Impact of the sintering parameters on the grain size, crystal phases, translucency, biaxial flexural strength, and fracture load of zirconia materials.

OBJECTIVES: To investigate the influence of the zirconia and sintering parameters on the optical and mechanical properties. METHODS: Three zirconia materials (3/4Y-TZP, 4Y-TZP, 3Y-TZP) were high-speed (HSS), speed (SS) or conventionally (CS) sintered. Disc-shaped specimens nested in 4 vertical layers of the blank were examined for grain size (GS), crystal phases (c/t'/t/m-phase), translucency (T), and biaxial flexural strength. Fracture load (FL) of three-unit fixed dental prostheses was determined initially and after thermomechanical aging. Fracture types were classified, and data statistically analyzed. RESULTS: 4Y-TZP showed a higher amount of c + t'-phase and lower amount of t-phase, and higher optical and lower mechanical properties than 3Y-TZP. In all materials, T declined from Layer 1 to 4. 3/4Y-TZP showed the highest FL, followed by 3Y-TZP, while 4Y-TZP showed the lowest. In 4Y-TZP, the sintering parameters exercised a direct impact on GS and T, while mechanical properties were largely unaffected. The sintering parameters showed a varying influence on 3Y-TZP. Thermomechanical aging resulted in comparable or higher FL. CONCLUSION: 3/4Y-TZP presenting the highest FL underscores the principle of using strength-gradient multi-layer blanks to profit from high optical properties in the incisal area, while ensuring high mechanical properties in the lower areas subject to tensile forces. With all groups exceeding maximum bite forces, the examined three-unit FDPs showed promising long-term mechanical properties.

Accuracy of digital complete-arch, multi-implant scans made in the edentulous jaw with gingival movement simulation: An in vitro study.

STATEMENT OF PROBLEM: The use of computer-aided design and computer-aided manufacturing (CAD-CAM) technologies is widely established, with single restorations or short fixed partial dentures having similar accuracy when generated from digital scans or conventional impressions. However, research on complete-arch scanning of edentulous jaws is sparse. PURPOSE: The purpose of this pilot in vitro study was to compare the accuracy of a digital scan with the conventional method in a workflow generating implant-supported complete-arch prostheses and to establish whether interference from flexible soft tissue segments affects accuracy. MATERIAL AND METHODS: An edentulous maxillary master cast containing 6 angled implant analogs was used and digitized with mounted scan bodies by using a high-precision laboratory scanner. The master cast was then scanned 10 times with 4 different intraoral scanners: TRIOS 3 with a complete-arch scanning strategy (TRI1) or implant-scanning strategy (TRI2), TRIOS Color (TRC), CEREC Omnicam (CER), and CEREC Primescan (PS). The same procedure was repeated with 4 different levels of free gingiva (G0-G3). Ten conventional impressions were obtained. Differences in implant position and direction were evaluated at the implant shoulder as mean values for trueness and interquartile range (IQR) for precision. Statistical analysis was performed by using the Kruskal-Wallis and post hoc Conover tests (α=.05). RESULTS: At G0, position deviations ranged from 34.8 µm (IQR 23.0 µm) (TRC) to 68.3 µm (12.2 µm) (CER). Direction deviations ranged from 0.34 degrees (IQR 0.18 degrees) (conventional) to 0.57 degrees (IQR 0.37 degrees) (TRI2). For digital systems, the position deviation ranged from 48.4 µm (IQR 5.9 µm) (PS) to 76.6 µm (IQR 8.1 µm) (TRC) at G1, from 36.3 µm (IQR 9.3 µm) (PS) to 79.9 µm (IQR 36.1 µm) (TRI1) at G2, and from 51.8 µm (IQR 14.3 µm) (PS) to 257.5 µm (IQR 106.3 µm) (TRC) at G3. The direction deviation ranged from 0.45 degrees (IQR 0.15 degrees) (CER) to 0.64 degrees (IQR 0.20 degrees) (TRC) at G1, from 0.38 degrees (IQR 0.05 degrees) (PS) to 0.925 degrees (IQR 0.09 degrees) (TRI) at G2, and from 0.44 degrees (IQR 0.07 degrees) (PS) to 1.634 degrees (IQR 1.08 degrees) (TRI) at G3. Statistical analysis revealed significant differences among the test groups for position (G0: P<.001; G1: P<.05; G2: P<.001; G3: P<.001) and direction (G0: P<.005; G1: P<.001; G2: P<.001; G3: P<.001). CONCLUSIONS: Without soft tissue interference, the accuracy of certain digital scanning systems was comparable with that of the conventional impression technique. The amount of flexible soft tissue interference affected the accuracy of the digital scans.

Time Efficiency of Digitally and Conventionally Produced Single-Unit Restorations.

The purpose of this in vitro study was to compare the time efficiency of digital chairside and labside workflows with a conventional workflow for single-unit restorations. The time efficiency in this specific sense was defined as the time, which has to be spent in a dental office by a dental professional performing the relevant steps. A model with interchangeable teeth on position 36 was created. These teeth were differently prepared, responding to several clinical situations to perform single-unit restorations. Different manufacturing techniques were used: For the digital workflows, CEREC Omnicam (CER) and Trios 3 (TN/TI) were used. The conventional workflow, using a dual-arch tray impression technique, served as the control group. For the labside workflow (_L) and the conventional impression procedure (CO), the time necessary for the impressions and temporary restorations was recorded and served as operating time. The chairside workflow time was divided by the time for the entire workflow (_C) including scan, design, milling and finishing the milled restoration, and in the actual working time (_CW) leaving out the chairside milling of the restoration. Labside workflow time ranged from 9 min 27 s (CER_L) to 12 min 41 s (TI_L). Entire chairside time ranged from 43 min 35 s (CER_C) to 58 min 43 s (TI_C). Pure chairside working time ranged from 15 min 21 s (CER_CW) to 23 min 17 s (TI_CW). Conventional workflow time was 10 min 39 s (CO) on average. The digital labside workflow and the conventional workflow require a similar amount of time. The digital chairside workflow is more time consuming.

Fracture Load of CAD/CAM Feldspathic Crowns Influenced by Abutment Material.

In vitro studies investigating the mechanical properties of dental reconstructions use various materials to replicate prepared teeth. However, no uniform recommendation exists as to which material is most suitable for standardized testing. The purpose of this study was to identify a material that resembles human dentin in fracture load tests. Sixteen human teeth were scanned with an intraoral scanner to obtain copies of the original crown morphology and were then prepared for crowns. Replica dies of the prepared teeth including the root morphology were fabricated with a Computer-aided design and computer-aided manufacturing (CAD/CAM) system and divided into four groups: (A) reinforced composite (RC); (B) human dentin (HD); (C) polymethyl methacrylate (PM); and (D) hybrid ceramic (HC). Sixty-four feldspar ceramic crowns were designed with the biocopy mode, fabricated with a CAD/CAM system, luted on the dies, and then with the roots embedded in polymethyl methacrylate. Care was taken to position all specimens of the same morphology identically. Thermo-mechanical load cycling was performed in a chewing simulator followed by fractural loading of the crowns. A mixed effect linear model was fitted to the data, and pairwise contrasts were estimated on the marginal means and corrected for multiple testing according to Tukey (α = 0.05). The means for fracture load (N) were 2435 N (95% CI (2162, 2709)) for hybrid ceramic, 1838 N (95% CI (1565, 2112)) for reinforced composite, 1670 N (95% CI (1396, 1943)) for human tooth and 1142 N (95% CI (868, 1415)) for polymethyl methacrylate abutment materials. Post-hoc pairwise contrasts revealed a statistically significant (p < 0.05) difference among all groups except for reinforced composite and human dentin (p = 0.76). The results indicate that the mechanical properties of abutment dies play a significant role for a possible substitution of natural teeth in in vitro studies.

Impact of interdental brush shape on interpapillary cleaning efficacy - a clinical trial.

This study aimed to investigate whether interdental brush shape influences cleaning efficacy, by comparing a waist-shaped interdental brush (W-IDB) with a cylindrical IDB (C-IDB); both provided with the same bristle texture. Cleaning efficacy of differently shaped IDBs was measured in proximal surfaces of teeth in a split-mouth cross-over design. Twenty-eight patients abolished oral hygiene for 4 d. Line angle plaque area was scanned with an intraoral camera after use of disclosing dye in baseline and after IDB application and analyzed planimetrically. Additionally, bacterial load in the IDBs was analyzed after usage by colony forming units (cfu). A Wilcoxon signed-rank test with continuity correction was used to compare the results of the waist-shaped and the cylindrically-shaped IDBs. The waist-shaped IDBs cleaned significantly better than their cylindrically-shaped counterparts (area cleaned: 23.1% vs. 18.3%), when applied at same interdental spaces (p < 0.001). However, no significant differences were found in comparison of bacterial load on the IDBs (median cfu counts: 2.3E9 vs. 2.7E9, p = 0.93). Irrespective of bristle texture or size, IDB shape have impact on cleaning efficacy. Waist-shaped IDBs are more effective in cleaning of the line angle area than cylindrically-shaped IDBs.

A volumetric assessment and follow-up of a granuloma gravidarum in the anterior maxilla.

AIM: Granuloma gravidarum (GG) is a benign lesion of the soft tissue. The aim of this technical note is the volumetric assessment and follow-up 3D measurement of a GG in the anterior maxilla. MATERIALS AND METHODS: A 35-year-old female patient who was 7 months pregnant was referred due to a soft tissue tumor in the papilla of tooth 21. A biopsy verified a pyogenic granuloma gravidarum. Initial and consecutive volumeatric measurements were made with an intraoral scanner during the patient's pregnancy and until 16 months postpartum. RESULTS: The volumetric assessment showed a continuous growth of the tumor and a consecutive volume reduction 16 months postpartum. In comparison with the level of the papilla of the contralateral incisor, there was an almost complete remission at the last follow-up. CONCLUSION: Intraoral scans can serve for the volumetric assessment of soft tissue tumors of the alveolar crest. Image superimposition enables the quantification of changes in morphology. This supports clinical follow-ups and enables the quantification of clinical observations.

Fracture load of three-unit full-contour fixed dental prostheses fabricated with subtractive and additive CAD/CAM technology.

OBJECTIVES: The aim of this study was to test the fracture load of ceramic and composite three-unit full-contour fixed dental prostheses (FDPs) fabricated with additive and subtractive computer-aided design (CAD)/computer-aided manufacturing (CAM) technology. MATERIALS AND METHODS: A newly developed alveolar socket replica model for a three-unit FDP replacing one molar was used in this study. Five CAD/CAM materials were used for fabrication of three-unit FDPs (each n = 12). The subtractive CAD/CAM fabrication method was used for groups BC (BRILLIANT Crios), TC (Telio CAD), EX (e.max CAD), and TZ (inCoris TZI C), and the additive method was used for group 3D (els 3D resin even stronger). FDPs were adhesively seated to the abutment dies (PANAVIA V5 system). Thermomechanical loading was performed prior to fracture testing with a universal testing machine. The data for maximum fracture load values was analyzed with one-way ANOVA and post hoc Scheffé test (α = 0.05). RESULTS: All FDPs survived the thermomechanical loading test. Statistically significant differences were found for the fracture load of three-unit FDPs fabricated from different CAD/CAM materials (p < 0.05). The highest mean fracture load was found for group TZ (2099.5 ± 382.1 N). Group 3D showed the lowest mean fracture load (928.9 ± 193.8 N). Group BC performed statistically significantly differently from group 3D with a mean fracture load of 1494.8 ± 214.5 N (p < 0.05). CONCLUSIONS: Particle-filled composite resin CAD/CAM materials showed fracture load values within the range of ceramic materials with a specific indication of use for three-unit FDPs. CLINICAL RELEVANCE: Particle filled composite CAD/CAM materials may offer new treatment possibilities for the CAD/CAM workflow.

Local accuracy of actual intraoral scanning systems for single-tooth preparations in vitro.

BACKGROUND: The authors evaluated the local accuracy of intraoral scanning (IOS) systems for single-tooth preparation impressions with an in vitro setup. METHODS: The authors digitized a mandibular complete-arch model with 2 full-contour crowns and 2 multisurface inlay preparations with a highly accurate reference scanner. Teeth were made from zirconia-reinforced glass ceramic material to simulate toothlike optical behavior. Impressions were obtained either conventionally (PRESIDENT, Coltène) or digitally using the IOS systems TRIOS 3 and TRIOS 3 using insane scan speed mode (3Shape), Medit i500, Version 1.2.1 (Medit), iTero Element 2, Version 1.7 (Align Technology), CS 3600, Version 3.1.0 (Carestream Dental), CEREC Omnicam, Version 4.6.1, CEREC Omnicam, Version 5.0.0, and Primescan (Dentsply Sirona). Impressions were repeated 10 times per test group. Conventional (CO) impressions were poured with type IV gypsum and digitized with a laboratory scanner. The authors evaluated trueness and precision for preparation margin (MA) and preparation surface (SU) using 3-dimensional superimposition and 3-dimensional difference analysis method using (95% - 5%) / 2 percentile values. Statistical analysis was performed using Kruskal-Wallis test. Results were presented as median (interquartile range) values in micrometers. RESULTS: The authors found statistically significant differences for MA and SU among different test groups for both trueness and precision (P < .05). Median (interquartile range) trueness values ranged from 11.8 (2.0) µm (CO) up to 40.5 (10.9) µm (CEREC Omnicam, Version 5.0.0) for SU parameter and from 17.7 (2.6) µm (CO) up to 55.9 (15.5) µm (CEREC Omnicam, Version 5.0.0) for MA parameter. CONCLUSIONS: IOS systems differ in terms of local accuracy. Preparation MA had higher deviations compared with preparation SU for all test groups. PRACTICAL IMPLICATIONS: Trueness and precision values for both MA and SU of single-unit preparations are equal or close to CO impression for several IOS systems.

Titanium Implant Characteristics After Implantoplasty: An In Vitro Study on Two Different Kinds of Instrumentation.

PURPOSE: To assess surface characteristics and implant stability after implantoplasty performed by two different instrument sequences regarding material loss, surface roughness, and fracture load resistance. Additionally, operators' subjective experience during instrumentation and the damage to neighboring teeth were evaluated. MATERIALS AND METHODS: Titanium implants were placed in the position of both first maxillary molars in models exposing 6 mm of their surface. Implantoplasty was performed in phantom heads: Exposed surfaces were instrumented with diamonds and Arkansas stones or abrasive stones and silicone polishers. Operators reported on abrasion, gloss, effectiveness, and tactility using a visual analog scale (VAS). Residual wall thickness of implants was measured on radiographs, material abrasion using three-dimensional (3D) scans, and surface roughness by contact profilometry. Maximum bending moments were measured. RESULTS: Residual thickness and weight loss were comparable after both treatments (0.3 ± 0.1 and 0.25 ± 0.07 mm and 0.22 ± 0.01 g, and 0.03 ± 0.01 mm and 0.02 ± 0.01 g, respectively, P > .05). Mean surface roughness was lower (P = .0001) for the group with the silicone polishers (0.4 ± 0.2 µm) compared with the group employing diamonds (0.8 ± 0.1 µm). Maximum bending moments showed neither intergroup differences nor stability loss compared with untreated implants. The stone-and-silicone polisher group showed less abrasion (4.6 ± 2.2) and higher gloss values (8.1 ± 1.4) than the diamond-and-Arkansas group (3.1 ± 1.3 and 4.1 ± 2.1, respectively). Superficial tooth injuries at proximal neighbor teeth were common (73% and 80%). CONCLUSION: Implantoplasty did not weaken implant stability. The use of silicone polishers revealed lower surface roughness. Regarding surface smoothness, the instrumentation sequence employing silicon carbide and Arkansas stones followed by silicone polishers seems to be superior to the combination of diamond and Arkansas stones.

Accuracy of complete- and partial-arch impressions of actual intraoral scanning systems in vitro.

OBJECTIVE: Intraoral scanners (IOSs) are widely used for obtaining digital dental models directly from the patient. Additionally, improvements in IOSs are made from generation to generation. The aim of this study was to evaluate the accuracy of new and actual IOS devices for complete- and partial-arch dental impressions in an in vitro setup. MATERIALS AND METHODS: A custom maxillary complete-arch cast with teeth made from feldspar ceramic material was used as the reference cast and digitized with a reference scanner (ATOS III Triple Scan MV60). One conventional impression technique using polyvinylsiloxane (PVS) material (President) served as the control (CO), and eight different IOS devices comprising different hardware and software configurations (TRn: Trios 3; TRi: Trios 3 insane; CS: Carestream Dental CS 3600; MD: Medit i500; iT: iTero Element 2; OC4: Cerec Omnicam 4.6.1; OC5: Cerec Omnicam 5.0.0; PS: Primescan) were used to take complete-arch impressions from the reference cast. The impressions were repeated 10 times (n = 10) for each group. Conventional impressions were poured with type IV gypsum and digitized with a laboratory scanner (inEos X5). All datasets were obtained in standard tessellation language (STL) file format and cut to either complete-arch, anterior segment, or posterior segment areas for respective analysis. Values for trueness and precision for the respective areas were evaluated using a three-dimensional (3D) superimposition method with special 3D difference analysis software (GOM Inspect) using (90-10)/2 percentile values. Statistical analysis was performed using either one-way analysis of variance (ANOVA) or Kruskal-Wallis test (α = 0.05). Results are given as median and interquartile range [IQR] values in µm. RESULTS: Statistically significant differences were found between test groups for complete- and partial-arch impression methods in vitro (p < 0.05). Values ranged from 16.3 [2.8] µm (CO) up to 89.8 [26.1] µm (OC4) for in vitro trueness, and from 10.6 [3.8] µm (CO) up to 58.6 [38.4] µm (iT) for in vitro precision for the complete-arch methods. The best values for trueness of partial-arch impressions were found for the posterior segment, with 9.7 [1.2] µm for the conventional impression method (CO), and 21.9 [1.5] µm (PS) for the digital impression method. CONCLUSION: Within the limitations of this study, digital impressions obtained from specific IOSs are a valid alternative to conventional impressions for partial-arch segments. Complete-arch impressions are still challenging for IOS devices; however, certain devices were shown to be well within the required range for clinical quality. Further in vivo studies are needed to support these results.

Fracture load of CAD/CAM-fabricated and 3D-printed composite crowns as a function of material thickness.

OBJECTIVES: Indirect CAD/CAM restorations can be fabricated using both subtractive and additive CAD/CAM technology. This study investigated the fracture load of crowns fabricated from three particle-filled composite CAD/CAM materials and one 3D-printed composite material. MATERIALS AND METHODS: Lava Ultimate, Cerasmart and Brilliant Crios were used as particle-filled composite CAD/CAM material and els-3D Harz as 3D-printed composite material. For each group, crowns with three different material thicknesses (0.5/1.0/1.5 mm) were fabricated. Control group was composed of ceramic-based CAD/CAM materials e.max CAD and Enamic. Totally, n = 180 crowns were fabricated and adhesively seated on SLA fabricated dies. Thermomechanical loading and fracture testing were performed. The data for fracture loading force were statistically analyzed by two-way ANOVA followed with multiple comparisons by post hoc Tukey's test (α = 0.05). RESULTS: In contrast to ceramics, all particle-filled composite crowns with 0.5-mm thickness survived fatigue testing. Forces varied statistically significantly. Brilliant Crios showed highest maximum loading force with 1580.4 ± 521.0 N (1.5 mm). Two-way ANOVA indicated that both the material and the thickness affected the fracture load (p < 0.05). CONCLUSIONS: Particle-filled composite resin CAD/CAM materials may have advantageous material characteristics compared to ceramic CAD/CAM materials for minimal restoration thicknesses. CLINICAL RELEVANCE: Composite-based CAD/CAM materials may offer new possibilities in minimally invasive restorative treatment concepts.

Precision of guided scanning procedures for full-arch digital impressions in vivo.

PURPOSE: System-specific scanning strategies have been shown to influence the accuracy of full-arch digital impressions. Special guided scanning procedures have been implemented for specific intraoral scanning systems with special regard to the digital orthodontic workflow. The aim of this study was to evaluate the precision of guided scanning procedures compared to conventional impression techniques in vivo. METHOD: Two intraoral scanning systems with implemented full-arch guided scanning procedures (Cerec Omnicam Ortho; Ormco Lythos) were included along with one conventional impression technique with irreversible hydrocolloid material (alginate). Full-arch impressions were taken three times each from 5 participants (n = 15). Impressions were then compared within the test groups using a point-to-surface distance method after best-fit model matching (OraCheck). Precision was calculated using the (90-10%)/2 quantile and statistical analysis with one-way repeated measures ANOVA and post hoc Bonferroni test was performed. RESULTS: The conventional impression technique with alginate showed the lowest precision for full-arch impressions with 162.2 ± 71.3 µm. Both guided scanning procedures performed statistically significantly better than the conventional impression technique (p < 0.05). Mean values for group Cerec Omnicam Ortho were 74.5 ± 39.2 µm and for group Ormco Lythos 91.4 ± 48.8 µm. CONCLUSIONS: The in vivo precision of guided scanning procedures exceeds conventional impression techniques with the irreversible hydrocolloid material alginate. Guided scanning procedures may be highly promising for clinical applications, especially for digital orthodontic workflows.

A validation study of reconstructed rapid prototyping models produced by two technologies.

OBJECTIVE: To determine the accuracy (trueness and precision) of two different rapid prototyping (RP) techniques for the physical reproduction of three-dimensional (3D) digital orthodontic study casts, a comparative assessment using two 3D STL files of two different maxillary dentitions (two cases) as a reference was accomplished. MATERIALS AND METHODS: Five RP replicas per case were fabricated using both stereolithography (SLA) and the PolyJet system. The 20 reproduced casts were digitized with a highly accurate reference scanner, and surface superimpositions were performed. Precision was measured by superimposing the digitized replicas within each case with themselves. Superimposing the digitized replicas with the corresponding STL reference files assessed trueness. Statistical significance between the two tested RP procedures was evaluated with independent-sample t-tests (P < .05). RESULTS: The SLA and PolyJet replicas showed statistically significant differences for trueness and precision. The precision of both tested RP systems was high, with mean deviations in stereolithographic models of 23 (±6) µm and in PolyJet replicas of 46 (±13) µm. The mean deviation for trueness in stereolithographic replicas was 109 (±4) µm, while in PolyJet replicas, it was 66 (±14) µm. CONCLUSIONS: Comparing the STL reference files, the PolyJet replicas showed higher trueness than the SLA models. But the precision measurements favored the SLA technique. The dimensional errors observed in this study were a maximum of 127 µm. In the present study, both types of reproduced digital orthodontic models are suitable for diagnostics and treatment planning.

In vivo tooth-color measurement with a new 3D intraoral scanning system in comparison to conventional digital and visual color determination methods.

STATEMENT OF PROBLEM: Three-dimensional (3D) intraoral scanning systems allow for the simultaneous acquisition of 3D information about tooth surfaces and a photorealistic view of the patient's tooth colors. AIM: The goal of this study was the in vivo comparison of a new 3D scanner with a color acquisition mode and conventional visual and digital color measurements. MATERIALS AND METHODS: The colors of 40 teeth of 20 patients were evaluated in seven ways: 1) By dentists using the Vita 3D-Master; 2) By dental technicians using the Vita 3D-Master; 3) With the 3Shape Trios device; 4) With the Vita Easyshade device; 5) With the Vita Easyshade Advance device; 6) With the SpectroShade device; and 7) With the SpectroShade Micro device. Digital measurements of Groups 3 to 7 were repeated three times for each tooth. For all groups, both the CIE Lab values and the Vita 3D-Master values were recorded. The repeatability and relative accuracy of the Vita 3D-Master values were analyzed statistically using Pearson's chi-squared test (α < 0.05). ΔE values were calculated from the CIE Lab values, which served as a basis for performing multidimensional scaling (MDS) and evaluating differences between the groups using the one-way ANOVA with post hoc Tamhane's test (α < 0.05). RESULTS: The results of the ΔE values showed that clinically relevant differences between the evaluation by dentists, dental technicians, and the intraoral scanning device (3Shape) are negligible. The intraoral 3D scanning device (Group 3) and the digital systems (Groups 4 to 7) did not differ significantly in the repeatability of color shade management. The SpectroShade Micro (Group 7) had significantly better relative accuracy than the other devices. CONCLUSIONS: The results demonstrate that intraoral scanning systems can be used to measure both tooth color and tooth surface in 3D. CLINICAL IMPLICATIONS: Intraoral optical scanning devices allow for the acquisition of accurate 3D surface data. Tooth color can be evaluated simultaneously and can be used to determine the color of restorations without requiring additional conventional color-measurement methods.

Trueness of four different milling procedures used in dental CAD/CAM systems.

OBJECTIVES: Milling is a crucial step in producing restorations using computer-aided design and computer-aided manufacturing (CAD/CAM) systems. In this study the trueness of currently available milling devices was evaluated. MATERIALS AND METHODS: Thirty clinical cases (ten inlays, ten crowns, ten onlays) were milled from ceramic blocks using four different milling approaches: five axis with IMES CORiTEC 450i, four axis with CEREC MCXL, four axis with CEREC MCXL-EF and five axis with inLab MCX5. The milled restorations were scanned and the occlusal and inner surfaces compared to the originally calculated 3D surface using difference analysis software. The (90-10 %) / 2 percentile of the distances were calculated and analysed using one-way ANOVA with the post hoc Scheffé test (α = 0.05). Chipping of marginal areas were visually examined and analysed using one-way ANOVA with a post hoc Tamhane test (α = 0.05). RESULTS: At inner surfaces, the milling trueness of IMES (33.9 ± 16.3 µm), X5 (32.3 ± 9.7 µm) and MCXL-EF (34.4 ± 7.5 µm) was significantly better (p < 0.001) than that of MCXL (62.1 ± 17.1 µm). At occlusal surfaces, MCXL-EF (25.7 ± 9.3 µm) showed significant higher accuracy (p < 0.001) than MCXL (48.7 ± 23.3 µm) and X5 (40.9 ± 20.4 µm). IMES produced the most chipping (p < 0.001). CONCLUSIONS: Five-axis milling devices yield high trueness. MCXL-EF is competitive and may allow chairside fabrication with good milling results. CLINICAL RELEVANCE: Accurate milling is required for well-fitting restorations and thereby requires fewer manual finishing steps, yields smaller marginal gaps, resistance to secondary caries and longevity of restorations.

Impact of digital intraoral scan strategies on the impression accuracy using the TRIOS Pod scanner.

OBJECTIVES: Little information is available on the impact of different scan strategies on the accuracy of full-arch scans with intraoral scanners. The aim of this in-vitro study was to investigate the trueness and precision of full-arch maxillary digital impressions comparing three scan strategies. METHOD AND MATERIALS: Three scan strategies (A, B, and C) were applied each five times on one single model (A, first buccal surfaces, return from occlusal-palatal; B, first occlusal-palatal, return buccal; C, S-type one-way). The TRIOS Pod scanner (3shape, Copenhagen, Denmark) with a color detector was used for these digital impressions. A cast of a maxillary dentate jaw was fabricated and scanned with an industrial reference scanner. This full-arch data record was digitally superimposed with the test scans (trueness) and within-group comparison was performed for each group (precision). The values within the 90/10 percentiles from the digital superimposition were used for calculation and group comparisons with nonparametric tests (ANOVA, post-hoc Bonferroni). RESULTS: The trueness (mean ± standard deviation) was 17.9 ± 16.4 µm for scan strategy A, 17.1 ± 13.7 µm for B, and 26.8 ± 14.7 µm for C without statistically significant difference. The precision was lowest for scan strategy A (35.0 ± 51.1 µm) and significantly different to B (7.9 ± 5.6 µm) and C (8.5 ± 6.3 µm). CONCLUSIONS: Scan strategy B may be recommended as it provides the highest trueness and precision in full-arch scans and therefore minimizes inaccuracies in the final reconstruction.

Marginal adaptation, fracture load and macroscopic failure mode of adhesively luted PMMA-based CAD/CAM inlays.

OBJECTIVES: To evaluate marginal adaptation, fracture load and failure types of CAD/CAM polymeric inlays. METHODS: Standardized prepared human molars (48) were divided into four groups (n=12): (A) PCG (positive control group); adhesively luted glass-ceramic inlays, (B) TRX; CAD/CAM polymeric inlays luted using a self-adhesive resin cement, (C) TAC; CAD/CAM polymeric inlays luted using a conventional resin cement, and (D) NCG (negative control group); direct-filled resin-based composite restorations. All specimens were subjected to a chewing simulator. Before and after chewing fatigue, marginal adaptation was assessed at two interfaces: (1) between dental hard tissues and luting cement and (2) between luting cement and restoration. Thereafter, the specimens were loaded and the fracture loads, as well as the failure types, were determined. The data were analysed using three- and one-way ANOVA with post hoc Scheffé test, two sample Student's t-test (p<0.05). RESULTS: Before and after chewing fatigue, marginal adaptation for interface 1 showed significantly better results for TRX and PCG than for TAC (p=0.001-0.02) and NCG (p=0.001-0.047). For interface 2, marginal adaptation for TAC was significantly inferior to TRX (p<0.001) and PCG (p<0.001). Chewing fatigue had a negative impact on the marginal adaptation of TAC and NCG. No significant differences in fracture load were found between all tested groups. SIGNIFICANCE: Self-adhesive luted polymeric CAD/CAM inlays showed similar marginal adaptation and fracture load values compared to adhesively luted glass-ceramic inlays.

Comparison of four monolithic zirconia materials with conventional ones: Contrast ratio, grain size, four-point flexural strength and two-body wear.

OBJECTIVES: To test the mechanical and optical properties of monolithic zirconia in comparison to conventional zirconia. MATERIALS AND METHODS: Specimens were prepared from: monolithic zirconia: Zenostar (ZS), DD Bio ZX(2) hochtransluzent (DD), Ceramill Zolid (CZ), InCoris TZI (IC) and a conventional zirconia Ceramill ZI (CZI). Contrast ratio (N=75/n=15) was measured according to ISO 2471:2008. Grain sizes (N=75/n=15) were investigated with scanning electron microscope. Four-point flexural strength (N=225/n=15/zirconia and aging regime) was measured initially, after aging in autoclave or chewing simulator (ISO 13356:2008). Two-body wear of polished and glazed/veneered specimens (N=108/n=12) was analyzed in a chewing simulator using human teeth as antagonists. Data were analyzed using 2-/1-way ANOVA with post-hoc Scheffé, Kruskal-Wallis-H, Mann-Whitney-U, Spearman-Rho, Weibull statistics and linear mixed models (p<0.05). RESULTS: The lowest contrast ratio values were found for ZS and IC and CZ. IC showed the largest grain size followed by DD and CZI. The smallest grain size was observed for ZS followed by CZ. There was no correlation between grain size and contrast ratio. The aging regime showed no impact on flexural strength. All non-aged and autoclave-aged specimens showed lower flexural strengths than the control group CZI. Within groups aged in chewing simulator, ZS showed significantly lower flexural strength than CZI. CZI showed higher material and antagonist wear than monolithic polished and glazed groups. Glazed specimens showed higher material and antagonist loss compared to polished ones. There was no correlation between roughness and wear. CONCLUSIONS: Monolithic zirconia showed higher optical, but lower mechanical properties than conventional zirconia.

In vivo precision of conventional and digital methods for obtaining quadrant dental impressions.

OBJECTIVES: Quadrant impressions are commonly used as alternative to full-arch impressions. Digital impression systems provide the ability to take these impressions very quickly; however, few studies have investigated the accuracy of the technique in vivo. The aim of this study is to assess the precision of digital quadrant impressions in vivo in comparison to conventional impression techniques. MATERIALS AND METHODS: Impressions were obtained via two conventional (metal full-arch tray, CI, and triple tray, T-Tray) and seven digital impression systems (Lava True Definition Scanner, T-Def; Lava Chairside Oral Scanner, COS; Cadent iTero, ITE; 3Shape Trios, TRI; 3Shape Trios Color, TRC; CEREC Bluecam, Software 4.0, BC4.0; CEREC Bluecam, Software 4.2, BC4.2; and CEREC Omnicam, OC). Impressions were taken three times for each of five subjects (n = 15). The impressions were then superimposed within the test groups. Differences from model surfaces were measured using a normal surface distance method. Precision was calculated using the Perc90_10 value. The values for all test groups were statistically compared. RESULTS: The precision ranged from 18.8 (CI) to 58.5 µm (T-Tray), with the highest precision in the CI, T-Def, BC4.0, TRC, and TRI groups. The deviation pattern varied distinctly depending on the impression method. Impression systems with single-shot capture exhibited greater deviations at the tooth surface whereas high-frame rate impression systems differed more in gingival areas. Triple tray impressions displayed higher local deviation at the occlusal contact areas of upper and lower jaw. CONCLUSIONS: Digital quadrant impression methods achieve a level of precision, comparable to conventional impression techniques. However, there are significant differences in terms of absolute values and deviation pattern. CLINICAL RELEVANCE: With all tested digital impression systems, time efficient capturing of quadrant impressions is possible. The clinical precision of digital quadrant impression models is sufficient to cover a broad variety of restorative indications. Yet the precision differs significantly between the digital impression systems.

In vivo precision of conventional and digital methods of obtaining complete-arch dental impressions.

STATEMENT OF PROBLEM: Digital impression systems have undergone significant development in recent years, but few studies have investigated the accuracy of the technique in vivo, particularly compared with conventional impression techniques. PURPOSE: The purpose of this in vivo study was to investigate the precision of conventional and digital methods for complete-arch impressions. MATERIAL AND METHODS: Complete-arch impressions were obtained using 5 conventional (polyether, POE; vinylsiloxanether, VSE; direct scannable vinylsiloxanether, VSES; digitized scannable vinylsiloxanether, VSES-D; and irreversible hydrocolloid, ALG) and 7 digital (CEREC Bluecam, CER; CEREC Omnicam, OC; Cadent iTero, ITE; Lava COS, LAV; Lava True Definition Scanner, T-Def; 3Shape Trios, TRI; and 3Shape Trios Color, TRC) techniques. Impressions were made 3 times each in 5 participants (N=15). The impressions were then compared within and between the test groups. The cast surfaces were measured point-to-point using the signed nearest neighbor method. Precision was calculated from the (90%-10%)/2 percentile value. RESULTS: The precision ranged from 12.3 µm (VSE) to 167.2 µm (ALG), with the highest precision in the VSE and VSES groups. The deviation pattern varied distinctly according to the impression method. Conventional impressions showed the highest accuracy across the complete dental arch in all groups, except for the ALG group. CONCLUSIONS: Conventional and digital impression methods differ significantly in the complete-arch accuracy. Digital impression systems had higher local deviations within the complete arch cast; however, they achieve equal and higher precision than some conventional impression materials.