## 2 Case Report
### Therapeutic Plan  
The treatment plan was to perform revascularization of tooth 35. After a detailed explanation of the treatment plan, written informed consent was obtained from the patient's parents.  
Under rubber dam isolation, the cavity was accessed with a high-speed air turbine. Purulent secretion was found in the chamber (Figure 1). The cavity was kept open for two days with a small cotton roll to establish drainage and relieve the acute symptoms. At the next appointment, under a rubber dam, the root canal was chemically debrided without mechanical instrumentation using 20 mL 0.5% sodium hypochlorite (NaOCl) assisted by Er: YAG laser irrigation with the photon-induced photoacoustic streaming (PIPS) procedure, that is, low energy (20 mJ), a low pulse repetition rate (15 Hz), and a very short pulse length (50 us) with a radial stripped novel fibre tip (Figure 2). The fibre tip was inserted in the pulp chamber (about 7 mm depth from the coronal reference) and kept in a stable position without advancement into the canal orifice (Figure 2). The procedure was four cycles of 20-s activation by PIPS followed by four rounds of 5-s off cycles. At the end of the irrigation phase, the canal was dried with paper points. A resin bond was applied without etching onto the access cavity walls and the coronal third of the root canal. A triple-antibiotic paste (1:1:1 ciprofloxacin: metronidazoleze: minocycline) was placed into the middle and apical thirds of the root canal, and the access was restored with CavitTM.  
Two weeks later, the tooth was asymptomatic and not tender to percussion and palpation. Under rubber dam isolation, the access cavity was reaccessed, and the triple-antibiotic paste was flushed out of the canal using 30 mL 0.5% NaOCl assisted by Er: YAG laser irrigation with the PIPS procedure. The canal was dried with paper points.  
After failing to induce enough blood into the canal system by over-instrumenting, a 9 mL sample of whole venous blood was drawn from the patient's forearm (right median cubital vein). The blood sample was collected into a test tube without anticoagulant and centrifuged immediately using a tabletop centrifuge by 30 s acceleration, 2 min at 2700 rpm (600 g), 4 min at 2400 rpm (400 g), 4 min at 2700 rpm (600 g), 3 min at 3000 rpm, and 36 s deceleration. Three distinct layers were formed in the tube: platelet poor plasma at the top, CGF in the middle, and red blood cells at the bottom (Figure 3). After centrifugation, sterile tweezers were inserted into the tube to gently grab and keep the CGF extracts. The CGF extracts close to the red blood cell layer were squeezed between the sterile dry gauge to drive out the fluids trapped in the fibrin matrix and thereby obtain an autologous fibrin membrane. The freshly prepared CGF membrane was fragmented, and the fragments were placed incrementally in the canal using a finger plugger up to the level of the cement-enamel junction (CEJ) (Figure 4). A 3-mm-thick layer of white mineral trioxide aggregate (MTA) was placed directly over the CGF matrix. The tooth was restored using glass-ionomer cement (GIC).  
Figure 2: Irrigation assisted by Er: YAG laser. (**a**) PIPS procedure; (**b**) Chemically debriding using 0.5% sodium hypochlorite assisted by Er: YAG laser with the PIPS procedure.  
Figure 4: The process of clinical revascularization. (**a**) The apical foramen under the microscope; (**b**) CGF membrane was placed into the canal; (**c**) 3-mm-thick layer of white MTA was placed directly over the CGF matrix; (**d**) MTA at CEJ level.  
Figure 3: The process of preparing a CGF membrane. (**a**) Nine millilitre sample of whole venous blood; (**b**) CGF extracts close to the red blood cell layer after centrifugation; (**c**) the retained CGF extracts; (**d**) the fibrin membrane obtained from squeezing the CGF extracts.