In Vitro Comparison of Internal and Marginal Adaptation between Printed and Milled Onlays.

STATEMENT OF PROBLEM: Nowadays, milling is still the gold standard for fabricating indirect restorations, but to overcome its disadvantages, there are alternatives, such as 3D printing. PURPOSE: This study aimed to compare the gaps between the prepared tooth and milled and printed onlays fabricated with the same CAD design. It also aimed to determine the gap reproducibility across onlays fabricated by 3D printing and milling. METHODS: A resin tooth was prepared for an onlay. After scanning the preparation, an onlay was designed with proprietary dental software. Next, 22 onlays were milled in a graphene-reinforced PMMA disc (Group 1), and 22 onlays were 3D-printed with a hybrid composite material (Group 2). After that, all fabricated restorations were scanned and superimposed on the scanned prepared resin tooth. Subsequently, a specific software was used to measure the margin, central, and intaglio-located gap between the milled or printed restoration and the preparation. Finally, measurements were compared with a multifactor analysis of variance. RESULTS: The results demonstrated that printed onlays (Group 2) adapted better to the prepared tooth than the milled ones (Group 1) (p < 0.05). The comparison of standard deviations showed the better gap reproducibility of printed onlays (p < 0.05). CONCLUSION: This study concluded that the printed onlays adapted significantly better to the prepared tooth than the milled onlays. Printed onlays also showed significantly better gap reproducibility.

A comparison of digital and conventional fabrication techniques for an esthetic maxillofacial prosthesis for the cheek and lip.

Maxillofacial prostheses have traditionally been manufactured by pouring silicone into molds. However, the development of computer-aided design and computer-aided manufacturing (CAD-CAM) systems allows the virtual planning, design, and manufacture of maxillofacial prostheses through the direct 3-dimensional printing of silicone. This clinical report describes the digital workflow as an alternative to the conventional method of restoring a large midfacial defect in the right cheek and lip. In addition, the approaches were nonblinded evaluated in relation to outcomes and time efficiency, while marginal adaptation and esthetics, including patient satisfaction, were assessed for both prostheses fabricated. The digital prosthesis had acceptable esthetics and fit with improved patient satisfaction, especially in terms of efficiency, comfort, and speed of the digital workflow.

A Systematic Study of Restorative Crown-Materials Combinations for Dental Implants: Characterization of Mechanical Properties under Dynamic Loads.

This study aimed to find the optimum mechanical characteristics of the restorative materials for the manufacture of implant crowns subjected to impact loading when different combinations of materials are used for the inner and outer crown. Several combinations of external-internal crown restorative materials were analyzed. The dynamic stresses at eight different zones of a dental implant subjected to an impact load and the influence of several mechanical properties, such as the Young's modulus, Poisson's ratio, density, and initial velocity, were analyzed and compared. A detailed 3D model was created, including the crown, the retention screw, the implant, and a mandible section. The model was then built by importing the 3D geometries from CAD software. The whole 3D model was carefully created in order to guarantee a finite element mesh that produced results adjusted to physical reality. Then, we conducted a numerical simulation using the finite element method (FEM). The results of the FEM analysis allowed for evaluating the effect that different combinations of restorative materials and mechanical properties had on the stress distribution in various regions of the implant. The choice of restorative material is a factor to be considered in order to preserve the integrity of osseointegration. Restorative materials transfer more or less stress to the dental implant and surrounding bone, depending on their stiffness. Therefore, an inadequate Young's modulus of the rehabilitation material can affect the survival of the implant over time. Eight interactive graphics were provided on a web-based surface platform to help clinical dentists, researchers, and manufacturers to select the best restorative materials combination for the crown.

In vitro assessment of PEEK and titanium implant abutments: Screw loosening and microleakage evaluations under dynamic mechanical testing.

STATEMENT OF PROBLEM: Polyetheretherketone (PEEK) has been advocated to replace metal components in dentistry. Although PEEK is a high-performance polymer with a white color, adequate biological response, and resistance to fracture, data to support PEEK as an alternative material for implant abutments are lacking. PURPOSE: The purpose of this in vitro study was to assess the mechanical and functional properties of PEEK implant abutments as a nonmetallic alternative to titanium abutments, which presents esthetic limitations and greater difficulty to customize clinically. MATERIAL AND METHODS: Implant abutments manufactured by using PEEK (n=24) or titanium grade 5 (n=24) were attached to MIS Implants type M4 3.75×16 mm with an internal screw tightened to 25 Ncm. Screw loosening and microleakage was assessed by submersion in a 2% methylene blue solution for 48 hours at 37 °C. Both groups were compared with and without applying dynamic loading; fatigue testing was performed following the International Organization for Standardization (ISO) 14801:2016 standard. All specimens were observed under a stereomicroscope at ×8 magnification. Statistically significant differences among the PEEK and titanium implant abutments were tested with 2-factor ANOVA and the chi-square analysis for nonpaired and paired data, respectively (α=.05). RESULTS: The implant abutments made of titanium were better in all mechanical tests. The torque loss of titanium abutments was approximately 10%, while PEEK showed a significantly higher (P<.05) torque loss of up to 50%. Moreover, 91.6% of the titanium abutments did not present microleakage, while there was no specimen of PEEK abutments without microleakage, once subjected to dynamic loading (P<.05). CONCLUSIONS: Titanium implant abutments (Ti6Al4V) were better in all tests performed. However, PEEK abutments may be suitable for long-term interim restorations, especially in the anterior area, in patients without parafunction.

Bone Stress Evaluation with and without Cortical Bone Using Several Dental Restorative Materials Subjected to Impact Load: A Fully 3D Transient Finite-Element Study.

Statement of problem. Previous peri-implantitis, peri-implant bone regeneration, or immediate implant placement postextraction may be responsible for the absence of cortical bone. Single crown materials are then relevant when dynamic forces are transferred into bone tissue and, therefore, the presence (or absence) of cortical bone can affect the long-term survival of the implant. Purpose: the purpose of this study is to assess the biomechanical response of dental rehabilitation when selecting different crown materials in models with and without cortical bone. Methods: several crown materials were considered for modeling six types of crown rehabilitation: full metal (MET), metal-ceramic (MCER), metal-composite (MCOM), peek-composite (PKCOM), carbon fiber-composite (FCOM), and carbon fiber-ceramic (FCCER). An impact-load dynamic finite-element analysis was carried out on all the 3D models of crowns mentioned above to assess their mechanical behavior against dynamic excitation. Implant-crown rehabilitation models with and without cortical bone were analyzed to compare how the load-impact actions affect both type of models. Results: numerical simulation results showed important differences in bone tissue stresses. The results show that flexible restorative materials reduce the stress on the bone and would be especially recommendable in the absence of cortical bone. Conclusions: this study demonstrated that more stress is transferred to the bone when stiffer materials (metal and/or ceramic) are used in implant supported rehabilitations; conversely, more flexible materials transfer less stress to the implant connection. Also, in implant-supported rehabilitations, more stress is transferred to the bone by dynamic forces when cortical bone is absent.

A 3D Finite Element Analysis Model of Single Implant-Supported Prosthesis under Dynamic Impact Loading for Evaluation of Stress in the Crown, Abutment and Cortical Bone Using Different Rehabilitation Materials.

In the literature, many researchers investigated static loading effects on an implant. However, dynamic loading under impact loading has not been investigated formally using numerical methods. This study aims to evaluate, with 3D finite element analysis (3D FEA), the stress transferred (maximum peak and variation in time) from a dynamic impact force applied to a single implant-supported prosthesis made from different materials. A 3D implant-supported prosthesis model was created on a digital model of a mandible section using CAD and reverse engineering. By setting different mechanical properties, six implant-supported prostheses made from different materials were simulated: metal (MET), metal-ceramic (MCER), metal-composite (MCOM), carbon fiber-composite (FCOM), PEEK-composite (PKCOM), and carbon fiber-ceramic (FCCER). Three-dimensional FEA was conducted to simulate the collision of 8.62 g implant-supported prosthesis models with a rigid plate at a speed of 1 m/s after a displacement of 0.01 mm. The stress peak transferred to the crown, titanium abutment, and cortical bone, and the stress variation in time, were assessed.

Comparison between experimental digital image processing and numerical methods for stress analysis in dental implants with different restorative materials.

The aim of this study is to evaluate the stresses transferred to peri-implant areas from single implants restored with different restorative materials and subjected to a static vertical load with low eccentricity. A total of 12 crowns were made with four types of materials: carbon fiber-composite, metal-ceramic, metal-composite, and full-metal, all of them cemented over a titanium abutment. Three different ways of approaching the problem have been used independently to verify the robustness of the conclusions. The experimental results of stress distribution around the implant were obtained by two image processing techniques: Digital Photoelasticity and Digital Image Correlation (DIC). The tests have been modelled by 3D Finite Element Method (FEM). The FEM models have also been used to study the sensitivity of the results to slight changes in geometry or loads, so that the robustness of the experimental techniques can be analyzed. In addition, the realistic bone morphology of the mandible has also been modelled by FEM, including the cortical and trabecular bone property distinctions.

A method for determining the position of the abutment screw of any cement-retained implant-supported prosthesis.

Removing cement-retained implant-supported prostheses may be challenging for clinicians. A method combining a cone beam computed tomography (CBCT) and a digital scan with a virtual surgical planning software program is described to identify the perforation site of a cement-retained implant-supported prosthesis to locate the abutment screw.

Fracture Resistance of Two Different Composite Resin CAD/CAM Crowns Bonded to Titanium Abutments.

PURPOSE: To determine the influence of thermal and mechanical cycling on fracture load and fracture pattern of resin nanoceramic crowns and polymer-infiltrated ceramic-network (PICN) crowns, both fabricated with CAD/CAM technology. MATERIALS AND METHODS: A total of 90 premolar crowns bonded to titanium abutments were divided into three groups of 30 crowns each: 30 resin nanoceramic crowns (LU); 30 PICN crowns (VE); and 30 metal-ceramic crowns (MC). The 30 specimens of each group were further divided into three subgroups of 10 each that underwent (1) no treatment, (2) thermocycling (2,000 cycles, 5°C to 55°C), and (3) thermocycling with subsequent mechanical cycling (120,000 cycles, 80 N, 2 Hz). The specimens were loaded to failure, and two-way ANOVA and chi-square test were used to determine differences in fracture resistance and pattern. RESULTS: Mechanical and thermal cycling significantly influenced the critical load to failure of the three materials; however, no significant differences were observed between the thermocycled materials and the materials that were thermocycled with subsequent mechanical cycling. The MC specimens experienced significantly higher fracture loads than those of the LU and VE specimens, which showed no differences from each other in fracture resistance. The fracture patterns showed chipping in MC crowns and partial or complete fracture in LU and VE crowns. The fracture pattern depended on the material and was unrelated to the type of treatment it underwent. CONCLUSION: All crowns showed adequate resistance to normal masticatory forces in the premolar area. The cyclic fatigue load negatively influenced all three materials.

Snoring intensity assessment with three different smartphones using the SnoreLab application in one participant.

STUDY OBJECTIVES: To compare the assessment of snoring using the SnoreLab application (app) using three different smartphones by one participant to validate SnoreLab as a method for collecting data for studies on the effectiveness of snoring treatment. METHODS: A person from the research group was monitored for 30 consecutive nights with the SnoreLab app using three different smartphones (Xiaomi MI8Pro, Samsung Galaxy Alpha, and BQ Aquaris V). The SnoreLab app instructions were strictly followed, and data were collected from the app. RESULTS: No significant differences were found in the measurements from the three smartphones in the time in bed, all snoring time, snoring percentage, and quiet time. BQ and Samsung smartphones determined significantly more light snoring time than did the Xiaomi smartphone. The Samsung smartphone assessed significantly less loud snoring time than did the Xiaomi smartphone and measured the shortest epic snoring time. The lowest Snore Score was calculated with the Samsung smartphone, the highest with the Xiaomi smartphone. Pearson's correlation coefficients demonstrated a relatively strong relationship between the Snore Score measured with the three smartphones. CONCLUSIONS: Even though there was a relatively strong relationship between the Snore Score measured with the three smartphones by one participant, the observed differences make it difficult to use this index as a method of collecting data for studies on snoring treatment effectiveness when patients use different smartphones; however, the SnoreLab app may be handy to quantify treatment effectiveness for a specific patient, provided the patient always uses the same smartphone.

Influence of Implant Position in Implant-Assisted Removable Partial Denture: A Three-Dimensional Finite Element Analysis.

PURPOSE: To determine the ideal position of a dental implant to assist a posterior extended partial removable dental prosthesis (PRDP), through stress values, displacement values, and deformation of periodontal ligament (PDL). MATERIALS AND METHODS: A finite element analysis of different implant positions was analyzed using a 3D mandible model from a human patient. Test models were created: model A (implant in second molar area), model B (implant in the first molar area), and model C (implant in premolar area). A control model without implant support was also created. Overall displacement values, von Mises stress distribution maps, and nonlinear deformations were evaluated. RESULTS: Some differences could be observed between test models. The introduction of an implant in the edentulous area, unlike a conventional removable partial denture without implant support, decreases stress values in the biological structures such as: mandible, tooth, soft tissue, and PDL. Placing the implant in the first molar area resulted in improved displacement values, and reduced maximum stress values at the peri-implant bone area, metal structure, and implant were observed. CONCLUSIONS: Within the limitations of this study we can conclude that placing the implant in the position of the first molar improves biomechanical behavior of implant-assisted PRDPs.

Comparison of the Marginal Fit of Cobalt-Chromium Metal-Ceramic Crowns Fabricated by CAD/CAM Techniques and Conventional Methods at Three Production Stages.

PURPOSE: The aim of this study was to compare the marginal fit of cobalt-chromium crowns fabricated using conventional casts and computer-aided design/computer-assisted manufacturing (CAD/CAM) techniques at three stages of production: metal coping, after porcelain firing, and after cementation. MATERIALS AND METHODS: A total of 80 metal-ceramic crowns were fabricated using four different techniques: lost wax casting, milling, laser sintering, and milling of a presintered metal block. Marginal fit was measured at each manufacturing stage. RESULTS: The porcelain firing stage improved marginal fit. CAD/CAM techniques resulted in better marginal fit than did conventional casting techniques at all manufacturing stages. CONCLUSION: CAD/CAM techniques improve marginal fit.

In-vitro development of a temporal abutment screw to protect osseointegration in immediate loaded implants.

PURPOSE: In this study, a temporal abutment fixation screw, designed to fracture in a controlled way upon application of an occlusal force sufficient to produce critical micromotion was developed. The purpose of the screw was to protect the osseointegration of immediate loaded single implants. MATERIALS AND METHODS: Seven different screw prototypes were examined by fixing titanium abutments to 112 Mozo-Grau external hexagon implants (MG Osseous®; Mozo-Grau, S.A., Valladolid, Spain). Fracture strength was tested at 30° in two subgroups per screw: one under dynamic loading and the other without prior dynamic loading. Dynamic loading was performed in a single-axis chewing simulator using 150,000 load cycles at 50 N. After normal distribution of obtained data was verified by Kolmogorov-Smirnov test, fracture resistance between samples submitted and not submitted to dynamic loading was compared by the use of Student's t-test. Comparison of fracture resistance among different screw designs was performed by the use of one-way analysis of variance. Confidence interval was set at 95%. RESULTS: Fractures occurred in all screws, allowing easy retrieval. Screw Prototypes 2, 5 and 6 failed during dynamic loading and exhibited statistically significant differences from the other prototypes. CONCLUSION: Prototypes 2, 5 and 6 may offer a useful protective mechanism during occlusal overload in immediate loaded implants.

Effect of implant design in immediate loading. A randomized, controlled, split-mouth, prospective clinical trial.

OBJECTIVES: The aim of this study was to evaluate the effect of two different designs, tapered vs cylindrical, on the primary stability of implants placed with an immediate loading protocol in edentulous mandibles to support fixed prostheses within occlusal contacts during the first 48 h. MATERIAL AND METHODS: Tapered and cylindrical implants were placed in a split-mouth study using the same implant protocol in ten patients with edentulous jaws. A total of 20 tapered implants (test group) and 20 cylindrical implants (control group) were placed. All implants were loaded immediately with provisional fixed prostheses during the healing period before the final restoration. The implants were evaluated at the implant placement by analyzing the insertion torque values (ITVs) and the resonance frequency analysis (RFA) and after the healing period of three months, the success of those implants and the marginal bone loss were evaluated. RESULTS: Two cylindrical implants were mobile within the same patient and no tapered implants failed, resulting in implant survival rates of 90% and 100%, respectively after three months. The ITVs were statistically significantly different (P = 0.0210) for the tapered implants than for the cylindrical implants. However, no statistically significant differences in RFA values were found (P = 0.6063) when comparing the implant designs and the primary stability measured with implant stability quotient (ISQ) values. The control group resulted in a mean bone loss after three months of 0.91 mm while the test group resulted 0.42 mm. CONCLUSION: The tapered implant achieved greater primary stability values measured with ITVs and less marginal bone loss than the cylindrical implants.

Short-term retrospective case series of implant-assisted removable partial dentures with locator abutments.

The purpose of this retrospective case series was to report on the clinical performance of implant-assisted removable partial dentures (IARPDs) with Locator abutments in different partial edentulism situations, with a mean follow-up period of 28.6 months. Twelve consecutive patients were treated with IARPDs. A total of 24 implants were placed in the edentulous area. Minimum follow-up period was 12 months. Overall patient satisfaction, health of peri-implant tissues, survival of implants and abutments, and prosthetic complications were reported. Overall implant survival was 91.6%; two implants failed. No major complications were reported-only one IARPD metal framework broke. No Locator abutment loosening was reported. Within the limitations of this retrospective study, treatment with IARPDs can improve the patient's function, phonetics, and esthetics without the need for extensive bone regeneration surgeries and prosthodontic rehabilitations. However, well-designed prospective clinical studies on IARPDs are needed to support their long-term use.

Adhesion of dental porcelain to cast, milled, and laser-sintered cobalt-chromium alloys: shear bond strength and sensitivity to thermocycling.

STATEMENT OF PROBLEM: New technologies have led to the introduction of new materials, so an evaluation of the adhesion of ceramics to these materials is needed. PURPOSE: The purpose of this study was to compare the shear bond strength of dental porcelain to cast, milled, and laser-sintered cobalt-chromium alloys, and to investigate the adhesive bond and failure type after thermocycling, 90 metal cylinders (10 mm diameter and 10 mm height) were prepared from cast (30 specimens), milled (30 specimens), and laser-sintered (30 specimens) alloys. MATERIAL AND METHODS: Ceramic cylinders (2.5 mm diameter and 4 mm length) were fused to the alloy cylinders. For each group, 15 specimens were thermocycled 5500 times at temperatures between 4°C and 60°C before testing. After testing, the specimen surfaces were visually examined to determine the failure mode. Differences in adhesion values according to manufacturing method, testing condition (thermocycling or no thermocycling), and interaction between the factors were evaluated with a 2-way ANOVA. The χ(2) test (95% confidence level) was performed to determine whether the failure mode was associated with the testing condition. RESULTS: Adhesion strengths for the nonthermocycled specimens were 42.79 ±14.14 MPa (cast), 37.56 ±9.18 MPa (milled), and 29.09 ±6.95 MPa (laser-sintered), and, for the thermocycled specimens, 16.52 ±8.96 MPa (cast), 22.21 ±13.25 MPa (milled), and 24.28 ±10.13 MPa (laser-sintered). Two-way ANOVA results indicated no statistically significant differences in adhesion among the manufacturing methods (P=.257), but statistically significant differences were observed according to both testing conditions (P<.001) and interaction between the factors (P=.015). The χ(2) test indicated that the failure mode was not associated with the testing condition (thermocycled, P=.280; nonthermocycled, P=.240). CONCLUSIONS: The porcelain adhesion values for all the materials were adequate for clinical applications. No significant adhesion differences were observed between cast, milled, and laser-sintered specimens, or among thermocycled and nonthermocycled laser-sintered specimens. However, significant adhesion differences were observed among the thermocycled and nonthermocycled cast and the milled specimens.

Use of polyetheretherketone in the fabrication of a maxillary obturator prosthesis: a clinical report.

To treat a patient who needed a replacement for a maxillary obturator prosthesis, a new obturator prosthesis was fabricated from polyetheretherketone (PEEK), a material often used in medicine but seldom in dentistry. This material provided the patient with a better-adjusted, more functional, and lighter prosthesis.

Marginal adaptation of zirconium dioxide copings: influence of the CAD/CAM system and the finish line design.

STATEMENT OF PROBLEM: Marginal adaptation is essential for the long-term success of dental restorations. Studies comparing the marginal gaps of computer-aided design/computer-aided manufacturing (CAD/CAM) restorations made from conventional and digital impressions are limited. PURPOSE: The purpose of this study was to evaluate the marginal adaptation of zirconium dioxide copings made with 2 different CAD/CAM systems, the Lava All-Ceramic System (scanning definitive dies made with conventional impressions) and the Lava Chairside Oral Scanner (scanning directly from the prepared tooth). In addition, the influences of 2 different finish line configurations were also compared. MATERIAL AND METHODS: Forty human molar teeth were prepared to receive complete crowns. Twenty were prepared with a 90-degree round shoulder and the other 20 with a 45-degree chamfer finish line. Zirconium dioxide copings were fabricated by using CAD/CAM technology. The specimens were randomized; they included 10 teeth with round shoulder and 10 with chamfer finish lines with the Lava All-Ceramic System, and 10 teeth with round shoulder and 10 with chamfer finish lines with the Lava Chairside Oral Scanner. The marginal gaps were measured at 5 points on each side with stereomicroscopy at 40× magnification. Data were analyzed with 2-way ANOVA (α=.05). RESULTS: The mean values of the measured marginal gap for the round shoulder group were 52.66 µm with the Lava All-Ceramic System and 14.98 µm with the Lava Chairside Oral Scanner. The mean values for the chamfer group were 64.06 µm for the Lava All-Ceramic System and 18.45 µm for the Lava Chairside Oral Scanner. Differences were identified when the marginal gaps between the specimens with different CAD/CAM systems were compared. However, differences in the finish line design were identified only between the round shoulder and chamfer with the Lava All-Ceramic System. CONCLUSIONS: Restorations fabricated with the Lava Chairside Oral Scanner displayed smaller marginal gaps than those made with the Lava All-Ceramic System. Nevertheless, all marginal gaps were within the range of clinical acceptability for both groups.

Comparison of the marginal adaptation of zirconium dioxide crowns in preparations with two different finish lines.

PURPOSE: The purpose of this study was to evaluate the marginal adaptation of zirconium dioxide crowns in preparations with two different finish line configurations before and after porcelain firing cycles, after a glaze cycle, and after cementation. MATERIALS AND METHODS: Twenty human molar teeth were prepared to receive full crowns; ten were prepared with a 90° round shoulder and another ten with a 45° chamfer finish line. Zirconium dioxide copings were fabricated using CAD/CAM technology (Lava™ system). They were then veneered with a low-fusing glass-ceramic (IPS e.max® Ceram). Finally, they were glazed and cemented with a resin-composite cement (RelyX™ Unicem, Aplicap™). Measurements for marginal adaptation using stereomicroscopy (40×) were performed at four stages: copings (S1), after porcelain firing cycles (S2), after glazing (S3), and after cementation (S4). One-way ANOVA was used to assess the influence of the finish line design on the marginal adaptation in each stage. Two-way ANOVA with repeated measurements was performed to assess the influence on the marginal adaptation of the porcelain firing cycles, glaze firing cycle, and cementation. RESULTS: The measured marginal gap mean values for the shoulder group (µm) were: 50.13 (S1), 54.32 (S2), 55.12 (S3), and 59.83 (S4). The values for the chamfer group were: 63.56 (S1), 71.85 (S2), 74.12 (S3), and 76.97 (S4). When comparing marginal gaps between specimens with two different finish lines, differences were noticed at the four studied stages (p = 0.0165, p = 0.0027, p = 0.0009, and p = 0.0009, respectively). No differences were manifested in the marginal gap measurements of the shoulder group at the different stages of fabrication (p = 0.4335); however, in the chamfer group, differences were noticed between S1 and S3 (p = 0.0042). CONCLUSIONS: Marginal adaptation was influenced by the finish line design. The firing cycles significantly affected the chamfer group; nevertheless, the marginal gap was within the range of clinical acceptability.

A method for registering the abutment screw position of cement-retained implant restorations.

The primary concern with cement-retained implant restorations is retrievability. A simple method is described that allows identification of the location of the abutment screw in cement-retained implant restorations by superposition of 2 digital photographs of the definitive cast with and without the restoration.