Internal porosities,retentive force,and survival of cobalt–chromium alloy clasps fabricated by selective laser-sintering

PurposeThe purpose of this study was to evaluate internal porosities, retentive force values and survival of cobalt–chromium (Co–Cr) alloy clasps fabricated by direct metal laser-sintering (DMLS) and compare them to conventionally cast clasps.MethodsEmbrasure clasps were digitally designed fitting teeth 35 and 36 on identical metal models (N = 32). Sixteen clasps were fabricated using DMLS (group DMLS) and another sixteen clasps were additively manufactured from wax and then cast from a Co–Cr alloy (group CAST). Internal porosities were examined using micro-focus X-ray (micro-CT) and analyzed applying Kolmogorov–Smirnov test, Mann–Whitney test, and T test (significance level: p < 0.050). A universal testing machine was used to determine the retentive force values at baseline and after 1095, 5475, 10,950 and 65,000 cycles of simulated aging. Data were analyzed employing Kolmogorov–Smirnov test, one-way ANOVA, and Scheffé’s post-hoc test (significance level: p < 0.050). Survival was estimated for 65,000 cycles of artificial aging using Kaplan–Meier analysis.ResultsMicro-CT analysis revealed a higher prevalence (p < 0.001), but a more homogeneous size and a significantly smaller mean (p = 0.009) and total volume (p < 0.001) of internal porosities for group DMLS. The groups showed mean initial retentive force values of 13.57 N (CAST) and 15.74 N (DMLS), which significantly declined over aging for group CAST (p = 0.003), but not for group DMLS (p = 0.107). Survival was considerably higher for group DMLS (93.8%) than for group CAST (43.8%) after 65,000 cycles of aging.ConclusionsClasps made by laser-sintering could be an alternative to conventional cast clasps for the fabrication of removable partial denture frameworks.     

Retention strength between veneering resin composites and laser-sintered cobalt–chromium alloy

The purpose of the present study was to evaluate the retention strength between a resin composite veneering material and three types of cobalt–chromium (Co–Cr) alloy substrates. Co–Cr alloy specimens with 81 retention devices (LSR), with 144 retention devices (LDR), and without retention device (LN) were fabricated using a laser-sintering system. The specimens were air-abraded with alumina, conditioned with a primer [Alloy primer (AP) or M.L. primer (ML)], and veneered with a light-polymerized resin composite (Gradia). Three control groups (LSR-N, LDR-N, and LN-N) without primer were also prepared. After 20,000 thermocycles in 4 and 60 °C water, tensile retention strengths were determined using a universal testing machine. Data were analyzed by analysis of variance and a post hoc Tukey–Kramer HSD test (α = 0.05, n = 8). The highest retention strengths were obtained in LSR-AP (28.3 MPa), LSR-ML (23.3 MPa), LDR-AP (26.9 MPa), and LDR-ML (27.8 MPa), and these values were not significantly different. In the absence of a retention device, the retention strengths were significantly different in the following order: LN-N (0.1 MPa) < LN-ML (12.4 MPa) < LN-AP (20.2 MPa). The specimens without primer were significantly different in the following order: LN-N (0.1 MPa) < LSR-N (15.4 MPa), LDR-N (17.1 MPa). No significant difference was found between the numbers of retention devices, which were 81 and 144. In conclusion, the combined use of the primers and the retention devices is recommended when the laser-sintered Co–Cr alloy is veneered with the resin composite materials to maximize the retention strength.     

Influence of thermo-mechanical cycling on porcelain bonding to cobalt–chromium and titanium dental alloys fabricated by casting,milling, and selective laser melting

Purpose

The aim has been to determine the effect of thermo-mechanical cycling on shear-bond-strength (SBS) of dental porcelain to Co–Cr and Ti-based alloys fabricated by casting, computer-numerical-controlled milling, and selective-laser-melting (SLM).

Comparison of marginal fit of cemented zirconia copings manufactured after digital impression with lava™ C.O.S and conventional impression technique

Background

Evaluation of the marginal fit of cemented zirconia copings manufactured after digital impression with Lava? Chairside Oral Scanner in comparison to that of zirconia copings manufactured after conventional impressions with polyvinyl siloxane.

Methods

A prepared typodont tooth #36, was replicated 40 times with a vinyl silicone and precise model resin. The dies were randomly divided into two groups according to the impression taking technique. Digital impressions with Lava? C.O.S. and conventional impressions were taken according to the group. Subsequently zirconia copings were manufactured and cemented on their respective dies with zinc oxide phosphate cement. After embedding in resin, mesio-distal section of each coping was performed with a diamond saw in order to obtain two slices. One half of the specimen was used for evaluation with an optical microscope (OM) and the other half for evaluation with a scanning electron microscope (SEM). Marginal gap (MG) and absolute marginal discrepancy (AMD) were measured mesial and distal on each slice.

Results

No significant difference of the marginal parameters between the digital and the conventional group was found. The mean values for MG in the digital group were 96.28 μm (+/?43.21 μm) measured with the OM and 99.26 μm (+/?48.73 μm) measured with the SEM, respectively. AMD mean values were 191.54 μm (+/?85.42 μm) measured with the optical microscope and 211.6 μm (+/?96.55 μm) with the SEM. For the conventional group the mean MG values were 94.84 μm (+/?50.77 μm) measured with the OM and 83.37 μm (+/?44.38 μm) measured with the SEM, respectively. AMD mean values were 158.60 μm (+/?69.14 μm) for the OM and 152.72 μm (+/?72.36) for the SEM.

Conclusions

Copings manufactured after digital impression with Lava? C.O.S. show comparable marginal parameters with the copings manufactured after conventional impression with polyvinyl syloxane. The mean MG values of both groups fit in the clinically acceptable range.

     

Evaluation of the marginal and internal discrepancies of CAD-CAM endocrowns with different cavity depths: An in vitro study

Statement of problem

The marginal and internal discrepancies of computer-aided design and computer-aided manufacturing (CAD-CAM) endocrowns are unknown.

Cobalt–chromium alloys fabricated with four different techniques: Ion release,toxicity of released elements and surface roughness

ObjectiveTo investigate the metal ion release, surface roughness and cytoxicity for Co–Cr alloys produced by different manufacturing techniques before and after heat treatment. In addition, to evaluate if the combination of materials affects the ion release.MethodsFive Co–Cr alloys were included, based on four manufacturing techniques. Commercially pure titanium, CpTi grade 4 and a titanium alloy were included for comparison. The ion release tests involved both Inductive Coupled Plasma Optical Emission Spectrometry and Inductive Coupled Plasma Mass Spectrometry analyses. The surface analysis was conducted with optical interferometry. Cells were indirectly exposed to the materials and cell viability was evaluated with the MTT (3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyltetrazolium bromide) method.ResultsAll alloys showed a decrease of the total ion release when CpTi grade 4 was present. The total ion release decreased over time for all specimens and the highest ion release was observed from the cast and milled Co–Cr alloy in acidic conditions.The cast and laser-melted Co–Cr alloy and the titanium alloy became rougher after heat treatment. All materials were within the limits of cell viability according to standards.SignificanceThe ion release from Co–Cr alloys is influenced by the combination of materials, pH and time. Surface roughness is influenced by heat treatment. Furthermore, both ion release and surface roughness are influenced by the manufacturing technique and the alloy type. The clinical implication needs to be further investigated.     

Torque resistance of impression copings after direct implant impression: An in vitro evaluation of impression materials with and without adhesive

Statement of problem

No data are available on the ability of an impression coping to resist the manual placement of an abutment replica (implant analog) during prosthodontic laboratory procedures after a direct (pick-up) impression.

Comparison of excursive occlusal force parameters in post-orthodontic and non-orthodontic subjects using T-Scan® III

Objective: Published studies indicate that orthodontically treated patients demonstrate increased posterior occlusal friction contributing to temporomandibular disorder (TMD) symptoms. This study investigated measured excursive movement occlusal contact parameters and their association with TMD symptoms between non- and post-orthodontic subjects.

Methods: Twenty-five post-orthodontic and 25 non-orthodontic subjects underwent T-Scan® computerized occlusal analysis to determine their disclusion time (DT), the excursive frictional contacts, and occlusal scheme. Each subject answered a TMD questionnaire to determine the presence or absence of TMD symptoms. Statistical analysis compared the within group and between group differences (p < 0.05).

Results: Statistically significant differences were observed in the disclusion time: DT = 2.69 s in the post-orthodontic and 1.36 s in the non-orthodontic group. In the non-orthodontic group, 72.7% working and 27.3% non-working side contacts were seen, while in the post-orthodontic group, (near equal) 54.7% working and 45.3% non-working side contacts were seen. Presence of canine guidance was seen in 60% of the non-orthodontic group and 24% in the post-orthodontic group. Seventy-two percent of the post orthodontics subjects presented with one or more TMD symptoms.

Conclusion: Significantly longer disclusion time, higher posterior frictional contacts, and more TMD symptoms were observed in the post-orthodontic group, suggesting that orthodontic treatment increases posterior tooth friction. Computerized occlusal analysis is an objective diagnostic tool determining the quality of excursive movements following orthodontic treatment.     

In vitro evaluation of marginal and internal adaptation after occlusal stressing of indirect class II composite restorations with different resinous bases and interface treatments. “Post-fatigue adaptation of indirect composite restorations”

The present study evaluated the influence of different composite bases and surface treatments on marginal and internal adaptation of class II indirect composite restorations, after simulated occlusal loading. Thirty-two class II inlay cavities were prepared on human third molars, with margins located in cementum. A 1-mm composite base extending up to the cervical margins was applied on all dentin surfaces in the experimental groups; impressions were made and composite inlays fabricated. The following experimental conditions were tested: no liner (control group), flowable composite treated with soft air abrasion (experiment 1), flowable composite sandblasted (experiment 2) and restorative composite sandblasted (experiment 3). All specimens were submitted to 1,000,000 cycles with a 100-N eccentric load. Tooth-restoration margins were analysed semi-quantitatively by scanning electron microscopy before and after loading; internal adaptation was also evaluated after test completion. The percentage of perfect adaptation in enamel was 79.5% to 92.7% before loading and 73.3% to 81.9% after loading. Perfect adaptation to dentin was reduced before loading (54.8% to 77.6%) and after loading (41.9% to 63%), but no difference was found among groups for pre- and post-loading conditions. No debonding occurred between the base and composite luting. A significant, negative influence of cyclic loading was observed. The results of the present study support the use of flowable or restorative composites as base/liner underneath large class II restorations. Soft air abrasion represents a potential alternative to airborne particle abrasion for treating cavities before cementation. The application of a composite base underneath indirect composite restorations represents a feasible non-invasive alternative to surgical crown lengthening to relocate cavity margins from an intra-crevicular to supra-gingival position.     

Prospective comparison study of one-year outcomes for all titanium total temporomandibular joint replacements in patients allergic to metal and cobalt–chromium replacement joints in patients not allergic to metal

We aimed to ascertain whether there are any early differences in outcome between all titanium temporomandibular joint (TMJ) prostheses in patients allergic to metal and standard cobalt–chromium prostheses in patients not allergic to metal. All patients who had primary TMJ prostheses placed with one-year follow-up between March 2003 and February 2011 were included. We reviewed the basic characteristics of patients. The outcome variables measured included disease, pain, mouth opening, and diet. A total of 55 patients with 77 joint replacements fulfilled the inclusion criteria. Forty patients had standard cobalt–chromium alloy (Co–Cr–Mo) prostheses (20 unilateral and 20 bilateral), and 15 had all titanium prostheses (13 unilateral and 2 bilateral). Osteoarthritis was the most common disease in both groups. There was significant improvement in pain score at reviews at 6 weeks (p = 0.001) and 12 months (p = 0.03). Values between groups were not significant (p = 0.48 at 6 weeks, and p = 0.10 at 1 year). Mouth opening in each group improved significantly with continued gains between assessments at 6 weeks and 12 months (p = 0.001) but there were no significant differences between groups. Diet scores were significantly improved one year postoperatively in both groups (p = 0.001), but differences between groups were not significant (p = 0.90). At one year, outcomes for all titanium prostheses in patients allergic to metal were similarly favourable to those in patients who had no hypersensitivity to metal and had standard prostheses. No patient developed a hypersensitivity reaction, and no all titanium prosthesis failed during the one-year follow-up period.     

Influence of the methodology and evaluation criteria on determining microleakage in dentin–restorative interfaces

This in vitro study compared microleakage along the dentin–restorative interface using a spectrophotometer protocol and two conventional single-surface methods (scores and percentages), using an organic dye (0.5% buffered methylene blue) or a tracer (50% silver nitrate). Occluso-proximal preparations with gingival margins in dentin were made in 40 human teeth. The teeth were divided into four groups (n=10) according to the solution dyes and adhesive system used: group 1, single bond/methylene blue; group 2, single bond/silver nitrate; group 3, Clearfil SE Bond/methylene blue; and group 4, Clearfil SE Bond/silver nitrate. The dye penetration measurements were made in all groups, using scores and percentages. Groups 1 and 3 were also assessed by UV spectrophotometer. For percentage measurement, the data were submitted to ANOVA and Tukey’s test. For the material factor, there was a statistically significant difference between groups 1 and 3. For the dye factor, there was a statistically significant difference between groups 3 and 4. The score results were submitted to Kruskall–Wallis test and showed differences between groups 1 and 3 and groups 2 and 3. For spectrophotometer measurement, no significant difference was observed between groups 1 and 3. The results of dye penetration suggest that there was a difference between dyes and measurement methods, and this should change the interpretation of microleakage tests.     

Quality of life in treatment of mandibular fractures using closed reduction and maxillomandibular fixation in comparison with open reduction and internal fixation – A randomized prospective study

Treatment of mandibular fractures by open reduction and internal fixation (ORIF) is often assumed to be superior to treatment by close reduction and maxillomandibular fixation (MMF) because patients managed by ORIF seem to be rehabilitated earlier according to functional and social aspects. This assumption is often from surgeon's perspective, not taking into account patient's view point. This study highlights a comparative assessment between ORIF and MMF from the patients' perspective.Fifty six patients with mandibular fractures within the tooth bearing areas of the mandible were prospectively studied in a randomized controlled pattern for postoperative Quality of Life (QoL) after ORIF versus MMF. Both groups were analyzed preoperatively, at 1 day, 6 and 8 weeks regarding their QoL using the General Oral Health Assessment Index questionnaire (GOHAI). No significant statistical difference was found between the groups regarding overall QoL. Patients managed by MMF were more affected by psychosocial and physical domains whereas patients managed by ORIF were more affected by the pain domain.The results demonstrate that the treatment affects the psychosocial, physical and pain domain differentially. When both treatments are possible the patient's should be enlightened on the advantages and disadvantages of both treatment modalities to guide their choice of treatment.     

A comparative evaluation of shear bond strength of porcelain and composite using different bonding agents — An in vitro study

Objective

The purpose of the present in vitro study is to compare and evaluate the shear bond strength of porcelain and composite using different bonding agents.

Materials and methods

Sixty-three porcelain pellets were prepared and were divided into 9 groups. Three surface treatment and two bonding agents were evaluated. The surface treatment were: 1) sandblasting; 2) etching with 35% phosphoric acid; and 3) etching with 8% hydrofluoric acid. Applying bonding agents Scotch bond adhesive and clearfil liner bond 2V and combination of these treatments. Composite resin was condensed and light cured for 60 seconds on the porcelain specimens which were stored in distilled water at 37°C for 24 hours before mechanical testing.

Results

The bond strength were significantly different according to ANOVA F-test (F = 6.28, p < 0.01) and Duncan’s Multiple Range Test. Eight percent hydrofluoric acid showed higher bond strength when compared to 35% phosphoric acid etching and sandblasting by 50 micron aluminum oxide. Highest bond strength was observed with hydrofluoric acid + clearfil.

Conclusion

Etching with 8% hydrofluoric acid + clearfil liner bond showed higher bond strength when compared to hydrofluoric acid alone. This is indicative that effect of silane and etching can be use to improve mechanico chemical bonding. Among bonding agents used clearfil liner showed higher bond strength when compared to scotch bond adhesive.     

Comparison of closure occlusal force parameters in post-orthodontic and non-orthodontic subjects using T-Scan® III DMD occlusal analysis

Objective: Balanced occlusal force distribution is a critical factor for restorative, prosthetic or orthodontic treatment. It has been postulated that orthodontic treatment may lead to occlusal discrepancies in the arch due to changing the occlusal relationships. This study was conducted to compare the occlusal force parameters between natural dentition patients and a post-orthodontic treatment group.

Method and Materials: Fifty Thai subjects were divided into non-orthodontic and post-orthodontic groups comprised of 25 subjects each (mean age 24.8 years). The T-Scan® III computerized occlusal analysis system was used to record a multi-bite closure for each subject. The initial occlusal contact location, the bilateral percentage force distribution, the percentage force in the anterior and posterior quadrants, and the individual tooth force percentages were calculated for both groups. The Student’s Paired t-Test compared the in-group differences, while a one-way ANOVA analyzed the differences between the two groups.

Results: The initial tooth contacts in both groups were found on the second molars and central incisors. Maximum force was most frequently observed on the left second molar tooth (15.9% non-orthodontic; 25.4% post-orthodontic). The bilateral right-to-left side force distribution (51.36% right–48.96% left) was not statistically different for all subjects, nor was it statistically different between the non-orthodontic (48.67% right–51.36% left) and the post-orthodontic groups (48.96% right–51.05% left). Statistically significant differences were found between the quadrants in both the groups (22.46% anterior–77.57% posterior in non-orthodontic subjects; 10.58% anterior–89.42% posterior in post-orthodontic subjects) (p < 0.01).

Conclusion: A significant occlusal force discrepancy was found in the post-orthodontic subjects, with higher force percentages observed posteriorly and much less percentage force anteriorly, when compared to the natural dentition subjects. T-Scan® III digital occlusal analysis may be recommended for orthodontic case finishing, to make visible to the clinician the severity of the orthodontically created occlusal force imbalance, such that it can be minimized during orthodontic case finishing.     

Prediction of cathode efficiency in electro-deposition of copper–tin using regression and artificial neural network model

The aim of this paper is to develop a model using artificial neural network for the electro-deposition of copper–tin alloy (bronze) based on the experimentally obtained data. The electro-deposition of copper–tin was carried out using an alkaline cyanide bath. Copper and tin contents of coatings were determined using X-ray fluorescence spectroscopy. Cathode efficiencies were determined from the actual and theoretical masses of the deposits. The results were used to create a model for the plating characteristics and also for studies using ANN. The ANN model was compared with the regression model for analysis.