Anterior Reconstruction: Beginning with the End in Mind
When starting any type of construction project, it essential that the builder use a well considered and calculated architectural design. The plan must clearly designate the building materials as well as provide enough support for the structure to sustain repeated stresses. In addition, the designer must pay extreme detail to the exterior appearance of the venture. With careful planning, the final project should have predictable longevity, outstanding visual appeal and the approval of the patron.
So too is the case with dental rehabilitation, where careful selection of materials, understanding of esthetics and protection against occlusal forces are all essential for a successful reconstruction.
The Leaning Tower of Pisa is an infamous example of poor engineering and the consequences that result from poor foundation design as well as an incomplete understanding of the forces on the structure.
It is through understanding the demands of the rehabilitation, especially the interaction of the upper and lower jaws, that the clinician will then be able to determine the materials of choice, design of restorations as well as the esthetic demands of the treatment.
As with a poorly engineered building, failure to understand and properly implement a correct guidance will result in poor stability of the final restorations, though the damages due to this instability may take several years to be manifest.
Anterior guidance, determines how the anterior and posterior teeth of each jaw interact with the other, and as such it is responsible for posterior function. Proper attention the forces of the occlusion will result in coordination of muscle function, successful phonetics and the complete comfort and stability of the oral facial complex.
Frank Lloyd Wright, a renowned early 20th century architect, coined the phrase: Form follows Function. Similarly, in dentistry, providing a well planned anterior guidance in harmony with phonetics and the neuromuscular zone of neutral forces will naturally provide an esthetic result.
Proper anterior guidance depends on the contact of the and lingual contours of the upper anterior teeth as well as the shape and position of the incisal edges of the lower anterior teeth, in centric relation, long centric, as well as protrusive and lateral excursions. The interactions between these two surfaces are the basis of anterior guidance.
The incisal edges of the lower teeth are visible when speaking, while the lingual contours of the upper incisors are invisible during normal social interaction, thus it is necessary to first define and determine the position of the mandibular incisors prior to developing the lingual contours of the upper incisors.
In the development of occlusion of a child, the erupting lower incisors are guided into position by the muscular forces of the lips and tongues prior to the eruption of the maxillary incisors and the upper incisors follow suit. Similarly, the desired position of the incisal edge of lower anterior teeth must be determined prior to the placement of any final restorations to the maxillary anterior teeth. Any changes to the lower incisal edges and/or the lingual contours of the upper teeth affect their interaction and consequently the anterior guidance. While changes to the lingual contours of the upper teeth are essentially invisible to an observer, the incisal edges of the lower anterior teeth are far more of a factor in esthetics. In fact, it is the incisal edges of the lower teeth that are most visible when speaking. Therefore, careful attention to the position and shape of the lower anterior incisal edges of the Mandibular incisal edge position must proceed treating the maxillary anterior teeth. This is crucial to a successful treatment.
However, mandibular incisal edge determination of the position of the lower incisors can not stand alone. It must be simultaneously be coordinated with the determination of the incisal edge position of the upper teeth. This can be accomplished by thorough examination of the patient, along with examination of the patient’s diagnostic records (photos, mounted models, radiographs, etc.). The determined restorative incisal position should be assesses by means of a diagnostic intra-oral mock-up. This diagnostic mockup allows the patient to test this position through a series of criteria including esthetics, phonetics and lip support, neutral zone. This upper incisal edge can be coordinated with the lower incisal edge position, but can not be finalized until the lower incisal edges are satisfactorily situated.
The clinician however may be tempted to start with the upper teeth are because the patient wants a quick fix to the front teeth. However, the lingual contours of these teeth may not be correctly developed for any necessary changes in the incisal position of the lower anteriors. This could result in over eruption of these teeth due to inadequate occlusal stops, or worse, the necessity of grinding the lingual contours of newly placed maxillary restorations to allow for the changed and now functional and esthetic position of the lower anteriors placed in a second stage of treatment.
Functional Anterior Guidance requires three basic criteria:
- No occlusal interferences to Centric Relation
- Complete disclusion of all posterior teeth when the mandible moves from centric relation to protrusive and lateral excursions. (This can be determined by the use of blue and red articulation paper. Have the patient tap into CR with the blue paper followed by placement of the red articulating paper between the teeth for marking any contacts that may occur during lateral and protrusive excursions. Any marks that appear on the posterior teeth in red alone are indicators for interferences and insufficient anterior guidance.)
- Lack of mobility of anterior teeth through excursive movements
In addition, a healthy anterior dentition must be in harmony with all neuromuscular forces, allow for clear phonetics and desired esthetic.
When starting to develop anterior guidance the first step after elimination of all interferences to centric relation, is to determine the incisal edge position, starting with the incisal position of the mandibular teeth. The clinician should perform a complete examination of the anterior dentition.
- Are the teeth relatively straight or would they benefit from either orthodontics or veneers’
- Are the anterior teeth severely worn with short clinical crowns due to over eruption’
- Does the patient require periodontal surgery to lengthen these clinical crowns’
- Are the lips fully supported, or are lips thin or excessively protrusive’
- Are the teeth excessively crowded’ This can often be remedied by simple orthodontic treatment, delaying maxillary anterior rehabilitation by only a few months.
- Is there super eruption of individual lower teeth’ This is due to absence of occlusal stops. These teeth should never be shortened without providing a stable maxillary occlusal stop or splinting to adjacent teeth, as the shortened teeth will continue to over erupt until reaching a centric stop
- Vertical Face Height:
- Has the vertical face height been lost due to wear and premature tooth loss’
- Does the bite require opening (increasing vertical face height) to restore proper facial dimensions and support of the facial musculature and soft tissue’
- Is there any mobility or drifting of these lower anterior teeth that may require splinting and/ or periodontal therapy’
- Is there active periodontal disease that will result in poor or unpredictable longevity of the rehabilitation’
- Evaluate ‘ssss’ to determine the adequacy of the air space between the upper and lower incisors or does the patient lisp due to placement of the tongue to fill the void between incisors
- Determine if the upper incisal edge position when enunciating ‘ffff’. It should be on the border between the wet and dry portion of the lower lip.
- Occlusal Plane:
- What is the patient’s occlusal plane’ Is there an excessively deep Curve of Spee or is it flat and possibly preventing anterior guidance during protrusive excursions
- Does the patient have any habits that prevent the anterior teeth from contacting’ This could include nail biting, lip biting, mouth breathing, pipe smoking and tongue thrusting. Some habits such as lip or tongue biting may actually be the patients’ subconscious attempts to avoid occlusal prematurities and may disappear follow equilibration of the occlusion
If the lower anterior teeth do not meet all the above criteria, then their inadequacies must be addressed prior to treating the upper anterior teeth.
Once desired treatment of the anterior teeth is determined, it should be first worked out on an accurately mounted diagnostic model with a semi-adjustable articulator using accurate centric, protrusive and lateral bite registrations. (The setting of the articulator to average protrusive and lateral movements is often acceptable, eliminating the need for protrusive and lateral check bites.)
It is on these mounted models that a diagnostic wax up is made. This wax up should precisely delineate the desired incisal edge position and provide all the requirements of proper anterior guidance. This wax up should be duplicated in stone and impressed with a putty matrix which is to be used as a template for the temporary restorations. The patient should be allowed to wear and function in the temporary restorations based on the diagnostic wax up to determine if all the above outline requirements of successful anterior guidance are met.
Should the patient have any dissatisfaction with the temporary restorations, these issues must be met while the patient is still in temporaries. It is relatively easy to make the necessary changes in the temporary restorations, but possibly disastrous once the final restorations have been placed.
Once the patient is fully satisfied with the temporary restorations, new impressions of these temporary restorations in the patient’s mouth should be made and forwarded to the laboratory technician along with a detailed description of the desired restorations. The technician will make a matrix of these temporary restorations. The mounted model will be used to produce a custom guide table to reproduce the lingual contours of the upper teeth as well as the matrix to reproduce the incisal and buccal contours of the acceptable temporary restorations.
By fully examining, evaluating and treating the lower anterior teeth, if required, the clinician can be sure of providing a stable, predictable and esthetic rehabilitation for the patient.