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Enhancing The Accuracy Of Planned Surgery With Computer Controlled Osteotomies
Naji Bou Zeid, M.D.1, Devansh Saini, PhD1, George R. Nahass, BS1, Weiqiao Zeng, PhD1, He Tong-Chuan, PhD2, Russel R. Reid, MD PhD2, Pravin K. Patel, MD1, Lee Alkureishi, MD1;
1University of Illinois at Chicago, Chicago, IL, USA, 2University of Chicago, Chicago, IL, USA

PURPOSE: The techniques used for bony deformation and creating osteotomies have changed little in the past decades. Using advanced technologies now available, we sought to develop a new workflow which permits more accurate translation of the surgical plan. We used computer-aided design (CAD) generated digital models to drive a computer-controlled (CNC) milling cutter, creating osteotomies several orders of magnitude more precise than those achievable by hand.
METHODS: 12-day-old porcine calvaria samples were scanned using micro-CT and machined using a CNC milling machine. A fractional factorial experimental design varied four parameters (spindle speed, feed per tooth, depth of cut, coolant type) across three levels, resulting in total of 27 experimental runs. During machining, temperatures were recorded using infrared thermal imaging to measure heat generation at the cutting site, while the cell viability was assessed using bone histology.
RESULTS: The model (R2=0.49, p=0.008) showed that spindle speed (p=0.015), depth of cut (p=0.041), and flood coolant (p=0.044) significantly affected temperature while the feed rates ranging from 0.0005-0.0015 inches did not. Temperatures varied from 25.5-42.8C, well below the cited cellular necrosis threshold of 47C. Aggressive cutting parameters produced no microstructural disruption or visible thermal damage during histological analysis.
CONCLUSION: The proposed workflow demonstrated excellent ability to be used on bone graft specimens, permitting accurate reproduction of fine osteotomy patterns while minimizing bony injury. This workflow allows for the significantly more accurate execution of presurgical plans than can be achieved by hand and opens the door to new technique modifications in craniomaxillofacial surgery and beyond.
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