Objective: To investigate the differences between temporomandibular articular fossa bone surface and the envelope surface of the mandibular condyle movement. Methods: Thirty-four healthy adults underwent skull base and mandible scans using CBCT and performed mandibular border movement using the mandibular movement recording system. Landmarks of the fossa and tubercle were indicated and distance and angle parameters were measured on the 3D models reconstructed from the CBCT. The condyle movement envelope surfaces were formed according to models reconstructed from CBCT and the mandibular movement trajectory using computer simulation. The highest and lowest points of the envelope surface were indicated to create parameters. The data were analysed using a paired t test in SPSS (version 24.0, IBM, Armonk, NY, USA). Results: The mandibular fossa bone surface was statistically different to the envelope surface for the height of the first peak of the envelope surface (3.280 ± 1.319 mm) and depth of the mandibular fossa (6.338 ± 2.389 mm) (the ratio was 51.75%), the height of the second peak of the envelope surface (1.463 ± 0.745 mm) and the height of the tubercle (2.000 ± 0.968 mm) (the ratio was 73.15%), and the downwards angle of the envelope surface (25.933 ± 7.539 degrees) and the posterior slope angle of the articular tubercle (35.059 ± 5.224 degrees) (the ratio was 73.97%). Conclusion: The downwards angle of the envelope surface was statistically significantly smaller than the posterior slope angle of the articular tubercle, suggesting that the condyle movement is flatter than the mandibular fossa bone surface. Keywords: artificial fossa component, condyle movement, envelope surface, mandibular fossa bone surface, temporomandibular joint

The irradiance of powered polymerisation activators for chairside use affects composite resin adhesive curing during the restorative process, whereas radiant accumulated temperature rise relates to clinical safety. Irradiance reduction and high radiant accumulated temperature will compromise the treatment results as there is a lack of curing output efficacy and safety awareness for powered polymerisation activators. Insufficient attention has been paid to the activator’s quality control, irradiance attenuation and radiant accumulated temperature excessive temperature rise during its lifetime. The present manuscript has been drafted by the Society of Dental Equipment, Chinese Stomatological Association to fill the quality control gap and guide the quality control process, following tested steps, using a metered radiometer and a thermometer to record the irradiance and radiant accumulated temperature separately. The testing result may indicate the equipment’s situation in service and provide information about the irradiance values and performance of the powered polymerisation activator for its usage and maintenance. Keywords: dental powered polymerisation activator, quality control

A severe public health crisis has been declared worldwide since coronavirus disease 2019 (COVID-19) was classified as a pandemic of acute respiratory infectious disease by the World Health Organisation (WHO). China has taken strict measures to curb the spread of the disease to save lives, and has managed to control the outbreak. COVID-19 is mainly transmitted through respiratory droplets and close physical contact, so it is challenging to prevent nosocomial infection and possible spread during dental treatment. Since the initial phase of the COVID-19 outbreak, a disease prevention and control strategy based on the new concept of population risk classification and rational use of personal protective equipment has been implemented by the Peking University Hospital of Stomatology. Nosocomial infection prevention and control concepts and measures relating to dental diagnosis and treatment are critically checked in the hospital. Our experiences in handling this situation are shared here and may have wide-ranging implications for infection prevention and control (IPC) for COVID-19 in dental practices worldwide. Keywords: coronavirus disease 2019, dentistry, health care personnel, infection prevention and control, personal protective equipment, population risk classification

Skull base surgery is an interdisciplinary subject. The anatomical structures in the skull base related to oral and maxillofacial surgery include the parapharyngeal space, the pterygopalatine fossa and the infratemporal space. This operative area is one of the most challenging surgical areas in oral and maxillofacial surgery due to its deep site, complex anatomy and high risk. Obtaining pathological information of the tumour preoperatively may help surgeons optimise their treatment plan. Needle biopsy is one of the major minimally invasive techniques that allows preoperative pathological results to be obtained. The navigation technology, which is developing rapidly nowadays, provides a reliable assistance for deep tissue biopsy surgery. Experts from the Society of Oral and Maxillofacial Surgery, Chinese Stomatological Association formulated an expert consensus on the procedures and operations of navigation-guided needle biopsy techniques for skull base tumours, so as to standardise and promote the application and operation of navigation-guided needle biopsy for skull base tumours. Keywords: skull base tumour, biopsy, surgical navigation, expert consensus

Deformities of the maxillofacial region following trauma and ablative surgery are devastating and not uncommon. Reconstruction of such defects is a surgically challenging procedure. Conventionally, reconstruction of dental arch defects lacks preoperative customised planning and relies heavily on the surgeon experience to ensure optimum surgical outcomes. The restoration of the dental arch shape and function has taken precedence after an extensive tumour resection surgery, especially in the current age of technological advancement. Thus, personalised and accurate reconstruction of dental arch defects has become a new goal. Computer-assisted surgery, especially navigation-assisted surgery, has gained popularity of late, in reconstructing deformities and restoring facial symmetry, appearance and function in the maxillofacial region. This technology provides a clearer three-dimensional visualisation of the area of interest and its relationship with the adjacent vital structures. Together with preoperative virtual surgical planning, it allows more specific and accurate osteotomies, thus reducing the ischemia and total operating times substantially. The risk of complications is also minimised whilst improving the final surgical outcomes. The use of the intraoperative navigation system and other computer-assisted surgical techniques during surgery can significantly improve the precision of the reconstruction of dental arch deformities, and achieve personalised and functional reconstructive goals while enhancing the quality of life of patients postoperatively. The Society of Oral and Maxillofacial Surgery, Chinese Stomatological Association provides the present professional perspective and treatment protocol for navigation-guided reconstruction of dental arch defects, to allow standardisation of the technique while promoting its application among oral and maxillofacial surgeons. Keywords: bone remodelling, jaw defect, reconstruction, navigation technique, digital surgery, expert consensus

The zygoma is located in the medial and lateral parts of the face, supporting the midfacial contour. The forward projection of the zygoma and the zygomatic arch often expose them to injury. Fractures of the zygoma can lead to the displacement of the zygoma and the zygomatic arch, causing facial collapse deformity. For delayed zygomatic fractures, the loss of normal anatomical landmarks caused by the malunion of the fracture lines and remodelling of the bony contour makes it difficult to determine the correct positions of the zygomatic bones. In such cases, ideal and steady outcomes with satisfactory midface symmetry have been difficult to obtain using traditional surgical methods. Nowadays, the application of digital surgical software and surgical navigation helps surgeons to perform accurate preoperative simulations to obtain ideal three-dimensional virtual surgical plans and achieve accurate reduction by intraoperative navigation systems, which increase the accuracy and predictability of fracture reduction outcomes. Experts from the Society of Oral and Maxillofacial Surgery, Chinese Stomatological Association have fully discussed and formulated an expert consensus on navigation-guided unilateral delayed zygomatic fracture reconstruction techniques to standardise the clinical operation procedures and promote the application. Keywords: delayed zygomatic fractures, digital navigation, unilateral

Orbital fracture and orbital floor reconstruction surgery is characterised by limited surgical exposure and high risks. Before the advent of digital technology, the design and implementation of the surgical scheme for orbital floor reconstruction surgery mainly depended on the intuitive understanding of imaging and the clinical experience of surgeons, with strong unpredictability and experience dependence. Surgical navigation systems with real-time positioning and imaging functions, when used in orbital reconstruction surgery, can detect the real-time intraoperative position, avoid risks, and assist in locating the reconstruction position to ensure the accuracy of orbital reconstruction, with the help of a preoperative surgical plan. Many studies have confirmed its effect. Unilateral orbital fracture and orbital floor reconstruction surgery is one of the earliest and most widely used surgical techniques in maxillofacial surgery. Experts from the Society of Oral and Maxillofacial Surgery, Chinese Stomatological Association have fully discussed and formulated this expert consensus on navigation-guided unilateral orbital fracture and orbital floor reconstruction techniques to standardise the clinical surgical procedures and promote its application. Keywords: navigation technique, orbit fractures, unilateral

The newly emerged coronavirus disease (COVID-19) is a respiratory disease caused by a novel coronavirus (2019-nCoV) which was first identified in China in December 2019. It is a highly contagious infection that can spread from person to person through close contact and respiratory droplets. The healthcare personnel of the Department of Oral and Maxillofacial Surgery are especially vulnerable to the infection due to their extensive and close exposure to patients' oral and nasal cavities and secretions. As one of the busiest specialised hospitals in the world, the Department of Oral and Maxillofacial Surgery of Peking University School and Hospital of Stomatology summarised the experience with disease prevention and control and clinical recommendations on the examination, diagnosis and treatment processes, clinical management, healthcare personnel protection and disinfection amid the continued spread of the pandemic. Keywords: diagnosis and treatment process, new coronavirus, oral and maxillofacial surgery, protection

Objective: To increase the awareness of oral squamous cell carcinoma (OSCC) metastasis to the parotid region and the characteristics of these cases, and to evaluate the outcomes and provide treatment suggestions. Methods: A retrospective study was conducted among the OSCC patients with metastasis to the parotid gland at the Peking University School and Hospital of Stomatology from 2000 to 2015. The demographic data and the medical records including primary tumour, treatment protocol, follow-up information and outcomes were collected and analysed. Results: A total of 10 patients with parotid metastasis (out of 1358 OSCC patients) were included in the study. The incidence of parotid metastasis was relatively low (0.74%). All the cases were poorly differentiated (Grade II/III) and the primary sites were in an advanced stage (T3/4). Parotid metastasis occurred frequently following neck dissection and radiotherapy, and the inferior parotid lymph nodes were most commonly involved. Surgery and radiotherapy were mainly salvage protocols for parotid metastasis. The 5-year survival rate of these patients was 38.9% by the Kaplan-Meier method. Conclusion: OSCC has the potential to metastasise into the parotid lymph nodes. The salvage rate and prognosis were relatively poor. Removing of the parotid tail along with the neck dissection is recommended for OSCC patients. Keywords: oral squamous cell carcinoma, parotid lymph node, metastasis

Objective: To evaluate the level of psychosocial difficulties in patients with temporomandibular disorders (TMD) by using the Symptom Checklist 90 revised (SCL-90-R), and determine whether there is an association between psychosocial status and chronic pain severity. Methods: One hundred and sixty-two female patients who came to the Center for TMD and Orofacial Pain of Peking University Hospital of Stomatology were randomly included in this study. SCL-90-R was used to assess the psychological status of the TMD patients. This instrument was also used to assess psychological status and pain-related disability in chronic pain patients and a seven-item questionnaire was used to grade chronic pain severity (GCP). Univariate analysis of variance and correlation analysis were performed to determine the association between psychological status and chronic pain severity. Results: A total of 126 female TMD patients complained of pain in the temporomandibular joint. One hundred and sixteen patients had low disability, with 83 (51.3%) having low intensity pain (Grade I), 30 (18.5%) having high intensity pain (Grade II) and only 13 (8%) with high disability (Grade III pain). The patients were divided into four groups according to their GCP scores. The scores of all the factors of SCL-90-R were significantly different among the groups. The incidence of psychosocial symptoms was also significantly different among the groups. The psychosocial status of patients with high disability was the worst among the four groups. Conclusion: The GCP severity is a suitable tool to assess the psychosocial and physical status of TMD chronic pain. Some TMD patients have psychological problems and symptoms of psychopathology, especially those with high disability. Physicians should keep this possibility in mind when treating patients with TMD chronic pain. Keywords: chronic pain, disorders psychology, Symptom Checklist 90, temporomandibular