the Objective of This Research is to Compare the Clinical Effectiveness of the Conventional Lingual Arch Space Maintainers With Three-dimensional Printed Space Maintainers.

Introduction and Review of literature Primary teeth serve to preserve inborn space until permanent teeth erupt, in addition they help with speech and mastication. It is appropriate to highlight the primary dentition's function as the best space maintainer for permanent teeth. It is possible that premature primary tooth loss will cause undesirable primary and permanent tooth movements, including a loss in arch length. If there is not enough arch length, it is more likely to predict malocclusions such as crowding and ectopic eruption as well as tooth impaction.

Since the largest space loss occurs within a month of losing the deciduous teeth, it is best to use a space maintainer as soon as possible after early tooth loss. Space maintainers are the orthodontic appliance of choice for preventing space loss because they preserve space within the oral cavity.

Conventional space maintainers have significant drawbacks despite their clinical effectiveness. These include the need for patient compliance, extended chairside times, multiple steps in the fabrication process, technique-sensitive impressions and lab procedures, solder failure, and caries formation at band margins.

These disadvantages in the conventional space maintainer recommend the need for more advanced appliance designs and materials, one of which is three-dimensional (3D) printing, The process involves creating 3D objects using a digitally scanned and layered design of the entire object. The design is preserved using a "Standard Tessellation Language" (STL) file.

So, the objective of this research is to compare the clinical effectiveness of the conventional lingual arch space maintainers with three-dimensional printed space maintainers.

Inclusion criteria

• Apparently, healthy cooperative children have recently prematurely loss of more than one mandibular primary molar in any of the quadrants, full erupted mandibular first permanent molars in both sides, and whose lower permanent incisors have erupted
• The permanent successors of the lost primary molars were not expected to erupt within 6 months
• Angle's class 1 occlusion with normal primary molar relation
• Caries-free and periodontally healthy abutment teeth
• Absence of parafunctional habits or abnormal occlusion conditions such as crossbite, open bite, or deep bite.
• Children's age ranges from 7 to 9 years-old
• Radiographically, presence of permanent successors, more than one millimeter of bone covering the successor tooth germ, and/or only about one-third of the root of the permanent tooth has been formed.
• Parents and children were accepting the new treatment modality.

Exclusion criteria

• children exhibited poor oral hygiene, para-functional oral habits, severe crowding, space loss, and abnormal occlusion
• Extraction of primary molars exceeding three months.
• Radiographically, absence of permanent successor.
• uncooperative children