T elusive dream of replacing missing teeth with artificial analogs has been part of dentistry for a thousand years. The coincidental discovery by Dr P-I Branemark and his coworkers of the tenacious affinity between living bone and titanium oxides, termed osseointegration, propelled dentistry into a new age of reconstructive dentistry. Initially, the essential tenets for obtaining osseointegration dictated the atraumatic placement of a titanium screw into viable bone and a prolonged undisturbed, submerged healing period. By definition, this required a 2-stage surgical procedure. To comply, a coupling mechanism for implant placement and the eventual attachment of a transmucosal extension for restoration was explored. The initial coronal design selected was a 0.7-mm-tall external hexagon. At its inception, the design made perfect sense, because it permitted engagement of a torque transfer coupling device (fixture mount) during the surgical placement of the implant into threaded bone and the subsequent second-stage connection of the transmucosal extension that, when used in series, could effectively restore an edentulous arch. As 20 years of osseointegration in clinical practice in North America have transpired, much has changed. The efficacy and predictability of osseointegrated implants are no longer issues.1–7 During the initial years, research focused on refinements in surgical techniques and grafting procedures. Eventually, the emphasis shifted to a variety of mechanical and esthetic challenges that remained problematic and unresolved.8–10 During this period, the envelope of implant utilization dramatically expanded from the original complete edentulous application to fixed partial dentures, single-tooth replacement, maxillofacial and a myriad of other applications, limited only by the ingenuity and skill of the clinician.11–13 The external hexagonal design, ad modum Branemark, originally intended as a coupling and rotational torque transfer mechanism, consequently evolved by necessity into a prosthetic indexing and antirotational mechanism.14,15 The expanded utilization of the hexagonal resulted in a number of significant clinical complications.8–11,16–22 To mitigate these problems, the external hexagonal, its transmucosal connections, and their retaining screws have undergone a number of modifications.23 In 1992, English published an overview of the thenavailable external hexagonal implants, numbering 25 different implants, all having the standard Branemark hex configuration.14 The external hex has since been modified and is now available in heights of 0.7, 0.9, 1.0, and 1.2 mm and with flat-to-flat widths of 2.0, 2.4, 2.7, 3.0, 3.3, and 3.4 mm, depending on the implant platform. The available number of hexagonal implants has more than doubled. The abutment-retaining screw has also been modified with respect to material, shank length, number of threads, diameter, length, thread design, and torque application (unpublished data, 1998).23 Entirely new secondand third-generation interface coupling geometries have also been introduced into the implant milieu to overcome intrinsic hexagonal deficiencies.24–28 Concurrent with the evolution of the coupling geometry was the introduction of a variety of new implant body shapes, diameters, thread patterns, and surface topography.26,27,29–36 Today, the clinician is overwhelmed with more than 90 root-form implants to select from in a variety of diameters, lengths, surfaces, platforms, interfaces, and body designs. Virtually every implant company manufactures a hex top, a proprietary interface, or both; “narrow,” “standard,” and “wide” diameter implant bodies; machined, textured, and hydroxyapatite (HA) and titanium plasma-spray (TPS) surface implants; and a variety of lengths and body shapes (Table 1). In the wide-diameter arena alone, there are 25 different offerings, 15 external hexagonal, and 10 other interfaces available in a number of configurations. 1Adjunct Professor of Prosthodontics, Graduate Prosthodontics, Indiana University, Indianapolis, Indiana; Assistant Research Scientist, Department of Restorative Dentistry, University of California at San Francisco; and Private Practice, Roseville, California.

/pdf/implants-and-components-entering-the-new-millennium-3eig9xnt5y.pdf

Implants and components: entering the new millennium.

https://www.fml.t.u-tokyo.ac.jp/~izumi/Bolt/WG/fem_bolted_joints_modelling_Korea.pdf

Finite element analysis and modeling of structure with bolted joints

Three-dimensional finite element analysis of threaded fastener loosening due to dynamic shear load

The primary stability of dental implants has been investigated before, but a study of the influence of implant shape, size and surface morphology (machined, acid etched or anodized), surgical technique (press-fit or undersized) and substrate (natural or simulated bone) on the primary stability of dental implants has not been reported. The present work intends to fill this gap. In this work, six different dental implants were inserted into and removed from synthetic and natural bone while measuring the torque. A total of 255 dental implants with three shapes, four sizes and three surface topographies were inserted into pig rib, PTFE and polyurethane. The implant sites were prepared using straight and tapered drills. The primary stability was estimated from the maximum insertion torque. Comparisons between samples were based on the maximum insertion torque (MIT), the maximum removal torque (MRT) and the torque ratio (TR=MRT/MIT). The insertion torque into pig ribs showed larger dispersion. All parameters (shape, size and surface morphology of the implant, surgical technique and substrate type) were found to have a significant influence on primary stability. The insertion of a tapered implant requires a higher torque than the insertion of a straight implant. Surface treatments improve the primary stability. The influence of the surgical technique is smaller than that of implant size and shape. The highest insertion torque was that of anodized tapered implants inserted into undersized sites. Finally, the primary stability of dental implants is highly dependent on implant design, surgical technique and substrate type.

Influence of implant shape, surface morphology, surgical technique and bone quality on the primary stability of dental implants

To date, there is no evidence that internal anti-rotation configurations are better than external ones. The purpose of this study was to evaluate the effect of eccentric cyclic loading on abutment screw loosening in internal and external hexagon implants with either of these two screw materials, titanium (Ti) alloy versus gold alloy. The reverse torque value of the abutment screw was measured before (initial preload) and after loading (post-loading). The prepared assemblies were divided into four groups (A to D). Groups A and B used internal hex implants with gold alloy and Ti alloy abutment screws respectively. Groups C and D used external hex implants with gold alloy and Ti alloy abutment screws respectively. In all the groups, post-loading preload was significantly (p<0.05) higher than initial preload. Further, two-way ANOVA indicated that the implant-abutment connection did not have an effect, but the abutment screw material did. In particular, Ti abutment screws were less likely to come loose.

/pdf/influence-of-lateral-oblique-cyclic-loading-on-abutment-5dm04atmnp.pdf

Influence of lateral-oblique cyclic loading on abutment screw loosening of internal and external hexagon implants.

Although the title of this book includes the word “introduction”, the treatment of the subject is extensive and complete. The material goes well beyond the coverage of bolted joint design received in a typical undergraduate machine design course. The easy-to-read text begins with the fundamentals of bolt strength, deformation, and material selection and proceeds to cover the topics of preload, torque, and stretch control. The emphasis is on practical considerations for the efficient design of joints, including cost, ease of assembly, inspection, and disassembly. This second, revised edition has expanded the coverage of corrosion, fatigue, gaskets, and ultrasonic measurement of bolt strain. Also included are discussions of the failure modes and mechanisms of bolted joints. Case histories from industry are presented throughout the text to illustrate key points. Many up-to-date references are presented at the end of each chapter to allow the reader to pursue individual topics further, if desired. The text contains several appendices with useful tables and formulas for quick reference. The author has broad experience in the subject area from many years as a consultant to the power generation and nuclear industry, active participation on society working groups such as ASME and PVRC, as well as the presentation of numerous seminars on the topic. This book would serve as a valuable desk reference for engineers concerned with the design and performance of bolted joints.

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Papers

An Introduction to the Design and Behavior of Bolted Joints