Influence of Prosthesis Material on the Loading of Implants That Support a Fixed Partial Prosthesis: In Vivo Study

In vivo measurement of three-dimensional load exerted on dental implants: a literature review

Background

For biomechanical consideration of dental implants, an understanding of the three-dimensional (3D) load exerted on the implant is essential, but little information is available on the in vivo load, including the measuring devices.

Purpose

This review aimed to evaluate studies that used specific load-measuring devices that could be mounted on an implant to measure the functional load in vivo.

Materials and methods

An electronic search utilizing the internet research databases PubMed, Google Scholar, and Scopus was performed. The articles were chosen by two authors based on the inclusion and exclusion criteria.

Results

In all, 132 studies were selected from the database search, and 16 were selected from a manual search. Twenty-three studies were finally included in this review after a complete full-text evaluation. Eleven studies were related to the force measurements using the strain gauges, and 12 were related to the piezoelectric force transducer. The principles of the two types of devices were completely different, but the devices produced comparable outcomes. The dynamics of the load magnitude and direction on the implant during function were clarified, although the number of participants in each study was small.

Conclusions

The load exerted on the implant during function was precisely measured in vivo using specific measuring devices, such as strain gauges or piezoelectric force transducers. The in vivo load data enable us to determine the actual biomechanical status in more detail, which might be useful for optimization of the implant prosthetic design and development of related materials. Due to the limited data and difficulty of in vivo measurements, the development of a new, simpler force measurement device and method might be necessary.

Peri-implant biomechanical responses to standard, short-wide, and double mini implants replacing missing molar supporting hybrid ceramic or full-metal crowns under axial and off-axial loading: an in vitro study

Background

The aim of this study was to evaluate the biomechanical response of the peri-implant bone to standard, short-wide, and double mini implants replacing missing molar supporting either hybrid ceramic crowns (Lava Ultimate restorative) or full-metal crowns under two different loading conditions (axial and off-axial loading) using strain gauge analysis.

Methods

Three single-molar implant designs, (1) single, 3.8-mm (regular) diameter implant, (2) single, 5.8-mm (wide) diameter implant, and (3) two 2.5-mm diameter (double) implants connected through a single-molar crown, were embedded in epoxy resin by the aid of a surveyor to ensure their parallelism. Each implant supported full-metal crowns made of Ni-Cr alloy and hybrid ceramic with standardized dimensions. Epoxy resin casts were prepared to receive 4 strain gauges around each implant design, on the buccal, lingual, mesial, and distal surfaces. Results were analyzed statistically.

Results

Results showed that implant design has statistically significant effect on peri-implant microstrains, where the standard implant showed the highest mean microstrain values followed by double mini implants, while the short-wide implant showed the lowest mean microstrain values. Concerning the superstructure material, implants supporting Lava Ultimate crowns had statistically significant higher mean microstrain values than those supporting full-metal crowns. Concerning the load direction, off-axial loading caused uneven distribution of load with statistically significant higher microstrain values on the site of off-axial loading (distal surface) than the axial loading.

Conclusions

Implant design, superstructure material, and load direction significantly affect peri-implant microstrains.

Use of stress analysis methods to evaluate the biomechanics of oral rehabilitation with implants

Because the biomechanical behavior of dental implants is different from that of natural tooth, clinical problems may occur. The mechanism of stress distribution and load transfer to the implant/bone interface is a critical issue affecting the success rate of implants. Therefore, the aim of this study was to conduct a brief literature review of the available stress analysis methods to study implant-supported prosthesis loading and to discuss their contributions in the biomechanical evaluation of oral rehabilitation with implants. Several studies have used experimental, analytical, and computational models by means of finite element models (FEM), photoelasticity, strain gauges and associations of these methods to evaluate the biomechanical behavior of dental implants. The FEM has been used to evaluate new components, configurations, materials, and shapes of implants. The greatest advantage of the photoelastic method is the ability to visualize the stresses in complex structures, such as oral structures, and to observe the stress patterns in the whole model, allowing the researcher to localize and quantify the stress magnitude. Strain gauges can be used to assess in vivo and in vitro stress in prostheses, implants, and teeth. Some authors use the strain gauge technique with photoelasticity or FEM techniques. These methodologies can be widely applied in dentistry, mainly in the research field. Therefore, they can guide further research and clinical studies by predicting some disadvantages and streamlining clinical time.

Implant platform switching: biomechanical approach using two-dimensional finite element analysis

In implant therapy, a peri-implant bone resorption has been noticed mainly in the first year after prosthesis insertion. This bone remodeling can sometimes jeopardize the outcome of the treatment, especially in areas in which short implants are used and also in aesthetic cases. To avoid this occurrence, the use of platform switching (PS) has been used. This study aimed to evaluate the biomechanical concept of PS with relation to stress distribution using two-dimensional finite element analysis. A regular matching diameter connection of abutment-implant (regular platform group [RPG]) and a PS connection (PS group [PSG]) were simulated by 2 two-dimensional finite element models that reproduced a 2-piece implant system with peri-implant bone tissue. A regular implant (prosthetic platform of 4.1 mm) and a wide implant (prosthetic platform of 5.0 mm) were used to represent the RPG and PSG, respectively, in which a regular prosthetic component of 4.1 mm was connected to represent the crown. A load of 100 N was applied on the models using ANSYS software. The RPG spreads the stress over a wider area in the peri-implant bone tissue (159 MPa) and the implant (1610 MPa), whereas the PSG seems to diminish the stress distribution on bone tissue (34 MPa) and implant (649 MPa). Within the limitation of the study, the PS presented better biomechanical behavior in relation to stress distribution on the implant but especially in the bone tissue (80% less). However, in the crown and retention screw, an increase in stress concentration was observed.

Impact of implant number, distribution and prosthesis material on loading on implants supporting fixed prostheses

The purpose of this study is to evaluate axial forces and bending moments (BMs) on implants supporting a complete arch fixed implant supported prosthesis with respect to number and distribution of the implants and type of prosthesis material. Seven oral Brånemark implants with a diameter of 3.75 mm and a length of 13 and 7 mm (short distal implant) were placed in an edentulous composite mandible used as the experimental model. One all-acrylic, one fibre-reinforced acrylic, and one milled titanium framework prosthesis were made. A 50 N vertical load was applied on the extension 10 mm distal from the most posterior implant. Axial forces and BMs were measured by calculating signals from three strain gauges attached to each of the abutments. The load was measured using three different models with varying numbers of supporting implants (3, 4 and 5), three models with different implant distribution conditions (small, medium and large) and three models with different prosthesis materials (titanium, acrylic and fibre-reinforced acrylic). Maximum BMs were highest when prostheses were supported by three implants compared to four and five implants (P < 0.001). The BMs were significantly influenced by the implant distribution, in that the smallest distribution induced the highest BMs (P < 0.001). Maximum BMs were lowest with the titanium prosthesis (P < 0.01). The resultant forces on implants were significantly associated with the implant number and distribution and the prosthesis material.

All-on-4 Immediate-Function Concept with Branemark SystemR Implants for Completely Edentulous Maxillae: A 1-Year Retrospective Clinical Study

BACKGROUND

Immediate implant function has become an accepted treatment modality for fixed restorations in totally edentulous mandibles, whereas experience from immediate function in the edentulous maxilla is limited.

PURPOSE

The purpose of this study was to evaluate a protocol for immediate function (within 3 hours) of four implants (All-on-4, Nobel Biocare AB, Göteborg, Sweden) supporting a fixed prosthesis in the completely edentulous maxilla.

MATERIALS AND METHODS

This retrospective clinical study included 32 patients with 128 immediately loaded implants (Brånemark System TiUnite, Nobel Biocare AB) supporting fixed complete-arch maxillary all-acrylic prostheses. A specially designed surgical guide was used to facilitate implant positioning and tilting of the posterior implants to achieve good bone anchorage and large interimplant distance for good prosthetic support. Follow-up examinations were performed at 6 and 12 months. Radiographic assessment of the marginal bone level was performed after 1 year in function.

RESULTS

Three immediately loaded implants were lost in three patients, giving a 1-year cumulative survival rate of 97.6%. The marginal bone level was, on average, 0.9 mm (SD 1.0 mm) from the implant/abutment junction after 1 year.

CONCLUSION

The high cumulative implant survival rate indicates that the immediate function concept for completely edentulous maxillae may be a viable concept.

Evaluation of factors influencing the marginal bone stability around implants in the treatment of partial edentulism

BACKGROUND

The original protocol of Brånemark to achieve predictable osseointegration for oral implants has substantially been modified. One may question whether results are influenced by those modifications, especially for the long-term prognosis.

PURPOSE

The goal of the present study was to investigate the impact of those parameters that deviate from the original protocol as defined by P-I Brånemark.

MATERIALS AND METHODS

In this study, 246 patients with 263 fixed partial prostheses supported by 668 Brånemark implants were followed from 1 to 15 years (mean: 6.3 yr). Radiographs were taken at the time of abutment connection, at 3 to 6 months, at 12 months, and then every 3 years. The bone level was rated mesially and distally from the implants on a total of 2588 radiographs.

RESULTS

A positive relation between abutment length and marginal bone level was found (p > .0001). The maxilla (p = .03), porcelain (p = .007), long abutments (p = .008), and regular-sized diameter implants (p = .001) all exhibited more bone loss in the first 6 months. After 6 months, only long implants showed more bone loss (p = .03).

CONCLUSIONS

Overall, the marginal bone level remained stable around Brånemark implants, never surpassing 2.2 mm, even after 15 years. Although longer implants lost more bone over time, this has to be interpreted with respect to higher resorption rates in less resorbed jaws.