###### Abstract  
Background: The aim of this study was to biomechanically evaluate the initial stability of a patient-specific root analogue implant (RAI) design with drilling protocol by comparing it to designs without drilling protocol through a 3D finite element analysis (FEA). Methods: A 3D surface model of an RAI for the upper right incisor was constructed. To evaluate the effect of root apex drilling, four modified RAI shapes were designed with the press-fit implantation method: Non-modified, wedge added at root surface, lattice added at root surface, and apex-anchor added at root apex (AA). Each model was subjected to an oblique load of 100 N. To simulate the initial stability of implantation, contact conditions at the implant-bone interface were set to allow for the sliding phenomenon with low friction (frictional coefficient 0.1-0.5). Analysis was performed to evaluate micro-displacements of the implants and peak stress on the surrounding bones. Results: Under all low frictional coefficient conditions, the lowest von Mises stress level on the cortical bone and fewest micro-displacements of the implant were observed in the AA design. Conclusion: In view of these results, the AA design proved superior in reducing the stress concentration on the supporting cortical bone and the micro-displacement of RAI. root analogue implant; initial stability; finite element analysis +
Footnote †: journal: Applied Mechanics and Physics Letters  
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Footnote 1: Department of Prostodontics, Korea University An-san Hospital, Gyung-gi do 15355, Korea; [EMAIL_ADDRESS]  
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Footnote 2: Department of Biomedical Engineering, College of Medicine, Seoul National University, Seoul 03080, Korea  
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Footnote 3: Department of Advanced Prostodontics, Graduate School of Clinical Dentistry, Korea University, Seoul 02841, Korea; [EMAIL_ADDRESS]  
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Footnote 4: Department of Prostodontics, College of Dentistry, Yonsei University, Seoul 03722, Korea; [EMAIL_ADDRESS]  
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Footnote 5: Department of Prostodontics, College of Dentistry, Yonsei University, Seoul 03722, Korea; [EMAIL_ADDRESS]  
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Footnote 6: Department of Prostodontics, School of Dentistry, Seoul National University, Seoul 03080, Korea; [EMAIL_ADDRESS]  
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Footnote 7: Department of Prostodontics Korea University Anam Hospital, Seoul 02841, Korea; [EMAIL_ADDRESS]  
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Footnote 8: Institute for Clinical Dental Research, Korea University, Seoul 02841, Korea  
placed implant in the maxillary anterior esthetic zone [5]. According to the previous anatomical studies it is suggested that the immediate placement position of a conventional screw type implant should be palatal side with the tooth extraction in order to maintain significant primary stability and avoid thin alveolar maxilla [6]. From the mechanical viewpoint, this is reasonable because of the larger lateral component of the occlusal force and the smallest implant-bone contact area. Therefore, the root-analogue implants, press-fit implants inserted immediately after extraction, that can obtain friction force from all contact areas of the tooth extraction socket after immediate implantation, have raised great attention among the researchers and dentists [7; 8; 9; 10; 11]. The concept of immediately replacing missing teeth with patient-specific root form implants has long been in place, with many laboratory experiments and clinic trials using root analogue implants (RAIs) [8; 9; 12]. However, due to initial instability and high failure rates over short follow-up periods, patient-specific implant systems are still considered experimental and not yet recommended for clinical use [12; 13]. With the recent rapid development of computer-aided design and computer-aided manufacturing (CAD/CAM) technology, the design of patient-specific RAIs has been reconsidered to resolve the discrepancy between the cylindrical-shaped conventional implant and an individual's tooth-extraction socket [7; 9; 10; 14; 15]. Conventional screw-type implants achieve initial stability through mechanical fixation by implant threads in the bone [16].