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Journal of Oral Science & Rehabilitation Volume 2 | Issue 3/2016 35 P u l p r e s p o n s e a f t e r c a p p i n g w i t h P D G F Introduction The dental pulp provides nutrition and sensory properties to dentin and has reparative capacity toreacttoinjury.Whentheinjuryresultsinodon- toblast death, a new generation of odonto- blast-like cells maydifferentiatefrom progenitor cells within the pulp and secrete a reparative dentin matrix.1 Pulp capping is a common proce- dure that induces reparative dentin formation after pulp exposure due to cavity preparation, cariesremovalortrauma.Calciumhydroxide,zinc oxide eugenol cements, composite resins, min- eral trioxide aggregate (MTA) and glass ionomer cements are used in clinical daily practice.2, 3 However, several concerns have been listed re- garding the use of these materials for pulp cap- ping, including cytotoxic effects,4 the lack of adequatebleedingcontrolafteracidetching5 and the new hard-tissue formation at the expense of pulp chamber width, causing narrowing of root canals.6 Although calcium hydroxide is the most widely used pulp capping agent to encourage hard-tissue bridging, the material is not able to effectively induce new tissue formation.7 Bridge formation remains unpredictable, with varying thickness and numerous tunnel defects,8 sug- gesting that it may be of insufficient quality to protect the pulp against bacterial microleakage along the restoration margins. Several articles have addressed the use of MTA for pulp capping and demonstrated a hard-tissue barrier beneath the MTA; however, pulpal soft tissue enclosed within the hard-tissue barrier and unpredictable dentin bridge formation were observed.9, 10 Recently, a growth factor delivery approach has been introduced to induce reparative dentin formation in noninflamed mechanicallyexposed pulps.11, 12 Rutherford et al. examined histologi- callythe reparative dentin formation of pulp tre- ated with osteogenic protein-1 (bone morpho- genetic protein [BMP] 7) in monkeys.13 They reported that BMP-7 has the potential to induce the formation of reparative dentin and related theamountofnewlyformeddentintotheamount of implanted protein. Nakashima observed his- tologicallythe induction oftubulardentinforma- tion in teeth capped with BMP-2 and -4 in mon- keys.11 An in vivo study has demonstrated with histomorphometric analysis the role oftransfor- ming growth factor-ʹ in promoting odontob- last-like cell differentiation and the secretion of extracellular matrix.14 The effects of enamel matrixproteinonpulpcappinghavebeenevalua- ted histologicallyand immunohistochemicallyin animal13 and human studies.15, 16 Afterapplication ofenamelmatrix protein,the damaged pulp sho- wed at first a reparative process with formation of a scar and moderate inflammatory infiltrate. Subsequently, neogenesis of normal dental pulp occurred and odontoblast-like cells produced reparative dentin.17 In the literature, there is con- verging evidencethat reparative processes reca- pitulate early developmental events that lead to dentaltissueformation.18 However,the effects of platelet-derived growth factor (PDGF) on repa- rativeprocessesafterpulpcappinghavenotbeen defined.PDGFisapotentmitogenic,chemotactic agent. It stimulates cells of mesenchymal origin to produce protein19 and promotes angiogenesis and the regeneration process of several tissues, such as bone, cementum and periodontal liga- ment.20 PDGFalsoregulatescellproliferationand dentin matrix protein production in dental pulp culture.21, 22 In their histochemical and immuno- histochemical study, Yokose et al. evaluated the effectsofthreePDGFdimers(PDGF-AA,-BBand -AB)onodontoblastdifferentiationofdentalpulp cells.23 The authors reportedthe different effects of the PDGF dimers on dentin formation during the repair process in damaged dental pulp. They observed that PDGF-AB and -BB stimulated the differentiation of odontoblastic cells, increasing thenumberofmatureodontoblasticcells.Incon- trast, PDGF-AA exerted inhibitory effects on odontoblastdifferentiation.23 Thesefindingssug- gest a role of PDGF-BB in dentinogenesis in the dentalpulp and in differentiation ofodontoblasts during repairprocesses afterinjurytothe mature pulp. The aims of this preliminary human study were to develop a regenerative approach to pulp capping using PDGF-BB andto describe histolo- gically the pulp tissue response. Materials and methods After a through explanation of the experimental rationale, clinical procedure and possible risks, written informed consent was obtained from both subjects to be entered in the study. The studyconformedtothe principles outlined inthe DeclarationofHelsinkiof1975,asrevisedin2013, on experimentation involving human subjects and was approved by the Ethics Committee of the Department ofHuman Morphologyand Bio- medicalSciences"CittàStudi",Milan,Italy.Before treatment, all patients gave written informed consent. Two completely erupted third molars thatneededtobeextractedfororthodontictreat- Volume 2 | Issue 3/201635