Overview

Between breakfast, lunch, dinner, and occasional snacking, the pH in our mouths is ever-changing.¹ Luckily, our oral cavity has a built-in buffer system to maintain a constant pH between 6.5-7, this is achieved by saliva.² A continuous disruption in this environment can lead to tooth decay, also known as caries.^2,3

In general, tooth decay is caused by acids because of bacterial metabolism of carbohydrates in particular. These acids dissolve tooth minerals and eventually cause a cavity if given enough time. It is important to note that the process of tooth decay takes time, it doesn’t just show up overnight, meaning that it is reversible in the early stages.²

The structure of the tooth

The tooth is composed of three prominent layers, enamel, dentin, and the pulp. The enamel is the outermost layer, covering the crown of the tooth. It is the hardest structure of the human body, able to withstand immense chewing forces and chemical and temperature changes.⁴ Phosphate and calcium ions play a crucial role in maintaining the integrity of the enamel.⁵

Underneath the enamel is the dentin, which is a softer material. Dentin is close to a rich blood supply and is innervated, this is made possible through the dental pulp, which is the innermost layer.⁴ 

A closer look into tooth decay and pH

Tooth decay is caused by demineralisation of the hard tissues of the teeth.⁶ Demineralisation refers to the release of important minerals such as calcium from the teeth, weakening the enamel, which allows the decay to reach the dentine and possibly the pulp if left untreated.^6,7 Acidic foods and beverages can initiate demineralisation, however, it is important to consider the ‘critical pH’ too.

Critical pH is when the pH of a substance is the same as the dental tissue, preventing demineralisation.⁶ Drinks such as orange juices, have a pH below 5.6-5.7, which is below the critical pH, thus demineralisation of the tooth occurs, initiating a cascade of events possibly resulting in a cavity.⁸

Acids are a key contributor to the initiation of the tooth decay process.⁶ They are released by bacteria in dental plaque which is adhered to the surface of the tooth^. An important bacteria found in plaque, Streptococcus mutans (S.mutans), metabolises sugary foods into lactic acids under specific conditions, thus lowering the pH.^9,10 The acid produced by S.mutans diffuses into the enamel and dissolves the essential minerals, eventually leading to tooth decay.² 

Symptoms of tooth decay

Here are some symptoms of tooth decay that may be experienced in the early to later stages of progression:¹¹

• Holes in the tooth that are visible 
• Staining on the surface of the tooth 
• Toothache 
• Pain when eating or drinking 
• Hypersensitivity of the tooth 
• Pain when biting down 

It is better to get symptoms checked by the dentist as soon as possible, as this maximises the chances of reversing tooth decay.¹¹

Treatment of tooth decay

There are several methods employed to manage tooth decay depending on the severity. Dentists will usually treat tooth decay accordingly once the mouth has been examined. Some of these include:¹¹

• Fluoride treatments - this is typically used when tooth decay is detected in the early stages to reverse the decaying process, this is achieved by restoring the enamel of the tooth 
• Fillings - this is a restorative approach where dental materials are used to fill the cavity once the decayed tooth material has been extracted by the dentist 
• Root canal treatment followed by placement of crowns - this method is used if there is a lot of decay and the infection has reached the pulp. The infected pulp is removed and a filling is used to replace it. The crown covers the entire surface of the tooth once the dentist has removed decayed tooth tissue and prevents any further fractures from occurring
• Tooth extractions - when tooth decay is past the point of using restorative methods, extractions are required. To fill the gap left by the extraction, dental implants or bridges can be used

Reducing the risk of tooth decay

Saliva acts as a natural buffer in the mouth by promoting remineralisation. This is a process in which minerals that were lost in demineralisation, have been restored to the enamel.⁵ Remineralisation depends on the presence of calcium, phosphate, and fluoride ions to rebuild the surface of the tooth.² The repetitive cycles of demineralisation and remineralisation determine the extent of mineral loss and regeneration, it is important to have these two processes balanced to limit the risk of tooth decay.^2,5

It has been established that sugar is the primary agent of tooth decay, therefore to reduce the chances of developing tooth decay is to limit sugar consumption. Avoiding sugary drinks such as fruit juices, energy drinks, and aerated fizzy drinks is beneficial in maintaining a healthy pH balance in the mouth, thus reducing the risk of tooth decay. It is key to remember that consuming sugar once will not lead to tooth decay, it is the consistent consumption that should be avoided.

Understandably, sugar cannot be completely eradicated from our diets, but it is a healthier option to be mindful of sugar consumption, additionally after drinking/eating sugary beverages/foods, drinking water afterwards will help reduce the risk of tooth decay.⁷

Oral hygiene is essential in the management of tooth decay. It is difficult to find tooth decay in people who consistently keep their teeth cleaned, this is because dental plaque gets disturbed by the action of brushing.⁷ Dental plaque has a role in tooth decay, so removal of this can help prevent tooth decay.⁶

Incorporating fluoride on the surface of the teeth may be crucial in the prevention of tooth decay.⁷ If fluoride is present on the enamel, it can prevent demineralisation by acids, protecting the teeth from erosion. Brushing twice daily with fluoride toothpaste can help to prevent tooth decay. Many clinical trials conclude the positive effect of fluoride toothpaste in reducing tooth decay.² Dental practitioners can also apply a fluoride varnish to the surface of the tooth which promotes remineralisation.⁷

The role of saliva

The mouth has a natural defence system against acids, which is saliva. Saliva is an essential component in the remineralisation process, as it contains all the necessary ions (phosphate and calcium) needed to repair the enamel after erosion.¹² Saliva also acts as a buffer system as it contains bicarbonate ions.^5,12 The concentration of bicarbonate ions varies with salivary flow. The buffering mechanism acts by neutralising the acidic and sugary foods/drinks ingested.¹²

Salivary clearance also regulates a constant, healthy, oral environment. This is a process in which the contents of the mouth are eliminated through swallowing and the rate of salivary flow.¹² 

Summary

The tooth is a complex structure comprising three distinct layers, enamel, dentin, and the pulp. Although enamel is the strongest substance in the human body, it is susceptible to erosion by acid.

To maintain a healthy oral environment, the pH should be kept between 6.5 and 7. The decrease in pH due to the metabolism of sugars results in tooth decay, acting on the enamel and if left untreated, it can progress to the pulp. Under normal conditions, saliva is the first defence system against the acids released by oral bacteria. Among the components of saliva, the main one is bicarbonate ions, which act as a buffer to neutralise the acids, protecting the enamel. Common symptoms include toothache, hypersensitivity, visible holes on the surface of the tooth, and many more.

Minerals from the tooth surface are removed when in contact with acid, also known as demineralisation, which is the beginning of the tooth decay process. To reduce the chances of tooth decay, sugar consumption can be limited as well as practising good oral hygiene, this includes brushing the teeth twice daily with a fluoride toothpaste. If a cavity is formed, there are a variety of treatments used to manage this, including tooth extractions, crowns, and many more, depending on the severity of the decay. Tooth decay does not show up overnight, so if preventative measures are put into action, there is a good chance of avoiding tooth decay altogether.