Internal pathological resorption is a rare tooth condition in which the inside of a tooth starts to break down. It often affects one tooth after injury, deep decay, or long-term inflammation, and some people have no symptoms until a dentist spots a change on an X-ray. For some, the first sign may be a pink area on the tooth, tooth pain, or sensitivity to heat and cold. Internal pathological resorption can continue over time if it is not treated, but it is not a life-threatening condition. Treatment usually aims to save the tooth with root canal care, and sometimes a crown or removal is needed if the damage is severe.
How many people live with Internal pathological resorption?
There are no reliable, widely used estimates for how many people worldwide or in the United States are living with internal pathological resorption. Published dental research usually measures how often this rare problem is found in individual teeth on dental X-rays, rather than counting affected people, so global and U.S. population totals are not consistently reported.
Overview
Internal pathological resorptionSymptoms
Internal pathological resorption often causes no symptoms at first and may be found on a dental X-ray. As it progresses, you may notice tooth pain, sensitivity, swelling, or a pinkish area on the tooth.
Outlook and prognosis
With internal pathological resorption, outlook is often good when it is found early and treated quickly, usually with root canal treatment. If damage is advanced, the tooth may become weak or need removal, so early symptoms of internal pathological resorption matter.
Causes and risk factors
Internal pathological resorption usually follows ongoing pulp inflammation, often after dental trauma, deep tooth decay, or restorative procedures. Poor oral hygiene and delayed dental care can raise risk. Clear genetic risk is not well established.
Genetic influences
Genetics do not seem to play a major, well-proven role in internal pathological resorption. In most people with internal pathological resorption, dentists look first at local triggers such as injury, inflammation, or dental procedures rather than inherited genetic variations.
Diagnosis
Internal pathological resorption is usually diagnosed with a dental exam and X-rays. If pictures are unclear, a 3D scan may help confirm the diagnosis of internal pathological resorption and show how much tooth structure is affected.
Treatment and drugs
Internal pathological resorption is usually treated by removing inflamed tissue inside the tooth with root canal treatment. If the tooth is badly weakened or perforated, repair or extraction may be needed. Early care often helps save the tooth.
Symptoms
Internal pathological resorption often causes few or no noticeable symptoms at first, so many people find out about it during a routine dental X-ray. You might notice small changes at first, but the early symptoms of internal pathological resorption are often mild or absent. When symptoms do appear, they usually involve color changes in the tooth, sensitivity, pain, or signs of infection if the damage becomes more advanced.
Many people with internal pathological resorption feel nothing unusual early on. The tooth may look normal and only show changes on a dental X-ray.
The tooth may look pink, reddish, or darker than the teeth around it. This can happen when thinning tooth structure lets the tissue inside show through.
Drinks, desserts, or brushing can trigger a sharp or lingering zing. Some may also notice sensitivity to sweets or air.
A dull ache or stronger toothache can develop if the inside of the tooth becomes more irritated or infected. Pain may come and go at first, then become more constant.
How people usually first notice Internal pathological resorption?
Internal pathological resorption is often first noticed during a routine dental X-ray, because many people with this condition do not feel anything unusual at first. When symptoms do show up, the first signs of internal pathological resorption can include a pinkish spot on the tooth, lingering tooth sensitivity, or pain if the process reaches deeper tissues or the tooth becomes inflamed. In many cases, a dentist is the first to spot it, which is why regular checkups matter even when a tooth seems completely normal.
Types of Internal pathological resorption
Internal pathological resorption can show up in a couple of recognized forms, and the differences mostly depend on what kind of tissue is being lost and what replaces it. In everyday life, many people do not notice anything at first, and the change is often found on a dental X-ray after an injury, deep decay, or long-standing inflammation inside the tooth. In medical terms, the main types of internal pathological resorption are inflammatory and replacement forms, and these variants of internal pathological resorption can differ in how quickly they progress and how likely they are to weaken the tooth.
Inflammatory type
This type happens when the inner dentin of the tooth is being broken down because inflamed pulp tissue remains active inside the root canal. Many people have no symptoms early on, but some may notice tooth pain, sensitivity, or discomfort when biting as the area grows. If it reaches the outer wall of the tooth, the tooth can become more fragile and harder to save.
Replacement type
In this less common form, the lost dentin is replaced by a hard tissue that looks more bone-like or cementum-like rather than normal tooth structure. Symptoms don’t always look the same for everyone, but this type is also often silent at first and usually shows up on imaging instead of causing clear day-to-day symptoms. Over time, the inside shape of the canal may look irregular, and treatment can be more complex because the normal canal space is partly filled in.
Can I slow down the onset of symptoms?
For internal pathological resorption, a problem where the inside of a tooth starts breaking down, there is no good evidence that lifestyle changes can meaningfully delay when symptoms begin; once it starts, it usually needs dental care rather than home measures. What may help is lowering the chance of the triggers that are linked to it, such as getting prompt care after a hit to the tooth, treating decay or infection early, and keeping up with regular dental visits, but this can reduce risk and support early detection rather than prevent the problem for sure. Early dental exams and X-rays are the main well-established way to find it before it gets worse, and while treatment can often stop further damage, it cannot guarantee that symptoms will never develop.
What genetics can tell you about symptoms
For internal pathological resorption, genetics does not currently tell doctors much about which symptoms you will have, how severe they will be, or when they will start. This condition is usually tied more closely to local tooth problems, such as injury, long-term inflammation, or damage inside the tooth, and many people have no symptoms until a dentist spots changes on an X-ray. Researchers are studying whether inherited differences in inflammation or tooth biology might slightly affect risk in some people, but these findings are not strong enough to predict day-to-day symptoms or guide care.
Causes and risk factors
Internal pathological resorption usually starts after the soft tissue inside a tooth becomes inflamed or injured. Common causes of internal pathological resorption include a past blow to the tooth, deep tooth decay, long-term infection, or irritation after dental treatment. Think of risk factors as pieces of a puzzle, not the whole picture. Poor oral hygiene, delayed dental care, and repeated stress on a tooth can raise the chance of the pulp damage that leads to internal pathological resorption. There are no strong known inherited causes, but age, overall dental health, and how badly a tooth has been injured can affect risk.
What are the most common causes or risk factors?
The most common causes of internal pathological resorption are long-lasting irritation or inflammation inside a tooth, often after a tooth injury, untreated deep tooth decay, or dental work such as large fillings or other procedures that affect the soft tissue in the center of the tooth. Less often, a crack in the tooth or serious gum disease may be linked to it. There is no clear, well-established inherited genetic risk, so for most people this problem is related to tooth damage or inflammation rather than family history.
Environmental and biological risk factors
Internal pathological resorption usually becomes more likely after the living tissue inside a tooth has been injured or irritated for some time. Doctors often group risks into internal (biological) and external (environmental). In practice, the main risk factors for internal pathological resorption are dental trauma, long-lasting pulp inflammation, and situations that let bacteria or repeated irritation reach the center of the tooth.
A blow to the mouth, a sports injury, or a tooth that has been knocked loose can injure the soft tissue inside the tooth. If that tissue stays partly alive but inflamed, internal pathological resorption is more likely to start.
A deep cavity can let bacteria move close to or into the pulp, which is the soft center of the tooth. Ongoing infection and inflammation can create the conditions that lead to internal pathological resorption.
Cracks in a tooth or gaps around an older filling or crown can allow repeated bacterial entry and irritation. Over time, that chronic irritation can keep the pulp inflamed and raise the risk.
When the pulp has been exposed during a fracture or dental treatment, the tissue may become persistently inflamed instead of fully healing. That long-running irritation can trigger the cells involved in resorption.
Genetic risk factors
If you’re wondering whether internal pathological resorption is hereditary, the answer is usually that it is not clearly inherited. Most cases appear sporadically, and no single gene has been confirmed as a common cause. Risk is not destiny—it varies widely between individuals.
Sporadic cases: Most internal pathological resorption happens without a known inherited cause. In other words, it usually does not follow a clear family pattern.
Rare syndromes: Very rare inherited conditions that affect the hard tissues of the teeth or jaw can include tooth resorption as one feature. When that happens, internal pathological resorption is usually part of a broader pattern, not the only finding.
Family history: If several close relatives have unusual tooth resorption or unexplained early tooth damage, dentists may think about an inherited predisposition. This can be more relevant when early signs of internal pathological resorption seem to cluster in one family.
Lifestyle risk factors
Lifestyle habits are not usually the primary cause of internal pathological resorption, but they can increase the chance of pulp inflammation, dental trauma, and delayed treatment that allow it to develop or worsen. When people ask about lifestyle risk factors for Internal pathological resorption, the most relevant issues are habits that raise the risk of deep decay, repeated injury, or untreated tooth damage. Good oral care and prompt dental attention can lower the chance that pulpal disease progresses to resorptive changes.
Inadequate brushing, flossing, and plaque control can increase the risk of deep tooth decay and gum disease. If decay or infection reaches the pulp, chronic inflammation may create conditions in which internal pathological resorption can begin or progress.
Frequent sugary snacks, sweet drinks, and constant grazing raise the risk of cavities. When decay advances toward the pulp, the resulting inflammation can make internal pathological resorption more likely.
Ignoring toothache, discoloration, or a history of dental injury can allow pulpal inflammation to persist for longer. That delay may give internal pathological resorption more time to enlarge before it is detected and treated.
Contact sports without a mouthguard and habits that increase falls or facial injury can raise the chance of tooth trauma. A previously injured tooth may develop pulpal damage that later contributes to internal pathological resorption.
Risk prevention
Internal pathological resorption cannot always be fully prevented, because it often starts after hidden irritation or injury inside a tooth. In day-to-day life, prevention mostly means lowering the chance of tooth damage and catching changes early, before the tooth weakens or breaks. Prevention works best when combined with regular check-ups. Many living with internal pathological resorption have no warning signs at first, so early dental care matters more than waiting for pain.
Regular dental visits help spot internal pathological resorption before it causes major damage. Small changes are often seen on dental X-rays even when the tooth feels normal.
A hit to the mouth from sports, a fall, or an accident can irritate the tissue inside a tooth and raise the risk of internal pathological resorption. Getting injured teeth checked quickly can lower the chance of long-term damage.
Deep cavities or untreated cracks can inflame the center of the tooth and make internal pathological resorption more likely. Prompt treatment of decay, leaking fillings, and broken teeth helps protect the pulp.
Wearing a mouthguard for contact sports or grinding can reduce repeated stress on teeth. Prevention isn’t about perfection, it’s about small steps that add up.
Can you prevent Internal pathological resorption?
You cannot always prevent internal pathological resorption, which is when a tooth starts to break down from the inside, but some cases may be less likely with early dental care. The most helpful steps are treating tooth injuries, deep cavities, and long-lasting tooth irritation or infection promptly, and keeping up with regular dental checkups. Getting pain, swelling, or a tooth that suddenly changes color checked early may also help limit damage.
Transmission
Internal pathological resorption cannot be transferred from one person to another, and it is not an infectious condition. If you are wondering whether internal pathological resorption is contagious, the answer is no; it develops inside a tooth, usually after irritation or damage to the tissue in the center of the tooth.
For many living with internal pathological resorption, this means there is no risk of “catching” it through kissing, sharing food, or close contact. It is also not generally thought of as an inherited condition, because it is usually linked to changes within the affected tooth rather than parent-to-child transmission.
When to test your genes
For internal pathological resorption, genetic testing is not part of early detection or personalized care because this condition is usually linked to local tooth injury, inflammation, or prior dental treatment, not inherited gene changes. What matters most is prompt dental evaluation and imaging if a tooth shows unexplained color change, pain, or root changes.
Diagnosis
Internal pathological resorption is usually found during a dental exam after a tooth changes color, feels sensitive, or shows up as an unexpected finding on an X-ray. This condition starts inside the tooth, so the diagnosis of internal pathological resorption often depends on imaging as well as what your dentist sees during the exam. Some diagnoses are clear after a single visit, while others take more time.
Your dentist will ask about tooth pain, past injury, deep decay, or earlier dental treatment. These details help show whether irritation or damage inside the tooth may have triggered the process.
The tooth is checked for color change, cracks, swelling, or tenderness when tapped. Dentists also look for signs that the nerve inside the tooth may be inflamed or no longer healthy.
Simple tests using cold, heat, or gentle electrical stimulation can show how the tooth nerve is responding. This helps your dentist judge whether the pulp is still alive and whether root canal treatment may be needed.
Regular dental X-rays are a key part of how internal pathological resorption is diagnosed. They may show a rounded area inside the root canal space where tooth structure has been lost.
How is Internal pathological resorption diagnosed?
Internal pathological resorption is usually diagnosed by a dentist, sometimes with help from a root canal specialist, after looking at the tooth and taking dental X-rays. Many living with this condition have no clear symptoms and it is found by chance on an X-ray, but if the picture is not clear, the dentist may use a 3D dental scan to see the damage inside the tooth and how far it has spread.
Stages of Internal pathological resorption
Internal pathological resorption does not have defined progression stages. This is because it is usually described by how much of the inside of the tooth has been affected on dental imaging, rather than by a standard step-by-step pattern that everyone goes through over time. Often the process begins when you notice changes in daily life, such as a tooth becoming sensitive, changing color, or being found unexpectedly on an X-ray during a routine dental visit. Dentists usually diagnose and monitor internal pathological resorption with a dental exam and imaging, and the early symptoms of internal pathological resorption can be mild or absent, so repeat scans may be used to check whether it is staying stable or getting worse.
Outlook and prognosis
The outlook for internal pathological resorption is generally good when it is found early and treated promptly, usually with root canal therapy or other endodontic care that removes the inflamed tissue and seals the defect. Prognosis depends mainly on how much tooth structure has already been lost, whether the resorption has perforated the root, and whether there is associated infection or fracture. Small, non-perforating lesions often allow long-term retention of the tooth, while advanced cases may have a guarded prognosis and sometimes require extraction if the tooth cannot be restored. Regular follow-up with clinical exams and dental imaging is important because progression can be silent until substantial damage has occurred. This condition is not associated with systemic mortality, and the main risks are tooth weakening, loss of the affected tooth, and the need for more complex dental treatment if diagnosis is delayed.
Long-term effects
Internal pathological resorption can quietly weaken a tooth over time, sometimes with no clear warning until a dentist spots it on an X-ray. If it is found early and treated, many people keep the tooth and avoid more serious damage. Long-term effects vary widely, depending on how much tooth structure has been lost and whether the problem has reached the outer root surface.
Internal pathological resorption can hollow out the inside of a tooth and make it more fragile over time. For many, this can mean a higher chance of cracking during normal biting or later dental treatment.
If the resorption keeps progressing, it may break through the wall of the root or crown. Once that happens, treatment becomes harder and the long-term outlook for saving the tooth is less certain.
Some people develop a pink, red, gray, or darker change in the tooth as the inside structure is altered. This color change may be one of the early symptoms of internal pathological resorption, although many teeth still cause no pain.
Internal pathological resorption is often painless at first, but later it can lead to sensitivity, toothache, or pain when biting. If the pulp dies or bacteria enter the area, an abscess or ongoing infection can develop.
How is it to live with Internal pathological resorption?
Living with internal pathological resorption can feel unsettling because a tooth may look normal for a while, yet changes are happening quietly from the inside. Many people have no symptoms at first, but some notice tooth discoloration, sensitivity, pain, or tenderness when chewing, which can make eating and daily oral care more stressful. In day-to-day life, the biggest impact is often the need for dental visits, imaging, and treatment to save the tooth if possible, since delaying care can weaken the tooth and increase the chance of fracture or tooth loss. For people around you, the effects are usually indirect, such as helping with appointments, costs, or emotional support, and the good news is that this condition is not contagious.
Treatment and drugs
Internal pathological resorption is treated by stopping the loss of tooth structure as early as possible, usually with dental procedures rather than medicines alone. If the inside of the tooth is affected and the tooth can still be saved, treatment often involves root canal therapy to remove the damaged tissue and seal the space; if the damage is too extensive, the tooth may need to be removed. If there is pain, swelling, or infection, dentists may use pain relievers and sometimes antibiotics, but these do not fix the resorption itself. Finding the right therapy can take some time, because treatment for internal pathological resorption depends on how far it has progressed, whether the outer tooth wall has been perforated, and whether nearby bone or gum tissue is involved.
Can you cure Internal pathological resorption?
Internal pathological resorption usually cannot be cured in the sense of reversing damage that has already happened inside the tooth. But a dentist can often stop it from getting worse with treatment such as a root canal, and if the damage is severe, surgery or removing the tooth may be needed. The sooner it is found, the better the chance of saving the tooth.
Non-drug treatment
Internal pathological resorption can quietly weaken a tooth from the inside, often after inflammation or injury to the pulp, the soft tissue in the center. Many people do not notice symptoms at first, so care often focuses on stopping the process, preserving the tooth, and restoring strength and comfort. For many, treatment begins not at the dental office alone, but with careful follow-up and good daily oral care to protect the treated tooth and the surrounding gums.
This is the main non-drug treatment for internal pathological resorption because it removes the inflamed or damaged pulp tissue driving the process. Cleaning and sealing the root canal space can help stop further tooth breakdown and lower the chance of pain or infection.
After the inside of the tooth is treated, a filling or crown may be used to rebuild strength and reduce the risk of cracking. This can matter in day-to-day life, such as when biting into firm foods or chewing on that side.
Regular dental X-rays and, in some cases, 3D scans help your dentist check whether internal pathological resorption has stopped and whether the tooth remains stable. This is especially important because early symptoms of internal pathological resorption may be mild or absent.
Gentle brushing, daily flossing, and routine dental cleanings help protect the tooth and surrounding gum tissue after treatment. Simple routines-like brushing twice a day and keeping dental visits-can have lasting benefits.
Your genes may have an impact on how drugs work for you
For internal pathological resorption, treatment is usually based more on dental procedures than on long-term medicine, so genes do not play as central a role as they do in some other conditions. Still, natural differences in how the body handles medicines can affect how well some people respond to pain relievers, numbing medicine used during treatment, or antibiotics if an infection is present, which may change how strong the effect feels or how likely side effects are. In everyday care, though, genetic testing is not a routine part of treating this condition, and dentists usually adjust treatment based on your symptoms, exam findings, and how you respond.
Pharmacological treatments
Internal pathological resorption is usually not treated with medicine alone, because the main problem is damage inside the tooth that often needs dental treatment such as root canal care. Medicines are mostly used to control pain, numb the area, lower inflammation, or manage infection when it is present. Some dentists also place medicated material inside the tooth during treatment to help stop ongoing tissue breakdown. If you are wondering about the best medication for internal pathological resorption, the answer often depends on whether there is pain, infection, or a planned dental procedure.
Dentists often use numbing medicines such as lidocaine or articaine so treatment can be done comfortably. These drugs do not treat the resorption itself, but they make procedures like root canal treatment much easier to tolerate.
Ibuprofen or naproxen may help with dental pain and swelling, and acetaminophen can also be used for pain relief. Some medicines work quickly, while others are mainly used for short-term comfort after treatment.
Antibiotics such as amoxicillin, amoxicillin-clavulanate, or clindamycin are not routine for internal pathological resorption on its own. They may be prescribed if there is a clear dental infection with swelling, fever, or spread into nearby tissues.
Calcium hydroxide may be placed inside the root canal between visits as a medicated dressing. It helps reduce bacteria and can support treatment when the tooth pulp is inflamed or infected.
Genetic influences
When people look into the causes of internal pathological resorption, family history often comes up. It’s natural to ask whether family history plays a role. At this point, internal pathological resorption is not thought to be a condition that is usually inherited, and there is no single gene known to cause most cases. Instead, it is more often linked to changes inside one tooth after injury, long-lasting inflammation of the inner soft tissue, deep decay, or sometimes dental treatment. Genetics may still have a small background effect on how tissues respond to inflammation or repair damage, but that link has not been clearly defined for internal pathological resorption. For most people with internal pathological resorption, the more useful clues are the tooth’s history, dental X-rays, and the dentist’s exam rather than a pattern across the family.
Is Internal pathological resorption genetic?
Genetics do not seem to play a major, well-proven role in internal pathological resorption. In most people with internal pathological resorption, dentists look first at local triggers such as injury, inflammation, or dental procedures rather than inherited genetic variations.
Having a genetic risk is not necessarily a diagnosis
Changes in genes are a normal part of being human and are widely seen across the population. Most of these changes do not directly affect health and simply reflect natural differences among people. For many genes, having a change tied to a condition points to a possible link, not a certain diagnosis, particularly when several genes and outside factors play a role. In some situations, though, one well-studied change in a certain gene is enough to confirm a diagnosis.
Pharmacogenetics—how genetics influence drug effects
For many, the biggest question is whether treatment for internal pathological resorption will stop the damage quickly enough to save the tooth. In most cases, genetics do not decide the main treatment, because dentists choose care based mostly on where the damage is, how far it has spread, and whether the tooth can still be repaired, often with root canal treatment or, in severe cases, removal. Not every difference in response is genetic, but inherited differences can affect how your body handles some medicines used around dental treatment, including certain pain relievers and, less often, some anesthetics. For example, some people break down codeine or tramadol unusually fast or unusually slowly, which can make these drugs work poorly or raise the risk of side effects. This means genetics may matter more for comfort and medication safety than for the core treatment for internal pathological resorption itself. Genetic testing is not a routine part of care for internal pathological resorption, but it may be worth discussing if you have had unusual reactions to medicines or if pain medicines have not worked as expected in the past.
Interactions with other conditions
Internal pathological resorption often does not happen in isolation. It is most often linked with ongoing inflammation inside the tooth, especially after dental trauma, deep decay, repeated dental procedures, or long-standing infection of the pulp, which is the soft tissue in the center of the tooth. Doctors call it a “comorbidity” when two conditions occur together, and in this case internal pathological resorption may appear alongside pulpitis, tooth infection, or damage after an injury. Someone might notice tooth pain or color change after a blow to the mouth, only to learn that the injured tooth also developed this quiet, inside-the-tooth breakdown. If internal pathological resorption is not found early, it can weaken the tooth and raise the chance of a crack, abscess, or spread of infection into the tissues around the root. In general, internal pathological resorption is not strongly tied to most body-wide diseases, but people living with conditions that affect healing or infection control may need closer dental follow-up if tooth damage or infection is present.
How genes can cause diseases
Humans have more than 20,000 genes, each carrying out one or a few specific functions in the body. One gene instructs the body to digest lactose from milk, another tells the body how to build strong bones and another prevents the body's cells from beginning to multiply uncontrollably and developing into cancer. As all of these genes combined are the building instructions for our body, a defect in one of these genes can have severe health consequences.
Through decades of genetic research, we know the genetic code of any healthy/functional human gene. We have also identified that in certain positions on a gene, some individuals may have a different genetic letter from the one you have. We call these hotspots "Genetic Variations" or "Variants" in short. In many cases, studies have been able to show that having the genetic letter "G" in the position makes you healthy, but having the letter "A" in the same position disrupts the gene function and causes a disease. Genopedia allows you to view these variants in genes and summarizes all that we know from scientific research, which genetic letters (Genotype) have good or bad consequences on your health or on your traits.
What other conditions can cause similar symptoms to Internal pathological resorption?
Tooth decay, a cracked tooth, and irritation or infection in the soft center of the tooth can all cause similar pain, sensitivity, or color changes. Dentists also need to tell it apart from damage that wears away the tooth from the outside, called external resorption, because it can look similar on an exam or dental X-ray. In many cases, the difference is only clear after a close dental exam and imaging.
History
People living with internal pathological resorption often do not know anything is happening until a dental X-ray shows a change inside a tooth, or a dentist notices a pinkish area near the crown. That quiet, hidden nature is one reason the condition took time to understand. Dentists and pathologists first recognized unusual loss of tooth tissue from the inside many decades ago, but early reports could only describe what was seen after symptoms appeared or after a tooth was removed.
As medical science evolved, doctors became better at separating internal pathological resorption from other causes of tooth damage, especially decay and wear on the outside of the tooth. Earlier descriptions were sometimes grouped together with other resorptive dental problems, which made the picture less clear. Over time, better dental imaging and closer study of tooth structure showed that this process begins within the pulp space, where the soft tissue and blood supply of the tooth sit, and then can slowly eat into the harder tooth tissue around it.
This clearer understanding changed how dentists think about early symptoms of internal pathological resorption. Many people with internal pathological resorption have no pain at first, while others may notice tooth sensitivity, mild discomfort, or changes in color. In some cases, a person goes in for routine care and learns that a tooth with an old injury, deep decay, inflammation, or prior dental treatment has developed this problem. That link with inflammation and damage inside the tooth became more widely accepted as dental research improved.
In recent decades, awareness has grown because modern X-rays, 3D scans, and improved endodontic care have made internal pathological resorption easier to spot earlier and treat more precisely. Researchers later identified that tooth biology and healing responses play an important role, although the full process is still being studied. Knowing the condition’s history helps explain why regular dental checkups matter: what was once easy to miss can now often be found before the tooth becomes badly weakened.