Dental Tribune United Kingdom

27August 1-7, 2011United Kingdom Edition Clinical I n this last article we looked at telescopic or double crowns and their appli- cation in the production of removable dentures. Here we will consider another al- ternative – attachments – that also make use of precision milling. Attachments are elements for linking removable prosthet- ics with existing teeth (abut- ment teeth). These require crowns in order to accept the attachment. They can be used with removable prosthetics and with crown and bridge tech- niques. They comprise a primary element that is permanently cemented in the oral cavity and the secondary component that is firmly linked with the actual prosthesis. Attachments are particularly applicable when it proves impossible to produce parallel abutment teeth sim- ply. The attachment is used to create a bridge between mis- aligned abutment teeth such that a secure insertion becomes possible. Types of attachments Attachments are divided into two groups, intracoronal at- tachments (within the crown of a tooth) and extracoronal attachments (exterior to the tooth crown). Both types are available either as prefabricated at- tachments ie they are manu- factured commercially and are then simply ‘assem- bled’ by the technician. They can be obtained in a wide va- riety of shapes, sizes and ma- terials. Alternatively, there are be- spoke attachments, which are wholly prepared in the labora- tory, though sub-units can be incorporated during construc- tion. Whether prefabricated or bespoke, an attachment is al- ways made of a male and female part. Both parts slide to- gether during the insertion of the prosthesis and result in a firm connection. At- tachments for removable prostheses are generally en- hanced by the addition of a stress breaker. The pros and cons of attach- ments Disadvantages: • Intracoronal attachments require a lot of space during preparation = loss of tooth ma- terial. • Extracoronal attachments placed at too great a distance can result in unfavourable le- ver and pressure distribution. • A loss of an abutment tooth at a later date does not permit a restoration of function. • Price disadvantage to tele- scope (double crown) solutions with two crowns or less. Advantages: • No solder or glued connec- tions (apart from with RSS at- tachments) • Patient-friendly insertion and removal of the prosthesis • Precision calibration of fric- tion settings • Ease with which female com- ponents can be interchanged in practice • Longevity and robust func- tionality as there are no com- plicated mechanics • Easily adapted to the local space constraints and therefore no reduction of the prosthesis aesthetics; more graceful than double crowns • Abutment teeth are coated in ceramics in contrast to tel- escope solutions • Price advantage over telescope crowns with 3 or more crowns Manufacturing Bespoke attachments require a high level of competence in milling and casting methods; however, they can be adapted to nearly all situations. If you compare the costs of prefab- ricated standard-sized attach- ments versus the bespoke at- tachments, (taking account of the work involved), then the cost difference is negligible as you either pay more for the parts with one or the labour with the other. I’ve worked almost exclu- sively with ROD attachments over the past 15 years. The ROD attachment is an extra- coronal connective element, which impresses through its simple functionality and lon- gevity. The male part is sup- plied as a modelling accessory and is cast together with the abutment crown. The female component is made from a Te- flon wear-resistant synthetic cap, which is available in three different frictions. Additionally, the adhesive strength can be adjusted via the length of the female component. Each piece of dental techni- cal work requires meticulous planning and this is particu- larly the case with combina- tion work. You need to take into account the number of abut- ment teeth, their condition, the required interlocking and last but not least, the number of re- quired attachments. As with any crown or bridge, the work on an attach- ment begins with the prepara- tion of the abutment teeth. The individual abutment blocks are taken into account when deter- mining the alignment direction for the attachment. The align- ment direction is determined in exactly the same way as for the planning of individual small bridges. Circumstances per- mitting, it is beneficial to create a bit more space on those den- tal surfaces where the attach- ments are to be fixed to bring the male components as close to the tooth axis as possible to avoid the creation of damaging lateral forces. The final casting of the preparations is no different to that for larger bridge work. The milling model is produced as usual then based on the model. The optimal alignment position for the attachment is deter- mined such that the rods on the male attachments are aligned parallel to one another. In order to protect the at- tachment from overloading by tension and pressure forces, each component is protected from these forces via a stress breaker: this avoids breakage of the male element or expan- sion of the female one. A horseshoe-shaped de- pression is milled into the crown(s), which has vertical grooves milled at either end. This prevents movement of the attachment along the sagittal axis. The ledge of the milled horseshoe depression is able to absorb axial pressure and dis- tribute it over the crown block. The stress breaker then fits No clasps please! A further attachment solution Ulrich Heker and Chris Thomas page 28DTà Bridge with male Parts of Rod attachments Complete work with inserted CoCr ‘Bespoke attachments require a high level of competence in milling and casting methods; however, they can be adapted to nearly all situations’