Acute toxicity of single and combined rare earth element exposures towards Daphnia similis.

The increasing use of Rare Earth Elements (REE) in emerging technologies, medicine and agriculture has led to chronic aquatic compartment contamination. In this context, this aimed to evaluate the acute toxic effects of lanthanum (La), neodymium (Nd) and samarium (Sm), as both single and binary and ternary mixtures on the survival of the microcrustacean Daphnia similis. A metal solution medium with (MS) and without EDTA and cyanocobalamin (MSq) as chelators was employed as the assay dilution water to assess REE bioavailability effects. In the single exposure experiments, toxicity in the MS medium decreased following the order La > Sm > Nd, while the opposite was noted for the MSq medium, which was also more toxic than the MS medium. The highest MS toxicity was observed for the binary Nd + La (1:1) mixture (EC50 48 h of 11.57 ± 1.22 mg.L-1) and the lowest, in the ternary Sm + La + Nd (2:2:1) mixture (EC50 48 h 41.48 ± 1.40 mg.L-1). The highest toxicity in the MSq medium was observed in the single assays and in the binary Sm + Nd (1:1) mixture (EC50 48 h 10.60 ± 1.57 mg.L-1), and the lowest, in the ternary Sm + La + Nd (1:2:2) mixture (EC50 48 h 36.76 ± 1.54 mg.L-1). Concerning the MS medium, 75 % of interactions were additive, 19 % antagonistic, and 6 % synergistic. In the MSq medium, 56 % of interactions were synergistic and 44 % additive. The higher toxicity observed in the MSq medium indicates that the absence of chelators can increase the concentrations of more toxic free ions, suggesting that the MS medium should be avoided in REE assays. Additive interactions were observed in greater or equivalent amounts in both media and were independent of elemental mixture ratios. These findings improve the understanding of environmental REE effects, contributing to the establishment of future guidelines and ecological risk calculations.

In silico dosimetry of low-dose rate brachytherapy using radioactive nanoparticles.

PURPOSE: Nanoparticles (NPs) with radioactive atoms incorporated within the structure of the NP or bound to its surface, functionalized with biomolecules are reported as an alternative to low-dose-rate seed-based brachytherapy. In this study, authors report a mathematical dosimetric study on low-dose rate brachytherapy using radioactive NPs. METHOD: Single-cell dosimetry was performed by calculating cellular S-values for spherical cell model using Au-198, Pd-103 and Sm-153 NPs. The cell survival and tumor volume versus time curves were calculated and compared to the experimental studies on radiotherapeutic efficiency of radioactive NPs published in the literature. Finally, the radiotherapeutic efficiency of Au-198, Pd-103 and Sm-153 NPs was tested for variable: administered radioactivity, tumor volume and tumor cell type. RESULT: At the cellular level Sm-153 presented the highest S-value, followed by Pd-103 and Au-198. The calculated cell survival and tumor volume curves match very well with the published experimental results. It was found that Au-198 and Sm-153 can effectively treat highly aggressive, large tumor volumes with low radioactivity. CONCLUSION: The accurate knowledge of uptake rate, washout rate of NPs, radio-sensitivity and tumor repopulation rate is important for the calculation of cell survival curves. Self-absorption of emitted radiation and dose enhancement due to AuNPs must be considered in the calculations. Selection of radionuclide for radioactive NP must consider size of tumor, repopulation rate and radiosensitivity of tumor cells. Au-198 NPs functionalized with Mangiferin are a suitable choice for treating large, radioresistant and rapidly growing tumors.

Knee radiosynovectomy with 153Sm-hydroxyapatite compared to 90Y-hydroxyapatite: initial results of a prospective trial.

INTRODUCTION: Radiosynovectomy (RS) with 90Y-hydroxyapatite (90Y-HyA) aims to control knee hemarthrosis in hemophiliac patients to prevent secondary arthropathy. However, knee RS using 153Sm-hydroxyapatite (153Sm-HyA) is considered less suitable due to the lower average soft tissue range and energy of 153Sm for large joints, such as the knees. PURPOSE: The objective of this investigation was to assess the efficacy and safety of knee RS with 153Sm-HyA, compared to 90Y-HyA. METHODS: Forty patients were prospectively assigned to undergo knee RS with 153Sm-HyA (n = 19) or with 90Y-HyA (n = 21). The frequency of hemarthrosis episodes before and after treatment were compared. RESULTS: After six months of knee RS, 153Sm-HyA and 90Y-HyA promoted a similar reduction of hemarthrosis episodes (50% and 66.7%, respectively). However, after 12 months of knee RS, the reduction of hemarthrosis episodes was significantly (p = 0.037) higher using 153Sm-HyA (87.5%) compared to 90Y-HyA (50.0%). This discrepancy was more pronounced (p = 0.002) for 153Sm-HyA compared to 90Y-HyA in adults/adolescents. CONCLUSION: Knee radiosynovectomy with 153Sm-HyA is safe, reduces hemarthrosis episodes after 12 months of treatments, especially in adults/adolescents and even with grades III/IV arthropathy, similar to 90Y-HyA. 90Y-HyA seems to promote better hemarthrosis control in small children.

Boron nitride nanotubes radiolabeled with 153Sm and 159Gd: Potential application in nanomedicine.

Boron nitride nanotubes (BNNTs) have been growing in notoriety in the development of systems aiming bioapplications. In this work we conducted an investigation about the mechanisms involved in the incorporation of samarium and gadolinium in BNNTs. The process was performed by the reduction of samarium and gadolinium oxides (Sm2O3 and Gd2O3, respectively) in the presence of NH3 gas (witch decomposes into N2 and H2) at high temperatures. Various characterization techniques were conducted to elucidate how Sm and Gd are introduced into the BNNT structure. Biological in vitro assays were performed with human fibroblasts and a human osteosarcoma cell line (SAOS-2). Our results show that the studied systems have high potential for biomedical application and can be used as non-invasive imaging agents, such as scintigraphy radiotracers or as magnetic resonance imaging (MRI) contrast medium, being able to promote the treatment of many types of tumors simultaneously to their diagnosis.

Biosorption of lanthanum and samarium by viable and autoclaved mycelium of Botryosphaeria rhodina MAMB-05.

The ascomycetous fungus, Botryosphaeria rhodina MAMB-05, secretes a (1→3)(1→6)-ß-D-glucan, and the scaled-up production of this ß-glucan results in large amounts of mycelial biomass being produced that represent a potentially cost-effective biosorbent for rare-earth elements. High sorption capacities for both La(III) and Sm(III) were demonstrated for viable and autoclaved lyophilized fungal mycelium. Fourier-transformed infra-red absorption spectra and the point of zero charge (PZC) were similar for the viable and inactive fungal mycelia. The rare-earth lanthanide elements (La and Sm) binding increased at initial pH values greater than 5.0, which was also observed for the PZC determination. The maximum La(III) uptake capacity was observed at lower amounts of La(III) ions in solution, decreasing from 100.0 to 25.3% when the initial lanthanide concentration increased from 15 to 100 mg/L. Lanthanide biosorption by B. rhodina MAMB-05 mycelia followed the Langmuir model, and the affinity of biosorbent functional groups was similar for La(III) and Sm(III).

Effect of acute/subchronic samarium exposure on the concentration, motility, and morphology of sperm in male mice.

Male ICR mice were orally administered samarium nitrate [Sm(NO3)3] to investigate its effects on sperm concentration and sperm quality. After acute exposure to ≥2880.00 mg/kg Sm(NO3)3 via intragastric gavage, sperm motility and acrosome integrity were decreased, and the sperm malformation percentage was increased (P < 0.05). After subchronic exposure to ≥500.00 mg/L Sm(NO3)3 administered via drinking water for 90 days, relative gonad weight, sperm concentration, and sperm quality significantly decreased (P < 0.05). Sperm malformation also increased after subchronic exposure to Sm, which was found to be the most sensitive index. Sperm head malformation accounted for the largest proportion of all types of sperm malformations evaluated. Of the six different subtypes of head malformation, irregular shape accounted for the largest proportion.

MgO:Li,Ce,Sm as a high-sensitivity material for Optically Stimulated Luminescence dosimetry.

The goal of this work was to investigate the relevant dosimetric and luminescent properties of MgO:Li3%,Ce0.03%,Sm0.03%, a newly-developed, high sensitivity Optically Stimulated Luminescence (OSL) material of low effective atomic number (Zeff = 10.8) and potential interest for medical and personal dosimetry. We characterized the thermoluminescence (TL), OSL, radioluminescence (RL), and OSL emission spectrum of this new material and carried out a preliminary investigation on the OSL signal stability. MgO:Li,Ce,Sm has a main TL peak at ~180 °C (at a heating rate of 5 °C/s) associated with Ce(3+) and Sm(3+) emission. The results indicate that the infrared (870 nm) stimulated OSL from MgO:Li,Ce,Sm has suitable properties for dosimetry, including high sensitivity to ionizing radiation (20 times that of Al2O3:C, under the measurement conditions) and wide dynamic range (7 µGy-30 Gy). The OSL associated with Ce(3+) emission is correlated with a dominant, practically isolated peak at 180 °C. Fading of ~15% was observed in the first hour, probably due to shallow traps, followed by subsequent fading of 6-7% over the next 35 days. These properties, together with the characteristically fast luminescence from Ce(3+), make this material also a strong candidate for 2D OSL dose mapping.

Comparison of the effect of knee synovectomy in haemophilic patients with 153Sm- and 90Y-labelled hydroxyapatite 1 year after.

To compare the use of 740 Mbq (20 mCi) of (153) Sm and 185 Mbq (5mCi) of (90) Y, both labelling hydroxyapatite (HA), for knee synovectomy in haemophilic patients, 1 year after the intervention. Thirty three men (36 knees) were studied, divided into two groups: 1 - treatment using 740 Mbq of (153) Sm-HA: 20 knees of 18 patients, with mean age of 21.4 ± 13.3 years (ranging from 7 to 56 years) and mean Pettersson score of 5.3; 2 - treatment using 185 Mbq of (90) Y-HA: 16 knees of 15 patients, with mean age of 26.3 ± 10.3 (ranging from 7 to 51 years) and mean Pettersson score of 6.3. The following criteria were adopted for the evaluation before and 1 year after synovectomy: reduction in haemarthrosis episodes and pain using a visual analogue scale, as well as improved joint mobility. The occurrence of adverse events in the treatment was also considered. The chi-square, Wilcoxon and Mann-Whitney tests were used with P ≤ 0.05 set as significant. The occurrence of haemarthrosis declined by 65.7% with the use of (153) Sm-HA and 82.6% for (90) Y-HA, with no statistical difference between the groups (P = 0.632); pain reduction was 42.5% in group 1 and 30.7% in group 2, once again with no statistical difference (P = 0.637). Improvement in joint mobility was not significant for both groups. Two cases of mild reactive synovitis were observed in group 1 and one in group 2, which cleared up without medical intervention. Although the beta energy from (90) Y is the gold standard for knee synovectomy, higher activities of (153) Sm may be used in places which have only production of this material.

The use of 185 MBq and 740 MBq of 153-samarium hydroxyapatite for knee synovectomy in haemophilia.

The penetration of beta energy of 153-samarium ((153) Sm) (0.8 MeV) is not only appropriate for synovectomy of median articulations but is possible to improve the radiobiological effect using increased activities. The aim of this study was to assess the effectiveness of 185 MBq and 740 MBq of 153-samarium hydroxyapatite ((153) Sm-HA) in knees of haemophilic patients. Thirty-one patients--36 knees, 30 males, were divided into two groups without coinjection of corticosteroid: A - 14 patients (17 knees) treated with intra-articular dose of 185 MBq of (153) Sm-HA, average age 23 years; B--17 patients (19 knees) with 740 MBq of (153) Sm-HA, average age 21.3 years. The evaluation before and after 1 year of synovectomy used the following criteria: reduction in the number of haemarthroses and use of the coagulation factor and improvement in articular motility. Adverse-effects occurrence was considered too. Early and late scintigraphic studies were performed after synoviorthesis and no joint immobilization was recommended. The reduction in haemarthrosis and use of coagulation factor were: group 1--31.3% and 25%; group 2--81.5% and 79% with P < 0.001 respectively; no significant improvement in knees motility was noted for both groups. Four cases of mild reactional synovitis were observed in each group. The scintigraphic control showed homogenous distribution of the radiopharmaceuticals with no articular escape; the material was considered safe by its permanence in the articulation. We have significant improvement in the synovectomy of haemophilic knees with 740 MBq of (153) Sm-HA; the less penetration of its beta radiation was compensated by the increased biological effect with the higher used activity.

Synthesis and characterization of calcium phosphate loaded with Ho-166 and Sm-153: a novel biomaterial for treatment of spine metastases.

Spine metastases are a common and painful complication of cancer. A novel concept of treatment combines the in situ vertebroplasty with radiotherapy employing radioactive bone cement into the human vertebrae. Thus, investigations concerning possible bioactive and radioactive cements become a relevant theme. In this work, we have synthesized calcium phosphate bioceramics incorporated with Ho and Sm nuclides using sol-gel technique. Characterizations were performed using X-ray diffractometry, infrared spectroscopy, scanning electron microscopy, instrumental neutron activation analysis, and gamma spectroscopy. Results showed bioceramics composed by multiphasic calcium phosphates along with holmium and samarium phosphates, with 8.9 and 13.7 % of Sm and Ho in weight, respectively. After neutron activation, the Ho-166 and Sm-153 beta-emitters were identified and quantified on the bioceramics with activities estimated at 32.5 and 14.5 MBq/mg of Sm-153 and Ho-166 bioceramic powder, respectively. These radioactive calcium phosphate bioceramics can compose suitable radioactive cements to radiovertebroplasty.

Radioactive synovectomy with (90) yttrium and (153) samarium hydroxyapatite in haemophilic joints: preliminary study on radiation safety.

Most countries still do not achieve 1 IU of factor VIII/capita sufficient for survival. Although primary prophylaxis prevents synovitis, is not universally used. Chronic synovitis is treated with arthroscopy at expense of considerable amount of coagulation factors, and specialized surgeons. Radioactive synovectomy (RS) is a minimally invasive and cost effective alternative to arthroscopy, often considered first the option for persistent synovitis. Even without established causation with cancer, RS is avoided by some, due to this concern. We aim contributing to the understanding of RS safety regarding malignancy, presenting a large number of treated patients, and a single case of cancer. Three centres in Brazil applied RS with (90) Yttrium Citrate, (90) Yttrium hydroxyapatite or (153) Samarium hydroxyapatite in haemophilic joints and performed a survey addressing cancer in these patients. Four hundred and eighty eight patients (ages 3-51) received 1-3 RS (total 842) and follow-up was 6 months to 9 years. One patient aged 14 years presented Ewing sarcoma, 11 months after RS. The tumour was treated successfully with surgery and chemotherapy. Causality of cancer by RS is improbable in this case. Accordingly, latency here is far below minimum 5-10 years for radio-induction of solid tumours. Moreover, ES is not a typically radio-induced tumour, even at high doses. In agreement with others, though recognizing limitations, this study suggests RS is safe regarding cancer induction. Synovitis is a known burden for patients. The decision of making reasonable usage of RS should be outweighed with the risks of leaving synovitis untreated.

Determination of Judd-Ofelt intensity parameters of pure samarium(III) complexes.

This work reports an alternative aproach to obtain the Judd-Ofelt intensity parameters of Sm(III) complexes with the general formula: [Sm(tta)(3)(L)(n)], with L = H(2)O, triphenylphosphine oxide (tppo), 2,2'-bipyridine (bipy) and 1,10-phenantroline (phen); n = 2 for H(2)O and tppo and n = 1 for phen and bipy, using the absorption spectra of rare earth complexes where the powders are dispersed in KBr pellets. This approach can be applied to other complexes of rare earth ions that have spin allowed transitions and it is validated by comparing the emission spectra of the complexes with those dispersed in KBr pellets.

Development of a voxel model of the heart for dosimetry.

This article investigates the dosimetry of a radioactive stent and radioactive liquid balloon placed into the heart vasculature to prevent restenosis after atherosclerosis treatment. The research aims to know the dosages to establish a suitable activity which achieves restenosis control and thereafter minimize radiation effects in the cardiac muscle. In order to accomplish the dosimetric analysis, a heart voxel model was assembled based on tomographic images. The computational model consists of a three-dimensional matrix taken from 60 tomographic images representing the major heart tissues. A radioactive ¹5³Sm liquid balloon is simulated as well as a ³²P radioactive stent, inserted in an arbitrary heart artery. After simulation processing, the absorbed dose rate was evaluated in the heart musculature. The models are presented in two- and three-dimensional previews and the dosage profiles are shown by isodose curves superimposed onto the heart model.

Effectiveness of radiation synovectomy with Yttrium-90 and Samarium-153 particulate hydroxyapatite in rheumatoid arthritis patients with knee synovitis: a controlled, randomized, double-blinded trial.

The aim of the present study was to investigate the long-term effectiveness of and tolerance to Yttrium-90 and Samarium-153-particulate hydroxyapatite radiation synovectomy in patients with rheumatoid arthritis (RA) and chronic knee synovitis. Eight-four patients (90 knees) with chronic knee synovitis and RA (according to the American College of Rheumatology criteria) participated in a controlled, double-blinded trial. Patients were randomized to receive an intra-articular injection with either 5 mCi Yttrium-90 plus 40 mg of triamcinolone hexacetonide (Y/TH Group), 15 mCi Samarium-153 hydroxyapatite plus 40 mg of triamcinolone hexacetonide (Sm/TH Group), or 40 mg triamcinolone hexacetonide alone (Control Group). Blinded examination at baseline, 1, 4, 12, 32, and 48 weeks post-intervention included a visual analog scale for joint pain and swelling, morning stiffness, range of motion, knee circumference, Likert scale, percentage of improvement, Stanford Health Assessment Questionnaire, Lequesne index, use of non-steroidal anti-inflammatory drugs and corticosteroids, events and adverse effects, calls to the physician, and hospital visits. There were three withdrawals prior to the injections. Regarding the pain, there was a significantly better response in the Y/TH Group versus the Sm/TH Group at T1 (p = 0.025) and versus TH alone at T48 (p = 0.026). The Sm/TH group had more adverse effects (p = 0.042), but these were mild and transitory. For the pain parameter alone, Yttrium-90 radiosynovectomy associated to TH proved superior to Samarium-153 hydroxyapatite radiosynovectomy associated to TH at T1 and to synovectomy with TH at T48. No other statistically significant inter-group differences were detected.

Gamma spectrometry and chemical characterization of ceramic seeds with samarium-153 and holmium-166 for brachytherapy proposal.

Ceramic seeds were synthesized by the sol-gel technique with Si:Sm:Ca and Si:Ho:Ca. One set of seeds was irradiated in the TRIGA type nuclear reactor IPR-R1 and submitted to instrumental neutron activation analysis (INAA), K(0) method, to determine mass percentage concentration of natural samarium and holmium in the seed as well as to determine all existing radionuclides and their activities. Attention was paid to discrimination of Si-31, Ca-40, Ca-45, Ca-47, Ca-49, Sm-145, Sm-155, Sm-153 and Ho-166. A second sample was submitted to atomic emission spectrometry (ICP-AES) also to determine samarium and holmium concentrations in weight. A third sample was submitted to X-ray fluorescence spectrometry to qualitatively determine chemical composition. The measured activity was due to Sm-153 and Ho-166 with a well-characterized gamma spectrum. The X-ray fluorescence spectrum demonstrated that there is no discrepancy in seed composition. The maximum ranges in the water of beta particles from Sm-153 and Ho-166 decay were evaluated, as well as the dose rate and total dose delivered within the volume delimited by the range of the beta particles. The results are relevant for investigation of the viability of producing Sm-153 and Ho-166 radioactive seeds for use in brachytherapy.

In vivo comparative study of hydroxyapatite labeled with different radioisotopes: evaluation of the scintigraphic images.

Radyosinovectomy (RSV) is a radiotherapeutic modality where a beta-emitting radionuclide is administered locally by intra-articular injection on the form of a colloid or radiolabeled particulate. RSV is a well-accepted therapeutic procedure in inflammatory joint diseases and has been successfully employed for more than 50 years as a viable alternative to surgical and chemical synovectomy. The aim of this work is to compare the in vivo stability of hydroxyapatite labelled with (177)Lu, (90)Y and (153)Sm. All radionuclides were labelled with high yield and were retained in the joint for 7 days, showing stability and usefulness as tools in the RSV treatment. A similar retention of the products in the muscle was observed when the particles were administrated in the muscle. However, the pure form of the radionuclides were rapidly cleared from the blood and accumulated in the liver when injected i.v.. Although (153)Sm-HA is already available for nuclear medicine procedures and clinical studies with (90)Y-HA have been developed, (177)Lu-labeled RSV agents will be economically more viable and has not been studied yet. Its favorable characteristics contribute to follow, to predict and asses the success of RSV by bone scintigraphy studies.

Effectiveness of radiation synovectomy with samarium-153 particulate hydroxyapatite in rheumatoid arthritis patients with knee synovitis: a controlled randomized double-blind trial.

OBJECTIVES: The aim of the present study was to investigate the effectiveness of Samarium(153)-particulate hydroxyapatite radiation synovectomy in rheumatoid arthritis patients with chronic knee synovitis. METHODS: Fifty-eight rheumatoid arthritis patients (60 knees) with chronic knee synovitis participated in a controlled double-blinded trial. Patients were randomized to receive either an intra-articular injection with 40 mg triamcinolone hexacetonide alone (TH group) or 40 mg triamcinolone hexacetonide combined with 15 mCi Samarium(153)-particulate hydroxyapatite (Sm/TH group). Blinded examination at baseline (T0) and at 1 (T1), 4 (T4), 12 (T12), 32 (T32), and 48 (T48) weeks post-intervention were performed on all patients and included a visual analog scale for joint pain and swelling as well as data on morning stiffness, flexion, extension, knee circumference, Likert scale of improvement, percentage of improvement, SF-36 generic quality of life questionnaire, Stanford Health Assessment Questionnaire (HAQ), Lequesne index, use of non-steroidal anti-inflammatory drugs or oral corticosteroids, events and adverse effects, calls to the physician, and hospital visits. RESULTS: The sample was homogeneous at baseline, and there were no withdrawals. Improvement was observed in both groups in relation to T0, but no statistically significant differences between groups were observed regarding all variables at the time points studied. The Sm/TH group exhibited more adverse effects at T1 (p<0.05), but these were mild and transitory. No severe adverse effects were reported during follow-up. CONCLUSION: Intra-articular injection of Samarium(153)-particulate hydroxyapatite (15 mCi) with 40 mg of triamcinolone hexacetonide is not superior to triamcinolone hexacetonide alone for the treatment of knee synovitis in patients with rheumatoid arthritis at 1 y of follow-up.

Application of a wrist dosimeter prototype for radiation monitoring ((153)Sm) during a therapeutic procedure simulation.

Gamma and beta radiation emitting radiopharmaceuticals are handled in nuclear medicine services, and in many cases there is only individual monitoring of gamma radiation. In this paper, the results obtained using a wrist dosimeter prototype (CaSO(4):Dy+Teflon pellets) show that the doses for workers occupationally exposed to beta radiation from (153)Sm are not negligible. It is important that this dose is evaluated, and it has to be taken into consideration in the individual monitoring system.

Absorbed dose profiles for (32)P, (90)Y, (188)Re, (177)Lu, (153)Sm and (169)Er: radionuclides used in radiosynoviortheses treatment.

The main objective of this paper was to obtain the absorbed dose profiles for radionuclides of frequent or potential use in radiosynoviortheses. These profiles reveal the absorbed dose per activity of injected radionuclide (Gy/h*MBq) in the synovial membrane and the articular cartilage. The researched radionuclides were (32)P, (90)Y, (188)Re, (177)Lu, (153)Sm and (169)Er. The therapeutic range of each radionuclides in synovial tissue were also calculated. This range determines the synovial thickness that can be sufficiently irradiated and thus successfully treated. The S values for the synovial membrane and articular cartilage were calculated using as a model a cylinder with the source uniformly distributed in its volume. The synovial membrane was simulated varying the radius of the cylinder (from 0.5cm to 9cm) and its height (from 0.01cm to 0.04cm). The area in the base of the cylinder represents different sizes of the synovial surface (small, medium and large joints). The height of the cylinder represents different stages of the progression of the rheumatoid arthritis. The same model was used to simulate the articular cartilage but, the source was uniformly distributed into a cylindrical slab (0.01cm height and 1cm of radius. The results obtained allow the estimation of the dose that will be delivered to the synovial membrane and the articular cartilage for different joint sizes and different stages of progression of the rheumatoid arthritis (RA).

Photoelastic analysis of stress distribution in different retention systems for facial prosthesis.

The aim of this study was to assess the behavior and stress distribution of 3 retention systems associated with implant for facial prosthesis by using the photoelasticity method. A photoelastic model was made from the replica of the orbital region on the left side of a dry skull with two 4-mm implants fixed in the superior orbital region. Three facial prosthetic retention systems were made for this study: O'ring, bar-clip, and magnets. The set (model/retention systems/prosthesis) was placed in a polariscope, and then traction began to be applied to the retention systems. The limit values for removal of the retention system were obtained by tests performed in an EMIC Universal test machine. The results were obtained by observation during the experiments and by photographic record of the stress behavior in the photoelastic model, resulting from the traction of the retention systems. In the magnet system, a lowest formation of fringes was verified both around and between the implants; in the O'ring system, the formation of photoelastic fringes was noted between the implants in the apical region; and in the bar-clip system, there was a greater concentration of colored fringes in the regions between the implants and cervical area. Based on the results obtained, it was concluded that the retention systems produced different stress distribution characteristics that, in general, were concentrated in the area around the implants, and the highest concentration of fringes, in increasing order, occurred in the retention systems of the magnets, O'ring, and bar-clip.