Fogorvosi szemle, 2002 (95. évfolyam, 1-6. szám)

2002-06-01 / 3. szám

FOGORVOSI SZEMLE ■ 95. évf. 3. sz. 2002.

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Perényi J, BeneL, Radnai M, Fazekas A:

Model-investigation of push-out test used for quantitative evaluation of dental implants’ osseointegration

A frequently used method for quantitative evaluation of implant-bone interface strength is the push-out test. The objective of the authors’ study was to determine the effect of implants’ geometric characteristics on the results of pushout method. The degree of osseointegration is determined by a complicated interaction of mechanical, biological and chemical factors.

As this study focused on the effects of geometrical characteristics of dental implants, the authors tried to reduce the influence of biological and chemical factors as much as possible. For this reason a model of push-out test was set up. Cylindrical metal rods were imbedded in acrylic resin and were pushed out, meanwhile the force needed to disrupt the connection between the surface of the metal rods and the resin was measured and push-out strengths were calculated. Metal rods with three different lengths (7, 9, and 13 mm) and three different diameters (3.4, 4, 4.5 mm) were investigated. No correlation was found between implant length and maximum push-out strength. The mean push-out strengths were 17.32 MPa, 15.99 MPa and 15.56 MPa in groups, with 3.4, 4 and 4.5 mm diameter, thus the push-out strength decreases with increasing metal rod diameter. This may be attributed to the different distance between the outer circumference of the metal rods and the hole of the supporting table.

Supporting this theory metal rods with identical diameter were examined, while the diameter of the hole on the supporting table was changed. The results demonstrated that larger holes on the supporting table resulted in higher pushout strengths. This indicates that comparisons of this variable should only be performed with standardized clearance of the hole on the supporting table.

Push-out strengths of groups of cylindrical and conical implants with 9° convergence were also investigated. The mean values were 16.57 MPa and 16.43 MPa, respectively. There was no statistically significant difference between the two groups. This means that results of experiments with all the above mentioned implant types are comparable, at least to that degree of conicity.

As masticatory forces act usually on a surface, which is not perpendicular to the implant axis, we compared forces and push-out strengths that acted on surfaces with 10° and 15° inclination. The calculated average push-out strengths were 24.89 MPa and 22.56 MPa, respectively.

More than twice as high push-out strengths were measured when threaded metal rods were compared to unthreaded ones (30.15 MPa, 14.89 MPa, respectively). Examining the effect of pitch of threads we compared the mean push-out strengths in three groups of threaded metal rods with pitch of threads 0.7, 1.0 and 1.25. The results were 28.86 MPa, 30.48 MPa, 31.12 MPa, respectively. The differences can be explained with the alteration in the dimension of the interface covered by the acrylic resin.

Thus the effect of diameter, inclined opposing surface and threads must not be ignored if one compares the osseointegration capacity of different implants.

Key words: dental implants, mechanical retention, push-out test, length, diameter, effect of convergence, pitch of thread