This study’s findings are presented following the CONSORT (Consolidated Standards of Reporting Trials) guidelines. The study protocol was approved by the Marmara University Faculty of Medicine Clinical Research Ethics Committee (approval no: 09.2021.725). The sample size estimation for this study was based on the number of donor sites rather than the number of patients. This approach was chosen because each patient could have more than one donor site, and our primary focus was on comparing the outcomes between the different surgical techniques at the level of individual donor sites. The sample size calculation was performed based on the primary outcome, which was the difference in osteotomy times between the piezosurgery and conventional methods. The calculation was performed using G*Power software, considering a significance level (alpha) of 0.05 and a power (1-beta) of 0.8. The effect size was determined from previous literature on similar procedures [16]. To strengthen the study’s findings, we decided to raise the sample size by 10%. This randomized controlled trial, consisting of conventional and piezosurgery groups (allocation ratio = 1:1), was conducted between September 2021 and March 2022 at Marmara University Faculty of Dentistry, Department of Oral and Maxillofacial Surgery. The trial did not employ stratification in patient allocation, focusing instead on a broadly representative sample without distinction based on age, gender, or comorbidities. All consecutive unrelated patients who presented to the clinic between these dates with the complaint of single or multiple missing teeth but who did not have sufficient horizontal bone for implants were invited to participate in the study. The preoperative analysis of the participants included obtaining a complete medical history, clinical and radiographic examination of the oral and maxillofacial region, and comprehensive analysis of the donor and recipient sites. The main inclusion criteria were severe alveolar ridge atrophy in the horizontal plane (≤ 4 mm) and no accompanying vertical defects according to preoperative cone-beam computed tomography scans (Morita Veraview IC5, Kyoto, Japan). Donor site selection for defect repair was determined by the defect morphology and recipient site location. Inclusion and exclusion criteria were determined as shown in (Table 1). The treatment process was explained to all patients, and written informed consent was obtained from patients who agreed to participate in the study. The protocol prepared before the start of the study was not modified until the end of the study.

For the random allocation of participants in our study, we utilized a computer-generated list of random numbers in two blocks (Excel, Microsoft Corp, Redmond, WA, USA), assigning participants to either the conventional or piezosurgery groups. Each new patient received a unique number from this list. Corresponding sealed, opaque envelopes were prepared, with their contents unknown to both participants and researchers. These envelopes were only opened after fulfilling the needed criteria and obtaining participant consent. Due to the inherent requirements of the surgical procedures, the physician was necessarily informed of the group allocation to perform the appropriate surgical technique. However, to maintain the integrity of the study and minimize potential bias, the investigator responsible for data collection and analysis was blinded to the technique used. This individual, who had access to medical data, was not involved in the surgical procedures and was unaware of the group assignments.

All procedures were performed under local anesthesia and standardized as much as possible. Oral hygiene education was given to all patients. Patients were asked to rinse with chlorhexidine 0.2% chlorhexidine three times a day, starting from the day after surgery to the day of suture removal. Mouth washing with 0.2% chlorhexidine solution was also performed preoperatively. A local anesthetic containing a vasoconstrictor (articaine hydrochloride) was infiltrated into the retromolar region, ascending ramus, and masseter area to block cervical innervation. When the donor and recipient sites were on the same side, the incision was made like the wisdom tooth incision, extended as distally as necessary, and the full-thickness flap was removed. When the recipient and donor sites were in different quadrants, the incision was similar to the sagittal split incision. The masseter was reflected laterally using the Minnesota retractor. Four osteotomies were performed as described by Misch (Fig. 1) [17]; (1) an external oblique cut was performed 4–6 mm medial to the external oblique ridge, and the length of the osteotomy was determined by the size of the area to be grafted (2); superior ramus cut: perpendicular to the external oblique cut in the lateral cortex of the ramus (3), inferior ramus cut: this osteotomy included only the cortex and was made parallel to the external oblique cut (4), anterior body cut: since the position of the mandibular canal is the most lateral at the wisdom tooth level, the vertical osteotomy was made at the level of the second or first molar, depending on the need for the graft, and the osteotomy was deepened until the spongious bone and hemorrhage were visible.

Clinical picture of surgical procedure of bone harvesting from retromolar area a) baseline situation, b) incision similar to wisdom tooth extraction, c) osteotomy with piezosurgery tip OT-12, d) inferior osteotomy with tip OT8-R, e) bone block separation with a chisel, f) modifying the harvested graft, g) adaptation of graft to the recipient site, h) final adaptation of graft, i) periosteal releasing incision for tension-free closure of the flap

Cortical incisions were made under sterile saline irrigation and maintained at a cooled temperature, for both the experimental and conventional groups. This procedure involved using a thin #9 fissure bur (HM 31 009, Hager & Meisinger, Neuss, Germany) and a surgical handpiece S-11 Straight tip (W&H Dentalwerk, Bürmoos, Austria) at 20,000 rpm. The physiodispenser settings (NSK Surgic Ap, Tokyo, Japan) adhered to the manufacturer’s recommendations. New round and fissure burs were used for each patient to ensure sterility and consistency.

During the use of the piezosurgery device (Mectron s.p.a., Carasco, Italy), a saline solution stored at 4 °C was used to increase the cooling effect, and 1-minute breaks were given for the handpiece to cool down for more than 5 min. The sound of the cut was used as acoustic feedback to ensure that the handpiece and tips were not pressed down too much, thus affecting the cutting efficiency and temperature of the bone. The device was used in boosted mode with high-frequency vibration for optimum bone-cutting capacity. Laser markings on the tips were used to control the depth of the incision. Superior, anterior body and external oblique incisions were made with OT-12, while the inferior ramus cut was made using OT8-L or OT8-R tips, depending on the studied quadrant (Mectron s.p.a., Carasco, Italy). The same tip was used up to 3 times if it was not broken before (Fig. 1).

After the osteotomies were completed in both groups, the block graft was carefully separated from the donor site and stored in 0.9% saline solution. The bone obtained was used for horizontal augmentation of the bone defect in the mandible and maxilla.

A full-thickness flap with a unilateral vertical incision accompanied by a sulcular incision at the recipient site was removed, and the bone defect was exposed. The length of the screw was decided using a caliper to measure the width of the recipient site. Fixing the graft to the recipient site was performed with one or two 1.6 mm microscrews. Any sharp edges were smoothed using a round bur. Maximum bone-to-bone contact between the harvested and native bone was attempted. No decortication was performed, and no membrane was applied. A periosteal-releasing incision was made for tension-free closure of the graft in the recipient site (Fig. 1). The flap was closed with resorbable simple sutures.

All patients were prescribed paracetamol for postoperative pain control and antibiotics for seven days, starting one day before surgery and administered every 12 h. A cold compress for 48 h was recommended. Sutures were removed after ten days.

The flap design for the second surgery at 4 months (re-entry surgery) was similar to that of the first surgery, but the releasing incision in the vestibule was shorter. Screws fixing the bone block were removed, and dental implants (Straumann AG, Basel, Switzerland or Megagen, Seoul, South Korea) were placed according to the patient’s preference and the standard surgical protocol.

The primary outcome measure of the study was to the compare osteotomy time between the conventional method and piezosurgery. In addition, flap elevation, graft adaptation time and total operation time were recorded using a stopwatch on the watch application on the iPad. The lap button was pressed when each stage was passed. The total operation time was recorded from the first incision to the last suture. Osteotomy time was the time from full-thickness flap removal to complete separation of the block graft from the donor site. Adaptation time was also recorded. This focus on osteotomy time as the primary outcome was selected to directly address and quantify the primary disadvantage associated with piezosurgery in the context of oral and maxillofacial surgical procedures.

Postoperative pain was recorded using the VAS scale. The patients were asked to score the pain in the relevant region using a visual analog scale, between 1 and 10 points according to the severity on the first day, third day, seventh day, and 14th day after surgery. In addition, patients were asked to record the number of analgesics used in the first week [18].

Trismus was evaluated by measuring the distance between the mesio-incisal corners of the upper and lower central incisors in millimeters, using a ruler, at maximum mouth opening. In our study, postoperative edema was assessed using the technique outlined by Neupert et al., which involves linear measurements with a tape measure. This approach entailed taking measurements from five specific points: (1) from the mandibular corner to the tragus (Go-Tr), (2) from the mandibular corner to the lateral canthus of the eye (Go-Ca), (3) from the mandibular corner to the nose wing (Go-An), (4) from the mandibular corner to the oral commissures (Go-Cm), and (5) from the mandibular corner to the pogonion (Go-Pog). We acknowledge the emergence of new three-dimensional assessment techniques for facial swelling, particularly in split-mouth studies, as highlighted in recent publications [19].

Piezo tip or bur fracture, osteosynthesis screw fracture, and nerve exposure were recorded as intraoperative complications, and mucosal dehiscence, infection and neurosensory disturbance were recorded as postoperative complications. A two-point discrimination test with calipers was used for postoperative neurosensory disturbance evaluation. Patients were asked to distinguish between the number of contacts on the oral mucosa and skin while their eyes were closed. If two points could be distinguished at less than 7 mm, it was considered normal; at a distance between 7 and 11 mm, it was considered slightly aberrant; and if it could only be distinguished at a distance greater than 11 mm, sensitivity was considered impaired [32]. The graft was considered successful when there was no infection or graft loss. Sufficient bone volume was obtained to allow implant placement.

For descriptive statistics, mean and standard deviation, median and minimum and maximum, frequency, and ratio values are presented. The distribution of variables was measured using the Kolmogorov–Smirnov test. Independent sample t tests and Mann–Whitney U tests were used for comparing operation and osteotomy times; Mann–Whitney U and Wilcoxon tests were used for comparing postoperative pain, edema and swelling parameters, and chi-squared tests were used for the analysis of qualitative independent data. SPSS v28.0 software (IBM SPSS Inc., Armonk, NY, USA) was used for the analysis. Intraoperative and postoperative complications were only recorded and not included in the intergroup analysis. This study analyzed data based on the actual treatments received by the participants, without applying an intention-to-treat approach.