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.     

The RPH Clasp Assembly: A Simple Alternative to Traditional Designs

One of the popular designs for the distal extension partial removable dental prosthesis is the RPI clasp assembly. A modification of the RPI clasp assembly is introduced. It incorporates a mesial rest (R), proximal plate (P), and a horizontal retentive arm (H—RPH). This clasp assembly provides benefits of the RPI clasp and can be used in clinical situations where the RPI clasp is contraindicated.     

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.     

Psammomatoid juvenile ossifying fibroma: an analysis of 2 cases affecting the mandible with review of the literature

Juvenile ossifying fibroma (JOF) is a rare fibro-osseous neoplasm, defined as a variant of the ossifying fibroma that arises within the craniofacial bones. Two subgroups, juvenile psammomatoid ossifying fibroma (PsJOF) and juvenile trabecular ossifying fibroma, have been delineated by their histology. PsJOF occurs predominantly in the sinonasal and orbital bones. This work reports on 2 cases of extensive PsJOF in the body of the right mandible as well as reviews the literature regarding the radiographic and histologic features, treatment, and prognosis of PsJOF of the jaws.     

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)     

Effects of Local Melatonin Application on Implant Osseointegration

Purpose: The aim of this study was to assess the effect of local melatonin administration on bone osseointegration around implants in rabbit tibiae. Material and Methods: Ten female, 6‐month‐old New Zealand rabbits were randomly divided into two groups: the experimental group, where five rabbits were treated with local application of melatonin (3 mg) to implant sites when placed into the rabbit tibia, and the control group, those who where without additive materials. Four weeks later, animals were sacrificed; tibiae were dissected from soft tissues and fixed in buffered formaldehyde, and then included in methacrylate. Histological sections were performed to be studied under light microscopy and analyzed morphometrically to evaluate the amount of bone to implant contact (BIC), trabecular area density, and cortical area density. One‐way analysis of variance test was used for statistical evaluation. p < .05 was considered to be significant. Results: Histological evaluation showed more trabecular reaction in the melatonin group. Morphometrical analysis showed a statistically significant increase in trabecular BIC in the melatonin group when compared with the control group (24.61% ± 2.87 vs 13.62% ± 1.44; p < .01). Cortical BIC was decreased in the melatonin group, without statistical significance (71.08 ± 3.63 vs 76.28 ± 2.57; p = 0.31). Trabecular area density was increased significantly in the melatonin group (8.68 ± 1.61 vs 4.02 ± 0.36; p < .05). Cortical area density was decreased significantly in the melatonin group (91.31 ± 1.6 vs 95.7 ± 0.5; p < .05). Conclusion: Within the limitation of this animal study, local melatonin application at the time of implant placement might induce more trabecular bone at implant contact and higher trabecular area density.     

Maxillary Sinus Augmentation Using Prehydrated Corticocancellous Porcine Bone: Hystomorphometric Evaluation after 6 Months

Background: Insufficient alveolar bone height often prevents the placement of standard dental implants in the posterior part of edentulous maxilla. In order to increase adequately the vertical dimension of the reabsorbed alveolar process, a sinus lift procedure is often necessary. The aim of this study was to evaluate histologic results of a prehydrated corticocancellous porcine bone used in maxillary sinus augmentation. Methods: Patients (age 18–70 years) with a residual bone height requiring a maxillary sinus augmentation procedure to place dental implants were eligible for this study. All patients were treated with the same surgical technique consisting of sinus floor augmentation via a lateral approach. The space obtained by elevation of the mucosa wall was grafted with prehydrated and collagenated corticocancellous porcine bone. Biopsies were harvested 6 months after the augmentation procedures. Results: Twenty‐four patients were enrolled. The mean percentage of new formed bone was 43.9 ± 18.6% (range 7.5–100%), whereas the mean percentage of residual graft material was 14.2 ± 13.6% (range 0–41.9%). The new bone/residual graft material ratio in the maxillary sinuses was 3.1. The mean soft tissues percentage was 41.8 ± 22.7% (range 0–92.5%). Conclusion: The present study suggested that porcine bone showed excellent osteoconductive properties and could be used successfully for sinus augmentation. Moreover, the porcine bone showed a high percentage of reabsorption after 6 months; this might be because of the presence of collagen and the porosity of the graft material.     

Cone Beam Computed Tomographic Measurement of Maxillary Central Incisors to Determine Prevalence of Facial Alveolar Bone Width ≥2 mm

Background: The initial thickness of maxillary bone has significant impact on the responding level of facial bone and soft tissue after extraction and immediate implant placement. A prevailing notion is that following implant placement in fresh extraction sites, at least 2 mm of facial bone is needed to prevent soft tissue recession, fenestration, and dehiscence. Purpose: The purpose of this study was to use cone beam computed tomography (CBCT) to measure horizontal width of facial alveolar bone overlying healthy maxillary central incisors and to determine prevalence of bone thickness ≥2 mm. Materials and Methods: Tomographic data from 101 randomly selected patients were evaluated by two independent observers. Assessments were made of facial bone width at levels 1.0 to 10.0 mm apical to the bone crest. Results: Healthy maxillary central incisors (n = 202) were measured from 101 patient scans. The percent of teeth with facial bone ≥2 mm at levels 1, 2, 3, 4, and 5 mm from the bone crest was 0, 1.5, 2.0, 3.0, and 2.5%, respectively. Overall mean thickness of the bone was 1.05 mm for right and left central incisors combined. The range of individual measurements for all levels was 0 to 5.1 mm. The occurrence of ≥2 mm thickness bone measurements increased with increasing depth. However, mean widths observed at levels 6 to 10 mm from the crest ranged only 1.0 to 1.3 mm because of apparent fenestration occurrence (0 mm bone) in approximately 12% of teeth. Overall, no significant differences in bone thickness were found between ethnic, gender, age, or scan groups. Conclusions: Using CBCT, occurrences of ≥2 mm maxillary facial alveolar bone were found on no more than 3% of root surfaces 1.0 to 5.0 mm apical to the bone crest in this sample of maxillary central incisors. The study evidenced prevalence of a thin facial alveolar bone (<2 mm) that may contribute to risk of facial bone fenestration, dehiscence, and soft tissue recession after immediate implant therapy.     

Long‐Term Follow‐Up of CeraOne™ Single‐Implant Restorations: An 18‐Year Follow‐Up Study Based on a Prospective Patient Cohort

Background: Knowledge on long‐term clinical performance of more than 5 years on the single‐implant CeraOne? (Nobel Biocare AB, Gothenburg, Sweden) concept is limited. Purpose: The aim of this study is to report the long‐term clinical performance of the first CeraOne single‐implant restorations, installed 17 to 19 years ago. Materials and Methods: The group comprised 57 patients provided with 65 CeraOne single‐tooth restorations. Sixty‐two all‐ceramic and three metal‐ceramic crowns were cemented between 1989 and 1991. Patients were followed up clinically and with intraoral radiographs at placement, after 1, 5, and between 17 and 19 years after placement. Results: Data were available for altogether 48 patients, followed up on an average time of 18 years. Excluding deceased patients (n = 2) and failed implant patients (n = 2), only five patients were lost to follow‐up (8.8%). Two implants failed, resulting in an 18‐year implant cumulative success rate (CSR) of 96.8%, and altogether eight original single‐crown restorations were replaced (CSR 83.8%). The most common reason for crown replacement was infra‐position of the implant crown (n = 3). Many of the remaining original crowns showed various signs of implant crown infraposition at the termination of the study. In general, the soft tissue at the restorations was assessed to be healthy and comparable with the gingiva at the adjacent natural teeth. Bone levels were on an average stable with only few patients exhibiting bone loss of more than 2 mm during 18 years in function. Conclusion: This long‐term follow‐up study of single‐implant restorations shows encouraging results with few implant failures and minimal bone loss over an 18‐year period. Original single‐crown restorations were replaced more frequently, because of, for example, implant crown infraposition and veneer fractures. The CeraOne concept proved to be a highly predictable and safe prosthodontic treatment.