The Mystery of Tooth Preparation

Loss of clearance on a molar. Have you ever done a tooth preparation and then found despite having reduced the prescribed amount of structure, you don't have the proper amount of clearance for your restoration? If you've ever had this happen, you know how puzzling and frustrating it can be.

I'm currently treating a patient who came in complaining of TMD symptoms. The indications became progressively worse after some recent crowns she had done in another office. During splint therapy one of her crowns came off; clearly the tooth had been reduced. The preparation was in contact with the opposing tooth. So what happened?

There are really only two possible causes for this. The first would be that the tooth was simply just not reduced enough. The second cause – which is more difficult and complicated to deal with – is that something changed with the patient's bite, which in this case appeared to be at least part of the problem.

So what can change in our patient's bite and cause the loss of occlusal clearance on a prepared tooth? Surprisingly it's pretty simple. If we accept, as documented in the literature, that the condyles on most of our patients are not seated, we must ask what's keeping them from doing so? Usually it's the patient's teeth that are causing this. So what happens if we prepare away the spots keeping the condyles from seating? You guessed it – they seat.

It's this seating that can cause you to lose the occlusal clearance you thought you made by reducing the tooth.

The simplest way to help manage this risk is to use a leaf gauge to find which teeth touch first when your patient's condyles are seated. The one I prefer, which you can order from Great Lakes Orthodontics, is simply several thin pieces of plastic fastened together.

Basically you just place it between the central incisors and adjust it so that no other teeth are touching when the patient tries to close. Then reduce the thickness of the gauge until you find the first teeth that contact.

In these cases it's best to take a step back and understand what you can expect to happen when you prepare these teeth and discuss how you plan to manage it with your patient.

John R. Carson, DDS, PC, Spear Visiting Faculty. [ www.johnrcarsondds.com ]

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Comments

Larry Gottesman, DDS
January 31st, 2013

In order to understand why this outcome can occur, I submit the following list of questions for review: 1. What is the role of occlusion, particularly the second molar, in the articulation of the TMJ? 2. When and where is the TMJ loaded? 3. When and where is the TMJ unloaded? 4. What is the correlation between EMG, bite force, muscle force, joint loads, and joint stability? 5. What is the composition of EMG? 6. How does the composition of EMG confer the properties of joint load? 7. Is low EMG associated with reduced muscle forces and joint loads? 8. Is high EMG in the elevator muscles associated with neuromuscular incoordination? 9. What is the definition of neuromuscular incoordination? 10. How does the occlusal scheme relate to joint loads? 11. How do we explain the difference between working and non-working side EMG and joint loads? 12. How does the EMG differential correlate with TM joint disorders? 13. How do we explain degenerative joint disorders and relate them to vulnerable malocclusions based upon EMG and occlusal schemes? 14. Why can appliances create an anterior open bite? 15. What is the role of long centric in joint kinematics and joint loads? 16. What is the differential role of the condyles during jaw movement? 17. What are the posterior determinants of occlusion? 18. How can the second molar dilemma be explained in terms of these principles? 19. Why does the frequency of CR/MIP differential displacement values approach 100%? 20. Why are the condyles down and back from CR in most studies, but almost always below CR? 21. Why did nature make so many mistakes? 22. HOW DOES VERTICAL DIMENSION RELATE TO JOINT LOADS, MUSCLE FORCES, STABILITY, EMG, ULTIMATE JOINT POSITION AND NUTRITION FOR THE TM JOINT? I will posit these final questions. In all joints which are diarthrodial, there is the necessity for both a loaded and unloaded position. Why would you want to attempt to achieve a full-time loaded position and can it be retained permanently? What do CR studies demonstrate long-term regarding this issue and CR/MIP differentials? I think a better question would be do you want to preserve the previous position or do you want to institute change in the occlusal scheme in relation to the joint position and what are the indications for such change? Sincerely, Larry Gottesman, DDS

John R. Carson
February 1st, 2013

Dr. Gottesman, Thank you for your comments. You pose a lot of great questions. As I am sure you know we could spend days (or longer) addressing and discussing these 25 questions you raise in full detail and attempting to do so here in this format would likely only raise further questions. This is not to say that the questions you pose are not important and should not be answered. Just that they would be better, more appropriately and more efficiently answered via an in person discussion such as a small workshop or class. In short what I can say well here is that there are many philosophies in regards to occlusion and how it should be managed. I am a firm believer that all these philosophies work some of the time and they all don’t work some of the time. The key is finding the right one for each patient. To do this requires that you be educated in multiple philosophies and that you develop a method that works for you and your patients to determine which is the most appropriate for each individual patient. Most if not all restorative dentists have been or will be faced with what I described above. Needless to say this can be difficult to deal with after the fact, especially if this risk was not discussed with the patient prior to treatment. My purpose here was to help others by presenting a simple way to evaluate a patient for this risk prior to treatment and thereby enabling a discussion and thought process to take place with the patient and doctor prior to treatment so together they can understand and discuss the risks and make a mutual decision as to the best way to proceed in that given case based on the patients desires and risk tolerance.

Lawrence Gottesman, DDS
February 1st, 2013

Dear Dr. Carson: Thank you for your response. You're right...we could spend a long time in discussing the questions I posed and I do! The truth be told, this often happens without splint therapy in many cases. This scenario poses a significant threat to the prepared tooth as the necessity for endodontic care looms larger because the requirement for aggressive preparation increases in response to altered condylar and tooth position augmented by local anesthesia. How will you preserve the original tooth position in patients who don't require splint therapy, but have lost interocclusal space subsequent to initial tooth preparation on the terminal 2nd molar? I think teaching your students a technique which preserves the original position would be highly beneficial. Especially when the unsuspecting dentist was not anticipating this outcome. I look forward to your response. Best, Larry Gottesman

John R. Carson
February 1st, 2013

Larry, In my experience I have found if you are going to prep away someone’s FPOC it is best to know what you can expect to happen PRIOR to doing this in the mouth. In cases like this in my experience it’s best to mount and analyze models, where you go from there, well honestly it all depends on what you see and learn and it case dependent. John

Larry Gottesman, DDS
February 2nd, 2013

Dear John: The loss of interocclusal space is going to occur whether you have mounted models or not (it's just how much). When you record your condylar hinge axis reference position in the open position, the condyles will be more loaded and seated to a task-dependent variable superior position. The necessity for 2 positions is apparent in kinematic studies whether they use a hinge axis, helical screw, or instantaneous center of rotation. The necessity for this differential exists across species and taxa that have a diarthrodial jaw joint. Take a look at the studies that document CR/MIP differentials like Frank Cordray. He describes differences or discrepancies 100% of the time in 596 patients. He is not the only one and percentages over 90% are described routinely in the literature and increase as you approach steeper mandibular plane angles and become more hyperdivergent. Also, take a look at the 1993 article by Pullinger and Seligman...what patients are most at risk for TMD symptoms? When you prepare a second molar for full coverage, you lose your posterior determinant of occlusion. I know this will come as a shock to the centric relation community, but it needs to be stated that CR is a border path position. So, where is the joint loaded and where is the joint unloaded? When you look at the studies on TMD you find that it is more closely associated with low EMG!!!! The dental community is rather surprised by this epiphany because they can't rectify the relationship. The reason they can't resolve the conundrum is because they don't understand the composition of EMG and it's derivation. Removing the occlusal contact of terminal molars is like chopping out the foundation for lyour home. While traditionally it is well tolerated, the damage to the tooth can be substantial as stated above. So, back to the original question.....how will you preserve the original position of the second molar and an asymptomatic joint patient when providing full coverage? Best, Larry

John R. Carson
February 2nd, 2013

Larry, In reference to your question on how to preserve the original position of a second molars, you seem to be implying that I stated mounted models were the fix for this, I did not mean to imply this, rather my intent was to state this is the first step in gaining a deeper understanding of that given patient. Then you proceed from there based upon these initial findings. How, exactly do you proceed after this? Well, frankly there is no black and white answer. Thanks for your input and comments. John

Lawrence Gottesman, DDS
February 3rd, 2013

Hi John: So, what insights do you gain from models mounted in CR? If you can anticipate that you will lose the interocclusal space, then what exactly are your mounted models telling you? As I stated above, it is normal for the differential to exist. What is the part of the picture that this adds clarity to? How do you put this in perspective when you take a normal phenomenon and call it a discrepancy and an abnormality? John, if you haven't figured it out yet, what I am attempting to accomplish is to have you look at these issues critically: you should challenge yourself and the dental community because when confronted by difficult questions like mine, the paradigm falls apart very quickly. Even very well trained dentists like yourself, who probably search for the answers to many problems reach that breaking point where they can't really adequately explain the rational for the issues that confront them and can only fall back upon a training and teaching philosophy that partially fails them; that's when dentists get frustrated! There are better black and white answers! I haven't asked you one question I don't already know the answer to. Best, Larry

John R. Carson
February 3rd, 2013

Larry, We do look at these issues critically both here at Spear and the other study clubs I am involved in. It is evident that you have an extensive knowledge of this subject. I am glad to you too, as do I and the others at Spear, seek to battle the frustrations so many in our profession face and agree questions like these deserve to be discussed, however I stand by my previous statements that a blog such as this is not the place due to their detailed nature. Thanks, John

Lawrence Gottesman, DDS
February 3rd, 2013

John: You probably have access to the email address I use as part of the required fields. The door is open. Thanks, Larry

Sharon Goodwin
February 7th, 2013

Larry thank you for your interesting comments!! Please can you share wth me how you preserve the position of the second molars and prevent this expected phenomenon from occuring? Thank you !! Sharon Goodwin

Michael Melkers
February 8th, 2013

Great blog John! This is such a critical concept. Once you pull the wrong apple from the cart, you cannot get it back. I actually have a CEREC Doctiors article on the technique I did a few years ago. Page 20: http://www.cerecdoctors.com/pdf/magazines/2009/CEREC-Magazine-Q2-2009.pdf I think that the concept of preserving the relationship is a natural curiosity. The challenge is if we strive to do that we replace the restoration into the same relationship which may have led to its failure in the first place. It is fairly consistent to see that first contact during the leaf gauge screen to be on that fracture line.

John R. Carson
February 8th, 2013

Thanks Mike, great points, nice article!

Sharon Goodwin
February 8th, 2013

Michael that was a very nice article and really had useful clinical tips.Thank you for sharing with us! Did you preserve one of the occluding cusps on the tooth (that would remain after the offending hyper occluding cusp was removed as identified by the articulating paper with the leaf gauge)and do an onlay restoration to be more conservative? I always find it easier and more predictable to do onlay restorations and preserve an occluding cusp on 2nd molars, if you are just treating that one tooth. Thank you! PS where do you get the reduction loop from?

Lawrence Gottesman, DDS
February 8th, 2013

Hi Sharon and anybody else who wishes to contact me: I will be happy to share with you the techniques available to preserve the 2nd molar position. I would prefer that you contact me on facebook under Lawrence Gottesman and then we can exchange personal emails and correspond from there. Even though this is a great blog going, I don't want to generate any resentment by dominating the site, as John thinks it would be best to discuss these topics elsewhere....so I will respect his wishes. Thanks, Larry

Lawrence Gottesman, DDS
February 8th, 2013

Just one more comment to the blog for anyone wishing to contact me> I have received a decent amount of correspondence as a result of this blog and others with respect to the questions I pose. Just so you know, I will try to contact you as soon as possible, but I am a "Sandy" victim and as I am trying to get my house back in order and deal with insurance issues, my time is often diverted away from my professional interests. Please don't hesitate to write though. This has beein a great distraction for me and has helped me refocus> Thanks, Larry

Michael Melkers
February 8th, 2013

Thanks Larry-the reduction loops are from Clinician's Choice and come in 1.0, 1.5 and 2mm. 1-I like to do onlays whenever I can...and still love to do gold whenever I can and the patient will allow. 2-I do not strive and actually make no attempt to maintain the 2nd molar position. As the screening can reveal, when the masseter and temporalis 'win' over everything and seat the condyle during parafunction-which is what we are screening to replicate with the leaf gauge, the lone second molar contact...that 1st contact in the seated position, is what takes all the force of parafunction. This is what leads to the breakage and fracture. Why we would strive to maintain and or replicate that deleterious contact is beyond me-perhaps you could explain your rationale on that Larry. If the load is going to be applied-parafunction-it is far better to distribute the load rather than place it all on one point.

Larry Gottesman
February 8th, 2013

Michael: I think that is a great question, so lets get real specific here. Firstly, which masseter and which temporalis are you talking about? You've got 2 portions to the masseter and 3 to the temporalis at the very least. Secondly, what kind of parafunction are you talking about....Is it clenching, universal bruxing, anterior holding, laterotrusive, or nail biting? What causes bruxis...how many of you can answer that question? Which is more dangerous....clenching or bruxism? How did the second molar become premature? When I practiced CR dentistry, it would be highly unusual for a patient to come to my care and during evaluation I would always find a CR/MIP differential...we call it a discrepancy. Why do you think nature made so many mistakes? How many of you have had the difficulty where you made a full arch centric relation splint verified in CR with a centric check or CPI and upon insertion of the appliance find the patient slamming on the second molars? If the approach is supposed to be so precise, why the difficulty? Why do most major teaching programs who integrate CR into their philosophy now advocate fabricating a splint with the anterior component delivered prior to including the posterior occlusion? Why....because they all had the problem!!!!! Have many of you have done a case mounted in CR and opened the vertical to find when you delivered the case you're grinding away way too much porcelain and you blame your lab for not being as fastidious as you? How many of you have done a case in CR and find that you get anterior fremitus..or in large cases, you might even have the centrals break off at the free gingival margin with crown prep stumps still in the crown, long bevel and all? How many of you can answer the questions I posed above? What happens to the disc, what happens to the synovial fluid, what happens to the retrodiscal tissue, what happens to venous outflow, what happens to the blood supply to the condyle, what happens to the vascular permeability, what happens to the synovial viscosity? Is the disc pulled forward by muscle? Can it be substantiated in studies? What is the functional heterogeneity of the muscles and why are we 40 years behind the times in this concept? Why has it never been presented to any dental audience by any major lecturer? What is task dependence? And what does it have to do with what you are doing for your patient? What is stability, where does it come from and how is it lost? Give me a definition for neuromuscular incoordination and tell me how that fits with the second molar that broke from your prematurity. Michael....where is the joint loaded and where is it unloaded? Where and when can you see it? Show me the literature with peer reviewed articles that implicates the prematurity on the second molar is the culprit? Take a look at the literature...if you wanted to ascribe to the literature in vogue with occlusal therapy, then separate the teeth any where from MIP and the EMG goes down. In your scenario, a prematurity would decrease the EMG and effectively treat the problem, because that's how splints work! Why do full occlusal contacts at MIP have the highest EMG? Why is it the most stable position but can't be retained long? Why do we spend much of our time with our teeth apart? So, how do you express occlusion through the sensorimotor system? If your second molar prematurity is not the problem, what is? Why do so many dentists who share the same problems and who have put all their eggs in one basket get stumped. Why do they go back to the same starting point and circuitously repeat the same things over again? Why, worse than that do they refuse to talk about it except in very close quarters or friendships? They have one size fit all and then can't get out of the hole. These are some of the difficulties I have had and now share with you and have sought the answers to. If some of you or all of have had similar problems and don't know where to go to find the answers, I have most of them. You don't have to be afraid or feel inadequate or insecure. I have failed many times and wanted to know the reason so I didn't become a repeat offender. Let's all talk and see what happens. I am not the enemy. Michael, let's see how well your side of what used to be my side too...holds up under scrutiny. Best, Larry So, Mike, let's here you side of the story and I will give you the direct answers. Larry

Michael Melkers
February 8th, 2013

Larry-I honestly don't care about CR...and without dissection I don't think there is anyway to really truly analyze it. I think laundry listing pargraphs of questions just leads and contributes to obfuscation of the issue. 24 questions in your response... I will make this really as straight forward as I can: if a tooth broke under contact of load, why would you strive to recreate the scenario?

Lawrence Gottesman, DDS
February 8th, 2013

Mike: You gave me the perception that the occlusion is the entire etiology of the fracture and you will make corrective care through the use of a leaf gauge in an altered position to alleviate the fracture problem and quiet down elevator muscle activity. When a patient presents to my care, if they have no signs of mobility, bone loss or fremitus on the tooth and their joints are asymptomatic, I choose to preserve the position of the tooth and as much of its original architecture as possible. If however, the tooth does have some mobility without the necessity for periodontal intervention I often elect to consider a position which would minimize tooth load during function. The reason I ask the above questions is because we clearly understand that the joint will influence tooth relationships. In those cases where the intraarticular space is larger than the posterior determinant of occlusion can tolerate, I choose change and reduce the gap. Also, second molars which have conical root forms may be more susceptible to load-related problems and unable to accept higher loads. Typically, I see patients with cracks and cuspal breakage that have had failed restorations, particularly amalgam. I do not see occlusal forces as the only expression of failure mode. Additionally, I want to try and avoid positioning a tooth that would load the joint adversely at the intercuspal position. In this case type, I choose a preservation procedure, particularly in Class II, Div. II patients where they have short clinical crowns and the altered position would obligate me to crown lengthening and/or RCT with post placement. Now, as far as my laundry list, I didn't get much of an answer from you... because during static clenching in the intercuspal position or excursive parafunctional movements, tell me how the second molar prematurity is involved in causing the problem. Larry

Lawrence Gottesman, DDS
February 8th, 2013

Mike: Furthermore, my questions are not meant to cloud any issues, but to help enlighten those who would seize the opportunity to learn not cease the opportunity to learn. l have come across many people like yourself, who have rich affiliations to institutes like Pankey and teach. I applaud your commitment and efforts on behalf of our fellow professionals, but I already know you can't answer the questions and you punted the ball your of your end-zone. Larry

Michael Melkers
February 8th, 2013

Larry-I like alot of what you say in the 2nd paragraph...and I am glad whatever i wrote clarified your understanding of what I was trying to say. I am sorry about not addressing the 24 questions...I did not see the point and thought it really took everything off track for this discussion. As to: ..."because during static clenching in the intercuspal position or excursive parafunctional movements, tell me how the second molar prematurity is involved in causing the problem." Which is it-interscuspal or just one tooth hitting? or do you mean hitting one tooth on the way to ICP....or from ICP to just the one tooth hitting? ;) I guess I have my own laundry list but it is a small load :)

Michael Melkers
February 8th, 2013

" ..but I already know you can’t answer the questions and you punted the ball your of your end-zone." Huh? Have a good weekend Larry...between your omniscience and semi veiled insults, I think I will step out of this one.

Lawrence Gottesman, DDS
February 8th, 2013

Mike: Maybe you need a larger capacity washer and dryer. ;) There is supposed to be a first point of contact on the way to ICP or have you missed the point. That's exactly what I have been trying to say! Upon closure, the 2nd molar is the first point of contact followed by a slide forward and as the condyle goes down and back. Take a look at the literature, which is extensive, related to joint kinematics. Come on, tell the truth...don't we all see this as the first point of contact in every patient? That slide forward is what we call long centric and it is shorter in some and longer in others. Lar

Lawrence Gottesman, DDS
February 8th, 2013

Mike: I think the insults are rather clear as being initially directed at me on your part. I am sorry if you were offended, but you didn't answer one question and you could not argue one positional point. My insults are not semi-veiled. I am a direct shooter. Larry

John Walker
February 8th, 2013

Larry, it would be more instructive if you would stop pointing out that no one knows the answers to your questions and just provide the answers for us, because it's obvious that we just do not yet know them.

John R. Carson
February 8th, 2013

Wow! What a back and forth today! I would like to clarify a few things: -Larry: I am fine with you and others discussing things here, my previous comments were not meant to say I wanted no further comments made here. My intent was to say for me this is not the place or format to have detailed discussions about such a detailed and intricate topic as we can see here this is a very passionate topic for people and in my experience these types of discussions are best had in person so for me personally that's where I choose to discuss them and avoid any potential misunderstandings. -All: feel free to answer each others questions and make comments let's just remember we are all professionals and we need to act as such and respect each others opinions and philosophies. This is not to say we must agree on them but we need to be respectful in our comments. John

Lawrence Gottesman, DDS
February 8th, 2013

Both Johns: Thank you both. To John Walker: I will be more direct now that I have your attention and if you have any kind of question or comment, I will be happy to answer it concisely with dignity and respect. Thanks you again, Larry

Lawrence Gottesman, DDS
February 8th, 2013

John Walker: To keep it short, I will answer a few or two at a time. Two of the most important answers are that the joint is UNLOADED at MIP and LOADED when there are opening gapes away from MIP. The best way to see this is by drawing two diagrams of Posselt's envelope of motion next to each other. One which will represent the incisal edge path and the other the condylar path. Most people don't recognize that there is a mirror inversion between the condyle and the incisal edge until you separate them on the diagram and that exactly what you see on a condylar position indicator when you compare MIP to a loaded superior anterior position, recognized currently as CR. Thanks, Larry

Lawrence Gottesman, DDS
February 11th, 2013

I received a fair amount of personal inquires. Most people wanted to know the technique I used to retain the original position of the second molar so I will give you some of the techniques I have used. I also received inquires about the rationale for CR implicating the second molar as the first point of contact as an interference to the arc of closure and the most seated position. I will handle these issues separately. First: How to preserve the original second molar position: Technique 1. This is a takeoff on the old FGP trays which you may be too young to know about. They aren't made anymore. So what you do is take an old quadrant plastic tray and cut off the flanges leaving about 1mm of flange. Index the 4 posterior teeth in the quad including the second molar before prepping (if you are happy with the morphology) and reserve it. I usually use a fast setting rigid bite registration material for this, but you can use a hard putty or a material like luxatemp to get an accurate indentation of the teeth. Take a quadrant tray impression for your temp..usually in VPS or alginate substitute like Alginot . DO NOT USE A TRIPLE TRAY FOR THIS TECHNIQUE. Prep the tooth and use your index as a reduction guide prep. Make your impression of the prep and send the index to the lab for a gold crown or pressed lithium disylicate crown. These two restorations are ideal for this technique because they can be waxed directly to the index and structurally preserving. Technique 2: Lets say you don't like the morphology of the existing 2nd molar. Take full arch models, articulate, wax the tooth at MIP or ICP however you like to call it, then index the tooth as above and make a quadrant impression from the model you revised for temporization. Technique3: As either 1 or 2 but split your temporary vertically down the middle. Record the bite registration of the single half tooth with GC pattern resin, remove the rest of the temp and record the rest with pattern resin. Now you can either index the adjacent teeth with the indexing technique, except in this case instead of having all negative indexes of the teeth, the opposing articulation will be recorded in the index as positive. By the way, all these techniques give a very stable articular relationship and most times there is minimal adjusting. Technique 4: As above, make your temp first and split it horizontally leaving the occlusal half or third intact. Pick it up in your bite registration and have the lab articulate this with a die model that has no spacer on it until the articulation is complete. 5: You could also index your temp in any one of these techniques if you like it better than what you had. That often works great for me. I adjust the temp, index it and send it to the lab with the quadrant impression. You need to just make sure your lab knows what your talking about with this technique because some younger technicians have never seen it. 6: If you're into the digital age, you can scan at any time with the original tooth or the waxup or your temp. Just that simple.. 7. Sometimes you can segmentally prepare a tooth. For example, if I am prepping an upper second molar, I will retain the lingual cusps and record the partial preparation of the buccal reduction in GC pattern resin with a seating tongue on the adjacent tooth. I then prepare the remaining tooth structure and replace the preliminary partial recording and capture the rest of the information in GC resin. ****It is real important that you check your reduction in comparison to the original tooth size. You can either do this by placing some fast-setting rigid bite registration material inside your original tooth index and then measuring the reduction with a caliper. ****** OR you can make a quick bis-gma temp and measure the thickness. Remember, with this technique, the amount of reduction should not be visualized by evaluating interocclusal clearance!!! Thanks to all who left me personal comments and words of encouragement, Larry

Lawrence Gottesman, DDS
February 11th, 2013

Here is the very basic premise to answer the next question. The Centric Relation community and philosophy have consistently found that the 2nd molar is the first point of contact. That is accurate. They watch the mandible slide forward (which it does) and they think AHA/ EUREKA! The lateral pterygoids are pulling that mandible forward and holding the condyle in a forward position precluding the condyle from fully seating. The assumption generated is that this mechanism contributes to the fatigue and pain in the lateral pterygoid because it is overworked. Overlooked was the rest of the movement. As the mandible slides forward, there is and arcuate component to the movement of the condyle down and back. This is like a child sitting on a rocking horse and pulling up on the horses ears (handles) while leaning back to create the analogous movement. Think of the handles as the coronoid process. If the condyle is going down and back, how can the lateral pterygoids be responsible for that movement? I have provided a link which demonstrates the real-time movement in a 3-D digitized graphic on you tube: https://www.youtube.com/watch?v=x5ikcZMUcYo watch carefully because it is hard to catch it the first time. Slide the time-line to 1:42 and stop it at 2:25. I do have a section of this which I rectified to one third of the normal motion time, however, I was unhappy with the transfer quality when I uploaded it to you tube. For those who want to see it, contact me on Facebook with your contact information and I will gladly send it. The second molar is supposed to hit first. The phenomenon you are witnessing is what we call "long centric" which exists in the general population to greater or lesser degrees. It is also the mechanism by which the condyle UNLOADS in a relative manner is you glide forward and the mandible arcs upward into MIP or ICP while the condyle moves down and back. This satisfies the relationship that basically 2 positions must exist in order for the biomechanics of the joint to succeed and provide for both stress relaxation phases along with productive loading to insure adequate nutrition, lubrication, and waste disposal through transsynovial exchange. The mechanism also allows for adequate blood supply from the arteriole/capillary side to oxygenate the complex and have compensatory venous outflow to carry out oxygen deficient blood. You might want to consider reading the article link I provided below: The Instantaneous Center of Rotation of the Mandible in Nonhuman Primates Claire E. Terhune,1,* Jose Iriarte-Diaz,† Andrea B. Taylor*,‡ and Callum F. Ross† Integr Comp Biol. 2011 Aug;51(2):320-32. This phenomenon runs across species and taxa that are herbivores and omnivores and have diarthrodial joints. There is a necessity for 2 positions: loaded and unloaded. While our kinematics are not the same, there must be 2 positions. Sorry for the long-winded explanation...I hope this clarifies some issues and no doubt will leave more questions to be answered. Thanks for the opportunity to share with you all. Larry

Marcelo Calamita
February 11th, 2013

Thanks Larry for all your insights! I learnt a lot from your didactical lessons. Very astute the observation of condyle movement and the comparison with a horse riding. Absolutely right! I never noticed it. It changed a lot of things in my mind. Also the explanation and differentiation about loaded and unloaded joints in the long centric. You are helping us to see things differently and think outside the box. Stay close!

John R. Carson
February 11th, 2013

Wow Larry, lots of info here, again I don't want to get into long discussion here (as I have said in past comments for me detailed discussions of topics such as these are best had in person) but I would like to say a few things. -You stated the TMJ is unloaded in MIP. To this I say it depends on what their MIP is, they may certainly be able to load their joint. -You give several techniques for maintaining the second molar position. First for me in my experience it may or may not be a good idea, for me again, it depends on the case, but generally I have not found this to be predictable long term for me. Please note I am NOT faulting you for doing something that is working for your and your patients. -You state "The Centric Relation community and philosophy have consistently found that the 2nd molar is the first point of contact. That is accurate." You seem to be implying (maybe I am wrong) that for the most part the FPOC is always on second molars. I would say while I often find a FPOC on second molars, this is far from always the case, it is not uncommon for me find an FPOC that is not on second molars. So again for me the bottom line is everything works some of the time and everything doesn't work some of the time. I agree, as I am sure you do and we need to be open to different way of thinking and understand that what works in one case may not work in another. John

Lawrence Gottesman, DDS
February 11th, 2013

John: I agree with you that nothing can exist all the time. Nature endorses diversity and that is clearly reflected in the clinical setting as well as the scientific literature. For me, it is about having the ability to select from a large diagnostic and treatment menu. And you are right, there are many case scenarios where the first point of contact is not on the second molar. Different disturbances in the joints and different types of malocclusions will manifest with a different presentation in the FPOC. In normal joints, the kinematic architecture will most often be on the second molar and is among the most common in the joint with DJD. There are many cases in my practice where joint effusions in the retrodiscal tissue will cause the patient to hit prematurely on the anterior teeth and even have a posterior open bite. We are not that far apart, John. Additionally, I provided a rationale for both preservation and change in the position of the second molar in my response to Michael. A time and place for everything. Most of all, I think blogs like these provide a great forum for interactive learning. I hope you watched and enjoyed the video. The article I suggested will help you further appreciate the genius of nature. Thanks for your comments and moderation, Larry

David Slaughter
February 13th, 2013

As much as I would love to get into this occlusion discussion with you guys, instead i am going to sidestep it and mention a few items that I think could be beneficial to those whose interest was peaked with the title of the article--and keep it really simple. If you can recognize that you could be in this situation before preparing the tooth, I think many dentists would be more comfortable as you plan your restoration and inform the patient. These patients are typically the ones who clench or squeeze their teeth together during the day. You know some of these guys who are not even your patients because you can see their muscles flexing as they sit by you on plane, bus, church, whatever. Look for signs of wear. If they display wear on the posterior teeth (might be heavy on second molars and decreasing anteriorly) and virtually no wear on the anterior teeth, there is a good chance you are in this situation. Use the deprogrammer of your choice and you will find that initial contact on a second molar. Leaf gauge is probably the fastest and easiest way to do this. For me, I already know I'm doing gold on this tooth. If this is the only tooth that requires treatment, I will equilibrate the patient before the treatment. If there is other future restorative work to be done or I am concerned that there is a considerable occlusal issue that requires significant change, I will mount deprogrammed models and do my equilibration there to find the end point so I can inform the patient where we are going--again, before treatment. Simple, doesn't take much time, and avoids a code brown. It's not a surprise when its expected.

John R. Carson
February 14th, 2013

David, Thanks for the comments and great points!

Lawrence Gottesman, DDS
February 14th, 2013

Gee Doug: I guess you scored some great points with John. Your second molar prematurity carries much more weight than mine. Larry

SMSDDS
February 15th, 2013

That makes good sense! Like Weinberg's liniar occlusion concepts. Thinking too mechanically. Please excuse spelling. Thanks

Alan Slootsky
February 17th, 2013

Kudos to all those who have posted. I have really enjoyed reading the posts, and thank Dr Gottesman for pushing me outside my own comfort level in treating my patients. I am sure we all get good results in spite of, or because of our techniques. But just as our awareness has been raised, how do we raise the awareness of our patients so they can make an informed decision to start treatment. The behavioral science side of this discussion would also be interesting. I am sure we all try to lead the horse to water, and realize they will not always take a drink. We take models, photo's etc, but what behavioral techniques develop a sincere trust before treatment begins? Here, certainly, there is no one approach, as the same clinical presentation with different personality types may have a different approach. Your thoughts? respectfully, Alan

John R. Carson
February 17th, 2013

Wow, great to see comments still coming, I have been having some email trouble so I was not aware of the all the continued traffic until today. Alan, a couple other blogs you may like are below and you are dead on- It does not matter what we see and know about what our patients need to do to reach their goals if we cannot communicate it with them properly to allow them to make the choice that it best for them. http://www.speareducation.com/spear-review/2013/02/is-something-missing-on-your-office-walls/ http://www.speareducation.com/spear-review/2013/02/get-the-picture/ John

Sharon Goodwin
March 12th, 2013

Larry thank you for your refreshing approach to this continuing mystery that seems to make our lives unnecessarily difficult..I have learnt a lot from you and you are making it easier to understand rather than more confusing and problematic...so many coencepts in occlusion get thrown in the air and we wait ti see where they land !!

Lawrence Gottesman, DDS
March 14th, 2013

Thank you for your comments Sharon. Decoding the mystery is so much fun.....happy to help. Larry

Dr.Andreas Aspros
April 8th, 2013

We have to consider centric relation as the best choice for large cases.We have to study the case in the articulator with the casts mounted in centric relation.Another important step is to see the anterior contacts.

Michelle Johnson CDA, RDA
March 1st, 2015

Dear Dr John Carson, After reading your article and ALL of the commentary that followed, would you please explain to me why my 2nd molars are NOT the first teeth that touch? With or without using a leaf gauge my left 1st premolars are the first contact I have. 1. I do wear a hard splint. 2. It has been checked and adjusted. 3. I still have TMD. 4. I know how the muscles work. 5. I have been in dentistry for 25 years. 6. I had ortho on my lower arch only to correct my slighty turned canines. I look forward to any responses to my question, be it from Dr Carson or not. I enjoyed this article and the commentary comments. Thank you in advance, Michelle

John R. Carson
March 1st, 2015

Michelle, It's not uncommon to find a first point of contact (FPOC) that is not on second molars or the most terminal tooth in the mouth. A few questions I would ask are: -Tell me about your TMD. -How long have you worn your splint? -Are you more comfortable in your splint? -Have you been equilibrated? -Are you confident that you have found CR when evaluating your FPOC -What is the direction and magnitude of your slide from CR to CO or MIP Thanks, John

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