This randomized clinical trial (RCT) will evaluate the effectiveness of cross-linked hyaluronic acid as an adjunct to endodontic microsurgery in adult patients with apical periodontitis affecting maxillary or mandibular first molars. Participants previously treated with non-surgical endodontic therapy will be allocated to either endodontic microsurgery with cross-linked hyaluronic acid application (test group) or the same surgical procedure without adjunctive material (control group), with 12 months of follow-up.

The study hypothesis is that cross-linked hyaluronic acid improves soft- and hard-tissue healing, reduces postoperative inflammation and pain, and supports more stable surgical outcomes. Primary outcomes include early soft tissue healing (Early Wound Healing Score, day 4) and postoperative pain (visual analogue scale). Secondary outcomes include periapical healing assessed by blinded evaluators on periapical radiographs (Molven criteria) at 3, 6, and 12 months, and on CBCT scans (PENN 3D criteria) at 6 and 12 months, as well as cortical plate healing (RAC/B index). This study aims to provide clinical evidence on the potential regenerative and anti-inflammatory benefits of cross-linked hyaluronic acid in endodontic microsurgery.

Background and Rationale:

Endodontic microsurgery is an established treatment for persistent apical periodontitis after non-surgical root canal treatment. Successful healing depends on appropriate surgical technique, infection control, and favorable soft and hard tissue regeneration. Cross-linked hyaluronic acid is a non-animal-origin biomaterial with hydrating, tissue-supportive, and bacteriostatic properties, and may support wound healing and tissue regeneration in oral surgery. In addition, it is stable at room temperature and radiolucent, which facilitates postoperative radiographic and CBCT evaluation.

The present study investigates whether adjunctive use of cross-linked hyaluronic acid during endodontic microsurgery improves clinical healing outcomes compared with standard endodontic microsurgery alone.

Scientific Question:

Does cross-linked hyaluronic acid improve hard and soft tissue regeneration in endodontic microsurgery?

Hypothesis:

The adjunctive use of cross-linked hyaluronic acid in endodontic microsurgery improves soft-tissue and bone-healing, reduces inflammation and postoperative pain, and enhances the long-term stability of surgical outcomes.

Study type: Interventional (Clinical Trial) Allocation: Randomized Intervention model: Parallel assignment Masking: Double-blinded (participant and outcome examiner/radiologist) Primary purpose: Treatment Setting: Single center Follow-up duration: 12 months

Study Population:

Adult patients (>18 years) with apical periodontitis in maxillary or mandibular first molars, previously treated with non-surgical endodontic therapy at least 12 months prior to enrollment, and meeting predefined periodontal and radiographic eligibility criteria.

Interventions:

Test Group (n=30 teeth) Endodontic microsurgery (open flap debridement) with adjunctive application of cross-linked hyaluronic acid (Hyadent BG, Regedent) into the osteotomy defect and under the flap before closure.

Control Group (n=30 teeth) Endodontic microsurgery (open flap debridement) with no adjunctive grafting/regenerative material.

Surgical Procedure (both groups):

All procedures will be performed under an operating microscope (Carl Zeiss Extaro 300) using a standardized microsurgical protocol under local anesthesia (articaine with epinephrine 1:100,000, 3.4 mL). The protocol includes:

Single flap approach (Trombelli 2009) combined with entire papilla preservation technique (Aslan et al.).

• Flap elevation
• Osteotomy with Lindemann bur under irrigation
• 3 mm root-end resection at approximately 90 degrees
• Root-end staining with 1% methylene blue
• Ultrasonic retrograde preparation
• Granulation tissue removal
• Hemostasis with epinephrine cotton pellets
• Root-end filling with mineral trioxide aggregate (MTA, Trioxident)
• Irrigation with 0.9% sodium chloride
• Periosteoplasty
• Tension-free flap repositioning and suturing with 7-0 monofilament sutures (Prolene)
• In the test group only, cross-linked hyaluronic acid will be applied via cannula to fill the osteotomy defect and placed beneath the flap prior to suturing.

Outcome Measures:

Primary Outcome: Early soft tissue healing Assessed on postoperative day 4 using the Early Wound Healing Score (EHS).

Secondary Outcomes

• Periapical healing on periapical radiographs (PA) Assessed by blinded evaluators using Molven criteria at 3, 6, and 12 months
• Periapical healing on CBCT Assessed by blinded evaluators using PENN 3D criteria at 6 and 12 months
• Cortical plate healing Assessed using the RAC/B index
• Postoperative pain Assessed using a Visual Analogue Scale (VAS).

Statistical Considerations

Sample size calculation was based on detecting a 2-point difference in the Early Wound Healing Score (range 0-10) between groups, assuming:

Alpha = 0.05 Power = 80% Standard deviation = 3 The calculated sample size was approximately 18 patients per group. To account for potential dropouts and ensure robustness, the final planned sample size is 23 patients per group. The protocol currently plans enrollment of 30 teeth per group, providing additional allowance for attrition and variability.

Inclusion Criteria:

• Written informed consent
• ≥18 years of age
• Apical peridontitis at maxillar or mandibular first molars ≥ 12 months after non-surgical endodontical treatment
• Full mouth plaque score (FMPS) and bleeding score (BoP) < or 20%
• Periapical lesion < or 10 mm
• Four-wall bone defect morphology

Exclusion Criteria:

• Smokers of more than 10 cigarettes a day
• Allergy to hyaluronic acid
• Pregnancy or lactation
• Uncontrolled Diabetes
• Untreated periodontal conditions
• Any conditions associated with poor compliance or failure to maintain good oral hygiene
• Acute infections lesions in areas intended for surgery
• Chemotherapy and radiotherapy treatment

The participants are in surgery not seeing the surgical intervention and not knowing if adjunctive HA will be applied. The outcome assessor is not involved in the patient allocation nor the surgical intervention.