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science & practice 31Show Preview IDS Cologne 2015 tically,wenotedthatnearinfra-redlaser wascapableofgeneratingreactiveoxy- gen species (ROS). This highly reactive, transient chemical intermediate was sensed by a key methionine residue on thelatentTGF-β1complexthatresulted in a change in its conformation, result- inginitsactivation.20 Study2:Dentinregeneration Having noted the effects of low powerlasersonpromotingoralmucosal wound healing in the prior study, we extended our clinical applications to dentin regeneration where TGF-β1 has been shown to play a pivotal role in dentin physiology.21–25 We noted the ability of low power lasers to promote dentin regeneration using human den- talstemcells.Tovalidatetheseobserva- tions, rodent pre-odontoblasts (MDPC- 23) cells grown in a polymeric scaffold, simulating a 3-D niche were treated withlowpowerlasers. Laser treatments were able to in- duce dentin differentiation as evident by increased dentin-specific matrix deposition and mineralisation. To con- firmtheroleofTGF-βinvivo,transgenic mice with lack of TGF-β receptor in all cells capable of inducing dentin (utilis- ing a Dentin Sialophosphoprotein spe- cifictransgene)weregenerated.Experi- ments in these mice did not demon- strate any significant dentin induction followinglasertreatmentvalidatingthe criticalroleofTGF-βactivationinmedi- atingitseffects. Previous studies have shown the therapeutic benefits of supplementing exogenous (recombinant) TGF-β for reparative dentin, this study suggests theuseoflowpowerlaserscanactivate endogenouslatentTGF-β1presentnatu- rallyinthepulp-dentincomplextodrive differentiation of resident dental stem cells (Fig. 2). Thus, this therapy can utilise the inherent repair-regenerative responses naturally present in native tissues. ClinicalApplications ofLaser-Dentininduction These observations have potent clinical implications where dentin wouldneedtobetherapeuticallygener- ated. The two directly relevant clinical scenariosareforpulpcappingfollowing deep carious lesions and for dentin de- sensitisation. In the former case, re- moval of decayed or damaged tooth structureapproximatingthepulp(close toorclearexposure)thatrequiretheuse ofpulpcappingagents(suchasCalcium hydroxide) could be potentially re- placedwithlowpowerlasertreatments. In the second scenario,the use of low power laser treatments on exposed dentinal tubules could potentially gen- erate an intrinsic dentin barrier that would relieve tooth sensitivity. This would be more effective than our cur- rent approach to extrinsically occlude exposedtubulesmodes. Thetwomajorlimitationsofthecur- rentstudywerethatwenotedcalcifica- tions interspersed throughout the pulp chamber, spatially distinct from the laser-biological tissue interface. We be- lieve this is perhaps a combination of the inherent near-infrared laser wave- length that readily permeates through- out biological tissue as well as the solu- ble nature of the activated molecules. This could be potentially addressed by better optical focusing techniques and use of specific reagents that absorb the radiantenergyandspatiallyrestrictthe biologicalinterphase. A second limitation in this study was the observation that laser-gener- ated dentin was a tertiary or reparative form that lacks pristine tubular struc- ture.Itappearsthatadditionalcuesboth biophysical(architecture)andbiochem- ical (soluble, organizational), are likely necessary to promote morpho-differen- tiationofthenewlyinduceddentin. Inattemptstofurtherexplorethese molecular mechanisms, we have more recently extended developed a poly- mericscaffoldsystemwithprecisemor- phogen fields.26 Using this model, we were able to extend our observations with dental stem cells and laser-acti- vatedTGF-β1mediateddentindifferen- tiation to mesenchymal stem cells sug- gestingthisapproachcouldhavesignif- icant potential with other stem cell typesaswell. Conclusion BothROSandTGF-βarecentralbio- logicalmediatorsinawiderangeofbio- logical responses.27–29 The ability to se- lectively activate them in a spatio-tem- porally defined manner in vivo using low power lasers provides a significant clinical tool for various therapeutic in- terventions. Questions on precise wavelengths, clinical protocol (delivery and dose ranges) and context of the pathophysio- logical response are all critical issues thatneedtobeexploredrigorouslytoen- able further effective clinical transla- tionofthistherapy.30 Further,theability to effectively move this therapy into mainstream clinical dentistry will re- quiremorebasicresearch,development of robust clinical standards and educa- tionatvariouslevels(basicdentaltrain- ingandcontinuededucation)(Fig.3). In the current era of personalised medicine and strategies to utilise so- phisticated technologies and pharma- ceuticals to individualise health care, the significant promise of lasers in clin- ical dentistry may indeed be the lead- ing, pivotal technology that ushers in theneweraofregenerativedentistry. Acknowledgement This work was supported by the in- tramural research program of the Na- tional Institute of Dental and Craniofa- cial Research, National Institutes of the Health. 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