The mandible constitutes the bony scaffolding of the lower 1/3 of the face, which is essential for maintaining facial shape and keeping chewing and other functions. Mandibular defects are relatively common among craniomaxillofacial defects and can be caused by a variety of diseases such as tumors and trauma. The resulting mandibular and adjacent soft tissue defects often lead to severe facial deformities and dysfunctions, which seriously affect the physical and mental health of patients. This article summarizes the current status and progress of mandibular defect repair and reconstruction. Mandibular defects are common among craniomaxillofacial defects, which can be caused by a variety of diseases, such as maxillofacial tumors, acute and chronic osteomyelitis of the jaws, radionecrosis, trauma, etc. The resulting mandibular and adjacent soft tissue defects often lead to severe facial deformities and dysfunctions. The resulting defects in the mandible and adjacent soft tissues often lead to severe facial deformities and dysfunctions such as mastication, speech, swallowing, breathing, etc., which seriously affect the patients’ quality of life. How to better restore these defects and functions is a major issue for head and neck surgeons. This article summarizes the current status and progress of mandibular defect repair and reconstruction. [The goal of restoration is not only to restore the continuity of the anatomical structure of the mandible, but also to restore the oral function of the patient. An ideal restoration should have the following characteristics1-2 ① The shape of the restoration is close to that of the mandible, which can be adapted to the oral environment for a long period of time, and is not easy to be infected, necrotic, or rejected by the foreign body; ② The restoration is of sufficient length, width, and quality, and it can provide a good structural shape for the fitting of prostheses and the placement of implants (iii) Restore the function of external skin, oral lining, floor of the mouth and adjacent organs (especially tongue) at the same time; (iv) Fixation is stable and accurate, not easy to be displaced, and can be used for function at an early stage; (v) Avoid and minimize the damage of nerves and blood vessels as much as possible. At present, there is no repair method that can satisfy the above conditions at the same time. [The modern viewpoint of prosthetic surgery is that as long as the defect affects the patient’s form or function, it should be considered for prosthetic repair if the technical conditions permit and the patient’s general condition is good, even for the patients whose local tumors can not be completely controlled and whose survival period is estimated to be short, prosthetic repair should be performed.2 For such patients, the improvement of their quality of life is even better than the active supportive treatment. There are one-stage and two-stage repair of mandibular defects, and one-stage repair is now accepted by most scholars, with the following features: ① Immediate restoration of mandibular continuity, restoring appearance and function. ①Immediate restoration of mandibular continuity, restoration of appearance and function. ②Avoidance of secondary surgery, shortening the course of treatment and reducing costs. ③It can maximize the survival period and improve the quality of life for the elderly and patients with short life expectancy. ④ Facilitates the installation of denture or implant in a short period of time and quick functional recovery. ⑤Good implant bed conditions, no obvious changes in local anatomy. The main reason why second-stage restoration is seldom used is because of the displacement of the fracture end of the residual bone and the insufficiency or fibrosis of the adjacent soft tissues, which leads to anatomical disorders and decreased conditions of the grafting bed, making it difficult to restore the bone in the second stage.3 [Prosthetic design] There are many types of mandibular defects, and there are large variations in the morphology of the mandible among individuals, which makes it difficult to simply replace the individual mandibular defects by the normal average value of the mandible. Simply using the normal average value of the mandible as a substitute for the individual mandible is not appropriate. Therefore, it is crucial to perform individualized design before mandibular repair and reconstruction. With the wide application of digital technology in the medical field, computer-aided design and computer-aided manufacturing have better solved such problems.CAD/CAM technology refers to the design of the ideal mandibular morphology and its anatomical relationship with the maxilla on the computer, and the reproduction of a solid model by rapid prototyping technology, which facilitates accurate measurement and analysis in vitro and surgical design.4 Bianchi et al.4 concluded that the advantages of CAD/CAM technology are as follows. Bianchi et al.4 believe that the advantages of CAD/CAM technology are: ① It can simulate the effect of surgery, accurately replicate the morphology of the defective tissue, reduce the surgical time and surgical injury, and make the surgical effect more ideal; ② Accurately determining the scope, size, and three-dimensional spatial relationship of the defective part, which is helpful for diagnosis and treatment and the teaching of scientific research intuitively and conveniently; ③ It is convenient for the communication between doctors and patients and telemedicine. At present, CAD/CAM technology has been used at home and abroad to design or manufacture dentures, orthognathic surgical measurements, predictions, and repair of large craniomaxillofacial defects caused by trauma or tumors.5,6 Domestic Yang Lianping et al.7 applied numerical control technology and mirroring technology for individualized mandibular reconstruction surgical design, and the results of the patient’s facial shape and the functional restoration of the mandible are more ideal. The application of CAD/CAM technology combined with tissue-engineered bone to repair mandibular defects is meaningful for improving the level of functional mandibular reconstruction and accurately reconstructing the anatomical morphology of the mandible, and this technology makes truly individualized mandibular reconstruction possible. [Selection of restoration program] 1. Bone grafting Including autogenous, allogeneic or xenograft bone grafting and artificial bone substitute grafting. Autologous bone grafts retain osteoconduction and osteoinduction with the presence of osteoblasts, and there is no risk of immune rejection or disease transmission. Autogenous bone grafts that are vascularized or tipped through anastomosis are easily viable and have a strong resistance to infection, with the most certain efficacy. Therefore, the commonly accepted method of mandibular reconstruction is to cut the autogenous bone flap for graft repair, and vascularized autogenous bone graft is the clinically preferred option. As the transplanted bone has a direct and sufficient blood supply, the bone cells remain alive, so that the mechanism of bone healing is transformed from the process of “creeping substitution” to the general fracture healing process, which makes bone grafting enter a new stage. There are many types of vascularized autografts that can be used for mandibular bone repair, such as rib grafts anastomosed with intercostal vessels, iliac bone grafts anastomosed with deep iliac vessels, and scapular flaps anastomosed with rotator scapulae or dorsal thoracic vessels. Since 1989, when Hidalgo8 first reported the use of the fibular muscle flap to repair mandibular defects, a large number of clinical and basic studies have confirmed that the fibular composite flap is a safe and effective tissue flap in repairing the morphology and function of the mandible. Its advantages are as follows: ① the adult fibula can provide bone tissue up to 25cm long, and can even repair the defects on both sides of the mandible at the same time; ② the double blood supply from the periosteum and bone marrow, strong resistance to infection, high survival rate, and the fibula can be divided into a number of segments without affecting the blood supply to each segment of the bone, which is convenient for the fibula to be molded and used to repair the mandible in different parts of the defect; ③ there is a relatively uniform geometry and the flap is mainly made of cortical bone, which is suitable for the repair of different parts of the mandible; ③ there are relatively uniform and consistent geometry and the flap is mainly made of cortical bone, which is suitable for the repair of different parts of the mandible. Mojallal et al11 evaluated the functional recovery of the donor and recipient areas in 42 patients with free fibular flap repair. After evaluating 42 patients with free fibula flap repair, they concluded that there were few complications in the donor area and good functional and esthetic recovery of the mandible in the recipient area. In order to solve the problem of insufficient height of fibula in repairing mandibular defects and simultaneous dental implantation, domestic Zhang Chen et al12 designed a dental implantation retractor which can be used for transverse retraction of fibula during the same period of dental implantation, completing the reconstruction of mandibular shape and function in one period, greatly simplifying the treatment procedure, and thus restoring the shape and function of the mandible during the same period of time. 2.Distraction osteogenesis Distraction osteogenesis (DO) is a technique to lengthen or widen the bone by completely cutting off the bone or only cutting the bone cortex, and applying appropriate traction to the bone segment that retains the soft tissue attachment and blood supply. Research has evolved from traction lengthening of limb bones to craniomandibular traction, from experimental animal studies to clinical applications, and from external to internal traction devices. McCarthy13 in his study of osteogenesis by traction in mandibular reconstruction found that the traction of the mandible was accompanied by functional expansion of the surrounding soft tissues, including the neural tissues, thus reducing the recurrence of traction. Stabilization of the traction force and the specific traction speed and frequency are the key factors determining the success or failure of the traction osteogenesis technique. Conventional traction devices require manual adjustment, which is time-consuming and tedious, and the traction parameters are often not constant.14 Ayoub et al14 recently reported the first case in which an electrically driven, automated traction device was used to lengthen the right branch of the mandible by 20 mm in a 65-year-old patient while maintaining appropriate, constant traction force, traction speed, and frequency.15 Osteosynthesis also has its own shortcomings, such as: (1) extra-oral traction access, resulting in scarring or infection of the skin. There are also some shortcomings such as: ① extra-oral traction access, which leads to scarring or infection of the skin and affects the aesthetics; ② the retractor itself affects the patient’s daily life; ③ the traction force on the inferior alveolar nerve and temporomandibular joints caused by the damage, and so on. 3.Bone tissue engineering Tissue engineering is an application of engineering and life science principles, using biological materials as a carrier combined with isolated cells, and can be degraded in the host body and release the cells, the formation of new functional tissue science. The basic method is to disperse the tissues obtained in vivo into single-cell suspensions by mechanical or enzymatic digestion, and then incubate and culture them under in vitro conditions that simulate the in vivo environment, so that the cells can survive, grow and spread. The cells cultured in vitro with a certain concentration are then planted onto a three-dimensional scaffolding material with a certain spatial structure for further cultivation to form tissues and organs with a certain structure and function through intercellular adhesion, growth, propagation, and secretion of extracellular matrix.15 Repairing bone defects with bone tissue engineering has the following advantages over other bone grafting methods (autologous, allogeneic, and xenogeneic bone grafting): 1) (i) less donor tissue is needed, and the damage to the donor is slight, which will not cause new morphological and functional deficits; (ii) precise three-dimensional plasticity can be performed according to the morphology of the defect; (iii) no antigenicity or little antigenicity; (iv) sufficient bone supply can meet the needs of repairing different parts and types of defects; (v) tissue-engineered artificial bone has vitality, and it is a kind of living bone graft, which can shorten the time of repairing the defects and improve the quality of repairing the bone defects. (5) Tissue engineered artificial bone has vitality and is a kind of living bone graft, which can shorten the time of bone defect repair and improve the quality of bone defect repair. Tissue engineering technology has shown good application prospects with its features of arbitrary shaping, restoring structure and function, and little damage to the organism, and is now the key research content for repairing various types of bone defects. Seed cells and biological scaffold materials are two key factors in bone tissue engineering. In recent years, more studies have been conducted on bone marrow stromal stem cells (BMSC) as seed cells, which have become the best source of cells for bone tissue engineering because of their characteristics of little damage to the organism when they are obtained, sufficient quantity after culture and expansion, and avoidance of immune rejection by autologous cells. Schliephake et al.16 used calcined bovine bone as a scaffold and composite BMSC to repair mandibular segmental defects in sheep, and the histologic results showed a significant increase in the amount of new bone formation compared with the material-only group. Tissue engineering has made great progress in the basic and clinical research of bone defects, but still faces many problems, such as the development of good biocompatible biodegradable scaffolds, the establishment of a cell culture system that mimics the stress environment in vivo, etc., so that the constructed bone tissues, after implantation in vivo, can adapt to the biomechanical environment in vivo very quickly, participate in the repair of the bone and restore its function, etc., are problems that need to be worked on and solved. [Prospect] The mandible constitutes the bony scaffolding of the lower 1/3 of the face, which is the key to maintaining facial shape, mastication, and other functions, and its deficiency seriously affects the physical and mental health of patients. The development of mandibular restorative and reconstructive surgery and bioengineering technology undoubtedly brings a broad therapeutic prospect to patients. Although the current vascularized autologous bone tissue transplantation has a high survival rate of transplanted bone tissue, it is morphologically different from autologous bone. However, the morphology of autogenous bone is always different from that of the mandible, and the grafting source will eventually require the creation of a second donor area, resulting in new morphological and functional deficits. Bone tissue engineering method can construct a three-dimensional, individualized bone tissue with the same morphology as the defective area with the assistance of computers, which makes it possible to repair the mandible precisely in morphology and function. Since the tissue cells are derived from the autologous body, the grafted bone is easy to survive and is not of immunogenic origin, therefore, it has the advantages that are incomparable with other repair methods. With the development of prosthetic and reconstructive surgery and bioengineering technology, we believe that the era of tissue-engineered bone repair of mandibular defects is coming.