Computer-aided Design And Computer-aided Manufacturing System Research Articles

Development of ZTA (80% Al2O3/20% ZrO2) pre-sintered blocks for milling in CAD/CAM systems

The present work aims to develop a production method of pre-sintered zirconia-toughened-alumina (ZTA) composite blocks for machining in a computer-aided design and computer-aided manufacturing (CAD-CAM) system. The ZTA composite comprised of 80% Al2O3 and 20% ZrO2 was synthesized, uniaxially and isostatically pressed to generate machinable CAD-CAM blocks. Fourteen green-body blocks were prepared and pre-sintered at 1000 °C. After cooling and holder gluing, a stereolithography (STL) file was designed and uploaded to manufacture disk-shaped specimens projected to comply with ISO 6872:2015. Seventy specimens were produced through machining of the blocks, samples were sintered at 1600 °C and two-sided polished. Half of the samples were subjected to accelerated autoclave hydrothermal aging (20h at 134 °C and 2.2 bar). Immediate and aged samples were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Optical and mechanical properties were assessed by reflectance tests and by biaxial flexural strength test, Vickers indentation and fracture toughness, respectively. Samples produced by machining presented high density and smooth surfaces at SEM evaluation with few microstructural defects. XRD evaluation depicted characteristic peaks of alpha alumina and tetragonal zirconia and autoclave aging had no effect on the crystalline spectra of the composite. Optical and mechanical evaluations demonstrated a high masking ability for the composite and a characteristic strength of 464 MPa and Weibull modulus of 17, with no significant alterations after aging. The milled composite exhibited a hardness of 17.61 GPa and fracture toughness of 5.63 MPa m1/2, which remained unaltered after aging. The synthesis of ZTA blocks for CAD-CAM was successful and allowed for the milling of disk-shaped specimens using the grinding method of the CAD-CAM system. ZTA composite properties were unaffected by hydrothermal autoclave aging and present a promising alternative for the manufacture of infrastructures of fixed dental prostheses.

Effect of resin cement selection on fracture resistance of chairside CAD-CAM lithium disilicate crowns containing virgilite: A comparative in vitro study

Studies on the fracture performance of a recently introduced computer-aided design and computer-aided manufacturing (CAD-CAM) lithium disilicate ceramic containing virgilite with different cements are lacking. The purpose of this in vitro study was to evaluate the fracture resistance of crowns made of a recently introduced chairside CAD-CAM lithium disilicate containing virgilite cemented with different types of adhesive luting cement. Sixty complete coverage crowns for a maxillary right central incisor were milled out of a lithium disilicate with virgilite (CEREC Tessera) (n=48) and a traditional lithium disilicate (e.max CAD) (n=12) using a chairside CAD-CAM system (Primescan). The central incisor tooth preparation included a 1.5-mm incisal reduction, a 1.0-mm axial reduction, and a 1.0-mm chamfer finish line. The restorations were bonded with different types of resin cement to 3D printed dies of the tooth preparation and were divided into 5 groups (n=12 per group): e.max CAD with Multilink Automix (E.Mu); Tessera with Multilink Automix (T.Mu); Tessera with Calibra (T.Ca); Tessera with Unicem (T.Un); and Tessera with Speedcem (T.Sp). The cemented restorations were stored in water for 30 days and then loaded until they were fractured in compression. The load at fracture was analyzed with a 1-way analysis of variance (ANOVA) and the honestly significant difference (HSD) Tukey test (α=.05). The mean fracture resistance of traditional lithium disilicate and virgilite lithium disilicate anterior crowns significantly differed depending on the type of resin cement used (P<.05). Group E.Mu displayed the highest values (946.35 ±155N), followed by group T.Un (819.59 ±232N), group T.Sp (675.52 ±153N), and group T.Mu (656.95 ±193N). The lowest values were displayed by group T.Ca (567.94 ±184N). The fracture resistance of lithium disilicate containing virgilite and traditional lithium disilicate crowns cemented with the same cement displayed statistically similar values. However, significant differences were observed when the virgilite lithium disilicate crowns were cemented with different types of adhesive luting cement. The crowns in the T.Ca group displayed the lowest fracture resistance.

Effect of the CAD-CAM and lost-wax framework fabrication techniques on the fracture strength of porcelain in metal-ceramic restorations.

Ceramic fracture is a common problem in metal-ceramic restorations (MCRs). The advent of computer-aided design and computer-aided manufacturing (CAD-CAM) technology eliminated the lost-wax technique, which was responsible for many of the problems associated with framework fabrication. However, the role of the CAD-CAM technology in decreasing porcelain fracture is not yet known. The aim of the present in vitro study was to compare the fracture strength of porcelain in MCRs with metal frameworks fabricated with the use of the lost-wax and CAD-CAM techniques. Twenty metal dies were prepared with a deep chamfer finish line, with a depth of 1.2 mm and the occlusal taper of the walls of 8°, a 2-millimeter occlusal reduction of the functional cusp, a 1.5-millimeter occlusal reduction of the nonfunctional cusp, and the functional cusp bevel. Ten frameworks were fabricated using the CAD-CAM system and 10 with the lost-wax technique. After porcelain veneering, the specimens underwent thermocycling and cyclic loading to simulate the aging process. The load test was then performed. The fracture strength of porcelain was compared between the 2 groups, and the mode of failure was also determined using a stereomicroscope. Two specimens were excluded from the CAD-CAM group. Thus, 18 specimens were statistically analyzed. The results revealed no significant difference in fracture strength between the 2 groups (p > 0.05). The mode of failure was mixed in all specimens from both groups. Our results indicated that the fracture strength of porcelain and the mode of failure did not depend on the metal framework fabrication technique (lost-wax or CAD-CAM).

Evaluation of marginal and internal fit of single crowns manufactured with an analog workflow and three CAD-CAM systems: A prospective clinical study.

This prospective clinical study evaluated and compared the marginal and internal fit of crowns fabricated with an analog workflow and three different computer-aided design and computer-aided manufacturing (CAD-CAM) systems. Twenty-five participants in need of a single complete-coverage molar or premolar crown were recruited in the study. Twenty-two completed the study, and three participants dropped out. Teeth were prepared according to a standardized protocol by one operator. For each participant, one final impression was made with polyether material (PP) and three intraoral scanners: CEREC Omnicam (C), Planmeca Planscan (PM), and True Definition (TR). For the PP group, crowns were fabricated with a pressable lithium disilicate ceramic, whereas for the other three groups (C, PM, and TR), crowns were designed and milled with dedicated CAD-CAM systems and materials. Marginal (vertical and horizontal) and internal discrepancies between the crowns and tooth preparation were measured at various locations with digital superimposition software. Data was analyzed for normality with Kolmogorov-Smirnov and Shapiro-Wilk tests and then compared with one-way ANOVA and Kruskal-Wallis tests. Mean vertical marginal gap values were 92.18±141.41μm (PP), 150.12±138.06μm (C), 129.07±109.96μm (PM), and 135.09±112.03μm (TR). PP group had statistically significantly smaller vertical marginal discrepancy (p=0.001) than all other groups, whereas no significant difference was detected among the three CAD-CAM systems (C, PM, and TR). Horizontal marginal discrepancies were 104.93±111.96μm (PP), 89.49±119.66μm (C), 113.36±128.49μm (PM), and 136.39±142.52μm (TR). A significant difference was detected only between C and TR (p<0.0001). Values for the internal fit were 128.40±49.31μm (PP), 190.70±69.79μm (C), 146.30±57.70μm (PM), and 168.20±86.67μm (TR). The PP group had a statistically significant smaller internal discrepancy than C (p<0.0001) and TR groups (p=0.001), whereas no significant difference was found compared to the PM group. Posterior crowns fabricated with CAD-CAM systems showed vertical margin discrepancy greater than 120μm. Only crowns fabricated with the conventional methodology had vertical margins below 100μm. Horizontal marginal discrepancy was different among all groups, and only CEREC CAD-CAM was below 100μm. Internal discrepancy was less for crowns fabricated with an analog workflow.

Evaluation of ridge lap accuracy and adaptation of the diagnostic tooth arrangement fabricated with CAD-CAM systems: An in vitro study

Statement of problemDigital light processing (DLP) and milling (MIL) are computer-aided design and computer-aided manufacturing (CAD-CAM) systems that have become popular for fabricating definitive complete dentures. However, few studies have compared the accuracy of the ridge laps of diagnostic tooth arrangements fabricated with these systems and their adaptation with the denture base sockets. PurposeThe purpose of this in vitro study was to comparatively analyze the accuracy of the ridge laps of the diagnostic tooth arrangements fabricated by using MIL and different layer thicknesses in DLP. Material and methodsA virtual definitive complete denture was designed with a CAD software program on a scanned virtual digital cast, divided into diagnostic tooth arrangement and a denture base that accommodated the arrangement, and saved as a standard tessellation language (STL) file. From this file, 27 diagnostic tooth arrangements were fabricated by DLP (50 μm and 100 μm) and MIL. The ridge laps were scanned and overlapped on the file (reference data) to analyze the accuracy (trueness and precision). The ridge laps of all groups were overlapped on the reference denture base data to analyze their adaptation with the sockets. The measurements of the trueness, precision, and adaptation were analyzed statistically by using the nonparametric Kruskal-Wallis test and post hoc Mann-Whitney U test with Bonferroni correction. ResultsThe diagnostic tooth arrangements showed significant differences among the groups (P<.001). The values were the lowest in the MIL group and highest in the DLP group for the following parameters: trueness root-mean-square (RMS) value, 173 ±7 μm versus 286 ±15 μm; precision RMS value, 22 ±3 μm versus 57 ±20 μm; and adaptation RMS value, 41 ±5 μm versus 112 ±13 μm. ConclusionsOf the 2 diagnostic tooth arrangements fabricated with the CAD-CAM systems, the one fabricated with MIL was clinically more appropriate.

Volumetric and dimensional accuracy assessment of CAD-CAM–manufactured dental prostheses from different materials

Statement of problemIn computer-aided design and computer-aided manufacturing (CAD-CAM) dentistry, the CAD of the prosthesis represents the clinical prerequisite design to restore the treated tooth. However, how closely the CAM prosthesis shape matches the CAD, particularly in relation to different materials, is unclear. PurposeThe purpose of this in vitro study was to evaluate onlays designed and manufactured with the same CAD-CAM system but manufactured with different materials. Material and methodsA single standard tessellation language (STL) model was used to produce 6 composite resin onlays, 6 leucite glass-ceramic onlays, and 6 lithium disilicate glass-ceramic onlays. The onlays were digitized by using an X-ray microtomographic protocol with a metrological calibration. The CAD model was then compared with the scans of the different onlays. An analysis by region of interest was then carried out to assess the accuracy and reliability of the dimensional accuracy. ResultsThe composite resin and the lithium disilicate glass-ceramic had the best dimensional accuracy. The leucite glass-ceramic exhibited a lack of trueness linked to consistent overmilling. The composite resin had less peripheral chipping than the glass-ceramics. ConclusionsThe composite resin and the lithium disilicate glass-ceramic material exhibited satisfactory dimensional accuracy. Milling the glass-ceramic before crystallization considerably improved dimensional accuracy.

Clinical performance of CAD-CAM crowns provided by predoctoral students at the University of Toronto

Statement of problemThe clinical success of monolithic lithium disilicate glass-ceramic (LDGC) crowns manufactured with computer-aided design and computer-aided manufacturing (CAD-CAM) technology provided by predoctoral students has not been fully investigated. PurposeThe purpose of this retrospective clinical study was to evaluate the performance of laboratory-fabricated monolithic posterior LDGC CAD-CAM crowns provided by predoctoral students at the University of Toronto. Specific patient- and provider-related factors were also investigated. Material and methodsA sample of posterior LDGC CAD-CAM crowns (IPS e.max) provided by predoctoral students was evaluated. Crown preparations were made according to specific criteria, and crowns were milled in an in-house laboratory by using the CEREC Bluecam system. The crowns were cemented with Rely-X Unicem (3M ESPE) and Calibra Universal (Dentsply Sirona) resin cements. Clinical assessments of the crowns and supporting periodontal structures were performed following the modified California Dental Association (CDA) criteria. Intraoral photographs and periapical and bitewing radiographs were obtained for further assessment by 2 evaluators. Descriptive statistics, McNemar, t test, log rank (Mantel-Cox) tests, Pearson chi-squared tests, simple logistic regression, odds ratios, and Kaplan Meier survival analyses were performed (α=.05). ResultsA total of 189 patients receiving 210 crowns (108 premolar and 102 molar) were examined with a follow-up period of up to 6 years. Altogether, 28 complications were observed (12 technical, 11 biological, and 5 esthetic). No significant association was found between patient age, sex, periodontal condition, tooth type, tooth vitality, cement type, and crown longevity. However, significantly lower survival and success rates were found for mandibular crowns than for maxillary crowns (P=.029). The provider’s experience had no significant effect on the clinical performance of LDGC CAD-CAM crowns. The 6-year cumulative survival rate was 93.0%, and the success rate was 86.4%. ConclusionsThe ease of use of the CAD-CAM system and clinical performance of LDGC suggest that this technology should be used in the dental school setting by predoctoral students.

Clinical evaluation of the fit of lithium disilicate crowns fabricated with three different CAD-CAM systems

Statement of problemThe fit and performance of prostheses fabricated using various computer-aided design and computer-aided manufacturing (CAD-CAM) systems have been evaluated. However, most studies were conducted in vitro, and relatively few have addressed gingival parameters and prosthesis fit under clinical conditions. PurposeThis clinical study aimed to compare the fit of lithium disilicate crowns produced using 3 CAD-CAM systems and evaluate clinical results up to 6 months after delivery. Material and methodsForty participants requiring a single crown were recruited. Three monolithic lithium disilicate crowns were fabricated per participant by using 3 different CAD-CAM systems (intraoral scanners, CAD software, and milling machines): CEREC group (CEREC Bluecam, CEREC AC, CEREC MC); EZIS group (EZIS PO, EZIS VR, EZIS HM); and TRIOS group (TRIOS 3, EXO-CAD, ARUM-4X). The fit of the prostheses was assessed via a silicone replica technique, and the most acceptable crown was delivered; 12 were selected from the CEREC group, 16 from the EZIS group, and 12 from the TRIOS group. Follow-up clinical examinations were performed at 1, 3, and 6 months after delivery. The Kruskal-Wallis test with the post hoc Mann-Whitney U test was conducted to analyze significant differences in crown fit and periodontal conditions among the groups (α=.05). ResultsThe marginal gap of the CEREC group was significantly higher than that of the EZIS group, and the occlusal gap of the EZIS group was significantly lower than those of the CEREC and TRIOS groups (P<.05). Probing depth, bleeding index, and plaque index showed no intergroup differences at 6 months (P>.05). ConclusionsThe lithium disilicate crowns of all groups showed clinically acceptable fit. No significant differences were found among the groups in terms of periodontal conditions after 6 months.

Effect of different fabrication techniques on the marginal precision of polyetheretherketone single-crown copings

Statement of problemDemand is increasing for polyetheretherketone (PEEK) as a fixed dental prosthesis core material. However, information is lacking about how the precision of these restorations is affected by the fabrication procedures. PurposeThe purpose of this in vitro study was to evaluate the influence of different fabrication techniques on the marginal precision of PEEK single-crown copings. Material and methodsA stainless-steel master die was designed to simulate a prepared mandibular second molar to receive ceramic crowns. Thirty PEEK copings were fabricated and divided into 3 groups (n=10) according to the fabrication technique: milled from a prefabricated PEEK blank by using a computer-aided design and computer-aided manufacturing (CAD-CAM) system (PC); pressed from prefabricated PEEK pellets (PP); and pressed from PEEK granules (PG); in addition, 3-mol yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) copings (n=10) were produced by using the same CAD-CAM system and served as a control. Marginal precision measurements (in μm) were recorded at 4 reference points on each coping by using a digital microscope. The data obtained were statistically analyzed by using 1-way ANOVA and the pair-wise Tukey (HSD) test to study the difference between group mean values (α=.05). ResultsThe overall mean ±standard deviation marginal gap at the marginal opening for the copings was 78 ±10 μm for PEEK granules copings, 72 ±9 μm for PEEK pellet copings, 45 ±6 μm for PEEK CAD-CAM copings, and 43 ±1 μm for the 3Y-TZP CAD-CAM control. A statistically significant difference was found between the milled and pressed copings as indicated by the ANOVA test (P<.001). The pair-wise Tukey honestly significant difference (HSD) test showed a nonsignificant difference (P>.05) between milled 3Y-TZP and milled PEEK copings; moreover, no significant difference was observed between the PEEK copings pressed from pellets or granules (P>.05). ConclusionsThe marginal precision of PEEK CAD-CAM–fabricated copings showed significantly lower mean marginal gap values than PEEK pressed copings. The marginal gap mean values recorded were all within a clinically acceptable range (120 μm).

Evaluation of the adaptation of complete denture metal bases fabricated with dental CAD-CAM systems: An in vitro study

Statement of problemConventional fabrication of complete denture metal bases is being replaced by the computer-aided design and computer-aided manufacturing (CAD-CAM) systems. However, a comparative analysis of subtractive and additive CAD-CAM manufacturing techniques is lacking. PurposeThe purpose of this in vitro study was to compare the adaptation of complete denture metal bases fabricated by milling (subtractive manufacturing) and stereolithography apparatus (SLA) and digital light processing (DLP) (additive manufacturing). Material and methodsThirty metal bases were manufactured by using the milling (MIL group), SLA (SLA group), and DLP (DLP group) techniques. The silicone replica technique was used to evaluate the adaptation of the complete denture metal bases, and 30 silicone blocks were fabricated. The silicone block was cut equally in the canine, first molar, and second molar areas. The gap between the model and the metal base was measured by using a digital microscope at the 3 locations, and the measured data were statistically analyzed by using a statistical software program (α=.05). ResultsThe gaps measured at the 3 areas showed significant differences in all 3 groups (P<.05). At the anterior, middle, and posterior areas, the SLA group showed the narrowest gap (302 ±31 μm, 241 ±39 μm, 201 ±43 μm, respectively). The SLA group also had the narrowest total gap of the metal bases (218 ±33 μm). ConclusionsThe adaptation of the fabricated metal bases varied significantly across the techniques used but fell within a clinically allowable range. The SLA group was the most precise in the fabrication of complete denture metal bases. Further studies are required to analyze the effects of the layer thickness setting, wax elimination, and casting temperature on the adaptation of metal bases manufactured by using SLA.

Comparison of nonscheduled, postinsertion adjustment visits for complete dentures fabricated with conventional and CAD-CAM protocols: A clinical study

Statement of problemUnscheduled denture-adjustment visits may disrupt both patients and clinicians. Denture-adjustment visits have not been correlated with denture-processing methods. PurposeThe purpose of this clinical study was to identify differences in the number of unscheduled postinsertion-adjustment visits of patients with complete dentures fabricated by injection molding (IM) versus dentures fabricated by computer-aided design and computer-aided manufacturing (CAD-CAM). Material and methodsOne hundred six participants were evaluated in the study. They were consecutively treated in a private practice setting and followed up for 1 year after the insertion of new complete dentures. The first 33 received dentures fabricated using an IM system, and the other 73 were milled using a CAD-CAM system. All participants had been edentulous for at least 1 year. Participant ages ranged from 29 to 83 years. IM dentures were fabricated by a commercial dental laboratory; CAD-CAM dentures were milled by a commercial manufacturer. All participants were scheduled for 1- or 2-week postinsertion office visits. Further adjustment visits were scheduled according to participant request. The results were tabulated, and univariable tests of association were performed including chi-square and the Fisher exact tests for categorical comparisons and the Wilcoxon rank sum test for comparison of ordinal continuous data. A multivariable logistic regression model was used to control for the influence of multiple predictor variables on the outcome of interest. ResultsEdentulous years ranged from 1 to 60. Approximately one half (n=56) of all participants returned for scheduled postinsertion visits approximately 1 to 2 weeks after insertion of the dentures. No significant demographic or clinical differences were noted between participants receiving CAD-CAM or conventional dentures. Return visits for unscheduled adjustments were not associated with the method of denture fabrication or any other demographic features (P=.55). ConclusionsBased on the results of this study, there were no significant differences in the number of unscheduled, postinsertion visits for participants whose dentures were fabricated following IM or CAD-CAM milling protocols. Clinicians may choose to fabricate complete dentures with either protocol and expect similar clinical results in terms of the number of unscheduled postinsertion visits.

Randomized controlled clinical trial of digital and conventional workflows for the fabrication of zirconia-ceramic posterior fixed partial dentures. Part II: Time efficiency of CAD-CAM versus conventional laboratory procedures

Statement of problemClinical trials are needed to evaluate the digital and conventional fabrication technology for providing fixed partial dentures (FPDs). PurposeThe purpose of the second part of this clinical study was to compare the laboratory production time for tooth-supported, 3-unit FPDs by means of computer-aided design and computer-aided manufacturing (CAD-CAM) systems and a conventional workflow. In addition, the quality of the 3-unit framework of each treatment group was evaluated clinically. Material and methodsFor each of 10 participants, a 3-unit FPD was fabricated. Zirconia was used as the framework material in the CAD-CAM systems and included Lava C.O.S. CAD software (3M) and centralized CAM (group L); CARES CAD software (Institut Straumann AG) and centralized CAM (group iT); and CEREC Connect CAD software (Dentsply Sirona) and centralized CAM (group C). The noble metal framework in the conventional workflow (group K) was fabricated by means of the traditional lost-wax technique. All frameworks were evaluated clinically before veneering. The time for the fabrication of the cast, the 3-unit framework, and the veneering process was recorded. In addition, chairside time during the clinical appointment for the evaluation of the framework was recorded. The paired Wilcoxon test together with appropriate Bonferroni correction was applied to detect differences among treatment groups (α=.05). ResultsThe total effective working time (mean ±standard deviation) for the dental technician was 220 ±29 minutes in group L, 217 ±23 minutes in group iT, 262 ±22 minutes in group C, and 370 ±34 minutes in group K. The dental technician spent significantly more time in the conventional workflow than in the digital workflow, independent of the CAD-CAM systems used (P<.001). ConclusionsIrrespective of the CAD-CAM system, the overall laboratory time for the dental technician was significantly less for a digital workflow than for the conventional workflow.

Marginal adaptation of CAD-CAM onlays: Influence of preparation design and impression technique

Statement of problemFactors that may affect the marginal adaptation of computer-aided design and computer-aided manufacturing (CAD-CAM) restorations include preparation design, impression technique, and CAD-CAM system. The influence of impression technique and preparation design on CAD-CAM partial coverage restorations has not been fully addressed. PurposeThe purpose of this in vitro study was to investigate the influence of direct and indirect digital scanning techniques and 2 preparation designs on the marginal adaptation of CAD-CAM onlays. Material and methodsTwo mesio-occlusal buccal onlay preparations with reduction of the mesiobuccal cusp were made: conventional preparation (CP) with a 1.2-mm modified shoulder margin and modified preparation (MP) flat cuspal reduction without shoulder. Virtual models were generated from each preparation by using a digital scanner (BlueCam; Dentsply Sirona) from the plastic teeth (direct digital scan) or from the stone dies (indirect digital scan). Onlays were designed using a CAD-CAM system (CEREC 4.0; Dentsply Sirona), and nanoceramic resin blocks (Lava Ultimate Restorative; 3M ESPE) were milled using the CEREC MCX milling machine. Marginal discrepancy was evaluated using an optical stereomicroscope at ×25 magnification in 18 locations distributed along the margins of the preparation. The data were analyzed by using 3-way ANOVA followed by the Tukey HSD test (α=.05). ResultsCP presented a statistically significant reduced average marginal adaptation (59 ±50 μm) than did MP (69 ±58 μm) (P<.001). The Tukey HSD test showed the presence of a significantly larger marginal discrepancy in the mesial and buccal locations of MP when compared with CP. Regarding impression techniques, the buccal location presented the smallest average marginal discrepancy in restorations fabricated with indirect impression when compared with direct impression (42 ±33 μm and 60 ±39 μm) (P<.001). ConclusionsThe results showed that conventional preparation with a modified shoulder margin presented improved marginal adaptation compared with modified preparation with flat cuspal reduction. Direct and indirect digital scanning techniques produced restorations within a clinically acceptable range; however, the indirect scanning technique resulted in the fabrication of restorations with superior marginal adaptation on the buccal location.

Marginal accuracy of computer-aided design- and computer-aided manufacturing-fabricated full-arch zirconia restoration.

ObjectiveThis study evaluated marginal accuracy of full-arch zirconia restoration fabricated from two digital computer-aided design and computer-aided manufacturing (CAD-CAM) systems (Trios-3 and CS3500) in comparison to conventional cast metal restoration.Materials and methodsA stainless steel model comprising two canine and two molar abutments was used as a master model for full-arch reconstruction. The canine and molar abutments were machined in a cylindrical shape with 5° taper and chamfer margin. The CAD-CAM systems based on the digital approach were used to construct the full-arch zirconia restoration. The conventional cast metal restoration was fabricated according to a conventional lost-wax technique using nickel–chromium alloys. Ten restorations were fabricated from each system. The marginal accuracy of each restoration was determined at four locations for each abutment. An analysis of variance (ANOVA) and Tukey’s honest significant difference (HSD) multiple comparisons were used to determine statistically significant difference at 95% confidence interval.ResultsThe mean values of marginal accuracy of restorations fabricated from conventional casting, Trios-3, and CS3500 were 48.59±4.16 μm, 53.50±5.66 μm, and 56.47±5.52 μm, respectively. ANOVA indicated significant difference in marginal fit of restorations among various systems. The marginal discrepancy of zirconia restoration fabricated from the CS3500 system demonstrated significantly larger gap than that fabricated from the 3Shape system (p<0.05). Tukey’s HSD multiple comparisons indicated that the zirconia restoration fabricated from either CS3500 or Trios-3 demonstrated a significantly larger marginal gap than the conventional cast metal restoration (p<0.05).ConclusionFull-arch zirconia restoration fabricated from the Trios-3 illustrated better marginal fits than that from the CS3500, although, both were slightly less accurate than the conventional cast restoration. However, the marginal discrepancies of restoration produced by both CAD-CAM systems were within the clinically acceptable range and satisfactorily precise to be suggested for construction full-arch zirconia restoration.

Influence of scanner, powder application, and adjustments on CAD-CAM crown misfit

Statement of problemThe manufacturers of computer-aided design and computer-aided manufacturing (CAD-CAM) systems emphasize that new technologies can improve the marginal fit of dental crowns. However, data supporting this claim are limited. PurposeThe purpose of this in vitro study was to investigate the differences among the following fabrication methods on the marginal discrepancy of dental crowns: intraoral optical scanners, powder application, and adjustments of intaglio surface. Material and methodsA single human premolar was fixed on a typodont and prepared to receive crowns prepared by the CEREC CAD-CAM system. Three fabrication techniques were used: digital scans using the CEREC Bluecam scanner with titanium dioxide powder (TDP), digital scans using the CEREC Omnicam scanner without TDP, and digital scans using the Omnicam scanner with TDP. Five experimental groups (n=10) were designated: Bluecam (group B), Bluecam with adjustments (group BA), Omnicam (group O), Omnicam with adjustments (group OA), and Omnicam with TDP (group OP). The specimens were scanned using microcomputed tomography to measure the vertical, horizontal, and internal fit and volumetric 3-dimensional (3D) internal fit values of each luting space. The paired t test was used to evaluate mean marginal fit change after adjustments within the same group. One-way analysis of variance and post hoc tests were used to compare groups B, O, and OP (α=.05). ResultsMean vertical fit values ±standard deviations of group B=29.5 ±13.2 μm; BA=26.9 ±7.7 μm; O=149.4 ±64.4 μm; OA=49.4 ±12.7 μm; and OP=33.0 ±8.3 μm. Adjustments in the intaglio surface and TDP application statistically influenced the vertical fit of group O (P<.001). The percentage of vertical fit values <75 μm in group B=89.3%, BA=92.7%, O=31.0%, OA=73.5%, and OP=92.0%. Mean horizontal fit values for group B=56.2 ±21.5 μm; 85.8 ±44.4 μm for group BA; 77.5 ±11.8 μm for group O; 102.5 ±16.2 μm for group OA; and 91.4 ±19.4 μm for group OP. Results from group B were significantly different from those of the other test groups (P<.05). The percentages of horizontal misfit were 61.2% in group B; 73.5% in group BA; 88.1% in group O; 92.4% in group OA; and 85.0% in group OP. Volumetric 3D internal fit values in group B were 9.4 ±1.3 mm3; 10.7 ±1.0 mm3 in group BA; 11.8 ±2.1 mm3 in group O; 11.0 ±1.3 mm3 in group OA; and 9.6 ±0.9 mm3 in group OP. The overall results from groups B and OP were better than those of group O, with regard to vertical misfit and volumetric 3D internal fit. ConclusionsDifferent intraoral optical scanners, powder application, and internal adjustments influenced the marginal discrepancy of crowns. Crowns fabricated using the Omnicam system had significantly higher vertical discrepancy and volumetric 3D internal fit than those fabricated using the Bluecam scanner with TDP. Adjustments of the intaglio surface improved the vertical fit of crowns made using the Omnicam scanner; however, TDP application before Omnicam scanning improved the vertical fit as well as the volumetric 3D internal fit value of the luting space of crowns.

Lithium silicate endocrown fabricated with a CAD-CAM system: A functional and esthetic protocol

An endocrown restoration is an alternative approach to complete crowns with intraradicular cores or dowels for the restoration of endodontically treated teeth. Endocrowns conserve tooth structure and require fewer dental visits. This approach has been widely used, and various materials and techniques have been reported. Computer-aided design and computer-aided manufacturing (CAD-CAM) systems can generate and store libraries of teeth with various anatomies in their database, and diagnostic tooth waxing may not be required. However, occlusal adjustments after the cementation of indirect restorations are often frustrating. Thus, a rapid and efficient way of addressing this challenge is necessary. This clinical report presents a protocol for the fabrication and delivery of an endocrown by using the biogeneric design mode with lithium silicate-based ceramic adjusted before its complete sintering.

Randomized controlled within-subject evaluation of digital and conventional workflows for the fabrication of lithium disilicate single crowns. Part II: CAD-CAM versus conventional laboratory procedures

Statement of problemClinical studies are needed to evaluate the entire digital and conventional workflows in prosthetic dentistry. PurposeThe purpose of the second part of this clinical study was to compare the laboratory production time for tooth-supported single crowns made with 4 different digital workflows and 1 conventional workflow and to compare these crowns clinically. Material and methodsFor each of 10 participants, a monolithic crown was fabricated in lithium disilicate-reinforced glass ceramic (IPS e.max CAD). The computer-aided design and computer-aided manufacturing (CAD-CAM) systems were Lava C.O.S. CAD software and centralized CAM (group L), Cares CAD software and centralized CAM (group iT), Cerec Connect CAD software and lab side CAM (group CiL), and Cerec Connect CAD software with centralized CAM (group CiD). The conventional fabrication (group K) included a wax pattern of the crown and heat pressing according to the lost-wax technique (IPS e.max Press). The time for the fabrication of the casts and the crowns was recorded. Subsequently, the crowns were clinically evaluated and the corresponding treatment times were recorded. The Paired Wilcoxon test with the Bonferroni correction was applied to detect differences among treatment groups (α=.05). ResultsThe total mean (±standard deviation) active working time for the dental technician was 88 ±6 minutes in group L, 74 ±12 minutes in group iT, 74 ±5 minutes in group CiL, 92 ±8 minutes in group CiD, and 148 ±11 minutes in group K. The dental technician spent significantly more working time for the conventional workflow than for the digital workflows (P<.001). No statistically significant differences were found between group L and group CiD or between group iT and group CiL. No statistical differences in time for the clinical evaluation were found among groups, indicating similar outcomes (P>.05). ConclusionsIrrespective of the CAD-CAM system, the overall laboratory working time for a digital workflow was significantly shorter than for the conventional workflow, since the dental technician needed less active working time.

In vitro evaluation of marginal discrepancy of monolithic zirconia restorations fabricated with different CAD-CAM systems

Statement of problemDental laboratories use different computer-aided design and computer-aided manufacturing (CAD-CAM) systems to fabricate fixed prostheses; however, limited evidence is available concerning which system provides the best marginal discrepancy. PurposeThe purpose of this in vitro study was to evaluate the marginal fit of 5 different monolithic zirconia restorations milled with different CAD-CAM systems. Material and methodsThirty monolithic zirconia crowns were fabricated on a custom-designed stainless steel die and were divided into 5 groups according to the type of monolithic zirconia crown and the CAD-CAM system used: group TZ, milled with an MCXL milling machine; group CZ, translucent zirconia milled with a motion milling machine; group ZZ, zirconia milled with a dental milling unit; group PZ, translucent zirconia milled with a zirconia milling unit; and group BZ, solid zirconia milled using an S1 VHF milling machine. The marginal fit was measured with a binocular microscope at an original magnification of ×100. The results were tabulated and statistically analyzed with 1-way ANOVA and post hoc surface range test, and pairwise multiple comparisons were made using Bonferroni correction (α=.05). ResultsThe type of CAD-CAM used affected the marginal fit of the monolithic restoration. The mean (±SD) highest marginal discrepancy was recorded in group TZI at 39.3 ±2.3 μm, while the least mean marginal discrepancy was recorded in group IZ (22.8 ±8.9 μm). The Bonferroni post hoc test showed that group TZI was significantly different from all other groups tested (P<.05). ConclusionsWithin the limitation of this in vitro study, all tested CAD-CAM systems produced monolithic zirconia restorations with clinically acceptable marginal discrepancies; however, the CAD-CAM system with the 5-axis milling unit produced the best marginal fit.

Evaluation of the marginal and internal discrepancies of CAD-CAM endocrowns with different cavity depths: An in vitro study

Statement of problemThe marginal and internal discrepancies of computer-aided design and computer-aided manufacturing (CAD-CAM) endocrowns are unknown. PurposeThe purpose of this in vitro study was to evaluate the marginal and internal discrepancies of endocrowns with different cavity depths by measuring them with microcomputed tomography (μCT). Material and methodsEndocrowns (n=48) of 2 different cavity depths (2 mm and 4 mm) were fabricated in 2 different chairside CAD-CAM systems (CEREC AC and E4D). A μCT scan was made before and after cementation. For analysis of the marginal and internal discrepancies, reference points were selected in 2-dimensional views of 3 buccolingual cross-sections and 3 mesiodistal cross-sections. To calculate the total discrepancy volume, the μCT sections were reconstructed 3-dimensional views, and changes in volume and surface area were examined. Statistical analysis was performed using 2-way ANOVA with Bonferroni correction (α=.05). ResultsAn endocrown with a 4-mm cavity showed a larger marginal and internal volume than one with a 2-mm cavity. Cementation did not show significant differences in total discrepancy thickness. Discrepancies on the pulpal floor were largest in other sites. Both chairside CAD-CAM systems showed similar discrepancy in the endocrowns. ConclusionsBased on the present study, marginal and internal discrepancies increased depending on cavity depth. Cementation did not increase the dimension of the discrepancy between the restoration and the cavity wall. The discrepancy on the pulpal floor appeared to affect these results.

Fracture resistance of computer-aided design and computer-aided manufacturing ceramic crowns cemented on solid abutments

BackgroundBecause no information was found in the dental literature regarding the fracture resistance of all-ceramic crowns using CEREC (Sirona) computer-aided design and computer-aided manufacturing (CAD-CAM) system on solid abutments, the authors conducted a study. MethodsSixty synOcta (Straumann) implant replicas and regular neck solid abutments were embedded in acrylic resin and randomly assigned (n = 20 per group). Three types of ceramics were used: feldspathic, CEREC VITABLOCS Mark II (VITA); leucite, IPS Empress CAD (Ivoclar Vivadent); and lithium disilicate, IPS e.max CAD (Ivoclar Vivadent). The crowns were fabricated by the CEREC CAD-CAM system. After receiving glaze, the crowns were cemented with RelyX U200 (3M ESPE) resin cement under load of 1 kilogram. For each ceramic, one-half of the specimens were subjected to the fracture resistance testing in a universal testing machine with a crosshead speed of 1 millimeter per minute, and the other half were subjected to the fractured resistance testing after 1,000,000 cyclic fatigue loading at 100 newtons. ResultsAccording to a 2-way analysis of variance, the interaction between the material and mechanical cycling was significant (P = .0001). According to a Tukey test (α = .05), the fracture resistance findings with or without cyclic fatigue loading were as follows, respectively: CEREC VITABLOCKS Mark II (405 N/454 N) was statistically lower than IPS Empress CAD (1169 N/1240 N) and IPS e.max CAD (1378 N/1025 N) (P < .05). The IPS Empress CAD and IPS e.max CAD did not differ statistically (P > .05). According to a t test, there was no statistical difference in the fracture resistance with and without cyclic fatigue loading for CEREC VITABLOCS Mark II and IPS Empress CAD (P > .05). For IPS e.max CAD, the fracture resistance without cyclic fatigue loading was statistically superior to that obtained with cyclic fatigue loading (P < .05). ConclusionsThe IPS Empress CAD and IPS e.max CAD showed higher fracture resistance compared with CEREC VITABLOCS Mark II. The cyclic fatigue loading negatively influenced only IPS e.max CAD. Practical ImplicationsThe CEREC VITABLOCS Mark II, IPS Empress CAD, and IPS e.max CAD ceramic crowns cemented on solid abutments showed sufficient resistance to withstand normal chewing forces.