Fourth molars, also called distomolars, are a variant in shape and number appearing as alterations during odontogenesis. They can be eumorphic or dismorphic, single or multiple, erupted or impacted, unilateral or bilateral, and can appear in both jaws. They are of unknown etiology, but there are several theories to justify these tooth alterations such as dental lamina duplication, its horizontal proliferation or its hyperactivity. Other factors can be hereditary factors, full division of tooth bud or phylogenetic regression.
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Fourth molars, also called distomolars, are a variant in shape and number appearing as alterations during odontogenesis. They can be eumorphic or dismorphic, single or multiple, erupted or impacted, unilateral or bilateral, and can appear in both jaws.
They are of unknown etiology, but there are several theories to justify these tooth alterations such as dental lamina duplication, its horizontal proliferation or its hyperactivity. Other factors can be hereditary factors, full division of tooth bud or phylogenetic regression.
Fourth molars are found in a very important space, and when their own existence or the suitable extraction techniques are unknown, severe complications can frequently occur during and after surgery.
A literature review was undertaken, examining different articles and texts of different years, in order to better determine the origins and formation of this supernumerary tooth.
The process of dental development which leads to formation of teeth within bones is called odontogenesis Figure 1. Teeth develop from epithelial invaginations which normally start to form in the anterior portion of the jaws to then advance to a posterior direction.
Although outlines possess a determined shape according to the tooth they are going to be the origin of, and possess their precise location in the jaw, all have a common development plan which takes place in a gradual manner. Supernumerary teeth are rare development alterations as a result of processes occurring during odontogenesis, they appear in all areas of dental arches, and can affect any sector of said arches.
Since they normally are asymptomatic, they are usually detected through routine x ray examinations. Within the Homo classification genre which groups all species considered human , dentition is of a heterodontic type, that is to say, exhibiting teeth of different morphology and function. Human dentition comprises four types of teeth: incisors, canines, premolars and molars. Teeth are of the utmost importance not only for mastication purposes, they are vital for phonetics and facial morphology.
It is well known that cavemen possessed stronger and harder teeth than modern men, it is considered they possessed up to four molars since they mainly lived on raw and fibrous meat, roots and vegetables. Nevertheless, when primitive men began to master fire, among other things, they used it to cook food, making them softer and easier to ingest, and therefore, development of the jaws experienced a decrease. In a research conducted at the Instituto Nacional de Antropologia e Historia National Institute of Anthropology and History it was reported that none of the specimens in the exposition exhibited fourth molars.
Pompa and Padilla mention that Australopithecus men did not exhibit fourth molars Figure 2. Fourth molars, also called distomolars or retromolars due to their distal or posterior location with respect to third molars, are a variant in shape and number which might take place during odontogenesis.
It can erupt or be retained or compacted, its eruption failure can be due to physical, dental bone or systemic origin factors. In some instances fourth molars fuse to third molars, and appear as a tubercle appended to its crown in the distal-lingual area, it is then called distomolar tubercle, it can even be appended to the third molar roots such as the palatine root in the case described by Gay-Escoda, Berini, Duarte and Azevedo 14 , 15 Figure 6.
Fourth molars are formed and develop like any other teeth although in some instances it might not possess the same evolutionary moment as teeth in the area, they can erupt into the arch in a position very similar to that of a molar, or they can remain within the bone. All the aforementioned syndromes exhibit in common the presence of facial cranial anomalies. Table I describes other examples. Nevertheless, development of supernumerary teeth in CCD patients has been delayed, in both primary and permanent dentitions, probably due to the incomplete dissolution of the dental lamina, giving thus rise to supernumerary teeth.
Etiology is yet unknown, since human dentition is composed of two dentitions and exhibits different morphology for each tooth group, number of teeth in each dentition and all sort of variations experienced during phylogenetic evolution favor their formation. During dental embryology processes, alterations in different development stages can occur, which can eventually affect teeth with respect to their number, shape or structure, giving thus rise to different anomalies.
Anomalies, or dental variations in number, as is the case of fourth molar or distomolar take place in the dental development initial stage, and can affect both dentitions, 23 among theories offering to explain this phenomenon we can count:. All cells of the tooth bud have same origin and same biological characteristics, therefore, in some situations, some cells can acquire properties of other specially differentiated cells, with resulting proliferation and formation of evaginations or invaginations which will give rise to new tooth tissues.
This new tooth formation can be formed from any of the following successive embryonic stages experienced by a tooth. Odontogenesis process begins at the 6 th week of intrauterine life, a week later dental bud is formed, due to proliferation of dental lamina cells, if alterations are present at this stage, they will result in a supernumerary tooth in the primary dentition. Once the crown of the permanent tooth has been formed, dental lamina is subjected to programmed cellular death, it degenerates resulting in epithelial pearls or remnants located within the jaws.
If proliferation excess or prolonged survival of dental lamina epithelial cells are stimulated through inductive factors, they can cause formation of a fourth molar, an odontoma or an erupting cyst. It has been reported that a lingual extension of the dental lamina will result in a eumorphic tooth Figure 10 , and epithelial remnants induced by dentition pressure will result in a dismorphic tooth Figure At the eighth week of intrauterine life, at the cap stage, the dental bud begins to separate from the dental lamina through an epithelial proliferation called epithelial cord or gubernaculum dentis.
Over-activity from the epithelial cord can originate formation of a fourth molar Figure An alteration of these processes will result in the presence of a fourth molar. It is the less accepted or defended theory, due to lack of supporting information. Different factors such as trauma or evolution mutations can cause accidental division of the dental follicle into two or more fragments. This cleavage can cause development of two teeth from one single tooth bud. Result will be either two similarly shaped teeth or one normal tooth and one dismorphic tooth.
This theory is supported by animal experiments where divided tooth buds were cultured in vitro. There is a case of fusion of left lower third and fourth molars reported by Hernandez-Guisado et al Figure 14 ; they state that the fact that the fourth molar possessed a volume similar to that of the third molar, and the union groove went from crown to apex, led them to believe existence of bonding union of two independent buds which were not separated by a bone septum during their development.
Nadal-Valldaura, in this subject, defines germination as the union taking place between a normal tooth and a fourth molar. Gemination can occur at the same levels as fusion Figure Generally, a fused fourth molar comes from the bud of the tooth to which it is fused. Duarte reported a case of an African American, 47 year old patient, with x-ray evidence of a radiopaque shape with characteristics of cementoblast or fourth molar; exploration clearly stated an inverted distomolar, fused to the palatal root of the third molar, additionally compromising the root canal Figure Another example was reported by Gomez Sosa: a 48 year old Venezuelan female, who exhibited fusion of lower third molar and distomolar, involving root canal and chamber.
These structures could be linked, either individually or separately according to the development stage at which the union took place 29 Figure Fusion and germination of molars is infrequent in permanent dentition, prevalence varies from 0. Fusion of a permanent tooth to a supernumerary tooth is less than 0. Dental fusion has, to this date, unknown etiology. It has been suggested that pressure of adjacent dental follicles might cause contact and fusion before calcification, hereditary factors of ethnic differences might predispose to fusion.
It is observed more frequently in people of Japanese extraction and in primary dentition, no differences have been observed with respect to gender. Combination of environmental and genetic factors, although hereditary transmission of fourth molars has not been yet proved. Non syndromic dominant autosomal transmission of multiple supernumerary teeth is new.
Kallay supports the hypothesis of a possible third molar or even second molar division. With respect to supernumerary teeth incidence, there are different authors, for instance Salcido Garcia, who reach the conclusion that these teeth can be found in a range of 0. Leco Berrocal report in his study that supernumerary teeth were present with onset frequency of 1. On the contrary, when reporting fourth molar incidence, there are different authors, for instance Daniela Nascimiento who place it in second place, after mesiodens, or Fernandez Montenegro who places it in third place, after paramolars, with variable percentage of incidence Table III.
Ohata H mentions that fourth molar incidence is very infrequent, from 0. Kurt H, Berkay ST presented a study with orthopantomographic X rays of 14, Turkish patients 6, females and 7, males in the time frame Out of the total 14, patients included in the study, 45 presented distomolar 14 female, 31 male , representing 0.
Out of 9 cases, 0. All were found in the upper jaw, with In the upper jaw, 5 cases Caseta M, Alteri F et al reported 61 posterior supernumerary teeth in 45 patients 32 males and 13 females out of a total of 25, patients. Nirmala and Tirupathi report in their study prevalence studies comparing supernumerary molars paramolar and distomolar and prevalence of distomolar or fourth molar with different authors, studies and reported cases 42 Tables VI and VII.
Most authors such as Reyes Velazquez concur in reporting that the area of most frequent apparition is the upper jaw, with respect to gender they are more frequently found in males Table VIII.
There are different opinions and percentages with respect to incidence related to race or ethnicity. Frequency in Caucasian population is 0. Moreover, it has been reported that these teeth are longer than those found in females. Duarte mentions it is more common in subjects of African descent, and that it affects 2. Prevalence according to ethnicity is as follows: 44 , The study conducted by Harris et al reported greater prevalence of fourth molars in African Americans, 2.
It was also mentioned that there has been no Latin American study to show predominance for a specific ethnicity or country where fourth molar occurrence would be more frequent. In Mexico, a prevalence of 0. Literature reports established consensus in the need of surgically treating this type of clinical situations since there is high percentage of derived complications, among them whether the tooth is or is not retained or impacted.
In some instances, eruption mechanisms fail giving rise to different retention varieties; in this case, the cause was the fourth molar Figure Mention is even made of keratocyst formation due to inclusion of numerous teeth, causing greater loss of bone tissue around the crowns of these teeth, and thus increasing mandibular fracture risks in a high percentage of cases.
Dentigerous cysts can be sizeable and cause bone expansion due to the fact they are asymptomatic and with remarkable growth ability. Although they normally are related to crowns of permanent teeth, with much lesser frequency they can be related to primary teeth or fourth molars Figures 22 and This type of cystic lesions, or like keratocysts, exhibit high incidence of appearing related to third molars due to their high impaction incidence, even more so when they are related to fourth molars.
Epithelial lining possesses transformation potential, enabling development of odontogenic tumors and carcinoma. Among odontogenic tumors we find ameloblastoma. When there are mucous cells in the cystic structure, there is possibility for a muco-epidermoid carcinoma to appear. Even metastasic potential has been reported, although it is not a habitual situation. Transformation into carcinoma would occur at advanced ages.
Bacteria Peptostreptococcus , Fusobacterium , bacteroides having a more direct entrance access, possess to greater root proportions, due to absence of root bone, thus causing intense local periodontitis.
Pressure of the molar along with sack surrounding the crown cause localized bone destruction, which might cause rhyzolysis , which in turn might lead to pain and fractures due to bone absence in the area. Ehsan Camarata described the case of a fourth molar in a 50 year old male patient.
The molar was located underneath and alongside the right mandibular canal; clinical manifestations initiated as a neurological picture: that is to say, atypical oral and facial pain and sensitivity alteration in the are of the right lower tooth nerve.
Fourth molars or distomolars, since they not always exhibit isolated symptomatology, are mostly found after X ray examinations conducted to treat third molar problems Figure Fourth molars are rarely found erupted, thus first findings are clinical.
Cone-beam computerized tomography CBCT enables to increase assessment ability in the clinic, with lesser distortion that that obtained with 3D images. With respect of tooth recording within clinical history, different formulae and nomenclatures are used, the most used one is that belonging to IDF International Dental Federation , thus, Sarjeev Singh Yadav and Sapna Sonkurla proprose the following nomenclature for supernumerary teeth. Early diagnosis, accurate assessment and suitable treatment of supernumerary teeth are essential.
There are two kinds of treatment: surgical extraction or frequent clinical and X-ray observation. Decision with respect to whether distomolars require treatment is based on their location, and the probability they might cause pathological alterations, or even dental arch alterations.
Early development of the human dentition revisited
Tooth agenesis: in search of mutations behind failed dental development. Tooth agenesis are the most common craniofacial malformations. Genetic linkage and molecular biology studies have allowed, in the last decade, the identification of mutations responsible for some patterns of syndromic and non-syndromic tooth agenesis. Current research would lead to the development of new classifications of tooth agenesis that took into account both the phenotypes and the genetic background.
Immunohistochemical analysis of CK14 and CK19 in tooth germ and ameloblastoma. Odontogenesis is the process by which teeth form, and where different molecules are expressed, among them some cytokeratins CK like CK14 and CK Remnants of odontogenic epithelium may persist once the development process is complete, which has been suggested to be involved in the development of ameloblastoma, one of the most common benign odontogenic tumors. It has been suggested that CK14 and CK19 are useful markers of ameloblast differentiation and that they could have implications for tumor behavior. The aim of this study was to describe the patterns of immunohistochemical expression of these cytokeratins in tooth germs and ameloblastomas.