Three treatment options exist for the replacement of congenitally missing lateral incisors. They include canine substitution, a tooth supported restoration or a single-tooth implant. Selecting the appropriate treatment option depends on the malocclusion, anterior relationship and specific space requirements.
In a previous article, I wrote about canine substitution as one treatment modality for young patients with congenitally missing lateral incisors. If the qualifications for using canine substitution aren’t met and the patient is opposed to the placement of an implant, a fixed restoration, such as a resin-fixed bridge, may be an option. Although there are differences in preparation design, the classic resin-bonded fixed partial denture relies solely on adhesion, without the use of pins or grooves.
The success rate of this type of restoration varies widely from a 54 percent failure rate over 11 months to 10 percent failure over 11 years, with de-bonding being the most common cause of failure.
Although these restorations can be used successfully, specific criteria must be addressed in order to ensure optimal esthetics and long-term predictability. The main criteria involve tooth position and mobility of the abutment teeth. Tooth position as it relates to the vertical overbite of the incisors can significantly impact the stresses placed at the bond interface.
Resin-bonded FPDs placed in a deep overbite relationship are associated with a higher incidence of failure. As the overbite increases, either the surface area available for bonding the retainer must decrease or the tooth must be prepared and the occlusion placed on the retainer.
Therefore, the ideal anterior relationship for a resin-bonded fixed partial denture is a shallow overbite.
The second concern regarding tooth position is inclination of the abutment teeth. The direction of normal occlusal forces on proclined incisors creates more of a tensile force at the bond interface, while occlusal forces on upright incisors create more of a shear force at the bond interface.
Knowing that something can be loaded with a shear force significantly more before it fails compared to that same thing being loaded with a tensile force, resin-bonded FPDs don’t do well on patients with proclined teeth.
Mobility of the abutment teeth negatively impacts the durability of the bond in two ways:
- Directional mobility: When placing a resin-bonded FPD from a mobile central incisor to a mobile canine, each abutment wants to move under occlusal load. The problem is their movement is on different vectors due to the position that each tooth occupies in the arch.
- Differential mobility: When one abutment is mobile and the other abutment is not, there is an increased stress placed on the bond when only one of the abutments moves under occlusal load. Generally, it is the least mobile of the two abutments that will debond as the restoration moves in the direction of the more mobile abutment.
As restorative dentists, our goal is to always treat our patients with the most conservative treatment possible. If the patient has a deep overbite, proclined, or mobile abutment teeth, then a resin bonded FPD may not be the best treatment option. It is with this in mind that today, resin bonded FPDs are often used as more of a long-term provisional, until the patient is old enough to have an implant placed.