Analysis of load transfer and stress distribution by splinted and unsplinted implant-supported fixed cemented restorations

In Vitro Reliability and Stress Distribution of Wide Diameter Extra-Short Implants as Support for Single Crowns and Fixed Partial Dentures

This study evaluated the reliability, failure mode, and stress distribution of wide-diameter extra-short dental implants (ESDI) as support for single crowns (SC) and fixed partial dentures (FPD) (3:1 crown-to-implant ratio [C:I]) for rehabilitation in the posterior atrophic mandible. For that, 126 ESDI (of 5 mm length) were allocated in four groups based on diameter (Ø4 and Ø6 mm) and prostheses (SC and FPD): SC4, SC6, FPD4, and FPD6. The fatigue test was performed by step-stress accelerated life testing (n = 21/group), failure mode by fractographic analysis, and stress distribution by finite element analysis: von Mises stress (σvM), maximum shear stress (τmax), and minimum principal stress (σmin). Reliability at 200 N was higher than 84% in both SC4 and SC6, with SC6 showing significantly higher reliability at 300 N. Failure mode involved the abutment (SC4 and SC6). The missions were suspended for the FPD groups due to 100% survival at the maximum load. The σvM showed a stress reduction of about 40% at the SC6 implant when compared to SC4 and FPD6 compared to FPD4. For the abutment, a minor decrease of at least 6.72% was observed comparing SC6 to SC4 and 2.78% for the FPD6 compared to FPD4. The τmax and σmin in the cortical bone demonstrated a stress reduction of at least 38.85% for the SC6 compared to SC4 and at least 3.78% in FPD6 compared to FPD4. The σmin in the cancellous bone showed an overall reduction of at least 8.46% for SC6 compared to SC4 and for FPD6 compared to FPD4. But, for τmax, in the cancellous bone, a 19.42% higher stress was found in SC6 compared to SC4 and 27.21% in FPD6 compared to FPD4. Finally, when splinting was used, a general stress reduction was found, about 50% in both diameters in the implant and abutment. According to the limitations of this in vitro study, it is possible to conclude that both groups (SC4 and SC6) showed high reliability in clinically relevant loads for the posterior atrophic mandible, SC6 having the lowest probability of failure at 300 N, with failure restricted to the abutment. Meanwhile, FPD6 has better stress distribution.

Clinical Evaluation of the Long-Term Survival and Success Rates of Different Types of Implant-Supported Prostheses

Background

Dental implants have been essential to the therapy of patients who are partially edentulous.

Aim

Clinical evaluation of the long-term survival and success rates of different types of implant-supported prostheses.

Materials and Methods

Patients who had a healthy edentulous ridge of three missing teeth in the posterior jaw in which two or three dental implants were placed having any of three prostheses, namely, three-unit fixed dental prostheses (FPD) on two implants, three splinted crowns on three implants, and three splinted crowns on three implants were included.

Results

The survival rate in all patients with dental implants having different types of prostheses was 94.9%. The survival rate in FPD, three splinted crowns, and three nonsplinted crowns was 100, 88.5, and 93.6% respectively.

Conclusion

FPD loaded on two dental implants was found to have a greater long-term survival rate and success rate with a lower frequency of peri-implantitis and prosthodontic complications.

Splinting or non-splinting of fixed prostheses on adjacent implants: A critical review

PURPOSE

The present study aimed to identify, through a critical review of the literature, the success factors associated with the splinting of fixed prostheses on adjacent implants of the posterior sectors in partially edentulous patients compared with those not splinted.

STUDY SELECTION

A MEDLINE strategy was implemented based on a research question to systematically search and extract information from databases (PubMed and Scopus) using MeSH terms/keywords identified for each domain. Systematic reviews, clinical and in vitro studies were selected and classified according to eligibility criteria based on the research question and level of evidence using the PRISMA flowchart.

RESULTS

A total of 32 studies were selected for data extraction and analysis according to study design (three systematic reviews, 14 clinical studies, and 15 in vitro studies). Overall, the studies found no significant difference in the association between the survival rate and prosthesis type. In clinical studies, there have been no differences in marginal bone loss between splinted and non-splinted prostheses, and the influence of peri-implant status and restorative materials has been poorly evaluated. The distribution of stress and loads determined in the in vitro studies showed results that could favor splinted prostheses; however, are generally associated with implant design.

CONCLUSIONS

The need for splinted or non-splinted adjacent implant-supported prostheses remains controversial. The reviewed evidence indicates that factors such as implant size and its relationship with coronal height could be important in decision-making.

Effect of bone mass density and alveolar bone resorption on stress in implant restoration of free-end edentulous posterior mandible: Finite element analysis of double-factor sensitivity

BACKGROUND

Osseous condition of the mandible was regarded as a key factor influencing stability of implants in the early stage. Finite element analysis was used to assess the effect of bone mass density and alveolar bone resorption (double factors) on stress in a four-unit implant restoration of a free-end edentulous posterior mandible.

METHODS

A 3D finite element model was constructed for a single-sided free-end edentulous mandible (from mandibular first premolar to mandibular second molar) containing threaded dental implants. Mandible sensitivity modes were constructed with different alveolar bone resorption levels for normal conditions as well as mild, moderate and severe periodontitis, respectively. Based on the mass density of cancellous bone for four types of bones as the sensitivity parameter, two implant design modes were constructed: Model A (four-unit fixed bridge supported by three implants, implant positions were 34, 36 and 37) and model B: 34 × 36, 37 (37: a single implant crown) (34 × 36: three-unit fixed bridge supported by two implants, implant positions were 34 and 36). A total of 32 sensitivity-based finite element models, grouped in two groups, were constructed. Stress distribution and maximum von Mises stress on cortical bone and cancellous bone around the implant, as well as the surface of implant were investigated by using ABAQUS when vertical loading and 45° oblique loading were applied, respectively.

RESULTS

When vertical loading was applied on the implant, maximum von Mises stress on the cortical bone around the implant was assessed to be 4.726 MPa - 13.15 MPa and 6.254 MPa - 13.79 MPa for groups A and B, respectively; maximum stress on the cancellous bone around the implant was 2.641 MPa - 3.773 MPa and 2.864 MPa - 4.605 MPa, respectively; maximum stress on the surface of implant was 14.7 MPa - 21.17 MPa and 21.64 MPa - 30.70 MPa, respectively. When 45° oblique loading was applied on the implant restoration, maximum von Mises stress on the cortical bone around the implant was assessed to be 42.08 MPa - 92.71 MPa and 50.84 MPa - 102.5 MPa for groups A and B, respectively; maximum stress on the cancellous bone around the implant was 4.88 MPa - 25.95 MPa and 5.227 MPa - 28.43 MPa, respectively; maximum stress on the surface of implant was 77.91 MPa - 124.8 MPa and 109.2 MPa - 150.7 MPa, respectively. Stress peak on the cortical bone and that on cancellous bone around the implant increased and decreased with the decrease in bone mass density, respectively. Stress peak on alveolar bone increased with alveolar bone resorption when oblique loading was applied.

CONCLUSION

1. Both alveolar bone resorption and bone mass density (double factors) are critical to implant restoration. Bone mass density may exhibit a more pronounced impact than alveolar bone resorption. 2. From the biomechanical perspective, types I and II bones are preferred for implant restoration, while implantation should be considered carefully in the case of type III bones, or those with less bone mass density accompanied by moderate to severe alveolar bone loss. 3. Splinting crowns restoration is biomechanically superior to single crown restoration.

Analysis of Strain Distribution in Common Clinical Designs of Posterior Implant-Supported Fixed Partial Restorations: Comparison between Six Configurations

The configuration of implant-supported prostheses is considered to influence the magnitude of stress concentrations, affecting their survival rate. The purpose of this study is to determine, through strain gauge measurements during load application, the dispersion and magnitude of strain concentrations in different implant-supported prosthesis designs. All designs matched those commonly used in posterior partially edentulous states. Three implants were inserted into an epoxy resin model (PLM-4B Vishay Measurements Group Inc., Raleigh, NC, USA), allowing for the delivery of three- and four-unit crowns in different cemented configurations. Loads were applied at vertical and oblique directions over the cast crowns in six different configurations representing various posterior partially edentulous restorations. The readings from the strain gauges adhered to the implant necks' presented data on implant strain. Prostheses including cantilevers showed the highest strain among the three-unit prostheses within the prosthetic complex, and three single units showed the least (8133 µs vs. 201 µs, respectively). Angulated load application also had a role in amplifying the strains recorded, resulting in total strains of between 3.5 and 20 times higher than during vertical loading in all configurations. It can be concluded that the configuration of implant-fixed partial prosthesis changes the loads engaging the restoration, the implant, and, probably, the supporting bone.

The Use of Splinted Versus Nonsplinted Prosthetic Design in Dental Implants: A Literature Review

The choice of a splinted or nonsplinted implant-supported prosthesis should be based on solid scientific evidence that considers the conditions and needs of each patient. This review elaborates on the factors that directly influence clinical decisions between splinted or nonsplinted dental implants. Digital and manual searches of the published literature were conducted to identify studies that examined splinted prostheses (SPs) and nonsplinted prostheses (NSPs). The search terms used, alone or in combination, were "splinting prosthesis," "nonsplinting prosthesis," "prosthetic design," "stress distribution in dental implant," "implant loading," "implant occlusion," and "crestal bone resorption." Ninety-four studies were selected to compare and address the details emphasized in this study. Thirty-four reported articles were not directly related to restoration design but were reviewed to better understand the influence of mechanical risk factors, finite element analysis limits, and criteria for implant survival and treatment success. There are advantages and disadvantages of splinting implants together. NSPs are the ideal choice because they resemble natural teeth. Splinting a restored implant will cause the implant to appear as part of one unit and is indicated in more compromised situations, unfavorable conditions, or when pontic spaces and cantilevers are needed in implant prostheses.

The effect of frontal trauma on the edentulous mandible with four different interforaminal implant-prosthodontic anchoring configurations. A 3D finite element analysis

PURPOSE

The present three-dimensional (3D) finite element analysis (FEA) was aimed to assess the biomechanical effects and fracture risks of four different interforaminal implant-prosthodontic anchoring configurations exposed to frontal trauma.

MATERIAL AND METHODS

A symphyseal frontal trauma of 1 MPa was applied to four dental implant models with different configurations (two unsplinted interforaminal implants [2IF-U], two splinted interforaminal implants [2IF-S], four unsplinted interforaminal implants[ 4IF-U], four splinted interforaminal implants [4IF-S]. By using a 3D-FEA analysis the effective cortical bone stress values were evaluated in four defined regions of interest (ROI) (ROI 1: symphyseal area; ROI 2: preforaminal area; ROI 3: mental foraminal area; and ROI 4: condylar neck) followed by a subsequent intermodel comparison.

RESULTS

In all models the frontal traumatic force application revealed the highest stress values in the condylar neck region. In both models with a four-implant configuration (4IF-U, 4IF-S), the stress values in the median mandibular body (ROI 1) and in the condylar neck region (ROI 4) were significantly reduced (P <0.01) compared with the two-implant models (2IF-U, 2IF-S). However, in ROI 1, the model with four splinted implants (4IF-S) showed significantly (P < 0.01) reduced stress values compared to the unsplinted model (4IF-U). In addition, all models showed increased stress patterns in the area adjacent to the posterior implants, which is represented by increased stress values for both 2IF-U and 2IF-S in the preforaminal area (ROI 3) and for the four implant-based models (4IF-U, 4IF-S) in the mental foraminal area.

CONCLUSION

The configuration of four splinted interforaminal implants showed the most beneficial distribution of stress pattern representing reduced stress distribution and associated reduced fracture risk in anterior symphysis, condylar neck and preforaminal region.

Influence of Different Implant Designs on Replacement of Four Teeth of The Posterior Free-end Edentulism: Three-dimensional Finite Element Analysis and Clinic Case Validation

BACKGROUND

With periodontal disease having an increasing incidence, mandibular free-end edentulism caused by periodontitis is clinically more common. Finite element analysis and clinical case reports were used to evaluate the influence of different designs on the load distribution of implant prosthesis in mandibular posterior free-end edentulism.

METHOD

A finite element model of a mandible with posterior free-end edentulism was established. Considering the implant position and selection of single crown repair or splint repair, four designs were conducted including model A: 3435×37(four-unit fixed bridge supported by three implants, implant positions were 34, 35, 37); model B: 34,35×37, (34: a single implant crown) (35×37: three-unit fixed bridge supported by two implants, implant positions were 35, 37); model C: 34×3637(four-unit fixed bridge supported by three implants, implant positions were 34, 36, 37); and model D: 34×36, 37(37: a single implant crown)(34×36: three-unit fixed bridge supported by two implants, implant positions were 34, 36). Stress distribution and the Von Mises stress value of the implants, the crown and the bone around the implants were analyzed at vertical and 45° inclined load.

RESULTS

Stress in the cortical bone was mainly concentrated around the implant neck, and maximum Von Mises stress (MVMS) of the four models was 11.6-16.1MPa at vertical load and 61.74-96.49MPa at 45° inclined load. Stress in the cancellous bone was concentrated around the implant base, and MVMS of four models was 3.075-3.899MPa at vertical load and 5.021-6.165MPa at 45° inclined load. Stress of the restoration crowns was mainly concentrated in the connector of the bridge, and MVMS of four models was 23.38-26.28MPa at vertical load and 53.14-56.35MPa at 45° inclined load. Stress of the implant interface was mainly concentrated on the surface of the smaller implants near the bridge, and MVMS of four models was 21.12-33.25MPa at vertical load and 83.73-138.7MPa at 45° inclined load.

CONCLUSION

There was favorable stress distribution of the four models at vertical load and 45° inclined load. Design of a three-unit fixed bridge combined with a partial crown may be an available option for devising patient treatment plans with mandibular free-end edentulism.

The significance of vertical platform discrepancies and splinting on marginal bone levels for adjacent dental implants

OBJECTIVE

The aim of this retrospective study was to investigate the influence of vertical platform discrepancies for splinted and non-splinted adjacent implants on radiographic marginal bone loss (RMBL).

METHODS

Data from January 2000 to February 2021 were collected from the electronic charts of 156 patients with 337 implants at the UCSF School of Dentistry. Five different implant restoration categories were evaluated for radiographic evidence of proximal RMBL. Patients with (1) two adjacent single crowns, (2) two adjacent splinted crowns, (3) three-unit bridges supported by two implants, (4) three adjacent single crowns, and (5) three adjacent splinted crowns. Inclusion required baseline radiograph taken at the time of prosthesis delivery or final impression, and follow-up radiographs at least 12 months after restorations have been in function. Measurements assessed included vertical distance between adjacent implant platforms and proximal RMBL around implants. Odds ratios (ORs) and 95% confidence interval (95% CI) of implants with ≥1 mm RMBL between different type of restorations were calculated.

RESULTS

In general, prostheses supported by splinted adjacent implants demonstrated a significant association with the presence of ≥1 mm RMBL (OR = 2.55, 95% CI = 1.17-5.17, p = 0.018) when compared to prostheses supported by non-splinted adjacent implants. In addition, prostheses with a vertical platform discrepancy ≥0.5 mm demonstrated a significant association with the presence of ≥1 mm RMBL (OR = 4.30, 95% CI = 1.85 to 10.01, p = 0.007) when compared to prostheses with a vertical platform discrepancy <0.5 mm. When adjacent implants had ≥0.5 mm vertical platform discrepancy, the majority (66.67%) of three splinted adjacent crowns had at least one implant with ≥1 mm RMBL. This was followed by two splinted adjacent crowns (58.97%), three-unit bridge (25.93%), two single adjacent crowns (24.24%), and three single adjacent crowns (18.18%). When adjacent implants had ≥1 mm vertical platform discrepancy, there was an increased percentage of implants with ≥1 mm RMBL. The restorative design associated with the highest percent of implants with bone loss was three splinted adjacent crowns (70%), two splinted adjacent crowns (61.11%), three single adjacent crowns (40%), and three-unit bridge and two single adjacent implants (21.05%). Three splinted adjacent crowns were significantly associated with ≥1 mm RMBL when compared to three-unit bridge (OR 6.56, 95% CI 1.59-27.07). Similarly, two splinted crowns were significantly associated with ≥1 mm RMBL when compared to two single crowns (OR = 2.50, 95% CI = 1.08-5.79).

CONCLUSION

Two or three adjacent implants placed with a vertical platform discrepancy, when splinted together, are associated with higherincidence of ≥1 mm RMBL than non-splinted restorations.

Biomechanical finite element analysis of short-implant-supported, 3-unit, fixed CAD/CAM prostheses in the posterior mandible

Objective

To assess the biomechanical effects of different prosthetic/implant configurations and load directions on 3-unit fixed prostheses supported by short dental implants in the posterior mandible using validated 3-D finite element (FE) models.

Methods

Models represented an atrophic mandible, missing the 2nd premolar, 1st and 2nd molars, and rehabilitated with either two short implants (implant length-IL = 8 mm and 4 mm) supporting a 3-unit dental bridge or three short implants (IL = 8 mm, 6 mm and 4 mm) supporting zirconia prosthesis in splinted or single crowns design. Load simulations were performed in ABAQUS (Dassault Systèmes, France) under axial and oblique (30°) force of 100 N to assess the global stiffness and forces within the implant prosthesis. Local stresses within implant/prosthesis system and strain energy density (SED) within surrounding bone were determined and compared between configurations.

Results

The global stiffness was around 1.5 times higher in splinted configurations vs. single crowns, whereby off-axis loading lead to a decrease of 39%. Splinted prostheses exhibited a better stress distribution than single crowns. Local stresses were larger and distributed over a larger area under oblique loads compared to axial load direction. The forces on each implant in the 2-implant-splinted configurations increased by 25% compared to splinted crowns on 3 implants. Loading of un-splinted configurations resulted in increased local SED magnitude.

Conclusion

Splinting of adjacent short implants in posterior mandible by the prosthetic restoration has a profound effect on the magnitude and distribution of the local stress peaks in peri-implant regions. Replacing each missing tooth with an implant is recommended, whenever bone supply and costs permit.

A comparison of marginal bone loss, survival rate, and prosthetic complications in implant-supported splinted and nonsplinted restorations: A systematic review and meta-analysis

Aim

To compare marginal bone loss (MBL), implant survival rate and prosthetic complications of implant-supported splinted and non-splinted restorations (NSR).

Settings and Design

This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines (PRISMA). The PROSPERO registry, which keeps track of prospective systematic reviews, also received this paper (CRD42021229477).

Material and Methods

An electronic search was done in PubMed, the Cochrane Central Trials Register, Scopus, Science Direct, and Google Scholar searches were carried out. The search was limited to articles published in English and covered the period from January 2010 to August 2020.

Statistical Analysis Used

To conduct the meta analysis, researchers employed methodologies such as continuous measurement and odds ratios.

Results

For both qualitative and quantitative analysis, 19 scientific studies were chosen. 3682 implants were placed in 2099 patients with a mean age of 59 years (splinted, 2529; non-splinted, 1153); the mean age was not provided in 5 trials. For splinted restorations, there were statistically significant differences in MBL, indicating the former has less MBL than for NSR. Splinted restorations had much greater survival rates than NSR, according to a qualitative study. Rest prosthesis complications with or without splinting were essentially the same.

Conclusions

Splinted implant restorations lost less bone than non-splinted implant restorations, according to this meta analysis. This was particularly true for posterior restorations. Lower implant failure was associated with splinted restorations. Restorations with and without splinting had the same level of prosthetic problems.

Effect of different fabrication methods of occlusal devices on periradicular stress distribution: A photoelastic analysis

STATEMENT OF PROBLEM

Investigations on the effectiveness of new methods for optimizing the fabrication of oral devices are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate stress distribution with photoelastic analysis in the periradicular area of teeth supporting occlusal devices fabricated by 5 different processes.

MATERIAL AND METHODS

The occlusal devices were fabricated by vacuum thermoforming, heat-polymerized acrylic resin, chemical polymerized acrylic resin, 3-dimensional printing, and milling (computer-aided manufacturing). The devices were evaluated regarding initial fit, number of adjustments for passive fit, and stress distribution under 100-N and 400-N loads in the periradicular locations of posterior teeth.

RESULTS

The 3-dimensional printing device did not require any adjustment for initial adaptation to the photoelastic model and presented a little friction with the model. The heat-polymerized acrylic resin device did not seat initially, requiring more sites of adjustment until passive adaptation. At 100-N and 400-N loads, the use of the computer-aided manufacturing occlusal device resulted in the lowest stresses in periradicular areas (0.744 and 1.583, respectively), and the 3-dimensional printing occlusal device produced the highest stresses with a 400-N load application (2.427). The lowest mean of fringe pattern was observed for the computer-aided manufacturing device, and the highest mean of fringe pattern was observed for the vacuum thermoforming device.

CONCLUSIONS

The computer-aided design and computer-aided manufacturing milled occlusal device presented the best initial adaptation and transferred lower stresses to the periradicular areas than the other evaluated devices.

Effect of different design of abutment and implant on stress distribution in 2 implants and peripheral bone: A finite element analysis study

STATEMENT OF PROBLEM

How adjacent dental implants with different sizes, designs, and abutment connection shapes affect stress on the prosthetic structure is unclear.

PURPOSE

The purpose of this finite element analysis (FEA) study was to analyze stress distribution around bone and around 2 implants with different sizes, diameters, shapes, and loading directions placed next to each other in splinted and unsplinted prostheses.

MATERIAL AND METHODS

On 3D FEA models representing the posterior right lateral segment of the mandible, 1 implant (Ø3.5×12 mm) and 1 implant (Ø5.5×8 mm) were placed adjacent. Three different contemporary implant models were created with different teeth, pitch, spiral numbers, and self-taping features, and different abutments for them were modeled in 3D. The implant-abutment connection was internal hexagonal (MIH), stepped conical (MSC), and internal conical (MIC). Vertical and oblique loads of 365 N for molar teeth and of 200 N for premolar teeth were applied as boundary conditions to the cusp ridges and grooves in a nonlinear FEA.

RESULTS

The MIH implants resulted in improved stress conditions. According to the von Mises stresses occurring on the screw, abutment, and implant, especially under oblique loads, MIH was exposed to less stress than MSC, and MSC was exposed to less stress than MIC.

CONCLUSIONS

When a standard implant and a short implant were placed adjacent and splinted by crowns, the implants, abutments, and screws had unfavorable stress levels; therefore, adjacent splinted implants should be of similar size. The form of the implant-abutment junction is also an important factor affecting stress.

Comparison of Conventional and Pontic Fixed Partial Dentures Over Implants Using the Finite Element Method: Three-Dimensional Analysis of Cortical and Medullary Bone Stress

Rehabilitation with implant prostheses in posterior areas requires the maximum number of possible implants due to the greater masticatory load of the region. However, the necessary minimum requirements are not always present in full. This project analyzed the minimum principal stresses (TMiP, representative of the compressive stress) to the friable structures, specifically the vestibular face of the cortical bone and the vestibular and internal/lingual face of the medullary bone. The experimental groups were as follows: the regular splinted group (GR), with a conventional infrastructure on 3 regular-length Morse taper implants (4 × 11 mm); and the regular pontic group (GP), with a pontic infrastructure on 2 regular-length Morse taper implants (4 × 11 mm). The results showed that the TMiP of the cortical and medullary bones were greater for the GP in regions surrounding the implants (especially in the cervical and apical areas of the same region) but they did not reach bone damage levels, at least under the loads applied in this study. It was concluded that greater stress observed in the GP demonstrates greater fragility with this modality of rehabilitation; this should draw the professional's attention to possible biomechanical implications. Whenever possible, professionals should give preference to use of a greater number of implants in the rehabilitation system, with a focus on preserving the supporting tissue with the generation of less intense stresses.

Prosthetic design related to peri-implant bone resorption in microvascular free fibular flap among patients with oral cancer: A retrospective clinical study

STATEMENT OF PROBLEM

Prosthetic rehabilitation is challenging after tumor excision in patients with oral cancer. Prosthetic parameters may be compromised because of the physical limitations of the oral cavity. Although microvascular free fibular flaps are a common treatment modality for mandibular reconstruction and allow the placement of dental implants, fibular resorption under long-term functional loading is still a controversial issue. Research focusing on how prosthetic design affects fibular resorption around dental implants in an oral cancer population is lacking.

PURPOSE

The purpose of this retrospective clinical study was to correlate the success of implant-supported prostheses in microvascular free fibular flaps with occlusal force and fibular resorption around the implants 7 years after functional loading.

MATERIAL AND METHODS

The T-Scan III was used to measure occlusal force in 13 participants with oral cancer. Forty-seven successful endosseous dental implants (Biomet 3i) under functional loading in the participants from 2010 to 2017 were analyzed retrospectively. Prosthetic design including fibular length, rehabilitated arch length, and crown-to-implant ratios was estimated from panoramic radiographs. The intergonial distance was used to calibrate the panoramic radiographs to enhance accuracy. To compensate for panoramic distortion, all parameters were represented as a ratio such as fibular length/mandibular width; implant-supported prosthesis length/mandibular dental arch length; implant-supported prosthesis length/maxillary dental arch length; and mandibular dental arch length/maxillary dental arch length. A generalized estimating equation was used for longitudinal analysis to estimate the impact of variables on fibular resorption around the implants.

RESULTS

Increased length of the implant-supported prostheses compared with maxillary and mandibular dental arch length significantly impaired the maximal occlusal force (P=.045 and P=.029). The crown-to-implant ratios in the fibular flaps were not correlated with fibular resorption around the implants under long-term functional occlusion (P>.05). The increased ratio of the implant-rehabilitated mandibular to maxillary dental arch length showed a statistically significant tendency to reduce fibular resorption around the implants (P=.007).

CONCLUSIONS

Crown-to-implant ratios were not significantly correlated with maximal occlusal force or fibular resorption around dental implants. Increasing the length of the reconstructed mandibular implant-supported prosthesis in the fibular flap will reduce occlusal force. The rehabilitated mandibular dental length should be as long as the maxillary arch for optimum occlusal stress distribution to maintain the peri-implant fibula bone level.

Splinted and Nonsplinted Crowns with Different Implant Lengths in the Posterior Maxilla by Three-Dimensional Finite Element Analysis

The aim of this study was to evaluate stress distribution in the implants/components and bone tissue for splinted and nonsplinted prostheses with different lengths of implants using three-dimensional finite element analysis. Six models from the posterior maxillary area were used in simulations. Each model simulated three Morse taper implants of 4.0 mm diameter with different lengths, which supported metal-ceramic crowns. An axial load of 400 N and an oblique load of 200 N were used as loading conditions. Splinted prostheses exhibited better stress distribution for the implants/components, whereas nonsplinted prostheses exhibited higher stress in the first molar under axial/oblique loading. Implant length did not influence stress distribution in the implants/components. In cortical bone tissue, splinted prostheses decreased the tensile stress in the first molar, whereas nonsplinted prostheses were subjected to higher tensile stress in the first molar; implant length had no influence on stress distribution. Within the limitations of this study, we conclude that splinted prostheses contributed to better stress distribution in the implant/abutment and cortical bone tissue; however, the reduction in the implant length did not influence the stress distribution.

Effect of Restorative Configurations and Occlusal Schemes on Strain Levels in Bone Surrounding Implants

AIM

This study investigated strain levels during and after implant insertion, and during and after simulated mastication, in splinted and nonsplinted restorations with different occlusal schemes.

MATERIALS AND METHODS

Fresh bovine bone resembling type I jawbone was collected. Strain gauges were placed at each implant's neck, one horizontally and one vertically. Strains at and after implant insertion were recorded. The restoration was loaded with cyclic load simulating mastication. Loading and residual strains were recorded for 6 experimental loading types.

RESULTS

At and after implant insertion, high horizontal strains were measured. Full splint loading presented higher vertical compared with horizontal strains (P < 0.05). Segmented cross-arch splint showed higher horizontal strains (P < 0.05). Premolar loading guidance presented the most favorable loading and residual strain results (P < 0.05).

CONCLUSIONS

Splinting implant restorations may reduce strain levels at implant neck area and provide preferable strain distribution during cyclic loading.

A comparison of peri-implant strain generated by different types of implant supported prostheses

AIMS AND OBJECTIVE

To find out and compare peri implant strain developed in four different types of implant supported prostheses i.e., cement retained splinted, cement retained non splinted, screw retained splinted, screw retained non splinted.

METHODOLOGY

Four implant analogues were placed in a polyurethane mandibular model at the position of left and right first and second molar. Abutments were fixed to the implant at a torque of 25Ncm. Two such models were made. Four different prostheses were placed on abutment of each model i.e screw retained splinted, screw retained nonsplinted, cement retained splinted, cement retained non splinted. Four strain gauges were attached on the model, two on the buccal and two on the lingual aspect of each implant. Static load of 400N was applied on the prosthesis using universal testing machine. Load application was done ten times for each model and peri implant strain was measured.

RESULTS

The mean peri implant strain (±SD) generated was found to be highest in non-splinted screw retained (1397.70 ± 44.47 microstrains and 1265.90 ± 42.76 microstrains) and least in splinted cement retained (630.70 ± 31.98 microstrains and 519.60 ± 32.48 microstrains) in both 1st and 2nd molars respectively.

CONCLUSIONS

Splinted crowns produce less peri implant strain when compared to non splinted crowns. Cement retained prosthesis produce less peri implant strain when compared to screw retained prosthesis. Least strain was observed in cement retained splinted crowns.

Short implants to support mandibular complete dentures - photoelastic analysis

This study evaluated the stress behavior around short implants in edentulous atrophic mandibles. Six groups included implants with two diameters regular and wide (4 and 5 mm) and three lengths (5, 7 and 9 mm) as follows: Ci9 (9 x 4 mm), Ci7 (7 x 4 mm), Ci5 (5 x 4 mm), Wi9 (9 x 5 mm), Wi7 (7 x 5 mm) and Wi5 (5 x 5 mm). These groups were compared to the control group CG (11 x 4 mm). The analysis was performed with the photoelastic method (n = 6). Each model comprised 4 implants with the same length and diameter connected by a chromium-cobalt bar that simulates a fixed denture. A 0.15 kg force was applied at the end of the cantilever (15 mm), and the maximum shear stress was recorded around the distal and subsequent implants. The stress values were determined, and the quantitative data (Fringes®) were submitted to statistical analysis with one-way ANOVA and the Dunnett test (p < 0.05). It was observed that the reduction in implant length increased stress values with a significant difference (p < 0.05) between CG Ci7 and Ci5, while the increase in implant diameter reduced the stress values without any differences found between short and long implants. Implants with 5 and 7 mm with regular diameter increased stress levels while short implants with larger diameters experienced similar stress to that of longer implants.

Magnet-Retained Two-Mini-Implant Overdenture: Clinical and Mechanical Consideration

Two-implant overdentures have become the accepted treatment for restoring mandibular edentulism. The dimensions of regular implants sometimes limit their use, such as in the case of narrow ridges. Mini-implants with reduced diameters (less than 3.0 mm) enable insertion into narrow ridges. A magnet-retained two-mini-implant overdenture system was developed and is described in this paper. Additionally, we describe a clinical mandibular procedure using the system and evaluate its biomechanical performance.

The Influence of Interproximal Contact on Implant-Supported Fixed Partial Dentures in the Posterior Jaw: A Photoelastic Analysis

The aim of this study was to analyze the effect of the separation of prosthetic crowns from fixed partial dentures by means of stress gradient evaluation. Three photoelastic models were created to examine contiguous implants with varying contact between the crowns (contact point [CP], contact surface [CS], splinted [SP]). The SP group presented the best results, followed by the CS group, indicating that the use of splinted prosthetic crowns and crowns with broad surface contacts is viable when considering the stress values.

The effect of implant splinting on the load distribution in bone bed around implant-supported fixed prosthesis with different framework materials: A finite element study

Analysing the influence of implant splinting and its relation to different framework materials is a complex issue. The stiffness of framework materials and the overload of the implant system directly affect the final transferred load of the bone around implants. A finite element model of a long-span cementable implant-supported fixed prosthesis was created. Three materials were analysed for the framework: Titanium, gold alloy, and zirconia. The connection screws were first preloaded with 200 N. Two loading conditions were studied: The implant at the molar region was first loaded without splinting to the framework, and in the second condition, the implant was splinted to the framework. A total force of 500 N and 1000 N in 30° from the long axis of the framework were applied in buccal or distal direction on the implant system. The stresses and strains within the framework materials, implant system, and bone bed around the supporting implants were analysed. Loading the implant distally was associated with high stresses within the implant system in comparison to buccal loading. By splinting the implant, the stress in the implant system was reduced from 5393 MPa to 2942 MPa. Buccal loading of the implant was more critical than the distal loading. In the splinted condition of the implant, the stresses in the cortical bone were reduced from 570 MPa to 275 MPa.

Photoelastic stress analysis in prosthetic implants of different diameters: mini, narrow, standard or wide

PURPOSE

This study investigated the biomechanical behavior of screwed partial fixed prosthesis supported by implants with different diameters (2.5 mm; 3.3 mm and 3.75 mm) by using a photoelastic analysis.

MATERIALS AND METHODS

Six photoelastic models were fabricated in PL-2 resin as single crowns or splinted 3-unit piece. Models were positioned in a circular polariscope and 100-N axial and oblique (45 degrees) loads were applied in the occlusal surface of the crowns by using a universal testing machine (EMIC). The stresses were photographically recorded and qualitatively analyzed using a software (Adobe Photoshop).

RESULTS

Under axial loading, the number of fringes was inversely proportional to the diameter of the implants in the single crown models. In the splinted 3-unit piece, the 3.75-mm implant promoted lower number of fringes regardless of loading area application. Under oblique loading, a slight increase of fringes number was observed for all groups.

CONCLUSION

The standard implant diameter promoted better stress distribution than the narrow and mini diameter implants. Additionally, the splinted crowns showed a more uniform stress distribution.

Treatment planning of implants when 3 mandibular posterior teeth are missing: a 3-dimensional finite element analysis

PURPOSE

To analyze the biomechanics of 3 designs of implant treatment for 3 teeth missing in posterior low arch quadrants.

MATERIAL AND METHODS

A posterior portion of the human mandible missing 44, 45, 46 and three 4.1 × 10 mm threaded ITI implants with crowns were used to construct the finite element model. According to 3 implants being single, splinted or 2 implants support fixed partial denture (FPD) fixed in bone segments. Three implant support conditions were prepared with ANSYS 10.0. A load of 100 N was applied at the central fossa of the occlusal surfaces of the crowns at 45 degrees buccolingually along the triangular ridge of the buccal cusp. The von Mises stress and strain distributions in periimplant bone were observed.

RESULTS

The results demonstrated that the von Mises stress in the supporting bone of the 2-implant supported FPD significantly increased compared with that in the 3-implant replacement. Meanwhile, when 3 implants were splinted, only the median implant had a decreased and more homogenous stress distribution, and the other implants did not exhibit significant differences when splinted.

CONCLUSION

This study suggests that when space and cost permit, a 2-implant supported FPD should not be used, and 1 implant for each missing tooth being single is recommended.