To stop further damage and restore function of primary molar teeth that are decayed or malformed, a dentist will usually use a filling (a soft material that is placed in the cavity and hardened) to restore the tooth to its original shape. Alternatively the dentist may place a crown over the tooth to cover it. This usually requires an injection in the gum to numb the tooth before trimming it down (conventional technique). These crowns are pre-made (i.e. preformed) in a variety of sizes and can be metal or white, with the correct size being chosen to fit the trimmed down tooth. The Hall Technique is an alternative method for fitting metal crowns, where there is no need for an injection or tooth trimming as the crown is simply pushed over the tooth. Preformed crowns are recommended by specialists in children’s dentistry for the management of baby back teeth (molars) when they are affected by moderate to advanced tooth decay, or where the enamel has malformed during development or the tooth has had to have root canal treatment.
What was the research?
A systematic review of the evidence to find out whether crowns are better than other ways of managing decay in children’s baby teeth for reducing ‘major failure’ (including toothache and dental abscess), pain during treatment and harm, and for improving satisfaction with treatment. It also asks whether metal or white crowns are better and whether a new fitting method called the Hall Technique is better than the conventional fitting technique. The review updates one originally published in 2007.
Who conducted the research?
The research was conducted by a team led by Nicola P.T. Innes of the University of Dundee on behalf of the Cochrane Oral Health Group. David Ricketts, Lee Yee Chong, Alexander J. Keightley, Thomas Lamont and Ruth M. Santamaria were also on the team.
What evidence was included in the review?
Data was extracted from 5 randomised controlled trials. Four studies compared crowns with fillings. Two of them compared metal crowns fitted using the conventional method with fillings and two compared metal crowns fitted using the Hall Technique with fillings. One of the studies also compared the Hall Technique with ‘non-restorative caries treatment’ (not using either a filling or crown but opening the cavity to make it possible to clean with a toothbrush, sealing with fluoride varnish and encouraging toothbrushing). The final study compared crowns made of two different materials (stainless steel versus stainless steel with a white covering). We looked at what happened for each treatment at the time of the dental appointment or within 24 hours of treatment, in the short term (less than 12 months) and long term (12 months to 48 months).
What did the evidence say?
Teeth restored with preformed crowns are less likely to develop problems (e.g. abscess) or cause pain in the long term, compared to fillings. Crowns fitted using the Hall Technique (no injections or tooth trimming) gave less discomfort at the time of the appointment, when compared with fillings. Crowns may increase the risk of gingival bleeding but this result was unclear. Only one small study compared crowns with non-restorative caries treatment and one small study compared metal and white crowns, and we could draw no reliable conclusions from these. Some of our outcomes of interest were not measured in any of the studies: these included time to restoration failure or retreatment, patient satisfaction and costs.
How good was the evidence?
The studies in this review were at high risk of bias because the participants knew which treatment they received and so did the people who treated them. There is moderate quality evidence that crowns are more effective than fillings for managing decay in primary molar teeth. There is moderate quality evidence that crowns fitted using the Hall Technique are less likely to cause abscesses and pain than fillings. The evidence comparing preformed crowns with non-restorative caries management, and comparing preformed metal crowns with preformed white crowns, is very low quality so we do not know which is better.
What are the implications for dentists and the general public?
Crowns placed on primary molar teeth with carious lesions, or where pulp treatment has been carried out, are likely to reduce the risk of major failure or pain in the long term compared to fillings. Crowns fitted using the Hall Technique may reduce discomfort at the time of treatment compared to fillings.
What should researchers look at in the future?
The population investigated included only fit and healthy children. The performance of restorative interventions is important for children with special needs and may be different in those children with limited ability to tolerate invasive dental procedures. This should be considered when designing future trials and considering generalisability of findings. As most restorative procedures in children are undertaken by non-specialists, these clinicians should be included in future research to improve generalisability of the results.
Future research should include discomfort at the time of treatment and pain following treatment. Reporting should include adequate detail about how these were assessed and who reported them, as well as consideration of the multi-dimensionality of pain and its expression, especially with children.
There were no studies that compared the Hall Technique to conventional crowns. So, although crowns outperformed fillings, it is not possible to say whether crowns should be fitted conventionally (involving local anaesthesia and removal of tooth substance), or fitted less invasively. This is an important question in terms of best clinical outcome (fewer major failures and less gingival bleeding), as well as from children’s and parents’ perspectives, and that of cost. There was very little measurement and reporting of patient-reported outcomes. Only the two trials that involved the Hall Technique investigated pain or discomfort at time of treatment. The studies investigated adverse events in a limited way, with gingival bleeding measured in three studies and bone resorption in one, but other adverse events, as well as cost and satisfaction with treatment, were not investigated. A core outcome set is not available yet for trials investigating restorative interventions, but would be helpful to guide researchers in the design of trials and would improve the ease of comparing and collating findings. Longer follow-up in studies should be considered. We found no studies that investigated the management of primary teeth with developmental defects. These should also be investigated in the future, as well as the implications of the depth of carious lesions.
Innes NPT, Ricketts D, Chong LY, Keightley AJ, Lamont T, Santamaria RM. Preformed crowns for decayed primary molar teeth. Cochrane Database of Systematic Reviews 2015, Issue 12. Art. No.: CD005512. DOI: 10.1002/14651858.CD005512.pub3.