How a composite filling works, and how it differs from amalgam
Amalgam doesn't adhere to teeth. It is packed into a cavity and held by the shape of that cavity, which means cutting undercuts so it can't come out. Some of the tooth removed for an amalgam was sound tooth, taken to give the filling something to hold.
Composite is held by adhesion. Enamel is etched so the surface becomes microscopically rough, bonding resin flows into it and is set hard with a light, and the composite joins chemically to that resin. Because the bond holds it in place, the cavity needs to be only as large as the decay plus enough access to reach it.
None of this makes amalgam a poor material. It tolerates a damp field better than composite does, and in very large restorations it retains an advantage in bulk strength.
Composite or amalgam
Each material suits different situations, and the question is which one suits the particular tooth being restored.
| Consideration | Composite | Amalgam |
|---|---|---|
| Appearance | Matched to your tooth shade | Clearly visible, and it can gray the tooth around it over time |
| How it is held | Bonded to enamel and dentine | Held by the shape of the cavity |
| Tooth removed | The decay, plus access to reach it | The decay, plus sound tooth cut away to retain it |
| Moisture | Bonding fails if the tooth stays wet | Much more tolerant of a damp field |
| Where it struggles | Large cavities, heavy grinding, deep margins | Anywhere appearance matters |
What happens at the appointment
The filling is made and finished in the tooth in a single visit, with no laboratory stage and no temporary.
-
Shade first, then numbing and isolation
We select the shade before anything else, because teeth dehydrate and lighten within minutes of being held open. Local anesthetic follows, and we isolate the tooth and keep it dry, because saliva reaching the prepared surface ruins the bond.
-
Removing the decay
We remove only the decayed tissue, plus enough sound tooth to reach its edges. Sometimes decay runs deeper than the x-ray suggested and the plan changes, and we'll let you know before treatment continues.
-
Etching, bonding and layering
Acid gel is applied and rinsed thoroughly, then bonding resin is cured with a light. Composite shrinks slightly as it sets, so we place it in increments, cured layer by layer, to limit stress on the bond.
-
Shaping, bite and polish
We contour the anatomy, check the contact with the neighboring tooth using floss, adjust the bite and polish the surface. A rough margin collects plaque, and a high bite causes sensitivity.
Where composite is not the right choice
- Very large restorations. Once most of the biting surface and a cusp are gone, composite is being asked to perform a structural role, and that tooth usually needs an onlay or a crown.
- Heavy grinding. Composite wears and chips under sustained load. It can still be appropriate for someone who grinds, alongside a night guard.
- Margins deep under the gum. Adhesion needs a dry field, and a margin where fluid seeps continuously makes reliable bonding difficult.
How long they last, and why margins stain
A small composite in a front tooth, or a modest one on the biting surface of a molar, often lasts many years. A large multi-surface composite in someone who grinds carries a heavier load and tends to need attention sooner. Size, position, the bite, diet and how dry the tooth was kept during bonding all influence the outcome.
Staining at the margin is what people notice first on a front tooth. The junction picks up color from coffee, tea and tobacco, and a thin brown line after several years is common. On its own, that is a cosmetic finding. It becomes significant when a gap lies behind it, and telling the two apart is what the x-ray is for.
Composite bonds to composite, so a chipped or stained restoration can often be repaired rather than remade. Every replacement cycle removes a little more tooth, so we repair what can be repaired. The same principle underlies preventive care.
Common questions about composite fillings
How much does a tooth-colored filling cost?
It depends on how many surfaces are involved and how large the cavity is. Plans often set the benefit for a back tooth at the amalgam equivalent and leave the difference to the patient, though every policy differs. Call (559) 683-4694 and ask, and see insurance.
Why is my tooth sensitive after a filling?
Some sensitivity for a few days to a couple of weeks is common, particularly with a deep filling. Pain on biting often means the bite is fractionally high, and that's a quick adjustment. Pain that lingers, or that wakes you at night, deserves a look, so please give us a call.
Are composite fillings as strong as silver ones?
For normal chewing in small and moderate cavities, modern composites handle the load well. In very large restorations amalgam retains an advantage in bulk strength, which is why the size of the cavity matters as much as the material.
Do white fillings whiten?
Composite keeps the shade it was made in, so it won't lighten. If you plan to brighten your teeth, complete the whitening first, let the shade settle, then have front fillings matched to it.