OCCLUSAL EQUILIBRATION BETWEEN OPTION AND CLINICAL REALTY
Sever Toma Popa1a, Sanda Mihaela Popescu2b*, Marian-Vladimir Constantinescu3c
- Department of Prosthetic Dentistry, Faculty of Dentistry, “Iuliu Hatieganu” University of Medicine and Pharmacy, Cluj-Napoca, Romania
- Oral Rehabilitation Department, Faculty of Dental Medicine, University of Medicine and Pharmacy of Craiova, Craiova, Romania
- Department of Prosthetic Dentistry, Faculty of Dental Medicine, “Carol Davila” University of Medicine and Pharmacy Bucharest, Bucharest, Romania
a DDS, PhD, Consultant Professor
b MDM, PhD, Associate Professor
c DDS, PhD, Professor
Associate Professor Sanda Mihaela Popescu, MDM, PhD
Faculty of Dental Medicine, University of Medicine and Pharmacy of Craiova, 2-4 Petru Rares Str., RO-200349 Craiova, Dolj, Romania.
Occlusal dysfunctions generated by occlusal interferences as a part of occlusal pathology actually have a growing frequency in oral pathology. Unfortunately because of theirs insidious appearance, they are unnoticed until injurious effects are observed or the patients have a dental, muscle or temporomandibular joints pains.
If, occlusal interferences would be observed at the beginning of their appearance, the occlusal adjustments will be rarely necessary. To practice the occlusal equilibration techniques need to respect some accurate steps by step technical stages. These principles and stages are revealed in the following text.
Key words: occlusal adjustment, occlusal equilibration, dental interferences, centric relation (CR), deflective contacts.
The mandibular neuromuscular complex has a strong adaptive capacity which permits function and protection of the masticatory system (Dawson, 1989, 2006). Deflective occlusal contacts will induce an irritable condition into neuromuscular system which will be continuously reinforced with each closure through proprioceptive feedback. This conditioned state (engrame) may induce the changes at the level of any components of masticatory system: teeth, muscles, periodontium, gingival mucosa and temporomandibular joints. Occlusal dysfunctions can be cured by use the deprogramming methods (Popa S, 2004).
One of the frequently used deprogramming techniques is occlusal equilibration (Wenneberg et al, 1988; Constantinescu, Ene, 1995) or selective grinding (Winstanley, 1986; Saito, 1990; Acosta, Roura, 2009). Occlusal equilibration is a therapeutical abrasive technique that can remove or correct occlusal interferences using a selective grinding of cuspal slopes or ridges of the teeth interfered with normal functional occlusal paths. This method of correcting occlusion can be applied at the occlusal surface of natural or prosthetic teeth using occlusal therapeutic grinding techniques. The best means to practice this method is to consider centric relation (CR) as best concept for the settlement, registration, transfer and reproducibility reference position of the mandible. This reasoning relies on the stability of physiologic hinge axis position during relaxed and asymptomatic function of elevator muscles of the mandible and the pain releasing of the temporomandibular joints dysfunction patients to whom occlusal adjustments are to be made. The recording of precise and reproducibility centric relation with a hinge axis around mandibular condyles can made a pure rotation movement, is the first step of a method claimed to provide a true and correct occlusal equilibration.
Kerstein et al (1990, 1991, 1992, 1997, 2010) published other technique called immediate complete anterior guidance development (ICAGD). This technique assisted by computer aimed to obtain a successful reduction in disocclusion time, reducing contractile muscle activity and interrupting fatigue and spasm in masticatory muscles. Compared with classical occlusal equilibration, this technique let all jaw movements free and unguided by the operator and the sequence of adjustments were completely reversed from that of traditional occlusal equilibration. All mandibular excursions were adjusted and immediate posterior disoclusion in all excursions was established before any habitual closure adjustments were done. Molar contact was decreased.
Occlusal equilibration is indicated because it removes the disagreement and occlusal and temporomandibular joints dysfunctions of the TMJ-dysfunction syndrome. Full functional maxillary and mandibular dental arches has the role to protect a harmonious occlusal function against parafunctional activity of neuromuscular system: pain around the temporomandibular joints or the masticatory muscles with or without clicking, inability to fully open the mouth, head and neck aches (Torii, Chiwata, 2007). The factors as interocclusal distance envelope of mandibular motion, chewing stroke, tooth to tooth relations and determinants of occlusion can be improved by occlusal adjustments at the level of working or balancing quadrants.
An equilibrated occlusal function can be also achieved by dental prosthesis or orthodontic devices (Gupta et al, 2012). Occlusal adjustments techniques can be applied on natural teeth or on the teeth of fixed prostheses applied on the natural or implant abutments. The purpose of occlusal adjustments is to obtain a functional occlusion not an ideal one. The ideal occlusion is not a practical functional occlusion; it is a theoretical, fictional one. The occlusal equilibration in the case of complete dentures is made somehow different from it is made on natural dental arches. It is coordinated according to the Gysi‘s occlusal prosthetic concept: occlusal support on at list three points on all functional paths: right, left sideways and protrusive.
- The improvement of functional mandibulo-maxillary interrelations and of physiologic dento-periodontal stimuli.
- To remove occlusal trigger factors and muscle spasms joined with pain and functional discomfort.
- The removal of pain dysfunction TMJ syndrome,
- The steadiness of an equilibrate occlusal function before of any prosthetic treatment,
- The used dental crowns can be contour with a view to improve masticatory efficacy and periodontal tissues protection,
- The stabilization of therapeutical results of orthodontic treatments.
The main targets of occlusal adjustments
- Primary occlusal trauma which affects odontal tissues: teeth and dental pulp, periodontium, temporomandibular joints, neuromuscular system, oral mucosa.
- Secondary occlusal trauma which affects physiological teeth mobility and hard and soft support tissues of the teeth.
- Generally occlusal adjustments are suggested to be made onto natural teeth before prosthetic treatments with a view to don’t be perpetuated occlusal cuspal incongruous slopes.
- The limitation of the envelope of masticatory movements.
Elemental occlusal dental topography
The cusp slope of every tooth resembles a gothic pyramid: it has a base, ridges (slopes) and tip (Fig 1). An image of teeth occlusal contacts between the ridges of the teeth in occlusal intercuspation is explanatory. Every maxillary and mandibular lateral tooth has buccal and lingual cusps. Every cusp has buccal and lingual ridges (slopes). Every ridges (slopes) of the lateral teeth have occlusal contacts during masticatory movements (green color), excepting buccal ridges (slopes) of buccal guidance cusps of maxillary teeth and lingual ridges (slopes) of lingual guidance cusps of mandibular teeth (red color). The buccal slopes of guidance cusps of maxillary teeth and the lingual slopes of guidance cusps of mandibular teeth are rarely adjusted (Fig 2).
Matherial and method
It is customary to use for occlusal adjustments different diamond burs: round-end tapered diamond, chamfer diamond, medium wheel diamond, round diamond burs, dura-white different size, white polishing stones of enamel, thin and extra fin articulating papers.
Occlusal equilibration using dental occlusal adjustment has some subsequent stages:
- The removal all occlusal interferences on intercuspation path of mandible movement around hinge terminal axis (centric relation). These occlusal interferencies arise between CR and OC points on Posselt’s diagram (Fig 3).
Thus, on the level of teeth of quadrant sliding towards cheeks are grinded buccal ridges of maxillary support cusps, or lingual ridges of mandibular support cusps: BULL
On the level of teeth of quadrant sliding towards tongue are grinded lingual ridges of maxillary and /or buccal ridges of the mandibular teeth: LUBL (Fig 2;7;8).
On the sagittal close arch in centric relation the mandible slides toward mesial direction when the occlusal interferences are present. These mesial slides are not symmetrical (99%): usually they are mesiolaterotrusives, and symmetrical (1%). On the sagittal close arch, when the mandible slides towards mesial, because of dental interferences, the mesial slopes of maxillary cusps of lateral teeth and distal slopes of mandibular cusps of lateral teeth must be grinded:
MUDL (Fig 9).
As a rule of occlusal equilibration technique is that the slope of cusp must be grinded is that one his tip is nearer the central groove of antagonistic tooth.
- The removal of occlusal interferences on the laterotrusive (diagonotransversal) paths of masticatory cycle. The removal of occlusal interferences on the laterotrusive functionally paths is coordinated by anterior (dental) and posterior (condylar) guidances of the mandible. The laterotrusive guidance is dependent of individual masticatory cycle.
On the mandibular laterotrusive functionally paths interferences can appear at the working or balancing dental arches. As a rule the occlusal interferences of balancing arches are removed first. The mandible is guided alternatively, right and left from centric relation position on the functionally masticatory paths with the purpose of occlusal interferences registration. At the level of balancing arches are removed buccal ridges of maxillary (upper) lateral teeth or lingual ridges of mandibular (lower) lateral teeth: BULL. At the working arches are removed lingual ridges of maxillary (upper) lateral teeth or buccal ridges of mandibular (lower) lateral teeth: LUBL (Fig 10 and 11).
On the protrusive functionally paths, the occlusal interferences can appear at the mesial slopes of maxillary (upper) teeth and/or distal slopes of mandibular (lower) teeth: MUDL, or at the level of the anterior (dental) guidance path on lingual surfaces of upper frontal teeth, or on labial surfaces of lower frontal teeth. Usually, the remove of the frontal dental interference are made first, then follows the removal of lateral dental interferences. If it is necessary more adjustments, they can be repeated in the same manner.
III. The removal of occlusal interferences on the protrusive path of masticatory cycle. These interferences hinder the disclussion of lateral teeth on the protrusive path of mandible. They deviate the protrusive trajectorial direction of the mandible toward left or right sides. So, having like functional mark of mandibular protrusive movement on posterior (condylar) and anterior (dental) guidance paths, must be removed the interferences from the level of mesial slopes of the maxillary dental cusps (upper) and distal slopes of the mandibular dental cusps (lower): MUDL (Fig 12).
Subject of controversy, occlusal equilibration is a tickler. Excellent results obtained after selective grinding in cases with temporomandibular disorders reported Winstanley in 1986, Saito in 1990, McHorris in 1985 and many others. Conversely, according to Koh and Robinson (2003, 2004) clear evidence that occlusal adjustment treats or prevents temporomandibular disorders is lacking. Therefore is need for well designed controlled studies to analyze the current clinical practices and effectiveness.
Occlusal equilibration is not an easy treatment because if it isn’t correctly conceived and performed, it will be more injurious than if it would not be made. That is why there are some rules respecting how to carry it into practice:
- The precise diagnosis and localization of occlusal interferences.
- The identification of abrasion facetes on the dental cusps.
- The verification on the casts mounted on semiadjustable articulators the occlusal interferences points registered in the patient’s mouth.
- A correct occlusal equilibration cannot be finalized during only one treatment seance.
- Wrong centric relation position of the mandible compromises occlusal equilibration by occlusal adjustments.
- The true centric relation of the mandible must be achieved having the mandibular condyles placed in their highest position in glenoide fosses, without occlusal teeth contacts
- Real centric relation isn’t obtained by “forced guidance” of the mandible but through mandibular muscles relaxation. Centric relation is a fibroligamentous connection between temporal glenoid fosse and mandibular condyles.
- Occlusal equilibration outside of centric relation position of the mandible brings about occlusal dysfunction.
The iatrogenic errors during occlusal equilibration have different reasons: the wrong initial diagnosis, a wrong premise or indication of occlusal adjustment, the insufficiency of dentist’s training in the field of occlusal adjustments and diminution of occlusal vertical dimension.
The masticatory system is a unitary functional biomechanical complex. That being so, the homogenous functional dentoperiodontal impulses have a great significance in favor of the development and maintenance of dentoperiodontal, temporomandibular joints and masticatory muscles in soundness functional capacity and resistance.
Occlusal adjustment techniques offer a direct and easy opportunity in order that obtain equilibrium of occlusal interrelations, thanks to the perception of the homogenous functional stimuli. In this way, the occlusal surfaces of the teeth are liable to a uniform, smoothly physiological abrasion process.
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