Introduction of courses, sections

Dental Education

Director Ryuta Kataoka
The Division of Dental Education at Showa University was founded in April 2008, and I was appointed as its director. As a part of the School of Dentistry, the Division of Dental Education Unit aims to promote interdisciplinary education with other education staff from the schools of medicine, pharmacy, and nursing and rehabilitation Sciences, to direct curriculum development and to develop educational research.
We are collaborating with the other schools of Showa University in educational activities such as interdisciplinary PBL for 1st-, 3rd- and 4th-year students, and an early exposure program. Training students to be able to work with other medical professionals is essential to our program and is consistent with our university’s educational spirit. We are making a concerted effort to acquire advanced knowledge and interdisciplinary skills, and to learn together by transcending departmental boundaries and utilizing the wide range of facilities of a medical university.

Oral Anatomy and Developmental Biology

Education

Our department is in charge of teaching and laboratory training for second-year undergraduate students in the anatomical course, including gross human anatomy, histology, embryology and tooth anatomy. Anatomical knowledge is essential for becoming a dentist and dissection of the human body provides students with not only an understanding of the structure of the body but also the opportunity to think about the dignity of life and medical ethics, with gratitude for the inspiring wishes of the donor and their families.

Research

Our on-going research projects are: 1) Ontogenic and phylogenic development of osteogenesis and hematopoiesis, 2) The effect of bisphosphonates on osteogenesis and hematopoiesis, 3) Structural and functional characterization of junctional epithelium, 4) Identification and function of exosomes on odontogenesis, and 5) Differences in the bone repair process due to osteogenesis and/or part of the bone. These projects are closely related. Our staff continue their own projects by using histological, biochemical, immunological and molecular biological analyses.

Oral Physiology

The long-term goal of our laboratory is to understand the neural circuit basis underlying oral motor behaviors such as sucking, chewing, swallowing, sleep bruxism, etc. Mechanisms responsible for controlling jaw movement during such behaviors exist in the brain; however, how and where these motor patterns are produced is poorly understood. To study these questions, we use a combination of anatomical, electrophysiological, imaging, molecular biological, and optogenetic techniques in a variety of animal models including brainstem slice preparations, arterially perfused decerebrate animals, and freely moving animals. Currently there are several main research projects in our laboratory:
1. Neural networks generating suckling, chewing, and swallowing
We have engaged in the analysis of neural networks generating suckling behavior using isolated brainstem-spinal cord preparations. In addition, we are currently developing experimental models of swallowing and chewing using arterially perfused decerebrate preparations, and analyzing the neural mechanisms of swallowing and chewing.
2. Development of neural circuits for feeding behavior
We have been examining the development of neural mechanisms responsible for feeding behavior during the early postnatal period using patch-clamp recording techniques.
3. Neural mechanisms of sleep bruxism (SB)
We have investigated the mechanisms of SB through physiological and genetic analysis. Recently, we have found that some kinds of selective serotonin reuptake inhibitors (SSRIs), one of the risk factors of SB, have facilitating effects on the jaw-closing muscle activity in non-rapid eye movement (non-REM) sleep.
4. Serotonergic modulation on jaw-closing motoneuron excitability
We have focused on the modulatory role that serotonin (5-HT) exerts on jaw-closing motoneurons. We are trying to reveal the role of the serotonergic system in mastication using optogenetic stimulations of 5-HT neurons in freely behaving mice.

Biochemistry

In many countries including Japan, a full-fledged aged society has arrived. Rapid aging of the general population has increased the number of individuals with bone diseases such as osteoporosis and osteoarthritis, which adversely affect quality of life. Therefore, in addition to the need to develop novel procedures for diagnosis and treatment of these diseases, clarification of the molecular basis of hard tissue development and metabolism is urgently required. The Department of Biochemistry of Showa University School of Dentistry has pursued a variety of biomedical research studies in regard to calcified tissues. Ongoing research is now touching several important areas of hard tissue science, including the molecular foundations of bone, cartilage, and teeth. We have a training program for graduate and postgraduate students that offers a wide variety of research opportunities with emphasis on molecular and cellular biochemistry. For further information, please contact us at biochem@dent.showa-u.ac.jp.

Oral Microbiology and Immunology

Our research topic is the relationship between oral flora and health. Numerous microorganisms inhabit the oral cavity and form a flora. Normally, humans have a healthy microbial flora that prevents the invasion of pathogenic microbes from outside the mouth and protects our bodies. However, once the balance of the microbial flora is disrupted for some reason, pathogens will settle and increase in the oral cavity, and as a result, not only oral health but also general health may be impaired. The oral cavity is the entrance to the human body and is connected to the digestive tract of the small and large intestines. Like the digestive tract, the oral cavity is covered with mucous membranes, and various immune cells such as macrophages and lymphocytes exist under the mucosa of periodontal tissues, palate and pharynx. However, their roles have not been fully elucidated, and there are many unexplored subjects of infection control mechanisms in the oral area. The microbial flora and immune system interact closely in the oral cavity, and the balance should be tightly controlled, but the molecular mechanism is not well understood. By elucidating this, we believe that the importance of the oral cavity in health care can be made clear.

Dental Pharmacology

Policy

We pledge to contribute to science, medicine and education through utmost efforts.

Staff

5 staff (1 professor (Dr. Masamichi Takami), 1 associate professor, 3 assistant professors, and 1 engineer), 8 graduate school students from the graduate school of dentistry or medicine, and 2 students of the dental school are conducting studies every day.

Research

Our laboratory is studying hard tissues including bone and teeth. We are investigating: 1) the molecular mechanisms of the bone resorbing function of osteoclasts using FIB-SEM, 2) bone regeneration mechanism after bone fracture, 3) effects of anti-bone-resorbing drugs such as denosumab and bisphosphonates on pregnancy, growth and periodontitis, 4) in-vivo imaging of bone-related cells by genetic recombination technology using Medaka fish, 5) relationships between hyperlipidemia and tooth development, 6) molecular function of mechanical sensors in bone, and 7) roles of osteoclasts in orthodontic treatment.

Education

We are teaching dental pharmacology to first-, second-, third-, fourth- and sixth-year students in Showa University. Although many teachers mainly use a slide projector in the classroom, we usually use a good textbook and write on a blackboard, which is the classical style of teaching, to make the students understand deeply.

Please visit our laboratory and enjoy the research and education.

Biomaterials and Engineering

It gives us great pleasure and is a privilege to introduce the Division of Biomaterials & Engineering in Showa University. Professor Yo Shibata, who is in charge of the division, has published his outstanding works in dentistry, biomaterials, and biomechanics journals. Some of his works have become cornerstones in their field, attracting remarkable attention and many citations over the years. He is perhaps one of a few authors who are able to publish their work in leading journals, such as the Journal of Dental Research, Biomaterials, Acta Biomaterialia, and Dental Materials. Professor Shibata demonstrated his superior ability and skills in developing international collaboration on some major initiatives. He has established strong partnerships with institutions in Australia, New Zealand, China and the US. Through such collaborations, he demonstrated vision and leadership by bringing together the expertise of leading domestic and international researchers. He also has exceptional ability and experience in research supervision: he has successfully supervised over 20 PhD students to completion in his career, including his visiting professorship appointments at the Universities of Otago and Sydney. He encouraged forward thinking and thorough research by students in an effective way. The way he implemented his research supervision was impressive, reflecting his supervising philosophy in effectively taking students to research frontiers to conduct world-class research.

Hygiene and Oral Health

The study of hygiene and oral health aims to improve life for humans through good oral health. Good oral health means more than good teeth; it means maintaining a good oral condition. Moreover, functional components are particularly important. Oral health is multi-faceted and includes the ability to eat, speak, breathe and convey a range of emotions through facial expressions. It is integral to general health and essential for physical and mental wellbeing.The following are the main research projects in our department:

1. Epidemiological survey on oral function and impairment of health
2. Influence of oral and pharynx morphology for the development of oral function in early childhood and decline of oral function in old age
3. Relationship between eating function and oral health /general health
4. Motion analysis of the oral and maxillofacial region
5. Food texture analysis and its analysis method

The following are the main clinical fields in our department:

1. Treatment for eating and swallowing disorders in children at the Center of Special Needs Dentistry
2. Oral health care for inpatients at the affiliate hospitals as a Showa University Oral Health Care Center. At each hospital the interdisciplinary team medicine approach is carried out to improve oral health.

Conservative Dentistry

Aesthetic Dentistry and Clinical Cariology

Aesthetic Dentistry was introduced as an academic course by the Department of Conservative Dentistry of the Showa University School of Dentistry, the first such initiative among Japanese universities. Minimal intervention is the key concept. We endeavor to minimize invasive treatment for patients while maximizing the benefits of intervention. Using aesthetic dental materials, we administer dental treatment focusing on improving oral cavity function as well as aesthetic aspects of the oral cavity including the maxillofacial area. The outpatient clinic is equipped with a full CAD/CAM system that enables us to offer cutting-edge dental work, including same-day repair using state-of-the-art aesthetic dental materials such as glass ceramics and zirconia. Students are also strongly supported and encouraged in their basic clinical training on repair work using the CAD/CAM system. We provide students with education that matches the contemporary needs of dentistry. We have established a Whitening Clinic for outpatients, where we provide regular treatment of dental whitening that meets individual patients’ needs. Research is another strength: we conduct a diverse range of research and experiments: basic and clinical research in the digital dentistry domain as well as in whitening, research into materials used for aesthetic repair such as composite resin and zirconia, research into the efficacy of polyphosphoric acid, and basic research into anti-aging, to name a few. The results of studies are published and presented widely in Japan and globally.

Endodontology

Endodontics is a field of clinical dentistry that deals with the teeth, dental pulp and periapical tissues, as well as the prevention and treatment of periapical periodontitis. It is widely known that endodontics is one of the most difficult procedures of dentistry, due to the complex morphology of the root canal system and oral-microbiological circumstances. Also, endodontic therapy has changed in recent years, including the use of the microscope, cone-beam computed tomography, Ni-Ti instruments and so on. There are nine dental chairs with microscopes in our department, enabling us to perform any observation and general root canal treatment under the microscope. This equipment enables us to provide a higher level of endodontic treatment.
In our department, we have engaged in not only clinical practice but also education and research. Throughout undergraduate and postgraduate education, we provide basic and advanced knowledge and the procedures of endodontics. Our research topics cover a wide range, including osteoimmunology of periapical periodontitis, analysis of mechanical properties of endodontic instruments, advanced use of cone-beam CT and latest technologies for clinical endodontics.

Periodontology

The Department of Periodontology actively engages in the research and treatment of periodontal diseases, as well as education of periodontology.
Research: Our current research projects are: 1. Analysis of junctional epithelium (e.g. we have succeeded in isolating junctional epithelium cells, and established cell line JE-1,2 expressing green fluorescent protein by using a bioengineered tooth technique in mice), 2. Analysis of gingival crevicular fluids, 3. Cellular and biochemical analysis of periodontal tissue, 4. Development of devices for visualizing and removing oral biofilm, 5. Prevention of peri-implantitis, and 6. Periodontal medicine.
Clinics: Our department possesses instructors, periodontists and trainers certified by the Japanese Society of Periodontology (JSP) Board. We strive to provide high-standard periodontal treatments.
Education: We give lectures and run clinical training programs on periodontal treatments for dental students and graduate school dentists. Our mission is to provide students with thorough skills and knowledge for periodontology, and to develop their careers as JSP Board Certified Periodontists.

Comprehensive Dentistry

We provide general dentistry services, especially for first-time patients who do not have a doctor’s referral letter. Clinical Comprehensive Dentistry is responsible for structuring and teaching comprehensive dentistry (formerly known as general dentistry) within the Showa University School of Dentistry. Our goal is to provide educational training courses in oral health care. Our courses are designed to expand the scope, depth of knowledge, and skills in providing comprehensive oral health care to patients. This program features an intensive clinical emphasis with lectures, seminars, conferences, and patient care experiences which will increase participants’ expertise in the field of comprehensive dentistry.

Prosthodontics

Prosthodontics

Overview

The primary responsibility of the Department of Prosthodontics is to educate undergraduate and postgraduate students in restoring damaged dentition to improve patients' quality of life, with a focus on achieving biological health, function, esthetics, and comfort. This is achieved by teaching and practicing modern restorative and prosthodontic clinical techniques, including implant dentistry and digital dentistry, based on current evidence from related sciences. The department integrates both undergraduate and postgraduate prosthodontics.

Undergraduate Prosthodontics Program

The Undergraduate Prosthodontics Program is responsible for educating undergraduate students to develop competency in treating and managing patients who require comprehensive diagnoses, treatment plans, and sequences of treatment in general prosthodontic therapy commonly encountered in general dental practices.

Postgraduate Prosthodontics Program (Ph.D. course)

The Postgraduate Prosthodontics course is a research-oriented program that involves conducting original research under supervision, as well as preparing and completing a thesis. The average time required to complete a postgraduate program is four years for full-time students. The Ph.D. course requires students to demonstrate their ability to understand the scientific process, including data collection, statistical analysis, and presentation at scientific meetings. The program is engaged in the following clinical and basic research associated with prosthodontics:

• Digital Dentistry
• Sleep Bruxism
• Pathophysiological Analysis using induced Pluripotent Stem Cells
• Oral Health-related Quality of Life
• Material Science such as Zirconia Implant and Antibacterial Agent for Dentures

Our research program is highly active, and our students frequently receive awards at scientific meetings. In addition, our Ph.D. course has regularly accepted international students. International students are always welcome to apply to our program.
Furthermore, the program aims to equip students holding a Japanese dental license with advanced knowledge and skills necessary to apply for the JPS Board Certified Prosthodontists of the Japan Prosthodontic Society, allowing them to provide highly complex prosthetic care. The curriculum is continually evolving and innovative, focusing on developing clinical decision-making and technical skills. Our objective is to train expert clinicians who exhibit ethical responsibility and professionalism. All students are able to receive hands-on training in CAD/CAM programs, such as 3Shape Dental System, 3Shape Implant Studio, DTX Studio, Geomagic Freeform, exocad, and Netfabb software, from faculty. In addition, Trios 3, Trios 4, Primescan, and Medit i700 intra-oral scanners are available for student use, along with a 3D printer. Our department boasts well-experienced full and part-time prosthodontists as clinical faculty.
For any additional inquiries, please do not hesitate to contact us using the address provided below.
For further information on university Ph.D. courses, please visit: /en/adm.html

Oral and Maxillofacial Surgery

Oral and Maxillofacial Surgery

Our division has acted as a clinically and academically pioneering facility in the field of oral surgery. We provide optimum treatments ranging from tooth extraction, removal of wisdom teeth, management of facial trauma, jawbone defects, facial deformities, temporomandibular joint disease, cleft lip and palate, and oral mucosal disease, to benign and malignant tumors. Especially, we perform orthognathic operations as well as tumor extirpation with safety, reliability, and accuracy by using navigation systems.
Our education program for undergraduate students is designed to acquire a broad and advanced level of skills and knowledge of oral and maxillofacial surgery. For graduate students, we provide evidence-based, integrated research training by expert staff.
We also accept international students at any time via the Showa University International Exchange Center, and have accepted many oral and maxillofacial surgeons from overseas including China, Myanmar, and Madagascar. We provide assistance with the acquisition of temporary Japanese dental licenses and practice in oral surgery in our department and other attached university hospitals.
The primary purpose of our research is to find solutions to improve the oral health of patients. We are committed to research linking basic science with clinical science, and the results may lead to benefits for patients and good results of our operations.

Oral Oncology

Education

The Division of Oral Oncology belongs to the Department of Oral and Maxillofacial Surgery of the dental school. We provide diagnostic procedures and treatment techniques for oral cancer and salivary gland disease to undergraduate dental students, as well as practical surgical techniques for head and neck cancer to graduate dental students.

Research

We specialize in the diagnosis and treatment of head and neck cancer and tumors.
1) Clinical study on resection of cervical schwannoma using narrow-band imaging
2) Clinical study on early detection of cervical lymph node metastasis of head and neck cancer using CT analysis

Medical Care

We belong to the Head and Neck Oncology Center, which consists of Head and Neck Surgery, Oral and Maxillofacial Surgery, Head and Neck Reconstructive Surgery and the Oral Rehabilitation team. The Center specializes in the medical care of head and neck cancer, head and neck tumors especially in cervical schwannomas, parotid gland tumors and thyroid gland tumors.

Orthodontics

Orthodontic treatment is performed in patients with malocclusions or jaw deformities to improve their dentition, occlusion, and facial harmony. In our department, we will use cone-beam computed tomography (CBCT), electromyography, mandibular movement analysis, and a three-dimensional scanner to formulate the three-dimensional and functional diagnosis, treatment plans, and associated research. Regarding the research, we will introduce advanced technologies from fields other than orthodontic, such as biomechanics and molecular biology. Also, We perform treatment using appliances, such as an aligner-type custom-made orthodontic appliance and the zirconia bracket MANEWVER, which was developed in our department to move teeth with weak force. We studied and developed the virtual patient robot, Showa Hanako for students to be utilized in clinical training and practical examinations. As a comprehensive medical university, multiple medical and dental departments collaborate in administering the treatments, and the Showa Cleft Palate Team（SCPT） has been organized for the orthodontic treatment of congenital diseases, such as cleft lip and palate. 
The Study Abroad Course includes the following:
1) One-year course without degree
2) Four-year course with degree
Students can participate in lectures, clinical training, technical training, and treatment assistance in our course curriculum.

Oral Diagnostic Sciences

Pathology

Dry mouth results from hypofunction of the salivary glands due to Sj?gren’s syndrome (SS), various medications, and radiation therapy for head and neck cancer. In severe cases of salivary gland hypofunction, sialagogue is not always effective due to loss of salivary parenchyma. Therefore, regenerative medicine using stem cell therapy is a promising treatment for these severe cases. Stem cells are classified into three groups: tissue stem cells, embryonic stem cells, and induced pluripotent stem cells. To date, it has been reported that tissue stem cells such as hematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and salivary stem/progenitor cells can recover irradiation-induced salivary gland hypofunction. Both HSCs and MSCs can recover salivary gland hypofunction through soluble factors in a paracrine manner, while salivary stem/progenitor cells can reconstitute the damaged salivary glands. We clarified that CD133-positive cells in mouse submandibular glands showed a stem cell feature, which reconstituted damaged salivary glands. Furthermore, we have focused on the challenge of producing functional salivary glands, which are 3-dimensionally induced from mouse ES cells. We have already succeeded in generating functional salivary glands from mouse ES cells (Nat Commun, 11;9:4216, 2018), and are now attempting to generate human functional salivary glands derived from human iPS cells for clinical application to treat dry-mouth patients and for analysis of salivary gland diseases.

Radiology

Dental (oral and maxillofacial) radiology is a field of dentistry, but at the same time it is also a field of radiology. This field has advanced by applying the knowledge and insights gained from radiation medicine in general to the dental field. Dental radiology is an area that connects physicians and teeth, and has contributed to the development of dental care.
In our division, there are three main areas of activity: clinical practice in dental hospitals, undergraduate and postgraduate education in dental radiology, and research on imaging. In clinical practice, we are responsible for imaging and diagnosing oral and maxillofacial lesions. We perform examinations of intraoral radiographs, panoramic radiographs, cone beam computed tomography (CBCT), MDCT, and ultrasonography. In the research field, we are focusing on the development and improvement of diagnostic imaging equipment, systematic analysis of image diagnosis capabilities, systematic analysis of image findings, establishment of criteria for selecting diagnostic imaging methods in dentistry, radiation dose measurement, and radiation protection. In student education, undergraduate students are taught about dental radiology through lectures and clinical practice, and about X-ray examination techniques such as intraoral radiography as well as imaging diagnosis.

Implant Dentistry

Overview

We conduct treatment, education and research on dental implants in general.

Education

Undergraduates learn about the flow of implant treatment through dental implant surgical training, prosthetic training and implant simulation training.
For postgraduates, our young dentists learn through assisting implantation and bone grafting, and treat patients in the prosthetic phase and maintenance phase under the guidance of specialists.

Research

Our research is mainly focused on clinical research, and also covers bone graft materials and dental implants.
International students are accepted from time to time, so please feel free to contact us.

Pediatric Dentistry

Outline

Showa University School of Dentistry was founded in 1977 and our department was established at the same time. We provide advanced dental management and care, including caries treatment, surgical operation, and dysphagia rehabilitation for children with and without disabilities. We also participate in specialized teams such as the Showa University Cleft Palate Team, and in maternity care in collaboration with the schools of medicine, nursing, and so on. Furthermore, we send our staff to administrative organizations to nurture develop pediatric dentists who can contribute to regional public health care.

Education

Senior staff allocate cases to young doctors based on their capacity, and support them in creating a treatment plan and treating patients. We have developed an oral phantom that can simulate the oral growth of children such as shedding and eruption.

Overseas Students

Our department has accepted eight overseas students from Bangladesh, Brazil, and China. We have also accepted short-term visitors from Indonesia, Canada, the U.K., etc.

Research

Dental Materials Journal 2019 Jan.; 35(1): 87–97
Journal of Oral Biosciences 2017 Aug.; 59(3): 172–178
Biochemical and Biophysical Research Communications 2017 Apr.; 485(h2): 461–467
Pediatric Dental Journal 2015 Apr.; 25(1): 1–7
Journal of Neurophysiology 2015 Jun.; 113(10): 3720–3735
Pediatric Dental Journal 2014 Sep.; 24: 159–166
Dental Materials Journal 2014 Sep.; 30(9): 1021–1028
Dental Medicine Research 2013 Jan.; 33(1): 88?99
Gene 2013 Feb.; 515(2): 291–297
Lasers in Medical Science 2012 Mar.; 27(2): 365–370

Oral Health Management

Oral Functional Rehabilitation Medicine

Our department focuses on the diagnoses of oral maxillofacial functional disorders such as eating, swallowing, speech function, obstructive sleep apnea syndrome and other functional disorders of the oral cavity. We conduct research on dysphagia and oral function using videofluoroscopic and videoendoscopic evaluation of swallowing. Moreover, we research the relationship between oral function and QOL in head and neck cancer patients. If you have these symptoms or are interested in our research, please feel free to contact our department.

Perioperative Medicine

Comprehensive Medicine

?As outstanding feature, our division is solely organized by medical stuff (MD), contributing for medical support for the patients in Showa University Dental Hospital.

Since established at April 2005, we participates education for dental student including bedside teaching, but excepting post graduate student including from foreign countries.

The first chief of division, professor Shin Inoue is specialist in cardiology, engaging the pathogenesis of the ischemic heart disease, various arrhythmia, cardiac myopathy or myocarditis.
Main achievement is depiction of the “slow pathway” as a target for catheter ablation procedure in atrioventricular reentrant tachycardia, co-authored with Dr. Anton E. Becker of Amsterdam University.

Dr. Koichi Ando, lecturer and chief assistant, is specialist in respiratory medicine and allergology. He also devoted in epidemiology in pulmonary diseases as appeared in Showa University Academic Resources.

Our clinic is opened Monday to Friday for outpatients mainly of cardio-pulmonary disease. However, in addition, we accept various diseases from psychosomatic disease in adolescence, to unexplained pains with ageing process.

As community based medicine in each disease state, clinical examination or practice should be cooperated with Showa University Hospital, but it should be noted that our stuff or operation has a room for change.

Medical and Dental Cooperative Dentistry

?Community-Based Comprehensive Dentistry was established in April 2009 as a means of further deepening collaboration with medical facilities in the community.
Regarding clinical services, patients with difficult conditions, such as severe dental phobia and gag reflex, who are difficult to treat by primary care dentists are referred to our department. We also perform dental treatment for high-risk patients who have systemic complications. For patients with dental phobia or a gag reflex, dental treatment is often performed under intravenous sedation or general anesthesia.
In education, we have been training dentists who can effectively treat these high-risk groups by conducting team medicine education in collaboration with other hospital departments and with Showa University as a whole. We also emphasize the importance of patient-centered treatment, safe and reassuring care, and face-to-face collaboration.
Research in our department focuses on the associations between oral management at Showa University Hospital and the basic medicine departments and includes topics such as the prevention of cerebral infarction and myocardial infarction, improvement of diabetes, shortening of length of hospital stay, and medical cost reduction. We are also conducting research on dental phobia with the goals of improving patient's QOL and eventually being able to provide normal dental care.

Dentistry for Persons with Disabilities

The Dental Clinic for Persons with Disabilities provides treatment for patients with special needs, such as those with intellectual disability, autism spectrum disorder, cerebral palsy, and genetic syndromes (such as Down syndrome) or mental retardation. Treatment methods include the outpatient clinic, intravenous anesthesia, and general anesthesia. Moreover, we provide dental treatment (such as for caries and periodontal disease) and dysphagia rehabilitation.
We strive to provide appropriate treatment in a feasible way taking into account the patient’s symptoms. Please feel free to contact us.