This study will evaluate the effectiveness of N-TPA appliance compared to Nance SM in maintaining the arch dimensions after bilateral premature extraction of primary molars in children.

In this randomized controlled clinical trial, 30 healthy children, 8-9 years of age with premature extraction of bilateral maxillary primary molars will be selected. Children will be randomly allocated into two equal groups of 15 children each according to the type of the appliance that will be used. Group I will receive a a Nance SM, and Group II a combined N-TPA appliance . Panoramic X-rays and study casts will be made, and baseline measurements will be recorded including arch circumference, intermolar width and arch depth. The appliances will be fabricated and cemented intra-orally.

The patients will be followed up at 3, 6 and 9 months for re-evaluation of arch circumference, intermolar width, arch depth, and patient acceptance.

Inclusion Criteria:

• Fully erupted maxillary permanent first molars.
• Angle's class I occlusion.(31)
• Adequate space for premolar eruption according to Moyer's arch length analysis.(31)
• Fair to good oral hygiene according to Silness and Loe plaque index.(32)
• No history of allergy to polymethyl methacrylate.

Exclusion Criteria:

• Children with congenitally absent permanent successors.
• Children with successors not covered by bone with 2/3 of the root formed.(33)