Arc of Rotation & Heavy Posterior Contacts

December 10, 2021 Lee Ann Brady DMD

Have you ever had a night guard or other full coverage dental device come back with contact only in the posterior or heavy in the posterior? It is a fairly common phenomenon. And it is a big challenge when doing two-jaw hybrid surgery and placing the temporary restorations on the day of the surgery.

I became aware of this big challenge when my oral surgeon came across the parking lot one day to discuss the upper and lower hybrid case of one of our mutual patients. This was the first hybrid case we would be doing together. He had been using a company with a software platform that does his implant planning and digital setup, and then produces his surgical guides and provisional restorations. It can even produce the final restorations. He related to me that when he tries in the initial prostheses, he always finds they are heavy in the posterior.

So, I asked him, “When they ask you for records, what do you send them?” He said they request either an upper and lower scan, or upper and lower BPS impressions, or upper and lower models. They also want a bite record and a shade. As he went down the list, something was missing that has to do with heavy posterior contacts.

Whether it is premade upper and lower provisional restorations when you are doing extractions, implants, and hybrids — or it is a nightguard you get back from the lab or Invisalign trays that you receive from Invisalign, there are occasions when we find prostheses are heavy on the posterior contacts. Sometimes there are no anterior contacts. That’s because, across the board, prostheses need to be fabricated knowing the arc of rotation, which is the distance between the hinge axis at the center of the condyle and the upper anterior teeth.

A full arch impression taken without a facebow transfer, either hand articulated or with a bite registration only over the prepared teeth, only provides the same information about maximum intercuspal position as a triple tray. If we mount the full arch impressions on a simple hinge articulator, the articulation used does not represent the arc of rotation. If we are digitizing the impressions for a digital system, we also are missing this essential piece of diagnostic information. We must have impressions mounted on an articulator with a facebow or dental-facial analyzer (DFA).

I explained this to my oral surgeon who became concerned he would not be able to deliver this information to the implant planning company he was using. But this story has a happy ending. He called the company to learn if they could use articulated models mounted with a DFA or facebow. It turns out they much prefer this! And they told him the specific articulator systems for which they have corollaries in the digital world. If he sends the models mounted on any of these, they can digitize them and know the arc of rotation.

Those who have been in my presentations have heard this many times before. The more esthetic and functional information we send to the laboratory the higher will be our ability to efficiently manage the functional and esthetic issues of the case precisely. A lesson we can learn from this story is the value of conversing with the specialists on our interdisciplinary teams and in our interdisciplinary study clubs about the importance of capturing and communicating the arc of rotation. If a laboratory is not requesting this information, have a conversation with the laboratory.

The primary purpose of Panadent’s DFA or any of the earbow/facebow systems is to capture this critical piece of information we call the arc of rotation. There is other information these systems capture but the arc of rotation is critical in establishing proper occlusion. I’ve written about Panadent’s DFA in a previous blog. For an in-person, hands-on lesson in the dento-facial analyzer, we invite you to attend our Essentials 1 Pankey course. You can also watch this video for a quick refresher.

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Lee Ann Brady DMD

Dr. Lee Ann Brady is passionate about dentistry, her family and making a difference. She is a general dentist and owns a practice in Glendale, AZ limited to restorative dentistry. Lee’s passion for dental education began as a CE junkie herself, pursuing lots of advanced continuing education focused on Restorative and Occlusion. In 2005, she became a full time resident faculty member for The Pankey Institute, and was promoted to Clinical Director in 2006. Lee joined Spear Education as Executive VP of Education in the fall of 2008 to teach and coordinate the educational curriculum. In June of 2011, she left Spear Education, founded leeannbrady.com and joined the dental practice she now owns as an associate. Today, she teaches at dental meetings and study clubs both nationally and internationally, continues to write for dental journals and her website, sits on the editorial board of the Journal of Cosmetic Dentistry, Inside Dentistry and DentalTown Magazines and is the Director of Education for The Pankey Institute.

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Dento-Facial Analyzer Technique: Capturing Records

October 1, 2018 Lee Ann Brady DMD

You can gather accurate functional and esthetic information using the Panadent Dento-Facial Analyzer for restorative cases. I’ve found this tool particularly effective compared to alternatives such as the Facebow or stick bite.

If you haven’t done so yet, make sure to check out the introduction to this series on the Dento-Facial Analyzer. It includes background information, armamentarium, and key reasons why the device can elevate patient care.

Without further ado, the Dento-Facial Analyzer technique:

Essentials of Dento-Facial Analyzer Technique

Once you have the white disposable plate – which is actually the piece you will send to the lab once the record is captured – snapped onto the Dento-Facial Analyzer, use VPS tray adhesive to lightly coat the plastic tray. You are only going to do this from about the canine position posteriorly because you aren’t going to put silicone on the anterior portion of that bite plate.

Next, attach the vertical reference bar to the Dento-Facial Analyzer. Without bite registration on it, take it to the patient’s mouth and seat the central incisors exactly against the white plastic in the front labially.

Verify that you can hold this level to the horizon in two planes of space and that you can touch the patient’s teeth. If not, you might need to build up the posterior.

If you’ve verified this, put bite silicone on the plate from the canine position back, then seat it again, making sure the central incisors are seated labially against the white plastic …

I’ll round up this fun technique with Part 3 in the series coming soon.

For a hands-on lesson in the Dento-Facial Analyzer from our talented educators, check out our Essentials 1 Pankey course. Also, watch this video for a quick refresher or pre-course overview.  

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About Author

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Lee Ann Brady DMD

Dr. Lee Ann Brady is passionate about dentistry, her family and making a difference. She is a general dentist and owns a practice in Glendale, AZ limited to restorative dentistry. Lee’s passion for dental education began as a CE junkie herself, pursuing lots of advanced continuing education focused on Restorative and Occlusion. In 2005, she became a full time resident faculty member for The Pankey Institute, and was promoted to Clinical Director in 2006. Lee joined Spear Education as Executive VP of Education in the fall of 2008 to teach and coordinate the educational curriculum. In June of 2011, she left Spear Education, founded leeannbrady.com and joined the dental practice she now owns as an associate. Today, she teaches at dental meetings and study clubs both nationally and internationally, continues to write for dental journals and her website, sits on the editorial board of the Journal of Cosmetic Dentistry, Inside Dentistry and DentalTown Magazines and is the Director of Education for The Pankey Institute.

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Who Captures The Facebow Record?

February 10, 2018 Roger Macias DDS

Do you feel reticent about having someone other than you use the facebow? 

A Spatial Reference Point Story

Recently over the holidays as I was “channel surfing” I came across the movie Apollo 13. This is one of those movies that no matter how many times I have watched it, I just have to stop and watch it one more time. Every time I do, I can’t help but get misty-eyed when it gets to the part when the crew make it back to Earth safely (SPOILER ALERT … But you probably read this in the history books anyway).

For me, there is one super exciting moment in the film when Astronaut James Lovell (aka Tom Hanks) has to find a reference point to correct their descent back to Earth from space or burn up on re-entry. Since he cannot use his on-board computers, he lines up his spaceship with the Earth in his window.

“Keep the Earth in the window!” A spatial reference point! Too much correction and their spaceship burns up on re-entry. Too little and they skip off the Earth’s atmosphere.

Make Your Facebow Process Simpler

In our dental offices, the facebow is used to give us a spatial reference point for mounting diagnostic or working models of our patient’s dentition. This is done onto an articulator that approximates the realities of our patient. Sure, you might be able to mount casts arbitrarily, but is your accuracy reproducible? The facebow is a simple tool in our armamentarium to make our life easier.

The question remains, “Is this a task that the dentist must perform?” In my office when we create exquisite dental mountings, I delegate this task to my awesome dental assistants.  With a little training they can do this immediately and the procedure only takes a few minutes.

This involvement is a great way for them to demonstrate their knowledge. It paves the way for more opportunities to open conversations about the Dentist’s Care, Skill, and Judgement. They become your chairside cheerleader and highlight your expertise. They will also express how a critical bite registration record or protrusive record performed by the dentist will only enhance the outcome of treatment.  

Information gathered through the use of a facebow makes our dentistry more predictable. It distinguishes you and your team as a highly trained dental practice.

Don’t burn up on re-entry or skip off into space. Glide effortlessly into beautiful predictable dentistry by using your facebow. Keep your Earth in the window!

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Roger Macias DDS

Dr. Macias obtained his dental education at the University of Texas Health Science Center Dental School at San Antonio and graduated in 1983. While establishing his private practice, Dr. Macias was an assistant professor in the Department of General Practice at the UT Dental School from 1983 until 1989. He is the team dentist for the San Antonio Rampage, the WNBA San Antonio Silver Stars, the San Antonio Missions Baseball Club as well as numerous college universities and high schools in the south Texas area. Dr. Macias is active in numerous dental study clubs and is currently a faculty professor at the world renowned L.D. Pankey Institute for Advanced Dental Education in Key Biscayne, Florida. Among Dr. Macias’s many accolades and awards, he has received his Fellowship in the American and the International College of Dentistry as well as the Pierre Fauchard Academy.

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