Biomedical subjects

Lisa A Lang

Publications and source records attributed to Lisa A Lang.

5 recordsLinked to original sources

PubMed2003

Finite element analysis to determine implant preload.

STATEMENT OF PROBLEM: The nature of the forces used to clamp implant components together, and how they are generated and sustained, is lacking in the literature. PURPOSE: This study examined the dynamic nature of developing the preload in an implant complex using finite element analysis. METHODS: The implant complex was modeled in accordance with the geometric designs for the Nobel Biocare implant systems. A thread helix design for the abutment screw and implant screw bore was modeled to create the geometric design for these units of the implant systems. Using the software programs HyperWorks and LS3D-Dyna, 2 3-dimensional finite element models of (1) a Branemark System 3.75 x 10-mm titanium Mark III implant, a CeraOne titanium abutment, a Unigrip gold alloy abutment screw, and (2) a Replace Select System 4.30 x 10-mm titanium implant, a Straight Esthetic titanium abutment, and a TorqTite titanium abutment screw were created. Modeling the threads to the machining specifications permitted simulation of screw tightening. The abutment screws were subjected to a tightening torque in increments of 1 Ncm from 0 to 64 Ncm using ABAQUS software. Using these models, the effect of the coefficient of friction on the development of preload amount in the implant complex during and after abutment screw tightening was determined. In the first experiment, the coefficient of friction was set to 0.20 between the titanium bearing surface of the abutments and the implant bearing surfaces, and 0.26 between the gold abutment screw and the titanium implant screw bore. In the second experiment, the coefficient of friction was varied; the titanium implant and titanium abutment bearing surfaces were set to a coefficient of friction of 0.20, whereas the Mark III gold and the Replace Select titanium abutment screws and their respective titanium screw bores in the implants were set to 0.12. The preload amount (N) was determined from the finite element analysis. RESULTS: The stress distribution pattern clearly demonstrated a transfer of preload force from the screw to the implant during tightening. A preload of 75% of the yield strength of the abutment screw was not established using the recommended tightening torques. CONCLUSION: Using finite element analysis, a torque of 32 Ncm applied to the abutment screws in the implant assemblies studied in the presence of a coefficient of friction of 0.26 resulted in a lower than optimum preload for the abutment screws. 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 should be 0.12.

Dental Abutments↗

PubMed2003

Introducing dental students to clinical patient care: the Complete Denture Prosthodontics Transition Clinic.

Using complete denture treatment as an introduction to clinical patient care for dental students, the purposes of the Complete Denture Prosthodontics Transition Clinic at the University of Colorado School of Dentistry are to reduce the time lapse between the preclinical complete denture prosthodontics course and the first denture patient experience, and to encourage development of student self-confidence and skills. In the 2002 spring semester, faculty at the University of Colorado School of Dentistry initiated the Complete Denture Prosthodontics Transition Clinic for DS-II (second-year) dental students, as an introduction to clinical patient care. Each patient was assigned to a team of two dental students. Three Division of Prosthodontics faculty members staffed each clinic session, providing a student-to-faculty ratio of approximately 6.6:1 and a patient-to-faculty ratio of approximately 3.3:1. All DS-II students in the Class of 2004 delivered their first complete dentures no later than 8 months (average, 184 days) after the last day of the preclinical complete denture prosthodontics course. The time from the diagnostic appointment through the denture placement appointment averaged 39 days for patients treated in this program, compared with an average of 98 days or more for previous classes. The program was successful in achieving the goal of reducing the time lapse between the preclinical complete denture prosthodontics course and the first denture patient experience.

Clinical Clerkship↗

PubMed2002

The influence of abutment screw tightening on screw joint configuration.

STATEMENT OF PROBLEM: Limiting abutment-to-implant hexagonal discrepancies and rotational movement of the abutment around the implant to less than 5 degrees would result in a more stable screw joint. However, the exact relationship after abutment screw tightening is unknown, as is the effect of a counter-torque device in limiting abutment movement during screw tightening. PURPOSE: This study examined the orientation of the abutment hexagon to the implant hexagon after tightening of the abutment screw for several abutment systems with and without the use of a counter-torque device. MATERIAL AND METHODS: Thirty conical self-tapping implants (3.75 x 10.0 mm) and 10 wide-platform Brånemark System implants (5.0 x 10.0 mm), along with 10 abutment specimens from the CeraOne, Estheticone, Procera, and AuraAdapt systems, were selected for this investigation. The implants were placed in a holding device prior to tightening of the abutments. When the tightening torque recommended for each abutment system was reached with the use of a torque controller, each implant abutment specimen was removed from the holding device and embedded in a hard resin medium. The specimens were sectioned in a horizontal direction at the level of the hexagons and cleansed of debris prior to examination. The hexagon orientations were assessed as the degree and direction of rotation of the abutment hexagon around the implant hexagon. RESULTS: The range of the maximum degrees of rotation for all 4 abutment groups tightened with or without the counter-torque device was slightly more than 3.53 degrees. The absolute degrees of rotation for all 4 abutment groups were less than 1.50 degrees with or without the use of the counter-torque device. CONCLUSION: The hexagon-to-hexagon orientation measured as rotational fit on all abutment systems was below the 5 degrees suggested as optimal for screw joint stability. The absolute degrees of rotation for all 4 abutment groups were less than 1.50 degrees regardless of whether the counter-torque device was used.

Dental Abutments↗

PubMed2002

Finite element analysis on dental implant-supported prostheses without passive fit.

PURPOSE: The purpose of this study is to use finite element analysis to investigate the effect of misfit prostheses, cantilever prostheses, and various occlusal forces on the stress distribution in the prostheses, implant components, and surrounding bone. MATERIALS AND METHODS: Two 3-dimensional finite element models were constructed: (1) a 2-implant-supported, 2-unit fixed partial denture and (2) a 2-implant-supported, 2-unit fixed partial denture with a distal cantilever. Variations of the standard finite element models were made by placing a 111-microm gap between the gold cylinder on either the mesial or distal implant. The effects of load of 100 N were tested on all models. Subsequently, loads of 50 N, 200 N, and 300 N were evaluated on the cantilever model. RESULTS: When the gap was positioned near to the applied force, the stress in both models increased significantly in the implant components and surrounding bone. The stress increase in each component ranged from 8% to 64% in the non-cantilever models and 43% to 85% in the cantilever models. The greatest stress was found in the distal gold screw. The effect of the gap was clearly shown by the pattern of stress distribution in both models. Additionally, the presence of a cantilever and excessive occlusal force amplified the effect of prosthesis misfit. CONCLUSIONS: Prosthesis misfit influenced the pattern and magnitude of stress distribution in the prosthesis, implant components, and surrounding bone, and the presence of the cantilever or greater occlusal force amplified the effect of misfit.

Bite Force↗

PubMedDate not supplied

Evaluation of the precision of fit between the Procera custom abutment and various implant systems.

PURPOSE: It has been suggested that the CAD/CAM Procera custom abutment may be universally applied with multiple implant systems. An acceptable fit between the internal hexagon of an abutment and the external hexagon of various implant systems, along with true interchangeability of the Procera abutment screw, would support this concept. This study determined the precision of fit of the CAD/CAM-produced Procera abutment onto the external hexagon and bearing surfaces of implants from 6 implant manufacturers and the interchangeability of the Procera abutment screw with these systems. MATERIALS AND METHODS: This investigation consisted of 3 parts: (1) direct measurement of the internal hexagon and bearing surface of each Procera abutment and the external hexagon and the bearing surface of 6 implants from 6 different systems, (2) radiographic examination of 30 Procera abutment-implant junctions following tightening to 32 Ncm to determine the precision of fit between the bearing surfaces and the top of the external hexagon of the implant with the superior surface of the internal hexagon of the abutment, and (3) examination of 3 abutment screws and 3 implants from the various manufacturers for interchangeability based on American National Standards. RESULTS: The mean flat-to-flat external hexagons of the implants measured between 2.67 and 2.69 mm. The Procera abutment's flat-to-flat internal hexagon measured 2.73 mm. The height of the various implant systems' external hexagon ranged from 0.69 to 0.81 mm. The height of the Procera abutment blanks was 0.90 mm. Radiographic examination demonstrated that not all of the manufacturers' screws fit appropriately within the internal screw bore of the Procera abutment. The internal bore of all implant systems studied had a metric thread designation of M2 x 0.4 - 6H. The metric thread designation of all abutment screws examined was M2 x 0.4 - 6g. The greatest variations in the dimensions of the abutment screws measured were seen in the diameter of the screw head, which ranged from 2.12 to 2.69 mm. DISCUSSION: The Procera abutment's internal hexagon fit the external hexagon of all implant systems evaluated. The Procera abutment screw fit the internal screw bore of the implant systems tested. CONCLUSION: The Procera abutment with its screw can be universally applied to the implant systems studied. This fact, plus the CAD/CAM feature of this system, would thus provide a dynamic approach to satisfying the design and spatial needs of implant placements observed clinically.

Computer-Aided Design↗