implants UK - the journal of oral implantology

I 17 research _ Toothless jaws I implants1_2011 When evaluating overdenture attachment con- structionsasfittingmeans,thevarioustypesandforms available must be considered. On the one hand, there are individually shaped bar attachments, and on the otherhand,thereistheclassicroundbar,whichcanbe manufactured either by casting or by combination of pre-fabricatedelements. Theoverdentureattachmentfittedonfourimplants is a classic fitting element for a purely implant-sup- ported cover denture prosthesis in a toothless upper or lower jaw. A retrospective study with 51 patients compared individually shaped bar attachments and roundbarsforthefittingofcoverdentureprostheses.9 Twenty-six patients were equipped with round bars, while25patientsreceivedasuperstructurewithanin- dividualbarattachmentonfourimplantseach.Aftera surveillanceperiodoffiveyears,thesurvivalrateofthe implants was 100 per cent. Larger technical complica- tionsthatrequiredarenewalofthemountingelements occurredintheroundbarsonlyintheformoffractures in the extension areas. The fractures on the extensions of the overdenture attachments, which were exposed tohighmechanicalstress,weredueeithertoporosities in the cast object or to inhomogeneities in the area of the points of attachment. Furthermore, it was deter- mined that low-grade complications (activation of hanks) occurred three times as often in the round bars as in the bar attachments. Thus, two causes of defects can be deduced: firstly, defects due to faults in the manufacturing technique (casting and joining proc- esses); and secondly, defects causatively connected withthedesignofthesuperstructure. Two versions are described in the literature for the fitting of attachments in the toothless upper jaw: the fittingofattachmentsonfourimplantsintheanterior segment and the fitting of two attachments on three to four implants on the lateral segments (mostly after a previous sinus floor augmentation). Additionally, for the application of attachments in the toothless upper jaw, data from clinical studies has been published.9 Both attachment concepts featured almost identical survival rates after five years: 98.4 per cent for the at- tachments in the anterior segment and 97.4 per cent for the attachments fitted on six to eight implants in the lateralsegmentsoftheupperjaw. In particular, fitting by bar attachments appears to be a therapeutic means with guaranteed success of the fitting of purely implant-supported cover den- ture prostheses in the upper and lower jaw. It excels with a low rate of technical complications, as well as low maintenance requirements. Hence, bar attach- ments constitute clinically tested fitting elements for implant-retained and implant-fitted removable superstructuresinthetoothlessupperandlowerjaws. No clinical data for the fitting of removable super- structures in the toothless upper jaw for magnets and for ball-head attachments is available. Additionally, the application of so-called locators for the fitting of removable implant superstructures cannot be consid- eredtobebasedonevidence,accordingtothecurrently available data. To date, no results of clinical studies havebeenpresentedforthisfittingelement. Telescopes as fitting elements for removable su- perstructures are popular particularly in the Ger- man-speakingcountries,astheyareveryhygienicand easy to expand. However, these advantages are offset by the high technical requirements and costs. Clinical studies on the suitability of double crowns as fitting elements in implant prostheses demonstrate that they are generally suitable and they point out the ad- vantage of combining the natural teeth with implants forthefittingofaremovableconstruction,asopposed toattachments. Fig. 2_Fracture of a bar attachment construction manufatured by casting in the area of the extension. Fig. 3_Casting of the implants in the pick-up technique with a high strength casting material Fig. 4 Fig. 5 Fig.4_Tooth arrangement produced on the work model. Fig. 5_Virtual construction with distal attachments Fig. 2 Fig. 3