Influência de uma superfície modificada por fluoretos na osseointegração de implantes dentais em ratos diabéticos

Pós-graduação em Odontologia - FOAR

Efeito de três sistemas de osteotomia - ultrassom cirúrgico, laser Er, Cr: YSGG e sistema rotatório - sobre o processo de osseointegração e reparo de defeitos ósseos em tíbia de ratos: estudo histomorfométrico, imuno-histoquímico e biomecânico

Pós-graduação em Odontologia - FOAR

Efeito da administração de alendronato, a longo prazo, sobre as propriedades mecânicas do tecido ósseo, sua reparação e mineralização ao redor de implantes osseointegráveis. Estudo em ratas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Biomechanical and histologic evaluation of non-washed resorbable blasting media and alumina-blasted/acid-etched surfaces

Objectives: To compare the biomechanical fixation and histomorphometric parameters between two implant surfaces: non-washed resorbable blasting media (NWRBM) and alumina-blasted/acid-etched (AB/AE), in a dog model. Material and methods: The surface topography was assessed by scanning electron microscopy, optical interferometry and chemistry by X-ray photoelectron spectroscopy (XPS). Six beagle dogs of similar to 1.5 years of age were utilized and each animal received one implant of each surface per limb (distal radii sites). After a healing period of 3 weeks, the animals were euthanized and half of the implants were biomechanically tested (removal torque) and the other half was referred to nondecalcified histology processing. Histomorphometric analysis considered bone-to-implant contact (BIC) and bone area fraction occupancy (BAFO). Following data normality check with the Kolmogorov-Smirnov test, statistical analysis was performed by paired t-tests at 95% level of significance. Results: Surface roughness parameters Sa (average surface roughness) and Sq (mean root square of the surface) were significantly lower for the NWRBM compared with AB/ AE. The XPS spectra revealed the presence of Ca and P in the NWRBM. While no significant differences were observed for both BIC and BAFO parameters (P>0.35 and P>0.11, respectively), a significantly higher level of torque was observed for the NWRBM group (P = 0.01). Bone morphology was similar between groups, which presented newly formed woven bone in proximity with the implant surfaces. Conclusion: A significant increase in early biomechanical fixation was observed for implants presenting the NWRBM surface.

Evaluation of chemically modified SLA implants (modSLA) biofunctionalized with integrin (RGD)- and heparin (KRSR)-binding peptides

Enhancing osseointegration through surface immobilization of multiple short peptide sequences that mimic extracellular matrix (ECM) proteins, such as arginine-glycine-aspartic acid (RGD) and lysine-arginine-serine-arginine (KRSR), has not yet been extensively explored. Additionally, the effect of biofunctionalizing chemically modified sandblasted and acid-etched surfaces (modSLA) is unknown. The present study evaluated modSLA implant surfaces modified with RGD and KRSR for potentially enhanced effects on bone apposition and interfacial shear strength during early stages of bone regeneration. Two sets of experimental implants were placed in the maxillae of eight miniature pigs, known for their rapid wound healing kinetics: bone chamber implants creating two circular bone defects for histomorphometric analysis on one side and standard thread configuration implants for removal torque testing on the other side. Three different biofunctionalized modSLA surfaces using poly-L-lysine-graft-poly(ethylene glycol) (PLL-g-PEG) as a carrier minimizing nonspecific protein adsorption [(i) 20 pmol cm⁻² KRSR alone (KRSR); or in combination with RGD in two different concentrations; (ii) 0.05 pmol cm⁻² RGD (KRSR/RGD-1); (iii) 1.26 pmol cm⁻² RGD (KRSR/RGD-2)] were compared with (iv) control modSLA. Animals were sacrificed at 2 weeks. Removal torque values (701.48-780.28 N mm), bone-to-implant contact (BIC) (35.22%-41.49%), and new bone fill (28.58%-30.62%) demonstrated no significant differences among treatments. It may be concluded that biofunctionalizing modSLA surfaces with KRSR and RGD derivatives of PLL-g-PEG polymer does not increase BIC, bone fill, or interfacial shear strength.

Osseointegration and biocompatibility of different metal implants-a comparative experimental investigation in sheep

Background In the present study, 4 different metallic implant materials, either partly coated or polished, were tested for their osseointegration and biocompatibility in a pelvic implantation model in sheep. Methods Materials to be evaluated were: Cobalt-Chrome (CC), Cobalt-Chrome/Titanium coating (CCTC), Cobalt-Chrome/Zirconium/Titanium coating (CCZTC), Pure Titanium Standard (PTST), Steel, TAN Standard (TANST) and TAN new finish (TANNEW). Surgery was performed on 7 sheep, with 18 implants per sheep, for a total of 63 implants. After 8 weeks, the specimens were harvested and evaluated macroscopically, radiologically, biomechanically (removal torque), histomorphometrically and histologically. Results Cobalt-Chrome screws showed significantly (p = 0.031) lower removal torque values than pure titanium screws and also a tendency towards lower values compared to the other materials, except for steel. Steel screws showed no significant differences, in comparison to cobalt-chrome and TANST, however also a trend towards lower torque values than the remaining materials. The results of the fluorescence sections agreed with those of the biomechanical test. Histomorphometrically, there were no significant differences of bone area between the groups. The BIC (bone-to-implant-contact), used for the assessment of the osseointegration, was significantly lower for cobalt-chrome, compared to steel (p = 0.001). Steel again showed a lower ratio (p = 0.0001) compared to the other materials. Conclusion This study demonstrated that cobalt-chrome and steel show less osseointegration than the other metals and metal-alloys. However, osseointegration of cobalt-chrome was improved by zirconium and/or titanium based coatings (CCTC, TANST, TAN, TANNEW) being similar as pure titanium in their osseointegrative behavior.

Biomechanical evaluation of the interfacial strength of a chemically modified sandblasted and acid-etched titanium surface

The functional capacity of osseointegrated dental implants to bear load is largely dependent on the quality of the interface between the bone and implant. Sandblasted and acid-etched (SLA) surfaces have been previously shown to enhance bone apposition. In this study, the SLA has been compared with a chemically modified SLA (modSLA) surface. The increased wettability of the modSLA surface in a protein solution was verified by dynamic contact angle analysis. Using a well-established animal model with a split-mouth experimental design, implant removal torque testing was performed to determine the biomechanical properties of the bone-implant interface. All implants had an identical cylindrical shape with a standard thread configuration. Removal torque testing was performed after 2, 4, and 8 weeks of bone healing (n = 9 animals per healing period, three implants per surface type per animal) to evaluate the interfacial shear strength of each surface type. Results showed that the modSLA surface was more effective in enhancing the interfacial shear strength of implants in comparison with the conventional SLA surface during early stages of bone healing. Removal torque values of the modSLA-surfaced implants were 8-21% higher than those of the SLA implants (p = 0.003). The mean removal torque values for the modSLA implants were 1.485 N m at 2 weeks, 1.709 N m at 4 weeks, and 1.345 N m at 8 weeks; and correspondingly, 1.231 N m, 1.585 N m, and 1.143 N m for the SLA implants. The bone-implant interfacial stiffness calculated from the torque-rotation curve was on average 9-14% higher for the modSLA implants when compared with the SLA implants (p = 0.038). It can be concluded that the modSLA surface achieves a better bone anchorage during early stages of bone healing than the SLA surface; chemical modification of the standard SLA surface likely enhances bone apposition and this has a beneficial effect on the interfacial shear strength.

Biomechanical comparison of different surface modifications for dental implants

Purpose: A satisfactory clinical outcome in dental implant treatment relies on primary stability for immediate load bearing. While the geometric design of an implant contributes to mechanical stability, the nature of the implant surface itself is also critically important. Biomechanical and microcomputerized tomographic evaluation of implant osseointegration was performed to compare alternative structural, chemical and biochemical, and/or pharmaceutical surface treatments applied to an identical established implant design. Materials and Methods: Dental implants with the same geometry but with 6 different surface treatments were tested in vivo in a sheep model (pelvis). Peri-implant bone density and removal torque were compared at 2, 4, and 8 weeks after implantation. Implant surfaces tested were: sandblasted and acid-etched titanium (Ti), sandblasted and etched zirconia, Ti coated with calcium phosphate (CaP), Ti modified via anodic plasma-chemical treatment (APC), bisphosphonate-coated Ti (Ti + Bisphos), and Ti coated with collagen containing chondroitin sulfate (CS). Results: All dental implants were well integrated at the time of sacrifice. There were no significant differences observed in peri-implant bone density between implant groups. After 8 weeks of healing, removal torque values for Ti, Ti + CaP, Ti + Bisphos, and Ti + collagen + CS were significantly higher than those for zirconia and Ti + APC. Conclusions: Whereas the sandblasted/acid-etched Ti implant can still be considered the reference standard surface for dental implants, functional surface modifications such as bisphosphonate or collagen coating seem to enhance early peri-implant bone formation and should be studied further.

Quantifying the influence of bone density and thickness on resonance frequency analysis: an in vitro study of biomechanical test materials

PURPOSE: Resonance frequency analysis (RFA) offers the opportunity to monitor the osseointegration of an implant in a simple, noninvasive way. A better comprehension of the relationship between RFA and parameters related to bone quality would therefore help clinicians improve diagnoses. In this study, a bone analog made from polyurethane foam was used to isolate the influences of bone density and cortical thickness in RFA. MATERIALS AND METHODS: Straumann standard implants were inserted in polyurethane foam blocks, and primary implant stability was measured with RFA. The blocks were composed of two superimposed layers with different densities. The top layer was dense to mimic cortical bone, whereas the bottom layer had a lower density to represent trabecular bone. Different densities for both layers and different thicknesses for the simulated cortical layer were tested, resulting in eight different block combinations. RFA was compared with two other mechanical evaluations of primary stability: removal torque and axial loading response. RESULTS: The primary stability measured with RFA did not correlate with the two other methods, but there was a significant correlation between removal torque and the axial loading response (P < .005). Statistical analysis revealed that each method was sensitive to different aspects of bone quality. RFA was the only method able to detect changes in both bone density and cortical thickness. However, changes in trabecular bone density were easier to distinguish with removal torque and axial loading than with RFA. CONCLUSIONS: This study shows that RFA, removal torque, and axial loading are sensitive to different aspects of the bone-implant interface. This explains the absence of correlation among the methods and proves that no standard procedure exists for the evaluation of primary stability.

Efeito da geometria do implante dentário e do protocolo de fresagem óssea na estabilidade primária e na osseointegração inicial: estudo experimental em cães

CHAPTER 1 - This study histologically evaluated two implant designs: a classic thread design versus another specifically designed for healing chamber formation placed with two drilling protocols. Forty dental implants (4.1 mm diameter) with two different macrogeometries were inserted in the tibia of 10 Beagle dogs, and maximum insertion torque was recorded. Drilling techniques were: until 3.75 mm (regular-group); and until 4.0 mm diameter (overdrillinggroup) for both implant designs. At 2 and 4 weeks, samples were retrieved and processed for histomorphometric analysis. For torque and BIC (bone-to-implant contact) and BAFO (bone area fraction occupied), a general-linear model was employed including instrumentation technique and time in vivo as independent. The insertion torque recorded for each implant design and drilling group significantly decreased as a function of increasing drilling diameter for both implant designs (p<0.001). No significant differences were detected between implant designs for each drilling technique (p>0.18). A significant increase in BIC was observed from 2 to 4 weeks for both implants placed with the overdrilling technique (p<0.03) only, but not for those placed in the 3.75 mm drilling sites (p>0.32). Despite the differences between implant designs and drilling technique an intramembranous-like healing mode with newly formed woven bone prevailed. CHAPTER 2 - The objective of this preliminary histologic study was to determine whether the alteration of drilling protocols (oversized, intermediate, undersized drilling) present different biologic responses at early healing periods of 2 weeks in vivo in a beagle dog model. Ten beagle dogs were acquired and subjected to surgeries in the tibia 2 weeks before euthanasia. During surgery, 3 implants, 4 mm in diameter by 10 mm in length, were placed in bone sites drilled to 3.5 mm, 3.75 mm, and 4.0 mm in final diameter. The insertion and removal torque was recorded for all samples. Statistical significance was set to 95% level of confidence and the number of dogs was considered as the statistical unit for all comparisons. For the torque and BIC and BAFO, a general linear model was employed including instrumentation technique and time in vivo as independent. Overall, the insertion torque increased as a function of drilling diameter from 4.0 mm, to 3.75 mm, to 3.5 mm, with a significant difference in torque levels between all groups (p<0.001). Statistical assessment of BIC and BAFO showed significantly higher values for the 3.75 mm (recommended) drilling group was observed relative to the other two groups (p<0.001). Different drilling dimensions resulted in variations in insertion torque values (primary stability) and different pattern of healing and interfacial remodeling was observed for the different groups. CHAPTER 3 - The present study evaluated the effect of different drilling dimensions (undersized, regular, and oversized) in the insertion and removal torques of dental implants in a beagle dog model. Six beagle dogs were acquired and subjected to bilateral surgeries in the radii 1 and 3 weeks before euthanasia. During surgery, 3 implants, 4 mm in diameter by 10 mm in length, were placed in bone sites drilled to 3.2 mm, 3.5 mm, and 3.8 mm in final diameter. The insertion and removal torque was recorded for all samples. Statistical analysis was performed by paired t tests for repeated measures and by t tests assuming unequal variances (all at the 95% level of significance). Overall, the insertion torque and removal torque levels obtained were inversely proportional to the drilling dimension, with a significant difference detected between the 3.2 mm and 3.5 mm relative to the 3.8 mm groups (P < 0.03). Although insertion torque–removal torque paired observations was statis- tically maintained for the 3.5 mm and 3.8 mm groups, a significant decrease in removal torque values relative to insertion torque levels was observed for the 3.2 mm group. A different pattern of healing and interfacial remodeling was observed for the different groups. Different drilling dimensions resulted in variations in insertion torque values (primary stability) and stability maintenance over the first weeks of bone healing.

A robotic apparatus that dictates torque fields around joints without affecting inherent joint dynamics

This manuscript describes how motor behaviour researchers who are not at the same time expert roboticists may implement an experimental apparatus, which has the ability to dictate torque fields around a single joint on one limb or single joints on multiple limbs without otherwise interfering with the inherent dynamics of those joints. Such an apparatus expands the exploratory potential of the researcher wherever experimental distinction of factors may necessitate independent control of torque fields around multiple limbs, or the shaping of torque fields of a given joint independently of its plane of motion, or its directional phase within that plane. The apparatus utilizes torque motors. The challenge with torque motors is that they impose added inertia on limbs and thus attenuate joint dynamics. We eliminated this attenuation by establishing an accurate mathematical model of the robotic device using the Box-Jenkins method, and cancelling out its dynamics by employing the inverse of the model as a compensating controller. A direct measure of the remnant inertial torque as experienced by the hand during a 50 s period of wrist oscillations that increased gradually in frequency from 1.0 to 3.8 Hz confirmed that the removal of the inertial effect of the motor was effectively complete.

Retorque de parafusos de pilares protéticos com recobrimento de carbono tipo diamante: uma análise da manutenção do torque após fadiga mecânica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Retorque de parafusos de pilares protéticos com recobrimento de carbono tipo diamante: uma análise da manutenção do torque após fadiga mecânica

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A novel cryo-mechanical approach for the removal of blocked nonretrievable implant components

The removal of nonretrievable implant components represents a challenge in implant dentistry. The mechanical approach involves the risk of damaging the implant connection or the bone-to-implant interface. This case report describes a cryo-mechanical approach for the safe removal of a nonretrievable implant component. A patient had an implant surgically placed in a private practice. When the patient returned to the restorative dentist to make a definitive impression, the healing abutment could not be loosened. The patient was referred to the Division of Fixed Prosthodontics (University of Bern, Switzerland), where the stripped screw hole was enlarged with a special drill from a service kit of the implant provider. Although an extraction bolt was screwed into the opening and the torque ratchet was activated, the healing abutment would not loosen. A novel approach was attempted whereby the healing abutment was cooled with dry ice (CO2). The cooling effect seemingly caused shrinkage of the healing abutment and a reduction of the connection forces between the implant and the nonretrievable component. The approach of creating an access hole for the application of reverse torque via the extraction bolt in combination with the thermal effect led to the successful removal of the blocked component. Neither the implant connection nor the bone-to-implant interface was damaged. The combined cryo-mechanical procedure allowed the implant to be successfully restored.