The confined conditions imposed on orcas in captivity are directly responsible for multiple health issues, including oral degradation. In captivity, it's common for separated orcas to bite down on the horizontal metal bars, or to "jaw-pop" through the gates. In addition, under-stimulated and bored animals also "chew" metal bars and mouth concrete pool corners, like the main stages and concrete slide outs. As a consequence, tooth fragments can sometimes be found on the bottom of the pools following these displays.

This breakage leaves the pulp of some teeth exposed which allows for decay, causing a cavity that then leads to food plugging, if left untreated the orcas own immune system will create inflammation and eventually a focus for systemic infection.

To try and avoid infection, captive orcas are subject to painful dental procedures were holes are drilled into their teeth (Pulpotomy) using a variable speed drill, the holes are then flushed 3 times a day. The whole procedure is performed without pain relief causing the orcas to suffer in great pain, during the procedures orcas often squeal, shudder and sink away from the person performing the procedure. And, as I said before, orcas are given a wide range of antibiotics to prevent tooth infections. 

A former SeaWorld trainer commented on the process, "The whales are conditioned to "accept" the noise, heat, vibration and obvious pain associated with drilling vertically through the tooth column and into the fleshy pulp below. Success is measured by blood spilling out of the hole, which apparently tells the bore is complete. Orcas only get one set of teeth to last a lifetime which are highly durable, yet in captivity almost all captive orcas, particularly in SeaWorld's collection, have broken, ground, drilled or missing teeth.

The chronic pain caused from poor dental health causes captive orcas to participate in the behaviour of grinding down the jaw itself leaving the orca with little, or no teeth.

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Part of the caption/provided information from @inherentwild (on IG)