Browsing by Subject "Abutment"

Now showing 1 - 3 of 3
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    CAD/CAM lithium disilicate crown performance cemented extraorally and delivered as a screw-retained implant restoration
    (2015-03) Lassle, Michael Jon
    Purpose: To determine if a novel technique combining the attributes of a cement-retained implant restoration fabricated extraorally and delivered to the patient as a screw-retained implant restoration has the necessary strength to provide a clinically acceptable and predicable restoration.Materials and Methods: Thirty specimens were fabricated and tested in this novel implant restoration technique, in which stock abutment was scanned using a bench top laboratory scanner and 30 lithium disilicate full contour crowns were designed and milled. In the first experimental group, the occlusal access channel was prepared in a pre-sintered crown using new high-speed diamond burs in a high-speed handpiece with ample irrigation as to keep the specimen cool. The access channel was prepared by the same operator for every specimen and the diameter was recorded. The specimens were allowed to air dry for 48 hours prior to being glazed, fired and finished. In the second experimental group, the screw access channel was prepared after the crown was fired and finished. In the control group, no screw access channel was prepared. Each finished crown intaglio surface was silinated per manufacturer specifications and luted with self-adhesive resin cement to its corresponding stock abutment. The cement was allowed to cure for at least 24 hours before testing. Each specimen was individually mounted in a custom-fabricated testing fixture and tested to failure on a servo-hydraulic testing system for static and dynamic tests. Each specimen was vertically loaded at a dynamic rate of 0.100 mm/min until failure and the highest force reached at the point of failure was recorded. Statistical analysis was performed by consultants from the Biostatistical Design and Analysis Center. Results: A total of thirty CAD/CAM lithium disilicate crowns were fabricated and tested to failure. The first experimental group had a mean failure of 990.64N. The second experimental group had a mean failure of 1167.65, and the control group had a mean failure of 188.68N. A two-sample t-test was used to compare the load among the three groups and because there are 3 comparisons, Bonferroni method is applied to adjust p-values for multiple comparisons. The results show that experimental group #1, experimental group #2 and the control group are statistically significantly different from each other. The diameter of the screw access channel did not make a statistically significant difference, most likely because the difference among the diameter wasn't that great between samples.Conclusions: The null hypothesis stated there will be no difference in the axial force required to fracture a lithium disilicate crown with and without a screw access channel prepared. The results of this study support rejecting the null hypothesis and accepting the alternative hypothesis. The preparation of a screw access channel in a lithium disilicate crown has statistical significance and reduces the axial load capacity from a crown without occlusal access. The diameter of the screw access channel did not make a statistically significant difference, most likely because the difference among the diameter wasn't that great between samples.
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    A Comparison Of Morse Taper And Sloped Shoulder Abutment Geometries Using Torque Angle Analysis
    (2024) Clark , Zane
    Abstract Background: Full arch fixed implant prostheses continue to become a popular treatment option for dentists when rehabilitating the completely edentulous patient as they can help to significantly restore function, esthetics and comfort paired with the well-documented predictability, success and longevity of dental implants. The connection of the prosthesis to the implant platform has also received much attention in the literature, however, many of these papers only report torque and de-torque values. Generally, torque values recommended by the manufacture are between 65-75% of that abutment screws yield potential, or in other words, the point at which the abutment screw will fracture. But a key concept to understand is that the implant-abutment connection maintains its stability through a mechanical force known as preload, which is a clamping force created from the elastic recovery of the abutment screw. But herein lies a well-documented issue that up to 90% of the torquing force applied to the abutment screw is lost to friction and other factors leaving only 10% available for conversion to preload. Although it has been reported that abutment geometry can aid in the stability of the connection, preload is the predominant force holding the implant, abutment and prosthesis together. If the preload can be maximized within the limits of the abutment screws yield potential, then a stronger implant abutment connection will be created. In a pilot study by Chow et al., they investigated whether abutment geometry contributes to preload of the abutment screw. Among their conclusions was a statistically significant difference between classical morse tapered engaging abutments and non-engaging abutments with the non-engaging abutments having higher preload values. This was because for the non-engaging abutments, much of the torque was lost to settling of the abutment into the morse taper. With the numerous dental implant companies a restorative dentist can choose from, it begs the question: are all implant-abutment connections created equal? More specifically, are some implant brands better suited for optimizing the implant-abutment connection and preload achieved in the abutment screw. Therefore, the purpose of this study is to investigate the effect of abutment geometry on preload with two widely used implant bodies and multiunit abutments. The hope of this pilot study is to report the data and utilize it for a larger future study that compares preload data between multiple implant brands. Purpose: This study aimed to evaluate preload on sloped shoulder and morse taper abutment geometries using torque angle signature analysis Materials and Methods: Three sloped shoulder (Straumann, BLX) implants were embedded into custom dies using Type V dental gypsum (Die-Keen Green). Two abutment designs were selected for this study, one having a morse taper geometry and the other with a morse taper and sloped shoulder component. Three morse tapered internal connection abutments and three sloped shoulder abutments were used in this study. An a priori power analysis was completed to determine sample size. Therefore, two experimental groups (n=3) were created. A custom fabricated device was milled out of aluminum to rigidly fixate both the imbedded implant and torque meter. A horizontal arm was also attached to the torque meter to allow for a consistent and controlled torque force to be applied. A torque driver was attached to the torque angle meter (HGTA-AMK Digital Torque Gauge with Angle Encoder, IMADA, PCB, Load &Torque, Inc.). Each abutment was torque to into the imbedded implants to 35 Ncm and a torque angle signature obtained. Upon reaching 35 Ncm, the torque meter was zeroed and samples were de-torqued producing a releasing curve. Analysis of the torque angle signatures allowed for extraction of insertion slope as well as insertion and releasing degree of rotation (torque angle). From these values, preload values were calculated using the preload formula outlined by Hagiwara and Ohashi (1994). Statistical analysis was conducted using non-paired student t-test. A p-value of 0.05 was used. Results: Morse Taper Abutments (blue) show an elongated rundown, alignment and elastic zone when compared to the sloped shoulder abutments. A mean insertion slope of 0.71 was calculated for sloped shoulder abutments (n=3, st. dev.= 0.102) with a 95% C.I. of ±0.115. A mean slope of 0.3 was calculated for morse taper abutments (n=3, st. dev.= 0.048) with a 95% C.I. of ±0.246. Non-paired student t-test produced a value of p=0.0039961. Analysis of the data shows a maximum mean insertion angle of 41.40° for sloped shoulder abutments (n=3, st. dev.= 3.176) and a 95% C.I. of ±3.59. Mean insertion angle for morse tapered abutments were 108.67° (n=3, st. dev. = 16.88) with a 95% C.I. of ±19.1. Non-paired student t-test produced a value of p=0.0105222. Similarly, upon releasing, releasing angles showed a maximum mean release angle of 31.6° for sloped shoulder abutments (n=3, st. dev. = 4.757) with a 95% C.I. of ±5.38°. Mean release angle for morse tapered abutments was 21.8° (n=3, st. dev. = 1.892) with a 95% C.I. of ± 2.14°. Non-paired student t-test produced a value of p=0.0222863. The mean preload for sloped shoulder abutments was 805.06N (n=3, st. dev. = 120.812) with a 95% C.I. of ±136.7. Mean preload for morse tapered abutments was 554.48N (n=3, st. dev. = 48.074) with a 95% C.I. of ±54.39. Non-paired student t-test produced a value of p=0.0.0222289. Conclusions: Higher preload levels were found in the sloped shoulder abutment than in the morse taper abutment. Longer rundown and alignment zones were found in the morse taper abutment than in the sloped shoulder abutment. The insertion slopes were less for the morse tapered abutment than for the non-engaging abutment. Additionally, insertion angles were greater and release angles shorter in morse tapered abutments. The lack of a positive stop and greater friction between components seen in the morse tapered abutment caused the torque limit to be reached before greater clamping force could be achieved. Although more studies are needed to take friction into account, this study demonstrates that the geometry of the implant-abutment connection does influence preload. With respect to multiple implant splinted prostheses, these factors can greatly impact the clinical outcome, longevity of the prosthesis, its various components, and underlying implants.
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    Evaluation of implant restoration retention on various custom abutment materials and surfaces
    (2018-05) McMillan, Kale
    Purpose: Clinical use of cement-retained implant crowns requires selecting the appropriate abutment materials, surface characteristics, and cement type, based on finding the right balance between the desired level of retention form and the potential need for retrievability for each patient case. The purpose of this study was to evaluate the forces needed to vertically displace a cement-retained implant crown, using a provisional cement and five different combinations of abutment materials and surface characteristics. Material & Methods: A clinical master cast with an implant analog in the maxillary right central incisor site was fabricated and facilitated the design and manufacturing of 25 implant custom abutments planned for cement-retained restorations. Although all 25 implant custom abutments were designed to be identical in contour, each group of five abutments was fabricated from different materials or had different surface characteristics. The five different implant abutment groups were titanium smooth surface (Ts), titanium with retentive grooves (Tr), titanium with a nitride coating and smooth surface (Gs), titanium with a nitride coating and retentive grooves (Gr), and zirconia (Z). A total of 25 lithium disilicate crowns were fabricated and each crown was cemented to its corresponding abutment with non-eugenol temporary resin cement. With the use of a universal testing machine, the maximum tensile strength needed to dislodge the crown from the abutment was recorded and evaluated. Results: The mean tensile force needed to decement the lithium disilicate crowns within each implant abutment group was 31.58 N for titanium smooth surface (Ts), 29.29 N for titanium with retentive grooves (Tr), 32.90 N for titanium with nitride coating with smooth surface (Gs), 28.75 N for the titanium with nitride coating with retentive grooves (Gr), and 139.49 N for zirconia (Z). The titanium abutment groups did not differ significantly (P=.92); however, the zirconia abutment group required a statistically significant higher tensile force to decement the lithium disilicate crowns cemented with non-eugenol temporary resin cement compared to the titanium abutment groups (P<.05) Conclusion: Surface characteristics of the titanium implant abutments, including retentive grooves and nitride coating, did not increase the tensile force required to decement the crowns compared to a smooth titanium surface. The fabrication of zirconia abutments has the potential to generate discrepancies in the size and shape of the zirconia abutments, especially compared to the milled titanium abutments. The possible discrepencies in the zirconia abutments, including larger surface areas and need for nonstandardized crowns to fit the zirconia abutments may contribute more significantly to the increased retention compared to the interaction of the abutment material and provisional cement.