The Dental Blog

Fundamental Occlusion Concerns: Orthodontics Achieving Esthetics and Function in Harmony

 

PART I

Orthodontic treatment is without a doubt one of the greatest marvels of dentistry. In addition to being a fundamentally important aspect of functional and aesthetic care, to see a case evolve from start to finish it as remarkable as watching one the masters paint a fine masterpiece. At the same time, orthodontics is both one of the most difficult disciplines in dentistry and one of the most important ones in so far as the long term integrity and health of the mouth is concerned.

Stephen Covey in his highly acclaimed book, The Seven Habits of Highly Successful People, suggests that we “Begin with the end in mind”. While this is great advice for any endeavor, it is fundamental to orthodontic care. Unless the clinician is crystal clear about their intended outcome long before a bracket is bonded or a wire is bent, there is little hope for a successful outcome.

Objectives for orthodontic treatment include

• Attractive, straight teeth
• Long-term stability
• Good functional occlusion

While aesthetics and stability are essential components of the orthodontic case, the focus of the article will be the on how we can combine the patients aesthetic requirements with good functional occlusion.

Three Separate But Interrelated Issues Concerning Occlusion

It is the opinion of the authors that there are three separate but related issues regarding occlusion in dentistry.

• Biomechanical stability and force and how they are best managed in the oral environment.
• Function of the jaw joint and minimization of stress on the joint structures and disc assembly.
• Hyper activity of the muscles of mastication and its relation to, head and neck pain as they relate to tooth clenching, grinding and associated head, neck and facial pain.

While each of these issues must be considered in concert for long term comfort, function and esthetics they are best considered and examined separately.

I. Biomechanical stability and force.

The laws of physics are applicable inside the oral cavity. The jaw is a class III lever. The condyle is the fulcrum and the muscles are the force. The resultant is expressed in the bolus of food or on the teeth. In any system, the force is the greatest close to the fulcrum and in the mouth that means in the area of the molars. Vertical forces are best tolerated in any system and horizontal ones are most destructive. Therefore we want to minimize all horizontal forces and where they are unavoidable, whether in functional activities such as chewing and swallowing, or even in para-functional tooth clenching or grinding, strive to locate them as far from the fulcrum as possible. The more surface area we can spread forces over, the less is the force per surface area. Therefore as the number of simultaneous contact areas increases, the force per unit area decreases.

The generally accepted prosthetic standards of a good functional occlusion are sometimes seen as controversial when words such as centric relation and canine guidance are introduced. Therefore the authors have modified some of those rules to be more general in nature so as not to evoke disagreement. Instead of the five traditional prosthetic rules as defined by Dr. Peter, E, Dawson in his book “Evaluation, Diagnosis, and Treatment of Occlusal Problems”, we have substituted three more general ones (A, B, and C below) that are accepted as standards in physics and engineering and therefore less likely to provoke disagreement in any field of endeavor, such as dentistry:

1. Even, simultaneous and non-deflective contacts of the posterior teeth when the jaw joints are centered and stable.
      A. Make the joints and teeth simultaneously stable
2. Posterior contacts must be directed in the long axis of the teeth.
      B. Create axis loading wherever possible
3. Anterior guidance such that the anterior teeth disclude the posterior teeth in protrusive.
4. Canine guidance such that the canines disclude the posterior teeth in lateral excursions.
5. No occlusal contacts on the balancing side.
      C. Move off axis loading as far from the fulcrum as possible

II. Stability of the T M Joint

The T M Joint is the most complicated joint in the body because of three complications that are present in no other joints in the human body.

• Both joints must move simultaneously and in harmony together.
• They are the only joints that can move in three dimensions: Forward and back, left and right, and rotate open and closed.
• They have has an external articulating element, the teeth. In every other joint, the position of the joint is determined by the bones and muscles of the joint. In the case of the T M Joint, the ultimate position of the joints is determined by the shape and position of the teeth. Teeth determine position of condyle in fossa. For this reason it is essential that an occlusal scheme is devised such that the jaw joint can be stable and centered in the fossa at the time that the teeth are in maximum intercuspation.

III. Muscle Spasm and Pain and Overload

If the condyles are not centered in the fossa at the time of maximum intercuspation and there are deflecting forces on the teeth, it will stimulate an increase in muscle activity that is required to stabilize the jaw joints in this non-centered position. Many studies have confirmed that posterior deflective incline contacts predictably lead to heightened EMG muscle activity. This muscle hyper activity and potential ultimate muscle fatigue has been found to head, neck and facial pain that may radiate and refer to different nt parts of the head neck and face. Other studies show that in some individuals this triggers tooth clenching and grinding which can lead to tooth damage, such as abfractures, gum recession, cracked, chipped and worn teeth.

Resistive / Adaptive Capacity

When considering any disease, including disorders associated with occlusion and the T M Joint, a very important variable to understand is the resistive / adaptive capacity of the individual. Most patients have a less than a perfectly balanced bite, especially an individual that is being considered for orthodontic intervention. But at the same time, not every individual suffers from significant biomechanical dental disease, joint derangement or head, neck and facial pain. The reason that they do not exhibit symptoms is that they have sufficient resistance / adaptive capacity to tolerate these imperfections without suffering a significant adverse reaction. This similar to individuals who are exposed to influenza viruses but does not get the flu or individuals that are exposed to long term high levels of sun light and do not develop skin cancer. In any disease state, there is always a balance between the resistance / adaptive capacity of the individual and the intensity of the stressors in the environment.

In light of this it is important to consider these aspects of an individual’s resistive capacity because resistance can vary from time to time and patient to patient.

• A patient with a prior history of head, neck and facial pain may be currently symptom free
• Intra-oral conditions are in flux during orthodontic treatment
• Current or prior history of head, neck or facial pain is an indication of lower resistive capacity
• Impact of changing occlusion during treatment and how the individual might react to the altered occlusion
• the resistive capacity of the individual might be different at the end of the treatment than at the start

Barriers to Orthodontic Success

Very few people, including most dentists really appreciate the complexity of orthodontic treatment. There are many variables that the orthodontist must carefully consider and manage during treatment, many of which are not under the control of the practitioner, including:

• Tooth size discrepancy. The dentist must work with the teeth that the patient presents with. Even with careful planning there is absolutely no certainly that the morphology of the teeth will naturally fit together.
• Asymmetrical arch forms. One limiting factor is the growth and development of the dental arches and their relationship to each other. This can be somewhat influenced by early treatment and tooth guidance, but in the end, genetics and other factors outside the control of the orthodontist will inevitably create some limitations in so far as tooth position, angulations and direction of forces.
• Changes over time. Even after the teeth are positioned as ideally as possible, in any system there can be unanticipated changes and movements that disrupt the in progress or completed case such as growth, habits and needs for restorative dentistry.
• Limitations of tooth movement. The mechanical requirements, such as bodily movement versus tipping are sometimes simply not possible without either extremely long treatment times or possible root or bone resorbtion.
• Unintended movements. Moving a tooth requires anchorage against other teeth and that may lead to unintended movements. For example counter movements, which need to be neutralized or reversed, often occur as the case develops even though one tooth is set against several in the arch.
• Functional vs. cosmetic requirements. A balance of cultural considerations of beauty and realistic considerations of what is possible as dictated by jaw size, arch forms, facial structures and other factors must be struck. Not everyone can have the exact “Julia Roberts Smile.”
• Patient compliance. Patient compliance is a fundamental of effective orthodontic care. Not wearing removable appliances, elastics l or simply keeping appointments on schedule as well as lack of cooperation can drastically reduce the effectiveness of the intended biomechanics.
• Duration of treatment. In orthodontic cases the teeth may not move as fast as the orthodontist desires due patient cooperation or simply individual variations of growth and development. Patients may not be wiling to pay for or endure additional treatment beyond the predicted schedule. And the duration of treatment combined with the mobility of the population often requires that patients have more than one practitioner treating them. This may result in less than ideal results as time is lost, patients lose interest, and techniques vary from practitioner to practitioner.

Adjunctive Treatment Planning may be required to achieve the final desired result given the multitude of considerations listed above, the orthodontist must also sometimes be able to take advantage of, or incorporate additional disciplines to achieve their goals for the patient. The necessity to include other modalities should be considered during the diagnostic phase and discussed with the patients well in advance so they understand why they are necessary and the benefits to them by doing so.

• Implants
• Bonding
• Veneers
• Reshaping
• Equilibration

Once we understand that the orthodontic process has as its end point to combine a pleasing appearance, the best possible force management, and minimal non-functional muscle activity as well as maximize joint stability, we are ready to begin.

Evaluation Before Treatment Starts

Before the active treatment is begun, we must perform a full evaluation of the existing occlusion, the muscles and the jaw joints. Specifically we are looking for following:

• Signs of biomechanical dental disease such as accelerated wear, cracked, loosened teeth or damage to the periodontal alveolar structures.
• Evidence of joint derangement such as popping, clicking or crepetice sounds from within the joint or any reduction in range of motion.
• History of head, neck and facial pain that is due to muscles secondary to a conflict between the teeth and the jaw joints.

Examination Process

1. Ask all of your patients, especially those with signs of clenching and grinding, if the get any head, neck or facial pain. Often the question must be rephrased several times, since most people do not associate their bite or dentist with headaches. Many dentists report that patients who suffer from daily headaches often fail to convey this information until they have been asked several times. If a patient has a history of head, neck or facial pain and is now symptom free it is important to note that changing a patients occlusion during orthodontic treat may cause the headaches to reoccur.

2. Examine the patient’s teeth for signs of occlusal wear or symptoms of biomechanical dental disease gum recession and “Cracked”, “chipped”, “abfractured” and “broken” teeth.

3. Ask the patient to close their teeth until the point of first occlusal contact and stop. Upon closing the rest of the way note any slide or movement of the lower teeth.

4. Palpate the lateral pterygoid, temporalis, massater, and muscles of the neck and shoulders, noting the level of sensitivity. If there is a painful response, ask the patient to palpate the muscles themselves.

Bite Records and Case Mounting

A fundamental tool for pre-treatment evaluation is mounted diagnostic models at a position where the jaw joints are centered and the muscle are relaxed. This will allow for evaluation both in the ideal long term treatment position (centered joint position) as well as in the current position of maximum intercuspation. Because heightened and irregular muscle activity is often seen in cases where these is a conflict between the centered jaw position and the position of maximum tooth intercuspation, it is necessary to first deprogram the muscles and take the bite record in an open bite position that is free of the influence of the teeth.

The process of deprogramming the muscles has been used and taught in dentistry for over 50 years by Doctors Long, Neff, Dawson, Roth, Williams and many others. While there are many ways to achieve this, the authors use a 4th generation deprogrammer developed by one of the co-authors, Dr. Jerry Simon which is available from Best-Bite.

Best-Bite is designed to be secured to the upper teeth with a PVS bite registration material so that it is fast and easy to use. Once set on the teeth Best-Bite discludes the posterior teeth which enables the lower incisors to move freely anterior-posterior and inferior-superior without tooth interference which in turn allows the condyles to move to the centered position in the fossa. Once the condyles were centered, the muscles no longer needed to brace the condyles in an unstable position which allows the muscles to relax. A sample patient sEMG taken before and 5 minutes after Best-Bite use confirms the relaxation of the muscles. In cases where patients are experiencing bite related occlusal muscle pain relieving the influence of occlusal interferences on the muscles can produce a remarkably rapid reduction in symptoms, both in cases where muscles are the primary cause of pain or a trigger for a secondary pain, such as tension or secondary migraines.

A bite record can easily be captured at this position for articulator mounting by placing a dab of polyvinyl adhesive was placed on the underside of the Discluder where the lower incisors line up. Next a small amount of bite registration material is dispensed on the under side of the Discluder and the patient passively, with totally relaxed muscles, closes against the flat surface to capture the anterior position. The last step is to inject a bolus of custom liner material, or PVS quick set putty in between the upper and lower posterior teeth and let it passively set. The result is a confirmed, passive, accurate, stable and repeatable bite record. The anterior discluder and posterior bite records are used to mount the casts on the semi adjustable articulator andy uses Panadent Articulator (WaterPik Technologies Denar Combi). Marking ribbion showing first contact verifies accurate transfer of the occlusal relationship from the mouth the to the articulator.

Case Study

As a demonstration of the principles described we are going to present a case for your consideration. Please examine the case photographs, the patient’s desires for treatment and the evaluation of the issues by Dr. Andy Giradot. In the next article next month we will take the readers through the process of treatment and ultimately finishing the case to achieve the principles outlined above.

Chief complaints and desires of the patient

1. Reduce buck tooth and facial appearance
2. Fix crooked and overlapped teeth
3. Make sure teeth are healthy and don’t get crooked again.

Clinical observations by the dentist

1. No TMJ of functional problems, mandibl easy to manipulate with CR bite, Hx neg
2. 1 in Red Zone (after Andrews)
3. 5mm 1 at rest, smile line at the cervical line
4. Lip strain and protrusion
5. Lower midline to right

Clinical outcomes to achieve the patients and clinicians objectives

1. Esthetics and patient’s chief complaint reduce protrusion of incisors and soft tissue lip posture
2. TMJ health (static and dynamic) – Achieve Seated Condylar position (CR) at CO and constant contact between condyle/disc/eminence in all jaw positions
3. Excellent Dental Occlusion (static and dynamic) – Eliminate crowding, correct midline discrepancy, Andrews’ 6 keys, multiple and even posterior contacts in CO, mutually protected occlusal scheme
4. Periodontal health achieve tooth movement with roots in bone, crowns over roots, and distribute forces optimally to supporting tissues
5. Achieve excellent stable and long term functional harmony between the teeth, neuro-musculature and TM Joints

PART II

Case Study

The purpose of this article is to explore and demonstrate the challenges that face all dentists in the field of orthodontics. That is namely that there is often a conflict between the various requirements of an orthodontic case and their satisfactory resolution is what determines whether the patient will be happy with the result in so far as being satisfied with the cosmetics of the case and equally important, will the patient be comfortable with the functionality and will there be long term stability in the final case.

Appearance of course is clearly one of the chief outcomes of any orthodontic case, so it is important to involve the patient is the analysis and treatment planning from the start. There are cultural and regional norms to be aware of as well. In this particular case the greatest concerns expressed by the patient were that she felt her front teeth protruded too much and she felt that she did not have a broad enough smile due to the narrowing of her arches. Both of these issues are plainly evident in the pre treatment photographs and study models. Completion of the case without satisfactorily solving these issues would have, from the view point of the patient, led to a failure regardless of the other issues.

Functionality hinges, no pun intended, on a coincidence of all the teeth inter-digitating with the forces most advantageously managed on a tooth to tooth basis, on an arch to arch basis and on a cranio-mandibular basis as well.

Tooth To Tooth Relationships

Teeth as we have described are subjected to the same laws of physics as other physical objects, so we must design tooth contacts so as to minimize force over load on the individual teeth. In this regard we are concerned with which teeth contact when the jaw is in static closure. Forces delivered perpendicular to the long axis of the teeth are much better resisted than forces that are off axis. For that reason we want to arrange tooth to tooth contacts so that in static vertical closure, as well as when it is moving into excursions that the forces are primarily directed as equally as possible to all of the teeth and as vertically in the long axis of the teeth as possible. Contacts should be between the tips of the cusps against a flat plane on the opposing tooth, generally a fossa. Intra arch considerations such as firm tooth to tooth contacts with not open spaces both for cosmetics as well as eliminating food impactions and subsequent periodontal disturbances would also come under this category.

Arch to Arch Relationships

The jaw operates as a lever with the fulcrum being in the TM Joint and the forces being the muscles and the resultant being expressed in the teeth. The forces are many times greater as you get closer to the fulcrum, so force management requires that contacts between the arches be controlled as well.

When the patient moves their jaws, all contacts will by definition be off axis so that we want to design the tooth contacts such that the forces are move as far as possible from the fulcrum. When the patient moves forward we want to direct forces as far as possible from the fulcrum so the contacts should be directed to the central incisors. When the patient moves laterally, we want the forces to be directed towards the canines. In any excursive movement off axis contacts are to be avoided where ever possible, and where they are inevitable, they need to be moved as far as possible from the fulcrum.

Cranio-mandibular Relationships

The condyle to glenoid fossa relationship is also a consideration when the teeth are in static closure and when the jaws are moving. The consideration is that when the condyles are centered in the fossa, that the joint is a stable as possible and that muscle bracing in minimized. Although this is regarded as the most controversial of the three considerations, it makes sense that if the condyle in forced to deviate from the most centered position in the fossa to accommodate to let the teeth inter-digit ate in MIP, that this inherently unstable position would require grater muscle activity to stabilize the joint in the socket and this has been bourn out in many electro-myographic studies that demonstrate that muscled activity is greater in patients with off axis loading of the teeth and whose jaws are not centered at the time of maximum intercuspation.

Long Term Stability

It is one thing to design the mechanics to successfully move teeth where you want them, but it is another matter entirely to get them into a position that is both aesthetically pleasing to the patient and the practitioner, functionally acceptable and also stable in that position. It dos the patient no good to leave the teeth and or jaw joints in a relationship that is inherently unstable and likely to shift. If the practitioner leaves the case with inclined plane contacts in posterior teeth or a conflict between the teeth and jaw joints and instructions for the patient to wear their retainer to bed at night, they must recognize that this is the dental equivalent of doing a nice job of parallel parking an automobile with the car parallel to the traffic lane, the tires nicely spaced from the curb, but leaving the car on a hill with only a short term parking break. Eventually the patient will stop wearing their retainer for a variety of reasons and if the practitioner walks away from the case in an inherently unstable position, the teeth, like the automobile will move as soon as the break is released. While the orthodontist cannot guarantee that there will not be some changes over time after the case is completed, it has to make sense that the more stable the teeth are when the case is released, the less likely the teeth are to move and that is true in the physical universe of teeth every bit as much as in automobiles.

As a demonstration of the principles described we are going to continue the case we introduced in the prior issue for your consideration. Please re-examine the case photographs, the patient’s desires for treatment and the evaluation of the issues by Dr. Andy Giradot in the previous article. In this article next month we will take the readers through the process of treatment and ultimately finishing the case to achieve the principles outlined above.

The practitioner must also realize that there are significant limits as to what orthodontic teeth movement can accomplish. In the previous article we detailed the potential problems that the practitioner faces. Briefly summarized they include:

• Tooth size discrepancies
• Asymmetrical arch forms
• Changes over time
• Limitations of tooth movement
• Unintended movements
• Functional vs. cosmetic requirements
• Patient compliance
• Duration of treatment conflicts

When you examine the case presented you can see that there are several issues that require tooth movement to solve. Please refer to the previous issue and you can see that there is significant narrowing of the arches and protruded anterior teeth. In addition the midlines are off the center of the face as well as not matching with each other. As a result of the lower midline being shifted to the right the lower posterior teeth are distal to the uppers resulting in a class II relationship on the right side and a somewhat class III relationship on the left. Lastly there is significant crowding in the anterior region of both the upper and lower teeth.

In her position of maximum intercuspation MIP, without any regards for a centered jaw joint position, the patient appears to come together in a class I alignment. And finally, despite the obvious malocclusion, the patient is free of any head, neck and facial pain or joint disturbances.

The challenge is to attempt to meet the intra arch requirement of tooth positioning and at the same time create a functional harmony between the arches and accomplish all of this and do so in a way that leaves the jaw joint centered and balanced with the teeth are in a MIP.

This is the challenge that every practitioner faces at the start of any case. The question is can all of this be accomplished with orthodontic treatment? Generally the answer is simply no. Orthodontic treatment can eliminate the crowding, widen the arches, reduce the maxillary protrusion and resolve the intra arch issues very well. Where we get into more complications is to make the individual arches work together.

Occlusal Evaluation Is Needed In Every Stage

• Pre-treatment assessment for accurate bite records and diagnosis of head, neck and facial pain
• Mid Treatment, assess functional relationships, manage transitional occlusion
• End of treatment Assessment of final occlusion and short term management of any head, neck and facial pain

Orthodontic treatment

• Deprogram to center the condyles
• Bite records & mount case
• Diagnostic wax up
• Tooth movement
• Equal contact on all teeth
• Vertical contacts on back teeth
• Canine guidance in lateral
• Incisor guidance in protrusive
• Final equilibration / retention

Evaluation of Treatment Progress

• Coincidence of CR and CO, lip support, anterior tooth alignment.
• Necessity for mid-course corrections
• Can we really get there from here?
• Spacing issues, cosmetic issues, potential for occlusal stability, growth and development

Before the braces come off, we need to evaluate if we achieved what we set out to do?

• Cosmetics, need for bonding, veneers, onlay, reshaping
• Function, CO vs. Centric Relation, 3 fundamental rules of occlusion
• If not, how can we mitigate them now? Communication prevents failures

Retention Phase

• Need to maintain aesthetics and function
• Best aesthetics is not always the most stable position of the teeth
• Long-term retention might be required
• Tooth movement indicates unbalanced forces not failure
• Esthetics and Patient’s Chief Complaint – Reduce protrusion of incisors and soft tissue lip posture
• TMJ health (static and dynamic) – Achieve Seated Condylar position (CR) at CO and constant contact between condyle/disc/eminence in all jaw positions
• Excellent Dental Occlusion (static and dynamic) – Eliminate crowding, correct midline discrepancy, Andrews’ 6 keys, multiple and even posterior contacts in CO, mutually protected occlusal scheme
• Periodontal health –roots in bone, crowns over roots, distribute forces optimally to supporting tissues
• Stability – achieve excellent functional harmony between teeth/neuromusculature/TMJoints

Clinical Exam

• No TMJ of functional problems, mandible easy to manipulate with CR bite, Hx neg
• 1 in Red Zone (after Andrews)
• 5mm 1 at rest, smile line at the cervical line
• Lip strain and protrusion
• Lower midline to right

Chief Complaint

• Reduce dental and lip protrusion
• Eliminate crowding
• Achieve healthy, stable gnathic system