Senin, 15 Desember 2008

dental implant

A dental implant is an artificial tooth root replacement and is used in prosthetic dentistry to support restorations that resemble a tooth or group of teeth. There are several types of dental implants. The major classifications are divided into osseointegrated implant and the fibrointegrated implant. Earlier implants, such as the subperiosteal implant and the blade implant were usually fibrointegrated . The most widely accepted and successful implant today is the osseointegrated implant, based on the discovery by Swedish Professor Per-Ingvar Brånemark that titanium can be successfully fused into bone when osteoblasts grow on and into the rough surface of the implanted titanium ]. This forms a structural and functional connection between the living bone and the implant. A variation on the implant procedure is the implant-supported bridge, or implant-supported denture.




History

The Mayan civilization has been shown to have used the earliest known examples of endosseous implants (implants embedded into bone), dating back over 1,350 years before Per Brånemark started working with titanium. While excavating Mayan burial sites in Honduras in 1931, archaeologists found a fragment of mandible of Mayan origin, dating from about 600 AD. This mandible, which is considered to be that of a woman in her twenties, had three tooth-shaped pieces of shell placed into the sockets of three missing lower incisor teeth. For forty years the archaeological world considered that these shells were placed under the nose in a manner also observed in the ancient Egyptians. However, in 1970 a Brazilian dental academic, Professor Amadeo Bobbio studied the mandibular specimen and took a series of radiographs. He noted compact bone formation around two of the implants which led him to conclude that the implants were placed during life.

In the 1950s research was being conducted at Cambridge University in England to study blood flow in vivo. These workers devised a method of constructing a chamber of titanium which was then embedded into the soft tissue of the ears of rabbits. In 1952 the Swedish orthopaedic surgeon, P I Brånemark, was interested in studying bone healing and regeneration, and adopted the Cambridge designed ‘rabbit ear chamber’ for use in the rabbit femur. Following several months of study he attempted to retrieve these expensive chambers from the rabbits and found that he was unable to remove them. Per Brånemark observed that bone had grown into such close proximity with the titanium that it effectively adhered to the metal. Brånemark carried out many further studies into this phenomenon, using both animal and human subjects, which all confirmed this unique property of titanium.

Although he had originally considered that the first work should centre on knee and hip surgery, Brånemark finally decided that the mouth was more accessible for continued clinical observations and the high rate of edentulism in the general population offered more subjects for widespread study. He termed the clinically observed adherence of bone with titanium as ‘osseointegration’. In 1965 Brånemark, who was by then the Professor of Anatomy at Gothenburg University in Sweden, placed the first titanium dental implant into a human volunteer, a Swede named Gösta Larsson.

Over the next fourteen years Brånemark published many studies on the use of titanium in dental implantology until in 1978 he entered into a commercial partnership with the Swedish defense company, Bofors AB for the development and marketing of his dental implants. With Bofors (later to become Nobel Industries) as the parent company, Nobelpharma AB (later to be renamed Nobel Biocare) was founded in 1981 to focus on dental implantology. To the present day over 7 million Brånemark System implants have now been placed and hundreds of other companies produce dental implants. The majority of dental implants currently available are shaped like small screws, with either tapered or parallel sides. They can be placed at the same time as a tooth is removed by engaging with the bone of the socket wall and sometimes also with the bone beyond the tip of the socket. Current evidence suggests that implants placed straight into an extraction socket have comparable success rates to those placed into healed bone.[4]. The success rate and radiographic results of immediate restorations of dental implants placed in fresh extraction sockets (the temporary crowns placed at the same time) have been shown to be comparable to those obtained with delayed loading (the crowns placed weeks or months later)[5]

Some current research in dental implantology is focusing on the use of ceramic materials such as zirconia (ZrO2) in the manufacture of dental implants. Although generally the same shape as titanium implants zirconia, which has been used successfully for orthopaedic surgery for a number of years, has the advantage of being more cosmetically aesthetic owing to its bright tooth-like colour[6]. Long-term clinical data is necessary before one-piece ZrO2 implants can be recommended for daily practice[7].

Procedure

A typical implant consists of a titanium screw (resembling a tooth root) with a roughened or smooth surface. The very first implants were made out of commercially pure titanium, however since it was discovered that the Ti6AlV4 alloy offered the same osseointegration level as commercially pure titanium, more and more implants were made out of Ti6AlV4 alloy due to its better tensile strength and thus fracture resistance. Today most implants are made out of the Ti6AlV4 alloy and treated either by plasma spraying, etching or sandblasting to increase the surface area and, thus the integration potential of the implant. An osteotomy or precision hole is carefully drilled into jawbone and the implant is installed in the osteotomy.

Implant surgery is performed as an outpatient under general anesthesia (if several implants are to be placed) or with local anesthesia (for simple cases) by trained and certified clinicians including general dentists, oral surgeons, prosthodontists, and periodontists. An increasing number of cosmetic dentists are also placing implants in relatively simple cases. In the UK the General Dental Council has guidelines on the training required for a dentist to be able to place dental implants in general dental practice [8]. The most common treatment plan calls for several surgeries over a period of months, especially if bone augmentation (bone grafting) is needed to support implant placements. In straight forward cases patients can be implanted and restored in a single surgery, in a procedure labeled "Immediate Loading". In such cases a provisional prosthetic tooth or crown is shaped to avoid the force of the bite transferring to the implant while it integrates with the bone.

A single implant procedure that involves an incision and "flapping" of the gum or gingiva (to expose the jawbone) takes about an hour, sometimes longer; multiple implants can be installed in a single surgical session lasting several hours.

Healing and integration of the implant(s) with jawbone occurs over three to six months in a process called osseointegration. At the appropriate time, the restorative Dentist uses the implant(s) to anchor crowns or a bridge (a prosthetic restoration containing several crowns). Since the implants supporting the restoration are integrated, which means they are biomechanically stable and strong, the patient is immediately able to masticate (chew) normally.

In an immediate function procedure, the gingiva is usually not flapped (Flapless). Instead, the surgeon removes a small plug of gingiva directly over the drilling site. The site is drilled and the implant is installed. Then a crown is immediately added.

There are different approaches to place dental implants after tooth extraction. The approaches are:

  1. Immediate post-extraction implant placement.
  2. Delayed immediate post-extraction implant placement (2 weeks to 3 months after extraction).
  3. Late implantation (3 months after tooth extraction).

According to the timing of loading of dental implants, the procedure of loading could be classified into:

  1. Immediate loading procedure.
  2. Early loading (1 week to 12 weeks).
  3. Staged loading (3-6 months).
  4. Late loading (more than 6 months).

Most patients need the longer treatment plan, which has an excellent history going back many years.[citation needed] Before surgery, with the patient fully awake or during an earlier office visit, a prudent clinician planning mandibular implants will conduct a neurosensory examination to rule out altered sensation, thus setting a base line on nerve function. Also prior to surgery, a panoramic X-ray will be taken using a metal ball of known dimension so that calibrated measurements can be made from the image (to accurately locate "vital structures" such as nerves and the position of critical anatomical features such as the mental foramen, which is the transit point in the jawbone for the nerve which innervates the lip and chin).

At edentulous (without teeth) jaw sites, a pilot hole is bored into the recipient bone, taking care to avoid vital structures (in particular the inferior alveolar nerve or IAN within the mandible). A zone of safety, usually 2 mm, is the standard of care for avoiding vital structures like the IAN. When computed tomography (3D X-ray imaging) is used preoperatively to accurately pinpoint vital structures, the zone of safety may be reduced to 1 mm through the use of computer-aided design of surgical guides.

Drilling into jawbone usually occurs in several separate steps. The pilot hole is expanded by using progressively wider drills (typically between three and seven successive drilling steps, depending on implant width and length). Care is taken not to damage the osteoblast or bone cells by overheating. A cooling saline spray keeps the temperature of the bone to below 47 degrees Celsius (approximately 117 degrees Fahrenheit). The implant screw can be self-tapping, and is screwed into place at a precise torque so as not to overload the surrounding bone (overloaded bone can die, a condition called osteonecrosis, which may lead to failure of the implant to fully integrate or bond with the jawbone). Typically in most implant systems, the osteotomy or drilled hole is about 1mm deeper than the implant being placed, due to the shape of the drill tip. Surgeons must take the added length into consideration when drilling in the vicinity of vital structures.

Once properly torqued into the bone, a cover screw is placed on the implant, then the gingiva or gum is sutured over the site and allowed to heal for several months for osseointegration to occur between the titanium surface of the implant and jawbone.

After several months the implant is uncovered in another surgical procedure, usually under local anesthetic by the restorative dentist or prosthodontist, and a healing abutment and temporary crown is placed onto the implant. This encourages the gum to grow in the right scalloped shape to approximate a natural tooth's gums and allows assessment of the final aesthetics of the restored tooth. Once this has occurred a permanent crown will be fabricated and placed on the implant.

An increasingly common strategy to preserve bone and reduce treatment times includes the placement of a dental implant into a recent extraction site. In addition, immediate loading is becoming more common as success rates for this procedure are now acceptable. This can cut months off the treatment time and in some cases a prosthetic tooth can be attached to the implants at the same time as the surgery to place the dental implants.

In all of these approaches, computer-based guidance has thrust itself onto the treatment stage. Not only will 3D digital imagery yield critical treatment guidance, the digital data can be used to manufacture precision drilling guides, virtually eliminating surgical errors.

Complementary procedures

Sinus lifting is a common surgical intervention. A dentist or specialist with proper training such as an endodontist, periodontist, prosthodontist, or oral surgeon thickens the inadequate part of atrophic maxilla towards the sinus with the help of bone transplantation or bone expletive substance. This results in more volume for a better quality bone site for the implantation.

Bone grafting will be necessary in cases where there is a lack of adequate maxillary or mandibular bone in terms of front to back (lip to tongue) depth or thickness; top to bottom height; and left to right width. Sufficient bone is needed in three dimensions to securely integrate with the root-like implant. Improved bone height -- which is very difficult to achieve -- is particularly important to assure ample anchorage of the implant's root-like shape because it has to support the mechanical stress of chewing, just like a natural tooth. If an implant is too shallow, chewing may cause a dangerous jawbone crack or full fracture.

Typically, implantologists try to place implants at least as deeply into bone as the crown or tooth will be above the bone. This is called a 1:1 crown to root ratio. This ratio establishes the target for bone grafting in most cases. If 1:1 or better cannot be achieved, the patient is usually advised that only a short implant can be placed and to not expect a long period of usability.

A wide range of grafting materials and substances may be used during the process of bone grafting / bone replacement. They include the patient's own bone (autograft), which may be harvested from the hip (iliac crest) or from spare jawbone; processed bone from cadavers (allograft); bovine bone or coral (xenograft); or artificially produced bonelike substances (calcium sulfate with names like Regeneform; and hydroxyapatite or HA, which is the primary form of calcium found in bone). The HA is effective as a substrate for osteoblasts to grow on. Some implants are coated with HA for this reason.

Bone graft surgery has its own standard of care. In a typical procedure, the clinician creates a large flap of the gingiva or gum to fully expose the jawbone at the graft site, performs one or several types of block and onlay grafts in and on existing bone, then installs a membrane designed to repel unwanted infection-causing microbiota found in the oral cavity. Then the gingiva is carefully sutured over the site. Together with a course of internal antibiotics and external antibiotic mouth rinses, the graft site is allowed to heal (several months).

The clinician typically takes a new panoramic x-ray to confirm graft success in width and height, and assumes that positive signs in these two dimensions safely predicts success in the third dimension, depth. Where more precision is needed, usually when mandibular implants are being planned, a 3D or cone beam X-ray may be called for at this point to enable accurate measurement of bone and location of nerves and vital structures for proper treatment planning. The same X-ray data set can be employed for the preparation of computer-designed placement guides.

Correctly performed, a bone graft produces live vascular bone which is very much like natural jawbone and is therefore suitable as a foundation for implants.

Considerations

For dental implant procedure to work, there must be enough bone in the jaw, and the bone has to be strong enough to hold and support the implant. If there is not enough bone, more may need to be added with a bone graft procedure discussed earlier. Sometimes, this procedure is called bone augmentation. In addition, natural teeth and supporting tissues near where the implant will be placed must be in good health.

In all cases, what must be addressed is the functional aspect of the final implant restoration, the final occlusion. How much force per area is being placed on the bone implant interface? Implant loads from chewing and parafunction can exceed the physio biomechanic tolerance of the implant bone interface and/or the titanium material itself, causing failure. This can be failure of the implant itself (fracture) or bone loss, a "melting" or resorption of the surrounding bone.

The dentist must first determine what type of prosthesis will be fabricated. Only then can the specific implant requirements including number, length, diameter, and thread pattern be determined. In other words, the case must be reverse engineered by the restoring dentist prior to the surgery. If bone volume or density is inadequate, a bone graft procedure must be considered first. The restoring dentist may consult with the periodontist, endodontist, oral surgeon, or another trained general dentist to co-treat the patient. Usually, physical models or impressions of the patient's jawbones and teeth are made by the restorative dentist at the implant surgeons request, and are used as physical aids to treatment planning. If not supplied, the implant surgeon makes his own or relies upon advanced computer-assisted tomography or a cone beam CAT scan to achieve the proper treatment plan.

Computer simulation software based on CAT scan data allows virtual implant surgical placement based on a barium impregnated prototype of the final prosthesis. This predicts vital anatomy, bone quality, implant characteristics, the need for bone grafting, and maximizing the implant bone surface area for the treatment case creating a high level of predictability. Computer CAD/CAM milled or stereo lithography based drill guides can be developed for the implant surgeon to facilitate proper implant placement based on the final prosthesis occlusion and aesthetics.

Treatment planning software can also be used to demonstrate "try-ins" to the patient on a computer screen. When options have been fully discussed between patient and surgeon, the same software can be used to produce precision drill guides.

Success rates

Dental implant success is related to operator skill, quality and quantity of the bone available at the site, and also to the patient's oral hygiene. The general consensus of opinion is that implants carry a success rate of around 95%[9]

Failure

Failure of a dental implant is often related to failure to osseointegrate correctly. A dental implant is considered to be a failure if it is lost, mobile or shows peri-implant (after implant) bone loss of greater than 1.0 mm in the first year and greater than 0.2mm a year thereafter.

Dental implants are not susceptible to dental caries but they can develop a periodontal condition called peri-implantitis. The cause may be infection that was introduced during surgery; or failure by the patient to follow correct oral hygiene routines. In either case, inflammation in the bone surrounding the implant causes bone loss (recession) which ultimately may lead to failure, often evidenced by the ability to "spin" an implant.

Peri-implantitis is often dealt with pre-emptively by clinicians who prescribe a course of antibiotics in the days prior to surgery; and post-surgically with another course of antibiotics and special oral rinses. Since peri-implantitis is generally easy to see on standard panoramic and periapical X-rays, prudent clinicians who suspect the problem will take an X-ray soon after surgery, and again at staged intervals post-operatively.

Risk of failure is increased in smokers. For this reason implants are frequently placed only after a patient has stopped smoking as the treatment is very expensive. More rarely, an implant may fail because of poor positioning at the time of surgery, or may be overloaded initially causing failure to integrate. If smoking and positioning problems exist prior to implant surgery, clinicians often advise patients that a bridge or partial denture rather than an implant may be a better solution.

Contraindications

There are no absolute contraindications to implant dentistry, however there are some systemic, behavioral and anatomic considerations that should be considered.

Particularly for mandibular (lower jaw) implants, especially in the vicinity of the mental foramen (MF), there must be sufficient alveolar bone above the mandibular canal also called the inferior alveolar canal or IAC (which acts as the conduit for the neurovascular bundle carrying the inferior alveolar nerve or IAN).

Failure to precisely locate the IAN and MF invites surgical insult by the drills and the implant itself. Such insult may cause irreparable damage to the nerve, often felt as a paresthesia (numbness) or dysesthesia (painful numbness) of the gum, lip and chin. This condition may persist for life and may be accompanied by unconscious drooling.

Lack of sufficient alveolar bone is another contraindication to the procedure. Typically, a preoperative in-office panoramic X-ray is taken to establish (with allowances for image distortion, a known problem with panoramic X-rays) in two dimensions (height and width) the amount of available bone. A bone graft or augmentation procedure may be performed and allowed to heal several months before implantation surgery. A new panoramic X-ray will help determine if the graft was successful.

This is an important step inasmuch as improved bone height is much more difficult to achieve than more increased bone depth. For mandibular grafts, a 3D or cone beam X-ray enables measurement of bone height (top to bottom), width (left and right) and depth (front to back) to an accuracy of 0.1mm. The precision of cone beam has stimulated a new industry that produces computer-designed surgical guides based on the cone beam X-ray's digital data. These surgery aids are employed by implantologists to precisely locate and drill into the mandible and maxilla, and to avoid vital structures.

Uncontrolled type II diabetes is a significant relative contraindication as healing following any type of surgical procedure is delayed due to poor peripheral blood circulation. Anatomic considerations include the volume and height of bone available. Often an ancillary procedure known as a block graft or sinus augmentation are needed to provide enough bone for successful implant placement.

There is new information about intravenous and oral bisphosphonates (taken for certain forms of breast cancer and osteoporosis, respectively) which may put patients at a higher risk of developing a delayed healing syndrome called osteonecrosis. Implants are contraindicated for some patients who take intravenous bisphosphonates.

The many millions of patients who take an oral bisphosphonate (such as Actonel, Fosamax and Boniva) may be advised to stop the administration prior to implant surgery, then resume several months later. But this protocol may not be necessary. As of January, 2008, an oral bisphosphonate study reported in the February 2008 Journal of Oral and Maxillofacial Surgery, reviewing 115 cases that included 468 implants, concluded "There is no evidence of bisphosphonate-associated osteonecrosis of the jaw in any of the patients evaluated in the clinic and those contacted by phone or e-mail reported no symptoms." (JOMS, Volume 66, Issue 2, Ppgs 223-230).

The American Dental Association had addressed bisphosphonates in an article entitled "Bisphosphonate medications and your oral health," (JADA, Vol. 137, page 1048, July 2006.) In an Overview, the ADA stated "The risk of developing BON [bisphosphonate-associated osteonecrosis of the jaw] in patients on oral bisphosphonate therapy appears to be very low...". The ADA Council on Scientific Affairs also employed a panel of experts who issued recommendations [for clinicians] for treatment of patients on oral bisphosphonates, published in June, 2006. The overview may be read online at ada.org but it has now been superseded by a huge study -- encompassing over 700,000 cases -- entitled "Bisphosphonate Use and the Risk of Adverse Jaw Outcomes." Like the 2008 JOMS study, the ADA study exonerates oral bisphosphonates as a contraindication to dental implants. (JADA, January 2008, 139:23-30).

Bruxism (tooth clenching or grinding) is another contraindication. The forces generated during bruxism are particularly detrimental to implants while bone is healing; micromovements in the implant positioning are associated with increased rates of implant failure. Bruxism continues to pose a threat to implants throughout the life of the recipient. Natural teeth contain a periodontal ligament allowing each tooth to move and absorb shock in response to vertical and horizontal forces. Once replaced by dental implants, this ligament is lost and teeth are immovably anchored directly into the jaw bone. This problem can be minimized by wearing a custom made mouthguard (such an NTI appliance) at night.

Postoperatively, after implants have been placed, there are physical contraindications that prompt rapid action by the implantology team. Excessive or severe pain lasting more than three days is a warning sign, as is excessive bleeding. Constant numbness of the gingiva (gum), lip and chin -- usually noticed after surgical anesthesia wears off -- is another warning sign. In the latter case, which may be accompanied by severe constant pain, the standard of care calls for diagnosis to determine if the surgical procedure insulted the IAN. A 3D cone beam X-ray provides the necessary data, but even before this step a prudent implantologist may back out or completely remove an implant in an effort to restore nerve function because delay is usually ineffective. Depending upon the evidence visible with a 3D X-ray, patients may be referred to a specialist in nerve repair. In all cases, speed in diagnosis and treatment are necessary.

Kamis, 27 November 2008

Diseases of the Teeth

Adults have 32 permanent teeth, including the incisors, canines, premolars, and molars. As shown in Figure 1, the crown of a tooth rises above the gingiva, and the root is the portion embedded in alveolar bone. The periodontal ligament suspends a tooth and its roots in the bone and is made up of collagen fibers. The major component of teeth is a bone-like substance called dentin. Inside the tooth lies the pulp, containing blood vessels and nerves. The crown is covered by enamel and the roots are covered by cementum.

Fig.1 Tooth Anatomy



Diseases of the teeth are frequently identified by clinical inspection of the oral cavity and by x-ray examination. Common radiographs include periapical views to identify the crown and root, bite-wing radiographs to examine the interproximal spaces, occlusal views to image large segments of the dental arch, and panoramic views to identify both dental arches and their supporting structures. Periapical, bite-wing, and occlusal radiographs are intraoral films made by placing film inside the patient's mouth and directing the x-ray beam through the area to be imaged. Panoramic radiographs, which are extraoral films requiring special equipment to obtain, are frequently used since they can display the entire maxillomandibular region on a single film.

Dental caries, or injury and destruction of the calcified structures of the teeth by Streptococcus species and other bacteria, continue to be extremely prevalent in the United States. Although less than 15% of US adults are free of caries, the absolute number of caries per individual during the past 50 years has declined. This is due in part to preventive measures such as water fluoridation and the use of toothpaste, supplements, and mouth rinses that contain fluoride.

Caries may occur on smooth tooth surfaces, chewing surfaces, and most commonly in pits and fissures (Fig 2). To prevent caries in the pits and grooves of occlusal surfaces of posterior teeth, dental sealants have been developed. These materials modify the resistance of teeth to caries by coating the occlusal grooves with an adherent material such as a plastic resin. Dental sealants are currently indicated for newly erupted teeth with significant pits and fissures or for patients with significant previous occlusal caries. Once dental caries occur, they are treated by removal of the affected tissue and replacement with a restorative material such as silver amalgam, gold, or composite. The primary goal, however, is prevention of caries through dietary modification, limitation of sucrose-containing food, use of fluoride supplements, and antibacterial measures such as daily personal oral hygiene and regular professional cleanings.

Fig 2. Pit and Fissure

taken from : http://www.medscape.com/viewarticle/410839

Rabu, 26 November 2008

dental composite


Dental composites (white fillings) are a group of restorative materials used in dentistry. As with other composite materials, a dental composite typically consists of a resin-based oligomer matrix, such as a bisphenol A-glycidyl methacrylate BISMA or urethane dimethacrylate (UDMA), and an inorganic filler such as silicon dioxide silica. Compositions vary widely, with proprietary mixes of resins forming the matrix, as well as engineered filler glasses and glass ceramics. The filler gives the composite wear resistance and translucency. A coupling agent such as silane is used to enhance the bond between these two components. An initiator package begins the polymerization reaction of the resins when external energy (light/heat, etc.) is applied. A catalyst package can control its speed.

Selasa, 25 November 2008

the teeth and your teeth

You bite into an apple and then try to start talking to your friend about yesterday's math homework. Suddenly something feels funny — one of your baby teeth has fallen out! It's been loose forever, and now there it is, right in your hand. And you have an empty space in your mouth big enough to poke a drinking straw through.

Before you put that tooth under your pillow, did you know that there is much more to that tooth than meets the eye? A single tooth has many different parts that make it work. And teeth play an important role in your daily life. They not only let you eat stuff like apples, they also help you talk. So let's talk teeth!

Tiny Teeth

Unlike your heart or brain, your teeth weren't ready to work from the day you were born. Although babies have the beginnings of their first teeth even before they are born, teeth don't become visible until babies are about 6 to 12 months old.

After that first tooth breaks through, more and more teeth begin to appear. Most kids have their first set of teeth by the time they are 3 years old. These are called the primary or baby teeth, and there are 20 in all. When a child gets to age 5 or 6, these teeth start falling out, one by one.

A primary tooth falls out because it is being pushed out of the way by the permanent tooth that is behind it. Slowly, the permanent teeth grow in and take the place of the primary teeth. By about age 12 or 13, most kids have lost all of their baby teeth and have a full set of permanent teeth.

There are 28 permanent teeth in all — eight more than the original set of baby teeth. Between the ages of 17 and 21, four more teeth called wisdom teeth usually grow in at the back of the mouth. They complete the adult set of 32 teeth.

Tooth Tour

Let's take a tour of your teeth. Look in the mirror at your own teeth or check out a friend's smile. The part of the tooth you can see, which is not covered by the gum (your gums are the pink, fleshy part), is called the crown. The crown of each tooth is covered with enamel (say: ih-nam-ul), which is very hard and often shiny. Enamel is a very tough substance and it acts as a tooth's personal bodyguard. Enamel works as a barrier, protecting the inside parts of the tooth.

tooth, teeth, diagramIf you were able to peel away the enamel, you would find dentin (say: den-tin). Dentin makes up the largest part of the tooth. Although it is not as tough as enamel, it is also very hard.

Dentin protects the innermost part of the tooth, called the pulp. The pulp is where each tooth's nerve endings and blood supply are found. When you eat hot soup, bite into a super-cold scoop of ice cream, fall and hurt a tooth, or get a cavity, it's your pulp that hurts. The nerve endings inside the pulp send messages to the brain about what's going on ("That ice cream is too cold!"). The pulp also contains the tooth's blood vessels, which feed the tooth and keep it alive and healthy.

The pulp goes all the way down into the root of the tooth, which is under the gum. Cementum (say: sih-men-tum) makes up the root of the tooth, which is anchored to the jawbone.

Tooth Types

You've probably noticed that you have different types of permanent teeth in your mouth. Each one has its own function.

Your two front teeth and the teeth on either side of them are incisors (say: in-sy-zurs). There are four on the top and four on bottom.

teeth mouthIncisors are shaped like tiny chisels, with flat ends that are somewhat sharp. These teeth are used for cutting and chopping food. Think back to that apple you ate: You used your incisors to crunch into the skin of the apple.

The pointy teeth beside your incisors are called canine (say: kay-nine) teeth. There are four of them, two on top and two on bottom. Because these teeth are pointy and also sharp, they help tear food.

Next to your canine teeth are your premolars (say: pree-mo-lurs), which are also called bicuspid teeth. You have eight premolars in all, four on top and four on the bottom. You'll need to open a bit wider to see these teeth, but when you do, you'll notice that their shape is completely different from both incisors and canines. Premolars are bigger, stronger, and have ridges, which make them perfect for crushing and grinding food.

If you open your mouth really wide, you'll see your molars (say: mo-lurs). You have eight of these, four on the top and four on the bottom. Sometimes these are called your 6-year molars and your 12-year molars because that is around the time when they come in.

Molars are the toughest of the bunch. They are even wider and stronger than premolars, and they have more ridges. Molars work closely with your tongue to help you swallow food. How? The tongue sweeps chewed-up food to the back of your mouth, where the molars grind it until it's mashed up and ready to be swallowed.

As we mentioned earlier, the last teeth a person gets are wisdom teeth. These are also called third molars. They are all the way in the back of the mouth, one in each corner.

Wisdom teeth aren't used for anything and they are often removed because they can cause problems in a person's mouth. Some people believe that wisdom teeth may have been used by people millions of years ago to help them chew food. It's believed that they're called wisdom teeth because they come in later in life, when a young person is older and wiser.

Tooth Talk

Your teeth are great for chewing, but you also need them to talk. Different teeth work with your tongue and lips to help you form sounds. Try saying the word "tooth" slowly and notice how your tongue first hits the inside of your incisors to produce the hard "t" sound and then goes in between your upper and lower teeth to make the "th" sound.

And if you love to sing "la la la la la," you can thank those teeth every time you sing a song. Pay attention to what happens to your teeth and tongue every time you make the "l" sound.

Treating Teeth Kindly

Brushing your teeth with fluoride toothpaste is your best bet when it comes to keeping your teeth in tip-top shape. Try to brush after eating or at least twice a day. It's especially important to brush before bedtime.

The best way to brush your teeth is in little circles — go around and around until you have covered every surface of every tooth. Brush up and down, rather than side to side. You'll also want to clean between your teeth with dental floss (a special string for cleaning your teeth) at least once a day. That removes food and plaque (sticky stuff that can cause cavities or gum disease) that get stuck in between your teeth. You can also brush your tongue to help keep your breath fresh!

It's also important to visit your favorite tooth experts — your dentist and dental hygienist. During your appointment, they'll look out for any problems and clean and polish your teeth. Sometimes the dentist will take X-rays to get a better picture of what is going on in your mouth. You also might get a fluoride treatment while you're there.

In between dentist visits, you can prevent problems by eating fewer sugary snacks and sugary drinks, such as soda. Sugar can hurt your teeth and cause tooth decay, or cavities. But if you take care of your teeth now, you'll be chewing like a champ for the rest of your life!

Reviewed by: Kenneth H. Hirsch, DDS, and Larissa Hirsch, MD
Date reviewed: May 2007

source : http://kidshealth.org/kid/htbw/teeth.html

the dentitry

Dentistry is the "evaluation, diagnosis, prevention and/or treatment (nonsurgical, surgical or related procedures) of diseases, disorders and/or conditions of the oral cavity, maxillofacial area and/or the adjacent and associated structures and their impact on the human body". Dentistry is necessary for complete oral health. Those in the practice of dentistry are known as dentists. Other people aiding in oral health service include dental assistants, dental hygienists. dental technicians, and dental therapists.



History

Evidence of ancient dentistry has recently been found in a Neolithic graveyard in the Indus River basin of Pakistan. Teeth dating from around 7000 to 5500 BC show evidence of holes from dental drills. The teeth were found in people of the Indus Valley Civilization. A Sumerian text from 5000 BC describes a "tooth worm" as the cause of dental caries. Evidence of this belief has also been found in ancient India, Egypt, Japan, and China. The legend of the worm is also found in the writings of Homer, and as late as the 1300s AD the surgeon Guy de Chauliac still promoted the belief that worms cause tooth decay.

The Edwin Smith Papyrus, written in the 17th century BC but which may reflect previous manuscripts from as early as 3000 BC, includes the treatment of several dental ailments. In the 18th century BC, the Code of Hammurabi referenced dental extraction twice as it related to punishment. Examination of the remains of some ancient Egyptians and Greco-Romans reveals early attempts at dental prosthetics and surgery.

Ancient Greek scholars Hippocrates and Aristotle wrote about dentistry, including the eruption pattern of teeth, treating decayed teeth and gum disease, extracting teeth with forceps, and using wires to stabilize loose teeth and fractured jaws. The first use of dental appliances or bridges comes from the Etruscans from as early as 700 BC. Roman medical writer Cornelius Celsus wrote extensively of oral diseases as well as dental treatments such as narcotic-containing emollients and astringents.



Medieval dentist extracting a tooth. London; c. 1360-75.

Historically, dental extractions have been used to treat a variety of illnesses. During the Middle Ages and throughout the 19th century, dentistry was not a profession in itself, and often dental procedures were performed by barbers or general physicians. Barbers usually limited their practice to extracting teeth, which not only resulted in the alleviation of pain, but often cured a variety of ailments linked to chronic tooth infection. Instruments used for dental extractions date back several centuries. In the 14th century, Guy de Chauliac invented the dental pelican[30] (resembling a pelican's beak) which was used up until the late 18th century. The pelican was replaced by the dental key which, in turn, was replaced by modern forceps in the 20th century.[citation needed]

The first book focused solely on dentistry was the "Artzney Buchlein" in 1530, and the first dental textbook written in English was called "Operator for the Teeth" by Charles Allen in 1685. It was between 1650 and 1800 that the science of modern dentistry developed. It is said that the 17th century French physician Pierre Fauchard started dentistry science as we know it today, and he has been named "the father of modern dentistry". Among many of his developments were the extensive use of dental prosthesis, the introduction of dental fillings as a treatment for dental caries and the statement that sugar derivate acids such as tartaric acid are responsible for dental decay.



source : http://en.wikipedia.org/wiki/Dentistry