Merle J. Jaarda

Effect of preload torque on the ultimate tensile strength of implant prosthetic retaining screws

The preload concept proposes that an optimal torque exists to which implant prosthetic retaining screws should be tightened. According to this theory, the preload prevents separation of implant components, thus protecting the screw from fracture. Recent research suggests that most implant-retained prostheses in function today were placed using improper preloads. The purpose of this investigation was to determine whether or not improper preloading of prosthetic implant-retaining screws would adversely affect their ultimate tensile strength. Fifteen Nobelpharma-slotted gold screws from one lot were tightened to 6, 10, and 15 N/cm with a torque gauge and ultimate tensile strength values determined. The procedure was duplicated using 15 Nobelpharma gold screws from another lot tightened to 0, 10, and 20 N/cm. Within each of the test groups, there was no significant difference in the ultimate tensile strength among the three preload torques. However, a paired t test (P = 0.005) determined that there was a significant difference between the two lots with respect to the ultimate tensile strength of the screws preloaded to 10 N/cm. Altering the preload torque applied to Nobelpharma gold-retaining screws does not affect their ultimate tensile strength. The ultimate tensile strength of the screws from the two lots differed, suggesting an unannounced change in component specifications. (Implant Dent 1994;3:17–21)

Geometric comparison of five interchangeable implant prosthetic retaining screws

Eight geometric parameters of five interchangeable prosthetic retaining screws (#1-3i Implant Innovation-gold, #2-Impla-Med-gold, #3-Nobelpharma-gold, #4-3i Implant Innovation-titanium, and #5-Implant Support Systems-titanium) were recorded with an Amray 1000-B scanning electron microscope at x20 to x200 magnification. Five screws of each type were measured and eight parameters were evaluated: (A) diameter of head, (B) screw length, (C) thread pitch, (D) major diameter, (E) neck diameter (F) length of neck, (G) crest width, and (H) root width. The Nobelpharma-gold prosthetic retaining screws served as controls. The results revealed significant differences between the control and test screws in all parameters except parameters C and G (ANOVA, p < 0.05) and Duncans multiple range test (significance level 0.05). On the basis of these differences, it was concluded that interchanging prosthetic retaining screws can introduce unknown variables in treating patients.

Measurement of composite resin filler particles by using scanning electron microscopy and digital imaging

Composite resins are routinely classified on the basis of filler particle size for purposes of research, clinical applications, and communications. The size and characterizations of filler particles have also been considered a significant factor in the rate of wear of composites. Making valid correlations between the filler particles within a composite and wear requires accuracy of filler particle size and characterization. This study was initiated to examine two methods that would (1) qualify the filler particle content of a composite resin and (2) quantify the number, size, and the area occupied by the filler particles in composite resins. Three composite resins, BIS-FIL I, Visio-Fil, and Ful-Fil, were selected as the materials to be examined, on the basis of their published composite classification type as fine particle. The findings demonstrated that scientific methods are available to examine qualitatively and measure quantitatively the composite resin filler particles in terms of their numbers, sizes, and area occupied by use of a scanning electron microscope and digital imaging. Significant differences in the filler particle numbers, sizes, and the area occupied were found for the three composite resins in this study that were classified as fine particle.

Ultimate tensile strength of five interchangeable prosthetic retaining screws

Implant prosthetic retaining screws have been reported to serve as built-in safety factors to protect against overload in the implants “vertical stack,” although loosening and fracture of retaining screws are often considered complications. Manufacturers have responded by introducing interchangeable prosthetic retaining screws, which can give the clinician the impression that interchanging screws will not have an adverse effect on the remainder of the implant complex and for the integration of the implant itself. The objective of this investigation was to measure the ultimate tensile strength of four retaining screws from three manufacturers and two alloy types (gold and titanium) using the Nobelpharma gold prosthetic retaining screw as a standard for the comparisons. Five screws of each type were loaded in tension in an Instron Universal Testing Machine until fracture occurred. A Tukey-Kramer Test (significance level =.05) analysis of the data showed that all of the interchangeable prosthetic retaining screws were significantly different from the control screws in respect to ultimate tensile strength. The data suggest that interchanging prosthetic retaining screws will influence their built-in safety feature.

Early detection of osseointegration using scanning electron microscopy and the interfacial biopsy chamber: a pilot study.

This pilot project attempted to demonstrate microscopic evidence of osseointegration in a controlled environment as originally presented by Brånemark. The Interfacial Biopsy Chamber was developed to collect titanium/tissue serial biopsies of the implant-tissue interface at various stages of wound healing. It was surgically placed in two Flemish giant rabbits and titanium/tissue biopsies were collected at 35 and 70 days. The biopsies were examined using scanning electron microscopy (x2000, x3200, and x7500) and light microscopy (x230). Osseous tissue was found in intimate contact with the titanium implant surface with no evidence of an intervening fibrous layer. Cells with the morphological characteristics of osteoblasts were observed covering the titanium surface. Processes extending from the main body of these cells were in intimate contact with the titanium surface, following the machining striations. The photomicrographs were similar to those presented earlier by Brånemark. The project also suggested the use of the Interfacial Biopsy Chamber as a research instrument for the collection of implant/tissue interface serial biopsy samples. (Implant Dent 1992;1:84–87)