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A filling is the repair most people picture when they think of going to the dentist for a cavity. This page explains what a filling is, what it is for, what they are made of, and how long they last. It does not describe what happens during an appointment, and it does not say whether your child needs one — that is your dentist’s call.
When decay has damaged part of a tooth, that damaged tissue is removed and the space it leaves is filled with a material that restores the tooth’s shape. That material is the filling. The tooth keeps its own structure; the filling replaces only the part that was lost.
The AAPD groups fillings under restorative treatment, alongside crowns and the other approaches described on How dentists treat cavities. A filling is the most common of them, not the only one, and not automatically the right one for a given tooth.
A filling is like a patch for a tooth. The dentist takes away the poorly part and puts something strong in its place, so the tooth is the right shape again and you can chew on it like normal. Some patches are white and some are silver-coloured.
A filling repairs damage; it does not treat the reason the damage happened. The AAPD states that restorative treatment of dental caries alone does not stop the disease process, and that the restorative plan must be prepared in conjunction with an individually tailored preventive programme. A filled tooth still needs brushing, fluoride and the same attention to snacking as every other tooth.
The AAPD sets out the objectives that any restorative treatment, a filling included, is meant to achieve:
Worth knowing before the conversation starts: the AAPD is explicit that not every caries lesion requires restoration, and that some lesions may not progress and therefore may not need restoring. A cavity being found does not automatically mean a filling follows.
There is more than one filling material, and the AAPD reviews the evidence for and against each rather than naming a single best one. Which material suits a particular tooth depends on where it is, how big the repair is and how much moisture can be kept off it while it is placed. That is your dentist’s judgement.
A resin-based material matched to the colour of the tooth. The AAPD notes it is technique sensitive and takes longer to place than amalgam, and that where isolation or a child’s cooperation is in question it may not be the material of choice.
A cement that releases fluoride, which the AAPD notes is taken up by the surrounding enamel and dentin. A resin-modified version exists and, per a meta-analysis the AAPD cites, is more successful than conventional glass ionomer as a restorative material.
The silver-coloured material. The AAPD describes it as a mixture of metals including silver, copper and tin, plus approximately 50 per cent mercury, and notes its use has declined. The questions families ask about it are addressed below.
Mercury in amalgam, and BPA in white fillings. Both are reasonable things to ask about and both have a documented answer. What follows is what the AAPD’s restorative dentistry document says, including the positions it reports from the US Food and Drug Administration and the American Dental Association. It is set out here so you can take the question to your dentist already knowing what the guidance says.
Not forever, and that is expected rather than a sign something went wrong. The AAPD states plainly that restorations have finite lifespans. A filling is checked at future visits like any other part of the mouth, and may eventually need repairing or replacing.
On how the two most-discussed materials compare, the AAPD cites a meta-analysis of 59 randomised controlled trials of Class I and Class II composite and amalgam restorations showing an overall success rate of about 90 per cent after ten years for both materials, with rubber dam use significantly increasing longevity. It also reports that the main reason for failure in both materials was recurrent caries — new decay around the existing repair — which brings the conversation back to prevention.
My child has been booked in for a filling. Ask your dentist which material they plan to use and why, what the alternatives are for that particular tooth, and what happens if you wait. If a material worries you, say so before the appointment rather than on the day. There is a list of questions to ask a dentist in the For Parents section. Nothing on this page is a second opinion, and none of it is based on your child’s teeth.
That is your dentist’s decision, made for the individual tooth. The AAPD reviews evidence for several materials rather than recommending one, and notes that factors such as the size of the repair, its position, and whether the tooth can be kept dry while the material is placed all bear on the choice. If you have a preference, raise it before the appointment.
On the evidence the AAPD cites, they are closely comparable. A meta-analysis of 59 randomised controlled trials of Class I and Class II restorations found an overall success rate of about 90 per cent after ten years for both composite and amalgam. The AAPD also notes that results comparing the longevity of amalgam to other materials are inconsistent across studies, and that many trials run only two to three years, at which point all materials reportedly perform similarly.
The guidance is unusually clear on this one. The AAPD reports that both the FDA and the ADA recommend existing amalgam fillings in good condition should not be removed or replaced unless medically necessary. If you are worried about a specific filling, that is a conversation to have with your dentist, who can look at it.
The AAPD’s restorative guidance covers primary teeth throughout rather than treating them as a lesser case, and it cites evidence on how particular materials perform in baby teeth specifically — including teeth expected to be lost within two years. Whether a particular tooth is filled is still a decision for your dentist. There is more on why decay in baby teeth is taken seriously on What is a cavity?
Possibly, in time. The AAPD states that restorations have finite lifespans, and reports that the main reason for failure in both composite and amalgam restorations was recurrent caries. A filling that needs redoing is usually a sign that decay has started again nearby, which is why the prevention conversation continues after the tooth is repaired.
Every clinical statement on this page comes from the American Academy of Pediatric Dentistry document below. Where the page describes what the FDA or the ADA recommends, it is reporting what that AAPD document says about them rather than citing those organisations directly.
This website is for education only and does not replace care from your dentist, physician, or emergency services.