Clinical challenges of fiber-reinforced direct bridges

Manufacturing fixed prostheses directly involves many technical, skill, and design challenges with which the dentist is not necessarily familiar.

When we receive a conventional bridge from the laboratory, we overlook many details that were covered during its manufacture, for example, the thickness of the material, the design of the connectors and the pontic, the polishing and detailing of the work, details that together cover the functions of a fixed prosthesis such as:

-Improve the patient's aesthetics and psychological needs.

-Stabilize the occlusion and maintain the relationships with the neighboring teeth.

-Restore chewing and phonetics.

-Allow for easy sanitization and facilitate plaque control.

-Respect the gingival tissues.

These are just some of the functions that a fixed prosthesis must have; if it does not fully cover all these points (there are more), the prosthesis is a failure.

Direct fiber-reinforced bridges, as their name suggests, are manufactured directly in the patient's mouth. This limits our access to detail in areas of intimate contact with soft tissue and challenges us to meet the mechanical needs of the prosthesis.

So let's walk through some of the challenges that dentists encounter when making direct fixed prostheses.

DESIGN OF THE PONTIC

The pontic is the component of a partial denture that replaces the missing tooth and must meet several requirements. It must restore function, be hygienically maintainable, be biologically and aesthetically acceptable, and be comfortable for the patient.

Extensive literature indicates that the Modified Ridge -Lap design (Fig. 1) offers several advantages over other pontic designs. In this design, the pontic surface may or may not have a small contact area with the soft tissue of the vestibular area. This has resulted in less inflammation of the surrounding mucosa because it reduces food trapping and facilitates cleaning while providing function and aesthetics.

Figure 1: Side view of the Modified Ridge-Lap pontic design.

This area of the pontic that is in contact with the mucosa of the edentulous space is called the Ridge Surface and can be easily detailed and polished by the laboratory in conventional bridges; however, due to lack of access, the dentist does not have the ability to polish and detail this area in bridges that are manufactured directly.

To ensure that this surface is as polished as possible, the technique known as the "hugging technique" or by its English name Hugging Mylar Band Technique (Fig 2) is applied, which translated into Spanish would be the mylar band hug technique.

Figure 2: The photograph shows the "Hugging Mylar Band Technique" used to obtain a perfectly polished Ridge Surface.

This technique aims to achieve an extremely polished surface (Ridge Surface) by allowing the material from which the pontic is made to cure or light cure in contact with a mylar strip.

According to the literature, the smoothest and most polished surface of a resin is achieved by curing it against a Mylar strip. This simple technique has significantly overcome one of the most challenging technical limitations in the fabrication of direct bridges.

ISOLATION

In the case of direct bridges, the insulation plays an additional role beyond keeping the medium free of fluids.

The thickness of the dam we use will affect the distance between the pontic and the soft tissue ; for this reason, it is recommended to use a thin or medium thickness rubber dam (approximately 0.15mm to 0.20mm) to maintain a minimum space between these two surfaces.

When isolating, the dentist should ensure an apical displacement of the papillae adjacent to the edentulous space by invaginating the rubber dam within the sulcus. This will create the necessary space to prevent food trapping and facilitate hygiene.

CENTRAL FIBER ANGULATION AND PHOTOPOLYMERIZATION

As we have already discussed in previous blog posts, the correct mechanical response of bridges to chewing loads is closely linked to the way in which the dentist arranges the fibers of the framework or structure.

The longitudinal or central fibers that are arranged from box to box of each abutment must have an apical angle (Fig 3), this curvature improves the dissipation of loads and allows the pontic material to have a good thickness in the occlusal area thus reducing the possibility of fractures.

Figure 3: Photograph showing the apical angulation of the longitudinal fibers

.

The length of these central fibers is determined using WetJet (Fig. 4) or dental floss, which the dentist adjusts according to the distance from one end of the tray to the other. The dentist must allow an additional distance when determining this length to account for the curvature of the fibers.

Figure 4: The WetJet is presented end-to-end across the pillars to measure the length of the central fibers.

When the dentist arranges the longitudinal fibers, he must ensure in one step that the fiber has intimate contact with the abutment while light-curing that end. The light pulse should be quick (1 sec) and focused. It is recommended to use lenses that localize the light emission to avoid light-curing the area of the fiber over the edentulous space, since it must then be given the desired curvature.

If an accessory lens to focus the light from the curing lamp is not available, the dentist can use a spatula-type instrument to block the light towards the central area of the fibers.

Once one end is light-cured, the clinician can provide the angulation in a more predictable way while ensuring intimate contact of the fibers with the missing abutment.

These techniques require skill and knowledge of the materials; it is highly recommended that the arrangement of the central fibers be done by four hands.

As you can see, direct fiber optic bridges involve many details to ensure they perform their function accurately 🫡, but don't stress 🙌🏼, this is a new topic and like any new topic it may seem complex, but believe me, with a little practice everything will flow smoothly.

I hope you find this information useful, best regards!

Dr. Marvin