Comparison of Dimensional Accuracy of Stone Models Fabricated by Three Different Impression Techniques Using Two Brands of Polyvinyl Siloxane Impression Materials.

AIM: The aim of this study is to check the dimensional precision of stone models made by two different brands of polyvinyl siloxane impression materials using the monophase, one-step, and two-step putty/light-body impression techniques. MATERIALS AND METHODS: A metal model, having two crown preparations, was fabricated. With each technique, 40 impressions were made using two types of polyvinyl siloxane impression materials (Aquasil and Virtual). A total of 240 impressions were made with both the polyvinyl siloxane impression materials. Monophase impressions were made with a medium body using an acrylic custom tray. By simultaneous usage of putty and light-body, one-step impressions were made with a perforated metal stock tray. For two-step impressions, a 25-40 microns thick cellophane sheet spacer was used. The stone casts were obtained from the impressions of the stainless steel model. Three different dimensions (height, diameter, and inter-abutment distance) on these resultant stone casts were compared with the standard die. The accuracy of two different brands of impression materials was also compared. The results were then statistically analyzed. RESULTS: The resultant casts obtained from the different impression techniques had significantly larger dimensions in height and diameter, but smaller dimensions were observed for the inter-abutment distance. Larger deviation in resultant casts was observed in the monophase than one-step impression technique and the least deviation was observed in the two-step impression technique. CONCLUSION: The two-step impression technique produced the most accurate results in terms of the resultant casts. Out of the two different brands, Aquasil produced more fare results. CLINICAL SIGNIFICANCE: Adequate marginal adaptation, proper fit and least distortion of the castings, and the final prosthesis can be achieved by using the adequate impression technique and impression material.

3D Finite Element Analysis to Assess the Stress Distribution Pattern in Mandibular Implant-supported Overdenture with Different Bar Heights.

AIM: Proper stress distribution on dental implants is necessary in bar-retained implant overlay dentures. The purpose of the study is to comparatively assess the stress distribution pattern on the crestal bone at the bone-implant interface due to different bar heights using finite element models (FEMs). MATERIALS AND METHODS: Eight 3D FEMs were developed from mandibular overdentures with two implants in the canine region separated by a distance of 20 mm. In these models, four different bar heights from the mucosa (0.5, 1, 1.5, and 2 mm) with 12 mm occlusal plane height were analyzed. A unilateral and a bilateral vertical load of 150 N were applied to the central occlusal fossa of the first molar and the stress of bone around the implant was analyzed by finite element analysis (FEA). RESULTS: By increasing the bar height, the maximum stress values around implants on the crestal bone were found to be increased in unilateral and bilateral loading models. In unilateral loading models, the maximum stress was found in a model with a 2 mm bar height (0.46 MPa) on the distal side of the ipsilateral implant, and in bilateral loading cases, the maximum stress was also found in a model with a 2 mm bar height (0.456 MPa). CONCLUSION: As the vertical cantilever increases (here the bar height), the maximum stress on the crestal bone increases. A minimum of 0.5 mm of space is sufficient between the mucosa and the inferior border of the bar to maintain oral hygiene. CLINICAL SIGNIFICANCE: From the present study, it can be concluded that an increase in bar height causes an increase in stress levels on the peri-implant crestal bone.

A Radiographic Evaluation of Peri-implant Bone Level in Immediate and Conventionally Loaded Implants Using Flap and Flapless Techniques.

AIM: The purpose of this research is to compare peri-implant bone level in immediate and conventionally loaded implants using flap and flapless techniques. MATERIALS AND METHODS: Forty patients were selected and were subjected into four groups. Group A: 10 patients with immediate loading (IL) by raising the flap. Group B: 10 patients with IL without raising the flap. Group C: 10 patients with conventional loading by raising the flap. Group D: 10 patients with conventional loading without raising the flap. RESULTS: It was observed that for most of the flapless techniques with IL cases, the bone loss settled at first thread or just below the implant collar after 6 months. CONCLUSION: It was seen that the crestal bone height was reduced in both flap and flapless techniques by immediate and conventional loading, respectively. On comparing the bone loss, the flapless approach by IL showed statistically significant lesser reduction as determined by radiovisiography. CLINICAL SIGNIFICANCE: Postoperative pain was less in the flapless technique as compared to the traditional flap technique. IL minimizes invasiveness, complexity, and also improves acceptance by patients.

Evaluation of Shear Bond Strength of Three Different Acrylic Resin and Artificial Denture Teeth with and without Monomer Application.

AIM: To compare and evaluate the shear bond strength of the tooth-denture base junction when three different commercially available acrylic resin base bonded to acrylic teeth with and without application of methyl methacrylate monomer on ridge lap area. MATERIALS AND METHODS: A three-stepped cylindrical shaped die was customized. Sixty samples were fabricated with heat cure and self-cure acrylic resin with and without monomer application. A total of 60 samples were divided into three groups and six subgroups. • Group A-Twenty samples of Trevlon-HI heat-activated acrylic resin. • Subgroup A1-Ten samples of acrylic teeth bonded with Trevlon-HI heat-activated acrylic resin with the application of monomer on ridge lap area. • Subgroup A2-Ten samples of acrylic teeth bonded with Trevlon-HI heat-activated acrylic resin without application of monomer on ridge lap area. • Group B-Twenty samples of Trevalon heat-activated acrylic resin. • Subgroup B1-Ten samples of acrylic teeth bonded with Trevlon heat-activated acrylic resin with the application of monomer on ridge lap area. • Subgroup B2-Ten samples of acrylic teeth bonded with Trevlon heat-activated acrylic resin without application of monomer on ridge lap area. • Group C-Twenty samples of Trevlon-RR self-activated acrylic resin. • Subgroup C1-Ten samples of acrylic teeth bonded with Trevlon-RR self-activated acrylic resin with the application of monomer on ridge lap area. • Subgroup C2-Ten samples of acrylic teeth bonded with Trevlon-RR self-activated acrylic resin without monomer application on ridge lap area. RESULTS: Samples obtained from high impact heat cure acrylic resin with monomer application shows higher bond strength when tested under the universal testing machine. CONCLUSION: With and without monomer application on high impact polymethylmethacrylate (PMMA) resin and Heat cured resin it was found that high impact shows better bond strength. Trevlon HI monomer shows a greater increase in strength due to the presence of cross-linking agents. CLINICAL SIGNIFICANCE: The incorporation of mechanical surface treatments followed by monomer application significantly influences the bonding between denture teeth and denture base resin.

Twelve-month prostate volume reduction after MRI-guided transurethral ultrasound ablation of the prostate.

PURPOSE: To quantitatively assess 12-month prostate volume (PV) reduction based on T2-weighted MRI and immediate post-treatment contrast-enhanced MRI non-perfused volume (NPV), and to compare measurements with predictions of acute and delayed ablation volumes based on MR-thermometry (MR-t), in a central radiology review of the Phase I clinical trial of MRI-guided transurethral ultrasound ablation (TULSA) in patients with localized prostate cancer. MATERIALS AND METHODS: Treatment day MRI and 12-month follow-up MRI and biopsy were available for central radiology review in 29 of 30 patients from the published institutional review board-approved, prospective, multi-centre, single-arm Phase I clinical trial of TULSA. Viable PV at 12 months was measured as the remaining PV on T2-weighted MRI, less 12-month NPV, scaled by the fraction of fibrosis in 12-month biopsy cores. Reduction of viable PV was compared to predictions based on the fraction of the prostate covered by the MR-t derived acute thermal ablation volume (ATAV, 55°C isotherm), delayed thermal ablation volume (DTAV, 240 cumulative equivalent minutes at 43°C thermal dose isocontour) and treatment-day NPV. We also report linear and volumetric comparisons between metrics. RESULTS: After TULSA, the median 12-month reduction in viable PV was 88%. DTAV predicted a reduction of 90%. Treatment day NPV predicted only 53% volume reduction, and underestimated ATAV and DTAV by 36% and 51%. CONCLUSION: Quantitative volumetry of the TULSA phase I MR and biopsy data identifies DTAV (240 CEM43 thermal dose boundary) as a useful predictor of viable prostate tissue reduction at 12 months. Immediate post-treatment NPV underestimates tissue ablation. KEY POINTS: • MRI-guided transurethral ultrasound ablation (TULSA) achieved an 88% reduction of viable prostate tissue volume at 12 months, in excellent agreement with expectation from thermal dose calculations. • Non-perfused volume on immediate post-treatment contrast-enhanced MRI represents only 64% of the acute thermal ablation volume (ATAV), and reports only 60% (53% instead of 88% achieved) of the reduction in viable prostate tissue volume at 12 months. • MR-thermometry-based predictions of 12-month prostate volume reduction based on 240 cumulative equivalent minute thermal dose volume are in excellent agreement with reduction in viable prostate tissue volume measured on pre- and 12-month post-treatment T2w-MRI.

The impact of expansive arterial remodeling on clinical presentation in carotid artery disease: a multidetector CT angiography study.

BACKGROUND AND PURPOSE: Atherosclerotic arterial remodeling has been described in the coronary circulation but has not been studied extensively for carotid atherosclerosis. The purpose of our study was to examine the association between carotid artery remodeling and clinical presentation in patients with significant stenosis by using multidetector row CT (MDCT). MATERIALS AND METHODS: One hundred eight patients with >or=50% stenosis (North American Symptomatic Carotid Endarterectomy Trial criteria) by MDCT angiography between January 2004 and June 2006 were identified. The study group included 37 symptomatic (65.9 +/- 13.0 years; 12 women; stenosis, 81.5 +/- 12.2%; 17 with stroke; 15 with transient ischemic attack; 5 with amaurosis fugax) and 71 asymptomatic patients (70.5 +/- 10.5 years; 28 women; stenosis, 78.8 +/- 11.1%). Remodeling ratio (RR) was calculated by dividing the outer vessel circumference at the site of greatest stenosis by a normal reference-segment vessel circumference. Maximum vessel thickness (MxVT) and eccentricity index (EI) of the plaque, defined as maximal thickness/minimal thickness at the site of greatest luminal narrowing, were also determined. Data were analyzed by using an independent t test. RESULTS: The RR was significantly higher in symptomatic patients (1.64 +/- 0.44) than in asymptomatic patients (1.41 +/- 0.5) (P=.02). There was no significant difference in MxVT in symptomatic (5.9 +/- 2.1 mm) and asymptomatic patients (5.6 +/- 2.4 mm) (P=.45) and no significant difference in EI (symptomatic, 4.7 +/- 2.7; asymptomatic, 4.3 +/- 2.2; P=.38). CONCLUSION: In this series of subjects with significant internal carotid artery stenosis, expansive carotid remodeling was significantly greater in patients with cerebral ischemic symptoms than in asymptomatic patients. The extent of expansive remodeling may indicate underlying atherosclerotic plaque vulnerability. MDCT has a role in the evaluation of carotid artery disease beyond examining luminal stenosis.