D. Harbrow

Orthodontic tooth movement in the prednisolone-treated rat.

Adverse effects of corticosteroids on bone metabolism raise concerns as to whether steroid treatment may influence orthodontic movement. This study examined the effect of prednisolone on orthodontic movement using an established rat model. The corticosteroid treated group (N = 6) was administered prednisolone (1 mg/kg) daily, for a 12-day induction period; the control group (N = 6) received equivalent volumes of saline. On day 12, an orthodontic appliance was placed which exerted 30 g of mesial force to the maxillary first molar. Animals were sacrificed on day 24 and tooth movement was measured. Sagittal sections of the molars were stained with haematoxylin and eosin, and for tartrate-resistant acid phosphatase (TRAP) activity. While there were no significant differences in the magnitude of tooth movement between the 2 groups, steroid-treated rats displayed significantly less root resorption on the compression side and fewer TRAP-positive cells within the PDL space on the same side. This suggests steroid treatment suppressed clastic activity.

Effect of ethylene vinyl acetate (EVA) closed cell foam on transmitted forces in mouthguard material

Objectives: To compare transmitted forces through ethylene vinyl acetate (EVA) mouthguard material and the same EVA material with gas inclusions in the form of a closed cell foam. Method: EVA mouthguard materials with and without foam gas inclusions and 4 mm thick were impacted with a constant force from an impact pendulum. Various porosity levels in the foam materials were produced by 1%, 5%, and 10% by weight foaming agent. The forces transmitted through the EVA after energy absorption by the test materials were measured with a force sensor and compared. Results: Only minor non-significant differences in transmitted forces through the EVA with and without foam were shown. Conclusions: The inclusion of gas in the form of a closed cell foam in 4 mm thick EVA mouthguard materials did not improve the impact performance of the EVA mouthguard material.

Disturbances of tooth form and eruption in the microphthalmic (mi) mouse: A light and electron microscopic study

Changes in the surrounding alveolar bone occur during tooth eruption. The microphthalmic (mi/mi) mouse suffers from osteopetrosis and lack of bone resorption; tooth form and eruption were examined in both affected mi/mi mice and unaffected litter-mates to determine the effect of osteopetrosis on tooth development and eruption. Paraffin sections of mandibles from 3, 7, 10, 13, 15 and 20-day-old mice were examined by light microscopy after staining with haematoxylin and eosin and for stable acid phosphatase activity. Mandibles from 15- and 20-day-old mice were examined by scanning electron microscopy. The ultrastructure of odontoblasts was observed in 15-day-old mice. Tooth eruption was significantly reduced in the mi/mi mice; the bone of affected mice increased in area with increasing age and marrow spaces narrowed. There was little bony remodeling in the mi/mi mouse, as indicated by layers of reversal lines. This lack of bone resorption affected tooth eruption and root formation. No abnormalities were detected in odontoblasts, suggesting functional normality, but the wide predentine layer in the mi/mi mouse may indicate an alteration in dentine mineralization.

The cervical wedge-shaped lesion in teeth: a light and electron microscopic study

BACKGROUND The cervical non-carious wedged-shaped lesion is controversial in that its aetiology may involve attrition, erosion, abrasion and stress-corrosion (abfraction). This study examined the histopathology of anterior teeth with cervical wedge-shaped lesions by light and electron microscopy to elucidate their pathogenesis. METHODS Ten undecalcified human teeth with cervical lesions were available for investigation. Patency of the dentine tubules was tested using red dye penetration from the pulp chamber. The morphology of normal and sclerotic dentine adjacent to the cervical wedge-shaped lesions was investigated by scanning electron microscopy. The numbers and diameters of dentinal tubules were measured at different levels beneath the surfaces of the lesions. RESULTS The gross and microscopic features of the worn teeth were described. Red dye penetration tests showed white tracts of sclerotic tubules contrasted with red tracts of patent tubules. Numbers of tubules per square area and diameters of patent and sclerotic tubules varied at different levels within the dentine due to deposits of intratubular dentine. CONCLUSIONS The cervical wedge is shaped by interactions between acid wear, abrasion and dentinal sclerosis. No histopathological evidence of abfraction was found. Clinical diagnosis, conservation and restoration of non-carious cervical lesions need to take into account the extent of sclerotic dentine beneath wedge-shaped lesions.

Ameloblast apoptosis and IGF-1 receptor expression in the continuously erupting rat incisor model.

Enamel-producing cells (ameloblasts) pass through several phenotypic and functional stages during enamel formation. In the transition between secretory and maturation stages, about one quarter of the ameloblasts suddenly undergo apoptosis. We have studied this phenomenon using the continuously erupting rat incisor model. A special feature of this model is that all stages of ameloblast differentiation are presented within a single longitudinal section of the developing tooth. This permits investigation of the temporal sequence of gene and growth factor receptor expression during ameloblast differentiation and apoptosis. We describe the light and electron microscopic morphology of ameloblast apoptosis and the pattern of insulin-like growth factor-1 receptor expression by ameloblasts in the continuously erupting rat incisor model. In the developing rat incisor, ameloblast apoptosis is associated with downregulated expression of the insulin-like growth factor-1 receptor. These data are consistent with the hypothesis that ameloblasts are “hard wired” for apoptosis and that insulin-like growth factor-1 receptor expression is required to block the default apoptotic pathway. Possible mechanisms of insulin-like growth factor-1 inhibition of ameloblast apoptosis are presented. The rat incisor model may be useful in studies of physiological apoptosis as it presents apoptosis in a predictable pattern in adult tissues.

A histochemical study of the effects of high doses of sodium fluoride on dipeptidyl peptidase II activity in the rat incisor ameloblast

Female Wistar rats, 3 weeks old, were given sodium fluoride in saline solution (isotonic) by intraperitoneal injection at a dose of either 0, 10 or 20 mg per kg body weight. This treatment was given 9 times over 4.5 days. After fixation by perfusion and demineralization in neutral EDTA, hemi-mandibles were sectioned in a cryostat. Sections were stained for dipeptidyl peptidase II activity, using the specific substrate Lys-Ala-MNA and the coupler Fast Blue B for histochemical localization. Staining indicative of dipeptidyl peptidase II was found in the enamel organ of the incisor, particularly in cells of the stratum intermedium and in both secretory and maturation ameloblasts. This staining was markedly reduced in ameloblasts of rats given either 10 or 20 mg sodium fluoride per kg body weight.

The effect of glucocorticosteroid treatment on dentine formation in the Lewis rat, a histological study.

Abstract Glucocorticosteroids are widely used in the treatment of chronic illnesses and have been reported to cause premature obliteration of the pulp space. During the active stages of dentinogenesis, odontoblasts are growth hormone receptor (GHr) positive. The aims of this study were to determine if the glucocorticosteroid, prednisone, affected the rate of dentine deposition and odontoblast expression of GHr in the rat molar. Following subcutaneous injection of 0.05 mg/kg, 1.0 mg/kg or 5.0 mg/kg prednisone for 20 days, immature and mature molars from rats aged 3 and 6 weeks respectively, were examined histologically. Distribution of GHr expression was determined immunohistochemically. No morphological differences were observed in molars from prednisone treated animals. Prednisone did not appear to enhance dentine deposition in immature molars but in mature molars significantly increased dentine deposition on the roof of the pulp chamber at a dosage of 5.0mg/kg (p > 0.001). In all immature molars, odontoblasts and pulp cells expressed GHr immunoreactivity. In mature molars, odontoblasts and pulpal cells from controls did not show GHr immunoreactivity. However, odontoblasts and pulp cells were GHr immunoreactive in mature molars from animals treated with prednisone.

Non-expression of insulin-like growth factor-I receptor is associated with apoptosis: an ultrastructural study on rat ameloblasts.

Insulin-like growth factor-I (IGF-I) is a pleiotrophic polypeptide which appears to have roles both as a circulating endocrine hormone and as a locally synthesized paracrine or autocrine tissue factor. IGF-I plays a major role in regulating the growth of cells in vivo and in vitro and initiates metabolic and mitogenic processes in a wide variety of cell types by binding to specific type I receptors in the plasma membrane. In this study, we report the distribution of IGF-I receptors in odontogenic cells at the ultrastructural level using the high resolution protein A-gold technique. In the pre-secretory stage, very little gold label was visible over the ameloblasts and odontoblasts. During the secretory stage the label was mostly seen in association with the cell membranes and endoplasmic reticulum of the ameloblasts. Lysosome-like elements in the post-secretory stage were labelled as well as multivesicular dense bodies. Very little labelling was encountered in the ameloblasts in the transitional stage, where apoptotic bodies were clearly visible. The maturation stage also exhibited labelling of the secretory-like granules in the distal surface. The presence of gold particles over the plasma membrane is an indication that IGF-I receptor is a membrane-bound receptor. Furthermore, the intracellular distribution of the label over the endoplasmic reticulum supports the local synthesis of the IGF-I receptor. The absence of labelling over the transitional ameloblasts suggests that the transitional stage may require the non-expression of IGF-I as a prerequiste or even a trigger for apoptosis.

Apoptosis in rat incisor ameloblasts: An ultrastructural study.

Corticosteroids are widely used today in the medical treatment of many chronic illnesss. It has hem well docunnented that corticosteroids affect hone metabolism and this rnaie concemas as so the effect of coeticosteroid treatent on orthodontic tooth movemiernt. The aimn of this study was to determine Ithe effect of an elevated physiologic level of corticosteroid on bone rmnodeling daring orthodontic movement. Twelve 9-weak old adult male Wisuar rate were divided into two groups- a corticosteroid treated group (n=6) and a control group (n=6). The corticosteroid treate group was admiinistered ltngik of oral prednisolone daily for a 12-day induction period, while the control group received the equivalent volumes of saline for the tame liTme period. Following thin induction period, an orthodontiC appiance was ligated between the maxillary first left molar and two nmaxillary central incisors such thata menia force of 30g wasW T R W generated. The molar on the right skide was used an the son-appliance control. All sanimals were sacrificedIT WDR after 12 days of appliance wear. The magnitude of tooth mnovement was recoorded. Maxillse were fixed, demineralised and processed to paraffin. Sagittal sections of the first molar were staned with harmatoxylin and cosin and for turtrate-resistant acid phosphatase (TRAP) activity. For thin dose of prednisolone, there are no significant differences (p<0.05) in the magnitude of tooth imovement between the treated and control groups. Steroid treaed rats displayed lens root resorption along the length of the root on the coespressive side as well as fewer TRAP positive cells widthin the PDL space of the comspressive side, conmpaed to the non-sterid control (p.Z0.05). There was more TRAP activity recorded along the tension-side alveolar bone surface (cervcal third) in the steroid treated rats comspared to the son steroid controls (pr0O05). The rate of orthodontic movements was unaffected by lessgIsa of orednisolone. The easth of root renemtion alon th menial comprenson side and the TRAP activity at the comoression side PDL were both reduced. suagenlise that a susorenion of clastic activity had taken place. This study was supported by an ADRF grat.