The eruption of the first permanent molars is very important as it provides the harmony of the growth of the face and sufficient occlusion support. A delay in the eruption of this tooth can cause morphological, functional and aesthetic disturbances. These include reduced vertical size of the lower face, extruding the antagonist teeth, malloclusion formation, follicular cyst formation, pericoronal inflammation, and roots resorbtion of the adjacent teeth, as well as functional problems of dentoalveolar area, etc. In this regard, the issue of etiology, pathogenesis, early diagnostics and further treatment of lower first permanent molars retention is very relevant for modern orthodontics. In the literary review, morphological and radiological diagnostic criteria of eruption of first permanent lower molars have been presented. Materials and methods of the research. The article reviews and analyzes literature on the etiology, pathogenesis, early diagnostics of retention of the lower first permanent molars. Results The analysis of the literature pointed to a small number of studies regarding the disrupted eruption of first lower permanent molars. In most cases, they are presented as clinical cases. According to the world literature, the prevalence of delayed eruption of the first molar of the mandible was 0.01% to 0.04%. Data from the world literature indicate that the retention of the lower first molar is a polyfactoral disease. According to the etiological factors authors distinguish general and local. Local factors causing delay in teeth eruption include impaired pathway for teeth eruption, abnormality of the tooth form, hyperplasia, displacement of the rudiment because of the cyst and the tumour, loss of space for eruption, gingival fibrosis, idiopathic conditions. Systemic factors include endocrine disorders such as hypothyroidism, hyperthyroidism, hypoparathyroidism, rickets, craniofacial hypertrophy. In the literary review morphological and radiological diagnostic criteria of eruption disturbance of the first permanent lower molars are presented. Thus, the Korean scientists proposed to determine the depth of the retention, the angle of inclination and the space for their eruption on panoramic radiographs. The review presents the classification of retention types for the first permanent molars of the mandible.

Dental anomalies are the leading ones among dental diseases in the period of mixed (79,96%) and permanent (84,33%) dentition. According to the results of our studies, frequency of distal occlusion (up to 40%) and dental crowding (up to 65%) are the largest in structure of orthodontic pathology. The aim of the study is to analyze and summarize knowledge about ways of enhancement of treatment and prophylaxis efficiency in patients with distal occlusion and dental crowding. Genetic predisposition, early childhood diseases (including upper respiratory tract infections), children's bad habits, pathological state of teeth (adentia, impaction, micro-, macrodentia), micro-, macrognathia, functional disorders of maxillofacial area contribute a high percentage in structure of "risk factors" which lead to formation of distal occlusion with dental crowding. For each particular patient distal occlusion, complicated by dental crowding, is formed under the influence of combination of several "risk factors", where the first place belongs to disturbances of dental area: breathing, closing of lips, swallowing, chewing, speech. Today it is well known that the first step in correction of distal occlusion of dentitions is to evaluate the patient's potential growth. Treatment in the period of mixed dentition is important with relation to protection of palate from trauma by mandibular incisors with a large sagittal gap, prophylaxis of dysfunction of temporomandibular joint, psychological rehabilitation of children during speech formation, as well as to improve the prognosis of treatment in older age. The best period of treatment is a peak of growth and development. Growth is the most important factor in planning treatment of distal occlusion, since dramatic changes in correction are related to growth rather than teeth movement. Orthodontists forbear from recommendations for teeth extraction in growing patients, as they believe that it leads to worsening of face profile and does not allow to achieve optimal relationships of jaw and occlusion. In adult patients, complete conservative correction of distal occlusion is possible only in the absence of skeletal disorders. Combined method, namely combination of orthodontic treatment and orthognathic surgery, is an alternative for adults treatment. Adequate individual approach to orthodontic treatment in patients with distal occlusion complicated by dental crowding is based on a comprehensive clinical examination, scientific analysis and results interpretation of additional examination methods. Full functional occlusion is possible if all elements of dentition: occlusion, periodontal tissues, temporomandibular joints, muscles and nervous system, are considered. Stable results and positive prognosis are provided by normalization of physiological state of masticatory and mimic muscles.

In modern dental practice, one of the complaints of patients is unsatisfactory appearance due to the visually disproportionate size of teeth. Diagnostic assessment of the smile reflects the amount of gum and tooth tissue exposed. This emphasizes the growing need for the exchange of information and scientific knowledge between orthodontists and periodontists, an integrated approach to the treatment of orthodontic patients. The position of the gums is clinicalу important because it is not static. Tooth eruption involves a complex of stages that have not yet been widely studied. According to the concept of continuous eruption, it does not stop, even when the teeth are in contact with their functional antagonists, but lasts a lifetime. The normal state of passive eruption should lead to the location of the cement-enamel joint (CEJ) approximately in the area of the base of the furrow and 2 mm from the ridge of the alveolar bone. The active eruption is the movement of teeth towards the occlusal plane, whereas the passive eruption is the exposure of teeth by apical migration of the gums. The passive eruption usually occurs after teething and continues in adolescents and finally stops after facial growth. Altered passive eruption (APE) (also known as delayed passive eruption) occurs when the edge of the gums is incorrectly (occlusively) located on the anatomical crown in adulthood and does not approach the CEJ. The "normal" position of the gingival margin to the CEJ is usually considered to be on or near the CEJ in the fully incised teeth of adults. The prevalence of APE in the adult population is currently poorly studied, possibly due to the lack of clear diagnostic criteria. Thus, Volchansky and Cleaton-Jones, based on a survey of 1,025 patients aged 24.2±6.2 years, recorded 12.1% of cases of APE. The analysis of the literature did not reveal any reliable etiological factors that cause the impossibility of the tooth eruption and cause such morphology of the CEJ. The greatest clinical significance of APE is its aesthetic consequences. As a rule, this is a change in dentofacial harmony, which is manifested in the following: the square appearance of the crowns, the exposure of the gums during a smile, smoothed gingival scallops. An integrated approach to the treatment of patients with APE includes consideration of periodontal interventions, restorative manipulations, and orthodontic treatment. Thus, the altered passive eruption is an unusual physiological variation in the morphology of the dental-gum complex, which leads to aesthetic disorders and is considered a risk factor for periodontal disease. Therefore, it is necessary to pay attention to the presence of altered teeth eruption when planning the orthodontic treatment. Correction of malocclusions should be integrative.