What's That Filling In My Tooth Cavity Made Of?

When it comes to dental caries, commonly known as cavities, the usual treatment involves a direct restoration, aka a filling. For those unfamiliar, dental caries is treated by accessing the decayed portion of the tooth and excavating all the decay out with hand and rotary instruments. Once the tooth is "prepared", the filling material is ready to be placed.

This post will describe the different materials used for direct restorations and the pros and cons of each. The indications of each will also be evaluated.

Indirect restorations, such as crowns and bridges, generally use different materials as they are fabricated in a dental laboratory. These will be discussed in a later blog post.

1) Amalgam

Dental amalgam, also known as silver fillings, have been used very successfully since the early 1900's.

The composition of amalgam includes silver, tin, copper, mercury, and small amounts of other metals such as zinc.

Many people are concerned with the toxicity of mercury present in dental amalgam, but after many decades of successful usage and even more research, the science says they are extremely safe for dental use.

Advantages of amalgam include

i) Faster placement.

This saves the patient time as amalgams can be placed in bulk much quicker than composite resins.

ii) High compressive strength.

They do not break easily when chewing on them.

iii) Moisture tolerance.

Amalgam restorations do not require the working area to be completely dry, so amalgams can successfully be placed even in difficult to isolate areas such as the teeth in the very back of the mouth or patients who gag if attempting to install a rubber dam

Disadvantages include -

i) Poor esthetics.

Amalgam is a metal alloy and is silver coloured, so in areas of esthetic concern it should not be used. It can also stain the tooth with a dark-grey shade over time.

Well-done amalgams with many years of service, but esthetically poor

ii) Minimal thickness required of 1.5mm.

This is because of its poor tensile and shear strength. For very small cavities, the dentist will have to drill deeper than required to provide necessary bulk for the amalgam.

iii) Galvanic shock.

When people with amalgam restorations eat with metal utensils, there is sometimes an electric jolt like a static electricity shock that occurs because of two different types of metals contacting each other.

iv) Environmental concerns.

Countries in Europe have started banning and phasing out dental amalgam entirely, not because of human safety, but because of environmental concerns. Amalgam scraps require special disposal methods, and when not properly treated, some of the heavy metals ends up back in the environment that harms our planet.

We use Solmetex's HG5© amalgam separator to ensure that we are playing our part in keeping our planet clean and sustainable.

2) Composite Resin

Composite resins are what are commonly known as white or tooth-coloured fillings. These are made of a resin matrix with filler particles dispersed throughout for strength.

When dental composites were first introduced in the 1960's, they were worse than amalgam in almost all aspects. They were weak, they would not adhere to teeth properly, and they were not colour stable either.

However, since the late 1990's, the technology has drastically improved.

A current-gen composite resin with all the advantages listed below

Below are some of the advantages of composite resins

i) High strength.

Composites are now close to matching amalgam in terms of strength. They also do not require a minimum thickness, so for very small cavities there is no need to remove more tooth structure than necessary.

ii) Bonded to teeth.

With current generations of bonding agents, the bond to tooth structure is now very good to excellent. Bonding to a tooth allows a better seal between restorative material and tooth.

iii) Excellent esthetics.

Composites now match the colours of most teeth extremely well. They also no longer suffer from discolouration over time.

Disadvantages of composites include -

i) Needing a dry working field.

Proper isolation, either with a rubber dam, a mouth prop such as Isolite©, or various types of cotton rolls, is crucial to ensure success with composites. For cavities that extend into the gum which may result in uncontrollable bleeding or fluids, composite is also not the best choice, as we cannot get a proper bond.

ii) More time-consuming.

Composites also take longer to place compared to amalgams, as they require a separate bonding step and many composites cannot be placed in bulk. This results in patients with multiple cavities requiring more visits.

iii) Higher cost.

Composite resins also cost more to the patient than dental amalgam because of more steps needed and more supplies needed for the dentist.

Please visit our Gallery on our website for some sample cases of composite resin restorations.

3) Glass Ionomer

Another category of materials are glass ionomers (GIs). These restorative materials are also tooth coloured, but they are not as esthetic as composite resins because of compositional differences. Few dentists would use this as the material of choice for most patients, but there are some strong indications for using GIs in specific cases.

The greatest advantages of GIs is that they are

i) Fluoride-releasing.

This enables them to reduce the risk of recurrent decay around the restoration. For patients that are at high risk of decay, this fluoride release is extremely beneficial.

ii) Moisture tolerant.

In cases where tooth isolation cannot be achieved in an ideal manner, glass ionomer is a fantastic alternative to composite resins.

Disadvantages of GIs:

i) Imperfect esthetics.

Glass ionomers tend to have one flat colour, so it is hard for them to look invisible compared to the surrounding tooth.

ii) Strength not as high.

Historically, GIs are not as strong as composite resins, so until recently, they have not been used to restore the biting surfaces of posterior teeth.

With recent advances, there are now hybrid GIs that combine the strength and esthetics of composite resins with the advantages of GIs called resin-modified glass ionomers (RMGIs) which allows a wider variety of applications.

Equia Forte is a current-gen RMGI with high strength

4) Pulpal Protector or Liner

For deep caries that is encroaching the pulp, otherwise known as the nerve of the tooth, irritants such as mechanical and thermal trauma can cause inflammation in the pulp. This can result in sensitivity after a filling was placed, or in the worst case scenario, for the tooth to need a root canal.

To minimize the chances of this happening, a pulpal protector or liner is placed in areas of close proximity to the nerve. This is usually a calcium hydroxide-based material or a resin-modified glass ionomer. These materials are soothing to the pulp, and help prevent it from inflammation. Then, the restorative material of choice is placed over the liner.

TheraCal liner is highly effective at protecting the pulp, and we have had great success with it

For most cases, the tooth will feel as good as new. In some teeth, there may be sensitivity over the next few days, then subsequently subside. In cases where the sensitivity worsens into pain, the tooth may need a root canal despite our best efforts.

Here at MC2 Dental, we only restore teeth with composite resin and resin-modified glass ionomers. Although amalgam is a fantastic material with many applications, I believe that its detrimental effect on the environment is something that shys me away from it. Most patients, including myself, also prefer tooth coloured restorations, and that is another reason why we do not use amalgam in our practice anymore.

Please contact me if there are any questions or comments, and look forward to my next blog post regarding indirect restorative materials.