Real, Rare, and Usually Something Else

Allergy to a dental material is real, documented, and uncommon. It also gets blamed for a great many things it is not causing, and separating the two is worth doing carefully because both errors are expensive.

What a genuine reaction looks like

The distinguishing feature is location.

A contact allergy produces a reaction in the tissue physically touching the material — a red or white patch on the inside of the cheek or the side of the tongue, exactly where it rests against a specific restoration.

The classic form is a lichenoid lesion: a white, lacy or striated patch, sometimes with redness or ulceration, sitting precisely opposite an amalgam filling. Mirror the tooth onto the cheek and the patch is there and nowhere else.

That geometry is what makes the diagnosis. If the corresponding site on the other side of the mouth is normal, the material is a suspect. If the symptom is everywhere, or nowhere in particular, it is not a contact allergy.

The materials that do it:

Nickel, by a distance the commonest contact allergen in general and relevant to some orthodontic components and older crowns.

Mercury, in amalgam, in a small number of genuinely sensitized people.

Components of composite resin, particularly certain acrylates, which can also affect the dental staff handling them uncured.

Gold, occasionally, which surprises people.

Latex, from gloves or dam, which is a reaction to the appointment rather than to the filling.

And the test exists

Patch testing, by a dermatologist. A panel of dental materials applied to the skin and read at 48 and 96 hours.

Which is the right escalation for somebody with a localized lesion adjacent to a restoration — because it distinguishes an allergy from the two much commoner alternatives below, and because replacing restorations on suspicion is expensive and irreversible.

What it usually turns out to be instead

Three things account for most of what gets attributed to allergy.

Galvanic reaction. Two different metals in a wet, salty, conductive environment form a small electrical cell. A gold crown opposing an amalgam filling can generate a measurable current, and people describe it as a metallic taste, a tingle, or a jolt when the teeth touch.

That is physics rather than immunology. It is harmless, it often settles, and if it does not, changing one of the two materials resolves it.

Mechanical irritation. A rough margin, a slightly overhanging edge, or a sharp point rubbing the tongue or cheek. It produces a sore patch in the tissue touching a filling — which is exactly the pattern of a contact allergy, and it is fixed in five minutes with a polishing bur.

Worth ruling out first for that reason alone.

And a high filling. A restoration standing fractionally proud is hit first and hardest every time the jaw closes, which produces tenderness, sensitivity and sometimes a dull ache. People experience this as my body is rejecting it, and it is corrected with a strip of colored paper and a few seconds of adjustment.

The amalgam question, briefly and honestly

Amalgam contains mercury bound in an alloy. Regulators including the FDA regard it as safe for most people while advising caution for a small number of groups — pregnancy, young children, people with impaired kidney function, and people with a demonstrated sensitivity.

Two points worth being clear about.

Removing sound amalgam releases more mercury vapour than leaving it alone. Drilling generates heat and particulate. So routine replacement of intact fillings on health grounds is a net exposure increase, not a reduction, and it also removes more tooth structure — every replacement takes some.

And the practitioners who offer whole-mouth amalgam removal for general symptoms are selling something the evidence does not support. It is expensive, it damages teeth, and the symptom it is aimed at is usually still there afterwards.

Replacing a specific filling that has a documented lichenoid lesion against it is a completely different proposition, and reasonable.

If you feel unwell and suspect your fillings

This deserves a straight answer rather than a dismissal, because the people asking are usually genuinely unwell.

The symptoms are real. Fatigue, a metallic taste, a burning mouth, brain fog — none of that is imagined.

And the fillings are the least likely explanation on a long list. A metallic taste has many commoner causes: medication, reflux, sinus infection, zinc or B12 deficiency, and a galvanic couple. Burning mouth syndrome is its own condition with its own workup. Fatigue has a differential the length of a textbook.

Which suggests a sensible order. Rule out the common things first, get a patch test if there is a localized lesion adjacent to a restoration, and treat whole-mouth replacement as the last option rather than the first.

Because the fillings can always be removed later. The tooth structure taken with them cannot be put back.

The short version

Contact allergy to dental materials is real and rare, and it shows itself as a reaction in the tissue physically touching the restoration — usually a white lacy patch against an amalgam.

Galvanic current, a rough edge and a high filling explain far more of what gets blamed on it, and all three are cheap to fix.

Patch testing exists. Removing sound amalgam releases more mercury than leaving it, and each replacement costs tooth that does not come back.