To maintain good oral health during childhood and to prevent the onset of tooth decay - the most common oral pathology at this age - it is vital that children have proper oral hygiene habits from the time they are born. 

The acquisition and maintenance of these habits means that as adults they will be able to keep their teeth throughout their lifetimes. However, needs are not the same in a newborn as in older children. Here we present some oral hygiene guidelines that should be followed at the different stages of development of the mouth to achieve a common goal: removal of dental biofilm to maintain a healthy mouth. 

From birth to old age, humans go through different stages, and each stage involves changes that may be anatomical, physiological, or psychological, etc. These changes affect the different parts of the body, including the mouth. Development of the oral cavity mainly occurs in childhood. 

Three different periods may be discerned: 

• From birth to age 2. The eruption of the primary teeth, also known as milk or deciduous teeth, takes place. 

• From age 2 to 6. At this stage, children have all their milk teeth and no dental eruption occurs. 

• From age 6 to 12. Children are at the so-called mixed dentition stage, since eruption of the permanent teeth begins while coexisting with the temporary teeth. 

Although milk teeth are replaced over time by the permanent teeth, they intervene in very important functions such as chewing, breathing, speech and aesthetics. What is more, their premature loss may affect the eruption of the permanent teeth, as they serve as a guide for the proper emergence thereof. 

It is vitally important to keep both milk teeth and permanent teeth in good health. To ensure dental health, it is essential to perform oral hygiene adapted to the needs of each age, since each stage requires specific care, but all share a common goal: the removal of dental biofilm (bacterial plaque). The build-up of dental biofilm causes the onset of the two most common oral diseases among children: tooth decay (caries) and gingivitis. 

TOOTH DECAY 

Caries is the leading cause of tooth loss in children, and involves localised destruction of the hard tissues of the teeth due to the acids produced by oral bacteria upon metabolising dietary carbohydrates. When this process is repeated continuously over time, cavitation occurs. Initially, localised destruction of the enamel occurs, and once it reaches the dentin, it extends, potentially affecting the pulp. 

In Spain, the prevalence of caries in six-year-old children is 33.9%, reaching nearly 100% in adults. In younger children, we talk about early childhood caries, formerly known as baby bottle tooth decay, which affects children aged up to 71 months. 

The progression of early childhood caries is rapid in deciduous teeth (the enamel is thinner than in permanent teeth). In addition, children with decay in their baby teeth are much more likely to have multiple cavities in their permanent teeth. 

The main risk factors are decay-producing bacteria, poor oral hygiene and a carbohydrate-rich diet. To reduce the risk of caries, the following factors should be addressed: 

Bacteria 

• Prevention of early transmission of bacteria through saliva contamination from parents to children, as when blowing on food to cool it, tasting food with the baby’s spoon, putting their pacifier in the adult’s mouth, etc. 

• Maintenance of proper oral hygiene. 

Carbohydrates (the substrate) 

• The simpler ones (sugars) are more cariogenic than the complex (starch). 

• The amount, and above all, the frequency of intake should be considered: the more often, the greater the risk of decay. 

GINGIVITIS 

Gingivitis is an infectious disease that causes redness, inflammation and bleeding of the gums. In Spain, only 48.2% of 12 year olds have healthy gums, and this percentage drops lower still in puberty. 

Gingivitis is essentially produced by the build-up of biofilm in the margin between gums and teeth, and between the teeth (interdental spaces). This biofilm induces a local response of the immune system that causes inflammation, redness and bleeding of the gums, all major signs of gingivitis. In very few cases it may develop into periodontitis - much less frequently than in adults - which involves the destruction of the supporting tissues, and potentially, tooth loss over time. 

The main preventive measure is to maintain good oral hygiene to prevent build-up of dental biofilm, in addition to check-ups at the dental clinic. 

RECOMMENDATIONS FOR ORAL HYGIENE AT DIFFERENT STAGES OF CHILDHOOD 

Eruption of temporary teeth (0-2 years) 

The eruption process usually begins at six months of age and ends after the age of two. Temporary dentition consists of a total of 20 milk teeth—five per dental quadrant. 

It is important to keep in mind that oral hygiene is advisable before the first teeth appear. When babies do not yet have teeth, it is recommended that the gums be cleaned with a damp gauze or with a silicone thimble after each feeding. 

The tooth eruption process may lead to greater restlessness, irritability and difficulty sleeping. The baby may show increased salivation, mild discomfort, redness and irritation of the gums. 

There are specially formulated gel balms for the gums to prevent and relieve this discomfort. The gel balm may be applied with a silicone thimble or gauze, by gently massaging the baby's sore gums. 

When the first tooth erupts, it is recommended on the one hand to take the child to the paediatric dentist, and on other, to start brushing it to prevent the build-up of dental biofilm. Brushing at this age should be done by the parents - or the adult caring for the baby. It is recommended to use a child's toothbrush that adapts to the adult's hand and to the baby's mouth, with ultra-soft filaments that facilitate proper hygiene while protecting gums and teeth. 

It is advisable to go to the paediatric dentist within the first year of a baby’s life. The check-up will aim at monitoring proper emergence of teeth and factors such as occlusion and alignment, and will facilitate the timely detection of oral disorders or pathologies, including the early detection of decay. 

In addition to the recommendations on oral hygiene, in order to prevent decay at this age, it is advisable to take into account the following habits: 

• Do not leave your baby in bed with a bottle containing any liquids other than water, as long exposure to sugars favours the development of caries. 

• Avoid wetting the pacifier with sweet sugary substances. 

• Avoid transmission of cariogenic bacteria via saliva as when cleaning the pacifier in your mouth or blowing directly on your baby’s food to cool it. 

Temporary dentition and acquiring oral hygiene habits (2-6 years) 

At this stage children have all their milk teeth and it is advisable that they begin to take care of their own oral hygiene and that they understand the need for this. The most important thing is to instil good habits. 

It is recommended the child begin to brush her own teeth for two minutes, at least twice a day - morning and especially at night - or preferably after meals. To help acquire the habit, there are certain strategies, such as parents brushing their teeth at the same time as the child, and numerous apps, games, songs, etc. 

For best results, the brush should adapt to the hand and mouth of the child, should have a very small head that can reach all the areas of the mouth and should have soft filaments which will protect both teeth and gums. 

The brush should also be easy to handle for the parents, who are advised to review the child’s daily brushing. Note that the child will probably not be fully efficient in removing the dental biofilm. Plaque revealers are available to help improve brushing technique. 

To prevent tooth decay - the most common oral pathology at this age - the use of dental gel with a concentration of fluoride suited to the child's age is recommended. According to the guidelines of the European Academy of Paediatric Dentistry (EAPD) and the Spanish Society of Paediatric Dentistry (SEOP), the fluoride concentration recommended from the age of two is 1,000 ppm fluoride ion. The estimated amount of fluoride gel to use would be about the size of a pea. Parents should make sure the child spits out the gel after brushing and that it is not swallowed. 

The child should be taken to the paediatric dentist at least once a year to prevent the possible onset of oral diseases. 

Regarding the use of a pacifier, some studies have shown that it can relieve discomfort during tooth eruption and even reduce the risk of sudden infant death. However, it is recommended that its use not go beyond the age of three years to avoid any bite-related sequelae (same for thumb sucking) or oral malformations. 

Emergence of permanent teeth (6-12 years) 

At this age the emergence of permanent teeth begins in a process that ends at around the age of 12. During this stage children have mixed dentition, since milk teeth coexist with permanent teeth. Final dentition consists of 32 teeth - eight per dental quadrant - including the third molars or wisdom teeth, which erupt as of age 18, although they may never emerge. 

The most common pathology at this age is still caries. It is recommended to use a brush adapted for handling by the child, with a small head, soft filaments and a narrow neck to reach all the areas in the mouth. 

Regarding dental gel, it is advisable the concentration of fluoride is increased. The EAPD and SEOP recommend the use of a concentration of 1,450 ppm fluoride ion, and the amount to be used would now be 1-2 cm - as for an adult - since all the teeth have by now formed, although they may not have emerged. 

During the eruption of the permanent teeth there may also be some discomfort or irritation of the gums. It would thus be advisable for the gel’s composition to include specific ingredients for the protection of the gums. 

Brushing should continue to be supervised by parents and reviewed as necessary until approximately 8-9 years of age. 

As of the age of six, children can usually control the swallowing reflex and can spit properly. So, if this is the case, the use of mouthwash may be introduced. Besides providing a pleasant taste, mouthwash will provide extra protection against decay and will help [active ingredients] reach all areas of the mouth. 

From this age onwards - especially in adolescence, due to changes in the hormone balance and in attitude - the build-up of biofilm between the teeth may lead to the onset of gingivitis. For this reason, it is advisable to introduce the habit of interdental hygiene, using either dental floss/tape or interproximal brushes. It is important to ensure that this is done with care and with a proper technique to prevent damage that may cause the child to evade interdental cleaning in the future. 

As the permanent teeth emerge, interceptive orthodontic treatment may be required to correct problems of occlusion, alignment of teeth, etc. Fixed orthodontics is only used in children who have all their permanent teeth, at around 12 years of age. 

Finally, visiting the dentist at least once a year is advised. At these ages, it is possible to detect incipient decay, established caries lesions requiring treatment and a need for the application of sealants to pits and fissures in high caries risk areas.