Compare two band and loop space maintainers made from two tooth colored materials; Polyetherethherketone (PEEK) and monolithic Zirconia (BruxZir) as regards to:

• Clinical performance of space maintainers in terms of frequency of debonding or fracture of the appliance and health of adjacent gingiva during a one-year follow up.
• Wear of the opposing teeth.

After extraction of the mandibular first primary molars in both mandibular quadrants, impressions will be taken with intraoral scanner. Then, it will be sent to the CAD/CAM laboratory to construct functional band and loop space maintainers using PEEK and monolithic zirconia 'BruxZir' blocks with proper shades.

After the fabrication of the space maintainers of both sides, they will be cemented with resin luting cement containing MDP monomer. Photographs will be taken after cementation for the space maintainers and the patient will be informed and educated about the oral hygiene measures. The parents will also be inquired to call if any discomfort, debonding or fracture of the appliances happens.

Inclusion Criteria:

• Clinical inclusion criteria:

  • Children requiring bilateral extraction of mandibular first primary molars or those with previously extracted molars no more than 6 months prior to intervention (11) .
  • Existence of teeth on the mesial and distal side of edentulous area.
  • Angle's Class I molar relationship and/or flush terminal/mesial step primary molar occlusion

Radiographic inclusion criteria:

• No periapical and/ or furcural pathological condition related to abutment teeth.
• Presence of tooth germ of the succeeding tooth (mandibular first premolars).
• Presence of more than 1 mm of bone overlying the successor tooth germ

Exclusion Criteria:

• Carious abutment teeth requiring pulp therapy.

  • Carious abutment primary teeth requiring a full coverage restoration.
  • Patients with history of bruxism or/and clenching.
  • Patients with medical, intellectual or physical disabilities.
  • Patients with abnormalities as posterior cross-bite, open bite, and deep bite

articipants will be blinded to the type of intervention. Teeth treated will be assigned codes so that outcome evaluators at the follow up appointments are blinded. On the other hand, the operator/ primary investigator cannot be blinded, as she is already familiar with the nature of the materials used. For statistical analysis, codes will also assure blinding and confidentiality. For the patient, both types of space maintainers will have the same color and design.