Influence of luting agent on the microleakage of all-ceramic crowns

PURPOSE: In this in-vitro study, microleakage of all-ceramic crowns was evaluated at enamel and dentin margins. MATERIALS AND METHODS: Forty maxillary central incisors were randomly divided into 4 groups (n = 10). While buccal and palatal margins were placed on enamel, mesial and distal margins were placed below the cementoenamel junction. In groups 1 to 3, IPS Empress 2 crowns were luted with Variolink 2/Syntac Classic (group 1), Bifix DC/Solobond Plus (group 2) and Calibra/Prime & Bond NT combinations (group 3), respectively. In the control group (group 4), porcelain-fused-to-metal crowns were luted with a zinc-phosphate cement. All specimens were subjected to 5000 thermocycles (at 5 degrees C to 55 degrees C; 30-s dwell time). After immersion in India ink for 48 h at 37 degrees C, the specimens were sectioned both buccolingually and mesiodistally. Each section was evaluated for microleakage under a stereomicroscope at 24X magnification. RESULTS: According to the Krukal-Wallis test, in all groups, there were significant differences in microleakage at the enamel margins (p = 0.001). Nevertheless, the margins finished in dentin showed no significant differences (p = 0.163). According to the Mann-Whitney U-test, statistically significant differences were observed in microleakage between groups 1 and 3 (p = 0.049), groups 1 and 4 (p = 0.001), groups 2 and 4 (p = 0.002), and between groups 3 and 4 (p = 0.045) at the enamel margin. In group 1, significantly greater microleakage was observed at the dentin margin compared to the enamel margin (p = 0.007). CONCLUSION: The adhesive luting technique demonstrated an excellent ability to minimize microleakage of all-ceramic crowns at the enamel margins. Water-based dentin bonding systems showed less microleakage than the water-free acetone-based dentin bonding system at the enamel margin.     

Effect of thermocycling on tensile strength and tear resistance of four soft denture liners

This study evaluated the effect of thermocycling on the tensile strength and tear resistance of four long-term soft denture liners. One light-activated (Astron Light, AL), two chemically activated (GC Reline Soft, GC; Silagum Comfort, SC), and one heat-cured (Molloplast-B, MLP) soft liner materials were tested. Dumbbell and trouser-leg specimen geometries were used for tensile strength and tear resistance tests, respectively. A total of 120 specimens were prepared. Test specimens for each material (n=5) were subjected to thermal cycling for 1000 and 3000 cycles between 5 degrees C and 55 degrees C in a thermocycler. Before thermocycling, AL gave the lowest tensile strength, while SC exhibited the highest tear resistance value among the materials tested (p < 0.05). Thermal cycling significantly affected the tensile strength of AL as well as the tear resistance values of AL, MLP, and GC materials. This in vitro study revealed that the tensile strength and tear resistance values of the soft liner materials tested varied according to their chemical compositions.     

The use of computerized tomography for diagnosis and treatment planning in implant dentistry

Preoperative radiographic imaging of recipient sites for implant placement is imperative to obtain a functional and aesthetic implant-supported prosthesis. Although conventional radiographic techniques have inherent problems that restrict accurate imaging, the main drawback of panoramic and periapical radiography is the two-dimensional image. Computerized tomography provides cross-sectional radiographic images that facilitate proper assessment of potential recipient sites for implant placement. This paper reviews the role of computerized tomography in implant dentistry.     

Dexmedetomidine versus midazolam in outpatient third molar surgery.

PURPOSE: The aim of this study was to compare the use of dexmedetomidine with the use of midazolam during intravenous conscious sedation in third molar surgery. PATIENTS AND METHODS: Twenty healthy patients with symmetrically impacted mandibular third molars were included in this double-blind, crossover, randomized study. Either dexmedetomidine (group D) (4 microg.kg(-1).h(-1)) or midazolam (group M) (0.4 mg.kg(-1).h(-1)) was administered intravenously for 15 minutes before the first operation. At the second operation, the other agent was applied. Cardiorespiratory data were collected. The intraoperative sedation level, patient cooperation, and postoperative performance were scored and any pain reaction during the local anesthetic injection was recorded. Visual analog scales were additionally used for the subjective assessment of pain and patient satisfaction. Amnesia was evaluated by the patients' ability to recall the objects shown during the operations and the local anesthetic injection. Patients' preferences were recorded during the interview at the end of the second operations. RESULTS: The mean heart rate and blood pressure measurements were significantly lower in group D. There was no significant difference in the respiratory findings. A significantly higher number of patients showed pain reactions in group M. Sedation level, postoperative performance, and VAS pain scores were not statistically significant, whereas the differences in cooperation score and VAS for patient satisfaction were significant. Adequate amnesia was obtained in group M, however, no amnesia was demonstrated in group D. Sixty-five percent of the patients indicated a preference for dexmedetomidine sedation. CONCLUSION: Dexmedetomidine may be a remarkable alternative to midazolam for intravenous sedation because it seems to be a reliable and safe method, with additional analgesic effect providing a satisfactory sedation level without any serious side effects during impacted third molar surgery.     

The anti-MMP activity of benzalkonium chloride

Objective

This study evaluated the ability of benzalkonium chloride (BAC) to bind to dentine and to inhibit soluble recombinant MMPs and bound dentine matrix metalloproteinases (MMPs).

Methods

Dentine powder was prepared from extracted human molars. Half was left mineralized; the other half was completely demineralized. The binding of BAC to dentine powder was followed by measuring changes in the supernatant concentration using UV spectrometry. The inhibitory effects of BAC on rhMMP-2, -8 and -9 were followed using a commercially available in vitro proteolytic assay. Matrix-bound endogenous MMP-activity was evaluated in completely demineralized beams. Each beam was either dipped into BAC and then dropped into 1 mL of a complete medium (CM) or they were placed in 1 mL of CM containing BAC for 30 days. After 30 days, changes in the dry mass of the beams or in the hydroxyproline (HYP) content of hydrolysates of the media were quantitated as indirect measures of matrix collagen hydrolysis by MMPs.

Results

Demineralized dentine powder took up 10-times more BAC than did mineralized powder. Water rinsing removed about 50% of the bound BAC, whilst rinsing with 0.5 M NaCl removed more than 90% of the bound BAC. BAC concentrations 0.5 wt% produced 100% inhibition of soluble recombinant MMP-2, -8 or -9, and inhibited matrix-bound MMPs between 55 and 66% when measured as mass loss or 76-81% when measured as solubilization of collagen peptide fragments.

Conclusions

BAC is effective at inhibiting both soluble recombinant MMPs and matrix-bound dentine MMPs in the absence of resins.     

The influence of functional forces on the biomechanics of implant-supported prostheses--a review

Objectives: To evaluate published evidence related to the influence of functional forces on the biomechanics of implant-supported prostheses.

Data and sources. The literature was searched for original research articles relating control of loads on dental implants, effects of early and late occlusal loads, the influence of bone quality, prosthesis type, prosthesis material, number of supporting implants, and engineering techniques employed for evaluating mechanical and biomechanical behavior of implants using MEDLINE^® and manual tracing of references cited in key papers otherwise not elicited.

Study selection. Current literature on implant biomechanics as main focus and pertinent to key aspects of the review.

Conclusions. The outcome of implant treatment is often maximized when implants are placed in dense bone, number of supporting implants are increased, implant placement configuration reduces the effects of bending moments, and when a fixed prosthesis is delivered to the patient.     

Comparison of post-gel shrinkage strains in light-polymerized composite resins

STATEMENT OF PROBLEM: Polymerization shrinkage is associated with light-polymerized and polyacid-modified composites. PURPOSE: This in vitro study compared the polymerization shrinkage of a light-polymerized hybrid composite, a posterior composite, and a polyacid-modified composite. MATERIAL AND METHODS: Five disk-shaped specimens (1 cm in diameter and 2 mm in thickness) were prepared in a mold from each of the following test materials: a light-polymerized hybrid composite (3M Valux Plus), a posterior composite (Filtek P60), and a polyacid-modified composite (Dyract AP). The hybrid composite served as the control material. A linear strain gauge was placed at the center of each specimen. After the specimens were light-polymerized for 60 seconds under 400-mW/cm(2) light intensity, microstrains were recorded with the strain indicator continuously every 4 seconds for 120 seconds. The data were evaluated with 1-way analysis of variance (P<.05) followed by a post hoc least significant difference test. RESULTS: During the first 20 seconds of light polymerization, all materials exhibited tensile strains between 6 and 55 mu epsilon that quickly converted into compressive strains and continued rising after the light source was removed. The strains for all materials increased at a declining rate until they reached a constant level between 148 and 180 seconds. The polymerization shrinkage recorded for Filtek P60 was the lowest (-190.56 mu epsilon), followed by 3M Valux Plus (-303.94 mu epsilon) and Dyract AP (-345.64 mu epsilon) (P<.05). The dimensional change between Filtek P60 and Dyract AP and between Filtek P60 and 3M Valux Plus was significant (P=.001). However, the difference between Dyract AP and 3M Valux Plus specimens was not significant (P=.208). CONCLUSION: Within the limitations of this study, the light-polymerized posterior composite tested demonstrated less polymerization shrinkage than the polyacid-modified and hybrid composites tested. Polymerization shrinkage velocity significantly affected the magnitude of strains.     

Impact of perioperative acute ischemic stroke on the outcomes of noncardiac and nonvascular surgery: a single centre prospective study

Background

Although ischemic stroke is a well-known complication of cardiovascular surgery it has not been extensively studied in patients undergoing noncardiac surgery. The aim of this study was to assess the predictors and outcomes of perioperative acute ischemic stroke (PAIS) in patients undergoing noncardiothoracic, nonvascular surgery (NCS).

Methods

We prospectively evaluated patients undergoing NCS and enrolled patients older than 18 years who underwent an elective, non-daytime, open surgical procedure. Electrocardiography and cardiac biomarkers were obtained 1 day before surgery, and on postoperative days 1, 3 and 7.

Results

Of the 1340 patients undergoing NCS, 31 (2.3%) experienced PAIS. Only age (odds ratio [OR] 2.5, 95% confidence interval [CI] 1.01–3.2, p < 0.001) and preoperative history of stroke (OR 3.6, 95% CI 1.2–4.8, p < 0.001) were independent predictors of PAIS according to multivariate analysis. Patients with PAIS had more cardiovascular (51.6% v. 10.6%, p < 0.001) and noncardiovascular complications (67.7% v. 28.3%, p < 0.001). In-hospital mortality was 19.3% for the PAIS group and 1% for those without PAIS (p < 0.001).

Conclusion

Age and preoperative history of stroke were strong risk factors for PAIS in patients undergoing NCS. Patients with PAIS carry an elevated risk of perioperative morbidity and mortality.