ANTERIOR GUIDANCE

Prior to dwelling into the intricacies of the “anterior guidance” it is prudent to bear a few basic concepts in mind that have a direct bearing upon the anterior guidance.

These are:-

1) The envelope of function2) Long centric

THE ENVELOPE OF FUNCTION:-

Every tooth in the mandible has an envelope of motion that outlines the outer limits to which each lower tooth can be moved. These limits of movements are imposed on the mandible. These limits are directly related to the limits imposed by ligaments, bone, and muscles on temporomandibular joint.

The envelope of function dictates the incisal edge position and consequentially determines the anterior guidance. Envelop of function is that functional movement of mandible occurring within the envelope of motion and can not be determined by recording border movements of condyle. Pantographic tracing records only the condylar border path but, there is not enough information to determine the envelope of function that occurs within the envelope of motion.

Variation in the envelope of function result naturally from how the anterior teeth were guided during eruption into their neutral position by the tongue and lips.

Mechano receptors in and around the teeth program the muscles for functional jaw movement. The incisal edge position should be in harmony with the envelope of function. The outer limits of potential jaw pathways are not a factor in location of the incisal edges or the envelope of function .The envelope of function is directly related to the neutral positioning of the anterior teeth In occlusal rehabilitations the restorations should be in harmony with envelope of function

When restorations are in harmony with the envelope of function, Stable

Results in best aesthetics, comfort and patient satisfaction

If the Incisal edges are too far posterior

Unstable

May result in Fremitus, excessive wear on the labio incisal contours of lower incisors or the lingual contours of upper incisors, tooth movement, or fracture of anterior laminate restorations

If the Incisal edges are too forward

Interferes with the lip closure and neutral zone

Unstable

May result in phonetic problems or feeling that teeth

are too large too forward

LONG CENTRIC:-

“LONG CENTRIC IS RELLY SHORT PROTRUSIVE”-FRANK CELENZA

Long centric is a freedom to close the mandible either into centric relation or slightly anterior to it without varying the vertical dimension at the anterior teeth.

Two conflicting schools of thought have given rise to the very concept of long centric:-

One school of thought is of the belief that horizontal freedom is a pre-requisite in an occlusion to accommodate a resilient relationship to the articular surfaces.

The other holds the belief that there is no resiliency of articulation at the centric relation position and hence horizontal freedom at this position is not an imperative entity.

A flat long centric is not needed in the posterior teeth even if it is incorporated in the anterior guidance

A. The condyles cannot move horizontally forward because they are up against the eminentiae at the centric relation

B. They must move downward from the centric relation to protrude the mandible. The molars must move down with the condyles

Long centric involves primarily anterior teeth

Long centric refers to freedom from centric, not freedom in centric

ANTERIOR GUIDANCE:-

Incisal guidance is the influence on mandibular movements provided by the contacting surfaces of the maxillary and mandibular anterior teeth. The steepness of the incisal guidance is influenced by the horizontal and vertical overlap of the anterior teeth.

In normal occlusion, the lingual inclines (surfaces) of the six upper anterior teeth may be considered as the incisal guide factor. The muscles of mastication and the temporomandibular joints control the movements of the mandible while the teeth are out of functional contact.

From the time the first tooth contact is made until all teeth are in full functional contact, the teeth play a progressively greater role in directing the movements of the mandible.

In the study of occlusion, we are more interested in the limited movements made by the condyles occurring while the teeth are in functional contact than we are in condylar movements made during the complete cycle of mastication.

Radical changes in lip support, incisal edge position, and lingual contours may change more than a patient's natural appearance. Along with the discomfort and the look of artificiality, improperly restored anterior teeth may contribute to the destruction of the entire dentition.

One thing that every dentist should know before he attempts to restore anterior teeth is that besides being nice to look at and to bite sandwiches with, the anterior teeth have the very important job of protecting the back teeth. So important is this job of the anterior guiding inclines that posterior teeth that are not protected from lateral or protrusive stresses by the anterior teeth will, in time, almost certainly be stressed beyond the resistance of their supporting structures.

In spite of how good the upper front teeth may look their chance of staying healthy and keeping the back teeth healthy depends on their lingual contours, specifically the contact of the lower anterior teeth against the upper anterior teeth in centric, "long centric", straight protrusive, and lateral excursions. This dynamic relationship of the lower anterior teeth against the upper anterior teeth through all ranges of function is called the anterior guidance. As such, it literally sets the limits of movement of the front end of the mandible

CONTROLLING FACTORS

In the occlusal rehabilitation of a natural dentition, there are three factors which have an influence upon or establish the occlusal contour of the posterior teeth.

1. They are the two posterior controls or the temporomandibular joints, and

2. The anterior control or the incisal guidance.

On the operator’s bench top these controlling factors are translated to the articulating instrument as:-

1. Two condylar guidances of the articulator, which represent the two temporomandibular joints, and

2. The incisal guidance formed by the incisal guide pin of the articulator and the surface upon which it functions. This mechanical incisal guidance represents the incisal guidance provided in the mouth by the anterior teeth.

These three controls function, to a degree, separately and independently, but if there is to be efficiency and harmony of functional occlusion, all intermediate occlusal contours will be influenced by them and must function in harmony with them.

IMPORTANCE OF INCISAL GUIDANCE:

Hypothesize that all the back teeth have been shortened through preparation so that they cannot touch in any position of the mandible. Now without any possibility of posterior tooth interference, we visualize the mandible closing in a terminal axis closure until the front teeth contact simultaneously against stable centric stops at the correct vertical dimension, the

First requirement of good anterior relationship has been fulfilled. The mandible should be closed into a stable tripod and the terminally braced condyles serving as the other two legs.

Since this mandible tripod is a lever that hinges at the condyle it will be apparent that the power for closing this lever is in muscles that exert the closing force between the condyles and the front teeth. The anterior teeth are all forward of the closing muscle power, so to exert stress on the anterior teeth. The mechanical result of the closing muscles would be like trying to crack a walnut by placing it at the tips of the handles of a nutcracker and squeezing the handles up by the hinge. This is the unique position of resistance to stress that the anterior teeth enjoy by virtue of their relationship to the condylar fulcrum and the source of muscle power.

The condyles braced firmly against bone and dense ligaments, form a very strong hinge that is completely capable of resisting the power of the closing muscles. The anterior teeth, when their position should be made to form a very stable stop for the front of the mandible and thereby limit its closing motion. If the closing motion of the mandible is stopped by the incisal edges of all six lower anterior teeth against stable holding contacts of the six upper anteriors, we have not only taken advantage of the position of the front teeth, we have also strengthened that position by distributing the stresses.

It is a popular fallacy, however, that whatever path the condyles follow must be duplicated in the lingual surfaces of the upper anterior teeth so that the lower anterior teeth can follow the same path. This is wrong. Condylar paths do not dictate anterior guidance, and there is no need or even advantage to try to make the anterior guidance duplicate condylar guidance. Advocates of such a concept have failed to recognize that the condyles can rotate as they move along their protrusive pathways. This allows the front end of the mandible to follow a completely different path without interfering with condylar path.

The path that the condyles travel dictates the outer limits to which the mandible can move. These outer limitations are referred to as the envelope of motion. The path that the front end of the mandible follows is dictated by functional movements of muscle as it relates the lower anterior teeth to the upper anterior teeth in the chewing cycle. The outer limits of these functional movements are referred to as the envelope of function; such functional movements occur within the limits of condylar border movements and consequently should be treated as separate entity.

To better understand how the anterior guidance differs from the condylar guidance, we return to our visualization of the upside-down tripod. Since the condyles on the back two legs of the tripod are rounded (so that the mandible can rotate around them), it is easy to see how the lower incisors that form the front leg of the tripod can slide forward on a variety of paths without conflict to either the front path or the condyle path. The same condylar path that permits the lower anterior teeth to follow a horizontal path forward will just as easily permit them to follow a 10-degree. a 30-dcgree, or even a steeper path. It does not matter whether the anterior path is flat or curved, concave, convex or parabolic; the rotating

condyles sliding down the unchanged condylar path permit the lower anterior teeth to follow any number of path variations without interference.

If the nature of the condyle path does not dictate the anterior guidance, it should be clear that the recording of condylar pathways does not in itself furnish enough information to optimally restore anterior teeth. The dentist who prepares all the teeth in either arch (or worse yet. in both arches) sometimes believes he has all the information needed if he mounts his models on a completely adjustable instrument. When he has properly recorded and transferred all the condylar pathways to a fine instrument, he may think that he "has the patient's head on his laboratory bench". Such is not the case. The best that any technician can do with such information is to guess at the contours of the anterior teeth. We do not wish to belittle the importance of condylar guidance. It is extremely important, and capturing the effect of condylar pathways by some method is one bit of information that is essential to the completion of the occlusal contours, but is only of the needed information.

Condylar pathways do not dictate the correct smile line. The precise incisal edge position varies greatly as the length of the lip and the degree of flaccidity or tightness of the lip varies. People with tight lips usually have anterior teeth that are positioned more vertically than those of people with flaccid lips, and even if the condylar guidance were the same in both types of patients, the anterior guidance would be different. It would almost always be steeper in the tight-lipped individual.

It is both practical and logical to work out the details of anterior contours in the mouth. When done in an orderly sequence, we can determine precisely how much "long centric" is needed, we can test variations in incisal edge position for phonetic correctness, and we can be guided by the mobility patterns of teeth as they are subjected to varying degrees of lateral stress. The greater the hyper mobility, the greater the need for minimizing lateral stresses. The less the mobility, the less need for changing even steep anterior inclines. By making any changes directly in the mouth, the patient is given the opportunity of approving the appearance and trying out the function comfort and phonetics before accepting the changed contours. Once the correctness of the incisal edge positions, labial contours, and lingual curvatures has been verified and accepted by the patient, the permanent restorations can be fabricated with confidence. All the information must be preserved in a usable manner, however, so that the finished anterior restorations duplicate the contours that have been tested in the mouth and confirmed as correct.

Lateral anterior guidance:

Reason for not using the term "incisal guidance" is that the connoted limitation to the four incisors is often confusing. Incisal guidance is frequently described in terms of protrusive movements only. Actually, the lateral pathways that are established on the anterior teeth have a far greater influence on posterior occlusal form, and the cuspids play a major role in determining the lateral stress-bearing capabilities of all the anterior teeth.

The occlusal contours of all the posterior teeth are dictated by both condylar guidance and anterior guidance. No posterior tooth should interfere with either anterior guidance or condylar guidance. Posterior teeth may either be dis-occluded from any lateral contact by the anterior teeth or they must be in perfect, harmonious group function with them and the condyles. Either way, the anterior guidance, as a determinant of posterior occlusal form, must be perfected before occlusal contours can be finalized.

Whenever it is practical to eliminate posterior contact while working out the anterior guidance, it is helpful. This can be accomplished in mouths that require posterior occlusal restorations by completing the preparation of the posterior teeth prior to working out the anterior guidance. If the posterior teeth do to require restorations, the anterior guidance must be worked out simultaneously with equilibration of the posterior teeth.

Since the anterior guidance is a protector of the posterior teeth, our goal is to make the anterior teeth as strong as possible so that they may carry out their protective function. Adjusting the anterior inclines when there is no support from posterior teeth enables us to fully evaluate the stress resistance capabilities of the anterior teeth and to correct them accordingly.

The ultimate goal of a correct anterior guidance is that is should be comfortable, functional, and stable even without posterior contact.

After the anterior guidance is perfected to the optimum degree possible, it can be determined how much help is needed from the posterior teeth. If the anterior teeth are strong enough to function on their own, posterior contact in centric relation may be sufficient. If the anterior teeth are weak in resisting lateral stresses, the posterior teeth may be brought into group function to help share the load of lateral forces. If the anterior guidance has been optimally corrected and is still too weak to serve its protective requirements, splinting may be necessary to bring the anterior teeth up to the necessary strength.

Close observation of the anterior teeth in the mouth is the best way to determine whether lateral movements are stressing them. Both visual and digital examination should be used to determine whether any teeth are being moved during lateral excursions. Noting the contact areas between the cuspid and the lateral incisor during lateral excursions is often a good indicator of stress. Movement of the cuspid will frequently open the contact as the jaw is moved laterally.

Upper anterior teeth that are noticeably moved by any functional excursion should be corrected. Correction usually consists of reshaping the upper lingual contours. Centric stops should always be established prior to refinement of excursive inclines, so the lower incisal edges are rarely involved in the correction of any lateral excursion interferences. Changes in the lower anterior teeth should be limited to minimal adjustments that do not involve the centric stops on the incisal edges.

Correction of upper lingual contours is patterned to accomplish two effects: re-direction of forces and improved distribution of forces. Forces are redirected by changing the shape of the contacting surfaces. The main vector of force is at a right angle to the surface contacted. Changing the surface changes the vector. The main vector of force against a steep incline is directed nearly horizontally. Changing the steep incline to a flat incline would redirect the forces more nearly up the long axis.

Improved distribution of forces is accomplished by bringing more teeth into simultaneous contact during excursions. This is often accomplished as a side benefit when force direction is improved, because more anterior teeth are brought into lateral function as steep convex inclines are changed to concave.

In mouths with poor periodontal support, poor crown root ratios, poorly shaped roots, or poor quality alveolar bone, drastic changes in contour may be necessary. To reduce stresses to the minimum, it is almost always necessary to both redirect and redistribute all lateral forces on the teeth.

Correction of upper lingual contours is accomplished by reducing the steepness of any inclines that, when contacted, cause the tooth to move. Steep inclines just lateral to the centric stops are the most common source of stress. The need for corrective flattening from centric stops out is greatest close to the stops and then diminishes as the jaw moves laterally. This most often produces concave lingual inclines that are flattest near the centric stops but may then curve into quite steep inclines to permit effective incising.

It is almost never necessary to reduce the length of aesthetically correct teeth. It is not necessary to flatten the lateral or protrusive angles all the way through the teeth to reduce stress. To do so in protrusion is aesthetically disastrous, and the resultant reverse smile line "ages" the patient many years. If lateral stresses cannot be minimized enough with concave contouring of upper lingual inclines, it would be better to stabilize the anterior teeth by splinting than to ruin the appearance of a person's smile.

The determination of whether splinting is needed or not is dependent on whether or not an aesthetically acceptable anterior guidance can be worked out that does not stress the anterior teeth to noticeable movement when firm excursions arc made.

It may be quite surprising how practically the correct concave inclines can be worked out in the mouth. As the mandible moves laterally, the orbiting condyle moves downward and the natural tendency of the jaw is to open as it moves to the side. The resultant over and down movement of the lower anterior teeth produces the concavity in the upper lingual contours, which permits lateral function with minimal stress.

An anterior occlusal problem that will have to be solved quite often involves hypermobile cuspids in a cuspid - protected occlusion. The lingual incline of the cuspids is too steep to permit any other tooth inclines from sharing the lateral stresses. Very often the cuspid inclines are convex, which forces the cuspid laterally when the jaw moves to the side.

If very little bone has been lost around the cuspids, it may be possible to eliminate the hyper-mobility with minimal changes to the cuspids. Changing the convexity to a straight steep incline with just a little concavity at and just lateral to the centric stops may solve the problem and be very compatible lo a vertical envelope of function. This may sometimes be accomplished without even bringing other teeth into group function. Slight changes very often make major improvements in function and stability. Making such corrections in the mouth, where patterns of tooth mobility can be observed, enables us to keep changes to the minimum.

The cuspid with steep or convex lingual inclines that has lost a considerable amount of bony support will need to have the inclines opened out to allow an almost flat area from centric relation laterally to accommodate the lateral side shift of the mandible (Bennett) and to permit other anterior teeth to come into group function with it. As more teeth are brought in to share the lateral stresses, the flat inclines can then curve into sleeper ones to produce the concavity. At the same time, the mobility of the cuspid will diminish until even moving the mandible laterally with firm help from the operator will not cause noticeable movement of the teeth.

Bringing more anterior teeth into group function not only distributes the stresses over more teeth, it distributes them to teeth that are progressively farther from the condylar fulcrum and in a better position to withstand the stresses. It is often possible to extend group function around to include both central teeth, and sometimes even the balancing side lateral incisor can contribute support.

While concave lingual contours usually work out quite naturally for normal to deep overbite patients, they may be contraindicated for patients with minimal overbite. The near end-to-end anterior relationship will end up with an anterior guidance that is almost flat. Lateral guide pathways may have no curvatures at all. As long as the inclines permit firm excursions without noticeable movement of teeth, the centric stops are stable, and the aesthetics and function are acceptable, all requirements for the anterior guidance have been fulfilled.

When anterior guidance inclines must fellow fairly straight paths, better aesthetics usually results from having protrusive inclines that are steeper than lateral inclines. This gives the upper smile line a more natural curvature. Flat protrusive paths in combination with steeper lateral paths accentuate the cuspids and produce a harsh, un-aesthetic, reversed smile line.

Steps in harmonizing the anterior guidance:

Preliminary Steps:

1. When indicated, lower anterior teeth should be reshaped or restored first. 2. All posterior occlusal contact should be eliminated {if posterior occlusal reconstruction is

indicated). When the occlusal surfaces of the posterior teeth are to be restored, it is advantageous to prepare them before harmonizing the anterior guidance. Taking the

posterior teeth out of contact eliminates their proprioceptive influence and makes it simpler to record centric relation slops on the anterior teeth. Functional border movements are more easily and more accurately harmonized since there are no restricting influences from posterior proprioception.

The four steps to harmony:

Step 1: Establish coordinated centric relation stops on all anterior teeth:

The dentist must manipulate the mandible and guide it into a terminal axis closure, marking with thin silk marking ribbon and adjusting until each layer incisor makes a definite mark. In most mouths, minimal adjustment is required to establish good centric stops.

Some of the common problems faced at this step are following. Deviation from first centric contact into a more closed position: All interferences should be eliminated so that the mandible may close the entire way to maximum closure without any deviation. This is the most common problem and the easiest to solve. No contact on some teeth after deviation is eliminated: This is the patient who has solid centric steps, but not on all teeth. What do we do with the teeth that are not in contact? We have three choices.

1. We can close the vertical by grinding down the centric stops until all teeth contact. This might sound harsh, but a slight closure of vertical does no harm. In teeth with severe bone loss, it may have an advantage by improving the crown-root ratio. Even with firm teeth, slight closure to gain contact is usually better than having to restore teeth to contact.

2. We can build up teeth to contact it is often necessary to make temporary restorations to build out the lingual contours into contact.

3. We can do nothing. Sometimes nothing is what we should do. Anterior teeth that are not in contact but that are stable because of a substitute contact such as lip or tongue position are sometimes better left as they are. We must just be certain that they are stable without tooth contact before selecting to leave them that they are stable without tooth contact for electing to leave them that way. If non-contacting teeth need to be restored and if we can establish enough centric stops from other teeth to program, the customized guide table, we do not have to worry about missing contacts. The restorations can be corrected on the articulator.

Missing anterior teeth: This problem is solved by making a temporary anterior bridge from articulated models and then finalizing all contours on the temporary bridge in the mouth. Correct aesthetics can be established right along with correct lingual contours.

Arch relationship problems that do not allow centric contact on all teeth: As a general rule, we must determine which teeth should contact in centric relation before proceeding to the next step. If lower anterior teeth need to be moved or reshaped, their position and contours must be corrected before proceeding with finalizing the anterior guidance.

Habits that keep anterior teeth from contacting: Before any noncontacting tooth is brought into contact, we must make sure it is not being held out of contact by an unbreakable habit. Many habits of lip biting actually result from unconscious attempts to cushion the teeth from interfering contacts. Such habits usually disappear when the occlusion is corrected. Equilibration procedures should be carried out to produce as much stability as possible prior to preparation. Any anterior teeth that could touch but do not should be evaluated carefully before they are brought into contact.

Contouring the centric stops:It is necessary for the entire incisal edge of the lower incisors to contact in centric relation. This usually produces too much of a ledge in the upper teeth. If upper contours are rounded, contact with just the labial portion of the incisal edge is sufficient. The shape of the upper contacts should direct the forces as near up the long axis as possible, but contacts on slight inclines are not as stressful as they may seem because the labial vector of force is counteracted by inward pressure from the lips. Posterior support that is harmonized to the anterior stops will also minimize the potential stress.

When all centric stops have been refined, each tooth should be checked digitally to make sure it is not being moved by centric closure.

Step 2: Extend centric stops forward at the same vertical to include light closure from the postural rest position:

This is when we determine how much long centric the patient requires. After centric stops have been established by manipulating the mandible into terminal axis closure, the patient should sit up in a postural position. The headrest is removed and the patient is instructed to tap lightly with the lips relaxed. Red silk ribbon is inserted between the teeth and the tapping is repeated. The mouth should be held open while the patients returned to the supine position and a manipulated centric closure into a darker marking ribbon made (green or blue works fine). If the red marks extend onto inclines forward of the centric marks, the centric stops should be extended at the same vertical so that the teeth can be closed either into centric relation or slightly forward of it without bumping into inclines. The amount of freedom from centric relation required rarely exceeds 0.5 mm. Regardless of the amount needed; it can be determined quite precisely by following this procedure.

Extension of the centric stops is accomplished with sharp inverted cone carborundum stone. Care should be taken not to touch the centric stops themselves. The results should be checked digitally to make sure that no teeth are jarred when the patient taps.

Step 3: Establish group function in straight protrusion:

Before protrusive pathways can be established, the precise location of each incisal edge must be determined. For simplicity's sake now, we will assume that all the aspects of lip

support, phonetics and aesthetics that dictate incisal edge position are correct. If so, all we need to do is selectively grind from the centric and "long centric" stops forward to the incisal edges. In most cases the four incisors fall right into group function as individual tooth interferences are reduced. All reductions should be done on the upper teeth. Interferences are marked by sliding forward on marking ribbon from centric to end-to-end. If one tooth marks by itself, the marked area is hollow ground until the second tooth shared the load and on until all four incisors have continuous contact forward.

At the completion of the protrusive movement, the incisal edges of the lower central incisors should meet the incisal edges of the upper centrals. If the lateral incisors can also meet edge to edge, so much the better, hut it is not always possible without ruining the aesthetics.

Step 4: Establish ideal anterior stress distribution in lateral excursions:

It is wrong to think that every mouth should have anterior group function in lateral excursions. It is just as big a fallacy as giving every mouth cuspid protection. However if the cuspid is showing signs of hyper-mobility. accelerated wear, or loss of periodontal support, both stress and wear can be diminished by bringing it into group function with other anterior teeth. While it is often advantageous to change a cuspid-protected occlusion to anterior group function, there appears to be no sound reason for changing anterior group function to cuspid protection.

The procedure for customizing the lateral anterior guidance starts with closing the mandible into centric contact. With firm help from the operator, the patient is asked to slide his jaw laterally and any movement of any teeth is noted. The excursion is repeated with marking ribbon interposed between the teeth and the marked lateral contacts selectively ground until there is continuous contact from centric to the incisal edge of the upper cuspid.

To reduce the lateral stress on any tooth or teeth, the contacting surfaces must be flattened from centric contact laterally. However, it is not necessary to extend the flat surface all the way through the teeth. The cuspid is the key tooth in lateral excursions, and as the jaw moves laterally on a fairly flat plane, teeth in front of the cuspid begin to share more of the load. This permits the lateral lingual inclines to be gradually steepened, forming concave pathway. The downward excursion of the balancing condyle also contributes to a tendency for a natural opening movement as the jaw moves laterally to form a concave over-and-down pathway of the lower front teeth.

For best aesthetics, protrusive inclines are almost always steeper than lateral inclines.

Once the dentist and the patient have accepted the anterior relationship as correct, we are ready to capture that relationship so that it cannot be lost. We must duplicate it carefully.

There are a number of ways of accomplishing this. Making a customized anterior guide table is a most effective yet simple method of transferring the guidance pathways to an instrument. It can be used with any instrument that has an anterior guide table.

Customized anterior guide table:

The customized anterior guide table is only needed when anterior teeth are being restored. If anterior teeth are not being restored, the teeth themselves (on the models) act to guide the front end of the articulator when the posterior teeth are being fabricated.

If both the anterior and the posterior teeth are to be completely fabricated on a fully adjustable articulator. the condylar guidances must all be set prior to making the custom guide table.

If the border movements of the posterior teeth are to be recorded directly through functionally generated path techniques, there is no need to precisely duplicated condyle pathways on the instrument. The result of condylar pathways will be captured three dimensionally by the functionally generated path technique at the site of the teeth themselves.

If the functionally generated path technique for later fabrication of the posterior teeth is chosen, the condyle paths may be set on the articulator arbitrarily. A practical approach is to set the horizontal path at 20 degrees and the lateral setting at 30 degrees. Condylar settings cannot be changed after the customized anterior guide table is fabricated.

Method of Fabrication:

1. After the anterior guidance has been finalized in the mouth, upper and lower impressions are made.

2. Using indentations in the bite record of posterior teeth only, a centric bite record is taken. If the posterior teeth have been prepared, the centric bite record can be taken at the correct vertical dimension with the front teeth touching.

3. After the centric bite record and the impression of the harmonized anterior teeth are completed, the preparation of the anterior teeth is begun. The model of the prepared anterior teeth should fit into the same bite record made before anterior preparations were completed. This will make the model of the harmonized anterior teeth and the model of the prepared anterior teeth interchangeable on the articulator.

4. With the model of the harmonized anterior teeth in place, the anterior guide table is flattened to 0 degrees and the special guide pin is raised about 1 mm.

5. Special acrylic with diatomaceous earth added is mixed and placed on the guide table and the articulator is closed. When the anterior teeth are in centric contact, the guide pin should indent about 3mm, into the doughy acrylic. The teeth on the upper model should then be slid over the lower anteriors from centric relation through protrusive and lateral excursions. As the front of the upper model is guided through all excursions from straight lateral to straight protrusive, the guide pin forms its own pathways in the acrylic on the guide table. The acrylic is then allowed to harden.

A customized guide table formed in this manner is in precise harmony with the guiding lingual inclines of the upper anterior teeth. As long as the condylar pathways are not

changed, the anterior guide pin, sliding on the custom guidance inclines, will produce the same movements of the upper bow of the articulator whether the model is on it or not. If the model of the prepared anterior teeth is mounted in exactly the same position as the model of the harmonized teeth, its pathways will be identical. This is of course accomplished by using the same centric bite record to mount both models.

When the customized guide table is completed, it should be checked for accuracy by making sure that during excursions the upper teeth maintain contact with the lower teeth and that the pin maintains contact with the guide table.

To cut a long story short;

Determinants of Anterior Guidance: Aesthetics Phonetics Condylar border movements Positional relationship of the maxillary and mandibular anterior teeth

Without the boundaries of the anterior teeth and the neuromuscular system the masticatory apparatus would destroy itself or muscle dysfunction would occur.

The functions of anterior guidance are: 1. To incise food 2. To aid in speech 3. To aid in aesthetics 4. To protect the posterior teeth, by directing the teeth together in centric occlusion so that the closing forces will be vertically directed onto the posterior teeth.

The anterior teeth must also allow the Bennett movement to occur so that the final closure forces will be directed along the long axis of the posterior teeth. This is of particular importance for the restoration of the canines. As more Bennett movement is introduced and the angle of the eminence is reduced more lingual concave curvature is needed. In contrast a steep eminence will be in harmony with a small amount of lingual curvature

DETERMING ANTERIOR TOOTH POSITION AND CONTOUR Step1: Refine and verify lower incisal edge position, shape, and plane. If upper anterior position ahs not been determined, it must be done in combination with lower determinations. Step2: Establish centric holding stops. This is always the first step. The correct anterior guidance cannot be determined until all interferences to centric relation have been eliminated. Step 3: Lip support in line with alveolar contour. The upper half of the labial contour can be determined fairly well on the cast. The upper impression must include the complete contour of the alveolar process Step 4: Lip-closure path. This is a critical determinant for the incisal half of labial contour. It can only be determined in the mouth. Step 5: Determine incisal edge length (using the smile line). This relationship is important for phonetics of the F and V position as well as for the best aesthetics. Step 6: Refine incisal edge position (using F and V sounds). Determination must be made with gentle, softly spoken sounds. Make sure incisal plane contacts inner vermillion border during gentles speech. Step 7: Adjust for long centric (if needed). Follow the rules for anterior guidance after centric relation and incisal edges have been determined. Step 8: Establish lingual contours (anterior guidance) in harmony with the envelope of function: a. In straight protrusive

b. In lateral excursions.

Step 9: Evaluate S sounds. The closest speaking position should produce no whistle or lisp. Step 10: Evaluate cingulum contours (using T and D). Round into centric stops.For optimum stability, comfort, and function, the anterior teeth must be:

In harmony with the neutral zone

In harmony with the lips

In harmony with phonetics

In harmony with centric relation

In harmony with the envelope of function

This results in tooth position and contours that are in harmony with a matrix of functional anatomy that also produces the most natural aesthetics