Cláudia Lopes Brilhante Bhering

Influence of the casting technique and dynamic loading on screw detorque and misfit of single unit implant-supported prostheses.

Abstract Objective. This study aimed to evaluate the influence of the casting procedure and cyclic loading of prosthetic frameworks on detorque of prosthetic screws and marginal misfit of single unit implant-supported prostheses. Materials and methods. Twenty specimens were obtained, each one consisting of a set of an implant (external hexagon 3.75 × 13 mm – Branemark type), a prosthetic abutment (entirely calcinable or overcasted UCLA) and a prosthetic screw. After the specimens were obtained, the prosthetic screws were tightened with 30 Ncm torque and released 24 h later in order to evaluate initial detorque. The screws were retightened and marginal gaps were assessed. All specimens were submitted to 106 loading cycles, performed with 2 Hz frequency and 130 N load. The specimens were re-evaluated for marginal misfit and detorque after the mechanical loading (final marginal misfit/final detorque). The results were submitted to analysis of variance for repeated measurements, followed by Tukey HSD test (α = 0.05). Results. No statistically significant differences were found on detorque values of the prosthetics screws for all groups and intervals evaluated (p = 0.8922). The entirely calcinable abutments showed higher initial marginal misfit compared to the overcasted ones (p = 0.0438). There was no statistically significant difference on marginal misfit before and after mechanical loading for both groups (p > 0.05). Conclusions. It can be concluded that the overcasted abutments showed lower misfit values when compared to the entirely casted abutments. No difference was observed on detorque values of prosthetic screws. After mechanical loading there was no difference on marginal misfit and detorque between the groups.

Loosening torque of Universal Abutment screws after cyclic loading: influence of tightening technique and screw coating

PURPOSE The purpose of this study was to evaluate the influence of tightening technique and the screw coating on the loosening torque of screws used for Universal Abutment fixation after cyclic loading. MATERIALS AND METHODS Forty implants (Titamax Ti Cortical, HE, Neodent) (n=10) were submerged in acrylic resin and four tightening techniques for Universal Abutment fixation were evaluated: A - torque with 32 Ncm (control); B - torque with 32 Ncm holding the torque meter for 20 seconds; C - torque with 32 Ncm and retorque after 10 minutes; D - torque (32 Ncm) holding the torque meter for 20 seconds and retorque after 10 minutes as initially. Samples were divided into subgroups according to the screw used: conventional titanium screw or diamond like carbon-coated (DLC) screw. Metallic crowns were fabricated for each abutment. Samples were submitted to cyclic loading at 106 cycles and 130 N of force. Data were analyzed by two-way ANOVA and Tukeys test (5%). RESULTS The tightening technique did not show significant influence on the loosening torque of screws (P=.509). Conventional titanium screws showed significant higher loosening torque values than DLC (P=.000). CONCLUSION The use of conventional titanium screw is more important than the tightening techniques employed in this study to provide long-term stability to Universal Abutment screws.

Fit and Stability of Screw-Retained Implant-Supported Frameworks Under Masticatory Simulation: Influence of Cylinder Type

PURPOSE The aim of the study was to evaluate the effect of a prosthetic cylinder and casting on the misfit and loosening torque of screw-retained multiple-unit implant-supported dental prostheses under masticatory simulation. MATERIALS AND METHODS Screw-retained, three-unit fixed dental prostheses (FDP) and screw-retained full-arch FDP frameworks were waxed using calcinable (plastic cylinders) or overcasted (premachined cast-on cylinders) on the dental implant abutments. The cylinders were cast in Co-Cr alloy to obtain four groups according to cylinder type and prosthesis type (n = 10). The screws were tightened with 20 N/cm (abutment) and 10 N/cm (prosthetic) torque according to the manufacturers recommendation. After 24 hours, the initial loosening torque was analyzed. The initial misfit measurements were performed according to the Schiffleger test. The screws were retightened, and the specimens were submitted to 10(6) mechanical cycles (2 Hz/280 N). Loosening torque and misfit were reevaluated (final measurements), and data were submitted to ANOVA, Tukeys HSD, and Pearsons correlation tests (α = 0.05). RESULTS The calcinable three-unit FDP demonstrated greater misfit (initial: 107.53 ± 40.36 μm; final: 99.00 ± 40.85 μm) than did the overcasted three-unit FDP frameworks (initial: 51.50 ± 22.98 μm; final: 44.33 ± 14.14 μm) (initial: p = 0.0005; final: p = 0.0007). No difference was noted between the calcinable and overcasted full-arch FDP frameworks (p > 0.05). Masticatory simulation did not affect the misfit (p > 0.05). The overcasted full-arch FDP presented a lower abutment screw loosening torque (12.05 ± 1.80 N/cm) than did the calcinable ones (14.75 ± 1.72 N/cm) in the final measurement (p = 0.0024). The calcinable groups presented a lower prosthetic screw loosening torque than did the overcasted groups in the final evaluation (p < 0.05). After masticatory simulation, the prosthetic screw loosening torque of the calcinable three-unit FDP decreased (initial: 5.49 ± 1.07 N/cm; final: 3.73 ± 1.15 N/cm; p = 0.0044). Correlation between misfit and loosening was observed only for the prosthetic screws (p < 0.05). CONCLUSIONS The overcasted components provided a better fit in three-unit FDPs but did not influence the fit of full-arch FDPs. Prosthetic screws of overcasted frameworks presented higher stability, whereas masticatory simulation did not influence misfit but did reduce the prosthetic screw loosening torque of calcinable three-unit FDP frameworks.

The effect of casting and masticatory simulation on strain and misfit of implant-supported metal frameworks.

The influence of casting and masticatory simulation on marginal misfit and strain in multiple implant-supported prostheses was evaluated. Three-unit screw retained fixed dental prosthesis (FDP) and screw retained full-arch fixed dental prosthesis (FAFDP) frameworks were made using calcinable or overcasted cylinders on conical dental implant abutment. Four groups were obtained according to the cylinder and prosthesis type (n=10). Frameworks were casted in CoCr alloy and subjected to strain gauge analyses and marginal misfit measurements before and after 10(6) mechanical cycles (2 Hz/280 N). Results were submitted to ANOVA, Tukeys HSD and Pearson correlation test (α=0.05). No difference was found on misfit among all groups and times (p>0.05). Overcasted frameworks showed higher strain than the calcinable ones (FDP - Initial p=0.0047; Final p=0.0004; FAFDP - Initial p=0.0476; Final p=0.0115). The masticatory simulation did not influence strain (p>0.05). No correlation was observed between strain and misfit (r=0.24; p>0.05). In conclusion, the marginal misfit value in the overcasted full-arch frameworks was higher than clinical acceptable data. It proved that overcasted method is not an ideal method for full-arch prosthesis. Overcasted frameworks generate higher strain upon the system. The masticatory simulation had no influence on misfit and strain of multiple prostheses.

Comparison between all-on-four and all-on-six treatment concepts and framework material on stress distribution in atrophic maxilla: A prototyping guided 3D-FEA study

We evaluated two treatment concepts for the rehabilitation of moderate atrophic maxilla with dental implants (all-on-four and all-on-six) and the effect of framework material on the stress distribution of implant-support system. A three-dimensional finite element model based on a prototype was built to simulate an entirely edentulous maxilla with moderate sinus pneumatization that was rehabilitated with a full-arch fixed dental prosthesis. Four standard implants were positioned according to the all-on-four concept and four standard implants and two short implants were placed according to the all-on-six concept. Three framework materials were evaluated: cobalt-chrome (CoCr), titanium (Ti) and zirconia (Zr), totalizing six groups. A unilateral oblique force of 150N was applied to the posterior teeth. The von Mises (σVM), maximum (σmax) and minimum (σmin) principal stress and displacements were obtained. All-on-six showed smaller σmin, σVM and σmax values on the cortical bone, implants and trabecular bone, respectively. All-on-four exhibited higher displacement levels. Ti presented the highest stress values on the cortical bone, implants, abutments, prosthetic screws and displacement levels. In conclusion, the all-on-six approach and framework stiffer materials showed the most favorable biomechanical behavior. However, the stress values did not exceed the bone resistance limits for both treatment concepts.

The Influence of Post System Design and Material on the Biomechanical Behavior of Teeth with Little Remaining Coronal Structure: Posts Restoring Weakened Teeth

PURPOSE To evaluate the influence of different post systems on the biomechanical behavior of teeth with a severe loss of remaining coronal structure. MATERIALS AND METHODS Fifty standardized bovine teeth (n = 10 per group) were restored with: cast post-and-core (CPC), prefabricated metallic post (PFM), parallel glass-fiber post (P-FP), conical glass-fiber post (C-FP), or composite core (no post, CC). The survival rate during thermomechanical challenging (TC), the fracture strength (FS), and failure patterns (FP) were evaluated. Finite element models evaluated the stress distribution after the application of 100 N. RESULTS All specimens survived TC. Similar FS was observed among post-containing groups. Groups P-FP and CC presented 100% repairable fractures. The von Mises analysis showed the maximum stresses into the root canal in groups restored with metallic posts. Glass-fiber posts and CC presented the maximum stresses at the load contact point. Glass-fiber groups showed lower stresses in the analysis of maximal contact pressure; CPC led to the highest values of contact pressure. The modified von Mises (mvM) stress in dentin did not show differences among groups. Moreover, mvM values did not reach the dentin fracture limit for any group. CONCLUSIONS The type of intracanal post had a relevant influence on the biomechanical behavior of teeth with little remaining coronal structure.

Estabilidade de parafusos protéticos com pilares calcinável e sobrefundido após diferentes períodos de simulação mastigatória

Resumo O efeito do tipo de pilar em próteses unitárias implantossuportadas foi avaliado a partir de vinte amostras, compostas por implante HE, pilar protético do tipo UCLA (10 calcináveis e 10 para sobrefundição), parafuso de retenção e coroa em CoCr. Divididos em quatro grupos de estudo (n=5): pilares sobrefundidos e submetidos a 1 milhão (S1) e 3 milhões (S3) de ciclos mecânicos, pilares calcináveis e submetidos a 1 milhão (C1) e 3 milhões (C3) de ciclos mecânicos (frequência= 2 Hz; e carga oblíqua= 130N). Os parafusos foram torqueados (30 N.cm) e estabilidade e desajuste marginal foram avaliados antes e após cada período de ciclagem mecânica. Os dados foram submetidos à ANOVA de dois fatores, teste Bonferroni e regressão linear (α=0,05).