Mandibular Flexure and Crestal Bone Stress Distribution on an Implant-Supported Fixed Full Arch Mandibular Prosthesis: Finite Element Analysis in Three Dimensions.

Aim This study's objective was to assess and analyze, using 3D Finite Element Analysis, the impact of four mandibular complete arch superstructures on the distribution of stress in the crestal bone during mandibular flexure. Materials and methods Four Finite element models of the mandible with different implant-retained framework designs have been developed. Three of these models had six axial implants placed at intervals of 11.8 mm, 18.8 mm and 25.8 mm from the midline, respectively. One model had two tilted implants and four axial implants splinted with a single piece of framework at intervals of 8.4 mm, 13.4 mm and 18.4 mm from the midline. For analyzing the stress distribution, the finished product was transferred to ANSYS R 18.1 software (Sirsa, Haryana, India) for finite element simulation, the models were constructed, the ends were restrained, and bilateral vertical loads of 50N, 100N and 150N were applied to the distal part of the framework. Results Bilateral loads were applied to each of the four 3D FEM and after assessment of Von Mises Stress and Total Deformation, a finding was made that the model with six axial implants supported by a single piece of framework underwent the highest total deformation and the model with four axial implants and two implants with distal tilts displayed most significant Von Mises stress. Conclusion Within the constraints of this 3D FEA, it was determined that mandibular flexure and peri-implant bone stress were affected by the way the framework is divided and the nature of mandibular movement. The three types of frames with the least bone stress are demonstrated by the mandibular deformation that results from two-piece frameworks on axial implants. Regardless of the number of implants, the single framework splinted with six implants shows a flexure in mandible with the highest bone stress around the implant irrespective of the angulation of the implant. Clinical significance When it comes to edentulous jaws, reducing stress in implant-supported restorative systems at varying degrees of the bone and implant interfaces and superstructures of prosthetics is one of the fundamental goals of implant treatment. A framework with proper design and a low modulus of elasticity reduces mechanical risk. Additionally, a larger number of implants helps to prevent cantilevers and spacing between the implants.

Comparative Effect of No Finish Line, Heavy Chamfer, and Shoulder Marginal Designs on the Fracture Resistance of Zirconia (Cercon) Ceramic Restoration: An In Vitro Study.

Background Because all-ceramic crowns are more aesthetic and biocompatible than metal-ceramic crowns, they have grown in popularity among patients and dentists. Poor finish line layout can result in restoration margin fracturing, hence, finish line arrangement is critical to maintaining the restoration's marginal integrity. The goal of this in-vitro study is to evaluate zirconia's resistance to fracture (Cercon) ceramic restorations with three marginal designs (no finish line, heavy chamfer, and shoulder). This study is important in contributing to the ongoing debate about the optimal finish line design for zirconia restorations. Methodology Three different finish lines, namely, biologically oriented preparation technique (BOPT) with a marginal width of less than 0.3 mm, heavy chamfer with a marginal width of up to 0.3 mm, and shoulder with a marginal width greater than 0.3 mm, were made on 10 extracted maxillary first premolar tooth to make 30 epoxy resin dies on which zirconia (Cercon) coping was done using CAD/CAM technology, and marginal discrepancies were measured using a three-dimensional scanner. All the copings were affixed to their respective dies using GIC luting cement, and fracture resistance was measured using a digital universal testing machine. Results The Kruskal-Wallis test revealed that the mean fracture resistance was more in the heavy chamfer finish line, followed by the no finish line (BOPT) and the shoulder finish line. No statistically significant difference was seen between the no finish line and the heavy chamfer finish line. There was a significant difference between the heavy chamfer and shoulder finish lines (p = 0.004). Conclusions To increase the biomechanical performance of posterior single zirconia restorations, heavy chamfer margins are indicated.

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.

Crestal Bone Changes around immediately loaded Single-piece Implants using Flap and Flapless Technique: A Radiographic Study.

AIM: With the trend shifting toward the minimally invasive surgeries in implant surgery, the flapless technique of implant placement is gaining popularity among the implantologists. This study was done to assess the crestal bone loss level in flap and flapless surgery at follow-up periods of 0, 1, and 3 months. MATERIALS AND METHODS: Patients presenting with missing teeth requiring dental implants for rehabilitation were included in the study. Implant placement was done in 10 patients with traditional flap technique, while in other 10 patients, flapless technique was performed after determining the availability of sufficient bone width with ridge mapping. Radiographical follow-up was done for 3 months at 0-, 1-, and 3-month intervals. RESULTS: It was observed that for most of the flapless cases, the bone loss settled at 1st thread or just below the implant collar after 3 months. CONCLUSION: It was seen that crestal bone height was reduced in both flap and flapless techniques. On comparing the bone loss, the flapless approach showed statistically significant lesser reduction as determined by radiovisiography. CLINICAL SIGNIFICANCE: The study has been done to evaluate crestal bone level using flap and flapless technique. It was seen that reduction of crestal bone height was seen in both flapless and with flap techniques. However, on comparison, less bone resorption was observed in flapless technique.

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.