Disturbed tooth eruption in osteopetrotic (op/op) mice: histopathogenesis of tooth malformation and odontomas

Histological characteristics of macrodontic cheek teeth of guinea pigs

Macrodontia is the enlargement of tooth dimensions of different ethologies. This work aims to show a histological evaluation of macrodontic teeth in guinea pigs. The material was obtained from animals postmortem. Ninety structural changes derived from 24 guinea pigs were evaluated. All teeth used in the study showed macrodontic changes. The samples were decalcified, dehydrated and embedded in paraffin. Material was cut in the transverse and longitudinal planes in relation to the alveolar bone. Histological evaluation included apical bud cells, pulp cavity cells, periodontium, dentin, enamel, cementum and alveolar bone tissue. Individual elements were evaluated with respect to their morphology and distribution. Moreover, the arrangement of the individual hard tooth structures was assessed on the teeth. No atypia was found among the cells that make up the apical bud, pulp or periodontal cavity. Displacement of periodontal cells or odontoblasts towards the pulp cavity as well as disorganization of the cell system in the pulp cavity were observed. Changes in the dentine ligaments and the reconstruction of the alveolar bone were also observed in areas where dentine and cement systems were affected. Dental slides were observed and showed that the enamel is also involved in structural remodelling of the pulp cavity. The histological assessment revealed that structural changes in macrodontic teeth involve the rearrangement of typical tooth tissues.

Complex Odontoma in a Young Captive Reticulated Giraffe (Giraffa camelopardalis reticulata)

Complex odontoma is a rare odontogenic lesion reported in rodents (order: Rodentia) and odd-toed ungulates (order: Perissodactyla), to name a few, and only in bovine animals of the order Artiodactyla. A 3-year-old female giraffe presented with a steadily proliferating, firm mass in the rostral mandible. With further expansion and ulceration of the mass, the general condition of the giraffe deteriorated and it was euthanized. Post-mortem examination revealed greyish-white tissue with an irregular arrangement of yellowish hard tissue arranged in thin plates and intermingled areas of greyish soft tissue. Histologically, irregular proliferated odontogenic epithelium and mesenchyme, dentin, cementum and empty spaces, suggestive of decalcified enamel, were present. These findings are consistent with a diagnosis of complex odontoma, which should be added to the differential diagnoses of oral tissue proliferations in giraffes. To our knowledge, this is the first description of a complex odontoma in a giraffe.

Nicotinamide Improves Delayed Tooth Eruption in Runx2+/- Mice

Patients with cleidocranial dysplasia (CCD) caused by mutations in RUNX2 have severe dental anomalies, including delayed or absent eruption of permanent teeth. This requires painful and expensive surgical/orthodontic intervention because of the absence of medicine for this condition. Here, we demonstrate that nicotinamide, a vitamin B3 and class III histone deacetylase inhibitor, significantly improves delayed tooth eruption in Runx2^+/- mice, a well-known CCD animal model, through the restoration of decreased osteoclastogenesis. We also found that Csf1 mRNA and protein levels were significantly reduced in Runx2^+/- osteoblasts as compared with wild type whereas RANKL and OPG levels had no significant difference between wild type and Runx2^+/- osteoblasts. The nicotinamide-induced restoration of osteoclastogenesis of bone marrow-derived macrophages in Runx2^+/- mice was due to the increased expression of RUNX2 and CSF1 and increased RANKL/OPG ratio. RUNX2 directly regulated Csf1 mRNA expression via binding to the promoter region of the Csf1 gene. In addition, nicotinamide enhanced the RUNX2 protein level and transacting activity posttranslationally with Sirt2 inhibition. Taken together, our study shows the potential and underlying molecular mechanism of nicotinamide for the treatment of delayed tooth eruption by using the Runx2^+/- murine model, suggesting nicotinamide as a candidate therapeutic drug for dental abnormalities in patients with CCD.

Role of osteoclasts in oral homeostasis and jawbone diseases

The jawbone is a unique structure as it serves multiple functions in mastication. Given the fact that the jawbone is remodeled faster than other skeletal bones, bone cells in the jawbone may respond differently to local and systemic cues to regulate bone remodeling and adaptation. Osteoclasts are bone cells responsible for removing old bone, playing an essential role in bone remodeling. Although bone resorption by osteoclasts is required for dental tissue development, homeostasis and repair, excessive osteoclast activity is associated with oral skeletal diseases such as periodontitis. In addition, antiresorptive medications used to prevent bone homeostasis of tumors can cause osteonecrosis of the jaws that is a major concern to the dentist. Therefore, understanding of the role of osteoclasts in oral homeostasis under physiological and pathological conditions leads to better targeted therapeutic options for skeletal diseases to maintain patients' oral health. Here, we highlight the unique features of the jawbone compared to the long bone and the involvement of osteoclasts in the jawbone-specific diseases.

Ectodermal and ectomesenchymal marker expression in primary cell lines of complex and compound odontomas: a pilot study

BACKGROUND

Odontomas are odontogenic tumors with hamartoma features that are classified as compound or complex. Our objective was to characterize the proliferation of ectodermal and ectomesenchymal profile markers of primary cell cultures of complex and compound odontomas.

METHODS

Four samples of compound odontomas (OdCm) and three of complex odontomas (OdCx) were obtained from patients attending the Oral Pathology and Medicine Clinic of the Graduate Dental School, National Autonomous University of Mexico for primary culture generation. MTT, immunocytochemistry and RT-PCR assays of CD34, Sox2, Amel, Ambn, p21, EDAR, Msx1, Msx2, Pax9, RUNX2, BSP, OPN, Barx1 and GAPDH (control) were performed. Additionally, six paraffin-embedded odontomas were obtained for immunocytochemistry and RT-PCR validation assays. The mean and standard deviation were determined, and ANOVA and Kruskall-Wallis tests were performed.

RESULTS

Cultured compound odontoma exhibited higher proliferation, and an ectomesenchymal immunocytochemistry profile with predominant expression of Amel, BSP, Pax9, EDAR, Barx and Msx2; in complex cultured odontoma Sox2, CD34, RUNX2 and OPN predominated. Our statistical analysis showed a significant difference in PCR analysis (P<0.05) for OPN and CD34. Paraffin-embedded odontomas showed similar pattern with difference for NGFR and Sox2 for immunohistochemistry and EDAR, BARX1 and PAX9 for RT-PCR assays.

CONCLUSIONS

The results suggested heterogeneous behavior for both odontoma cell lines, because in compound odontomas predominant biomarkers are related to the enamel knot, late-stage odontogenesis and ectomesenchymal interactions; and in complex odontoma the significant expression of CD34 and OPN could be responsible for the difference behavior and mineralized amorphous structure.

Matrix Metalloproteinase-1 and Acid Phosphatase in the Degradation of the Lamina Propria of Eruptive Pathway of Rat Molars

The comprehension of dental pathogenesis and disorders derived from eruption failure requires a deep understanding of the molecular mechanisms underlying normal tooth eruption. As intense remodelling is needed during tooth eruption, we hypothesize that matrix metalloproteinase-1 (MMP-1) and acid phosphatase (ACP) play a role in the eruptive pathway degradation. We evaluated MMP-1-immunoexpression and the collagen content in the lamina propria at different eruptive phases. Immunohistochemistry and ultrastructural cytochemistry for detection of ACP were also performed. In the maxillary sections containing first molars of 9-, 11-, 13-, and 16-day-old rats, the birefringent collagen of eruptive pathway was quantified. MMP-1 and ACP-2 immunohistochemical reactions were performed and the number of MMP-1-immunolabelled cells was computed. Data were analyzed by one-way ANOVA and Tukey post-test (p ≤ 0.05). ACP cytochemistry was evaluated in specimens incubated in sodium β-glycerophosphate. In the eruptive pathway of 13- and 16-day-old rats, the number of MMP-1-immunolabelled cells increased concomitantly to reduction of collagen in the lamina propria. Enhanced ACP-2-immunolabelling was observed in the lamina propria of 13- and 16-day-old rats. Fibroblasts and macrophages showed lysosomes and vacuoles containing fragmented material reactive to ACP. MMP-1 degrades extracellular matrix, including collagen fibers, being responsible for the reduction in the collagen content during tooth eruption. The enhanced ACP activity at the mucosal penetration stage indicates that this enzyme plays a role in the degradation of remnant material, which is engulfed by macrophages and fibroblasts of the eruptive pathway. Therefore, enzymatic failure in the eruptive pathway may disturbs tooth eruption.

Apical Elongation of Molar Teeth in Captive Microtus Voles

Molar apical elongation (MAE) was the leading cause for euthanasia or death in a captive breeding colony of endangered Amargosa voles ( Microtus californicus scirpensis). Clinical signs included ocular discharge, abnormal mastication, dyspnea, abnormal mentation, weight loss, and death. Although the severity varied, all molars in all quadrants were affected. When severe, the overgrown molar reserve crown and apex protruded into the nasal meatuses, the orbit, the calvarial vault and through the ventral margin of the mandible. Overall prevalence in the colony was 63% (92/146 voles) and increased to 77% in aged voles (>1 year). Mean age of onset was 5.3 months (1.7-11.2 months). Progression to extreme severity occurred over 1 to 3 months. Mean survival was 10.9 months (7.1-21.7 months). Histologically, the lesion was characterized by odontogenic hyperplasia and dysplasia. MAE was also documented in museum specimens of 2 other M. californicus subspecies ( M. californicus californicus, M. californicus vallicola) and 3 other Microtus species ( M. montanus, M. pennsylvanicus, M. socialis). In the M. californicus californicus collection, overall prevalence was 35.1% (129/368 skulls) and increased to 77.3% in aged voles (>1 year). A probable genetic influence was identified in the museum collection of M. californicus californicus. The etiopathogenesis of MAE is likely multifactorial, due to (1) inherent continuous odontogenic proliferation, (2) inadequate occlusal attrition, and (3) possible heritable disease susceptibility. In captivity, dietary or other management of occlusal attrition to prevent or delay MAE is a fundamental concern.

Anatomy and Disorders of the Oral Cavity of Rat-like and Squirrel-like Rodents

The order Rodentia comprises more than 2000 species divided into 3 groups based on anatomic and functional differences of the masseter muscle. Myomorph and sciuromorph species have elodont incisors and anelodont cheek teeth, unlike hystrichomorph species which have full anelodont dentition. Diseases of incisors and cheek teeth of rat-like and squirrel-like rodents result in a wide variety of symptoms and clinical signs. Appropriate diagnostic testing and imaging techniques are required to obtain a definitive diagnosis, formulate a prognosis, and develop a treatment plan. A thorough review of elodontoma, odontoma, and pseudo-odontoma is provided, including treatment of pseudo-odontomas in prairie dogs.

Clinical parameter of odontoma with special emphasis on treatment of impacted teeth-a retrospective multicentre study and literature review

OBJECTIVES

Odontoma-separated into complex (CxOD) and compound (CpOD) subtypes-represents the most frequent odontogenic malformation. Retention of permanent teeth is a common symptom. Therefore, in a series of odontomas, an analysis of the management of retained teeth was conducted.

MATERIALS AND METHODS

In a retrospective multicenter study of two University Medical Centers and one private praxis in Germany, demographic and clinical data regarding odontomas from 01/2000-03/2015 were obtained. In particular, the influence of operative therapy on the dentition and on the treatment of impacted teeth was analyzed.

RESULTS

Forty-five patients with 15 CxOD and 30 CpOD were included. Initial symptoms were delayed eruption of permanent teeth (n = 11), pain (n = 4), and swellings (n = 2); 28 cases were discovered by incidence, all of them via panoramic radiographs. The mandible/maxilla ratio was about 1:0.55 (29/16). Thirty-five out of 45 odontomas were in close proximity of at least one tooth (n = 16 at molars). A total of 14 teeth were extracted (CxOD: n = 5; CpOD: n = 9). Extractions had to be conducted more often in older patients (mean age 39.8 vs. 25.6 years). Of the non-extracted teeth, 8 teeth were displaced and retained. Of those, 4 teeth were aligned in the dental arch via orthodontic help and 2 teeth erupted spontaneously after operation during the follow-up period. In all cases, no relapse was seen.

CONCLUSION

Odontomas can cause displacement as well as malformation and resorption of the adjacent teeth.

CLINICAL RELEVANCE

Mostly, removal of odontomas is conducted. Extirpation of odontoma can allow for normal tooth eruption, often rendering extractions avoidable. Orthodontic alignment, though sometimes challenging, is a reasonable therapeutic option. These findings underline the value of the panoramic radiograph in preventive dentistry in younger patients.

Root and Eruption Defects in c-Fos Mice Are Driven by Loss of Osteoclasts

c-Fos homozygous mice lack osteoclasts with a failure of the teeth to erupt and with an arrest of root development. Here, we characterize the defects associated with the failure in root development and the loss of the tooth-bone interface, and we investigate the underlying causes. We show that, while homozygous c-Fos mice have no multinucleated osteoclasts, heterozygous mice have a reduction in the number of osteoclasts with a reduction in the tooth-bone interface during development and subtle skeletal defects postnatally. In the homozygous mutants bone is found to penetrate the tooth, particularly at the apical end, physically disrupting the root forming HERS (Hertwig's epithelial root sheath) cells. The cells of the HERS continue to proliferate but cannot extend downward due to the presence of bone, leading to a loss of root formation. Tooth germ culture showed that the developing tooth invaded the static bone in mutant tissue, rather than the bone encroaching on the tooth. Although c-Fos has been shown to be expressed in developing teeth, the defect in maintenance of the tooth-bone interface appears to be driven solely by the lack of osteoclasts, as this defect can be rescued in the presence of donor osteoclasts. The rescue suggests that signals from the tooth recruit osteoclasts to clear the bone from around the tooth, allowing the tooth to grow, form roots, and later erupt.

Elodontoma in Two Guinea Pigs

Elodontoma was diagnosed in two pet guinea pigs, one involving a maxillary premolar tooth and the other affecting a mandibular incisor tooth. Diagnostic imaging, including radiographs, computed tomography, and oral endoscopy was performed in order to quantify dental disease. Diagnostic imaging was also used to guide treatment of acquired dental disease, which included intraoral restoration of normal occlusal plane and tooth extraction using an extraoral approach. These are the first histologically confirmed cases of elodontoma in guinea pigs.

Infant cynomolgus monkeys exposed to denosumab in utero exhibit an osteoclast-poor osteopetrotic-like skeletal phenotype at birth and in the early postnatal period

RANKL is a key regulator of bone resorption and osteoclastogenesis. Denosumab is a fully human IgG2 monoclonal antibody that inhibits bone resorption by binding and inhibiting the activity of RANKL. To determine the effects of denosumab on pre- and postnatal skeletal growth and development, subcutaneous injections of 0 (control) or 50 mg/kg/month denosumab were given to pregnant cynomolgus monkeys from approximately gestation day (GD) 20 until parturition (up to 6 doses). For up to 6 months postpartum (birth day [BD] 180/181), evaluation of the infants included skeletal radiographs, bone biomarkers, and oral examinations for assessment of tooth eruption. Infant bones were collected at necropsy for densitometry, biomechanical testing, and histopathologic evaluation from control and denosumab-exposed infants on BD1 (or within 2 weeks of birth) and BD181, and from infants that died or were euthanized moribund from BD5 to BD69. In all denosumab-exposed infants, biomarkers of bone resorption and formation were markedly decreased at BD1 and BD14 and slightly greater at BD91 vs. control, then similar to control values by BD181. Spontaneous long bone fractures were detected clinically or radiographically in 4 denosumab-exposed infants at BD28 and BD60, with evidence of radiographic healing at ≥BD60. In BD1 infants exposed to denosumab in utero, radiographic evaluations of the skeleton revealed decreased long bone length; a generalized increased radio-opacity of the axial and appendicular skeleton and bones at the base of the skull with decreased or absent marrow cavities, widened growth plates, flared/club-shaped metaphysis, altered jaw/skull shape, and reduced jaw length; and delayed development of secondary ossification centers. Densitometric evaluations in these infants demonstrated a marked increase in bone mineral density at trabecular sites, but cortical bone mineral density was decreased. Histologically, long bone cortices were attenuated and there was an absence of osteoclasts. Bones with active endochondral ossification consisted largely of a dense network of retained primary spongiosa with reduced marrow space consistent with an osteopetrotic phenotype. A minimal increase in growth plate thickness largely due to the expansion of the hypertrophic zone was present. Retained woven bone was observed in bones formed by intramembranous ossification, consistent with absence of bone remodeling. These changes in bone tissue composition and geometry were reflected in reduced biomechanical strength and material properties of bones from denosumab-exposed infants. Material property changes were characterized by increased tissue brittleness reflected in reductions in calculated material toughness at the femur diaphysis and lack of correlation between energy and bone mass at the vertebra; these changes were likely the basis for the increased skeletal fragility (fractures). Although tooth eruption was not impaired in denosumab-exposed infants, the reduced growth and increased bone density of the mandible resulted in dental abnormalities consisting of tooth malalignment and dental dysplasia. Radiographic changes at BD1 persisted at BD28, with evidence of resumption of bone resorption and remodeling observed in most infants at BD60 and/or BD90. In 2 infants euthanized on BD60 and BD69, there was histologic and radiographic evidence of subphyseal/metaphyseal bone resorption accompanied by multiple foci of ossification in growth plates that were markedly increased in thickness. In infants necropsied at BD181, where systemic exposure to denosumab had been below limits of quantitation for approximately 3months, there was largely full recovery from all bone-related changes observed earlier postpartum, including tissue brittleness. Persistent changes included dental dysplasia, decreased bone length, reduced cortical thickness, and decreased peak load and ultimate strength at the femur diaphysis. In conclusion, the skeletal and secondary dental effects observed in infant monkeys exposed in utero to denosumab are consistent with the anticipated pharmacological activity of denosumab as a monoclonal antibody against RANKL and inhibitor of osteoclastogenesis. The resulting inhibition of resorption impaired both bone modeling and remodeling during skeletal development and growth. The skeletal phenotype of these infant monkeys resembles human infants with osteoclast-poor osteopetrosis due to inactivating mutations of RANK or RANKL.

A rare association of compound odontome with missing lateral incisor

Odontomas are a common type of odontogenic tumor, usually asymptomatic and mostly detected on routine radiographic examination. An 11-years-old male child with the chief complaint of mobility of deciduous dentition in the upper front region was diagnosed with an odontome with an impacted central incisor, missing lateral incisor and retained deciduous incisors following radiographic analysis. Histopathology revealed a compound odontoma following a conservative enucleation. Odontomas associated with primary dentition, impacted teeth and erupting into oral cavity have been described, but the association with a missing lateral incisor makes this an interesting case report.

How to cite this article: Nammalwar RB, Moses J. A Rare Association of Compound Odontome with Missing Lateral Incisor. Int J Clin Pediatr Dent 2014;7(1):50-53.

Interactions of the tooth and bone during development

The tooth works as a functional unit with its surrounding bony socket, the alveolar bone. The growth of the tooth and alveolar bone is co-ordinated so that a studied distance always separates the 2, known as the tooth-bone interface (TBI). Lack of mineralization, a crucial feature of the TBI, creates the space for the developing tooth to grow and the soft tissues of the periodontium to develop. We have investigated the interactions between the tooth and its surrounding bone during development, focusing on the impact of the developing alveolar bone on the development of the mouse first molar (M1). During development, TRAP-positive osteoclasts are found to line the TBI as bone starts to be deposited around the tooth, removing the bone as the tooth expands. An enhancement of osteoclastogenesis through RANK-RANKL signaling results in an expansion of the TBI, showing that osteoclasts are essential for defining the size of this region. Isolation of the M1 from the surrounding mesenchyme and alveolar bone leads to an expansion of the tooth germ, driven by increased proliferation, indicating that, during normal development, the growth of the tooth germ is constrained by the surrounding tissues.

Osteoclasts and odontoclasts: signaling pathways to development and disease

Osteoclasts are cells essential for physiologic remodeling of bone and also play important physiologic and pathologic roles in the dentofacial complex. Osteoclasts and odontoclasts are necessary for tooth eruption yet result in dental compromise when associated with permanent tooth internal or external resorption. The determinants that separate their physiologic and pathologic roles are not well delineated. Clinical cases of primary eruption failure and root resorption are challenging to treat. Mineralized tissue resorbing cells undergo a fairly well characterized series of differentiation stages driven by transcriptional mediators. Signal transduction via cytokines and integrin-mediated events comprise the detailed pathways operative in osteo/odontoclastic cells and may provide insights to their targeted regulation. A better understanding of the unique aspects of osteoclastogenesis and osteo/odontoclast function will facilitate effective development of new therapeutic approaches. This review presents the clinical challenges and delves into the cellular and biochemical aspects of the unique cells responsible for resorption of mineralized tissues of the craniofacial complex.

Administration of the bisphosphonate zoledronic acid during tooth development inhibits tooth eruption and formation and induces dental abnormalities in rats

Bisphosphonates (BPs) are potent inhibitors of osteoclastic bone resorption and widely used for the treatment of osteoporosis and metastatic bone diseases. Recently, BPs have also been shown to benefit children with primary and secondary osteoporosis, including osteogenesis imperfecta; however, their long-term safety has not been established yet. Clinical and experimental studies have demonstrated that BPs delay or inhibit tooth eruption. The failure of tooth eruption causes several dental abnormalities. In this study, to determine the effects of BPs on tooth formation, the BP zoledronic acid (ZOL) was injected into 7- and 14-day-old rats, and the development of the mandibular teeth was examined. X-ray analysis demonstrated that ZOL inhibited the eruption of both incisors and molars and their formation, especially in the molar roots. Histological examination showed that, in ZOL-treated animals, alveolar bone remained unresorbed around tooth crowns, which injured ameloblasts and enamel matrix, leading to defects of the enamel. Furthermore, haphazard proliferation of odontogenic epithelium and mesenchyme associated with primitive tooth structures, which resembles human odontomas, was induced at the basal end of incisors but not around the molars. Tooth ankylosis to alveolar bone was occasionally observed in molars. These results suggest that administration of BPs during tooth development has the potential to inhibit tooth eruption and formation and to induce several types of dental abnormalities, which may be attributed to the altered osteoclastic activities.

A new osteopetrosis mutant mouse strain (ntl) with odontoma-like proliferations and lack of tooth roots

A new spontaneous mouse mutant (ntl) with autosomal-recessive osteopetrosis was characterized. These mice formed tartrate-resistant acid phosphate (TRAP)-positive osteoclasts but their osteoclasts had no ruffled border and did not resorb bone. These mice displayed no tooth eruption or tooth root formation. Adult mutant mice developed odontoma-like proliferations near the proximal ends of the incisors. Intraperitoneal injection of progenitor cells from the liver of 16.5 days postcoitum wild-type embryos into newborn mutants rescued the osteopetrosis phenotype, indicating that the defects were intrinsic to the osteoclasts. Our findings not only provide further support for a critical role of osteoclasts in tooth eruption and tooth root development, but also suggest that the perturbation of the homeostasis of the odontogenic precursors of the incisors is primarily responsible for the development of the odontoma-like proliferations in this osteopetrosis mutant. Genetic mapping has narrowed down the location of the mutant allele to a genetic interval of 3.2 cM on mouse chromosome 17.

OPG knockout mouse teeth display reduced alveolar bone mass and hypermineralization in enamel and dentin

Recent studies showed that local injection or upregulation of OPG gene would result in early temporal retardation of tooth development. It was assumed that this retardation might cause defective tooth mineralization and pulp formation as the long-term effects. However, since those OPG treatments were transient, any possible long-term effects of OPG addition could not be assessed previously. In the present study, a high-resolution microCT was used to evaluate the long-term effect of OPG gene deprivation on the mineralization and morphology of mouse tooth. Our results showed that the mineralization of alveolar bone in OPG(-/-) mouse tooth was decreased while those of enamel and dentin were increased, compared with the wild-type (WT) group. The labial and lingual dentin thicknesses of OPG(-/-) group were significantly higher and with larger area in enamel and dentin than those of WT group. The size of pulp chamber was also substantially decreased in OPG(-/-) mouse incisor. Different responses in mineralization and morphogenesis to OPG gene deprivation were found between bone and tooth. These effects may be independent of the early odontogenesis, and further studies are warranted to investigate the molecular mechanism of the effect of OPG gene expression on bone formation and later tooth development.

Increased connective tissue extracellular matrix in the op/op model of osteopetrosis

Mice that are homozygous for the recessive osteopetrosis spontaneous mutation (op/op) develop severe osteopetrosis due to a defect in the production of macrophage colony-stimulating factor (M-CSF) and a deficiency in monocyte-derived osteoclasts. Our study describes a novel soft tissue finding in an osteopetrosis (B6C3Fe a/a-Csf1(op)/J) mouse model. Tissues were obtained from B6C3Fe a/a-Csf1(op)/J mice and age-matched wild-type mice, processed for hematoxylin and eosin sections, and comprehensive light microscopic tissue evaluation was performed. Mutant mice had characteristic traits of op/op deficiency including missing incisors and domed skulls. Histologically, the bone marrow cavity was effaced by interweaving thick bony trabeculae consistent with osteopetrosis. An increase in a finely granular, basophilic interstitial extracellular matrix (ECM) was observed in the subcutaneous connective tissue of the op/op mice when compared with controls. Histochemically, the ECM was negative with periodic acid Schiff and stained dark blue with alcian blue at a pH of 2.5, indicating that it is composed primarily of nonsulfated glycosaminoglycans (GAGs). This work suggests an increased ECM that is composed mainly of GAGs located in the subcutaneous tissue in op/op mice. This increase in ECM may be related to altered matrix production or turnover because of changes in M-CSF production.

Erupted compound odontoma: case report of a 15-year-old Sudanese boy with a history of traditional dental mutilation

A rare case of an erupted compound odontoma associated with a malformed and dilacerated maxillary left lateral incisor is reported. The patient, a 15-year-old immigrant Sudanese boy, had a malformed right lateral maxillary incisor and missing centrals. His guardian reported he had undergone traditional extraction of his primary teeth as a child whilst in Africa. Treatment and possible mechanisms for development of the condition are discussed. The number of refugees and migrants from Africa to developed countries has increased in the past 20 years. Australia in particular with its large population of recent migrants from areas in Africa where tooth mutilation is practised will likely see more patients with dental abnormalities in the respective populations.

Characterization of excess hard tissue occurring in the mesio-buccal surface of the mandibular first molar in microphthalmic mouse

OBJECTIVE

The aim of the present study was to characterize the excess hard tissue on the mandible of the microphthalmic mouse having a mutation at the mitf locus.

DESIGN

Homozygous mutant (mi/mi) and wild-type (+/+) mice were obtained by mating a breeding pair (strain name, B6C3Fe a/a-Mitf(mi)/J). We used mi/mi and +/+ mice at ages 6, 7, 8, 9, 28, and 49 days for micro-computed tomographic and histologic analyses.

RESULTS

Excess hard tissue was found on the mesio-buccal surface of the mandibular first molar in all 11mi/mi mice, but none was found in the 8mi/+ or 14 +/+ mice. The excess hard tissue was located in the mental foramen connected to the mandibular canal. The mandibular canal passed near the basal part of the incisor and the root of the mandibular first molar due to aberrant development of the teeth and mandible. The excess hard tissue contained predentine immunostained for dentine sialoprotein, a marker for early stages of dentinogenesis, which was first observed at about 7 days of age. Dentine, predentine, pulp, and root-like structures were observed in the excess hard tissue, but neither enamel nor enamel organ was observed.

CONCLUSION

Odontogenic cells in the basal part of the incisor and/or the mandibular first molar with the ability to develop into odontoblasts and pulp cells appeared to migrate through the mandibular canal to the mental foramen, where they developed into odontoblasts and pulp-like cells, and then formed dentine and predentine-like structures.

Targeted expression of csCSF-1 in op/op mice ameliorates tooth defects

OBJECTIVE

The aim of this study was to characterize the tooth phenotype of CSF-1-deficient op/op mice and determine whether expression of csCSF-1 in these mice has a role in primary tooth matrix formation.

DESIGN

Ameloblasts and odontoblasts, isolated from wt/wt frozen sections using laser capture microdissection, were analysed for csCSF-1, sCSF-1 and CSF-1R mRNA by RT-PCR. Mandibles, excised from 8 days op/op and wt/wt littermates, were examined for tooth morphology as well as amelogenin and DMP1 expression using in situ hybridisation. op/opCS transgenic mice, expressing csCSF-1 in teeth and bone using the osteocalcin promoter, were generated. Skeletal X-rays and histomorphometry were performed; teeth were analysed for morphology and matrix proteins.

RESULTS

Normal dental cells in vivo express both CSF-1 isoforms and CSF-1R. Compared to wt/wt, op/op teeth prior to eruption showed altered dental cell morphology and dramatic reduction in DMP1 transcripts. op/opCS mice showed marked resolution of osteopetrosis, tooth eruption and teeth that resembled amelogenesis imperfecta-like phenotype. At 3 weeks, op/op teeth showed severe enamel and dentin defects and barely detectable amelogenin and DMP1. In op/opCS mice, DMP1 in odontoblasts increased to near normal and dentin morphology was restored; amelogenin also increased. Enamel integrity improved in op/opCS, although it was thinner than wt enamel.

CONCLUSIONS

Results demonstrate that ameloblasts and odontoblasts are a source and potential target of CSF-1 isoforms in vivo. Expression of csCSF-1 within the tooth microenvironment is essential for normal tooth morphogenesis and may provide a mechanism for coordinating the process of tooth eruption with endogenous matrix formation.

Odontoma-like Tumours of Squirrel Elodont Incisors—Elodontomas

Since 2003, nine squirrels were presented at a South African veterinary dental practice with lesions in the maxilla consistent with the clinical, radiological and histological features of odontomas as described in prairie dogs, rats and mice. These odontoma-like masses have not previously been described in squirrels. This report describes the clinico-pathological features and possible pathogenesis of the lesions and proposes the term "elodontoma" for these hamartomatous odontogenic lesions in the jaws of animals with continuously erupting (elodont) teeth.

Osteoclast diseases and dental abnormalities

Tooth eruption depends on the presence of osteoclasts to create an eruption pathway through the alveolar bone. In diseases where osteoclast formation, or function is reduced, such as the various types of osteopetrosis, tooth eruption is affected. Diseases in which osteoclast formation or activity is increased, such as familiar expansile osteolysis and Paget's disease, are associated with dental abnormalities such as root resorption and premature tooth loss. Less is known about the origin of the dental problems in these conditions as there are no rodent models of these diseases as yet. In this short review, the genes currently known to be mutated in human osteoclast diseases will be reviewed and, where known, the effect of osteoclast dysfunction on dental development described. It will focus on human conditions and only mention rodent disease where no clear data in the human are available.

Delayed tooth eruption: pathogenesis, diagnosis, and treatment. A literature review

Delayed tooth eruption (DTE) is the emergence of a tooth into the oral cavity at a time that deviates significantly from norms established for different races, ethnicities, and sexes. This article reviews the local and systemic conditions under which DTE has been reported to occur. The terminology related to disturbances in tooth eruption is also reviewed and clarified. A diagnostic algorithm is proposed to aid the clinician in the diagnosis and treatment planning of DTE. The sequential and timely eruption of teeth is critical to the timing of treatment and the selection of an orthodontic treatment modality. This review addresses the need for a more in-depth understanding of the underlying pathophysiology of DTE and gives the clinician a methodology to approach its diagnosis and treatment.

Recruitment of osteoclasts in the mandible of osteopetrotic (op/op) mice

Osteoclasts in osteopetrotic (op/op) mice are substantially reduced by the absence of functional activities of macrophage colony-stimulating factor (M-CSF). However, it is known that osteoclasts appear in op/op skeletal bones with aging, although the molecular mechanism for this is unknown. In order to investigate osteoclastic recruitment in the jaw bones of op/op mice, osteoclastic distribution was analysed for 2 yr after birth by histochemistry for tartrate-resistant acid phosphatase activity and immunohistochemistry for cathepsin K. Osteoclasts in op/op mandibular bones decreased rapidly in number after birth and disappeared by 3 d, although there was no difference in the osteoclastic distribution between op/op and normal littermates at birth. At 2 wk, osteoclasts began to reappear around op/op tooth germs, where no apparent connective tissue layer intervened between tooth germs and bone trabeculae. They increased in number and were scattered over the mandible, reaching a maximum at 8 wk, when periodontal ligament-like structures were recognizable around incisor germs. Osteoclasts then again decreased gradually, and after 62 wk few osteoclasts were seen in op/op mandibular bones, whose marrow space disappeared. These findings suggest that osteoclasts are recruited in an M-CSF-independent manner in op/op mandibles, especially in areas around tooth germs.

No developmental failure of cultured tooth germs from osteopetrotic (op/op) mice

BACKGROUND

Incisor tooth germs of osteopetrotic (op/op) mice are known to fail to erupt, but form odontomas in their root apices instead, due to invasion of alveolar bone trabeculae into the tooth germs. The purpose of this study is to determine if the tooth developmental failures in op/op mice are intrinsic or secondarily arise as a result of the defective bone metabolism due to lack of macrophage colony-stimulating factor (M-CSF).

METHODS

We isolated mandibular first molar tooth germs from normal and op/op mice and cultured them under conditions with or without bone tissues which had been formed around tooth germs.

RESULTS

Tooth germs from normal mice, cultured for a week, showed almost the same developmental features as those of mice with the corresponding age. They were surrounded with dental follicular tissues and were never invaded by bone trabeculae. On the other hand, op/op tooth germs cultured in the presence of bone components were invaded by alveolar bone trabeculae around tooth germs in the same manner as shown in vivo. When cultured without bone, they developed without any interruptions.

CONCLUSIONS

These findings indicated that op/op tooth germs had potential for normal development and that their abnormal development was a secondary phenomenon caused by lack of bone remodeling in the early phase of odontogenesis.