked to original sources
PubMed1996

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.

Alveolar Process↗
PubMed1995

Transition and determinants of orthodontic root resorption-repair sequence.

When severe root resorption is observed during orthodontic treatment the clinician needs to know how the active process can be stopped. It is generally assumed that if active force is discontinued, the root resorption will end. The determinants of the resorption/repair sequence are, however, not well understood. The aim of the present study was to register and analyse determinants that may influence the extent of resorbed root surface, as well as the transition of a process of active root resorption into a process of tissue deposition/repair in the resorption lacunae. Using an experimental model that would simulate the first force-activation cycle, the upper first molars of rats were moved mesially by a fixed orthodontic appliance for periods between 2 and 21 days. The results revealed that (1) the extent of root resorption after 21 days corresponded with the maximal extent of the hyalinized zone; (2) a process of repair started from the periphery in the resorbed lacunae where the periodontal ligament (PDL) had been re-established, while ongoing active resorption was observed beneath the existing hyalinized tissue; and (3) root resorption continued in the area where hyalinized tissue persisted even after active force had terminated. It is hypothesized that determinants of continued resorption/repair generally seem to be associated with the persistence and removal of the necrotic tissue.

Animals↗
PubMed1995

The repair of orthodontic root resorption: an ultrastructural study.

It has previously been shown by light (LM) and scanning electron microscopy (SEM), that after force is terminated, repair of the orthodontic root resorption lacunae occur by deposition of new cementum. The ultrastructural details of the process are not well established. Since it has been hypothesized that a new barrier to protect the root surface is formed during the reparative phase, new information on this aspect of orthodontic root resorption may be valuable. The aim of the present investigation was, by using transmission electron microscopy (TEM), to study in more detail the repair of orthodontic root resorption lacunae and the re-establishment of the adjacent periodontal membrane (PM). Three experimental tooth movement groups of rats (age 40-45 days) were used. The maxillary first molar was moved mesially by a closed coil spring for 10, 14, and 21 days. The results indicate that transition of active root resorption into a process of repair which occurs even in the presence of a light force, is associated with invasion of fibroblast-like cells from the circumference into the active root resorption site. After 10 days, formation of new tooth supporting structures was seen in the periphery of the resorption lacunae, while active resorption by multinucleated odontoclast-like cells (OD) took place in the central parts. In the later phases, after termination of force, the repair process is similar to the early cementogenesis occurring during tooth development. New mineralized cementum was observed on the resorbed root surface by 21 days. After deposition of the new cementum, the structures of a new periodontal ligament (PDL) were comparable with the control specimens.

Animals↗
PubMed1995

Effects of orthodontic magnets on cutaneous epithelial thickness and tibial bone growth in rats.

The use of permanent magnets in orthodontic treatment has increased significantly over the past years, triggered by the introduction of rare earth magnetic alloys. Concerns about possible side effects have been expressed relating to their use in orthodontic treatment. In previous experimental studies evidence of a reduction in bone formation and epithelial turnover close to rare earth magnets has been presented. The aim of the present study was twofold: to confirm earlier results and to study whether the observed changes are reversible. One hind leg in each of 45 rats was fitted with aluminum rings with Co5Sm magnets, whereas the other hind leg was fitted with sham rings. After 8 weeks 25 rats were killed, and the rings in the remaining rats were removed. The latter group was killed after another 11 weeks. The epithelial and bone reactions were evaluated histomorphometrically. Previous results showing thinner epithelium and retarded rate of bone formation close to Co5Sm magnets were confirmed. These effects were also shown to be largely reversible. It was concluded on the basis of this and the magnitude of the effects that any local side effects from orthodontic rare earth magnets appear negligible when extrapolated to the clinical situation.

Animals↗
PubMed1994

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).

Adult↗
PubMed1994

Root resorption beneath the main hyalinized zone.

A previous investigation on the initial phase of root resorption associated with orthodontic overcompression of local areas of the periodontal ligament (PDL), indicated that a differentiation should be made between two stages: (1) the very first resorption occurring in the periphery of the main necrotic zone; and (2) the root resorption occurring on that part of the root surface situated beneath the main bulk of necrotic tissue (Brudvik and Rygh, 1993a). The aim of the present investigation was to study the latter stage. Attention was focused on: (1) the possible association between the presence of necrotic tissue and root resorption; and (2) the cells that invaded and removed the necrotic tissue, as well as the cells that started to remove/resorb the cementum. Mesial movement of the upper first molars (rats) and lower first molars (mice) was performed by a fixed orthodontic appliance. The results indicate an association between the root resorption, and the presence and active removal of the hyalinized tissue. Root resorption beneath the main hyalinized zone occurred in areas where invading cells were observed close to the root surface. The majority of the cells involved in removal of the necrotic tissue and resorption of the root surface were multi-nucleated and TRAP-positive. It is hypothesized that multi-nucleated TRAP-positive cells when reaching the subjacent contaminated and damaged root surface after having removed necrotic PM tissue, continued to remove the cementum surface.

Acid Phosphatase↗
PubMed1994

Multi-nucleated cells remove the main hyalinized tissue and start resorption of adjacent root surfaces.

Recent studies revealed that the initial root resorption occurred in the peripheries of the necrotic periodontal ligament (PDL) and was performed by mono-nucleated non-clast macrophage- and fibroblast-like cells (Brudvik and Rygh, 1993a, b). The aim of the present transmission electron microscopic (TEM) investigation was to study in more detail the cells involved in removal of the main hyalinized tissue and those involved in root resorption, occurring on the root surface situated beneath the main hyalinized tissue. Twelve male Wistar rats were used. The maxillary first molar was moved mesially by a fixed orthodontic appliance for 7 and 10 days. The results indicate that multi-nucleated giant cells (MNGC) without a ruffled border surface, as well as mono-nucleated macrophage-like cells were responsible for removal of the necrotic tissue and also for resorption of the surface parts of the root cementum. Although the present MNGC showed many morphological traits similar to the observed odontoclasts and osteoclasts, except for their lack of ruffled borders, it is assumed that they are derived from the mono-nucleated phagocytic system. Multi-nucleated clast-like cells with ruffled border were never observed near the remnants of the necrotic tissue. Such cells were found only in the resorption lacunae on root and bone surfaces.

Acid Phosphatase↗
PubMed1993

The initial phase of orthodontic root resorption incident to local compression of the periodontal ligament.

The present light microscopic investigation was undertaken in order to study the initial phase of orthodontic root resorption in areas of pressure and, more specifically, to focus on the first cells that penetrate the root surface. Twenty-one upper first molars (rats) and 31 lower first molars (mice) were moved mesially by a fixed orthodontic appliance. The experimental periods were 1, 2, 3, 4, and 5 days in rats, and 1, 2, 3, 4, 5, 6, 7, and 8 days in mice. Tartrate-resistant acid phosphatase (TRAP) and Haematoxylin Eosin (H&E) stains were used. Root resorption related to a hyalinized zone showed a consistent pattern: Root resorption started in the circumference of the necrotic hyalinized tissue. In the central parts of the hyalinized zone frontal root resorption occurred 3-4 days later than in the periphery. Indications that the mechanisms for circumferential and central resorption differed was the reason for presenting only the periphery stage in this paper. The initial penetration of cells into precementum/cementum occurred at the peripheries or at a short distance from the peripheries of the hyalinized zone. These cells were TRAP-negative, indicating that they were not clasts or clast precursors. Before this happened TRAP-negative macrophage-like cells were observed at the borderline between the hyalinized tissue and vital periodontal membrane (PM). TRAP-positive cells were first observed in the bone marrow spaces. During the later stages mono- and multi-nucleated TRAP-positive cells were participating in active removal of the hyalinized tissue toward the root surface, and in resorption of cementum and dentine.

Alveolar Process↗
PubMed1993

Non-clast cells start orthodontic root resorption in the periphery of hyalinized zones.

Previous research has indicated that orthodontically-induced root resorption is regularly associated with local trauma, most often with over-compression of the periodontal ligament (PDL). Recent research has revealed that the initial root resorption occurs in the periphery of the necrotic PDL, where mononucleated cells not stained by tartrate resistant acid phosphatase (TRAP), are the first cells to penetrate the root surface. The aim of the present transmission electron microscopic (TEM) investigation was to study in more detail the root surface during the initial penetration of cells into precementum and mineralized cementum. In 21 Wistar rats (age 40-45 days) the maxillary first molar was moved mesially by a closed coil spring for 6 and 12 hours, 1, 2, 3, 4, and 5 days. The results clearly indicate a role for mononucleated non-clast cells in the initial local removal of precementum and mineralized acellular cementum in the periphery not only near, but also at some distance from the compressed PDL. 1. Macrophage-like cells phagocytosed necrotic tissue in the middle of the PDL after 6 hours and near the root surface close to the hyalinized zone after 24 hours. 2. Fibroblast-like cells seemed to break down by phagocytic and collagenolytic activity the precementum near the hyalinized zone after 24 hours. 3. The surface layers of mineralized cementum were removed by mononucleated cells which occurred on the mineralized cementum after 3 days. 4. Multinucleated cells without ruffled border occurred in the PDL at some distance from the root surface after 24 hours. Multinucleated cells with a ruffled border towards the mineralized root surface were rare during the 5 days' period.

Animals↗
PubMed1993

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).

Cephalometry↗
PubMed1993

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.

Adolescent↗
PubMed1993

Maxillary protraction: different effects on facial morphology in unilateral and bilateral cleft lip and palate patients.

Since 1977 patients with anterior/posterior crossbites in the care of the Bergen CLP team have undergone an interceptive orthopedic protraction phase during the deciduous and mixed dentition period. Eighty-seven cases with complete clefts (63 unilateral and 24 bilateral) displaying anterior crossbite (negative overjet) were treated to normal occlusion. A fixed quad-helix appliance was used in combination with a facial mask. In the unilateral complete cleft lip and palate (UCLP) group, mean age at start of treatment was 6 years 10 months and mean duration was 12 months. In the bilateral complete cleft lip and palate (BCLP) group, mean age at start of treatment was 7 years and mean duration 15 months. The protraction force was 700 g. The sagittal changes during protraction in the UCLP and BCLP groups were compared, and related to the growth changes in a group of noncleft children at the same age. Dentofacial treatment effect was different in the UCLP and BCLP groups. Significant increase of maxillary prognathism (angle s-n-ss) was found only in the UCLP group, whereas the treatment effect in the BCLP group was mainly dentoalveolar. However, after protraction there was no longer a significant difference in maxillary prognathism between the two CLP groups, and the sagittal position of the upper molars was normalized in both groups. The upper incisors remained retroclined in both groups, significantly more in the BCLP group. Increase of the upper facial height (n-sp") and clockwise rotation of the occlusal line were significantly greater in the BCLP group. The computerized occlusal line was unsuitable as a reference standard for the evaluation of sagittal dentofacial treatment changes when the occlusal line was rotated during treatment.

Cephalometry↗
PubMed1993

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.

Cephalometry↗
PubMed1992

Orthodontic magnets: effects on gingival epithelium and alveolar bone in monkeys.

The purpose of the present study was to examine soft and hard oral tissues in contact with or close to orthodontic magnets following an extended exposure time. Two male monkeys were used in the experiment. Individual silver splints covering the teeth from 17 to 27 in the upper jaw and 32-42 in the lower jaw were made. Co5Sm magnets were inserted with cold-curing acrylic buccally and lingually in the splints. The monkeys were injected with tetracycline at the start of the experiment and after 4 weeks. The epithelial thickness in buccal and lingual mucosa under the magnets and corresponding sites on the control side were estimated. The intensity of tetracycline fluorescence in the bone under the magnets and corresponding control sites was assessed semiquantitatively. A thinner epithelium compared to the controls and a patchy tetracycline-incorporation in the bone adjacent to orthodontic magnets in contrast to a homogeneous tetracycline fluorescent pattern in the controls were the most conspicuous findings. It cannot be excluded that the magnetic field or corrosion products from the magnetic material influenced vital processes in the epithelium and the bone close to the magnets. However, it cannot be concluded from the present study what cellular processes were affected.

Alveolar Process↗
PubMed1991

Root resorption after local injection of prostaglandin E2 during experimental tooth movement.

The purpose of this study was to investigate the occurrence of orthodontic root resorption in connection with local injection of prostaglandin E2 (PGE2). The material consisted of 25 male Wistar rats. The control group comprised six animals where no force was applied. In five animals 0.1 ml of 0.1 micrograms/microliter PGE2 was injected in the gingival area of the upper right first molar. In one animal no PGE2 was injected. The animals were killed after 3 days. The experimental tooth movement groups consisted of 19 animals. Duration of experiments was 3 days, 7 days, and 10 days. The maxillary first molars on both sides were each moved mesially by means of a coil spring. On the right side 0.1 ml of PGE2 0.1 micrograms/microliters was injected in the gingiva on the buccal side of the upper first molar on days 0, 3, 5, and 7. On the left side no injection of PGE2 was performed. In three animals in the 7-day group the vehicle (Waymouth medium) was injected. There was no significant difference in root resorption between the experimentally moved teeth with and without local injection of PGE2, but a trend towards more root resorption was registered on the teeth where such injections had been performed.

Animals↗
PubMed1990

[New treatment modalities for patients with cleft lip, jaw and palate].

Cleft lip/palate patients are reported at birth to a national register and are referred to one of the cleft palate teams in Oslo or Bergen. The teams coordinate the active treatment periods by plastic surgery, orthodontics/jaw orthopedics, logopedics, otology, pediatrics, psychology and orthognatic surgery. Presurgical orthopedics is performed early after birth in some total clefts with very asymmetric jaw segments. Lip is closed at 3 months, hard and soft palate at 1 1/2 years. Only a few cases now need early protraction of the upper jaw due to growth restraint. Many need orthodontic repositioning of the jaw segments and establishment of good occlusion. Bone from the ileac crest is grafted to the cleft prior to eruption of the canine. This permits normal development of the alveolar bone and eruption or, if the lateral is missing, orthodontic mesialization of the canine, excluding prosthetic replacement.

Adolescent↗