Digital wear analysis and retention of poly-ether-ether-ketone retentive inserts versus conventional nylon inserts in locator retained mandibular overdentures: in-vitro study.

OBJECTIVE: this study aimed to digitally compare wear behavior and retention between PEEK and nylon retentive inserts used in locator-retained, mandibular implant overdentures when attachment design and size were standardized. MATERIALS AND METHODS: A total of sixty-four inserts (32 PEEK and 32 nylon inserts); were picked-up in implant overdentures. Overdentures of both groups were submerged in artificial saliva and mounted to chewing simulator. After 480,000 chewing cycles (equivalent to 2 years of clinical use) all inserts were scanned by scanning electron microscope (SEM), then all acquired images were digitally analyzed by software to detect and compare quantitative and qualitative changes of inserts in both groups. On the other hand, retention of both groups was measured by universal testing machine and the collected data was statistically analyzed using one-way Analysis of Variance (ANOVA) test with significance level set at P ≤ 0.05. RESULTS: PEEK inserts showed significantly higher mean retentive values compared to the nylon inserts in the control group. Also, PEEK retentive inserts exhibited statistically lower mean wear values than the control group P ≥ 0.000. Qualitative investigation revealed significant and more pronounced changes in the surface roughness of nylon inserts compared to PEEK ones. CONCLUSIONS: Regarding retention, wear behavior and dimension stability, PEEK can be recommended as retentive insert material in cases of locator-retained mandibular implant overdentures. CLINICAL RELEVANCE: PEEK inserts offer enhanced retention, reduced wear, and greater dimensional stability over two years time interval. Clinically, this reduces prosthodontic maintenance and adjustments, improving patient satisfaction and long-term prosthetic success.

The Journey of Additive Manufacturing in Prosthodontics from the Early Dawn till the Current State of Art. A Narrative Review.

Additive manufacturing (AM) also known as 3D-printing has become one of the pillars of digital technology in the dental field particularly in prosthodontics. With the burgeoning development in the already existing AM technology and the evolution of new techniques, concurrent with the development of printable biomaterials, the range of application of the technology has broadened from the construction of diagnostic models to more complex applications such as maxillofacial prosthetics and implant planning. Full understanding of the technology and the related fabrication parameters will enable the maximum benefit from such technology. Therefore, the aim of this review is to represent a road trip along which the prosthodontists and dental technicians can cast a closer look on different AM technologies, advantages and disadvantages of each technique, the application of technology in the field of Prosthodontics, areas of current research in the field and finally recommendations for areas of future investigations.

Influence of different designs of bulb support structures on the accuracy and weight of 3D printed maxillary obturators. An in vitro study.

STATEMENT OF PROBLEM: Evidence is lacking on the influence of different designs of bulb support structures on the accuracy of 3-dimensional (3D) printed obturators. PURPOSE: The purpose of this in vitro study was to evaluate the influence of various infill designs (hollow, honeycomb, and gyroid) for the bulb of an obturator on the accuracy and weight of digital light projection (DLP) 3D printed maxillary obturators. MATERIAL AND METHODS: A maxillary obturator was virtually designed and used to obtain 3 digital reference files which were defined based on the design of the infill support structure within the bulb: hollow, honeycomb, and gyroid. The resultant standard tessellation language (STL) files were used to fabricate the obturators using a DLP 3D-printer in FREEPRINT denture resin material (n=10 per each group design). The fitting surfaces of all printed specimens (n=30) were digitized using a laboratory scanner, and the scan STL files were exported to the Geomagic control X program for dimensional accuracy analysis (trueness and precision) using the digital subtraction technique. One-way analysis of variance (ANOVA) was used for analysis (α=.05) RESULTS: Quantitative analysis revealed no significant difference in root mean square estimate (RMSE) values among the test groups for trueness (P=.326) and precision (P=.140). Hollow bulb design was significantly lighter in weight than both honeycomb and gyroid infill designs (P<.001). Colormaps revealed increased areas of negative deviation around the circumference of the bulb wall in the hollow design compared with both the gyroid and honeycomb groups and the close surface matching of fitting surfaces in the 3 groups. CONCLUSIONS: The lack of significant difference in accuracy among the tested groups and the significantly lighter hollow design obturator compared with honeycomb and gyroid designs favors the selection of the hollow bulb design in the digital fabrication of maxillary obturators.

Additive Manufacturing Technologies: Where Did We Start and Where Have We Landed? A Narrative Review.

Additive manufacturing (AM), also known as 3D printing, is gaining burgeoning interest among various dental disciplines. The import of this technology stems not only from its ability to fabricate different parts but from the solutions it provides for the customization and production of complex designs that other methods cannot offer-all to the end of enhancing clinical treatment alternatives. There is a wide range of AM machinery and materials available to choose from, and the goal of this review is to provide readers and clinicians with a decision tool for selecting the appropriate technology for a given application and to successfully integrate AM into the digital workflow.

Influence of Fabrication Technique on Adhesion and Biofilm Formation of Candida albicans to Conventional, Milled, and 3D-Printed Denture Base Resin Materials: A Comparative In Vitro Study.

The aim of this study was to evaluate the adhesion and biofilm formation of Candida albicans (C. albicans) on conventionally fabricated, milled, and 3D-printed denture base resin materials in order to determine the susceptibility of denture contamination during clinical use. Specimens were incubated with C. albicans (ATCC 10231) for 1 and 24 h. Adhesion and biofilm formation of C. albicans were assessed using the field emission scanning electron microscopy (FESEM). The XTT (2,3-(2-methoxy-4-nitro-5-sulphophenyl)-5-[(phenylamino) carbonyl]-2H-tetrazolium hydroxide) assay was used for the quantification of fungal adhesion and biofilm formation. The data were analyzed using GraphPad Prism 8.02 for windows. One-way ANOVA with Tukey's post hoc testing were performed with a statistical significance level set at α = 0.05. The quantitative XTT biofilm assay revealed significant differences in the biofilm formation of C. albicans between the three groups in the 24 h incubation period. The highest proportion of biofilm formation was observed in the 3D-printed group, followed by the conventional group, while the lowest candida biofilm formation was observed in the milled group. The difference in biofilm formation among the three tested dentures was statistically significant (p < 0.001). The manufacturing technique has an influence on the surface topography and microbiological properties of the fabricated denture base resin material. Additive 3D-printing technology results in increased candida adhesion and the roughest surface topography of maxillary resin denture base as compared to conventional flask compression and CAD/CAM milling techniques. In a clinical setting, patients wearing additively manufactured maxillary complete dentures are thus more susceptible to the development of candida-associated denture stomatitis and accordingly, strict oral hygiene measures and maintenance programs should be emphasized to patients.

Influence of scan technology on the accuracy and speed of intraoral scanning systems for the edentulous maxilla: An in vitro study.

PURPOSE: To compare the accuracy of three intraoral scanners in terms of trueness and precision relative to the scanner acquisition technology and scan capture mode. Scan speed of each scanner was also evaluated. MATERIALS AND METHODS: An edentulous maxillary arch was digitized (reference model) and 3D-printed using an SLA-based 3D-printer (XFAB; DWS, Italy) (n = 10). Each model was scanned using three intraoral scanners, each with different scan technologies: confocal (Trios 3; 3Shape, Copenhagen, Denmark), parallel confocal (iTero; Align Technology), and triangulation (Medit i700). Scan time and scanning accuracy (trueness and precision) were calculated using digital subtraction technique (Geomagic Control X v2020, 3DSystems, USA). One-way analysis of variance (ANOVA) test was used to detect differences in trueness, precision, and scanning time between the tested groups (p < 0.05). RESULTS: ANOVA results showed statistically significant differences in trueness, precision, and scan time among the tested groups. Confocal scanning technique (Trios 3) showed the highest trueness and precision (root mean square estimate [RMSE] 0.094 and 0.096, respectively) followed by iTero displaying parallel confocal technique (RMSE 0.113 and 0.133, respectively); the difference was not significant (p = 0.849, p = 0.488). Further, Trios showed the longest scanning time (100 s) compared to iTero and Medit i700 (p = 0.011 and 0.002, respectively). Medit i700 presenting triangulation scan technology revealed lowest trueness and precision (RMSE 0.268) (p = 0.000, p = 0.001) and fastest scan time (59 s) close to iTero (66 s) (p = 0.802). CONCLUSIONS: Scanner technology had an influence on the accuracy and scan speed of the acquired intraoral scans. The Trios 3 scanner featuring the confocal acquisition technology displayed the highest trueness, precision, and longest scan time. Medit i700 IOS with triangulation acquisition concept featured the lowest trueness, precision, and fastest scan speed. There is no ideal scanner with the best combination of accuracy and scan speed.

Does the palatal vault form have an influence on the scan time and accuracy of intraoral scans of completely edentulous arches? An in-vitro study.

PURPOSE: The purpose of this study was to evaluate the influence of different palatal vault configurations on the accuracy and scan speed of intraoral scans (IO) of completely edentulous arches. MATERIALS AND METHODS: Three different virtual models of a completely edentulous maxillary arch with different palatal vault heights-Cl I moderate (U-shaped), Cl II deep (steep) and Cl III shallow (flat)-were digitally designed using CAD software (Meshmixer; Autodesk, USA) and 3D-printed using SLA-based 3D-printer (XFAB; DWS, Italy) (n = 30; 10 specimens per group). Each model was scanned using intraoral scanner (Trios 3; 3Shape™, Denmark). Scanning time was recorded for all samples. Scanning accuracy (trueness and precision) were evaluated using digital subtraction technique using Geomagic Control X v2020 (Geomagic; 3DSystems, USA). One-way analysis of variance (ANOVA) test was used to detect differences in scanning time, trueness and precision among the test groups. Statistical significance was set at α = .05. RESULTS: The scan process could not be completed for Class II group and manufacturer's recommended technique had to be modified. ANOVA revealed no statistically significant difference in trueness and precision values among the test groups (P =.959 and P =.658, respectively). Deep palatal vault (Cl II) showed significantly longer scan time compared to Cl I and III. CONCLUSION: The selection of scan protocol in complex cases such as deep palatal vault is of utmost importance. The modified, adopted longer path scan protocol of deep vault cases resulted in increased scan time when compared to the other two groups.

Zirconia versus Titanium Implants: 8-Year Follow-Up in a Patient Cohort Contrasted with Histological Evidence from a Preclinical Animal Model.

Zirconia ceramic (ZC) implants are becoming more common, but comparisons between preclinical histology and long-term clinical trials are rare. This investigation comprised (1) 8-year clinical follow-up of one-piece ZC or titanium (Ti) implants supporting full overdentures and (2) histomorphometric analysis of the same implants in an animal model, comparing implants with various surface treatments. METHODS: (1) Clinical trial: 24 completely edentulous participants (2 groups of N = 12) received 7 implants (one-piece ball-abutment ZC or Ti; maxilla N = 4, mandible N = 3) restored with implant overdentures. Outcomes after 8-years included survival, peri-implant bone levels, soft-tissue responses, and prosthodontic issues. (2) Preclinical trial: 10 New Zealand sheep received 4 implants bilaterally in the femoral condyle: Southern Implants ZC or Ti one-piece implants, identical to the clinical trial, and controls: Southern ITC® two-piece implants with the same surface or Nobel (NBC) anodised (TiUnite™) surface. %Bone-implant contact (%BIC) was measured after 12 weeks of unloaded healing. RESULTS: 8 of 24 participants (33%) of an average age of 75 ± 8 years were recalled; 21% of original participants had died, and 46% could not be contacted. 80.4% of implants survived; excluding palatal sites, 87.5% of Ti and 79% of ZC implants survived. All failed implants were in the maxilla. Three ZC implants had fractured. Bone loss was similar for Ti vs. ZC; pocket depths (p = 0.04) and attachment levels (p = 0.02) were greater for Ti than ZC implants. (1.7 ± 1.6 mm vs. 1.6 ± 1.3 mm). All implants in sheep femurs survived. %BIC was not statistically different for one-piece blasted surface Ti (80 ± 19%) versus ZC (76 ± 20%) or ITC® (75 ± 16 mm); NBC had significantly higher %BIC than ITC (84 ± 17%, p = 0.4). CONCLUSION: Short-term preclinical results for ZC and Ti one-piece implants showed excellent bone-implant contact in unloaded femoral sites. This differed from the long-term clinical results in older-aged, edentulous participants. While ZC and Ti implants showed equivalent performance, the risks of peri-implantitis and implant loss in older, completely edentulous patients remain a significant factor.

Influence of Different Fabrication Techniques on the Accuracy of Radiographic Scan Templates in Cases of Full-Arch Computer-Guided Implant Placement: An In Vitro Study.

PURPOSE: To evaluate the influence of using different fabrication techniques, including intraoral scans, CBCT scans of patients' existing dentures, or denture duplicates, on the accuracy of radiographic scan templates. The influence of selecting different segmentation threshold values during reconstruction of CBCT data was also evaluated. MATERIALS AND METHODS: A reference model was obtained by scanning five pairs of maxillary and mandibular acrylic complete dentures using a desktop laboratory laser scanner (DWOS 7Series, Dental Wings). Test scans were obtained from intraoral scans of dentures, CBCT scans of dentures and denture duplicates reconstructed at different grayscale segmentation thresholds, and a laboratory scan of denture duplicates. The resultant STL scan files were imported to an open source and cloud storage software (Medit Link) for the accuracy measurements by calculating root mean square estimate (RMSE) between reference and test scans. Collected data were then analyzed. Qualitative analysis was also performed using 3D color maps. RESULTS: The lowest RMSE (352.7) was found with intraoral denture scans. The highest RMSE (1,336.3) was found with the CBCT scans of the denture duplicates at segmentation threshold of -700 grayscale level. Qualitative analysis revealed that the intraoral denture scans exhibited the most homogenous deviation pattern relative to reference lab scans. CONCLUSION: Within the limitations of this study, the intraoral scans of the patients' existing dentures resulted in the fabrication of the most accurate radiographic scan templates. The improved accuracy of scan templates fabricated using the intraoral scanners can eliminate the possible laboratory errors associated with the conventional technical procedures as well as reduce the inaccuracies resulting from the image processing and segmentation of CBCT data.

Clinical evaluation of implant overdentures fabricated using 3D-printing technology versus conventional fabrication techniques: a randomized clinical trial.

AIM: To evaluate the oral health-related quality of life (OHRQoL) of patients rehabilitated with conventional or 3D-printed implant overdentures. MATERIALS AND METHODS: A randomized clinical trial (RCT) was designed. Twenty-eight completely edentulous participants were randomly allocated into two equal groups. All participants received two implants with ball attachments. Participants in the control group were rehabilitated with conventionally manufactured polymethyl methacrylate (PMMA) maxillary complete dentures (CDs) and mandibular implant overdentures, while those in the intervention group received digital light processing (DLP)-printed photopolymerizable PMMA maxillary CDs (NextDent) and mandibular implant overdentures. Follow-up appointments were scheduled at 3, 6, and 12 months where Oral Health Impact Profile 19 (OHIPEDENT19) data were used to assess the OHRQoL of the participants. Denture retention was measured using a digital force gauge device. RESULTS: The OHRQoL values were significantly higher (less improvement) in the conventional overdenture group at 6 months (P = 0.02) and 12 months (P = 0.04). A statistically significant difference was found between the mean retention values of the conventional and 3D-printed overdenture groups. For all the follow-up periods, the mean retention values were higher for the 3D-printed overdenture group (P = 0.001). CONCLUSION: 3D-printed overdentures may represent an alternative to conventionally fabricated ones. This study represents a stepping stone and proof of concept that support the potential future use of 3D-printed dentures.

Stain Susceptibility of 3D-Printed Nanohybrid Composite Restorative Material and the Efficacy of Different Stain Removal Techniques: An In Vitro Study.

Recent burgeoning development in material science has introduced a 3D-printable, nanohybrid composite resin restorative material. However, its performance has not yet been investigated. This study evaluates the stain susceptibility and efficacy of different stain removal techniques. A total of 120 labial veneers were fabricated using milling (n = 60) and SLA 3D-printing (n = 60). Based on the immersion media: coffee, tea and artificial saliva, each group was divided into three sub-groups (n = 20). Stain susceptibility was evaluated by calculating color difference (∆E00) at 12 and 24 days using a spectrophotometer against black and white backgrounds. Collected data were analyzed with ANOVA and Tukey's post hoc test (p < 0.05). A significant interaction effect was found between the staining mediums and fabrication methods in both black and white backgrounds (p < 0.001). 3D-printed restorations showed significantly higher stain susceptibility than milled restorations (p < 0.001). Prolonged immersion time increased the color difference in both groups. In-office bleaching was more effective in stain removal in both 3D-printed and milled restoration groups. The susceptibility of the presented novel 3D-printed restorative material to color changes in different immersion mediums was clinically not-acceptable. The clinicians might expect the need to replace the restoration after 1-2 years and thus, recommendation for the use of such a material as a permanent restoration cannot be made but rather as a long-term temporary restoration.

Biomechanics of 3-implant-supported and 4-implant-supported mandibular screw-retained prostheses: A 3D finite element analysis study.

STATEMENT OF PROBLEM: The number of implants required for the rehabilitation of completely edentulous mandibles has been controversial. The use of a greater number of implants can produce favorable biomechanical outcomes. However, this will lead to high costs and may require complex surgical procedures. Therefore, the minimum number of implants that can produce desirable outcomes should be used. PURPOSE: The purpose of this 3D finite element study was to compare the biomechanics of mandibular 3-implant-supported to 4-implant-supported prostheses. The opposing occlusion was a maxillary complete denture or natural dentition. MATERIAL AND METHODS: Two finite element analysis mandibular anatomic models were created. Implants were virtually placed in the mandibular lateral incisor and second premolar region bilaterally in the 4-implant-supported prosthesis model. For the 3-implant-supported model, they were placed in the midline and bilaterally in the second premolar region. Screw-retained polymethyl methacrylate prostheses were designed. Reverse engineering was used to convert standard tessellation language files into computer-aided design solid models. Vertical and oblique loading was applied twice: simulating an opposing maxillary complete denture and a natural dentition. Von Mises stresses and equivalent strains generated in the peri-implant bone, implants' von Mises stresses and the maximum vertical displacement of the prosthesis were recorded. RESULTS: All recorded outcomes reported higher values for the 3-implant-supported prosthesis compared with the 4-implant-supported models for both applied loads. When opposed by a maxillary complete denture, maximum strain values for the 3-implant-supported (2.3×103 µÎµ) and 4-implant-supported (1.6×103 µÎµ) models were less than the different threshold limits for the bone resorption reported (3×103, 3.6×103, 6.6×103 µÎµ). When opposed by a maxillary natural dentition, maximum strain values for the 3-implant-supported (4.10×103 µÎµ) and 4-implant-supported (3.88×103 µÎµ) models were less than the highest reported threshold limit for bone resorption (6.6×103 µÎµ) in contrast with other reported threshold limits (3×103, 3.6×103 µÎµ). In both designs irrespective of the magnitude and direction of loading, the maximum recorded von Mises stresses of the implants (126 MPa) and denture displacement (3.24×102 µm) were less than titanium's yield strength of (960 to 1180 MPa) and the displacement values (5.2×103 to 8.8×103 µm) reported in the literature. CONCLUSIONS: When opposed by a complete denture, recorded biomechanical outcomes for the 3- and 4-implant-supported designs were within physiologic limits. When opposed by a natural dentition, the von Mises stresses of the implants and denture displacement values for both designs were within a favorable mechanical range, whereas peri-implant stresses and strain exceeded most reported physiologic tolerance levels of bone except for the 6.6×103 µÎµ threshold limit for the bone resorption reported.

A histomorphometric study on treated and untreated ceramic filled PEEK implants versus titanium implants: Preclinical in vivo study.

OBJECTIVES: To investigate the osseo-integrative behavior of untreated (UCFP) and sandblasted ceramic filled PEEK (SCFP) implants in comparison with titanium implants through measurement of bone implant contact (BIC) and bone density (BD). MATERIALS AND METHODS: Nine implants from each type were inserted into 9 dogs in which every experimental dog received the three different implants in the lower border of the mandible. The animals were euthanized after 3 months and extracting bone blocks containing implants followed by blocks preparation for histological examinations. RESULTS: BIC and BD were significantly higher in titanium and SCFP compared with UCFP group (p = .007) and (p = .012), respectively. Aluminum blasting increased the bone ingrowth and bone implant contact when compared to machined surfaces of untreated PEEK implants. CONCLUSION: In conclusion, sandblasting with 110 µm aluminum oxide particles can be proposed as a suitable surface treatment that enhances hydrophilicity of CFP. Further in vivo animal studies are still needed to confirm the findings of this study.

Osseodensification in Implant Dentistry: A Critical Review of the Literature.

INTRODUCTION: Osseodensification is a technique that aims at bone preservation and compaction either through nonsubtractive drilling or implants with a special thread design. This can increase quantity and density of periimplant bone. This review represents a summary and a critical appraisal of the studies regarding osseodensification in the literature. MATERIALS AND METHODS: Three databases were searched: PubMed (MEDLINE), Cochrane Library, and Latin American and Caribbean center on health sciences information (LILACS). Studies were screened by title/abstract according to predetermined eligibility criteria. Full texts of 7 eligible articles were read among which 2 were excluded and 5 articles were included and underwent qualitative synthesis. DISCUSSION: Studies advocating osseodensification are sparse and mainly animal studies of low evidence level. High risk of bias and low correlation between used animal models and human bone were detected in most of the studies. CONCLUSION: Although osseodensification seems to be a very promising technique, the findings are inconclusive and should be cautiously interpreted. Well-designed animal and human studies of longer follow-up periods are required before implementing such technique in regular daily practice.

Three-dimensional evaluation of marginal and internal fit of 3D-printed interim restorations fabricated on different finish line designs.

PurposeTo evaluate the influence of fabrication method and finish line design on marginal and internal fit of full-coverage interim restorations. MethodsFour typodont models of maxillary central-incisor were prepared for full-coverage restorations. Four groups were defined; knife-edge (KE), chamfer (C), rounded-shoulder (RS), rounded-shoulder with bevel (RSB). All preparations were digitally scanned. A total of 80 restorations were fabricated; 20 per group (SLA/3D-printed n=10, milled n=10). All restorations were positioned on the master die and scanned using micro-computed tomography. The mean gaps were measured digitally (ImageJ). The results were compared using MANOVA (α=.05). ResultsInternal and marginal gaps were significantly influenced by fabrication method (P=.000) and finish-line design (P=.000). 3D-Printed restorations showed statistically significant lower mean gap compared to milled restorations at all points (P=.000). The mean internal gap for 3D-printed restorations were 66, 149, 130, 95µm and for milled restorations were 89, 177, 185, 154µm for KE, C, RS, RSB respectively. The mean absolute marginal discrepancy in 3D-printed restorations were (30, 41, 30, 28µm) and in milled restorations were (56, 54, 52, 38µm) for KE, C, RS, RSB respectively. ConclusionsThe fabrication methods showed more of an influence on the fit compared to the effect of the finish-line design in both milled and printed restorations. SLA-printed interim restorations exhibit lower marginal and internal gap than milled restorations. Nonetheless, for both techniques, all values were within the reported values for CAD/CAM restorations. Significance3D-printing can offer an alternative fabrication method comparable to those of milled restorations.

Can PEEK Be an Implant Material? Evaluation of Surface Topography and Wettability of Filled Versus Unfilled PEEK With Different Surface Roughness.

Polyetheretherketone (PEEK) composites are biocompatible materials that may overcome the esthetic and allergic problems of titanium dental implants. However, their potential for osseointegration with a subsequent survival rate is still questionable. The aim of this study was to evaluate the surface roughness and wettability of different surface-treated filled and unfilled PEEK specimens, which may be indicative of the osseointegration behavior and potential use of PEEK as an implant material. Unfilled, ceramic-filled (CFP) and carbon fiber-reinforced (CFRP) PEEK discs were prepared and left untreated or were surface treated with 50 µ, 110 µ, or 250 µ aluminum oxide particles. The roughness average (Ra) value of each disc was evaluated using a contact stylus profilometer. Their contact angles were measured to evaluate their wettability, which was compared among PEEK discs using ANOVA, followed by Bonferroni test for pairwise comparisons ( P ≤ .05). Regarding the surface roughness, a significant difference was found between unfilled and filled PEEK when untreated and bombarded with 50 or 110 microns of aluminum oxide particles. For the contact angle, a significant difference was found only among the untreated PEEK materials. Among the evaluated PEEK materials, CFRP50, CFRP110 and CFP110 showed the most favorable Ra values with good wettability properties, thus being potential substrates for dental implants.

3D-printing zirconia implants; a dream or a reality? An in-vitro study evaluating the dimensional accuracy, surface topography and mechanical properties of printed zirconia implant and discs.

PURPOSE: The aim of this study was to evaluate the dimensional accuracy, surface topography of a custom designed, 3D-printed zirconia dental implant and the mechanical properties of printed zirconia discs. MATERIALS AND METHODS: A custom designed implant was 3D-printed in zirconia using digital light processing technique (DLP). The dimensional accuracy was assessed using the digital-subtraction technique. The mechanical properties were evaluated using biaxial flexure strength test. Three different build angles were adopted to print the specimens for the mechanical test; 0°(Vertical), 45° (Oblique) and 90°(Horizontal) angles. The surface topography, crystallographic phase structure and surface roughness were evaluated using scanning electron microscopy analysis (SEM), X-ray diffractometer and confocal microscopy respectively. RESULTS: The printed implant was dimensionally accurate with a root mean square (RMSE) value of 0.1mm. The Weibull analysis revealed a statistically significant higher characteristic strength (1006.6MPa) of 0° printed specimens compared to the other two groups and no significant difference between 45° (892.2MPa) and 90° (866.7MPa) build angles. SEM analysis revealed cracks, micro-porosities and interconnected pores ranging in size from 196nm to 3.3µm. The mean Ra (arithmetic mean roughness) value of 1.59µm (±0.41) and Rq (root mean squared roughness) value of 1.94µm (±0.47) was found. A crystallographic phase of primarily tetragonal zirconia typical of sintered Yttria tetragonal stabilized zirconia (Y-TZP) was detected. CONCLUSIONS: DLP prove to be efficient for printing customized zirconia dental implants with sufficient dimensional accuracy. The mechanical properties showed flexure strength close to those of conventionally produced ceramics. Optimization of the 3D-printing process parameters is still needed to improve the microstructure of the printed objects.

Additive Manufacturing Techniques in Prosthodontics: Where Do We Currently Stand? A Critical Review.

PURPOSE: The aim of this article was to critically review the current application of additive manufacturing (AM)/3D-printing techniques in prosthodontics and to highlight the influence of various technical factors involved in different AM technologies. MATERIALS AND METHODS: A standard approach of searching MEDLINE, EMBASE, and Google Scholar databases was followed. The following search terms were used: (Prosth* OR Restoration) AND (Prototype OR Additive Manufacture* OR Compute* OR 3D-print* OR CAD/CAM) AND (Dentistry OR Dental). Hand searching the reference lists of the included articles and personal connections revealed additional relevant articles. Selection criteria were any article written in English and reporting on the application of AM in prosthodontics from 1990 to February 2016. RESULTS: From a total of 4,290 articles identified, 33 were seen as relevant. Of these, 3 were narrative reviews, 18 were in vitro studies, and 12 were clinical in vivo studies. Different AM technologies are applied in prosthodontics, directly and indirectly for the fabrication of fixed metal copings, metal frameworks for removable partial dentures, and plastic mock-ups and resin patterns for further conventional metal castings. Technical factors involved in different AM techniques influence the overall quality, the mechanical properties of the printed parts, and the total cost and manufacturing time. CONCLUSION: AM is promising and offers new possibilities in the field of prosthodontics, though its application is still limited. An understanding of these limitations and of developments in material science is crucial prior to considering AM as an acceptable method for the fabrication of dental prostheses.

Build Angle: Does It Influence the Accuracy of 3D-Printed Dental Restorations Using Digital Light-Processing Technology?

PURPOSE: The aim of this study was to evaluate the effect of the build orientation/build angle on the dimensional accuracy of full-coverage dental restorations manufactured using digital light-processing technology (DLP-AM). MATERIALS AND METHODS: A full dental crown was digitally designed and 3D-printed using DLP-AM. Nine build angles were used: 90, 120, 135, 150, 180, 210, 225, 240, and 270 degrees. The specimens were digitally scanned using a high-resolution optical surface scanner (IScan D104i, Imetric). Dimensional accuracy was evaluated using the digital subtraction technique. The 3D digital files of the scanned printed crowns (test model) were exported in standard tessellation language (STL) format and superimposed on the STL file of the designed crown [reference model] using Geomagic Studio 2014 (3D Systems). The root mean square estimate (RMSE) values were evaluated, and the deviation patterns on the color maps were further assessed. RESULTS: The build angle influenced the dimensional accuracy of 3D-printed restorations. The lowest RMSE was recorded for the 135-degree and 210-degree build angles. However, the overall deviation pattern on the color map was more favorable with the 135-degree build angle in contrast with the 210-degree build angle where the deviation was observed around the critical marginal area. CONCLUSIONS: Within the limitations of this study, the recommended build angle using the current DLP system was 135 degrees. Among the selected build angles, it offers the highest dimensional accuracy and the most favorable deviation pattern. It also offers a self-supporting crown geometry throughout the building process.

Factors Influencing the Dimensional Accuracy of 3D-Printed Full-Coverage Dental Restorations Using Stereolithography Technology.

PURPOSE: The aim of the present study was to evaluate the effect of the build angle and the support configuration (thick versus thin support) on the dimensional accuracy of 3D-printed full-coverage dental restorations. MATERIALS AND METHODS: A full-coverage dental crown was digitally designed and 3D-printed using stereolithography-additive manufacturing (SLA-AM) technology. Nine different angles were used during the build process: 90, 120, 135, 150, 180, 210, 225, 240, and 270 degrees. In each angle, the crown was printed using a thin and a thick support type, resulting in 18 specimens. The specimens were digitally scanned using a high resolution optical surface scanner (IScan D104i; Imetric 3D). The dimensional accuracy was evaluated by digital subtraction technique. The 3D digital files of the scanned printed crowns (test model), exported in standard tessellation language (STL) format, were superimposed with the STL file of the designed crown (reference model) using Geomagic Studio 2014 (3D Systems). RESULTS: The root mean square estimate value and color map results suggest that the build angle and support structure configuration have an influence on the dimensional accuracy of 3D-printed crown restorations. Among the tested angles, the 120-degree build angle showed a minimal deviation of 0.029 mm for thin support and 0.031 mm for thick support, indicating an accurate fit between the test and reference models. Furthermore, the deviation pattern observed in the color map was homogenously distributed and located further away from the critical marginal area. CONCLUSIONS: Within the limitations of this study, the selection of build angle should offer the crown the highest dimensional accuracy and self-supported geometry. This allows for the smallest necessary support surface area and decreases the time needed for finishing and polishing. These properties were mostly observed with a build angle of 120 degrees combined with a thin support type.