The first anti-rotational abutment system was the Branemark external hex. Originally designed solely to allow the engagement of a driver to seat the implant, it was ultimately adapted to prevent the rotation of abutments placed on the implant body. The short height of the hex, and the lack of an abutment with correct tolerances, made it a poor choice for stabilization of a single tooth restoration[i]. In addition, the flat to flat abutment connection allowed percolation of fluids and a bacterial component into the implant connection[ii]. This pumping action during cyclical loading ultimately places stress on the retaining screw[iii]. Screw loosening became endemic in this design with failure of the prosthetic components and soft tissue volume[iv]. The move from external to internal attachments began as a means to mitigate the loosening of abutments as they were being subjected to clinical functional forces. A clinical byproduct of this change, as noted radiographicaly, was a decrease in crestal bone remodeling.
Percolation of fluids during the normal micro-mobility that occurs at the implant-abutment interface leads to bacterial infiltration[v]. Chronic inflammation results in the production of matrix metalloproteanases (collagenase, gelatinase, elastase) which cause soft tissue breakdown and the potentiation of osteoclastic activity[vi]. The challenge, therefore, was to reduce microleakage at the implant/abutment interface.
Intra-Lock™ engineers proceeded to develop a ferrule attachment in combination with both inside and outside stabilization (Figure 4).
Figure 4. SEM cross section of Intra-Lock® abutment
In a recent study conducted by New York University Department of Biomaterials and Biomimetics, some of the leading abutment designs were tested and compared for microleakage. The Intra-Lock® abutment was shown to be superior. It clearly and significantly reduces microleakage when compared to various attachment designs of its competitors[vii]. This significant reduction in microleakage will reduce the concentration of inflammatory compounds being produced, which helps to prevent resorption of the interdental bone and thereby preserve papillary support for aesthetics. A more stable joint will also decrease stress to the retaining screw. Retention of the abutment should be borne primarily by the abutment at the joint interface. There should be stability of the abutment after primary torque even if the retaining screw is removed. The ferrule attachment gives us this kind of stability and is responsible for the dramatic reduction in microleakage. In addition, there is a choice of abutment diameters, giving the clinician an option for a platform shifted emergence profile.
When evaluating an abutment system, the clinician should be looking for several features. First is prosthetic variability. Is there sufficient adaptability for all types of prosthesis planning, from removable overdentures to complex fixed restorations, both in the provisional and definitive stages? Second is the accuracy of impression and record taking. Third is the stability of the abutment interface if the final abutment must be transferred from lab model to the mouth several times during the try-in phase. Finally, the abutment should eliminate flexural opening at the margins during function to reduce microleakage at the implant-abutment interface. The Intra-Lock® abutment clearly meets all of these parameters as demonstrated by university studies. This gives clinicians the confidence needed for long-term success in prosthetic rehabilitation.
[i] Binon PP. The effect of implant/abutment hexagonal misfit on screw joint stability. Int J Prosthodont. 1996;9:149
[ii] Brogginni N, McManus LM, Hermann JS, Medina R Schenk RK, Buser D et al. Peri-implant inflammation defined by the implant-abutment interface. J Dent Res.2006;85:473
[iii] Khraisat A, Hashimoto A, Normura S, Miyakawa O. Effect of lateral cyclic loading on abutment screw loosening of an external hexagon implant system. J Prosthet Dent. 2004;91:326
[iv] Brogginni N, McManus LM, Hermann JS, Medina RU, Oates TW, Schenk RK et al. Persistent acute inflammation at the implant-abutment interface. J Rest Dent Res.2003;82:232
[v] Steinebrunner L, Wolfart S, Bossmann K, Kern M. In vitro evaluation of bacterial leakage along the implant-abutment interface of different implant systems. Int J Oral Maxillofac Implants. 2005;20:875
[vi] Becker W, Becker BE, Newman MG, Nyman S, Clinical and microbiological findings that cause failure of dental implants. Quintessenz.1991;42:9
[vii] Coelho PG, Sudack P, Suzuki M,