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Technical Discussion: Mid-Line Fracture

Technical Discussion: Mid-Line Fracture

Problem: I have a patient with a chronic mid-line fracture problem. What can be done?

L.T. Armstrong, DMD: Look at the denture from the back as if you were standing in the patient’s throat. If the upper molars are buccal to the crest of the upper ridge (even slightly), you will have a mid-line fracture problem. Every time the patient chews, swallows, or bites down, they touch their upper and lower posterior teeth together. This produces a flex in the upper denture across the mid-line. Over time, as it flexes back and fourth, the plastic work-hardens and breaks. I call this the “Coat-Hanger Effect.” This problem is made worse if the patient has natural posterior teeth opposing the denture because they can bite harder.

Why didn’t the patient have this problem with his/her old denture?

Probobly because the old denture was made when the patient had a less-resorbed ridge. As the ridges resorb, the posterior support diminishes. The upper ridge resorbs superiorly and inward toward the midline, making the ridge smaller.

What can be done?

The traditional approach by labs is to place a mesh, strengthening bars, or more acrylic along the fracture. This will NOT work because the problem has nothing to do with the strength of the appliance.

The real solution is to set the teeth according to the current position of their ridges. This often means setting the teeth in cross-bite. This may feel unnatural to the patient. You will need to explain that this change is necessary to avoid the headache of repairing the appliance every six months.

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