Occlusal Considerations, Concepts and Treatment Planning for Full Mouth Rehabilitation of Mutilated Dentition

Headnote

Abstract

Complete occlusal rehabilitation of a breakdown dentition to its full form and function is a challenging task. The aim of the restorative procedure is to provide an ordered pattem of occlusal contact and articulation, which will optimize oral function, occlusal stability and esthetics. It involves not only replacement of lost teeth or tooth structures but also restoration and maintenance of health and functional integrity of the dental arches by the use of inlays, crowns, and fixed and/or removable partial denture prostheses. Restorations are complex in nature. Many concepts have been discussed in the literature. This article analyses PankeyMann-Schuyler (PMS), and Hobo's Twin Stage concept.

Keywords: Occlusal rehabilitation; Pankey-Mann-Schuyler; Twin Stage; gnathological concept; vertical dimension of occlusion.

Introduction

Rehabilitating the occlusion of a mutilated dentition is biologically and technically a challenging task. The challenges faced by the restorative dentists are to achieve the comprehensive treatment goal to maintain the optimal health of the stomatognathic system by restoring the lost anatomic form and functional harmony, and also occlusal stability. The masticatory system is the functional unit of the body, primarily responsible for chewing, speaking and swallowing.1 The system is made up of teeth and their supporting structures, craniomandibular articulations, mandible, positioning and accessory musculatures, tongue, lips, cheeks, oral mucosa and associated neurologic complex.2 The most common shortcoming in analyzing or rehabilitating occlusal relationship is the failure to consider all the parts of the masticatory system. Occlusion is not limited to occlusal contact of maxillary and mandibular teeth alone. The teeth are merely apart of this system, and frankly there is no way to evaluate occlusal relationship until we have first ascertained that the temporomandibular articulation is in harmony. Deterioration of anatomic form of teeth and its supporting structures due to microbial cause or stress factors can produce occlusal instability that may lead to temporomandibular problems, or vice versa. Some developmental anomalies like emelogenesis imperfecta can also contribute to such decimation of natural dentition. Extensive generalized destruction of natural form of teeth and supporting structure make an individual physically and esthetically handicapped. Often demand for esthetics, motivates these patient to seek dental treatment.3 4

Functional and esthetic rehabilitation of mutilated occlusion is started with careful evaluation of every component of the masticatory system, diagnosis, conceptual analysis of need and proper treatment planning for such complex restoration.5 7 Many concepts have been described.810 Pankey-Mann-Schuyler (PMS) philosophy, and Hobo's-Twin Stage Gnathological concept is in a brief showcase of this article.

Occlusal Consideration

To establish the occlusal contact relationship of the maxillary and the mandibular teeth during complete occlusal rehabilitation of a mutilated dentition, the restorative dentists should have proper knowledge and understanding of the same that exists in natural dentition during centric relation, centric occlusion and as well as during lateral movement of the mandible. In a dentate adult individual centric occlusion may not identically coincide with the centric relation. However, during complete occlusal reconstruction centric occlusion should be built only in centric relation position.

A) Types of centric relation contact: The 2 basic centric occlusal contact relationships that exist in natural dentition are: cusp tip to fossa contact, and cusp-marginal contact relationship. Cusp tip to fossa contact relation is less common in natural dentition; but it is a better choice for restoring the natural occlusal relation of a mutilated dentition. This type of occlusion is easy to build and the easiest to equilibrate. When cusp tips are located in the most advantageous fossae, they can direct the occlusal forces as near parallel as possible to the long axis of each tooth. Thus, these types of occlusal contacts offer excellent function, resistance to wear, and stability, with the flexibility to choose any degree of distribution of lateral forces that is warranted.11

B) Types of occlusal contact in mandibular lateral excursion: Occlusal contact relation during mandibular lateral excursion is thought to be crucial for the diagnosis and evaluation of restorative and reconstructive dental treatment.12 Dawson divided the excursive contact relations as working side occlusion and non-working side occlusion.11 He described that the non-working condyle is not solidly fixed against the unyielding bone and ligaments. Rather, it can move little up, since the mandible band is slightly under firm mus ele pressure. Consequently, such contacts should be avoided in permanent dentition. It has also been proposed that non-functional interference might cause damage to supporting tissues, jaw muscles, and tempormandibular joints.12 Three types of working side occlusal contacts can be seen in natural dentition:

1. Group function

2. Partial group function

3. Posterior disclusion

1. Group function contact: It was first described by Schuyler as the unilateral contact of a group of teeth on the working side, also referred to as unilateral balanced articulation.13'14 This type of contact relation intends to distribute the harmful lateral occlusal forces to all the teeth in group contact rather than assigning all the forces to one particular tooth. However, only 8% of the natural dentition shows even contact between maxillary and mandibular teeth on the working side during lateral movement.15

2. Partial group function contact: It refers to allowing some of the posterior teeth to share the load in excursions whereas others contacts only in centric relation. Thus, weaker teeth with poor periodontal support can be kept out of occlusion in order to protect them from lateral forces.

3. Posterior disclusion: It refers to no contact of any posterior teeth in any position but in centric relation. Stuart and Stallard proposed this occlusal scheme as "mutually protected articulation". In this scheme all posterior teeth prevent excessive contact of the anterior teeth in maximum intercusp ation and the anterior teeth disengage the posterior teeth in all mandibular excursive movements.16

Posterior disclusion can be achieved by 2 different type of anterior guidanc e :

A) Anterior group function- It refers to contact of a group of anterior teeth that disclude the posterior teeth. This type of contact is considered beneficial as because the anterior contacts are progressively farther from condyle fulcrum. It produces less stresses that are distributed to more teeth. Despite these advantages, anterior group function is not applicable in all cases because some arch relationships do not permit the incisors to contact in lateral excursions.

B) Cuspid protected occlusion- It refers to disclusion of all other teeth by the cuspid of the working side. Cuspids serve as the cornerstone in mutually protected occlusion, provided they are in good state of health to withstand the lateral stress load without any help from other teeth. The fact is that minimal lateral stresses are produced by this contact if the lingual contour of the cuspids is in harmony with the functional border movement of the mandible. D'Amico stated cuspid-protected occlusion and disclusion as the natural adaptation for preventing a destructive occlusion.17

Diagnosis and treatment planning

Successful treatment of a patient who seeks complex dental restoration requires a thorough evaluation for correct diagnosis of the problems and developing a proper treatment plan. However, the extent of problems for many of these patients frequently makes the diagnosis and treatment planning a difficult task. Patients with skeletal and dental abnormalities, severe occlusal disease, or extensive periodontal disease coupled with multiple missing teeth, collapsed occlusions, and years of dental neglect and/or inadequate dental care can present with an extremely complicated and initially confusing set of circumstances. Therefore, it is imperative that a consistent and systemic approach to planning treatment for rehabilitation of such patients be made. These patients require multidisciplinary treatment, the most logical and orderly approach is to execute through an evaluation of the existing occlusion and comparison of that condition to an occlusal scheme that would be physiologically, functionally and esthetically most durable.

Dawson adopted 2 of the best rides to follow for staying out oftrouble with restorative procedures as follows:11

1. Never begin any restorative procedures unless all the procedures that follow are outlined in advance and properly related to one another in correct sequence.

2. Never begin any restorative procedure unless the result is visualized and understood.

Preliminary mouth preparation

All the preliminary procedures should be completed before starting the actual restorative procedures.

1. Oral hygiene measures and proper home care instruction should be given. Patients should demonstrate the ability and interest in home care before extensive restorative procedures are started.

2. Caries control should be achieved. Adequate conservative procedures and if indicated endodontic therapy should be completed. Sometimes intentional endodontic therapy also has to be performed in order to establish the occlusal plane.

3. Periodontal therapy should be completed and adequate time should be allowed for tissue maturation before final preparations are started.

4. Orthodontic procedures for required orthodontic correction and stabilization of occlusion.

5. Necessary extraction should be done and tissues healed before final preparation is made. Selection and placement of implant should also be considered.

Once these required preliminary procedures have been completed, evaluation of the existing dentition is done in the following order to draw out the actual restorative treatment planning.

Centric relation: Maxillary and mandibular diagnostic casts are mounted to a semi adjustable/fully adjustable articulator by means of face bow transfer. This enables to both evaluate and test the current state of health of the patient's TMJs, as well as to relate the intercuspal position of the teeth to the centric relation position. If any interference between these 2 positions exists, occlusal equilibration should be done. It may be necessary to fabricate provisional fixed restorations or splints in order to optimize preliminary mouth preparation. The goal of such procedures is to make TMJs comfortable, restore the health and status of the teeth and periodontium before final preparation of teeth and cementation of fixed restorations.

Vertical dimension of occlusion: Following evaluation of the centric relation position, the VDO is assessed. The vertical dimension in physiologic rest position is assessed to determine the existing inter occlusal clearance. If sufficient inter occlusal clearance exists, the restorative dentist can judge to alter the VDO to establish the adequate height of the face. The alteration may require in few of the many clinical situations with "posterior bite collapse" that do not present with enough inter arch space to accommodate a new prosthesis to restore lost form, function, aesthetics, and health and comfort of the patients.

Plane of occlusion: The occlusal plane is "the average plane established by the incisal and occlusal surfaces of the teeth".2 This plane, the dental arches, and teeth have a speci fic relationship to the temporomandibular joints (TMJs) and to the horizontal plane. Correct positioning of the dental cast on an articulator, which replicates these relationships in the patient, is a pre-requisite for the functional and esthetic success of the prosthesis. Correct mounting of the maxillary cast by means of face bow transfer with third point reference facilitates this job taking the 'axis orbital plane' as the horizontal reference plane. The occlusal plane is established parallel to the ala tragus (camper) line.

Maxillary incisal edge position: In the intact and healthy Class I occlusion, the maxillary incisal edge position represents the anterior extension of the posterior occlusal plane. Hence, when the posterior teeth are missing or the plane of occlusion is so deviated that it must be re-established, posterior extension of a line from properly positioned incisal edges of the maxillary incisors, closely parallel with the ala-tragus line, will establish a plane to which the posterior teeth may be set in the reconstruction. There is obviously some variability in maxillary incisor edge position based upon esthetic and phonetic concerns.

Mandibular incisal edge position: Initial consideration of mandibular incisal edge position also begins early in the diagnostic phase of treatment, when the VDO is assessed. Dynamic relationship of the mandibular incisal edges with the lingual inclines of the maxillary incisors will determine the type and amount of incisal guidance that will be established for the final restoration.

Concepts of Occlusal Rehabilitation

Many concepts have evolved based on different theories.18 However, the modem schools of occlusion believe in developing a biologic/physiologic occlusion with its philosophical goal of function and maintaining the health and comfort of the stomatognathic system.

Goals of Biological Occlusion

- No interferences between centric occlusion and centric relation

- No balancing contacts

- Cusp-to-fossa occlusal scheme

- Cuspid protected or group function

- No posterior contacts with protrusive jaw movements

- No cross-tooth balancing contacts

- Eliminate all possible fremitus

Many of the modem concepts including PMS and Hobo's twin-stage (Gnathological) concepts substantiate the philosophies ofbiologic occlusion.818

Pankey, Mann, Schuyler System

In the late 1920s, groups of researchers began to formulate systematic approaches to restoring the natural dentition. Pankey and Mann are examples of this evolutionary process of formulating concepts for natural dentitions while also devising a systematic approach to reconstructive dentistry. The Pankey- Mann system was originally an amalgamation of the Monson theory and the Meyer functionally generated path technique, where they attempted to gain bilateral balance in eccentric movements (a holdover from complete denture occlusal theories).18 The technique involved restoring the mandibular posterior occlusion to a 4-inch sphere as described by Monson. The maxillary posterior occlusion was then fabricated to the mandibular occlusal form by using the maxillary anterior teeth as guides for the "chew in" registration as advocated by Meyer. A few years later Schuyler joined with Pankey and Mann to evolve what is now known as the PMS (Pankey, Mann Schuyler) System. This occlusal system retained the Monson spherical theory and the functionally generated path technique ; however, under Schuyler's influence the balancing side contacts were eliminated and the importance of incisal guidance was elevated. The concept of "long centric" or "functional centric occlusion" was proposed in which centric occlusion is thought of as an area of contact rather than a point contact. The Hanau occlusal instrument with arbitrary face bow and Broadrick occlusal plane analyzer was adopted. Thus, restoration of decimated occlusion using PMS philosophy can be performed in the following sequential steps:

I) Preparation and restoration of mandibular anterior teeth followed by maxillary anterior teeth in harmonization of the anterior guidance for best possible esthetics, function, and comfort (Figure lato Id)

II) Restoration of mandibular posterior teeth: Occlusal plane is established using Broadrick occlusal plane analyzer and indexes for occlusal reduction of mandibular posterior teeth are made. After preparation of teeth, fossa contour guide is prepared using anterior guidance index on the incisal guide table of the articulator. Provisional restorations are fabricated to cusp tip to fossae occlusion using the diagnostic wax-up as guide. Final restorations are fabricated into the same occlusal scheme (Figure 2a to 2i)

III) Restoration of maxillary posterior teeth using functionally generated technique (Figure 3a to 3e)

Hobo's Twin Stage Concept

The basic principle of this concept is to provide disclusion by designing cuspid protected occlusion. After a thorough evaluation and required preliminary procedures this concept is selected. All the maxillary and mandibular teeth are prepared before final impressions are made. The Broadrick occlusal plane analyzer is used to establish the occlusal plane and also to make indexes to guide the amount of occlusal preparation. Provisional restorations are given based on the diagnostic wax-up. Hobo had designed "Twin Hobo Articulator" for this concept. The rehabilitation work is completed in centric relation position by methodical approach in twin-stage referred as :

Condition I- Reproduce the occlusal morphology of posterior teeth without the anterior segment and produce a cusp angle coincident with the standard values of effective cusp angle (Figure 4, above) by adjusting the articulators as below:

Sagittal condylar guidance: 225°

Bennet angle: 15°

Incisal guidance: Sagittal inclination 25°, Lateral wing angle 10°

Condition II- Reproduce anterior morphology with the anterior segment and provide anterior guidance which produce a standard amount of disclusion. The articulator is adjusted to the following mechanical values (Figure 4, below):

Sagittal condylar guidance: 40°

Bennet angle: 15°

Incisal guidance: Sagittal inclination 45°, Lateral wing angle 20°

In condition I the occlusal morphologies are designed to balance articulation without anterior teeth so the cusp angles become parallel to cusp path of opposite teeth during eccentric movement. Waxing up the anterior teeth to Cus- pid protected occlusion in condition II by readjusting the articulator to mechanical equivalent i.e., greater than the condition I provided anterior guidance to produce standard amount of disclusion.

Discussion

Rehabilitation of a decimated occlusion with a primary therapeutic goal to restore and maintain the health, function, and beauty of the stomatognathic system is not an easy task. Thorough evaluation to draw out a systemic treatment planning keeps the restorative dentist out of trouble with the restorative procedures.6 7 One should not start the restorative procedures before visualizing the end result.11 Skeletal and dental abnormalities coupled with years of negligence make these restorative works very complex. The restorative dentists should seek help of multidisciplinary expert hand to solve all the preliminary procedures.

Many concepts of occlusal rehabilitation have been evolved.9'10 The early concepts proposed before 1930 in part are based on theory and interrelated, contributing to evolution of new concepts. Most of the early concepts were being basically formulated for complete denture patients in which bilateral balanced occlusion in eccentric movements was considered essential. Concept of balanced articulation was not acceptable for natural dentition. Based on the understanding of the 3D mandibular movements, McCollum, Stallard, Stuart and predecessors worked on the Gnathologic concept and designed sophisticated 3-D articulators to reproduce the mandibular movement.101 Modem occlusal concepts basically believe on biologic principles to restore and maintain the health and function of the masticatory system.

PMS-system as improvised and described by Dawson is a very flexible concept. The most impressive advantage of PMS philosophy is the latitude it permits.11 Treatment model within this concept can be varied from the simplest technique for the beginning restorative dentists to the most precise details of the master reconstmctionist. Again PMSphilosophy is not limited to any specific instruments unlike the Twin-stage philosophy introduced by Hobo and Takayama.s 1920 This was categorized as an improving concept in Gnathology with introduction of fully adjustable 3-D Twin Hobo Articulator. However, the author has successfully rehabilitated few cases (Figure 5 shows one such case before and after completion of restorative therapy) by using semiadjustable (Hanau wide view) articulator with equivalent mechanical values. Both the concepts rationalized the necessity of disclusion to reduce the horizontal stresses by developing canine protected or mutually protected occlusion. However, the need of group function and partial group function in some periodontally compromised condition and implant occlusion was not overruled. The disadvantage of the Twin stage includes restrictions for achieving ideal occlusion when altering the vertical dimension, occlusal plane and embrasure development.2122 The Twin stage procedure are not recommended for few cases with abnormal curve of Spec, curve of Wilson, abnormally rotated tooth, and abnormally inclined tooth.8 Yet, Hobo's Twin stage technique is an easy, less time consuming method of occlusal rehabilitation which can be conveniently adopted to provide predictable results.23

Conclusion

With the advent of new materials and techniques, mainly tremendous progress in the field of adhesive technology, continuous evolution of dental ceramics and implant dentistry, treatment modalities are being changed. With growing of industrializations, esthetic demands of dental patients have also been increased. Considering this paradigm shift, restorative dentists should select the occlusal concepts and related techniques and materials for reconstructing breakdown occlusion. However, the importance of thorough and meticulous evaluation before starting the restorative procedures should not be overlooked, to achieve desired long-term structural and functional success of the complete occlusal reconstructive therapy.

References

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