Sarah Turner, Jayne E. Harrison, Fyeza N.J. Sharif, Darren Owens, Declan T. Millett
What are crowded teeth?
When teeth erupt (come through the gum into the mouth), they may twist, stick out, drop back, or overlap if there is not enough space in the mouth. Losing baby teeth early from tooth decay or trauma can lead to crowded permanent teeth. If crowded teeth affect a child's self‐esteem or cause pain, damage or chewing problems, the child may be referred to a specialist dentist known as an orthodontist to correct them. Orthodontics is about the growth of the jaws and face, and development of the teeth and bite.
What is orthodontic treatment?
Crowded teeth can be prevented or corrected using braces if crowding is mild (less than 4 mm). Removal of some teeth (extraction) may also be needed if crowding is moderate (4 to 8 mm) or severe (more than 8 mm). Fixed braces are used on permanent teeth. Removable braces can be used on baby or permanent teeth, or both. Baby or permanent teeth can be extracted.
Fixed braces attach parts to each tooth using dental glue, with brackets holding a wire that puts a force on the teeth, to move and straighten them. The wire is secured with metal ties, small rubber bands or a clip that is built into the bracket ('self‐ligating').
A lower lingual arch (LLA) or lip bumper (LB) retains the lower back teeth (molars) while allowing the lower front teeth to straighten and move forwards. To remove pressure on the teeth, an LLA wire lies on the inner side of the teeth; an LB wire lies on the outer side. The 0.9 mm stainless steel wires are attached to metal bands around the back (molar) teeth at either end, with the LB wire having a plastic coating at the front.
Sometimes extra items are used with fixed braces, such as headgear (straps attached to a frame outside the mouth), vibrating plates or lacebacks (thin wires holding teeth together).
Removable braces are usually made from hard plastic that joins together active parts that move the teeth and clips that secure the brace. Some removable braces are made from moulded flexible plastic.
The Schwarz appliance has a screw that is turned once a week by parents, to widen the arch of the lower jaw and make more space into which the permanent teeth can move.
The eruption guidance appliance guides permanent teeth into a better position as they erupt. It is a combined upper and lower brace that holds the lower jaw forwards and has guiding slots to align the front teeth and improve the side teeth bite.
Baby eyeteeth (canines) are extracted when children have a mix of adult and baby teeth, to provide space into which other teeth can move.
Wisdom teeth (third molars) may be removed any time from when they form (early teenage years) until adulthood, to help prevent them from putting forward pressure on the other teeth.
What did we want to know?
We aimed to evaluate scientific research on the effectiveness of orthodontic treatments (fixed braces, removable braces, tooth extraction) used to prevent or correct crowded teeth in children aged 16 years old or younger. We searched for studies that compared these treatments against no treatment, delayed treatment, placebo (pretend treatment) or another orthodontic treatment.
What studies did we find?
We included 24 studies that presented results from 1314 children aged from 7 to 16 years in different countries. Twenty studies tested fixed braces, two tested removable braces and two tested extractions.
What were the main results?
Fixed braces and related items
A lower lip bumper may prevent crowding when the adult teeth are starting to come through. Nickel‐titanium wires may correct crowding better than wires made of copper nickel‐titanium, and twisted multi‐stranded (co‐axial) nickel‐titanium archwires may be better than single‐stranded ones. However, we cannot be sure of these findings.
For the other comparisons evaluated, it was not possible to show that one group did better or worse than the other for reducing crowding.
Removable braces and related items
The Schwarz appliance may reduce crowding in the lower arch, when measured at nine months. Use of an eruption guidance appliance, for a year, may reduce likelihood of crowding, but there may be other explanations for this. Again, we cannot be sure of these findings.
Taking out wisdom teeth (third molars) does not seem to affect crowding later in life, while taking out the pointy baby teeth (canines) from the lower jaw, may reduce crowding in the short term, but we cannot be sure of this. There are probably other explanations for this finding.
What are the limitations of the evidence?
The evidence is uncertain. It consists of small, individual studies testing different treatments. Some of them have problems with how they were carried out. We cannot be sure about our findings and future research may change them.
How up to date is the evidence?
The evidence is up to date to January 2021.
Turner S, Harrison JE, Sharif FNJ, Owens D, Millett DT. Orthodontic treatment for crowded teeth in children. Cochrane Database of Systematic Reviews 2021, Issue 12. Art. No.: CD003453. DOI: 10.1002/14651858.CD003453.pub2.