A preliminary evaluation of the structural integrity and fracture mode of minimally prepared resin bonded CAD/CAM crowns

Clinical performance comparison between lithium disilicate and hybrid resin nano-ceramic CAD/CAM onlay restorations: a two-year randomized clinical split-mouth study

A total of 20 lithium disilicate glass-ceramics (IPS e.max CAD, Ivoclar Vivadent) and 20 resin nano-ceramic (Voco Grandio Blocks) onlay restorations were performed in 20 patients using a split-mouth design to compare the two-year clinical performance of lithium disilicate and resin nano-ceramic onlay restorations. Both restorations were evaluated at baseline, one-year, and two-year clinical follow-ups based on the modified United States Public Health Service (USPHS) criteria. Chi-square and Fisher's exact tests showed no statistically significant difference between Voco Grandio and IPS e.max ceramic restorations for all evaluated parameters during the different follow-up periods (p > 0.05). Cochrane's and MC-Nemar's tests indicated statistically significant differences regarding color match within the Voco Grandio group. They also indicated statistically significant differences in marginal discoloration, marginal adaptation, surface texture, and postoperative hypersensitivity within both ceramic material groups (p < 0.05). Kaplan-Meier curve indicated that the survival rate of both ceramic materials was 90%. After two years of clinical service, IPS e.max CAD and Voco Grandio onlay restorations exhibited similar clinical performance.

Yousief S, Tammam R, M. Galal R, Brakat A, Mohamed El Sayed H, Kamal A, Noushad M, Nassani MZ. Biomechanics of Central Incisor Endocrowns with Different Lengths and Milled Materials after Static and Vertical Loading: A Finite Element Study

Purpose

The aim of this study was to compare and assess the stress distribution and failure possibility of endodontically treated central incisor protected with endocrowns with different heights, with various CAD-CAM blocks such as IPS e.max CAD, Katana Zirconia, and Zolid Fx Zirconia.

Materials and Methods

A root canal-treated central incisor (plastic model) restored with an endocrown was scanned with a laser scanner to prepare a control model with a CAD software and then transferred to an FEA software. Proposed crown heights were 2, 4, and 6 mm. The model that was duplicated and restored with CAD-CAM blocks, IPS e.max CAD, Katana Zirconia, and Zolid Fx Zirconia were tested as endocrown materials. Bone geometry was simplified to be two coaxial cylinders in all models. Stress distributions under 50 N axial and oblique (with 135° angle from the vertical plane) loading were analyzed. Each model was then subjected to two occlusal loading conditions-the lingual slope of the incisal edge and the junction between incisal and middle thirds. Eighteen runs and calculations were performed to determine the endocrown height and material effect.

Results

The results showed a minor or negligible effect of changing the endocrown material. Increasing endocrown height was shown to reduce stresses and deformations on most of the model components (bone, gutta-percha, periodontal ligament, and endocrown), except root and cement. Differences in deformations and stresses between the two models of 4 and 6 mm were relatively smaller (ranged between 1% and 30%) compared to those between the 2 and 4 mm models (ranged between 10% and 400%).

Conclusions

The material used to fabricate endocrowns did not show considerable effect on the underlying structures. However, the endocrown design (2, 4, and 6 mm height) was shown to affect all components of the studied systems. Increasing endocrown height is recommended for bone, periodontal ligaments, and endocrown body, as it reduces stresses and deformations. On the other hand, it dramatically increases stresses on the root and cement layer. Smaller endocrown sizes represent an acceptable treatment option when there is a healthy periodontal state, while using larger sizes will be more suitable when there is a periodontal compromise with bone loss.

Ultrathin lithium disilicate and translucent zirconia crowns for posterior teeth: Survival and failure modes

PURPOSE

To evaluate the reliability and failure modes of ultrathin (0.5 mm) lithium disilicate, translucent and ultra-translucent zirconia crowns for posterior teeth restorations.

MATERIALS AND METHODS

Fifty-four mandibular first molar crowns of three ceramic materials: (1) Lithium disilicate (e.max CAD, Ivoclar Vivadent), (2) 3Y-TZP (Zirconn Translucent, Vipi), and (3) 5Y-PSZ (Cercon XT, Dentsply Sirona), with 0.5 mm of thickness were milled and cemented onto composite resin abutments. Eighteen samples of each group were tested under mouth-motion step-stress accelerated life testing in a humid environment using mild, moderate, and aggressive profiles. Data was subjected to Weibull statistics. Use level curves were plotted and reliability was calculated for a given mission of 100,000 cycles at 100, 200, and 300 N. Fractographic analyses of representative samples were performed in scanning electron microscope.

RESULTS

Beta (β) values suggest that failures were dictated by material's strength for lithium disilicate and by fatigue damage accumulation for both zirconias. No significant differences were detected in Weibull modulus and characteristic strength among groups. At a given mission of 100,000 cycles at 100 N, lithium disilicate presented higher reliability (98% CB: 95-99) regarding 3Y-TZP and 5Y-PSZ groups (84% CB: 65%-93% and 79% CB: 37&-94%, respectively). At 200 N, lithium disilicate reliability (82% CB: 66%-91%) was higher than 5Y-PSZ (20% CB: 4%-44%) and not significantly different from 3Y-TZP (54% CB: 32%-72%). Furthermore, at 300 N no significant differences in reliability were detected among groups, with a notable reduction in the reliability of all materials. Fractographic analyses showed that crack initiated at the interface between the composite core and the ceramic crowns due to tensile stress generated at the intaglio surface.

CONCLUSIONS

Ultrathin lithium disilicate crowns demonstrated higher reliability relative to zirconia crowns at functional loads. Lithium disilicate and zirconia crown's reliability decreased significantly for missions at higher loads and similar failure modes were observed regardless of crown material. The indication of 0.5 mm thickness crowns in high-load bearing regions must be carefully evaluated.

CLINICAL SIGNIFICANCE

Ultraconservative lithium disilicate and zirconia crowns of 0.5 mm thickness may be indicated in anterior restorations and pre-molars. Their clinical indication in high-load requirement regions must be carefully evaluated.

Two‑year clinical performance of indirect restorations fabricated from CAD/CAM nano hybrid composite versus lithium disilicate in mutilated vital teeth. A randomized controlled trial

TRIAL DESIGN

This is a randomized, controlled, superiority, double-blinded, parallel-group, two-arms trial with an allocation ratio of 1:1. The aim of this trial was to compare the two-year clinical performance of partial indirect restorations fabricated from CAD/CAM nano-hybrid composite and ceramic lithium disilicate blocks using the modified USPHS criteria.

METHODS

In two parallel groups (n = 50 restorations), fifty participants having mutilated vital teeth with a minimum of two remaining walls were randomly enrolled in this trial and received indirect restorations of either nano-hybrid composite resin blocks (Brilliant, Coltene, Switzerland) or Lithium Disilicate (IPS Emax CAD). The restorations were assessed using modified USPHS criteria by two independent blinded assessors at baseline, six months, one-year and two years follow-up visits. Categorical and ordinal data were presented as frequencies and percentages. Categorical data were analyzed using the chi-square test. Ordinal data were analyzed using the Mann-Whitney U test for intergroup comparisons and Freidman's test followed by the Nemenyi post hoc test for intragroup comparisons. Numerical data were presented as mean and standard deviation values. They were analyzed for normality using the Shapiro-Wilk test. Data were found to be normally distributed and were analyzed using the independent t-test. The significance level was set at p ≤ 0.05 within all tests.

RESULTS

Forty-eight participants received the allocated intervention and completed the follow-up periods. There was a statistically significant difference between both tested materials for all USPHS criteria regarding Marginal integrity and Marginal discoloration at six-months Follow-up, but with no statistically significant difference at one- and two-year follow-up.

CONCLUSIONS

Both materials showed an acceptable, successful clinical performance along the two-years follow-up period.

CLINICAL RELEVANCE

The CAD/CAM nano-hybrid composite blocks are as reliable as Lithium disilicate for restoring mutilated vital teeth.

The Structural Integrity and Fracture Behaviour of Teeth Restored with PEEK and Lithium-Disilicate Glass Ceramic Crowns

Polyetheretherketone (PEEK) is a unique polymer material which has recently been introduced to dentistry. This study aimed to assess the structural integrity of PEEK as a posterior tooth crown and compared it with ceramic-based material. A total of 31 monolithic CAD-CAM PEEK (JuvoraTM, Strumann, Andover, MA, USA) crowns and 31 lithium disilicate (IPS e.max®CAD, Voclar Vivadent AG, Liechtenstein) crowns were created and cemented on dentin-like teeth (AlphaDie®MF, Schütz Dental GmbH, Rosbach, Germany) in a precise procedure mimicking the physical and mechanical properties of natural teeth and periodontal ligaments. A static compressive strength test using a universal testing machine and a dynamic fatigue test using a chewing simulator machine were used until crown failure to assess the fracture behaviour by mode of fracture (fractographic analysis) and 3D digital subtraction analysis. The results showed that PEEK has a greater fracture resistance than IPS e.max®CAD by 2060 N to 703 N. Additionally, in fatigue limit, IPS e.max®CAD showed a constant failure under 2.0 Kg (=320 N) before 5000 chewing cycles while PEEK survived at a significantly higher load > 11 Kg (930 N). Furthermore, PEEK showed a continued survival at >1,250,000 cycles while the mean fatigue life of IPS e.max®CAD was around 133,470 cycles. PEEK illustrated a significantly less catastrophic failure mode with some plastic deformation at the fractographic stereomicroscope and in the 3D digital subtraction analysis. Using PEEK for crowns looks very promising, however, further clinical studies are required to assure this study’s results.

Fatigue failure and success rate of lithium disilicate table-tops as a function of cement thickness

PURPOSE

Under thin, partial coverage restoration the proper cement thickness to be clinically employed still remains an issue. The aim of this study was to determine the failure and success rates of simplified lithium disilicate occlusal veneers as a function of cement thickness. The null hypothesis was that cement thickness has no effect on the fatigue resistance.

METHODS

Sound human molars were severed in a plane parallel to the occlusal surface to create a flat dentin surface surrounded by enamel edges. Forty-five occlusal veneers 1.0 mm thick (IPS e.max CAD LT) were luted to the teeth with Multilink Automix resin cement, creating 3 experimental groups (n=15) with cement thicknesses of 50, 100, and 200 µm. The restorations were fatigue-cycled using a ball mill machine containing zirconia and stainless steel spheres. Twelve 60 min cycles were performed. Survival statistics were applied to "failure" and "success" events, comparing the three groups using a log-rank Mantel-Cox test and a log-rank test for trends (alpha = 0.05).

RESULTS

The failure and success rates were not significantly influenced by cement thickness (P = 0.137 and P = 0.872, respectively); thus, the null hypothesis was accepted. However, when log-rank test for trends was applied to failure events, the tendency to have less failures with increasing thicknesses was found statistically significant (P = 0.047).

CONCLUSIONS

The cement thickness within the range adopted here did not have a significant effect on the failure or success rate of lithium disilicate occlusal veneers when exposed to randomized impact stresses generating fatigue phenomena.

Effect of etching with low concentration hydrofluoric acid on the bond strength of CAD/CAM resin block

The effect of etching for 90 s with low concentrations (0.5, 1.0, 2.0, 3.0, 3.5, and 4.0%) of hydrofluoric acid (HF) on the adhesiveness of computer-aided design/computer-aided manufacturing (CAD/CAM) resin blocks [CERASMART (CS), SHOFU BLOCK HC (HC), KATANA AVENCIA Block(KA), and VITA ENAMIC (EN)] was investigated. Energy dispersive spectroscopy revealed that the silicon content of HC, KA, and EN groups remained almost constant with HF etching of ≤4%. HF etching increased the surface roughness of all blocks. The HF concentration resulting in the highest shear bond strength in each group was as follows: CS (2.0%), HC (3.0%), KA (3.5%) and EN (0.5%). Scanning electron microscopy revealed that the bonding interface of etched surfaces differed significantly from that of airborne-particle abrasion surfaces. Thus, low concentration HF etching is effective for surface treatment of CAD/CAM resin blocks. The etching effect and optimum HF concentration differ with the block composition and structure.

Degradation of Computer-aided Design/Computer-aided Manufacturing Composites by Dietary Solvents: An Optical Three-dimensional Surface Analysis

CLINICAL RELEVANCE

Computer-aided design/computer-aided manufacturing (CAD/CAM) composite resins are susceptible to degradation by dietary solvents. Dietary counselling is prudent when placing such CAD/CAM restorations.

SUMMARY

This study determined the effect of dietary solvents on the surface roughness (Ra) of direct, indirect, and computer-aided design/computer-aided manufacturing (CAD/CAM) dental composites. The materials evaluated were a direct composite (Filtek Z350 XT [FZ]), an indirect composite (Shofu Ceramage [CM]), and four CAD/CAM composites (Lava Ultimate [LU], Shofu Block HC [HC], Cerasmart [CS], and Vita Enamic [VE]). Specimens (12×14×1.5 mm) of each material were prepared, measured for baseline Ra, ranked, divided into six groups (n=12), and conditioned in the following media for 1 week at 37°C: air (control), distilled water, 0.02 N citric acid, 0.02 N lactic acid, heptane, and 50% ethanol-water solution. The composite specimens were then subjected to postconditioning Ra testing using an optical three-dimensional surface analyzer (G4e, Alicona Imaging GmbH, Raaba, Austria). Inter-medium and inter-material comparisons were performed with one-way analysis of variance and post hoc Bonferroni test at a significance level of α=0.05. Mean Ra values ranged from 0.086 ± 0.004 μm to 0.153 ± 0.005 μm for the various material/medium combinations. For all materials, conditioning in air (control) and distilled water generally resulted in significantly lower mean Ra than exposure to other dietary solvents. Conditioning in citric acid presented the roughest surfaces for FZ, CM, and CS. For LU, HC, and VE, exposure to lactic acid, heptane, and ethanol solution resulted in the highest mean Ra. Regardless of conditioning media, FZ had the highest and VE the lowest mean Ra compared with other composites. The CAD/CAM composites remained susceptible to surface degradation by dietary solvents despite their industrial polymerization.

Fracture resistance and 3D finite element analysis of machined ceramic crowns bonded to endodontically treated molars with two planes versus flat occlusal preparation designs: an in vitro study

Background: The flat occlusal preparation design (FOD) of posterior teeth offers promising results of fracture resistance and stress distribution, but its application in vital teeth is limited as there may be a danger of pulp injury. Although this danger is omitted in endodontically treated teeth, there is no research work assessing the impact of FOD on the fracture resistance and distribution of stresses among these teeth. The aim of this study was to assess the impact of FOD of endodontically treated molars on the fracture resistance and distribution of stresses among a ceramic crown-molar structure when compared to the two planes occlusal preparation design (TOD). Methods: 20 human mandibular molars were endodontically treated and distributed equally to two groups: Group I (TOD) and Group II (FOD). Ceramic CAD/CAM milled lithium disilicate (IPS e.max CAD) crowns were produced for all preparations and adhered using self-adhesive resin cement. Using a universal testing machine, the fracture resistance test was performed. The fractured samples were examined using a stereomicroscope and scanning electron microscope to determine modes of failure. Stress distribution was evaluated by 3D finite element analysis, which was performed on digital models of endodontically treated mandibular molars (one model for each design). Results: Group II recorded statistically non-significant higher fracture resistance mean values (3107.2± 604.9 N) than Group I mean values (2962.6 ±524.27 N) as indicated by Student's t-test (t=0.55, p= 0.57). Also, Group II resulted in more favorable failure mode as compared to Group I. Both preparation designs yielded low von-Mises stresses within the factor of safety. However, the stress distribution among different layers of the model differed. Conclusions: FOD having comparable fracture strength to TOD and a more favorable fracture behavior can be used for the preparation of endodontically treated molars.

Comparative Evaluation of Marginal Adaptation and Fracture Strength of Different Ceramic Inlays Produced by CEREC Omnicam and Heat-Pressed Technique

Objective

The aim of this in vitro study was to evaluate marginal adaptation and fracture strength of inlays produced by CEREC Omnicam using different types of blocs and heat-pressed technique. Methods: Seventy-five extracted human mandibular molars were divided randomly into 5 groups (n=15). 60 molars in four groups received MOD inlay preparations. Experimental groups were CO: Intact teeth, EC: IPS e.max CAD and CEREC, LU: Lava Ultimate and CEREC, EL: IPS Empress CAD and CEREC, EP: IPS Empress Esthetic ingots and heat-pressed technique. Marginal gap measurements were taken with a stereomicroscope. Restorations were cemented with Variolink N and stored in distilled water at 37°C for 24 hours. All samples were subjected to thermocycling. The fracture strength of specimens was determined at a 0.5 mm/min crosshead speed until fracture. Fracture modes were determined. Statistical analyses were performed using one-way analysis of variance for fracture strength data and Kruskal–Wallis for marginal gap data (p=0.05).

Results

The mean marginal gap size of EC, LU, EL, and EP were 33.54 µm, 33.77 µm, 34.23 µm, and 85.34 µm, respectively. EP had statistically higher values than other groups. The fracture strength values were significantly higher in the intact teeth group (3959,00 ± 1279,79 N) than those of restored groups EC (2408,00 ± 607,97 N), LU (2206,73 ± 675,16), EL (2573.27 ± 644,73) ve EP (2879,53 ± 897,30).

Conclusion

Inlays fabricated using CEREC Omnicam demonstrated better marginal adaptation than inlays produced with heat-pressed technique, whereas fracture strength values of inlays fabricated with different type of blocks using CEREC Omnicam exhibited similarity to those fabricated with heat-pressed technique.

LED and Halogen Light Transmission through a CAD/CAM Lithium Disilicate Glass-Ceramic

The effect of thickness, shade and translucency of CAD/CAM lithium disilicate glass-ceramic on light transmission of light-emitting diode (LED) and quartz-tungsten-halogen units (QTH) were evaluated. Ceramic IPS e.max CAD shades A1, A2, A3, A3.5, high (HT) and low (LT) translucency were cut (1, 2, 3, 4 and 5 mm). Light sources emission spectra were determined. Light intensity incident and transmitted through each ceramic sample was measured to determine light transmission percentage (TP). Statistical analysis used a linear regression model. There was significant interaction between light source and ceramic translucency (p=0.008) and strong negative correlation (R=-0.845, p<0.001) between ceramic thickness and TP. Increasing one unit in thickness led to 3.17 reduction in TP. There was no significant difference in TP (p=0.124) between shades A1 (ß1=0) and A2 (ß1=-0.45) but significant reduction occurred for A3 (ß1=-0.83) and A3.5 (ß1=-2.18). The interaction QTH/HT provided higher TP (ß1=0) than LED/HT (ß1=-2.92), QTH/LT (ß1=-3.75) and LED/LT (ß1=-5.58). Light transmission was more effective using halogen source and high-translucency ceramics, decreased as the ceramic thickness increased and was higher for the lighter shades, A1 and A2. From the regression model (R2=0.85), an equation was obtained to estimate TP value using each variable ß1 found. A maximum TP of 25% for QTH and 20% for LED was found, suggesting that ceramic light attenuation could compromise light cured and dual cure resin cements polymerization.

Fracture resistance of monolithic zirconia molar crowns with reduced thickness

OBJECTIVES

The purpose of the present study was to analyze the relationship between fracture load of monolithic zirconia crowns and axial/occlusal thickness and to evaluate the fracture resistance of monolithic zirconia crowns with reduced thickness in comparison with that of monolithic lithium disilicate crowns with regular thickness.

MATERIALS AND METHODS

Monolithic zirconia crowns (Lava Plus Zirconia, 3M/ESPE) with specified axial/occlusal thicknesses and lithium disilicate crowns (IPS e.max press, Ivoclar/Vivadent) with regular thickness were fabricated using a dental CAD/CAM system and a press technique, respectively. The crowns cemented onto dies were loaded until fracture. Based on measurements of the crown thickness made by micro-CT and the fracture load, multiple regression analysis was performed.

RESULTS

It was revealed that the occlusal thickness significantly affected the fracture load (p < 0.01), but the axial thickness did not (p = 0.2828). Although the reduction of the occlusal thickness decreased the fracture resistance of the monolithic zirconia crowns, the fracture load of the zirconia crowns with the occlusal thickness of 0.5 mm (5558 ± 522 N) was significantly higher than that of lithium disilicate crowns with an occlusal thickness of 1.5 mm (3147 ± 409 N).

CONCLUSION

Within the limitations of the present study, it is suggested that monolithic zirconia crown with chamfer width of 0.5 mm and occlusal thickness of 0.5 mm can be used in the molar region in terms of fracture resistance.

Resin-composite blocks for dental CAD/CAM applications

Advances in digital impression technology and manufacturing processes have led to a dramatic paradigm shift in dentistry and to the widespread use of computer-aided design/computer-aided manufacturing (CAD/CAM) in the fabrication of indirect dental restorations. Research and development in materials suitable for CAD/CAM applications are currently the most active field in dental materials. Two classes of materials are used in the production of CAD/CAM restorations: glass-ceramics/ceramics and resin composites. While glass-ceramics/ceramics have overall superior mechanical and esthetic properties, resin-composite materials may offer significant advantages related to their machinability and intra-oral reparability. This review summarizes recent developments in resin-composite materials for CAD/CAM applications, focusing on both commercial and experimental materials.

Intraoral Digital Impression Technique: A Review

With the techniques of computer-aided design and computer-aided manufacturing (CAD/CAM) being applied in the field of prosthodontics, a concept of intraoral digital impressions was put forward in the early 1980s. It has drawn comprehensive attention from dentists and has been used for dental prosthesis fabrication in a number of cases. This new digital impression technique is expected to bring about absolute digitization to the mode of prosthodontics. A few published articles have indicated that dental prostheses fabricated from intraoral digital impressions have exhibited remarkable advantages over those from conventional impressions in several respects. The present review discusses intraoral digital impression techniques in terms of the following aspects: (1) categories and principles of intraoral digital impression devices currently available; (2) operating characteristics of the devices; and (3) comparison of the manipulation, accuracy, and repeatability between intraoral digital impression and conventional impression.

Fatigue resistance of CAD/CAM complete crowns with a simplified cementation process

STATEMENT OF PROBLEM

Various computer-aided design and computer-aided manufacturing (CAD/CAM) materials are available to fabricate complete crowns. The type of material may have an effect on the longevity of these restorations.

PURPOSE

To evaluate the fatigue resistance, load-to-failure, failure mode, and antagonistic wear of complete molar computer-aided design and computer-aided manufacturing (CAD/CAM) crowns made of resin nanoceramic (RNC), feldspathic glass ceramic (FEL), or lithium disilicate (LD) placed with a simplified cementation process.

MATERIAL AND METHODS

Forty-five molars received a standardized complete crown preparation and were restored with CAD/CAM crowns (1.5-mm thickness, n=15) made of RNC, FEL, and LD. After cementation, the restorations were submitted to cyclic isometric loading: 200 (×5000), 400, 600, 800, 1000, 1200, and 1400 N at a maximum of 30 000 cycles each. Surviving specimens were axially loaded until failure or to a maximum load of 4500 N. The specimens were analyzed as to failure mode: catastrophic, possibly repairable, and repairable. The groups were compared by using the life table survival analysis and the t test (α=.05).

RESULTS

All the specimens survived the fatigue process until the 800-N step. The survival rate of RNC was 80%, LD 93.3%, and FEL 6.6%. The survival of RNC and LD crowns did not differ from each other but exceeded that of FEL. Postfatigue load-to-failure test was 2500 N (FEL), 3122 N (RNC), and 3237 N (LD). No catastrophic failure occurred in the fatigue test, whereas all of the specimens in the load-to-failure test exhibited catastrophic fractures. Crowns made of RNC seemed to generate the least amount of antagonistic wear.

CONCLUSIONS

Posterior crowns made of RNC and LD were not statistically different, and both had significantly higher fatigue resistance than FEL. All materials survived beyond the normal range of masticatory forces, and all failures were possibly re-restorable except those in the load-to-failure test. RNC crowns seemed to cause less wear of the antagonist.

The Evaluation of Working Casts Prepared from Digital Impressions

Objective

The aim of this study is to evaluate the reproducibility of working casts of a digital impression system by comparing them with the original, virtual, and rapid prototyping casts.

Materials and Methods

A total of 54 cast sets in clinically stable occlusion were used. They were scanned by an iTero intraoral scanner and converted into STL format virtual casts. Rapid prototyping casts and polyurethane casts were fabricated from the iTero milling system based on the virtual casts. Several horizontal and vertical measurements were performed from the four types of casts, that is, original stone casts, virtual casts, rapid prototyping casts, and polyurethane casts of iTero. Measurement error, intraclass correlation coefficient (ICC), and differences among the casts were calculated and compared.

Results

Casts from iTero milling machines exhibited greater dimensional differences and lower ICC values than did other casts. In addition, many of the measurements of the iTero working casts showed statistically significant differences in comparison to the three other types of casts. In contrast, there were no statistically significant differences between the virtual and original casts.

Conclusion

Virtual casts made by the iTero intraoral scanner exhibited excellent reproducibility. However, the casts from the iTero milling machine showed greater dimensional differences and lower reproducibility compared to other types of casts.

WITHDRAWN: Clinical fitting of CAD/CAM zirconia single crowns generated from digital intraoral impressions based on active wavefront sampling

OBJECTIVES: The aim of this clinical trial was to test the accuracy of single all-ceramic zirconia crowns resulting from digital intraoral impressions with active wavefront sampling technology by measuring the marginal and internal fits of the crowns. MATERIALS AND METHODS: Thirty-seven teeth (24 anterior and 13 posterior) in fifteen patients were restored with single zirconia-ceramic crowns (Lava/Lava Ceram; 3M ESPE) generated from a digital intraoral scanner (Lava Chairside Oral Scanner; 3M ESPE). Before definitive insertion, silicone replicas were produced for all 37 crowns. The sample was cut in four sections; each section was evaluated in four points: marginal gap, mid-axial wall, axio-occlusal edge and centro-occlusal. A total of 592 measurements (148 for each evaluation point) was examined using stereomicroscopy with a magnification of 50×. The Mann-Whitney U test was used to evaluate whether there were differences between anterior and posterior values (alpha=0.05). RESULTS: The mean values for each point were: 48.65μm (SD 29.45μm) for the marginal gap, 112.25μm (SD 55.54μm) at the mid-axial wall, 137.81μm (SD 71.31μm) at the axio-occlusal edge of the abutments, and 157.25μm (SD 75.51μm) at the centro-occlusal location. No statistical differences were found between the anterior and posterior group for each point (p-values: P1=0.39; P2=0.38; P3=0.07; P4=0.30). CONCLUSIONS: The marginal and internal fitting values obtained were within literature agreed as clinically acceptable for both anterior and posterior teeth. CLINICAL RELEVANCE: Single crown restorations obtained using digital intraoral impressions based on active wavefront sampling technology presented enough accuracy to be used as an alternative to the conventional impression techniques.

Marginal gap, internal fit, and fracture load of leucite-reinforced ceramic inlays fabricated by CEREC inLab and hot-pressed techniques

PURPOSE

This in vitro study was designed to evaluate and compare the marginal gap, internal fit, and fracture load of resin-bonded, leucite-reinforced glass ceramic mesio-occlusal-distal (MOD) inlays fabricated by computer-aided design/manufacturing (CAD/CAM) or hot pressing.

MATERIALS AND METHODS

Fifty caries-free extracted human molars were prepared for standardized MOD inlays. Impressions of each specimen were made and poured using type IV dental stone. Dies were randomly divided into two equal groups. Twenty-five ceramic inlays were fabricated by the hot-pressed technique using IPS Empress leucite-reinforced glass ceramics, and the other 25 ceramic inlays were produced by CAD/CAM technology using ProCAD leucite-reinforced ceramic blocks and CEREC inLab facilities. Inlays were bonded to the teeth using a dual-cured resin cement. The specimens were stored in distilled water at 37°C for 24 hours and then thermocycled for 5000 cycles. The marginal gap measurements were taken with a stereomicroscope. Specimens in each group of inlay systems were randomly divided into two subgroups of 10 and 15 specimens each. Ten specimens in each subgroup were sectioned mesiodistally for evaluation of the internal fit. The fracture load of specimens in the second subgroup (n = 15) of the two inlay systems was determined under compressive load in a universal testing machine. Data were analyzed using Student's t-test at a significance level of p < 0.05.

RESULTS

The mean marginal and internal gap size in both IPS Empress and ProCAD inlays were less than 100 μm; however, the marginal gap for the IPS Empress restorations was significantly higher than that of ProCAD restorations (p < 0.05). There was no significant difference in the mean internal fit or the fracture load between the two glass ceramic inlays (p > 0.05).

CONCLUSIONS

The leucite-reinforced glass ceramic inlay restorations fabricated by CEREC inLab (CAD/CAM) and the hot-pressed technique provided clinically acceptable marginal and internal fit with comparable fracture loads after luting.