Correlation of Occlusal-Plane-Inclination with Functional Condylar Displacement inDifferent Skeletal Classes

Objective: The aim of this study was to investigate the correlation between different skeletal classes, functional condylar displacement and the inclination of the upper posterior and upper anterior occlusal planes. Methods: 150 patients out of a total of 700 were selected for the study based on recorded occlusal parameters, both genders from 18 years, using cephalostat, condylograph and Cadiax Diagnostic, Reference SL Articulator, Gamma dental software version 7.7.14. Results: Condylar displacement was found in almost every second patient with different skeletal classes. The majority of patients show an aboveaverage steepness of occlusal plane (upper posterior occlusal plane more than the anterior one). Conclusion: Over average steep Anterior Occlusal Plane (AOP) and Posterior Occlusal Plane (POP) is significantly correlated with retrusive mandibular/ condylar displacement in all skeletal classes, whereas in Skeletal class II the correlation is highly significant (Class II>I>III). We conclude that it is very important to determine the upper posterior and anterior occlusal planes for a detailed diagnosis to identify patients at risk of inducing functional complaints by dental treatment and to create an optimized treatment plan for each patient.


Introduction
The skull/craniofacial system is the most complicated part in the human skeletal system with the main functions as connecting the brain [1] and participating in sensory and motor activities (smiling [2], talking and mastication [3]). The scope of this thesis pertains to the craniofacial system and the skeletal types that influence the motor functions of the craniofacial system. Furthermore, dynamics of the craniofacial system [4] is related to the anatomy of the system [5] and the variety depends on the individual skeletal type.
Accordingly, the angular differences between upper and lower jaw influence the functioning of the craniofacial system [6,7]. This is also known as the proper or malocclusion of mandibular and maxillary system [8,9].
Most important is the angle between the occlusal and the mandibular plane OP-MP [14]. Normally, the OP-MP angle is maintained constant [15,16]. However, during excessive displacement of the occlusal plane [17], a backward rotation of the mandible [18] takes place, which leads to an increase in the OP-MP angle [19]. Furthermore, during another instance of excessive displacement of the occlusal plane there is an insufficient vertical support of occlusion [20,21] and hence the mandibular condyle stays restricted to grow [22,23] (Figures 1-4).
The Upper Anterior Occlusal Plane (UAOP) [24] is established by connecting the tip of upper central incisor with the cusp of the upper second premolar.
The Upper Posterior Occlusal Plane (UPOP) [24] is represented by the line that connects the cups of the upper second premolar with the occlusal surface of the upper second molar.
According to Angle's classification of malocclusions we differentiate between skeletal classes I (Neutroocclusion), II (Distocclusion, mandibular retrognathism/Overjet) and class III [25] (Mesiocclusion, mandibular prognathism/negative overjet).   Based on the concepts of occlusion by Professors Slavicek and Sato [26], we have taken up the case study of several patients in this thesis.
Here we have analyzed a number of patients of different age groups and gender, healthy and with different dento-alveolar or functional anomalies.
For condylar position the orthodontists' purpose is a treatment result [27], where the upward and forward or a reference position [28,29] of a condyle is constant with respect to the intercuspal position if the patient closes the mandible [30,31]. Is there a larger discrepancy between the seated condyle and tooth intercuspation pretreatment should be aimed for [32,33].
Moreover, the reference position, also known as the centric relation [34], provides a clear clinical indication whether the mastication process takes place properly or whether there is an excessive overbite or overjet. Furthermore, to classify the patients, we have also determined the facial skeletal types of the subjects using the cephalometric analysis by Ricketts, Slavicek, Jarabak. In addition, facial skeletal types and resulting condylar displacements [35,36] have a profound influence on the facial muscles [37] as well.
Our study's aim is to determine the correlation between different skeletal classes, condylar displacement [38,39] and the inclination of the upper posterior and upper anterior occlusal planes [40][41][42].
Accordingly, the hypotheses for our study are: • There is an evident correlation between an upper anterior and upper posterior occlusal plane with a condylar displacement in different skeletal classes.
• Condylar displacement is associated with a steeper posterior occlusal plane, especially in class II skeletal patterns.

Materials and Methods
A retrospective cephalometric and condylographic study was done with 150 patients out of a total of 700 patients. 500 of which were from Viesid database and 200 patients were the sample group for this study.
The selection criteria were: • Recorded occlusal parameters of all patients • Male and female from 18 years • Patients with all teeth from inferior central incisor to second molar in all quadrants, with or without third molars • Previously obtained informed consent to use patient data.
The methods used for the research were as follows: • Historical method • Descriptive and analytical epidemiology • Biostatistics • Information transfer method All patients took part in a standardized process: • Questionnaire and special medical analysis (recent infections, problems with cardiovascular, respiratory, digestive or metabolic system, allergies, urogenital problems, problems related to the central nervous system, psychological problems, rheumatic disease, hormonal disorders or any special problems not listed here?) • Dental history analysis • Muscle and joint diagnosis (the state of muscles, both in the left and right sides of shoulders and neck, atlanto-occipital regions, anterior, medial and posterior temporal is muscles, superficial and deep masseter muscles, tuber maxillae muscles, pterygoideus medialis muscles, mylohyoideus muscles, digastricus muscles, supra and infra hyoidale muscles, laryngeal, sterno-cleidomastoeideus, omohyoideus and tongue muscles; for bone and joint assessments, the examinations involved comparative palpation of jaw joints, lateral poles statically, lateral points in rotation, retral joint space and temporomandibular ligament) • Occlusogram-Brux checker • Photographs of the patient (facial and oral) • Study models (RP bite, face-bow) • Condylography-Cadiax • X ray-Panoramic [43], lateral and front cephalometric views [44,45].
A total of 49% of patients showed condylar displacement while the remaining 51% did not show any condylar displacement.

Skeletal class-wise distribution of condylar displacements
The majority of patients in the skeletal class II (n=36/63.15%) had condylar displacement. Amongst the patients classified in skeletal class I and skeletal class III there was an approximately equal percentage of patients with (w/d) and without (wo/d) condylar displacements (Class i: w/d n=36/47, 36%; wo/d n=40/52, 63) (Class III: w/d n=7/41, 2%; wo/d n=10/58, 8%) ( Figure 5).        The X axis represents the angle of displacement and the Y axis represents the number of patients.

Discussion
An effective treatment of skeletal and dentoalveolar anomalies [46] including obtaining stable results [47] in time is primarily based on a detailed diagnosis [48] of all components of the stomatognathic system [49]. The condylar position is undoubtedly very important for a normal functionality of the temporomandibular joint [50] what International Journal of Dentistry and Oral Health Open Access Journal has been demonstrated by the results of previous studies [51][52][53].
Compiling this data with the results of our study, we can conclude the following.
The majority of patients show an above-average steepness of the occlusal plane (upper posterior occlusal plane more than the anterior one).
A retruded condyle is an unfavorable "starting" position for the functions of the masticatory organ and is very often associated with functional disorders [29] (Weinberg LA, etc.).
A steep anterior occlusal plane [54] involves an avoidance pattern [55] due to the avoidance of too strong front tooth contacts in the transversal, retrusive or protrusive direction [56], leading to a load of the structures of the temporomandibular joint [57,58] and to a constant hypertonicity of the muscles. This additional load involves a neurological reaction of the body leading to even more muscle activity [26,1,39].
Moreover, in the majority of cases a steep posterior occlusal plane provides a significantly higher chance for the occurrence of laterotrusive and mediotrusive or even retrusive posterior interferences [59], again making an avoidance-which in turn will lead to more compensatory necessity of the system to increase the activity of the neurological system, enhanced muscle activity [60] and condylar displacement.
The analysis of data obtained from our study revealed that a majority of class II patients has condylar displacement. Also, almost every second investigated person with class I or III has condylar displacement.
Most patients with class I and condylar displacement have an upper posterior occlusal plane angle with values near 76-77 degrees. Most patients with class II and condylar displacement have the same angle with values between 67 and 81 degrees. Respectively, in class III this angle is about 77 degrees.
If we refer to the upper anterior occlusal plane angle, most patients with class I and condylar displacement reveal values between 76 and 81 degrees. Most patients with class II and condylar displacement have the same angle of 77 degrees. Respectively, in class III this angle is about 86 degrees.
So, if the majority of patients in all skeletal classes show this unfavorable starting position for dynamic function, it is absolutely necessary to pay special attention in dental treatment to the anterior and posterior occlusal plane [61] because there could be a high chance of overstraining the system in its adaptive capacities as they are already compensated in the majority of the cases [62].
According to Sato's concept [63] about the skeletal class II pattern with a steep posterior occlusal plane [9] and also reiterating the rapid historical increase of the class II incidence, we conclude that it is highly important to determine the upper posterior and anterior occlusal planes for a complex and detailed diagnosis.
Customized dentistry following the VieSID Sequential Occlusion with Canine Dominance concept should be based on an individual, thorough diagnosis using model analysis, cephalometric radiography, condylography, etc. It is highly recommended to use the upper anterior and posterior occlusal plane method to identify risk patients because of disclosed compensation and to choose the most reasonable treatment plan.

Conclusion
Over average steep Anterior Occlusal Plane (AOP) and Posterior Occlusal Plane (POP) is significantly correlated with retrusive mandibular/condylar displacement in all skeletal classes, whereas in Skeletal class II the correlation is highly significant (Class II>I>III). Steep Anterior and Posterior Occlusal Planes (AOP/POP) reduce the intercoronal functional freedom of functional mandibular movements and seems to induce muscular avoidance pattern with significant loading of the intra-articular structures of the temporo-mandibular joint and hereby bearing great risk of causing signs and symptoms of temporo-mandibular disorders such as muscle hypertonicity, muscle pain, internal derangement of the TMJ (capsulitis, synoviitis, tendinitis) and TMJ-pain.
We conclude that it is very important to determine the upper posterior and anterior occlusal planes for a detailed diagnosis to identify patients at risk of inducing functional complaints by dental treatment and to create an optimized treatment plan for each patient.

Acknowledgment
It is my great pleasure to say "thank you" to Professor Rudolf Slavicek and Sadao Sato for their historical wisdom, sharing of invaluable knowledge and friendly criticism.
Special thanks to my colleague, friend and a role model Valeriu Fala for his motivation and support.
I would also like to express appreciation to the most important teacher of my life who taught me not only to look but to see, to