Tooth resorption

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Root resorption
Specialty Dentistry

Tooth resorption, or root resorption, is the progressive loss of dentine and cementum by the action of osteoclasts. [1] This is a normal physiological process in the exfoliation of the primary dentition, caused by osteoclast differentiation due to pressure exerted by the erupting permanent tooth. However, in the secondary dentition the process is pathological.



Pulp necrosis, trauma, periodontal treatment, orthodontics and tooth whitening are the most common stimulants of inflammatory resorption. [2] Some other less common causes include pressure from ectopic teeth, cysts, and tumours. These cause damage to the periodontal ligament (PDL), cementum, or pre-dentine. These tissues provide protection from resorption when intact and healthy.

Regardless of the reason, tooth resorption is due to an inflammatory process in response to an insult on one of the above. [3] [4]


Osteoclasts are the cells responsible for the resorption of the root surface. [5] Osteoclasts can break down bone, cartilage and dentine.

Receptive activator of nuclear factor kappa-B ligand (RANKL), also called osteoclast differentiation factor (ODF) and osteoprotegerin ligand (OPGL), is a regulator of osteoclast function. [6] [7] In physiological bone turn over, osteoblasts and stromal cells release RANKL, this acts on macrophages and monocytes which fuse and become osteoclasts. [8] Osteoprotegerin (OPG) is also secreted by osteoclasts and stromal cells; this inhibits RANKL and therefore osteoclast activity.

The pathophysiology of stimulation of osteoclasts in the process of inflammatory resorption is unknown.

One thought is that the presence of bacteria plays a role. Bacterial presence leads to pulpal or peri-periapical inflammation. These bacteria are not mediators of osteoclast activity but do cause leukocyte chemotaxis. Leukocytes differentiate into osteoclasts in the presence of lipopolysaccharide antigens found in Porphyromonas, Prevotella and Treponema species (these are all bacterial species associated with pulpal or periapical inflammation). [9]

Osteoclasts are active during bone regulation, there is constant equilibrium of bone resorption and deposition. Damage to the periodontal ligament can lead to RANKL release activating osteoclasts. [10] Osteoclasts in close proximity to the root surface will resorb the root surface cementum and underlying root dentin. This can vary in severity from evidence of microscopic pits in the root surface to complete devastation of the root surface.

When there is insult leading to inflammation (trauma, bacteria, tooth whitening, orthodontic movement, periodontal treatment) in the root canal/s or beside the external surface of the root, cytokines are produced, the RANKL system is activated and osteoclasts are activated and resorb the root surface.

If the insult is transient, resorption will stop and healing will occur, this is known as transient inflammatory resorption. [11] If the insult is persistent, then resorption continues, and if the tooth tissue is irretrievably damaged, complete resorption may occur. [12]


The maxillary (upper) left (right in photograph) lateral incisor (2nd tooth from the center) is afflicted with internal resorption (termed a pink tooth of Mummery). Mummery.jpg
The maxillary (upper) left (right in photograph) lateral incisor (2nd tooth from the center) is afflicted with internal resorption (termed a pink tooth of Mummery).

Internal resorption

Internal resorption defines the loss of tooth structure from within the root canal/s of a tooth.

It may present initially as a pink-hued area on the crown of the tooth; the hyperplastic, vascular pulp tissue filling in the resorbed areas. This condition is referred to as a pink tooth of Mummery, after the 19th century anatomist John Howard Mummery. It may also present as an incidental, radiographic finding. Radiographically a radiolucent area within the root canal may be visible and/or the canal may appear sclerosed.

Chronic pulpal inflammation is thought to be a cause of internal resorption. The pulp must be vital below the area of resorption to provide osteoclasts with nutrients. If the pulp becomes totally necrosed the resorption will cease unless lateral canals are present to supply osteoclasts with nutrients.

If the condition is discovered before perforation of the crown or root has occurred, endodontic therapy (root canal therapy) may be carried out with the expectation of a fairly high success rate. Removing the stimulus (inflamed pulp) results in cessation of the resorptive process.

External resorption

external root resorption 25 Wurzelresorption Zahn 25 und keilfoermiger Defekt PD 4.jpg
external root resorption 25

External resorption is the loss of tooth structure from the external surface of the tooth. It can be further divided in the following classifications: [4]


External inflammatory resorption occurs following prolonged insult leading to continuing pathological resorption. It is commonly caused by damage to the periodontal ligament (PDL), drying of root surface following avulsion, exposure of dentine tubules, and pressure. This process can occur rapidly.


Also known as transient inflammatory resorption. It is a self-limiting process and is a often and incidental radiographic finding. Transient inflammatory resorption undergoes healing and should be monitored only.

It is caused by localised and limited injury to root surface or surrounding tissues. [11] [13] There is 2–3 weeks of osteoclast activity before healing then occurs. If cementum alone is involved in the resorptive process then complete healing will occur, but if dentine is involved there will be re-contouring in the area of lost dentine. [11]


External cervical resorption is a localised resorptive lesion in the cervical area of the tooth, below the epithelial attachment. This rarely involves the pulp. Prolonged insult leads to vertical and horizontal growth of the lesion. It is commonly caused by trauma, periodontal treatment, or tooth whitening.

Multiple idiopathic cervical resorption is when a minimum of 3 teeth are affected by cervical resorption for no evident cause.


x-ray of external root resorption 25 Wurzelresorption Zahn 25 und keilfoermiger Defekt PD 5.jpg
x-ray of external root resorption 25

External replacement resorption occurs following ankylosis of the root of the alveolar bone. The tooth tissue is resorbed and replaced with bone. This process is poorly understood.

It is thought that following the union of bone and tooth and the obliteration of the PDL, the protective regulators released by the PDL to protect the root from resorption are no longer present. This results in the tooth tissue being resorbed by osteoclasts and replaced with bone like it was part of the continuous homeostatic process of bone turnover.

There is currently no single best  intervention or treatment for the management of external root resorption. Treatments are usually case-dependent and therefore more research is needed in this area. [14]

See also

Related Research Articles

Human tooth Calcified whitish structure in humans mouths used to break down food

The human teeth function to mechanically break down items of food by cutting and crushing them in preparation for swallowing and digesting. Humans have four types of teeth: incisors, canines, premolars, and molars, which each have a specific function. The incisors cut the food, the canines tear the food and the molars and premolars crush the food. The roots of teeth are embedded in the maxilla or the mandible and are covered by gums. Teeth are made of multiple tissues of varying density and hardness.


Cementum is a specialized calcified substance covering the root of a tooth. The cementum is the part of the periodontium that attaches the teeth to the alveolar bone by anchoring the periodontal ligament.


An osteoclast is a type of bone cell that breaks down bone tissue. This function is critical in the maintenance, repair, and remodelling of bones of the vertebral skeleton. The osteoclast disassembles and digests the composite of hydrated protein and mineral at a molecular level by secreting acid and a collagenase, a process known as bone resorption. This process also helps regulate the level of blood calcium.


Osteoprotegerin (OPG), also known as osteoclastogenesis inhibitory factor (OCIF) or tumour necrosis factor receptor superfamily member 11B (TNFRSF11B), is a cytokine receptor of the tumour necrosis factor (TNF) receptor superfamily encoded by the TNFRSF11B gene.

Pulp (tooth) Part in the center of a tooth made up of living connective tissue and cells called odontoblasts

The pulp is the part in the center of a tooth made up of living connective tissue and cells called odontoblasts. The pulp is a part of the dentin–pulp complex (endodontium). The vitality of the dentin-pulp complex, both during health and after injury, depends on pulp cell activity and the signaling processes that regulate the cell's behavior.

Periodontal fiber

The periodontal ligament, commonly abbreviated as the PDL, is a group of specialized connective tissue fibers that essentially attach a tooth to the alveolar bone within which it sits. It inserts into root cementum one side and onto alveolar bone on the other.

Enamel organ

The enamel organ, also known as the dental organ, is a cellular aggregation seen in a developing tooth and it lies above the dental papilla. The enamel organ is responsible for the formation of enamel, initiation of dentine formation, establishment of the shape of a tooth's crown, and establishment of the dentoenamel junction.

Pulpitis is inflammation of dental pulp tissue. The pulp contains the blood vessels the nerves and connective tissue inside a tooth and provides the tooth’s blood and nutrients. Pulpitis is mainly caused by bacterial infection which itself is a secondary development of caries. It manifests itself in the form of a toothache.

Dental follicle

The dental follicle, also known as dental sac, is made up of mesenchymal cells and fibres surrounding the enamel organ and dental papilla of a developing tooth. It is a vascular fibrous sac containing the developing tooth and its odontogenic organ. The dental follicle (DF) differentiates into the periodontal ligament. In addition, it may be the precursor of other cells of the periodontium, including osteoblasts, cementoblasts and fibroblasts. They develop into the alveolar bone, the cementum with Sharpey's fibers and the periodontal ligament fibers respectively. Similar to dental papilla, the dental follicle provides nutrition to the enamel organ and dental papilla and also have an extremely rich blood supply.

Alveolar process

The alveolar process is the thickened ridge of bone that contains the tooth sockets on the jaw bones that hold teeth. In humans, the tooth-bearing bones are the maxilla and the mandible. The curved part of each alveolar process on the jaw is called the alveolar arch.


Receptor activator of nuclear factor κ B (RANK), also known as TRANCE receptor or TNFRSF11A, is a member of the tumor necrosis factor receptor (TNFR) molecular sub-family. RANK is the receptor for RANK-Ligand (RANKL) and part of the RANK/RANKL/OPG signaling pathway that regulates osteoclast differentiation and activation. It is associated with bone remodeling and repair, immune cell function, lymph node development, thermal regulation, and mammary gland development. Osteoprotegerin (OPG) is a decoy receptor for RANKL, and regulates the stimulation of the RANK signaling pathway by competing for RANKL. The cytoplasmic domain of RANK binds TRAFs 1, 2, 3, 5, and 6 which transmit signals to downstream targets such as NF-κB and JNK.


Receptor activator of nuclear factor kappa-Β ligand (RANKL), also known as tumor necrosis factor ligand superfamily member 11 (TNFSF11), TNF-related activation-induced cytokine (TRANCE), osteoprotegerin ligand (OPGL), and osteoclast differentiation factor (ODF), is a protein that in humans is encoded by the TNFSF11 gene.

Dens invaginatus (DI), also known as tooth within a tooth, is a rare dental malformation found in teeth where there is an infolding of enamel into dentine. The prevalence of condition is 0.3 - 10%, affecting more males than females. The condition is presented in two forms, coronal and radicular, with the coronal form being more common.

Feline odontoclastic resorptive lesion

Feline Tooth Resorption (TR) is a syndrome in cats characterized by resorption of the tooth by odontoclasts, cells similar to osteoclasts. TR has also been called "feline odontoclastic resorption lesion" (FORL), neck lesion, cervical neck lesion, cervical line erosion, feline subgingival resorptive lesion, feline caries, or feline cavity. It is one of the most common diseases of domestic cats, affecting up to two-thirds. TRs have been seen more recently in the history of feline medicine due to the advancing ages of cats, but 800-year-old cat skeletons have shown evidence of this disease. Purebred cats, especially Siamese and Persians, may be more susceptible.

Scaling and root planing

Scaling and root planing, also known as conventional periodontal therapy, non-surgical periodontal therapy or deep cleaning, is a procedure involving removal of dental plaque and calculus and then smoothing, or planing, of the (exposed) surfaces of the roots, removing cementum or dentine that is impregnated with calculus, toxins, or microorganisms, the etiologic agents that cause inflammation. It is a part of non-surgical periodontal therapy. This helps to establish a periodontium that is in remission of periodontal disease. Periodontal scalers and periodontal curettes are some of the tools involved.

In dentistry, enamel matrix derivative (EMD) is an extract of porcine fetal tooth material used to biomimetically stimulate the soft and hard tissues surrounding teeth to regrow following tissue destruction.

Pulp necrosis is a clinical diagnostic category indicating the death of cells and tissues in the pulp chamber of a tooth with or without bacterial invasion. It is often the end result of many cases of dental trauma, caries and irreversible pulpitis.

Dental avulsion

Dental avulsion is the complete displacement of a tooth from its socket in alveolar bone owing to trauma.

Tooth ankylosis is the pathological fusion between alveolar bone and the cementum of teeth, which is a rare phenomenon in the deciduous dentition and even more uncommon in permanent teeth. Ankylosis occurs when partial root resorption is followed by repair with either cementum or dentine that unites the tooth root with the alveolar bone, usually after trauma. However, root resorption does not necessarily lead to tooth ankylosis and the causes of tooth ankylosis remain uncertain to a large extent. However, it is evident that the incident rate of ankylosis in deciduous teeth is much higher than that of permanent teeth.

Tooth replantation is a form of restorative dentistry in which an avulsed or luxated tooth is reinserted and secured into its socket through a combination of dental procedures. The purposes of tooth replantation is to resolve tooth loss and preserve the natural landscape of the teeth. Whilst variations of the procedure exist including, Allotransplantation, where a tooth is transferred from one individual to another individual of the same species. It is a largely defunct practice due to the improvements made within the field of dentistry and due to the risks and complications involved including the transmission of diseases such as syphilis, histocompatibility, as well as the low success rate of the procedure, has resulted in its practice being largely abandoned. Autotransplantation, otherwise known as intentional replantation in dentistry, is defined as the surgical movement of a tooth from one site on an individual to another location in the same individual. While rare, modern dentistry uses replantation as a form of proactive care to prevent future complications and protect the natural dentition in cases where root canal and surgical endodontic treatments are problematic. In the modern context, tooth replantation most often refers to reattachment of an avulsed or luxated permanent tooth into its original socket.


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