Pulp biology update: Is regeneration possible or is it just pulp fiction?

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1 Pulp biology update: Is regeneration possible or is it just pulp fiction? Hal Duncan, Division of Restorative Dentistry and Periodontology, Dublin Dental University Hospital, Trinity College Dublin, Ireland NVvE Voorjaarscongres, 2 nd April 2016

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3 What is possible in the lab and what is translatable to your clinic?

4 Saturday afternoon s pulp biology agenda Briefly consider 4 questions 1. What are the current and future developments for damaged pulp tissue? 2. Are targeted regenerative restorative biomaterials a pipe dream or viable treatment option? 3. Are cell-homing techniques predictable or likely to become a gold standard in endodontic practice? 4. Will stem cell-based solutions ever be realistic options in dental practice or developing countries?

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6 Biologically-based therapies

7 The promise of stem cells may someday help kids say good bye to the dreaded root canal, scientists report.

8 What problems do we want regenerative solutions to? Pulp vitality affected by microbial, chemical or mechanical irritants (Kakehashi et al. 1965; Levin, 2003). Removal of injurious stimulus can allow dental tissue regeneration (Mjör & Tronstad, 1974). Problem number Reactionary dentinogenesis Reparative dentinogenesis Smith et al. 1995

9 What problems do we want regenerative solutions to? Problem number Root-end closure with MTA (apexification) Cell-homing technique (revitalization)

10 Do we want to solve this by a regenerative approach? Problem number Problem number Necrotic pulp mature root Edentulous space

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12 What are the limitations of current restorative treatments? Cox et al Nair et al. 2008

13 Potential targeted solutions? Smith et al JOE

14 Dental materials, which biologically stimulate repair? Dentine treatments (e.g. EDTA) Material supplementation (e.g. NAC, Simvastatin) Direct application of growth factors Gene therapy Epigenetic modifiers (HDAC inhibitors) Pharmacological inhibitors Cell-based and non-cell based regenerative therapies The ready release of these bioactive molecules by the various tissue preparation agents, medicaments, and materials commonly used in endodontics highlights the opportunities for translational regenerative strategies exploiting these molecules with little change to existing clinical practice (Smith et al. 2016)

15 Epigenetics

16 What are epigenetic modifications? Duncan et al IEJ

17 Target cell nuclear function by acetylation of histone/non-histone proteins induces transcriptional and cellular processes (Duncan et al. 2011, 2012, 2013, 2015, 2016)

18 Primary Cells: Rat pulp (α-mem, 10% FCS, P<3) 1. Protein expression ELISA quantitative assessment total MMP-13 Time course analysis up to 21 days (NM, MM, SAHA) Cell pellet lysates, rather than culture supernatants 3. Mineralisation Assay Alizarin Red S (after 14d in mineralising medium) Mineralisation-medium +/- SAHA controls (24h) MMP-13i in range of concentrations ( 1 & 2µM) Reverse staining (Gregory et al. 2004) 5. Gene Expression (qrt-pcr) Selected mineralisation markers (24 h) Range of up/down regulated marker genes for validation of microarray (1, 14d) Complex basic laboratory research SAHA (1µM- 3µM) MMP-13 inhibitor (0.5-10µM) 6-/12-/96-well dishes seeding 4, ,000, n=3 Culture: Up to 21 days (95% humidity, 5% CO 2, 37 C) 2. MMP-13 enzyme activity Inhibitor specificity determined with 50ng/ml recombinant MMP-13 Optimal inhibitor concentrations selected Early and late mineralization activity assessment 1 and 14 day cell pellet lysates (MMP-13i, SAHA) Commercial MMP-13 fluorometric assay kit 4. Evaluation of Cell Growth Cell counts proliferation/ viability (24h, 5d) SAHA and range on MMP-13i concentrations 6. Cell migration Assays Vertical migration: Chemotaxis Transwell assay Cells pass through 8 μm-pore membrane in unsupplemented media (3 hours) Fluorogenic staining Horizontal migration: Wound healing assay (24 h)

19 What potential benefts have we demonstrated? Duncan et al. 2016b IEJ

20 Gene expression microarray Microarray (1 and 14d), 1µM SAHA Whole rat genome (Agilent 4 x 44k, 2-colour) 4 biological replicates Specific MMP investigation MMP-13 (collagenase-3) involved in ordered bone remodelling.expression increased in pathogenesis and repair HDAC-4 binds the MMP-13 promoter and suppresses MMP-13 gene transcription in the rat osteoblast cells (Shimizu et al. 2010) Gene expression analysis

21 Cell migration Wound healing scratch assay : representative plates Wound healing: quantified

22 Pharmacological inhibitors and mineralisation MMP-13 inhibition promotes mineralisation dose-dependently in DPCs in both the presence and absence of SAHA Mineralising medium (control) 1µM MMP-13i 2µM MMP-13i

23 Duncan et al JCP

24 Bone morphogenetic proteins Dentine matrix component release Neurotrophic growth factors Angiogenic growth factors Other growth factors From Duncan et al. 2016a IEJ

25 Recent research conclusions Short-term low-dose SAHA-exposure promoted mineralisation in DPCs, partly by epigenetic modulation of MMP expression and activity at relatively early time-points. MMP-13 inhibition further increased mineralisation-associated events, but decreased cell migration indicating a potentially novel role for MMP-13 in pulpal repair processes. Translationally, the use of low-dose pharmacological inhibitors (HDAC and MMP-13) have the potential to accelerate mineralisation in regenerative vital pulp treatment and promote regeneration within endodontic tissue engineering procedures.

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27 Revascularisation to revitalisation Pulp tissue? Cost? Protocol? Predictability? Banchs and Trope 2004

28 Cell-free or cell-homing The future regenerative therapies Tissue engineering approach requires cells, growth factors, matrix. It can be done, problems? what are the

29 Cell-free regenerative therapies Conclusions (Shimizu et al. 2012, 2013 JOE) Regeneration of pulp-like tissue was only possible after revascularization in teeth with preserved root sheath and without apical periodontitis.

30 From Smith et al JOE

31 Broad conclusions (Galler 2016a & b IEJ) >70 cases reports and case-series with 320 teeth Stimulation of bleeding brings stem cells into root Irrigants and medicaments create most conducive environment to repair No mechanical cleaning of dentine advocated EDTA in combination with NaOCl (1-3% 20 ml 5 min) Triple antibiotic paste, is being replaced by Ca(OH) 2 MTA over blood clot approx. 3 mm apical to ACJ Discolouration an issue, calcium silicate alternatives In majority of cases no odontoblasts, often fibrous tissue, cementum or bone inside root canal Not pulp-dentine regeneration; but biological tissue Positive vitality response Root thickening not consistent? How many cases? Case reports and positive reporting

32 Method: Retrospective cohort study compared clinical and radiographic outcomes of endodontic treatment performed in immature non-vital permanent teeth by apexification (calcium hydroxide or apical barrier with mineral trioxide aggregate) versus revascularization. 31 teeth (19 revascularization and 12 apexificaton), recall rate 63%, follow up 17 months Success: From a patient-based perspective, whether it is truly pulp or not may be irrelevant as long as the length and thickness of the root are increased by mineralized tissue apposition and the alveolar bone heals and is maintained Galler et al IEJ Results: 97% survival, more adverse events in revascularisation group. Although more revascularization cases than apexification cases showed an increase in radiographic root area and width, the effect was not statistically significant. Conclusions: Revascularization was not superior to other apexification techniques in either clinical or radiographic outcomes. Alobaid et al JOE

33 The goal of regenerative endodontics is to reinstate normal pulp function in necrotic and infected teeth that would result in reestablishment of protective functions, including innate pulp immunity, pulp repair through mineralization, and pulp sensibility Cao et al JDR

34 Cell-based or cell-free

35 Conclusions: On the basis of histobacteriologic observations, the failure of this revascularized/ revitalized tooth could be due to inadequate root canal disinfection without mechanical debridement Lin et al JOE In order to induce blood/stem cells into root canal system would have to widen apical constriction. What size? Is this preferable to RCT? Biological root filling perhaps, how predictable? Role of infection

36 Cell-based approaches

37 Although pulpal regeneration requires the cell-based approach, several challenges in clinical translation must be overcome-including aging-associated phenotypic changes in pulpal MSCs, availability of tissue sources, and safety and regulation involved with expansion of MSCs in laboratories. Cao et al JDR Duncan et al. 2016b IEJ

38 Editorial thoughts (Nair 2014) Microbe-free canal not predictably attainable Biofilm will disturb regenerative procedures Cell-based regeneration of pulp-like tissue, only so far been illustrated in sterile root canals Breakthrough more likely in new generative medicine i.e. whole tooth generation Perhaps regen endo not a paradigm shift Review conclusions (Volponi & Sharpe 2013 BDJ) Periodontal ligament regeneration difficult Bioengineered tooth development (implantation, growth and eruption) of mouse tooth takes weeks, the equivalent time to create a functional human tooth takes months.

39 What is clinically translatable today?

40 Potential chairside regenerative protocols cell-homing (cell-free) technique

41 Alternative chairside regenerative protocols Calcium silicate pulpotomy

42 How I d like to see Regen Endo developing

43 The development of new materials, which harness natural regenerative capacity and control inflammation is a priority To conclude In order to be accepted..solutions must be cost-effective and comparative to existing high street solutions Cell-based therapies are not yet the answer, but should not be ignored as a priority area for research. Cell-free revitalisation procedures are currently available, but require high quality multi-centred clinical investigations to answer key questions.

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