Brånemark Implant® Screws

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Evaluation of the Interchangeability of Implant Abutment Screws
The Effect of Coefficient of Friction on Preload With a Given Tightening Torque
Determining Preload Contact Force During Abutment-Implant Assembly Using Ultrasound
Determining Preload Contact Force During Abutment-Implant Assembly Using FEA

Abstract: The purpose of this investigation was to determine if abutment screws from 6 dental implant manufacturers are interchangeable with implant fixtures other than their manufacturer specific complement. A previous study concluded that the Procera® custom abutment, designed and fabricated using CAD/CAM technology, should easily accept the external hexagon when the abutment is placed onto each of several different implant fixtures. While the Unigrip gold screw is delivered with the Procera® custom abutment, the question arises about its’ use with other implant systems. Three screws and 3 implants, of the standard 4.0 mm size, from each of several manufacturers were measured and categorized according to ANSI/ASME B1.13M-1983(R1989) American National Standard. The standard assesses the major determinants of interchangeability by the screw profile (ANSI/ASME B1.21M), the pitch and tolerance. These measures of interchangeability are expressed by the M value and by the tolerance class 6h/6g. The following chart categorizes on the first line the internal bore of the various implants while the second line refers to the dimensions of threads of the abutment screws.
BrånemarkLifecoreImplamed3ISteri-OssParagon
M2 - .4 6g M2 - .4 6g M2 - .4 6h M2 - .4 6g M2 - .4 6g M2 - .4 6g
M2 - .4 6h M2 - .4 6h M2 - .4 6h M2 - .4 6h M2 - .4 6h M2 - .4 6h
All implant and screw combinations were standard 4.0 mm sizes.
Conclusions: From the measurement data it would appear that the Unigrip gold screw should be easily accepted by any of the implants studied.

Abstract: There is little information in the dental literature on the effect of the coefficient of friction on the preload when the abutment screw is tightening during the assembly of the abutment onto an implant. This study examined the effect of the coefficient of friction on the development of preload stress in the implant complex during abutment screw tightening. Using the software program HyperWorks®, two three-dimensional finite element models of 1) a Brånemark® System 3.75 X 10 mm Mark III implant, a CeraOne® abutment, a Unigrip abutment screw, and 2) a Replace Select™ System 4.25 X 10 mm implant, a Straight Esthetic abutment, and a TorqTite abutment screw) were developed. The abutment screws were subjected to a tightening torque in increments of 1 Ncm from 0-32 Ncm using ABAQUS® software. The coefficient of friction was set to a baseline of 0.26 between all components of the implant model and then varied until a preload of 75% of the yield strength of the abutment screw was reached. The von Mises values in each element of interest were measured and converted to the preload in Newtons. Preload measurements were determined for 1) the base of the screw head, 2) screw head and shank junction, 3) the screw shank, and 4) screw threads.
Conclusions: In order to reach the desired preload of 75% of the yield strength, using a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied, the coefficient of friction between the implant components would need to be 0.10.

Abstract: The direct measurement of the magnitude of the preload force developed during tightening of the abutment screw in an implant complex has not been reported. The objective of this study was to measure the preload contact forces using a miniature ultrasonic transducer positioned in the head of the abutment screw. An experimental Testing System consisting of a 20 MHz ultrasonic transducer, an ultrasonic pulser-receiver USD-15 (Krautkramer) unit, and a TDS-520 (Tektronix) oscilloscope connected to a computer through a GPIB port (IEEE488) was designed for this study. An implant screw was positioned within the holding devices of a Test Stand that was capable of delivering and measuring a force up to 2000 N. An ultrasonic transducer positioned in the head of the screw was continuously activated using the USD-15 unit, and load-upload pulses were transmitted by the transducer to the screw. Echo-pulses or an A-scan were received and transmitted by the USD-15 to the TDS-520 oscilloscope for digitizing that represented baseline “time of flight” data of the initial stress in the screw. An upward movement of the upper member of the Test Stand was initiated producing an applied tensile load to the screw. A second A-scan following screw loading was received, processed, and digitized. The software for the system used the two digitized A-scans for determining the variation in the time of flight (TOF) between the two A-scans. The screw was subjected to multiple tensile loads that ranged between zero (0) and 400 N.
Conclusions: Direct comparisons between the applied load and the stress in the abutment screw as determined by the TOF values were used to evaluate the accuracy of the adaptation of ultrasound acoustic technology to measure the preload in the implant screw. During load applications from zero (0) N to 400 N, the preload measured using the ultrasonic method varied by less than 2.0 N.

Abstract: The preload induced in the implant complex during abutment screw tightening is fundamental to our understanding of the biomechanical principles in load transfer. The objective of this study was to measure the magnitudes of the preload contact force using the finite element analysis method (FEA). A (FEA) model of a Brånemark® System Mark III implant, a CeraOne® abutment, a Unigrip abutment screw and its torque wrench were created with a thread helix using the software programs HyperWorks and LS3D-Dyna. The implant model was positioned with in a bone models. Using the torque wrench,a 320 Nmm torque moment was applied followed by removal of the wrench using the software ABAQUS. The contact force (N) was measured at the interfaces between the: 1) Abutment Screw and Abutment Bearing surface (ASAB), 2) Abutment and Implant Bearing Surface (AIBS), and 3) Abutment screw Thread and Implant internal Thread bore (ATIT). The contact force direction of ATIT was normal to the thread contact flank. The preload was calculated from the ATIT contact forces. The contact forces after 320 Nmm torque tightening were: (ASAB) 554.4 N, (AIBS) 554.4 N, (ATIT) 573.9 N and the preload 522.17 N. Following torque wrench removal, the contact force were reduced: (ASAB) 549.0 N, (AIBS) 549.0 N, (ATIT) 538.2 N and the preload 489.7 N.
Conclusions: The horizontal motion of the horizontal torque moment applied by the torque wrench lead to a vertical motion by the helix thread geometry of the ATIT interface. At the point of contact between the thread surfaces, the horizontal moment force was transformed to the contact forces at ASAB, AIBS and ATIT. The torque-contact forces demonstrated a simple regression during the torque moment application (R2=1.000) but changed to a polynomial regression after wrench removed for all interfaces with the exception of ATIT.

Abstract: The purpose of this study was to determine the influence of instrumentation and operator experience on the torque generated during manual tightening of slotted gold screws. Sixteen subjects (12 dentists and 4 dental students), divided into four groups based on experience, were instructed to tighten five screws into implant analogs with 20-mm and 37-mm slotted screwdrivers. The screws were then removed with a torque gauge. All groups were able to generate significantly greater torque with the 37-mm slotted screwdrivers. Dentists with no implant treatment experience generated significantly less torque than the other three groups. Of the 12 dentist subjects, only three generated the optimal amount of torque when using the 20-mm screwdriver.
Conclusions: Operators who had little experience dealing with implant prostheses were not able to provide the recommended torque and experienced operators tended to generate more than the recommended amount. None of the subjects were able to generate consistent torque values.

Abstract: In this project, the maximum preload torque of implant prosthetic retaining screws from four manufacturers: 3i Implant Innovations, Impla-Med Inc., Nobel Biocare USA Inc., and Implant Support Systems, and of two alloy types (gold and titanium) were measured to determine one index of interchangeability of intersystem components. Five screws of each type were tightened down against a gold cylinder in an in vitro patient simulation model using a Tohnichi BTG-6 torque gauge until fracture occurred. The 3i Implant Innovations gold and the Nobelpharma gold screws were not significantly different. The 3i Implant Innovations titanium and the Impla-Med gold screws were able to withstand less preload torque than the 3i Implant Innovations gold and the Nobelpharma gold screws. The Implant Support Systems titanium screw was able to withstand significantly more preload torque than all the other screws.
Conclusions: Interchanging implant prosthetic retaining screws could introduce new and unknown variables that may affect the long-term survival of implant fixtures and/or the implant prostheses.

Abstract: In this project, eight geometric parameters of five “interchangeable” prosthetic retaining screws: 3i Implant Innovation-gold, Impla-Med-gold, Nobelpharma-gold, 3i Implant Innovation-titanium, and Implant Support Systems-titanium were recorded using an AMRAY 1000-B scanning electron microscope at 20-200X magnification. Five screws of each type were measured. The eight parameters evaluated were: (A.) head 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 the controls to which all other screws were compared. Significant differences between the control and test screws were found in all parameters except parameters C and G (ANOVA P<.05 and Duncan multiple range statistic significance level=.05).
Conclusions: It may be concluded that interchanging prosthetic retaining screws will introduce unknown variables when treating patients.

Abstract: The purpose of this study was to measure the ultimate tensile strength of four retaining screws from three manufacturers and two alloy type (gold and titanium) using the Nobel Biocare 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.
Conclusions: All of the interchangeable prosthetic retaining screws were significantly different from the control screws with respect to ultimate tensile strength. The data suggests that interchanging prosthetic retaining screws will influence their built-in safety feature.

Abstract: The purpose of this investigation was to determine whether improper preloading of prosthetic implant-retaining screws would adversely affect their ultimate tensile strength. Fifteen Brånemark System (Nobel Biocare, AB) slotted gold retaining screws from one lot were tightened to 6, 10, and 15 Ncm with a torque gauge and ultimate tensile strength values determined. The procedure was replicated using 15 Brånemark System gold screws from another lot tightened to 0, 10, and 20 Ncm. Within each test group, there was no significant difference in the ultimate tensile strength among the three preload torques tested. 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 Ncm.
Conclusions: Altering the preload torque applied to the Brånemark System gold retaining screws does not affect their ultimate tensile strength.