Why a perfect crown may not always be the best option for a patient

November 6, 2017

Article

Putting in ‘ideal’ crowns without considering other factors can lead to restoration failure.

When we look at crown restorations, they often mimic the form an ideal tooth in color, translucency and contour. But while the replication may be “ideal” in the broadest sense of the term, it may not be ideal for any particular patient.

That’s because wear patterns in patients’ mouths are as unique as the patients themselves, so putting in a crown that hasn’t been designed for that patient is asking for the restoration to fail.

“The challenge is that, for most patients presenting a need for a crown, there is some sort of wear on the tooth, but when technicians close their eyes to design a tooth, they are thinking of the most natural looking tooth,” says Adam Hodges, DMD, a general dentist practicing in Asheville, North Carolina. “When dentists start thinking about that, they realize that if the lab knows what the dentist is trying to do, they can actually make crown procedures more predictable and make the results better for patients.”

Why restorations should not be made into the 'ideal' tooth

Every lab technician wants to create the most beautiful, functional crown possible, but there are limits to how “ideal” a crown should be.

“The tooth structure of a 50- or 60-year-old does not look like the tooth structure of a 20-year-old,” Dr. Hodges says. “For most patients presenting a need for a crown, there is some sort of wear on the tooth. It could be because of an existing filling or because of a wear pattern in their mouth.”

If a technician creates the most natural looking tooth, he or she will include the ideal contours and form of the tooth. But that can pose a problem if those contours are in violation to the contours the patient has created, Dr. Hodges says. If that happens, it’s likely that the restoration will fail.

“There is a very high likelihood that the patient will return to the practice with either the crown knocked off or a sore tooth,” he says. “It is like walking down the street in the same way that you have walked for thousands of years. There is probably a line in the street where you walk. If you change that topography just a little bit, you could stub your toe. The same thing happens with the teeth. If you have a contour that the patient spent the last 40 years milling into their mouth and you do not replicate that contour or a contour that is short of that, there is a very high likelihood that the patient will end up with pain.

The patient could even end up needing root canal therapy, which could have been avoided had the crown mimicked their teeth’s natural form.

“We like to think that if you cut down that wear and make an ideal tooth that everything is fine, but actually it creates a lot of problems,” Dr. Hodges says. “If you are doing single-tooth dentistry, which is the lion’s share of what is being done out there, you must pay attention to and respect the contours that are there. If you don’t, you are going to end up with those situations.

“I have a new patient who has had a crown cemented four times over the last three years, and now this tooth is going to be extracted,” he continues. “I know the crown was put in in a way that violated the contours and rather than respect and recognize that those contours were violated, the dentist kept recementing the tooth, thinking it was a cement problem. Our cements are fantastic, so if a tooth keeps coming off, you had better learn the lesson, or something is going to happen. In this case, the tooth broke, so we are going to extract it.”

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Digital scanners help replicate the patient’s natural tooth

Most dentists don’t send preoperative models to their labs, but digital scans can fix that.

“With a digital scan, it can actually make the process quite simple by allowing you to take a preoperative scan and then take a postoperative scan after preparing the tooth,” Dr. Hodges says. “If you are going to give them a new crown, your best bet is to replicate the existing tooth in a stronger form. We all like the beauty of the brand-new tooth and what can be possible if a technician gets their artistry involved in making the perfect-looking tooth with perfect-looking anatomy. But we all hate crowns coming off or increasing patient sensitivity. Replication of the pre-operative form is a paradigm shift that should happen more often, and digital impressioning machines make that simple. It can also be digitized and created in the digital world by the labs, which mostly work in the digital world now.”

“For the patient to be able to choose their own smile design is the biggest thing,” says Jason Atwood, CDT and digital integration specialist at Core3dcentres NA. “There is even an option now to have a ‘donor smile’ where the patient can choose someone else’s smile.”

This is a good option specifically for patients who want to recreate the natural, beautiful smile of their youth. Thanks to digital scanners and the phenotype of a younger generation, dentists can look to a more youthful copy of their mouth to create their patient’s ideal smile.

“We did a case recently where a mother was getting restorations done and said her daughter’s teeth looked like hers when she was younger,” Atwood says. “The dentist took a scan of both of their teeth and we were able to copy the daughter’s smile for the mother. By copying her daughter’s smile, we were able to open the fountain of youth for the mother and make her feel like she had gone back 30 years.”

This is a significant change from the “old days,” when a dentist would make most of the decisions, leaving little room for patient involvement.

“It is not just make it function anymore, it is much more of a personal connection,” Atwood says. “The traditional way, most of the decisions were left up to the doctor. You would get impressions taken and they would be sent off to the lab and the doctor and the lab would discuss a diagnostic wax-up. The lab would send it back to the dentist, who would show the patient a model and ask if it looked nice and the patient would say yes or no. There was not a lot of input from the patient.”

With digital scanners and design software, everyone is now more involved, from the dentist to the lab tech to the patient. That saves time on reducing chairside adjustments, ensures a more predictable and successful restoration, and allows the dentist to place the most ideal restoration for each patient, who can go home with a smile that looks and functions at the highest level possible.