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Freedom in centric allows for function and comfortable, well-fitting dentures.
Freedom in centric is a concept many denture professionals have forgotten. However, it is vital for denture teeth design because it allows for excellent function and a comfortable, well-fitting denture for patients.
Marc Wagenseil, CDT, DD lectures for VITA North America with an advanced denture course “Freedom of Movement: ‘Understanding Occlusion’ Hands-On Denture Workshop.” The course seeks to impart a greater understanding of biomechanics, to instruct dentists, prosthodontists, denturists and technicians on the importance of minimizing deflective contacts and deliver dentures that have more flexibility and improved freedom of movement for patients.
“I'm on a mission to help raise a profession-we can do better,” Wagenseil says.
Wagenseil has 32-years’ experience as a denturist in Canada. He commented early on in his career, he had successes and patients would bake him cookies and sing his praises, while conversely others would tell him off. The dichotomy between the outcomes led him to wonder what he was missing.
It was freedom in centric, or more specifically, using teeth that have it. Wagenseil says that when freedom in centric is built into a denture, it fits comfortably and increases patient satisfaction while also decreasing the set-up time, as well as the need to reset and adjust the denture after delivery.
What is freedom in centric?
The clinical definition of freedom in centric is “A flat area in the central fossae upon which opposing cusps contact which permits a degree of freedom (0.5–1 mm) in eccentric movements uninfluenced by tooth inclines.”1 The less clinical definition for the term is how when we hold our natural teeth together we can wiggle them around a little bit when they are touching.
A professional builds dentures by setting up teeth with consideration of the centric contact without interference between the teeth. However, few denture teeth are constructed to have freedom in centric once they come together in occlusion.
“A patient cannot accurately reproduce centric every time,” Wagenseil says. “That’s why you have freedom in centric in your natural teeth. Yet, we have built denture teeth that are locked together that do not have that phenomenon in them.”
Wagenseil says dentures don’t have nerves, so the denture patient cannot feel them, and as a result cannot feel if there is interference in occlusion.
Most denture teeth are of a flatter design than a natural tooth. The denture is built with working and balancing contacts with the mindset of balancing on the soft tissue. When the patient chews, the denture rocks. The rocking is a result of a deflective contact defined as a cusp hitting the guide plane of its antagonist, not the fossa. The rocking of the denture creates friction which in turn causes sores. Wagenseil says dental professionals often misdiagnose that as “just being a denture.”
“When we misdiagnose, then we reline the denture, or we adjust it. Eventually, the patient gets tired of coming in and paying for adjustments. They end up just buying denture adhesive, and that's why the adhesive market in the U.S. is estimated at a $150 million a year market,” Wagenseil says.
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Wagenseil recommends the VITAPAN EXCELL® and VITAPAN LINGOFORM® denture teeth that allow the interproximal fit that mimics our natural teeth. The maxillary lingual cusp tip doesn’t lock with the opposing fossa, and the maxillary buccal cusps do not contact, which is what creates the “freedom.” The chances of a cusp hitting the guide plane of its opposing tooth is greatly reduced. Unlike most denture teeth, only the lingual cusp of the upper has centric contact with the lower fossa in VITA’s premium denture teeth. When you design the denture with these teeth and employ a lingualized occlusion, these features allow for more stability and less risk of interference while the patient chews.
Wagenseil says the denture industry forgot about freedom in centric due to complacency and a lack of understanding of its significance. Many dental professionals have forgotten how a denture patient chews and how characteristics of natural teeth work differently than those of most denture teeth.
“I was taught a denture patient needs working and balanced occlusion because it's not going to tip the denture. Well, natural teeth don't have working balanced occlusion,” he says.
Wagenseil discovered that when he provided freedom in centric to a patient’s denture, the adjustments and problems decreased while satisfaction increased. He also has eliminated the use of soft liners in his office. Before designing dentures with freedom in centric and lingualized occlusion, his average adjustment rate per patient was two to five. Now, his adjustment rate is down to one, and many times zero, consistently.
If a denturist charges $200 to $400 an hour, two adjustments a day can affect their bottom line quickly. Wagenseil estimates that denturists in Canada hold anywhere from one to one and a half hours a day for adjustments, which works out to the equivalent of a work-day for free.
“When you provide freedom in centric in the denture, you can cut that time you set aside in half. You have more time, and you're less stressed,” he says.
Wagenseil’s freedom in centric mission
“My mission and mandate are to help a dental professional understand dentures better,” Wagenseil says. “This two-day course is successful because I'm retraining a profession to think differently.”
On what he describes as his holistic journey to this point, Wagenseil realized he thought he knew it all, but he didn't. For example, he used to tell patients to bite together when they put dentures in their mouth. In one course, Wagenseil has people put up their hand and promise they won’t use the word “bite,” a problematic word that means to cut through something.
“How do they know they're biting together? There are no nerves in the denture. How do they know their teeth are together?” Wagenseil says. “I had to start thinking like a denture patient-who cannot feel their teeth!”
Wagenseil explains our brains and central nervous system work on repetition and patterns. If the patient has had dentures for ten or fifteen years, they know biting creates a certain amount of pressure on the gum and hydraulics internally. People get used to that feeling and try to reproduce it.
However, opening the vertical dimension of a denture changes the patient’s bite and chewing pattern. When a patient is overclosed, they have to close their mouth more to make their teeth touch, this flattens their bite pattern. When you open the vertical dimension in a new denture, the pattern becomes more like a teardrop, elongating it, which is more like a natural bite pattern of a person with healthy natural teeth and vertical dimension, per Wagenseil.
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When you instruct a patient to bite down in a new denture, the patient is going to want to make the old, flatter patternThe teeth hit on the guiding planes, and the plate rocks loose. The patient can't feel the denture teeth; they feel the result, which is the loose denture.
“You're changing what they holistically know and have developed a pattern to. After wearing a denture for years there is a distinct pattern developed. A practitioner not recognizing this trait can cause for poor treatment planning and misdiagnosis of problems,” Wagenseil says.
While you can purchase denture teeth with freedom in centric, Wagenseil says you should also incorporate into treatment an articulator that can move horizontally which has side shift built-in. He says it will “up your game.” When you deliver better fitting dentures that don’t rock and cause sores, you get more referrals and improve the revenue stream of your office.
“Consider this, if you fabricate a denture to fit better, the dentist is providing a superior- fitting denture, resulting in more patient referrals, ergo sending more dentures back to the lab,” Wagenseil says. “It is significant when a denture patient experiences a new denture without pain. They will be loyal to you.”
Another issue from using denture teeth without freedom in centric is premature wearing of the nylon locator attachment which secures the denture to the head of the implant. When using locators, the denture should sit on the undercut, engaging it and without wear on the locaters. The nylon wears when the denture is physically moved on and off the undercut. This happens as a result of the moving or tipping over the top of the undercut of the head of the implant as a result of a locked-in bite. On occasion, the patient misinterprets the tipping/rocking denture as a failure of implant expectations.
“Patients say, ‘I don't like feeling the swaying. I want it solid,’” Wagenseil says “Professionals sell them a screw-retained denture instead. One must now consider what are you doing to the patient’s temporomandibular joint? (TMJ) This is the last thing now that'll wear out as a result of a locked in bite and that doesn't happen in five days, it happens in 15 to 20 years.”
With a (TMJ) injury, the patient could experience ringing, or hissing in the ears, vertigo, pain behind the eyes and popping in the jaw when they move it. By the time they get to their doctor, who figures out it’s the TMJ, it's too late, Wagenseil says. The joint is damaged.
Mills and the 3D printers have the potential for freedom in centric design, but the technology needs to have the appropriate scans which include freedom in centric posterior tooth design says Wagenseil. He cautions the denture industry to remember that the streamlined manufacture of dentures must not come at the cost of excellent fit and function. Otherwise, the technician or dentist will have to make another one, which is frustrating and expensive.
“What I'm hearing and experiencing now with digital milled dentures is you need to master the conventional way before you transition into the digital way. You need to know what you're doing so you know how to troubleshoot and how to make the software work for you,” Wagenseil says.
Wagenseil is lecturing at least two times a month in North America and has begun traveling the world with his message about freedom in centric. He has some people come back to his lecture three times and tell him how much it is helping them, which makes the time away from his family worthwhile to him. He feels fortunate to give back to a profession that he feels has given him a lot over the years.
“I want to give back and say, ‘We can do better,’” he says. “This is the next level. Where do you want to be? It is so much more than slapping plastic teeth together!”
1. Schuyler CH. “Freedom in centric.” Dent Clin North Am. 1969 Jul; 13(3):681-6. From web. 1 April 2019: https://www.ncbi.nlm.nih.gov/pubmed/5255322