Regular and platform switching: bone stress analysis varying implant type

Purpose: This study aimed to evaluate stress distribution on peri‐implant bone simulating the influence of platform switching in external and internal hexagon implants using three‐dimensional finite element analysis. Materials and Methods: Four mathematical models of a central incisor supported by an implant were created: External Regular model (ER) with 5.0 mm × 11.5 mm external hexagon implant and 5.0 mm abutment (0% abutment shifting), Internal Regular model (IR) with 4.5 mm × 11.5 mm internal hexagon implant and 4.5 mm abutment (0% abutment shifting), External Switching model (ES) with 5.0 mm × 11.5 mm external hexagon implant and 4.1 mm abutment (18% abutment shifting), and Internal Switching model (IS) with 4.5 mm × 11.5 mm internal hexagon implant and 3.8 mm abutment (15% abutment shifting). The models were created by SolidWorks software. The numerical analysis was performed using ANSYS Workbench. Oblique forces (100 N) were applied to the palatal surface of the central incisor. The maximum (σ_max) and minimum (σ_min) principal stress, equivalent von Mises stress (σ_vM), and maximum principal elastic strain (ε_max) values were evaluated for the cortical and trabecular bone. Results: For cortical bone, the highest stress values (σ_max and σ_vm) (MPa) were observed in IR (87.4 and 82.3), followed by IS (83.3 and 72.4), ER (82 and 65.1), and ES (56.7 and 51.6). For ε_max, IR showed the highest stress (5.46e‐003), followed by IS (5.23e‐003), ER (5.22e‐003), and ES (3.67e‐003). For the trabecular bone, the highest stress values (σ_max) (MPa) were observed in ER (12.5), followed by IS (12), ES (11.9), and IR (4.95). For σ_vM, the highest stress values (MPa) were observed in IS (9.65), followed by ER (9.3), ES (8.61), and IR (5.62). For ε_max, ER showed the highest stress (5.5e‐003), followed by ES (5.43e‐003), IS (3.75e‐003), and IR (3.15e‐003). Conclusion: The influence of platform switching was more evident for cortical bone than for trabecular bone, mainly for the external hexagon implants. In addition, the external hexagon implants showed less stress concentration in the regular and switching platforms in comparison to the internal hexagon implants.     

A Novel Framework to Eliminate the Effects of Casting Distortion when Fabricating a Fixed,Detachable Screw‐Retained Prosthesis

The ideal fixed, detachable framework sits passively on the implants and does not introduce any stress. Several techniques in the literature compensate for an ill‐fitting framework. These techniques require extra visits, chairtime, and laboratory time and only mitigate the stress; the stress is not eliminated. A framework is presented here that eliminates the stress transmitted to the implants by encircling the abutment cylinders and not directly incorporating them into the framework. Furthermore, the framework mitigates the stress from the polymerization distortion of acrylic when processing the acrylic onto the prosthesis.     

A Case Series: Herpes Simplex Virus as an Occupational Hazard

ABSTRACT

Statement of the Problem: Herpes labialis infections are common and present a serious risk to the dental team. Purpose of the Study: The purpose is to make dentists aware of the risks involved with treatment of patients with active herpes labialis. In addition, evidence‐based risk‐management strategies are presented. Methods and Materials: The incidence and natural history of herpes simplex virus type 1 (HSV‐1) are reviewed. Four previously unreported case histories are presented to illustrate the impact common sequelae of HSV‐1 can have on the dental team. The differences between HSV‐1 and the blood‐borne diseases which are the focus of universal precautions are discussed. In particular, the highly contagious, highly transmissible nature of HSV‐1 and its transmission through aerosols are highlighted. Finally, the need to include protection against aerosols in the profession's understanding of universal precautions is noted. Results: The authors suggest limiting the treatment of patients with active lesions to urgent care only, and treating active HSV‐1 lesions to reduce time of healing. For four common clinical situations involving HSV‐1 infections, evidence‐based methods for protecting the dental team and the patient from cross‐contamination are also presented. Conclusion: While it is clear that the treatment of patients with active herpes labialis lesions increases risk of cross‐infection, there are good protocols for controlling this risk.

CLINICAL SIGNIFICANCE

By bringing common vectors of cross‐infection to light and providing evidence‐based protocols for preventing them, this article provides practitioners with positive steps that can be taken for controlling the risk of spreading herpes infections to the dental team. (J Esthet Restor Dent 24:61–67, 2012)     

Self‐Adhesive Resin Cements—Part II

This is the second part of a two‐part piece on self‐adhesive resin cements; Part I was presented in the previous issue of the Journal. Here in Part II, the specific topics concerning self‐adhesive cements are clinical performance, post‐cementation sensitivity, and cementation of endodontic posts.