Permanent teeth in hypophosphatasia: light and electron microscopic study

Root resorptions induced by genetic disorders: A systematic review

OBJECTIVES

Root resorption in permanent teeth is a common pathological process that often follows dental trauma or orthodontic treatment. More rarely, root resorption is a feature of genetic disorders and can help with diagnosis. Thus, the present review aims to determine which genetic disorders could induce pathological root resorptions and thus which mutated genes could be associated with them.

METHODS

We conducted a systematic review following the PRISMA guidelines. Articles describing root resorptions in patients with genetic disorders were included from PubMed, Embase, Web of Science, and Google Scholar. We synthesized the genetic disorder, the type, severity, and extent of the resorptions, as well as the other systemic and oral symptoms and histological features.

RESULTS

The synthetic analysis included 25 studies among 937 identified records. We analyzed 21 case reports, three case series, and one cohort study. Overall, we highlighted 14 different pathologies with described root resorptions. Depending on the pathology, the sites of resorption, their extent, and their severity showed differences.

CONCLUSION

With 14 genetic pathologies suspected to induce root resorptions, our findings are significant and enrich a previous classification. Among them, three metabolic disorders, three calcium-phosphorus metabolism disorders, and osteolysis disorders were identified.

Diagnosis and initial management of children presenting with premature loss of primary teeth associated with a systemic condition: A scoping review and development of clinical aid

BACKGROUND

Premature loss of primary teeth (PLPT) can be a rare presentation of systemic medical conditions. Premature loss of primary teeth may present a diagnostic dilemma to paediatric dentists.

AIMS

To identify systemic conditions associated with PLPT and develop a clinical aid.

DESIGN

OVID Medline, Embase and Web of Science were searched up to March 2023. Citation searching of review publications occurred. Exclusion occurred for conference abstracts, absence of PLPT and absence of English-language full text.

RESULTS

Seven hundred and ninety-one publications were identified via databases and 476 by citation searching of review articles. Removal of 390 duplicates occurred. Following the exclusion of 466 records on abstract review, 411 publications were sought for retrieval, of which 142 met inclusion criteria. Thirty-one systemic conditions were identified. For 19 conditions, only one publication was identified. The majority of publications, 91% (n = 129), were case reports or series. Most publications, 44% (n = 62), were related to hypophosphatasia, and 25% (n = 35) were related to Papillon-Lefèvre. Diagnostic features were synthesised, and a clinical aid was produced by an iterative consensus approach.

CONCLUSIONS

A diverse range of systemic diseases are associated with PLPT. Evidence quality, however, is low, with most diseases having a low number of supporting cases. This clinical aid supports paediatric dentists in differential diagnosis and onward referral.

A Review of Selected Dental Anomalies With Histologic Features in the Pediatric Patient

Unique dental conditions in children include odontogenic cysts and tumors, hereditary dental diseases, developmental anomalies, and lesions associated with the eruption of the primary or permanent teeth. Many of these conditions have long lasting effects on the adult dentition in terms of affecting esthetics, function, and overall quality of life. Inherited dental syndromes affect the dental hard tissues specifically the enamel, dentin, and/or cementum in a generalized manner, involving both primary and permanent teeth. These conditions manifest in altered quality or quantity of the hard tissues, leading to fragility, tooth loss and dental diseases such as caries, periapical pathology, and periodontal disease. This category includes amelogenesis imperfecta, dentinogenesis imperfecta, dentin dysplasia, hypophosphatasia, and hypophosphatemia. Developmental defects such as regional odontodysplasia are defined by involvement of the primary and permanent dentition in a localized manner, identified in early childhood. This review will elaborate on the histologic findings in these selected dental conditions with a discussion on clinical and radiographic findings, as well as molecular features wherever appropriate.

Different Dental Manifestations in Sisters with the Same ALPL Gene Mutation: A Report of Two Cases

Hypophosphatasia (HPP) is an inherited disease caused by mutation of the alkaline phosphatase (ALPL) gene in an autosomal dominant or an autosomal recessive manner. The main symptoms of HPP are bone hypomineralization and early exfoliation of the primary teeth. Some of the mutations identified in autosomal dominant families are reported to have dominant negative effects. In addition, the penetrance can vary among patients with the same variant even within the same family, resulting in various phenotypes of systemic symptoms. However, differences in dental symptoms between patients with HPP and carriers with the same ALPL variant have not been reported. Herein, we report on two sisters who had the same heterozygous ALPL variant with dominant negative effects. The older sister had bone and dental symptoms and was diagnosed with childhood HPP. In contrast, the younger sister was a carrier with no bone and dental symptoms. It can be inferred that this phenomenon was caused by the difference in penetrance. This case revealed that carriers with the ALPL mutation may have no dental symptoms characteristic of HPP. Because HPP is sometimes progressive, it is very important to carefully monitor carriers to detect the possible onset of dental and systemic symptoms.

Dental manifestation and management of hypophosphatasia

Hypophosphatasia is an inherited metabolic disorder characterized by defective mineralization of bones and teeth with a wide variety of manifestations, ranging from stillbirth to dental symptoms alone. Recently, the prognosis of severe hypophosphatasia patients has been greatly improved by the introduction of enzyme replacement therapy. The typical dental manifestation is early exfoliation of primary teeth due to disturbed cementum formation, so dentures are recommended to ensure that important oral functions are acquired. Some studies have shown that enzyme replacement therapy improves dental mineralization, resulting in the stabilization of periodontal tissues and better growth of tooth roots. A nationwide Japanese survey revealed the common genetic and dental manifestations of patients with mild hypophosphatasia, which markedly differ from those of the severe forms. There may be many undiagnosed mild patients, so dentists should contribute to the early diagnosis by screening possible cases based on the typical finding of early exfoliation of primary teeth. Early diagnosis is important for patients to receive early intervention in both medical and dental fields. The establishment of fundamental dental therapy to solve the dental problems is still underway and is eagerly anticipated.

GSK3β rephosphorylation rescues ALPL deficiency-induced impairment of odontoblastic differentiation of DPSCs

Background

Premature exfoliation of the deciduous teeth is a common manifestation in childhood patients with hypophosphatasia (HPP), which is an autosomal inherited disease caused by ALPL mutations. Dysplasia of the cementum, dentin, and alveolar bone has been proposed to be the main reasons for the exfoliation of teeth, while the extraordinarily complex intracellular mechanisms remain elusive. Dental pulp stem cells (DPSCs) have been demonstrated to successfully regenerate functional pulp-dentin-like tissue. Dental pulp cells derived from HPP patients impaired mineralization; however, insight into the deeper mechanism is still unclear.

Methods

The effects of ALPL on odontoblastic differentiation of DPSCs from HPP patient were assessed by Alizarin Red staining, immunofluorescent staining, Western blot and RT-PCR, and micro-CT assays.

Result

Here, we found DPSCs from HPP patient exhibited low ALP activity and impaired odontoblastic differentiation. Meanwhile, we found that loss of function of ALPL reduced phosphorylation of GSK3β in DPSCs. While GSK3β rephosphorylation improved odontoblastic differentiation of HPP DPSCs with LiCl treatment. Finally, we demonstrated systemic LiCl injection ameliorated tooth-associated defects in ALPL^+/− mice by enhanced phosphorylation of GSK3β in the teeth.

Conclusions

Our study indicates that ALPL regulates odontoblastic differentiation of DPSCs and provides useful information for understanding how ALPL deficiency led to tooth dysplasia and, ultimately, may inform efforts at improvement tooth defects in HPP patients.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02235-7.

Dental defects in the primary dentition associated with hypophosphatasia from biallelic ALPL mutations

ALPL encodes tissue-nonspecific alkaline phosphatase (TNAP), an enzyme expressed in bone, teeth, liver, and kidney. ALPL loss-of-function mutations cause hypophosphatasia (HPP), an inborn error-of-metabolism that produces skeletal and dental mineralization defects. Case reports describe widely varying dental phenotypes, making it unclear how HPP comparatively affects the three unique dental mineralized tissues: enamel, dentin, and cementum. We hypothesized that HPP affected all dental mineralized tissues and aimed to establish quantitative measurements of dental tissues in a subject with HPP. The female proband was diagnosed with HPP during childhood based on reduced alkaline phosphatase activity (ALP), mild rachitic skeletal effects, and premature primary tooth loss. The diagnosis was subsequently confirmed genetically by the presence of compound heterozygous ALPL mutations (exon 5: c.346G>A, p.A116T; exon 10: c.1077C>G, p.I359M). Dental defects in 8 prematurely exfoliated primary teeth were analyzed by high resolution micro-computed tomography (micro-CT) and histology. Similarities to the Alpl^-/- mouse model of HPP were identified by additional analyses of murine dentoalveolar tissues. Primary teeth from the proband exhibited substantial remaining root structure compared to healthy control teeth. Enamel and dentin densities were not adversely affected in HPP vs. control teeth. However, analysis of discrete dentin regions revealed an approximate 10% reduction in the density of outer mantle dentin of HPP vs. control teeth. All 4 incisors and the molar lacked acellular cementum by micro-CT and histology, but surprisingly, 2 of 3 prematurely exfoliated canines exhibited apparently normal acellular cementum. Based on dentin findings in the proband's teeth, we examined dentoalveolar tissues in a mouse model of HPP, revealing that the delayed initiation of mineralization in the incisor mantle dentin was associated with a broader lack of circumpulpal dentin mineralization. This study describes a quantitative approach to measure effects of HPP on dental tissues. This approach has uncovered a previously unrecognized novel mantle dentin defect in HPP, as well as a surprising and variable cementum phenotype within the teeth from the same HPP subject.

Dental manifestations of hypophosphatasia in children and the effects of enzyme replacement therapy on dental status: A series of clinical cases

The most frequent dental signs of hypophosphatasia in children are premature loss of primary teeth, decrease in height of alveolar bone, and malocclusions. Enzyme replacement therapy with Asfotase alfa might be associated with stabilization of dental status.

Evaluating the possible association between systemic osteoporosis and periodontal disease progression in postmenopausal women

To evaluate the association between systemic osteoporosis and periodontal diseases in postmenopausal women. A total of 300 women aged (50-70 years) were divided into an osteoporotic (OP) group (n = 150) and non-osteoporotic (NOP) group (n = 150) depending on BMD measured using (DXA) at the femoral neck and lumbar spine. Periodontal examination including PI, GI, PPD, and CAL was measured. A standard digital dental panoramic radiograph was taken for each patient and analyzed using specially developed software graphic program to assess the alveolar bone level and BMD. Elemental analysis of root surfaces of extracted teeth was done for detecting Ca, P, F, Mg, and K using (LIBS). Results showed the differences between both groups were not statistically significant in PI, GI, and PPD. A statistically significant difference was found between both groups in CAL, the distance between CEJ-AC and alveolar bone density. Elemental analysis of the root surfaces revealed that Ca was statistically significantly less in the OP group while the differences between both groups regarding F and P were not statistically significant. Mg and K found to be significantly more in the OP group than in the NOP group. To conclude osteoporosis is certainly a risk factor for periodontal disease and seems to plays a vital role in disease progression.

Hypophosphatasia: oral cavity and dental disorders

Dental anomalies exist in every subtype of hypophosphatasia (HPP), from the most severe to the most moderate, called odontohypophosphatasia. The forms are defined by the age at onset of the initial symptoms. These anomalies affect all dental mineralized tissues from enamel, dentin and cementum to alveolar bone in a gradient proportional to the severity of the disease. Early loss of the deciduous teeth, before 3 years of age, and then possibly of the permanent teeth, is due to an abnormality of the cementum, the tissue attaching the teeth to alveolar bone, and is the most frequent abnormality. Tooth loss is a very important diagnostic sign and needs to be recognized. Patients with HPP need specialized oral and dental care in coordination with the reference and expert centers. The oral and dental signs and their treatment remain poorly known. The recording of the abnormalities and their treatment in a registry is indispensable in order to enhance patient management and oral and dental health.

Hypophosphatasia: An overview For 2017

Hypophosphatasia (HPP) is the inborn-error-of-metabolism that features low serum alkaline phosphatase (ALP) activity (hypophosphatasemia) caused by loss-of-function mutation(s) of the gene that encodes the tissue-nonspecific isoenzyme of ALP (TNSALP). Autosomal recessive or autosomal dominant inheritance from among >300 TNSALP (ALPL) mutations largely explains HPP's remarkably broad-ranging severity. TNSALP is a cell-surface homodimeric phosphohydrolase richly expressed in the skeleton, liver, kidney, and developing teeth. In HPP, TNSALP substrates accumulate extracellularly. Among them is inorganic pyrophosphate (PPi), a potent inhibitor of mineralization. Superabundance of extracellular PPi explains the hard tissue complications of HPP that feature premature loss of deciduous teeth and often rickets or osteomalacia as well as calcific arthropathies in some affected adults. In infants with severe HPP, blocked entry of minerals into the skeleton can cause hypercalcemia, and insufficient hydrolysis of pyridoxal 5'-phosphate (PLP), the major circulating form of vitamin B₆, can cause pyridoxine-dependent seizures. Elevated circulating PLP is a sensitive and specific biochemical marker for HPP. Also, the TNSALP substrate phosphoethanolamine (PEA) is usually elevated in serum and urine in HPP, though less reliably for diagnosis. Pathognomonic radiographic changes occur in pediatric HPP when the skeletal disease is severe. TNSALP mutation analysis is essential for recurrence risk assessment for HPP in future pregnancies and for prenatal diagnosis. HPP was the final rickets/osteomalacia to have a medical treatment. Now, significant successes using asfotase alfa, a mineral-targeted recombinant TNSALP, are published concerning severely affected newborns, infants, and children. Asfotase alfa was approved by regulatory agencies multinationally in 2015 typically for pediatric-onset HPP.

Early Tooth Loss in Children: A Warning Sign of Childhood Hypophosphatasia

Premature exfoliation of primary teeth may be the first manifestation of this serious condition and the general dental practitioner plays an important role in recognizing dental anomalies and referring patients at an appropriate time. This is imperative to ensuring early diagnosis and good quality patient care. This article describes the case of a 4-year-old boy affected by childhood hypophosphatasia, who presented with premature exfoliation of his primary teeth as the first manifestation of this condition. An overview of the condition is outlined including a discussion of the likelihood of permanent dentition involvement. Clinical relevance: Oral manifestations of hypophosphatasia may be the first and the only signs of this condition and may be the basis upon which a diagnosis is made.

Cementum and Dentin in Hypophosphatasia

Hypophosphatasia (HPP) often leads to premature loss of deciduous teeth, due to disturbed cementum formation. We addressed the question to what extent cementum and dentin are similarly affected. To this end, we compared teeth from children with HPP with those from matched controls and analyzed them microscopically and chemically. It was observed that both acellular and cellular cementum formation was affected. For dentin, however, no differences in mineral content were recorded. To explain the dissimilar effects on cementum and dentin in HPP, we assessed pyrophosphate (an inhibitor of mineralization) and the expression/activity of enzymes related to pyrophosphate metabolism in both the periodontal ligament and the pulp of normal teeth. Expression of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) in pulp proved to be significantly lower than in the periodontal ligament. Also, the activity of NPP1 was less in pulp, as was the concentration of pyrophosphate. Our findings suggest that mineralization of dentin is less likely to be under the influence of the inhibitory action of pyrophosphate than mineralization of cementum.

Hypophosphatasia - aetiology, nosology, pathogenesis, diagnosis and treatment

Hypophosphatasia is the inborn error of metabolism characterized by low serum alkaline phosphatase activity (hypophosphatasaemia). This biochemical hallmark reflects loss-of-function mutations within the gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). TNSALP is a cell-surface homodimeric phosphohydrolase that is richly expressed in the skeleton, liver, kidney and developing teeth. In hypophosphatasia, extracellular accumulation of TNSALP natural substrates includes inorganic pyrophosphate, an inhibitor of mineralization, which explains the dento-osseous and arthritic complications featuring tooth loss, rickets or osteomalacia, and calcific arthopathies. Severely affected infants sometimes also have hypercalcaemia and hyperphosphataemia due to the blocked entry of minerals into the skeleton, and pyridoxine-dependent seizures from insufficient extracellular hydrolysis of pyridoxal 5'-phosphate, the major circulating form of vitamin B6, required for neurotransmitter synthesis. Autosomal recessive or dominant inheritance from ~300 predominantly missense ALPL (also known as TNSALP) mutations largely accounts for the remarkably broad-ranging expressivity of hypophosphatasia. High serum concentrations of pyridoxal 5'-phosphate represent a sensitive and specific biochemical marker for hypophosphatasia. Also, phosphoethanolamine levels are usually elevated in serum and urine, though less reliably for diagnosis. TNSALP mutation detection is important for recurrence risk assessment and prenatal diagnosis. Diagnosing paediatric hypophosphatasia is aided by pathognomic radiographic changes when the skeletal disease is severe. Hypophosphatasia was the last type of rickets or osteomalacia to await a medical treatment. Now, significant successes for severely affected paediatric patients are recognized using asfotase alfa, a bone-targeted recombinant TNSALP.

Malformations of the tooth root in humans

The most common root malformations in humans arise from either developmental disorders of the root alone or disorders of radicular development as part of a general tooth dysplasia. The aim of this review is to relate the characteristics of these root malformations to potentially disrupted processes involved in radicular morphogenesis. Radicular morphogenesis proceeds under the control of Hertwig's epithelial root sheath (HERS) which determines the number, length, and shape of the root, induces the formation of radicular dentin, and participates in the development of root cementum. Formation of HERS at the transition from crown to root development appears to be very insensitive to adverse effects, with the result that rootless teeth are extremely rare. In contrast, shortened roots as a consequence of impaired or prematurely halted apical growth of HERS constitute the most prevalent radicular dysplasia which occurs due to trauma and unknown reasons as well as in association with dentin disorders. While odontoblast differentiation inevitably stops when growth of HERS is arrested, it seems to be unaffected even in cases of severe dentin dysplasias such as regional odontodysplasia and dentin dysplasia type I. As a result radicular dentin formation is at least initiated and progresses for a limited time. The only condition affecting cementogenesis is hypophosphatasia which disrupts the formation of acellular cementum through an inhibition of mineralization. A process particularly susceptible to adverse effects appears to be the formation of the furcation in multirooted teeth. Impairment or disruption of this process entails taurodontism, single-rooted posterior teeth, and misshapen furcations. Thus, even though many characteristics of human root malformations can be related to disorders of specific processes involved in radicular morphogenesis, precise inferences as to the pathogenesis of these dysplasias are hampered by the still limited knowledge on root formation.

Counter-regulatory phosphatases TNAP and NPP1 temporally regulate tooth root cementogenesis

Cementum is critical for anchoring the insertion of periodontal ligament fibers to the tooth root. Several aspects of cementogenesis remain unclear, including differences between acellular cementum and cellular cementum, and between cementum and bone. Biomineralization is regulated by the ratio of inorganic phosphate (P_i) to mineral inhibitor pyrophosphate (PP_i), where local P_i and PP_i concentrations are controlled by phosphatases including tissue-nonspecific alkaline phosphatase (TNAP) and ectonucleotide pyrophosphatase/phosphodiesterase 1 (NPP1). The focus of this study was to define the roles of these phosphatases in cementogenesis. TNAP was associated with earliest cementoblasts near forming acellular and cellular cementum. With loss of TNAP in the Alpl null mouse, acellular cementum was inhibited, while cellular cementum production increased, albeit as hypomineralized cementoid. In contrast, NPP1 was detected in cementoblasts after acellular cementum formation, and at low levels around cellular cementum. Loss of NPP1 in the Enpp1 null mouse increased acellular cementum, with little effect on cellular cementum. Developmental patterns were recapitulated in a mouse model for acellular cementum regeneration, with early TNAP expression and later NPP1 expression. In vitro, cementoblasts expressed Alpl gene/protein early, whereas Enpp1 gene/protein expression was significantly induced only under mineralization conditions. These patterns were confirmed in human teeth, including widespread TNAP, and NPP1 restricted to cementoblasts lining acellular cementum. These studies suggest that early TNAP expression creates a low PP_i environment promoting acellular cementum initiation, while later NPP1 expression increases PP_i, restricting acellular cementum apposition. Alterations in PP_i have little effect on cellular cementum formation, though matrix mineralization is affected.

The rachitic tooth

Teeth are mineralized organs composed of three unique hard tissues, enamel, dentin, and cementum, and supported by the surrounding alveolar bone. Although odontogenesis differs from osteogenesis in several respects, tooth mineralization is susceptible to similar developmental failures as bone. Here we discuss conditions fitting under the umbrella of rickets, which traditionally referred to skeletal disease associated with vitamin D deficiency but has been more recently expanded to include newly identified factors involved in endocrine regulation of vitamin D, phosphate, and calcium, including phosphate-regulating endopeptidase homolog, X-linked, fibroblast growth factor 23, and dentin matrix protein 1. Systemic mineral metabolism intersects with local regulation of mineralization, and factors including tissue nonspecific alkaline phosphatase are necessary for proper mineralization, where rickets can result from loss of activity of tissue nonspecific alkaline phosphatase. Individuals suffering from rickets often bear the additional burden of a defective dentition, and transgenic mouse models have aided in understanding the nature and mechanisms involved in tooth defects, which may or may not parallel rachitic bone defects. This report reviews dental effects of the range of rachitic disorders, including discussion of etiologies of hereditary forms of rickets, a survey of resulting bone and tooth mineralization disorders, and a discussion of mechanisms, known and hypothesized, involved in the observed dental pathologies. Descriptions of human pathology are augmented by analysis of transgenic mouse models, and new interpretations are brought to bear on questions of how teeth are affected under conditions of rickets. In short, the rachitic tooth will be revealed.

Extracellular matrix mineralization in periodontal tissues: Noncollagenous matrix proteins, enzymes, and relationship to hypophosphatasia and X-linked hypophosphatemia

As broadly demonstrated for the formation of a functional skeleton, proper mineralization of periodontal alveolar bone and teeth - where calcium phosphate crystals are deposited and grow within an extracellular matrix - is essential for dental function. Mineralization defects in tooth dentin and cementum of the periodontium invariably lead to a weak (soft or brittle) dentition in which teeth become loose and prone to infection and are lost prematurely. Mineralization of the extremities of periodontal ligament fibers (Sharpey's fibers) where they insert into tooth cementum and alveolar bone is also essential for the function of the tooth-suspensory apparatus in occlusion and mastication. Molecular determinants of mineralization in these tissues include mineral ion concentrations (phosphate and calcium), pyrophosphate, small integrin-binding ligand N-linked glycoproteins and matrix vesicles. Amongst the enzymes important in regulating these mineralization determinants, two are discussed at length here, with clinical examples given, namely tissue-nonspecific alkaline phosphatase and phosphate-regulating gene with homologies to endopeptidases on the X chromosome. Inactivating mutations in these enzymes in humans and in mouse models lead to the soft bones and teeth characteristic of hypophosphatasia and X-linked hypophosphatemia, respectively, where the levels of local and systemic circulating mineralization determinants are perturbed. In X-linked hypophosphatemia, in addition to renal phosphate wasting causing low circulating phosphate levels, phosphorylated mineralization-regulating small integrin-binding ligand N-linked glycoproteins, such as matrix extracellular phosphoglycoprotein and osteopontin, and the phosphorylated peptides proteolytically released from them, such as the acidic serine- and aspartate-rich-motif peptide, may accumulate locally to impair mineralization in this disease.

Current concepts in hypophosphatasia: case report and literature review

BACKGROUND.  Hypophosphatasia (HP) is characterized by defective mineralization of bone and teeth because of deficient alkaline phosphatase activity. There are generally six recognized clinical forms, of which the most severe is often lethal prenatally or early in life. In milder forms, such as odontohypophosphatasia (OHP), premature exfoliation of primary teeth may be the only clinical manifestation. CASE REPORT.  A 20-month-old girl was referred to the Specialist Paediatric Salaried Dental Service within the Harrogate and District NHS Foundation Trust with mobility of tooth numbers 71 and 81. Clinical examination revealed grade III mobile 71 and 81, with minimal gingival inflammation and plaque deposits. There were no other dental findings and no significant medical history. Tooth numbers 71 and 81 exfoliated prematurely with no evidence of root resorption, shortly after presentation. Haematological and urinary investigations showed no abnormalities. Histological examination showed a complete absence of cementum. A diagnosis of OHP was made. After 10 months of dental follow-up, no further teeth have increased mobility. CONCLUSION.  Odontohypophosphatasia should be included as a differential diagnosis in children presenting with early loss of primary teeth. The dentist may be the first health care professional to whom the patient presents.

Tooth root dentin mineralization defects in a mouse model of hypophosphatasia

Tissue-nonspecific alkaline phosphatase (TNAP) is expressed in mineralizing tissues and functions to reduce pyrophosphate (PP(i) ), a potent inhibitor of mineralization. Loss of TNAP function causes hypophosphatasia (HPP), a heritable disorder marked by increased PP(i) , resulting in rickets and osteomalacia. Tooth root cementum defects are well described in both HPP patients and in Alpl(-/-) mice, a model for infantile HPP. In Alpl(-/-) mice, dentin mineralization is specifically delayed in the root; however, reports from human HPP patients are variable and inconsistent regarding dentin defects. In the current study, we aimed to define the molecular basis for changes in dentinogenesis observed in Alpl(-/-) mice. TNAP was found to be highly expressed by mature odontoblasts, and Alpl(-/-) molar and incisor roots featured defective dentin mineralization, ranging from a mild delay to severely disturbed root dentinogenesis. Lack of mantle dentin mineralization was associated with disordered and dysmorphic odontoblasts having disrupted expression of marker genes osteocalcin and dentin sialophosphoprotein. The formation of, initiation of mineralization within, and rupture of matrix vesicles in Alpl(-/-) dentin matrix was not affected. Osteopontin (OPN), an inhibitor of mineralization that contributes to the skeletal pathology in Alpl(-/-) mice, was present in the generally unmineralized Alpl(-/-) mantle dentin at ruptured mineralizing matrix vesicles, as detected by immunohistochemistry and by immunogold labeling. However, ablating the OPN-encoding Spp1 gene in Alpl(-/-) mice was insufficient to rescue the dentin mineralization defect. Administration of bioengineered mineral-targeting human TNAP (ENB-0040) to Alpl(-/-) mice corrected defective dentin mineralization in the molar roots. These studies reveal that TNAP participates in root dentin formation and confirm that reduction of PP(i) during dentinogenesis is necessary for odontoblast differentiation, dentin matrix secretion, and mineralization. Furthermore, these results elucidate developmental mechanisms underlying dentin pathology in HPP patients, and begin to explain the reported variability in the dentin/pulp complex pathology in these patients.

Enzyme replacement prevents enamel defects in hypophosphatasia mice

Hypophosphatasia (HPP) is the inborn error of metabolism characterized by deficiency of alkaline phosphatase activity, leading to rickets or osteomalacia and to dental defects. HPP occurs from loss-of-function mutations within the gene that encodes the tissue-nonspecific isozyme of alkaline phosphatase (TNAP). TNAP knockout (Alpl(-/-), aka Akp2(-/-)) mice closely phenocopy infantile HPP, including the rickets, vitamin B6-responsive seizures, improper dentin mineralization, and lack of acellular cementum. Here, we report that lack of TNAP in Alpl(-/-) mice also causes severe enamel defects, which are preventable by enzyme replacement with mineral-targeted TNAP (ENB-0040). Immunohistochemistry was used to map the spatiotemporal expression of TNAP in the tissues of the developing enamel organ of healthy mouse molars and incisors. We found strong, stage-specific expression of TNAP in ameloblasts. In the Alpl(-/-) mice, histological, µCT, and scanning electron microscopy analysis showed reduced mineralization and disrupted organization of the rods and inter-rod structures in enamel of both the molars and incisors. All of these abnormalities were prevented in mice receiving from birth daily subcutaneous injections of mineral-targeting, human TNAP at 8.2 mg/kg/day for up to 44 days. These data reveal an important role for TNAP in enamel mineralization and demonstrate the efficacy of mineral-targeted TNAP to prevent enamel defects in HPP.

Hypophosphatasia-associated deficiencies in mineralization and gene expression in cultured dental pulp cells obtained from human teeth

INTRODUCTION

Mutations in the gene ALPL in hypophosphatasia (HPP) reduce the function of tissue nonspecific alkaline phosphatase, and the resulting increase in pyrophosphate (PP(i)) contributes to bone and tooth mineralization defects by inhibiting physiologic calcium-phosphate (P(i)) precipitation. Although periodontal phenotypes are well documented, pulp/dentin abnormalities have been suggested in the clinical literature although reports are variable and underlying mechanisms remains unclear. In vitro analyses were used to identify mechanisms involved in HPP-associated pulp/dentin phenotypes.

METHODS

Primary pulp cells cultured from HPP subjects were established to assay alkaline phosphatase (ALP) activity, mineralization, and gene expression compared with cells from healthy controls. Exogenous P(i) was provided to the correct P(i)/PP(i) ratio in cell culture.

RESULTS

HPP cells exhibited significantly reduced ALP activity (by 50%) and mineral nodule formation (by 60%) compared with the controls. The expression of PP(i) regulatory genes was altered in HPP pulp cells, including reduction in the progressive ankylosis gene (ANKH) and increased ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). Odontoblast marker gene expression was disrupted in HPP cells, including reduced osteopontin (OPN), dentin matrix protein 1 (DMP1), dentin sialophosphoprotein (DSPP), and matrix extracellular phosphoprotein (MEPE). The addition of P(i) provided a corrective measure for mineralization and partially rescued the expression of some genes although cells retained altered messenger RNA levels for PP(i)-associated genes.

CONCLUSIONS

These studies suggest that under HPP conditions pulp cells have the compromised ability to mineralize and feature a disrupted odontoblast profile, providing a first step toward understanding the molecular mechanisms for dentin phenotypes observed in HPP.

PHEX neutralizing agent inhibits dentin formation in mouse tooth germ

The mutation of phosphate-regulating gene with homologies to endopeptidases on the X-chromosome (PHEX) can lead to human X-linked hypophosphatemic rickets which displays hypo-mineralization in bone and dentin. To study its possible roles in teeth, PHEX antibody was injected into pregnant mice on E15 to explore its roles on the formation of enamel and dentin. Mallory trichrome staining results showed that arrangements of ameloblasts and odontoblasts were irregular after PHEX antibody treatment. Differentiation of odontoblasts and the formation of dentin were inhibited. Spatiotemporal distribution of PHEX protein was observed in various stages of tooth germ. Immunohistochemical results showed positive PHEX signals appeared in the inner enamel epithelium on E16 and became stronger on E18. Ameloblasts and odontoblasts showed much higher PHEX expression on P1 and P3. Expression of PHEX in odontoblasts decreased accordingly. However, enamel formation was only slightly affected. The findings proved that a decrease in PHEX expression could suppress dentin formation.

Enzyme replacement therapy prevents dental defects in a model of hypophosphatasia

Hypophosphatasia (HPP) occurs from loss-of-function mutation in the tissue-non-specific alkaline phosphatase (TNALP) gene, resulting in extracellular pyrophosphate accumulation that inhibits skeletal and dental mineralization. TNALP-null mice (Akp2(-/-)) phenocopy human infantile hypophosphatasia; they develop rickets at 1 week of age, and die before being weaned, having severe skeletal and dental hypomineralization and episodes of apnea and vitamin B(6)-responsive seizures. Delay and defects in dentin mineralization, together with a deficiency in acellular cementum, are characteristic. We report the prevention of these dental abnormalities in Akp2(-/-) mice receiving treatment from birth with daily injections of a mineral-targeting, human TNALP (sALP-FcD(10)). sALP-FcD(10) prevented hypomineralization of alveolar bone, dentin, and cementum as assessed by micro-computed tomography and histology. Osteopontin--a marker of acellular cementum--was immuno-localized along root surfaces, confirming that acellular cementum, typically missing or reduced in Akp2(-/-) mice, formed normally. Our findings provide insight concerning how acellular cementum is formed on tooth surfaces to effect periodontal ligament attachment to retain teeth in their osseous alveolar sockets. Furthermore, they provide evidence that this enzyme-replacement therapy, applied early in post-natal life--where the majority of tooth root development occurs, including acellular cementum formation--could prevent the accelerated tooth loss seen in individuals with HPP.

Genetic Etiology and Dental Pulp Cell Deficiency of Hypophosphatasia

Hypophosphatasia is caused by mutations of the tissue-non-specific alkaline phosphatase ( TNSALP) gene with deficiency of dentin structure. The aim of this study was to examine whether TNSALP mutation in dental pulp cells contributes to dentin dysplasia in hypophosphatasia. Mutation analysis showed that compound heterozygous mutations of TNSALP were identified in three hypophosphatasia patients, including 3 novel mutation sites. Exfoliated teeth from the patients showed abnormal dentin mineralization and loss of cementum, as assessed by ground sections and scanning electron microscope analysis. Dental pulp cells isolated from one of the patients showed a significantly reduced TNSALP activity and mineralization capacity when compared with those in dental pulp cells from the unaffected individuals. Our results suggested that dentin dysplasia in hypophosphatasia may be associated with the decreased mineralization ability of dental pulp cells.

Orodental phenotype and genotype findings in all subtypes of hypophosphatasia

Background

Hypophosphatasia (HP) is a rare inherited disorder characterized by a wide spectrum of defects in mineralized tissues and caused by deficiency in the tissue non-specific alkaline phosphatase gene (ALPL). The symptoms are highly variable in their clinical expression, and relate to numerous mutations in this gene. The first clinical sign of the disease is often a premature loss of deciduous teeth, mostly in the moderate forms.

Aim

The purpose of this study was to document the oral features of HP patients and to relate theses features to the six recognized forms of HP in 5 patients with known genotype and to investigate the genotype-phenotype correlations.

Methods

Clinical and radiographic examinations were carried out. We collected medical and dental history in the kindred and biochemical data. Finally, mutations in the ALPL gene were tested by DNA sequencing in SESEP laboratory.

Results

We have for the first time related the known dental anomalies which occur as integral features of HP to the recognized clinical forms of HP. We also pointed out striking dental abnormalities which were never described in association with this rare disease. Accurate genotype-phenotype severity correlations were observed.

Conclusion

This work allowed us to compare orodental manifestations in all the clinical forms of HP within the patient's sample. According to the severity of the disorder, some dental defects were infrequent, while other were always present. The long term prognosis of the permanent teeth varies from a patient to another. As premature loss of primary teeth is often the first, and sometimes the only visible symptom of the milder forms, the paediatric dentist plays a critical role in the detection and diagnosis of the disease.

Expression of bone associated markers by tooth root lining cells, in situ and in vitro

Periodontal disease is marked by inflammation and subsequent loss and/or damage to tooth-supporting tissues including bone, cementum, and periodontal ligament. A key tissue in the initial process of periodontal development as well as regeneration following periodontal disease is cementum. Research efforts aimed toward understanding mechanisms involved in periodontal development and regeneration, and in particular the formation of root cementum, have been hampered by an inability to isolate and culture cells involved in cementum production (i.e., cementoblasts). Much has been learned regarding the processes and mechanisms involved in bone formation and function from experiments using bone cell cultures. Therefore, the purpose of this study was to develop a strategy whereby cementoblasts could be isolated, cultured, and characterized. As a first step, using in situ hybridization, we determined the timed and spatial expression of mineral-associated proteins during first molar root development in CD-1 mice. These proteins included dentin sialoprotein (DSP), osteopontin (OPN), bone sialoprotein (BSP), osteocalcin (OCN), and type I collagen. During root development in mice BSP, OPN, and OCN mRNAs were expressed selectively by cells lining the tooth root surface--cementoblasts--with high levels of expression at day 41. Importantly, at this time point BSP, OPN, and OCN mRNAs were not expressed throughout the periodontal ligament. These findings provided us with markers selective to root-lining cells, or cementoblasts, in situ, and established the time (day 41) for isolating cells for in vitro studies. To isolate cells from tissues adherent to the root surface, enzymatic digestion was used, similar to what are now considered classical techniques for isolation of osteoblasts. To determine whether cells in vitro contained root-lining cells and cementoblasts, cultured cells were analyzed for expression of mineral-associated proteins. Cells within this heterogeneous primary population expressed type I collagen, BSP, OPN, and OCN as determined by in situ hybridization. In contrast, cells within this population did not express dentin sialoprotein, an odontoblast-specific protein. These procedures have provided a means to obtain root-lining cells in vitro that can now be cloned and used for studies directed at determining the properties of root-lining cells, or cementoblasts, in vitro.

Hypophosphatasia affecting the permanent dentition

Reports on dental abnormalities in connection with hypophosphatasia almost exclusively describe changes in primary teeth. A 23-year-old man with hypophosphatasia, first diagnosed at the age of 8 months, is described; histologically and radiographically verified signs of the condition were present in the permanent dentition. The findings included a reduced level of the marginal alveolar bone supporting the upper central incisors, which had to be extracted. The molars displayed large coronal pulp chambers. Histologically, the upper incisors demonstrated abnormal root cementum, with areas of dentin resorption, as well as disturbances of the mineralization of the coronal dentin. The patient also had signs of abnormal root resorption of molars. The potential involvement of permanent teeth puts children with hypophosphatasia at risk of developing oral complications during adolescent and adult life.

Light and SEM observation of internal root resorption of a traumatized permanent central incisor

A clinical case report is presented which illustrates internal root resorption of a traumatized tooth. Light and scanning electron microscope were used to further examine the defect. An explanation of the morphological structure of the resorption is discussed.

Observations of root surfaces from patients with early-onset periodontitis and leukocyte adhesion deficiency

The purpose of this investigation was to report observations of the root surfaces of teeth from 2 siblings with leukocyte adhesion deficiency (LAD). In previous publications, the clinical, radiographic and immunologic findings in the family were presented. 38 permanent teeth from the 2 siblings were prepared for microscopic examination, 11 for light microscopy (LM), and 27 for scanning electron microscopy (SEM). In addition, 8 healthy teeth obtained from 2 patients requiring extractions for orthodontic treatment served as controls. LM observations on healthy teeth revealed cementum with normal structural appearance which exhibited a mosaic or mogul-like pattern with SEM. In LAD specimens, cementum apical to the dentogingival junction exhibited resorption lacunae and areas of poor structural definition characterized by aplasia and hypoplasia (hypomineralization). Areas of hypoplasia presented as distinct irregular surfaces with a pebbly or globular-like appearance. Alteration in cementum formation and maturation may play a role in the etiology of early-onset periodontitis.

Periodontal manifestation of hypophosphatasia. A family case report

Hypophosphatasia is a rare inherited disease, the 1st clinical sign of which is often a premature loss of deciduous teeth. We describe clinical, histological and SEM findings of 2 cases of hypophosphatasia from a single family and discuss the pathological mechanisms with reference to the literature.

Hypophosphatasia: dental aspects and mode of inheritance

Hypophosphatasia is rare enzymopathy that normally presents within the first few years of life and often has profound effects upon the periodontium. It is a heritable disorder characterised by defective mineralisation of the skeletal and dental structures of the body and a deficiency in the liver/bone/kidney (L/B/K) isoenzyme of alkaline phosphatase (ALP). There has been a tremendous advance in our knowledge of this condition over the last decade due to the advent of highly specific DNA probes and novel microanalytical techniques. This paper aims to review current literature about hypophosphatasia with special reference to the dental aspects of the condition and to shed light upon the controversial area of its mode of genetic inheritance. It is concluded that hypophosphatasia may result from the existence of 2 defective alleles, which alone or in combination may cause the condition. One allele is expressed in an autosomal dominant manner producing milder phenotypic characteristics, whilst the other is expressed in an autosomal recessive manner producing the more severe clinical form that often results in neonatal death. The milder phenotypes may go undiagnosed and the consequence of this in genetic counselling terms is extremely important.

A quantitative enzyme histochemical analysis of the distribution of alkaline phosphatase activity in the periodontal ligament of the rat incisor

The spatial distribution of alkaline phosphatase (ALP) activity was examined in the periodontal ligament of the continuously growing rat incisor. With the indoxyl-tetrazolium salt method, enzyme activity was demonstrated in undecalcified cryosections, and the amount of reaction product was quantified. ALP activity appeared to be distributed heterogeneously. Its highest activity was found in the bone-related compartment of the ligament. In the tooth-related compartment and the supracrestal extension of the ligament, enzyme activity was significantly lower, but still higher than in the lamina propria of the gingiva. In the part of the ligament bordering the cementum, highest activity was found in the apical region just occlusal to Hertwig's epithelial root sheath, where formation of acellular cementum begins. From there toward the incisal edge, the activity of the enzyme gradually decreased. It is suggested that differences among the various parts of the periodontal ligament are related to local variations in phosphate metabolism and cementum deposition.