Odontoblast dysfunction in osteogenesis imperfecta: an LM, SEM, and ultrastructural study

Dental tissue changes in juvenile and adult mice with osteogenesis imperfecta

Osteogenesis imperfecta (OI), a disorder of type I collagen, causes skeletal deformities as well as defects in dental tissues, which lead to increased enamel wear and smaller teeth with shorter roots. Mice with OI exhibit similar microstructural dentin changes, including reduced dentin tubule density and dentin cross-sectional area. However, the effects of these mutations on gross dental morphology and dental tissue volumes have never been characterized in the osteogenesis imperfecta murine (OIM) mouse model. Here we compare mineralized dental tissue measurements of OIM mice and unaffected wild type (WT) littermates at the juvenile and adult stages. The maxillary and mandibular incisors and first molars were isolated from microCT scans, and tissue volumes and root length were measured. OIM mice have smaller teeth with shorter roots relative to WT controls. Maxillary incisor volumes differed significantly between OIM and WT mice at both the juvenile and young adult stage, perhaps due to shortening of the maxilla itself in OIM mice. Additionally, adult OIM mice have significantly less crown enamel volume than do juveniles, potentially due to loss through wear. Thus, OIM mice demonstrate a dental phenotype similar to humans with OI, with decreased tooth size, decreased root length, and accelerated enamel wear. Further investigation of dental development in the OIM mouse may have important implications for the development and treatment of dental issues in OI patients.

Morphological and Ultrastructural Collagen Defects: Impact and Implications in Dentinogenesis Imperfecta

Collagen is the building block for the extracellular matrix in bone, teeth and other fibrous tissues. Osteogenesis imperfecta (OI), or brittle bone disease, is a heritable disorder that results from defective collagen synthesis or metabolism, resulting in bone fragility. The dental manifestation of OI is dentinogenesis imperfecta (DI), a genetic disorder that affects dentin structure and clinical appearance, with a characteristic feature of greyish-brown discolouration. The aim of this study was to conduct a systematic review to identify and/or define any ultrastructural changes in dentinal collagen in DI. Established databases were searched: Cochrane Library, OVID Embase, OVID Medline and PubMed/Medline. Search strategies included: Collagen Ultrastructure, DI and OI. Inclusion criteria were studies written in English, published after 1990, that examined human dental collagen of teeth affected by DI. A Cochrane data extraction form was modified and used for data collection. The final dataset included seventeen studies published from 1993 to 2021. The most prevalent findings on collagen in DI teeth were increased coarse collagen fibres and decreased fibre quantity. Additional findings included changes to fibre orientation (i.e., random to parallel) and differences to the fibre organisation (i.e., regular to irregular). Ultrastructural defects and anomalies included uncoiled collagen fibres and increased D-banding periodicity. Studies in collagen structure in DI reported changes to the surface topography, quantity, organisation and orientation of the fibres. Moreover, ultrastructural defects such as the packing/coiling and D-banding of the fibrils, as well as differences in the presence of other collagens are also noted. Taken together, this study provides an understanding of the changes in collagen and its impact on clinical translation, paving the way for innovative treatments in dental treatment.

Morphological Study of Dental Structure in Dentinogenesis Imperfecta Type I with Scanning Electron Microscopy

Background: Dentinogenesis imperfecta type I (DGI-I) is a hereditary alteration of dentin associated with osteogenesis imperfecta (OI). Aim: To describe and study the morphological characteristics of DGI-I with scanning electron microscopy (SEM). Material and methods: Twenty-five teeth from 17 individuals diagnosed with OI and 30 control samples were studied with SEM at the level of the enamel, dentin–enamel junction (DEJ) and four levels of the dentin, studying its relationship with clinical–radiographic alterations. The variables were analysed using Fisher’s exact test, with a confidence level of 95% and asymptotic significance. Results: OI teeth showed alterations in the prismatic structure in 56%, interruption of the union in the enamel and dentin in 64% and alterations in the tubular structure in all of the cases. There is a relationship between the severity of OI and the morphological alteration of the dentin in the superficial (p = 0.019) and pulpar dentin (p 0.004) regions. Conclusions: Morphological alterations of the tooth structure are found in OI samples in the enamel, DEJ and dentin in all teeth regardless of the presence of clinical–radiographic alterations. Dentin structural anomalies and clinical dental alterations were observed more frequently in samples from subjects with a more severe phenotype of OI.

Case Report: A Novel COL1A1 Missense Mutation Associated With Dentineogenesis Imperfecta Type I

Background: Osteogenesis imperfecta (OI) is a clinical and genetic disorder that results in bone fragility, blue sclerae and dentineogenesis imperfecta (DGI), which is mainly caused by a mutation in the COL1A1 or COL1A2 genes, which encode type I procollagen. Case Report: A missense mutation (c.1463G > C) in exon 22 of the COL1A1 gene was found using whole-exome sequencing. However, the cases reported herein only exhibited a clinical DGI-I phenotype. There were no cases of bone disease or any other common abnormal symptom caused by a COL1A1 mutation. In addition, the ultrastructural analysis of the tooth affected with non-syndromic DGI-I showed that the abnormal dentine was accompanied by the disruption of odontoblast polarization, a reduced number of odontoblasts, a reduction in hardness and elasticity, and the loss of dentinal tubules, suggesting a severe developmental disorder. We also investigated the odontoblast differentiation ability using dental pulp stem cells (DPSCs) that were isolated from a patient with DGI-I and cultured. Stem cells isolated from patients with DGI-I are important to elucidate their pathogenesis and underlying mechanisms to develop regenerative therapies. Conclusion: This study can provide new insights into the phenotype-genotype association in collagen-associated diseases and improve the clinical diagnosis of OI/DGI-I.

Dentine disorders and adhesive treatments: A systematic review

OBJECTIVES

A better understanding of the microstructure and mechanical properties of enamel and dentine may enable practitioners to apply the current adhesive dentistry protocols to clinical cases involving dentine disorders (dentinogenesis imperfecta or dentine dysplasia).

DATA/SOURCES

Publications (up to June 2020) investigating the microstructure of dentine disorders were browsed in a systematic search using the PubMed/Medline, Embase and Cochrane Library electronic databases. Two authors independently selected the studies, extracted the data in accordance with the PRISMA statement, and assessed the risk of bias with the Critical Appraisal Checklist. A Mann-Whitney U test was computed to compare tissues damage related to the two dentine disorders of interest.

STUDY SELECTION

From an initial total of 642 studies, only 37 (n = 164 teeth) were included in the present analysis, among which 18 investigating enamel (n = 70 teeth), 15 the dentine-enamel junction (n = 62 teeth), and 35 dentine (n = 156 teeth). Dentine is damaged in cases of dentinogenesis imperfecta and osteogenesis imperfecta (p = 2.55E-21 and p = 3.99E-21, respectively). These studies highlight a reduction in mineral density, hardness, modulus of elasticity and abnormal microstructure in dentine disorders. The majority of studies report an altered dentine-enamel junction in dentinogenesis imperfecta and in osteogenesis imperfecta (p = 6.26E-09 and p = 0.001, respectively). Interestingly, enamel is also affected in cases of dentinogenesis imperfecta (p = 0.0013), unlike to osteogenesis imperfecta (p = 0.056).

CONCLUSIONS

Taking into account all these observations, only a few clinical principles may be favoured in the case of adhesive cementation: (i) to preserve the residual enamel to enhance bonding, (ii) to sandblast the tooth surfaces to increase roughness, (iii) to choose a universal adhesive and reinforce enamel and dentine by means of infiltrant resins. As these recommendations are mostly based on in vitro studies, future in vivo studies should be conducted to confirm these hypotheses.

Phenotypic features of dentinogenesis imperfecta associated with osteogenesis imperfecta and COL1A2 mutations

OBJECTIVE

Dentinogenesis imperfecta (DI) requires dental treatment. This study investigated the characteristics of DI teeth associated with osteogenesis imperfecta (OI) and COL1A2 mutations.

STUDY DESIGN

Whole exome and Sanger sequencing were performed. Three primary teeth (called "OIDI teeth") obtained from 3 unrelated COL1A2 patients were investigated and compared with 9 control teeth from age-matched healthy individuals using colorimetry, micro-computed tomography, Knoop microhardness, energy dispersive X-ray spectroscopy, scanning electron microscopy, and histology.

RESULTS

All patients were identified with heterozygous glycine substitutions in COL1A2. The COL1A2 mutations, c.1531G>T and c.2027G>T, were de novo, whereas c.3106G>C was inherited. OIDI1, 2, and 3 teeth had a substantial decrease in dentin microhardness and lightness. OIDI2 enamel microhardness was significantly reduced, whereas OIDI1 and 3 had enamel microhardness comparable to that of control individuals. The OIDI1 pulp cavity was large; OIDI2 was narrow; and OIDI3 was obliterated. OIDI1 and 3 had significantly higher carbon levels than those in control individuals. Numerous ectopic calcified masses, sparse and obstructed dentinal tubules, dentin holes, and collagen disorientation were observed.

CONCLUSIONS

OIDI teeth had reduced lightness and variable pulp morphology. Weak dentin, mineral disproportion, and abnormal ultrastructure could contribute to the brittleness of OIDI teeth and adhesive restoration failure. Here, we expand the phenotypic spectrum of COL1A2 mutations and raise awareness among dentists seeing patients with OI.

Tooth ultrastructure of a novel COL1A2 mutation expanding its genotypic and phenotypic spectra

OBJECTIVES

To investigate tooth ultrastructure and mutation of two patients in a family affected with osteogenesis imperfecta (OI) type IV and dentinogenesis imperfecta (DGI).

METHODS

Mutations were detected by whole exome and Sanger sequencing. The permanent second molar obtained from the proband (DGI1) and the primary first molar from his affected son (DGI2) were studied for their color, roughness, mineral density, hardness, elastic modulus, mineral content, and ultrastructure, compared to the controls.

RESULTS

Two novel missense COL1A2 variants, c.752C > T (p.Ser251Phe) and c.758G > T (p.Gly253Val), were identified in both patients. The c.758G > T was predicted to be the causative mutation. Pulp cavities of DGI1 (permanent teeth) were obliterated while those of DGI2 (primary teeth) were wide. The patients' teeth had darker and redder colors; reduced dentin hardness; decreased, disorganized, and scattered dentinal tubules and collagen fibers; and irregular dentinoenamel junction (DEJ), compared to controls. Lacunae-like structures were present in DGI2.

CONCLUSIONS

We reported the novel causative mutation, c.758G > T (p.Gly253Val), in COL1A2 for OI type IV and DGI. The DGI dentin demonstrated inferior mechanical property and ultrastructure, suggesting severe disturbances of dentin formation. These could contribute to fragility and prone to infection of DGI teeth. This study expands phenotypic and genotypic spectra of COL1A2 mutations.

Mutations in COL1A1 Gene Change Dentin Nanostructure

Although many studies have attempted to associate specific gene mutations with dentin phenotypic severity, it remains unknown how the mutations in COL1A1 gene influence the mechanical behavior of dentin collagen and matrix. Here, we reported one osteogenesis imperfecta (OI) pedigree caused by two new inserting mutations in exon 5 of COL1A1 (NM_000088.3:c.440_441insT;c.441_442insA), which resulted in the unstable expression of COL1A1 mRNA and half quantity of procollagen production. We investigated the morphological and mechanical features of proband's dentin using atomic force microscope (AFM), scanning electron microscope, and transmission electron microscope. Increased D-periodic spacing, variably enlarged collagen fibrils coating with fewer minerals were found in the mutated collagen. AFM analysis demonstrated rougher dentin surface and sparsely decreased Young's modulus in proband's dentin. We believe that our findings provide new insights into the genetic-/nano- mechanisms of dentin diseases, and may well explain OI dentin features with reduced mechanical strength and a lower crosslinked density.

Tooth dentin defects reflect genetic disorders affecting bone mineralization

Several genetic disorders affecting bone mineralization may manifest during dentin mineralization. Dentin and bone are similar in several aspects, especially pertaining to the composition of the extracellular matrix (ECM) which is secreted by well-differentiated odontoblasts and osteoblasts, respectively. However, unlike bone, dentin is not remodelled and is not involved in the regulation of calcium and phosphate metabolism. In contrast to bone, teeth are accessible tissues with the shedding of deciduous teeth and the extractions of premolars and third molars for orthodontic treatment. The feasibility of obtaining dentin makes this a good model to study biomineralization in physiological and pathological conditions. In this review, we focus on two genetic diseases that disrupt both bone and dentin mineralization. Hypophosphatemic rickets is related to abnormal secretory proteins involved in the ECM organization of both bone and dentin, as well as in the calcium and phosphate metabolism. Osteogenesis imperfecta affects proteins involved in the local organization of the ECM. In addition, dentin examination permits evaluation of the effects of the systemic treatment prescribed to hypophosphatemic patients during growth. In conclusion, dentin constitutes a valuable tool for better understanding of the pathological processes affecting biomineralization.

New perspectives on osteogenesis imperfecta

A new paradigm has emerged for osteogenesis imperfecta as a collagen-related disorder. The more prevalent autosomal dominant forms of osteogenesis imperfecta are caused by primary defects in type I collagen, whereas autosomal recessive forms are caused by deficiency of proteins which interact with type I procollagen for post-translational modification and/or folding. Factors that contribute to the mechanism of dominant osteogenesis imperfecta include intracellular stress, disruption of interactions between collagen and noncollagenous proteins, compromised matrix structure, abnormal cell-cell and cell-matrix interactions and tissue mineralization. Recessive osteogenesis imperfecta is caused by deficiency of any of the three components of the collagen prolyl 3-hydroxylation complex. Absence of 3-hydroxylation is associated with increased modification of the collagen helix, consistent with delayed collagen folding. Other causes of recessive osteogenesis imperfecta include deficiency of the collagen chaperones FKBP10 or Serpin H1. Murine models are crucial to uncovering the common pathways in dominant and recessive osteogenesis imperfecta bone dysplasia. Clinical management of osteogenesis imperfecta is multidisciplinary, encompassing substantial progress in physical rehabilitation and surgical procedures, management of hearing, dental and pulmonary abnormalities, as well as drugs, such as bisphosphonates and recombinant human growth hormone. Novel treatments using cell therapy or new drug regimens hold promise for the future.

Dentinogenesis imperfecta in children with osteogenesis imperfecta: a clinical and ultrastructural study

AIM

The aim of this study was to assess the correlation between osteogenesis imperfecta (OI) and dentinogenesis imperfecta (DI) from both a clinical and histological point of view, particularly clarifying the structural and ultrastructural dentine changes.

DESIGN

Sixteen children (6-12 years aged) with diagnosis of OI were examined for dental alterations referable to DI. For each patient, the OI type (I, III, or IV) was recorded. Extracted or normally exfoliated primary teeth were subjected to a histological examination (to both optical microscopy and confocal laser-scanning microscopy).

RESULTS

A total of ten patients had abnormal discolourations referable to DI: four patients were affected by OI type I, three patients by OI type III, and three patients by OI type IV. The discolourations, yellow/brown or opalescent grey, could not be related to the different types of OI. Histological exam of primary teeth showed severe pathological change in the dentin, structured into four different layers. A collagen defect due to odontoblast dysfunction was theorized to be on the base of the histological changes.

CONCLUSIONS

There is no correlation between the type of OI and the type of discolouration. The underlying dentinal defect seems to be related to an odontoblast dysfunction.

Increased Young's modulus and hardness of Col1a2oim dentin

Mice harboring the Col1a2(oim) mutation (oim) express dentinogenesis imperfecta. To determine the effect of Col1a2 genotype on tissue mechanical properties, we compared Young's modulus and hardness of dentin in the 3 Col1a2 genotypes. Upper incisors were tested by nanoindentation. Genotype had a significant effect on Young's modulus, but there was not a simple mutant allele dosage relationship. The effect of genotype on hardness did not reach significance. Hardness and Young's modulus were greater near the dento-enamel junction than near the pulp chamber. Greater hardness and Young's modulus values near the dento-enamel junction reflected continued mineralization of the dentin following its initial synthesis. Analysis showed the mechanical data to be consistent with Fourier transform infrared and backscattered electron microscopy studies that revealed increased mineralization in oim bone. Analysis of the data suggests that clinical fragility of teeth in oim mice is not due to deficiencies of hardness or Young's modulus, but may be due to defects in post-yield behavior or resistance to fatigue damage.

Abnormal dentin structure in two novel gene mutations [COL1A1, Arg134Cys] and [ADAMTS2, Trp795-to-ter] causing rare type I collagen disorders

Histological and ultrastructural observations of dentin of two patients affected with rare types of type I collagen disorders are presented. In the first case, a homozygous nonsense mutation in ADAMTS2 (substitution of a codon for tryptophan by a stopcodon) causes type VIIC Ehlers-Danlos syndrome (EDS) with multiple tooth agenesis and focal dysplastic dentin defects. In the second case, a missense mutation in COL1A1 (substitution of arginine by cysteine) results in a type I EDS phenotype with clinically normal-appearing dentition. Tooth samples are investigated by using light microscopy (LM), transmission electron microscopy (TEM) and immunostaining for types I and III collagen, and tenascin. These are compared with samples from patients with types III and IV osteogenesis imperfecta (OI) in association with dentinogenesis imperfecta (DI), showing a consistently abnormal appearance of the dentin in all specimens, with variations being primarily those of degree of change. Similarities in histological changes include the alternating presence of normal and severe pathological areas in primary and secondary dentin, the latter being characterized by large canal-like structures in atubular areas. Ultrastructural evidence of pathological dentinogenesis include abnormal distribution, size and organization of collagen fibers, which may also be found in clinically unaffected teeth. The histological and ultrastructural changes seen can be explained on the basis of odontoblast dysfunction which may be secondary to the collagen defect, interfering with different levels of odontoblast cell function and intercellular communication. These observations on (ultra)structural dentin defects associated with the two novel gene mutations are the first ever reported.

Association of bovine dentine phosphophoryn with collagen fragments

Bovine dentine phosphophoryn (BDP), a protein rich in aspartyl (Asp) and O-phosphoseryl (Ser(P)) residues, is synthesized by odontoblasts and believed to be involved in matrix-mediated biomineralization of dentine. Phosphophoryn was purified from bovine dentine using EDTA extraction, Ca(2+) precipitation, anion exchange and size exclusion chromatography. The purified protein migrated on SDS-PAGGE as a single band. The protein was dephosphorylated using a chelex alkaline dialysis procedure, repurified using anion exchange and size exclusion chromatography and then subjected to cleavage with trypsin. The digest was subjected to reversed-phase HPLC and analysed by Q-TOF mass spectrometry. The only non-trypsin peptides that could be identified were two collagen Type I alpha2 peptides whose sequence was determined by fragmentation analysis. The association of collagen fragments with highly purified phosphophoryn suggests that the EDTA extraction method yields BDP that is strongly bound to collagen fragments. This association now helps explain discrepancies in molecular weight and amino acid composition data for various phosphophoryn preparations compared with the same data calculated from the C-terminal extension of mouse, rat and human dentine sialophosphoprotein (DSPP) gene products. Analysis of the mutation pattern of the clinical disorder Osteogenesis Imperfecta within the region enclosed by the identified collagen fragments reveals that phosphophoryn associates with a segment of collagen that is crucial for structure and/or function.