Three-dimensional Finite Element Stress Pattern Analysis in Bone around Implant-supported Abutment with Different Angulations under Axial and Oblique Load.

AIM: The goal of this research was to compare the stress distribution in the bone adjacent to the implant where three different angled abutments were loaded in both the axial and oblique directions. MATERIALS AND METHODS: The premaxilla region was digitally recreated in 3-dimension (3D) using a finite element model, with a solid 4.2 mm by 13 mm implant and abutments at 0°, 15°, and 25° of rotation. Axial load (100 N) and oblique load were also applied to the abutments (178 N). Six models were made and used with a fixed bases. The coefficient of friction was set at a constant value of 0.02. The CITIA program was used for the stress analysis. In this investigation, we employed linear static analysis. Each abutment and crown in the model has subjected to an arbitrary vertical load as well as the oblique load. RESULTS: The cortical bone around the implant with a 25° angled abutment experienced a maximum von Mises stress of 187.692 Mpa under oblique load. This stress was increased with the degree of abutment angulation. CONCLUSION: As abutment angulation was increased, axial and oblique burdens were also increased. In both cases, we were able to identify the source of the observed growth. When we looked at the effect of stress on angulation, we found that the peaks were seen in the area of abutment and cortical bone. Since it was difficult to predict the stress distribution around implants with varying abutment angles in a clinical setting, finite element analysis (FEA) was chosen for this investigation as a more cutting-edge approach. CLINICAL SIGNIFICANCE: It is a herculean task calculating the prompted forces clinically, FEA has opted for this study as it's a progressively wielded tool to prognosticate the stress allocation in the region of the implants with different angled abutments.

A 3-D Finite Element Analysis of Stress Distribution on Implant-supported Fixed Prosthesis with Four Different Commercially Available Implant Systems.

AIM: To investigate by the finite element analysis comparison of stress distribution on the cortical and cancellous bone in an implant-supported yttrium tetragonal zirconia polycrystals (Y-TZP FPD) in four different widely used implant systems under different loading conditions. MATERIALS AND METHODS: Four 3-D finite element analysis (FEA) models of mandible having different implant systems with dimensions 8.0 mm × 5 mm in the second premolar and molar region were developed. In these models, abutment was tightened and 3-unit implant-supported Y-TZP FPD were cemented. A lateral force component of 100 N at 30° to the occlusal plane and a vertical intrusive force component of 250 N were applied to the central fossa of the FDP and the stress on bone around the implant was analyzed by FEA. RESULTS: In the four implant systems, the maximum stress values on the crestal bone differ for the different implant systems for the two loading conditions applied. In both cases, the maximum stress values on the cortical bone were in ADIN Touareg Closefit WP implants and the maximum stress on the cancellous bone was observed in the Nobel Speedy Groovy implants. CONCLUSION: The ADIN Touareg Closefit WP implant system induced maximum stress on the crestal bone in both axial and buccolingual loading. Nobel Speedy Groovy implant system favored more equitable load distribution to the peri-implant crestal bone when compared to the other three implant systems. CLINICAL SIGNIFICANCE: From this study, it was found that out of all the implants used for the study, the Nobel Speedy Groovy implant system favored more equitable load distribution due to the platform switch design contrary to the other systems and at the cancellous bone the least load was transferred by the Nobel Active implants due to the reverse buttress thread design and larger thread pitch.

Comparative Analysis of Marginal Accuracy of Complete Crowns Fabricated by Using Ringless and Metal Ring Investment Systems: An In Vitro Study.

AIM: To compare the vertical margin accuracy of lost wax castings produced by the conventional casting technique with all metal (WIRONIUM®) and PFM alloy (WIRON®99) using a metal ring and ringless system. MATERIALS AND METHODS: A brass die assembly was used to fabricate standardized wax pattern crowns. A total of 100 wax patterns were made with both ringless and metal ring investment systems. Wax patterns were readapted and refined on the master die and divided into two groups, namely, group I and group II with 50 wax patterns in each group. Group I (ringless system) and group II (metal ring system) were further divided into subgroups having a sample size of 25 in each group. Each coping was invested and cast individually. The marginal discrepancy between the metal die and the castings were measured by a stereomicroscope and AutoCAD software 2013. Measurement was made on the facial area of the metal die. RESULTS: The resultant casts obtained from different casting systems show statistically significant difference found between the marginal discrepancies using metal ring and ringless castings system, and statistically nonsignificant difference was found between the marginal discrepancies using all metal alloy (WIRONIUM®) and PFM alloy (WIRON®99) within the same group. CONCLUSION: The marginal discrepancy for castings made with ringless casting system was less when compared to metal ring casting system, and there was no difference in marginal discrepancy when compared to all metal alloy (WIRONIUM®) and PFM alloy (WIRON®99) within the same group. CLINICAL SIGNIFICANCE: Marginal fit is influenced by several factors including type of crown, tooth preparation geometry, dimensional accuracy of impression materials, factors related to dental casting, type of cement, luting pressure, duration of cementation, and use of occlusal vents or die spacers.

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.

Evaluating the Effect of Different Impression Techniques and Splinting Methods on the Dimensional Accuracy of Multiple Implant Impressions: An in vitro Study.

AIM: This study was done to determine more accurate impression technique and splinting method for multiple implant impressions in edentulous patients. MATERIALS AND METHODS: A prefabricated maxillary reference model was taken on which four implants were placed parallel to each other using vertical milling machine. Forty custom trays having different tray designs were fabricated using autopolymeri-zing acrylic resin on the stone cast obtained from the reference model. A total of 40 samples (n = 40) were divided into five groups, in which group I included casts obtained from impressions made with closed-tray technique, group II: open-tray impression technique, group III: open-tray impressions splinted with acrylic, group IV: open-tray impressions splinted with light cure material, and group V acted as a control group (reference model). Casts obtained were poured with dental stone. The interimplant distances were checked using coordinate measuring machine to evaluate the three-dimensional (3D) positional accuracy in X, Y, and Z axes. RESULTS: Casts obtained from impressions made with closed-tray technique showed highest mean deviation from the reference model while those obtained from open-tray splinted with light cure showed the least deviation. The casts obtained from open-tray nonsplinted and open-tray acrylic splinted showed intermediate mean deviations. CONCLUSION: The casts obtained from open-tray impression technique were more accurate as compared with the closed-tray technique. Among splinting, the impressions obtained from light cure splinting showed more accuracy than the impressions obtained from acrylic splinting. CLINICAL SIGNIFICANCE: The accuracy of the multiple implant impression is influenced by the type of impression material used which ultimately leads to an accurate cast on which precisely fitting prosthesis is fabricated. Several factors including material accuracy, time span before the impression is poured, and extent of intraoral undercuts are to be kept in mind while choosing an impression material.

Comparative evaluation of fracture resistance of various post systems using different luting agents under tangential loading.

OBJECTIVE: The purpose of this in vitro study was to evaluate the fracture resistance of various post system using different luting agents under tangential loading after wet thermocycling. MATERIAL & METHODS: Seventy freshly extracted maxillary central incisors were endodontically treated and post-spaces were prepared to receive different post system. They were assigned to 7 groups. Composite resin was used as core material in all the groups. Three type of post system: prefabricated post system (ParaPost(®) XP™), fibre post (ParaPost(®) fiber Lux™), cast nickel-chromium alloy post and two type of luting cements dual cure resin cement (ParaCem(®), Whaledent) and glass ionomer cement (Fuji I, GC) were used. The specimens were thermocycled and subjected to tangential loading at a crosshead speed of 1.5 mm/min. The failure loads were recorded and data were statistically analyzed with one-way ANOVA (p < 0.05) and Student's t tests (p < 0.001). RESULTS: Significant differences of fracture resistance were detected among groups (p < 0.001). The greatest number of repairable fracture mode was recorded in fibre posts and resin cement system. CONCLUSIONS: Within the limitations of this in vitro study, it can be stated that fibre posts can be recommended as a better alternative to the cast post and cores and prefabricated metallic posts in the anterior region and resin cement might give additional fracture resistance when used for post and crown cementation.