This study is a prospective, randomized, single-blind, split-mouth, national multicenter trial, comparing the efficacy of a self-etch adhesive system combined (SAM) with a flowable composite to that of a fluoride varnish for the prevention of spontaneous dental abscesses in children with XLH. For each patient, according to randomization, one side of the oral cavity is treated with the experimental treatment (application of the adhesive system to healthy anterior and posterior temporary teeth, and application of the flowable composite to healthy posterior temporary teeth), and the other side with the active comparator (fluoride varnish). The application process for both treatments is similar and will be renewed every 6 months (visits at 6, 12, 18 and 24 months) systematically for the SAM and the varnish, and in case of partial or total loss of the composite.

X-linked hypophosphatemia (XLH) is a vitamin D-resistant familial rickets resulting from a mutation of the PHEX gene. One of the major clinical disorders is dental pulp necrosis, which results in "spontaneous" dental abscesses not related to carious lesions or trauma. These abscesses, which occur in about 67% of children with XLH, can lead to serious complications: loss of teeth, disorders of masticatory, phonetic and aesthetic functions, disorders of occlusion and alveolar-dental development, cervicofacial cellulitis, consequences on the psychological development of the child. this study is the first randomized controlled trial for the prevention of these abscesses.

Primary objective is to evaluate whether a non-invasive adhesive technique, combining the application of a self-etch adhesive system (SAM) to all faces (smooth, proximal and occlusal) of all temporary teeth (anterior and posterior) and a flowable composite applied in the grooves of the posterior temporary teeth, is effective in preventing the development of spontaneous abscesses in children with XLH, compared to the application of a fluoride varnish.

Inclusion Criteria:

• X-linked hypophosphatemia diagnosed by the doctor specializing in the disease.
• Patients with at least two healthy contralateral quadrants (right and left) at inclusion defined by the absence of symptomatic or asymptomatic spontaneous abscess, carious lesion and trauma (concussion, subluxation, dislocation, crack, fracture) on all teeth in the quadrant.

Exclusion Criteria:

• Antibiotic treatment within 15 days prior to inclusion
• Patients with a mental disability,
• Patients with cancer, heart disease, sickle cell anemia, pathological bruxism
• Patients with contraindications to study treatments