Immediate Rehabilitation of the Extremely Atrophic Mandible with Fixed Full‐Prosthesis Supported by Four Implants

Purpose: To prospectively assess the outcome of immediate rehabilitation of extremely atrophic mandibles by a full‐arch fixed bridge anchored to four implants. Material and Methods: Twenty patients with edentulous mandibles were included in the study. Each patient received a full‐arch fixed bridge supported by two axial and two distal tilted implants. Prosthetic loading was applied within 48 hours of surgery. Patients were scheduled for follow‐up every 6 months up to 2 years and annually until 5 years. Radiographic evaluation of marginal bone level change was performed at 1 year. Results: All patients were followed for a minimum of 1 year (range 20–48 months, mean 30.1 months). No failures were recorded to date. The 1‐year implant survival rate and prosthesis success rate were 100%. Marginal bone loss around axial and tilted implants was similar at 12‐month evaluation, being, respectively, 0.6 ± 0.3 (standard deviation) mm and 0.7 ± 0.4 mm. High patient's level of satisfaction was recorded for function, phonetics, and aesthetics. Conclusion: This technique could be considered a viable treatment option for the rehabilitation of the atrophic mandible.     

Influence of Tapered and External Hexagon Connections on Bone Stresses Around Tilted Dental Implants: Three‐Dimensional Finite Element Method With Statistical Analysis

Background: The purpose of this study is to analyze the tension distribution on bone tissue around implants with different angulations (0°, 17°, and 30°) and connections (external hexagon and tapered) through the use of three‐dimensional finite element and statistical analyses. Methods: Twelve different configurations of three‐dimensional finite element models, including three inclinations of the implants (0°, 17°, and 30°), two connections (an external hexagon and a tapered), and two load applications (axial and oblique), were simulated. The maximum principal stress values for cortical bone were measured at the mesial, distal, buccal, and lingual regions around the implant for each analyzed situation, totaling 48 groups. Loads of 200 and 100 N were applied at the occlusal surface in the axial and oblique directions, respectively. Maximum principal stress values were measured at the bone crest and statistically analyzed using analysis of variance. Stress patterns in the bone tissue around the implant were analyzed qualitatively. Results: The results demonstrated that under the oblique loading process, the external hexagon connection showed significantly higher stress concentrations in the bone tissue (P <0.05) compared with the tapered connection. Moreover, the buccal and mesial regions of the cortical bone concentrated significantly higher stress (P <0.005) to the external hexagon implant type. Under the oblique loading direction, the increased external hexagon implant angulation induced a significantly higher stress concentration (P = 0.045). Conclusions: The study results show that: 1) the oblique load was more damaging to bone tissue, mainly when associated with external hexagon implants; and 2) there was a higher stress concentration on the buccal region in comparison to all other regions under oblique load.     

Biomechanical Evaluation of Subcrestal Placement of Dental Implants: In Vitro and Numerical Analyses

Background: This study investigates the effect of depth of insertion in subcrestal cortical bone (SB) and thickness of connected cortical bone (CB) for a subcrestal implant placement on bone stress and strain using statistical analyses combined with experimental strain‐gauge tests and numerical finite element (FE) simulations. Methods: Three experimental, artificial jawbone models and 72 FE models were prepared for evaluation of bone strain and stress around various equicrestal and subcrestal implants. For in vitro tests, rosette strain gauges were used with a data acquisition system to measure bone strain on the bucco‐lingual side. The maximum von Mises stresses in the bone were statistically analyzed by analysis of variance for FE models. Results: The experimental bone strains reduced significantly (22% to 49%) as the thickness of CB increased. FE analyses indicated that the suggested CB thickness for efficiently minimizing bone stress was 0.5 to 2.5 mm. The results for the depth of SB were not absolute because obvious stress reductions only presented at a certain range of depth (0.6 to 1.2 mm). Conclusion: Within the limitations of this study, increasing the thickness of CB and maintaining the depth of SB within a limited range can provide the benefit of decreasing the stress and strain in surrounding bone for subcrestally placed implants.     

Attachment‐Retained Gingival Prosthesis for Implant‐Supported Fixed Dental Prosthesis in the Maxilla: A Clinical Report

The rehabilitation of edentulous maxillae is a complex procedure due to the involvement of esthetic and functional requirements. A trial maxillary denture can be used to identify the need for adequate upper lip support when replacing removable complete dentures by implant‐fixed dental prostheses. This clinical report describes the outcome of the rehabilitation of an edentulous atrophic maxilla with unfavorable maxillomandibular relationship and deficient upper lip support. A trial denture was fabricated and used to diagnose the need for a prosthesis capable of restoring the upper lip support. The reduced upper lip support was also confirmed by a lateral cephalogram. The patient was rehabilitated by an implant‐fixed dental prosthesis associated with an attachment‐retained gingival prosthesis. The case presented shows that when loss of upper lip support is detected and the patient does not wish to undergo further surgical reconstruction procedure, the retention of a gingival prosthesis using a ball attachment is a satisfactory treatment option.     

Cortical Bone Stress Distribution in Mandibles with Different Configurations Restored with Prefabricated Bar‐Prosthesis Protocol: A Three‐Dimensional Finite‐Element Analysis

Purpose: To evaluate stress distribution in different horizontal mandibular arch formats restored by protocol‐type prostheses using three‐dimensional finite element analysis (3D‐FEA). Materials and Methods: A representative model (M) of a completely edentulous mandible restored with a prefabricated bar using four interforaminal implants was created using SolidWorks 2010 software (Inovart, São Paulo, Brazil) and analyzed by Ansys Workbench 10.0 (Swanson Analysis Inc., Houston, PA) to obtain the stress fields. Three mandibular arch sizes were considered for analysis, regular (M), small (MS), and large (ML). Three unilateral posterior loads (L) (150 N) were used: perpendicular to the prefabricated bar (L1); 30° oblique in a buccolingual direction (L2); 30° oblique in a lingual‐buccal direction (L3). The maximum and minimum principal stresses (σ_max, σ_min), the equivalent von Mises (σ_vM), and the maximum principal strain (σ_max) were obtained for type I (M.I) and type II (M.II) cortical bones. Results: Tensile stress was more evident than compression stress in type I and II bone; however, type II bone showed lower stress values. The L2 condition showed highest values for all parameters (σ_vM, σ_max, σ_min, ?_max). The σ_vM was highest for the large and small mandibular arches. Conclusion: The large arch model had a higher influence on σ_max values than did the other formats, mainly for type I bone. Vertical and buccolingual loads showed considerable influence on both σ_max and σ_min stresses.     

Relevant Anatomic and Biomechanical Studies for Implant Possibilities on the Atrophic Maxilla: Critical Appraisal and Literature Review

Purpose: The purpose of this review was to highlight anatomic and biomechanical aspects of atrophic maxillae for implant possibilities. Materials and Methods: A MEDLINE electronic search of the years 1966 to 2009 was conducted with the keywords “atrophic,”“resorbed,”“edentulous,” and “maxilla.” Results: Twenty papers presented the following findings: (1) previous use of a removable prosthesis is a risk factor for resorption, with flabby tissues related to the severity of resorption; (2) implants in the reconstructed maxilla (≤5 mm) and supporting overdentures had a higher risk for bone loss based on the worse periimplant soft‐tissue health observed; (3) bleeding on probing was found with pocket depths ≥5 mm in half of the zygomatic implants; (4) prevalence of bone septa is higher in atrophic maxillae, and changes on nasopalatine canal can reduce up to 44.4% of the full length of buccal bone plates; (5) female patients have less medullar bone quantity and connectivity than male patients; (6) transectioning of nutrient vessels is easier and accelerates resorption; (7) stress does not concentrate on maxillary sinus base cortical bone contiguous to trabecular bone; (8) splinted implants receive nine times less load than nonsplinted implants even under oblique loading; (9) implant stability quotient (ISQ) values for implants ranged between 60 and 65; (10) in vivo force transfer to implants is similar between fixed prostheses and overdentures; (11) inclined implants generate better biomechanical responses; (12) masticatory efficiency and bite forces improve in maxillectomized patients who receive obturators with milled bar attachments. Conclusion: Sound implant‐supported choices for an atrophic maxilla must be made with a thorough understanding of its anatomic and biomechanical factors.     

Comparison of stress distribution between complete denture and implant-retained overdenture-2D FEA

The aim of this study was to compare the stress distribution induced by posterior functional loads on conventional complete dentures and implant-retained overdentures with different attachment systems using a two-dimentional Finite Element Analysis (FEA-2D). Three models representative of edentulous mandible were constructed on AutoCAD software; Group A (control), a model of edentulous mandible supporting a complete denture; Group B, a model of edentulous mandible supporting an overdenture over two splinted implants connected with the bar-clip system; Group C, a model of edentulous mandible supporting an overdenture over two unsplinted implants with the O-ring system. Evaluation was conducted on Ansys software, with a vertical force of 100 N applied on the mandibular left first molar. When the stress was evaluated in supporting tissues, groups B (51.0 MPa) and C (52.6 MPa) demonstrated higher stress values than group A (10.1 MPa). Within the limits of this study, it may be concluded that the use of an attachment system increased stress values; furthermore, the use of splinted implants associated with the bar-clip attachment system favoured a lower stress distribution over the supporting tissue than the unsplinted implants with an O-ring abutment to retain the mandibular overdenture.     

A Comparison Study of the Osseointegration of Zirconia and Titanium Dental Implants. A Biomechanical Evaluation in the Maxilla of Pigs

Objectives: The purpose of the present study was to investigate the osseointegration of microstructured zirconia implants in comparison with sandblasted and acid‐etched (SLA) titanium implants in a biomechanical study. Materials: Zirconia implants (4.1 mm in diameter, 10 mm in length) were produced using a new low pressure injection molding technique. After that the implants were acid‐etched with hydrofluoric acid. Standard Ti‐SLA implants of the exact same shape served as controls. Six months after extraction of incisors 2 and 3, 16 adult pigs received a total of 64 implants in the maxillae. After 4, 8, and 12 weeks the animals were sacrificed, and 59 implants could be analyzed to removal torque (RTQ) testing. Results: The mean RTQ values for zirconia implants were 42.4 Ncm at 4 weeks, 69.6 Ncm at 8 weeks, and 69.3 Ncm at 12 weeks of healing, whereas RTQ values for the Ti‐SLA implants were 42.1 Ncm, 75.0 Ncm, and 73.1 Ncm at corresponding time intervals. There is no statistical difference in RTQ values between Ti‐SLA and zirconia implants at 8 weeks. Conclusions: Within the limits of the present study it was concluded that acid‐etching of zirconia implants enhances bone apposition resulting in RTQ values which were equivalent to that of Ti‐SLA.     

计算机辅助下颌骨个体化功能性修复的三维有限元分析

目的:探讨下颌骨缺损个体化功能性修复三维有限元模型的初步建立和生物力学分析,为下颌骨缺损的个体化功能性修复提供生物力学指导。方法: 在CT扫描获取下颌骨断层解剖信息的基础上进行三维重建,重建模型实体化后模拟颌骨缺损,设计个体化带种植体三维钛网修复体加以修复,然后进行三维有限元建模和应力分析。结果:所建下颌骨缺损个体化功能性修复的三维有限元模型几何相似性好,力学分析证实这种个体化功能性三维网状修复体早期能对骨缺损断端起到良好的固定作用,后期骨应力遮挡影响不大。结论:采用CT扫描获取下颌骨原始解剖信息的基础上,利用计算机可以建立下颌骨个体化功能性修复的三维有限元模型,利用此模型进行生物力学分析可以指导下颌骨缺损的个体化功能性修复。     

One‐Year Results of a Clinical and Radiological Prospective Multicenter Study on NEOSS® Dental Implants

Background: NEOSS® (Neoss Ltd., Harrogate, UK) dental implant system was introduced on the clinical arena in 2003. It is important that novel implant systems are systematically evaluated in a multicenter setting. Purpose: The aim of this study was to follow a large number of consecutively treated patients, with NEOSS dental implant system, both clinically and radiographically. The current report constitutes the 1‐year data of a planned 5‐year study. Materials and Methods: The study included a total of 177 patients treated with 590 NEOSS implants at 13 clinics in Sweden. The material was composed of 72 males and 105 females treated for single, partial, and total edentulism. Clinical, radiographic, and subjective evaluations were performed. Results: Out of 590 implants, 13 early failures have been reported, corresponding to a 1‐year cumulative survival rate (CSR) of 97.8%. Evaluation of function and esthetics at the 1‐year visit resulted in 100% success for function and 98% success for the esthetic outcome. The mean marginal bone loss was 0.6 mm (SD 1.1) after 1 year in clinical function. No adverse effects of the NEOSS dental implants were reported, and complications were few and similar to those reported for implant treatment in general. Conclusion: The CSR in the present study was 97.8%. No adverse effects of the NEOSS implants were reported, and complications during the study period were few and similar to those reported to for other well‐documented implants system. Based on the present data, we conclude that NEOSS dental implant is a safe and predictable implant system. However, the high number of dropouts in the radiological evaluation must be considered when interpreting the data.     

倾斜角度对种植体骨界面生物力学影响的三维有限元分析

目的 :分析不同倾斜种植对种植体界面应力、应变及位移分布状况的影响。方法 :在第一磨牙区分别垂直及向舌侧倾斜10°、20°、30°植入种植体 ,建立下颌骨三维有限元模型。模拟咀嚼肌力加载 ,分析在正中咬合情况下种植体骨界面应力、应变及位移分布情况。结果 :随着倾斜角度的增大 ,种植体骨界面应力、应变及位移均增加。倾斜30°种植时 ,种植体骨界面应力显著性增大(P<0.01)。结论 :种植体倾斜角度应小于30°。     

Effect of framework material and vertical misfit on stress distribution in implant-supported partial prosthesis under load application: 3-D finite element analysis

Abstract

Objective. This study evaluated the influence of framework material and vertical misfit on stress created in an implant-supported partial prosthesis under load application. Materials and methods. The posterior part of a severely reabsorbed jaw with a fixed partial prosthesis above two osseointegrated titanium implants at the place of the second premolar and second molar was modeled using SolidWorks 2010 software. Finite element models were obtained by importing the solid model into an ANSYS Workbench 11 simulation. The models were divided into 15 groups according to their prosthetic framework material (type IV gold alloy, silver-palladium alloy, commercially pure titanium, cobalt-chromium alloy or zirconia) and vertical misfit level (10 µm, 50 µm and 100 µm). After settlement of the prosthesis with the closure of the misfit, simultaneous loads of 110 N vertical and 15 N horizontal were applied on the occlusal and lingual faces of each tooth, respectively. The data was evaluated using Maximum Principal Stress (framework, porcelain veneer and bone tissue) and a von Mises Stress (retention screw) provided by the software. Results. As a result, stiffer frameworks presented higher stress concentrations; however, these frameworks led to lower stresses in the porcelain veneer, the retention screw (faced to 10 µm and 50 µm of the misfit) and the peri-implant bone tissues. Conclusion. The increase in the vertical misfit resulted in stress values increasing in all of the prosthetic structures and peri-implant bone tissues. The framework material and vertical misfit level presented a relevant influence on the stresses for all of the structures evaluated.