What is a dental onlay?

Over the years there have been great advances in the science of dental materials and techniques that we use to restore teeth with.

First there were the old silver mercury amalgam fillings, then came the development of white tooth coloured composite fillings. Previously for teeth that were particularly badly broken down or weakened by very large cavities, placing a crown over the entire tooth was  often the favoured treatment. In recent years however, the use of tooth coloured porcelain onlays has superseded crowns as the preferred treatment of choice to restore and protect weak, cracked and badly damaged teeth. 

But why is this and what exactly is an onlay? Both onlays and crowns are precision laboratory made restorations where by an impression of the prepared tooth is sent to a dental technician, who then designs and constructs them to precisely fit the prepared tooth, as well as the adjacent teeth beside it  and the opposing teeth it bites against. The main disadvantage of crowns however is that they often require quite destructive preparation of the teeth. The recent introduction of stronger porcelains and more reliable bonding cements means that instead we can now place porcelain tooth coloured onlays which involve much less tooth preparation. An onlay fits  directly over the top biting surface of the tooth, but unlike a crown does not need to extend all the way down to the gum line,  so more natural tooth is retained. The design of onlays is such  that they simultaneously replace any existing fillings, filling in any cavities present, as well as stabilising the rest of the tooth, strengthening it, so any inherent cracks or potential weaknesses are prevented from worsening. This puts an end to the traditional need for fillings to be repeatedly replaced over time as so often happens.

As dentists we regularly see patients with large old fillings where either the filling has started to wear out, allowing further decay to develop, or part of the tooth  around the filling has cracked.  It is important to recognise that fillings do nothing to reinforce  a weak tooth. As a cavity becomes larger there is less tooth to hold the filling in place. If a filling is repeatedly replaced  with larger and larger fillings, the sides of the tooth eventually become very thin and prone to fracture.  To avoid these ongoing potential problems, cost and pain, a more long term preventative approach is to recognise when the tooth has reached this limit and restore the tooth properly with an onlay. The conservative yet protective nature of porcelain onlays means that they are an ideal solution to prevent this cycle of tooth break down and replace those unsightly silver fillings with a  strong and beautiful  tooth coloured restoration. The end result is a durable, longer lasting restoration that fits perfectly and looks and feels completely natural.

Preventative. Protective, Conservative. Aesthetic. Cost effective.  Onlays really have revolutionised the way we restore teeth! Keep in mind there are still instances where a crown may still be necessary. Your dentist will evaluate your teeth fully before deciding what is most appropriate for you and your teeth.


Brad Ngan BDS (Otago)