Study on the Effect of Inter-Layer Cooling Time on Porosity and Melt Pool in Inconel 718 Components Processed by Laser Powder Bed Fusion

This paper investigates the effects on the material microstructure of varying the Inter-Layer Cooling Time (ILCT) during the printing process in laser powder bed fusion (L-PBF) multi-laser machines. Despite these machines allowing higher productivity rates compared to single laser machines, they are affected by lower ILCT values, which could be critical for material printability and microstructure. The ILCT values depend both on the process parameter sets and design choices for the parts and play an important role in the Design for Additive Manufacturing approach in L-PBF process. In order to identify the critical range of ILCT for this working condition, an experimental campaign is presented on the nickel-based superalloy Inconel 718, which is widely used for the printing of turbomachinery components. The effect of ILCT on the microstructure of the material is evaluated in terms of porosity and melt pool analysis on printed cylinder specimens, considering ILCT decreasing and increasing in the range of 22 to 2 s. The experimental campaign shows that an ILCT of less than 6 s introduces criticality in the material microstructure. In particular, at an ILCT value of 2 s, widespread keyhole porosity (close to 1‱) and critical and deeper melt pool (about 200 microns depth) are measured. This variation in melt pool shape indicates a change in the powder melting regime and, consequently, modifications of the printability window promoting the expansion of the keyhole region. In addition, specimens with geometry obstructing the heat flow have been studied using the critical ILCT value (2 s) to evaluate the effect of the surface-to-volume ratio. The results show an enhancement of the porosity value (about 3‱), while this effect is limited for the depth of the melt pool.

Long-term follow-up of single crowns supported by short, moderately rough implants-A prospective 10-year cohort study

OBJECTIVES

To evaluate prospectively the clinical and radiographic outcomes after ten years of short (6 mm) implants with a moderately rough surface supporting single crowns in the posterior region.

MATERIAL AND METHODS

Forty 6 mm modified sandblasted large-grit acid-etched (mod-SLA), soft tissue level implants were installed in the distal segments of 35 consecutive patients. After 6 weeks of healing, abutments were tightened, and single porcelain-fused-to-metal crowns were cemented. Implant survival, marginal bone loss, and clinical crown/implant ratio were evaluated at various time intervals up to 10 years after loading.

RESULTS

Two out of the 40 implants were lost before loading, one implant was lost after 7 years because of peri-implantitis. One patient with two implants died and was excluded from analysis. Two patients did not come at the 10-year follow-up and were considered as drop out (2 implants). The survival rate was 91.7% (n = 36). Thirty-three implants were available for marginal bone loss evaluation. A mean marginal bone loss after 10 years of function was 0.8 ± 0.7 mm. Between 5 and 10 years, the loss was 0.2 ± 0.4 mm. No technical complications were registered during the 10-year period. The clinical crown/implant ratio increased with time from 1.6 at the delivery of the prosthesis to 2.0 after 10 years of loading with no increase between 5 and 10 years.

CONCLUSION

Short (6 mm) implants with a moderately rough surface supporting single crowns in the posterior region and loaded after 6-7 weeks maintained full function for at least 10 years with low marginal bone resorption.

Association of Smoking Habits and Height of Residual Bone on Implant Survival and Success Rate in Lateral Sinus Lift: A Retrospective Study

The primary aim was to evaluate the association of patient-related factors, biomaterials, and implant characteristics on complications' rate of sinus graft surgery and on implant survival rate in grafted sinus. Secondary aims were to measure bone remodeling around implants and patient satisfaction. A retrospective cohort study was designed. Patients who had computerized tomography (CT) before sinus surgery (T0), orthopantomography after implant surgery (T1) and at follow-up (T2), were included. Specific forms were used to collect clinical data. Radiographic measures were: height of residual bone before sinus surgery measured on CT (T0) and apical and marginal bone levels around implants measured on orthopantomography at T1 and T2. Forty-three lateral sinus lifts were performed. Three grafts failed before implant insertion. Out of 83 implants inserted in 29 patients, a total of 19 failed. Mean follow-up (T2) was 6 ± 1.8 years [4; 11.2 years]. The multilevel models analysis showed no association between complications rate and patient-related factors, biomaterials, and implant characteristics. Smoking (odds ratio [OR]: 8.3; 95% CI 1.46-48.05, P = .0173) and height of residual bone (OR: 0.32 for each mm; 95% CI 0.15-0.68, P = .0034) were associated with implant failure. Bone remodeling between T1 and T2 was -0.8 ± 0.2 mm for apical bone and -0.6 ± 0.3 mm for marginal bone. General therapy satisfaction measured in a visual analogue scale was 8.4 ±1.4. In conclusion, lower height of residual bone before sinus surgery and smoking habits had a negative prognostic effect on survival rate of dental implants placed in grafted sinuses.

[Effectiveness of depot diltiazem in stable effort angina: a double-blind study compared with placebo]

AIM OF THE STUDY

The antianginal efficacy of slow-release (SR) Diltiazem and change in ergometric parameters during treatment were evaluated in patients with stable effort angina.

METHODS

Forty eight patients with documented ischemic cardiopathy were studied. The study design was double blind randomised cross over versus placebo. After a 7 days run-in period of pharmacological washout, patients were randomised to treatment with diltiazem SR (120 mgs bid) or placebo for 1 week, followed by crossover of treatments. No concomitant antianginal therapy, except sublingual nitro-glycerine was allowed during the trial. Exercise tests were performed during the run-in period and at the end of each week of treatment.

RESULTS

After diltiazem administration, exercise duration increased significantly in comparison with placebo (645.6 +/- 196.31 vs 563.9 +/- 244.52 s, p < 0.01). Similarly, time to onset of angina and time to ischemic threshold increased in comparison to placebo (603.78 +/- 198.50 vs 459.69 +/- 239.40 s, p < 0.01 and 576.06 +/- 208.88 vs 463.16 +/- 246.12 s, p < 0.01 respectively). No significant changes in heart rate, blood pressure and double product at ischemic threshold and peak exercise were detected.

CONCLUSIONS

SR-diltiazem is effective and well tolerated in the treatment of patients with stable angina.

Chest thump and ventricular tachycardia

Chest thump is a simple method of treatment of some paraxysmal arrhythmias. Its therapeutic efficacy, electrophysiological bases and clinical utility have been studied in 17 patients during 45 episodes of ventricular tachycardia (VT). Thumping the precordium interrupted the VT in 22 episodes. Three types of interruption of VT have been observed: (1) In 15 episodes, single ventricular premature beats induced by the blow, occurring randomly in the cycle, stopped the arrhythmia; (2) In 5 episodes, a run of premature beats, induced by a rapid succession of blows, interrupted the tachycardia; (3) In 2 episodes, chest thump caused a short period of asystole followed by sinus rhythm. Chest thump is an antiarrhythmic treatment of definite clinical utility. The complications are rare, although there is a possibility of ventricular fibrillation. Therefore, it should be performed only under careful supervision.

Leukocytotoxic Antibodies in Patients Suffering from Various Forms of Leukemia

The results of a study on the leukocytotoxic activity of sera from patients with acute or chronic, myeloid or lymphoid leukemia are reported and discussed. In almost all cases circulating antibodies were found, active –- in isolation or simultaneously –- against suspensions of granulocytes and/or lymphocytes of normal subjects, and autologous and homologous leukemic cells from subjects with acute or chronic, myeloid or lymphatic leukemia. The presence of an immunologic process appeared to be independent of the type of leukemia, though the rate of positives in chronic lymphatic leukemia was lower. Antileukemic immunisation proved to be independent of the leukocyte count; however, the cases with anti-autologous leukocyte antibodies were among the leukopenics. These findings support the hypothesis that there is an immunologic humoral process of the antileukocytic type, though it does not seem to be active against specific neoformed antigens of the autologous leukemic cells. The probable autoimmune pathogenesis of these antibodies is discussed.