Q: What is the Normal Sequence of Tooth Eruption?
At 6 months, your child’s first teeth (the lower central incisors) will emerge from the gums, and by the time your child is 2.5 to 3 years old, he or she will have a complete set of 20 milk teeth. This is known as the primary dentition phase. The mixed dentition phase starts when your child is about 6-7 years old, marked by the emergence of the first permanent teeth (usually the first molars or the lower central incisors).
The mixed dentition phase is usually when the sequence of teeth eruption becomes most crucial, and any premature loss of the milk tooth (most commonly due to tooth decay) or delay in eruption of the adult teeth may cause shifting of the adjacent teeth and result in alignment and bite problems. By 12-13 years old, your child will now have entered the permanent dentition phase once the last milk tooth is shed, and with the exception of the wisdom teeth, he or she should have 28 adult teeth in total.
The wisdom teeth pose a unique set of problems as there is a tendency to have insufficient space in the jaw to accommodate them, resulting in impaction and other eruption problems. You can read more about the wisdom teeth in another article here.
Read more: Is it Wise to Remove My Wisdom Tooth?
You may refer to the series of graphics below showing the normal sequence of tooth eruption:
Q: How Do I Know If There’s Something Wrong With My Child’s Permanent Teeth Eruption?
There is a possible cause of concern if the same tooth on the opposite side (but in the same arch) has not erupted after 6 months
In general, teeth usually erupt in pairs in the same jaw (i.e., upper jaw) and if one side has not erupted more than 6 months after the other side (right vs left, or vice versa), then a radiograph may be required to check on the position of the unerupted tooth. Sometimes, there may be an additional tooth present (known as a supernumerary tooth) which may be blocking the adult tooth from erupting properly. In other instances, the adult tooth is congenitally absent, or positioned wrongly and such, will unlikely every erupt.
In the example above, the upper left central incisor (UL1) has erupted in an 8-year-old, but the upper right central incisor (UR1) has not. An X-ray was taken and it was discovered that there is a supernumerary (extra tooth), called a mesiodens (M), which was obstructing the eruption of the right central incisor. In this situation, the mesiodens has to be surgically removed, and the unerupted right central incisor has to be “helped” to erupt into its proper position, with braces.
The radiograph below was taken for a 14-year-old patient whose upper right canine (UR3) and first premolar (UR4) have long erupted but the upper left canine and first premolar have yet to erupt, with the milk teeth still present. The upper left canine (UL3) and first premolar (UL4) are both lying horizontally above the roots of the milk teeth (C and D), and they will likely remain there unless removed surgically.
The X-ray below shows a 10-year-old with absent lower left second premolar (5). As such, she will retain her primary second molar (E) well into her adulthood as it will not exfoliate on its own. However, the milk tooth usually does not last long as the roots are significantly shorter, and the tooth itself is more easily worn down due to its smaller size and thinner enamel, leading to sensitivity and possibly pain.
Let’s contrast the X-ray with the other X-ray below, which shows what is normally seen in a 8- to 9-year-old in the mixed dentition stage. As disturbing as it looks, the X-ray image needs to be scrutinised closely and the teeth counted to ensure no missing or extra teeth are present. Luckily for this patient, none of the permanent teeth are missing and the sequence of teeth eruption looks to be in order.
Do take note that the “more than 6 months” rule only applies to teeth in the same arch or the same jaw. For example, if the lower canines have erupted but the upper canines have not, that is actually normal since the upper canines generally erupt a lot later than the lower canines.
Q: One of My Child’s Upper Front Tooth is Now Biting Behind His Lower Front Tooth. Do We need To Do Anything?
The upper incisors are usually placed in front of the lower incisors when the teeth come together in a biting position. However, there are situations where the upper incisors end up behind the lower incisor, this is known as a crossbite.
Yes, an early intervention is possible to correct a single tooth crossbite while the teeth are erupting, as not only does the crossbite look unaesthetic, it also causes functional problems by creating an interference to your child’s bite. The most common way to correct the single tooth crossbite is by getting your child to wear a removable appliance with an activated spring which will push the erupting upper tooth forward into the correct position.
There is a small window of time for which the removable appliance will work, once this window is missed, then your child has to wait until he or she is 12-13 years old and ready to wear braces (also known as fixed orthodontic appliance) to correct the crossbite. As such, you will need to consult the dentist as soon as you notice a crossbite developing on the incisors.