use of platelet-rich plasma in endodontic procedures in

Regenerative Endodontics

Use of Platelet-rich Plasma in EndodonticProcedures in Adults: Regeneration or Repair? AReport of 3 Cases with 5 Years of Follow-up
Jos�e Francisco Gavi~no Ordu~na, DDS,* Javier Caviedes-Bucheli, DDS, MSc,†
Mar�ıa C. Manzanares C�espedes, PhD, MD, DDS,‡ Esther Ber�astegui Jimeno, PhD, MD, DDS,*Benjam�ın Mart�ın Biedma, PhD, MD, DDS,§ Juan Jos�e Segura-Egea, PhD, MD, DDS,¶

and Jos�e L�opez-L�opez, PhD, MD, DDSk

Abstract

SignificanceEndodontic therapywith PRPof necrotic teethwithopen apices and apical periodontitis appears to bepredictable at a 5-year follow-upandagoodoptionin adults.

Introduction: Regenerative endodontic procedures(REP) are a promising alternative for necrotic immatureteeth in adolescents and children, but very littleevidence is available on this alternative in long-lastingnecrotic teeth with open apices in adults. REPs aredesigned to replace damaged structures of the pulp-dentin complex, but no regeneration has been obtainedin any of the cases described in necrotic immature per-manent teeth with apical periodontitis with histologicresults. The results are limited to periapical tissue repairwith increasing root length, thickening of the root walls,and apical closure in young patients. In this series ofcases, we report on the outcomes of the adjuvant useof autologous platelet-rich plasma (PRP) in endodontictherapy in adults by monitoring periapical tissue healingwith periodic periapical radiographs and cone-beamcomputed tomographic scanning. Methods: Threeteeth with apical periodontitis and open apices in 3different patients from 21 to 35 years-old were evalu-ated. An REP was performed with the adjuvant use ofPRP. Results: At controls, complete disappearance ofthe radiolucent lesions and the presence of calcifiedstructures forming bridges occupying the pulp lumenwere observed but not an ostensible thickening ofroot walls with a regeneration of pulp-dentin complex.Conclusions: The repair of periapical tissues withREPs of open apex teeth with apical periodontitis andin nonsurgical endodontic retreatment appears to befeasible in adults, but no regeneration was obtained inany of the present cases. The use of PRP may be agood choice as an autologous matrix because of its sta-bility and induction; it contains growth factors and

From the *Department of Odonto-Stomatology, School of DentisOdontologicas (CIO) Pontificia Universidad Javeriana, Bogota, ColomSantiago de Compostela, Santiago de Compostela, Spain; ¶DepartmeBarcelona University/Oral Health and Masticatory System Group (BeBarcelona, Spain.

Address requests for reprints to Dr Jos�e Francisco Gavi~no Ordu~naGobierno, C/ Feixa LLarga s/n, L’Hospitalet de Llobregat 08907, Bar0099-2399/$ - see front matter

Copyright ª 2017 American Association of Endodontists.http://dx.doi.org/10.1016/j.joen.2017.04.010

1294 Gavi~no Ordu~na et al.

bioactive molecules like transforming growth factor beta, bone morphogenic proteins,insulinlike growth factors, and angiogenetic growth factors, which stimulate collagenproduction, angiogenesis, and cell differentiation. Anti-inflammatory and antibacterialproperties have also been reported for this preparation, which are involved in all pro-cesses of repair. (J Endod 2017;43:1294–1301)

Key WordsAdult regenerative endodontic procedure, apical periodontitis, open apex necrotictooth, plasma-rich growth factors

Early dental trauma toimmature teeth can

result in a loss of neuro-vascular supply, leadingto pulp necrosis, interrup-tion of rhizogenesis, andsubsequent formation of
periapical lesions. The management of necrotic immature teeth with open apices hasbeen performed classically using apexification with long-term application of calciumhydroxide (1). More recently, root-end barriers with mineral trioxide aggregate(MTA) have shown predictable clinical results (2). However, the difficulty in obtainingthe apical stop as well as failure in the continuity of root development and the increasedrisk of subsequent fracture during or after treatment (77% in teeth with the least devel-oped roots for calcium hydroxide apexification) make the retention of these teethdifficult (3).
Regenerative endodontic procedures (REPs) are designed to replace damagedstructures including dentin and root structures as well as cells of the pulp-dentincomplex (4). REPs follow the basic principles of tissue regeneration, being a moreconservative and biological endodontic treatment. The ultimate goal of REPs is theregeneration of tooth pulp based on 3 pillars: the source of stem cells (genesis), thesupply of growth factors (induction), and the presence of a scaffold (conduction)(5). No regeneration of the dentin-pulp complex has been obtained in any of the cases

try and ‡Faculty of Dentistry, University of Barcelona, Barcelona, Spain; †Centro de Investigacionesbia; §Unit of Dental Pathology and Therapeutics II School of Medicine and Dentistry University ofnt of Stomatology, School of Dentistry, University of Seville, Seville, Spain; and kSchool of Dentistry,llvitge Biomedical Research Institute), IDIBELL, University of Barcelona, L’Hospitalet de Llobregat,

, Bellvitge University Campus, Department of Odontoestomatology, School of Dentistry, Pabell�on decelona, Spain. E-mail address: [email protected]

JOE — Volume 43, Number 8, August 2017

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http://dx.doi.org/10.1016/j.joen.2017.04.010

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described with histologic results in immature permanent necrotic teethwith apical periodontitis. Despite this, REPs provide 3 advantages overtraditional methods of apexification: they promote root developmentand increase root length, they allow thickening of the root dentinalwalls, and they provide apical closure (6, 7).
Disinfection of the root canal using calcium hydroxide and anti-biotic pastes (8–10), obtaining a biological scaffold with bleedinginto the canal, and sealing with a biocompatible material seem to bethe main methods to produce the necessary environment for thesuccess of REPs (6). To achieve vascularization of a necrotic toothwith an open apex with a diameter <1 mmmay require instrumentationto approximately 1–2 mm to allow bleeding into the root canal systemand thus obtain a greater likelihood of repair (4).

Despite this, sometimes it is difficult to generate the blood clot; theuse of autologous growth factors and a matrix may offer an alternativethat is worth investigating. Platelet-rich plasma (PRP) is an autologousscaffold that is obtained by platelet activation and fibrinogen polymer-ization. Several studies have shown the capacity of this preparation tostimulate collagen production, angiogenesis, and cell differentiation,and anti-inflammatory and antibacterial properties have also beenreported for this preparation (11–13).

Most of the cases that reported using REPs have been limited topatients aged 8–16 years (14). This series of cases describes the tech-nique and long-term outcome of the adjuvant use of PRP in endodontictherapy on teeth with pulp necrosis and apical periodontitis in adultpatients to show that this therapy is effective in the repair and formationof mineralized tissue in open apex teeth in adults.

Case ReportsCase 1

A 35-year-old white female patient presented to the University ofBarcelona Dental Hospital, Barcelona, Spain, complaining of dentalpain and discomfort of 2 weeks’ duration. The signs and symptomswere related to the maxillary left central incisor. Her medical historywas not relevant. The patient reported a traumatic injury when shewas 8 years old, but she did not remember what kind of injury; therewas no history of pain or discomfort until 2 weeks before attendingthe clinic. Clinical examination revealed a discolored left maxillarycentral incisor and an intraoral sinus draining buccally. Percussionand cold vitality tests (Endo Ice; Colt�ene/Whaledent Inc, Cuyahoga Falls,OH) were negative. Periodontal probing performed using a periodontalprobe (CP-12; Hu-Friedy, Chicago, IL) was normal. A periapical radio-graph using the paralleling technique revealed incomplete root devel-opment, thin dentinal walls, and an open apex, corresponding toNolla’s ninth stage of root development. A radiolucent periapical lesion(3� 3 mm) was also evident (Fig. 1A). The clinical and radiographicexaminations were sufficiently obvious, and a diagnosis of pulp necrosisand chronic apical abscess was established.

Taking into account that the tooth exhibited an open apex, an REPwith autologous PRP was considered for treatment. The patient agreed,and written informed consent was obtained.

At the first appointment, after placing a rubber dam, adequateaccess to the pulp cavity was obtained without administration of a localanesthetic. Drainage of hemorrhagic and purulent exudates was thenperformed. The root canal was irrigated with 10 mL 5.25% sodium hy-pochlorite (NaOCl) using Endo-Eze Irrigator Tips (Ultradent, SouthJordan, UT) without instrumentation, and the canal was dried usingsterile paper points. An approximation of the working length was deter-mined with an apex locator (Root ZX; Morita, Tokyo, Japan) using a #15K-file. The working length was confirmed using a periapical radiograph.Then, minimal mechanical instrumentation was performed 2 mm above


the apex with an ISO #70H-file and copious irrigation with 5.25%NaOClsolution. After drying the canal, a triantibiotic paste (TAP) (metronida-zole 250mg, ciprofloxacin 250mg, andminocycline 100mg), obtainedafter mixing with sterile water until a creamy paste was generated, wasintroduced into the canal using a #1 Buchanan hand plugger (Sybro-nEndo, Orange, CA) and paper points up to the apex. The access cavitywas temporarily restored with 3 mm Cavit (3M ESPE, Seefeld,Germany).

At the second appointment 2 weeks later, the patient remainedasymptomatic, and the intraoral sinus draining had disappeared. Localanesthesia was administered with 3% mepivacaine without a vasocon-strictor (Scandinibsa 3%; Laboratorios Inibsa SA, Llic�a de Vall, Barce-lona, Spain). The root canal was accessed and irrigated with sterilesaline to remove the TAP. The canal was then washed with 5.25% NaOClsolution that remained in the root canal for 10 minutes (renewing every5 minutes). Then, a final irrigation with sterile saline was performedagain. The canal was dried, and a #25 K-file was introduced until thebone to provoke bleeding from the periapical tissue into the pulpchamber.

PRP (PRGF-Endoret; BTI Biotechnology Institute SL, Vitoria,Spain) was prepared according to the instructions of the manufacturer.Briefly, 18 mL peripheral blood was extracted by venipuncture into two9-mL extraction tubes containing 3.8% sodium citrate as anticoagulant(BTI Biotechnology Institute SL). The tubes were centrifuged at 580 gfor 8 minutes at room temperature using a BTI System centrifuge(BTI Biotechnology Institute SL). Then, the plasma column was dividedinto 2 fractions: fraction 2 (F2) was defined as the 2 mL plasma justabove the buffy coat, and fraction 1 (F1) was defined as the plasmacolumn above the F2. This gave a total of 4 mL F2, and the volume ofF1 depended on the hematocrit value of the patient. At that point, thePRP was used in the REP as follows. First, 1 mL F2 without activationwas injected into the apical third of the root canal using a sterile syringe.The remaining 3 mL F2 was gently poured in a sterile glass containerand activated by adding 150 mL 10% calcium chloride solution; thelatter triggered the formation of a 3-dimensional fibrin clot and therelease of growth factors and proteins by autologous platelets. Theobtained clot of F2 was used to fill the apical third of the root canal,extruding it through the apical foramen to the periapical tissues. Inaddition, the activated F1 fraction, maintained at 37�C to obtain a hemo-static and elastic fibrin membrane, was placed over the F2 clot to 3 mmbelow the cementoenamel junction.

Mineral trioxide aggregate (MTA) (Dentsply Tulsa Dental, John-son City, TN) was mixed with saline solution and placed on top of thePRP to 1 mm below the cementoenamel junction to prevent the stainingof the crown from worsening. The consistency of the F1 fibrin mem-brane allowed us to place the MTA safely and to control the level atwhich it was placed. A moistened cotton pellet was positioned in thepulp chamber, and then a provisional restoration with 3 mm Cavitwas placed to seal the access cavity. A postoperative radiogram wastaken (Fig. 1B).

After 1 week, the tooth was asymptomatic. A protocol of internalbleaching was initiated, and the final restoration was performed usingan adhesive composite. Esthetic restoration was performed after the lastcontrol at 50 months because the patient did not want to do it earlier.

Follow-up visits were then scheduled after 1, 2, 6, 12, 24, 36, and50 months of treatment. The patient remained asymptomatic andexhibited negative percussion, palpation, and thermal tests. At radio-graphic controls, the widening of the walls and the reduction of periap-ical radiolucency were not clear; for this reason, cone-beam computedtomographic (CBCT) imaging was obtained at the 36-month appoint-ment, revealing the presence of periapical radiolucency and the lossof vestibular cortical bone in the root apical third. The apex remained

Endodontic Therapy with PRP 1295

Figure 1. (A) The initial periapical radiograph of case 1: a maxillary left central incisor with incomplete development of the root, an open apex, and a radiolucentperiapical lesion (3 � 3 mm). (B) Immediately after the revascularization procedure. (C) The periapical radiograph taken at the 50-month follow-up visit. Thepatient remained asymptomatic. Note the complete disappearance of the periapical radiolucency. (D and E) Images of CBCT scans visualized by Kodak DentalImaging Software 3D Module v 2.4 (Kodak, Rochester, NY), cuts at 76 mm. (D) The sagittal plane at 36 months. The presence of calcified structures formingbridges and the maintenance of apical radiolucency with a loss of vestibular cortical bone in the apical area. The apex remained open and thin root walls too.(E) The sagittal plane at 50 months, presence of bone occupying the periapical area, vestibular cortical, and invagination into the open apex.


open, but the oblique was cut at 76 mm; a calcified bridgelike structureof dentin occupying the lumen pulp partially or completely was found insome scans (Fig. 1D).

Another CBCT image was obtained at 50 months because of theabsence of complete resolution of the periapical lesion obtained at36 months. The radiography and CBCT image at 50 months showedcomplete disappearance of the periapical radiolucency and the exis-tence of vestibular cortical bone completing the bone healing aroundthe root apex. A slight invagination of bone inside the canal wasobserved also (Fig. 1C and E).


Case 2A 21-year-old patient who reported a history of trauma in the ante-

rosuperior area 13 years earlier was referred for endodontic treatmentof the right upper central incisor to the University of Barcelona DentalHospital. Clinical examination showed a maxillary right central incisorwith an incisal edge fracture (FDI 11). The tooth did not respond to acold sensitivity test (Endo Ice). Responses to percussion and probingpocket depths (CP-12) were all within normal limits when comparedwith other teeth. Periapical radiography using the parallel techniquerevealed incomplete development of the root, thin root walls, and an


open apex corresponding to the eighth stage of root developmentaccording to the Nolla stages. A radiolucent periapical lesion(3 � 3 mm) was observed (Fig. 2A). Clinical and radiographic exam-inations were sufficiently obvious to avoid a concomitant CBCT scan,and a diagnosis of asymptomatic granulomatous apical periodontitiswas established. Informed consent was obtained, and an REP withPRP was performed as described in case 1 (Fig. 3A–E).
At 6 months, a slight decrease of the periapical radiolucency wasobserved (Fig. 2B). The radiography and CBCT scan obtained at 5 yearsrevealed resolution of the periapical lesion and the presence of intactcortical plates with complete bone healing around the root apex and

Figure 2. (A) The initial periapical radiograph of case 2: a maxillary right centraland a radiolucent periapical lesion (3� 3 mm). (B) The periapical radiograph takeosseous healing of the lesion. (C) The periapical radiograph taken at the 5-year follocortical plates with complete bone healing. (D) The CBCT scan at the 5-year follow-around the root apex and invagination of bone inside the canal forming irregular


invagination of the bone inside the canal forming irregular calcifiedstructures; a slight increase of root length was observed also (Fig. 2Cand D).

Case Report 3A 24-year-old woman was referred for pain in the maxillary left

lateral incisor (FDI 22). There was a history of endodontic treatmentwhen she was 10 years old. The patient was asymptomatic until shewas 22 years old when she received a nonsurgical endodontic retreat-ment to solve an infection related to this tooth, but the pain and discom-fort persisted. There was no relevant medical history.

incisor with incomplete development of the root, thin root walls, an open apex,n at the 6-month follow-up visit. The patient was asymptomatic. Note the partialw-up visit. Note the resolution of the periapical lesion and the presence of intactup visit. Note the resolution of the periapical lesion with complete bone healingcalcified structures.


Figure 3. Intraoperative photographs of case 2. (A) Detailed view of the extraction tubes after centrifugation at 580 g for 8 minutes at room temperature using aBTI System centrifuge. (B) Detailed view of the F2 clot activated. (C and D) Detailed view of the elastic fibrin membrane introduced and placed to 3 mm below thecementoenamel junction. (E) The periapical radiograph immediately after the revascularization procedure.


Clinical examination revealed the tooth was tender to percussionand palpation. Sensibility tests were negative. Periodontal probingdepths were normal. Radiographic examination revealed a big compos-ite restoration with a metal post, a poorly filled apical third, and a radio-lucent periapical lesion with an open apex (Fig. 4A). The tooth wasdiagnosed with symptomatic apical periodontitis with previous end-odontic treatment. The treatment plan was nonsurgical endodonticretreatment and an REP with PRP. The treatment plan was agreed on,and appropriate consent was obtained.

For the nonsurgical retreatment, the intraradicular metal post wasremoved using ultrasonic tip CPR 1 (SybronEndo), the remains of gutta-percha were removed using an R25 file (VDW GmbH, Munich, Ger-many), and the REP was performed as described in cases 1 and 2.

At follow-up examinations, the patient did not show any kind ofpain, discomfort, swelling, or sinus tract. The response for percussionand palpation was asymptomatic.

At 48 months, radiography and the CBCT scan showed the pres-ence of cortical plates and the resolution of the periapical lesion. Radi-ography showed the repair of the periodontal ligament around the apex,and the CBCT scan indicated the presence of a calcified structure justbelow the MTA barrier and irregular calcified tissue over the entireinternal root walls, especially in the apical third of the canal (Fig. 4Cand D).

DiscussionA series of cases of endodontic therapy with PRP of necrotic maxil-

lary incisors in patients from 21 to 35 years old have been presented.The solution of the radiolucent lesion with the presence of a calcifiedstructure forming bridges and occupying the pulp lumen as well asthe retention of the treated tooth after a 5-year follow-up indicate thesuccess of treatment. The review of the scientific literature shows thatREPs provide significantly greater tooth survival (100%) for MTA apex-ification (95%) compared with teeth treated with Ca(OH)2 apexification(77%) (15).

The patients suffered a traumatic injury when teeth had not yetfinished root maturation, and the clinical and radiographic signssupported the diagnosis of pulp necrosis and apical periodontitis.


A review of the literature reveals that about 34% of necrotic and in-fected teeth treated with REPs had trauma as the etiology for pulpalnecrosis and the periapical lesion (16).

In the present cases, copious irrigation with NaOCl and TAP(ciprofloxacin, metronidazole, and minocycline) as the intracanalmedicament were used in the disinfection protocol. NaOCl has beenshown to provide proper disinfection for treatment success as previ-ously published studies confirmed in vitro, in situ, and in vivo(6, 7, 9, 17–19). The decision to use the NaOCl concentration inREPs must be driven by the objective of reaching maximumdisinfection. Full-strength (5%–6%) NaOCl concentrations have beenused in 36% of the published cases of REPs (16). However, it hasbeen shown that 6% NaOCl decreases the survival of human stem cellsof the apical papilla (SCAPs) in a PRP scaffold (20).

TAP used in the presented cases was introduced in REPs in 2004(6) and has become the most commonly used intracanal medicament(16). The preparation of the paste (metronidazole 250 mg, ciproflox-acin 250 mg, and minocycline 100 mg mixed with sterile water) until acreamy paste is generated provides a higher concentration than recom-mended by the standardized protocol for REPs of the American Associ-ation of Endodontists (0.01–0.1 mg/mL) (16, 21). The concentrationof the antibiotic mix used in REPs would be greatly effective againstbacteria while being innocuous to the stem cells (16). It has beenreported that paste formulations may be used at 0.1 mg/mL, which iseffectively antimicrobial while having a minimal effect on SCAP survival(21). However, a recent study showed that concentrations of 0.1 mg/mLwere not capable of completely eliminating bacteria from simulatednecrotic immature permanent teeth; TAP at a concentration of10 mg/mL was the most effective medicament in eliminating bacteriafrom the root canal system while allowing for the survival of a smallpercentage of SCAPs (22). The decision about higher concentrationsof TAP must be driven by the objective of reaching maximum disinfec-tion, maintaining stem cell viability.

In the first reported case, the side effect of crown discolorationcaused by minocycline was evident (23). Sealing the dentinal tubulesof the chamber with flowable composite can avoid unwanted staining(24). There have been similar results performing the treatment with cal-cium hydroxide, biantibiotic paste (metronidazole and ciprofloxacin),


Figure 4. (A) The initial periapical radiograph of case 3: a maxillary left lateral incisor with nonsurgical endodontic retreatment and an open apex; note thepresence of a radiolucent periapical lesion. (B) The periapical radiograph of MTA placed in the coronal part of the canal 1 mm below the cementoenamel junction;note the lack of MTA in the mesial part of the canal. It was necessary to add more MTA in this part. (C) The periapical radiograph taken at the 48-month follow-upvisit. Note the mineralized tissue just below the MTA plug and in the apical third of the canal. (D) CBCT scan at the 48-month follow-up visit. Note the presence of acalcified structure just below MTA barrier and irregular calcified tissue over the entire internal root walls, especially in the apical part of the canal.


or triantibiotic paste (ciprofloxacin, metronidazole and amoxicillin)preventing discoloration (8, 25) so the other options might bepreferred in cases of revascularization. If the discoloration is alreadypresent, internal bleaching with sodium perborate is a good optionto reduce the unwanted effects (26).

In the cases reported, PRP was used as the intrapulpal matrix. InREPs, a matrix is necessary to provide a physiochemical and biologicalmicroenvironment that supports the growth, migration, and differenti-ation of dental stem cells (27). PRP is versatile, easy to prepare, and canbe used as amatrix for REPs. First, it provides the conduction; the fibrin-ogen present in plasma is cleaved to form fibrin. Then, the fibrin is


cross-linked with factor XIIIa, creating a 3-dimensional fibrin scaffoldthat retains part of the released protein content, maintains the regener-ative space, and serves as a matrix for endogenous cells. Moreover, thismatrix helps for the placement of MTA to the optimal level (11, 28).Second, it provides the induction, supplying the growth factors andbioactive molecules (transforming growth factor beta, bonemorphogenic proteins, insulinlike growth factor, and angiogeneticgrowth factors) needed for the repair and/or regeneration of thedentin pulp system (13, 29).

Most of the growth factors are stored in the alpha granules of theplatelets and are released after activation. Platelet-derived growth


factor, transforming growth factor beta, epidermal growth factor, andvascular endothelial growth factor are some of the many growth factorsand proteins available in PRGF-Endoret. Other growth factors comefrom the blood plasma such as insulinlike growth factor 1 and hepato-cyte growth factor. All these biologically active proteins are able toinfluence recruitment, growth, and morphogenesis of cells in orderto promote the healing process (11, 13).
In comparison with a blood clot, PRP has shown a better clinicaloutcome in terms of periapical healing, apical closure, and rootdentinal wall thickening (30). PRP is the first choice when the bloodclot is insufficient or no bleeding is found when irritating the apicaltissue (31).

In a recent study in dogs, REPs with NaOCl, TAP, and PRP showedmaximal improvement in the percentage of teeth showing histologicapical closure (34.5%) and vital tissue within the canal space(68.8%) compared with other protocols with a blood clot or withoutTAP (32).

Following the position statement about the use of CBCT imaging inendodontics from the European Society of Endodontology, a CBCT scanin endodontics may only be considered when the additional informationobtained will potentially help to formulate a diagnosis and/or improvethe management following the ‘‘as low as reasonable achievable’’ prin-ciple (33).

In the present cases, the diagnosis was clear enough with clinicalexamination and conventional radiographs to avoid the use of CBCTimaging at this stage, but it was absolutely necessary in subsequentcontrols because of the impossibility to appreciate clearly the positiveevolution with the thickening of the root canal walls, calcified bridgelikestructures, and the size of the periapical radiolucent lesions at radio-graphic controls.

Based on the criteria of the clinical considerations for a regener-ative procedure of the American Association of Endodontics, thesuccess of REPs is evaluated by 3 different goals. The primary goal isthe elimination of symptoms and the evidence of bony healing, thesecondary goal is to increase root wall thickness and/or increaseroot length, and the tertiary goal is to obtain a positive response tovitality testing (34). In the present cases, the primary goal was obtainedin all cases, and the secondary goal was obtained with differentresponses in all 3 cases. The mineralized tissue was obtained, like acalcified structure dentin bridge occupying the lumen pulp in the firstcase, a slight increase of root length with invagination of the bone insidethe canal forming irregular calcified structures in the second case, andmineralized tissue just below the MTA barrier and irregular calcified tis-sue over the entire internal root walls in the third case, but in any casewe obtained a total thickening or elongation of the root. The tertiary goalwas not obtained in any of the cases.

It was suggested that this result was related to the existence ofSCAPs, existing even in necrotic teeth (35, 36). Their potential forself-renewal and to differentiate into chondroblasts, osteoblasts, andadipocytes has been confirmed (37). The validation of SCAPs to differ-entiate into functional dentinogenic cells has been shown (35).

Histologic results from animal and human species have describedthe formation of cementoid/osteoid tissue deposited on the canal walls,which increases their thickness (7). Moreover, bridge formation bycementum- and/or bonelike tissue has been also described (38, 39).

In the present cases, all the patients are adults, and the possibility ofmaintaining the apical papilla is low; other sources of apical mesen-chymal stem cells (MSCs) are needed. Thus, the cells from inflamedperiapical tissues or periodontal ligaments with MSC properties presentin adults are transferred into root canals by periapical overinstrumenta-tion and bleeding (40). These cells have the capacity to form a mineral-ized matrix in vitro and in vivo and could be responsible for the


formation of cementum- and/or bonelike tissue in REPs (41, 42).Apical MSCs are probably responsible for the formation of mineralizedtissue obtained in these cases which no longer have the presence ofthe apical papilla. For this reason, the apical closure and root dentinalwall thickening are not obtained, which is in contrast to the resultsobtained in cases of REPs in young patients.

Different mineralized responses were obtained in the presentcases in adults with long-lasting endodontic infections. This is suggestedto be related to unknown host factors or the nature and duration of theetiology (eg, duration and virulence of an endodontic infection), butthere was no correlation with age, sex, tooth type, or previous treatment(40). For this reason, it was possible to obtain the same results in case 3with previous nonsurgical root canal retreatment.

Although with age the ability of multipotent stem cells to replacedamaged tissues decreases (43), this could be related to the fact thatthe differentiation capacity of MSCs decreases over time but not tothe amount of inflow of MSCs into the root canal system in adultsbecause this amount does not change with age (40). However, the heal-ing pattern in cases of REPs with histologic results has shown tissuerepair but not regeneration of a new pulp-dentin complex with thesame original architecture and biological function. In fact, it wouldbe a clinical success but not a biological regeneration.

In the present cases, we obtained a repair according to the clinicaland radiographic criteria but no regeneration because we have no his-tologic or clinical evidence to prove these results.

ConclusionEndodontic therapy with PRP of necrotic teeth with open apices

and apical periodontitis and with nonsurgical endodontic retreatmentappears to be predictable and a good option in adults, obtaining peri-apical tissue repair according to clinical and radiographic criteria. Inthe present cases, because it was not possible to obtain a histologic eval-uation, we could not conclude if tissue repair or regeneration was ob-tained. Further studies on this promising therapeutic treatment arenecessary in adults. The use of PRP helps control the level of placementof MTA and could be a good choice to promote the healing process.

AcknowledgmentsThe authors deny any conflicts of interest related to this study.

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