| BACKGROUND:The lower face bony contour, namely that facial contours mandibular body shape affected. Asians in recent years more and more emphasis on facial appearance, obtain an oval or oval face is female in this era of beauty common orientation. Improve this profile is accomplished through a series of plastic surgery. The cosmetic surgical procedures include mandibular angle osteotomy and genioplasty.Mandibular angle hypertrophic shape is a common face at oriental. Orientals are therefore generally desirable to have plastic surgery to improve their facial appearance generally. Currently mandibular angle osteotomy surgery is accepted to correct its hypertrophic shape of mandibular angle. Because of the small surgical perspective and other reasons, the stereoscopic vision of surgeons are greatly limited, they tend to make the surgeons to make mistakes of osteotomy line, so the operation is very difficult. Not only the osteotomy surgery can correct the lower facial contour, but also get the aesthetic effect. As large as possible to cut mandibular angle bone, does not damage blood vessels, nerves, and also after the completion of symmetrical shape of the mandible, lack of vision is very difficult to finish the operations. Surgeons not only need to consider surgical approach, the degree of intraoperative injury, postoperative appearance and other specific conditions, also taking into account the patient’s own individual needs and other factors. Therefore, more effective and precise "personalized surgery" is increasing.Short chin deformity is the main reason of the following section lines which are not smooth, soft contours. The dissatisfied chin contour in eastern population mainly affect the lower 1/3 outline very obviously. If the contour associated with hypertrophic mandibular angle, it is even more highlighted the shortcomings of the lower facial shape and contour. Currently the methods improve its appearance are surgical chin implants augmentation and genioplasty, but no matter what kind of surgery, and are used in the mouth incision, has been to avoid the formation of facial scar. Chin implants augmentation and genioplasty have their own advantages and disadvantages, but more and more patients do not want to implanted prosthesis, often choose genioplasty which through its own bone forward to achieve a more beautiful shape of chin. This surgical approach for the intraoral gingival sulcus lingual horizontal incision, postoperative complications in terms of feeling the cut caused mainly lower lip and chin skin numbness. The main reason for the cause of the symptoms is the lower lip and chin branch of mental nerve injury. Current surgical incisions tend to damage the nerve, so how to improve the surgical incision is necessary to become a problem.Traditional mandibular angle osteotomy, surgeons mainly make their plans depend on their personal experiences. And during the surgery surgeons are in the semi-blindness, the surgery is in great risk. In the vast majority of our primary hospitals, surgeons are still in the stage which they make their preoperative plans by thinking. Depend on x-ray, CT, and other two-dimensional (2D) images were conceived preoperative surgical planning, although preoperative patients have bone shape a certain understanding, but the actual operation still need even with a surgeon’s experience, virtual design in the pre-operation and actual operation cannot be consistent. Lack of peripheral vascular mandibular nerve anatomical structure described anatomical measurements difficult to precisely, standardized surgery performed to develop design solutions that fit the specific cases is difficult to determine optimal surgical options, it is also difficult to predict the operation effect. Surgeons often sketched by virtue of their experience intraoperative three-dimensional (3D) scene, conceived and surgical experience shared in the brain is also difficult for the surgery group assistant, the operation is more difficult to reach an understanding, and results of operations often rely on clinical experience of individual surgeons and the skills. Experience and surgical proficiency determines the success of the surgery.In the recent 10 years, the rapid development of digital medical technology, especially the development of a variety of digital medical image processing application software. Using computer-aided technology, the surgeons perform three-dimensional reconstruction, virtual surgery with CT data. Facial bones contour operation also changed, namely the use of a computer reconstruction of the individual patient digitized three-dimensional images of internal structures observed in surgical planning software, measuring three-dimensional model of insight into the surgical site, and precisely designed osteotomy path and scope to make surgery more accurate, safe and minimally invasive surgery to enhance the quality and reliability, but also precisely because of these advantages, digital technology has been widely used in plastic and maxillofacial surgery field. Digital technology can be precisely designed surgical options, make surgery more precise, improve operation quality and reliability, but they still exist in the virtual operating stage. How do virtual surgery program designed to achieve practical implementation of surgery, how to bridge the gap between virtual and reality is an important issue in digital technology applications. With 3D printing technology, virtual models of any shape can be printed as a solid model, and reduced costs, improvement of the mechanical strength of the print model, printing model accuracy and speed of their printing, all of them for solving the above problems provides a rare opportunity. Through the front improve the computer-aided preoperative evaluation, surgical planning and design, using 3D printing technology will be put operation plan accurately into the actual operation, paving the way for a virtual surgical planning and actual surgery.PURPOSE:1. To research the safe range of operation instruments after mandibular ramus in the operations by measuring the distances between the retro-mandibular vein traveling and three points in mandibular body ramus posterior border.2. To research incision line improved design in genioplasty by measuring the angle between lower lip branches of the mental nerve and the face midline;3. To achieve precise mandibular angle, personalized osteotomy by designing optimal navigation template of mandibular angle osteotomy, combined with 3D printing technology and then performing the mandibular angle osteotomy in mandible specimens and fresh cadavers.METHODS:1. The measurement of distances between the retro-mandibular vein traveling and three points of mandibular body ramus posterior border:First, determine the three fixed points in mandibular body ramus posterior border, respectively, as a starting point of osteotomy line in mandibular body ramus posterior border, gonion and the midpoint between above two points in mandibular body ramus posterior border. There are four kinds of measured data, respectively, the distance between a starting point of osteotomy line in mandibular body ramus posterior border in the occlusal horizontal direction, in the direction of elongation osteotomy line and retro-mandibular vein; the distance between gonion in the occlusal horizontal direction and retro-mandibular vein; the distance between the mid-point of above two points in mandibular body ramus posterior border and retro-mandibular vein. Total sample measurement data set 90, which was input into SPSS20.0 software for statistical analysis, the positional relationship between the retro-mandibular vein and the mandibular body ramus. According to its location, characteristics, guiding swing saws performance, to determine the relative safety range, while provide the reference range to stripping.2. The angle measurement between lower lip branch of mental nerve and the midline of face:collecting cadavers 30 cases, micro-dissection each lower lip branch which were measured at the level of labio-mental angle with face midline, a total of 127 sets of data. The measurement data were imported into SPSS20.0 for statistical analysis, get the positional relationship of lower lip branches of mental nerve at the level of labio-mental angle and face midline, thereby improving analysis genioplasty incision line design.3. Mandible specimens experimental verification of the mandibular angle osteotomy digital optimization design:the use of normal human mandible with a tooth specimens in 10 cases, thin-section CT scans performed, then three-dimensional reconstruction, virtual osteotomy, digital navigation guides design optimization, virtual navigation osteotomy and performing operation in accordance with the digital implementation of the program mandible mandibular angle osteotomy specimens under the guidance of the navigation template. Postoperative CT scanning and three-dimensional reconstruction again, consistency prior to the measurement and comparative analysis of preoperative virtual surgery and the actual results of the evaluation in the navigation template assisted mandibular angle precision, feasibility and personalized surgery accuracy.4. Fresh specimens experimental verification of the mandibular angle osteotomy digital design optimization:The normal skull with dental 10 fresh specimens, get thin-section CT scans performed, then three-dimensional reconstruction, virtual osteotomy, digital navigation guides design optimization, virtual navigation osteotomy and performing operation in accordance with the digital implementation of the program mandible mandibular angle osteotomy specimens under the guidance of the navigation template. Postoperative CT scanning and three-dimensional reconstruction again, consistency prior to the measurement and comparative analysis of preoperative virtual surgery and the actual results of the evaluation in the navigation template assisted mandibular angle precision, feasibility and personalized surgery accuracy and security.RESULTS:1. By measuring distances between the retro-mandibular vein traveling and three points of mandibular body ramus posterior border group of 90 samples from the data and results into SPSS20.0 software for statistical analysis:The distances between the starting point of osteotomy line in mandibular body ramus posterior border in the direction of elongation osteotomy line and retro-mandibular vein was 8.58±1.85mm; the distances between the starting point of osteotomy line in mandibular body ramus posterior border in the occlusal horizontal direction and retro-mandibular vein was 8.70±1.86mm; the distances between gonion in the occlusal horizontal direction and retro-mandibular vein was 11.82±2.10mm; the distances between the midpoint of above two points in mandibular body ramus posterior border in the occlusal horizontal direction and retro-mandibular vein was 12.15±2.41mm.2. The angle measurement between lower lip branch of mental nerve and the midline of face in 127 sets of data, then import the results into SPSS20.0 software for statistical analysis:the angle between lower lip branch of mental nerve at the level of labio-mental angle and face midline was 62.07±16.27°.3. No significant differences (.P>0.05) were observed between the virtual post-operation and actual post-operation in seven sets of data for ten mandible specimens. The mean deviation between the left virtual postoperative gonial angle (L-Vir-A) and left actual postoperative gonial angle (L-Act-A) was 0.16±0.31°. The mean deviation between the right virtual postoperative gonial angle (R-Vir-A) and right actual postoperative gonial angle (R-Act-A) was 0.30±0.43°. The mean deviation between the left virtual postoperative gonial displacement distance (L-Vir-D) and left actual postoperative gonial displacement distance (L-Act-D) was 0.22±0.31mm. The mean deviation between the right virtual postoperative gonial displacement distance (R-Vir-D) and right actual postoperative gonial displacement distance (R-Act-D) was 0.13±0.21mm. The mean deviation between the left virtual postoperative length of mandibular ramus (L-Vir-L) and left actual postoperative length of mandibular ramus (L-Act-L) was 0.17±0.44mm. The mean deviation between the right virtual postoperative length of mandibular ramus (R-Vir-L) and right actual postoperative length of mandibular ramus (R-Act-L) was 0.05±0.69mm. The mean deviation between the virtual postoperative mandibular width (Vir-W) and actual postoperative mandibular width (Act-W) was 0.03±0.21mm.4. No significant differences (P>0.05) were observed between the virtual post-operation and actual post-operation in seven sets of data for ten fresh cadavers. The mean deviation between the left virtual postoperative gonial angle (L-Vir-A) and left actual postoperative gonial angle (L-Act-A) was 0.16± 0.57±. The mean deviation between the right virtual postoperative gonial angle (R-Vir-A) and right actual postoperative gonial angle (R-Act-A) was 0.59±0.98°. The mean deviation between the left virtual postoperative gonial displacement distance (L-Vir-D) and left actual postoperative gonial displacement distance (L-Act-D) was 0.27±0.48mm. The mean deviation between the right virtual postoperative gonial displacement distance (R-Vir-D) and right actual postoperative gonial displacement distance (R-Act-D) was 0.25±0.40mm. The mean deviation between the left virtual postoperative length of mandibular ramus (L-Vir-L) and left actual postoperative length of mandibular ramus (L-Act-L) was 0.04±0.54mm. The mean deviation between the right virtual postoperative length of mandibular ramus (R-Vir-L) and right actual postoperative length of mandibular ramus (R-Act-L) was 0.22±0.45mm. The mean deviation between the virtual postoperative mandibular width (Vir-W) and actual postoperative mandibular width (Act-W) was 0.26±0.70mm.Conclusions:The lower face contour plastic surgery because of its surgical approach and the way individual differences, their personalized surgical programs, safe and accurate surgery is primarily through the anatomic measurement results, the quality of preoperative optimization of digital design and intraoperative 3D printing technology implemented. By measuring the positional relationship between retro-mandibular vein and mandibular body ramus posterior border, the chance of vein injury in the cutting line will be greatly reduced when swing saws performance and stripping in the starting point of osteotomy line, gonion and the midpoint are in the range of control within the range of statistical analysis. In genioplasty through improved design inverted "V" shaped incision, the surgeon will effectively reduce the risk of nerve damage to the lower lip branch of mental nerve, greatly reducing the incidence of postoperative numbness of the lower lip and chin skin complications. Combined with 3D printing technology through the development of digital technology to achieve optimization and personalized preoperative surgical plan, navigational 3D printing templates to accurately guide the osteotomy operated, it is possible to complete the precise mandibular angle osteotomy. With 3D printing navigational template, pre-operative surgical planning and the aid of digital design, to achieve a precise and optimized mandibular angle osteotomy in mandible specimens and fresh cadavers, surgical results obtained with preoperative planning consistent mandible profile, verify the feasibility of accurate and personalized surgery under the guidance of 3D printing navigational template. Preliminarily it verified the application value in performing personalized mandibular angle osteotomy with 3D printing technology. |
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