readingmaterials口腔专业阅读材料

1、Reading Materials1. Tooth developmentTooth development or odontogenesis is the complex process by which teeth form from embryonic cells, grow, and erupt into the mouth. Although many diverse species have teeth, non-human tooth development is largely the same as in humans. For human teeth to have a h

2、ealthy oral environment, enamel, dentin, cementum, and the periodontium must all develop during appropriate stages of fetal development. Primary (baby) teeth start to form between the sixth and eighth weeks, and permanent teeth begin to form in the twentieth week. If teeth do not start to develop at

3、 or near these times, they will not develop at all.A significant amount of research has focused on determining the processes that initiate tooth development. It is widely accepted that there is a factor within the tissues of the first branchial arch that is necessary for the development of teeth. In

4、 vertebrates several specializations of epithelial tissue generate after thickening specific structures: keratinized structure (hair, nails) or exoskeletons structure (scales, teeth). Placoids scales and teeth of sharks are considered homologous organs.2. Tooth StructureAn individual tooth consists

5、of an exposed crown and a root, buried in the gum and jaw. The crown is usually at least partly covered by an outer layer of an especially hard substance related to bone called enamel. Beneath the enamel (and sometimes exposed to the surface if the enamel is missing or worn away) is an intermediate

6、layer of material called dentine, which is also similar to bone but is not nearly as hard as enamel. It surrounds an inner pulp cavity filled with pulp (a living, vascular and well innervated tissue). Blood vessels and nerves reach the pulp cavity through a channel, the root canal, that penetrates t

7、he root. An additional layer of bony material, cementum, usually surrounds the root.As most teeth mature, the root canal gradually closes and the pulp cavity is sealed off. These teeth are called rooted. In contrast, rootless teeth are those in which the root canal remains open and the tooth continu

8、es to grow indefinitely. Rodent incisors and the molars of many arvicoline rodents are examples of rootless or evergrowing teeth; the molars of dogs and humans are rooted.Teeth are present in most vertebrates (turtles and modern birds are notable exceptions), and in some groups the diversity of teet

9、h rivals that seen in mammals. A significant distinction of mammals, however, is that mammalian teeth are restricted to just three bones, the maxillary and premaxillary of the upper jaw and the dentary of the lower jaw.Finally, a note on orientation: mammalogists refer to labial, lingual, and occlus

10、al surfaces. The labial side of the tooth is the side closest to the lips; the lingual side lies next to the tongue. The occlusal surface is the surface that meets a tooth or teeth in the opposite jaw during chewing.3. CariesDental caries, also known as tooth decay, is a disease where bacterial proc

11、esses damage hard tooth structure (enamel, dentin and cementum). These tissues progressively break down, producing dental cavities (holes in the teeth). Two groups of bacteria are responsible for initiating caries, Streptococcus mutans and Lactobacilli. If left untreated, the disease can lead to pai

12、n, tooth loss, infection, and, in severe cases, death. Today, caries remains one of the most common diseases throughout the world. Cariology is the study of dental caries.The presentation of caries is highly variable, however the risk factors and stages of development are similar. Initially, it may

13、appear as a small chalky area which may eventually develop into a large cavitation. Sometimes caries may be directly visible, however other methods of detection such as radiographs are used for less visible areas of teeth and to judge the extent of destruction.Tooth decay is caused by specific types

14、 of acid-producing bacteria which cause damage in the presence of fermentable carbohydrates such as sucrose, fructose, and glucose. The mineral content of teeth is sensitive to increases in acidity from the production of lactic acid. Specifically, a tooth (which is primarily mineral in content) is i

15、n a constant state of back-and-forth demineralization and remineralization between the tooth and surrounding saliva. When the pH at the surface of the tooth drops below 5.5, demineralization proceeds faster than remineralization (i.e. there is a net loss of mineral structure on the tooths surface).

16、This results in the ensuing decay. Depending on the extent of tooth destruction, various treatments can be used to restore teeth to proper form, function, and aesthetics, but there is no known method to regenerate large amounts of tooth structure. Instead, dental health organizations advocate preven

17、tive and prophylactic measures, such as regular oral hygiene and dietary modifications, to avoid dental caries. All cavities occur where carbohydrate like sugar or starch is in the food left on teeth after every meal or snack and changed to acid demineralisation of tooth by plaque bacteria.Though mo

18、re than 95% of trapped food is left packed between teeth after every meal or snack, over 80% of cavities develop inside pits and fissures in grooves on chewing surfaces where the brush cannot reach and there is no access for saliva and fluoride to neutralise acid and remineralise demineralised tooth

19、. Few cavities occur where saliva has easy access.Chewing fibre like celery after eating helps force saliva into trapped food to dilute carbohydrate like sugar, neutralise acid and remineralise demineralised teeth.4. PulpitisPulpitis is medical condition in which the dental pulp becomes inflamed.Sym

20、ptoms Increased sensitivity to stimuli, specifically hot and cold, is a common symptom of pulpitis. A prolonged throbbing pain is also associated with the disease.CausesPulpitis may be caused by a dental caries that penetrate though the enamel and dentin to reach the pulp, or it may be a result of t

21、rauma, such as thermal insult from repeated dental procedures.Inflammation associated with a bacterial infection, as in the case of penetrating decay, the pulp chamber is no longer sealed off from the environment of the oral cavity.When the pulp becomes inflamed pressure begins to build up in the pu

22、lp cavity exerting pressure on the nerve of the tooth and the surrounding tissues. Pressure from inflammation can cause mild to extreme pain, depending upon the severity of the inflammation. Often, pulpitis can create so much pressure on the tooth nerve the individual will have trouble locating the

23、source of the pain, confusing it with neighbouring teeth. Inflammation in the tooth provides a difficult environment for reducing the inflammation in the pulp cavity. Unlike other parts of the body where pressure can dissipate through the surrounding soft tissues and where lymph can reach, the pulp

24、cavity is very different. The dentin surrounding the pulp is hard and does not give under the pressure of the inflammation so the pressure has very little chance of dissipating before pulpal necrosis occurs. The pulp cavity inherently provides the body with an immune system response challenge, which

25、 makes it very unlikely that the bacterial infection can be eliminated. The pain will usually stop once the pulp has died, however the infection can spread to the ancillary anatomy.TreatmentOnce the pulp has become inflamed the tooth can be diagnostically divided into two categories. reversible pulp

26、itis irreversible pulpitis Reversible pulpitisOnce the irritant is removed the pulp remains vital and is not unduly affected by the changes, and the tooth can be restored vital by filling.Irreversible pulpitisThe pulp is irreversibly damaged and necrosis will follow. Pain may not subside after remov

27、al of the irritant. Pain may be sharp or dull and throbbing. If there is any drainage, then the severity of pain is reduced.The tooth may be endodontically treated where by the pulp is removed and replaced by gutta percha. An alternative is extraction of the tooth. This may be required if there is i

28、nsufficient coronal tissue remaining for restoration once the root canal therapy has been completed.5. Herpes simplexHerpes simplex is a viral disease caused by both herpes simplex virus 1 (HSV-1) and herpes simplex virus 2 (HSV-2). Infection with the herpes virus is categorized into one of several

29、distinct disorders based on the site of infection. Oral herpes, the visible symptoms of which are colloquially called cold sores or fever blisters, infects the face and mouth. Oral herpes is the most common form of infection. Genital herpes, known simply as herpes, is the second most common form of

30、herpes. Other disorders such as herpetic whitlow, herpes gladiatorum, ocular herpes (keratitis), cerebral herpes infection encephalitis, Mollarets meningitis, neonatal herpes, and possibly Bells palsy are all caused by herpes simplex viruses.Herpes viruses cycle between periods of active diseasepres

31、enting as blisters containing infectious virus particlesthat last 221 days, followed by a remission period, during which the sores disappear. Genital herpes, however, is often asymptomatic, though viral shedding may still occur. After initial infection, the viruses move to sensory nerves, where they

32、 reside as life-long, latent viruses. Causes of recurrence are uncertain, though some potential triggers have been identified. Over time, episodes of active disease reduce in frequency and severity.Herpes simplex is most easily transmitted by direct contact with a lesion or the body fluid of an infe

33、cted individual. Transmission may also occur through skin-to-skin contact during periods of asymptomatic shedding. Barrier protection methods are the most reliable method of preventing transmission of herpes, but they merely reduce rather than eliminate risk. Oral herpes is easily diagnosed if the p

34、atient presents with visible sores or ulcers. Early stages of orofacial herpes and genital herpes are harder to diagnose; laboratory testing is usually required. Twenty percent of the U.S. population has antibodies to HSV-2, although not all of them have a history of genital lesions. A cure for herp

35、es has not yet been developed. Once infected, the virus remains in the body for life. However, after several years, some people will become perpetually asymptomatic and will no longer experience outbreaks, though they may still be contagious to others. Vaccines are in clinical trials but have not de

36、monstrated effectiveness. Treatments can reduce viral reproduction and shedding, prevent the virus from entering the skin, and alleviate the severity of symptomatic episodes.Herpes simplex should not be confused with conditions caused by other viruses in the herpesviridae family such as herpes zoste

37、r, which is a viral disease caused by varicella zoster virus. There is also a possibility of confusion with hand, foot and mouth disease due to apparition of lesions on the skin.6. CandidiasisCandidiasis or thrush is a fungal infection (mycosis) of any of the Candida species, of which Candida albica

38、ns is the most common. Candidiasis encompasses infections that range from superficial, such as oral thrush and vaginitis, to systemic and potentially life-threatening diseases. Candida infections of the latter category are also referred to as candidemia and are usually confined to severely immunocom

39、promised persons, such as cancer, transplant, and AIDS patients.Superficial infections of skin and mucosal membranes by Candida causing local inflammation and discomfort are however common in many human populations. While clearly attributable to the presence of the opportunistic pathogens of the gen

40、us Candida, candidiasis describes a number of different disease syndromes that often differ in their causes and outcomes. Commonly referred to as a yeast infection, it is also technically known as candidosis, moniliasis, and oidiomycosis. Most candidial infections are treatable and result in minimal

41、 complications such as redness, itching and discomfort, though complication may be severe or fatal if left untreated in certain populations. In immunocompetent persons, candidiasis is usually a very localized infection of the skin or mucosal membranes, including the oral cavity (thrush), the pharynx

42、 or esophagus, the gastrointestinal tract, the urinary bladder, or the genitalia (vagina, penis). Candidiasis is a very common cause of vaginal irritation, or vaginitis, and can also occur on the male genitals. In immunocompromised patients, Candida infections can affect the esophagus with the poten

43、tial of becoming systemic, causing a much more serious condition, a fungemia called candidemia. Children, mostly between the ages of three and nine years of age, can be affected by chronic mouth yeast infections, normally seen around the mouth as white patches. However, this is not a common conditio

44、n.Symptoms of candidiasis may vary depending on the area affected. Infection of the vagina or vulva may cause severe itching, burning, soreness, irritation, and a whitish or whitish-gray cottage cheese-like discharge, often with a curd-like appearance. These symptoms are also present in the more com

45、mon bacterial vaginosis. In a 2002 study published in the Journal of Obstetrics and Gynecology, only 33 percent of women who were self-treating for a yeast infection actually had a yeast infection, while most had either bacterial vaginosis or a mixed-type infection. Symptoms of infection of the male

46、 genitalia include red patchy sores near the head of the penis or on the foreskin, severe itching, or a burning sensation. Candidiasis of the penis can also have a white discharge, although uncommon. However, having no symptoms at all is common, and a more severe form of the symptoms may emerge late

47、r.7. History of anesthesiaMethods for lessening the sensation of pain during surgery date back to ancient times. Before the discovery of substances that produced general anesthesia, patients needing surgery for illness or injury had to rely on alcohol, opium (a natural narcotic derived from the opiu

48、m poppy), or fumes from an anesthetic-soaked cloth to deaden the pain of the surgeons knife. Often a group of men held the patient down during an operation in case the opium or alcohol wore off. Under these conditions, many patients died of shock from the pain of the operation itself.Nitrous oxide,

49、ether, and chloroform. The gases nitrous oxide, ether, and chloroform were first used as anesthetics in the nineteenth century, ushering in the modern era of anesthesia. Nitrous oxide, or laughing gas, was discovered as an anesthetic by English chemist Humphry Davy (17911867) in 1799. Davys finding

50、was ignored until the next century, when Connecticut dentist Horace Wells (18151848) began to experiment using nitrous oxide as an anesthetic during tooth surgery. In 1845, he attempted to demonstrate its pain-blocking qualities to a public audience but was unsuccessful when he began to pull a tooth

51、 before the patient was fully anesthetized. The patient cried out in pain and, as a result, another 20 years passed before nitrous oxide was accepted for use as an anesthetic.The first use of ether as an anesthetic during an operation was claimed by surgeon Crawford W. Long (18151878) of Georgia in

52、1842. The operation, however, was unrecorded, so official credit went instead to Massachusetts dentist William Morton (18191868) for his 1846 public demonstration of an operation using ether performed in a Boston hospital. While Morton administered the gas to the patient through an inhaling device,

53、John C. Warren (17781856) removed a neck tumor without the patient feeling any pain. Following this landmark use of ether as an anesthetic, general anesthesia began to be practiced all over the United States and Europe.Chloroform was introduced as a surgical anesthetic by Scottish obstetrician James

54、 Young Simpson (18111870) in 1847. After first experimenting with ether, Simpson searched for an anesthetic that would make childbirth less painful for women. Although it eased the pain of labor, chloroform had higher risks than those associated with ether. Neither ether nor chloroform are used in s

55、urgery today.8. What is a dry socket?A dry socket occurs when the blood clot is lost from an extraction site prematurely. Basically, the blood clot in the socket serves the same two functions as a scab on a skin surface cut. First, it assists in the cessation of bleeding and second, it protects unde

56、rlying structures during the healing process. Like the child who picks at a scab the area heals in time but is painful for far longer than if the scab had been left alone. When the blood clot is lost before the underlying structres have had time to heal, bone is exposed to the oral environment along

57、 with fine nerve endings. This is an exquisitely painful but otherwise relatively harmless situation. There are packing materials which the oral surgeon can place to help ease the discomfort both by physically blocking the wound and by the action of the chemicals in the pack on local nerve endings.

58、Generally, patients return to have the pack changed every day or two and most patients do not require more than 2 or three dressing changes. Some patients require no dressing while others may require 4 or 5 changes of packing. Tincture of time and good oral hygiene usually resolve the situation. The

59、re are some activities which may increase the propensity for dry socket formation.smoking, drinking carbonated beverages in the first 24 hours after surgery, spitting or drinking through a straw in that same time period.but often dry sockets occur for no particular reason at all. 9. Bone fractureA bone fracture (sometimes abbreviated FRX or Fx, Fx) is a medical condition in which there is a break in the continuity o