The goal of this randomized double-blinded controlled clinical trial is to determine whether piezosurgery can reduce complications and improve outcomes compared to conventional osteotomy techniques in patients undergoing bilateral sagittal split osteotomy (BSSO), with or without concurrent Le Fort I osteotomy (bimaxillary surgery).

The main questions this study aims to answer are:

• Does piezosurgery reduce inferior alveolar nerve impairment following BSSO compared to conventional techniques?
• Does piezosurgery affect surgical duration, intraoperative blood loss, rates of bad splits, postoperative infections, costs, and environmental sustainability compared to conventional techniques?

Researchers will compare BSSO performed with piezosurgery versus BSSO performed with conventional oscillating saw and burr techniques to see if piezosurgery leads to better sensory outcomes, reduced morbidity, and improved cost-effectiveness and sustainability.

Participants will be:

• Dutch or English-speaking adults aged 18-65 scheduled for BSSO or BIMAX surgery at Erasmus Medical Centre (Rotterdam) or St. Anna Hospital (Geldrop, Netherlands).
• Exclusions include bone healing disorders, coagulation issues, facial trauma history, smoking, craniofacial anomalies, and planned simultaneous genioplasty.

Participants will:

• Undergo preoperative assessment of inferior alveolar nerve function (two-point discrimination test, validated questionnaire).

• Be randomized into:

  • Intervention group: BSSO performed entirely using piezosurgery.
  • Control group: BSSO performed with conventional burr and saw techniques.

• Have their surgery performed by experienced maxillofacial surgeons following standardized protocols.

• Have operative time and blood loss recorded during surgery.

• Be followed up at 1 week, 3 months, 6 months, and 1 year for nerve function, sensory recovery, and infection assessment.

• Complete postoperative questionnaires on sensory changes at 3 months and 1 year.

• Have surgical outcomes evaluated by blinded examiners.

• Contribute to a life cycle cost analysis (LCC) and life cycle assessment (LCA) comparing equipment cost, maintenance, energy use, waste generation, and environmental impact between techniques.

This is a randomized, double-blinded controlled clinical trial designed to evaluate the efficacy, safety, cost-effectiveness, and environmental impact of piezosurgery compared to conventional osteotomy techniques in orthognathic surgery. The study focuses on patients undergoing bilateral sagittal split osteotomy (BSSO), either as a standalone procedure or combined with Le Fort I osteotomy (bimaxillary surgery).

Orthognathic surgery is a well-established treatment for dentofacial deformities, performed to correct occlusal discrepancies and improve both function and aesthetics. The conventional technique for mandibular osteotomy employs rotary and oscillating instruments, which may increase the risk of iatrogenic injury to the inferior alveolar nerve, intraoperative bleeding, and postoperative swelling. Piezosurgery, a technique utilizing ultrasonic microvibrations for selective bone cutting, has been proposed to minimize trauma to adjacent soft tissues, potentially reducing sensory deficits and improving recovery.

Study Rationale Preliminary evidence from smaller clinical studies suggests that piezosurgery may lower the incidence of inferior alveolar nerve impairment, reduce intraoperative bleeding, and lessen postoperative morbidity, but it may also increase operative time. Many prior studies have been limited by small sample sizes, heterogeneous methodologies, and lack of standardized neurosensory assessment. This trial addresses these limitations with adequate statistical power, standardized testing, and rigorous blinding procedures.

Intervention and Control

Intervention arm: All osteotomy cuts performed using piezosurgical devices.

Control arm: Osteotomy performed using a Lindemann burr for horizontal and vertical cuts, followed by a reciprocating saw to connect osteotomies.

The allocation ratio is 1:1, determined via block randomization in Castor EDC with variable block sizes (2, 4, and 6).

Blinding Participants will remain blinded to treatment allocation. Postoperative neurosensory assessments will be conducted by independent examiners blinded to group assignment.

Procedures All participants will undergo standardized preoperative assessment of inferior alveolar nerve function, including the static two-point discrimination test and a validated questionnaire on subjective sensory changes. Surgeries will be performed by experienced maxillofacial surgeons using the Hunsuck modification of the BSSO technique.

Intraoperative metrics will include surgical duration (from incision to final suture) and quantified blood loss (suction volume minus irrigation fluid plus gauze weight). Adverse intraoperative events such as "bad splits" will be documented. Postoperative infection will be defined according to CDC criteria.

Follow-up will occur at 1 week, 3 months, 6 months, and 12 months postoperatively. Neurosensory function will be reassessed at each visit, and the validated patient questionnaire will be completed at 3 months and 12 months.

Cost and Sustainability Assessment A life cycle cost analysis (LCC) will compare acquisition, operation, maintenance, and disposal costs between the two techniques. A life cycle assessment (LCA) will evaluate environmental impact, including CO₂ emissions, energy consumption, sterilization requirements, and waste generation.

Sample Size Sample size calculations were based on detecting clinically meaningful differences in operative time, blood loss, and nerve injury rates. The largest required sample size was 31 participants per group to detect differences in nerve impairment at 3-6 months with 80% power and α = 0.05.

Statistical Analysis Primary outcome (time to functional sensory recovery) will be analyzed using Kaplan-Meier survival curves and the log-rank test. Neurosensory scores will be compared using Chi-square or Fisher's exact tests. Continuous secondary outcomes will be analyzed using Student's t-test or Mann-Whitney U test depending on distribution. Categorical outcomes (e.g., bad split, infection) will be compared using Chi-square or Fisher's exact tests. The relationship between surgeon experience with piezosurgery and operative time will be explored using linear regression. A p-value < 0.05 will be considered statistically significant.

This trial is designed to provide robust evidence regarding both clinical and economic implications of adopting piezosurgery in orthognathic surgery.

4.2 Inclusion criteria

We will include:

• Dutch or English-speaking patients
• Patients 18-65 years of age

4.3 Exclusion criteria

The following patients will be excluded from the study:

• Patients with any underlying comorbidities or medication use that may impair bone healing, i.e., radiotherapy in the head- and neck region or the use of antiresorptive drugs.
• Patients with coagulation disorders or those using of anticoagulative medication
• Patients with a history of facial trauma or previous facial surgery
• Patients who smoke
• Patients with facial cleft(s) or other craniofacial anomalies
• Patients undergoing simultaneous genioplasty