THE ROLE OF ELECTROMYOGRAPHY IN IMPROVING THE EFFECTIVENESS OF PROSTHETICS UNILATERAL END DEFECTS USING IMPLANTS

Introduction Rehabilitation of patients with octal tooth loss with uni­ lateral terminal defect (second class according to Kennedy) is a difficult task in orthopedic dentistry. Such patients are adapted to chewing on one side for a long time and get to the doctor with advanced pathology due to the prolonged absence of complaints from the dental-maxillary system [1,2,4,5]. When chewing food on one side, due to increased func­ tional load, a pathological symptom complex develops de­ formation of the dentition, erasure of the teeth of anagonists, restructuring of the receptor field of the oral cavity, changes in the chewing muscles [3,4]. With a unilateral term inal defect on the side of teeth having antagonists, signals go from periodontal proprioreceptors to the sensitive nucleus of the trigeminal nerve, then to the motor nucleus, and then to the masticatory muscles, which contributes to the restructuring of the function of the masticatory muscles. A unilateral type of chewing and forced occlusion is formed [6]. According to Zhulev E. N., 2000, with partial loss of teeth, a decrease in the frequency and amplitude of surface EMG was revealed and a violation of the synchronous activity of the masticatory muscles was indicated [9]. There are several methods of orthopedic treatment of the second class according to Kennedy (unilateral distally unlimited defects of dentition) removable and non-remov­ able structures. According to a number of authors, the preferred method of treat­ ment for partial tooth loss is fixed structures supported by implants [7,8]. Fixed structures supported on implants are also the most comfortable for the patient in the absence of contraindications. However, in the available literature there is not a significant amount of data on the effectiveness of this method of treatment for unilateral terminal defect according to the description of electromyography of the masticatory muscles.


Introduction
Rehabilitation of patients with octal tooth loss with uni lateral terminal defect (second class according to Kennedy) is a difficult task in orthopedic dentistry. Such patients are adapted to chewing on one side for a long time and get to the doctor with advanced pathology due to the prolonged absence of complaints from the dental-maxillary system [1,2,4,5].
When chewing food on one side, due to increased func tional load, a pathological symptom complex develops -de formation of the dentition, erasure of the teeth of anagonists, restructuring of the receptor field of the oral cavity, changes in the chewing muscles [3,4].
W ith a unilateral term inal defect on the side of teeth having antagonists, signals go from periodontal proprioreceptors to the sensitive nucleus of the trigeminal nerve, then to the motor nucleus, and then to the masticatory muscles, which contributes to the restructuring of the function of the masticatory muscles. A unilateral type of chewing and forced occlusion is formed [6]. According to Zhulev E. N., 2000, with partial loss of teeth, a decrease in the frequency and amplitude of surface EMG was revealed and a violation of the synchronous activity of the masticatory muscles was indicated [9].
There are several methods of orthopedic treatment of the second class according to Kennedy (unilateral distally unlimited defects of dentition) -removable and non-remov able structures.
According to a number of authors, the preferred method of treat ment for partial tooth loss is fixed structures supported by implants [7,8]. Fixed structures supported on implants are also the most comfortable for the patient in the absence of contraindications. However, in the available literature there is not a significant amount of data on the effectiveness of this method of treatment for unilateral terminal defect according to the description of electromyography of the masticatory muscles. f t Th e aim of our study was to study the data of surface elec tromyography of the masticatory muscles before and after the restoration of masticatory function during prosthetics on implants of unilateral terminal defects.

M aterials and methods of research
32 patients of both sexes aged 37-53 years were examined to study the dynamics of adaptation to fixed structures based on implants that restore unilateral terminal defects. All patients, from anamnesis, had a unilateral disal-unlimited defect for at least one year. Patients with the absence of 2 to 4 teeth in the lateral section were fitted with 4x10 mm or 4x12mm Conmet implants according to a two-stage method. After the integra tion of the implants, orthopedic treatment was performed. All patients received metal-ceramic prostheses with screw fixation. The formation of the occlusal surface was performed in an articulator in accordance with generally accepted recommen dations [1,3].
Adaptation to dentures was assessed using surface electro myography of the masticatory and temporal muscles before and after fixation of the denture on implants. The study used a portable electromyograph FREELY by De Gotzen (Italy), which automatically processes the data obtained with a spe cial set of programs compatible with Windows and allows you to present the results of EMG in the form of tables and diagrams. EMG control was carried out on the 7-th, 14-th day, 1 time a month for six months. Disposable cutaneous bipolar electrodes with a dimeter of 10 mm with an interelectrode distance of 21 mm were used for EMG. One electrode was fixed as a reference on the forehead (Fig. 1).

Conclusions and recomendations
The total electrobiopotential of all muscles -1151+ 263 pV*sec was obtained before the start of orthopedic treatment. At the same time, the index of lateral displacement of the lower jaw (normally up to 10 %) was -19.9+ 5.5 %, and the index of symmetry of the temporal muscles and masticatory muscles (in the norm of 80-100 %) was 57.2+ 6.8 % and -75.68+ 5.8 %, respectively.
After fixation of the denture on implants, the total electrobiopotential of all muscles decreased to 1113+ 180 pV*sec. While the index of symmetry of the temporal muscles increased to 83.29+ 0.93 % (p<0.05), which corresponds to the norm, and the masticatory muscles increased to 84.34+ 1.16 %. The index of lat eral displacement of the mandible decreased to normal values, and amounted to 10.37 + 0.75 %.
After a month, the total electrobiopotential of all muscles increased to 1468+ 202 pV*sec, the index of lateral displacement of the mandible approached zero (0.8+ 0.04 %), and the indices of symmetry of the temporal and masticatory mus cles were recorded within the normal range (87.07+ 0.67 % (p<0.05) and 86.33+ 0.84 %, respectively). Electromyography performed after 6 months showed an increase in the total electrobiopotential to 1703+ 207 pV*sec, and the remaining indicators did not statistically significantly differ from the values recorded in previous periods of the study.
A clinical case. Patient T., 47 years old, went to the clinic complaining of an aesthetic defect and difficulty chewing food. There are 2.4, 2.5, 2.6, 2.7 teeth missing on the upper jaw, which were removed for various reasons more than a year and a half ago. To replace the defect of the dentition in the area of the missing 2.4, 2.6, 2.7, Conmet implants were installed using a two-stage 4x12 mm technique. After 3 months, gum shapers were installed (Fig. 2).
According to the traditional method, a metal-ceramic conditionally removable structure with screw fixation was made (Fig. 3,4).
EMG analysis before applying a bridge-like prosthesis supported by implants on the right side of the maxilla revealed asymmetries in the work of the temporal muscles 50, 26 %, and the masticatory muscles 74, 55 %. The norm for symmetrical operation is 80-100 % Analysis of the work of the same muscles criss-cross -sym m etry of the masticatory on the right and temporal on the left, and vice versa, that is, the index of lateral displacement of the lower jaw was 35, 84 %, while the norm is up to 10 %. The total potential of all muscles was 996 pV*sec, which is within the normal range (from 500 to 2500 pV*sec) (Fig. 5).
A fter applying the denture, sym metry in the work of the masticatory and temporal muscles was obtained by 84, 51 % and 83, 16 %, respectively, the index of lateral displacement was 10, 64 %. The total potential of all m us cles decreased and am ounted to 783 pV*sec (Fig. 6).
After 1 month, the total potential of all muscles increased by 1064 pV*sec.  Fig. 6. EMG after applying and fixing the prothesis After 6 months, the total potential of all muscles increased and amounted to 1228 pV*sec. The remaining indicators retained the previously obtained values of the activity of the masticatory and temporal muscles. The symmetry of the muscles remained at the previously obtained level, and the lateral displacement index approached zero.
From all of the above, a preliminary conclusion can be drawn. The restoration of a unilateral distal-unlimited defect of the dentition with dentures on implants is an effective meth od of prosthetics and actually restores the masticatory function within up to 1 month after the fixation of the prosthesis, which is objectively confirmed by the restoration of symmetrical work of the masticatory muscles and, as a consequence, the formation of a bilateral type of mastication.