## 2 Materials and Methods
### Operative Procedure  
The CS scaffolds were fabricated according to the protocol in our previous study [23]. Intravenous injection of Xylazine (Seton, Barcelona, Spain) at a dose of 2% mg/kg was introduced in the jugular vein using a 25-gauge needle 1 cc/mL to sedate the animals. Subsequent injections of ketamine (TEKAM(r), London, UK) were maintained every half an hour and controlled by a veterinarian [24]. Pre-operative radiographs were taken to confirm pathosis absence. Next, teeth were locally anesthetized with infiltration technique using Xylocaine Dental Adrenaline 20 mg/mL + 12.5 mg/mL Standard, 1.8 mL (Dentsply Ltd., Surrey, UK). Teeth were isolated with a rubber dam and disinfected with cotton soaked in 75% ethanol. Under a 4X microscope (System Contraves & Sec, Carl Zeiss, Thornwood, NY, USA), access was opened using a sterile water-cooled tapered diamond bur (Komet Dental, Lemgo, Germany), and root canal treatment was performed with Protaper Gold rotary files (Dentsply Sirona, Baden, Switzerland). The canals were irrigated with 2.5% sodium hypochlorite (NaOCL) and dried with sterile paper points then obtutrated with single matching gutta-percha cones (Dentsply Sirona, York, NC, USA) using AH26 silver-free sealer (Dentsply De- Trey GmbH, Konstanz, Germany). A 2 mm diameter perforation (equal to the width of the used round diamond bur to standardize the size among all teeth) was created in the pulp chamber floor, except for the negative control group. The depth of the perforation was between 2 and 4 mm according to the depth of the tooth's pulpal floor to invade completely through the furcal dentin into the periodontitis. Irrigation protocol using 2.5% NaOCL was followed. Afterwards, teeth were left open for four weeks to ensure inflammatory lesion formation in the furcation area. No medication was used to inhibit new variables' effects. After a month, animals were sedated following the same previous protocol and under aseptic technique and rubber dam isolation, the perforation site was curetted using a small spoon excavator to remove the food remnants, debris, and inflamed tissue, cleaned with 2.5% NaOCL, and dried with paper points and cotton pellets. The teeth were randomly treated as follows:  
* Group 1: Negative control. No perforation was created in the pulp chamber after finishing the root canal filling. The access cavity was left open without coronal filling;
* Group 2: Positive control. The furcal perforation and access cavity were left open without coronal filling;
* Group 3: CollaCote (CollaCote(r); Zimmer, Warsaw, IN, USA). CL was placed in the furcal perforation then white MTA (ProRoot MTA; Dentsply Tulsa Dental Specialties, Johnson City, TN, USA) mixed with sterile saline (3 parts powder to 1 part liquid) was carried into the furcal site with amalgam carrier and compacted with a size 1 Buchanan hand plugger with light pressure, followed by a 2-3 mm resin-modified glass ionomer (GC Fuji II LC Capsule; GC Corporation, Tokyo, Japan);
* Group 4: Chitosan. CS scaffold with no SIM was placed in the furcal perforation site then the same procedure was repeated as in group 3;
* Group 5: Chitosan scaffold impregnated with SIM was placed in the furcal site, then the same procedure was repeated as in group 3. Group distribution is illustrated in Figure 1.  
The procedures were all performed by one operator. The goats were continuously monitored for any changes in habits and food intake during the post-treatment evaluation periods. The clinical steps and radiographic images were documented in one animal for illustration purposes (Figure 2).  
Figure 1: Group Distribution. –ve: negative; +ve: positive; CL: CollaCote; CS: Chitosan; SIM: Simvastatin; M: month.  
Figure 2: Clinical photographs and radiographic images of (**A**) pre-operative, (**B**) access opening, (**C**) obturation, (**D**) fraction induction, (**E**) perforation repair.