A biomechanical effect of wide implant placement and offset placement of three implants in the posterior partially edentulous region

Finite Element Analysis of Dental Implants with Zirconia Crown Restorations: Conventional Cement-Retained vs. Cementless Screw-Retained

The present study was designed to compare the stress distributions in two restoration types of implants and the surrounding bone. The first restoration type was a conventional cement-retained zirconia crown, and the second was a novel cementless screw-retained zirconia crown with a base abutment. A three-dimensional finite element method was used to model the implants, restorations, and supporting bone. A comparative study of the two implants was performed under two masticatory loads: a vertical load of 100 N and a 30-degree oblique load of 100 N. Under both loading conditions, the maximum von Mises stress and strain values in the implant and supporting bone were higher in the conventional cement-retained restoration model than in the cementless screw-retained model. In terms of stress distribution, the cementless screw-retained zirconia crown with base abutment may be considered a superior restoration option compared to the conventional cement-retained zirconia crown.

Correlation between abutment angulation and off-axial stresses on biomechanical behavior of titanium and zirconium implants in the anterior maxilla: A three-dimensional finite element analysis study

Aim

The aim of the present study was to evaluate the stress distribution around the titanium and zirconium implant with different abutment angulations in the anterior maxilla to off-axial load.

Setting and Design

In vitro - Comparative study.

Materials and Methods

Two models of titanium and zirconium implants (4 mm × 13 mm) and abutment with at 0°, 15°, 25° angulations were modeled to replace missing right central incisor using three-dimensional finite element analysis. A bite force of 178 N was applied on the lingual fossa of crowns at an angle of 120° off-axial to the long axis of implant.

Statistical Analysis Used

Nil.

Results

Von Misses stresses observed are as follows: (1) at the implant-bone interface Ti 0 (8.31 MPa), Zr 0 (8.57 MPa), Ti 15 (83.59 MPa), Zr 15 (98.07 MPa), Ti 25 (197.8 MPa), and Zr 25 (265.77 MPa); (2) at the implant-abutment interface Ti 0 (5.90 MPa), Zr 0 (6.45 MPa), Ti 15 (19.13 MPa), Zr 15 (19.32 MPa), Ti 25 (38.65 MPa), and Zr 25 (38.26 MPa); and (3) within superstructure Ti 0 (3.11 MPa), Zr 0 (5.02 MPa), Ti 15 (6.17 MPa), Zr 15 (5.02 MPa), Ti 25 (8.15 MPa), and Zr 25 (6.131 Mpa).

Conclusion

Stress behavior of titanium and zirconium implant with tested abutment angulation at implant-abutment interface and within the superstructure was similar, except at implant-bone interface.

Stress distribution pattern of screw-retained restorations with segmented vs. non-segmented abutments: A finite element analysis

Background. Screw-retained restorations are favored in some clinical situations such as limited inter-occlusal spaces. This study was designed to compare stresses developed in the peri-implant bone in two different types of screw-retained restorations (segmented vs. non-segmented abutment) using a finite element model. Methods. An implant, 4.1 mm in diameter and 10 mm in length, was placed in the first molar site of a mandibular model with 1 mm of cortical bone on the buccal and lingual sides. Segmented and non-segmented screw abutments with their crowns were placed on the simulated implant in each model. After loading (100 N, axial and 45° non-axial), von Mises stress was recorded using ANSYS software, version 12.0.1. Results. The maximum stresses in the non-segmented abutment screw were less than those of segmented abutment (87 vs. 100, and 375 vs. 430 MPa under axial and non-axial loading, respectively). The maximum stresses in the peri-implant bone for the model with segmented abutment were less than those of non-segmented ones (21 vs. 24 MPa, and 31 vs. 126 MPa under vertical and angular loading, respectively). In addition, the micro-strain of peri-implant bone for the segmented abutment restoration was less than that of non-segmented abutment. Conclusion. Under axial and non-axial loadings, non-segmented abutment showed less stress concentration in the screw, while there was less stress and strain in the peri-implant bone in the segmented abutment.

Influence of platform diameter in the reliability and failure mode of extra-short dental implants

PURPOSE

To evaluate the influence of implant diameter in the reliability and failure mode of extra-short dental implants.

MATERIALS AND METHODS

Sixty-three extra-short implants (5mm-length) were allocated into three groups according to platform diameter: Ø4.0-mm, Ø5.0-mm, and Ø6.0-mm (21 per group). Identical abutments were torqued to the implants and standardized crowns cemented. Three samples of each group were subjected to single-load to failure (SLF) to allow the design of the step-stress profiles, and the remaining 18 were subjected to step-stress accelerated life-testing (SSALT) in water. The use level probability Weibull curves, and the reliability (probability of survival) for a mission of 100,000 cycles at 100MPa, 200MPa, and 300MPa were calculated. Failed samples were characterized in scanning electron microscopy for fractographic inspection.

RESULTS

No significant difference was observed for reliability regarding implant diameter for all loading missions. At 100MPa load, all groups showed reliability higher than 99%. A significant decreased reliability was observed for all groups when 200 and 300MPa missions were simulated, regardless of implant diameter. At 300MPa load, the reliability was 0%, 0%, and 5.24%, for Ø4.0mm, Ø5.0mm, and Ø6.0mm, respectively. The mean beta (β) values were lower than 0.55 indicating that failures were most likely influenced by materials strength, rather than damage accumulation. The Ø6.0mm implant showed significantly higher characteristic stress (η = 1,100.91MPa) than Ø4.0mm (1,030.25MPa) and Ø5.0mm implant (η = 1,012.97MPa). Weibull modulus for Ø6.0-mm implant was m = 7.41, m = 14.65 for Ø4.0mm, and m = 11.64 for Ø5.0mm. The chief failure mode was abutment fracture in all groups.

CONCLUSIONS

The implant diameter did not influence the reliability and failure mode of 5mm extra-short implants.

Influence of Abutment Surface Treatments on Screw Loosening of Morse Taper Implants

PURPOSE

To evaluate the effect of blasting and bonding on abutment surface to prevent screw loosening in Morse taper connections.

MATERIAL AND METHODS

Twenty-eight Morse taper connection implants were divided into 4 groups: no treatment (G1), blasting (G2), bonding (G3), and blasting + bonding (G4). In groups G2 and G4, the abutments were blasted with aluminum oxide granules; in groups G3 and G4, the conical abutment region was covered with a thin layer of bond thread lock agent. In all implants, the abutment-implant joint was tightened at a torque of 35 Ncm. The specimens were submitted to the mechanical cycling, under an oblique load for 1.0 × 10 cycles. The torque was measured with a digital torque meter. Data were analyzed by the t test, one-way analysis of variance, and Tukey tests (95%).

RESULTS

The loosening strength was significantly higher in group G4 (35.83 ± 3.02 Ncm). There was no significant difference among groups G1 (25.86 ± 1.96 Ncm), G2 (25.86 ± 3.29 Ncm), and G3 (26.14 ± 2.12 Ncm).

CONCLUSION

The association of blasting and bonding on abutment surface can be used to prevent screw loosening in Morse taper implants.

Retrospective clinical study of ultrawide implants more than 6 mm in diameter

Background

The prognosis of wide implants tends to be controversial. While wider implants were initially expected to result in a larger osseointegration area and have higher levels of primary stability, they were reported to have a relatively high rate of failure. The clinical outcome of ultrawide implants of more than 6 mm in diameter was evaluated through a retrospective study.

Methods

The investigation was conducted on patients who had received ultrawide implant (≥6 mm diameter) placements in Seoul National University Bundang Hospital from January 2008 to December 2013. Complications were investigated during the maintenance period, and marginal bone loss was measured using periapical radiography. Primary stability immediately after the implant placement and second stability after second surgery or during impression were measured using Osstell^® Mentor (Osstell, Sweden) as an implant stability quotient (ISQ).

Results

Fifty-eight implants were placed in 53 patients (30 male, 23 female), and they were observed for an average of 50.06 ± 23.49 months. The average ISQ value increased from 71.22 ± 10.26 to 77.48 ± 8.98 (P < 0.005). The primary and secondary stability shows significantly higher at the mandible than at the maxilla (P < 0.001). However, mean survival rate shows 98.28 %. Average marginal bone loss of 0.018 and 0.045 mm were measured at 12 and 24 months after the loading and 0.14 mm at final follow-up date (mean 46.25 months), respectively. Also in this study, the bone loss amount was noticeably small compared to regular implants reported in previous studies.

Conclusions

The excellent clinical outcome of ultrawide implants was confirmed. It was determined that an ultrawide implant can be used as an alternative when the bone quality in the posterior teeth is relatively low or when a previous implant has failed.

Biomechanical effects of offset placement of dental implants in the edentulous posterior mandible

Background

Proper implant placement is very important for long-term implant stability. Recently, numerous biomechanical studies have been conducted to clarify the relationship between implant placement and peri-implant stress. The placement of multiple implants in the edentulous posterior mandible has been studied by geometric analysis, three-dimensional finite element analysis (FEA), model experimentation, etc. Offset placement is a technique that reduces peri-implant load. However, few studies have used multiple analyses to clarify the value of the offset placement under identical conditions.

The present study aimed to clarify the biomechanical effects of offset placement on the peri-implant bone in edentulous posterior mandibles by comparative investigation using FEA and model experimentation with strain gauges.

Methods

Three implants were embedded in an artificial mandible in the parts corresponding to the first premolar, the second premolar, and the first molar. A titanium superstructure was mounted to prepare models (experimental models). Three load points (buccal, central, and lingual) were established on the part of the superstructure corresponding to the first molar. Three types of experimental models, each with a different implant placement, were prepared. In one model, the implants were placed in a straight line; in the other two, the implants in the parts corresponding to the second premolar and the first molar were offset each by a 1-mm increment to the buccal or lingual side. Four strain gauges were applied to the peri-implant bone corresponding to the first molar.

The experimental models were imaged by micro-computed tomography (CT), and FEA models were constructed from the CT data. A vertical load of 100 N was applied on the three load points in the experimental models and in the FEA models. The extent of compressed displacement and the strain in the peri-implant bone were compared between the experimental models and the FEA models.

Results

Both experimental and FEA models suffered the least compressed displacement during central loading in all placements. The greatest stress and compressive strain was on the load side in all types of placements.

Conclusions

Offset placement may not necessarily be more biomechanically effective than straight placement in edentulous posterior mandibles.

Survival analysis of wide dental implant: systematic review and meta-analysis

OBJECTIVE

Wide-diameter implants are frequently placed in molar sites to obtain appropriate restoration profiles, to rescue implants that lack stability, and to engage bone in extraction sites. However, studies of wide-diameter implant placement have provided conflicting evidence regarding clinical outcomes. This systematic review aims to analyze survival rates of wide-diameter implants (platform diameter ≥5 mm) and assess clinical variables potentially affecting failure rates.

MATERIAL AND METHODS

Electronic search was conducted using MEDLINE (PubMed), Cochrane Central Register of Controlled Trials (CENTRAL) and EMBASE from January 1980 to October 2014. Publication screening, data extraction, and quality assessment were performed. Failure rate per implant-year was analyzed using mix-effects Poisson regression model to obtain summary estimates of the 5-year survival rate. Relative risk (RR) was calculated to evaluate the association of different clinical variables with estimated failure rates.

RESULTS

Eleven retrospective studies and eight prospective studies having at least 1-year follow-up period were included in the analysis. The estimated 5-year survival rate was 92.67% (95% confidence interval: [79.60, 97.50]) in the retrospective studies and 97.76% (Confidence interval: [93.25, 99.27]) in the prospective studies. Implant surface and implant diameter were significantly associated with the failure events in the retrospective studies.

CONCLUSIONS

Placement of wide-diameter implants demonstrated a promising survival rate during 5-year follow-up. Further controlled trials with the control group and longer follow-up period are needed to provide the direct evidence comparing survival rates of wide implants with survival rates of narrower implants.

A biomechanical investigation of mandibular molar implants: reproducibility and validity of a finite element analysis model

Background

Three-dimensional finite element analysis (FEA) is effective in analyzing stress distributions around dental implants. However, FEA of living tissue involves many conditions, and the structures and behaviors are complex; thus, it is difficult to ensure the validity of the results. To verify reproducibility and validity, we embedded implants in experimental models and constructed FEA models; implant displacements were compared under various loading conditions.

Methods

Implants were embedded in the molar regions of artificial mandibles to fabricate three experimental models. A titanium superstructure was fabricated and three loading points (buccal, central, and lingual) were placed on a first molar. A vertical load of 100 N was applied to each loading point and implant displacements were measured. Next, the experimental models were scanned on micro-computed tomography (CT) and three-dimensional FEA software was used to construct two model types. A model where a contact condition was assumed for the implant and artificial mandible (a contact model) was constructed, as was a model where a fixation condition was assumed (a fixation model). The FEA models were analyzed under similar conditions as the experimental models; implant displacements under loading conditions were compared between the experimental and FEA models. Reproducibility of the models was assessed using the coefficient of variation (CV), and validity was assessed using a correlation coefficient.

Results

The CV of implant displacement was 5% to 10% in the experimental and FEA models under loading conditions. Absolute values of implant displacement under loading were smaller in FEA models than the experimental model, but the displacement tendency at each loading site was similar. The correlation coefficient between the experimental and contact models for implant displacement under loading was 0.925 (p < 0.01). The CVs of equivalent stress values in the FEA models were 0.52% to 45.99%.

Conclusions

Three-dimensional FEA models were reflective of experimental model displacements and produced highly valid results. Three-dimensional FEA is effective for investigating the behavioral tendencies of implants under loading conditions. However, the validity of the absolute values was low and the reproducibility of the equivalent stresses was inferior; thus, the results should be interpreted with caution.

Management of a fractured, nonremovable implant: a clinical report with a 12-month follow-up

Implant failures could be due to biological or mechanical factors, which also include fracture of the fixture. The present report presents a case of a single fractured implant placed in the left mandibular molar region. Since the residual portion of the fixture was perfectly osseointegrated with no signs of peri-implantitis, and in direct contact with the roof of the inferior alveolar nerve canal, it was decided to treat the patient with a short implant positioned on top of the fractured, and not removing the fractured implant. Clinical and radiographical follow-up was performed for 12 months after loading. Periimplant soft tissues healing and implant osseointegration were achieved 6 months after implant placement; at the end of the follow-up a periimplant bone remodeling of 0.3 mm was observed. In conclusion, short implants could be taken into consideration as a treatment option in cases of nonremovable implants and sufficient residual bone height.

Noninvasive method for retrieval of broken dental implant abutment screw

Dental implants made of titanium for replacement of missing teeth are widely used because of ease of technical procedure and high success rate, but are not free of complications and may fail. Fracturing of the prosthetic screw continues to be a problem in restorative practice and great challenge to remove the fractured screw conservatively. This case report describes and demonstrates the technique of using an ultrasonic scaler in the removal of the fracture screw fragment as a noninvasive method without damaging the hex of implants.

Effect of Offset Implant Placement on the Stress Distribution Around a Dental Implant: A Three-Dimensional Finite Element Analysis

There are some anatomical restrictions in which implants are not possible to be inserted in their conventional configuration. Offset placement of implants in relation to the prosthetic unit could be a treatment solution. The aim of this study was to evaluate the effect of the offset placement of implant-supported prosthesis on the stress distribution around a dental implant using 3D finite element analysis. 3D finite element models of implant placement in the position of a mandibular molar with 4 configurations (0, 0.5, 1, 1.5 mm offset) were created in order to investigate resultant stress/strain distribution. A vertical load of 100 N was applied on the center of the crown of the models. The least stress in peri-implant tissue was found in in-line configuration (0 mm offset). Stress concentration in the peri-implant tissue increased by increasing the amount of offset placement. Maximum stress concentration in all models was detected at the neck of the implant. It can be concluded that the offset placement of a single dental implant does not offer biomechanical advantages regarding reducing stress concentration over the in-line implant configuration. It is suggested that the amount of offset should be as minimum as possible.

Biomechanical rationale for six splinted implants in bilateral canine, premolar, and molar regions in an edentulous maxilla

PURPOSE

To determine the influence of number and location of implants loaded on the stress to the bone in an edentulous maxilla using a three-dimensional finite element model (3D FEM).

MATERIAL AND METHODS

Computed tomographic data with the bone density of a dry skull were used to construct a 3D FEM. Titanium implants were simulated in the configuration as 14 unsplinted implants (US14), 14 splinted implants (S14), 6 splinted implants (canine, premolar, and molar regions, S6), 4 splinted implants (S4), and 6 anterior implants (incisors and canines, A6). Distributed loads of 200 N were applied on the occlusal table of the superstructures.

RESULTS

The S6 model was subjected to a similar amount of stress and deformation to the US14 and the S14. The S4 and A6 models were subjected to approximately three times of stress under the vertical load, and approximately five times of stress under the inclined load, respectively, compared with the S6 model.

CONCLUSIONS

The 3D FEM analyses suggest that the six splinted implants configuration has a similar stress and deformation pattern as compared with naturally positioned splinted 14 implants in the edentulous maxilla.

Analysis of the biomechanical feasibility of a wide implant in moderately atrophic maxillary sinus region with finite element method

OBJECTIVE

The aim of this study was to evaluate the biomechanical feasibility of a short wide implant in a moderately atrophic posterior maxilla.

STUDY DESIGN

A normal maxillary posterior section with a standard screwed implant (model 1) and a moderately atrophic maxillary posterior section with a short wide screwed implant (model 2) were created. The maximum von Mises stresses in maxilla and the maximum displacements in the implant-abutment complex were evaluated.

RESULTS

When the implant diameter exceeded 5.0 mm, the most stable and minimal value of stress in maxilla and displacement in the implant-abutment complex could be achieved in model 2, which were almost all lower than those in model 1.

CONCLUSIONS

The effect of a short wide implant in the moderately atrophic maxillary sinus region is favorable and similar to that of the standard implant in the normal sinus region. From the biomechanical point of view, implant diameter exceeding 5.0 mm is a relatively optimal selection in a moderately atrophic maxilla.

Fractures related to occlusal overload with single posterior implants: a clinical report

This clinical report describes 2 patient situations in which fractures related to occlusal overload occurred with a single posterior implants. The initial clinical presentation of both patients appeared to be screw loosening, but upon further examination, implant and abutment fractures were identified. Several factors are described that have been implicated in the etiology of implant fractures, including occlusal overload, implant location, inadequate fit of the prosthesis, design of the prosthesis, progressive bone loss, metal fatigue, implant diameter, manufacturing defects, and galvanic activity. This article describes the management of implant and abutment fractures and discusses possible mechanisms of failure for the patient situations presented. Careful treatment planning and execution of implant therapy is necessary to minimize the risk of implant and component fractures.

[New estimation method for displacement characteristic of teeth with occlusal force records]

OBJECTIVES

To establish adequate occlusion for prostheses, evaluation of degree of displacement of teeth and implant is essential. However, it cannot be attained without complex equipment, which limits clinical application. To develop a new estimation method for displacement characteristic of teeth and implant by both occlusal force of individual teeth and existing data on degree of displacement, the relationship between increase of total occlusal force and occlusal force of individual teeth was evaluated.

METHODS

Ten male subjects (mean age: 28.5, [range: 26-31] years) with clinically normal healthy dentition were selected. Electromyograms at maximum clenching at intercuspal position were recorded as 100 MVC. Then, clenching at 80, 60, 50, 30, 20, and 10 MVC was instructed with visual feedback. Occlusal forces were recorded with pressure-sensitive sheet (Dental-Prescale). The occlusal contacts were recorded by a silicone occlusal contact checking material (Black Silicone). The change of occlusal forces at first premolar was converted to displacement with existing data of degree of displacement (Goto et al). Then displacement characteristic of second premolar and first molar was calculated.

RESULTS

The displacement characteristic of second premolar was similar to existing data on first premolar. Although the displacement characteristic of first molar was similar, the degree of displacement was small, which means occlusal force at the first molar increased more than at the first premolar as increase of the displacement.

CONCLUSION

The results of this study, indicating similarity to past studies with complex equipment, suggest that the displacement characteristic of teeth could be estimated with both occlusal force of individual teeth and existing data on degree of displacement.

Influence of length and diameter of implants associated with distal extension removable partial dentures

PURPOSE

The aim of this study was to evaluate the influence of the length and diameter of the implant incorporated under the saddle of a distal-extension removable partial denture, acting as support.

MATERIALS AND METHODS

Six hemi-mandibular models were made with the presence of left inferior cuspid and first bicuspid, with the following differences: model A, without removable partial denture; model B, removable partial denture only; model C, removable partial denture and implant of 3.75 x x mm; model D, removable partial denture and implant of 3.75 x x3 mm; model E, removable partial denture and implant of 5 x x mm; and model F, removable partial denture and implant of 5 x x3 mm. These models were designed with the aid of AutoCAD 2000 (Autodesk, Inc., San Rafael, CA) and processed for finite element analysis by ANSYS 5.4 (Swanson Analysis Systems, Houston, PA). The loads applied were 50 N vertical on each cuspid point.

RESULTS

It was noted that the presence of the removable partial denture overloaded the supporting tooth and other structures. The introduction of the implant reduced tensions, mainly at the extremities of the edentulous edge. Both the length and diameter tended to reduce tensions as their dimensions increased.

CONCLUSIONS

Increasing the length of the implant had a great influence on the decrease of displacement and von Mises tension values. Increasing the diameter of the implant had a great influence on the decrease of von Mises tension values, but did not influence the displacement values. According to the results of this study, it is a good choice to use the greater and larger implant possible in the association between implant and distal extension removable partial denture.

The staggered installation of dental implants and its effect on bone stresses

PURPOSE

The aim of this study was to investigate the effect of offsetting the middle or peripheral implant on the compressive stress values in the crestal bone around the neck of the dental implant.

MATERIALS AND METHODS

Three finite element models describing three titanium implants installed in quadrilateral pieces of bone was executed. A 2-mm nickel chromium superstructure representing a bridge was modeled over the implant abutments. In model 1, implants were installed along a straight line. Model 2 had the middle implant installed outside the line connecting the two peripheral implants buccally. Model 3 had the mesial implant installed out of alignment. Six 100-N loads were modeled on top of the mesial and middle implants of the three models individually. Loads 1 and 2 were directed vertically on the mesial and middle implants, while loads 3 and 4 represented the horizontal loads in the buccal direction. Loads 5 and 6 were directed mesially on the mesial and central implants. Maximal compressive stress levels in the crestal bone of the three models were then investigated.

RESULTS

The results demonstrated that offset implant installation revealed slightly lower bone stresses under buccally or lingually directed horizontal forces. Slightly higher bone stresses under vertical loads were observed. Horizontal mesial or distal loads resulted in slightly higher bone stresses than those caused by buccal or lingual loading.

CONCLUSIONS

The in-line implant alignment clearly had the safest compressive stress outcome on the surrounding structure under vertical loads. Under buccolingual loads, implant alignment with peripheral offset would have, relatively, the safest compressive stress outcome on bone.

Three-dimensional finite elemental analysis of zygomatic implants in craniofacial structures

The objective of this study was to analyse stress distribution in craniofacial structures around zygomatic osseointegrated implants. An integrated system for Digital Imaging and Communications in Medicine (DICOM) data were utilized to create a three-dimensional model of craniofacial structures. The amount and distribution of the main stresses were compared using three-dimensional finite elemental analysis. The system allowed visual confirmation and analysis of stress distribution as well as the convenient and simple construction of a digital biomechanical model that provided details of anatomical structures in the regions of interest. Zygomatic implants with or without connected implants supporting the superstructure were compared. Stresses in severely resorbed maxillae with connected implants were not concentrated around the alveolar bone supporting the zygomatic implants. Stresses where there were no connected implants tended to be generated in the zygomatic bone, at the middle part of the zygomatic implant and at the joint of the fixture-abutment. Stress due to occlusal forces is mainly supported by the zygomatic bone, is transferred predominantly through the infrazygomatic crest, and is divided between the frontal and temporal processes of the zygomatic bone in different directions.

Wide-Diameter Implants: Analysis of Clinical Outcome of 304 Fixtures

BACKGROUND

In the last decade, the use of wide-diameter implants (WDIs; diameter >3.75 mm) has increased. Although good clinical outcomes have been reported in recent literature, there are few reports on this topic. Thus, we planned a retrospective study on a large series of WDIs to evaluate the clinical outcome.

METHODS

From October of 1996 to December of 2004, 205 patients were operated on, and 304 WDIs were inserted. The mean postloading follow-up was 30 months. Implant diameter and length ranged from 5.0 to 6.5 mm and from 8.0 to 15 mm, respectively. Because only five of 304 implants were lost (i.e., a survival rate of 98.4%) and no statistical differences were detected among the studied variables, no or reduced crestal bone resorption (CBR) was considered an indicator of success to evaluate the effect of several host-, surgery-, and implant-related factors. A general linear model (GLM) was performed to detect variables that were associated statistically with CBR.

RESULTS

Only five of 304 WDIs were lost, and no differences were detected among the studied variables. On the contrary, the GLM showed that distal teeth (i.e., premolars and molars), small implant diameter (i.e., 5.0 and 5.5 mm), and short implant length (i.e., <13 mm) correlated with a statistically significant lower CBR.

CONCLUSION

The use of WDIs is a viable treatment option, and it may provide benefits in posterior regions for long-term maintenance of various implant-supported prosthetic rehabilitations.

Stress analysis of implant-supported partial prostheses in anisotropic mandibular bone: in-line versus offset placements of implants

Three-dimensional, anisotropic finite element models were executed to investigate the biomechanical effects of in-line and offset placements of implants on implant-supported partial prostheses. Three implant placements of finite element models were created: in-line, buccal offset and lingual offset placements. The mesh models of a cadaver mandibular segment and a three-united crown containing the 2nd premolar, the 1st molar and the 2nd molar were constructed by computer tomography images. The material properties of mandible were applied as transversely isotropic and linearly elastic. Two loading modes (100N), vertical and oblique, were evaluated in all models. Insignificant difference was observed in implant stresses between the in-line and offset placements under the vertical loading mode. Under the oblique loading, however, the offset placement decreased the implant stress by a maximum of 17%. The maximum stress at cortical bone and trabecular bone around each implant did not show conspicuous difference between the in-line and offset placements. This study demonstrated the mechanisms of how stresses were distributed between the in-line and offset placements. Even though the offset placements showed the benefit of decreasing implant stresses, justified from the bone stress the offset placements provided no advantage for the stress decreasing over the in-line placement.

The use of short, wide implants in posterior areas with reduced bone height: a retrospective investigation

STATEMENT OF PROBLEM

Reduced bone height frequently presents a challenge for implant-assisted tooth replacement in partially edentulous patients.

PURPOSE

This retrospective study evaluated the success rate of short, wide hydroxyapatite (HA)-coated implants placed in mandibular and maxillary molar areas with reduced bone height.

MATERIAL AND METHODS

A total of 168 HA-coated implants (6-mm diameter x 8-mm length) were placed in 167 patients in a private-practice setting. A minimal 6-mm workable ridge height and 8-mm ridge width was available in all situations. Patients were referred back to 1 of 7 referring restorative dentists for restoration of the implants. No attempt was made to standardize the restoration of the implants except to avoid working and nonworking contacts in lateral excursions. Implant success was evaluated according to the following criteria: (1) absence of complaints, (2) absence of recurring peri-implant infection or suppuration, (3) absence of perceptible implant mobility, and (4) absence of radiolucencies at implant-bone junction. The data were analyzed with descriptive statistics.

RESULTS

Fifty-four (32.1%), 35 (20.8%), 36 (21.4%), and 42 (25.0%) implants replaced maxillary first and second and mandibular first and second molars, respectively. There were 128 implant-supported single crowns. Thirty-eight implants served as abutments for fixed partial dentures connected to other implants of various sizes. Two implants were involved in cantilevered fixed partial dentures. Patients were followed for up to 68 months (mean=34.9 months) after loading of implants. The overall cumulative success rate was found to be 100%.

CONCLUSIONS

For residual ridges with minimal height but adequate width, the use of short, wide HA-coated implants may offer a simple and predictable treatment alternative in posterior areas.

Removal of a fractured implant abutment screw: a clinical report

The failure of dental implants is due not only to biological factors, such as unsuccessful osseointegration or the presence of peri-implantitis, but may also result from technical complications. Fracture of the implant abutment screw can be a serious problem, as the fragment remaining inside the implant may prevent the implant from functioning efficiently as an anchor. The procedure used for the removal of fractured screw fragments and the successful utilization of the existing prosthesis are described in this clinical report.

The influence of functional forces on the biomechanics of implant-supported prostheses--a review

OBJECTIVES

To evaluate published evidence related to the influence of functional forces on the biomechanics of implant-supported prostheses.

DATA AND SOURCES

The literature was searched for original research articles relating control of loads on dental implants, effects of early and late occlusal loads, the influence of bone quality, prosthesis type, prosthesis material, number of supporting implants, and engineering techniques employed for evaluating mechanical and biomechanical behavior of implants using MEDLINE and manual tracing of references cited in key papers otherwise not elicited.

STUDY SELECTION

Current literature on implant biomechanics as main focus and pertinent to key aspects of the review.

CONCLUSIONS

The outcome of implant treatment is often maximized when implants are placed in dense bone, number of supporting implants are increased, implant placement configuration reduces the effects of bending moments, and when a fixed prosthesis is delivered to the patient.