J Endod 2008;36:536–541

Before 2004 : Apexification :  Apexification has proven to be highly predictable  increased susceptibility to cervical fracture

The artificial apical barrier technique  The material of choice : MTA  The technique is predictable and successful Mineral trioxide aggregate (MTA) was introduced in 1993 by Loma Linda University, the commercial version of MTA introduced in 1998 tooth-colored MTA was introduced in 2002

first revascularization research efforts :  immature tooth was treated with irrigation and disinfection using two antimicrobial agents (metronidazole and ciprofloxacin) with successful revascularization Banchs and Trope 2004

 Stem Cell Therapy  Gene Therapy Reference

 stem cells  Morphogens or Signaling molecules  scaffold of extracellular matrix

 they exist as undifferentiated cells and maintain this phenotype  they have an ability to self-replicate for prolonged periods  they maintain their multiple differentiation potential throughout the life of the organism Barry FP. Biology and clinical applications of mesenchymal stem cells. Birth Defects Res Part C, Embryo Today Rev 2003;69:250 –6. Reference

 Progenitor cells retain the differentiation potential and high proliferation capability, but have lost the self-replication property unlike stem cells.

 dental pulp stem cells (DPSCs)  stem cells from human exfoliated deciduous teeth (SHED)  stem cells from the apical papilla  dental follicle progenitor cells  periodontal ligament stem cells

 biological three-dimensional microenvironment for cell growth and differentiation  promoting cell adhesion, and migration.  serves as a carrier for morphogen in protein therapy

 should be effective for transport of nutrients, oxygen, and waste.  It should be gradually degraded and replaced by regenerative tissue  They should have biocompatibility, nontoxicity, and proper physical and mechanical strength

degradation rate, microstructure, and mechanical strength

 Fibronectin  Bone sialoprotein  Alginate hydrogel facilitates pulpal wound healing with hydration properties and tethering growth factors  Mineral trioxide aggregate (MTA), promotes reparative dentin formation

The morphogenetic signaling networks include the five major :  bone morphogenetic proteins (BMPs),  fibroblast growth factors (FGFs)  wingless and int-related proteins (Wnts)  Hedgehog proteins (Hhs)  tumor necrotic factor (TNF) families Although five distinct families of morphogens are involved in embryonic tooth development, BMPs appear to be sufficient for tooth regeneration in adults

 BMP2, BMP4, BMP6, BMP7, and Gdf11 are also expressed during odontoblast differentiation  BMP4 and Bmp5 during ameloblast differentiation

 There are many similarities between morphogenic factors regulating dentinogenesis and the factors that regulate reparative dentinogenesis  transforming growth factor ß, (BMPs), platelet-derived growth factor, fibroblast growth factor, and vascular endothelial growth factor (VEGF) are incorporated into the dentin matrix during dentinogenesis and are retained there As “fossilized” molecules.

 interestingly, calcium hydroxide has been shown to solubilize Dentin and allow The release Of bioactive molecules that can potentially regenerate dentin.

 BMPs, Dentin matrix protein (DMP)-1, bone sialoprotein (BSP) can also stimulate the differentiation of pulp cells into cells that are capable of secreting mineralizable matrices in pulp exposure sites.

These studies demonstrated that dentin-derived BMP-2, but not BMP-7, is necessary for the differentiation of stem cells into odontoblasts. Reference

 recently observed that SHED have the potential to differentiate into functional vascular endothelial cells via a process that closely resembles that of vasculogenesis  VEGF induces the differentiation of DPSCs (i.e., SHED) into endothelial cells Reference

 It is noteworthy that members of the BMP family have pronounced effects on neurogenesis  Thus, it is likely BMPs can be used for regenerative pulpal therapy and dentinogenesis may have concurrent beneficial effects on nerve regeneration. Lein P, Guo X, Hedges AM, Rueger D, Johnson M, Higgins D. The effects of extracellular matrix and osteogenic protein-1 on the morphological differentiation of rat sympathetic neurons. Int J Dev Neurosci 1996;14:203–15. Adler J, Jayan A, Melia CD. A method for quantifying differential expansion within hydrating hydrophilic matrixes by tracking embedded fluorescent microspheres. J Pharm Sci 1999;88:371–7. Mabie PC, Mehler MF, Kessler JA. Multiple roles of bone morphogenetic protein signaling in the regulation of cortical cell number and phenotype. J Neurosci 1999; 19:7077– 88. White PM, Morrison SJ, Orimoto K, Kubu CJ, Verdi JM, Anderson DJ. Neural crest stem cells undergo cell- intrinsic development changes in sensitivity to instructive differentiation signals. Neuron 2001;29:57–71. References

 There is a risk of unfavorable transformation of the stem cells, and there is also a risk of unwanted contamination of these cells with pathogens during these procedures.

 In vivo methods : Add gene in vivo to induce new function, examples: angiogenesis  Ex Vivo methods : Culture cells ex vivo, add gene, transplant back to host examples: re- growth of cartilage and bone

 In Vivo Gene Therapy: the ultrasound-mediated Gdf11 gene transfer together with microbubbles also induced differentiation of pulp stem cells into odontoblasts in vitro and complete reparative dentin formation in vivo

 Ex Vivo Gene Therapy: The in vivo gene therapy does not have much effect on reparative dentin formation in case of severe inflammation and few stem/progenitor cells in the pulp tissue The transplantation of cultured dermal fibroblasts transduced with Bmp7 using a recombinant adenovirus also induced reparative dentin formation in the exposed pulp with reversible pulpitis. Bmp-transduced cells directly contributed to reparative/regenerative dentin formation

 The field of stem cell-based regenerative dentistry is complex and multidisciplinary by nature. Progress will depend on the collaboration between clinicians and researchers from diverse fields (e.g., biomaterials, stem cell biology, endodontics) working together toward the goal of developing biological approaches to regenerate dental and craniofacial tissues.

 begins with chemical disinfection by copious irrigation of the root canal space with NaOCl, combination of NaOCl/chlorhexidine or NaOCl/hydrogen peroxide  followed by placement of an intracanal medicament at the first visit. Several medicaments like triple antibiotic mixture (metronidazole, ciprofloxacin, and minocycline), calcium hydroxide, and formocresol have been used successfully. At the next visit  which should be at least 1 week after the initial session or more  in the absence of clinical signs of inflammation, the clinician removes the intracanal medicament  induces bleeding inside the root canal space by irritating the periradicular tissue.  After clot formation, the clinician seals the root canal space by placing an MTA plug over the blood clot J Endod 2012;38:14 28–1434

 An 11-year-old boy  maxillary second premolar tooth had been accidently extracted and immediately replanted developed pulpal  necrosis and symptomatic apical periodontitis.  After preparing an access cavity, its necrotic pulp was removed. The canal was irrigated with 5.25% NaOCl solution and dried with paper points. A triple antibiotic mixed with distilled water was packed in the canal and left for 22 days.

 Twenty milliliters of whole blood was drawn from the patient’s forearm for preparation of PRP.  After removal of the antibiotic mixture, the PRP was injected into the canal space up to the cementoenamel junction level. Three millimeters of grey mineral trioxide aggregate was placed directly over the PRP clot.  Three days later, the tooth was double-sealed with permanent filling materials.

 Clinical examination 5 1/2 half months later revealed no sensitivity to percussion or palpation tests.  Radiographic examination of this tooth showed resolution of the periapical lesion, further root development, and continued apical closure.  Sensitivity tests with cold and an electric pulp test elicited a positive response similar to those found in the first premolar tooth

 Discoloration : use of minocycline in the triple antibiotic paste  Treatment Period: The required time for disinfection of the root canal space with triple antibiotic paste or calcium hydroxide and increased number of clinical sessions J Endod 2012;38:14 28–1434

 Challenging Histologic Outcomes: generated tissue inside the root canal space after regenerative endodontic treatment was basically ingrowth of periodontal connective tissue instead of pulpal connective tissue.  No odontoblastic cell layer,dentin-like structure, and pulp-like tissue were detected  3 types of tissues: cementum-like tissue that was responsible for increase in root length and thickness, bone-like tissue and periodontal ligament (PDL)–like tissue inside the canal space

 Poor Root Development :absence of increase in root wall thickness, or lack of formation of tooth apex  Insufficient Bleeding  Root Canal Calcification/Obliteration

 A healthy 14-year-old female  history of impact trauma to the anterior maxillary teeth 6 years before initial visit  Clinical examinations revealed extensive caries of tooth #8  Both teeth showed normal mobility  Cold test by using Endo-Frost cold spray did not elicit any response in maxillary central incisors  whereas maxillary lateral incisors responded normally to the test  maxillary central incisors were sensitive to percussion and palpation

 After local anesthesia with 3% plain mepivacaine  access cavities on teeth #8 and #9 were prepared  Each root canal was passively irrigated with 20 mL NaOCl 5.25% without instrumentation, Canals were gently dried with paper points  A triple antibiotic mixed with distilled water was packed in the canal and left for 4 weeks  A sterile size 40 K-file was overextended and initiate bleeding  approximately 3 mm of MTA was placed in the coronal third of the canals

 The patient was recalled yearly  The teeth were not sensitive to percussion and palpation.  The response to the cold test was negative in all follow-up sessions.  In radiographic examinations the radiolucent lesions healed, and the apices formed.  However, there was no increase in the length and thickness of the roots

 Six years after initial treatment the patient complained about the appearance of her maxillary central incisors.  severity of discoloration, full crown restoration for both teeth was suggested  root canal therapy of both central incisors

 In the present case, passage of a long time (6 years) without any treatment after traumatic impact might be related to damaged Hertwig epithelial root sheath and, subsequently, decreased root development potential

J Endod 2012;38:14 28–1434