White zirconia crowns for damaged baby molar teeth are very popular in many parts of the world. At the American Academy of Pediatric Dentistry Conference’s trade exhibition, there were at least 4 or 5 companies e.g. Nusmile, Kinder Krowns, Cheng Crowns, Sprig EZ Crowns, promoting zirconia crowns as state of the arts treatment for damaged baby molar teeth. Currently in Australia, only 1 brand of prefabricated white zirconia crowns for baby teeth is available.
Crowns are recommended for severely damaged baby molar teeth where full coverage is necessary for function, protection and for restoring structural form (please refer to Tooth Bunny’s “Crowns for Baby Teeth” article)(1,2). Crowns offer optimal sealing of the entire damaged tooth, thereby protecting the tooth structures from risk factors e.g. acids and decay-causing bacteria in the oral environment.
They are prefabricated in pre-set sizes and contours suitable for primary teeth. Dental practitioners select the “correct” size to fit the dimensions of the damaged tooth, usually after some tooth reduction and removal of damaged /softened tooth structure. The most fitting crown is then attached to the tooth using dental cement. In most cases, cemented crowns stay in place until the crown-covered baby tooth becomes wiggly and falls out.
Commonly, parents / carers are given the option of either prefabricated white molar crowns vs. prefabricated silver molar crowns. So how do these crowns compare?
No doubt, white zirconia crowns are more appealing than silver stainless steel crowns, when it comes to aesthetics (3). However, if the crown fitting surface is affected by blood during the preparation or cementation procedures, the colour of the crown may be compromised.
It is worth noting that colour selection is not possible, but the colours of the crowns differ between companies. Most dental practitioners will have 1 brand of zirconia crowns and 1 brand of stainless steel crowns available in the surgery. So, parents are asked to select either white or silver only, as different shades of white or silver are not available.
The length of time needed to complete crown treatment varies from case to case and from practitioner to practitioner. In general, treatment using zirconia crowns take longer than treatment using stainless steel crowns.
Tooth Reduction / Preparation
Tooth reduction and preparation is usually performed on the damaged baby tooth, regardless of the choice of crowns.
There is one exception: using the “Hall Technique”, stainless steel crowns may be placed with no tooth reduction or preparation, no cleaning out of dental decay and no local anaesthetics.
When comparing the amount of tooth reduction required, white zirconia crowns require a lot more “cutting down” of the damaged tooth than stainless steel crowns (4). Typically, both stainless steel crowns and zirconia crowns require the height of the baby tooth to be reduced by 1-2mm. For stainless steel crowns, minimal selective tooth preparation, approximately <0.5mm, is carried out in order to fit a stainless steel crown; whereas all crown surfaces must be reduced by 1-2mm to fit a zirconia crown in addition to 0.2mm thickness reduction circumferentially under the gum line, extending 1-2mm below the gingival margin.
Crown Fit and Adaptation
Stainless steel crowns can be adjusted by trimming or crimping at the margin to improve the fit and is flexible enough to engage minor undercuts to provide a tight fit and close adaptation. Stainless steel crown margins are usually at or just under the gum line. In contrast, zirconia crowns cannot be adjusted to improve fit and adaptation. Passive fit is required as zirconia crowns are more rigid and not able engage undercuts. Zirconia crown margins must be placed well below the gum line. Tooth reduction and preparation must be carried out precisely in order to provide excellent fit of a zirconia crown.
Wear and Fracture Risks
Stainless steel crowns can wear over time under excessive forces. Sometimes the wear is so significant that the stainless steel crown becomes perforated through the cement layer, exposing the damaged tooth. When this happens, the crown will need to be repaired e.g. using adhesive filling materials or replaced with a new stainless steel crown.
Zirconia crowns are more susceptible to fracture than wear when under excessive eating, chewing, grinding or clenching pressures (5). A fractured zirconia crown cannot be repaired but must be replaced.
Performance and Durability
Stainless steel crowns are generally stronger and more durable than zirconia crowns. Stainless steel crowns on baby teeth have a recognized survival rate of 95% (6-9), whereas the long term survival rate of zirconia crowns on baby teeth is not yet known as only limited research is available (10-11).
Anecdotally, zirconia crowns are at greater risk of failure because it relies solely on dental cement to hold it onto the tooth, and blood and saliva can both negatively interfere with the strength of the cement. The risk of pulp damage leading to failure or the need for pulp therapy prior to crown placement is high when using zirconia crowns because of the need for extensive tooth reduction and preparation, exposing the pulp of the tooth to heat and physical trauma.
Zirconia crowns cost more than stainless steel crowns by roughly 40-60%.
The decision whether to choose white zirconia crowns or silver stainless steel crowns for our children’s baby teeth is not a simple one. Many factors contribute to the decision-making process. Ultimately, the decision depends on the primary aim of treatment and our priorities.
Three questions to ask ourselves before making the final decision:
- Is strength and durability more important than aesthetics?
- If in order to fit a white crown, pulp therapy needs to be completed first but a stainless steel crown on the same tooth can be done without pulp therapy, what would be my choice?
- Is the colour silver acceptable to my child?
Something New on the Horizon?
At the AAPD Conference, I came across another type of prefabricated crowns for baby teeth, made of fibreglass and resin. They are white and claims to be easier to work with than zirconia crowns but looks just as nice. It’s currently only available in America and Canada. I’ll write about them soon.
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