Aim: Decrease in the interalveolar distance (IAD) that develops during a period of permanent occlusion as a result of progressive primary dental diseases: Increased abrasion of hard tissues of the teeth, extensive edentulous space, and generalized form of periodontitis is accompanied by morphofunctional changes in the masticatory muscles and the development of temporomandibular joint (TMJ) dysfunction. The objective of the study was to identify development mechanisms of the reduced occlusion syndrome (ROS) that develops as a result of decrease in the IAD caused by primary dental diseases. Material and Method: 395 people 28-68 years of age with primary dental diseases of the dentofacial apparatus. Of the overall examined, 293 (74.2%) patients with decrease in the IAD constituted the active treatment group. The control group included 102 patients without sign symptoms of reduced occlusion. Patients in the control group had different types of dental prothesis in the oral cavity at the time of examination. The morphological examination object included 138 certified skulls with lower jaws. Anamnestic and clinical data were analyzed. Radiological methods were used rehabilitation capabilities of the dentofacial apparatus, a functional and physiological method for determining the jaw relation was applied, facial electromyography of the chewing muscles, and neck muscles was used. Results and Discussion: The work presents and scientifically grounds the diagnostic system for integral assessment of morphofunctional linkages of dentofacial apparatus and reduced occlusion syndrome patients, its stomatogenic and general manifestations have been defined, an effective treatment regimens and rehabilitation of reduced occlusion syndrome patients of varying severity have been developed. The combination of resulting data enables to reduce complications developed on the background of primary dental diseases accompanied by a decrease in the interalveolar distance of different origin. Conclusion: The study revealed that of 293 examined patients with a decrease in the IAD, 231 (78.8%) patients were diagnosed with the ROS of different severity. The ROS is a persistent pathological process characterized by progressiveness, which includes: Anatomical and functional changes resulting in compression of bilaminar region of the TMJ, as well as in an impaired functions of chewing-speech apparatus with somatogenic and general manifestations, developing on the background of a decrease in the efficiency of vegetative regulation of the region and the patient's body.