Phenotypic Properties of Collagen in Dentinogenesis Imperfecta Associated with Osteogenesis Imperfecta

Dental abnormalities in rare genetic bone diseases: Literature review

Currently, over 500 rare genetic bone disorders are identified. These diseases are often accompanied by dental abnormalities, which are sometimes the first clue for an early diagnosis. However, not many dentists are sufficiently familiar with phenotypic abnormalities and treatment approaches when they encounter patients with rare diseases. Such patients often need dental treatment but have difficulties in finding a dentist who can treat them appropriately. Herein we focus on major dental phenotypes and summarize their potential causes and mechanisms, if known. We discuss representative diseases, dental treatments, and their effect on the oral health of patients and on oral health-related quality of life. This review can serve as a starting point for dentists to contribute to early diagnosis and further investigate the best treatment options for patients with rare disorders, with the goal of optimizing treatment outcomes.

Microfabrication-based engineering of biomimetic dentin-like constructs to simulate dental aging

Human dentin is a highly organized dental tissue displaying a complex microarchitecture consisting of micrometer-sized tubules encased in a mineralized type-I collagen matrix. As such, it serves as an important substrate for the adhesion of microbial colonizers and oral biofilm formation in the context of dental caries disease, including root caries in the elderly. Despite this issue, there remains a current lack of effective biomimetic in vitro dentin models that facilitate the study of oral microbial adhesion by considering the surface architecture at the micro- and nanoscales. Therefore, the aim of this study was to develop a novel in vitro microfabricated biomimetic dentin surface that simulates the complex surface microarchitecture of exposed dentin. For this, a combination of soft lithography microfabrication and biomaterial science approaches were employed to construct a micropitted PDMS substrate functionalized with mineralized type-I collagen. These dentin analogs were subsequently glycated with methylglyoxal (MGO) to simulate dentin matrix aging in vitro and analyzed utilizing an interdisciplinary array of techniques including atomic force microscopy (AFM), elemental analysis, and electron microscopy. AFM force-mapping demonstrated that the nanomechanical properties of the biomimetic constructs were within the expected biological parameters, and that mineralization was mostly predominated by hydroxyapatite deposition. Finally, dual-species biofilms of Streptococcus mutans and Candida albicans were grown and characterized on the biofunctionalized PDMS microchips, demonstrating biofilm-specific morphologic characteristics and confirming the suitability of this model for the study of early biofilm formation under controlled conditions. Overall, we expect that this novel biomimetic dentin model could serve as an in vitro platform to study oral biofilm formation or dentin-biomaterial bonding in the laboratory without the need for animal or human tooth samples in the future.

Atomic force microscopy-mediated mechanobiological profiling of complex human tissues

Tissue mechanobiology is an emerging field with the overarching goal of understanding the interplay between biophysical and biochemical responses affecting development, physiology, and disease. Changes in mechanical properties including stiffness and viscosity have been shown to describe how cells and tissues respond to mechanical cues and modify critical biological functions. To quantitatively characterize the mechanical properties of tissues at physiologically relevant conditions, atomic force microscopy (AFM) has emerged as a highly versatile biomechanical technology. In this review, we describe the fundamental principles of AFM, typical AFM modalities used for tissue mechanics, and commonly used elastic and viscoelastic contact mechanics models to characterize complex human tissues. Furthermore, we discuss the application of AFM-based mechanobiology to characterize the mechanical responses within complex human tissues to track their developmental, physiological/functional, and diseased states, including oral, hearing, and cancer-related tissues. Finally, we discuss the current outlook and challenges to further advance the field of tissue mechanobiology. Altogether, AFM-based tissue mechanobiology provides a mechanistic understanding of biological processes governing the unique functions of tissues.

Correlative Atomic Force Microscopy and Raman Spectroscopy in Acid Erosion of Dentin

Physical properties and chemical composition are fundamentally defining and interconnected surface characteristics. However, few techniques are able to capture both in a correlative fashion at the same sample location and orientation. This is especially important for complex materials such as dentin, which is an inner tooth structure and is a heterogeneous, composite inorganic-organic material with open channels (tubules) that extend toward the tooth pulp. Here, a combined microscope system consisting of an atomic force microscope and a confocal Raman spectrometer was used to study the correlative physical and chemical properties of human dentin. The local hardness of dentin was highly correlated with the Raman signal ratio of inorganic to organic material, and this was enhanced in the peritubular regions of dentin. When the samples were etched with citric acid, Young's modulus, hardness, and inorganic-to-organic material ratio decreased significantly, collagen fibrils on the surface were exposed, the peritubular regions were removed, and the tubule diameters increased. Thus, the combined atomic force microscopy (AFM)-Raman approach allows for comprehensive and correlative physical-chemical analysis of material surfaces and will be invaluable for evaluating oral therapeutic strategies.

A seminal perspective on the role of chondroitin sulfate in biomineralization

Chondroitin sulfate (CS) is an important extracellular matrix component of mineralized tissues. It participates in biomineralization, osteoblast differentiation and promotes bone tissue repair in vitro. However, the mechanism in which CS functions is unclear. Accordingly, an in-depth investigation of how CS participates in mineralization was conducted in the present study. Chondroitin sulfate was found to directly induce intrafibrillar mineralization of the collagen matrix. The mineralization outcome was dependent on whether CS remained free in the extracellular matrix or bound to core proteins; mineralization only occurred when CS existed in a free state. The efficacy of mineralization appeared to increase with ascending CS concentration. This discovery spurred the authors to identify the cause of heterotopic ossification in the Achilles tendon. Chondroitin sulfate appeared to be a therapeutic target for the management of diseases associated with heterotopic calcification. A broader perspective was presented on the applications of CS in tissue engineering.

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.

Nanomechanical and Molecular Characterization of Aging in Dentinal Collagen

Methylglyoxal (MGO) is an important molecule derived from glucose metabolism with the capacity of attaching to collagen and generating advanced glycation end products (AGEs), which accumulate in tissues over time and are associated with aging and diseases. However, the accumulation of MGO-derived AGEs in dentin and their effect on the nanomechanical properties of dentinal collagen remain unknown. Thus, the aim of the present study was to quantify MGO-based AGEs in the organic matrix of human dentin as a function of age and associate these changes with alterations in the nanomechanical and ultrastructural properties of dentinal collagen. For this, 12 healthy teeth from <26-y-old and >50-y-old patients were collected and prepared to obtain crown and root dentin discs. Following demineralization, MGO-derived AGEs were quantified with a competitive ELISA. In addition, atomic force microscopy nanoindentation was utilized to measure changes in elastic modulus in peritubular and intertubular collagen fibrils. Finally, principal component analysis was carried out to determine aging profiles for crown and root dentin. Results showed an increased presence of MGO AGEs in the organic matrix of dentin in the >50-y-old specimens as compared with the <26-y-old specimens in crown and root. Furthermore, an increase in peritubular and intertubular collagen elasticity was observed in the >50-y-old group associated with ultrastructural changes in the organic matrix as determined by atomic force microscopy analysis. Furthermore, principal component analysis loading plots suggested different "aging profiles" in crown and root dentin, which could have important therapeutic implications in restorative and adhesive dentistry approaches. Overall, these results demonstrate that the organic matrix of human dentin undergoes aging-related changes due to MGO-derived AGEs with important changes in the nanomechanical behavior of collagen that may affect diagnostic and restorative procedures in older people.

Manifestation and Mechanisms of Abnormal Mineralization in Teeth

Tooth biomineralization is a dynamic and complicated process influenced by local and systemic factors. Abnormal mineralization in teeth occurs when factors related to physiologic mineralization are altered during tooth formation and after tooth maturation, resulting in microscopic and macroscopic manifestations. The present Review provides timely information on the mechanisms and structural alterations of different forms of pathological tooth mineralization. A comprehensive study of these alterations benefits diagnosis and biomimetic treatment of abnormal mineralization in patients.

Bacterial adhesion to collagens: implications for biofilm formation and disease progression in the oral cavity

Collagen is the most abundant structural protein in the body and the main component of the extracellular matrix of most tissues, including dentine and periodontal tissues. Despite the well-characterized role of collagen and specifically type-I collagen, as a ligand for host cells, its role as a substrate for bacterial adhesion and biofilm formation is less explored. Therefore, the purpose of this review is to discuss recent findings regarding the adhesion of oral bacteria to collagen surfaces and its role in the progression and severity of oral and systemic diseases. Initial oral colonizers such as streptococci have evolved collagen-binding proteins (cbp) that are important for the colonization of dentine and periodontal tissues. Also, periodontal pathogens such as Porphyromonas gingivalis and Tannerella forsythia utilise cbps for tissue sensing and subsequent invasion. The implications of bacteria-collagen coupling in the context of collagen biomaterials and regenerative dentistry approaches are also addressed. Furthermore, the importance of interdisciplinary techniques such as atomic force microscopy for the nanocharacterization of bacteria-collagen interactions is also considered. Overall, understanding the process of oral bacterial adhesion onto collagen is important for developing future therapeutic approaches against oral and systemic diseases, by modulating the early stages of biofilm formation.

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.

Nanoscopic wear behavior of dentinogenesis imperfecta type II tooth dentin

OBJECTIVES

The aim of this study was to investigate the wear behavior of Dentinogenesis imperfecta type II (DGI-II) dentin and elucidate the correlation between its tribological properties and components.

METHODS

The mid-coronal dentin of normal and DGI-II teeth were divided into two groups: perpendicular and parallel to the dentin tubules. The microstructure of dentin was detected using atomic force microscopy (AFM). The wear behavior of dentin was evaluated by nanoscratch tests and scanning electron microscopy (SEM). Meanwhile, changes in molecular groups and chemical composition were analyzed by Raman and Energy-Dispersive X-ray (EDX) tests, respectively. Nanohardness was also evaluated.

RESULTS

AFM images of DGI-II dentin illustrated a decrease in the number of tubules and the tubule diameter. Nanoscratch test showed a higher friction coefficient and a greater depth-of-scratch in DGI-II dentin. The wear resistance of DGI-II dentin was reduced independent of tubule orientation. EDX results indicated that DGI-II dentin mineral content decreased and Raman spectra results showed DGI-II dentin had a decreased collagen matrix structure stability coupled with hypomineralization. Furthermore, a significant reduction in nanohardness and elastic modulus of DGI-II dentin was observed. Regression analysis revealed a close correlation between dentin components and inferior wear resistance.

CONCLUSIONS

All results indicated the wear behavior of DGI-II dentin was significantly deteriorated, presumably caused by the disorder in microstructures and the reduction of chemical composition.

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.

Comparison and Contrast of Bone and Dentin in Genetic Disorder, Morphology and Regeneration: A Review

The bone and dentin have distinct healing processes. The healing process of bones is regenerative, as newly formed tissues are morphologically and functionally similar to the original bone structures. In contrast, the healing process of dentin is reparative due to its failure to replicate some of its key morphological features. In this review, we compare and contrast the healing processes of bone and dentin. We describe how distinct morphological and physiological structures of the 2 tissues translate into different signaling molecules, growth factors, and matrix protein secretion.

Human dentin characteristics of patients with osteogenesis imperfecta: insights into collagen-based biomaterials

Osteogenesis imperfecta (OI), also known as "brittle bone disease", is a rare genetic disorder of the skeleton, whose most benign form I corresponds to autosomal dominant mutations in the genes encoding type I collagen (COLA1, COLA2). Several associated skeletal manifestations are often observed but, surprisingly, while dentin defects often reflect genetic bone disorders, about half of OI patients have no obvious oral manifestations. Here, we investigated the collagen, mineral and mechanical properties of dentin from deciduous teeth collected from patients with mild form of OI and displaying no obvious clinical signs of dentinogenesis imperfecta. For the first time, an increase in the hardness of OI dentin associated with an increase in mineral content compared to healthy patients was reported. In addition, OI altered the tissue characteristics of the dentin-enamel junction but the interfacial gradient was preserved. The impact of changes in molecular structure due to mutations in OI was assessed by Raman microspectroscopy. Our results highlighted a change in the hydroxyproline-proline ratio in direct association with collagen mineralization. Our findings suggest that the evaluation of teeth could be an important aid for mild types of OI that are often difficult to diagnose clinically and provide experimental evidence that hydroxyproline content should be considered in future studies on collagen-based biomaterials.

CircRNA hsa_circ_0008500 Acts as a miR-1301-3p Sponge to Promote Osteoblast Mineralization by Upregulating PADI4

Circular RNAs (circRNAs) are regarded as pivotal regulators in bone metabolism. However, the role of circRNAs in osteoblast mineralization remains largely unknown. Herein, we explored the expression profiles of circRNAs in 4 groups of osteoblasts with varying mineralization processes. Hsa_circ_0008500 (circ8500), which is upregulated in the RNA-seq data, is sifted through 194 candidate circRNAs in osteoblasts during mineralization. We characterize the features of novel circRNAs and find that the elevated expression of circ8500 promotes osteoblast mineralization. Mechanistically, circ8500 contains a critical binding site for miR-1301-3p. We further show that circ8500 competitively binds miR-1301-3p to abolish its suppressive effect on peptidyl arginine deiminase 4 (PADI4). PADI4 works as a binding partner of RUNX2 and stabilizes its protein expression levels by inhibiting the ubiquitin-proteasome pathway. This work provides new insights on the circRNA patterns in osteoblasts and the role of PADI4 in matrix mineralization.

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.