Regression models of individual linear sizes of molars depending on the features of cephalometric indices in practically healthy men of the Western and Eastern regions of Ukraine

Restoration of missing teeth should be done as close as possible to the natural anatomical features of the person's tooth-jaw apparatus. That is why the problem of aesthetics in dentistry has ceased to be only orthopedic and has shifted towards a constitutional and ethnic odontology. The purpose of the study is to construct and carry out analyzes obtained by regression analysis, models of computed-tomographic size of molars, depending on the features of cephalometric indices of practically healthy men of the Western and Eastern regions of Ukraine. A computed-tomographic study of molars with the following odontometry and cephalometry of 36 practically healthy men of the Western region of Ukraine residents of Volyn, Rivne, Lviv, Chernivtsi, Ternopil, Khmelnytskyi, Transcarpathian and Ivano-Frankivsk regions and 35 men of the Eastern region of Ukraine residents of Kharkiv, Donetsk and Luhansk regions was performed with the help of the Dental Cone-ray Tomography Veraviewepocs-3D (Morita, Japan). Regression models of linear sizes of molars, depending on cephalometric indices, were conducted using the statistical software package Statistica 6.1. As a result of the conducted research, reliable models of computed-tomographic size of the upper and lower jaws molars were constructed in practically healthy men of the Western [7 models of mesio-distal dimensions (R2 = 0.532-0.646), most of which include sagittal arc (12.5%), outer-eye width, nose depth, distance between nasion and inter-cutter point, body length of the lower jaw on the left, largest head circumference and maximum head length (by 7.5%); 6 models of vestibular-tongue dimensions (R2 = 0.527-0.646), which most often include nasal depth (20.0%), body length of the lower jaw to the left (16.0%), physiological face length and morphological face length (by 12.0%); 1 model of crown height (R2 = 0.579)] as well as Eastern [3 models of crown height (R2 = 0.5380.682), which most often include nose depth (15.0%), face type, physiological face length, morphological face length, smallest width head and sagittal arc (by 10.0%); 2 models of mesio-distal sizes (R2 = 0.572 and 0.556), which most often include inter eye fossa width (15.4%)] regions of Ukraine. Thus, in practically healthy men from the Western and Eastern administrative-territorial regions of Ukraine, based on the specifics of cephalometric indicators and face type, reliable regression models (with determination coefficient R2 greater than 0.5) of computed-tomographic size of molars of the upper and lower jaws (out of 40 possible 14 for the western and 5 for the eastern regions of Ukraine).


Introduction
One of the main issues of orthodontics is the prevention and correction of the wrong bite, as well as other tooth-jaw anomalies.The current level of orthodontic development allows to restore the form and function of the tooth-jaw system by various methods [9,10,21].The progress of dentistry, the emergence of new technologies, materials, methods of treatment gradually formed a new direction -aesthetic dentistry.When working, you must strive not only to close the defect and deprive the patient of pain, but also to reproduce the natural beauty of the teeth [3,7,8,26].
In order to achieve stable and guaranteed clinical success, a comprehensive approach is needed.That is, the problem of returning the natural form of teeth does not belong to the category of exclusively aesthetic.Restoration of missing teeth should be done as close as possible to the natural anatomical features of the person's tooth-jaw apparatus.That is why the problem of aesthetics in dentistry has ceased to be only orthopedic and has shifted towards the constitutional and ethnic odontology [13,15,17,19,22].
The process of competent modeling of anatomical forms leads to the fact that newly created designs from restoration materials are harmoniously combined with craniofacial structures.The work on predicting the size of the teeth -this is a daily task facing the dentist, but it was solved earlier, as a rule, intuitive [5,14,27,28,30].
Previously, methods for modeling the teeth parameters were based mainly on simplified models with numerous assumptions, but now it is important to simulate the size of the teeth, which requires deep knowledge of anatomy and, in particular, the consideration of individual dimensional features of the tooth-jaw and craniofacial system [2,4,6,11,12].
The purpose of the study is to construct and carry out analyzes obtained by regression analysis, models of computed-tomographic size of molars, depending on the features of cephalometric indices of practically healthy men of the Western and Eastern regions of Ukraine.

Materials and methods
On the basis of the medical center "WinIntermed LTD", for 200 somatologically healthy men aged from 19 to 35 years from different administrative regions of the regions of Ukraine done a cone-ray computer tomography using the Veraviewepocs-3D Dental Cone-ray Tomography (Morita, Japan).Among them: the western region -36 inhabitants of Volyn, Rivne, Lviv, Chernivtsi, Ternopil, Khmelnytsky, Transcarpathian and Ivano-Frankivsk regions; Eastern region -35 inhabitants of Kharkiv, Donetsk and Luhansk regions.Bioethics Committee of National Pirogov Memorial Medical University, Vinnytsya found that the studies fully met ethical and moral-legal requirements in accordance with the order of the Ministry of Health of Ukraine No. 281 of November 1, 2000 and do not contradict the basic bioethical norms of the Helsinki Declaration, the Council of Europe Convention Human Rights and Biomedicine (1977).
On cone-ray computed-tomograms of molars of the upper and lower jaws, measurements were made: height of the crown of the corresponding tooth; vestibular-tongue dimensions of the crown and neck of the tooth; mesio-distal dimensions of the crown and neck of the corresponding tooth [20].
A cephalometric study was conducted taking into account the generally accepted recommendations and anatomical points [1] with the help of a large sliding compass with a scale of the real size of the Martin system and a soft centimeter ribbon.The shape of the head was determined according to the following formula [30]: EU_EU / G_OP x 100.Up to 75.9, men belonged to dolichocephals; 76.0-80.9-to mesocephals; 81.0-85.4-for brachycephals; 85.5 and more -to hyperbrachycephals.The value of the face index (Garson morphological index) was obtained by the corresponding formula [18]: N_GN / ZY_ZY x 100.Up to 78.9 men belonged to the group with a very wide face; 79.0-83.9-with a wide face; 84.0-87.9-with middle face; 88.0-92.9-with a narrow face; 93.0 and more -with a very narrow face.
For the determination of computed-tomographic linear dimensions of molars, according to the features of cephalometric indices, craniotype and the type of the face of practically healthy men from the Western and Eastern regions of Ukraine, a direct stepwise regression analysis was conducted using the licensed statistical software package "Statistica 6.1".For the analysis of the obtained results, only models in which the determination coefficient (R 2 ) was not less than 0.50 and the value of the F-criterion was not less than 2.5 were taken into account.
Models of all other linear dimensions of molars in practically healthy men of the Western and Eastern regions of Ukraine have a determination coefficient less than 0.5 and therefore have no significance for practical dentistry.

Discussion
Knowledge of odontology of different groups of the population allows to develop an individual approach in the course of activities aimed at the treatment and restoration of teeth and dental-jaw system in general, extends the importance of other specialties, including forensic medicine and anthropology [12,20,23,29].Specialists engaged in this branch of odontology, seek to identify general patterns of structure and development of the dental system, individual and sexual variability of teeth, the laws of their morphogenesis, the relationship between different elements of the system, the correlation of the size and structure of individual teeth between themselves and the skull.As a result, with a number of known morphometric parameters of the patient's teeth, by calculating on the basis of regression equations, we obtain the individual parameters of missing teeth and their tissues [11,16,24,25].
Using regression analysis, based on the characteristics of cephalometric indices, craniotype and face type, reliable models (with determination coefficient R 2 greater than 0.5) of linear computed-tomographic sizes of molars of the upper and lower jaws in practically healthy men of the Western (4 models of mesio-distal sizes of the crown of the teeth of the upper and lower jaws, R 2 = 0.575-0.646;3 models of mesiodistal dimensions of the neck of the teeth of the mandible, R 2 = 0.532-0.581;3 models of vestibular-tongue crowns of the lower teeth R 2 = 0.527-0.646; 1 model of the height of the crown of the tooth of the upper jaw, R 2 = 0.579) and the Eastern (3 models of the height of crowns of the teeth of the upper jaw, R 2 = 0.538-0.682; 1 model of mesio-distal size of crown of tooth of upper jaw, R 2 = 0.572; 1 model of mesio-distal size of the neck of the mandible tooth, R 2 = 0.556) of the regions of Ukraine.
Constructed models of computed-tomographic sizes of molars of the upper and lower jaws with a determination coefficient of more than 0,5 most often include: in men of the Western region of Ukraine -parameters of the facial part of the head 72.6% (nose depth -11.0%, the length of the body of the mandible on the left -9.6%, the distance between the nasion and the inter-cutter point and the morphological length of the face -by 6.8%, exterior eye width, the height of the upper face and physiological face length -by 5.5%) and the parameters of the cerebral head were 24.7% (sagittal arc -6.8%; transverse arc, greatest head width, largest head girth and largest head length -by 4.1%); individually for models of mesio-distal teeth sizesagittal arc (12.5%), exterior eye width, nasal depth, distance between nasion and inter-cutter point, length of the body of the mandible on the left, largest head circumference and maximum head length (by 7.5%); to the models of vestibulartongue sized teeth -the depth of the nose (20.0%), the length of the body of the lower jaw to the left (16.0%), physiological face length and morphological face length (by 12.0%); in men of the Eastern region of Ukraine -parameters of the facial part of the head 72.7% (nose depth, morphological length of the face and inter-orbital width -by 9.1%, nose length, exterior eye width and physiological facial lengthby 6.1%), parameters of the cerebral head 18.2% (sagittal arc -9.1%; lowest head width -6.1%) and face type 9.1%; separate to the models of the height of crowns of teethnose depth (15.0%), face type, physiological face length, morphological length of face, smallest head width and sagittal arc (by 10.0%); to models of mesio-distal dimensions of teeth -inter-orbital width (15.4%).
When comparing our results with the results of modeling the linear dimensions of premolars in similar regions [16] it is necessary to note: for men of the Western region of Ukraine constructed 4 models of mesio-distal sizes of premolars (R 2 = 0.535-0.659),which most often include the largest girth the head and distance between the nasion and the intercutter point (by 14.8%), the transverse arc, the width of the mouth gap and the length of the body of the mandible on the right (by 11.1%); 1 model of the height of crowns of premolars (R 2 = 0.522); men of the Eastern region of Ukraine had 6 models of mesio-distal premolars sizes (R 2 = 0.505-0.641),most of which included sagittal arc, mouth width and forehead height (by 12.8%), average facial width (10.3%), and length of the body of the mandible on the left (7.7%); 2 models of the vestibular-tongue dimensions of premolars (R 2 = 0.519 and 0.559), which most often include the transverse arc, the width of the mouth, exterior eye width, the width of the mandible, and the length of the nose (by 14.3%); 1 model of height of crown of premolars (R 2 = 0.603).
Constructed regression models of linear dimensions of molars, depending on the features of cephalometric indices and the type of face of men of the Western and Eastern regions of Ukraine, will allow dentists to more correctly carry out treatment and diagnostic measures of various tooth-jaw anomalies.

Conclusion
In practically healthy men from the Western and Eastern administrative-territorial regions of Ukraine, based on the specifics of cephalometric indices and face type, reliable regression models (with determination coefficient R 2 greater than 0.5) of computed-tomographic size of molars of the upper and lower jaws (out of 40 possible 14 for the Western and 5 for the eastern regions of Ukraine) have been constructed.