Hot isostatic pressing as an alternative thermo-mechanical treatment for metallic full-arch implant-supported frameworks obtained by additive and subtractive manufacturing technology: Vertical and horizontal fit, screw removal torque, and stress analysis

PURPOSE

To assess vertical and horizontal fit, screw removal torque, and stress analysis (considered biomechanical aspects) of full-arch implant frameworks manufactured in Ti-6Al-4V through milling, and additive manufacturing Direct Metal Laser Sintering (DMLS) and Electron Beam Melting (EBM), and the effect of the thermo-mechanical treatment Hot Isostatic Pressing (HIP) as a post-treatment after manufacturing.

MATERIAL AND METHODS

Maxillary full-arch implant frameworks were made by milling, DMLS, and EBM. The biomechanical assessments were screw removal torque, strain-gauge analyses, and vertical and horizontal marginal fits. The vertical fit was assessed by the single-screw test and with all screws tightened. All frameworks were submitted to a standardized HIP cycle (920°C, 1000 bar pressure, 2 h), and the tests were repeated (α = 0.05).

RESULTS

At the initial time, milled frameworks presented higher screw removal torque values, and DMLS and EBM frameworks presented lower levels of strain. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally, higher fit values were found for milled frameworks, followed by DMLS and EBM. After HIP, milling and EBM frameworks presented higher screw removal torque values; the lowest strain values were found for EBM. Using the single-screw test, milled and DMLS frameworks presented higher vertical fit values, and with all screws tightened and horizontally no differences were found.

CONCLUSIONS

DMLS and EBM full-arch frameworks presented adequate values of screw removal torque, strain, and marginal fit, although the worst values of marginal fit were found for EBM frameworks. The HIP cycle enhanced the screw removal torque of milled and EBM frameworks and reduced the strain values of milled frameworks. The HIP represents a reliable post-treatment for Ti-6Al-4V dental prostheses produced by milling and EBM technologies.

Targeting Biomechanical Endurance of Dental-Implant Abutments Using a Diamond-Like Carbon Coating

Abutment components (i.e., fixtures associated with oral implants) are essentially made of titanium (Ti), which is continuously exposed to the hash oral environment, resulting in scratching. Thus, such components need to be protected, and surface treatments are viable methods for overcoming long-term damage. Diamond-like carbon (DLC), an excellent protective material, is an alternative surface-treatment material for Ti abutments. Here, we demonstrate that a silicon interlayer for DLC film growth and the pulsed-direct current plasma-enhanced chemical vapor deposition (DC-PECVD) method enables the deposition of an enhanced protective DLC film. As a result, the DLC film demonstrated a smooth topography with a compact surface. Furthermore, the DLC film enhanced the mechanical (load-displacement, hardness, and elastic modulus) and tribological properties of Ti as well as increased its corrosion resistance (16-fold), which surpassed that of a bare Ti substrate. The biofilm formed (Streptococcus sanguinis) after 24 h exhibited an equal bacterial load (∼7 Log colony-forming units) for both the groups (Ti and DLC). In addition, the DLC film exhibited good cytocompatibility, owing to its noncytotoxicity toward human gingival fibroblast cells. Therefore, DLC deposition via DC-PECVD can be considered to be a promising protective and cytocompatible alternative for developing implant abutments with enhanced mechanical, tribological, and electrochemical properties.

Factors and clinical outcomes for standard and mini-implants retaining mandibular overdentures: A systematic review and meta-analysis

STATEMENT OF PROBLEM

Standard-diameter dental implants are not always applicable because of anatomic limitations of the residual ridge. Thus, mini-implants have been increasingly used and offer an alternative. However, data regarding prosthetic complications, maintenance factors, and clinical outcomes are limited.

PURPOSE

The purpose of this systematic review and meta-analysis was to compare prosthetic complications and maintenance events and clinical outcomes in residual ridges rehabilitated with mandibular implant overdentures (IODs) by using standard implants or mini-implants.

MATERIAL AND METHODS

Nine electronic databases were searched. Quantitative analyses to measure the risk ratio (RR) and standardized mean difference (SMD) were applied. Those methods were used to assess prosthetic complications and maintenance events (abutment adjustments, replacement of retentive element, occlusal adjustment, and overdenture fracture) and clinical outcomes related to postoperative pain, probing depth (PD), plaque index (PI), marginal bone loss (MBL), and implant survival rate.

RESULTS

Altogether, 7 publications were selected. Mini-implants presented reduced abutment adjustments (RR 0.23 [0.07, 0.73], P=.01), replacement of retentive element (RR 0.41 [0.31, 0.54], P<.001), occlusal adjustment (RR 0.53 [0.31, 0.91], P=.02), and overdenture fracture (RR 0.46 [0.23, 0.94], P=.03) compared with standard implants. Additionally, mini-implants presented lower values for PI at 6 months (SMD -0.27 [-0.47, -0.08], P=.006) and 12 months (SMD -0.25 [-0.46, -0.05], P=.01). No additional tangible differences were noted.

CONCLUSIONS

Mini-implants might be an alternative choice based on the number of prosthetic complications and maintenance events. This was also confirmed by the comparable clinical data between standard implants and mini-implants.

Funding assistance and global productivity in the field of implant overdentures: A bibliometric analysis of 35 years

STATEMENT OF PROBLEM

Implant overdentures have been widely used as a treatment option for edentulous patients. However, the development of implants, aside from commercial growth, requires funding assistance to determine scientific reliability and clinical applications. Nonetheless, bibliometric studies in the implant overdenture field are lacking.

PURPOSE

The purpose of this bibliometric analysis was to evaluate the prevalence of funding and its bibliometric associated parameters according to the financial assistance granted and the implant overdenture documentation over time.

MATERIAL AND METHODS

Six databases were assessed, and 12 bibliometric parameters related to the economy, geographical origin, publication details, and corresponding author metrics were recorded. An incidence rate ratio was applied by using a multiple Poisson regression model (α=.05) to assess the association between funding and each bibliometric parameter.

RESULTS

In total, 1369 studies published between 1986 and 2021 were assessed bibliometrically. The prevalence of funded studies was 34.8% (n=477). The parameter associated with the presence of funding was country income (P<.01), with those having a high and upper-middle income being more funded than those with a lower-middle and low income. Oceania and South America were the continents more frequently funded (P<.05), with Africa being the least frequent. Randomized and nonrandomized controlled trials, in vitro studies, and in silico studies were more funded (P<.001) than case reports and series. Stud and ball attachment systems were more funded (P<.01) than studies with more than 1 retention system. Funding increased over time (P<.01), and corresponding authors with a higher h-index had more studies funded (P<.05).

CONCLUSIONS

The number of funded studies on implant overdentures increased over the years. Other bibliometric parameters such as country income, continent, study design, retention system, and corresponding author h-index were associated with the frequency of funded studies published.

Clinical efficacy of triclosan-containing toothpaste in peri-implant health: A systematic review and meta-analysis of randomized clinical trials

STATEMENT OF PROBLEM

Recent evidence suggests that toothpaste containing 0.3% triclosan (TCS) is more effective than regular toothpaste in improving clinical periodontal conditions. However, a consensus on whether TCS favors a healthy peri-implant environment is limited.

PURPOSE

The purpose of this systematic review and meta-analysis of randomized clinical trials was to determine the effects of TCS-containing toothpaste on dental implant health based on clinical, immunological, and microbiological parameters, as well as on reported adverse events.

MATERIAL AND METHODS

Clinical studies comparing peri-implant conditions in participants by using TCS toothpaste versus conventional fluoride toothpaste (control) were extracted from 9 databases. The studies were assessed with the Cochrane risk-of-bias tool for randomized clinical trials (RoB 2). Datasets for bleeding on probing (BOP), probing depth (PD), clinical attachment level (CAL), gingival index (GI), plaque index (PI), osteo-immunoinflammatory mediators, and bacterial load were plotted, and the standard mean difference (SMD) quantitative analysis was applied by using the Rev Man 5.3 software program. Adverse effects reported by the studies were also tabulated. The certainty of evidence was assessed by using the grading of recommendations assessment, development, and evaluation approach.

RESULTS

Six studies were included in the meta-analyses. BOP was higher in the control group than in the TCS toothpaste group at 3 months (SMD -0.59 [-1.11, -.07] P=.002, I2=77%) and 6 months (SMD -0.59 [-0.83, -0.34] P=.009, I2=79%). PD (SMD -0.04 [-0.08, -0.00] P=.04, I2=0%) was also deeper in the control group versus TCS toothpaste at 6 months (SMD -0.41 [-0.73, -0.10] P=.04, I2=77%). CAL, GI, and PI did not differ between groups (P>.05). Among the osteo-immunoinflammatory mediators, IL-10 levels increased, and IL-1β and osteoprotegerin levels decreased in the TCS toothpaste group (P<.05). Microbiological findings found that TCS toothpaste prevented the growth of periodontal pathogens, specifically in up to approximately 20% of the Prevotella intermedia. Adverse effects were not reported after toothbrushing in either group. However, most studies had "some" or "high" risk of bias, and the certainty of the evidence was considered to be "very low."

CONCLUSIONS

Most studies were short-term (3 and 6 months) analyses, and the results found that, although TCS-containing toothpaste had positive osteo-immunoinflammatory and microbiologic results, clinical parameters, including CAL, GI, and PI, were not influenced.

Bibliometric assessment in implant-retained overdenture articles: Mapping citation and journal impact factor trends

STATEMENT OF PROBLEM

Implant-retained overdentures are a recognized treatment option. However, a comprehensive assessment of all articles on implant-retained overdentures to identify publication standards such as mean citation and the Journal Citation Reports (JCR) impact factor is lacking.

PURPOSE

The purpose of this bibliometric assessment was to evaluate the association of mean citation and JCR impact factor with bibliometric parameters in articles on implant-retained overdentures.

MATERIAL AND METHODS

Articles reporting randomized controlled clinical trials (RCTs) and nonrandomized controlled clinical trials (N-RCTs); case reports and series; retrospective studies; and in silico, in vitro, or systematic reviews in 6 databases were included. Data were extracted, and 2 multiple Poisson regressions analyses were applied (α=.05). The dependent variables were mean citation and JCR impact factor, which were evaluated to identify their association with bibliometric parameters by using prevalence ratio (PR) values.

RESULTS

A total of 1369 articles published from 1986 to 2021 were included. The data revealed a high mean citation and high JCR impact factor for RCT, N-RCT, retrospective, and in vitro studies (P<.05). In silico studies presented a high mean citation (P<.001). Senior researchers with a high h-index were more likely to have a high mean citation and publications with a high JCR impact factor (P<.001). Also, senior authors associated with an international network were more likely to have a high mean citation (P=.001). High-income countries had more studies with a high mean citation and JCR impact factor (P<.05). Higher JCR impact factors were associated with articles evaluating only the maxilla or mandible (P<.05). The topics "implant setting" and "macrodesign" were associated with a high mean citation (P<.05).

CONCLUSIONS

The publication trends suggest a high mean citation and a high JCR impact factor for clinical designs (RCT, N-RCT, retrospective) and in vitro studies. The same pattern was also displayed for researchers with a high h-index and located in high-income countries.

Additive Manufacturing of Metallic Frameworks Supported by the All-on-Six Implant Concept: Dimensional Precision After Veneer Layering and Spark Erosion

PURPOSE

To compare frameworks manufactured by selective laser melting (SLM) and electron beam melting (EBM) with frameworks manufactured by milling, regarding dimensional precision after veneer layering and spark erosion for the all-on-six implant concept.

MATERIALS AND METHODS

Frameworks (n = 5/group) were manufactured by milling, SLM, and EBM. Dimensional precision of the frameworks was evaluated by marginal fit, screw loosening torque, and strain. Marginal fit was assessed by the single screw protocol. The screw-loosening torque was measured for the evaluation of screw stability. Tension distribution was analyzed with strain gauges. All frameworks received veneer layering followed by the marginal fit, screw-loosening torque, and strain gauge tests. Subsequently, the frameworks were subjected to the spark erosion process. The analyses were repeated after each stage (baseline, veneer layering, and spark erosion). Data was explored by two-way repeated-measures analysis of variance (ANOVA) with the Bonferroni test (α = .05).

RESULTS

At baseline, the highest (worst) marginal fit values were displayed by SLM frameworks (mean ± standard deviation [SD]: 186.13 ± 21.27 μm), while the milling group (83.30 ± 12.03 μm) showed the lowest (best) values (P < .05). After veneer layering, EBM presented the worst marginal fit values (222.55 ± 52.56 μm; P < .05) among the groups. Over time (from the baseline to veneer layering), the marginal fit values increased (became worse) for milling (P = .002) and EBM (P < .001), while for SLM (P = .002) the values decreased (improved). Compared with veneer layering data, spark erosion improved the marginal fit values only for EBM (P = .005). Irrespective of time, the screw-loosening torque for the milling group showed higher values. The lowest strain was found for the SLM at baseline (P < .05), but it increased after veneer layering (P = .015) and after spark erosion (P = .028).

CONCLUSION

Additive technologies are promising for dental applications. In addition, all technologies demonstrated accuracy in the manufacturing of implant-supported frameworks, especially the EBM technology, which demonstrated biomechanical behavior similar to the milling technology after the intervals (baseline, veneer layering, and spark erosion) assessed in the study.

Clinical efficacy of anodized dental implants for implant-supported prostheses after different loading protocols: A systematic review and meta-analysis

OBJECTIVES

To summarize the clinical performance of anodized implants connected to different prostheses design after immediate/early (IL) or conventional loading (CL) protocols.

MATERIALS AND METHODS

Seven databases were surveyed for randomized (RCTs) and non-randomized controlled clinical trials (CCTs). Studies comparing IL vs. CL protocol of anodized implants supporting single crown, fixed partial denture (FPD), full-arch fixed dental prosthesis (FDP), or overdenture were included. Risk-of-bias was evaluated using Cochrane Collaboration tools. Meta-analyses for different follow-up were analyzed, followed by heterogeneity source assessment and GRADE approach. The outcomes included implant survival rate, marginal bone loss (MBL), implant stability quotient (ISQ), probing depth (PD), plaque index (PI), and peri-implantitis prevalence.

RESULTS

From 24 eligible studies, 22 were included for quantitative evaluation. Most RCTs (58%, n = 11) and all the 5 CCTs had high and serious risk-of-bias, respectively. Overall, pooling all prosthesis design, no difference between IL vs. CL protocols was observed for all outcomes (p > .05). However, according to prosthesis type subgroups, CL reduced MBL for full-arch FDP (p < .05). In a point-in-time assessment, with overdenture, although IL presented higher PI (12 months), it showed lower MBL (≥24 months), higher ISQ (3 months), and lower PD (6 and 12 months) (p < .05). Conversely, PD was higher for IL in single crown (3 and 6 months) (p < .05). Regarding MBL, IL demonstrated higher mean difference for full-arch FDP (36 months) and FPD (12 and 36 months) (p < .05).

CONCLUSION

Within the limitations of this study, overall, there is no significant difference in the outcomes between IL and CL loading protocols.

Biomechanical behavior of CAD/CAM cobalt-chromium and zirconia full-arch fixed prostheses

PURPOSE

To verify the influence of computer-aided design/computer-aided manufacturing (CAD/CAM) implant-supported prostheses manufactured with cobalt-chromium (Co-Cr) and zirconia (Zr), and whether ceramic application, spark erosion, and simulation of masticatory cycles modify biomechanical parameters (marginal fit, screw-loosening torque, and strain) on the implant-supported system.

MATERIALS AND METHODS

Ten full-arch fixed frameworks were manufactured by a CAD/CAM milling system with Co-Cr and Zr (n=5/group). The marginal fit between the abutment and frameworks was measured as stated by single-screw test. Screw-loosening torque evaluated screw stability, and strain analysis was explored on the implant-supported system. All analyses were performed at 3 distinct times: after framework manufacturing; after ceramic application in both materials' frameworks; and after the spark erosion in Co-Cr frameworks. Afterward, stability analysis was re-evaluated after 10⁶ mechanical cycles (2 Hz/150-N) for both materials. Statistical analyses were performed by Kruskal-Wallis and Dunn tests (α=.05).

RESULTS

No difference between the two materials was found for marginal fit, screw-loosening torque, and strain after framework manufacturing (P>.05). Ceramic application did not affect the variables (P>.05). Spark erosion optimized marginal fit and strain medians for Co-Cr frameworks (P<.05). Screw-loosening torque was significantly reduced by masticatory simulation (P<.05) regardless of the framework materials.

CONCLUSION

Co-Cr and Zr frameworks presented similar biomechanical behavior. Ceramic application had no effect on the biomechanical behavior of either material. Spark erosion was an effective technique to improve Co-Cr biomechanical behavior on the implant-supported system. Screw-loosening torque was reduced for both materials after masticatory simulation.

Patient-reported outcome measures and clinical assessment of implant-supported overdentures and fixed prostheses in mandibular edentulous patients: A systematic review and meta-analysis

STATEMENT OF PROBLEM

A consensus based on patients' perceptions as to whether to use overdentures or fixed prostheses to rehabilitate mandibular edentulous arches is limited.

PURPOSE

The purpose of this systematic review and meta-analysis was to compare the patient-reported outcome measures (PROMs) and clinical outcomes associated with implant-supported overdentures and fixed prostheses in edentulous mandibles.

MATERIAL AND METHODS

Nine electronic databases were searched for randomized clinical trials (RCTs) and nonrandomized clinical trials (N-RCTs). The risk of bias was assessed by the revised Cochrane risk of bias tool for RCTs (RoB 2) and N-RCT (ROBINS-I). Data sets for oral health-related quality of life (OHRQoL), satisfaction, survival rate, implant probing depth, and marginal bone loss were plotted, and the appropriate analyses were applied by using the Rev Man 5.3 software program. Certainty of evidence was also evaluated by means of the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach.

RESULTS

Ten eligible trials were included and evaluated quantitatively. For 3 domains of OHRQoL, fixed prostheses showed significantly higher quality of life when compared with overdentures regarding functional limitation (P<.001), physical disability (P=.001), and physical pain (P=.003). Fixed prostheses also improved satisfaction, when compared with overdentures for comfort (P=.02), ease of chewing (P<.001), retention (P<.001), and stability (P<.001). The same pattern was observed for overall OHRQoL (P=.01) and satisfaction (P=.01) in which fixed prostheses improved patient satisfaction. Only ease of cleaning presented greater satisfaction for the overdenture group. Clinical parameters did not differ statistically (P>.05) between both types of prosthesis.

CONCLUSIONS

Fixed rehabilitations for mandibular edentulous patients seem to be a well-accepted treatment from the patients' oral health perspective. However, mandibular overdentures are no less efficient than fixed prostheses in terms of clinical outcomes.

Can ceramic veneer spark erosion and mechanical cycling affect the accuracy of milled complete-arch frameworks supported by 6 implants?

STATEMENT OF PROBLEM

Milling is a well-established method for manufacturing prosthetic frameworks. However, information about the influence of ceramic veneer and spark erosion on the accuracy of the all-on-six complete-arch fixed frameworks manufactured from different materials is lacking.

PURPOSE

The purpose of this in vitro study was to compare the accuracy of milled complete-arch fixed frameworks with zirconia, cobalt-chromium, and titanium at different steps of their manufacturing process and the influence of mechanical cycling.

MATERIAL AND METHODS

Fifteen milled complete-arch fixed frameworks, supported by 6 implants, were made in zirconia, cobalt-chromium, and titanium (n=5). The fit was measured by the single-screw test protocol. Stress was measured by photoelastic analysis. The loosening torque was evaluated by tightening the screws, retightening them after 10 minutes, and then evaluating the loosening torque 24 hours later. Thereafter, all frameworks received ceramic veneer, and the previous tests were repeated. Cobalt-chromium and titanium frameworks received spark erosion after ceramic veneer, and all analyses were repeated. Before and after mechanical cycling, loosening torque was evaluated. The results were subjected to 2-way repeated-measures ANOVA and the Bonferroni test (α=.05).

RESULTS

Titanium presented higher fit values than zirconia (P=.037) and similar to cobalt-chromium frameworks (P>.05) at baseline. After ceramic veneer, higher fit levels were observed for zirconia (P=.001) and cobalt-chromium (P=.008). Titanium showed higher stress values (P<.05) regardless of time. Baseline for all materials presented lower stress values (P<.05). Higher loosening torque values were found for the titanium group at baseline (P<.001) and after ceramic veneer (P<.001). Spark erosion improved fit and loosening torque values only for cobalt-chromium (P<.05). Mechanical cycling did not influence the loosening torque (P>.05).

CONCLUSIONS

Titanium milled complete-arch fixed frameworks presented poorer fit values than zirconia, although the loosening torque at baseline was higher. Ceramic veneer increased the fit levels for zirconia and cobalt-chromium, decreased the loosening torque values for cobalt-chromium, and enhanced stress levels. Spark erosion can be a reliable technique to improve fit and loosening torque for cobalt-chromium frameworks. Mechanical cycling did not decrease loosening torque.

3D metal printing in dentistry: An in vitro biomechanical comparative study of two additive manufacturing technologies for full-arch implant-supported prostheses

The use of 3D technologies is progressing in the dental field. However, little is known about the biomechanical behavior of the additive manufacturing of full-arch fixed dental prostheses (FAFDPs) for the establishment of clinical protocols. We investigated the influence of three CAD/CAM technologies: milling (control), Selective Laser Melting (SLM) and Electron Beam Melting (EBM) for FAFDP manufacturing. Also, the effects of ceramic veneer and spark erosion on marginal misfits of FAFDPs, the stability of prosthetic screws, strain and stress on the implant-supported system, as well as the effect of chewing simulation on screw stability were evaluated. Fifteen Ti-6Al-4V alloy FAFDPs were obtained by means of CAD/CAM systems: milling, SLM and EBM (n = 5/group). The marginal misfit was analyzed according to the single-screw test protocol. Screw stability was analyzed by screw-loosening torque. Strain-gauge analysis investigated the strain on the mini-abutment analog, and photoelastic analysis investigated the stress on the peri-implant region. Subsequently, all frameworks underwent ceramic veneer and spark erosion procedures. Marginal misfit, screw-loosening and strain and stress analyses were assessed after each evaluation time: initial, ceramic veneer and spark erosion. Finally, all prostheses were subjected to 10⁶ mechanical cycles (2 Hz/150 N), and screw-loosening was re-evaluated. Data were subjected to two-way ANOVA for repeated measures, and the Bonferroni test as a post hoc technique (α = 0.05). At the initial time, the milling group presented the lowest marginal misfit (p < 0.001). Ceramic veneer did not alter marginal misfit for all groups (p > 0.05); spark erosion decreased the misfit values for the SLM and EBM groups (p < 0.05). Evaluation time did not alter screw-loosening values for all groups (p = 0.191), although the milling group presented the highest screw-loosening values (p < 0.05). Ceramic veneer and spark erosion reduced strain in the components regardless of the manufacturing technology used (p < 0.05). The milling group presented the lowest stress values regardless of evaluation time (p = 0.001), and lower stress values were found after spark erosion regardless of the manufacturing group (p = 0.016). In conclusion, although milled frameworks exhibited the best biomechanical behavior, frameworks manufactured by additive technologies presented acceptable values of screw-loosening torque, strain and stress. Ceramic veneer did not negatively interfere in the biomechanical tests of the study, and clinically acceptable marginal misfit was achieved after spark erosion. Therefore, such 3D printing technologies seem to be feasible for the manufacturing of full-arch implant-supported frameworks.

Is one dental mini-implant biomechanically appropriate for the retention of a mandibular overdenture? A comparison with Morse taper and external hexagon platforms

STATEMENT OF PROBLEM

Limited information is available to clinicians on the use of dental mini-implants (MI) as opposed to standard-diameter implants (SDIs) for the stabilization of implant-retained mandibular overdentures (MOs).

PURPOSE

The purpose of this in vitro and finite element analysis study was to analyze and compare the biomechanical behavior of MOs with either 1 or 2 implants with external hexagon (EH), Morse taper (MT) SDIs, and MIs.

MATERIAL AND METHODS

Thirty photoelastic models (n=30) of each group (n=5) of SDIs (EH-1, EH-2, MT-1, MT-2) and MI (MI-1, MI-2) were fabricated for posterior, peri-implant, and total maximum shear stress evaluation by quantitative photoelastic analysis. One specimen of each group was further used to create the 6 computational models to be analyzed by finite element analysis. The maximum von Mises values and stress maps were plotted for each ductile component. Two types of load were applied to the overdenture: a150-N load bilaterally and simultaneously on the first molar and a 100-N load on the incisal edge of the central incisors at a 30-degree angle. The data were subjected to the 2-way ANOVA test and the Tukey honestly significant difference test (α=.05).

RESULTS

The EH-2 and MT-2 showed the lowest posterior (P<.001) and total (P<.05) mean shear stress values. For peri-implant shear stress, no difference was found among all groups (P>.05). Regardless of the loading area, the MI-1 and MI-2 groups showed the lowest von Mises stress values. However, for implant housing, the MI-1 group, under incisor loading, presented greater stress, followed by MT-1, EH-1, EH-2, MI-2, and MT-2. The attachment was the most overloaded structure, with high values under incisor loading, especially for the groups with 2 implants (MT-2, EH-2) as compared with the other models.

CONCLUSIONS

Biomechanically, regardless of the implant number, MI is a promising rehabilitation method with similar peri-implant shear stress and lower von Mises stress on the implant when compared with SDIs for MOs.

Biomechanical behavior of overdentures supported by different implant position and angulation using Micro ERA® system

Aim: The aim of this study was to investigate the biomechanical behavior of implant-retained mandibular overdentures using Micro ERA® system with different implant position and angulation by finite element analysis (FEA). Methods: Four 3D finite element models of simplified mandibular overdentures were constructed, using one Bränemark implant with a Micro ERA® attachment. The implant was positioned on the canine or lateral incisor area with an angulation of either 0º (C-0º; LI-0º) or 17º (C-17º, LI-17º) to the vertical axis. A 100 N axial load was applied in one side simultaneously, from first premolar to second molar. In all models it was analyzed the overdenture displacement, compressive/tensile stress in the bone-implant interface, and also the von Mises equivalent stress for the nylon component of the housing. The stresses were obtained (numerically and color-coded) for further comparison among all the groups. Results: The displacement on the overdenture was higher at the posterior surface for all groups, especially in the C-17º group. When comparing the compressive/tensile stress in the bone-implant interface, the lateral-incisor groups (LI-0º and LI-17º) had the highest compressive and lowest tensile stress compared to the canine groups (C-0º and C-17º). The von Mises stress on the nylon component generated higher stress value for the LI-0º among all groups. Conclusions: The inclination and positioning of the implant in mandibular overdenture interferes directly in the stress distribution. The results showed that angulated implants had the highest displacement. While the implants placed in the lateral incisor position presented lower compressive and higher tensile stress respectively. For the attachment the canine groups had the lowest stress.

Photoelastic and finite element stress analysis reliability for implant-supported system stress investigation

Aim: To compare the reliability between photoelastic and finite element (FE) analyses by evaluating the effect of different marginal misfit levels on the stresses generated on two different implant-supported systems using conventional and short implants. Methods: Two photoelastic models were obtained: model C with two conventional implants (4.1×11 mm); and model S with a conventional and a short implant (5×6 mm). Three-unit CoCr frameworks were fabricated simulating a superior first pre-molar (P) to first molar (M) fixed dental prosthesis. Different levels of misfit (µm) were selected based on the misfit average of 10 frameworks obtained by the single-screw test protocol: low (<20), medium (>20 and <40) and high (>40). Stress levels and distribution were measured by photoelastic analysis. A similar situation of the in vitro assay was designed and simulated by the in silico analysis. Maximum and minimum principal strain were recorded numerically and color-coded for the models. Von Mises Stress was obtained for the metallic components. Results: Photoelasticity and FE analyses showed similar tendency where the increase of misfit generates higher stress levels despite of the implant design. The short implant showed lower von Mises stress values; however, it presented stresses around its full length for the in vitro and in silico analysis. Also, model S showed higher µstrain values for all simulated misfit levels. The type of implant did not affect the stresses around pillar P. Conclusions: Photoelasticity and FEA are reliable methodologies presenting similarity for the investigation of the biomechanical behavior of implant-supported rehabilitations.

Influence of spark erosion on the fit of screw-retained Co-Cr fixed complete denture frameworks veneered with different materials

STATEMENT OF PROBLEM

Spark erosion is a fit corrective technology that can be used even after the veneering material has been applied. The framework does not require sectioning, thus preserving its mechanical resistance. However, the spark erosion effect on veneered Co-Cr fixed complete denture (FCD) frameworks has not been investigated.

PURPOSE

The purpose of this in vitro study was to evaluate whether spark erosion is effective in improving marginal fit on screw-retained Co-Cr FCD frameworks veneered with different materials. A comparison between ceramic applications and simulated ceramic firing cycles was also investigated.

MATERIAL AND METHODS

Forty FCD frameworks were fabricated with a Co-Cr alloy. Four groups (n=10) were obtained according to the veneer material used on frameworks: HR (heat-polymerized resin); LR (light-polymerized resin); C (ceramic); and SC (simulated ceramic firing cycle). The spark erosion process was conducted for all groups. The marginal fit was analyzed according to the single-screw test protocol, and the measurements were performed at 3 evaluation times: initial, after veneer material application, and after spark erosion process. The results were submitted to a 2-way repeated measures ANOVA and the Tukey honest significant differences test (α=.05).

RESULTS

Poorer marginal fit (in micrometers) was noted after veneer material application, where the HR and C groups presented the worst values (HR: 170; LR: 72; C: 165; SC: 86; P<.05). The spark erosion process was effective in improving the fit for all groups (HR: 109; LR: 52; C: 110; SC: 60; P<.05).

CONCLUSIONS

Spark erosion improved the fit of Co-Cr FCD frameworks veneered with different materials. An actual ceramic application should be used to assess distortions generated by veneer material application instead of using only simulated ceramic firing cycles.

Can the alendronate dosage be altered when combined with high-frequency loading in osteoporosis treatment?

Alendronate therapy has been associated with serious side effects. Altering the alendronate concentration and combining with high-frequency loading as mechanical intervention was explored in this animal study as a treatment for osteoporosis. The bone anabolic potency of high-frequency loading was overruled by the different alendronate dosages applied in the present study. Further exploration of reduced hormonal therapy associated with mechanical interventions in osteoporosis treatment should be sought.

INTRODUCTION

The aim of the present study was to investigate the effect of alendronate (ALN) administration at two different dosages, associated or not with high-frequency (HF) loading, on the bone microstructural response.

METHODS

Sixty-four female Wistar rats were used, of which 48 were ovariectomized (OVX) and 16 were sham-operated (shOVX). The OVX animals were divided into three groups: two groups were treated with alendronate, at a dosage of 2 mg/kg (ALN(₂)) or at a reduced dosage of 1 mg/kg (ALN(₁)) three times per week. A third OVX group did not receive pharmaceutical treatment. All four groups were mechanically stimulated via whole body vibration (WBV) at HF (up to 150 Hz) or left untreated (shWBV). ALN and HF were administered for 6 weeks, starting at 10-week post-(sh)OVX. Tibia bone structural parameters were analyzed using ex vivo microcomputed tomography.

RESULTS

Trabecular bone loss and structural deterioration resulting from ovariectomy were partially restored by ALN administration, demonstrated by the improvement of trabecular patter factor (Tb.Pf), trabecular separation (Tb.Sp), and structure model index (SMI) of the ALN groups compared to that of the OVX group, regardless of the applied dosage [ALN(₂) or ALN(₁)] or mechanical loading regime (shWBV or WBV). However, a significant positive effect of the ALN(₁) administration on trabecular (decrease of Tb.Sp and SMI) and cortical bone (increase of cortical thickness) microarchitecture compared to that of the OVX status group was observed for both loading regimes was not seen for ALN(₂). Furthermore, HF loading resulted in cortical bone changes, with an increased trabeculary area and endocortical perimeter. Finally, the benefits of a combined therapy of ALN with HF loading could not be discerned in the present experimental conditions.

CONCLUSIONS

The bone anabolic potency of HF loading was overruled by the ALN dosages applied in the present study. Further altering the ALN dosage combined with robust mechanical stimuli needs to be considered in osteoporosis research and eventually therapy.

Comparison of the Accuracy of Different Transfer Impression Techniques for Osseointegrated Implants

The aim of this study was to evaluate 3 transfer techniques used to obtain working casts of implant-supported prostheses through the marginal misfit and strain induced to metallic framework. Thirty working casts were obtained from a metallic master cast, each one containing 2 implant analogs simulating a clinical situation of 3-unit implant-supported fixed prostheses according to the following transfer impression techniques: group A, squared transfers splinted with dental floss and acrylic resin, sectioned, and re-splinted; group B, squared transfers splinted with dental floss and bis-acrylic resin; and group N, squared transfers not splinted. A metallic framework was made for marginal misfit and strain measurements from the metallic master cast. The misfit between the metallic framework and working casts was evaluated with an optical microscope following the single-screw test protocol. In the same conditions, the strain was evaluated using strain gauges placed on the metallic framework. The data were submitted to one-way analysis of variance followed by the Tukey test (α = 5%). For both marginal misfit and strain, there were statistically significant differences between groups A and N (P &lt; .01) and groups B and N (P &lt; .01), with greater values for group N. According to the Pearson test, there was a positive correlation between the misfit and strain variables (r = 0.5642). The results of this study showed that the impression techniques with splinted transfers promoted better accuracy than the nonsplinted technique, regardless of the splinting material used.

Biomechanical Analysis of Implant-Supported Prostheses with Different Implant-Abutment Connections

This study evaluated the influence of implant-abutment connections on stress distribution through 3D finite element analysis. Three-dimensional models of an implant-supported fixed prosthesis in the jaw retained by four implants with different connection systems (external hex and Morse taper) were analyzed. External hex connection promoted higher microstrain values, which were concentrated on the cervical region of the distal implants extending into the trabecular bone, while Morse taper connection provided a more even distribution of the microstrain on all implants. Implant-supported fixed prostheses with external hex connections tend to concentrate strain in the distal implants, while Morse taper connection promoted a better situation. On the other hand, there was greater demand on the prosthetic screws and abutments of Morse taper connections than on external hex connections.

Electrochemical behavior of bioactive coatings on cp-Ti surface for dental application

The surface characteristics and electrochemical properties of bioactive coatings produced by plasma electrolytic oxidation (PEO) with calcium, phosphorous, silicon and silver on commercially pure titanium were evaluated. PEO treatment produced a porous oxide layer, which improved the surface topography, and enriched the surface chemistry with bioactive elements, responsible for mimicking bone surface. The surfaces with higher calcium concentration presented antibacterial and biocompability properties with better responses for corrosion and barrier properties, due to the presence of rutile crystalline structure. PEO may be a promising surface treatment option to improve the electrochemical behavior of dental implants mitigating treatment failures.

Toothpastes containing abrasive and chemical whitening agents: efficacy in reducing extrinsic dental staining

This in vitro study evaluated the efficacy of toothpastes containing abrasive and chemical whitening agents in reducing the extrinsic discoloration of dental enamel. Sixty slabs of dentin from human teeth were sealed so that only the enamel surface was exposed. The enamel surfaces were photographed for initial color assessment. Staining was performed by immersing the dental slabs in 0.2% chlorhexidine solution for 2 minutes and then in black tea for 60 minutes. This process was repeated 15 times. Photographs were taken at the end of the staining process, and the slabs were divided into 5 groups (n = 12), 3 to be brushed with toothpastes containing chemical whitening agents (2 containing phosphate salts and 1 containing phosphate salts plus hydrogen peroxide) and 2 to represent control groups (ordinary/nonwhitening toothpaste and distilled water). The dental slabs were subjected to mechanical toothbrushing with toothpaste slurry or distilled water, according to each group's specifications. After brushing, more photographs were taken for color analysis. The results showed a significant reduction in luminosity after the staining process in addition to an increase in the colors red and yellow (P < 0.001). After brushing, there was a significant increase in luminosity and a reduction in both red and yellow (P < 0.001). However, there was no observed difference between the changes in color values in dental enamel slabs brushed with whitening toothpastes and the changes found in slabs brushed with ordinary toothpaste. The whitening toothpastes did not outperform an ordinary toothpaste in the removal of extrinsic staining.

Overdenture retaining bar stress distribution: a finite-element analysis

OBJECTIVE

Evaluate the stress distribution on the peri-implant bone tissue and prosthetic components of bar-clip retaining systems for overdentures presenting different implant inclinations, vertical misfit and framework material.

MATERIALS AND METHODS

Three-dimensional models of a jaw and an overdenture retained by two implants and a bar-clip attachment were modeled using specific software (SolidWorks 2010). The studied variables were: latero-lateral inclination of one implant (-10°, -5°, 0°, +5°, +10°); vertical misfit on the other implant (50, 100, 200 µm); and framework material (Au type IV, Ag-Pd, Ti cp, Co-Cr). Solid models were imported into mechanical simulation software (ANSYS Workbench 11). All nodes on the bone's external surface were constrained and a displacement was applied to simulate the settling of the framework on the ill-fitted component. Von Mises stress for the prosthetic components and maximum principal stress to the bone tissue were evaluated.

RESULTS

The +10° inclination presented the worst biomechanical behavior, promoting the highest stress values on the bar framework and peri-implant bone tissue. The -5° group presented the lowest stress values on the prosthetic components and the lowest stress value on peri-implant bone tissue was observed in -10°. Increased vertical misfit caused an increase on the stress values in all evaluated structures. Stiffer framework materials caused a considerable stress increase in the framework itself, prosthetic screw of the fitted component and peri-implant bone tissue.

CONCLUSIONS

Inclination of one implant associated with vertical misfit caused a relevant effect on the stress distribution in bar-clip retained overdentures. Different framework materials promoted increased levels of stress in all the evaluated structures.

Stress Evaluation of Implant-Abutment Connections Under Different Loading Conditions: A 3D Finite Element Study

This study evaluated the effects of axial and oblique occlusal loading on implant-supported partial dentures with different connection systems (external hexagon, internal hexagon, and Morse taper). Upon axial loading, all systems presented similar stress values. Stress values increased under oblique loading. Stress distribution changed for some of the internal connection structures. It can be concluded that oblique load increases stress on bone structures and prosthetic components. Internal connection system implants present more favorable stress distribution patterns than do external connection system implants.

Influence of Different Soft Liners on Stress Distribution in Peri-Implant Bone Tissue During Healing Period. A 3D Finite Element Analysis

The aim of this study was to evaluate the stress distribution in the bone adjacent to submerged implants during masticatory function in conventional complete dentures with different soft liners through finite element analysis. Three-dimensional models of a severely resorbed mandible with 2 and 4 submerged implants in the anterior region were created and divided into the following situations: (1) conventional complete dentures (control group); and conventional complete dentures with different soft liner materials, (2) Coe-Comfort, (3) Softliner, and (4) Molteno Hard. The models were exported to mechanical simulation software and 2 simulations were done with the load in the inferior right canine (35 N) and the inferior right first molar (50 N). The data were qualitatively evaluated using the maximum principal stress and microstrain values given by the software. The use of soft liners provides decreased levels of stress and microstrains in peri-implant bone when the load was applied to canine teeth. Considering all of the values obtained in this study, the use of softer materials is the most suitable for use during the period of osseointegration.

Effect of chlorhexidine and ethanol on push-out bond strength of fiber posts under cyclic loading

PURPOSE

To investigate the effects of pretreatment with 2% chlorhexidine in a gel base (CHX) and 100% ethanol (EtOH) on the bond strength between fiber posts relined with resin composite and root dentin under cyclic loading.

MATERIALS AND METHODS

Forty bovine incisor roots were divided into four groups after phosphoric acid etching: group 1 (control), irrigation with physiological saline solution; group 2, 5 min pretreatment with CHX; group 3, 1 min pretreatment with EtOH; group 4, 5 min pretreatment with CHX followed by 1 min with EtOH. Fiber posts relined with resin composite were cemented with RelyX ARC and the etch-and-rinse adhesive system Scotchbond Multi-Purpose. Each group was randomly divided into two subgroups: 24 h of storage (immediate groups) and cyclic loading (loading groups) with 250,000 cycles in a controlled chewing simulator. All roots were sectioned transversely and push-out tests were performed. Failure modes were observed and the bond strength means were analyzed using ANOVA and Tukey's test (a = 0.05).

RESULTS

The mean values for the bond strength test (MPa) in immediate groups were: group 1, 5.44 ± 1.48; group 2, 5.57 ± 1.41; group 3, 5.49 ± 1.48; group 4, 5.57 ± 1.42. Immediate groups showed similar bond strength values (p > 0.05). In the cyclic loading groups, the bond strength values were: group 1, 2.80 ± 0.79; group 2, 4.02 (1.30); group 3, 4.50 ± 1.67; group 4, 4.97 ± 2.00. After cyclic loading, a significant decrease in the control group was observed (p < 0.05), while CHX pretreatment resulted in intermediate values (p < 0.05) and EtOH alone or associated with CHX preserved the bond strength values (p > 0.05).

CONCLUSION

Chlorhexidine and/or ethanol pretreatment preserved the bond strength of the fiber post after cyclic loading.

Effect of framework material and vertical misfit on stress distribution in implant-supported partial prosthesis under load application: 3-D finite element analysis

OBJECTIVE

This study evaluated the influence of framework material and vertical misfit on stress created in an implant-supported partial prosthesis under load application.

MATERIALS AND METHODS

The posterior part of a severely reabsorbed jaw with a fixed partial prosthesis above two osseointegrated titanium implants at the place of the second premolar and second molar was modeled using SolidWorks 2010 software. Finite element models were obtained by importing the solid model into an ANSYS Workbench 11 simulation. The models were divided into 15 groups according to their prosthetic framework material (type IV gold alloy, silver-palladium alloy, commercially pure titanium, cobalt-chromium alloy or zirconia) and vertical misfit level (10 µm, 50 µm and 100 µm). After settlement of the prosthesis with the closure of the misfit, simultaneous loads of 110 N vertical and 15 N horizontal were applied on the occlusal and lingual faces of each tooth, respectively. The data was evaluated using Maximum Principal Stress (framework, porcelain veneer and bone tissue) and a von Mises Stress (retention screw) provided by the software.

RESULTS

As a result, stiffer frameworks presented higher stress concentrations; however, these frameworks led to lower stresses in the porcelain veneer, the retention screw (faced to 10 µm and 50 µm of the misfit) and the peri-implant bone tissues.

CONCLUSION

The increase in the vertical misfit resulted in stress values increasing in all of the prosthetic structures and peri-implant bone tissues. The framework material and vertical misfit level presented a relevant influence on the stresses for all of the structures evaluated.

Effect of chemical cleaning agents on the flexural strength of acrylic and hard denture line resins

This study sought to evaluate the disinfectants, Efferdent (EF) and 0.5% sodium hypochlorite (SH), and their effects on the flexural strength and modulus of elasticity of the hard denture liners, Kooliner (K) and New Truliner (NT), and a thermoacrylic resin, QC-20. Ninety specimens were made (50 mm x 10 mm x 3 mm) and divided into 9 groups (n = 10). The 3 control groups were Group 1: QC-20 without disinfection cycles, Group 2: K, and Group 3: NT. The 6 experimental groups were Group 4: QC-20 in EF, Group 5: K in EF, Group 6: NT in EF, Group 7: QC-20 in SH, Group 8: K in SH, and Group 9: NT in SH. Specimens were subjected to 360 cycles of disinfection involving 35-minute cycles of immersion in cleaning solutions. The materials' flexural strength and modulus of elasticity were determined using a universal testing machine at a 5 mm/minute speed of compression. The data were subjected to ANOVA, Tukey, Kruskal-Wallis, and Dunn tests (α = 0.05). Regardless of the disinfection method used, the NT hard denture liner showed the lowest flexural strength values (P < 0.05) and modulus of elasticity (P < 0.0001) compared to K and QC-20. However, flexural strength values increased after applying SH and EF (P < 0.05). QC-20 showed a higher modulus of elasticity (P < 0.033), which increased after EF was applied (P = 0.005). It can be concluded that the disinfection methods changed the mechanical properties of the tested materials.

Stress distribution in Co-Cr implant frameworks after laser or TIG welding

Lack of passivity has been associated with biomechanical problems in implant-supported prosthesis. The aim of this study was to evaluate the passivity of three techniques to fabricate an implant framework from a Co-Cr alloy by photoelasticity. The model was obtained from a steel die simulating an edentulous mandible with 4 external hexagon analog implants with a standard platform. On this model, five frameworks were fabricated for each group: a monoblock framework (control), laser and TIG welding frameworks. The photoelastic model was made from a flexible epoxy resin. On the photoelastic analysis, the frameworks were bolted onto the model for the verification of maximum shear stress at 34 selected points around the implants and 5 points in the middle of the model. The stresses were compared all over the photoelastic model, between the right, left, and center regions and between the cervical and apical regions. The values were subjected to two-way ANOVA, and Tukey's test (α=0.05). There was no significant difference among the groups and studied areas (p>0.05). It was concluded that the stresses generated around the implants were similar for all techniques.

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

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 10(6) 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.

Linear dimensional change, compressive strength and detail reproduction in type IV dental stone dried at room temperature and in a microwave oven

The type IV dental stone is widely used for the fabrication of dyes and master casts for fixed and removable partial prostheses. It is typically normal to wait at least 24 hours for the casts to dry prior to beginning the laboratory procedures. The waiting time has been shown to be greatly reduced by using microwave drying.

Evaluation of resistance to displacement of metal posts with different lengths

AIMS AND OBJECTIVES

to evaluate the resistance to displacement of metal intraradicular retainers of different lengths by means of the shear test.

MATERIAL AND METHODS

Thirty-six maxillary central incisors were cross-sectioned at 16 mm from the root apex, endodontically treated and randomly divided into three groups that were treated as follows: G1 (control) preparation of 2/3 (10.6 mm) of the total root length; G2: preparation of 1/2 (8 mm) of the total root length and G3: preparation of 1/3 (5.3 mm) of the total root length. After canal preparation, a matrix was made of the coronal and radicular portions using Duralay to obtain metal intraradicular retainers. These retainers were cemented with zinc phosphate cement and subjected to the compression shear test in a Universal Test Machine (EMIC DL 2000) at a crosshead speed of 0.5 mm/minute. The results were subjected to statistical analysis by analysis of variance (ANOVA) and Newman- Keuls, which showed statistically significant difference (P < 0.01).

RESULTS

The means in Newtons and their respective standard deviations were: G1 = 972.05 (±81.36); G2 = 921.15 (±112.25); G3 = 686.66 (±113.02).

CONCLUSION

It could be concluded that metal retainers of 2/3 and 1/2 the length of the root portion showed higher resistance to displacement values when compared with the group that had been prepared for 1/3 of the root length.

Effect of chemical and microwave disinfection on the surface microhardness of acrylic resin denture teeth

PURPOSE

The purpose of this study was to evaluate the effect of simulated disinfections (2% glutaraldehyde, 1% sodium hypochlorite, and microwave energy) on the surface hardness of Trilux, Biocler, Biotone, New Ace, and Magister commercial artificial teeth.

MATERIALS AND METHODS

Specimens (n = 10) were made with the teeth included individually in circular blocks of acrylic resin, leaving the labial surface exposed. Cycles of simulated chemical disinfection were accomplished with the specimens immersed in the solutions at room temperature for 10 minutes, followed by tap water washing for 30 seconds and storage in distilled water at room temperature for 7 days until the next disinfection. Simulated disinfection by microwave energy was carried out in a domestic oven with 1300 W at a potency of 50% for 3 minutes with the specimens individually immersed in 150 ml of distilled water. Control (no disinfection) and the experimental groups (first and third disinfection cycles) were submitted to Knoop hardness measurements with indentations at the center of the labial tooth surface. Data were submitted to repeated measure two-way ANOVA and Tukey's test (α = 0.05).

RESULTS

Biocler, Magister, and Trilux showed lower surface microhardness when submitted to microwave. Lower microhardness for Biotone was promoted by hypochlorite, while no significant difference was shown for New Ace. The third disinfection cycle significantly decreased the tooth surface hardness only for microwave.

CONCLUSIONS

Different disinfection methods promoted different effects on the microhardness of different types of artificial teeth. Surface microhardness of the teeth was less affected by the simulated chemical disinfections when compared to microwaved specimens.

Análise radiográfica de uniões soldadas a laser executadas no titânio comercialmente puro fundido, em diversas situações clínicas simuladas

Esse estudo foi conduzido para avaliar a possibilidade de visualização de porosidade interna em radiografias periapicais de uniões soldadas a laser, confeccionadas em estruturas de titânio cp, em diferentes situações de soldagem. Foram confeccionados halteres em resina acrílica, com diâmetros centrais de 1,5; 2,0; e 3,5 mm, por meio de uma matriz metálica bipartida. Os halteres em resina foram fundidos em Ti cp e após acabamento e polimento, seccionados em duas partes iguais. As partes foram alinhadas e fixadas de tal forma que as distâncias entre elas fossem 0,0 e 0,6 mm. A combinação entre as variáveis (distância de soldagem e diâmetro dos halteres) gerou seis grupos (n=10). A soldagem a laser foi realizada com as seguintes especificações: 360V/8ms (1,5 e 2,0 mm) e 380V/9ms (3,5 mm), com foco e freqüência regulados em zero, em um aparelho de soldagem a laser Desktop-F. As uniões obtidas receberam acabamento, polimento e foram submetidas à análise radiográfica com exposição à radiação (90 KV, 15 mA, 0,6 seg e 10 a 13 mm de distância) utilizando filme periapical. As radiografias foram analisadas visualmente quanto à presença de porosidade nas uniões soldadas, e os dados obtidos, submetidos ao teste Qui-Quadrado (5%). Com isso, verificou-se ser possível visualizar porosidade interna nessas uniões. Em corpos de prova de menores diâmetros, 1,5 e 2,0 mm, a incidência é maior quando a distância é 0,6 mm. Entretanto, em corpos de prova de 3,5 mm, a incidência é alta para ambas as uniões, não diferindo estatisticamente entre si

Influence of thickness and area of reline on the stress distribution in peri-implant bone during the healing period: a three-dimensional finite element analysis

The current study used finite element analysis to evaluate how the thickness of reline material and the area of its placement in conventional complete dentures affected the stress distribution in peri-implant bone during function in the healing period. For this study, three-dimensional models were created to simulate a severely resorbed mandible with two implants placed recently in the anterior region. Two of these models received a layer of soft liner material that covered the entire length of the denture base (1.5 mm or 3.0 mm); for the other sample models, soft liner material was placed (in thicknesses of 1.5 mm or 3.0 mm) in the implant region only. The models were exported to mechanical simulation software; two simulations were performed by placing a load in the mandibular right canine (35 N) and the mandibular right first molar (50 N). Data were quantitatively and qualitatively evaluated by means of maximum principal stress. In all cases, models that received 3.0 mm of soft liner material showed lower values of stress concentration than those receiving 1.5 mm of soft liner material. Likewise, localized application of soft liner in the implant region showed lower stress concentration compared with models in which the entire denture base was relined. These results indicate that the thickness and area of reline in conventional complete dentures has a direct effect on stress distribution in the peri-implant bone tissue during the healing period.

An in vitro comparison of joint stability of implant-supported fixed prosthetic suprastructures retained with different prosthetic screws and levels of fit under masticatory simulation conditions

PURPOSE

This study sought to determine an optimal postinsertion retorque protocol to maintain implantsuprastructure joint stability after being subjected to a 1-year in vitro masticatory simulation.

MATERIALS AND METHODS

Ten mandibular implant-supported dentures were manufactured and 20 epoxy resin models were obtained for two fit levels: passive fit and misfit. Eight groups (n = 20) were created on the basis of vertical fit (passive or misfit) and prosthetic screw material (titanium or gold). The single-screw test was performed and the vertical misfit was quantified using an optical microscope. Loosening torque was measured after simulations of two types of clinical use: (1) 6 months of use, torque loosening, retightening, another 6 months of use, and loosening torque; and (2) 1 year of use followed by loosening torque. Data were analyzed by means of two-way analysis of variance and the Tukey test.

RESULTS

The factors of cycling time and condition use (fit level and screw type), as well the interaction between these factors, significantly influenced the loosening torque (P < .05). After 6 months and another 6 months of clinical use simulation, titanium screws showed higher loosening torque values than did gold screws for the same fit level (P < .05). After 1 year of clinical use simulation, titanium and gold screws in passively fit dentures showed higher loosening torque values than they did in misfit dentures (P < .05). The titanium screws presented a decrease in the loosening torque after 1 year in misfit dentures.

CONCLUSIONS

The stability of titanium screws was higher than that of gold screws after 6 months of simulation because of their lower plastic deformation. When the cycling time was analyzed, titanium screws were less stable after 1 year of simulation because of loss of torque in the presence of misfit.

Fatigue performance of joints executed in pure titanium structures with several diameters

This study evaluated fatigue strength of CP-Ti laser-welded joints. Sixty (20/diameter) CP-Ti casted dumbbell rods with diameters of 1.5, 2.0, and 3.5 mm were sectioned and welded using two joint openings (0.0 (00) and 0.6 mm (06)). Six groups were formed, amounting to a total of 9 (n=10) with inclusion of intact groups. Welding was executed using 360 V/8 ms (1.5 and 2.0 mm) and 380 V/9 ms (3.5 mm). Joints were finished, polished, and submitted to radiographic examination to visually analyze presence of porosity (PP). Specimens were submitted to cyclic tests, and the number of cycles until failure (NC) was recorded. Fractured surfaces were examined by SEM. Kruskal-Wallis and Dunn (α=0.05) tests demonstrated that NC was lower for all diameters with 06, and for 3.5 mm/00. NC and PP were found to have a negative correlation (Spearman Coefficient). For CP-Ti frameworks with thin diameters, laser welding is better when structures are juxtaposed.

Effect of monomer content in the monomer-polymer ratio on complete denture teeth displacement

The purpose of the study was to verify the linear displacement of teeth in maxillary complete dentures influenced by different monomer-polymer ratios - according to the manufacturer's instructions, with 25% excess or 25% less monomer content - in the conventional and microwaved polymerization techniques. Wax base plates and wax planes were made on edentulous maxillary stone casts according to traditional method. The set was assembled in semi-adjustable articulator with a lower toothed stone cast as guide to mounting of the maxillary artificial teeth. Impressions were taken from this tooth arrangement with silicone and the mold was used to standardize the mounting of the teeth of all dentures. Referential points were made on the artificial teeth for linear measurements with optical microscope before processing of the dentures and after deflasking. Denture bases were conventionally packed with acrylic resin according to the monomer-polymer ratio protocol. Tooth displacement data were submitted to ANOVA and Tukey test (α=0.05). There were no statistically significant differences (p>0.05) between the group with monomer content recommended by the manufacturer and groups with 25% more and 25% less monomer, in both conventional and microwaved polymerizations. Excess or less monomer in the monomer-polymer ratio and polymerization types did not change the linear distance between teeth.

The influence of storage on dimensional changes in maxillary acrylic denture bases and the effect on tooth displacement

This study investigated the influence of both room temperature storage and water storage on tooth displacement in complete dentures. Thirty maxillary dentures were manufactured and processed using 3 different curing cycles; long, short conventional and microwaved. Distances between fixed points on teeth were measured and the dentures stored at room temperature for 24 weeks. After storage, the distances were measured again and the dentures then stored in water at 37 degrees C for 24 weeks, when the distances were re-evaluated. Anteroposterior distances demonstrated contraction in all acrylic resins. Incisor-incisor (air = -8.5% and water = -7.0%) and molar-molar (room = -1.8% and water = -1.1%) distance changes were greater in the Onda-Cryl resin (p < 0.05), whereas the premolar-premolar (room = -2.2% and water = -1.7%) distance was higher in the QC-20 resin (p < 0.05).

Misfit of pure titanium frameworks: effect of veneer coverage and spark erosion process

OBJECTIVE. The purpose of this study was to evaluate the influence of veneer application on the misfit level of implant-supported frameworks. MATERIALS AND METHODS. Thirty commercially pure titanium (Tritan, Dentaurum, Pforzheim, Germany) frameworks were fabricated from a metallic index containing five Branemark-type multi-unit abutments. Analogs of the abutments were positioned into the framework to manufacture an index for each framework, which permitted the evaluation of the marginal gap caused only by the veneer coverage. The frameworks were grouped (n = 10) in the following manner: (G1) heat-cured acrylic resin (Clássico, Clássico, São Paulo, Brazil); (G2) light-cured resin (Versyo.com, Heraeus Kulzer, Brazil); and (G3) porcelain (Triceram, Dentaurum, Pforzheim, Germany). Marginal refinement with spark erosion was then conducted. The marginal gap was verified before and after the veneer coverage and the spark erosion procedure, following the single screw test protocol (tightening force of 10 Ncm). Data were submitted to an analysis of variance (ANOVA) in a split-plot design for repeated measurements followed by a Tukey test (p = 0.05). RESULTS. The veneer application was associated with a significant increase in the mean misfit values of all groups. The lowest values were presented by G2. After the spark erosion process, the mean misfit value decreased only on G3. CONCLUSIONS. Heat-cured acrylic resin and porcelain produced the highest values of marginal gaps, whereas light-cured acrylic resin produced the lowest. In addition, the spark erosion process was effective only in the marginal gap of the porcelain application group.