Clinical, Radiographic, and Histologic Outcome of Regenerative Endodontic Treatment in Human Teeth Using a Novel Collagen-hydroxyapatite Scaffold Ali Nosrat, DDS, MS, MDS,* † Alireza Kolahdouzan, DDS, MS, ‡§ Amir Hossein Khatibi, DDS, MS, ¶ Prashant Verma, DDS, MS, FAGD, † Davoud Jamshidi, DDS, MS, ‡ Alan J. Nevins, DDS, k and Mahmoud Torabinejad, DDS, MSD, PhD** Abstract Introduction: Histologic examination of teeth after regenerative endodontic treatment (RET) shows that the type, quality, and quantity of tissues formed in the root canal space are not predictable. The aim of this study was to examine clinically, radiographically, and histologically the outcome of RET in immature nonin- fected human teeth using SynOss Putty (Collagen Matrix Inc, Oakland, NJ) as a scaffold. Methods: Three pairs of maxillary/mandibular first premolars in 3 patients sched- uled for extraction were included. Sensibility tests confirmed the presence of vital pulps. After informed consent, anesthesia, and rubber dam isolation, the pulps were removed. RET was performed using the following scaffolds: SynOss Putty + blood in both teeth in patient #1, SynOss Putty with or without blood in patient #2, and SynOss Putty + blood or blood only in patient #3. After a follow-up period of 2.5–7.5 months, the teeth were clinically and radiographically evaluated, ex- tracted, and examined histologically. Results: Patients remained asymptomatic after treatment. Radiographic examination of the teeth showed signs of root develop- ment after treatment. In teeth treated with SynOss Putty + blood, histologic examination showed formation of intracanal mineralized tissue around the scaffold par- ticles solidifying with newly formed cementumlike tissue on the dentinal walls. The tooth treated with SynOss Putty without blood showed the formation of a periap- ical lesion. The tooth treated with a blood clot only showed tissues of periodontal origin growing into the root canal space. Conclusions: SynOss Putty + blood showed a predictable pattern of tissue formation and mineralization when used as a scaffold for RET in human immature noninfected teeth. The newly formed mineralized tissue solidifies with newly formed cementum on the dentinal walls. (J Endod 2019;45:136–143) Key Words Immature tooth, regenerative endodontic treatment, revascularization, revitalization, scaffold, SynOss Putty P ulp necrosis in imma- ture teeth creates a complicated situation for clinicians. The immature root/canal is difficult to disinfect, difficult to seal, and prone to fracture because of its thin root structure. Apexification using mineral trioxide aggregate (MTA) has shown promising results regarding the res- olution of endodontic disease and the survival of treated teeth (1, 2). Although traditional apexification methods promote healing of the periapical lesion, they do not promote root development. Regenerative endodontic treatment (RET) is a biologically based treatment aiming to regenerate the pulp-dentin complex (3, 4) and promote continued root development (5). Root development might increase the overall structural strength of the tooth (6) and, possibly, the survival. The outcome of RET can be assessed from 2 perspectives: 1. healing of the endodontic disease (ie, successful infection control) and 2. root development (ie, successful tissue regeneration) (7). As shown in many clinical studies, infection control and healing of the periapical lesion are predictable and reliable outcomes with this treatment (2, 8, 9). However, the rate for root development varies from 20% (8) to 100% (10). This means that 1 of the From the *Iranian Center for Endodontic Research, Dental Research Center, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran; † Division of Endodontics, Department of Advanced Oral sciences and Therapeutics, School of Dentistry, University of Maryland Baltimore, Maryland; ‡ Department of Endodontics, School of Dentistry, Ghazvin University of Medical Sciences, Ghazvin, Iran; § Department of Endodontics, School of Dentistry, Shahed University of Medical Sciences, Tehran, Iran; ¶ Private Practice, Tehran, Iran; k Private Practice, Southampton, New York; and **Torabinejad Institute of Surgical Education and Research Venues, Irvine, California. Address requests for reprints to Dr Ali Nosrat, Division of Endodontics, Department of Advanced Oral sciences and Therapeutics, School of Dentistry, University of Maryland Baltimore, 650 West Baltimore Street, 4th Floor, Baltimore, MD 21201. E-mail address: Nosrat@umaryland.edu 0099-2399/$ - see front matter Copyright ª 2018 American Association of Endodontists. https://doi.org/10.1016/j.joen.2018.10.012 Significance Using SynOss Putty with blood as a scaffold can make the outcome of regenerative endodontic treatments more predictable. The formation of an intracanal mineralized tissue that solidifies with the dentin-associated mineralized tissue might improve the structural integrity of immature teeth. Regenerative Endodontics 136 Nosrat et al. JOE — Volume 45, Number 2, February 2019