الفهرس 
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Abstract
The first mandibular molar is one of the teeth most frequently lost in a posterior segment., The mesiodistal dimension usually ranges from 8 to 14 mm, depending on the original tooth size cause biomechanical challenge. As the occlusal forces are greatest in the molar region, leading to possible increased stress on the implant components as well as the surrounding bone. So the concept of replacing teeth with custom-made root analogue implants represented a solution of such a problem, especially with widespread application of digital technology in dentistry and the introduction of cone beam computed tomography (CBCT) scan technology, and considerable progress had been made in the development of computer-aided design/ computer-aided manufacturing (CAD/CAM) techniques. A CBCT scan of a tooth could be virtual processed and converted into a model which could be scanned and milled in order to obtain a precise zirconia root analogue prior to tooth extraction, thus allowing immediate implant replacement and avoiding the need for subsequent surgery.
Materials: fourteen root analogue zirconium implants (RAI) immediately replacing extracted mandibular first molars and 14 Zirconium discs. Methods: The study was divided into a clinical, and laboratory study: the clinical evaluation was divided into 2 groups, each contain 7 RAI, In group I, Zirconia root analogue implants were sintered according to the manufacturer instructions, then sand-blasting from a distance of 10 mm with 150-μm Al2O3 at 0.4 MPa air pressure was made and the same in group II, application of UV surface treatment after sand-blasting. A clinical and a densitometric evaluation were made on both groups. In the laboratory evaluation, 21 zircomium discs were also, divided into 3 groups with the same surface treatments as in the clinical study. Then, surface topograghy and surface energy changes were assessed by
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Atomic force microscopy, electron microscopy and contact angle test. Results: in the clinical study, all of the RAI in both groups failed to osseointegrate within 3 to 5 months after placement, in the laboratory study, both air abrasion group, air abrasion and UV treatments created a low scale nano- rough surface as evidenced by SEM and AFM. Also, they convert the zirconia surface into a hydrophilic one but not a super hydrophilic surface.