Poly Methyl Methacrylate Block Research Articles

Measurement of computed tomography modulation transfer function with a novel polymethyl methacrylate phantom.

A novel phantom for measuring the 10% and 50% values of the modulation transfer function (MTF) for computed tomography scanners (CT) was investigated. The phantom was constructed by drilling rows of holes of different sizes and frequencies into a small block of polymethyl methacrylate (PMMA). The MTF at a given frequency was determined from the ratio of the range of Hounsfield units within the rows of holes at different frequencies, and the difference in Hounsfield units between air and PMMA. A MTF curve was plotted from measurements at different frequencies and the 10% and 50% MTF values were obtained from a cubic spline interpolation. The MTF results obtained with the drilled hole phantom method were compared to a conventional method - using a thin wire and Spice-CT ImageJ Plugin- and with identical acquisition and reconstruction parameters. The drilled hole phantom measured the 50% MTF with reasonable accuracy but underestimated the 10% MTF by 8.2% on average. MTF measurements were reproducible for repeated image acquisitions and with different users analysing the images, and the phantom was able to accurately measure the change in MTF when measured on images using different reconstruction kernels. The tool may find application as a cheap, easy to use method for routine QC testing of CT scanners.

The Effect of the Incorporation of a 3D-Printed Titanium Framework on the Mechanical Properties CAD/CAM Denture Base Materials

Background: Complete dentures should withstand occlusal forces and wear. However, over time, dentures can suffer fatigue and develop cracks, chipping, and fractures. Conventional methods for the fabrication of complete dentures involve injection molding, thermal curing, and the use of microwaves with polymethyl methacrylate (PMMA)-based materials. These methods have served well for many years. More recently, the incorporation of computer-aided design and computer-aided manufacturing (CAD/CAM) to fabricate complete dentures has been shown to enhance the dentures’ mechanical properties, including resistance to wear and impact strength. This study aims to investigate the mechanical properties and fracture types of CAD/CAM denture base materials (both milled and printed) as compared to a novel proprietary method that embeds a 3D-printed framework within PMMA-milled blocks. The null hypothesis is that incorporating a 3D-printed framework does not affect the mechanical properties of milled PMMA blocks. Methods: Three groups of bars were fabricated using CAD/CAM methods: printed (P), milled (M), and milled with a 3D-printed metallic framework reinforcement (M + F). A three-point bending test evaluated deformation, followed by an impact fracture test for fracture toughness. A descriptive fractographic analysis assessed the fracture characteristics. A statistical analysis using a paired t-test compared the differences between the groups. Results: The P group showed more elastic deformation than the M and M + F groups (p < 0.05). The M + F group achieved a higher fracture toughness as compared to the M and P groups (p < 0.05). Conclusions: Within the limitations of this experimental study, the null hypothesis can be rejected. Milled samples with an embedded 3D-printed titanium framework possess higher resistance to impact than milled samples without frameworks, and printed samples and milled samples with embedded 3d-printed titanium frameworks present increased flexural strength and lower elastic deformation as compared to milled samples without frameworks and printed samples.

Comparative Evaluation of the Flexural Strength of Heat-Activated Polymethyl Methacrylate Denture Base Resin With and Without 0.2% by the Weight of Silver Nanoparticles Cured by Conventional and Autoclave Methods: An In Vitro Study.

Heat-activated polymethyl methacrylate (PMMA) is the most common and widely accepted denture base material. Two important drawbacks are the development of denture stomatitis and the high incidence of fracture of denture bases. The present study investigated the effect of adding 0.2% by weight of silver nanoparticles (AgNps) and using the autoclave method of terminal boiling on the flexural strength of heat-activated PMMA denture base resin. A total of 40 samples of heat-activated PMMA blocks were divided into four groups, with 10 samples (n = 10) in each group. Group 1 consisted of unmodified heat-activated PMMA resin (PMMA-1) polymerized by the conventional method of terminal boiling (conventional curing); Group 2 consisted of 0.2% by weight AgNPs added to heat-activated PMMA resin (PMMA-2) polymerized by conventional curing; Group 3 consisted of PMMA-1 polymerized by the autoclave method of terminal boiling (autoclave curing); and Group 4 consisted of PMMA-2 polymerized by autoclave curing. The flexural strength was tested using a universal testing machine. Descriptive statistics were expressed as mean ± SD and median flexural strength. Kruskal-Wallis ANOVA with Mann-Whitney U post hoc test was applied to test for statistical significance between the groups. The level of significance was set at p<0.05. The results showed a statistically significant reduction in flexural strength in Group 2 compared to Group 1. The samples from Group 4 showed a statistically significant increase in flexural strength compared to Group 2. The Group 4 denture base had the highest flexural strength (115.72 ± 7.27 MPa) among the four groups, followed by Group 3 (104.16 ± 4.85 MPa). The Group 1 samples gave a flexural strength of 101.45 ± 3.13 MPa, and Group 2 gave the lowest flexural strength (85.98 ± 3.49 MPa) among the four groups tested. The reduction in flexural strength of the heat-activated PMMA denture base after adding 0.2% by weight of AgNP as an antifungal agent was a major concern among manufacturers of commercially available denture base materials. It was proved in the present study that employing the autoclave curing method of terminal boiling for the polymerization of 0.2% by weight of AgNp-added heat-activated PMMA denture base resulted in a significantly higher flexural strength compared to the conventional curing method of terminal boiling for polymerization. Unmodified heat-activated PMMA gave higher flexural strength values when polymerized by autoclave curing compared to the conventional curing method of terminal boiling.

Effects of various beverages on characteristics of provisional restoration materials.

To investigate the effect of common beverages on four currently used provisional restoration materials: Protemp®4, Integrity®, polymethyl methacrylate(PMMA) block, and acrylic resin. Flowable resin composite is included as a control group. Each material was formed into disks of 10-mm diameter and 4-mm thickness (N = 40) by loading the material into acrylic molds. The exposed surface in the mold was covered using a glass slide to prevent an oxygen inhibition layer, and polymerization then proceeded. The solidified disks were placed in distilled water for 24 h. These samples (n = 8) were then immersed for 14 days in one of four different beverages: water, orange juice, cola, and coffee. Changes in color dimension, hardness, and roughness were observed and then analyzed using two-way repeated analysis of variance. The provisional materials had more obvious changes in all three color dimensions than the flowable resin composite. Integrity showed the biggest changes, followed by acrylic resin and PMMA block, whereas Protemp had the smallest changes. The hardness of all the materials significantly decreased after immersion in any of the beverages for 14 days. There were no changes in surface roughness when the materials were immersed in distilled water. The surface roughness of the PMMA block significantly decreased in orange juice whereas that of Integrity and acrylic resin significantly increased in cola. Different kinds of provisional materials had different degrees of staining due to their composition. Moisture had a significant influence on the hardness of materials, and the acidity of cola significantly roughened the surface of the provisional materials.

Comparison and Evaluation of Fracture Toughness of Milled, 3D-Printed, and Conventional Polymethyl Methacrylate: An in vitro Study

ABSTRACT Introduction: Dentures aim to replicate natural dentition’s esthetics and functions as much as possible. With computer-aided design/computer-aided manufacturing (CAD/CAM) technology, dentistry had a new renaissance with workflow and materials. Aim: The aim is to compare the fracture toughness of the milled, 3D-printed, and conventional polymethyl methacrylate (PMMA) to those processed conventionally. Materials and Methods: 10 CAD MILLED PMMA BLOCKS, 10 3D PRINTED PMMA BLOCKS, and 10 CONVENTIONAL (HEAT CURE) PMMA BLOCKS. Results: A significant difference was seen in the mean flexural module when compared among three study groups as P &lt; 0.05. It was found to be maximum in CAD/CAM PMMA, followed by conventional heat cure and 3D-printed PMMA. Conclusion: Formlabs and Dentca (3D-printed) were significantly weaker in fracture toughness compared to Leucitone 199 (conventional) (P &lt; 0.05). Leucitone 199 (conventional) was significantly weaker in fracture toughness compared to Avadent (CAD CAM) (P &lt; 0.05).

Evaluation of accuracy and position of milled and printed teeth in digital complete dentures.

To compare the accuracy of milled vs printed complete denture bases and teeth and to assess the position of the teeth on the corresponding denture bases. Two different manufacturing techniques were used in this study. In group A, 10 complete dentures were digitally designed and fabricated by milling prepolymerized blocks of polymethyl methacrylate. In group B, 10 complete dentures were digitally designed and fabricated using the 3D printing technique. The accuracy of the maxillary and mandibular denture bases and teeth and the position of the teeth on the corresponding denture bases were evaluated using Geomagic Control X software. Data were presented as mean and SD values. Statistical analysis of the resultant data was performed using Student t test. The significance level was set at P ≤ .05. The results revealed lower surface deviations of the maxillary and mandibular milled denture bases (group A) with values of 0.158 ± 0.024 and 0.117 ± 0.022, respectively. Lower surface deviations of the printed teeth (group B) were found with values of 0.18 ± 0.016 for the maxillary teeth and 0.153 ± 0.02 for the mandibular teeth, and for position of teeth on the corresponding denture bases, the values were 0.4 ± 0.08 for the maxillary teeth and 1.003 ± 0.027 for the position of the mandibular teeth. The milling technique yields complete denture bases with superior accuracy, while printing technology provides denture teeth with better accuracy and positioning on the corresponding denture bases.

Influence of Windowing and Evaluation of Metal Artifact Reduction Algorithm on Five Different Restorative Materials by Using Different Cone Beam Computed Tomography (CBCT) Scanners: A CBCT Study.

To assess the influence of windowing, and to evaluate, and compare the effect of the metal artifact reduction (MAR) and non-metal artifact reduction (non-MAR) algorithms on different high-density restorative dental materials using different cone beam computed tomography (CBCT) devices. Height and diameter of all cylindrical shape metals including amalgam, cobalt-chromium, composite, gutta-percha, and titanium were measured using a digital caliper device. Polymethylmethacrylate block and arch phantom with a cylindrical-shaped perforation containing five different metals were submitted to tomographic acquisition with six different cone beam computed tomographic devices in small fields of view with their MAR enabled and disabled. Windowing was done using ITK-SNAP software (3.8.2) which was used as a contrast medial tool for window level and window width. The data was analyzed for probability distribution using theKolmogorov-Smirnov test, where a p-value of <0.05 indicated that the data were not normally distributed. The comparison of length and width was done using the Wilcoxon sign rank test. Comparison of categorical variables was done using theChi-square test where a p-value of <0.05 was considered statisticallysignificant. Length and width of all these metals measured using MAR and non-MAR CBCT were found to be statistically non-significant (p-value of >0.05). MAR algorithm significantly reduces metals artifact produced by high-density restorative materials (p-value of <0.05). Amalgam and cobalt-chromium produced more artifacts while composite and gutta-percha did not produce enough artifacts to be reduced by the MAR algorithm. Large window width and high window level would be beneficial to reduce the metal artifact.

Does continuous chemical disinfection affect mechanical properties of CAD/CAM PMMA?

This study was aimed at analyzing the effect of disinfectants on the roughness and mechanical properties of computer-aided design/computer-aided manufacturing (CAD/CAM) polymethylmethacrylate (PMMA) dentures. Two groups of denture base resins were tested: heat-polymerized and milled blocks. The specimens were shaped (n=80) for flexural strength (FS), flexural modulus (FM), and (n=240) for the properties of roughness (Ra) and microhardness alterations (KHN). They were categorized into the following groups based on immersion: control (deionized water), H1 (1% sodium hypochlorite), H05 (0.5% sodium hypochlorite), and C2 (2% chlorhexidine) groups. The immersion periods were 0 (T0), 130 (T1), and 260 (T2) cycles. Statistical analyses were performed for flexural properties using the three-way analysis of variance (ANOVA). Microhardness and surface roughness were analyzed using repeatedmeasures ANOVA. A significance level of 5% was set. CAD/CAM PMMA showed higher FS (P = .001) and FM (P < .001) than conventional PMMA. The KHN value was superior to the conventional PMMA (P < .001). The chemical solution affected the surface roughness of both resins (P = .007). The CAD/CAM PMMA block showed increased Ra values when H1 was used. Cycling separately increased the FS of conventional PMMA (T1 vs. baseline; P < .05). However, the FM of CAD/CAM PMMA was higher (T1 and T2 vs. baseline; P < .05). The time factor increased the microhardness of both resins (T2 vs. baseline; P < .05). The CAD/CAM resin showed higher values compared to conventional PMMA in all tests, regardless of the chemical solution used; however, the values obtained for both resins were clinically acceptable. Int J Prosthodont 2023. doi: 10.11607/ijp.8301.

Evaluation of the machinability and machining accuracy of polymer-based CAD/CAM blocks using merlon fracture test model.

The aims of this study were to estimate the machinability and machining accuracy of polymer-based CAM blocks using the merlon fracture test model specified in ISO 18675: 2022. Three hybrid disc blanks (MazicDuro, HC Disk, and Enamic) and three polymethyl methacrylate (PMMA) disc blanks (PMMA Disk, PMMA Block, and MazicTemp Hybrid) were tested in this study. The machinability was evaluated by assigning scores according to the fracture range of merlons with areas divided by ten vertical planes. The machining accuracy was evaluated by superimposing methods via CAD reference data and CAD specimen data. Within the limits of this study, a thickness of 0.3 mm is recommended for the clinical application of polymer-based CAD/CAM blocks in dental restorations that require superior machinability and accuracy. In addition, the machinability and machining accuracy tests of polymer-based CAM blocks are expected to provide guidelines for preparing accurate dental restorations.

Surface properties and initial bacterial biofilm growth on 3D-printed oral appliances: a comparative in vitro study

ObjectivesTo investigate the initial bacterial adhesion on 3D-printed splint materials in relation to their surface properties.Materials and methodsSpecimens of five printable splint resins (SHERAprint-ortho plus UV, NextDent Ortho Rigid, LuxaPrint Ortho Plus, V-Print Splint, KeySplint Soft), one polymethylmethacrylate (PMMA) block for subtractive manufacturing (Astron CLEARsplint Disc), two conventional powder/liquid PMMA materials (FuturaGen, Astron CLEARsplint), and one polyethylene terephthalate glycol (PETG) thermoplastic sheet for vacuum forming (Erkodur Thermoforming Foil) were produced and finished. Surface roughness Ra was determined via contact profilometry. Surface morphology was examined under a scanning electron microscope. Multi-species bacterial biofilms were grown on entire splints. Total biofilm mass and viable bacterial counts (CFU/ml) within the biofilms were determined. Statistical analyses were performed with a one-way ANOVA, Tukey’s post hoc test, and Pearson’s test (p < 0.05).ResultsAstron CLEARsplint and KeySplint Soft specimens showed the highest surface roughness. The mean total biofilm mass on KeySplint Soft splints was higher compared to all other materials (p < 0.05). Colony-forming unit per milliliter on FuturaGen, Astron CLEARsplint, and KeySplint Soft splints was one log scale higher compared to all other materials. The other four printable resins displayed overall lower Ra, biofilm mass, and CFU/ml. A positive correlation was found between Ra and CFU/ml (r = 0.69, p = 0.04).ConclusionsThe 3D-printed splints showed overall favorable results regarding surface roughness and bacterial adhesion. Thermoplastic materials seem to display a higher surface roughness, making them more susceptible to microbial adhesion.Clinical relevanceThe development of caries and gingivitis in patients with oral appliances may be affected by the type of material.

Does Multifunctional Acrylate's Addition to Methacrylate Improve Its Flexural Properties and Bond Ability to CAD/CAM PMMA Block?

This study investigated the effects of a multifunctional acrylate copolymer-Trimethylolpropane Triacrylate (TMPTA) and Di-pentaerythritol Polyacrylate (A-DPH)-on the mechanical properties of chemically polymerized acrylic resin and its bond strength to a CAD/CAM polymethyl methacrylate (PMMA) disk. The methyl methacrylate (MMA) samples were doped with one of the following comonomers: TMPTA, A-DPH, or Trimethylolpropane Trimethacrylate (TMPTMA). The doping ratio ranged from 10 wt% to 50 wt% in 10 wt% increments. The flexural strength (FS) and modulus (FM) of PMMA with and without comonomer doping, as well as the shear bond strength (SBS) between the comonomer-doped PMMA and CAD/CAM PMMA disk, were evaluated. The highest FS (93.2 ± 4.2 MPa) was obtained when doped with 20 wt% of TMPTA. For TMPTMA, the FS decreased with the increase in the doping ratio. For SBS, TMPTA showed almost constant values (ranging from 7.0 to 8.2 MPa) regardless of the doping amount, and A-DPH peaked at 10 wt% doping (8.7 ± 2.2 MPa). TMPTMA showed two peaks at 10 wt% (7.2 ± 2.6 MPa) and 40 wt% (6.5 ± 2.3 MPa). Regarding the failure mode, TMPTMA showed mostly adhesive failure between the CAD/CAM PMMA disk and acrylic resin while TMPTA and A-DPH showed an increased rate of cohesive or mixed failures. Acrylate's addition as a comonomer to PMMA provided improved mechanical properties and bond strength to the CAD/CAM PMMA disk.

Marginal and internal fit and fracture resistance of three-unit provisional restorations fabricated by additive, subtractive, and conventional methods.

To compare the marginal and internal fit and fracture resistance of three-unit provisional fixed dental prostheses (FDPs) fabricated by additive, subtractive, and conventional methods. Eighty 3-unit FDPs were fabricated on metal dies of the maxillary right second premolar and second molar by four different techniques (n = 20): The direct method by using autopolymerizing polymethyl methacrylate (PMMA), indirect method by the compression molding technique, subtractive manufacturing by using PMMA blocks, and additive manufacturing by using digital light processing technology. The adaptation of restorations at the marginal, axial, cuspal, and fossa areas was assessed by using the silicone replica technique. After thermocycling and cyclic loading, the fracture resistance was measured by a universal testing machine. Data were analyzed by atwo-wayanalysis of variance (ANOVA), ANOVA, and Tukey test (α = .05). The mean gap measured in the additive group was lower than that in all other groups at all points (p < .05); however, the difference in the marginal gap with the subtractive group was not significant (p = .995). The mean marginal and axial gaps in the subtractive group were significantly lower than the corresponding values in both conventional groups (p < .05). A significant difference existed between all groups regarding the mean cuspal and fossa gaps (p < .05). The mean fracture resistance of the additive group was significantly higher than that of indirect (p = .018) and direct (p < .001) groups, and the fracture resistance of the subtractive group was significantly higher than that of the direct group (p = .020). The digitally fabricated provisional FDPs showed superior marginal and internal fit and higher fracture resistance than the conventionally fabricated FDPs. Between the digital methods, the additive technique yielded superior internal fit.

An Interdisciplinary Study Regarding the Characteristics of Dental Resins Used for Temporary Bridges.

Background and Objectives: The surface condition of the materials that are used for temporary prostheses influences their microbial colonization, with a direct impact on the oral tissues. This study aims at a comparative analysis of three types of resins for temporary bridges using conventional and digital technologies. The attention was focused on the analysis of the surface characteristics and mechanical strength of these materials. Materials and Methods: The surface condition was assessed for three distinct materials both before and after polishing- heat-curing resin Superpont C + B (SpofaDental, Jicin, Czech Republic) used unconventional technology, Zotion dental milling polymethyl methacrylate (PMMA) block (Zotion, Chongqing, China) for provisional crowns/bridges used in digital subtractive technologies and Freeprint Temp (Detax GmbH & Co. KG, Ettlingen, Germany) resin for temporary crowns and bridges that are used in 3D printing technologies. The two-way ANOVA analysis indicated that polishing leads to a statistically significant increase in roughness coefficients for all the three resins that were tested (p < 0.001). While the highest roughness coefficients were displayed in the 3D cured sample, the largest decrease was reported by the milled sample Results: The results revealed that surface roughness was significantly influenced by both the type of resin that was used (p < 0.001) and the treatment that was induced by finishing and polishing (p < 0.001). Similar p-values were obtained for each of the three resins. Conclusions: The results demonstrated a significant optimization of the surfaces after finishing and polishing and statistically significant differences between the surface parameters and the mechanical properties of the samples. The low values of the roughness and the acceptable values of the mechanical resistance for the conventional samples indicate these materials for the long-term temporary bridge’s realization, allowing the correct restoration of the functions and the rehabilitation at the oral level.

Comparison of the Accuracy between Denture Bases Produced by Subtractive and Additive Manufacturing Methods: A Pilot Study

Today, two different types of CAD-CAM fabrication methods for complete denture bases are available besides the conventional protocols: a subtractive milling process from a prepolymerized block of polymethylmethacrylate and an additive manufacturing process that built the denture base using a light-cured liquid in a VAT-polymerization process. The aim of this study was to evaluate and to compare the accuracy and precision of denture prosthetic bases made with subtractive and additive manufacturing technologies and to compare them with a denture base with the conventional method in muffle. From the results obtained, 3D printing dentures show a statistically significant higher accuracy than milled prosthetic bases. Milled prosthetic bases have similar accuracy than conventional fabricated dentures.

Customized Two-Dimensional Computed Tomography-Guided Preoperative Pectus Bar Shaping.

Successful minimally invasive repair of pectus excavatum relies on a pectus bar that closely conforms to the desired shape of the sternum and ribs to produce optimal elevation and remodeling. However, the present method of empirical intraoperative bar shaping is tedious and risks trauma to surrounding structures. To overcome this, we devised a technique using a life-sized computed tomography (CT) printout of the patient's chest wall to guide preoperative bar bending. A 5-cm-wide polymethylmethacrylate block placed on the sternum as the patient underwent chest CT was used as a marker to guide scaling of an axial screenshot of the patient's chest to life-size. This life-size image was printed and the planned correction of the patient's chest wall was traced onto it. The pectus bar was bent according to this template. Patient demographics, Haller index, surgical indications, operative technique, complications, aesthetic and functional improvements, and overall satisfaction were assessed. Thirty patients (4 women) underwent primary minimally invasive repair of pectus excavatum with a single pectus bar shaped preoperatively over an 8-year period. The average age and Haller index was 20.6 years and 5.4, respectively. The mean operative time was 66.4 minutes. Satisfactory sternal elevation was attained with a single attempt at bar insertion in all cases. Two patients had pneumothoraxes that resolved without intervention. The mean follow-up period was 50.1 months. There were no cases of bar migration or recurrence of deformity after bar removal. On a 5-point Likert scale, all patients indicated an improvement in aesthetic appearance (4.6), and patients with physical symptoms (10) reported an improvement in function (4.4). The overall satisfaction score was 4.7. This technique of CT-guided preoperative pectus bar shaping is straightforward, eliminates the need for intraoperative revisions to bar shape, and achieves effective correction of the pectus excavatum deformity. All patients were satisfied with the aesthetic, functional, and overall outcomes.

Scanning Electron Microscopic Evaluation of the Internal Fit Accuracy of 3D-Printed Biphasic Calcium Phosphate Block: An Ex Vivo Pilot Study.

The aim of this study was to assess the internal fit accuracy of a three-dimensional (3D)-printed biphasic calcium phosphate (BCP) block compared with a 3D-milled poly methyl methacrylate (PMMA) block by scanning electron microscope (SEM) analysis. In a total of 20 porcine rib bones, two different types of defects having two adjacent walls and a floor were produced: a defect with a flat floor (flat defect; N = 10) and a defect with a concave floor (curved defect; N = 10). Each defect was grafted with either the 3D-printed BCP block or the 3D-milled PMMA block fabricated following the computer aided design. The defects were then cut cross-sectionally and evaluated under the SEM. The extents of internal contact and gap were measured and statistically analyzed (p < 0.05). All blocks in both BCP and PMMA groups were successfully fit to the flat and curved defects. The internal contact ratio was significantly higher in the BCP group (flat defect: 0.47 ± 0.10; curved defect: 0.29 ± 0.05) compared with the PMMA group (flat defect: 0.21 ± 0.13; curved defect: 0.17 ± 0.04; p < 0.05). The internal gap area was similar between the two groups regardless of the defect types (p > 0.05). The internal fit accuracy of the 3D-printed BCP block was reliable in both the flat and curved defects when compared with the accuracy of the 3D-milled PMMA block.

Passive fit analysis of laser-sintered, three-unit implant prostheses: an in-vitro study.

To assess whether implant-retained prostheses produced with a laser-sintering technique present accuracy and passive fit comparable to their milled counterparts. Two Regular Neck Straumann analogs were placed in a block of polymethyl methacrylate (PMMA) at 15 mm of distance and parallel to one another. The PMMA block was then scanned, and two groups of cobalt-chromium (Co-Cr) screw-retained, three-unit implant prostheses were fabricated using milling (control) and laser sintering (test) techniques. The prostheses were then screwed on the PMMA block, and the vertical marginal gap between the prostheses and the analogs at the implant-abutment junction was measured twice: (1) when only one screw was tightened, and (2) when both screws were fully tightened. The mean marginal gap measurements were compared to assess the difference in terms of passive fit between the laser-sintered and milled prostheses. The mean marginal gap of the milled and laser-sintered groups was 23.18 μ (SD = 6.2) and 23.71 μ (SD = 19.5), respectively. Laser-sintered prostheses presented a marginal fit comparable to milled.

Fibula Jaw-in-a-Day with Minimal Computer-Aided Design and Manufacturing: Maximizing Efficiency, Cost-Effectiveness, Intraoperative Flexibility, and Quality.

The vascularized fibular flap has been the mainstay for mandibular reconstruction for over 30 years. Its latest evolutionary step is the jaw-in-a-day operation, during which the fibula flap and dental prosthesis restoration are performed in a single stage. Computer-aided design and manufacturing technology in mandibular reconstruction has gained popularity, as it simplifies the procedure and produces excellent outcomes. However, it is costly, time-consuming, and limited in cases that involve complex defects, including bone and soft-tissue coverage. Moreover, it does not allow for intraoperative changes in the surgical plan, including defect size and recipient vessel selection.The authors describe their approach, including a conventional technique for fibula osteoseptocutaneous flap harvest without the need for a premanufactured cutting guide, using bundled wooden tongue spatulas instead, a stereolithographic model to customize commercially ready-made reconstruction plates, and two pieces of resin to maintain occlusive alignment of the remaining jaw segments during mandibular osteotomy. Dental implants are inserted free-hand. Vector guides are then connected to the implants following insertion into the fibula to confirm acceptable alignment and subsequently replaced with scan sensors. An intraoperative digital scan is used to design and to produce a dental prosthesis by in-house milling of a polymethylmethacrylate block. From our 10-case experience over the past 3 years, we have found that our approach offers a reliable method that matches the excellent outcomes seen using full computer-assisted design and manufacturing technology. It is time- and cost-effective, not limited to relatively simple jaw defects, and can readily accommodate intraoperative changes of surgical plan.

Fracture resistance of additive manufactured and milled implant-supported interim crowns

Statement of problemInterim dental prostheses can be fabricated by using subtractive or additive manufacturing technologies. However, the fracture resistance of implant-supported interim crowns fabricated by using vat-polymerization additive manufacturing methods remains unclear. PurposeThe purpose of this in vitro study was to evaluate the fracture resistance of anterior and posterior screw-retained implant-supported interim crowns fabricated by using subtractive and vat-polymerization direct light processing (DLP) additive manufacturing procedures. Material and methodsAn implant (Zinic Implant RP ∅4.0×10 mm) was placed in a 15×15-mm polymethylmethacrylate block. An implant abutment (ZiaCam, nonrotatory RP) was positioned on each implant. The virtual implant abutment standard tessellation language (STL) file provided by the manufacturer was imported into a software program (exocad v2.2 Valletta) to design 2 anatomic contour crowns, a maxillary right central incisor (anterior group) and a maxillary right premolar (posterior group). Each group was subdivided into 2 subgroups depending on the manufacturing method: milled (milled subgroup) and additive manufacturing (additive manufacturing subgroup). For the milled subgroup, an interim material (Vivodent CAD Multi) and a milling machine were used to fabricate all the specimens (N=40, n=10). For the additive manufacturing subgroup, a polymer interim material (SHERAprint-cb) and a DLP printer (SHERAprint 30) were used to manufacture all the specimens at a 50-μm layer thickness and 45-degree build orientation as per the manufacturer’s instructions. Then, each specimen was cemented to an implant abutment by using composite resin cement (Multilink Hybrid Abutment HO) as per the manufacturer’s instructions. A universal testing machine was used for fracture resistance analysis, and the failure mode was recorded. The Shapiro-Wilk test revealed that data were normally distributed. One-way ANOVA and Tukey multiple comparison were selected (α=.05). ResultsOne-way ANOVA revealed significant differences among the groups (P<.05). The anterior milled subgroup obtained a significantly higher fracture resistance mean ±standard deviation value of 988.4 ±54.8 N compared with the anterior additive manufacturing subgroup of 636.5 ±277.1 N (P<.001), and the posterior milled subgroup obtained significantly higher mean ±standard deviation of 423.8 ±68 N than the additive manufacturing subgroup of 321.3 ±128.6 N (P=.048). All groups presented crown fracture without abutment fracture. ConclusionsManufacturing procedures and tooth type influenced the fracture resistance of screw-retained implant-supported interim crowns. Milled specimens obtained higher fracture resistance compared with the DLP additive manufacturing groups. The anterior group was higher than the posterior group.

Effect of pulp chamber depth on the accuracy of endocrown scans made with different intraoral scanners versus an industrial scanner: An in vitro study

Statement of problemThe accuracy of intraoral scanners (IOSs) has been evaluated. However, testing their performance when scanning deep endocrown preparations is lacking. PurposeThe purpose of this in vitro study was to assess the effect of pulpal chamber extension depth (PCED) on scanning accuracy and to compare the accuracy of different IOSs on scanning different PCEDs. Material and methodsSix different IOSs were compared: TRIOS 3, CEREC Omnicam, CEREC Primescan, Planmeca Emerald, iTero Element2, and Virtuo Vivo. Endocrown preparations were digitally designed with a computer-aided design and computer-aided manufacturing (CAD-CAM) software program (Rhicoceros), and the PCEDs of preparations were 2, 3.5, and 5 mm. Designed preparations were milled from a polymethylmethacrylate block (Telio CAD) with a milling unit. Reference scans were obtained from an industrial scanner (ATOS), and 5 test scans of each cavity were made with 6 IOSs. All scans were converted into standard tessellation language (STL) files. The data sets obtained from the IOSs were superimposed on the reference scan to evaluate trueness and on each other within groups to determine precision by using a 3D analysis software program (Geomagic Control X). Obtained data were analyzed with 1-way ANOVA and Tukey HSD tests (α=.05). ResultsCEREC Primescan was found to have the best trueness and precision among the evaluated IOSs (P<.05), while Planmeca Emerald was found to have the lowest trueness (P<.05). For all tested PCEDs, statistically significant differences were found among IOSs. A PCED with a 2-mm depth (18.57 ±4.80 μm) showed significantly better scanning trueness than that with a 5-mm depth (23.81 ±6.53), while no significant differences were found between 2 and 3.5 mm (P>.05). ConclusionsDeep pulpal chamber extensions of endocrown restorations could negatively affect scanning accuracy, and scanning accuracy varies depending on the selected IOS. CEREC Primescan appears to be the best IOS choice for scanning endocrowns with deep pulpal chamber extensions.