Browsing by Subject "Implant"

Now showing 1 - 6 of 6
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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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    The Effect of a Screw Access Channel on the Fracture Resistance of Cement-Retained Metal- Ceramic Implant Crowns
    (2018-05) McMillan, Dane
    Purpose: To determine if the presence of a screw-access channel results in a statistically significant difference in fracture strength of molar and premolar cemented metal-ceramic implant crowns. Materials and Methods: Twenty abutment-crown specimens were fabricated and tested in this study. Ten metal-ceramic premolar crowns and 10 metal-ceramic molar crowns were fabricated on their respective custom abutments. Of the 10 specimens in both the premolar and molar groups, five were fabricated as the experimental group with a screw access channel while the other five had their occlusal surface intact and served as the control group. Polytetrafluoroethylene tape was inserted in the screw access channel of the custom abutment for all specimens and the crowns were cemented using resin-modified glass ionomer cement. Following cementation, the screw access channels of the 10 specimens in the two experimental groups were filled with composite resin. Specimens were individually mounted onto a custom fixture with an implant analog and tested on a servohydraulic testing machine at a crosshead speed of 0.5 mm/min at least 24 hours after cementation. Specimens were tested until failure with the highest force at the point of failure being recorded. Results: The mean axial load at failure for the molar crown without a screw access channel was 2032 N while the molar crown with an access channel was 1505 N. Comparatively, the mean axial load at failure for the premolar crown without a screw access channel was 1338 N while the premolar crown with an access channel was 964.5 N . Using a one-way ANOVA, the presence of a screw access channel in molar restorations led to a significant decrease in the axial load needed to fracture the restorations (P<.05); however, the screw access channel did not significantly affect the premolar restorations (P=.12). Molar restorations also required significantly more axial load to fracture relative to premolar restorations in specimens without a screw access channel (P<.01) and those with a screw access channel (P<.05). Conclusions: Metal-ceramic molar crowns, with or without a screw access channel, required a significantly higher axial load to fail than metal-ceramic premolar crowns. The presence of a screw access channel resulted in a significantly lower axial load force required for failure in the molar restorations; however, the difference was not statistically significant in the premolar restorations.
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    Effect of a screw-access channel on the fracture resistance of monolithic zirconia crowns
    (2019-06) Loeb, Mitchell
    Purpose This in-vitro study was designed from a clinical case and investigated the effect of the presence of a screw assess channel, created either during the milling phase or following cementation, on the fracture strength of a monolithic zirconia cement-retained implant-supported fixed prosthesis (ISFP). Material & Methods A definitive cast from a clinical case restoring a mandibular right first molar implant was utilized to fabricate three different styles of monolithic zirconia cement-retained ISFP. Group 1 had no screw-access channel (CR), Group 2 had a screw-access channel milled in the green phase (MA), and Group 3 had a screw-access channel created by hand preparation after cementation (HA). With 3 groups and 5 samples in each group, there were a total of 15 monolithic zirconia crowns fabricated on custom abutments in preparation for testing. The maximum force required for crown fracture was measured using a universal testing machine. Results The mean loads to fracture from highest to lowest were: the milled screw-access channel group (MA), followed by the hand-made screw-access channel group (HA), and lastly by the cement-retained group without a screw-access channel (CR). One-way ANOVA analysis indicated the fracture strength of the MA was statistically significantly different than the cement-retained samples (P<0.05). No statistically significant differences were found between the milled screw-access channel and the access channel created by hand. Conclusion The presence of a screw-access channel, whether milled or prepared by hand, does not negatively affect the fracture strength of a monolithic zirconia ISFP.
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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.
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    Optical and electrophysiological technologies for monitoring cortex-wide brain activity
    (2023-06) Hu, Jia
    Recording cortex-wide brain activity and decoding the brain’s neural computations are required to mediate behaviors. Such an understanding will help formulate better treatments for neurological disorders and improve the quality of life. Technologies for sensing neural activities have been continuously developed over the past century. These technologies have gradually improved to recording from larger brain regions at high temporal and spatial resolution. Miniaturized devices have been developed for performing such imaging in freely-behaving animals. Along these lines, this thesis first aimed to develop a high-accessibility neural activity sensing technology and developed a fully desktop-fabricated flexible Graphene electrocorticography (ECoG) arrays that can be completely built using commonly used laboratory tools without the need for specialized cleanroom facilities. The ECoG arrays could be implanted chronically for up to 180 days allowing high-quality measurement surface field potentials. Building on this work, I developed a 3D-printed transparent ECoG array that simultaneously performs ECoG recordings and mesoscale Calcium (Ca2+) imaging from multiple sites. This device allowed the combination of high temporal resolution electrophysiological measurements with high spatial resolution optical readout of neural activities. In in vivo recording, the 3D-printed ECoG recorded stimuli-evoked and anesthesia drug-induced brain activity in mice and showed strong correlations between the optical and electrical signals with a cross-correlation factor > 75%. In the third aim, I developed a miniaturized micro-camera array microscope (mini-MCAM) for cortex-wide Calcium imaging at single-cell resolution in head-fixed or freely behaving mice. Mini-MCAM is an array of 4 microcameras generating a large computationally stitched FOV of 30-40 mm2 with a central resolution of 9.9 µm. The mini-MCAM recorded spontaneous brain activities at head-fixed and freely behaving states where distinctive neurons’ activities were recorded and identified. In this thesis, all three neural activity sensing technologies share a common goal to improve the existing neural activity sensing technologies and accelerate fundamental neuroscience research, which will bring new insights into the brain.
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    Proximal bone levels of plateau-designed, press fit implants adjacent to a natural teeth and implants.
    (2009-12) Imeri, Alfredo Montes
    STATEMENT OF PROBLEM. Successful implant treatment requires a favorable biological response of living tissues to a foreign material. Even with a favorable pre-surgical evaluation, negative changes such as crestal bone loss can occur after the implant is placed, which can result in an esthetic failure. Controlling crestal bone loss around an implant placed adjacent to a natural tooth or to another implant represents an important challenge for present day prosthodontics. Guidelines on the distance between an implant and a natural tooth or another implant have been published as being an important factor in proximal bone preservation. PURPOSE. The purpose of this study was to retrospectively evaluate pre-treatment and post-treatment proximal bone levels of a single tooth, plateau-designed, press fit implants (Bicon®) utilizing a locking tapered, implant to abutment connection adjacent to a natural teeth and to a plateau design Bicon® implants. The bone levels were evaluated separately for those implants that were closer to a natural tooth or to another implant than the recommended guidelines. Bone levels were also measured on mesial and distal surfaces of all implants as well as the crestal bone levels between 2 implants. The relationship between implant spacing and crestal bone levels was to be determined. MATERIAL AND METHODS. A retrospective cohort study was designed to evaluate pre-treatment and post-treatment proximal bone levels of a single tooth, plateau-designed, press fit implants (Bicon®) utilizing a locking tapered, implant to abutment connection adjacent to a natural teeth and to a plateau design Bicon® implants. The cohort was derived from patients who received 1 or more single tooth, plateau-designed, press fit implants between 1995 and 2005. One hundred and sixty-nine implants with 338 proximal surfaces were included in this study. Of the 338 proximal surfaces, 120 were adjacent to a natural tooth, 192 were adjacent to an implant, and the remaining 26 surfaces were adjacent to an edentulous area. The mean follow-up time was 4 ± 2.3 years. Bone levels and changes in bone levels over time were determined by direct measurement of non-standardized digital periapical radiographs. All measurements were made by using a software measuring tool (DIGORA; Soredex, Tuusula, Finland) at ×3.0 magnification. Student T-tests were used to evaluate the statistical significance between pre-treatment and post-treatment proximal bone levels of natural teeth adjacent to implants. Level of significance was set to alpha 0.05. Descriptive statistics were used to report bone levels on implants adjacent to a natural tooth, another implant, or an edentulous area, as well as the crestal bone levels between 2 implants. RESULTS. There was no significant difference (P=0.25) between pre-treatment proximal bone levels and post-treatment proximal bone levels on a single tooth, plateau-designed, press fit implants (Bicon®) utilizing a locking tapered, implant to abutment connection adjacent to a natural teeth and plateau design Bicon® implants. CONCLUSIONS. Bone levels on implant surfaces adjacent to another implant and bone levels on natural teeth adjacent to implants can be expected to remain unchanged post-treatment when a single tooth, plateau-designed, press fit implant is placed closer than the recommended distance away from the natural tooth or to another implant.