Jaap C. Maltha

Optimum Force Magnitude for Orthodontic Tooth Movement: A Systematic Literature Review

The aim of this study was to perform a meta-analysis of the literature concerning the optimal force or range of forces for orthodontic tooth movement. Over 400 articles both on human research and animal experiments were found in Medline and by hand searching of main orthodontic and dental journals. Articles on animal experiments were in the majority. A wide range of animal species such as rat, cat, rabbit, beagle dog, monkey, mouse, and guinea pig were used. Besides variation in species, there was also a wide range of force magnitudes, teeth under study, directions of tooth movement, duration of experimental period, and force reactivation. Furthermore, hardly any experiments were reported that provide information on the relation between the velocity of tooth movement and the magnitude of the applied force. Data from human research on the efficiency of orthodontic tooth movement appeared to be very limited. The large variation in data from current literature made it impossible to perform a meta-analysis. Therefore, we have systematically reviewed the literature. It appeared that no evidence about the optimal force level in orthodontics could be extracted from literature. Well-controlled clinical studies and more standardized animal experiments in the orthodontic field are required to provide more insight into the relation between the applied force and the rate of tooth movement.

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.

Medication effects on the rate of orthodontic tooth movement : a systematic literature review

INTRODUCTION Recently, several reviews have been published on the effects of medications on bone physiology and the clinical side effects in orthodontics. However, the effects of medications on the rate of orthodontic tooth movement have not been evaluated. METHODS A systematic literature review on the effects of medications and dietary supplements on the rate of experimental tooth movement was performed by using PubMed (1953-Oct 2007), Web of Science, and Biosis, complemented by a hand search. RESULTS Forty-nine articles were included in the review, but their interpretation was hindered by the variability in experimental design, magnitude of force applied during tooth movement, and medication regimens. Therapeutic administration of eicosanoids resulted in increased tooth movement, whereas their blocking led to a decrease. Nonsteroidal anti-inflammatory drugs (NSAIDs) decreased tooth movement, but non-NSAID analgesics, such as paracetamol (acetaminophen), had no effect. Corticosteroid hormones, parathyroid hormone, and thyroxin have all been shown to increase tooth movement. Estrogens probably reduce tooth movement, although no direct evidence is available. Vitamin D3 stimulates tooth movement, and dietary calcium seemed to reduce it. Bisphosphonates had a strong inhibitory effect. CONCLUSIONS Medications might have an important influence on the rate of tooth movement, and information on their consumption is essential to adequately discuss treatment planning with patients.

Mechanobiology of tooth movement

This review describes the mechanical and biological signalling pathways during orthodontic tooth movement and provides an update of the current literature. A theoretical model is introduced to elucidate the complex cascade of events after the application of an orthodontic force to a tooth. In this model, the events are divided into four stages: matrix strain and fluid flow, cell strain, cell activation and differentiation, and remodelling. Each stage is explained in detail and discussed using recent literature.

Changes in the Periodontal Ligament After Experimental Tooth Movement Using High and Low Continuous Forces in Beagle Dogs

The aim of this study was to evaluate histological changes in the periodontal structures of beagle dogs after using high and low continuous forces during experimental tooth movement. An orthodontic appliance was placed on the second premolar and the first molar by exerting a continuous and constant reciprocal force of 25 cN on one side and 300 cN on the other side of the mandible. Tooth movement was recorded weekly. Dogs were sacrificed after one, four, 20, 40, and 80 days for histological evaluation. Hematoxylin and eosin (HE) staining was used for tissue survey, staining for alkaline phosphatase as a marker was used for active osteoblasts, and tartrate-resistant acid phosphatase staining was used for osteoclasts. After 24 hours, the remodeling process had already started at the pressure and tension side, and in some samples hyalinization was found. In contrast to earlier studies, hyalinization was found throughout the entire experimental period, both in molars and in premolars. In the periodontal ligament of some teeth, small patches of hyalinization were found at the pressure side, mostly located buccally or lingually of the mesiodistal plane, whereas others showed large areas of necrotic tissue. It is concluded that hyalinization limits tooth movement, but there is no relationship with the force level.

Fluid shear stress inhibits TNFalpha-induced osteocyte apoptosis.

Bone tissue can adapt to orthodontic load. Mechanosensing in bone is primarily a task for the osteocytes, which translate the canalicular flow resulting from bone loading into osteoclast and osteoblast recruiting signals. Apoptotic osteocytes attract osteoclasts, and inhibition of osteocyte apoptosis can therefore affect bone remodeling. Since TNF-α is a pro-inflammatory cytokine with apoptotic potency, and elevated levels are found in the gingival sulcus during orthodontic tooth movement, we investigated if mechanical loading by pulsating fluid flow affects TNF-α-induced apoptosis in chicken osteocytes, osteoblasts, and periosteal fibroblasts. During fluid stasis, TNF-α increased apoptosis by more than two-fold in both osteocytes and osteoblasts, but not in periosteal fibroblasts. One-hour pulsating fluid flow (0.70 ± 0.30 Pa, 5 Hz) inhibited (−25%) TNF-α-induced apoptosis in osteocytes, but not in osteoblasts or periosteal fibroblasts, suggesting a key regulatory role for osteocyte apoptosis in bone remodeling after the application of an orthodontic load.

Time-dependent mechanical behaviour of the periodontal ligament

Abstract 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 μm within 4 s and a more gradual (creep) displacement reaching a maximum of 60.00 ± 9.92 μm 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 × 10−14m4/Ns, the remaining 97 per cent was assigned a permeability of 2.5 × 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.

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.

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.

Myofibroblasts in Palatal Wound Healing: Prospects for the Reduction of Wound Contraction after Cleft Palate Repair

The surgical closure of orofacial clefts is considered to impair maxillary growth and dento-alveolar development. Wound contraction and subsequent scar tissue formation, during healing of these surgical wounds, contribute largely to these growth disturbances. The potential to minimize wound contraction and subsequent scarring by clinical interventions depends on the surgeon’s knowledge of the events responsible for these phenomena. Fibroblasts initiate wound contraction, but proto-myofibroblasts and mature myofibroblasts are by far the most important cells in this process. Myofibroblasts are characterized by their cytoskeleton, which contains alpha-smooth-muscle actin. Additionally, their contractile apparatus contains bundles of actin microfilaments and associated contractile proteins, such as non-muscle myosin. This contractile apparatus is thought to be the major force-generating element involved in wound contraction. After closure of the wound, the myofibroblasts disappear by apoptosis, and a less cellular scar is formed. A reduction of contraction and scarring might be obtained by inhibition of myofibroblast differentiation, stimulation of their de-differentiation, stimulation of myofibroblast apoptosis, or impairment of myofibroblast function. In this review, we will discuss all of these possibilities, which ultimately may lead to a better outcome of cleft palate surgery.