Crowns, Bridges and Dentures

Fixed prostheses are cemented to the teeth with special adhesives and cannot be removed by the patient. Removable dentures are made for patients who have lost many or all of their teeth and for whom fixed work is not possible.

• Crown: a fixed restoration for a single tooth.
• Bridge: a fixed restoration for missing teeth, made of joined crowns supported by the neighbouring teeth.

The main types of fixed prosthesis are:

• Metal-ceramic (porcelain-fused-to-metal) crowns and bridges
• Zirconia-based ceramic crowns and bridges
• Metal-free glass-ceramic crowns
• Porcelain veneers (laminates)

Preparation is the shaping of a tooth to receive a crown or bridge. With a shoulder preparation, a defined step is created around the tooth, which helps the restoration fit the tooth and gum tissues more closely.

What matters is not whether the margin of the restoration sits below, at or above the gumline, but that it is smooth and fits precisely wherever it is. Hiding a poorly fitting margin under the gum is not acceptable practice. Restorations that impinge on the gum or leave a ledge can, over time, lead to:

• Bleeding gums when brushing
• Bad breath and discoloured gums
• Gum recession
• Decay beneath the crown (secondary caries)
• Bone loss

A poor fit is one of the most common reasons for bleeding gums around crowns and bridges. Mouthwashes or special toothpastes will not resolve it; the restoration usually needs to be removed, the gums treated if necessary, and a new restoration made on a proper preparation.

Metal-ceramic systems have been used for many years and are clinically well proven. The bond between metal and porcelain is strong. Although zirconia withstands high forces, it does not flex, so for very long bridges metal-ceramic can still be the first choice.

Because the metal framework does not let light through, it can limit aesthetics, particularly at the front of the mouth, and where the gum is thin a dark line may be visible at the crown margin.

Cast versus laser-sintered frameworks

With conventional casting, distortion of the wax pattern and shrinkage caused by temperature changes during casting can compromise the fit. With laser sintering (CAD/CAM), the framework is produced entirely by computer technology, the fit is more precise, and a biocompatible cobalt-chromium alloy is used.

Our clinic does not make cast-metal prostheses; when a metal-ceramic restoration is needed, the laser-sintering method is used for its accuracy and tissue compatibility.

Zirconia is impact-resistant, light, does not conduct heat and transmits light to some degree, so it can replace the metal beneath porcelain. As it is produced with CAD/CAM, the fit is very good when careful impressions and a proper shoulder preparation are made. It costs more than metal-ceramic.

However, fracture (chipping) of the porcelain layered on zirconia is more likely than with metal-ceramic. Zirconia is not the most aesthetic choice in every situation; it can be preferred for long bridges that include front teeth. For single front teeth and short bridges, metal-free glass-ceramic crowns give a more natural look.

Zirconia as a framework

The zirconia is made as a thin framework covering the tooth and is then layered with porcelain, so the zirconia itself is not visible in the mouth.

Monolithic zirconia

With more translucent zirconia blocks, monolithic crowns that need no porcelain layer, and bridges of up to 4–5 units in the back of the mouth, can be made. Because their aesthetics are limited, they suit back teeth where appearance is less critical, and since they can be produced quickly with CAD/CAM they can be a preferred option for back bridges. See our Zirconia page for more detail.

All-ceramic crowns without metal or zirconia have light transmission and colour very close to natural enamel, so they give a natural appearance, especially at the front of the mouth.

Because they are translucent, the colour of the underlying tooth affects the result; they may not be suitable for discoloured, root-filled teeth, for example. Preparation, try-in and bonding are more demanding than with metal- or zirconia-based crowns and require special adhesive cements. Good oral hygiene is important for patients choosing these crowns.

Empress

An aesthetic ceramic containing no metal or zirconia, preferred for front teeth, particularly where biting load is low. It can only be used for single crowns and is not suitable for bridges.

e.max

Developed to be stronger than Empress. It can be used for single crowns in higher-load aesthetic areas and on back teeth, and for short three-unit bridges replacing a single missing front tooth. The risk of fracture increases in longer bridges, and it should be used with caution in patients who clench or grind (bruxism). See our e.max page for more detail.

Porcelain veneers are very thin ceramic shells bonded with strong adhesive systems to the front surface of the teeth, after minimal reduction of that surface or, in some cases, none at all. They are made from Empress or e.max ceramic.

For patients unhappy with the colour or shape of their teeth, a key advantage is that the other surfaces of the tooth are left untouched. A good result requires thorough planning beforehand.

Veneers can also be made from composite, but composite is affected sooner by tea, coffee and smoking, so porcelain is generally considered the better option. Ceramic keeps its colour for a long time. See our Veneers page for more detail.

Complete dentures

Complete (full) dentures are used when no natural teeth remain. Many patients with a lower complete denture struggle with retention and stability. Placing 2 or 4 implants in the lower jaw can markedly improve retention and stability, considerably reducing problems such as sore spots, food getting underneath and the denture moving. Upper complete dentures usually do not need implant support.

Partial dentures

Partial dentures come in clasp-retained (conventional), precision-attachment and hybrid designs. Each has different advantages and drawbacks in terms of aesthetics, durability and cost, and the most suitable type is chosen according to the patient’s mouth and remaining teeth.