Treatment planning of implants when 3 mandibular posterior teeth are missing: a 3-dimensional finite element analysis. IMPLANT DENT. 2012;21:340-343. [PMID: 22814561 DOI: 10.1097/id.0b013e31825cbc67]

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.

Comparative evaluation of short or standard implants with different prosthetic designs in the posterior mandibular region: a three-dimensional finite element analysis study

The purpose of this study is to evaluate the stress distribution of splinted or nonsplinted restorations supported by 2 short or 2 standard dental implants in the mandibular molar region using three-dimensional finite element analysis. Two standard implants (4.8 × 10mm) were placed in the mandibular molar area. Two short implants (4.8 × 6 mm) were located in the mandibular molar atrophied area. Implant-supported prostheses were simulated with splinted or nonsplinted crowns design. Vertical load of 200 N and oblique load of 100 N were applied on the central fossa and the buccal cusps. Evaluation of stress distribution in implants and peri-implant cortical bone using the finite element analysis software (Ansys, Version 2020, R2), a multipurpose computer design program. The maximum principal stress of cortical bone around the implants was higher in nonsplinted crowns when compared to splinted crowns. The stress concentration of cortical bone surrounding implants increased as the implant length decreased either splinted crowns or nonsplinted crowns. The short implants with nonsplinted crowns showed lower stresses when compared to standard implants with nonsplinted crowns. The results suggest that the nonsplinted prostheses supported by short dental implants might be considered in the molar area of the atrophic mandible.

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.

Three-dimensional finite element analysis of buccally cantilevered implant-supported prostheses in a severely resorbed mandible

PURPOSE

The aim of the study was to compare the lingualized implant placement creating a buccal cantilever with prosthetic-driven implant placement exhibiting excessive crown-to-implant ratio.

MATERIALS AND METHODS

Based on patient's CT scan data, two finite element models were created. Both models were composed of the severely resorbed posterior mandible with first premolar and second molar and missing second premolar and first molar, a two-unit prosthesis supported by two implants. The differences were in implants position and crown-to-implant ratio; lingualized implants creating lingually overcontoured prosthesis (Model CP2) and prosthetic-driven implants creatingan excessive crown-to-implant ratio (Model PD2). A screw preload of 466.4 N and a buccal occlusal load of 262 N were applied. The contacts between the implant components were set to a frictional contact with a friction coefficient of 0.3. The maximum von Mises stress and strain and maximum equivalent plastic strain were analyzed and compared, as well as volumes of the materials under specified stress and strain ranges.

RESULTS

The results revealed that the highest maximum von Mises stress in each model was 1091 MPa for CP2 and 1085 MPa for PD2. In the cortical bone, CP2 showed a lower peak stress and a similar peak strain. Besides, volume calculation confirmed that CP2 presented lower volumes undergoing stress and strain. The stresses in implant components were slightly lower in value in PD2. However, CP2 exhibited a noticeably higher plastic strain.

CONCLUSION

Prosthetic-driven implant placement might biomechanically be more advantageous than bone quantity-based implant placement that creates a buccal cantilever.

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.

Stress distribution of three-unit fixed partial prostheses (conventional and pontic) supported by three or two implants: 3D finite element analysis of ductile materials

In implantology, when financial or biological feasibility limitations appear, it is necessary to use prostheses with geometries that deviate from the conventional, with a pontic in the absence of an intermediate implant. The aim of this study was analyze and understand the general differences in the stresses generated in implants, components and infrastructures according to the configuration of the prosthesis over three or two implants. Thus, this paper analyzes the von Mises equivalent stresses (VMES) of ductile materials on their external surfaces. The experimental groups: Regular Splinted Conventional Group (RCG), which had conventional infrastructures on 3 regular-length Morse taper implants (4x11 mm); Regular Splinted Pontic Group (RPG), which had infrastructures with intermediate pontics on 2 regular-length Morse taper implants (4x11 mm). The simulations of the groups were created with Ansys Workbench 10.0 software. The results revealed that the RPG presented greater areas of possible fragility due to higher stress concentrations, for example, in the cervical area of the union between the implant and component the top platform of the abutment, as well as greater coverage of the stress by the cervical implant threads. The RPG infrastructure was also more affected by stresses in the connection areas between the prostheses and on the occlusal surface. There is an advantage to using prostheses supported by a greater number of implants (RCG) because this decreases the stress in the analyzed structures and consequently improves stress dissipation to the supporting bone, which would preserve the system.

Periprosthetic biomechanical response towards dental implants, with functional gradation, for single/multiple dental loss

The differences in shape and stiffness of the dental implants with respect to the natural teeth (especially, dental roots) cause a significant alteration of the periprosthetic biomechanical response, which typically leads to bone resorption and ultimately implant loosening. In order to avoid such clinical complications, the implant stiffness needs to be appropriately adapted. In this study, hollow channels were virtually introduced within the designed implant screws for reduction of the overall stiffness of the prototype. In particular, two opposing radial gradients of increasing hollow channel diameters, i.e., outside to inside (Channel 1) and inside to outside (Channel 2) were considered. Two clinical situations of edentulism were addressed in this finite element-based study, and these include a) loss of the first molar, and b) loss of all the three molars. Consequently, two implantation approaches were simulated for multiple teeth loss - individual implantation and implant supported dental bridge. The effects of implant length, approach and channel distribution on the biomechanical response were evaluated in terms of the von Mises stress within the interfacial periprosthetic bone, under normal masticatory loading. The results of our FE analysis clearly reveal significant variation in periprosthetic bone stress between the different implant designs and approaches. An implant screw length of 11 mm with the Channel 2 configuration was found to provide the best biomechanical response. This study also revealed that the implant supported dental bridge approach, which requires lower bone invasion, results in favorable biomechanical response in case of consecutive multiple dental loss.

Mini Implants Supporting Fixed Partial Dentures in the Posterior Mandible: A Retrospective

Small-diameter, or mini, dental implants have been successfully used to support removable and fixed oral prostheses. These implants impart about twice the per-square-millimeter force on the supporting bone and this should be addressed during treatment planning. In the posterior jaws, bite forces are of a higher magnitude than in the anterior jaws and may induce an overload of the supporting bone and failure of the osseointegration. Thus there should not be occlusal contact in functional excursions that induce off axial loads. The cases presented herein demonstrate that mini dental implants may be used successfully to support fixed partial dentures in mandibular sites in highly selected patients. Attention should be given to the bone density of the site, very slow seating rotation of the implant with intermissions or cooling during insertion, observation of a 4-month healing time, flapless placement, treatment of any existing periodontitis, an insoluble cement, and exclusion of occlusal contact in functional excursions. Importantly, a narrow, rounded occlusal table should be used to minimize off axial loads and an insoluble luting cement should be used to prevent loosening of the crowns due to dissolution of the cement and an overload of the retained implant with any residual cement-retained in the retainer. The implant that supports the cement retained retainer will be subjected to leveraged rotation that may destroy the osseointegration and result in exfoliation of the implant.

Posterior partially edentulous jaws, planning a rehabilitation with dental implants

AIM: To discuss important characteristics of the use of dental implants in posterior quadrants and the rehabilitation planning.

METHODS: An electronic search of English articles was conducted on MEDLINE (PubMed) from 1990 up to the period of March 2014. The key terms were dental implants and posterior jaws, dental implants/treatment planning and posterior maxilla, and dental implants/treatment planning and posterior mandible. No exclusion criteria were used for the initial search. Clinical trials, randomized and non randomized studies, classical and comparative studies, multicenter studies, in vitro and in vivo studies, case reports, longitudinal studies and reviews of the literature were included in this review.

RESULTS: One hundred and fifty-two articles met the inclusion criteria of treatment planning of dental implants in posterior jaw and were read in their entirety. The selected articles were categorized with respect to their context on space for restoration, anatomic considerations (bone quantity and density), radiographic techniques, implant selection (number, position, diameter and surface), tilted and pterygoid implants, short implants, occlusal considerations, and success rates of implants placed in the posterior region. The results derived from the review process were described under several different topic headings to give readers a clear overview of the literature. In general, it was observed that the use of dental implants in posterior region requires a careful treatment plan. It is important that the practitioner has knowledge about the theme to evaluate the treatment parameters.

CONCLUSION: The use of implants to restore the posterior arch presents many challenges and requires a detailed treatment planning.