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.

Bone Healing at Implants Placed in Sites Prepared Either with a Sonic Device or Drills: A Split-Mouth Histomorphometric Randomized Controlled Trial.

PURPOSE: To evaluate histomorphometrically early healing at implants placed in sites prepared with either a sonic device or conventional drills. MATERIALS AND METHODS: Sixteen volunteer patients were recruited. Two titanium mini-implants were placed in the distal segments of the maxilla in recipient sites prepared with either a sonic device or conventional drills. Biopsy specimens containing the mini-implants were retrieved after 2 weeks in eight patients, and after 6 weeks in the other eight patients. Histomorphometric analyses were performed. RESULTS: Histologic slides were available from seven patients for both 2-week and 6-week periods. After 2 weeks of healing, small amounts of new bone were found in contact with the implant surface, with 5.5% ± 7.3% and 3.8% ± 10.0% at the sonic and drill groups, respectively. After 6 weeks of healing, new bone was 46.9% ± 15.5% at the sonic group, and 46.4% ± 14.9% at the drill group. None of the differences was statistically significant. CONCLUSION: The percentage of new bone in contact with the implant surface was similar in the sonic and drill groups.

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.