This parallel-group randomized controlled trial will compare the clinical performance of prefabricated zirconia and Bioflx crowns for restoring primary maxillary anterior teeth in children aged 3 to 5 years. Eligible participants will be randomly assigned in a 1:1 ratio to receive either a zirconia crown or a Bioflx crown.

Clinical outcomes will be assessed at 3, 6, and 12 months after crown placement. Evaluations will include gingival health, plaque accumulation, wear of the opposing tooth, crown retention, and clinical symptoms of the treated tooth. Parent satisfaction with the esthetic outcome will also be evaluated.

The study aims to provide comparative clinical evidence on the effectiveness of zirconia and Bioflx crowns for restoration of primary maxillary anterior teeth.

Primary maxillary anterior teeth are important for esthetics, speech, mastication, and maintenance of normal oral function in young children. Extensive caries and hypomineralization may result in substantial loss of tooth structure and require full-coverage restoration. Prefabricated zirconia and Bioflx crowns are esthetic restorative options; however, comparative clinical evidence for their use in primary maxillary anterior teeth remains limited.

This study is a parallel-group randomized controlled clinical trial conducted in children aged 3 to 5 years who require full-coverage restoration of primary maxillary anterior teeth. Eligible participants must have an opposing tooth and at least two carious surfaces on the target tooth, caries involving the incisal edge, or discoloration associated with hypomineralization. Children with acute systemic disease, allergy to the luting cement, pulp exposure before treatment, inadequate remaining tooth structure, severe bruxism or deep bite, advanced root resorption, previous trauma affecting the target tooth, or other predefined exclusion criteria will not be enrolled.

A minimum of 120 teeth will be included. Randomization will be performed at the participant level using a computer-generated variable block sequence with a 1:1 allocation ratio. Allocation concealment will be maintained using sequentially numbered opaque sealed envelopes.

Participants will receive either prefabricated zirconia crowns or prefabricated Bioflx crowns. Clinical and radiographic examinations will be completed before treatment. Crown preparation and cementation procedures will be standardized, and Fuji IX Extra glass ionomer cement will be used for crown placement.

The primary outcome will be gingival health at 6 months after crown placement. Secondary outcomes will include plaque accumulation, wear of opposing teeth, crown retention, clinical symptoms of crowned teeth, and parent satisfaction with crown esthetics. Follow-up assessments will be performed at 3, 6, and 12 months. Statistical analyses will account for clustering when more than one tooth is included from the same participant.

Inclusion Criteria:

• Children aged 3 to 5 years.
• Children requiring full-coverage restoration of one or more primary maxillary anterior teeth.
• Presence of an opposing tooth.
• Target tooth with at least two carious surfaces, caries involving the incisal edge, or discoloration associated with hypomineralization.
• Written informed consent from a parent or legal guardian and willingness to comply with treatment and follow-up visits.

Exclusion Criteria:

• Allergy to Fuji IX Extra glass ionomer cement.
• Acute systemic disease.
• Crowded teeth affecting crown placement.
• Pulp exposure before treatment.
• Inadequate remaining clinical crown structure after tooth preparation.
• Absence of an opposing tooth.
• Bruxism or deep bite.
• Tooth close to exfoliation or root resorption exceeding one-half of the root length.
• Caries limited to a single surface without proximal involvement.
• History of trauma affecting the target tooth.