A Nonlinear Three-Dimensional Finite Element Analysis of Stress Distribution and Microstrain Evaluation in Short Dental Implants with Three Different Implant-Abutment Connections in Single and Splinted Conditions in the Posterior Mandible.

Background: Stress distribution plays a vital role in the longevity and success of implant-supported prosthesis. This study evaluated the von Mises stress and microstrain in the peri-implant bone and the implant-abutment junction of short dental implants with three different implant-abutment connections in splinted and unsplinted conditions using finite element analysis (FEA). Materials and Methods: In this experimental study, nine transversely isotropic finite element models were developed, and randomly divided into three equal groups (n = 3): control, (Group AC) single-standard 4.3 × 10 mm bone level implant-supported restorations with external hexagonal (EH) connection, internal conical (IC) and internal trichannel (ITC) connection, single short implant-supported restorations (Group AT), and splinted short implant-supported restorations (Group B) for each of the three implant-abutment connections, respectively. A 200 N load was applied along the long axis of the implants and a 100 N (45°) oblique load was applied and von Mises stress and microstrain values were evaluated. Results: Single standard implants demonstrated the highest von Mises stress and microstrain values followed by single short implants and splinted short implants, respectively. Among the implant-abutment connections, the IC connection showed the highest values and the ITC connection showed the least values. Conclusion: Within the limitations of this study, it was concluded that splinting of short dental implants demonstrated lesser and more homogeneous stress and microstrain, especially on oblique loading. The microstrain values for all connections evaluated were within the physiological loading limit (200-2,500 N) and were hence considered safe for clinical use.

Cytotoxicity of dental cement on soft tissue associated with dental implants at different time intervals.

Background: To investigate and compare the effect of four commercially used dental cement at 24 hours, 48 hours,72 hours (h) and 6 days on the cellular response of human gingival fibroblast (HGF). Methods: 3 cement pellet samples were made for each 4-test cement (n=12). The cement used for this study were zinc phosphate (ZP), zinc oxide non-eugenol (ZOE), RelyX U200 (RU200), and glass ionomer cement (GIC). The cytotoxicity of peri-implant tissues was investigated using one commercial cell line. All processing was done following International Organization for Standardization (ISO) methods 10993-5 and 10993-12 (MTT assay Test). Cell cultures without dental cement were considered as control. Standard laboratory procedures were followed to permit cell growth and confluence over 48 hrs after sub-cultivation. Before being subjected to analysis, the cells were kept in direct contact with the cement samples for the suggested time period. To validate the results the specimens were tested three times each. Cell death and inhibition of cell growth were measured quantitatively. Results were analyzed using 1-way ANOVA (a=0.05) followed by Tukey B post hoc test. Results: The study showed the dental cement test material was cytotoxic. ZOE, ZP, GIC, and RU200 were cytotoxic in decreasing order, respectively, significantly reducing cell viability after exposure to HGF (p <0.001). Conclusions: Within the limitations of this in-vitro cellular study, results indicated that HGF were vulnerable to the test the dental cement. The highest cytotoxicity was observed in ZOE, followed by ZP, GIC, and RU200.

An In Vitro Study on the Shear Bond Strength of Feldspathic Porcelain to Nickel Chromium Alloy and Cobalt Chromium Alloy after Various Surface Treatments.

Background: To evaluate and compare the shear bond strength of feldspathic porcelain to four distinctively surface-treated Ni-Cr and Co-Cr alloys and to assess the impact of oxidation-heat treatment on porcelain to base metal alloy bond strength. Methods: 40 specimens each of nickel-chromium alloy and cobalt-chromium alloy were cast. A total of four groups of specimens were created. Group I was surface-treated by sandblasting with 50 µm alumina particles, Group II was surface-treated by sandblasting with 110 µm alumina particles, Group III and Group IV were surface-treated with 250 µm alumina particles. In Group IV, after sandblasting initially with 250 µm alumina particles, the alloys were subjected to oxidation and resandblasting with 250 µm alumina particles. Each of the specimen was coated with opaque and body porcelain and fired to a total thickness of 2 mm porcelain. A universal measuring machine was used to assess shear bond strength at a crosshead speed of 0.5 mm/min. Results: Two-way ANOVA followed by Tukey's post hoc test was used to assess the significant difference within the groups. Unpaired t-test was used for the intergroup comparison of the obtained data. The study showed that the size of the air abrasion particles used for sandblasting significantly influenced the porcelain to metal surface bond strength, with p value <0.001. The bond strength values of the two alloys tested showed no major variations. Result also showed that oxidation influences the metal-ceramic bond strength. Conclusions: The bond strength of the metal-ceramic interface is influenced by the alloy's surface treatment. The oxidation process impacts the bond strength of the metal-ceramic system.

Effect of Different Surface Treatments on the Micro-Shear Bond Strength and Surface Characteristics of Zirconia: An In Vitro Study.

Purpose: To study the effect of different surface treatments on the micro-shear bond strength and surface characteristics of zirconia. Methods: Two types of zirconia ceramics were tested: opaque (O) and translucent (T). Each type of zirconia was further allotted into four groups based on the type of surface treatment method. The four groups were: control (C), air abrasion with 110 µm Al2O3 particles (A), etching with Zircos-E Etching solution for 2 hours (E), and a combination of air abrasion and etching (AE). After the surface treatment, all specimens were ultrasonically cleaned and 10 resin cement cylinders were attached to the zirconia discs in each group. A micro-shear bond strength test was performed in a universal testing machine at a crosshead speed of 0.5 mm/min. The fracture surfaces were assessed under a compound microscope. SEM, EDAX, and AFM analyses were done for the zirconia specimens after being subjected to surface treatment. Statistical analysis for the bond strength test was done using the Shapiro-Wilk test, one-way analysis of variance (ANOVA), and Post hoc Tukey test. Results: The micro-shear bond strength values for the groups were as follows in megapascals (MPa): OC 18.96 (5.54), OA 22.66 (2.51), OE 28.48 (4.50), OAE 28.63 (4.53), TC 22.82 (5.46), TA 25.36 (5.17), TE 28.12 (4.76), and TAE 32.00 (3.47). The one-way analysis of variance (ANOVA) and post hoc Tukey HSD tests were done which showed significant results in the groups. In opaque zirconia, significant differences were seen in the etching and air abrasion with etching groups when compared with the control and air abrasion groups. There was no difference between the etching and air abrasion with etching groups. For translucent zirconia, the only significant difference was seen in the air abrasion with etching group in comparison with the control and air abrasion groups. The mode of failure was majorly adhesive. The surface topography and surface roughness showed significant differences between the groups. The EDAX results showed material loss that occurred due to sandblasting in the air abrasion groups. Conclusions: Etching with Zircos-E Etching solution significantly increased the bond strength of zirconia to resin cement when compared with other surface treatment methods. In translucent zirconia, the best results can be achieved by combining etching with air abrasion.

Biomechanical Stress Analysis of Platform Switch Implants of Varying Diameters on Different Densities of Bone.

PURPOSE: The purpose of this study was to evaluate and compare the strain developed in D2 and D3 types of bones on vertical loading by platform switch implants of different diameters. MATERIALS AND METHODS: Implants of diameters 3.25 mm, 4.2 mm, and 5.0 mm and of length 11.5 mm were taken and placed each on D2 and D3 bone models. Strain gauges were attached on the buccal and the lingual sides on each of these samples, and a vertical load of 190N was placed on the samples. The strain was recorded using a data logger. The data obtained was analysed using one-way ANOVA and post hoc Tukey test. RESULTS: In D2 and D3 bone models, 3.25 mm significantly showed greater bone strain values. The buccal side strain was higher irrespective of the implant diameter and density of bone. CONCLUSION: Within the limitations of the study, it may be concluded that the narrow diameter implant produces greater strain than 4.2 and 5.0 mm diameter implants, respectively. The buccal side consistently produced higher bone strain values.

Cytotoxicity of Dental Cements on Soft Tissue Associated with Dental Implants.

PURPOSE: To investigate and compare the cellular host response of human gingival fibroblasts (HGF) on four currently used cements. Methods and Material. 5 cement pellet samples were made for each of the 4 test cements (n = 20). The cements used for this study were zinc phosphate, zinc oxide noneugenol (ZOE), RelyX U200, and glass ionomer cement (GIC). One commercially available cell line was used to investigate the cytotoxicity of peri-implant tissues. Direct contact cell culture testing was conducted following International Organization for Standardization (ISO) methods 10993-5 and 10993-12 (MTT assay test). Cell cultures without dental cement were considered as control. Cells were allowed to grow and confluence over 48 hours after subcultivation according to standard laboratory procedures. The cells were kept in direct contact with the cement samples for 24 hours before being subjected to analysis. All specimens were tested in triplicate to validate the results. Quantitative evaluation of cytotoxicity was done to measure cell death and inhibition of cell growth. Results were analyzed using 1-way ANOVA (a = 0.05) followed by Tukey B post hoc test. RESULTS: The results of the study showed that HGF was vulnerable to the dental cement test material. GIC, zinc phosphate, ZOE, and resin cement were cytotoxic in decreasing order, respectively, and significantly reduced the cell viability after exposure to HGF (p < 0.001). CONCLUSIONS: Within the limitations of this in vitro cellular study, results indicated that the test dental cements were cytotoxic to HGF. The highest cytotoxicity was observed in GIC followed by zinc phosphate, ZOE, and resin cement.

The prevalence and outcomes of in-hospital acute myocardial infarction in the Department of Veterans Affairs Health System.

BACKGROUND: Most studies of the epidemiology and treatment of acute myocardial infarction (AMI) have focused on patients who experienced onset of their symptoms in the community and then presented to the hospital. There are, however, patients whose symptoms of AMI begin after hospitalization for other medical conditions. The purposes of this study were to determine the prevalence of in-hospital AMI in the Veterans Health Administration (VHA) and to compare baseline characteristics, treatments, and outcomes according to whether individuals presented with AMI or had an in-hospital AMI. METHODS: This was a retrospective cohort study of 7054 veterans who were hospitalized for AMI in 127 VHA medical centers between July 2003 and August 2004. The main outcome measure was 30-day mortality. Key covariates included age, body mass index, admission systolic blood pressure, heart rate, previous use of lipid-lowering drugs, elevated admission troponin value, prolonged and/or atypical chest pain on admission, and ST-segment elevation on the initial electrocardiogram. RESULTS: There were 792 patients (11.2%) who had AMI while hospitalized for other medical conditions. These patients differed substantially from those who presented to the hospital with AMI. The odds of 30-day mortality were greater in the in-hospital group (odds ratio, 3.6; 95% confidence interval, 3.1-4.3; P<.001) and remained higher after statistical adjustment (odds ratio, 2.0; 95% confidence interval, 1.7-2.4; P<.001). CONCLUSION: Although most attention has been paid to patients with AMI admitted via the community emergency medical system or through the emergency department, AMI occurring during hospitalization for other medical problems is an important clinical problem.