2020, Number 1
The role of the occlusal plane in joint health in orthodontic diagnosis (Part I)
Full text
Language: English/Spanish [Versión en español]
References: 28
Page: 60-68
PDF size: 219.67 Kb.
ABSTRACT
The occlusal plane runs sagittally from the most distal occlusal surface of the last molar past the cusp tips of the canine teeth and continues down to the incisal area, it is not completely flat as it must have some curvature, and it also has a transverse arrangement. It is formed by the occlusal surfaces and incisal edges of all dental organs. Several types of occlusal planes can be used in the same patient depending on the area to be assessed, and also for diagnostic or therapeutic purposes when associated with other anatomical or cephalometric planes. We are clear about the role of the occlusal plane in joint health and stability, regardless of the patient's age, the need for rehabilitation, orthodontic treatment, surgery or aesthetic considerations. Shaping the final occlusion is undoubtedly one of the most important functional principles to consider when correcting malocclusion. Establishing the desired and necessary joint health translates into occlusal, muscular and skeletal stability. The aesthetic aspect will be another factor to consider when determining the final position of the occlusal plane, since it can generate important differences that have to do with the amount of teeth and gum that is shown, especially in the smile of the patient.INTRODUCTION
Over time there have been a large number of authors who have proposed different occlusal planes, Downs in 1949, Steiner in 1949, Ricketts in 1950, Wright in 1966, Delaire in 1981, Karkazis in 1986, etc. It has even been related to cranial cephalometric planes as a diagnostic tool, which we will not mention because it is part of another topic.1-4
In 2008 Okeson,5 defined the occlusal plane as that which is formed by drawing an imaginary line through all the buccal cusp tips and incisor edges of the lower teeth, and then running a plane that encompasses the lingual cusp tips and continues through the arch including the opposite side buccal and lingual cusp tips, introducing three-dimensional occlusal thinking.
To understand and analyse it is important to carefully examine each of the structures that make up the occlusal plane, as well as the position necessary to achieve an optimal relationship with the structures that control jaw movement, the temporomandibular joints (TMJs).
It is important to carefully examine each of the structures that make up the occlusal plane, as well as the position in which they are positioned in order to achieve an optimal occlusal relationship. These are determining factors in achieving the best functional relationship with the TMJs.
The structures that control mandibular movement are divided into two types: 1) those that influence the movement of the posterior portion of the mandible and 2) those that influence the movement of the anterior portion of the mandible. The TMJs are considered the posterior controlling factors and the anterior teeth the anterior controlling factors. The posterior teeth are positioned between these two controlling factors and thus can be affected by both to varying degrees.4-6
From the point of view of occlusion, the appearance of the incisors marks for the first time the conformation of an occlusal tripodism, given by the anterior teeth and the TMJs. From this moment on, important anatomical and functional changes begin to take place, basically the development of the zygomatic tubercle before the modification of mandibular movements, which have become more complex cycles that include vertical, lateral and protrusive movements.
As the primary dentition is completed, the occlusal plane descends, which in the newborn is practically at the level of the TMJs. By virtue of the direction of the growth centres of the upper jaw, which is downward and forward, the first occlusal plane is established, since, unlike in the permanent dentition, it does not have the basic features for three-dimensional diagnosis of the occlusal plane (Figure 1), such as the curve of Spee and/or Wilson, where sagittal and transverse relationships are analysed together with the vertical dimension.3,7,8
Spee's curvature refers to a sagittal curve that runs from the cusp of the lower canines and moves backwards past the cusps of the premolars and molars, if the curvature were to continue backwards, it would pass through the condyle (Figure 2).
The sagittal curve of the occlusal plane is designed to allow disocclusion of the posterior teeth in the protrusive movement and thus avoid premature occlusal contacts, in combination with the anterior and condylar guidance. When separation of the posterior teeth occurs through incisal contact, the levator muscles exert pressure (load and not overload) on the anterior teeth and condyles. If this synchrony of movement and force, which is regulated by the sensor system, is not achieved, a series of direct damage to the tooth mass, muscles, joints and periodontal structure will undoubtedly begin.
The Wilson Curve is very important in the occlusal plane, it is transverse and contacts the buccal and lingual cusps on each side of the arch. The lingual cusps should be lower than the buccal cusps in the lower arch, and in the upper arch the palatal cusps are lower than the buccal cusps. The inclination of the posterior teeth allows for load resistance and correct masticatory function when the tongue and buccinators muscles work in synchrony.2,6,8,9
We have to understand that the seating of the occlusal plane is a primary functional structure and is not only an aesthetic consideration. The literature considers that the gingival exposure of the upper jaw should be 0-2 mm when smiling and that the incisal edges of the upper teeth should show 2-4 mm when the lip is at rest. However, certain considerations must be taken into account, such as the fact that the upper incisors become less exposed with age, for example young patients have more exposure of the upper teeth, while adults show more of the lower teeth. These considerations are very important and should be taken into account when determining which type of functional aesthetic occlusal plane (FAOP) we want to leave, according to the age of the patient (Figure 3).10,11
The shape and inclination of the occlusal plane as well as its individual characteristics are related to the function of the stomatognathic system as well as to dentofacial aesthetics. It is very important to determine which occlusal plane the diagnostic or therapeutic interpretation of the patient will be based on, as in addition to having different occlusal planes within the same mouth, for example, the functional occlusal plane (POF) or the bisected occlusal plane (PLB), we find differences in occlusal seating in class II and class III patients or in patients with vertical growth and horizontal growth.7,11-13
The prediction of craniofacial growth is a fundamental goal in craniofacial biology and is a major concern within orthodontics and any area of odontology, as it is key in the diagnosis, prevention, interception and treatment of malocclusions. To date it is not completely clear how abnormal growth occurs in the different dentoskeletal schemes, due to the different factors that are involved and their interactions. Among the factors are cranial base flexion, dental eruption, vertical dimension, occlusal plane, maxillary and mandibular intrinsic growth, genetic factors and environment. Particularly the significance of occlusal plane inclination as a primary determinant in the establishment of mandibular position remains poorly understood.2,9,14
Shudy pointed out that the relationship between effective vertical condylar growth (horizontal growth) and vertical growth of the molars determines whether the mandible rotates downward or forward, or simply does not rotate. The occlusal plane is the effect, not the cause of the anatomical relationship attributable to condylar growth (related to vertical growth) as the key to vertical growth changes.15,16
The transverse planes become altered not only dentally but also dento-skeletally, which may be congenital or developmental alterations.
Structural cranio mandibular asymmetries are congenital (heredofamilial) or acquired (traumatic and/or infectious) in origin, which can be accentuated during growth, depending on the severity or manifestation of the asymmetry. The alterations have repercussions on the settling of the occlusal plane and in most cases lead to different occlusal planes, meaning that on one side there is one occlusal plane and on the contralateral side there is another, depending on the severity of the asymmetry. The loads or forces of the muscular system are also of utmost importance for the development and correct functioning of the occlusion, because they determine to a large extent the adaptation or disadaptation of the musculoskeletal system.17-19
Asymmetries are present in the three planes of space and can manifest themselves in the three thirds of the face, however, the lower third presents the greatest problem, perhaps because it is where the components of the stomatognathic system (muscles, ligaments, teeth, joints, etc.) participate. The occlusal plane will be a determining factor in the position and adaptation of the mandible, varying the degrees of inclination of the occlusal plane or planes that the patient's occlusion presents. Therefore, the degree of inclination of the occlusal plane or planes will be directly proportional to the degrees of deviation of the mandible, both of its hard and soft tissues and with respect to the facial midline or elements of assessment of facial symmetry.11,14,17,18,20
It is common to find that temporomandibular disorders (TMD) develop in facial asymmetries, both on the side towards which the mandibular deviation is present, as well as towards which the occlusal plane canthus is located, where it is more frequent on the ipsolateral side (side towards which the canthus is located), than on the contralateral side. Most studies of facial asymmetry focus on mandibular deviation, and some have described the relationship between lateral mandibular deviation and occlusal plane inclination.
There is a strong correlation between lateral deviation of the mandible and maxillary canthus, which tends to be the inclination towards which the mandible deviates. However, on some occasions the mandible can be deviated to one side and the occlusal plane can be inclined to the contralateral side.
Generally, the areas of greatest occlusal force and occlusal contact area are on the side to which the mandible is deviated and to which the occlusal plane is inclined, although it should be noted that this is not necessarily the side where joint symptomatology predominates (Figures 4 and 5).11,12,18,19,21
The correction of dentolabial deformities often requires bimaxillary surgery to achieve an adequate aesthetic and functional result, which should be corroborated by essential cephalometric and clinical criteria, but the decision certainly depends on the angulation of the occlusal plane to be obtained. Leaving a functional occlusal plane will be determined primarily by cephalometric assessment.
Among the considerations we must take into account regarding the TMJs, first of all, we must evaluate the status in which they are prior to surgery, particularly in cases in which the inclination of the occlusal plane will be reduced. The movement(s) carried out to reposition the occlusal plane should always be carried out without overloading the muscles on the joints, soft tissue and dentoalveolar structures so that they have the opportunity to readapt (Figure 6).11,22-24
Opdebeeck et al.25 established the morphometric and anatomical differences by cephalometry in patients with long-face and short-face syndrome. The main morphological difference is associated with the rotation of the mandible, which in the former syndrome is downward and backward (clockwise). In contrast, in patients with short-face syndrome the mandible rotates anteriorly and superiorly (counterclockwise), which represents changes in condylar position, due to mandibular rotation, and in other anatomical structures that change position such as the hyoid bone and even the tongue.
The recognition of the occlusal plane seems to be straightforward, but when the clinician is confronted with alterations of excessive curvatures, open or deep bites or severe malocclusion where it is complicated to determine the occlusal plane, Reyneke suggests working with the use of two different occlusal planes, the upper and lower occlusal planes, which are fully applicable to surgical planning.19,24,26-28
CONCLUSIONS
Determining the occlusal plane is a simple procedure that should not have any major errors or complications when it comes to locating it, as long as we are clear about the criteria (diagnostic, therapeutic, dental and facial aesthetics, smile, functional aspects, stability, etc.) that will be applied to carry out a given treatment. There are different occlusal planes that we can use in our planning, depending on the type of treatment that we will carry out (preventive or early phase, interceptive or corrective orthodontics, orthognathic surgery treatment, etc.).
The establishment of the occlusal plane is primordial and basic during the treatment of a malocclusion, because it has a direct relationship with the function and stability of the treatment to be chosen; and it will depend to a large extent on the harmony and good functioning of the TMJs, as both must have a complete functional synchrony relationship.
In the second part of this article we will show how the inclination of the occlusal plane is proportional to the inclination of the articular eminence and is directly related to the inclination of the anterior teeth, which allows the temporomandibular joint to really function as an orthopaedic joint in centric relation, free of overload and where the muscles that are involved work in neuro-pacification.
REFERENCES
AFFILIATIONS
1 Expresidente del Colegio de Ortodoncia y Ortopedia Dentomaxilofacial del Distrito Federal. México.
2 Profesora invitada en el Posgrado de Ortodoncia de la Universidad Autónoma de Baja California (UABC Campus Mexicali). México.
CORRESPONDENCE
Dr. Lorenzo Puebla Ramos. E-mail: lorenzopr_1@hotmail.comReceived: Agosto 2019. Accepted: Octubre 2019.