The goal of this clinical trial is to evaluate the effect of platelet-rich fibrin for revascularization of immature permanent teeth in comparison to standard apexification using calcium hydroxide (as a 12 months follow up for previous study) through using clinical outcomes and radiographically using cone beam computed tomography the main questions it aims to answer are

• is the platelet-rich fibrin an effective mean for management of necrotic immature permanent teeth
• is the platelet-rich fibrin has a superior clinical and radiographic effects than calcium hydroxide apexification participants were treated either by platelet-rich fibrin revascularisation or calcium hydroxide apexification

This study is an extension of a previous study [12], encompassing a 12-month fol-low-up period. The protocol for this study received approval from the ethical committee of the Faculty of Dentistry at Mansoura University (11111218) as a randomized con-trolled-clinical trial with a 1:1 allocation ratio for groups and subgroups. The sample size for this study was calculated based on Nagy et al.'s study [13], which determined a re-quired sample size of 28 teeth.

Inclusion and diagnostic criteria:

A total of 28 children, including both boys and girls, were recruited through daily pa-tient screenings in the Clinics of Pediatric Dentistry and dental public health department, Faculty of Dentistry at Mansoura University, following specific inclusion and diagnostic criteria:

• Patients were free of chronic systemic diseases.
• Clinically, a negative response to electric pulp sensibility testing confirmed the pres-ence of immature necrotic permanent teeth.
• Teeth were categorized as uncontaminated if, during the examination, there were no signs of pain, no tenderness during apical percussion, no tenderness of adjacent soft tissues, and no history of open sinus, fistula or swelling.
• Radiographically, teeth were with roots exhibiting thin dentin walls and open apical foramina larger than 1 mm, along with apical periodontitis (considered as contami-nated) or without apical periodontitis (considered as uncontaminated).

Patients' allocation:

The included 28 children were divided into two main groups, each consisting of 14 children: Group I (contaminated teeth) and Group II (uncontaminated teeth). Within each group, children were further divided into two subgroups based on the treatment tech-nique. The allocation was determined through simple randomization, resulting in a Platelet-Rich Fibrin subgroup (n=7 for each) and a Calcium Hydroxide (CH) apexification subgroups (control) (n=7 for each),

Inclusion Criteria:

• • Patients were free of chronic systemic diseases.

  • Clinically, a negative response to electric pulp sensibility testing confirmed the pres-ence of immature necrotic permanent teeth.
  • Teeth were categorized as uncontaminated if, during the examination, there were no signs of pain, no tenderness during apical percussion, no tenderness of adjacent soft tissues, and no history of open sinus, fistula or swelling.
  • Radiographically, teeth were with roots exhibiting thin dentin walls and open apical foramina larger than 1 mm, along with apical periodontitis (considered as contami-nated) or without apical periodontitis (considered as uncontaminated).

Exclusion Criteria:

• other than inclusion criteria