TO JUSTIFY A DIFFERENTIATED APPROACH TO PRESERVATION OF THIRD MOLARS DURING ORTHODONTIC TREATMENT BY DETERMINING THEIR CONDITION AND POSITION IN THE JAW
Authors: Doroshenko S.І. , Kuzmenko I.S. , Storozhenko K.V. , Irkha S.V. , Demianchuk Kh.M. 
Published: March 2021

No tooth is as problematic for patients as it is for third molars. After erupting later than all teeth, they often have little space in the dentition, or rather in the retromolar space, which should appear, above all, with further growth of the jaws. Therefore, the timing of their eruption varies considerably and is often accompanied by the appearance of significant morphological and functional disorders. That is why it is necessary to take a balanced approach to the preservation of third molars in the dental arch, providing them with a place in the retromolar space by timely detecting their condition and position in the jawbones and thus preserving the integrity of the dentition and implementing the fourth and last stage of bite raising in orthodontic patients with dental anomalies.
The purpose of the study. To substantiate a differentiated approach to the preservation of third molars in orthodontic treatment by determining their condition and position in the jaw.
Material and methods of research. For this purpose, 44 patients aged 15-30 years with different dentofacial anomalies having full permanent dentition including third molars confirmed by clinical and X-ray data were examined and given orthodontic treatment. Additional methods of the study included analysis of diagnostic model measurements (by Pont Korkhaus method). Furthermore, retromolar space was measured to find out if there is a space for third molars in the row of teeth by measuring its length and height using a silicone index (by S.I. Doroshenko and Ye.A. Kulhinskyi's method, 2009). X-ray studies included analysis of orthopantomograms (OPG), teleradiography (TRG), computed tomography (CT) scan, etc. The OPG analysis was conducted using K.V. Storozhenko's method (2013) which involved measuring the inclination of teeth, especially third and second molars relative to the jaw base. OPG showed a lack of space for third molars using S.I. Doroshenko and Ye.A. Kulhinskyi's method (2009). Measurement data were processed using mathematical statistics. The mean and the confidence interval for the data sample were calculated according to GOST R 8.736 – 2011.
Results. The analysis of data showed significant variability in inclination of third molars relative to the jaw base and second molars on both sides of the jaws (on the left and the right). The largest difference in inclinations of third and second molars was observed in the lower jaw (LJ) both on the left and the right, with an insignificant deviation of 0.3° ± 0.2°, and the least difference was in the upper jaw (UJ), especially on the left, but with a larger deviation of 3.6° ± 0.2°.
The conducted studies suggested that the larger the difference in inclinations of third lower molars relative to second ones is, the more problematic their eruption is, since they erupt later. Lower third molars incline medially at their crowns and therefore they have a smaller angle of inclination relative to the LJ base. While erupting upper third molars incline distally at their crown with an increased angle of inclination relative to the UJ base. In 44 patients aged 15-30 years, 106 (60.2%) third molars were in retention, including 35 (33.1%) teeth in physiological retention in younger people, 40 (37,7%) teeth in half-retention, and 31 (29.2%) third molars in constant retention.
An important factor in predicting the eruption of third molars became the presence of space for them in retromolar space, both sagittally and vertically. The presence of space in the row of teeth, i. e. sagittally, was observed in 25 (14.2%) of 176 third molars: in LJ in 15 (8.5%) molars, especially on the left in 7 (4.0%), and on the right in 8 (4.5%) teeth; in UJ in 10 (5.7%) teeth – 6 (3.4%) and 4 (2.3%) respectively.
The presence of space for the third molars also depended on width at the equator, which appeared to be the smallest in UJ and varied from 10 mm to 15 mm with a mean of 11.7 mm, and the largest in LJ – from 12 mm to 19 mm, the mean was 14.17 mm. Differences in the means between left and right UJ third molars were not detected (11.8 mm and 11.8 mm respectively), and in LJ it was insignificant (14.2 mm and 14.1 mm). In individual cases, the difference was 2.0-4.0 mm, and 1.0 mm in LJ. The latter confirms some scientists’ conclusions that the sizes of upper third molars vary more widely.
Retention of third molars in the subjects was associated with different dentofacial anomalies most commonly reported in 17 (38.6%) patients with distal occlusion (class ІІ) and in 13 (29.5%) persons with deep occlusion, and more rarely seen with medial (class ІІІ) – 4 (9.1%) – and open occlusion – 4 (9.1%).
Clinical studies suggested that when selecting a tactic for treatment of retained teeth, apart from determining their position in jawbones and the presence of a sagittal space in the row of teeth, it is also necessary to determine the size of vertical retromolar space for them which was measured using silicone indexes. Persons with deep and distal occlusion had the narrowest alveolar space from 0.5 mm to 4 mm, while in those with neutral occlusion it was from 5 mm to 7 mm.
Thus, the conducted studies showed the importance of the differentiated approach to the preservation of third molars, especially during orthodontic treatment.