Tag Archives: occlusal scheme


Facebows … Optimizing the Data

It is nearly impossible to find a textbook related to prosthodontics or restorative dentistry that does not mention the facebow as a technique to orient the upper cast to the articulator of choice. The general inference is … the more sophisticated and involved the treatment … the better the results (or the fewer adjustments required) when using a facebow.

Are you getting what you are looking for?
Early published “research” on the use of a facebow can be found in Dental Cosmos from WGA Bonwill in 1878 basically pertaining to the construction of complete removable denture prostheses. The idea is to begin the process of establishing a point reference for setting teeth.

Why make a facebow record?
The facebow is used to relate the maxillary cast to the condylar elements of your instrument or articulator of choice. The overall goal is to use this information to minimize the amount of adjustment at the time of delivery. One advantage of making a facebow record is the visible cue to the patient that there is something different going on in your office all part of the process of creating value for the treatment provided.

At what point do we need more accuracy?
In general, an earbow oriented facebow is an estimated measurement of the hinge axis position provides enough information for the majority of restorative treatment, particularly if our goal is to provide a mutually protected occlusal scheme with anterior guidance and shallow cuspal inclines in the posterior segments. Certainly, if the restorative goal includes a group function occlusal scheme, then more information is required. The additional information related to the functional pathways of each temporomandibular joint complex is obtained with something like a pantographic tracing with a fully adjustable articulator that optimally has customizable condylar elements.

Specifically, if our interocclusal record is made with a leaf gauge or Lucia Jig to record a repeatable hinge axis position, then it is safe to assume the bite registration is made at a vertical dimension of occlusion that is open from maximum intercuspation position (MIP). It is with this information whether as a close estimate (earbow) or more precise measurement (pantographic tracing) that we then feel comfortable altering the vertical dimension on the articulator by moving the pin up or down on the instrument.

Can we get by without a facebow?
Challenge yourself with this point. Talk to your laboratory technician to gain some insight on what is done on a regular basis and how they manage without the information gained from a facebow record. The goal is to plan our restoration based on the facial features of our patient … the final result must fit the patient’s face to be truly esthetic. Think about what we do to coordinate the position of the anterior teeth: a stick bite, a digital facebow showing facial features, and more specifically – modifying the position of the facebow/earbow to fit the horizontal plane that we are looking for in order to position the maxillary cast in a way to communicate the occlusal plane. What if the ears are asymmetrical? What if we have to “tug” the earbow element up, down, forward or back on one ear in order to make the record parallel to the desired horizontal plane? Are the estimates of the facebow record in terms of hinge axis position accurate at this point? How does this affect or influence the impact of the condylar elements on the articulator?

Think about this a little more. A Randomized Controlled Trial (RCT) published in the Journal of Prosthetic Dentistry (Hickey, et. al.) compared two methods of denture construction: One with hinge axis location and facebow transfer to an “advanced” articulator, and the other with arbitrary mounting to a simple articulator. The results after 20 year follow up (Ellinger et. al.) stated that were no significant difference between patient groups. Is that for real?

One technique that is used to teach laboratory technicians how to make dentures without the information gained by a facebow involves the use of a set up template. The idea is to make use of average value articulator settings using shallow denture teeth. The critical factor here is that the most important piece of information is an interocclusal record must be made at the anticipated vertical dimension of occlusion. This little detail minimizes the error attributed to the articulator.

The set up template is used to serve as a reference point based on the information provided by a properly contoured maxillary wax rim. The idea is that the clinician is able to see the wax rim clinically and is able to modify it to fit the esthetic landmarks of the patients face. The midline and the arch width are recorded so that if changes in tooth position are required, then it becomes a much more precise endeavor. A huge benefit when thinking about how wax alters tooth position three-dimensionally based on temperature changes.

ModelThe clinical photos (Figs. 1, 2, 3, 4) included show a denture tooth set up at the wax evaluation appointment. The desired changes include a slight modification of the midline position at the incisal as well as modification of the occlusal plane – bring the right side down and the left side up. How would you communicate this to the lab? How would you check the modifications that were made after the case is returned?

mustachioDoes this apply to natural dentition?
Dr. Kinzer demonstrates a technique in the Worn Dentition Workshop where we can get the best of both – a facebow record to mount the maxillary cast and a custom made plane of reference … a set up template. The technique provides the opportunity to facilitate communication, and, more importantly, track changes that are made while working with the dental laboratory. This type of information is useful during a diagnostic wax up based on the mounted study models.

How do you use the facebow record?

References:
Bonwill, WGA. The science of articulation of artificial dentures. Dental Cosmos 1878;20:321.

Hickey, JC, et. al. Patient response to variations in denture technique. I. Design of a study. Journal of Prosthetic Dentistry 1969;22:158-170.

Ellinger CW, et. al. Patient response to variations in denture technique. Part VII: twenty-year patient status. Journal of Prosthetic Dentistry 1989;62:45-48.

 

Douglas G. Benting, DDS, MS, FACP, Spear Visiting Faculty and Contributing Author. [ www.drbenting.com ]

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How to Make a Custom Incisal Guide Table

Once the decision is made to make a custom incisal guide table, the following sequence of steps should be followed. Determine if you are going to restore the patient in a seated condylar position (CR) or in maximum intercuspal position (MIP). If the two positions do not coincide, decide if you want to perform an equilibration.

1. Make accurate impressions and casts of the maxillary and mandibular teeth.

2. Take a facebow transfer.

3. Take a protrusive bite registration record.

4. Mount the maxillary cast with the facebow jig, and then hand-articulate the mandibular cast to mount it to the upper. The protrusive record is used to set the condylar inclinations.

5. The materials that can be used for the custom incisal guide table are as listed below.  Place a small amount of the material approximately 1.0 cm thick onto a stock incisal table. If Triad is used, it is light cured after the movements are all completed. All of the other materials are auto-curing, so you must move efficiently to avoid distortions.

6. Lubricate the incisal guide pin with Vaseline so it glides smoothly through the material you have selected.

7. Close the articulator with condyles locked so the incisal guide pin penetrates through the material and strikes the top of the table. This establishes the home position which represents maximum intercuspation.

8. Open the articulator and release the condylar locks. Position the casts so the incisal edges are now touching as in straight protrusive position. Confirm the teeth are touching as you move the maxillary cast to the home position. This establishes the straight protrusive incline on the custom incisal guide table.

9. Open the articulator and position the casts in a pure right lateral edge-to-edge position. Move the maxillary cast to the home position making certain the teeth are touching. This records the right lateral incline on the guide table. Repeat for the left side. The pathways have been recorded after completing the protrusive, right and left, movements.

10. Now record all the lateral protrusive movements by moving the maxillary cast.  Repeated movements will be necessary to establish a smooth custom guide table.

After completion of these steps, all of the functional movement patterns have been recorded for this patient. If the patient goes into cross-over during parafunction, this will need to be addressed in the new occlusal scheme.

 

Learn more about occlusion in addition to techniques relating to esthetics and treatment planning from the Spear Digital Suite.
View the free lesson: Bite Records in Restorative Dentistry.

 

Is Group Function Really Bad?

Most of us have been taught that ideal occlusion means canine guidance, or mutually protected occlusion. In fact, that is the preferred occlusal scheme in many instances. It requires the least amount of muscle activity for the mandible to move into excursions when the teeth are touching. It separates the back teeth so they are out of harm’s way during parafunction.

Most of us were also taught that group function is BADDD! It causes too much muscle activity and destroys teeth.

So what if we just can’t get the canines to touch when the teeth are closed? There are some choices—orthodontics, change the shape of the teeth, and even orthognathic surgery can be a possibility.

Practically though, unless there is a compelling reason to do the other treatments, the easiest thing is to “share the load” with group function. This simply means that when the jaw moves from side to side the guiding teeth may be premolars. The goal is to transition the guidance so that when the jaw moves side to side, even if the guidance begins on premolars it transitions to the canines.

The clinical slide shows this exact instance. Even after braces the canines didn’t touch. The solution was to start the guidance on the first premolar and transition it to the canine—group function!

 

The Importance of Incisal and Occlusal Planes

To achieve the most ideal esthetic and functional outcome for the patient, the goal in virtually all dental therapies is to level the incisal and occlusal planes to horizon. Orthodontics, orthognathic surgery, periodontal procedures, full denture prosthodontics, and restorative therapies all use horizon as the standard reference.

Once the incisal plane is level the gingival heights can be adjusted accordingly, and the maxillary midline can be made perpendicular to this horizontal plane.

Why is this so important? Because successful design of the occlusal scheme provides an esthetic result that is more visually pleasing, and enhances the patient’s envelope of function. To accomplish this you must have an accurate means of transferring the existing condition of the patient to the articulator, generally through the use of an esthetically corrected facebow.

It is important that this information is captured and communicated to all appropriate members of the dental team. It is my strong recommendation that the procedures needed to capture this information are completed during the initial diagnosis and treatment planning phase, and again during the provisionalization stage. In my last article, I provided you with guidelines for composing a photograph that accurately portrays where the patient’s planes are relative to horizon. Following those steps facilitates an accurate gathering of the necessary information.

In the laboratory, a facebow transfer is used to mount the maxillary cast. Freehand mounting can lead to an error in the occlusal plane and midline if a cant exists, because unless told otherwise, the technician will assume the planes are level. A photograph of the facebow is recommended and should be sent to the lab with your restorative case, to provide the technician with verification of the accuracy of the transfer.


For a detailed look at occlusal guidance patterns, history and research, view our free lesson: Understanding Occlusal Guidance.  

 

 

Alignment Showdown: Orthodontics Vs. Restorative Dentistry

Restorative dentists have been conflicted for quite some time over when to use orthodontics or restorative dentistry when esthetically treating their patients. Many patients don’t want to wear braces especially when the result obtained can be accomplished restoratively.

When treating a patient who wants their teeth aligned but doesn’t necessarily want orthodontics, it’s helpful to ask yourself the following six questions to compare the modes of treatment options.

1.Will restorative dentistry need to be done whether orthodontics is performed or not? One of the biggest advantages to orthodontics is that it eliminates the need to restore teeth if they are in good condition. If your patient’s teeth need to be restored anyway, it may be more efficient and conservative to align them restoratively.

2. Can the desired occlusal scheme be created without orthodontic movement? A good thing to know is that there are patients who must have orthodontics in order to avoid future issues with their teeth. If restorative dentistry offers an occlusion that isn’t ideal, it’s best to suggest referring your patient to an orthodontist to align the teeth.

3. Are the existing papilla levels esthetically acceptable? If the papilla levels aren’t acceptable, it’s very easy to move them apically with surgery. It is virtually impossible to move those levels coronally with anything besides orthodontics. When you evaluate all the esthetic parameters of your patient, take note of the gingiva and papilla heights – if they aren’t symmetrical it may be time for the patient to see the orthodontist.

4. Is the most apical-free gingival margin level acceptable? If you have an under-erupted tooth without recession and the gingiva is too apical, you must erupt the tooth orthodontically. If the tooth does have some recession and root exposure it’s easy to alter gum levels with surgery.

5. Can restorative dentistry create an acceptable contour and arrangement? This question usually comes up in cases of diastemas or crowding. Making a diagnostic wax-up of your patient’s teeth should allow you to see whether the case needs to be treated orthodontically or restoratively.

6. Can teeth be prepared and restoratively aligned without destroying them structurally? In most cases, even if it’s only one tooth that will lose structure, orthodontics will be the preferred method of treatment. However, there are some patients that will opt to have troublesome teeth extracted in order to avoid braces.

As with many procedures, it’s important to inform your patient of all the possible options of treatment. Although many patients don’t want to wear braces, laying out the pros and cons of each method will help your patient understand each option and choose the treatment appropriate for them.