dentistry Dominic Thorncroft

Case Study – Defective Filling

Case Study

Consent is a complex subject and although there are universally agreed principles there are also certain “grey areas” when the dental team needs to make their own balanced judgements. For consent to be valid, the patient must have received enough information to make the decision.

This is what we mean by ‘informed consent’. Giving and getting consent is a process, not a one-off event. It should be part of an ongoing discussion between the dentist and the patient. The Montgomery ruling with regards to consent has replaced the previous ruling with Bollam. The dentist must therefore share all material risks as well as those that he thinks that the individual patient would want to know.

The guidance states that the dentist needs to find out what your patients want to know, as well as telling them what you think they need to know. So examples of information which patients may want to know include:

  • Why you think the proposed treatment is necessary.
  • The risks and benefits of the proposed treatment.
  • What might happen if the treatment is not carried out?
  • And other forms of treatment, their risks and benefits.
  • And whether or not you consider the treatment is appropriate.

This case was discussed whereby a patient came in and the examination revealed a defective filling in LL5. The notes revealed that this restoration had only been done in the last 6 months at another dentist.

Furthermore, the reason had been to remove a previous overhang. The patient was informed and it was proposed to correct the filling material and the options were given to the patient including demonstrating on the patient’s own radiographs. In the end, the patient decided not to have further treatment as this was now going to be the third lot of treatment for this tooth.

In addition, the patient made it clear that should she experience any symptoms, then she would have an extraction. It was therefore decided to keep the tooth under observation.

dentistry Dominic Thorncroft

Composite Filling Materials Disadvantages


Composites are extremely technique sensitive. The dentist’s technique must be 100% perfect otherwise the composite is likely to cause problems and fail. All dentists have seen posterior composite being placed and caries being evident sometime later. Composite is very technique sensitive and does not like any moisture at all.

This is extremely problematic for posterior teeth where there is moisture present and even from the patient’s own breath or the bleeding/crevicular fluids around the gingival margins.


Most composites now are light cured and therefore have to be placed in layers in order for the light to penetrate fully to cause polymerisation setting reactions. This means that composite takes longer to place and in addition if the light does not reach the full extent or deeper layer of the cavity, this will result in unset composite. Composite which is unset will cause the body of the filling to move resulting in micro leakage and secondary dental caries.


Polymerisation shrinkage is a major disadvantage of composite resin. This means that the unset material occupies a larger volume than the polymerised set material. This then results in a gap between the filling material and the cavity walls. This causes bacteria to get in there and cause secondary or recurrent caries.

In addition the gap picks up stains and every dentist has seen a brown line along the margins of a composite restoration. This is worse in avid smokers although also in people who have strong tea and coffee or red wine habits. Polymerisation shrinkage can also cause physical stress inside the cavity/restoration interface. 

One of the ways in which polymerisation shrinkage effects can be reduced is to place the composite in layers. It is important however to understand that the amount of polymerisation shrinkage is the same whether the composite is light cured or whether it is chemically cured.

The difference is the manner in which the polymerisation shrinkage occurs. When composite is light cured, the polymerisation shrinkage occurs very rapidly but in chemically cured composite, the polymerisation shrinkage occurs more gradually. This is relevant when considering how the composite is to be bonded onto the enamel and dentine.

As composite does not have the inherent ability to bond chemically onto enamel or dentine, it is necessary to use extra steps for bonding. However, if the polymerisation shrinkage is too rapid, this can cause breakage of the bond or it can cause the composite to pull on the walls of the cavity. If the bond breaks, this leads to micro leakage but if the bond does not break, the pulling effect can even cause cracks within the enamel.

Patients will often come back to the dentist after a composite filling material has been used complaining of pain. One way to reduce the polymerisation shrinkage is to have good enamel and dentine bonding but also to cure/set the composite in layers rather than in one go. Newer composites have been formulated to have a reduced polymerisation shrinkage change which helps reduce microleakage.


Composite is nowhere near in getting a good contact point as amalgam. This is extremely important in class II cavities where a good contact point is required. However, modern posterior composite filling materials have fairly good contact ability but even so, a wedge is needed in conjunction with a clear matrix band.

The earlier composites were too stiff but difficult to pack and manipulate in order to meet this demand or they were too soft making them easier to pack and manipulate but difficult to press hard against the matrix band.


Composite does not inherently bond onto enamel or dentine and therefore extra steps are required for this to occur. There are two separate phenomena occurring here. Firstly, enamel bonding occurs by etching the enamel with 37% phosphoric acid for 20 seconds.

This acts on the enamel prisms and causes differential dissolving resulting in a roughened surface which acts to give micro mechanical retention. Dentine bonding is slightly different in that the acid attacks the mineral component of the dentinal tubules. Dentine is 70% mineral and 30% organic. This then causes a collagen mesh to remain and resin will then flow into the collagen mesh.

This is a form of micro mechanical retention. However, drilling into a tooth causes crushed hydroxyapatite debris and this is known as the smear layer which must be removed prior to etching and bonding. Creation of the smear layer prevents the usage of resin-tags. 

Fortunately, bonding systems have dramatically transformed and now, one step bonding systems exist which etch both enamel and dentine, remove the smear layer and create micro mechanical retention simultaneously. Older dentists will remember the original systems which used 8 or 9 separate steps with lots of potential for errors at any point.


Composites according to the specific brand can sometimes can be difficult to discern on the radiographs due to their radiopacity similar to dentine and this can be a disadvantage when trying to assess for secondary or recurrent caries.