Study design

Eighteen patients (age range 17–70 years) who needed dental implantation and had narrow alveolar ridges were included in this study. Forty-three implants were inserted with the performance of delayed expansion of the alveolar ridge, and the width of the alveolar ridge was measured before and after the surgery for each implant.

Surgical procedure

A representative case is illustrated in the figures. Clinical and radiological examinations of the patient revealed that both mandibular first molars were missing and the alveolar ridge was too narrow for the placement of dental implants ( Fig. 1 ). Therefore the delayed expansion technique was chosen for alveolar ridge augmentation.

Preoperative CBCT scan.

This procedure was divided into two surgeries. Before the first surgery, the patient rinsed with chlorhexidine solution for 1 min. After routine disinfection, both inferior alveolar nerves were blocked for pain control. A mucoperiosteal flap was raised with a paracrestal to palatal incision, followed by vertical releasing incisions. The alveolar ridge was extremely narrow. A trapezoid bone block was designed and shaped using an ultrasonic flat chisel. For this technique, the incision should penetrate the cortex of the alveolar bone and part of the cancellous bone. The wound was then closed to await revascularization between the bone block and mucoperiosteum ( Fig. 2 ).

Trapezoid bone blocks were designed.

Four weeks later, the second surgery was performed ( Fig. 3 ). After routine disinfection and anaesthesia, a small part of the mucoperiosteum was separated, and the designed trapezoid bone block was pushed to the buccal side along with the buccal mucoperiosteum, without damaging the new blood supply. Two implants (4.3 × 10 mm, NobelActive) were inserted separately and the residual space was filled with particulate bone and autologous bone, which was collected during drilling. A platelet-rich fibrin membrane (PRF) was used to cover the incision.

The designed trapezoid bone blocks were pushed to the buccal side with the buccal mucoperiosteum, and two implants were inserted separately.

Seven months later, two healing abutments were inserted separately into the implants to facilitate the formation of soft tissue sulci. Finally, two permanent teeth, smaller than normal molars, were placed in the limited space ( Fig. 4 ). The patient’s postoperative recovery was uneventful.

Healing abutments and permanent teeth were placed separately.

Measurement of alveolar ridge width

The width of the alveolar ridge was measured before implantation (T1), immediately after implantation (T2), and after the final restoration (T3). At T1, the width was measured at 1 mm below the alveolar ridge. All implants were inserted 1 mm below the alveolar ridge, and the width (T2) was measured at the top of the implant. After the final crown had been mounted, the width (T3) was measured at the top of the implant again. Measurement of the alveolar width is illustrated in Fig. 5 . In the axial plane ( Fig. 5 a), one of the cross lines is parallel to the long axis of the alveolar bone and the other line is perpendicular to the target implant; in the coronal plane ( Fig. 5 b), one of the cross lines passes through the implant. Finally, the measurement is made in the sagittal plane, as marked with a red line in Fig. 5 c.

Measurement of alveolar width.

The data analysis was performed using IBM SPSS Statistics version 19.0 software (IBM Corp., Armonk, NY, USA).