Leaving decay inside a baby tooth and covering it with a metal cap sounds like the opposite of what a dentist should do. Yet for many decayed baby molars that is exactly what the Hall technique does, and it does it well. The bacteria in the cavity need sugar from the mouth to keep making acid. Seal them off under a well-fitting crown and the decay generally stops progressing, without any drilling or local anaesthetic.
The method is named after Dr Norna Hall, a Scottish dentist who used it for years before it was formally tested in trials.
Why sealing works on baby molars
Decay is a slow process driven by plaque bacteria feeding on sugars. Cut off that food supply and the bacteria left inside the tooth become largely inactive. A preformed stainless steel crown covers the whole tooth and is cemented in place, so nothing from the mouth reaches the cavity. Research on sealed decay, including studies where lesions were later re-examined, has found that the soft decayed dentine tends to harden and the bacterial count drops once it is properly sealed.
Fissure sealants use a related idea to keep decay out of healthy grooves, as our article on dental sealants for children explains. The Hall technique applies it to a tooth where decay has already started. For more on how cavities form in the first place, see our guide to cavities and tooth decay.
Which teeth are suitable
The technique is used on baby molars, not on front teeth or adult teeth. The decay must not have reached the pulp. Before choosing it, the dentist checks for signs that the nerve is involved, such as pain that wakes your child at night, swelling, a gum boil, or changes around the roots on an X-ray. Our article on dental X-rays covers why that image matters and how low the dose is.
It may not be the right choice when the nerve is affected or infected, when there is too little tooth left to hold a crown, or when the baby molar is due to fall out soon anyway. In those cases another treatment, or sometimes simply monitoring, may suit better.
What the visits involve
Many children need a little space between the decayed molar and its neighbours first. At a short visit, small rubber rings called orthodontic separators are slipped between the teeth. They can make the area feel tight or achy for a day or two, and they are usually removed at the next visit a few days later.
At that second visit the dentist chooses a crown of the right size, fills it with cement, and places it over the tooth. Your child then bites down firmly, sometimes on a cotton roll, to push it into place. Excess cement is cleaned off. There is no drilling and usually no injection, and the appointment itself is short.
The bite tends to feel high for a few days because the crown props the jaws slightly apart. This usually settles within a few weeks as the teeth adjust. The crown is designed to stay on until the baby tooth falls out naturally, and it comes out with the tooth.
How well it holds up
The best known trial, run in Scottish general practices by Innes and colleagues, compared Hall crowns with conventional fillings placed in the same children. After five years, around 3 percent of Hall crowns had a major failure, such as an inflamed or dying nerve, an abscess or a tooth that could no longer be restored, compared with around 17 percent of the conventional fillings. In the same trial, most children, parents and dentists who stated a preference chose the Hall technique. Later trials and reviews have generally supported these results for suitable baby molars, and the technique now appears in paediatric dental guidance and expert consensus statements.
Like any treatment, it is not guaranteed. Crowns can occasionally come loose, and a small number of teeth go on to develop nerve problems despite being sealed. Regular check-ups keep an eye on this.
The trade-offs parents ask about
Appearance
The crown is silver. On a back baby molar it is not usually very visible, and it is lost with the tooth, but some families are bothered by it. Tooth-coloured preformed crowns exist, though they generally need more tooth preparation and are not used with the Hall approach.
Cost
As a rough guide, typical Australian market fees for a preformed metal crown on a baby tooth are often in the range of $200 to $400 per tooth. These are general market figures only, not Lumi fees. Some children are eligible for the Child Dental Benefits Schedule, and our team can confirm which items apply to your child.
Does the decay need removing later?
Usually not. The crown is designed to stay until the tooth is shed, and the sealed decay is lost along with the baby tooth.
If you are weighing up whether a cavity in a baby tooth needs treating at all, our article on whether cavities in baby teeth need treating sets out the options.
Asking about the Hall technique
If your child has a cavity in a baby molar, our dentists can examine it, take an X-ray and talk through whether a Hall crown, a filling or another approach makes sense. Read about our general dental care or see current deals to book an assessment at our Melrose Park practice.
