# Regenerative Endodontics > Regenerative endodontics for NEET-MDS Conservative Dentistry: the tissue engineering triad, antibiotic pastes, blood clot scaffolds, MTA barriers and outcomes. - Canonical URL: https://prepelephant.com/topics/neet-mds/conservative-dentistry/regenerative-endodontics-mds - Exam / course: NEET-MDS · Subject: Conservative Dentistry - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Regenerative Endodontics", PrepElephant, https://prepelephant.com/topics/neet-mds/conservative-dentistry/regenerative-endodontics-mds ## Direct answer Regenerative endodontics aims to replace a necrotic pulp with living, vascularised tissue so that an immature permanent tooth thickens its walls, lengthens its root and closes its apex — the triad of tissue engineering applied chairside: stem cells from the apical papilla surviving beneath the infection, a scaffold (the induced blood clot, with its growth factors), and effective disinfection. The protocol is two visits: chemomechanical disinfection without aggressive instrumentation, dressing with an antibiotic paste or calcium hydroxide, then at a second visit deliberate over-instrumentation past the apex to provoke bleeding, sealing the clot with a tricalcium silicate barrier and composite. Apexification remains the alternative for the same teeth — an MTA apical plug seals quickly and well, but the walls stay thin forever, which is exactly the disadvantage regeneration exists to erase. ## What you must remember - Case selection: immature permanent teeth with necrotic pulp and open, divergent apices — typically traumatic necrosis of young incisors; a sinus tract or apical radiolucency is compatible, absent acute symptoms. - The triad: stem cells (SCAP — stem cells of the apical papilla — and dental pulp stem cells), scaffold (blood clot, collagen), growth factors (released from dentine matrix by EDTA). - First visit: access, minimal or no mechanical instrumentation, irrigation with low-concentration sodium hypochlorite (about 1.5-3 per cent) and saline, dressing with triple antibiotic paste (ciprofloxacin, metronidazole, minocycline), double antibiotic paste or calcium hydroxide, sealed one to four weeks. - Minocycline discolours crowns: the double antibiotic paste or cefaclor substitution exists to prevent it, and coronal barriers (for example, a collagen plug or dentine-bonded layer) keep MTA grey from showing through. - Second visit: on resolution of symptoms, irrigate and finish with 17 per cent EDTA (avoiding residual hypochlorite, which is cytotoxic to stem cells), induce bleeding two millimetres past the apex with a K-file, allow the clot to form level with the cementoenamel junction, and place a 3-4 mm tricalcium silicate (MTA or Biodentine) barrier, sealed with composite. - Expected outcomes, in order of frequency: apical healing with resolution of lesions (most predictable), continued root thickening and lengthening, apical closure, and — least reliably — positive vitality responses. - Apexification contrast: one-visit MTA apical plugs of 4-5 mm or classical long-term calcium hydroxide (months of changes) produce a barrier but no wall thickening, and long calcium hydroxide dressing itself embrittles thin roots. - Histologically the regenerated tissue is commonly pulp-like with cementum or bone components — "revitalised", not a faithful pulp, a distinction examiners increasingly probe. ## Treating a blunderbuss necrotic incisor A nine-year-old's upper left central incisor, traumatised two years earlier, is discoloured, tender to percussion, with a periapical radiolucency and a wide-open divergent apex. First visit: isolate with rubber dam and remove necrotic debris with copious gentle 1.5-3 per cent hypochlorite irrigation without rotary shaping — these canals will be repopulated, not filled. Dry the canal and place a creamy antibiotic paste (double paste, avoiding minocycline in a front tooth), sealed with a cotton pellet and temporary cement for two weeks. Second visit, symptoms resolved: irrigate with saline, and finish with 17 per cent EDTA for several minutes to chelate the smear layer and liberate dentine growth factors. Bleed the canal deliberately: pass a K-file two millimetres beyond the apex until blood wells, and let it clot at the coronal level. Lay a collagen barrier, then 3-4 mm of white MTA or Biodentine over the clot, and close with bonded composite. Recall with radiographs: expect lesion resolution first, then measurable wall thickening and apical maturation. ## Where students slip Three answers decide this viva. "Which component of the triple paste is dropped and why?" — minocycline, for crown discolouration; candidates who do not know the substitution have not engaged with the protocol's complications. "Why EDTA last?" — because it releases growth factors from dentine matrix and because residual hypochlorite is cytotoxic to the very stem cells the technique depends on. "What actually forms inside?" — a pulp-like, vascularised tissue often containing cementum or bone, not identical native pulp; "new pulp, same as before" is the naive answer examiners set as bait. ## Frequently asked questions ### What is the tissue engineering triad in regenerative endodontics? Stem cells (chiefly of the apical papilla), a scaffold (the induced blood clot), and signalling molecules — growth factors released from dentine by EDTA. ### Why is minocycline often dropped from the triple antibiotic paste? It discolours crowns; the double paste or cefaclor substitution keeps antimicrobial cover without staining. ### Why is 17 per cent EDTA the final irrigant? It removes the smear layer, liberates dentine growth factors and washes out hypochlorite residues toxic to apical cells. ### How is the scaffold created? Over-instrumentation two millimetres past the apex induces bleeding; the clot forms to the cementoenamel junction beneath the MTA barrier. ### How do outcomes differ from apexification? Regeneration pursues wall thickening and root lengthening with apical closure; apexification seals the apex but leaves walls thin. ### What tissue actually regrows? A vascularised pulp-like tissue often containing cementum or bone — revitalisation, not histologically native pulp.