Periodontal Regeneration and Scaffold Research

• The demand for dental tissue and whole-tooth regeneration is increasing with life expectancy.
• Dental tissues' complex structure poses challenges to regenerative dentistry despite medical progress.
• Cellular biologists, material scientists, and clinical odontologists are collaborating to find solutions for dental tissue regeneration.
• Recent discoveries include signaling pathways and factors influencing calcified tissue genesis in teeth.
• Novel biocompatible scaffolds and polymer-based drug release systems are in development for clinical use.
• These biomaterials have the potential to modulate signaling cascades involved in dental tissue genesis and regeneration.
• Approaches for whole-tooth regeneration use adult stem cells, induced pluripotent stem cells, or tooth germ cell transplantation.
• These are promising alternatives to overcome existing in vitro tissue generation hurdles.
• This review discusses recent advances in cellular signaling, novel materials, odontogenic cell sources, and tooth regeneration methods.
• Review provides an up-to-date overview of tooth regeneration and hints at future directions in regenerative dentistry.

Keywords

• Dentogenesis
• Amelogenesis
• Dentinogenesis
• Cementogenesis
• Drug release materials
• Scaffolds
• Odontogenic cells
• Stem cells
• Whole-tooth regeneration

Introduction

• Dental injuries and diseases affect significant portions of populations worldwide.
• Caries lesions cause enamel resorption and dentin damage due to oral microbiota.
• Untreated caries causes excessive dentin damage, requiring reparative treatment.
• Periodontitis is an inflammatory disease that damages gingiva, periodontal ligament, cementum, and alveolar bone.
• Specialized soft and hard calcified tissues regeneration approaches are needed due to the fact excessive periodontitis damage cannot be regenerated naturally.
• Heritable disorders, like amelogenesis imperfecta, affect tooth formation, eruption, calcification, or maturation.
• Dental diseases create an unaesthetic oral cavity, thus affecting patients emotionally.
• Dental tissues have limited self-regeneration.
• Enamel becomes acellular after formation.
• Dentin regeneration is limited and dependent on the dental pulp stem cell pool.
• Cementum has limited regrowth in disease-induced resorption.
• Each dental tissue contains inorganic matter, matrix proteins, and microstructures.
• The complex microarchitecture of the tooth requires biocompatible and wear-resistant replacement materials.
• The development of enamel and dentin relies on mesenchymal-epithelial interactions.
• Signaling patterns in dental tissue differentiation in vitro, postnatal calcified tissue metabolism, and regeneration are being actively studied.
• Whole tooth regeneration efforts include biological, bioengineering, and genetic approaches.
• Revitalizing the odontogenic potency of the successional dental lamina (SDL) rudiment may induce tooth formation in adults.
• Whole-tooth restoration utilizes autologous tooth germ cells and bioengineered tooth germ transplantation.
• Due to limited tooth germ cell sources and immune rejection risks, adult stem cells or induced pluripotent stem cells (iPSCs) may be used instead.
• Combining cells of mesenchymal and epithelial origin with novel culture methods is being explored for tooth regeneration.
• The combination with scaffold material may improve tooth formation.
• Scaffolds influence cell behavior and provide mechanical support.
• Their degradation parallels native extracellular matrix formation.
• Artificial scaffolds for tooth regeneration are rare due to the complex nature of teeth.
• Recent developments in biomaterial involve hybrids/composites of inorganic/organic components to mimic natural tooth composition.
• Functionalization of scaffolds using cell-free methods is possible.
• Vesicles, small RNAs, or exosomes can be used to address regenerative functions.
• Scaffolds can be loaded with drugs, growth factors, and/or receptor ligands to guide stem cell differentiation.
• Very few artificial materials have been tested clinically.
• This review summarizes discoveries about cellular signals guiding dental tissue differentiation in vitro and in vivo.
• Current developments of biocompatible functionalized scaffolds, drug-release materials, and their applications are addressed as well.
• Whole-tooth generation approaches and dilemmas are elucidated using an interdisciplinary approach covering molecular, structural, and biological dental regeneration issues.

Hard Dental Tissues and Their Genesis

• Tooth formation starts in embryogenesis and continues throughout childhood and adolescence.
• Each dental tissue forms uniquely and in a regulated manner, with one tissue guiding the others.
• Early odontogenesis involves epithelial-mesenchymal interaction.
• Epithelium derives from embryonic endoderm, mesenchyme from cranial neural crest.
• Placodal thickenings of the oral epithelium induce cellular condensation of the mesenchyme.
• The tooth primordium undergoes morphological stages forming bud, cap, and later bell.
• Epithelium gives rise to enamel, mesenchyme to pulp, periodontal apparatus, dentine, and cementum.
• Epithelial components lose odontogenic competence, reciprocal induction starts from mesenchyme.
• Signaling program governs reciprocal crosstalks involving molecules interacting in signaling pathways.
• Morphogenetic inducers include BMPs, FGFs, Wnt, Hh, and EDA.
• Morphogenesis is driven by signaling centers orchestrating tissue interactions and influencing tooth size and shape.
• Tissue forces involving epithelial contraction, mesenchymal condensation, or bone biomechanics participate in tooth morphology.
• Epithelial stem cells are located in the cervical loop and active until tooth root formation during development.
• Hertwig's epithelial root sheath is the signaling center for tooth root formation.
• Interaction with developing alveolar bone is essential for whole tooth regeneration.
• The mature tooth consists of non-vascularized hard tissues, enamel, dentin, and vascularized innervated dental pulp.
• The dental pulp is associated with dentin and harbors cell populations.
• Blood vessels nourish resident cells, nerves exchange sensory information.
• Odontoblasts, precursors, and DPSCs from the dental pulp are recruited for dentin repair in excessive dental injury.
• The periodontal ligament is a complex attachment tissue harboring odontogenic stem cells, linking the tooth to the alveolar jawbone.

Signaling Pathways Modulating Hard Dental Tissue Generation

• Signaling cascades like FGF, Shh, TGF-β, BMPs, and Wnt/ß-catenin regulate dentogenesis during development and adulthood.
• Specific functions are elicited during tooth differentiation phases; some for cell stemness and proliferation (FGF, Shh), and others for differentiation, migration, and calcification (Wnt, TGF-ẞ, and BMPs).
• Purinergic signaling function is gaining attention in dental tissues metabolism.
• Most ligands activate transcription factors like Runx2, osterix (Osx or Sp7), and ERK1/2, which are central regulators of gene sets for calcified tissues.
• Epithelial–mesenchymal interactions also play a role in odontogenic and cementogenic differentiation.

Amelogenesis

• Amelogenesis is tooth enamel formation by ameloblasts.
• Ameloblasts secrete proteins like amelogenin, ameloblastin, and enameling to serve as scaffolds for mineral deposition.
• Amelogenin and amelotin phosphorylation is essential for enamel rod formation.
• Matrix proteases degrade scaffolds later, and ameloblasts undergo apoptosis, making enamel acellular and highly mineralized.
• Enamel cannot be regenerated due to its acellular nature.
• Several cell sources have amelogenic capacity: keratinocyte stem cells, epithelial cell rests of Malassez (ERM), odontogenic oral epithelial stem cells (OEpSCs), adipose tissue-derived mesenchymal stem cells (AT-MSCs), and iPSCs.
• Since ameloblasts undergo apoptosis after enamel production, studies rely on in vitro models like murine immortalized ameloblast-lineage cell (ALC) line, organotypic cultures, or rodent models.
• Shh, a major ligand expressed in the enamel knot, has a direct effect on amelogenin and ameloblastin expression via activated Glil.
• Gli1 was proposed as marker for selecting stem cells with odontogenic potential for tooth regeneration.
• Runx2 and ODAM regulate matrix metalloproteinase 20 (MMP20) expression, the key enamel matrix-degrading enzyme.
• WDR72 is an intracellular protein abundant in ameloblasts during enamel maturation and a function in amelogenin endocytosis is proposed.
• Studies indicate the importance of the mentioned pathways in dentogenesis.
• Shh and FGF8 stimulate proliferation of ameloblast precursors.
• Runx2 regulates amelotin expression during enamel maturation.
• Cytoplasmatic B-cell CLL/lymphoma 9 protein (Bcl9), its paralog B-cell lymphoma 9-like protein (Blc91), and partners Pygopus regulate amelogenin secretion.
• Expression of β-catenin shapes tooth development by modulating developmental signaling pathways.
• The β-catenin pathway is also involved in ameloblast polarity and motility.
• TGF-ẞ superfamily ligands such as BMPs and TGF-ẞs are regulating enamel structural genes and matrix metalloproteinases expression.
• MMP20 regulates TFG-ẞ isoforms activity.
• BMP knock-outs result in downregulated matrix proteins and metalloproteinase expressions.
• Timely regulation of ligands important for cell stemness maintenance is crucial for enamel formation.
• Proper enamel scaffolding protein deposition, phosphorylation state, and timely cleavage are needed, which allow ameloblast migration and crystals deposition.
• Enamel integrity depends on proper enamel scaffolding, protein deposition, phosphorylation state, and timely cleavage, crystals deposition is enabled.

Dentinogenesis

• Dentin made out mostly hydroxyapatite is produced by odontoblasts.
• Process entails building scaffold then minerals precipitation.
• Mineralized part connects through tubules in pulp.
• Projections of odontoblasts is involved stimuli reaction by cells.
• Dentin regeneration capacity depends on remaining dental stem cell pool.

Cementogenesis

• Cementum, a thin calcified tissue, is produce by bone.
• Bone is composed of collagen I, bone sialoprotein, osteopontin, glycoproteins and hydroxyapatite.
• Cementoblast precursors are present, mobilization is possible.

Cell Sources and Signaling Modulators

• Several signaling molecules promote hard tissue genesis.
• Amelogenin controls cementogenesis by proteins expression modulation.
• Osx key transcription actor for dentin, dentinogenesis has same key transcriptor.

Scaffolds and Drug Release Materials for Tooth Regeneration

• Scaffolds and biomaterials are essential for dental tissue regeneration.
• These act as a template for tissue regeneration or delivery platform for implantable cells.
• They can also be used to transport bioactive molecules such as drugs or growth factors, enhancing regenerative potential.
• Scaffold materials need to be available and biocompatible + biodegradable, without toxic metabolites.
• Tooth regeneration scaffolds are subjected to challenges of the oral cavity environment (mechanical forces, microorganisms, temperature, pH).
• The intended biomaterial has to face these challenges without limitations in its biocompatibility.
• Properties besides biocompatibility mimic tissue intended to regenerate. Categories for biomaterials used in tooth regeneration are natural organic, synthetic organic materials, or inorganic materials.
• Organic materials involve peptides/polysaccharides, synthetic include PLA and PCL, inorganic are bioactive glasses/Calcium Phosphates, Polymeric materials establish porous providing highly hydrated matrix.
• Engineered inorganic tissues comprise preferable properties. Combination components gains rising tissue interest.

Enamel Formation

• Acellularity stands as main challenge regeneration, ameloblasts need finalized structure vitro.
• Model unique HA crystals not successful, studies follow Bioemetic approach.
• Amino peptide fragments as template, promote calcium phosphate surrounding entrapment.

Dentin Formation

• Pulp capping main therapy vital maintain. Pulp capping comes infection, is essential vitality desired.
• Regenerating the pulp is key need.
• Canal induced, clot scaffold, leads regeneration, dentin mix tissue. Nanobiocement showed bioactive in vivo w/ Sr.
• Glass promoted odontogenesis, composite promoted layer deposit.

Cementum Formation

• Cementum re-growth closely connected ligaments/gingiva.
• Promote various recruitment and homing factor surroundings. Multi-compartment different solve defect scale.

Scaffolds Summarized

• Retro significantly higher formed, addition improve the biodegradation.
• BMP-2 promoted for increased results from the scaffold.

Drug Release Systems Useful in Tissue Engineering

• Whole tooth most challenger w/ drug aspect, as precise combinations and amounts differentiation needs are key Appropriate is that compounds development for tooth formation

Whole Tooth Regeneration

• Goal is to regenerate as replacement decay or lost, using either implants to fill gaps.
• Strategy where biological parts can form w/ metal or ceramic implants used is alternative (bio-root)
• Regrow teeth bio likely focus future if efforts.

Reactivation the Odontogenic Potency

• Fishes and reptiles from teeth, evolution reduced.
• Dental lamina (SDL) for tooth replacement approach as it has the ability to carry out odontogenesis.
• Level replacement is related by genes with SOX express to BMP signaling needed.

Tissue Recombination

• Basic to tissue mimic natural tissue building processes.
• Tooth mass transplanted from the mouth used generate pulp, dentin, enamel.
• Used collagen drops with cells implant animals get "Biotooth."

Adult Stem Cell Approaches

• Autologous is to use cells from patient needing tooth tissue growth.
• Adult + embryo "Tooth inducers" cells

Problems in Whole Tooth Regeneration

• Tissue environment or bone/jaw can interfere.
• In Vitro growth needed to not lose potential 3D micro help prevent, rescue cells w signaling.

This quiz covers research on periodontal ligament regeneration, focusing on scaffold materials and cell types used in regenerative therapies. Questions address the function of macroporous compartments, cell sheet composition, and the regenerative potential of different scaffold types containing BM-MSCs and PDLCs. It further explores the effect of specific peptides on dental caries.