Amalgam and composite fillings are the most widely used direct filling materials by dentists to restore teeth. Direct fillings are the fillings where the material is mixed at the chair side, followed by its placement, carving and polishing into the prepared cavity.
Composition of dental amalgam
Dental amalgam is a mixture of metals, consisting of liquid (elemental) mercury and a powdered alloy composed of silver, tin, and copper.
Currently, the alloys used in amalgam contain silver (40–70%), tin (12–30%) and copper (12–24%), indium 0–4%, palladium 0.5% and zinc (1%).
This alloy powder is mixed with liquid mercury in a high-speed amalgamator to produce amalgam. Amalgam is available in capsules separated by a membrane that is broken in the amalgamator to allow the mix to occur.
The mixed amalgam is then placed in the prepared cavity and carved with the instruments. The material takes 24 hours to gain its full strength and patients are instructed not to eat from the treated side for the next 24 hours.
Composition of composite
Fillers in the composite fillings are obtained from glass, quartz or silica and are processed into a microscopically fine powder. There are different varieties of dental composites available based on the filler content, shape (spherical, fibres or flakes) and size of filler particles.
The matrix of composite fillings is generally composed of monomers of resin that lack strength and are therefore mixed with filler to provide strength to the material. These monomers polymerise into long chains of polymers on exposure to UV radiation.
Composite is available in syringes that contain a thick paste of resin monomers, fillers, catalysts and initiators. Most composites used in dental practice are light activated. On exposure to the UV light, the material sets into a hard solid. Before turning the light on, the matrix is pressed into the cavity and carved to the desired shape.
Pros and cons of amalgam and composite fillings
Amalgam and composite fillings has their own pros and cons. We shall now see how one is better than the other:
Amalgam or silver fillings are not approved by most patients because of their silver appearance but due to their high strength, they are still used in the back teeth, especially the molars that are massively destroyed by tooth decay. The back teeth or molars are subjected to enormous forces of chewing and require filling that can bear these heavy forces.
Amalgam has high wear and compression resistance because of its high value of hardness.
The recent varieties/brands of composite now contain more filler and different filler size particles that impart enough strength to the filling to be used in high-stress bearing areas.
Composite fillings are available in different shades to match exactly your tooth colour and are hence more preferred by patients. On the contrary, amalgam or silver fillings are often a concern for patients because of their silver appearance. Moreover, over the years metals in the fillings corrodes can cause tooth staining.
Bonding to the tooth
Another advantage of the composite over amalgam is its property to bond to the teeth and thus requires less removal of healthy tooth substance. However, amalgam doesn’t bond to the teeth and is mechanically retained in the tooth i.e, the amalgam cavity is prepared in a box shape with its walls converging towards the biting surface. Amalgam placement, therefore, requires more removal of tooth structure to retain it in the tooth.
The composite completely sets after the exposure to UV light and patients can start eating from the treated side the same day, however, amalgam is weak when the patient leaves the clinic and takes 24 hours to completely set.
Dimensional change in material on setting
Composite tends to shrink while setting. Shrinkage of material on setting leaves a tiny space between material and tooth. Composite shrinkage can be dealt by placing and curing the material in thin layers or sections.
On setting, initially amalgam contracts slightly due to diffusion of mercury into the alloy particles. The material then expands as amalgam is setting and new compounds of metal crystals grows. Overall, The expansion takes precedence over the contraction.
From a clinical viewpoint, the combination of these two phenomena does not lead to any significant expansion or contraction.
Because of presence metals in the amalgam, it has a high value of thermal diffusivity. It transmits sensitivity or pain to the inner pulp when a hot or a cold drink or food is taken. The filling also expands and contracts on hot and cold food, respectively. It has three times the ability to expand than the dentin (second layer of teeth).
On contraction, a micro-gap between the cavity wall and the filling is formed that allow fluids to leak into the space and can lead to secondary tooth decay. Deep cavities are therefore lined with a layer of insulating material that acts as a barrier between the filling and tooth and to prevent any pain or sensitivity.
Dental composite is a thermal insulator and doesn’t transmit sensitivity or pain to the dental pulp. However, it contains monomers that can irritate the pulp and require a lining of a soothing material on the cavity floor in deep cavities.
Composite filling cost more than the amalgam filling. Amalgam fillings are still used extensively to restore molars in developing countries due its low cost.
A single amalgam filling costs $50 to $150 whilst a composite filling is at $300 to $400. The tooth inlays and onlays (cast-gold or porcelain) are even more costly (cast-gold or porcelain) with a range of $900 to $4,500.
An amalgam filling can last up to 12-15 years due to their increase strength.
A composite is technique sensitive and requires good moisture control for the longevity of the restoration. On average it lasts for at least 10 years.
Which is better and what to choose between an amalgam and composite fillings?
Composite is the choice of material for the front teeth because if its colour matching property. For back teeth that are mild to moderately destroyed (one or two walls of tooth are destroyed), a composite filling is better choice.
For teeth that are largely destroyed with 3 or more walls lost due to decay, its better to go for inlays or onlays. The inlays and onlays can be expensive but if you are looking a more affordable alternative, an amalgam filling is the option.
Amalgam and composite fillings are most widely used fillings for the restoration of a decayed or broken tooth. Both fillings have their own advantages and disadvantages.
Composite is better in-terms of its tooth colour-matching and bonding property, decrease need to remove healthy tooth structure in small cavities, complete setting on exposure to UV light etc.
Amalgam or silver fillings are popular due to their increase resistance to wear, hardness, increase compressive strength and affordability. For this reason, they are still extensively used for molar restoration in developing countries.