Dental caries, (decay), is often described as one of the most common diseases to affect adults and children.
Our mouths harbour bacteria and the food and drink that we consume contains sugar, which mouth bacteria feeds from and then go on to produce a substance called lactic acid. The acid is then free to break down some of the calcium which is one of the many minerals found in tooth enamel, the outer surface of our teeth. This is known as demineralisation. The damage caused by demineralisation can be repaired however by our saliva, which is one of our mouths natural defences. Saliva contains bicarbonate, which counteracts the acid produced by bacteria by helping to neutralise it. Saliva also delivers essential minerals such as calcium and phosphate to the tooth. By putting these minerals back into the enamel, the risk of caries forming is greatly reduced as the tooth has now been re-mineralised. So, demineralisation occurs when acid attacks the tooth, removing minerals from the enamel and remineralisation occurs when the same minerals found in our saliva are put back into the enamel. Dental caries occurs when there is more demineralisation than remineralisation, as the tooth surface becomes vulnerable due to the lack of essential minerals.
Dental caries in permanent teeth is divided into two categories: location and classification. There are two types of caries depending on the locations that they form: pit and fissure caries and smooth surface caries. Caries is divided into two locations as the factors involved in the development of caries in each location are different. Caries is also divided into classification depending on the location. G.V Black who died in 1915, created the “Black’s classification of caries lesions” which is still in wide use today.
Pit and Fissure caries: Class I.
This is the most common type of caries. Pits are like small dimples which are often found where there is a groove in a tooth. A common example is a buccal pit in a molar tooth. Fissures occur in premolar and molar teeth in the occlusal (biting) surface. Because pits and fissures are difficult to clean due to all the nooks and crannies, especially in fissures, they are a perfect breeding ground for bacteria. If these surfaces are not cleaned properly, then caries can form quickly and easily and once it has penetrated the enamel and reached the dentin underneath, it can spread rapidly.
Smooth surface caries: Class II caries.
Three types of caries fall under this category. Proximal caries/inter-proximal caries, root caries and the last type is caries that forms on any other of the smooth surfaces.
Proximal/Inter-proximal caries:
This type of caries often affects premolar and molar teeth and is described as the hardest to detect as it can only be detected through an x-ray. This is because the caries forms in between two teeth, usually in the mesial surface of one tooth and the distal of another. For example, the distal surface of LR6 and mesial surface of LR7.
Root caries:
This type of caries occurs when the root of a tooth becomes exposed due to gum recession. The root of a tooth is a lot more vulnerable as demineralisation occurs quicker due to the absence of enamel, however with fluoride application, it can be re-mineralised if detected early.
Caries that forms on any other smooth surface: For example: the lingual surface.
There are further classifications;
Class III: This is proximal caries which forms on anterior teeth, (incisors, lateral incisors and canines) and does not include the incisal edge, (biting surface).
Class IV: The same as above but does include the incisal edge.
Class V: This is caries that forms near the gum margin on the labial and lingual surfaces.
Class VI: This is caries that forms on the incisal edges of anterior teeth or the cusps of molar teeth.
Dental caries in children.
Dental caries in children is often described as “baby bottle caries.” Breast milk or formula, although very nourishing and healthy to a baby or toddler, can lead to caries formation. As with adults, children have naturally occurring bacteria in their mouths. If milk is regularly consumed from a bottle and the teeth are not cleaned afterwards, then this can cause problems with deciduous teeth. For example; if a baby or toddler falls asleep drinking a bottle at their afternoon nap and bedtime every day, then the milk is left coating the teeth, almost waiting for the acid produced from mouth bacteria to react with it and start destroying the enamel. It is difficult for new parents as babies and toddlers are instantly soothed with a nice bottle of warm milk before sleep but what we need to remember is that over a prolonged period of time this can cause devastating results, which frequently lead to deciduous extractions and fillings. Parents can help prevent caries by giving their children water before bedtime and also by helping their child brush their teeth using fluoride toothpaste.
Pathophysiology
Enamel is the hardest and most highly mineralized part of the tooth. It is made up of enamel rods which, depending on the surface of the tooth, follow a certain direction. Demineralisation follows the direction of the enamel rods, hence proximal caries will spread inwards and fissure caries will spread downwards. As caries progresses, the enamel develops different zones:
Translucent zone: The early sign of caries, often indicated by a chalky appearance.
Dark zone: Some remineralisation has occurred and one of two things will happen. The caries will halt and a cavity will not form or it will progress leading to a cavity.
Body of the lesion: The area of advanced demineralisation and destruction.
Surface zone: This area is fairly mineralised and stays this way unless demineralisation occurs, leading to a cavity.
Once caries has penetrated through the enamel and reaches the dentin, this is when caries becomes more obvious. Dentin, unlike enamel, reacts to caries because the dentin tubules have pathways to the nerve of the tooth, leading to pain sensation. Dentin also differs to enamel in the sense that it is always being produced by odontoblasts, (biological cells found where the dentin joins the pulp). Once enamel has been lost, it will never regenerate. As caries progresses, the dentin also develops different zones:
Translucent zone: Where the initial demineralisation begins. This zone also represents the advancement of caries.
Zone of bacterial penetration: Location of bacteria which have penetrated through the enamel to the dentin.
Zone of destruction: Ultimately, the area where dentin has been destroyed.
Dental caries can sometimes be given another name to describe how the caries developed and why. This is referred to as Etiology. For example; “baby bottle caries.” As suggested, the caries is linked to the consumption of milk before bedtime. Another example is, “rampant caries.” This indicates decay which has affected many teeth.
What are the signs and symptoms of dental caries?
The first sign of caries tends to be a chalky mark on the tooth where demineralisation of the enamel has taken place. At this point, the patient can be completely unaware of this and the process can be reversed by remineralisation. Teeth that have had early caries reversed can leave marks of discolouration but the area is caries-free. If remineralisation has not occurred, the area of demineralisation may then turn a darker colour and at this point, a cavity may occur. Once a cavity has appeared, there is no way the caries can be reversed. If the cavity is left, caries can spread to the dentin and start to expose the dentin tubules which will cause pain, as they have passages to the nerve of the tooth. An advanced cavity can make the tooth sensitive to cold, hot and sweet sensations. The cavity itself can also have a soft, leathery texture when probed, due to the presence of caries.
How can dental caries be diagnosed?
Caries can be diagnosed by a Dentist during an examination using a dental mirror and probe. Some Dentists may also use special microscopic glasses called “loupes” to inspect the tooth more closely. Caries can sometimes be difficult to detect, especially proximal caries and in this case, an x-ray is required as a diagnostic aid to determine diagnosis.
Treatment of dental caries
For early caries, fluoride therapy can help re-mineralise a tooth in order to halt the progression of caries. Once a cavity has been diagnosed however, treatment is needed. Usually under local anaesthetic, the Dentist cleans away all the caries in the tooth using a handpiece and bur and sometimes puts a lining in the cavity to calm down any inflammation caused by the caries. The Dentist can then restore the cavity with a silver or white filling, (amalgam or composite). If the cavity is too large and there is not enough tooth substance to support a filling, then the Dentist may restore the tooth with a porcelain, ceramic or gold inlay/onlay or a crown. The other option is to have the tooth removed.
How can dental caries be prevented?
Good oral hygiene is very important in the prevention of caries. Effective tooth-brushing twice a day combined with oral aids such as dental floss and inter-dental brushes minimize the build-up of plaque. Plaque is bursting with bacteria, all ready to feed off the sugars that we consume which leads to the bacteria producing lactic acid which attacks the teeth. Six monthly examinations with a Dentist and Hygienist will enable them to assess whether any further prevention is needed such as fluoride therapy, fissure sealants etc. It is also very important to limit the frequency of sugar that we consume. It is not the amount of sugar that determines the likeliness of caries but the frequency. Limiting sugar intake to 3 times a day will help massively with the prevention of caries and this can be achieved by limiting snacking and drinking water between meals.
Epidemiology
It has been estimated that approximately 90% of adults world-wide have suffered from dental caries with the disease most commonly affecting Asian and Latin American countries. African countries have had the least occurrences of dental caries. In the USA, dental caries is the most common chronic childhood disease, being at least five times more common that asthma. It is the primary pathological cause of tooth loss in children.*
