Glass-fibre ribbon (Splinting of teeth/reinforcing restorations)
A glass-fibre ribbon consists of glass drawn to very thin strands (diameter 10 µm to 20 µm). The resulting glass-fibres (“long fibres” >10 mm) can simply be twisted together (cords, mats) in the same direction lying next to each other or linked as with textiles to woven fabrics or meshes to increase significantly the dimensional stability and resistance to forces from different directions.
A composite material is created by embedding the glass-fibres in a different material (matrix). Though loose glass-fibres were first used in dentistry sporadically for reinforcing in the 1970s, the use of glass-fibre ribbons has become established since the 1990s.
Glass-fibres have a decisive advantage compared with other technically used fibres (e.g. carbon fibres), as they are transparent and aesthetically inconspicuous. The glass-fibre surfaces are silanized to improve the bond with the resin matrix. They are then impregnated (wetted) with a bonder/dental adhesive. The prefabricated ribbons in standard use today in the dental sector are divided into non-preimpregnated and preimpregnated (so-called prepregs).
Glass-fibre ribbons are used in different disciplines in dentistry with or without prepreparation of the tooth structure, e.g. in:
The glass-fibre ribbons must be handled with great care using metal instruments to avoid contamination of the bond surface with subsequent failure of the adhesive. Protected storage prevents drying out, material ageing or premature polymerisation. Application from a light-protected bottle greatly facilitates dispensing and significantly increases the shelf-life.
Many dental materials exhibit high compressive strength. Glass-fibres mainly improve the tensile strength and are, therefore, most effective when placed in tensile zones. Mechanical properties of the bond are influenced by various factors: the proportion of fibre and matrix should be in the region of 50% each to utilise the advantages of the glass-fibre and avoid cohesive fractures within excessively thick composite regions. Pre-impregnated ribbons are already manufactured in this manner. They should be placed close to the tooth (with splinting, collar-shaped in the interdental space) and fill the framework to be fabricated as completely as possible.
After a splint or restoration is finished, the glass-fibres should always be covered thinly but completely by composite (to prevent chipping and swelling due to water intake). Generally, flowable, low-filled composite materials (flowables) are applied using the brush technique for covering the fibres.
... or need professional advice?
Get in touch with us or click Contact.
English | German |
---|---|
elongation at rupture | Bruchdehnung |
Wax build-up technique Wax build-up technique The various anatomical structures (such as cusp tips and slopes as well as marginal ridges) are usually built up one after another by adding small portions of wax (often using differently coloured waxes for didactic purposes). The firm, special waxes first have to be melted at room temperature. This can be carried out by warming small portions on differently shaped working tips of hand instruments in an open flame (such as a gas burner) or using electrically heated instruments which provide for more accurate temperature control and avoid contamination (e.g. electric wax-knife, induction heaters, wax dipping units). The wax is applied drop-by-drop to ensure that the warmer molten wax added last fuses seamlessly with the firm, cooler material. After hardening, the wax pattern can be reduced by sculpting, milling guidance surfaces or drilling to add retainers. Modern procedures include flexible, occlusal preforms for adding contours to soft wax. In addition, wax preforms, such as for occlusal surfaces or bridge pontics, are available in various shapes and sizes. Recently, irreversible, light-curing materials have been introduced for use instead of reversible thermoplastic waxes. Wax preforms To ensure that the wax pattern can be released without being damaged, model surfaces, opposing dentition and preparations must be hardened/sealed with special lacquer (applied by spraying, brushing or dipping). These waxes are mostly relatively rigid/elastic after cooling. Attaching wax sprues to a removable framework supported on double crowns using a hand instrument When employing the lost wax technique, prefabricated wax sprues, bars and reservoirs are attached to the patterns. Once the pattern has been released and its sprues waxed onto the crucible former, it is invested in a casting ring with refractory investment material. The wax can then be burnt out residue-free and casting completed. Unlike standard wax build-up techniques, a diagnostic wax-up is not intended for fabricating an indirect restoration, but rather for simulating the appearance and/or external contouring for producing orientation templates. |