Biomedical subjects

J C Maltha

Publications and source records attributed to J C Maltha.

At least 37 records · Page 2Linked to original sources

PubMed2000

Myofibroblasts and matrix components in healing palatal wounds in the rat.

In order to identify wound contraction and scar formation during palatal mucoperiosteal wound healing in growing rats, the temporal and spatial distribution of myofibroblasts and matrix components were determined immunohistochemically. Myofibroblasts were found in the mucosal part of the palatal wound tissue between 4 and 22 days, with the highest density at 8 days post-wounding. The number of collagen type I and type III fibers gradually increased until about 8 days postwounding, and thereafter the staining intensity of collagen type III decreased. At 60 days post-wounding there were more transversely oriented collagen type I fibers and less type III fibers and elastin present in the submucosa than in normal tissue. The results suggest that in this model wound contraction mainly takes place in the mucosa between 4 and 22 days postwounding. Furthermore, palatal wounds made in young rats heal with distinct scar tissue formation. Therefore, this model is useful to test the effects of therapies that aim to reduce wound contraction and scarring after cleft palate surgery.

Actins↗

PubMed2000

Local injection of IFN-gamma reduces the number of myofibroblasts and the collagen content in palatal wounds.

Wound contraction and scar formation after cleft palate surgery impair maxillary growth and dentoalveolar development. Since myofibroblast numbers and scar formation are reduced by interferon-gamma (IFN-gamma) in the healing of dermal wounds, the hypothesis was tested that local administration of IFN-gamma reduces the numbers of myofibroblasts and the elevated amount of collagen during palatal mucoperiosteal wound healing. Standardized mucoperiosteal excision wounds were made in the palatal mucoperiosteum of young rats. Either IFN-gamma or vehicle alone (sham group) was repeatedly injected into the wound site between 4 and 29 days post-wounding. The results were compared with unmanipulated control wounds. Samples of wound tissue were prepared for biochemical and microscopic analysis. The hydroxyproline, sulfated glycosaminoglycan and DNA contents of the wound tissues were analyzed biochemically. The degree of re-epithelialization, tissue thickness, the numbers of myofibroblasts, and the amounts of elastin and collagen types I and III were evaluated on histological sections. Injection of vehicle alone affected almost all healing parameters, compared with the controls, and delayed the wound-healing process. IFN-gamma stimulated re-epithelialization and decreased the numbers of myofibroblasts when compared with vehicle-treated wounds. It also decreased the hydroxyproline and glycosaminoglycan contents of 60-day-old wound tissue, but the histological characteristics of scar tissue persisted. Therefore, IFN-gamma is able to reduce the numbers of myofibroblasts and the collagen content of scar tissue after palatal wound healing. It may be a promising pharmaceutical agent for the reduction of wound contraction and scarring after cleft palate surgery.

Actin Cytoskeleton↗

PubMed2000

Time-dependent mechanical behaviour of the periodontal ligament.

The process of tooth displacement in response to orthodontic forces is thought to be induced by the stresses and strains in the periodontium. The mechanical force on the tooth is transmitted to the alveolar bone through a layer of soft connective tissue, the periodontal ligament. Stress and/or strain distribution in this layer must be derived from mathematical models, such as the finite element method, because it cannot be measured directly in a non-destructive way. The material behaviour of the constituent tissues is required as an input for such a model. The purpose of this study was to determine the time-dependent mechanical behaviour of the periodontal ligament due to orthodontic loading of a tooth. Therefore, in vivo experiments were performed on beagle dogs. The experimental configuration was simulated in a finite element model to estimate the poroelastic material properties for the periodontal ligament. The experiments showed a two-step response: an instantaneous displacement of 14.10 +/- 3.21 microns within 4 s and a more gradual (creep) displacement reaching a maximum of 60.00 +/- 9.92 microns after 5 h. This response fitted excellently in the finite element model when 21 per cent of the ligament volume was assigned a permeability of 1.0 x 10(-14) m4/N s, the remaining 97 per cent was assigned a permeability of 2.5 x 10(-17) m4/N s. A tissue elastic modulus of 0.015 +/- 0.001 MPa was estimated. Our results indicate that fluid compartments within the periodontal ligament play an important role in the transmission and damping of forces acting on teeth.

Animals↗

PubMed2000

[Biological basis of orthodontic tooth movement].

The effect of orthodontic therapy is dependent of the biological possibilities and limitations of the dento-alveolar complex. Biomechanical effects determine the first phase of tooth movement. In the second phase hyalinisation occurs in almost all cases. Elimination of the hyalinised tissue is associated with undermining bone resorption. Next, 'real' tooth movement starts. At the pressure side the normal structure of the periodontal ligament is destroyed and so is the tooth attachment. At the tension side deposition of trabecular bone is found and the tooth attachment remains. The regulation of these processes is still not completely understood, but cytokines and growth factors play an important role. The biological system does not react according to a simple dose-response relation and large individual differences in susceptibility of the system exist.

Biomechanical Phenomena↗

PubMed2000

[Myth of optimal pressure].

Orthodontic tooth movement always follows the same pattern. Four phases can be distinguished. During the last phase, the linear phase, the tooth moves through the alveolar bone. One could assume that the rate of tooth displacement is related to the magnitude of the force or to the pressure in the periodontal ligament. No consensus exists on the optimal pressure for orthodontic tooth movement. In literature pressures are advocated, ranging from 2 to 30 KPa. Animal experiments show that a large range of force magnitudes results in an equal rate of tooth movement. A dose-response relation is only feasible when forces are used which are far below those used in an everyday practice.

Animals↗

PubMed1999

Effects of interferons on proliferation and collagen synthesis of rat palatal wound fibroblasts.

The purpose was to select drugs that specifically reduce collagen synthesis by palatal granulation fibroblasts without affecting their proliferation. Granulation fibroblasts were obtained from 8-day-old palatal mucoperiosteal wounds and normal fibroblasts from palatal tissue of unwounded rats. Cultured cells were treated with interferon-alpha2b, interferon-beta and interferon-gamma (0, 100, 1000, and 10000 U/ml). Cell proliferation was measured by [3H]thymidine incorporation. Collagen synthesis and non-collagenous protein synthesis were determined from the incorporation of [3H]proline. None of the interferons significantly inhibited the proliferation of either type of fibroblasts. Interferon-alpha2b had no effect on the variables studied at the dosages used. Interferon-beta reduced collagen synthesis of granulation fibroblasts without affecting their non-collagenous protein synthesis or protein synthesis by normal fibroblasts. Interferon-gamma reduced collagen synthesis of both types of fibroblast and the non-collagenous protein synthesis of granulation fibroblasts. These data show that interferon-beta specifically reduces collagen synthesis by oral granulation fibroblasts without affecting normal palatal fibroblasts.

Animals↗

PubMed1999

Incorporation of three types of bone block implants in the facial skeleton.

The regenerative response on autogenous cancellous and cortical bone grafts, and on a commercial available xenogenous resorbable bone mineral (RBM) (Bio-Oss, Geistlich-Pharma, Wolhusen, Switzerland) was compared in standardized bony defects related to a paranasal sinus. On 15 skeletally mature goats four critical sized full thickness bone defects were trephined in the frontal bone. These defects were filled at random with a cortical bone plug, a cancellous bone plug, a plug of spongious RBM cut into shape or left empty. Fluorochrome bone markers were injected subcutaneously 1 and 5 weeks after transplantation, and one week before the animals were killed. The animals were killed at 3, 6, 12 and 24 weeks after surgery. Histological evaluation showed that autogenous bone grafts were all accepted and incorporated in a similar way as in calvarial defects. RBM was only osteoconductive. New bone was formed at the margins of the defects, and only little of the RBM was incorporated. Most of the RBM was gradually resorbed by multinucleated osteoclast-like cells.

Absorbable Implants↗

PubMed1999

Incorporation of particulated bone implants in the facial skeleton.

The purpose of this study was to compare the regenerative response of autogenous cortical and cancellous bone chips and a natural particulate resorbable bone mineral (RBM) (Bio-Oss, Geistlich-Pharma, Wolhusen, Switzerland) in standardized bony defects relating paranasal sinuses to one another and to bone blocks. On 13 skeletally mature female goats four standardized critical-sized full thickness bone defects were made in the frontal bone overlying the frontal sinus. These defects were filled at random with cortical bone chips, cancellous bone chips, spongiosa granules of a RBM or left empty. Fluorochrome bone markers were injected subcutaneously 1 and 5 weeks after transplantation, and one week before the animals were killed. The animals were killed at 3, 6, 12 and 24 weeks after surgery. Autogenous cancellous bone chips is the material of choice for bridging a bony defect in the maxillofacial area where there is no need for mechanical strength. They heal in the same way as cancellous bone blocks do. Cortical bone chips are not reliable enough to be used as a solitary bone-grafting material under these conditions. A cortical block as a solitary implant gives better results. RBM granules as solitary implant in a critical-sized defect do not stimulate osteoconduction but give rise to an extensive osteoclastic activity stimulated by the mutual loose relation. A solid block of RBM is in a similar case more reliable.

Absorbable Implants↗

PubMed1999

Palatal mucoperiosteal wound healing in the rat.

The objective of this study was to analyze the changes in tissue architecture and matrix composition during healing of palatal wounds of immature rats, and to compare this with rats of the same age that did not receive mucoperiosteal wounds. Wounds were made in the mucoperiosteum of the palate of 35-d-old rats. Samples were evaluated histologically at numerous points in time after wounding. The DNA, hydroxyproline and sulphated glycosaminoglycan contents were determined at 8, 15, 30, and 60 d post-wounding. Eight-d-old granulation tissue contained 43% less hydroxyproline, and 100% more glycosaminoglycans and cells than unwounded palatal tissue of 43-d-old rats. Sixty-d-old wounds contained 100% more DNA and 39% more hydroxyproline than unwounded tissue of 95-d-old rats. At the same time, densely packed and transversely aligned collagen fibres were present. It is concluded that palatal mucoperiosteal wounds made in 35-d-old rats heal with distinct scar tissue formation. The scar contains more collagen than non-wounded palatal tissue of rats of the same age. Therefore, this model may be of use for the development of therapies aiming to reduce palatal scarring.

Animals↗

PubMed1999

Tooth movement with light continuous and discontinuous forces in beagle dogs.

In orthodontics, no consensus exists on how to move teeth most efficiently. The aim of the present study was to investigate the effect of two different force regimes and two different force magnitudes on tooth displacement. A split mouth design study was conducted in young adult beagle dogs. In each dog, both mandibular third premolars were extracted, and orthodontic appliances were placed for bodily distalization of the second premolars. The forces (10 cN or 25 cN) were applied, either continuously (24 h a day) or discontinuously (active 16 h daily from 17.00 till 9.00). Individual time-displacement curves of the second premolars were constructed. Four phases of tooth movement could be distinguished. Statistical analysis showed that the choice of regime had an influence on the duration of the hyalinisation phase, while force magnitude had not. The rate of tooth movement in the linear phase was mainly regime dependent. However, force magnitude also appeared to have some influence. The individual tissue response in each dog appeared to have an influence on both the duration of the second phase and the rate in the fourth phase. It was concluded that under these experimental conditions, force regime has more influence on the rate of orthodontic tooth movement than force magnitude.

Analysis of Variance↗

PubMed1999

The healing process of palatal tissues after operations with and without denudation of bone: an experimental study in dogs.

The aim of this study was to evaluate wound healing clinically and histologically in beagle dogs after palatal repair during growth by the partially split flap technique and the von Langenbeck technique. A standardised soft tissue defect was created in the medial region of the palate. The partially split flap technique was performed in 14 dogs (age 12 weeks). Von Langenbeck repair was simulated in 12 dogs (age 12 weeks). Four dogs (age 12 weeks) served as controls. Standardised slides of the palate were taken on eight occasions and the wound surface areas were measured. Histological sections were prepared at three different ages. The animals were studied until the age of 25 weeks. Re-epithelialisation was complete in roughly two weeks in dogs after palatal repair by the partially split flap technique. The histological features of this group were close to normal limits. After the von Langenbeck's procedure re-epithelialisation took about three weeks and scar tissue was firmly attached to bundle bone by Sharpey's fibres. We conclude that the histological appearance of the palatal tissues in dogs after palatal repair during growth by the partially split flap technique was close to normal. We assume that this is reason for more favourable dentoalveolar development after the partially split flap technique compared with von Langenbeck's repair.

Animals↗

PubMed1998

The healing process of palatal tissues after palatal surgery with and without implantation of membranes: an experimental study in dogs.

The aim of this study was to evaluate the wound-healing process clinically and histologically in growing beagle dogs after palatal repair according to von Langenbeck, with and without implantation of membranes of a copolymer of polyhydroxybutyrate 80%-hydroxyvalerate 20% (=PHB-co-HV 80/20). Von Langenbeck's repair was performed in 12 dogs (age 12 wk), while von Langenbeck's repair followed by implantation of PHV-co-HV membranes was carried out in 11 dogs (age 12 wk). Four dogs (age 12 wk) served as unoperated controls. Standardized intra-oral slides of the palate were taken and measurements of the wound surface areas were carried out. Histological sections were prepared at three different ages. The animals were studied until the age of 25 wk. It was found that wound closure after the von Langenbeck's procedure took about 3 wk, while the use of PHB-co-HV membranes after von Langenbeck's repair resulted in complete wound closure after approximately 7 wk after the membranes had sequestered. At the age of 25 wk, the histologic results after the von Langenbeck procedure showed that the entire scar tissue covering the former denuded bony areas was attached to the bone by means of Sharpey's fibres, while after implantation of the membranes only local scar tissue attachment by means of Sharpey's fibres was found. Further research is necessary to develop a membrane which allows wound closure without sequestration of it.

Journal Article↗

PubMed1997

Three-dimensional morphometric analysis of the effects of subperiosteal palatal soft-tissue expansion in growing cats.

A prospective longitudinal study in 75 growing cats was conducted to evaluate palatal soft-tissue expansion in cleft lip and palate surgery. In 31 cats, palatal scars were induced by simulated Langenbeck surgery at the age of 8 weeks. At the age of 14 weeks, custom-made tissue expanders were inserted in 61 animals. Tissue expansion was performed by weekly inflation in 33 cats (16 without and 17 with scars) for an 8-week period. The remaining 28 cats (14 without and 14 with scars) served as sham groups. A control group was formed by 14 animals (without scars and without tissue expander). The effects of the experimental interventions were evaluated on a series of dental casts during the inflation period and until 8 weeks after removal of the tissue expander. The results indicate that soft-tissue expansion of the palatal mucoperiosteum is feasible. Until 20 weeks of age, no differences were found between both expansion and sham groups. Thereafter, significant soft-tissue surface-area gain was quantified in relation to the base surface and base diameter of the tissue expander. Iatrogenic side-effects of active tissue expansion consisted of significant transversal growth retardation in the anterior part of the bony palate and dentoalveolar structures. After removal of the tissue expanders, some accelerated growth in the tissue-expansion, scarred-tissue group was seen. It is concluded that palatal soft-tissue expansion is possible in growing cats, with and without the presence of palatal scars; however, this technique, like other kinds of palatal surgery, impairs dentomaxillary growth and development.

Age Factors↗

PubMed1997

Tooth eruption through autogenous and xenogenous bone transplants: a histological and radiographic evaluation in beagle dogs.

The effect of implanting autogenous and xenogenous (Bio-Oss) bone transplants into metabolically active sites within beagle dog mandibles during permanent premolar tooth eruption was examined. Ten 14-week-old beagles were used. Before commencing the radiographic experiments, metal bone markers were placed in the caudal margin of the mandible at the age of 10 weeks. The deciduous first and third molar teeth were extracted and their sockets over the permanent second and fourth premolars were implanted with autogenous particulate enchondral iliac crest bone, autogenous particulate membraneous mandibular body bone, xenogenous bovine anorganic bone mineral spongiosa granules (1-2mm3) (Bio-Oss, Geistlich Pharma, Switzerland) of left empty. The third premolar served as control site. Standardized oblique lateral radiographs were taken once a week. A number of coordinates of defined points and structures were determined by means of a coordinate digitizing system. Animals were killed 4, 10 and 16 weeks after bone transplantation for histological examination of the transplantation sites. All premolars showed no delay in eruption or disruption of crown and root development. On histology, the Bio-Oss particles were not resorbed or integrated in the alveolar bone but were pushed forward into the gingiva. We have demonstrated that there is on difference in the eruption curve of the permanent premolars in the four groups (ANOVA P > 0.5) and that bone transplantation has no inhibitory effect on eruption (ANOVA P > 0.3) and crown development of the underlying permanent premolar but that Bio-Oss does not have the same resorbable or integrating capability as autogenous bone grafts.

Alveolar Process↗

PubMed1997

Contribution of interdigitation to the occlusal development of the dentition in Macaca fascicularis.

The contribution of interdigitation to the development of the dentition of juvenile Macaca fascicularis was studied on a series of dental casts and at the histological level by the use of vital staining. Fourteen laboratory-born monkeys were allocated to a control group (n = 7) or an experimental group (n = 7). They were followed from 31 to 152 weeks of age. In the animals of the experimental group, interdigitation was eliminated by gradually grinding the cusps of the molars and canines in both dental arches as soon as possible after emergence. Silicone impressions of the dental arches of each monkey were taken at regular intervals. Two experimental and two control animals received vital staining at regular intervals and were processed for histological evaluation at the end of the experimental period. Changes over time in the dimensions of the dentition were analysed. Locally, the maxillary dental arch in the experimental group broadened significantly faster than in the control group. No significant differences between the experimental and the control group were found for any of the mandibular parameters. The experimental intervention also led to less prevalence of anterior open bite in the experimental group than in the control group. It is concluded that interdigitation plays a role in the development of the maxillary dental arch and does not seem to affect mandibular dental arch development.

Animals↗

PubMed1997

Two-dimensional cephalometric analysis of the effects of subperiosteal palatal soft-tissue expansion in growing cats.

The feasibility and possible effects of palatal soft-tissue expansion in palatal repair were studied. A prospective longitudinal animal experiment was performed in 75 growing cats assigned to 5 groups. In 31 cats, a midline defect was made, and bipediced flaps were raised at the age of 8 weeks (stimulated Langenbeck operation) in order to create palatal scars. At the age of 14 weeks, custom-made tissue expanders were inserted palatally in 61 animals. Tissue expansion was performed by weekly inflation in 33 cats (16 without and 17 with scars) for an 8-week period. The remaining 28 cats (14 without and 14 with scars) served as sham groups. A control group was formed by 14 animals (without scars and without tissue expanders). Soft-tissue gain and its effects on maxillofacial growth and development were measured in the midsagittal plane on tracings from standardized lateral radiographs. The effects of the experimental interventions were evaluated for 8 weeks after removal of the tissue expanders. Not all the cats yielded results at all time periods. This study showed that soft-tissue expansion of palatal mucoperiosteum is feasible. The surgically induced scars did not cause significant differences between the different groups in the midsagittal plane, and the data from both expansion and sham groups could be pooled. Significant soft-tissue gain was achieved by the tissue-expansion technique. Iatrogenic side effects were significant anteroposterior growth retardation at the level of the bony palate and an increase in vertical growth of the anterior nasomaxillary height and the posterior skull height during active tissue expansion. After removal of the tissue expanders, some accelerated growth was found in the tissue expansion in the scarred tissue group, with initial correction of the abnormal growth at the cranial base level. It is concluded that palatal soft-tissue expansion is possible in growing cats. This technique, however, impaired maxillofacial growth and development.

Analysis of Variance↗

PubMed1996

Magnitude of orthodontic forces and rate of bodily tooth movement. An experimental study.

The relationship between the magnitude of a constant continuous orthodontic force and rate of bodily tooth movement was studied. In 25 young adult male beagle dogs, lower third premolars were extracted and bone markers were implanted in the mandible. Sixteen weeks later, an orthodontic appliance was placed, and elastics exerting 50, 100, or 200 gm were attached to the lower second premolar to produce bodily distalization. In each dog, different forces were used on the left and the right sides. As a control group, orthodontic appliances were placed without elastic on eight sides. Tooth movement was measured directly with a digital caliper twice a week during 16 weeks. Resulting curves could be divided in four phases. Large individual differences were found in the rate of tooth movement. Tooth movements on the left and right sides of each dog, however, were highly correlated. No significant differences in the duration of each phase nor in the mean rate of tooth movement during each phase were found between the three force groups. Maximum rate of tooth movement was about 2.5 mm per month in all force groups. There were no significant differences in the mesial movement of the anchorage unit between the force groups. It is concluded that under the circumstances of this study magnitude of force is not decisive in determining the rate of bodily tooth movement, but individual characteristics are.

Analysis of Variance↗

PubMed1996

The role of interdigitation in sagittal growth of the maxillomandibular complex in Macaca fascicularis.

The role of the interdigitation of posterior teeth in maxillomandibular growth and development was studied longitudinally in Macaca fascicularis monkeys. Fourteen monkeys were divided into a control group (n = 7) and an experimental group (n = 7). At the start of the study, the mean age of the animals was 29 weeks. At that stage the interdigitation in the experimental group was eliminated by grinding the cusps of the molars and canines. The animals were followed until 143 weeks of age and studied with the aid of tantalum implants and lateral radiographs. The findings indicated that elimination of the interdigitation resulted in a deviating anteroposterior relationship between the jaws and a significant inhibition of the vertical growth of the maxilla in the second half of the experimental period, while total face height was not noticeably affected. As a result, a more prognathic mandible and a more mesial occlusion developed. It can be concluded that the interdigitation plays a role in the regulation of vertical and anteroposterior facial growth and constitutes an important factor in the jaw relation in Macaca fascicularis monkeys.

Animals↗