Showing papers in "Journal of Prosthetic Dentistry in 2017"

Evaluation of the accuracy of 7 digital scanners: An in vitro analysis based on 3-dimensional comparisons.

Abstract: Statement of problem As digital impressions become more common and more digital impression systems are released onto the market, it is essential to systematically and objectively evaluate their accuracy. Purpose The purpose of this in vitro study was to evaluate and compare the trueness and precision of 6 intraoral scanners and 1 laboratory scanner in both sextant and complete-arch scenarios. Furthermore, time of scanning was evaluated and correlated with trueness and precision. Material and methods A custom complete-arch model was fabricated with a refractive index similar to that of tooth structure. Seven digital impression systems were used to scan the custom model for both posterior sextant and complete arch scenarios. Analysis was performed using 3-dimensional metrology software to measure discrepancies between the master model and experimental casts. Results Of the intraoral scanners, the Planscan was found to have the best trueness and precision while the 3Shape Trios was found to have the poorest for sextant scanning ( P iTero >3Shape TRIOS 3 >Carestream 3500 >Planscan >CEREC Omnicam >CEREC Bluecam. The order of precision for complete-arch scanning was as follows: CS3500 >iTero >3Shape D800 >3Shape TRIOS 3 >CEREC Omnicam >Planscan >CEREC Bluecam. For the secondary outcome evaluating the effect time has on trueness and precision, the complete- arch scan time was highly correlated with both trueness (r=0.771) and precision (r=0.771). Conclusions For sextant scanning, the Planscan was found to be the most precise and true scanner. For complete-arch scanning, the 3Shape Trios was found to have the best balance of speed and accuracy.

Marginal adaptation and CAD-CAM technology: A systematic review of restorative material and fabrication techniques

Abstract: Statement of problem The comparative assessment of computer-aided design and computer-aided manufacturing (CAD-CAM) technology and other fabrication techniques pertaining to marginal adaptation should be documented. Limited evidence exists on the effect of restorative material on the performance of a CAD-CAM system relative to marginal adaptation. Purpose The purpose of this systematic review was to investigate whether the marginal adaptation of CAD-CAM single crowns, fixed dental prostheses, and implant-retained fixed dental prostheses or their infrastructures differs from that obtained by other fabrication techniques using a similar restorative material and whether it depends on the type of restorative material. Material and methods An electronic search of English-language literature published between January 1, 2000, and June 30, 2016, was conducted of the Medline/PubMed database. Results Of the 55 included comparative studies, 28 compared CAD-CAM technology with conventional fabrication techniques, 12 contrasted CAD-CAM technology and copy milling, 4 compared CAD-CAM milling with direct metal laser sintering (DMLS), and 22 investigated the performance of a CAD-CAM system regarding marginal adaptation in restorations/infrastructures produced with different restorative materials. Conclusions Most of the CAD-CAM restorations/infrastructures were within the clinically acceptable marginal discrepancy (MD) range. The performance of a CAD-CAM system relative to marginal adaptation is influenced by the restorative material. Compared with CAD-CAM, most of the heat-pressed lithium disilicate crowns displayed equal or smaller MD values. Slip-casting crowns exhibited similar or better marginal accuracy than those fabricated with CAD-CAM. Cobalt-chromium and titanium implant infrastructures produced using a CAD-CAM system elicited smaller MD values than zirconia. The majority of cobalt-chromium restorations/infrastructures produced by DMLS displayed better marginal accuracy than those fabricated with the casting technique. Compared with copy milling, the majority of zirconia restorations/infrastructures produced by CAD-CAM milling exhibited better marginal adaptation. No clear conclusions can be drawn about the superiority of CAD-CAM milling over the casting technique and DMLS regarding marginal adaptation.

Comparison of digital intraoral scanner reproducibility and image trueness considering repetitive experience.

Abstract: Statement of problem Because the digital workflow can begin directly in the oral cavity, intraoral scanners are being adopted in dental treatments. However, studies of the relationship between the experience of the practitioner and the accuracy of impression data are needed. Purpose The purpose of this clinical study was to investigate the effect of the experience curve on changes in trueness when a patient's complete dental arch is scanned. Material and methods Twenty dental hygienists with more than 3 years of experience in dental clinical practice (group 1 had 3 to 5 years; group 2 had >6 years) were recruited to learn to operate 2 intraoral scanner systems. All learners scanned the assigned patient's oral cavity 10 times during the experience sessions. Precision was calculated as the mean deviation among all superimposition combinations from the 10 scanned data sets of each learner [n= 10 C 2 =45]. Trueness was evaluated by superimposing the 10 consecutive intraoral scan data onto the impression scan data from each patient's rubber impression body (n=10). The acquired images were processed and analyzed using a 3-dimensional analysis software. For statistical analysis, the independent 2-sample t test and repeated measures ANOVA were performed (α=.05). Results The mean precision of the Trios scanner was greater than that of the iTero (Trios, 52.30 μm; iTero, 60.46 μm; P P P >.05). In the iTero group but not in the Trios group, the length of clinical experience influenced the change of trueness as a result of repeated experience ( P P Conclusions The single-image based system required repeated learning sessions for effective clinical application. The newer system offered better trueness and precision and was less likely to be influenced by the length of clinical career or the region being scanned.

Removable partial dentures: The clinical need for innovation

Abstract: Statement of problem The number of partially dentate adults is increasing, and many patients will require replacement of missing teeth. Although current treatment options also include fixed partial dentures and implants, removable partial dentures (RPDs) can have advantages and are widely used in clinical practice. However, a significant need exists to advance materials and fabrication technologies because of the unwanted health consequences associated with current RPDs. Purpose The purpose of this review was to assess the current state of and future need for prosthetics such as RPDs for patients with partial edentulism, highlight areas of weakness, and outline possible solutions to issues that affect patient satisfaction and the use of RPDs. Material and methods The data on treatment for partial edentulism were reviewed and summarized with a focus on currently available and future RPD designs, materials, means of production, and impact on oral health. Data on patient satisfaction and compliance with RPD treatment were also reviewed to assess patient-centered care. Results Design, materials, ease of repair, patient education, and follow-up for RPD treatment all had a significant impact on treatment success. Almost 40% of patients no longer use their RPD within 5 years because of factors such as sociodemographics, pain, and esthetics. Research on RPD-based treatment for partial edentulism for both disease-oriented and patient-centered outcomes is lacking. Conclusions Future trials should evaluate new RPD materials and design technologies and include both long-term follow-up and health-related and patient-reported outcomes. Advances in materials and digital design/production along with patient education promise to further the application of RPDs and improve the quality of life for patients requiring RPDs.

Mechanical and optical properties of monolithic CAD-CAM restorative materials.

Abstract: Statement of problem Achieving natural tooth appearance with sufficient mechanical strength is one of the most challenging issues of computer-assisted design and computer-assisted manufacturing (CAD-CAM) materials. However, limited evidence is available regarding their optical and mechanical properties for proper and evidence-based material selection in clinical practice. Purpose The purpose of this in vitro study was to assess and compare the translucency and biaxial flexural strength of 5 monolithic CAD-CAM restorative materials. Material and methods Disk-shaped specimens (n=30) of each material (Lava Ultimate [LU], Vita Enamic [VE], Vitablocs Mark II [VMII], Vita Suprinity [VS], and IPS e.max CAD [IPS]) with a diameter of 12 mm and a thickness of 1.2 ±0.05 mm were prepared. A spectrophotometer was used to measure the translucency parameter. The specimens were then subjected to a biaxial flexure test using 3 balls and loaded with a piston in a universal testing machine at a cross-head speed of 0.5 mm/min until failure occurred (International Organization for Standardization standard 6872). Weibull statistics were used to evaluate the characteristic strength and reliability of each material. Chemical compositions were analyzed using an energy dispersive spectrometer, and microstructural analysis was conducted using scanning electron microscopy. Data were analyzed using 1-way ANOVA and the Tukey honest significant difference test (α=.05). Results Significant differences were found among the materials concerning translucency and biaxial flexural strength ( P Conclusions Based on the results of the present study, zirconia-reinforced glass-ceramic revealed higher mean translucency and biaxial flexural strength than resin nanoceramic, feldspathic ceramic, lithium disilicate ceramic, and dual-network ceramic.

Mechanical properties and internal fit of 4 CAD-CAM block materials

Abstract: Statement of problem Recent polymer-based computer-assisted design and computer-assisted manufacturing (CAD-CAM) materials have been commercialized for inlay restorations, a polymer-infiltrated ceramic-network (PICN) and composite resin nanoceramics Little independent evidence regarding their mechanical properties exists Internal adaptation is an important factor for the clinical success and longevity of a restoration, and data concerning this parameter for inlays made with these blocks are scarce Purpose The purpose of this in vitro study was to evaluate and compare the mechanical properties (flexural strength, flexural modulus, Vickers hardness, fracture toughness) and the internal adaptation of these recent polymer-based blocks with a lithium disilicate glass-ceramic block Material and methods The materials tested in this study were a PICN material (Vita Enamic), 2 composite resin nanoceramics (Lava Ultimate; 3M ESPE and Cerasmart; GCDental Products), and a lithium disilicate glass-ceramic (IPS emax CAD) Mechanical properties were evaluated according to ISO norm DIS 6872:2013 Bar-shaped specimens (18×3×3 mm) were prepared and submitted to a 3-point bend test using a universal testing machine at a cross-head speed of 05 mm/min In addition, identical cavities were prepared in 60 human mandibular extracted molars (n=15) and optically scanned to receive mesioocclusodistal inlays milled with the 4 materials tested in a CEREC Inlab milling machine The replica technique and a stereomicroscope (×20) were used to measure the internal fit of the inlays at 9 preselected locations All data were statistically analyzed using 1-way ANOVA and the post hoc Tukey multiple comparison or Games-Howell test (α=05) Results The mean flexural strength of the tested blocks ranged from 1487 ±95 MPa (Vita Enamic) to 2165 ±283 MPa (Cerasmart) The mean flexural modulus ranged from 233 ±64 GPa (Vita Enamic) to 528 ±105 GPa (IPS emax CAD) The mean Vickers hardness ranged from 066 ±002 GPa (Cerasmart) to 598 ±069 GPa (IPS emax CAD) The mean fracture toughness ranged from 12 ±017 MPam 1/2 (Cerasmart) to 18 ±029 MPam 1/2 (IPS emax CAD) The values for internal discrepancy ranged from 119 ±55 μm to 234 ±51 μm The mean internal discrepancy was significantly higher for Lava Ultimate ( P P 2 =0941; P Conclusions The mechanical properties of the CAD-CAM block materials tested were within the acceptable range for fabrication of single restorations according to the ISO standard for ceramics (ISO 6872:2008) IPS emax CAD and Cerasmart were observed to have superior flexural strength and better internal fit

Comparison of retention between maxillary milled and conventional denture bases: A clinical study

Abstract: Statement of problem Clinical studies comparing the retention values of milled denture bases with those of conventionally processed denture bases are lacking. Purpose The purpose of this clinical study was to compare the retention values of conventional heat-polymerized denture bases with those of digitally milled maxillary denture bases. Material and methods Twenty individuals with completely edentulous maxillary arches participated in this study. Definitive polyvinyl siloxane impressions were scanned (iSeries; Dental Wings), and the standard tessellation language files were sent to Global Dental Science for the fabrication of a computer-aided design and computer-aided manufacturing (CAD-CAM) milled denture base (group MB) (AvaDent). The impression was then poured to obtain a definitive cast that was used to fabricate a heat-polymerized acrylic resin denture base resin (group HB). A custom-designed testing device was used to measure denture retention (N). Each denture base was subjected to a vertical pulling force by using an advanced digital force gauge 3 times at 10-minute intervals. The average retention of the 2 fabrication methods was compared using repeated ANOVA (α=.05). Results Significantly increased retention was observed for the milled denture bases compared with that of the conventional heat-polymerized denture bases ( P Conclusions The retention offered by milled complete denture bases from prepolymerized poly(methyl methacrylate) resin was significantly higher than that offered by conventional heat- polymerized denture bases.

Accuracy of CAD-CAM-fabricated removable partial dentures

Abstract: Statement of problem The conventional fabrication of removable partial dentures (RPDs) is a complex, error-prone, time-consuming, and expensive process. The use of computer-aided design and computer-aided manufacturing (CAD-CAM) techniques, especially rapid prototyping, promises a more effective method for fabricating RPD frameworks. Purpose The purpose of this in vitro study was to evaluate the fit of RPD clasps fabricated by means of 4 different CAD-CAM-systems and to compare those fittings with that of the conventional lost-wax casting technique (LWT). Material and methods A master model of a partially edentulous maxilla with the canines and second molars as the remaining teeth was fabricated. After the model was optically scanned, we designed a quadrangularly supported RPD with 4 clasps and a palatal strap major connector. A standard tessellation language data set was used to fabricate 12 identical RPDs by using 4 different CAD-CAM techniques: indirect rapid prototyping (wax inject printing combined with LWT), direct rapid prototyping (selective laser melting), indirect milling (wax milling with LWT), and direct milling (resin milling [polyetheretherketone]). Three conventionally cast RPDs (LWT) served as the control group. The fit accuracy of the clasps (n=12 for each group) was determined in both the horizontal and vertical dimensions by using light microscopy. Results Indirectly milled RPDs (117 ±34 μm horizontal and 45 ±21 μm vertical) and directly milled RPDs (43 ±23 μm horizontal, and 38 ±21 μm vertical) showed significantly better ( P Conclusions Compared with the LWT, milling techniques enabled fabrication of RPDs with comparable or better fit. However, RPDs fabricated with rapid prototyping techniques showed distinct fitting irregularities.

Accuracy of intraoral digital impressions using an artificial landmark

Abstract: Statement of problem Intraoral scanners have been reported to have limited accuracy in edentulous areas. Large amounts of mobile tissue and the lack of obvious anatomic landmarks make it difficult to acquire a precise digital impression of an edentulous area with an intraoral scanner. Purpose The purpose of this in vitro study was to determine the effect of an artificial landmark on a long edentulous space on the accuracy outcomes of intraoral digital impressions. Material and methods A mandibular model containing 4 prepared teeth and an edentulous space of 26 mm in length was used. A blue-light light-emitting diode tabletop scanner was used as a control scanner, and 3 intraoral scanners were used as experimental groups. Five scans were made using each intraoral scanner without an artificial landmark, and another 5 scans were performed after application of an artificial landmark (a 4×3 mm alumina material) on the edentulous area. The obtained datasets were used to evaluate trueness and precision. Results Without an artificial landmark on the edentulous area, the mean trueness for the intraoral scanner ranged from 36.1 to 38.8 μm and the mean precision ranged from 13.0 to 43.6 μm. With an artificial landmark on the edentulous area, accuracy was improved significantly: the mean trueness was 26.7 to 31.8 μm, and the mean precision was 9.2 to 12.4 μm. Conclusions The use of an alumina artificial landmark in an edentulous space improved the trueness and precision of the intraoral scanners tested.

Fit of interim crowns fabricated using photopolymer-jetting 3D printing.

Abstract: Statement of problem The fit of interim crowns fabricated using 3-dimensional (3D) printing is unknown. Purpose The purpose of this in vitro study was to evaluate the fit of interim crowns fabricated using photopolymer-jetting 3D printing and to compare it with that of milling and compression molding methods. Material and methods Twelve study models were fabricated by making an impression of a metal master model of the mandibular first molar. On each study model, interim crowns (N=36) were fabricated using compression molding (molding group, n=12), milling (milling group, n=12), and 3D polymer-jetting methods. The crowns were prepared as follows: molding group, overimpression technique; milling group, a 5-axis dental milling machine; and polymer-jetting group using a 3D printer. The fit of interim crowns was evaluated in the proximal, marginal, internal axial, and internal occlusal regions by using the image-superimposition and silicone-replica techniques. The Mann-Whitney U test and Kruskal-Wallis tests were used to compare the results among groups (α=.05). Results Compared with the molding group, the milling and polymer-jetting groups showed more accurate results in the proximal and marginal regions ( P P Conclusions Polymer-jet 3D printing significantly enhanced the fit of interim crowns, particularly in the occlusal region.

Machinability of CAD-CAM materials.

Abstract: Statement of problem Although new materials are available for computer-aided design and computer-aided manufacturing (CAD-CAM) fabrication, limited information is available regarding their machinability. The depth of penetration of a milling tool into a material during a timed milling cycle may indicate its machinability. Purpose The purpose of this in vitro study was to compare the tool penetration rate for 2 polymer-containing CAD-CAM materials (Lava Ultimate and Enamic) and 2 ceramic-based CAD-CAM materials (e.max CAD and Celtra Duo). Material and methods The materials were sectioned into 4-mm-thick specimens (n=5/material) and polished with 320-grit SiC paper. Each specimen was loaded into a custom milling apparatus. The apparatus pushed the specimens against a milling tool (E4D Tapered 2016000) rotating at 40 000 RPM with a constant force of 0.98 N. After a 6-minute timed milling cycle, the length of each milling cut was measured with image analysis software under a digital light microscope. Representative specimens and milling tools were examined with scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy. Results The penetration rate of Lava Ultimate (3.21 ±0.46 mm/min) and Enamic (2.53 ±0.57 mm/min) was significantly greater than that of e.max CAD (1.12 ±0.32 mm/min) or Celtra Duo (0.80 ±0.21 mm/min) materials. SEM observations showed little tool damage, regardless of material type. Residual material was found on the tools used with polymer-containing materials, and wear of the embedding medium was seen on the tools used with the ceramic-based materials. Edge chipping was noted on cuts made in the ceramic-based materials. Conclusions Lava Ultimate and Enamic have greater machinability and less edge chipping than e.max CAD and Celtra Duo.

An update on computer-engineered complete dentures: A systematic review on clinical outcomes.

Abstract: Statement of problem Reports on computer-engineered complete dentures (CECDs) continue to increase Systematic reviews on clinical outcomes and applications associated with CECDs are lacking in the literature Purpose The purpose of this systematic review was to determine the clinical outcomes and applications of CECDs Material and methods Electronic searches of the English literature from January 1984 to May 2016 were performed in MEDLINE and Cochrane databases, with the results enriched by hand searches and citation mining to address 2 relevant population intervention comparison outcome (PICO) questions: What are the clinical outcomes associated with CECDs? Are there specific applications and significant advantages for CECDs? Results A review of the selected articles on CECDs revealed significantly better retention and reduced clinical time for the milled CECDs compared with conventional complete dentures An advantage associated with CECDs is the possibility of electronically archiving data using digital technology for rapid fabrication Applications reported in the literature with CECDs were also identified Conclusions A positive trend was seen in the outcomes with CECDs, although patient selection might have also contributed to favorable outcomes Significantly reduced clinical time, improved retention, and digital archiving were the main advantages associated with CECDs

Influence of aging on flexural strength of translucent zirconia for monolithic restorations

Abstract: Statement of problem Concern has been raised with regard to the low-temperature degradation (LTD) of translucent yttria-stabilized tetragonal zirconia polycrystalline (Y-TZP) for monolithic zirconia restorations. Purpose The purpose of this in vitro study was to assess the LTD behavior of 4 commercially available translucent Y-TZP materials by accelerated aging specimens in steam at 134°C, 0.2 MPa. Material and Methods Thin bars (22×3×0.2 mm) of Y-TZP, including Katana ML (Kuraray Noritake Dental Inc), Katana HT13 (Kuraray Noritake Dental Inc), Prettau (Zirkonzahn), and BruxZir (Glidewell Laboratories) (n=30 for each group), were machined from sintered blocks. Control specimens were assessed in the nonaged condition. Artificially ageing (n=5 per group at 5, 50, 100, 150, and 200 hours) was conducted in steam at 134°C at 0.2 MPa. The specimens were characterized, tested in 4-point flexure, and the fracture surfaces were analyzed. The monoclinic-to-tetragonal (m/t) peak intensity ratio measured by x-ray diffraction was used to calculate the monoclinic phase fraction and monitor LTD. Linear regression with heteroscedasticity-consistent robust standard errors was used to test for the effect of LTD (aging time) on (σ f ) and m/t. The Spearman rank correlation coefficient was used to assess the relationship between σ f and monoclinic phase fraction (α=.05). Results Artificial aging resulted in LTD as shown by an increase in the monoclinic phase fraction for all specimens. After aging for 200 hours, the mean ±SD monoclinic phase fraction increased from 2.90 ±0.34% to 76.1 ±0.64% for Prettau, 2.69 ±0.18% to 76.0 ±0.26% for BruxZir, 4.6 ±0.19% to 35.8 ±0.80% for Katana HT13, and 3.57 ±0.35% to 33.2 ±1.1% for Katana ML (all P P P P =.45); and from 875 ±130 to 909 ±70 MPa ( P =.82) for Katana ML. The mean flexural strength values of Prettau and BruxZir decreased with an increase in the monoclinic phase with Spearman rank correlation coefficients of −0.80 ( P =.001) for Prettau and −0.63 ( P =.022) for BruxZir. No significant changes in flexural strength were measured for Katana ML or Katana HT13 ( P >.05). Conclusions The LTD of Y-TZP resulted in a significant decrease in flexural strength of Prettau and BruxZir, whereas Katana ML and Katana HT13 exhibited less LTD and no significant decrease in flexural strength.

Clinical marginal fit of zirconia crowns and patients’ preferences for impression techniques using intraoral digital scanner versus polyvinyl siloxane material

Abstract: Statement of problem The use of digital intraoral scanners is increasing; however, evidence of its precision in making crown impressions clinically remains scarce. Patients should also feel more comfortable with digital impressions, but only a few studies evaluating this subject have been performed. Purpose The purpose of this clinical study was to evaluate the marginal fit of monolithic zirconia crowns and patients' preferences for digital impressions versus polyvinyl siloxane (PVS) impressions. Material and methods Sixteen participants with indications for single molar crowns were included. After crown preparation, digital impressions by intraoral scanner and PVS impressions were made. The participants were asked to complete a 6-item questionnaire with a visual analog scale related to perceptions of each of the following topics: time involved, taste/smell, occlusal registration, size of impression tray/scanner, gag reflex, and overall preference. Computer-aided design and computer-aided manufacturing monolithic zirconia crowns were fabricated from both impressions. The crowns were evaluated intraorally, and a blinded examiner measured the marginal discrepancy of silicone replicas under a stereomicroscope. Intraexaminer reliability was evaluated by calculating the intraclass correlation coefficient. Data for patients' preferences and marginal discrepancies were analyzed using the paired t test (α=.05). Results Visual analog scale scores for digital impressions were statistically significantly higher than those for PVS impressions in every topic ( P P >.05). Conclusions No differences were found in the clinical marginal fit of zirconia crowns fabricated from either digital impressions compared with PVS impressions. Furthermore, patients' satisfaction with digital impressions was significantly higher than with conventional impressions.

Influence of abutment tooth geometry on the accuracy of conventional and digital methods of obtaining dental impressions.

Abstract: Statement of problem Direct (intraoral) and indirect (desktop) digital scanning can record abutment tooth preparations despite their geometry. However, little peer-reviewed information is available regarding the influence of abutment tooth geometry on the accuracy of digital methods of obtaining dental impressions. Purpose The purpose of this in vitro study was to evaluate the influence of abutment tooth geometry on the accuracy of conventional and digital methods of obtaining dental impressions in terms of trueness and precision. Material and methods Crown preparations with known total occlusal convergence (TOC) angles (−8, −6, −4, 0, 4, 8, 12, 16, and 22 degrees) were digitally created from a maxillary left central incisor and printed in acrylic resin. Each of these 9 reference models was scanned with a highly accurate reference scanner and saved in standard tessellation language (STL) format. Then, 5 conventional polyvinyl siloxane (PVS) impressions were made from each reference model, which was poured with Type IV dental stone scanned using both the reference scanner (group PVS) and the desktop scanner and exported as STL files. Additionally, direct digital impressions (intraoral group) of the reference models were made, and the STL files were exported. The STL files from the impressions obtained were compared with the original geometry of the reference model (trueness) and within each test group (precision). Data were analyzed using 2-way ANOVA with the post hoc least significant difference test (α=.05). Results Overall trueness values were 19.1 μm (intraoral scanner group), 23.5 μm (desktop group), and 26.2 μm (PVS group), whereas overall precision values were 11.9 μm (intraoral), 18.0 μm (PVS), and 20.7 μm (desktop). Simple main effects analysis showed that impressions made with the intraoral scanner were significantly more accurate than those of the PVS and desktop groups when the TOC angle was less than 8 degrees ( P P =.002). Visual analysis revealed that the intraoral scanner group showed a homogeneous deviation pattern across all TOC angles tested, whereas scans from the PVS and desktop scanner groups showed marked local deviations when undercuts (negative angles) were present. Conclusions Conventional dental impressions alone or those further digitized with an extraoral digital scanner cannot reliably reproduce abutment tooth preparations when the TOC angle is close to 0 degrees. In contrast, digital impressions made with intraoral scanning can accurately record abutment tooth preparations independently of their geometry.

A comparative study of additive and subtractive manufacturing for dental restorations.

Abstract: Statement of problem Digital systems have recently found widespread application in the fabrication of dental restorations. For the clinical assessment of dental restorations fabricated digitally, it is necessary to evaluate their accuracy. However, studies of the accuracy of inlay restorations fabricated with additive manufacturing are lacking. Purpose The purpose of this in vitro study was to evaluate and compare the accuracy of inlay restorations fabricated by using recently introduced additive manufacturing with the accuracy of subtractive methods. Material and methods The inlay (distal occlusal cavity) shape was fabricated using 3-dimensional image (reference data) software. Specimens were fabricated using 4 different methods (each n=10, total N=40), including 2 additive manufacturing methods, stereolithography apparatus and selective laser sintering; and 2 subtractive methods, wax and zirconia milling. Fabricated specimens were scanned using a dental scanner and then compared by overlapping reference data. The results were statistically analyzed using a 1-way analysis of variance (α=.05). Additionally, the surface morphology of 1 randomly (the first of each specimen) selected specimen from each group was evaluated using a digital microscope. Results The results of the overlap analysis of the dental restorations indicated that the root mean square (RMS) deviation observed in the restorations fabricated using the additive manufacturing methods were significantly different from those fabricated using the subtractive methods ( P P =.466). Similarly, no significant differences were found between wax and zirconia, the subtractive methods ( P =.986). The observed RMS values were 106 μm for stereolithography apparatus, 113 μm for selective laser sintering, 116 μm for wax, and 119 μm for zirconia. Microscopic evaluation of the surface revealed a fine linear gap between the layers of restorations fabricated using stereolithography apparatus and a grooved hole with inconsistent weak scratches when fabricated using selective laser sintering. In the wax and zirconia restorations, possible traces of milling bur passes were observed. Conclusions The results indicate that the accuracy of dental restorations fabricated using the additive manufacturing methods is higher than that of subtractive methods. Therefore, additive manufacturing methods are a viable alternative to subtractive methods.

Influence of object translucency on the scanning accuracy of a powder-free intraoral scanner: A laboratory study

Abstract: Statement of problem Limited information is available regarding the influence of object translucency on the scanning accuracy of a powder-free intraoral scanner. Purpose The purpose of this in vitro study was to evaluate the scanning accuracy of a confocal microscopy principle powder-free intraoral scanner on ceramic copings and to analyze the relationship between scanning accuracy and object translucency. Methods Six slice specimens (12×10 mm) and 6 offset copings (1.00-mm thickness) were made from different translucent homogeneous ceramic blocks (CEREC Blocs, S0-M to S5-M, highest to lowest translucency). The primary sintered zirconia offset coping was produced in the same way as the control. Optical parameters related to the translucency of each slice were measured with a spectrophotometer. Three-dimensional (3D) datasets of the surface morphology of offset copings were obtained by using the intraoral scanner. The same white wax resin bases were used for registration. Quantitative parameters of scanning trueness and precision were measured. One-way ANOVA was used to analyze the values of each parameter among the 6 ceramic blocks. Bivariate correlation was used to analyze the relationships between each parameter of scanning accuracy and translucency (α=.05). Results Translucent copings showed a positive 3D bias (S0-M to S5-M: 0.149 ±0.038 mm to 0.068 ±0.020 mm), a narrower collar diameter (Dd=−0.067 mm), larger convergence angle (ΔΦ=2.79 degrees), and larger curvature radius of the internal gingivoaxial corner (Δρ=0.236 mm). The smaller the percentage sum of scattering and absorption, the greater was the occurrence of scanning bias (r=−0.918) and curvature (r=−0.935) decrease. Conclusions Use of the tested powder-free intraoral scanner, higher translucency objects (greater translucency than S1-M/A1C) resulted in lower scanning accuracy and morphological changes. Therefore, more suitable methods of measurement are still required.

Effect of different restorative crown and customized abutment materials on stress distribution in single implants and peripheral bone: A three-dimensional finite element analysis study

Abstract: Statement of problem In recent years, the use of resin-matrix ceramics and polyetheretherketone (PEEK) abutments has been suggested to absorb excessive stresses on dental implants. However, only a few studies have evaluated the effect of these materials on stress distribution in implants and peripheral bone structure. Purpose The purpose of this finite element analysis was to evaluate the biomechanical behaviors of resin-matrix ceramics and PEEK customized abutments in terms of stress distribution in implants and peripheral bone. Material and methods Three-dimensional (3D) models of a bone-level implant system and a titanium base abutment were created by using the standard tessellation language (STL) data of original implant components. An anatomic customized abutment and a maxillary right second premolar crown were then modeled over the titanium base abutment. A bone block representing the maxillary right premolar area was created, and the implant was placed in the bone block with 100% osseointegration. Six different models were created according to combinations of restoration materials (translucent zirconia [TZI], lithium disilicate glass ceramic [IPS], polymer-infiltrated hybrid ceramic [VTE]), and customized abutment materials (PEEK and zirconia). In each model, the implants were loaded vertically (200 N) and obliquely (100 N). The stress distribution in the crown, implant, and abutments was evaluated through the von Mises stress analysis, and the stress distribution in the peripheral bone was examined through the maximum and minimum principal stress analyses. Results The oblique load resulted in high stress values in the implant components, restorative crown, and cortical bone. Low stress values were observed in the VTE crowns. Zirconia customized abutments exhibited higher stress values than PEEK customized abutments. The stress distributions in the implant and peripheral bone were similar in all models. Conclusions Changes in restoration and customized abutment material did not affect stress distribution in the implant and peripheral bone.

A digital approach integrating facial scanning in a CAD-CAM workflow for complete-mouth implant-supported rehabilitation of patients with edentulism: A pilot clinical study

Abstract: Statement of problem Complete-mouth implant-supported rehabilitations are challenging because of the multiple surgical and prosthetic steps involved in clinical evaluations to assure passive prosthesis fit and optimal esthetic and functional outcomes As a result, these rehabilitations are usually associated with substantial clinical time, patient discomfort, and high treatment cost Purpose The purpose of this pilot clinical study was to evaluate a novel digital approach integrating digital intraoral dental and extraoral facial scanning information to design and mill a computer-aided design and computer-aided manufacturing (CAD-CAM) implant-retained prosthesis for patients with complete edentulism Material and methods Ten patients in need of complete-mouth rehabilitation were included in this pilot study Digital intraoral records were obtained through optical scanning the duplicate interim prosthesis using a laboratory scanner, while digital extraoral records were obtained through facial scanning using an in-office scanner The scanned impressions and occlusal records were used to create a virtual tooth arrangement, which was matched to the patient’s 3-dimensional face scan to create a virtual clinical evaluation phase After applying the necessary adjustments, the virtual arrangement was submitted to a CAM procedure where a 5-axis industrial milling machine was used to fabricate an interim prosthesis Results Digital intraoral and extraoral records were integrated and used to fabricate CAD-CAM milled interim prostheses, which were inserted and assessed for clinical fit, occlusion/articulation, and esthetics The prostheses remained in function for at least 6 months with no notable technical or biological complications except for 1 prosthesis that fractured Conclusions A novel digital workflow incorporating facial scanning in a CAD-CAM workflow was used to fully digitally design and mill 10 implant-retained interim prostheses More research is required to further develop and assess the accuracy and applicability of this approach

Digital versus conventional implant impressions for partially edentulous arches: An evaluation of accuracy

Abstract: Statement of problem To the authors' knowledge, while accuracy outcomes of the TRIOS scanner have been compared with conventional impressions, no available data are available regarding the accuracy of digital scans with the Omnicam and True Definition scanners versus conventional impressions for partially edentulous arches. Purpose The purpose of this in vitro study was to compare the accuracy of digital implant scans using 2 different intraoral scanners (IOSs) with that of conventional impressions for partially edentulous arches. Material and methods Two partially edentulous mandibular casts with 2 implant analogs with a 30-degree angulation from 2 different implant systems (Replace Select RP; Nobel Biocare and Tissue level RN; Straumann) were used as controls. Sixty digital models were made from these 2 definitive casts in 6 different groups (n=10). Splinted implant-level impression procedures followed by digitization were used to produce the first 2 groups. The next 2 groups were produced by digital scanning with Omnicam. The last 2 groups were produced by digital scanning with the True Definition scanner. Accuracy was evaluated by superimposing the digital files of each test group onto the digital file of the controls with inspection software. Results The difference in 3-dimensional (3D) deviations (median ±interquartile range) among the 3 impression groups for Nobel Biocare was statistically significant among all groups ( P P =.003), except for the conventional impression (22 ±5 μm) and True Definition (17 ±5 μm) groups; the median ±interquartile range for the Omnicam group was 26 ±15 μm. The difference in 3D deviations between the 2 implant systems was significant for the Omnicam ( P =.011) and conventional ( P P =.247). Conclusions Within the limitations of this study, both the impression technique and the implant system affected accuracy. The True Definition technique had the fewest 3D deviations compared with the other 2 techniques; however, the accuracy of all impression techniques was within clinically acceptable levels, and not all differences were statistically significant.

Patient outcomes and procedure working time for digital versus conventional impressions: A systematic review

Abstract: Statement of problem Limited evidence is available comparing digital versus conventional impressions from the point of view of patient preference. Purpose The purpose of this systematic review was to identify and summarize the available literature related to patient-centered outcomes for digital versus conventional impression techniques. Material and methods The databases Medline, Cochrane, Science Direct, Scopus, and Embase were electronically searched and complemented by hand searches. All published papers available on the databases from 1955 to July 2016 were considered for title and abstract analysis. Results A total of 2943 articles were initially identified through database searches, of which only 5 met the inclusion criteria for qualitative analysis. Four studies comparing patient-reported outcome measures (PROMs) between conventional and digital impressions revealed that the digital technique was more comfortable and caused less anxiety and sensation of nausea. Only 1 study reported no difference between the techniques regardless of patient comfort. Two studies reported a shorter procedure for the conventional technique, whereas 3 studies reported a shorter procedure for the digital technique. Conclusions A lack of clinical studies addressing patient outcomes regarding digital prosthodontic treatments was observed among the included articles. However, current evidence suggests that patients are more likely to prefer the digital workflow than the conventional techniques.

Effect of different treatments on the flexural strength of fully versus partially stabilized monolithic zirconia.

Abstract: Statement of problem Recent monolithic zirconia materials used for indirect restorations are predominantly fully stabilized zirconia with claims of enhanced optical properties. These restorations may behave differently from the conventional partially stabilized zirconia restorations, which may negatively affect some of the core properties required for restoration success. Purpose The purpose of this in vitro study was to evaluate and compare the effects of staining, airborne-particle abrasion, and artificial aging on the flexural strength of fully and partially stabilized zirconia material. Material and methods Each partially stabilized monolithic zirconia (PSZ) and fully stabilized zirconia (FSZ) material and a zirconia core material (control) were prepared as bar-shaped specimens (2×2×25 mm) and divided into 6 groups (n=8/subgroup): regular sintering, vacuum sintering, stained, airborne-particle abrasion, artificially aged regular sintering, and artificially aged vacuum sintering. Critical load to fracture was determined for all groups by using monotonic uniaxial loading in accordance with International Organization for Standardization standard 6872. Data were analyzed using univariate analysis of variance, followed by the Tukey honest significant difference post hoc test (α=.05). Results The control and PSZ (1034 and 1008 MPa) displayed a significantly higher (P Conclusions Fully stabilized zirconia may behave differently from conventional PSZ, especially with regard to airborne-particle abrasion, which may weaken the FSZ. The strength of PSZ is approximately double the strength of FSZ. Both of the zirconia materials showed resistance to artificial aging.

Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part III: marginal and internal fit

Abstract: Statement of problem Trials comparing the overall performance of digital with that of conventional workflows in restorative dentistry are needed. Purpose The purpose of the third part of a series of investigations was to test whether the marginal and internal fit of monolithic crowns fabricated with fully digital workflows differed from that of crowns fabricated with the conventional workflow. Material and methods In each of 10 participants, 5 monolithic lithium disilicate crowns were fabricated for the same abutment tooth according to a randomly generated sequence. Digital workflows were applied for the fabrication of 4 crowns using the Lava, iTero, Cerec inLab, and Cerec infinident systems. The conventional workflow included a polyvinyl siloxane impression, manual waxing, and heat-press technique. The discrepancy between the crown and the tooth was registered using the replica technique with polyvinyl siloxane material. The dimensions of the marginal discrepancy (Discrepancy marginal ) and the internal discrepancy in 4 different regions of interest (Discrepancy shoulder , Discrepancy axial , Discrepancy cusp , and Discrepancy occlusal ) were assessed using light microscopy. Post hoc Student t test with Bonferroni correction was applied to detect differences (α=.05). Results Discrepancy marginal was 83.6 ±51.1 μm for the Cerec infinident, 90.4 ±66.1 μm for the conventional, 94.3 ±58.3 μm for the Lava, 127.8 ±58.3 μm for the iTero, and 141.5 ±106.2 μm for the Cerec inLab workflow. The differences between the treatment modalities were not statistically significant ( P >.05). Discrepancy shoulder was 82.2 ±42.4 μm for the Cerec infinident, 97.2 ±63.8 μm for the conventional, 103.4 ±52.0 μm for the Lava, 133.5 ±73.0 μm for the iTero, and 140.0 ±86.6 μm for the Cerec inLab workflow. Only the differences between the Cerec infinident and the Cerec inLab were statistically significant ( P =.036). The conventionally fabricated crowns revealed significantly lower values in Discrepancy cusp and Discrepancy occlusal than all the crowns fabricated with digital workflows ( P Conclusions In terms of marginal crown fit, no significant differences were found between the conventional and digital workflows for the fabrication of monolithic lithium disilicate crowns. In the occlusal regions, the conventionally manufactured crowns revealed better fit than the digitally fabricated crowns. Chairside milling resulted in less favorable crown fit than centralized milling production.

Facially generated and cephalometric guided 3D digital design for complete mouth implant rehabilitation: A clinical report.

Abstract: Harmony among the teeth, lips, and facial components is the goal of prosthodontic treatment, whether performed by conventional or digital workflow methods. This clinical report describes a facial approach to planning computer-guided surgery and immediate computer-aided designed and computer-aided manufactured (CAD-CAM) interim complete-arch fixed dental prostheses on immediately placed dental implants with a digital workflow. A single clinical appointment for data collection included dentofacial documentation with photographs and videos. On these photographs, facial reference lines were drawn to create a smile frame. This digital smile design and sagittal cephalometric analysis were merged with 3-dimensional scanned casts and a cone beam computed tomographic file in virtual planning software, thus guiding virtual waxing and implant positioning. Computer-guided implant surgery and CAD-CAM interim dental prostheses allowed esthetic and functional rehabilitation in a predictable manner and integrated with the patient's face.

Integrating a facial scan, virtual smile design, and 3D virtual patient for treatment with CAD-CAM ceramic veneers: A clinical report

Abstract: This clinical report describes a digital workflow using the virtual smile design approach augmented with a static 3-dimensional (3D) virtual patient with photorealistic appearance to restore maxillary central incisors by using computer-aided design and computer-aided manufacturing (CAD-CAM) monolithic lithium disilicate ceramic veneers.

A microcomputed tomography evaluation of the marginal fit of cobalt-chromium alloy copings fabricated by new manufacturing techniques and alloy systems

Abstract: Statement of problem Although new digital manufacturing techniques are attracting interest in dentistry, few studies have comprehensively investigated the marginal fit of fixed dental prostheses fabricated with such techniques. Purpose The purpose of this in vitro microcomputed tomography (μCT) study was to evaluate the marginal fit of cobalt-chromium (Co-Cr) alloy copings fabricated by casting and 3 different computer-aided design and computer-aided manufacturing (CAD-CAM)-based processing techniques and alloy systems. Material and methods Single Co-Cr metal crowns were fabricated using 4 different manufacturing techniques: casting (control), milling, selective laser melting, and milling/sintering. Two different commercial alloy systems were used for each fabrication technique (a total of 8 groups; n=10 for each group). The marginal discrepancy and absolute marginal discrepancy of the crowns were determined with μCT. For each specimen, the values were determined from 4 different regions (sagittal buccal, sagittal lingual, coronal mesial, and coronal distal) by using imaging software and recorded as the average of the 4 readings. For each parameter, the results were statistically compared with 2-way analysis of variance and appropriate post hoc analysis (using Tukey or Student t test) ( α =.05). Results The milling and selective laser melting groups showed significantly larger marginal discrepancies than the control groups (70.4 ±12.0 and 65.3 ±10.1 μm, respectively; P P =.004). The milling groups showed significantly larger absolute marginal discrepancy than the control groups (137.4 ±29.0 and 139.2 ±18.9 μm, respectively; P P P =.935) or smaller ( P Conclusions The findings of this in vitro μCT study showed that the marginal fit values of the Co-Cr alloy greatly depended on the fabrication methods and, occasionally, the alloy systems. Fixed dental prostheses produced by using the milling/sintering technique can be considered clinically acceptable in terms of marginal fit.

Effects of the type and thickness of ceramic, substrate, and cement on the optical color of a lithium disilicate ceramic.

Abstract: Statement of problem Reproducing the characteristics of natural teeth in ceramic crowns remains a complex and difficult process. Purpose The purpose of this in vitro study was to evaluate the effect of the substrate, cement, type, and thickness of the ceramic on the resulting color of a lithium disilicate ceramic. Material and methods Forty ceramic disks were prepared from IPS e.max Press LT (low translucency) and HO (high opacity) in 2 different thicknesses (1.5 and 2 mm). The LT groups were composed of monolithic ceramic disks, and the HO groups were composed of disks fabricated with a 0.5-mm thickness combined with a 1- or 1.5-mm veneering ceramic thickness. Disks made of composite resin (R) and alloy (A) were used as substrate structures. The resin cement used was Variolink II. Color was measured with a spectrophotometer and expressed in CIELAB coordinates. Color differences (ΔE) were calculated. The data were analyzed with ANOVA and the Tukey HSD test (α=.05). Results When the ΔE of ceramic disks with both substrates, with and without cement, were compared, the lowest value (3) was obtained for ceramic HO with a 2-mm thickness/alloy substrate/without cement; the highest value (10) was obtained for ceramic LT with a1.5-mm thickness/alloy substrate/with cement. This difference was statistically significant. When the effect of cement on the ΔE of ceramics in both substrates was compared, the lowest value (1.1) occurred with ceramic HO with a 1.5-mm thickness/resin substrate, and the highest was observed for ceramic LT with a 1.5-mm thickness/alloy substrate (6.4). This difference was statistically significant. Conclusions The substrate color, type and thickness of ceramic, and presence of the cement significantly influenced the resulting optical color. The ΔE values of cemented HO ceramics were lower than that of the LT ceramic.

Influence of remaining tooth structure and restorative material type on stress distribution in endodontically treated maxillary premolars: A finite element analysis.

Abstract: Statement of problem How tooth preparation and material type affect the stress distribution of endodontically treated teeth restored with endocrowns remains unclear Purpose The purpose of this finite element (FE) study was to determine the influence of the quantity of remaining dental tissues and material type on stress distribution in endodontically treated maxillary premolars using 3-dimensional FE analysis Material and methods Five 3-dimensional FE models were constructed on the basis of the restorative methods used and the quantity of preserved tooth tissues: a sound maxillary premolar, an endodontically treated maxillary premolar restored with composite resin, and endodontically treated maxillary premolars restored with endocrowns with thicknesses of 10 mm, 20 mm, and 30 mm The following endocrown materials were used: Paradigm MZ100, IPS Empress, IPS emax CAD, and In-Ceram Zirconia Stress distributions were analyzed under vertical and oblique loads Results As the quantity of preserved dental tissues increased, the von Mises stress in dentin decreased, and the peak von Mises strain value of the cement layer increased When the elastic modulus of the endocrown material increased, the von Mises stress in endocrown and dentin increased, and the peak von Mises strain value of the cement layer decreased Conclusions Although the conservative preparation of teeth for endocrowns is likely to protect the residual tooth structure, it may cause future cohesive bonding failure An increase in the elastic modulus of the material may benefit the durability of bonding between the endocrown and the abutment tooth; however, it may cause fracture of the residual tooth structure

Survival of 2039 complete arch fixed implant-supported zirconia prostheses: A retrospective study.

Abstract: Statement of problem Presently, data for the survival of 1-piece complete arch fixed implant-supported zirconia prostheses are limited. Purpose The purpose of this retrospective study was to evaluate the survival outcomes of 1-piece complete arch fixed implant-supported zirconia prostheses fabricated by a single dental laboratory supporting several clinicians. Material and methods Outcome data were collected over a 5-year period from a large commercial dental laboratory that fabricated 2039 1-piece complete arch fixed implant-supported monolithic zirconia prostheses. All prostheses were fabricated using the same zirconia system from 1 manufacturer, using standardized protocols. The zirconia prostheses were predominantly monolithic, with veneered porcelain restricted to the gingival region. Because a 5-year warranty against fracture was offered by this dental laboratory, prostheses that were returned to the laboratory for remake because of catastrophic failure (fracture) or technical complications were identified, and data were analyzed using a life table. Results Of the 2039 zirconia prostheses evaluated, at least 319 prostheses had a minimum of 3 years of clinical service, and 69 prostheses had a minimum of 4 years of clinical service. A total of 6 fractures were reported, resulting in a first-year interval survival rate of 99.8% and a 5-year cumulative survival rate of 99.3%. Six zirconia prostheses were returned to the laboratory during the 5-year period because of technical complications related to the debonding of titanium cylinders, and 3 prostheses were returned because of fracture of the titanium cylinders. No prostheses were returned because of chipping of the veneered gingival porcelain. Conclusions Practice-based evidence from this large sample, short-term retrospective study showed that 1-piece complete arch fixed implant-supported zirconia prostheses with veneered porcelain restricted to the gingival region showed a cumulative survival rate of 99.3% in a 5-year period. The technical complication rate related to this type of prosthesis was minimal.

Effect of coloring and sintering on the translucency and biaxial strength of monolithic zirconia

Abstract: Statement of problem The influences of coloring and sintering procedures on the optical and mechanical properties of monolithic zirconia have not been thoroughly investigated. Purpose The purpose of this in vitro study was to investigate the effects of the coloring procedure and of varying final sintering temperatures on the translucency parameter (TP) and biaxial flexural strength (BFS) of monolithic zirconia. Material and methods Disk-shaped specimens (N=210) of 2 different monolithic zirconia brands (Vita YZ HT White [VYZa]; Vita YZ HT Color A2 [VYZb]; Prettau Zirkonzahn [PZ]; Prettau Anterior Zirkonzahn [PZA]) with a diameter of 15 mm and a thickness of 1.0 ±0.05 mm were prepared. Half of the specimens prepared from noncolored blocks (VYZa, PZ, and PZA) received coloring liquid application. Then, the specimens were divided into 3 subgroups (n=10) according to the final sintering temperatures (1350°C, 1450°C, and 1600°C). The TP was determined by using a reflection spectrophotometer, and the BFS was tested with the piston-on-3-ball method in a universal testing machine. Data were statistically analyzed by multivariate multiple regression and Bonferroni tests (α=.05). Results Significant differences were obtained among the groups based on the results of the TP and BFS ( P P P >.05). Conclusions Increased sintering temperature leads to increased translucency with minimal impact on the BFS. The coloring procedure should be considered at the time of material selection to avoid possible reduction in translucency.