Flávio Domingues das Neves

Relation between implant/abutment vertical misfit and torque loss of abutment screws

This study investigated whether there is a direct correlation between the level of vertical misfit at the abutment/implant interface and torque losses (detorque) in abutment screws. A work model was obtained from a metal matrix with five 3.75 x 9 mm external hex implants with standard platform (4.1 mm). Four frameworks were waxed using UCLA type abutments and one-piece cast in commercially pure titanium. The misfit was analyzed with a comparator microscope after 20 Ncm torque. The highest value of misfit observed per abutment was used. The torque required to loose the screw was evaluated using a digital torque meter. The torque loss values, measured by the torque meter, were assumed as percentage of initial torque (100%) given to abutment screws. Pearsons correlation (alpha=0.05) between the misfit values (29.08 +/- 8.78 microm) and the percentage of detorque (50.71 +/- 11.37%) showed no statistically significant correlation (p=0.295). Within the limitations of this study, it may be concluded that great vertical misfits dot not necessarily implies in higher detorque values.

Prosthetic laboratory influence on the vertical misfit at the implant/UCLA abutment interface

An inadequate fit at the abutment/implant interface can generate mechanical and biological problems. The laboratorial stages could induce misfit in such interface when the castable UCLA abutment type is used. The purpose of this study was to comparatively evaluate the performance of three prosthetic laboratories (Labs A, B and C) by vertical fit analysis of castable UCLA abutments on the casting and soldering stages of the same prosthesis. Four fixed prostheses were built by each laboratory using castable UCLA abutments. The evaluation was made by scanning electron microscopy under 500x magnification in the mesial and distal regions of each element of the prosthesis, totalizing 24 measurements per laboratory. The results were analyzed statistically by Kruskal-Wallis test (p<0.05). In the casting process, the values presented by the laboratories differed significantly to each other (p=0.004). After soldering, the values presented by the laboratories showed no significant difference (p=0.948). It may be concluded that the fit values obtained in the casting stage of UCLA abutments can be influenced when processed by different laboratories, and that conventional soldering itself increased the degree of framework misfit, regardless of which laboratory made it.

Implant/abutment vertical misfit of one-piece cast frameworks made with different materials

This study compared vertical and passive fit of one-piece cast frameworks made with 3 different materials: commercially pure titanium (CP Ti - G1), cobalt-chromium alloy (Co-Cr - G2) and nickel-chromium-titanium alloy (Ni-Cr-Ti - G3). Fifteen frameworks were obtained simulating bars for fixed prosthesis in a model with 5 implants. The passive and vertical fit of the framework interface was measured using an optical microscope at x30 magnification. Data were statistically analyzed by ANOVA and LSD tests (α=0.05). Mean and standard deviation values for passive fit and vertical fit were, respectively: G1 [472.49 (109.88) µm and 29.9 (13.24) µm], G2 [584.84 (120.20) µm and 27.05 (10.30) µm], and G3 [462.70 (179.18) µm and 24.95 (11.14) µm]. For vertical fit, there were no significant differences among G1, G2 and G3 (p=0.285). There were no significant differences for passive fit between G1 and G3 (p=0.844), but both differed significantly from G2 (p=0.028 and p=0.035, respectively), which showed the highest misfit values. It may be concluded that the vertical fit of frameworks was not affected by the tested materials, and that one-piece cast frameworks resulted in inadequate passive fit. The Co-Cr alloy presented the worst values for passive fit.

Shear bond strength of dental porcelains to nickel-chromium alloys

The continuous technological advance and increasing availability of new base metal alloys and ceramic systems in the market, coupled to the demands of daily clinical practice, have made the constant evaluation of the bond strength of metal/porcelain combinations necessary. This study evaluated the metal/porcelain shear bond strength of three ceramic systems (Duceram, Williams and Noritake) in combination with three nickel-chromium (Ni-Cr) alloys (Durabond, Verabond and Viron). Thirty cast cylinder specimens (15 mm high; 6 mm in diameter) were obtained for each alloy, in a way that 10 specimens of each alloy were tested with each porcelain. Bond strength was measured with an Emic screw-driven mechanical testing machine by applying parallel shear forces to the specimens until fracture. Shear strength was calculated using the ratio of the force applied to a demarcated area of the opaque layer. Mann-Whitney U test was used for statistical analysis of the alloy/ceramic combinations (p<0.05). Viron/Noritake had the highest shear bond sregnth means (32.93 MPa), while Verabond/Duceram (16.31 MPa) presented the lowest means. Viron/Noritake differed statistically from other combinations (p<0.05). Viron/Duceram had statistically significant higher bond strengths than Verabond/Duceram, Verabond/Williams and Durabond/Noritake (p<0.05). It was also found significant difference (p<0.05) between Verabond/Noritake, Verabond/Duceram and Durabond/Noritake. No statistically significant difference (p>0.05) were observed among the other combinations. In conclusion, the Noritake ceramic system used together with Viron alloy presented the highest resistance to shear forces, while Duceram bonded to Verabond presented the lowest bond strength. Viron/Duceram and Verabond/Noritake provided intermediate results. The combinations between the Williams ceramic system and Ni-Cr alloys had similar shear strengths among each other.

Management of fractured dental implants: a case report.

An implant fracture may be one of the major causes of late implant failures. Complications, such as loosening or fracture of the prosthesis restorative components, or even fracture of the implant, may occur and dental professionals should be aware of the causes of these complications. This study reports a clinical situation involving a patient restored with a mandibular overdenture that presented a fractured implant 2 years after placement. The probable cause of the implant fracture was dueto biomechanical overload caused by parafunctional habits. The implant head was flattened to make it smooth, retapping the internal screw, installing a new abutment (longer), and fabricating part of the overdenture bar. This treatment was timesaving for the patient in that the prosthesis was repaired in the shortest time possible.

Bond strength of three dental porcelains to Ni-Cr and Co-Cr-Ti alloys

Ceramometal bond strength has played an important role for the replacement of gold alloys by nickel-chromium alloys in dentistry. This study evaluated the metal/porcelain bond strength of three ceramic systems (Vita VMK 88, Williams and Duceram) associated with three nickel-chromium alloys (Durabond, Lite Cast B and Resistal P) and one experimental cobalt-chromium-titanium alloy. Thirty cast cylinder specimens (15 mm in height; 6 mm in diameter) were obtained for each alloy, in away that 10 specimens of each alloy were tested with each porcelain. Bond strength was measured with an Emic screw-driven mechanical testing machine by applying parallel shear forces to the specimens until fracture. Kruskal-Wallis and Mann-Whitney U tests were used for statistical analysis of the alloy/ceramic combinations (p<0.05). Resistal P/Duceram had significantly higher bond strength (44.38+/-9.12 MPa) (p<0.05) than the other combinations, except for Co-Cr-Ti alloy/Vita VMK 88 (38.41+/-12.64 MPa). The association of the experimental Co-Cr-Ti alloy with Williams porcelain had significantly higher bond strength (28.20+/-3.86 MPa) than the combination of other alloys with the same porcelain (p<0.05). Based of these results and within the limitations of an in vitro study, it may be concluded that the bond strength of the three ceramic systems to the Ni-Cr and Co-Cr-Ti alloys varied significantly, indicating that metal/ceramic compatibility was very important to the bond strength.

Evaluation of intracanal post removal using ultrasound.

The aim of this study was to determine the effect of ultrasonic vibration on the force necessary to remove pre-fabricated and anatomic and cast posts. Two hundred and forty teeth were divided into two groups. In group I, a 0.8-mm metallic pre-fabricated post, Unimetric-Maillefer, was utilized; in group II, cast copper-aluminum alloy posts measuring 0.8, 1.0 and 1.2 mm in diameter were used. The root canals were prepared in three different diameters: 0.8, 1.0 and 1.2 mm, with a length of 10 mm. The posts were cemented with glass ionomer cement resulting in 20 specimens for each subgroup. Half of the sample was submitted to ultrasonic vibration for 3 min, while the other half did not receive any vibration. The specimens were submitted to traction in a universal testing machine. The results were analyzed by non-parametric Mann-Whitney U, Wilcoxon and Kruskal-Wallis tests. The application of ultrasonic vibration significantly reduced the retention provided by the glass ionomer cement in the fixation of intracanal posts. The ultrasonic action was effective in both pre-fabricated and anatomic and cast posts. The effectiveness of the ultrasonic vibration was not related to the cementation line or the diameter of the post.

Evaluation of screw loosening on new abutment screws and after successive tightening

This study evaluated the loss of the torque applied after use of new screws and after successive tightening. Four infrastructures (IE), using UCLA castable abutment type, were cast in cobalt-chromium alloy and new abutment screws (G1) were used in a first moment. Subsequently, the same abutment screws were used a second time (G2) and more than two times (G3). The values of the torques applied and detorques were measured with a digital torque wrench to obtain the values of initial tightening loss (%). Data were analyzed by ANOVA and Tukeys test (?=0.05). Significant differences were observed between the G1 (50.71% ± 11.36) and G2 (24.01% ± 3.33) (p=0.000) and between G1 (50.71% ± 11.36) and G3 (25.60% ± 4.64) (p=0.000). There was no significant difference between G2 and G3 (p=0.774). Within the limitations of the study, it may be concluded that the percentage of the initial torque loss is lower when screws that already suffered the application of an initial torque were used, remaining stable after application of successive torques.

Micro-leakage at the implant-abutment interface with different tightening torques in vitro

Objectives This study evaluated the microleakage at the implant/abutment interface of external hexagon (EH) implants and abutments with different amounts of bacteria and tightening torques. Material and Methods A bacterial suspension was prepared to inoculate the implants. The first phase of this study used nine EH implants and abutments that were divided into three groups with different amounts of bacterial suspension (n=3): V0.5: 0.5 µL; V1.0: 1.0 µL e V1.5: 1.5 µL, and tightened to the manufacturers recommended torque. The second phase of this experiment used 27 assemblies that were similar to those used in the first phase. These samples were inoculated with 0.5 µL of bacterial suspension and divided into three groups (n=9). T10: 10 Ncm; T20: 20 Ncm and T32: 32 Ncm. The samples were evaluated according to the turbidity of the broth every 24 hours for 14 days, and the bacteria viability was tested after that period. The statistical evaluation was conducted by Kruskal-Wallis testing (p<.05). Results During the first phase, groups V1.0 and V1.5 was presented with bacterial contamination in all samples after 24 h. During the second phase, two samples from group T10 and one from T20 presented positive results for bacterial contamination. Different amounts of bacterial solution led to overflow and contamination during the first 24 h of the experiment. The tightening torques did not statistically affect the microleakage in the assemblies. However, the group that was tightened to 32 Ncm torque did not show any bacterial contamination. Conclusion After 14 days of experimentation, the bacteria were proven to remain viable inside the implant internal cavity.

In vitro integrity of implant external hexagon after application of surgical placement torque simulating implant locking

The aim of this study was to evaluate the integrity of the external hexagon of an implant system with internal and external hexagons but with prosthetic connection through the external hexagon (Internal Torque, IT) in comparison with that of an implant system with external hexagon with mount (External Hexagon, EH). A device was made to measure the rotational freedom angles between implant and abutment hexagons in 10 implants from each group after the application of surgical placement torques of 45, 60 and 80 Ncm simulating implant locking. The distances between the vertices of the external hexagon were also obtained. Rotational freedom data were subjected to ANOVA and Tukeys test (P < .05) showing no significant difference between the angles of the intact implants (EH - 3.31 +/- 0.41 degrees and IT - 3.30 +/- 0.17 degrees ) and after application of a 45 Ncm torque (EH - 3.27 +/- 0.38 degrees and IT - 3.31 +/- 0.22 degrees ). However, after application of a 60 Ncm torque there were significant differences (IT - 3.40 +/- 0.20 degrees and EH - 4.03 +/- 0.54 degrees ). After application of a 80 Ncm torque, the IT implant presented values of 3.39 +/- 0.21 degrees whereas the EH did not support the torque, suffering deformation of its external hexagon. Within the limits of this study, it can be concluded that the IT implant system may be preferable in clinical situations where implant placement within a certain bone density could generate torques higher than 60 Ncm.