Removable plates can be used in many orthodontic situations to help develop arches or straighten teeth. Each plate is usually designed for a specific orthodontic application. If the top teeth protrude forward and there is space between them a plate can be used to close the spaces and pull the top teeth backwards. If the upper arch is narrow and the upper teeth are in cross bite with the lower teeth a plate can be used to expand the upper arch. If a baby tooth were lost early and back teeth have come forward resulting in a loss of space then a plate can be used to lengthen the arch and regain space. Plates can also be used as space maintainers to prevent space loss when a baby tooth is lost early or needs to be removed for other dental reasons.
In order to construct a plate an impression is taken of the dental arch. A design is created to achieve the desired orthodontic outcome and the impression and prescription are sent to a dental laboratory. A technicion at the lab will pour plaster into the impression forming a working model. They will then bend the prescribed clips and springs and add any screws before creating the acrylic base. Once the plate is polished it is returned to our practice and ready to fit at the next appointment. (please note that all of our lab work is carried out in Melbourne, Australia and is not sent overseas)
An OPG radiograph is usually ordered when the impression is taken and this is a full mouth scan x-ray that shows all teeth and the bones that support them. This x-ray is checked to ensure there is no pathology, anomalies in the root structures or any extra or missing teeth.
The plate arrives back from the lab in a sealed bag and is opened and washed to remove the packing solution. Dr. Ferguson will fit and adjust the plate and then instructions are given on taking the plate in and out and general care.
Appointments are arranged every six weeks to check on progress, tighten clips, tighten springs or ease acrylic as required. The cost of a plate and all adjustment visits is $1800.
A twin block appliance is a type of plate that is called a functional appliance. Functional appliances are used to encourage growth of the lower jaw and reduce large protrusions of upper front teeth. On average, the upper teeth protrude by 2-3mm ahead of the lower teeth. Functional appliances are suitable for cases where the teeth protrude by 6-8mm of more. Extreme protrusions of 12-14mm can also be successfully treated with a twin block appliance.
The twin block consists of two plates, one for the upper arch and one for the lower arch. The upper plate has blocks towards the back and the lower plate has blocks towards the front. When the teeth bite together the lower jaw is guided forward so that the blocks will lock together. The action of the muscles provides gentle functional force to encourage forward growth of the lower jaw and change the position of the front teeth.
A twin block should only be used around the pubertal growth spurt. In a girl this is usually between 11 and 12 years of age and in a boy this is usually between 12 and 13 years of age. Starting functional appliance treatment too early or too late will produce reduced results because the patient will not be growing at the maximum rate.
Twin blocks are usually worn for about 12 months. Sometimes the corrections will occur relatively quickly but the plates are still worn to allow growth to catch up with the dental changes that have occurred. Twin blocks cost $2000 and this fee includes all adjustment visits over the 12 months. Prior to taking the impressions for a twin block appliance a full set of orthodontic records is taken. The fee for this is $150. Another set or records will be taken at the end of twin block treatment and a formal discussion carried out where the before and after records and tracings are compared. This allows assessment of the treatment outcome and also allows for further planning of fixed braces.
Plates vs Fixed Braces
Plates and fixed braces produce different types of orthodontic movement. Plates can tip teeth, expand arches, open or close space and maintain space. Fixed braces produce 3D control over the position of the tooth crown and root. The bracket slot allows for correction of rotations and bodily movement of teeth.
Plates are usually used in the mixed dentition where a mixture of first and second teeth are present. The first permanant molars and the four incisor teeth need to be erupted before a plate can be used. This is ususally around 9-10 years of age. Twin block timing is a little later around the pubertal growth spurt and fixed braces can only be used once all of the permanent teeth have erupted. This varies from person to person and depends on sex but on average ranges from about 11-13 years of age.
Plates and braces are often used in conjunction to produce the best results. Twin blocks are used to advance the lower jaw in Phase I treatment and then fixed braces are used to correct the alignment of the teeth and establish a good bite in Phase II of treatment. In this type of treatment extractions of teeth can often be avoided.