The Dental Denture Detective by Tim Lane, CDT

Investigating the culprits behind some of the most common denture problems

by Tim Lane, CDT

Many cases come into the dental lab with a prescription that simply says, “Fix.” Replacing a part, putting a tooth back on or putting a denture back together is simple enough to do but won’t “fix” the problem without a little dental sleuthing.

The Case of the Midline Fracture

The victim: A denture split down the middle. Normally it’s between the centrals, but it can be as far off as the lateral/cuspid area.

The accusation: “Bread broke my denture.” Yes, it would be nice if just once a patient would say, “I was chewing on a ham bone when it broke.” But, honestly, if they did, chances are that didn’t break the denture either. That would more likely break a tooth—a misdemeanor. But this belief that it broke because of whatever they were doing when it broke is why most prescriptions simply say “fix/repair.”

The investigation: Unless you investigate the cause of the fracture, you can’t fix the denture—you can only put it back together and wait for it to break, again, despite the attempt of some to double up the acrylic around the frenum, make the palate thicker, or incorporate wire or Perma Mesh in the repair. Most midline fractures are a result of constant flexing over time till the denture eventually breaks from fatigue.

The usual suspect: Tissue Support (or lack thereof) over the ridges, turning the palate into a fulcrum that will constantly stress and flex the denture along the midline until it breaks. This can occur with immediate dentures or older dentures where ridge resorption has taken place over a longer period. This is easy to visualize and simple to confirm. A wash will produce thin areas of impression material in the palate and thick areas over the ridges. A simple reline will address this issue and fix it.

The guilty party: There is a culprit that is often given a free pass: Improperly Directed Occlusal Forces. When the upper posterior teeth are set too far to the buccal, the masticating forces, using the hard palate as a fulcrum, will push the denture base outward, stretching and flexing at the midline till it eventually cracks. Properly directed occlusal forces directed to the center of the palate will compress the denture and, like that standard architectural arch, can withstand more force. Push on the top of an arch and it holds up. Push outwardly at the base of the arch and it will come tumbling down. Arches are an interesting study. Understanding the arch is how we convert masticating forces into compressive stresses and not tensile stresses. Just something to put in your dental forensic file and to think about. The Hoover Dam is one big horizontal arch—not the usual way we think about arches.

Forensic File #81173: A dental assistant needed a full upper denture opposing lower naturals and crowns. We mounted the case and knew instantly that she needed to be in a crossbite. At try-in, she rejected the crossbite, saying her naturals weren’t in a crossbite. We explained that the rules for a denture are different than natural dentition. She insisted. We made it, as instructed. Within a month, she split it down the middle. We told her it needed to be in a crossbite. She said it was too thin and just needed to be thicker. We made it thicker. Three months later, she split it down the middle. We told her it needed to be in a crossbite. She said she needed a metal palate. We made her a metal palate. Six months later, she split it down the middle. We told her it needed to be in a crossbite. She finally relented. We made her a new denture, normal thickness, set in a crossbite. It lasted more than 10 years.

The Case of the Lifting Lingual Plate

The victim: A lower partial with lingual plate and free-end saddles.

The accusation: “The lingual plate lifts up from the lingual surfaces of teeth.”

The investigation: This crime is generally perpetrated on the lower arch. The upper framework has the advantage of palatal coverage, making lifting of the lingual plate more difficult while making ridge resorption easy to pick out of a lineup of suspects. Many witnesses claim the lingual plate is the culprit, and many have stopped requesting them and have relied on lingual bars to solve this “crime.”

The usual suspect: This is gang activity. Ridge Resorption, Free-End Saddles and Framework Rotation all gang up and Lingual Plate gets the blame. Lingual Plate is not a victim; he is an innocent bystander. The real victims of this situation are Clasps and Abutment Teeth, because they’re the ones who will suffer the stresses of this gang activity.

The guilty party: The Physics Gang. It begins with the ringleader, Ridge Resorption. As the tissue resorbs, Free-End Saddle drops, and Rotational Axis comes into play, causing Lingual Plate to lift. Lingual Plate isn’t a part of the gang! He’s your silent alarm notifying you that your partial needs a reline. Lingual Plate isn’t alone in his fight against this gang. He can be helped greatly by the vigilante Retromolar Pad. Retromolar Pad isn’t called “the hidden abutment” for nothing. He can help keep Free-End Saddle from dropping, possibly reduce Ridge Resorption and make the need for a reline more apparent.

Forensic File #4154: This partial impression, taken in place, shows the separation between plate and teeth (Figs. 1 and 2). A little relieving of the stone, where the impression material did not flow, allows Lingual Plate to seat flush against the teeth. I wouldn’t be surprised (as the saddle area does not appear to have ever been relined) if this torqueing isn’t the reason why #21 had to be added (by someone else) and why the clasp on #27 that I was tasked to “fix” broke. I, reluctantly, replaced it and advised a reline of the saddle areas.

Fig. 1

Fig. 2

The Case of the Impinging Lingual Bar

The victim: Lingual Bar.

The accusation: “The bottom of the lingual bar begins to impinge on the tissue and is rubbed out.”

The investigation: Copycat crime. The MO of the Physics Gang is all over this. The only difference is, as Lingual Plate and his silent alarm aren’t on the scene, Framework Rotation isn’t detected until Lingual Bar begins to “lay into” the tissue.

The usual suspect: The Physics Gang, Ridge Resorption and Framework Rotation are at it again and laughing as Lingual Bar takes the blame and the heat.

The guilty party: The dentist/tech who rubbed out Lingual Bar, an innocent bystander, to relieve the pressure.

Forensic File #31778: Received the remains of Lingual Bar battered and beaten almost to the point of breakage. Doc request that I bulk up Lingual Bar … but he was too far gone. He snapped. I sent him back for a decent burial.

The Case of the Broken Clasp

The victim: Clasp.

The accusation: “He just broke.”

The investigation: Clasp never wanted to be a tough guy. He was supposed to be that sleek and elegant man-about-town. But with that name, “Clasp,” too many see him in conjunctive cahoots with the Clamp and Grasp Brothers. They grab a tooth, and twist and pull, and pull and twist until they can run away with it. They are responsible for recruiting Partials into the Slow Extractors Gang.

The usual suspect: Clasp. But in his defense, his choices were: break or pull the tooth. In which case one might consider a broken clasp as a blessing in disguise.

The guilty party: Clasp is misunderstood. He was never meant to be a snatch-and-run guy. He was meant to be an elegant, almost passive locking device that engages an undercut and, when possible, disengages under masticating force. His job was to hold the partial down, not lock the tooth down. Unfortunately, Clasp can provide a false sense of security because his partials “snap” in. Poor Design and Excessive Movement are Clasp’s worst enemies. They need to be under constant surveillance—a doc and patient neighborhood watch with regular checkups to keep an eye out for Ridge Resorption.

Forensic File #92774: This case reminds me of an older case but one that, unlike this one, was painfully obvious: the Broken CEKA attachment. They had a superior “snap-in” feel to them. When CEKAs got to the point where they were metal to metal, it became a classic domestic dispute between male and female. Occasionally the female would triumph and push the male through the occlusal surface—an easy enough repair if done to also address the loss of tissue support. But too often, the female just snaps and is replaced with a new crown and a new female … or wire clasp. Many attachments aren’t designed to hold a partial up but to hold them down. Get to know your attachments!

I hope I’ve given you something to think about and maybe a new way to look at things. I know I’ll never see the Hoover Dam as anything but the Hoover Arch.

Tim Lane, CDT grew up in his father’s removable lab, becoming a full-time tech in 1973 and a certified dental technician in 1981. In 1983, Lane moved to Jackson, Tennessee, where he opened Cynosure Dental Laboratory and served 10 years as the president of the Tennessee Dental Laboratory Association. He moved his lab to Memphis in 1997.
Lane developed the all-soft hallowed bulb obturator technique (Journal of Dental Technology, October 1995) and the Omega (Nesbit) partial. He is an enthusiastic supporter and promoter of the Luckman postdam. He has published articles for LMT magazine and the JDT and is now enjoying his new hobby, screenwriting. He has completed two feature scripts and one TV pilot.