Currently, prefabricated zirconia crowns have been used as an aesthetic restorative material for primary teeth for a few years. Another recently introduced esthetic crown is the Bioflx™ crown. It is made of a resin polymer and claimed to have high strength , flexibility and durability. The aim of this study is to evaluate and compare the clinical and radiographic success of zirconia crowns to that of Bioflx™ crowns in carious primary molars.

Background: Little is known about aesthetic management of decayed primary posterior teeth in children which often requires full-coverage restorations.

Aim: The aim of this study is to evaluate and compare the clinical and radiographic success of zirconia crowns to that of Bioflx™ crowns in carious primary molars.

Methods: this study design is a split mouth randomized controlled clinical trial including children ages between 4-10 years old. Each patient will receive a zirconia crown and Bioflx™ crown on either side of the maxillary or mandibular arch. Clinical procedure: The patients will be randomly allocated to receive either crown on the first visit, and the other type on the next visit which will be 1-2 weeks after. Children and teeth meeting the inclusion criteria will be included. Crowns will be prepared under local anesthesia and rubber dam isolation. Crowns will be evaluated at 1, 6, 12 and 24-month recall appointments according to pre-set success and failure criteria.

Inclusion Criteria:

• Ages 4-10 years
• Healthy child
• Child is cooperative
• Subject has a minimum of two bilateral carious upper or lower primary molars
• Teeth exhibiting carious lesions clinically and radiographically
• Teeth selected should be fully erupted, with no evidence of tooth fracture, and could be isolated adequately for crown cementation

Exclusion Criteria:

• Tooth close to exfoliation
• Medical problems in sbjects
• Children requiring advanced behaviour management
• Those not available for future recalls/ follow up