In this study, patients with unilateral cleft lip and palate are enrolled in a multicenter stepped wedge randomized trial ithat compares alveolar cleft closure using autologous bone harvested form the mandibular symphysis with an osteoinductive biphasic calcium phosphate putty.

Rationale: Patients who undergo alveolar cleft grafting have to deal with postoperative pain and comorbidity due to harvesting of autologous bone.

Objective: To evaluate if using calcium phosphate based scaffolds for alveolar cleft grafting is as effective as the use of an autologous bone graft.

Study design: A 'stepped wedge' randomized controlled trial will be conducted by four centres.

Study population: Children between the ages of 8 to 12 years with a unilateral alveolar cleft.

Intervention: Study group undergoes alveolar cleft grafting with the use of a calcium phosphate based scaffold, the control group undergoes the same procedure, but with the use of an autologous chin bone graft.

Main study parameters/endpoints: Main study outcome is one year postoperative residual bone volume in the reconstructed alveolar cleft. Secondary objectives of importance are postoperative pain and eruption of the tooth adjacent to the cleft through the reconstructed area.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: Patients in the control group will undergo a procedure that is currently seen as the gold standard. Patients in the study group will undergo the exact same risks as the control group, except there is no risk for donor site morbidity and postoperative pain is significantly less. Postoperative clinical and radiological evaluation of both groups is according to current treatment standards.

Inclusion Criteria:

• unilateral alveolar cleft, early secondary alveolar cleft closure

Exclusion Criteria:

• cleft lip and palate in a syndromic context