Mechanical control in dental and jaw morphogenesis and remodeling

Abstract

Tooth and maxillomandibular bone development is a synergistic process precisely and coordinately regulated by genetic programs, molecular signaling networks, and external environmental factors. Recent rapid progress in in situ biomechanical measurement techniques, cellular mechanical imaging, and molecular tracing technologies has greatly promoted research in developmental biomechanics. Accumulating evidence indicates that mechanical stimuli can be converted into biochemical signals via cellular mechanotransduction pathways, thereby modulating key cellular processes, including proliferation, differentiation, and apoptosis, and further regulating tissue morphogenesis and remodeling. In this review, we focus on the role of mechanical control in dental and jaw morphogenesis and remodeling. We first summarize the sources and spatiotemporal distribution features of mechanical stress during dentofacial development. Subsequently, we elaborate on the regulatory roles and underlying molecular mechanisms of mechanical signals in key dentofacial developmental processes, including crown development, root morphogenesis, tooth eruption and replacement, as well as maxillomandibular bone development and remodeling. Finally, we discuss the current research gaps in the field of mechanical stress regulation of dentofacial development and propose potential future research directions.

Introduction

As core components of the oral and maxillofacial region, tooth and maxillomandibular bone support mastication, pronunciation, and aesthetics, and their proper development underpins oral health and normal maxillofacial morphology.¹ The development of tooth and maxillomandibular bone is a complex process regulated by multiple factors, involving the synergistic effects of genetics, molecular signals, cellular behaviors, and external environments.^2–4 Among them, genetic factors determine the basic framework of development, while external mechanical stimulation, as a critical environmental regulator, plays an irreplaceable role in tooth germ differentiation, maxillomandibular growth and modeling, and the establishment of occlusal relationships.^5,6

For a long time, studies on tooth and maxillomandibular bone development have predominantly focused on genetic pathways and molecular mechanisms,^7–10 leaving the regulatory role of the mechanical microenvironment relatively underexplored. In recent years, the systematic development of cross-scale in situ force measurement techniques has provided powerful tools for the precise quantification of the mechanical properties of developing tissues.¹¹ At the tissue scale, ferrofluid droplets and Brillouin microscopy enable quantification of tissue viscoelasticity and local mechanical properties through deformation tracking and non-invasive optical approaches, respectively.^12–16 At the multicellular-to-cellular scale, velocity fields captured through particle image velocimetry (PIV) can be used to assess tissue rheological properties and phase transitions;^17–19 laser ablation and force-indentation spectroscopy using atomic force microscopy (AFM) allow approximation of local tension and extracellular matrix (ECM)/cortex stiffness, respectively;^20–24 and traction force microscopy enables direct measurement of traction forces generated by cells via adhesion receptors on the substrate.^25,26 At the cellular and molecular scale, micropipette aspiration and optical tweezers facilitate characterization of cortex mechanics and cell adhesion forces,^27–29 while Förster resonance energy transfer (FRET) tension sensors and Flipper-TR probes further enable real-time quantification of forces across single adhesion molecules and membrane tension.^30,31 The combined application of these multi-scale measurement approaches allows researchers to systematically resolve the spatiotemporal distribution and transmission of mechanical signals during development, driving the rapid advancement of mechanobiology. Empowered by these technical tools, growing evidence has confirmed that mechanical stimuli are not merely passive physical inputs, but can be transduced into biochemical signals through cellular mechanotransduction pathways, thereby regulating cell proliferation, differentiation, and apoptosis, as well as tissue morphogenesis and remodeling.^32–34 The regulatory role of mechanical stress in organ morphogenesis has been widely demonstrated across diverse biological processes, including intestinal looping,^35,36 alveolar development,^37,38 and digit formation.³⁹ To precisely describe this regulatory role, it is first necessary to clarify the mechanical terminology as summarized in Table 1.

Table 1.

Definitions and contextual usage of mechanical terminology in this review

Term	Definition	Unit	Context of use in this review
Force	External mechanical load applied to a tissue or structure	N	Macroscopic mechanical input, e.g., occlusal force, orthodontic force, and traction forces generated by cells
Stress	Internal force per unit area generated within a tissue, cell, or subcellular structure in response to an external force	Pa	General term bridging macroscopic force input and microscopic biological responses across tissue, cellular, and molecular scales
Strain	Relative deformation of a material resulting from stress	/	Tissue and cellular deformation, e.g., as captured by ferrofluid droplet tracking and PIV-based rheological analysis
Tension	Stress generated along a stretching/pulling direction	Pa	Cytoskeletal and cortical tension, junctional forces across single adhesion molecules, and membrane tension
Pressure	Compressive or hydrostatic stress acting perpendicular to a surface	Pa	Periodontal ligament compression side; interstitial or hydrostatic pressure within developing tissues
Stiffness	Intrinsic mechanical property of a tissue, cell, or matrix describing its resistance to deformation under an applied force	Pa	Tissue viscoelasticity and local mechanical properties quantified by Brillouin microscopy; ECM/cortex stiffness assessed by AFM force-indentation spectroscopy

During the development of the tooth and maxillomandibular bone, abnormal mechanical stimulation, such as abnormal mechanical loads caused by occlusal disorders and bad oral habits, often leads to dentomaxillofacial deformities, including malocclusion, delayed tooth development, and insufficient or excessive maxillomandibular bone growth.^5,40 Therefore, understanding how mechanical forces regulate tooth and maxillomandibular bone development may improve our understanding of developmental theory and guide clinical strategies in orthodontics, tooth anomaly intervention, and maxillomandibular bone regeneration. In this review, we first introduce the sources of mechanical stress during tooth and maxillomandibular bone development, and then focus on current understanding of the mechanical regulation of development and remodeling of tooth and maxillomandibular bone, exploring how mechanical forces cooperate with genetic and molecular programs to govern morphogenesis and maintain tissue homeostasis throughout life.

Sources of mechanical stress during the development and remodeling of teeth and maxillomandibular bones

Mechanical stress plays an indispensable role in regulating tooth and maxillomandibular bone morphogenesis, cell fate determination, and tissue homeostasis. The major sources of mechanical stress during tooth and jaw development fall into two distinct categories: micro mechanical stress, arising from cytoskeletal dynamics and differential tissue growth, and macro mechanical stress, imposed by occlusal loading, muscle contraction, orthodontic appliances, and the physical constraints of surrounding osseous structures (Fig. 1).

Fig. 1.

The major sources of mechanical stress during tooth and maxillomandibular bone development. The major sources of mechanical stress during tooth and jaw development fall into two distinct categories: micro mechanical stress, arising from cytoskeletal dynamics and differential tissue growth, and macro mechanical stress, imposed by occlusal loading, muscle contraction, orthodontic appliances, and the physical constraints of surrounding osseous structures

Micro mechanical stress

Micro mechanical stress encompasses forces generated by cytoskeletal contractility and differential tissue growth, representing the primary mechanical driving forces during the early stages of tooth and maxillomandibular bone development. The ability of the cytoskeleton to coordinate cellular functions and integrate diverse signals is particularly crucial during development. Cells contain three major classes of cytoskeletal filaments: actin filaments, microtubules, and intermediate filaments.^41,42 This filamentous network acts as a sensor for biochemical and mechanical changes external to the cell, transmitting this information to the cell interior and thereby influencing alterations in gene expression and cellular behavior.⁴³ Concurrently, modulating the organization and function of the cytoskeleton can generate mechanical forces and activate biochemical signaling pathways to remodel the extracellular space.⁴³ The pushing force is generated by actin polymerization during the process of cellular protrusion establishment, and the tension is produced when non‑muscle myosin II (MyoII) binds to filamentous actin (F‑actin) and hydrolyzes ATP, converting chemical energy into mechanical force.^33,44–46 This spatiotemporally regulated actomyosin activity drives a range of critical morphogenetic events, including apical constriction during invagination of the lens placode, inner ear placode, and lingual circumvallate papillae,^47–51 as well as tissue convergent extension and elongation during mandibular arch morphogenesis driven by polarized junctional myosin.^52–55 Forces generated by actomyosin contractility are transmitted across tissues via cell–cell adhesion junctions, enabling the conversion of individual cellular forces into global alterations in tissue morphology.^56–60 Beyond cell–cell adhesion, cell-ECM adhesion is also essential for transmitting or buffering intratissue forces during morphogenesis.^10,61,62 The physical linkage of cells to the ECM through focal adhesions (FAs) is critical for cellular rearrangement and migration. Furthermore, the ECM serves as an instructive biochemical cue that, upon recognition by integrin receptors, modulates downstream signaling pathways and regulates diverse cellular behaviors throughout developmental processes.^61,63 During tooth development, actomyosin contractile forces drive highly actin-dependent cell motility and oriented cell division in elongating epithelia,⁶⁴ while YAP, a mechanosensitive protein regulated by α-catenin at the enamel knot, transduces tissue pressure changes induced by differential growth to inhibit cell proliferation and specifies signaling cell fate.^56,65 Beyond actin‑based mechanics, non-centrosomal microtubules complement actin mechanics by bearing compressive loads^66,67 and coordinating anisotropic pushing forces during epithelial folding.^68,69 Mutations disrupting microtubule dynamics are linked to vertebrate craniofacial defects.^70,71

Intermediate filaments (IFs) differ from actin filaments and microtubules in both structural diversity and functional roles. Regardless of their type, IFs are composed of proteins that form uniform filamentous structures with a diameter of approximately 10 nanometers and exhibit an organized α‑helical conformation.⁴² Intermediate filaments constitute highly dynamic components of the cytoskeleton and perform multiple functions, such as participating in apoptosis, cell migration, adhesion, and interactions with other cytoskeletal elements.^41,42

Micro stress arising from differential tissue growth originates from spatiotemporal disparities in cell proliferation, apoptosis, and volumetric change. These disparities generate compressive and tensile stresses at the interface between regions with distinct growth rates, which in turn provide feedback regulation of cell behavior, differentiation, and rearrangement, establishing a bidirectional coupling between growth and mechanics.^72–74 In tooth development, epithelial cells surrounding the enamel knot (EK) proliferate faster than the EK itself. This differential growth, constrained by the underlying mesenchyme,⁷⁵ elevates pressure within the EK and produces pronounced buccal-lingual anisotropic deformation that shapes the molar crown.⁶⁴

Macro-mechanical stress

Macro-mechanical stress serves as a persistent regulatory factor throughout tooth and maxillomandibular bones development and remodeling, including four main categories: occlusal forces, muscular forces, orthodontic forces, and the physical constraints imposed by the maxillomandibular bone. Occlusal forces, the periodic mechanical loads produced by tooth contact during mastication, are the dominant macro stress on the dentition and maxillomandibular bone, and serve as a key target of natural selection for jaw morphology. In carnivores, for example, craniofacial morphology is significantly associated with masticatory function, a relationship driven jointly by dietary adaptation and non-feeding ecological variables.⁷⁶ Analyses of diet’s influence on bite force and morphology conducted within sigmodontine rodents indicated that diet is more likely to shape bite force, with natural selection modulating bite force through alterations in the size and shape of the skull and mandible.⁷⁷ Nevertheless, the relationship between occlusal forces and odontogenic stem cell behavior remains incompletely understood. While incisor truncation in rodents enhances mesenchymal stem cell proliferation and eruption rate, initially suggesting loss of occlusal loading as a triggering factor, unilateral truncation showed no significant changes, indicating that simple elimination of occlusal force is not sufficient.⁷⁸

Muscular forces generated by muscle contraction represent another important category of macro mechanical input, playing a critical regulatory role in the morphogenesis of the musculoskeletal system, including craniofacial bones, cartilage, tendons, and joints.⁷⁹ Loss-of-function studies across multiple vertebrate models have unequivocally demonstrated that muscle activity is essential for normal skeletal growth, eminence formation, tendon development, and maintenance of joint progenitor cell fate.^80,81 In muscular dystrophy models, chronically reduced forces elicit characteristic craniofacial abnormalities.^82,83 Consistently, deletion of tenogenic or myogenic components in the developing mandible led to micrognathia, masseter degeneration, and reduced mechanical sensing in mandibular bone, confirming that loss of masseter tendon‑transmitted mechanical force causes micrognathia.⁸⁴

Orthodontic appliances apply controlled exogenous strain to the dentoalveolar complex, triggering inflammatory, osteogenic, and angiogenic responses that remodel the alveolar bone and periodontal ligament (PDL).^3,85–87 These responses are mediated by mechanosensitive bone progenitor cells that detect altered matrix strain and adjust patterns of bone formation and resorption.⁸⁷ Beyond periodontal remodeling, orthodontic forces may also influence dental stem cell maintenance and tooth root resorption,^88,89 though the molecular mechanisms and clinical implications remain to be fully characterized.

The physical constraints imposed by the jaw on tooth development also constitute an important component of macro mechanical stress. The alveolar bone and jaw skeleton provide essential physical boundary conditions for the developing tooth germ, which are indispensable for establishing correct tooth morphology. Experimental evidence demonstrates that teeth cultured in vitro lose species-specific morphological characteristics, while combined computational simulations and in vitro mechanical constraint experiments have shown that lateral compression mimicking in vivo alveolar bone confinement is sufficient to generate offset cusps, a phenomenon observable even in mouse teeth.⁹⁰ These findings indicate that, although dental progenitor cells possess intrinsic morphogenetic capacity, the physical constraints imposed by the surrounding osseous tissue are a necessary condition for the formation of complete, species-specific tooth morphology.⁹¹ This also suggests that accurate computational prediction of tooth shape requires simultaneous incorporation of tissue mechanical properties and the boundary conditions imposed by surrounding structures.

The spatiotemporal distribution of mechanical forces defines the magnitude, direction, and duration of the stimuli that cells experience, yet converting these cues into biochemical signals requires a tightly coordinated mechanotransduction machinery. Three core modules underpin this process: the cytoskeleton–adhesion module (integrin-focal adhesion complexes) captures extracellular cues as the upstream mechanoreceptor; mechanosensitive ion channels (Piezo1/2, TRPV1/4) gate cation influx in response to membrane tension; and the Hippo effectors YAP/TAZ act as terminal transcriptional co-activators whose nucleocytoplasmic shuttling governs proliferation, differentiation, and morphogenesis. Together they form an integrated cascade redeployed in a stage-specific manner across successive events-epithelial invagination, crown morphogenesis, root formation, eruption, and jaw remodeling-where each mechanical microenvironment elicits a distinct response.

Mechanical regulation of dental epithelial invagination

The initiation of odontogenesis is fundamentally characterized by dental epithelial invagination, a pivotal process that transforms the flat oral epithelial placode into a three-dimensional bud structure, establishing the initial architecture for subsequent tooth germ development.^92–94 Accumulating evidence indicates that mechanical forces, intricately coupled with chemical signaling networks, govern this dynamic process, with distinct cellular and molecular mechanisms identified in the early primary dental lamina (DL).^6,10,75,95

Vertical cell movement

The development of the tooth germ begins with the invagination of the epithelium, marking the transition of tooth germ development into the bud stage (Fig. 2a). An alternative mechanism of epithelial invagination without classic cell wedging has been described as “vertical telescoping” in mammalian teeth and salivary glands. Here, peripheral placodal cells extend apical, centripetally polarized protrusions while remaining attached to the basal lamina. Cells migrate upwards and centripetally. This upward movement depresses the central cells, effectively driving epithelial invagination into the mesenchyme (Fig. 2b). Significantly, inhibition of protrusion formation blocks this process, highlighting the critical importance of active cell-on-cell migration.^95,96 Tooth morphogenesis is an integrated process involving vertical telescoping with canopy-driven contraction.⁹⁵

Fig. 2.

Mechanical regulation of dental epithelial invagination. a Dental epithelium invaginates into the mesenchyme to form the epithelial bud. b Cell vertical telescoping contributes to epithelial invagination. c Suprabasal cells intercalate toward the center of the tooth bud, generating contractile forces (blue arrows) in the plane of the basement membrane. These suprabasal cells organize their actomyosin cables in the planar orientation, pulling basal layer cells toward the center of the bud to promote epithelial invagination (green arrows). d The cytoskeleton is involved in the mechanotransduction and response to mechanical stress. Forces from the extracellular matrix (ECM) are sensed by focal adhesions and cell–cell junctions, activating Rho-ROCK signaling to drive actin stress fiber formation and cytoskeletal remodeling. Tension across the cytoskeleton is transmitted to the nucleus via LINKs complexes (linkers of nucleoskeleton and cytoskeleton), which in turn modulate chromatin conformation via LADs (Lamina-Associated Domains), regulating YAP/TAZ nucleocytoplasmic shuttling. Nuclear YAP/TAZ mediates mechanosensitive gene expression, coordinating cell proliferation and directional intercalation

Planar contraction and cell intercalation

A core mechanism of dental epithelial invagination involves the planar contraction of the suprabasal layer. Horizontally elongated suprabasal cells generate tensile forces through the assembly of actin bundles and phosphomyosin, which collectively drive epithelial bending.^6,97 Experimental incisions in the suprabasal layer of developing molar tooth germs result in bidirectional recoil, confirming that this layer exerts the required contraction forces essential for downward epithelial invagination.⁶Cell intercalation further contributes to this contraction: peripheral basal cells near the placode edge intercalate with suprabasal cells while maintaining anchorage to the basal lamina, consequently pulling the basal layer inward (Fig. 2c). This inward movement facilitates epithelial buckling, which is often coupled with underlying cell proliferation.^6,98 This mechanism of suprabasal cell intercalation-mediated contraction, forming a shrinking canopy over the underlying epithelial cells, is mechanistically conserved across ectodermal organs, promoting invagination through E-cadherin-based cell–cell coupling dependent on tissue-wide tension.⁹⁷ During this process, the cytoskeleton is involved in the mechanotransduction and response to mechanical stress, regulating cell proliferation and directional insertion (Fig. 2d).

Integration with signaling pathways

Chemical signaling pathways tightly integrate with these mechanical processes. Fibroblast Growth Factor (FGF) signaling induces suprabasal tissue formation through asymmetric cell division, which is a prerequisite for invagination. Subsequently, Sonic hedgehog (Shh) signaling promotes post-stratification cell rearrangement, including convergent migration and intercalation, to drive invagination to the bud stage.⁹⁵ Shh inhibition hinders suprabasal canopy contraction and cell intercalation, resulting in shallow, widened tooth germs.^6,98 This result underscores the role of Shh signaling in regulating tensile force generation. Furthermore, theoretical modeling supports the role of mechanical interactions: differential growth rates between peripheral and interior epithelial cells, combined with mesenchymal growth restriction, are sufficient to induce spontaneous epithelial buckling, a process that recapitulates the bud-to-cap transition.⁷⁵ Nuclear deformation analysis in molar placodes corroborates these findings, revealing that suprabasal cells experience planar tensile forces, stretching their nuclei into a flattened shape, consistent with the mechanical tension driving invagination along both the lingual-buccal and proximo-distal axes.⁹⁸

Mechanical regulation of tooth crown morphogenesis

Following invagination of the dental epithelium to form the tooth bud, the tooth germ sequentially progresses through the cap and bell stages, during which crown morphogenesis is ultimately established (Fig. 3a).^99–101 From the early stages of dental lamina formation to the final shaping of tooth cusps and eruption, mechanical stress has emerged as a pivotal mediator that orchestrates the proliferation, differentiation, and rearrangement of dental epithelial and mesenchymal cells.

Fig. 3.

Mechanical Regulation of Tooth Crown Morphogenesis. a Following the bud stage, tooth development proceeds sequentially through the cap stage and the bell stage. b Epithelium-derived Sema3f and Fgf8 induce mesenchymal condensation. Compressive stress generated during mesenchymal condensation acts on mesenchymal cells, triggering Ca²⁺ influx through Piezo1 to activate the Wnt-Runx2 signaling pathway, while promoting the secretion of Pax9, Msx1, and Bmp4. c Mechanical signaling cascade during enamel knot (EK) formation. The tooth germ displays circular proliferation gradients that produce tissue-wide mechanical compression and initiate EK formation, accompanied by elevated central Shh expression. In the peripheral fast-growth region outlined by the orange dashed line, cells elongate along tissue anisotropy axes. αE-catenin physically links the cytoskeletons of neighboring cells to mediate intercellular mechanical transmission, resulting in robust nuclear YAP enrichment. Severe compression in the central core region diminishes nuclear YAP accumulation, represses cell proliferation, and triggers Shh transcription, ultimately facilitating enamel knot morphogenesis

Mechanical regulation of mesenchymal condensation

Mesenchymal condensation, a critical early event in odontogenesis, involves the aggregation of dental mesenchymal cells around the developing epithelial bud, leading to increased cell density, reduced intercellular spaces, and the initiation of odontogenic differentiation.^102–104 Mechanical stress, particularly compressive stress resulting from cell aggregation and epithelial signaling, is a key driver of this process. Mammoto et al. demonstrated that FGF8 and SEMA3F, functioning as a chemoattractant and a repulsive signal, respectively, are secreted by the early dental epithelium to orchestrate mesenchymal cell condensation. The resulting mechanical compaction directly upregulates the expression of odontogenic transcription factors PAX9 and MSX1, as well as the growth factor BMP4.^102,105 Notably, mechanical compression alone is sufficient to induce mesenchymal differentiation, as mimicking cell compaction in vitro, either by culturing cells on micro-patterned adhesive islands or directly compressing mandibular mesenchyme, triggers the expression of Pax9 and Msx1 even in the absence of epithelial FGF signaling (Fig. 3b).¹⁰⁶

The stabilization of mesenchymal condensation by the ECM further emphasizes the mechanical regulation of this process. Collagen type VI, expressed in the condensed mesenchyme, is cross-linked by lysyl oxidase (LOX) to form a stable ECM scaffold that sustains cell compaction and differentiation.¹⁰⁶ Inhibition of LOX reduces mesenchymal condensation and downregulates Pax9 expression, highlighting the importance of ECM-mediated mechanical stabilization. ECM remodeling may contribute to the physical stabilization of cell shape changes induced during tooth development, whereas RhoA-dependent cytoskeletal prestress, together with alterations in cell geometry, play a central role in governing fate transitions of adult mesenchymal stem cells.¹⁰⁵ Furthermore, studies have shown that epithelial-derived LAMB3 can promote odontogenic differentiation of dental papilla cells by enhancing ECM stiffness.¹⁰⁷ Additionally, syndecan, tenascin, and fibronectin in the ECM may contribute to cell–cell and cell–matrix interactions, further modulating the mechanical microenvironment of the condensed mesenchyme.^108,109

Recent studies have identified Piezo1, a mechanosensitive ion channel, as a key mediator of stress-induced mesenchymal differentiation. In stem cells from human exfoliated deciduous teeth, hydrostatic pressure (HP) promotes odontogenic differentiation by activating Piezo1, which coordinates WNT signaling and ciliogenesis. Piezo1 activation by Yoda1 inhibits cell proliferation, induces primary cilia formation, and promotes nuclear translocation of RUNX2, a master transcription factor for odontogenesis. Conversely, silencing Piezo1 abrogates HP-induced odontogenic differentiation, indicating that Piezo1 functions as a mechanotransducer linking mechanical stress to intracellular signaling cascades during mesenchymal condensation (Fig. 3b).¹¹⁰ It should be noted that these findings were derived from stem cells from human exfoliated deciduous teeth, an in vitro postnatal progenitor model that, while retaining certain odontogenic differentiation capacities, does not fully recapitulate the in vivo cellular context of the dental papilla mesenchyme during early crown morphogenesis. Whether Piezo1-mediated mechanotransduction similarly governs mesenchymal condensation in the developing tooth germ remains to be directly established.

Mechanical regulation of enamel knot formation

The enamel knot (EK), a transient signaling center located at the tip of the enamel organ, plays a fundamental role in coordinating tooth morphogenesis, cusp patterning, and epithelial-mesenchymal communication.^4,111,112 Recent studies have unequivocally demonstrated that stress, particularly proliferation-driven compressive stress, is a key determinant of EK specification and maintenance. Direct mechanical measurements in developing rodent incisors revealed that cell proliferation generates compressive stresses that are resisted by the surrounding tissue, forming a circular pattern of mechanical anisotropy with a high-stress center that differentiates into the EK. Pharmacological inhibition of cell proliferation reduces these compressive stresses and suppresses EK formation, while exogenous application of pressure rescues EK development in proliferation-inhibited conditions, confirming the causal relationship between mechanical compression and EK specification.¹¹³

The transduction of mechanical stress into EK formation is mediated by the Hippo signaling pathway effector YAP and its homolog TAZ, which act as mechanosensors to relay mechanical information intracellularly. In the high-compressive stress region destined to become the EK, YAP localizes to the cytoplasm, leading to reduced cell proliferation and the acquisition of a specialized signaling phenotype. Conversely, in the surrounding stretched anisotropic cells that resist pressure buildup, YAP translocates to the nucleus, promoting cell proliferation. αE-catenin plays a crucial role in this process by inhibiting nuclear YAP/TAZ localization, thereby restricting cell proliferation and enabling the formation of the non-proliferative EK (Fig. 3c). Loss of αE-catenin disrupts EK formation, which can be rescued by combined deletion of Yap and Taz, highlighting the centrality of YAP/TAZ inhibition in EK specification.^113,114

YAP expression dynamics during tooth development further underscore its role in EK function. During the cap stage, YAP is critical for suppressing the primary EK and patterning secondary EKs, which give rise to future cusps. Stage-specific knockdown of Yap during the cap stage results in persistent primary EK activity and ectopic cusp formation.¹¹² In contrast, YAP overexpression leads to deformed tooth morphogenesis, including mislocalization of the EK to the upper portion of the enamel organ, depletion of key signaling molecules (e.g., Shh, Fgf4, Wnt10a) in the EK, and arrested cap stage development.^4,111 These findings indicate that precise spatiotemporal regulation of YAP activity, modulated by mechanical stress, is essential for normal EK formation and function.

Intracellular αE‑catenin is essential for physically linking the cytoskeletons of neighboring cells, enabling them to mechanically resist the buildup of tissue pressure caused by proliferation. Tissue resistance to graded cell proliferation leads to elevated tissue compression at the center of the circular anisotropy pattern, resulting in reduced nuclear YAP, suppressed cell proliferation, and triggered Shh expression, ultimately driving the formation of the enamel knot (EK).

Micro mechanical forces contribute to tooth morphology

The reciprocal interaction between dental epithelium and mesenchyme is essential for tooth morphogenesis, and micro mechanical stress plays a critical role in mediating this crosstalk. Epithelial invagination, a central process in tooth germ formation, is driven by mechanical forces generated within the epithelial layer and modulated by mesenchymal signals. In developing molars, planar contraction of the suprabasal epithelial layer, resulting from cell intercalation and actin-dependent tensile forces, generates lateral forces that bend the epithelium downward into the mesenchyme.⁶ Live imaging and tissue incision experiments have confirmed that the suprabasal layer exerts a contractile force, and attachment to the flanking non-dental epithelium resists this contraction, facilitating epithelial bending.

The mesenchyme provides mechanical constraints that modulate epithelial morphogenesis. Computational models and experimental evidence suggest that the mesenchyme acts as a mechanical scaffold to aid the bud-to-cap transition of the epithelium.^6,75 Abundant F-actin and phosphomyosin in the mesenchyme indicate its capacity to generate mechanical inputs for epithelial folding and invagination. For example, during feather and gut villus development, the mesenchyme drives epithelial curvature, and a similar mechanism may operate in tooth development. Additionally, mesenchymal condensation generates a mechanical signal that induces epithelial differentiation, as demonstrated by the ability of compressed mesenchymal scaffolds to induce dental epithelial invagination in vitro and in vivo.¹⁰³ In avian skin and follicle patterning, mesenchymal condensation activates β-catenin in neighboring epithelial cells via mechanical sensing, suggesting that the regulation of epithelial morphogenesis by tissue-derived mechanical forces is evolutionarily conserved.¹⁰²

The Hippo-YAP/TAZ pathway is a key mediator of epithelium-mesenchyme crosstalk regulated by stress. YAP is expressed dynamically in both epithelial and mesenchymal cells during tooth development, with nuclear localization promoting cell proliferation and cytoplasmic localization associated with differentiation.¹¹⁵ In the dental epithelium, YAP deficiency reduces cell proliferation and impairs ameloblast differentiation, while YAP overexpression disrupts epithelial invagination and EK formation.^4,116 YAP regulates epithelial-mesenchymal communication by controlling the expression of signaling molecules such as Shh, Fgf3, Fgf10, and Hox genes (Hoxa1, Hoxc13).^116,117 In the mesenchyme, YAP/TAZ activity is regulated by αE-catenin, and deletion of YAP rescues EK defects caused by loss of αE-catenin, confirming the role of YAP/TAZ in mediating epithelial-mesenchymal crosstalk.¹¹⁴ Moreover, the ITGA3-FAK-CDC42 signaling axis in mesenchymal cells promotes nuclear YAP expression, maintaining epithelial cell proliferation and inhibiting premature differentiation.¹¹⁵ These findings indicate that stress-induced YAP/TAZ signaling integrates epithelial and mesenchymal responses to ensure coordinated tooth morphogenesis.

Effects of macro mechanical forces on tooth morphology

In addition to local micro-forces, macro-scale mechanical forces, such as those generated by the surrounding maxillomandibular bones, mastication, and muscle activity, play a crucial role in shaping tooth morphology. Comparative studies of mouse and bank vole molars revealed that cusp offset, a species-specific morphological trait, is dependent on lateral mechanical constraints from the developing jaw. Vole molars cultured without jaw-derived mechanical support lose their cusp offset, while mouse molars cultured with artificial braces develop offset cusps, demonstrating that external mechanical forces regulate tooth cusp patterning. Computational modeling confirmed that lateral compression, similar to that imposed by the alveolar bone in vivo, is sufficient to induce cusp offset, highlighting the importance of jaw-tooth mechanical integration in dental diversity.⁹⁰

Masticatory forces and orthodontic loading also influence tooth development and stem cell behavior. Mechanical strain applied to the PDL during orthodontic treatment activates osteogenic, angiogenic, and inflammatory responses, promoting bone remodeling and tooth movement. In ever-growing rodent incisors, clipping the incisors to reduce occlusal force increases the proliferation rate of dental mesenchymal stem cells, suggesting that mechanical loading modulates stem cell activity and tooth eruption.⁹⁰ However, the role of occlusal forces in stem cell regulation remains controversial, as some studies have failed to observe changes in tooth growth rates after reducing occlusion. Nevertheless, the integrin-YAP signaling axis in dental stem cells is capable of mechanotransduction, implying that macro-mechanical forces may regulate stem cell proliferation and differentiation through this pathway.⁶ Muscle-generated forces also contribute to tooth positioning and morphology.

Mechanical regulation of tooth root morphogenesis

Tooth root development is a complex postnatal morphogenetic process that relies on the coordinated interplay between mechanical forces, signaling pathways, and cellular behaviors. Mechanical cues, as essential regulators, are transduced into biochemical signals to modulate key events, including root apex formation, PDL homeostasis, cementum or bone deposition, and the fate determination of dental mesenchymal progenitors. Accumulating evidence from in vivo and molecular studies has uncovered distinct mechanotransduction mechanisms that underpin root morphogenesis, providing a foundational theoretical framework for understanding stress-related regulation in this process.^118,119

Mechanotransduction during root development

A novel neuro-Mechanotransduction mechanism has been identified, wherein Piezo2⁺ mechanosensory neurons serve as master regulators of root morphogenesis by converting mechanical forces into paracrine signals. During postnatal mouse molar development, a subpopulation of Piezo2-expressing mechanosensory neurons in the trigeminal ganglia specifically detects root-associated mechanical forces. Mechanical activation of neuronal Piezo2 triggers calcium-dependent secretion of platelet-derived growth factor A (PDGFA), which acts as a paracrine factor to orchestrate mesenchymal cell behavior and root development. This Piezo2-calcium-PDGFA axis is supported by direct functional evidence: neuronal-specific knockdown of Pdgfa via trigeminal ganglion injection significantly impairs root elongation, mesenchymal proliferation, and Gli1⁺ progenitor maintenance in vivo. Furthermore, sensory neuron-specific ablation of Piezo2 (AvCreERT2; Piezo2^fl/fl) markedly reduces root growth in a kidney capsule transplantation model, and this phenotype is substantially rescued by local delivery of recombinant PDGFAA, demonstrating that PDGFA acts downstream of neuronal Piezo2 to sustain mesenchymal proliferation.¹¹⁹ This mechanism expands the theoretical understanding of root development by highlighting the previously unrecognized role of neural circuits in transducing mechanical cues (Fig. 4a). Nevertheless, several experimental limitations should be taken into account when generalizing the above conclusions. Rescue assays were implemented using ectopic transplantation models, which may not fully recapitulate the endogenous jaw microenvironment. Moreover, the Advillin-CreERT2 strain broadly labels all sensory neurons rather than exclusively marking Piezo2-expressing subpopulations. In addition, the exact spatial diffusion range and cellular sources of endogenous PDGFA in native tissues have not been thoroughly characterized. Collectively, further investigations are required to validate the broader applicability of these findings.

Fig. 4.

Mechanical Regulation during tooth root development and tooth renewal. a Piezo2⁺ mechanosensory neurons in the trigeminal ganglion play a pivotal role in sensing mechanical forces and transducing them into the chemical signal PDGFA via calcium influx. Nerve-derived PDGFA binds to PDGFA receptors on dental mesenchymal cells in the molar, thereby regulating normal tooth root development. b During tooth root development, FGF signaling in progenitor cells modulates cell proliferation and differentiation by regulating mechanotransduction and WNT signaling. Knockout of Fgfr1 in Gli1⁺ progenitor cells results in upregulated and ectopic expression of Piezo2, which in turn activates WNT signaling through the β-catenin pathway. c Before the eruption of the deciduous tooth, biomechanical stress exists between the deciduous tooth and the successional dental lamina (SDL) of the permanent tooth. This biomechanical stress maintains the successional dental lamina in a quiescent state by upregulating the expression of Integrin β1-Runx2–Fibulin-1 in dental follicle mesenchymal cells. After the eruption of the deciduous tooth, the loss of biomechanical stress downregulates Integrin β1-Runx2-Fibulin-1 expression, thereby initiating the development of the permanent tooth

During root formation, Gli1⁺ apical stem/progenitor cells act as a central coordinating node. Lineage tracing shows that Gli1⁺ cells of the apical dental papilla and dental follicle contribute to root dentin, dental pulp, and periodontal tissues.¹²⁰ Gli1⁺ progenitor cells serve as the central cellular substrate through which mechanical signals are transduced and integrated during root development. Fgfr1 is dynamically expressed in mesenchymal progenitors and their progeny throughout root development. Loss of Fgfr1 in Gli1⁺ progenitors leads to progenitor hyperproliferation and aberrant differentiation, resulting in narrowed PDL space, abnormal cementum/bone formation, and ultimately tooth ankylosis. Mechanistically, FGF signaling suppression induces aberrant activation of Piezo2, a key mechanosensitive ion channel, and WNT signaling. Notably, downregulation of WNT signaling rescues tooth ankylosis in Fgfr1 mutant mice.¹²¹ These findings reveal a critical FGF/Piezo2/WNT signaling cascade that modulates mechanotransduction in mesenchymal progenitors, ensuring proper PDL spacing and preventing ectopic cementum/bone fusion during root development (Fig. 4b).

Direct mechanical forces modulate root apex morphology and cellular behavior

Macro-mechanical forces exerted on developing teeth directly impact root apex development, with effects dependent on the duration of force application. In a 21-day-old rat model, prolonged force application (7 days) significantly shortened roots, caused apical bending, reduced apical cell proliferation, disrupted gene expression, and impaired Hertwig’s epithelial root sheath (HERS). These findings suggest that mechanical force directly regulates HERS function and apical cellular activity, and such damage is irreversible after force removal.¹²² Furthermore, studies have shown that applying light orthodontic force to the maxillary first molars of P28 mice for 3 days results in deformed dentin, disorganized odontoblast arrangement, reduced apical cell proliferation, and significantly shorter root length.¹²³ This indicates that the developing root apex exhibits a window of mechanical sensitivity, where sustained mechanical stress can irreversibly alter root morphogenesis by disrupting cell proliferation and HERS integrity.

Mechanical regulation of tooth eruption and tooth renewal

Several hypotheses have been proposed to interpret the driving mechanism of tooth eruption. Early-stage hypotheses include biophysical traction forces exerted by the PDL or mechanical pushing of tooth root against the surrounding bone.¹²⁴ However, these hypotheses have been fundamentally challenged by substantial experimental evidence: rootless teeth, whether congenitally absent or experimentally induced, have been shown to erupt normally into the oral cavity in both humans and multiple animal models, demonstrating that root formation is not a prerequisite for eruption.^125,126 The most widely accepted theory today holds that the principal driving force of tooth eruption originates from the asymmetric remodeling of the alveolar bone surrounding the tooth: bone overlying the crown undergoes directional resorption, eliminating the hard tissue resistance along the eruption pathway, while bone at the base of the follicle is continuously deposited, driving the axial coronal displacement of the tooth.^127,128 In this process, the dental follicle is considered to play a pivotal regulatory role: its coronal portion recruits osteoclasts to mediate bone resorption, while its basal portion recruits osteoblasts to promote bone formation, with both processes operating in a polarized and coordinated manner.¹²⁹ The classic experiments by Cahill and Marks further demonstrated that when the tooth germ was replaced by a metal or silicone replica, eruption proceeded on schedule as long as the dental follicle remained intact, whereas removal of the follicle completely arrested eruption.¹²⁵ Finite element analysis has been employed by researchers to demonstrate that tooth eruption results from bone remodeling driven by bite forces sensed by soft tissue dental follicles.¹³⁰ These findings establish the dental follicle as an absolute prerequisite for tooth eruption, and its polarized recruitment of osteoclasts and osteoblasts as the central regulatory mechanism governing the bone remodeling that drives this process.

It is important to emphasize that tooth eruption is a multifactorial physiological process. While follicle-mediated bone remodeling serves as the core mechanism governing intraosseous tooth movement, it cannot fully explain the complete eruption process. Remodeling of the PDL itself—including collagen fiber turnover and reorganization, as well as traction forces generated by PDL fibroblasts—has been hypothesized to facilitate tooth movement.^127,131 Furthermore, tooth eruption does not terminate upon the establishment of functional occlusion. Post-eruptive eruption sustains throughout life via continuous remodeling of alveolar bone and the PDL.^132–134 In addition, forces generated by the orofacial musculature are critical for the precise positioning of teeth within the jaws. This is clearly demonstrated by the marked labial or lingual displacement of teeth that occurs following the loss or gain of facial or lingual soft tissues, respectively.^135,136

In studies using the American alligator, a model capable of lifelong tooth renewal, researchers have found that quiescent odontogenic progenitor cells can be activated following physiological tooth exfoliation or artificial tooth extraction.¹³⁷ In mammals, the transition of permanent teeth from the resting to the initiation stage is tightly linked to the eruption of deciduous teeth. Studies using a miniature pig model have demonstrated that permanent tooth development remains dormant until deciduous tooth eruption releases the accumulated mechanical stress within the mandible. Prior to eruption, this mechanical stress suppresses permanent tooth initiation by modulating the integrin β1-ERK1-RUNX2 signaling axis in the surrounding mesenchyme.¹³⁸ Furthermore, RUNX2 can bind to the enhancer region of Fbln1 (Fibulin‑1 gene). The biomechanical force‑mediated RUNX2‑Fibulin‑1 axis inhibits the activation of the successional dental lamina (SDL) by maintaining the homeostasis of the SDL niche (Fig. 4c).¹³⁹ However, the specific mechanical cues and signaling cascades that trigger the SDL to exit quiescence and undergo subsequent invagination remain largely unexplored.

Mechanical regulation of maxillomandibular bone and temporomandibular joint biology

Mechanical regulation of maxillomandibular bone development and remodeling

During embryogenesis, mechanical forces cooperate with key molecular pathways to pattern the jaw skeleton. In the mouse mandibular arch, oscillatory cortical forces drive three-dimensional mesenchymal cell intercalations, with Wnt5a coordinating cell polarity and cytoskeletal dynamics; YAP/TAZ and Piezo1 act downstream to orient these intercalations via actomyosin regulation and calcium transients.⁵⁵ In zebrafish craniofacial cartilage, Pthlha restricts hypertrophic zone formation, and muscle contraction-derived mechanical force is required for normal expression of hypertrophic zone markers and subsequent ossification—paralysis abolishes this process.¹⁴⁰ YAP and TAZ also combinatorially promote postnatal bone development through osteoblast activation, matrix collagen organization, and suppression of osteoclast activity. The homozygous loss produces an osteogenesis imperfecta-like phenotype with spontaneous fractures.¹⁴¹

Mechanical loading during mastication is a primary determinant of mandibular morphology and bone quality. Rodent soft-diet models consistently demonstrate that reduced masticatory demand decreases condylar bone volume, inhibits ramus growth, and reduces condylar articular cartilage thickness alongside suppressed IGF-1r expression in chondroblasts.^142,143 Conversely, experimentally increased temporomandibular joint (TMJ) loading via incisal bite planes reduces condylar chondrocyte layer thickness, suppresses endochondral bone formation, and diminishes total mandibular length and ramus height.¹⁴⁴ In humans, larger masseter and temporalis cross-sectional areas correlate with a wider ramus, more robust coronoid process, and more rectangular mandibular body, confirming that muscle force is encoded in adult mandibular morphology.¹⁴⁵

BMP signaling and masticatory loading regulate mandibular morphogenesis through spatially distinct mechanisms. Conditional knockout of Bmpr1a in osteoblasts and chondrocytes (Osterix-Cre) produces shorter anterior mandibular lengths and a posteriorly inclined ramus. The superimposed imaging demonstrates that BMP signaling governs the posterior condyle while masticatory loading governs the anterior part.¹⁴⁶ At the systemic skeletal level, Bmpr1a loss sensitizes osteoblasts to mechanical stimuli, treadmill exercise further increases trabecular bone volume and normalizes cortical porosity exclusively in knockout mice, indicating that BMPR1A signaling modulates mechanosensitivity.¹⁴⁷

Dietary hardness enables a controlled in vivo study of mechanical loading effects on jaws. Soft-diet rodents exhibit hypoplastic craniofacial skeletons due to insufficient masticatory force, independent of nutrition.¹⁴⁸ Anthropological evidence further reveals consistent jaw morphological disparities between hunter-gatherers and agricultural/urban populations, concentrated at load-bearing regions. Masticatory mechanical stimulation, dictated by food texture, has long shaped human jaw morphology via developmental plasticity and evolutionary selection.^149–151 Collectively, masticatory force serves as a physiological mechanical cue analogous to orthodontic loading, acting through conserved mechanosensitive pathways to remodel jaw form across development, functional adaptation, and human evolution.

Mechanical regulation in alveolar bone and periodontal ligament formation

The periodontium is maintained by heterogeneous periodontal ligament stem cells (PDLSC) populations that sense and respond to occlusal forces. Leptin receptor-positive (Lepr⁺) PDLSCs, identified by single-cell RNA sequencing as a perivascular multipotent subpopulation, mediate periodontal homeostasis through Piezo1-dependent mechanosensing. Their ablation disrupts tissue homeostasis, while the Piezo1 agonist Yoda1 markedly promotes periodontal tissue growth.¹⁵² TRPV4 is a second key mechanosensitive channel: compressive force activates TRPV4, alters PDLSC stemness toward a pro-inflammatory, pro-osteoclastic phenotype, and regulates the RANKL/OPG ratio via ERK signaling.¹⁵³ Temperature-sensitive TRPV1/TRPV4 and mechanosensitive Piezo1/2 together constitute a multimodal sensory network in PDL cells that converts physical stimuli into osteoblastic and osteoclastic signals.¹⁵⁴

Complementing the Lepr⁺ PDLSC population, Gli1⁺ cells constitute a perivascular, multipotent stem population that gives rise to the PDL, alveolar bone, and cementum, sustaining periodontal homeostasis and injury repair.¹⁵⁵ Postnatally, Gli1⁺ PDL cells colonize perivascular sites, proliferate, and migrate toward the bone and cementum surfaces to maintain alveolar bone homeostasis in young animals, before entering quiescence in adulthood.¹⁵⁶ Physiological occlusal force regulates Gli1⁺ PDLSC activity via an osteocyte–Wnt axis: alveolar bone osteocytes secrete the Wnt inhibitor sclerostin to suppress Gli1⁺ cell activation, while occlusal loading downregulates sclerostin, relieving this inhibition and promoting PDLSC proliferation and osteogenic differentiation. Conversely, loss of occlusal force upregulates sclerostin and markedly suppresses PDLSC activation, revealing how occlusal force precisely maintains periodontal homeostasis through this osteocyte–Gli1 stem cell axis.¹⁵⁵

Site-specific mechanotransduction has been demonstrated between maxillary and mandibular PDLSCs: high-throughput kinase profiling under static compression reveals jaw origin-dependent signatures, with maxillary PDLSCs dominated by serine/threonine kinase activation and mandibular PDLSCs showing reduced protein tyrosine kinase signaling. Only a small subset of kinases are shared between regions.¹⁵⁷ This molecular heterogeneity provides a basis for clinically observed differences in orthodontic tooth movement (OTM) rates and alveolar bone remodeling across jaw regions.

Mechano-growth factor (MGF), generated by PDL under occlusal force, amplifies mechanical signals through a Fyn-FAK kinase axis and downstream ERK1/2/p38 MAPK activation to enhance PDLSC differentiation into fibroblasts and promote PDL regeneration in vivo.¹⁵⁸ At the ECM level, mechanical loading induces distinct architectural changes in PDL collagen: type VI collagen increases on the mesial side to support collagen fibrogenesis, type XII collagen accumulates at the PDL-cementum boundary on the distal side, and PDGF signaling emerges as a key regulator of matrisome homeostasis under load.¹⁵⁹

Cyclic tensile stress enhances PDLSC osteogenic differentiation through mitophagy activation, linking mitochondrial quality control to osteogenic commitment on the tension side of orthodontic loading.¹⁶⁰ YAP and TAZ, as Hippo pathway effectors, convert mechanical signals into biochemical cascades governing osteogenesis/osteoclastogenesis balance and periodontal homeostasis, with distinct versus overlapping roles depending on the specific regulatory context.³ Under pathological conditions, occlusal trauma, excessive force, or bacterial inflammation, PDLSCs shift toward a remodeling-dysregulated phenotype that drives root resorption and alveolar bone loss, underscoring their dual role as homeostatic regulators and disease mediators.¹⁶¹

Periodontal ligament and maxillomandibular bone remodeling during orthodontic tooth movement

OTM is fundamentally a biomechanical process in which externally applied force is transmitted through the PDL to generate an asymmetric distribution of compressive and tensile stress, which is subsequently converted into differential cellular and molecular responses. The PDL is a nonlinear viscoelastic tissue whose mechanical behavior, characterized by stress relaxation, creep, and hysteresis, depends on loading frequency, duration, and location, such that identical force magnitudes can produce markedly different internal stress/strain states depending on how the force is applied over time.¹⁶² This viscoelasticity underlies the classical concept of “optimal force,” originally proposed by Schwarz, which holds that the ideal continuous force is one that alters periodontal tissue pressure to approximate capillary blood pressure, thereby avoiding vascular occlusion in the compressed PDL.¹⁶³ Systematic reviews of clinical and animal data suggest that forces in the range of roughly 50–100 cN are generally most favorable for the rate of bodily tooth movement and patient comfort, although considerable heterogeneity exists across studies using forces from 18 to 360 cN.¹⁶⁴ Beyond magnitude, the temporal pattern of force delivery also shapes the biological outcome: continuous forces tend to sustain PDL cell proliferation and remodeling activity more effectively than intermittent forces of the same magnitude, while excessively heavy or prolonged compressive loading can exceed capillary pressure, causing local ischemia, hyalinization, and a corresponding delay in the resorptive response.¹⁶⁵ These biomechanical parameters—force magnitude, duration, and PDL viscoelastic properties— together determine the spatial pattern and intensity of stress transmitted to periodontal cells, forming the physical basis for the asymmetric bone resorption and formation described below.¹⁶⁶

On the compression side, the vasculature within the PDL collapses upon application of orthodontic force, causing a rapid drop in local oxygen tension and triggering an aseptic inflammatory response characterized by prompt recruitment and infiltration of macrophages, monocytes, and dendritic cells¹⁶⁷; this hypoxic state is itself a direct driver of inflammatory initiation, under the combined effects of mechanical strain and reduced oxygen supply, PDL fibroblasts upregulate HIF-1α, accompanied by increased RANKL expression and decreased osteoprotegerin (OPG) expression, thereby promoting osteoclast differentiation and driving compression-side alveolar bone resorption.¹⁶⁸ On the one hand, osteoclastogenesis is primarily regulated through the RANKL/OPG axis. Autophagy, mediated by ATG7, acts as a restraining mechanism: compression force activates autophagy and elevates RANKL/OPG in hPDLSCs, while ATG7 knockdown suppresses autophagy, further increases RANKL/OPG, and accelerates tooth movement in vivo, demonstrating that ATG7-dependent autophagy brakes the rate of OTM by limiting osteoclast activity.¹⁶⁹ On the other hand, TRPV4-activated PDLSCs reinforce compression-side resorption through ERK-mediated RANKL/OPG upregulation.¹⁵³ In addition, orthodontic compressive force induces macrophage M2 polarization via histone H3 hyperacetylation, and Piezo1-mediated impairment of cementoblast function has been implicated in compression-side external apical root resorption.¹⁷⁰

On the tension side, ERK1/2 serves as a universal and rapid mechanotransduction node in osteoblasts. A systematic review of 33 in vitro studies confirms that ERK1/2 is consistently activated within minutes across all major mechanical stimuli, fluid shear stress, substrate stretching, and hydrostatic pressure, and is linked to osteoblast proliferation and differentiation underpinning new bone formation during OTM.⁸⁶ This ERK-centric signaling is reinforced by MGF-FAK-ERK1/2/p38 mechanochemical coupling¹⁵⁸ and TRPV4-ERK pathways,¹⁵³ identifying MAPK activation as a convergent mechanism integrating multiple mechanosensory inputs into bone-forming responses. Notably, the same mechanical parameters that determine compression-side hydrostatic stress also govern tension-side strain magnitude, such that the biomechanical properties of the PDL effectively couple the compressive and tensile responses into a single, spatially coordinated remodeling program rather than two independent processes.

During OTM, YAP/TAZ function as mechanotransduction hubs that synchronize osteogenesis and osteoclastogenesis, orchestrating the coupled bone remodeling required for tooth movement. Their selective activation is regarded as a strategy to accelerate OTM and prevent orthodontically induced dental dysplasia.³ Under orthodontic loading, Gli1⁺ cells in the PDL proliferate markedly on the tension side and differentiate toward the osteoblast lineage. Both pharmacological and genetic inhibition of Gli1⁺ cells arrests orthodontic force-induced bone remodeling. The classical mechanotransducer YAP is highly expressed in Gli1⁺ cells, and conditional ablation of Yap in this population similarly impairs bone remodeling, providing direct evidence that Gli1⁺ cells are bona fide force-responsive cells that mediate orthodontic bone remodeling through the YAP mechanotransduction axis.¹⁷¹

Beyond the PDL, Gli1⁺ cell-mediated mechanosensing has also been characterized at the craniofacial suture level, where Gli1⁺ suture stem cells (SuSCs) serve as key effector cells that respond to orthopedic expansion forces. Jing et al. demonstrated that tensile stress markedly upregulates Wnt/β-catenin signaling in Gli1⁺ SuSCs, while conditional knockout of β-catenin substantially suppresses both the activation of Gli1⁺ SuSCs and bone remodeling under physiological and expansion conditions.¹⁷² In a zygomaticomaxillary suture distraction osteogenesis model, Jin et al. further found that the primary cilia of Gli1⁺ cells can sense mechanical stimuli, thereby activating the Hedgehog (Hh) signaling pathway and promoting osteogenic differentiation of Gli1⁺ cells.¹⁷³ At the level of intracellular mechanotransduction, Huang et al. demonstrated that mechanical force can be sensed by Gli1⁺ cells in the suture via the inositol 1,4,5-trisphosphate receptor (IP3R) calcium channel on the endoplasmic reticulum, by which intracellular Ca²⁺ concentration is raised, and osteogenesis is thereby mediated—revealing an additional mechanosensing pathway in Gli1⁺ cells.¹⁷⁴

Furthermore, bidirectional substance P (SP) signaling between PDL fibroblasts and sensory neurons constitutes an additional regulatory loop: compressive force induces TAC1 expression and SP secretion in PDL fibroblasts, which activates sensory neurons; activated neurons in turn drive pro-inflammatory responses and osteoclastogenesis in PDL fibroblasts.¹⁷⁵ This neuro-immune crosstalk amplifies the local remodeling response and is a key contributor to orthodontic pain, representing a potential therapeutic target for pain management without compromising treatment efficacy.

Mechanical regulation of temporomandibular joint development and remodeling

Mechanical stress is intrinsic to the entire lifecycle of the TMJ, serving as a core regulator in joint organogenesis, cavitation, and fibrocartilage remodeling while maintaining homeostasis via metabolic pathways.^176–178 During the embryonic stage, mechanical stimuli such as fetal mandibular movements provide an indispensable biophysical environment for the formation of the TMJ blastema, cavitation differentiation, and condylar cartilage development; notably, the absence of these loads leads to profound structural dysgenesis.^179–181 During the cavitation phase, mechanical signals modulate the differentiation of the upper and lower joint spaces and disc formation through the Ihh signaling pathway,^182–184 subsequently triggering microcavity fusion via hyaluronic acid (HA)–hyaluronan binding protein (HABP) interactions.^185–188

Postnatally, physiological masticatory loads drive the adaptive growth of the condyle and articular tubercle. The condyle exhibits a distinct asymmetric growth pattern from birth to adulthood: while longitudinal growth remains limited, the mediolateral diameter approximately doubles. This disparity is attributed to the differential distribution of shear strains—high shear strain inhibits chondrogenesis while promoting osteogenesis.^189,190 Specifically, elevated shear gradients along the anteroposterior axis may suppress cartilage formation, thereby restricting longitudinal expansion. At the cellular level, the Piezo1 ion channel acts as a pivotal mechanoreceptor, regulating the proliferation and differentiation of fibrocartilage stem cells to maintain cartilage stability.¹⁹¹ At the stem cell level, Gli1⁺ cells reside in the superficial condylar cartilage and subchondral bone and are critical for cartilage maturation and bone formation.¹⁹² In a TMJ osteoarthritis model induced by aberrant mechanical loading, an early and abnormal increase in YAP activity suppressed Hhip expression, thereby releasing the negative-feedback restraint on Hh-Gli1 signaling and driving excessive osteogenic differentiation of Gli1⁺ progenitor cells, which ultimately led to pathological subchondral bone remodeling and articular cartilage degradation. Specific inhibition of YAP activity in Gli1⁺ cells restored Hhip expression, suppressed excessive osteogenesis, and mitigated the osteoarthritis-like phenotype, whereas further activation of Hh-Gli1 signaling aggravates this pathological phenotype, suggesting that the YAP-Hhip-Gli1 axis constitutes a mechanosensitive negative-feedback regulatory loop.^192,193

Furthermore, mechanical strain modulates the TMJ disc microenvironment by reducing water content and porosity, which decreases the diffusion coefficients of essential nutrients like glucose. Ultimately, abnormal mechanical loading triggers metabolic dysfunction and exhaustion of the stem cell pool, culminating in degenerative conditions such as TMJ osteoarthritis.^194,195 Under physiological conditions, condylar cartilage of the TMJ resides in a relatively hypoxic microenvironment (~5% O₂), with HIF-1α continuously expressed at low levels as a key regulator maintaining cartilage homeostasis.¹⁹⁶ When mechanical loading exceeds the joint’s adaptive capacity (e.g., occlusal trauma, chronic overloading), intracartilaginous oxygen tension declines further, HIF-1α expression rises significantly, and this is accompanied by increased VEGF and cleaved Caspase-3 expression, indicating that excessive mechanical stress promotes chondrocyte apoptosis and matrix degradation primarily by exacerbating local hypoxia rather than through direct mechanical injury alone.^196,197 Notably, HIF-1α and HIF-2α exhibit opposing expression trends and functional roles in this pathological process: HIF-1α is protective for cartilage homeostasis, whereas HIF-2α expression progressively increases with sustained abnormal occlusal loading and exerts negative feedback inhibition on HIF-1α, accelerating condylar cartilage degeneration, a key molecular mechanism underlying the progression of TMJ osteoarthritis (TMJ-OA).¹⁹⁸ In addition, the inflammatory cytokine IL-1β interacts with mechanical loading in a complex manner: mechanical loading has been shown to partially suppress IL-1β-induced MMP-13 expression, suggesting that moderate mechanical stimulation may exert a chondroprotective effect within an inflammatory context. This offers a new perspective on the nonlinear interplay among mechanical loading, hypoxia, and inflammation in TMJ-OA.¹⁹⁹

In summary, mechanical signals dictate the trajectory of TMJ development and pathological degeneration through the dual pathways of structural modeling and metabolic regulation.

Abnormal mechanical stress and dentomaxillofacial deformities

Normal dentofacial development depends on tight mechanical homeostasis within the stomatognathic system. Physiological masticatory loading is transmitted through the PDL-bone axis and activates osteocyte mechanotransduction via fluid shear stress within the lacunar-canalicular network, thereby coordinating osteoblast and osteoclast activity to maintain alveolar bone homeostasis.^2,200–202 When the magnitude, direction, frequency, or duration of a mechanical force exceeds the adaptive threshold of the target tissue, this finely tuned regulation collapses, triggering imbalanced alveolar remodeling and aberrant skeletal growth. The aberrant forces that perturb dentofacial development fall into five categories: (i) abnormal occlusal forces, including occlusal trauma, premature contacts, loss of occlusal stimulation, and bruxism; (ii) maxillofacial trauma, typified by pediatric condylar fractures that directly injure the mandibular growth center; (iii) structural anomalies, of which cleft palate is representative, where the congenital defect and postsurgical scarring together act as persistent abnormal forces; (iv) abnormal oral soft-tissue forces, encompassing altered tongue posture, tongue thrusting, digit sucking, mouth breathing, and other parafunctional habits or muscle imbalances; and (v) improper orthodontic/orthopedic loading, including excessive force and mistimed rapid palatal expansion. The specific sources, resulting dentofacial deformities, and principal mechanistic pathways for each category are summarized in Table 2.

Table 2.

Abnormal mechanical forces causing dentofacial developmental anomalies

Category	Specific source	Dentofacial deformity	Principal mechanism	Refs
Abnormal occlusal force	Occlusal trauma/premature contact	Localized alveolar bone resorption, tooth loosening, and local arch-form change	Focal compressive stress activates the RANKL–RANK axis, promoting osteoclastogenesis while suppressing osteogenesis; impaired PDL vascularity destabilizes bone metabolism	201
	Loss of occlusal stimulation (anterior open bite)	Increased anterior alveolar ridge height, thinned buccolingual cortical bone, and masticatory dysfunction	Insufficient mechanical loading impairs type-H angiogenesis, reducing alveolar bone mass; cortical thickness correlates negatively with occlusal force	202,203
	Bruxism	Severe crown wear, reduced vertical dimension, altered occlusal plane, jaw asymmetry	Supraphysiological cyclic loading causes tooth-tissue loss; unilateral/asymmetric bruxing forces produce muscle imbalance; a neurophysiological feedback loop links malocclusion and bruxism	204,205
Maxillofacial trauma	Pediatric condylar fracture	Mandibular growth retardation, facial asymmetry, TMJ ankylosis, mandibular retrusion, unilateral posterior crossbite, midline deviation	Traumatic stress disrupts condylar cartilage proliferation and differentiation; ankylosis restricts mandibular movement and disturbs the functional-matrix control of jaw growth	206–208
Structural anomaly (cleft palate)	Cleft palate (congenital structural defect)	Maxillary arch collapse, maxillary hypoplasia, Class III malocclusion	The cleft abolishes three-dimensional maxillary support, allowing abnormally distributed occlusal stress to suppress vertical and transverse growth on the cleft side	209,210
	Scar contracture after cleft repair	Restricted anteroposterior and transverse maxillary expansion, aggravated maxillary hypoplasia, high prevalence of Class III malocclusion	Scar tissue persistently constricts the maxilla (“hoop” effect); finite-element analysis confirms asymmetric cleft-side stress that channels remodeling along unfavorable directions	210,211
Abnormal oral soft-tissue force	Tongue thrusting/altered tongue posture	Anterior open bite, deficient maxillary arch width, altered palatal morphology	Sustained anterior tongue thrust blocks vertical incisor eruption; lateral tongue pressure shapes the palate and limits arch width	212,213
	Digit sucking/pacifier habit	Incisor labial inclination, anterior open bite, narrowed maxillary arch, posterior crossbite	Inward buccal pressure from sucking, coupled with loss of lingual support, disrupts the equilibrium of oral soft-tissue forces	214
	Mouth breathing / incompetent lip seal	Narrowed maxillary arch, high-vaulted palate, maxillary protrusion, deep overjet	Weakened labial restraint on the upper incisors and a low tongue position withdraw palatal support; perioral muscle-tone pattern is altered	215,216
	Neonatal intubation pressure	Deep palatal vault, maxillary protrusion, tooth anomalies	Direct abnormal compression of the palate by the tube; disruption of normal suckling/swallowing deprives the jaw of the functional stimuli required for growth	217,218
	Occlusion-related muscle imbalance	Deviated growth direction of the maxillofacial skeleton, skeletal asymmetry	Class II children show lower tongue pressure and bite force than Class I	219,220
Improper orthodontic/orthopedic loading	Excessive orthodontic force (tooth movement)	Orthodontically induced inflammatory root resorption (OIIRR), alveolar bone loss, and reduced long-term arch stability	PDL pressure exceeding the capillary-closure pressure causes hyalinization and activates osteoclasts; compressive force upregulates IL-6, COX-2, PGE2, and the RANKL/OPG ratio, thereby driving osteoclast differentiation	221–223
	Mistimed/excessive rapid palatal expansion (RPE)	Buccal tooth tipping (dental compensation), cortical dehiscence, gingival recession, marginal bone loss	Once the suture ossifies, RPE force produces a dental rather than skeletal effect; circummaxillary sutures respond unevenly, and more ossified sutures resist expansion	224–226

In summary, abnormal mechanical forces, arising from diverse clinical sources, collectively disrupt the mechanobiological homeostasis of the craniofacial complex and represent a major etiological driver of occlusal and dentofacial developmental anomalies. Early identification and timely elimination of aberrant mechanical stimuli are therefore essential for the prevention and clinical management of malocclusion.

Conclusion and outlook

In summary, the development and homeostatic maintenance of the orofacial system is a highly dynamic biomechanical process, in which mechanical stress serves as a core regulatory signal with irreplaceable roles in cell-lineage fate determination, tissue morphogenesis, and homeostatic remodeling. Current evidence from diverse animal models has systematically established the regulatory action of mechanical signals across stages of dentofacial development; the principal animal models, methods, mechanotransduction pathways, and core findings discussed in this review are summarized in Table S1.

Currently, although certain progress has been made in elucidating the mechanisms by which mechanical signals regulate the development of diverse craniofacial structures, there are several limitations of the existing evidence base that should be noted. First, studies remain heavily concentrated on mice and rats, whereas primate and human samples are underrepresented; given the substantial differences between small rodents and humans in jaw size, bite-force magnitude, and tooth-replacement pattern, extrapolation to the clinic requires caution. Second, most studies do not explicitly group or separately analyze animals by sex, despite marked sex- and age-related heterogeneity in bone and tooth development, which may limit the generalizability of the mechanobiological responses summarized in this review. Third, the complete regulatory network, from stress perception and signal transduction to downstream effectors, remains largely undefined. Fourth, the highly spatiotemporally specific mechanical microenvironment of the craniofacial region is difficult to replicate in vitro, so translational research targeting pathways such as Piezo and YAP/TAZ continues to face bottlenecks.

To address these gaps, future work can advance systematically along the four complementary strategies depicted in Fig. 5: (i) Precise quantification of mechanical stress. Further improving stress detection methods and achieving precise quantification of mechanical stress at the tissue and cellular levels represent important prerequisites for in-depth investigations into biomechanical mechanisms. (ii) In vivo and in vitro mechanical-intervention models. Establishing in vivo models, such as cell-type-specific conditional knockout or overexpression models of Piezo and YAP, combined with the in vitro mechanical-intervention models to define causal relationships between mechanical signals and biological responses, represents an essential complementary strategy. (iii) Focus on mechanosensitive molecular components. Centered on Piezo channels and YAP/TAZ, single-cell and spatial transcriptomics can resolve their spatiotemporal activation across cell subpopulations, while the regulation of Piezo mechanical gating by post-translational modifications (phosphorylation, ubiquitination) can be examined. (iv) Epigenomic decoding of sustained mechanical signals. Epigenomic approaches, including chromatin accessibility profiling and DNA methylation sequencing, offer substantial potential for revealing how sustained mechanical signals remodel epigenetic landscapes and direct cell fate decisions. In parallel, single-cell and spatial transcriptomic technologies permit high-resolution characterization of cell type-specific and spatiotemporally constrained stress-responsive transcriptional programs. More broadly, mechanical stress does not act in isolation, and how stress stimulation forms multi-level crosstalk with systems such as nervous, immune microenvironment remodeling, and endocrine regulation remains to be further explored.

Fig. 5.

Four strategies for integrating the biomechanical regulatory network. (i) Precise quantification of mechanical stress. (ii) In vivo and in vitro mechanical-intervention models. (iii) Focus on mechanosensitive molecular components. (iv) Epigenomic decoding of sustained mechanical signals

At the translational application level, orofacial tissue regeneration and organoid construction based on mechanical-microenvironment modulation and targeting of Piezo/YAP/TAZ pathways are becoming a frontier of regenerative medicine. Nevertheless, two major hurdles impede clinical translational applications. First, Piezo1/2 and YAP/TAZ exert pleiotropic, context-specific regulatory effects in disparate craniofacial tissues, making it difficult to achieve tissue-specific targeting while sparing other mechanosensitive signaling networks. Second, there is a lack of well-validated non-invasive biomarkers to quantify mechanotransduction activity in human tissues, which hinders the extrapolation of rodent experimental results to clinical orthodontics and TMJ research.

To address these challenges, several strategic directions merit exploration. Pharmacological modulation of Piezo channels and YAP/TAZ activity—through small-molecule agonists, antagonists, or upstream regulators—may offer approaches to fine-tune mechanotransduction during OTM, TMJ remodeling, or PDL and condylar regeneration. In parallel, biomaterial- and scaffold-based strategies that engineer defined mechanical microenvironments, together with optimized three-dimensional culture systems and tissue engineering technologies, can enable precise simulation of the craniofacial mechanical stress microenvironment and directional induction of odontogenic stem cell differentiation. Collectively, these approaches may provide new strategies for repairing tooth defects, mitigating maxillomandibular resorption, achieving periodontal regeneration, and rescuing abnormal tooth development, though most remain to be functionally and clinically validated in craniofacial-specific contexts.

Supplementary information

Table S1 ^{(321.2KB, pdf)}

Author contributions

X.J. Yang contributed to conceptualization, visualization, writing, original draft, and funding acquisition; X.T. Zhang and Q.P. Gao contributed to writing, review & editing; S.L. Wang and X.S. Wu contributed to conceptualization, supervision, writing, review & editing, and funding acquisition.

Competing interests

The authors declare no competing interests.

Consent for publication

All authors have reviewed the full manuscript and agreed to publish.

Supplementary information

The online version contains supplementary material available at https://doi.org/10.1038/s41368-026-00462-3.