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Dermal bone

Dermal bone refers to the mineralized skeletal elements that form directly within the dermis layer of the skin in vertebrates, constituting the primary component of the exoskeleton and providing external protection.^[1] Unlike endochondral bones, which develop by replacing a cartilaginous model, dermal bones arise through intramembranous ossification, where osteoblasts deposit hydroxyapatite crystals in the connective tissue of the skin without an intervening cartilage stage.^[2] This process originated in early jawless vertebrates as protective armor or tooth-like odontodes around the basal membrane of the skin or throat, evolving under predation pressures to enhance survival and mobility.^[3] In vertebrate anatomy, dermal bones are distinguished by their superficial position and diverse forms, including flat plates, scales, and scutes that cover the body or reinforce specific regions.^[1] Prominent examples include the bony scales of sharks and bony fishes, the osteoderms in crocodilians and some lizards, the clavicle and parts of the shoulder girdle in tetrapods, and the roof of the skull in mammals, such as the frontal and parietal bones.^[2] These structures often feature enameloid or dentine coatings for added durability, reflecting their homology to ancient dermal armor in fossil jawless fish like ostracoderms.^[3] The evolutionary history of dermal bone traces back to the origins of vertebrates around 500 million years ago, marking a key innovation in skeletal mineralization that preceded the endoskeleton.^[3] Initially forming as acellular bone in primitive forms, it later incorporated cellular elements and spread into deeper dermal layers, contributing to the transition from exoskeletal dominance in aquatic vertebrates to integrated skeletal systems in terrestrial ones.^[3] Developmentally, cranial dermal bones typically derive from neural crest cells, while trunk elements like fish scales often originate from mesodermal tissues, with neural crest contributions observed in some species such as basal bony fish.^[2]^[4] This duality underscores the adaptability of dermal bone across vertebrate clades, from agnathans to amniotes.

Definition and Characteristics

Definition

Dermal bones are ossified structures that form directly from mesenchymal connective tissue within the dermis of the skin, bypassing any cartilaginous precursor and undergoing intramembranous ossification to produce flat or plate-like elements of the vertebrate skeleton.^[5] This process involves the differentiation of mesenchymal cells into osteoblasts, which deposit bone matrix without an intermediate cartilage stage, distinguishing dermal bones from those formed through endochondral ossification.^[6] The term "dermal bone" originated in the early 19th century within the field of comparative anatomy, where it was used to describe intramembranous or "membrane" bones, particularly those forming the roof of the vertebrate skull, in contrast to replacement bones derived from cartilage.^[7] The earliest documented use appears in 1833 by British surgeon and paleontologist Gideon Algernon Mantell, reflecting observations of fossilized vertebrate remains that highlighted these skin-derived skeletal components.^[7] Etymologically, "dermal" derives from the Greek derma (skin), emphasizing the bone's developmental origin in the dermal layer of the integument, while the contrasting term "endochondral" (from Greek endon, within, and chondros, cartilage) underscores the cartilage-mediated formation of other bone types.^[7] This nomenclature has persisted in vertebrate biology to classify bones based on their embryological and histological origins rather than solely on anatomical position.^[2]

Key Characteristics

Dermal bones are characterized by their superficial location within the dermis and formation through intramembranous ossification, resulting in flat, plate-like structures that lack a cartilaginous precursor. These bones exhibit a compact, dense composition, particularly in early developmental stages, where they form without a central marrow cavity, consisting primarily of lamellar cortical bone that provides structural integrity. Growth occurs mainly by apposition, or accretion, on external surfaces, allowing for incremental layering of new bone tissue directly from osteoblasts.^[8] A distinctive morphological feature of dermal bones is their frequent ornamentation with surface modifications such as pits, ridges, tubercles, or vascular grooves, which facilitate muscle attachments, sensory functions, or protection against external forces. These ornamentations often include odontogenic tissues like enameloid or dentine in basal vertebrates, enhancing durability. In the head region, dermal bones derive from neural crest cells, contributing to their rapid formation supported by high vascularity through periosteal channels and haversian systems, which enable efficient nutrient delivery and quick remodeling.^[9]^[10]^[8] Mechanically, dermal bones demonstrate high stiffness and resistance to bending, owing to their dense lamellar organization and superficial positioning, making them well-suited for protective roles such as shielding underlying tissues from impact. This combination of traits distinguishes them from endochondral bones, emphasizing their adaptation for external load-bearing rather than internal support.^[8]^[11]

Development and Formation

Embryological Origin

Dermal bones originate from undifferentiated mesenchymal cells located within the dermis, which differentiate directly into osteoblasts without an intervening cartilaginous stage. These mesenchymal precursors condense to form membranous templates that serve as the foundation for bone deposition during intramembranous ossification. In the cranial region, this process is heavily influenced by the migration of neural crest cells, which contribute significantly to the mesenchymal population responsible for forming the dermatocranium, including flat bones of the skull vault. In contrast, postcranial dermal bones, such as scales in fish or osteoderms in reptiles, primarily derive from mesodermal mesenchyme in the trunk and appendicular regions.^[2] The formation of dermal bones commences during early embryogenesis. In human development, mesenchymal condensations for cranial dermal bones begin to appear around the 6th to 7th week of gestation, with ossification centers initiating shortly thereafter. This timeline aligns with the broader establishment of the skeletal framework, where neural crest-derived mesenchyme in the head region proliferates and patterns the prospective bone sites. Genetic regulation plays a pivotal role in the patterning and differentiation of these mesenchymal cells into dermal bone. Hox genes, particularly those in the HoxA and HoxB clusters (such as Hoxa1, Hoxb1, and Hoxa2), are essential for specifying cranial neural crest identity and regionalizing the pharyngeal arches, thereby directing the precise positioning and morphology of dermal bones like the mandible and maxilla. Concurrently, bone morphogenetic protein (BMP) signaling pathways, including BMP2 and BMP4, promote osteogenic commitment in the neural crest-derived mesenchyme by inducing preosteoblast formation and regulating the balance between osteogenesis and chondrogenesis.^[12]^[13] Unlike endochondral bones, which develop through a hypertrophic cartilage intermediate formed from chondroblasts, dermal bones exhibit direct differentiation of mesenchymal cells into osteoblasts, bypassing chondrogenesis entirely. This intramembranous pathway allows for the rapid formation of protective, flat skeletal elements, particularly in the cranium, and is conserved across vertebrates for dermal armor and skull components.^[6]

Ossification Process

The ossification of dermal bones occurs through intramembranous ossification, a direct process that bypasses cartilage formation and involves the transformation of mesenchymal tissue into bone without an endochondral intermediate. This process begins with the condensation of mesenchymal cells at sites of future bone formation, such as in the cranial vault or dermal shields, where these cells aggregate into dense clusters to establish the foundational template for bone development. Derived from mesenchymal origins as outlined in the Embryological Origin section, these condensations provide the progenitor population for subsequent differentiation.^[13] Following condensation, the mesenchymal cells differentiate into osteoblasts, the primary cellular actors responsible for bone formation; these osteoblasts arise from precursor cells such as pericytes or fibroblast-like mesenchymal stem cells within the connective tissue membrane. Osteoblasts then secrete an organic bone matrix known as osteoid, composed mainly of type I collagen and other proteins, which is deposited around the cells to form the initial unmineralized framework. Mineralization follows rapidly, as calcium and phosphate ions precipitate within the osteoid, hardening it into mature bone and trapping some osteoblasts as osteocytes embedded in the matrix; osteoclasts, derived from hematopoietic precursors, contribute to remodeling by resorbing excess bone to refine the structure.^[14] At the molecular level, transcription factors play critical roles in committing cells to the osteoblast lineage during differentiation. Runx2, a key regulator, initiates osteoblast commitment by activating genes for early matrix proteins and promoting the transition from preosteoblasts to mature osteoblasts, with its absence preventing any ossification. Osterix (Osx), acting downstream of Runx2, further drives osteoblast maturation by regulating genes such as bone sialoprotein and osteocalcin, ensuring proper matrix deposition and mineralization in intramembranous bones.^[14]^[15] Dermal bone growth proceeds via appositional mechanisms, where new bone layers are added peripherally by osteoblasts on the periosteal surface, allowing expansion without internal cartilage replacement or endochondral invasion. This mode supports the rapid formation of flat, protective structures like those in the skull, with ongoing remodeling by osteoclasts maintaining structural integrity.^[13]

Anatomical Locations

In the Skull and Head

Dermal bones in the skull and head of vertebrates form the dermatocranium, an outer layer that covers the chondrocranium and contributes to the overall structure of the cranial vault and facial region. These bones arise through intramembranous ossification directly from mesenchymal tissue in the dermis, providing a protective overlay without an intervening cartilage stage. In mammals, prominent examples include the frontal and parietal bones, which form the superior aspect of the skull roof, as well as the nasal and lacrimal bones in the facial skeleton. In fish, the dermatocranium comprises multiple plate-like elements, such as the dermosphenotic bone, which associates with sensory canals and contributes to the superficial skull covering. These dermal bones serve key functions in the head, including forming the rigid skull roof to shield the brain and underlying structures, while dermal jaw elements like the premaxilla and dentary provide the foundational framework for the upper and lower jaws, respectively, supporting feeding and oral functions. The premaxilla bears anterior teeth and articulates with the maxilla, whereas the dentary forms the bulk of the mandible in advanced vertebrates. In humans, cranial dermal bones—such as the frontal, two parietals, two nasals, two lacrimals, and vomer—contribute significantly to both the neurocranium (protecting the brain) and viscerocranium (forming facial contours). During development, these bones grow appositionally and eventually fuse along fibrous joints called sutures, allowing for brain expansion in infancy. However, these sutures are vulnerable to premature fusion in craniosynostosis, a condition where accelerated intramembranous ossification restricts skull growth and can result in abnormal head shapes and increased intracranial pressure.

In the Postcranial Skeleton

Dermal bones are notably scarce in the postcranial skeleton of vertebrates, contrasting with their prevalence in the cranial region, and primarily appear as specialized supportive elements rather than load-bearing structures. The most prominent example is the clavicle, a key component of the pectoral girdle that originates as a dermal bone across many vertebrate lineages. In mammals, including humans, the clavicle exhibits a mixed ossification pattern, with intramembranous formation in the main shaft from mesenchymal tissue and endochondral contributions at the ends from cartilaginous precursors, reflecting evolutionary adaptations for shoulder mobility.^[16]^[17] This dermal origin underscores the clavicle's role in bridging the appendicular skeleton to the axial framework, often as a slender strut that enhances leverage without adding substantial mass. In aquatic vertebrates like fish, postcranial dermal bones manifest as the lepidotrichia, or fin rays, which are rod-like dermal ossifications embedded in the fin membranes to provide flexibility and structural integrity during locomotion. These segmented, bilateral elements form via intramembranous processes and articulate with internal radials, enabling precise control of fin shape and propulsion.^[18]^[19] Among reptiles, dermal bones contribute to protective exoskeletal features, such as the scales and plates in various species; a quintessential case is the turtle plastron, the ventral shell component composed entirely of dermal ossicles that ossify intramembranously in the dermis to form a rigid, lightweight barrier.^[20] These ossicles interlock to create a seamless plate, integrating with the overlying keratinous scutes for enhanced defense against predators. In amphibians and birds, postcranial dermal bones are even more restricted, typically limited to sesamoid-like elements embedded in tendons or occasional gastralia—ventral abdominal ribs that serve as dermal ossifications for abdominal support. In extant amphibians, such structures are minimal, with sesamoids providing localized reinforcement at joint interfaces, while fossil forms occasionally show more extensive dermal armor.^[21] Birds, similarly constrained, retain dermal contributions primarily in the furcula (fused clavicles), but lack widespread gastralia, emphasizing lightweight adaptations for flight.^[22] Gastralia, when present in related archosaurs like crocodilians, function as thin dermal struts to stabilize the ventral body wall.^[23] Overall, these postcranial dermal bones tend to be thin and plate-like, prioritizing tensile support and flexibility over compressive strength to accommodate dynamic movements without impeding agility.^[24]

Evolutionary Aspects

In Vertebrates

Dermal bones first emerged in early jawless vertebrates (agnathans) around 500 million years ago, with significant development in jawed vertebrates (gnathostomes) by the Silurian-Devonian periods (approximately 440-360 million years ago), primarily serving to protect the skull and sensory structures in these primitive aquatic forms.^[3] In early jawless vertebrates like ostracoderms, these formed protective head shields and body armor, predating the more integrated cranial structures in gnathostomes. These structures originated as intramembranous ossifications within the dermis, forming a robust exoskeleton that encased the head and, in some lineages, extended to the body for enhanced defense against environmental hazards and predation.^[25] In placoderms, an early group of armored gnathostomes, dermal bones expanded dramatically to create extensive plated armor, which provided mechanical protection and supported the evolution of powerful biting jaws, marking a key adaptation for survival in Devonian seas.^[26] Across vertebrate evolution, dermal bones have been conserved in all major groups, from chondrichthyans and osteichthyans to tetrapods and mammals, underscoring their fundamental role in cranial architecture despite varying degrees of elaboration.^[27] However, their number and prominence have progressively reduced, particularly during tetrapod evolution around 375 million years ago, where the extensive dermal skull roofing seen in early osteichthyan fishes (comprising around 30 or more individual elements) underwent simplification, reducing to approximately 41 in stem-tetrapods and further to about 8 major flat bones in the human calvaria, reflecting adaptations to terrestrial locomotion and reduced need for heavy armor.^[28] This regression intensified in mammals, where endochondral ossification dominates the postcranial skeleton, relegating dermal bones mainly to the cranium and leaving only vestiges like the clavicle in the shoulder girdle.^[29] Fossil evidence from Devonian and Carboniferous deposits has been instrumental in tracing these evolutionary shifts, with well-preserved dermal skull elements in transitional forms such as Eusthenopteron and Ichthyostega revealing patterns of bone loss and fusion that facilitated the shift from aquatic to terrestrial environments.^[21] These fossils highlight how dermal bones acted as diagnostic markers for identifying early tetrapod lineages, providing insights into the biomechanical trade-offs between protection and mobility during the conquest of land.^[30]

Comparative Examples

In teleost fishes, the dermal skeleton is extensive and includes prominent elements such as the opercular bones, which form part of the gill cover and exhibit diverse shapes across species to accommodate varied feeding and respiratory functions.^[31] Scales in teleosts also represent dermal ossifications, serving as protective coverings that develop directly from the dermis and influence the patterning of underlying sensory structures like the lateral line system. These features highlight the prevalence of dermal bone in the integumentary and cranial regions of teleosts, contrasting with more limited distributions in tetrapods.^[32] Among reptiles, crocodilians possess dermal armor in the form of osteoderms, which are bony plates embedded in the dermis of the dorsal and ventral skin, providing mechanical protection and structural support.^[33] In turtles, the carapace and plastron originate from dermal ossifications, where multiple osteoderms fuse with underlying endoskeletal elements like ribs to form the rigid shell structure.^[34] This dermal contribution to the shell underscores a specialized adaptation for defense, differing from the more fragmented osteoderms in crocodilians.^[35] In mammals, dermal bones are largely restricted to cranial elements, such as parts of the skull roof and palate, and the clavicle, which is the primary postcranial dermal bone retained in many species.^[2] This contrasts with marsupials, where the clavicle is often more prominent and robust, maintaining a stronger connection to the pectoral girdle for enhanced forelimb mobility in arboreal or fossorial lifestyles.^[36] The reduction or absence of the clavicle in some placental mammals, such as carnivorans, further illustrates the diminished role of postcranial dermal bone in this group.^[37] Birds exhibit a near-complete absence of postcranial dermal bones, an adaptation linked to the lightweight requirements for flight, with the skeleton relying predominantly on endochondral ossification for elements like the limb bones.^[2] However, dermal bone contributes to the beak through the ossification of upper jaw elements, such as the premaxilla and maxilla, which form the bony core supporting the keratinous rhamphotheca.^[38] This cranial specialization reflects a selective retention of dermal elements in the head, while postcranial dermal structures were evolutionarily lost to minimize mass.^[39]

Functions and Physiological Roles

Protective Functions

Dermal bones primarily serve to shield vital organs from mechanical damage, with those in the vertebrate skull forming a robust roofing layer over the brain and sensory structures such as the eyes and nasal capsules.^[40] In early vertebrates, extensive dermal armor extended across the body, providing a defensive barrier against environmental hazards and predation, as seen in the plated exoskeletons of ancient jawless fishes and placoderms.^[41] This protective role is evident in the skull roof, where dermal elements like the frontal and parietal bones encase the neurocranium, distributing external forces to prevent direct trauma to underlying neural tissues.^[40] Biomechanically, dermal bones exhibit high compressive strength due to their dense, mineralized matrix, enabling them to withstand substantial loads without fracturing; cortical bone in these structures typically achieves a Young's modulus of 10–20 GPa in the longitudinal direction.^[42] Ornamentation, such as tubercles on placoderm dermal plates, further enhances impact absorption by promoting energy dissipation through layered deformation, where harder outer layers (e.g., with hardness up to 4.5 GPa) transfer stress to tougher inner bone (toughness of 2–7 kJ·m⁻²).^[43]^[42] This hierarchical structure confers resistance to penetration and cracking, optimizing protection under dynamic predatory attacks.^[43] In placoderms, the multilayered dermal armor functioned as a key anti-predator adaptation during the Devonian period, with scales resisting biting forces from contemporaries like Dunkleosteus through graded material properties that absorbed energy via plasticity in basal bone layers (yield stress ~180 MPa).^[43] Similarly, in humans, the frontal bone—of dermal origin—demonstrates superior trauma resistance, requiring the highest failure forces (elastic modulus 3.79–15.54 GPa) and absorbing more energy than adjacent parietal bones during impacts, thereby safeguarding the frontal lobe and orbits.^[44] The rapid formation of dermal bones via intramembranous ossification provides a developmental advantage, allowing mesenchymal condensations to differentiate directly into ossified tissue without an intermediate cartilaginous stage, thus enabling early embryonic protection for vulnerable structures like the developing brain.^[5] This process facilitates quicker skeletal maturation compared to endochondral ossification, enhancing survival in nascent vertebrates by establishing a protective exoskeleton ahead of full organ development.^[5]

Other Physiological Roles

In reptiles such as crocodilians, dermal bones, particularly osteoderms, play a key role in ion buffering by storing calcium carbonate that helps regulate acidosis during prolonged apnea. During submersion, when lactic acid accumulates due to anaerobic metabolism, the vascular network within osteoderms facilitates the transport of lactate into the bone matrix, where osteoclasts release calcium and magnesium carbonates to neutralize protons and maintain blood pH. This mechanism is analogous to processes observed in turtles, where mineralized tissues contribute significantly to extracellular buffering of lactic acid, with carbonates providing up to 40% of the total buffering capacity in some species.^[45]^[46]^[47] Beyond acid-base balance, osteoderms in crocodiles contribute to thermoregulation through their extensive vascular networks, which enable efficient heat exchange during basking. When exposed to solar radiation, these dermal structures absorb external heat, raising their temperature above that of the surrounding body by up to 5–10°C, thereby facilitating convective heat transfer to the core via blood flow. This vascularization allows semiaquatic crocodilians to compensate for heat loss in water and achieve stable body temperatures, supporting ectothermic behavioral strategies.^[48] In fishes, dermal bones of the skull and scales incorporate vascular grooves that integrate with the lateral line system, enhancing sensory perception of water movements. These grooves house neuromasts within canal systems, where underlying vascular bone layers supply nutrients and oxygen, ensuring the functionality of this mechanosensory organ for detecting vibrations and pressure changes. Such adaptations are evident in early bony fishes, where compact vascular bone directly borders the horizontal canal systems, supporting ecological roles in predator avoidance and schooling.^[49]^[50] Dermal bones also serve as metabolic calcium reservoirs in various vertebrates, differing from endochondral bones by prioritizing mineral storage over hematopoiesis. In species like armadillo lizards, osteoderms exhibit higher density and compactness in females, providing labile calcium for reproductive demands such as eggshell formation, with up to 20–30% of total skeletal calcium potentially mobilized from these structures. This role underscores the evolutionary persistence of dermal bone as a phosphate and carbonate depot, particularly in reptiles lacking extensive marrow cavities.^[51]^[52]

Clinical and Pathological Considerations

Disorders Involving Dermal Bones

Disorders involving dermal bones encompass both congenital and acquired pathological conditions that disrupt intramembranous ossification, primarily impacting the craniofacial skeleton where these bones predominate. Congenital disorders often stem from genetic mutations affecting osteoblast differentiation and suture patency, while acquired issues like infections exploit the thin cortices and vascular networks of dermal elements, such as the mandible. These conditions highlight vulnerabilities in the ossification process, where disruptions can lead to structural deformities or inflammatory destruction.^[53]^[54]^[55] Craniosynostosis represents a key congenital disorder of dermal bones, defined by the premature fusion of one or more cranial sutures—the fibrous articulations between flat skull bones formed via intramembranous ossification. This early closure restricts skull expansion perpendicular to the fused suture, resulting in characteristic deformities such as scaphocephaly from sagittal suture involvement or brachycephaly from coronal suture fusion, alongside risks of elevated intracranial pressure and neurodevelopmental delays. Syndromic forms, like Apert syndrome, involve multisuture craniosynostosis due to FGFR2 gene mutations, producing a tower-like skull (turribrachycephaly), midface hypoplasia, and syndactyly. The condition exerts a higher impact on craniofacial development, altering facial proportions and potentially impairing vision or hearing. Prevalence is estimated at approximately 1 in 2,000 to 2,500 live births, with nonsyndromic cases comprising about 70-80% of occurrences.^[53]^[56]^[57]^[58] Cleidocranial dysplasia (CCD) is another hereditary disorder targeting intramembranous ossification, caused by heterozygous mutations in the RUNX2 transcription factor gene on chromosome 6p21, which regulates osteoblast activity. This leads to hypoplasia or complete aplasia of the clavicles—dermal bones essential for shoulder girdle stability—resulting in narrow shoulders and the ability to approximate them anteriorly. Cranial manifestations include delayed fontanelle closure, persistent metopic suture, and multiple wormian bones, increasing fracture risk and hydrocephalus potential; dental issues, such as supernumerary teeth and delayed eruption, further complicate the phenotype. CCD affects approximately 1 in 1,000,000 individuals, with variable expressivity even within families.^[54]^[59]^[60] Acquired infections, such as osteomyelitis, preferentially involve dermal bones like the mandible due to their thin, vascular cortices and proximity to oral flora. Osteomyelitis here begins as a medullary infection, often from odontogenic sources like dental abscesses, progressing to cortical involvement, sequestrum formation, and potential pathologic fractures if chronic. The mandible's rich blood supply facilitates rapid bacterial dissemination, particularly from Staphylococcus aureus or mixed anaerobes, leading to swelling, trismus, and fistula development. While less common than in long bones, mandibular osteomyelitis accounts for the majority of craniofacial cases, underscoring the regional vulnerability of dermal elements.^[55]^[61]^[62]^[63]

Surgical and Therapeutic Implications

Surgical interventions for dermal bone anomalies, particularly in the cranium, often involve cranioplasty to address premature suture fusion known as craniosynostosis. Autologous bone grafts, such as split calvarial grafts harvested during the procedure, are commonly used to reconstruct the cranial vault, promoting integration through intramembranous ossification and minimizing rejection risks.^[64]^[65] These autografts mimic the natural dermal bone structure, providing structural support and facilitating normal brain growth. Alternatively, 3D-printed implants, including custom titanium meshes or low-cost polymer-based prosthetics, offer precise fitting based on preoperative imaging, reducing operative time and improving aesthetic outcomes in resource-limited settings.^[64]^[66] In orthodontics, treatments targeting dermal bones of the jaw, such as the maxilla, leverage biomechanical forces to induce bone remodeling and correct malocclusions. Rapid maxillary expansion (RME) appliances apply controlled forces to separate the midpalatal suture, stimulating new bone formation via intramembranous ossification and increasing transverse maxillary dimensions.^[67] This approach enhances skeletal alignment, reduces dental crowding, and improves facial aesthetics, with studies showing sustained bone deposition in the palatal suture post-treatment.^[68] Bone-borne expanders, which anchor directly to the maxilla, further optimize skeletal effects by minimizing dental tipping and promoting targeted dermal bone expansion.^[69] Regenerative therapies increasingly focus on stem cell-based strategies to repair dermal bone defects through intramembranous ossification pathways. Mesenchymal stem cells (MSCs), particularly those derived from bone marrow or periosteum, are directed to differentiate into osteoblasts, directly forming bone matrix without a cartilaginous intermediate.^[70] These cells, when combined with growth factors like BMP-2, enhance defect healing in preclinical models by promoting vascularization and osteogenesis.^[71] Skeletal stem cells identified in perivascular niches further support this process, contributing to robust intramembranous regeneration in calvarial defects.^[72] As of 2025, advances in bioengineered scaffolds offer promising options for reconstructing dermal bones affected by dysplasia, such as the clavicle in cleidocranial dysplasia. These scaffolds, often composed of biodegradable polymers like poly(ε-caprolactone) integrated with cell-laden hydrogels, provide a biomimetic matrix that supports osteoblast differentiation and bone ingrowth.^[73] In genetic models of dysplasia, gene-corrected induced pluripotent stem cells (iPSCs) seeded onto such scaffolds have demonstrated improved engraftment and regeneration in skeletal defects, paving the way for personalized clavicular repairs.^[74] This approach builds on prior disorders involving dermal bones by emphasizing targeted tissue engineering to restore function.^[75]

References

[1]
Morphology of the Vertebrates
Dermal bone consists of bony structures (plates and scales) that develop in the skin. The bony armor of the earliest jawless fish was dermal bone; so are shark ...Missing: characteristics | Show results with:characteristics
[2]
Evolution of the vertebrate skeleton: morphology, embryology, and ...
In contrast, the exoskeleton consists of dermal bones (sensu [7]), which are homologous with bony armor and are often coated with enameloid or dentine tissues ...
[3]
Where did bone come from? An overview of its evolution - PMC
Bone is specific to vertebrates, and originated as mineralization around the basal membrane of the throat or skin, giving rise to tooth-like structures and ...Missing: characteristics | Show results with:characteristics
[4]
Dermal Bone - an overview | ScienceDirect Topics
Dermal bone forms via a process known as intramembranous ossification, with mesenchymal condensations differentiating directly into bone without a ...
[5]
Embryology, Bone Ossification - StatPearls - NCBI Bookshelf - NIH
Intramembranous ossification directly converts the mesenchymal tissue to bone and forms the flat bones of the skull, clavicle, and most of the cranial bones.
[6]
dermal bone, n. meanings, etymology and more
The earliest known use of the noun dermal bone is in the 1830s. OED's earliest evidence for dermal bone is from 1833, in the writing of Gideon Mantell, surgeon ...Missing: origin | Show results with:origin
[7]
https://www.oed.com/dictionary/dermal-bone_n
[8]
Histology of “placoderm” dermal skeletons - Wiley Online Library
Feb 2, 2013 · The dermal skeleton comprises three principal divisions: a superficial lamellar layer, including the ornament; a medial layer with a large ...
[9]
https://onlinelibrary.wiley.com/doi/full/10.1002/jmor.20119
[10]
Evolvability of the vertebrate craniofacial skeleton - PMC - NIH
Dec 13, 2017 · ... dermal bone. Population of the PAs with CNC gave rise ... Additionally, mechanical simulations have shown that the strength and stiffness ...
[11]
Scales, scutes, and embryonic origins of the vertebrate dermal ... - NIH
Aug 2, 2023 · The story of vertebrate origins is one of novel cell types and shifting germ layer fates—and at the center of this story lies the neural crest.Missing: characteristics | Show results with:characteristics
[12]
Coupling the roles of Hox genes to regulatory networks patterning ...
Dec 1, 2018 · Hox genes have been shown to play important roles at multiple stages in cNCC development, including specification, migration, and differentiation.
[13]
Regulation of skeletogenic differentiation in cranial dermal bone
Sep 1, 2007 · Intramembranous bones are classified into three categories: the sesamoid bones, which form in tendons as a result of mechanical stress (such as ...
[14]
Transcriptional Regulatory Cascades in Runx2-Dependent Bone ...
The process of intramembranous ossification begins with mesenchymal stem cells (MSCs), and the bone tissue is generated by the development of MSCs into ...
[15]
Osteoblast-specific Transcription Factor Osterix (Osx) Is an ... - NIH
Both endochondral and intramembranous ossification require Runx2, which is involved in the differentiation of mesenchymal cells into preosteoblasts (3). As a ...
[16]
Developmental origin of the clavicle, and its implications for ... - NIH
The pectoral appendage is comprised of endochondral portions, such as the humerus and the scapula, and a dermal portion, such as the clavicle, that contributes ...
[17]
Development of the clavicles in birds and mammals - ResearchGate
Aug 8, 2025 · In mammals the clavicles show a combination of intramembranous and endochondral ossifications (Hall 2001) . Growth hyaline cartilages are ...
[18]
ZFIN Anatomy Ontology: lepidotrichium
fin ray; lepidotrichia. Definition: Dermal bone that is rod-like, formed and usually contained in a fin membrane, and jointed to or adjacent to distal radials.
[19]
Dermal fin rays and scales derive from mesoderm, not neural crest
May 6, 2013 · Post-cranial dermal exoskeletal elements such as the bony fin rays (lepidotrichia), scales, bony armour and turtle plastrons have been ...
[20]
Development of the turtle plastron, the order-defining skeletal structure
Apr 25, 2016 · Although the recruitment of the ossification pathways used in other intramembranous bones seems evident in the turtle plastron ... dermal bone ...
[21]
Dermal bone in early tetrapods: a palaeophysiological hypothesis of ...
Apr 25, 2012 · Many early tetrapods possessed dermal bones of the skull and pectoral girdle with an external (superficial) surface heavily sculptured by pits, ...
[22]
(PDF) Cartilage on the furculae of living birds and the extinct bird ...
Jul 22, 2021 · As the only dermal bone in the avian postcranium, the furcula is a potential site for the formation of furcular secondary cartilage and merits ...
[23]
[PDF] DINOSAUR GASTRALIA; ORIGIN, MORPHOLOGY, AND FUNCTION
ABSTRACT—Gastralia are dermal ossifications situated in the ventral abdominal wall. Gastralia may be plesiomorphic for tetrapods, but are only retained in ...
[24]
Evolution of the vertebrate skeleton: morphology, embryology, and ...
Jan 13, 2015 · Exoskeletal bones are located superficially in the body in ancestral conditions, but some exoskeletal bones, such as the dentary and clavicle ...
[25]
The origin and early phylogenetic history of jawed vertebrates - PMC
Nov 17, 2015 · Early Devonian (419 Ma) mandibulate gnathostomes were already ecologically diverse and, by the close of the Devonian (360 Ma), the first ...
[26]
New findings in a 400 million-year-old Devonian placoderm shed ...
Aug 10, 2017 · Their highly evolved blade-like dermal jaw bones have been used as exemplars in analyses of the early evolution of jaws and teeth. However, ...
[27]
Bony Beginnings: The Rise of Vertebrate Innovation in the Devonian
Many fish from this period were characterized by bony plates of protective armor. These are called the Osteostracans and the Placoderms.
[28]
Problems in Fish-to-Tetrapod Transition: Genetic Expeditions Into ...
Even though a large number of dermal bones have been lost in the transition from fish, tetrapods still possess comparable developmental pathways of dermal bones ...
[29]
Earliest land animals had fewer skull bones than fish, restricting their ...
Sep 9, 2022 · The skulls of tetrapods had fewer bones than extinct and living fish, limiting their evolution for millions of years, according to a latest study.
[30]
Step changes in evolution - ScienceDirect.com
Jan 20, 2020 · Dermal bone has become less important in terrestrial tetrapods, although it is still present in structures like our skull and clavicle, and most ...Missing: reduced | Show results with:reduced
[31]
Early tetrapod cranial evolution is characterized by increased ...
Sep 9, 2022 · We find that bone loss across the origin of tetrapods is associated not only with increased complexity of bone-to-bone contacts but also with decreasing ...
[32]
A rich diversity of opercle bone shape among teleost fishes - PMC
Dec 27, 2017 · We surveyed the shapes of this bone among 110 families spanning the teleost tree and examined its pattern of occupancy in a principal component-based ...
[33]
[PDF] The phylogenetic significance of bone types in euteleost fishes
The study provided the opportunity to review theories of the association between bone and teeth in teleost fishes.
[34]
A survey of osteoderm histology and ornamentation among ...
Osteoderms of eight extant and extinct species of crocodylomorphs are studied histologically and morphologically.
[35]
The integumentary skeleton of tetrapods: origin, evolution, and ...
All osteoderms share a common origin within the dermis (at or adjacent to the stratum superficiale) and are composed primarily (but not exclusively) of osseous ...
[36]
[PDF] The origin of the turtle body plan: evidence from fossils and embryos
The prevailing scenario involved the formation of the carapace in turtles through fusion of dermal bony plates (osteoderms) to the underlying ribs (Versluys ...Missing: armor crocodilians
[37]
[PDF] Evolutionary Development of the Mammalian Presternum
The interclavicle, which sits between the sternal Page 12 12 bands and the clavicle, is present in the marsupial embryo. However, Klima argues that this ...
[38]
On the development of the shoulder girdle in Crocidura russula ...
In monotremes the clavicle is completely dermal, so it can be concluded that the presence of secondary cartilage as part of the clavicle in Placentalia is a ...
[39]
The Cells that Fill the Bill: Neural Crest and the Evolution of ...
Birds display magnificent variation in their beak morphology. Despite this diversity, all beaks originate from equivalent embryonic primordia, tissues, and ...
[40]
From fish to modern humans – comparative anatomy, homologies ...
This study, which reports the second part of the research project, focuses mainly on sarcopterygians and particularly on how the pectoral and forelimb muscles ...Missing: dermal | Show results with:dermal
[41]
None
### Summary of Protective Functions of Dermal Bones in the Skull
[42]
Ancient vertebrate dermal armor evolved from trunk neural crest
Aug 2, 2023 · The body of early vertebrates was covered from the head to tail with extensive dermal armor, comprised of dentin and bone.
[43]
Biomechanics and mechanobiology of the bone matrix - PMC - NIH
Aug 30, 2022 · The bone matrix has both high strength and strong toughness, indicating that bone requires both high strength to deal with the impact of ...
[44]
[PDF] Materials design principles of ancient fish armour - MIT
Jul 27, 2008 · Romer in. 1933 hypothesized that dermal armour served as a protection from predators4 and subsequently a number of additional mechanical and ...
[45]
Investigation of the elastic modulus, tensile and flexural strength of ...
They found that the frontal bone specimens required the highest forces upon failure and prior to failure absorbed the most energy, compared to the parietal ...Missing: origin resistance
[46]
Vascularization in Ornamented Osteoderms: Physiological ...
Oct 10, 2017 · During apnea (submerged), the osteoderm vascular network would convey the lactate into the bone matrix and may be supplied with osteoclasts ...ABSTRACT · INTRODUCTION · DISCUSSION · CONCLUSION
[47]
The evolution of dermal shield vascularization in Testudinata ... - NIH
Bone acidosis buffering during apnea has also been identified in crocodylian osteoderms, which are also known to employ heat transfer when basking. Although ...
[48]
Bone and shell contribution to lactic acid buffering of submerged ...
Based on this study and the earlier in vitro study (13), we now believe that Ca2+, Mg2+, and Na+ carbonates are mobilized to supplement extracellular buffering.
[49]
The crocodylian skull and osteoderms: A functional exaptation to ...
Dec 12, 2018 · Our results show that the osteoderms collect the external heat during the basking periods as they become significantly warmer than the ...
[50]
Scales and Dermal Skeletal Histology of an Early Bony Fish ...
Apr 9, 2013 · Under the vascular bone layer lies the base, which consists of one keel flanked by two ledges (Figure 3D). Histologically the keel and two ...
[51]
[PDF] Scales and Dermal Skeletal Histology of an Early Bony Fish ...
Apr 9, 2013 · The vascular bone below the horizontal canal system is poorly developed in Psarolepis (Figure 11C, D). Occasionally, the compact bone layer lies ...
[52]
Osteoderms as calcium reservoirs: Insights from the lizard ... - NIH
May 3, 2022 · We demonstrate that female Armadillo lizards (Ouroborus cataphractus) have denser, more compact osteoderms than males of similar body sizes.
[53]
Osteoderms as calcium reservoirs: Insights from the lizard ...
May 3, 2022 · In this study, we use micro-computed tomography to investigate inter- and intrasexual variation in osteoderm density in the viviparous lizard ...
[54]
UNDERSTANDING CRANIOSYNOSTOSIS AS A GROWTH ...
Craniosynostosis is a condition of complex etiology that always involves the premature fusion of one or multiple cranial sutures and includes various anomalies ...
[55]
Cleidocranial Dysplasia Spectrum Disorder - GeneReviews - NCBI
Jan 3, 2006 · CCD spectrum disorder affects most prominently those bones derived from intramembranous ossification, such as the cranium and the clavicles, ...
[56]
Osteomyelitis of the Craniofacial Skeleton - PMC - PubMed Central
Osteomyelitis is defined as an inflammatory condition of the bone that commences as an infection of the medullary cavity, rapidly involving the Haversian ...
[57]
Signaling Mechanisms Underlying Genetic Pathophysiology of ... - NIH
Craniosynostosis, is the premature fusion of one or more cranial sutures which is the second most common cranial facial anomalies. The premature cranial sutures ...
[58]
Craniosynostosis - StatPearls - NCBI Bookshelf - NIH
Jan 19, 2025 · Epidemiology. The prevalence of craniosynostosis is 1 in 2000 to 2500 live births.[8][7] Risk factors include maternal smoking, in utero ...
[59]
Apert Syndrome - StatPearls - NCBI Bookshelf
Apr 12, 2025 · Apert syndrome, also known as acrocephalosyndactyly type I, is a genetically inherited syndrome characterized by multisuture craniosynostosis, midface ...
[60]
A rare presentation of cleidocranial dysplasia - PMC - NIH
Aug 8, 2012 · Cleidocranial dysplasia (CCD) is an autosomal-dominant skeletal dysplasia affecting intramembranous ossification. The diagnosis of CCD is based ...
[61]
Cleidocranial dysplasia - PMC - PubMed Central - NIH
Cleidocranial dysplasia is a rare autosomal dominant condition leading to disturbance in ossification of the bones of cranial and facial skeleton. The ...
[62]
Mandibular blastomycosis: A case report and review of the literature
Osteomyelitis is an inflammatory process of the medulla of the bone. Osteomyelitis of the mandible is rare but is more common than maxillary involvement due to ...
[63]
A rare case of candida osteomyelitis of the mandible associated with ...
Jul 18, 2024 · Candida osteomyelitis, in general, is a relatively rare manifestation compared to its bacterial counterparts. The mandible's involvement is rarer.
[64]
Current Concepts in Cranial Reconstruction: Review of Alloplastic ...
Aug 19, 2022 · Advantages. The main advantage of 3D-printed custom titanium implants is the predictable fit. A preoperative high-resolution computed ...
[65]
Review of Nonsyndromic Patients Treated With a Novel Technique
Open cranial vault remodeling (CVR) with autologous split calvarial bone grafts redistributes and recontours an abnormal calvarium to create an expanded cranial ...
[66]
Low-Cost Cranioplasty—A Systematic Review of 3D Printing in ... - NIH
Budget 3D-printed endoprostheses are reliable and are reported to be significantly cheaper than the popular counterparts manufactured from polypropylene ...
[67]
Maxillary Expansion and Its Effects on Circummaxillary Structures
Jan 13, 2023 · There is less tissue resistance in structures around the maxilla, and there is an increase in bone formation in the mid-palatine suture.
[68]
Early Maxillary Expansion-Induced Bone Remodeling Guides ...
This study focuses on early arch expansion treatment for maxillary arch stenosis during the mixed dentition period. It investigates the synergistic effects ...
[69]
Are there benefits from using bone-borne maxillary expansion ...
Feb 25, 2019 · The suggested benefits of such appliances include greater skeletal expansion of the maxilla and facial bones, reduced burden and adverse effects ...
[70]
Close-to-native bone repair via tissue-engineered endochondral ...
Oct 13, 2022 · In the case of intramembranous ossification (IMO), MSCs are directly stimulated to differentiate into bone cells, namely osteoblasts, which ...
[71]
Stem Cells in Bone Regeneration - PMC - PubMed Central - NIH
In this review, we discuss the key principles underlying bone healing, efforts to characterize bone stem and progenitor cell populations,
[72]
How faithfully does intramembranous bone regeneration ...
Aug 19, 2020 · Some studies suggest that perivascular skeletal stem cells contribute to intramembranous bone regeneration in the absence of endochondral ...
[73]
3D- Printed Poly(ε-caprolactone) Scaffold Integrated with Cell-laden ...
Oct 17, 2017 · We concluded that the CSG incorporated PCLscaffold is a promising 3D scaffold for potential in vivo bone and subchondral bone defect repair.
[74]
Targeted reversion of induced pluripotent stem cells from patients ...
Jan 22, 2018 · Reverted iPSCs improved the abnormal osteoblast differentiation which resulted in much better engraftment into the rat calvarial bone defect.
[75]
Generation of cleidocranial dysplasia-specific human induced ...
The main clinical features of CCD include persistently open skull sutures with bulging calvaria, hypoplasia or aplasia of the clavicles permitting abnormal ...Missing: scaffolds | Show results with:scaffolds