It depends on which tooth it is and how rotten it is. You may have to have it pulled. You need to take care of it immediately, though. There was a 12 year old boy who died from an infected tooth. It was in the news yesterday. The infection spread to his brain. Go to the dentist immediately.
I have a rotten tooth in the back of my mouth but i have no pain. will i need a root canal or just a filling?
well, it depends on how deep the cavity is.....
Reply:so funny that u ask this cuz i just went to the dentist on monday for the same reason only i had pain. if there is no pain probably not going to need a root canal but if you let it go too long like i did and pain starts you will need one and let me tell you they are not cheap or painless to get. so get to the dentist my best advice and get that thing filled asap.
Reply:Root canals are the long passages full of soft tissue deep within the dentin of a tooth, adjoining the pulp chamber. In dentistry, a pulpectomy is an endodontic treatment to cure an infection of the root canal; informally a root canal. A root canal, coupled with internal tooth bleaching, is also used to fix teeth that have blackened because of infiltration of decayed soft tissue into the dentin in the teeth, most often seen in frontal incisors that have been injured through a sudden impact.
 Tooth structure
At the center of a tooth is a hollow area that houses soft tissue, known as pulp. This hollow area contains a relatively wide space towards the chewing surface of the tooth called the pulp chamber. This pulp chamber is connected to the tip of the root of the tooth via thin hollow pipe-like canals—hence, the term "root canal". Human teeth normally have one to four canals, with teeth toward the back of the mouth having the most. These canals run through the centre of the roots like pencil lead runs through the length of a pencil. The tooth receives nutrition through the blood vessels and nerves traversing these canals. Occasionally, a cavity on the outside of the tooth may allow this soft tissue to become infected. If left untreated, a serious jaw infection can result. The infection and inflammation is very painful in most cases. Treatment should take place before this happens.
 Root canal treatment
Sometimes a tooth is considered so threatened (because of internal cracking, etc.) that future infection is considered likely or inevitable, and a pulpectomy is advisable to prevent it. But usually some inflammation and/or infection is already present, within or below the tooth. To cure the infection and save the tooth, it is necessary for the dentist to drill into the pulp chamber, and remove the infected pulp by scraping it out of the root canals. Once that is done, the dentist fills the cavity with an inert material and seals up the opening. This procedure is known as root canal therapy. If enough of the tooth has been damaged, or removed as a result of the treatment, a crown may be required.
The standard filling material is Gutta-percha, a thermoplastic polymer of isoprene, which is melted and injected to fill the root canal passages. Barium is added to the isoprene so the material will be opaque to X-rays, allowing verification afterwards that the passages have been properly completely filled in, without voids.
Lower right first molar (center) after root canal therapy and crown: right-most two nerves have incomplete root canal and may need further therapy.For patients, root canal therapy is one of the most feared procedures in all of dentistry; dental professionals assert that modern root canal treatment is relatively painless because the pain can be controlled. Lidocaine is a commonly used local anesthetic. Pain control medication may be used either before or after treatment. However, in some cases it may be very difficult to achieve pain control before performing a root canal. For example, if a patient has an abscessed tooth, with a swollen area or "fluid-filled gum blister" next to the tooth, the pus in the abscess may contain acids that inactivate any anesthetic injected around the tooth. In this case, it is best for the dentist to drain the abscess by cutting it to let the pus drain out. Releasing the pus releases pressure built up around the tooth; this pressure causes much pain. The dentist then prescribes a week of antibiotics such as penicillin, which will reduce the infection and pus, making it easier to anesthetize the tooth when the patient returns one week later. The dentist could also open up the tooth and let the pus drain through the tooth, and could leave the tooth open for a few days to help relieve pressure. At this first visit, the dentist must ensure that the patient is not biting into the tooth, which could also trigger pain. Sometimes the dentist performs preliminary treatment of the tooth by removing all of the infected pulp of the tooth and applying a dressing and temporary filling to the tooth. This is called a "pulpectomy". The dentist may also remove just the coronal portion of the dental pulp, which contains 90% of the nerve tissue, and leave intact the pulp in the canals. This procedure, called a "pulpotomy", tends to essentially eliminate all the pain. A "pulpotomy" may be a relatively definitive treatment for infected primary teeth. The pulpectomy and pulpotomy procedures eliminate most all pain until the follow-up visit for finishing the root canal. But if the pain returns, it means any of three things: the patient is biting into the tooth, there is still a significant amount of sensitive nerve material left in the tooth, or there is still more pus building up inside and around the infected tooth. All of these cause pain.
Lower right first molar (center) after root canal therapy, this time complete and without crownAfter removing as much of the internal pulp as possible, the root canals can be temporarily filled with calcium hydroxide paste. This strong alkaline base is left in for a week or more to disinfect and reduce inflammation in surrounding tissue . Ibuprofen taken orally is commonly used before and/or after these procedures to reduce inflammation.
After receiving a root canal, the tooth should be protected with a crown that covers the cusps of the tooth. Otherwise, over the years the tooth will almost certainly fracture, since root canals remove tooth structure from the tooth and undermine the tooth's structural integrity. Also, root canal teeth tend to be more brittle than teeth not treated with a root canal. This is commonly due to the fact that the blood supply to the tooth, which nourishes and hydrates the tooth structure, is removed during the root canal procedure, leaving the tooth without a source of moisture replenishment. Placement of a crown or cusp-protecting cast gold covering is recommended also because these have the best ability to seal the root canaled tooth. If the tooth is not perfectly sealed, the root canal may leak, causing eventual failure of the root canal. Also, many people believe once a tooth has had a root canal it cannot get decay. This is not true. A tooth with a root canal still has the ability to decay, and without proper home care and an adequate fluoride source the tooth structure can become severely decayed – without the patient's knowledge since the nerve has been removed, leaving the tooth without any pain perception. Therefore it is very important to have regular X-rays taken of the root canal to ensure that the tooth is not having any problems that the patient would not be aware of.
The procedure is often complicated, depending on circumstances, and may involve multiple visits over a period of weeks. The cost is high, by local standards. In the United States, it would typically cost US$400-1,000—though exceeded by the even more expensive related crown procedure, typically around US$500-1,500 with usually only 50% being covered by the dental insurer (DMO or DPO). In India, the root canal procedure would typically cost INR 1,500, when performed by an endodontist — and the crown procedure, for a ceramic crown, would cost around INR 2,000.
In the last ten to twenty years, there have been great innovations in the art and science of root canal therapy. Dentists now must be educated on the current concepts in order to optimally perform a root canal. Root canal therapy has become more automated and can be performed faster, thanks to advances in automated mechanical instrumentation of teeth and more advanced root canal filling methods. Dentists also possess newer technologies that allow more efficient, scientific measurements to be taken of the dimensions of the root canal that must be filled. Many dentists use microscopes to perform root canals, and the consensus is that root canals performed using microscopes or other forms of magnification are more likely to succeed than those performed without them. Although general dentists are becoming versed in these advanced technologies, they are still more likely to be used by specialist root canal doctors (known as endodontists). Dr. Arnaldo Castellucci, an Italian dentist, has recently authored a three-volume treatise on endodontics which thoroughly covers these modern concepts.
Laser root canal procedures are a controversial innovation. Lasers may be fast but not thoroughly disinfect the whole tooth, and may cause damage .
Sometimes root canals fail. Patients should be educated on some of the reasons why root canals may fail. They may fail if the dentist does not find, clean and fill all of the root canals within a tooth. For example, on a top molar tooth, there is a more than 50% chance that the tooth has four canals instead of just three. But the fourth canal, often called a "mesio-buccal 2 (MB2)", tends to be very difficult to see and often requires special instruments and magnification in order to see it. So it may be missed, and this infected canal may cause a continued infection or "flare up" of the tooth. Any tooth may have more than one canal, which may be missed while performing the root canal. Sometimes the canal may be unusually shaped, making it impossible to fill it completely, so that some infected material is still left in the canal. Sometimes the canal filling does not extend deeply enough into the canal, or it does not fill the canal as much as it should. Sometimes a tooth root may be perforated while the root canal is being performed, making it difficult to fill the tooth. The hole may be filled with a material derived from natural cement called "MTA", although usually a specialist would perform this procedure. Fortunately, a specialist can often re-treat and definitively heal up these teeth, often years after the initial root canal procedure.
 Systemic issues
An infected tooth may endanger other parts of the body. People with special vulnerabilities, such as prosthetic joint replacement or mitral valve prolapse, may need to take antibiotics to protect from infection spreading during dental procedures. Both endodontic therapy and tooth extraction can lead to subsequent jaw bone infection, such as Neuralgia Inducing Cavitational Osteonecrosis . The American Dental Association (ADA) asserts that any risks can be adequately controlled .
Claims have been made that it is impossible to fully sterilize a tooth internally, or fill it in a perfectly inert biocompatible permanent fashion. There is an ongoing risk of infection, which may pose dangers to the rest of the body. But there is generally no satisfactory alternative. Pulling the tooth leaves a gap which poses both aesthetic and functional problems, and endangers the structure of the adjacent teeth . 
 Advice for patients requiring root canal treatment
If a tooth requires root canal treatment it is unlikely that any other form of therapy (other than extraction of the tooth) will be successful in the long term.
In the short term, for controlling pain and discomfort, many over the counter NSAIDs (non-steroidal anti-inflammatory drugs) such as ibuprofen can be used.
In certain cases (if prescribed by the dentist) antibiotic therapy may be of benefit to control a severe infection of the tooth.
Despite popular belief to the contrary, modern root canal treatment can be performed quite comfortably. Avoiding or delaying the treatment can reduce the chances of a positive outcome for the infected tooth.
Dental fillings are inserted as restorations in the treatment of dental cavities, after drilling out the cavities. The purpose of drilling is to remove the enamel and dentin that has had its structural integrity compromised by the invasion of acid-producing bacteria. However, once the infected hard tissues have been removed, the resulting cavity preparation must be filled in order to restore structural integrity to the tooth. This will prevent further damage to the tooth and hopefully avoid the eventual need for the tooth to be extracted.
Amalgam fillings, (also called silver fillings) are a mixture of mercury (from 43% to 54%) and powdered alloy made mostly of silver, tin, zinc and copper commonly called the amalgam alloy., Due to the known toxicity of the element mercury, there is some controversy about the use of Amalgams. see Amalgam controversy
The Chinese were the first to use a silver amalgam to fill teeth in the 7th century; in 1816, Auguste Taveau developed his own dental amalgam from silver coins and mercury. This amalgam contained a very small amount of mercury and had to be heated in order for the silver to dissolve at an appreciable rate. Taveau's formula offered lower cost and greater ease of use compared to existing materials such as gold, but had many practical problems, including a tendency to significantly expand after setting. Because of these problems, this formula was abandoned in France. In 1833, however, two untrained Europeans, the Crawcour brothers, brought Taveau's amalgam to the United States under the name "Royal Mineral Succedaneum"
 Gamma 2 phase amalgams
After widespread adoption and wildly varying standards, the multitude of formulas for making amalgams were standardised into the gamma-2-phase amalgam formula in 1895.
The gamma-2-phase amalgams contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:
%26gt; 65% silver (Ag)
%26lt; 29% tin (Sn)
%26lt; 6% copper (Cu)
%26lt; 2% zinc (Zn)
%26lt; 3% mercury (Hg)
The resulting amalgam is composed of the gamma phase (the silver-tin eutectic Ag3Sn, which reacts with mercury, yielding the gamma-1 phase (Ag2Hg3) and gamma-2 phase (Sn7-8Hg). The gamma phase is prone to corrosion and its mechanical strength is low. The alloy tends to undergo crevice corrosion and form local galvanic cells.
Around 1970, the ingredients changed to the new non-gamma-2 form, with lower manufacturing cost, greater mechanical strength, and better corrosion resistance. The reduced-gamma-2 amalgams (sometimes referred to as "high-copper" amalgams) contain approximately equal parts 50% of liquid mercury and 50% of an alloy powder containing:
%26gt; 40% silver (Ag)
%26lt; 32% tin (Sn)
%26lt; 30% copper (Cu)
%26lt; 2% zinc (Zn)
%26lt; 3% mercury (Hg)
The amalgam alloy is strengthened by presence of Ag-Cu particles. The gamma-2 phase reacts with the Ag-Cu particles to form eta phase Cu6Sn5 and gamma-1 phase.
The possible difference in toxicology between the two has not been studied conclusively. Amalgams continue to be used today because they are hard, durable and inexpensive.
 Galvanic shock
When aluminium foil makes contact with some amalgam fillings, saliva in the mouth can act as an electrolyte. This can generate small electrical currents which are felt through the nerves in the tooth as (often extremely painful) electrical "jolts" or shocks.
 Composite resin (also called white or plastic filling )
Composite resin fillings are a mixture of powdered glass and plastic resin, and can be made to resemble the appearance of the natural tooth. They are strong, durable and cosmetically superior to silver or dark grey colored amalgam fillings. Composite resin fillings are usually more expensive than silver amalgam fillings. Bis-GMA based materials contain Bisphenol A a known endocrine disrupter chemical. PEX based materials do not.
Most modern composite resins are light-cured photopolymers. Once the composite hardens completely, the filling can then be polished to achieve maximum aesthetic results. Composite resins experience a very small amount of shrinkage upon curing, causing the material to pull away from the walls of the cavity preparation. This makes the tooth slightly more vulnerable to microleakage and recurrent decay. With proper technique and material selection, microleakage can be minimized or eliminated altogether.
Besides the aesthetic advantage of composite fillings over amalgam fillings, the preparation of composite fillings requires less removal of tooth structure to achieve adequate strength. This is because composite resins bind to enamel (and dentin too, although not as well) via a micromechanical bond. As conservation of tooth structure is a key ingredient in tooth preservation, many dentists prefer placing composite instead of amalgam fillings whenever possible.
Generally, composite fillings are used to fill a carious lesion involving highly visible areas (such as the central incisors or any other teeth that can be seen when smiling) or when conservation of tooth structure is a top priority.
Composite resin fillings require a clean and dry surface to bond correctly with the tooth, so cavities in areas that are harder to keep totally dry during the filling procedure may require a less moisture-sensitive filling. The use of a rubber dam is highly recommended.
 Glass Ionomer Cement
These fillings are a mixture of glass and an organic acid. Although they are tooth-colored, glass ionomers vary in translucency. Although glass ionomers can be used to achieve an aesthetic result, their aesthetic potential does not measure up to that provided by composite resins.
The cavity preparation of a glass ionomer filling is the same as a composite resin; it is considered a fairly conservative procedure as the bare minimum of tooth structure should be removed.
Conventional glass ionomers are chemically set via an acid-base reaction. Upon mixing of the material components, there is no light cure needed to harden the material once placed in the cavity preparation. After the initial set, glass ionomers still need time to fully set and harden.
Glass ionomers do have their advantages over composite resins:
1. They are not subject to shrinkage and microleakage, as the bonding mechanism is an acid-base reaction and not a polymerization reaction.
2. Glass ionomers contain and release fluoride, which is important to preventing carious lesions. Furthermore, as glass ionomers release their fluoride, they can be "recharged" by the use of fluoride-containing toothpaste. Hence, they can be used as a treatment modality for patients who are at high risk for caries. Newer formulations of glass ionomers that contain light-cured resins can achieve a greater aesthetic result, but do not release fluoride as well as conventional glass ionomers.
Glass ionomers are about as expensive as composite resin. The fillings do not wear as well as composite resin fillings. Still, they are generally considered good materials to use for root caries and for sealants.
 Resin modified Glass-Ionomer Cement
A combination of glass-ionomer and composite resin, these fillings are a mixture of glass, an organic acid, and resin polymer that harden when light cured. (The light activates a catalyst in the cement that causes it to cure in seconds.) The cost is similar to composite resin. It holds up better than glass ionomer, but not as well as composite resin, and is not recommended for biting surfaces of adult teeth.
In general, resin modified glass-ionomer cements can achieve a better aesthetic result than conventional glass ionomers, but not as good as pure composites.
 Porcelain (ceramic)
Porcelain fillings are hard, but can cause wear on opposing teeth. They are brittle and are not always recommended for molar fillings.
Gold fillings have excellent durability, wear well, and do not cause excessive wear to the opposing teeth, but they do conduct heat and cold, which can be irritating. There are two categories of gold fillings, cast gold fillings ( gold inlays and onlays ) made with 14 or 18 kt gold, and gold foil made with pure 24 kt gold that is burnished layer by layer. For years, they have been considered the benchmark of restorative dental materials. Recent advances in dental porcelains and consumer focus on aesthetic results have caused demand for gold fillings to drop in favor of advanced composites and porcelain veneers and crowns. Gold fillings are usually quite expensive, although they do last a very long time. It is not uncommon for a gold crown to last 30 years in a patient's mouth.
 Other historical fillings
Lead fillings were used in the 1700s, but became unpopular in the 1800s because of their softness. This was before lead poisoning was understood.
According to U.S. Civil War-era dental handbooks from the mid-1800s, since the early 1800s metallic fillings had been used, made of lead, gold, tin, platinum, silver, aluminum, or amalgam. A pellet was rolled slightly larger than the cavity, condensed into place with instruments, then shaped and polished in the patient's mouth. The filling was usually left "high", with final condensation — "tamping down" — occurring while the patient chewed food. Gold foil was the most popular and preferred filling material during the Civil War. Tin and amalgam were also popular due to lower cost, but were held in lower regard.
One survey of dental practices in the mid-1800s catalogued dental fillings found in the remains of seven Confederate soldiers from the U.S. Civil War; they were made of:
Gold foil: Preferred because of its durability and safety.
Platinum: Was rarely used because it was too hard, inflexible and difficult to form into foil.
Aluminum: A material which failed because of its lack of malleability but has been added to some amalgams.
Tin and iron: Believed to have been a very popular filling material during the Civil War. Tin foil was recommended when a cheaper material than gold was requested by the patient, however tin wore down rapidly and even if it could be replaced cheaply and quickly, there was a concern, specifically from Harris, that it would oxidise in the mouth and thus cause a recurrence of caries. Due to the blackening, tin was only recommended for posterior teeth.
Thorium: Radioactivity was unknown at that time, and the dentist probably thought he was working with tin
Lead and tungsten mixture, probably coming from shotgun pellets. Lead was rarely used in the 19th century, it is soft and quickly worn down by mastication, and had known harmful health effects.
Amalgam: The most popular amalgam was a mixture of silver, tin and mercury. According to the authors of the article " It set very hard and lasted for many years, the major contradiction being that it oxidized in the mouth, turning teeth black. Also the mercury contained in the amalgam was thought at that time to be harmful." as explained in the pre-eminent dental textbook of that century, The Principles and Practice of Dental Surgery by Chapin A. Harris A.M., M.D., D.D.S.. 
 Replacement fillings
Fillings have a finite lifespan: an average of 12.8 years for amalgam and 7.8 years for composite resins . Fillings fail because of changes in the filling, tooth or the bond between them.
Amalgam fillings expand with age, possibly cracking the tooth and requiring repair and filling replacement. Composite fillings shrink with age and may pull away from the tooth allowing leakage. As chewing applies considerable pressure on the tooth, the filling may crack, allowing seepage and eventual decay in the tooth underneath.
The tooth itself may be weakened by the filling and crack under the pressure of chewing. That will require further repairs to the tooth and replacement of the filling.
If fillings leak or the original bond inadequate, the bond may fail even if the filling and tooth are otherwise unchanged.
Reply:If the tooth is rotten it will probably need to be filled. If it just has a cavity and is not rotten as you say then they will just fill it. See your dentist to get this checked out before it causes problems.
Reply:I had a deep cavity (with pain). Luckily, It just needed a filling, but dentist said if it had gone deeper to the pulp, it would have needed a lot more. Better to get it filled before it gets any bigger.
Reply:It depends on whether the cavity has reached the root or not.
I asked the same question from my dentist and he said that you could figure it out by tapping lightly on the tooth and if it results in pain then the cavity has probably reached the root.
Reply:Consider yourself lucky.
Pain from a cavity results from the decay getting involved in the nerve chamber. While you may have a large cavity, it may involved more surface area, rather than depth. (where the nerve is).
See your dentist asap. You may still have time before the decay gets to the nerve, therefore avoiding the need for a root canal, but the longer you wait, the bigger chance you take. Dentists can do a treatment if the decay is close to the nerve called a pulp cap, which is essentially a liner between the tooth and the filling.