A tooth that fails to develop in the process of tooth germ formation is called congenital edentulous. According to its severity and whether it is accompanied by systemic symptoms, it can be divided into several categories, but different documents have different classification standards and names for congenital missing teeth. In the past, most of the literatures divided congenital tooth loss into: tooth loss, that is, missing one or several teeth; Absence of teeth means that most teeth are not formed, usually accompanied by systemic abnormalities; Toothless refers to extremely serious tooth loss and complete toothlessness. Another classification standard is similar to the above, but the words are different, which are divided into: individual tooth loss, partial edentulous, and total edentulous. Raymond et al. [1] think that the word "partial missing teeth" used in the previous classification is literally self-contradictory and unscientific.
At present, most scholars [2 ~ 4] divide congenital tooth loss into two categories: lower tooth loss, which means congenital loss of one or more teeth, usually without systemic symptoms. Oligodontia refers to the congenital absence of six or more teeth (excluding the third molar), which is usually accompanied by systemic abnormalities and/or partial manifestations. Absence of teeth is considered to be a serious manifestation of congenital absence of most teeth.
2 Related factors of congenital missing teeth
Congenital tooth loss occurs in the early stage of tooth formation, that is, tooth germ formation. The reasons are different: ① the development of embryonic dental plate is physically hindered or the dental plate is broken. For example, in the mouth-face-toe syndrome, the lower incisor area is covered by hyperplastic ligaments, which will cause mechanical interference to the dental plate. ② Space is limited, resulting in pressure, which leads to tooth germ degeneration and lack of minimum nutrition, especially for the third molar. (3) lead to the dysfunction of epithelial tissue below it and/or the failure of mesenchymal induction.
The chewing organs of human beings tend to degenerate and decrease, so congenital tooth loss is related to the evolution of human race. As early as 1865, Darwin pointed out that the atrophy of human teeth and the congenital absence of teeth were related to the trend of the maxilla and mandible becoming smaller during evolution.
At present, many studies have proved that the occurrence of congenital tooth loss is related to genetic factors, but scholars have different views on the exact genetic transmission mode and mechanism. Among them, the main viewpoints are as follows: (1) Congenital tooth loss has autosomal dominant genetic characteristics; ② autosomal recessive inheritance; ③ Characteristics of polygenic inheritance. Most scholars' views tend to be polygenic inheritance influenced by environment [4].
In recent years, with the localization of transfer factors, growth factors, receptor molecules, cell surface molecules, intercellular molecules and other molecules in tooth development, and the study of their regulatory role in tooth development, the research on genetic factors of congenital missing teeth has become more in-depth, but scholars have different opinions. For example, Vastardis et al. [5] found that when the MXS 1 gene locus was mutated, most teeth in mice could be severely missing. Human beings are characterized by congenital absence of second premolars and third molars. In addition, some scholars have found that epidermal growth factor (EGF), epidermal growth factor receptor (EGFR) and fibroblast growth factor (FGF) play an important role in tooth development. Therefore, scholars suggest that gene mutation of EGF, EGFR, FGF and other factors can lead to congenital tooth loss. Arte et al. [6] investigated the pedigree of seven Finnish families with three generations of congenital individual tooth loss, and analyzed their fingerprints by PCR, but excluded the gene sites of EGF, EGFR and FGF-3 as the mutation sites of congenital individual tooth loss. Nieminen et al. [7] did not find the abnormality of MXS 1 gene locus when studying the genes of patients with congenital loss of incisors and premolars.
At present, two genes related to congenital edentulous syndrome have been cloned, one is ectodermal dysplasia (EDA), and the other is Rieger syndrome [8].
3. Incidence of congenital missing teeth
3. 1 Incidence of congenital absence of permanent teeth and deciduous teeth
Congenital tooth loss rarely occurs in mammals. But when it happens to humans, permanent teeth are more common than deciduous teeth. The incidence of congenital tooth loss of permanent teeth is 2.3% ~ 9.6% (excluding the third molar), and that of deciduous teeth is 0. 1% ~ 0.7%, with obvious racial differences. Eskimos, Indians and orientals have a higher incidence rate, while blacks have a lower incidence rate, with a ratio of 2: 3. The incidence of congenital absence of deciduous teeth and subsequent permanent teeth is 75% ~ 80% [9].
Most reports on the incidence of congenital missing teeth are not classified according to the classification of congenital missing teeth, and the third molar is not included. The reason may be that the incidence of congenital missing teeth and edentulous teeth is very low. No x-rays were taken during the large-scale population survey.
3.2 Incidence of congenital missing teeth in different tooth positions
There are many reports about the tooth position of congenital missing teeth, and there are obvious racial differences. It has been reported in literature that congenital tooth loss in Europe is more common in mandibular second premolar, in North America it is more common in maxillary lateral incisors, and in Japan it is more common in mandibular incisors [1]. The incidence of congenital absence of the third molar varies greatly among different races. The incidence of African blacks is 1.0%, while that of Japanese is 30%. According to most data, the incidence of congenital tooth loss of permanent teeth is the highest in the third molar, about 30%, followed by the mandibular second premolar (0.8% ~ 6.4%) and maxillary lateral incisors (1. 1% ~ 3.2%). The order of incidence of deciduous teeth from high to low is: mandibular deciduous teeth, maxillary deciduous teeth and deciduous teeth. Anthropologists suggest that human dentition is in a transitional period, and the teeth on one side of dentition in the future may be: 1 incisors, 1 canines, 1 premolars, 2 molars [1, 9].
3.3 Congenital edentulous and edentulous cases account for the majority.
The incidence of most congenital missing teeth is 0.3% in permanent dentition, and it is even rarer in deciduous dentition [10]. Congenital edentulous jaw is very rare, only in patients with severe ectodermal dysplasia. According to the literature, in 125 cases of congenital edentulous jaws, deciduous dentition and permanent dentition occurred simultaneously or only permanent dentition occurred independently [1].
4. Clinical manifestations of congenital edentulous patients with abnormal dentition
Congenital tooth loss is characterized by congenital tooth loss, which can occur alone, but it is more common to be accompanied by other dentition abnormalities. It is reported that congenital edentulous and microdefect often occur in the same dentition, so some scholars think that microdefect and conical teeth are also a manifestation of congenital edentulous [1 1].
Other dentition abnormalities related to congenital edentulous dentition include: congenital absence of other teeth, undersize teeth, conical teeth, enlarged dentition, delayed tooth development, abnormal eruption sequence, sinking of deciduous molars, dislocation of permanent teeth, ectopic eruption of first permanent molars, widening of dentition space, crowded dentition and alveolar bone hypoplasia [9 ~ 12]. Symons et al. [1 1] made statistics of various dentition deformities in 176 patients with congenital absence of one or more second premolars. The results showed that 63.6% of the other teeth were congenital missing, 65,438+03.1%of the permanent teeth were embedded, 9.7% of the deciduous molars were depressed, 6.8% of the dentition was crowded, 6.8% of the midline was deviated (maxilla), 3.6% of the dentition gap was widened, 2.8% of the teeth were ectopic and 2.8% of the teeth were delayed.
Among other dentition abnormalities related to congenital tooth loss, the most common one is congenital tooth loss. Among the patients with congenital absence of the third molar, the incidence of congenital absence of other teeth is higher than that of the normal population, specifically: mandibular second premolar 32%, maxillary lateral incisor 2 1%, maxillary second premolar 15%, mandibular lateral incisor 12%, maxillary canine 7%, mandibular central incisor 4%, and mandible.
5 principles of treating congenital missing teeth
The choice of treatment scheme for congenital missing teeth must be determined after comprehensive examination according to the profile of the child, the position and number of missing teeth and the arrangement of dentition [1, 9]. Generally, patients with congenital anterior tooth loss should first consider aesthetic problems, while patients with congenital posterior tooth loss should focus on function. At present, the commonly used orthodontic methods include closing the gap, concentrating the gap or maintaining the gap with implants or dentures. For most edentulous and edentulous patients with alveolar bone hypoplasia, surgical bone grafting and postoperative implant or denture repair can be used.
6. Systemic diseases with congenital missing teeth.
Congenital tooth loss can occur alone or as a part of systemic abnormality and/or syndrome. Congenital tooth loss has been described in more than 120 syndromes. The following systemic abnormalities or syndromes are usually accompanied by congenital majority tooth loss [1, 9, 12].
6. 1 ectodermal dysplasia (ectodermal dysplasia)
Some scholars classify ectodermal dysplasia as 1 17, but there is no unified view on the definition and classification of ectodermal dysplasia. The clinical manifestations of the patient are lack or scarcity of hair and body hair, dry skin, partial or total lack of sweat glands, prominent forehead, saddle nose, and the most prominent manifestations in the oral cavity are congenital absence of most teeth, widening of the gap between the remaining teeth, short conical teeth and labial frenum's dysplasia.
6.2 Oral and facial finger I and II syndrome.
The patient's lower incisors are undeveloped, with few teeth, fingers (toes) and fingers (toes), and fingers (toes) are too short or bent.
6.3 Rieger syndrome.
Partial facial bone defect, maxillary hypoplasia, congenital absence of maxillary anterior teeth, corneal and iris hypoplasia.
6.4 craniomandibular skin malnutrition (craniomandibular skin malnutrition)
This is a very rare disease, with hypoplasia of upper and lower jaws and congenital absence of central mandibular incisors. ■
Author: Deng Qing (Institute of Pediatric Stomatology, Railway University, Shanghai 200072)