The Effects of Loading on the Preload and Dimensions of the Abutment Screw for a 3-Unit Cantilever-Fixed Prosthesis Design

Authors

Setia, Gaurav DDS, Yousef, Hoda DMD, MS, Ehrenberg, David DDS, MS, Luke, Allyn BA, BSCE, MSCE, Weiner, Saul DDS

Abstract

Objective: The purpose of this study was to use an in vitro model system to compare the effects on the screw torque and screw dimensions within 2 commercially available implant systems from occlusal loading on a cantilevered-fixed partial denture. Materials and Methods: Cantilevered implant-supported 3-unit prostheses with 2 premolar abutments and 1 premolar pontic (7.3 mm in length) were made on resin casts containing 2 implant analogs for 2 implant systems: BioLok Silhouette Tapered Implant System (Birmingham, AL) and Zimmer Tapered Screw-Vent Implant System (Carlsbad, CA) with 10 samples in each group. Each sample was loaded with either of 2 protocols: (1) a load of 50 N on the cantilevered pontic unit and (2) a loading of 150 N on all 3 units. The outcome measures were (1) changes in residual torque of the abutment screws and (2) changes in screw dimension. Results: The BioLok Silhouette Tapered Implant group demonstrated slight but statistically significant torque loss 18.8% to 28.5% in both abutment screws for both protocols, P <= 0.05, without any changes in screw dimension. In the Zimmer Tapered Screw-Vent Implant group, there was a significant elongation of the abutment screws and a markedly significant 44.4%, (P <= 0.01) loss in torque in the mesial screw and a 28.5%, (P <= 0.05) loss in torque in the distal screw when the cantilever alone was loaded. Conclusions: Differences in screw design influence the maintenance of preload and distortion of the shank. The influence of the interface design, namely an internal hex of 1 mm versus an external hex did not influence the preload. Cantilevered prostheses can cause loss of torque and dimensional changes in abutment screws.

Link to Article

http://dx.doi.org/10.1097/ID.0b013e31829c227a

Matrix generation within a macroporous non-degradable implant for osteochondral defects is not enhanced with partial...

Title

Matrix generation within a macroporous non-degradable implant for osteochondral defects is not enhanced with partial enzymatic digestion of the surrounding tissue: evaluation in an in vivo rabbit model

Authors

Aaron J. Krych, Florian Wanivenhaus, Kenneth W. Ng, Stephen Doty, Russell F. Warren, Suzanne A. Maher

Abstract

Articular cartilage defects are a significant source of pain, have limited ability to heal, and can lead to the development of osteoarthritis. However, a surgical solution is not available. To tackle this clinical problem, non-degradable implants capable of carrying mechanical load immediately after implantation and for the duration of implantation, while integrating with the host tissue, may be viable option. But integration between articular cartilage and non-degradable implants is not well studied. Our objective was to assess the in vivo performance of a novel macroporous, nondegradable, polyvinyl alcohol construct. We hypothesized that matrix generation within the implant would be enhanced with partial digestion of the edges of articular cartilage. Our hypothesis was tested by randomizing an osteochondral defect created in the trochlea of 14 New Zealand white rabbits to treatment with: (i) collagenase or (ii) saline, prior to insertion of the implant. At 1 and 3-month post-operatively, the gross morphology and histologic appearance of the implants and the surrounding tissue were assessed. At 3 months, the mechanical properties of the implant were also quantified. Overall, the hydrogel implants performed favorably; at all time-points and in all groups the implants remained well fixed, did not cause inflammation or synovitis, and did not cause extensive damage to the opposing articular cartilage. Regardless of treatment with saline or collagenase, at 1 month post-operatively implants from both groups had a contiguous interface with adjacent cartilage and were populated with chondrocyte-like cells. At 3 months fibrous encapsulation of all implants was evident, there was no difference between area of aggrecan staining in the collagenase versus saline groups, and implant modulus was similar in both groups; leading us to reject our hypothesis. In summary, a porous PVA osteochondral implant remained well fixed in a short term in vivo osteochondral defect model; however, matrix generation within the implant was not enhanced with partial digestion of adjacent articular cartilage.

Link to Article

http://dx.doi.org/10.1007/s10856-013-4999-x

Effect of cell-seeded hydroxyapatite scaffolds on rabbit radius bone regeneration

Authors

C. R. Rathbone, T. Guda, B. M. Singleton, D. S. Oh, M. R. Appleford, J. L. Ong, J. C. Wenke

Abstract

Highly porous hydroxyapatite (HA) scaffolds were developed as bone graft substitutes using a template coating process, characterized, and seeded with bone marrow-derived mesenchymal stem cells (BMSCs). To test the hypothesis that cell-seeded HA scaffolds improve bone regeneration, HA scaffolds without cell seeding (HA-empty), HA scaffolds with 1.5 × 104 BMSCs (HA-low), and HA scaffolds with 1.5 × 106 BMSCs (HA-high) were implanted in a 10-mm rabbit radius segmental defect model for 4 and 8 weeks. Three different fluorochromes were administered at 2, 4, and 6 weeks after implantation to identify differences in temporal bone growth patterns. It was observed from fluorescence histomorphometry analyses that an increased rate of bone infiltration occurred from 0 to 2 weeks (p < 0.05) of implantation for the HA-high group (2.9 ± 0.5 mm) as compared with HA-empty (1.8 ± 0.8 mm) and HA-low (1.3 ± 0.2 mm) groups. No significant differences in bone formation within the scaffold or callus formation was observed between all groups after 4 weeks, with a significant increase in bone regenerated for all groups from 4 to 8 weeks (28.4% across groups). Although there was no difference in bone formation within scaffolds, callus formation was significantly higher in HA-empty scaffolds (100.9 ± 14.1 mm3) when compared with HA-low (57.8 ± 7.3 mm3; p ≤ 0.003) and HA-high (69.2 ± 10.4 mm3; p ≤ 0.02) after 8 weeks. These data highlight the need for a better understanding of the parameters critical to the success of cell-seeded HA scaffolds for bone regeneration.

Link to Article

http://dx.doi.org/10.1002/jbm.a.34834

Porous Tantalum Coatings Prepared by Vacuum Plasma Spraying Enhance BMSCs Osteogenic Differentiation and Bone Regeneration In Vitro and In Vivo

Authors

Ze Tang, Youtao Xie, Fei Yang, Yan Huang, Chuandong Wang, Kerong Dai, Xuebin Zheng, Xiaoling Zhang

Abstract

Tantalum, as a potential metallic implant biomaterial, is attracting more and more attention because of its excellent anticorrosion and biocompatibility. However, its significantly high elastic modulus and large mechanical incompatibility with bone tissue make it unsuitable for load-bearing implants. In this study, porous tantalum coatings were first successfully fabricated on titanium substrates by vacuum plasma spraying (VPS), which would exert the excellent biocompatibility of tantalum and alleviate the elastic modulus of tantalum for bone tissue. We evaluated cytocompatibility and osteogenesis activity of the porous tantalum coatings using human bone marrow stromal cells (hBMSCs) and its ability to repair rabbit femur bone defects. The morphology and actin cytoskeletons of hBMSCs were observed via electron microscopy and confocal, and the cell viability, proliferation and osteogenic differentiation potential of hBMSCs were examined quantitatively by PrestoBlue assay, Ki67 immunofluorescence assay, real-time PCR technology and ALP staining. For in vivo detection, the repaired femur were evaluated by histomorphology and double fluorescence labeling 3 months postoperation. Porous tantalum coating surfaces promoted hBMSCs adhesion, proliferation, osteogenesis activity and had better osseointegration and faster new bone formation rate than titanium coating control. Our observation suggested that the porous tantalum coatings had good biocompatibility and could enhance osseoinductivity in vitro and promote new bone formation in vivo. The porous tantalum coatings prepared by VPS is a promising strategy for bone regeneration.

Link to Article

http://dx.doi.org/10.1371/journal.pone.0066263

The Effect of Implant Shape and Screw Pitch on Microdamage in Mandibular Bone

Authors

Chendi Xu BDS, MS, Zhong Wei BS, Nizhou Liu BDS, MS, Fei Sun BDS, MS, Hui Chen BDS, Tingting Lin BDS, MS, Baowei Zhang DDS, Tingting Tang MD, PhD, Eryi Lu DDS, PhD

Abstract

The aim of this study was to investigate the effect of implant shape and screw pitch on microdamage in bone during insertion of dental implants. Thirty custom-made implants (length, 10 mm; diameters, 4.1 mm; cylindrical, tapered, and taper-cylindrical shapes; screw pitches, 1.25 and 0.8 mm; classified as 1.25C, 0.8C, 1.25T, 0.8T, 1.25TC, 0.8TC) were placed with a surgical device in the mandibles of eight goats. Two implant sites were prepared in the edentulous area on each side of the mandible. Implants were placed in a randomized order. Immediately after placement of the implants, the bone blocks with the implants were collected, bulk stained with basic fuchsin, embedded in methyl methacrylate, and sectioned. Histomorphometric quantification of the microcrack length (Cr.Le, μm); microcrack surface density (Cr.Le/B.Ar, μm/mm2), and damaged bone area fraction (DB.Ar/B.Ar, %) were measured. The Cr.Le, Cr.Le/B.Ar, and DB.Ar/B.Ar values of 0.8TC group were 80.96 ± 17.55, 478.75 ± 51.85, and 4.40 ± 0.36, respectively. All these parameters of microdamage induced by 0.8TC were significantly lower than those induced by other five types of implants (p < .05). Taper-cylindrical implants with 0.8 mm screw pitch caused the least microdamage to the bone in comparison with the other five types of implants during placement of implants.

Link to Article

http://dx.doi.org/10.1111/cid.12100

Bone Formation Under Sinus Using Venous Coagulum

Authors

Kathleen A Beaudry, DMD, MS, Nicolaas C Geurs, DDS, MS, Jack E Lemons, PhD, Michael S Reddy, DMD, DMSc

Abstract

Introduction: Insufficient bone height is a common obstacle to placing dental implants in the posterior maxilla. Sinus grafts have been shown to be a highly predictable way to increase bone height in the posterior maxilla. This case series illustrates a technique using venous coagulum and simultaneous implant placement under the elevated sinus. Bone formation is demonstrated clinically, radiographically, and histologically. To our knowledge, this is the first report of histomorphometric results and micro computed tomography using this technique. Case Presentation: A total of 5 sinus elevations with simultaneous placement of 2 dental implants were performed with venous blood coagulum as the sole filling biomaterial. At the time of uncovery, following 8-9 months healing, biopsies were harvested from the lateral wall of the maxilla. This article illustrates bone formation under 5 elevated sinuses, with simultaneous placement of dental implants, using venous coagulum as the sole filling material. Results show significant gains in bone height adjacent to the implant. MicroCT shows well-structured trabecular bone. Histomorphometry of biopsies show 38-74% vital bone. Conclusions: This case series illustrates that bone grafting materials in the subsinus cavity are not required for successful placement of implants. Utilization of ones own blood as filling material removes any objections to grafting including religious, ethical, or fear of disease transmission. Venous coagulum is a simple, inexpensive biomaterial and its systematic use during a sinus lift may be a relevant option, ultimately leading to increased access to implant treatment options for patients.

Link to Article

http://dx.doi.org/10.1902/cap.2013.120120