OSS DENTAL LABORATORY

Consider about eighty percent of restorations for the past forty years or more globally have been made by hand held models or mounted to some sort of plastic articulator and finished by guessing. Worse, probably sixty percent of bridges made never are mounted to a suitable manufactured articulator. Now we think digital dentistry has solved that issue by digital alignment. Not quite. So if your are wasting time with adjustments which might even warrant a remake, time and money and patient disappointment, then ask yourself why is this a wise spread issue?

CONE BEAM IS ABOUT HOW WE CAN SIMPLIFY, RE-ADDRESS AND MANAGE YOUR DAY TO DAY DENTISTRY TO AVOID ERRORS THAT ARE SEEN IN CLASSICAL RECONSTRUCTIONS AND MORE SO IN IMPLANT CASEWORK THAT CAN OFTEN BECOME ANTAGONISTIC OR DESTRUCTIVE.

BY USING CBTC TECHNOLOGY WE CAN ALIGN THE ENTIRE DENTITION CORRECTLY NOW TO YOUR PATIENTS GEOMETRIC SKELETAL PARAMETERS WITHIN A SCIENCE THAT MANY DENTISTS MOVED AWAY FROM BECAUSE IT BECAME TOO COMPLICATED AND TOO TIME CONSUMING TO MANAGE. NOW IT IS SIMPLE, BY USING CONE BEAM TO RE-CONNECT CASEWORK CORRECTLY TO THE SKELETAL SYSTEM ELIMINATING DISTRUCTIVE OUTCOMES BY USING A FULLY FUNCTIONAL ARTICULATOR AND PROGRAMMING THE SOFTWARE TO FOLLOW. THE REASON IS NOT HOW YOU DESIGN A CASE, BUT HOW YOU OPTIMIZE IT BEFORE FITTING.

When the dentition is restored classically we have a base of dentition to study. When all the dentition is extracted, the muscles have no idea what to do as all the contacts have suddenly gone. The mandible will remain in the habitual bite for a short time but it will not move back to CR on its own. That means retraining the muscles and checking where the mandible is positioned. I am developing new techniques to reset the CO-CR at the first appointment, not the extraction day. Its never too late but a totally edentulous patient will add time to the treatment.

A record is required prior to extractions that we can reference and CONE BEAM can record it. A Cone Beam scan can capture those parameters or any change which will tell me whats taking place similar to when we were pantographing patients to create reconstructions. The extracted parameters from the Cone Beam images can be used to correct years of mandibular movement that created the malocclusion. When implants are placed the techniques are a bit different and some planning is required and that can be done at the healing stage from the first week to twelve weeks to relocate the mandible back to CR.

The temporaries then can be setup to de-program the patient during the healing phase and still be functional to return the mandible permanently back to CR and the patient can enjoy a new smile at the same time. Cone Beam can then be a far easier route than the old days of pantographing which I was involved with through to 2014 to gather parameters for a CR treatment plan. Last no one wants to go back to those days either.

We do not want to go back to the past, but what we should avoid is reproducing the misplaced mandibular position of the original situation but record that position as a reference. Then plan out how to get the mandible back into CR. Then the treatment can be established to be stable in centric and dynamic in function to avoid damage to the casework from interferences and clashing.

HOW TO UNDERSTAND THESE IMAGE MAPS BELOW; These are two dimensional illustrations (flat maps) that indicate axis rotation tracking pathways of cusps to examine where and how interferences are developed and where they likely will develop by associated to changes in intercondylar distance measurements. They are created from three-dimensional video frames within a project environment called OCCLUDY (C) which is a video animated teaching platform currently under development by OSS DENTAL to teach static and dynamic occlusion. These illustrations cannot be applied to semi-adjustable articulators as they are fixed 110 mm instruments.

Nature created dentition to occlude but we use the term occlusion as a description that needs to be more defined. Dentition then has to function. What does that mean. I break this down to two separate states. "To Occlude" and "To Function", as that is easier to understand. When the upper and lower dentition is touching at the rest position (static) in MIP (maximum intercuspal position) that means it has Occluded, it does not mean the occlusion is correct or harmonic. If the condyles are in CR (centric relation) the teeth will be harmonic or correctly aligned. In CO (centric occlusion) is rarely seated in CR and the dentition will suffer more wear and the mandible will have no guidance and no repeatable position will exist. The question then is what position is the mandible in CO or CR ?

When dentition is in function the condyles are in motion (dynamic-function) sliding in contact, known as group function or separating meaning dislcuding and the mandible will move from CR which is a repeatable seating. If the mandible is in CO it is in a non-repeatable position. CR is termed as correct with lower tooth wear and rested muscles and CO is not and suffers far greater tooth wear and applies more force to the system and TMJ's'. Either way the mandible can translate and can be described as being in translation by being in rotational motion, protrusive motion or medial motion. This then can be tracked to include surtrusive, detrusive, retrusive and detrusive distractions as condylar positioning related to both the horizontal plane and the sagittal plane. That then means the mandible can translate in all three planes X,Y,Z or a mix of any at any time driven by associations and neuromuscular activity. That communication process is then between your brain, nerves, and muscles that creates the direction's of function. Errors are then detected by neuromuscular activity which triggers paranormal function to wear away the interference/s.

With that said the skeletal system is the base where the geometry resides within the TMJ and should link to the anterior guidance. This then can be called The Five Principles of Occlusion, if the geometry is setup correct and is harmonic as a protective system. In CR chipping, fractures or other abnormalities are greatly or completely eliminated if the geometric parameters are correct. In CO that cannot be achieved as the CO mandibular condition is free and not controlled by definitive guidance. Cone Beam can provide the incorrect skeletal associations by tracking a Cone Beam image and slicing it to extract accurate positioning, which can be included in a digital design and checked on a fully functional articulator.

This why I use a fully adjustable articulator and now in the process of developing a new one to accommodate new features and ease of use with digital dentistry.

Manufactured by Charles E. Stuart in 1953, this articulator in its day was recognized as the first ARCON computer in dentistry and that is engraved on the upper bow along with its patent number. Owned by Dr.J. Bunyan, Harley St - London in 1996 this was one of two sets used by PK Thomas while giving Gnathology courses in London at that time. Although I had been working with Stuart articulators since 1993 this Stuart and its Pantograph was given to me by Wilky Bunyan in 2014 to which I have used ever since. Brilliant in concept and as far I know nothing has ever surpassed it's abilities and accuracy.

I DO NOT MAKE FLAT PLANE OCCLUSIONS. BUT HERE ARE SOME GUIDELINES

This illustration explains what will happen if you totally ignore the skeletal system but are using an articulator for the convenience of aligning models only to create basic restorations or AOX designs.

It represents a flat plane occlusion which is often requested. Flat Plane occlusions are for non-interfering cusp arrangements that is intended usually by prosthodontists prescribing dentures. When applying composite or ceramics as onlays CONE BEAM can be used to plot accurate cuspal positioning. As a rule of thumb set your design with an occlusal plane of 10 degrees minium inclination and check all xyz translations for interferences or clashing and adjust canine guidance to coincide correctly with the condylar inclination and set the curve of Spee shallow or slightly higher than flat to avoid posterior clashing. This is not a good design but dentists now ask for this to ovoid grinding.

When using monolithic designs with stain and glazing or labial layered ceramic consider the loadings on classical restorative implant reconstructions. Vertical forces will not be absorbed through the ZR structure as the material is too dense and non absorbing. Force will be applied directly to the spiral and bottom of the implants in contact with the bone. Zirconia, Titanium and Chrome absorbs very little force, if any at all. Repeatable seatings of the condyles in CR configurations will help create correct harmonic occlusion to the casework when every tooth has equal contact with the arch of closure. I apply an 8 micron occlusion tolerance to finalize bites. CO will not do that as the mandible is unstable in CO, plus it is destructive by nature as it has no correct retrusive guidance.

A mandible in a CO configuration is what breaks most of your restorations, bars debond or midline fractures caused by offset forces are common.

If your patients are aware of interferences, paranormal function will be triggered to reduce the offending cusp's. That will not work as zirconia does not wear away, bone just loses mass and tissue and root resorption can be common symptoms. Flat plane occlusion involving ceramic needs to be setup correctly on very accurate instruments and tested carefully before fitting. This is not something I would undertake only when other options are not favorable. In my entire career I have made this type of setup about twice.

OBSERVATIONS THAT CREATES DAMAGE

Intecondylar distance not known.

The entire arch is designed by software.

Curve of Spee not considered or is incorrect

No immediate side-shift or progressive shift considered

Condylar inclination is not known.

Occlusal plane requested to be flat

Incisal guidance ignored or is incorrect

Canine guidance is not considered correctly or set by the software.

OUTCOME

JAW ROTATION DOWNWARDS WILL BE OKAY

ARC OF CLOSURE WILL BE IN SOME CASES TO TIGHT ON CLOSING

CONSEQUENCES - IMPLANT FAILURES, TMJ ISSUES - PAIN OR FRACTURES OF RESTORATIONS

USING A SEMI-ADJUSTABLE ARTICULATOR OR JUST USING STATIC SOFTWARE - WHAT HAPPENS

The illustration above show us how tracing pathways related to cusp positions will increase or decrease interferences related to how the TMJ components are configured. If the occlusal plane is shallow or almost flat the dentition will clash in the protrusive translation following the sagittal plane even though the anterior two front incisors direct the mandible downwards and forwards to an edge to edge position. To stop the clashing of the posterior dentition we are relying on the condyle inclination being mid point not too flat and not to steep around 25 to 30 degrees inclination. Incisal distance is reliant on the curve of spee being calculated to work with the condylar inclination as well. Opening the VDO (vertical dimension) too much is going to strain the ligaments and over stretch muscles which causes pain and tmj issues. Conebeam allows for an easy set up. Intercondylar distance if not set accurately will position all your cusps inaccurately.

When you take your work to the mouth as a try in or finished product the patients intecondylar distant may be completely different. You may not be aware of this unless a tracing was sent with the case before you started work on it or some indication of the intecondylar distance. The dentition, especially the cusps will be in the wrong place and the cusp hights too high or too low. Either way tooth wear increases by uncontrolled forces being applied by uneven, inefficient or non functional cuspal positioning.

OKAY - WHEN DOES ONE SIZE NOT FIT ALL

One of the indicators the intercondylar distance is not correct is that the distal aspects of the upper laterals will chip or fracture in translations and the upper and lower cusps of the posterior molars may follow the same fate, both are quite common to failure or adjustments in dental ceramics. Technically if you built your case with a 110 mm intercondylar distance on an fixed semi-adjustable articulator or designed within software and the patients intercondylar distance is the same in situ the lowers cusp positions will function with the upper opposing dentition as per the red pathways as they will coincide.

When the patients intercuspal distance is different and the pathways are wider or narrower the cusps hight may be too high or too low and interferences will be recorded on the mesial and distal inclinations of the posterior dentition related to the pathways that the other colors in the illustrations above are tracking to interferences can be many from minor to very obstructive because I have not included immediate side-shift in these illustrations which is another discussion best explained in a detailed animation or better explained in a hands on video.

The masticatory system is super sensitive to contact pressure, wrong parameters and incorrect that are being subjected to any interference or force. The neuromuscular system will trigger a reaction regardless of how small the inaccuracy maybe. The patient wil pick this up also and may point it out that the bite is high or wrong, often immediately. You may be able to adjust this out if it is minor around 0.2 mm or less or your guidance settings may drop the mandible downwards in the posterior quadrants and it might not be noticed. But it will be noticed as the jaw starts to come back into occlusion as it returns by a different pathway. Jaw opening is rotational, closing is elliptical and occlusal cusp inclinations dictate the arc of closure at the last 0.1mm of closure. The system can work to this accuracy and will react to the force being applied by the interference.

Remember these are flat two dimensional illustrations I have traced will give you an idea of how close or tight these pathways can be. Pathways will effect every tooth in the arch. When in a medial translation the problem gets far worse and if the patient is not within the tolerance of 110 mm and is 109 or 111 mm you might get away with with a few adjustments. After that you may face a lot of time wasted grinding which often ruins the morphology. At 115 mm to 120 mm you will probably face a total remake.

I have tracked only two cusps at four different medial pathways positions, (red-pathways) not sixteen teeth, only two but this is enough to show how the other curves will or might be different. Occlusion and function indicates how easy and unaware many of us are to how easy ceramic and other materials fail. I spent years working with pantographing techniques. Now using CONE BEAM CT for my reconstructions they take a lot less time and are far more accurate. Countries today are now multi-national with far more skeletal variations in skull sizing to accommodate. ONE SIZE NEVER FITTED ALL and it never will. Cases I have dealt with ranged from 87mm to 122mm, all with very different outcomes. CONE BEAM foe me has been a refreshing solution to the years of tracing patients. This is basically all lab-based.

PART - 1

IF YOU ARE EXPERIENCING CHIPPING OR FRACTURING OF CERAMIC RESTORATIONS IN RECONSTRUCTIONS TECHNIQUES WE OFFER SOLUTIONS TO ELIMINATE THIS PROBLEM

CONE BEAM IS ABOUT HOW WE CAN SIMPLIFY, RE-ADDRESS AND MANAGE YOUR DAY TO DAY DENTISTRY TO AVOID ERRORS THAT ARE SEEN IN CLASSICAL RECONSTRUCTIONS AND MORE SO IN IMPLANT CASEWORK THAT CAN OFTEN BECOME ANTAGONISTIC OR DESTRUCTIVE.

A FAMOUS DENTIST ONCE SAID - "ONE SIZE DOES NOT FIT ALL" WHAT DID HE MEAN

The masticatory system is a complex combination of geometry, function and aesthetics, how do you restore it when it no longer works or it looks tired.

PART - 2

WHAT WORKS AND WHAT WILL FAIL