QUESTION

In orthodontics, what is an "active" retainer as opposed to the passive retainer worn post-orthodontically?

ANSWER

Although called "retainers" these appliances are actually used to achieve minor tooth movement. Active retainers are used primarily to tip teeth. In many cases, they are practical because the amount of tooth movement desired is not extensive enough to warrant banding of the teeth. Active retainers are also frequently used in minor treatment for adults. They are also commonly used in early mixed dentition cases (when primary cuspids and molars are still present) in which it is necessary to intercept a developing orthodontic problem.

The forces applied by active retainers are supplied by a variety of springs, spring-loaded screws, and elastics. Various additional features may be incorporated in order to enhance the development of a better occlusion. An anterior or posterior shelf or bite plane, for example, may be used to open the bite, close the bite, or clear interferences during tooth movement. Active retainers generally require clasps in order to resist the dislodging forces of their component springs.

QUESTION

I have an adolescent patient with a congenitally missing mandibular second premolar. The orthodontist has maintained the space, rather than closing it. Future treatment plans include either restoration with a single implant and crown or a three-unit PFM fixed bridge, probably after the age of 18. Other than with the use of a removable orthodontic retainer, what can be done to hold this space for at least 5 years?

ANSWER

This is a somewhat common dilemma for dentists. The patient could continue to wear their orthodontic retainer, but compliance and oral hygiene are legitimate concerns. At this age, these retainers can often be found anywhere but in the patient's mouth. Also, after a lengthy and costly orthodontic treatment, the patient's parents cannot initially afford the costlier treatment options of implants or porcelain full-coverage bridgework. Other parents may have concerns about a surgical procedure at this age for implants or the extensive removal of sound tooth structure on adjacent teeth for full-coverage bridge abutments.

What are other possible space maintenance treatment options for an intermediate length of service?

One choice may be an acid-etched resin-bonded bridge, also known as a Maryland Bridge. This bridge has cast metal retainers that partially encircle the abutment teeth. Minimal tooth preparation is necessary and the bridge is cemented with a resin-bonded composite cement. The cost is substantially less than a fixed PFM Bridge. The drawback, though, is retention. The bridges tend to come unbonded, often at the resin-metal interface. They either need to be re-etched at the lab and rebonded, or if the metal is warped, a new bridge needs to be fabricated.

Another type of bonded bridge for intermediate lengths is a Sculpture/FibreKor Bridge. Consisting of an outer layer of composite for wear resistance and esthetics, and fiber reinforcement for strength and rigidity, Sculpture/FibreKor may provide adequate time for carefully selected cases. The lack of long-term clinical experience with these materials makes it hard to estimate longevity. However, these composite polymer bridges may offer the ability for intra-oral repair, and in the hands of a skilled technician, they are quite esthetic.