Composite fillings, also known as composite resins or dental composites are tooth colored filling materials. These dental composites are made up of resins and glass fillers.
They are the filling materials of choice when restoring a mild to moderately sized tooth cavity, because of their ability to withstand moderate amounts of pressure (the bite pressure). Let’s get to know where these dental composites are commonly used.
Composite Filling Uses
- As the dental composite is a tooth-colored material, when there is tooth decay or cavities in the front teeth, the composite filling is given.
- Dental composites are also used as dental veneers.
- Composites are also used for a process called core build up. The core build-up is usually carried out to replace the part of missing tooth structure that may have been damaged due to a fracture or tooth decay.
- Due to the new advancements and inventions in the field of dental materials, nowadays composite filling materials are also used for posterior teeth (the back teeth), like premolars and molars.
- Dental composites are used for splinting in cases of mobile teeth. Dental splints are used for stabilizing the teeth that are mobile.
- Composite fillings are also used as sealants and preventive resin fillings.
- Are frequently used for inlays.
- If an individual is allergic to dental amalgam, dental composites are the materials of choice.
Pros and Cons of Composite Filling
Below are some pros and cons of using dental composite.
Pros of composite filling
- As this is a tooth-colored or white filling material, it’s aesthetically pleasing and isn’t easily visible.
- The dentist doesn’t need to prepare a big cavity when doing a composite filling, unlike dental amalgam. Composite demands only conservative tooth preparation.
- If a composite filling in your mouth fractures it is easily repairable or redoable.
Cons of Dental Composites
- Shrinkage and secondary caries
- Plaque and calculus formation around the filling margins with poor oral hygiene
- The chances of staining and discoloration are higher.
- There may be mild to moderate level of tooth sensitivity after the composite filling is done.
- These fillings tend to fracture on the margins.
- Composites have a comparatively shorter life span than dental amalgam
- Even a slight amount of moisture in the mouth can hinder the process fabrication of composites.
- The procedure involved is time-consuming and is expensive when compared to amalgam.
Unique Properties of Composite Resins
- No direct bonding: When giving a composite filling it can’t be directly applied inside the tooth cavity. There is no direct bonding of the resin to the tooth but via the micromechanical method. So a process called etching is required prior to the insertion of the composite filling material.
- Dental composites have higher thermal expansion and contraction than the tooth.
- They have better compressive and tensile strength than tooth.
- Elastic modulus is less than tooth and the composite resin is brittle if used in thin sections.
- There is a process called polymerization shrinkage(shrinkage of the resin creating a gap in between the filling and the tooth) over time.
Components of Composite Resin
Composite is a mixture of resin and fillers.
Resins are BIS-GMA (Bis-phenol A and glycidyl methacrylate), also called Bowen resin or urethane di-methacrylate. Acrylate diluents such as TEGDMA(tri-ethylene glycol di-methacrylate) are also present.
Fillers such as quartz,silica,glasses like borosilicate and aluminosilicate are commonly present in dental composites.
The fillers added to the resin help the resin matrix by increasing the aesthetic property and the strength and toughness of the final composite filling. These fillers also decrease the thermal expansion and curing shrinkage of dental composites.
These agents help the process of binding of resin to fillers. Eg: organosilanes, titanates, zirconates.
These are added in small amounts to increase the shelf life of the material and also to get sufficient working time.
Eg: Butylated hydroxytoluene
Opacifiers like titanium dioxide and aluminum oxide are added in small amounts. The ratio of resin: filler composition affects the refractive index of the material and hence the aesthetics.
Types of Composites Used in Dentistry
Based on the size of the filler particles, the composite resin is divided into the following types:
Macrofill or coarse
They are the conventional ones with larger filler particles. They have good wear resistance but poor aesthetics .they are also difficult to polish, so roughens soon. These composites are prone to plaque accumulation and staining.
They have smaller filler particles with good aesthetic property and easy to polish, so they are preferred for anterior teeth filling.
They have poor wear resistance, so not suitable for filling in the posterior tooth.
This is a mixture of macro and microfill particles to achieve better mechanical properties as well as aesthetics.
It is a mixture of nanometric particles and nanoclusters in the conventional resin. This is a newer composite which the manufacturers claim to be having better wear resistance and easy to polish with good luster.
There are newer composites with different properties like
Due to its flowing consistency, it is used for small fillings, repair of margins or as liners.
This is a type of resin which can be used for posterior teeth filling as it is stiffer and harder.
Composite with antibacterial property
Composite resins that have antibacterial elements.
Organically modified ceramic
Polyacid modified resin with fluoride release on reaction. It is used as pit and fissure sealant and filling of deciduous teeth.
Hybrid of resin and glass ionomer cement.
Ceramic optimized resin
Direct and Indirect Composites
Direct composites are the ones used directly inside the individual’s mouth. These are done in a single sitting. Whereas indirect composites are fabricated in the lab and then inserted in the individual’s mouth in the dental clinic. These require two visits to the clinic.
Composite Resin Setting Reaction
The setting of the resin is by the formation of polymerized chain reactions or polymerization.
The dispensing of the resin is done two ways
- Two-paste system
- Single paste system
In two paste system (chemically activated), there is an initiator and activator which when mixed undergoes polymerization.
Benzoyl peroxide is the initiator and tertiary amine is the activator.
In single paste system(light activated) there is a diketone( Camphorquinone), a photosensitizer in case of visible light and a tertiary amine initiator which is cured by the light source. The wavelength of light used is 460-470nm. This is most widely used.
In case of ultraviolet light cure, the initiator is Benzion alkyl ester.
The resin comes in syringes, small bottles, and compules. The curing light systems are visible light and ultraviolet light.
The different modes of polymerization
The reaction takes place when two components are mixed together. This is chemically activated. The working time with this resin is limited.
This requires a light source for activation of the resin. There are three types of light source: Quartz Tungsten Halogen(QTH),
Plasma arc light and Light-emitting diode(LED). This system gives more working time and color stability is better. The dentist and the patient need to take care of their eyes while using the light source. Eyewear or a safety shield has to be worn by the patient during this process and also it is better to close the eyes during this process. The dentist usually looks away from the light source during the curing process.
In this, there is a light source which initiates the curing process and then chemical curing continues throughout the entire restoration.
The patient is prepared for the procedure in the following way. Some individuals may require local anesthesia before tooth preparation. Scaling and polishing of the teeth may be recommended before receiving the composite resin filling.
The dentist will do the shade selection before the procedure using the shade guide provided by the manufacturer. The shade selection is better done under natural light. Tooth preparation is done accordingly.
This is a very important step in composite fillings. Composite needs a dry area to work. Use of proper isolation methods like rubber dam, cotton rolls, gingival retraction cords if needed, and the good suction system will be done.
The prepared tooth is then etched using acid(etchant), for the resin to bond to the tooth. The etchant comes in a solution or a gel form which is applied onto the tooth surface. It is kept for 15-30 seconds, rinsed with water and the surface is dried with air. There are different types of etchants like 37% phosphoric acid, polyacrylic acid, maleic acid, etc.
Now the etched enamel is porous and has high surface energy which helps the bonding of the resin to give micromechanical retention. When dentine is cut during tooth preparation, the debris forms a smear layer on the surface of the cut dentine. This smear layer will compromise with the bonding of the resin.
The smear layer may clog the dentinal tubules, but this may be beneficial for reducing tooth sensitivity. So Dentine bonding agents are used to aim at modifying or partially removing the smear layer.
This can be done by acid etching and then using a primer like EDTA or maleic acid, followed by a dentine adhesive.
The dentin bonding agent is applied on the etched tooth surface and cured using a light source.
There are different generations of dentine bonding agents available. Newer bonding agents have one bottle system with a single application which has etchant, primer and the bonding agent in one.
Composite resin is then placed in increments using hand instruments or a compule or syringe. Then the curing is done in stages.
Finishing is done using mylar strips to contour the margins, refining with tungsten carbide burs or microfine diamond burs under water spray. Polishing is done with polishing pastes and abrasive impregnated discs.