Dentition

DENTITION (tooth eruption). The term D. is used to denote only the eruption of teeth. Based on the process of tooth eruption, vertebrates are divided into 3 groups: monophyodonts - one eruption, diphyodonts - two eruptions, and polyphyodonts - multiple eruptions. Monophyodont animals possess only permanent teeth, mostly of the same shape, and are therefore also called homodonts. Diphyodont animals undergo two sets of teeth during their lifetime - deciduous and permanent, with teeth of different shapes, and are therefore called heterodonts. Polyphyodont animals have no specific period of eruption, and throughout their lives (as for example in fish), as teeth wear out, they are replaced by others. Humans, along with most mammals, belong to the diphyodont group. The time of eruption of deciduous and permanent teeth varies considerably depending on genetic and paratypic conditions. The actual process of tooth eruption consists of the gradual appearance of the tooth crown above the gum surface. Tooth eruption continues until the entire crown appears above the gum. The latter may sometimes not occur. It is often observed (for example, during the eruption of wisdom teeth) that only part of the crown appears above the gum, and at this point the process of tooth eruption and protrusion ceases - partial retention of the tooth, incomplete eruption, occurs. Sometimes a tooth does not erupt at all - complete retention of the tooth. From comparative anatomical data, it is evident that diphyodonty, characteristic of humans, is an eruption system inherent in highly organized vertebrates, and diphyodonty is accompanied by the differentiation and specialization of different types of teeth (heterodonty), corresponding to the improvement of the vertebrate. Diphyodonty and heterodonty should be considered not only as phenomena accompanying each other, but also as interconnected. In certain cases in humans, there may appear to be a return to polyphyodonty. Thus, the ability of the oral epithelium to produce a large number (sometimes hundreds) of teeth was established by Luksky in the study of odontogenic tumors. The mechanism of tooth eruption is very complex and not fully understood. Most theories are unsatisfactory, as they usually consider eruption as a purely mechanical process. Thus, according to the root theory, it is believed that the tooth is pushed out by the growing root (Wedl, Colembrun-Mercu). Another explanation is proposed, where the main role is assigned to the mechanical force of growth of the pulp - the pulp theory (Hunter, Eichler, Wallisch, Walkhoff, Zuckerkandl). Other researchers see the cause of tooth eruption in external local forces acting directly on the tooth; Baume attributes a special pushing force to the growth of granulating bone marrow at the bottom of the alveolus; Nessel, Albrecht, and others believe that the tooth is squeezed out by the contractile force of the jaw bones; Berten attributes this action to the masticatory muscles; Robin - to the act of chewing as a whole. The general and basic objection to examining these eruption theories concerns their mechanical concept. Since the forces moving the tooth are characterized as purely mechanical, none of the theories individually nor all theories together can provide a satisfactory explanation. It is also incorrect to reduce the process of tooth eruption to mechanical phenomena of isolated movement of the tooth in the bone mass. - A physiological viewpoint was put forward by Adloff, who based the process of eruption on the physiological properties of the developing protoplasm of dental tissues, acquired by the protoplasm in the process of phylogenetic and ontogenetic development. - Later (1923) Landsberger, based on research on human embryos and experiments on dogs, came to the conclusion that during its development the tooth does not move, does not leave its place of formation, and does not come out of contact with the surrounding tissues - the movement of the tooth is apparent. The part of the alveolar bone tissue separating the neck of the tooth from the oral mucosa gradually disappears due to resorption. Parallel to the process of resorption, the opposite process occurs, which is so characteristic of bone - the process of deposition of bone substance. This process occurs in the part of the alveol located between the root opening of the tooth and the body of the jaw [see separate table (for article Dental Cysts), fig. 1 and 3]. This is how tooth eruption occurs, which appears to us as the 'movement' of the tooth to the periphery of the alveolar process. - Finally, mention should be made of the theory of hormonal morphogenesis of the dental apparatus, put forward by Robinsohn, who attributes to the tooth-forming epithelium and its remnants an endocrine function regulating odontogenesis, in particular the process of tooth eruption. Robinsohn's theory lacks factual basis, and since its publication (1926) to the present time, factual data supporting the theory have not been reported. First eruption. Local phenomena during tooth eruption are as follows. Before tooth eruption, the gum in a child appears as a small but rather sharply defined ridge, the so-called dental cartilage (cartilago gingivalis). On palpation, the ridge is very firm. As the erupting crown approaches the oral mucosa of the gum, the latter gradually thins and becomes softer. Further, through the mucous covering of the gum, the contour of the erupting tooth's crown begins to outline itself; the gum in this place becomes elevated, sometimes slightly reddens, and then pales. Finally, the crown erupts through the completely thinned mucous membrane. In multicuspid teeth, usually the front cusp of the chewing surface appears first, then the back. Along with the resorption of the coronal part of the alveolus described above, as the tooth approaches the oral mucosa, resorption of the latter begins. The part of the soft tissues facing the crown of the tooth is resorbed, as well as the part facing the oral mucosa itself. In the place where the mucous covering is resorbed to a thin strip, the integrity of the mucous membrane is disrupted. The two resulting flaps of the dental follicle gradually contract and become part of the circular ligament of the tooth. Remnants of the enamel epithelium at the neck of the tooth merge with the epithelium of the oral cavity [see separate table (appendix to article Dental Cysts), fig. 2 and 3]. From an anatomical point of view, pain sensations during tooth eruption can occur due to dissociation between the development of the alveolo-dental complex and the thinning of the mucous membrane at the cutting edge of the crown in the sense of delay of the latter. The easiest and fastest eruption is given by the group of incisors. Complications are most often observed during the eruption of canines. Surgical therapy in the form of incisions in the gum, etc., for painful eruption of deciduous teeth is contraindicated. - Disorders of eruption of deciduous teeth can manifest as 1) early eruption, 2) late eruption, 3) anomalies in the number and position of teeth. Fleischmann (L. Fleischmann) explains the possibility of early tooth eruption as follows: 1) premature formation of the germ followed by normal development, 2) normal formation of the germ with accelerated development, 3) superficial formation of the germ, which caused early eruption of an underdeveloped tooth. Second eruption. The moment that causes the shedding of deciduous teeth is the resorption of the root of the deciduous tooth, which is facilitated by the presence of a special formation - Tomes' resorbing organ (Tomes; 1861), which represents granulation tissue, the layer of which, adjacent directly to the root of the deciduous tooth, consists of the so-called osteoclasts - cells that resorb hard tissues. The resorption of the roots of deciduous teeth is closely related to the eruption of the permanent tooth, being one of the components of the eruption process. Resorption of the root begins from the place where the erupting crown of the permanent tooth approaches more closely [see separate table (appendix to Dental Cysts), fig. 11. Cementum, dentin, and pulp of the root are resorbed, then part of the enamel at the neck. The coronal pulp remains mostly untouched. - Disorders of eruption of permanent teeth manifest as delayed or accelerated appearance of teeth or violation of the order of eruption. Sometimes some teeth do not erupt at all. The absence of teeth in the dental arch may be due to retention - delay of the tooth. In such cases, the tooth remains in the bone substance of the jaw in a normal position, but usually it is in an incorrect position. This most often happens with the third molars, with canines, and lateral incisors. In such cases, an X-ray usually reveals the retained tooth. The second reason for the absence of one or more teeth in the jaw row is the absence or improper development of the corresponding germ, which can be accurately determined by X-ray. Such anomalies are called anodontia or adentia.

Lukomsky. Difficult teething. The doctrine of difficult teething refers mainly to the eruption of deciduous teeth, to which a significant role in the pathogenesis of all sorts of diseases has been ascribed since ancient times. Modern pediatric views have considerably narrowed the significance of this act, however complete consensus has not yet been established. There are no severe diseases associated with teething; antidentionists (Kassowitz, Karnitsky and others) believe that teething never causes any painful phenomena; whereas according to the opinion of the majority of dentionists this act can cause the onset of either only local or both local and general painful symptoms. Local symptoms include: swelling, tension, redness of the gum, pain or itching, increased salivation, catarrhal inflammation; general symptoms include: irritability, capriciousness, restless sleep, decreased appetite (partly due to pain during sucking), paleness, arrest or relative deficiency in weight gain, slight elevation of temperature in the presence of local causes. In very labile children, habitual diseases of the digestive tract, respiratory tract, rashes (eczema, urticaria) are aggravated or manifested, and in spasmophiliacs - convulsions. These painful phenomena are more often observed during the eruption of canines and molars, less often of incisors, mainly in weak children, anemics, rachitics, or neuropaths; in strong, properly developing children, they are either absent or weakly expressed only in the form of local phenomena. Antidentionists base their opinion on the following propositions: teething is a physiological act, and therefore it must be painless. Limited stomatitis - a result of traumatic injury by hard objects given to the child - is observed no more frequently during the period of teething than before or after it, salivation is a normal phenomenon, fluctuations in weight gain occur also in healthy children (Kassowitz), and all other phenomena are accidental coincidences. Dentionists consider the main argument to be: the simultaneity of the onset of the described painful phenomena with the moment of tooth eruption, their disappearance or diminution after eruption, repetition of the phenomena during the eruption of a new tooth, and the absence of other clinical data to explain them. According to Filatov and Geibner, stomatitis begins and is more strongly expressed at the place on the gum where the tooth is cutting. Also unconvincing is the a priori position that eruption as a physiological act must be painless (menstruation, childbirth). - Thus, from a scientific point of view, one cannot deny the possibility of a pathogenic influence of the eruption of deciduous teeth, especially in weak, anemic, rachitic children, but on the other hand, it is undoubtedly necessary to fight against the age-old prejudice of attributing all diseases, especially severe ones, during teething to this act.