Full Crown Research Articles

Can Dental Office Lighting Intensity Conditions Influence the Accuracy of Intraoral Scanning?

The aim of this study was to evaluate the influence of different settings of ambient light intensity inside the dental office on the accuracy (trueness and precision) of an intraoral scanner (IOS). A full crown preparation was conducted on a resin molar which was scanned using a high resolution extraoral scanner to obtain a reference model. Six light settings were chosen based on the most clinically relevant light conditions inside the workspace, and the preparation was scanned using an intraoral scanner (PlanScan, Planmeca). The obtained data was analyzed using a professional 3D quality control software (Geomagic Control X). There was no statistically relevant difference between the groups when regarding trueness, although a slight influence of the light intensity could be observed on the trueness values. Regarding precision, the best results were obtained in the 3800 lux group, with the other groups presenting close values, excepting the extreme values (400 lux and 11 000 lux) groups that proved to be the most deficient.

Adjacent surface trajectory planning of robot-assisted tooth preparation based on augmented reality

Dental caries is a common disease affecting the health of humans. Tooth preparation is an essential method for the treatment of dental caries, and its effect determines the quality of dental caries restoration directly. At present, the doctor-patient ratio of dentistry is incredibly unbalanced, and it is challenging to meet the increasing demand for tooth preparation. Besides, it is prone to produce visual deviation and positioning error if the tooth preparation is operated manually by doctors. This paper focuses on the adjacent surface tooth preparation of the full crown. By analyzing the preparation process, the robot body as well as the end-effector are selected. Further, the pose and position between the robot and the tooth are established. Through the inverse calculation and interpolation of the NURBS curve, the robot-assisted trajectory planning of adjacent surface tooth preparation is realized. On the basis of the traditional offline programming method, mobile App “Dental Preparation Assisting Software” is developed based on augmented reality, which can interactively display the planned adjacent preparation curves and preparation information. And the robot can be controlled by the mobile App, which improves the visualization and efficiency of the preparation process. Finally, the experimental system based on the Dobot Magician robot is established, and the robot experiments of adjacent surface tooth preparation are carried out. The maximum relative fixed-point error of each feature point in the XYZ axis is 0.24 mm, 0.29 mm and 0.37 mm, respectively. The confidence interval width of each feature point in the XYZ direction is stable at about 0.31 mm on average, and the correlation between the feature points in the three directional variables is not strong. The proposed method of robot-assisted trajectory planning based on augmented reality for adjacent surface tooth preparation can improve the efficiency of tooth preparation and relieve the pressure of manual tooth preparation within the margin of error, and its feasibility and validity are verified.

English

BACKGROUND Inadequate marginal fit of fixed restorations leads to plaque accumulation, recurrent caries and periodontal problems. The purpose of this experimental study is to evaluate and compare the marginal fit/gap of computer-aided design and computeraided manufacturing (CAD/CAM) fabricated zirconia copings and zirconia full contoured monolith crowns fabricated on type IV gypsum die having a definite cement spacer thickness of 0.05mm. METHODS This is an in-vitro experimental study carried out from November 2018 to November 2019. A master stainless steel die was used to make 52 type IV die stone models which were randomly divided into 2 groups of 26 samples each. Group 1: zirconia copings and group 2: zirconia monolith full contoured crowns. These restotations were fabricated using CAD/CAM. The marginal gap of each zirconia copings and zirconia full contoured crowns was assessed using scanning electron microscopic analysis on four different pre-marked points (GEMINI SEM 500; ZEISS). Observations were tabulated and analyzed statistically. Independent t-test was used to compare the measurements between zirconia copings & zirconia monolith crowns. RESULTS The least marginal gap observed was for group 2 (zirconia full contoured crown) with a mean value of 29.88 ± 9.16 μm while that of group1 (zirconia coping) was 73.64 ± 28.13 μm. There was a statistically significant difference in the measurements between zirconia copings and zirconia full contoured monolith crowns (P - value < 0.001). There was statistically significant difference in each side of zirconia monolith crowns when compared to the corresponding side of zirconia copings (P - Value < 0.001). CONCLUSIONS CAD/CAM milled full contoured zirconia crowns showed least marginal discrepancy when compared to zirconia copings. All samples had marginal gap within the clinically acceptable range of 120 μm. KEY WORDS Monolith, Zirconia Crowns, Zirconia Copings, Full Contoured Crowns, CAD-CAM

Relative amount of tooth structure removal in different partial- and full-crown preparation designs.

To assess the effect of tooth morphology on the amount of tooth structure removal and the effect of different assessment methods on the detected amount of removed tooth structure. Eight test groups (n = 10) of standardized artificial teeth were prepared for partial and full crowns. All teeth were prepared by the same operator following predefined preparation parameters. Tooth structure removal was measured using three different assessment methods: digital volumetric analysis (DVA), weight analysis (WA), and combined computer-aided manufacture and weight analysis (CAMWA). Nonparametric repeated-measures analysis of variance and post hoc analyses were used to determine the influence of tooth morphology and assessment method on the detected amount of tooth structure removal. For partial crown preparations, only the tooth morphology had a significant impact on the detected amount of tooth structure removal (P < .0001), not the different assessment methods used (P = .08). Tooth structure removal was not significantly different between the canine and incisor groups, but was for the other groupwise comparisons. For full crown preparations, the tooth morphology (P = .047) and different assessment methods (P = .01) had an impact on the detected tooth structure removal. However, only a few groupwise comparisons reached the significance level. The amount of tooth structure removal depended on the tooth morphology and the type of assessment method, which should be taken into account when comparing results across studies. The detected amount of tooth structure removal was below the values described in the literature, independent of the assessment method used.

Influence of Post-Core and Crown Type on the Fracture Resistance of Incisors Submitted to Quasistatic Loading.

The aim of this paper was to evaluate the fracture resistance and failure type of maxillary incisor teeth, rebuilt with various types of post-core restorations and full crowns made of either direct conventional particulate filler composite (PFC, G-aenial Anterior, GC, Tokyo, Japan) or indirect CAD/CAM restorations (composite Cerasmart 270 and glass ceramic LiSi Block from GC). One hundred (n = 10/group) central incisors were cut and divided into 10 experimental groups restored with different approaches. In approach A, teeth were restored with a core build-up composite (Gradia Core, GC) for a core and full crown of PFC. Approach B had teeth restored using composite core and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. Approach C contained teeth restored with a core of short fiber-reinforced composite (everX Flow, GC) and prefabricated fiber posts, and a complete crown of either PFC or CAD/CAM. In approach D, the teeth had a core of short fiber-reinforced composite only, and a complete crown of either PFC or CAD/CAM restorations. The root canals were prepared, and when posts were used, they were luted with either a dual-cure resin cement (LinkForce, GC) or everX Flow. As the control, sound teeth (n = 10) were used. Restorations were quasi-statically loaded until fracture. Failure type was visually investigated. The interface between the fiber post and luting cement was investigated using SEM, before and after completion of the loading test. The data were analyzed by analysis of variance (p = 0.05) followed by Tukey’s test. None of the restorative approaches restored the fracture load strength of intact teeth (p < 0.05). Restorations with additional fiber posts (Approaches B and C) had higher load-bearing capacity (p < 0.05) than restorations without fiber posts (Approaches A and D). Restorations that had short fiber-reinforced composite cores with or without fiber posts presented more repairable failures. Using short fiber-reinforced composite as post-luting and core build-up material with conventional fiber posts proved to be a promising method to strengthen severely damaged incisors.

Finish line for full coverage crown: A systematic review

Finish line for full coverage crown: A systematic review

Análise em micro-CT de dente rachado em segundo molar mandibular com anatomia em C após trauma oclusal: Relato de caso

O objetivo do presente estudo foi analisar em micro-CT dente extraído por fissura. Uma mulher de 38 anos, branca, com queixa de desconforto ocasional após morder caroço de milho de pipoca, procurou a urgência. Após exame clínico intra-oral e radiográfico, o segundo molar mandibular direito (dente 47) foi diagnosticado com polpa viva e fratura das cúspides linguais, e após remoção de restauração de amálgama constatou-se fratura incompleta iniciada na crista proximal distal da coroa. O plano de tratamento iniciou-se com reabilitação protética através de coroa total. Três meses após pulpite irreversível sintomática foi diagnosticada. A cavidade pulpar foi acessada através da coroa protética e o dente foi tratado endodonticamente. Dois anos depois a paciente apresentou fístula próxima a sulco gengival e sondagem periodontal de 12mm no centro da superfície distal. Ao exame tomográfico de feixe cônico observou-se extensa perda óssea atingindo o canal mandibular. O plano de tratamento foi a exodontia do elemento dentário e posterior planejamento de implante. O dente extraído foi então submetido ao escaneamento no micro-CT. Na análise das imagens do micro-CT do dente extraído, constatou-se dente rachado, com trinca estendendo-se da coroa até a raiz proximal (face distal). Foi verificado também má adaptação do cone de guta-percha no terço apical do tratamento endodôntico realizado. Através deste relato, podemos inferir que, o diagnóstico de dente rachado é um desafio na prática clínica, e a propagação corono-radicular da rachadura está associada a infiltração microbiana e consequente risco de perda do elemento dental.

Influence of different material substrates on the accuracy of 3 intraoral scanners: A single-blinded in vitro study.

To compare the accuracy of three commercially available intraoral scanners when imaging various dental material substrates.A maxillary dentate typodont model with 11 different dental material substrates was prepared and scanned using three intraoral scanners (TRIOS 3, 3Shape; CS 3600, Carestream; and Emerald S, Planmeca). The model was further scanned with a laboratory scanner (7series, Dental Wings) for reference. Files were exported in standard tessellation language format and inserted into a metrology 3D mesh software (CloudCompare).In terms of influence of different substrates on IOS trueness, a significant effect on the performance of TRIOS 3 and Emerald S was revealed. Concerning the accuracy of different intraoral scanners when scanning more translucent and reflective materials, pairwise comparisons revealed significant differences among scanners. In terms of complete-arch trueness and precision, pairwise comparisons revealed that TRIOS 3 had significantly higher trueness and precision compared to CS3600 and Emerald S. The complete-arch trueness and precision of CS3600 and Emerald S did not differ significantly.Dental material substrates influenced the accuracy of all three tested scanners. The full metal crown exhibited significantly lower trueness compared to other substrates across all three scanners. For the high-translucency substrate group, TRIOS 3 exhibited significantly higher trueness compared to CS 3600. Polished and unpolished class II amalgam restorations of similar dimensions did not exhibit significant differences in trueness regardless of intraoral scanner. In terms of complete-arch accuracy, TRIOS 3 had significantly higher trueness and precision compared to CS 3600 and Emerald S. All three scanners exhibited complete-arch average accuracy below 100 μm.

Coronal Restoration as a Predictor of Periapical Disease in Non-Endodontically Treated Teeth.

ObjectivesTo compare the frequency of apical periodontitis (AP) in non-endodontically treated teeth restored with full coverage crowns, amalgam and resin composite fillings, and to disclose the association of type and quality of coronal restoration with periapical disease.Material and MethodsThe cross-sectional study involved 597 subjects who attended the Dental Clinic of the Clinical Hospital Centre, Rijeka, Croatia for the first time. Data were collected by means of a clinical and radiological survey. The following data were recorded for all permanently restored non-endodontically treated teeth: the type, the quality of coronal restoration according to clinical and radiographic criteria for marginal integrity as well as the recurrent caries presence, periapical status and marginal bone loss. Chi-square tests were used to analyze the difference in periapical status regarding the type and the quality of restoration. The multivariate logistic regression analysis was used to assess the effect of explanatory tooth-specific variables on periapical status.ResultsThere was no significant difference in the proportion of AP with regards to the type and material of adequate quality coronal restorations (χ2=5.000, P=0.082). The regression analysis revealed significant positive associations with outcome variable (AP) for crowns (OR=3.39; P<0.001), recurrent caries (OR=4.67; P<0.001) and premolar teeth (OR=1.73; P=0.002).ConclusionIf the quality of restorations is adequate, there is no difference in the periapical status of non-endodontically treated teeth regarding the type and material of coronal restoration.

Quantitative analysis on the wear of monolithic zirconia crowns on antagonist teeth

BackgroundThe present study aimed to quantitate the wear of the highly transparent Yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) ceramic monolithic zirconia crown on the enamel in vivo and discuss the prone position of the wear and the underlying mechanism.Methods A total of 43 patients with 43 posterior teeth were selected for full zirconia crown restoration and examined immediately, at 6 months, and at 1 year after restoration. During the follow-up visit, the fine impression of the patients’ monolithic zirconia crowns, the antagonist teeth, the corresponding contralateral natural teeth, the super plaster cast, and epoxy resin model was ontained. The model of epoxy resin was observed under a stereo microscope, and the microstructure parts were observed under a scanning electron microscope.ResultsAfter 1 year, the mean depth and volume of wearing of the monolithic zirconia crown were the smallest (all P < 0.01), while those of the antagonist teeth were significantly larger than those of the natural teeth (P < 0.0001), and no significant difference was found among the natural teeth (P = 0.3473, P = 0.6996). The amount of wear after one year was remarkably higher than that at 6 months (P < 0.0001). The microscopic observation revealed the tendency of wearing of the monolithic zirconia crown on the antagonist teeth at the protruding early contact points. Electron micrographs of tooth scars showed that the wearing mechanism of the monolithic zirconia crown on natural teeth was mainly abrasive and fatigue wear.ConclusionsAlthough the self-wearing is insignificant, the monolithic zirconia crown can cause wear of the antagonist teeth via occlusal or early contact significantly; the amount of wearing is higher than that of natural teeth and increases over time. The wearing mechanism is mainly abrasive and fatigue wear.

&amp;ldquo;Conservative Bonded Restoration (An Alternative to Full Coverage Crown): A Case Report on Endocrown

ABSTRACTBackgroundThe restoration of endodontically treated tooth (ETT) with substantial loss of the tooth structure is challenging as it carries a higher chance of biomechanical failure than vital tooth in restorative dentistry. Post combined with complete coverage restoration is a well-established technique to save such teeth from fracture, but it does not follow the minimal invasive principles of adhesive dentistry.Case descriptionThis case report describes the management of endodontically treated mandibular premolar with lithium disilicate glass-ceramic endocrown (Emax).ConclusionEndocrown is a feasible option for the restoration of extensively damaged posterior tooth after endodontic treatment. Since posterior teeth are vulnerable to tooth loss, endocrown, which is a single partial restoration, can be regarded as replacing a single crown with intraradicular retention.How to cite this articleBejoy BM, Anitha S, George L. Conservative Bonded Restoration (An Alternative to Full Coverage Crown): A Case Report on Endocrown. Cons Dent Endod J 2020;5(2):42–47.

Evaluation of fracture strength of two kinds of zirconia all-ceramic crowns with different edge compensation angles

Objective To evaluate the effects of different edge compensation angles on the fracture strength of multilayer zirconia all-ceramic crowns and traditional uniform zirconia all-ceramic crowns. Methods The resin tooth preparation specimen of the mandibular first molar with a knife-edge was fabricated. A 3D digital model of the specimen was obtained by scanning it with a 3D dental model scanner. The 3D digital model was imported into computer aided design (CAD) software, and three 3D digital models of the full crown with the same surface shape are designed with the edge compensation angles of 30°, 45° and 60°, respectively. Then, the designed 3D digital model is imported into computer aided manufacturing (CAM) software. Three kinds of multilayer and homogeneous zirconia all-porcelain crowns with different edge compensation angles were fabricated, 10 each for a total of 60. The fracture load of each crown was measured under the electronic universal testing machine. Results Fracture load of multilayer and uniform zirconia all-ceramic crowns, (4 322.86±610.07) N and (5 914.12±596.80) N in the 30° group, (5 264.82±883.76) N and (5 220.83±563.38) N in the 45° group and (4 900.42±345.41) N and (5 050.22±560.24) N in the 60° group, respectively. The fracture load of multi-layer zirconia all-ceramic crowns in the 30° group was significantly lower than that of homogeneous zirconia all-ceramic crowns(P 0.05). In the multi-layer zirconia all-ceramic crowns: the fracture load of the 30° group was significantly lower than that of the 45° group (P 0.05).In uniform zirconia full crown group: the 30° group was higher than the 45° group, the 30° group was higher than the 60° group (P 0.05). Conclusion The fracture loads of three kinds of uniform and multilayer zirconia all ceramic crowns with different edge compensation angles can meet the clinical requirements. A smaller edge compensation angle is recommended when using traditional zirconia all-ceramic crowns, while 45° is recommended when using multi-layer zirconia all-ceramic crowns.

Analysis of The Reproducibility of Subgingival Vertical Margins Using Intraoral Optical Scanning (IOS): A Randomized Controlled Pilot Trial.

Background: The aim of this randomized controlled trial was to evaluate the capability of an IOS (Intra Oral Scanner) device, used in standardized conditions, to detect margins of abutments prepared with knife-edge finishing line located at three different levels in relation to the gingival sulcus. Methods: sixty abutment teeth for treatment with full crowns were selected and randomly divided in three groups accordingly to the depth of the finishing line: Group A: supragingival margin; Group B: 0.5–1.0 mm into the sulcus; Group C: 1.5–2.0 mm into the sulcus. Temporary crowns were placed for two weeks and then digital impressions (Aadva IOS 100, GC, Japan) were made of each abutment. As controls, analog impressions were taken, poured, and scanned using a laboratory scanner (Aadva lab scanner, GC, Japan). Two standard tessellation language (STL) files were generated for each abutment, subsequently processed, and superimposed by Exocad software (Exocad GmbH, Darmstadt, Germany), applying the “best-fit“ algorithm in order to align the scan of the conventional with the digital impressions. The distances between each preparation margin and the adjacent gingival tissue were measured. Four measures were taken, two interproximally and buccally, for a total of six measures of each abutment considering three modes of impressions. The data were statistically evaluated using two-way analysis of variance (ANOVA) for each site and the Bonferroni test. Results: there was no difference between the two kinds of impression in Group A in both sites, in Group B a difference of 0.483 mm and 0.682 mm at interproximal and buccal sites, respectively, and in Group C 0.750 mm and 0.964 mm at interproximal and buccal sites, respectively. The analysis performed on a site level (mesial/distal/vestibular) for the depth of both vertical preparations revealed significant differences (p < 0.0001). After a post hoc analysis (Bonferroni), vestibular sites of the shallow vertical preparations resulted in significantly lower values compared to the other sites prepared deeply. Conclusions: the results showed that the location of the margin is an important factor in making a precise and complete impression when IOS (Intra Oral Scanner) is used. Moreover, deep preparation into the sulcus is not recommended for IOS (Intra Oral Scanner) impressions.

Smile Designing Using Laminate Veneers – A Case Report

Aim: To describe a treatment plan that serves as a functional and aesthetic alternative to orthodontic treatment options that may be time-consuming, for mild crowding in anterior teeth wherein only aesthetics is of concern. Background: Laminate veneers are a conservative alternative to full coverage crowns for improving the appearance of the anterior teeth. Adhesive technologies make it possible to bond the prosthesis whilst preserving the tooth structure.[3] Immediate results are achieved since the prosthesis could be delivered within a few days. Ceramics are aesthetic, biocompatible, wear- resistant, exhibit excellent colour stability, and present a thermal coefficient of expansion similar to enamel. Hence prove to be the most desired material for laminate veneers. Case Description: Laser gingivoplasty was done on the maxillary anterior (13 to 23) to align the gingival zenith. Veneer preparation was done on the same teeth with minimal tooth reduction (0.5 mm) on the enamel only. All-ceramic veneers were bonded to the teeth with light cure resin cement to achieve the desired aesthetic results. Conclusion: Smile aesthetics can be achieved only when there is harmony between the teeth and the gingival zenith. With proper diagnosis and treatment planning, a desirable aesthetic result was achieved. Clinical Signification: Smile designing includes scientific and artistic principles, which helps in creating an aesthetic smile. These norms were found through the collection of data from patients, diagnostic casts, mock wax-ups, measurements, concepts of beauty, and golden proportions.

Evaluation of Polishing Systems for CAD/CAM Polymer-Infiltrated Ceramic-Network Restorations.

The purpose of this study was to evaluate the effectiveness of five different polishing systems on a computer-aided design and computer-aided manufacturing (CAD/CAM) polymer-infiltrated ceramic-network restoration with nanoscale assessment using atomic force microscopy (AFM) and visual assessment performed by dental school senior students and faculty members. Forty-eight full coverage crowns were milled out of polymer-infiltrated ceramic-network CAD/CAM blocks (Vita Enamic) for polishing with one company proprietary, two ceramic and two composite polishing systems. The prepared crowns were divided into six groups: (1) no polishing (control); (2) polishing with Vita Enamic Polishing Kit (VEna); (3) polishing with Shofu Porcelain Laminate Polishing Kit (SCer); (4) polishing with Brasseler Dialite Feather lite All-Ceramic Adjusting & Polishing System (BCer); (5) polishing with Shofu Composite Polishing Kit (SCom); and (6) polishing with Brasseler Composite Polishing Kit (BCom). The polished crown surface topography was observed, and surface roughness and area were measured with AFM. In addition, polished crowns were visually assessed by 15 senior dental students and 15 dental school faculty members. All polishing treatments significantly reduced the surface roughness and area of the crown compared with the control. SCom and BCom showed significantly higher surface area than VEna, and the SCer and BCer groups were intermediate, showing no significant difference from either VEna or SCom and BCom. There were no significant differences in surface roughness between any of the systems. Dental students and faculty members classified the groups polished with VEna, SCer, and BCer groups as clinically acceptable, and they selected BCer group as the best polished restorations and the control group as the least polished restorations. Ceramic and composite polishing systems produced similar polishing results as that observed using a company proprietary polishing system. However, effectiveness for polishing using a company proprietary and ceramic polishing system tends to be higher than composite polishing systems.

Comparison of microleakage between different restorative materials to restore marginal gap at crown margin.

BackgroundAn occurrence of secondary caries around the indirect restoration margin is reported to remain a leading cause of failures.ObjectiveThis study aimed to test the interfacial microleakage of conventional glass-ionomer (CGI), resin-modified glass ionomer (RMGI) and Nano-hybrid composite (CR) restorations at a full veneer margin crown.MethodsNinety human extracted molar teeth were divided into three groups (n = 30). Each group was subdivided into three subgroups (n = 10) according to the extent of the structural defects; The structural defect in G1 had a depth of 1.5 mm, width and length at 2 mm and 1 mm intrusion within the crown cervical margin. The corresponding structural defect dimension values for G2 were 2, 5, 4 and 2 mm with defects extending onto the root structure. Meanwhile, G3: structural deficiency of 2 mm depth, 3 mm width and 3 mm length and with 1.5 mm extension into the prepared teeth. These structural defects in each subgroup were restored with CGI, RMGI and CR. Artificial carious lesion formation was induced at the cervical finish line with a demineralizing solution. The artificial carious lesions were restored as per the group distribution. Subsequently, teeth samples were prepared and cemented with Nickel-chromium full coverage restorations utilizing glass-ionomer luting cement. Teeth samples were thermocycled, isolated with nail varnish, and immersed in 0.1% methylene blue for 24 h. The teeth samples were sectioned longitudinally, dye penetration was evaluated with a stereomicroscope. The data were analyzed with Kruskal–Wallis and Mann–Whitney U tests.ResultsCGI-G1 recorded the highest micro-leakage score at 1.450; while CR-G3 recorded the least score (0.350). At a cementum-restoration interface, CR-G1 (0.850) documented the lowest micro-leakage; RMGI-G3 had a greater value at 1.700.ConclusionsThe hybrid CR could be effectively used to restore the restoration of a marginal gap around crown margins.

Accuracy of four different intraoral scanners according to different preparation geometries.

To evaluate the accuracy (trueness and precision) achievable with four intraoral scanners (IOSs) and different preparation geometries. A model of a maxillary arch with different preparation geometries (onlay, inlay, veneer, full-crown) served as the reference master model (RMM). The RMM was scanned 10 times using four commonly used IOSs (Trios 2 [TR], 3Shape; Omnicam [OC], Dentsply Sirona; True-Definition [TD], 3M ESPE; and Primescan [PS], Dentsply Sirona). Scans were matched using a 3D measurement software (Inspect 2019, GOM) and a best-fit algorithm, and the accuracy (trueness and precision) of the preparation types of the scanning data was evaluated for positive and negative deviations separately. All data were subjected to univariate analysis of variance using SPSS version 24 (IBM). Mean (± SD) positive deviations ranged from 4.6 ± 0.7 μm (TR, veneer) to 25.9 ± 2.4μm (OC, full crown). Mean negative deviations ranged from -7.2 ± 0.6 μm (TR, veneer) to -26.4 ± 3.8 μm (OC, full crown). There were significant differences (P < .05) in terms of trueness and precision among the different IOSs and preparation geometries. The transfer accuracy of simple geometries was significantly more accurate than those of the more complex prosthetic geometries. Overall, however, the IOSs used in this study yielded results that were clinically useful for the investigated preparation types, and the mean positive and negative deviations were in clinically acceptable ranges.

In Vitro Comparison of Marginal and Internal Fit of Zirconia Copings Fabricated by One CAD/CAM System with Two Different Scanners.

Objectives: Marginal and internal fit of restorations are two important clinical factors for assessing the quality and durability of computer-aided design/computer-aided manufacturing (CAD/CAM)-fabricated monolithic zirconia restorations. The purpose of this study was to evaluate the marginal and internal fit of CAD/CAM zirconia crowns with two different scanners (i3D scanner and 3Shape D700). Materials and Methods: Twelve extracted sound human posterior teeth were prepared for full zirconia crowns. Two different extraoral scanners namely i3D scanner and 3Shape D700 were used to digitize type IV gypsum casts poured from impressions. The crowns were milled from presintered monolithic zirconia blocks by a 5-axis milling machine. The replica technique and MIP4 microscopic image analysis software were utilized to measure the marginal and internal fit by a stereomicroscope at ×40 magnification. The collected data were analyzed by paired t-test. Results: The mean marginal gap was 203.62 μm with 3Shape D700 scanner and 241.07 μm with i3D scanner. The mean internal gap was 192.30 μm with 3Shape D700 scanner and 196.06 μm with i3D scanner. The results of paired t-test indicated that there was a statistically significant difference between the two scanners in marginal fit (P=0.04); while, there was no statistically significant difference in internal fit (P=0.761). Conclusion: Within the limitations of this study, the results showed that type of extraoral scanner affected the marginal fit of CAD/CAM fabricated crowns; however, it did not have a significant effect on their internal fit.

Three-Dimensional Finite Element Analysis of Stress Distribution in a Tooth Restored with Full Coverage Machined Polymer Crown

The effect of a restored machined hybrid dental ceramic crown–tooth complex is not well understood. This study was conducted to determine the effect of the stress state of the machined hybrid dental ceramic crown using three-dimensional finite element analysis. Human premolars were prepared to receive full coverage crowns and restored with machined hybrid dental ceramic crowns using the resin cement. Then, the teeth were digitized using micro-computed tomography and the teeth were scanned with an optical intraoral scanner using an intraoral scanner. Three-dimensional digital models were generated using an interactive image processing software for the restored tooth complex. The generated models were imported into a finite element analysis software with all degrees of freedom concentrated on the outer surface of the root of the crown–tooth complex. To simulate average occlusal load subjected on a premolar a total load of 300 N was applied, 150 N at a buccal incline of the palatal cusp, and palatal incline of the buccal cusp. The von Mises stresses were calculated for the crown–tooth complex under simulated load application was determined. Three-dimensional finite element analysis showed that the stress distribution was more in the dentine and least in the cement. For the cement layer, the stresses were more concentrated on the buccal cusp tip. In dentine, stress was more on the cusp tips and coronal 1/3 of the root surface. The conventional crown preparation is a suitable option for machined polymer crowns with less stress distribution within the crown–tooth complex and can be a good aesthetic replacement in the posterior region. Enamic crowns are a good viable option in the posterior region.

Impact of Layer Thickness and Storage Time on the Properties of 3D-Printed Dental Dies.

The purpose of this study was to evaluate the effect of printing layer thickness on the repeatability and surface roughness of 3D-printed dies and detect the effect of layer thickness and storage time on the dimensional stability of 3D-printed dies. One stereolithography (STL) file of an upper molar prepared for a full ceramic crown was used to print three groups of dies: 25 µm, 50 µm, and 100 µm. Repeatability was evaluated by linear and area measurements with a digital caliper and a digital metrology microscope. Dimensional stability was analyzed at 3 weeks, 6 months, and 1 year of storage time. Surface roughness parameters were measured with a 3D confocal laser scanning microscope. Statistics were completed using one-way analysis of variance and Tukey’s post hoc tests, p < 0.05. Printing time decreased as layer thickness increased. All groups showed high repeatability and comparable surface roughness while showing differences in their linear dimensions and surface areas. At the 3 week storage interval, dimensional changes were observed in all groups. Within this experimental study’s constraints, it can be concluded that changing the 3D-printing layer thickness does not affect the repeatability or the surface roughness of the product; meanwhile, changes to the layer thickness and storage time influence the dimensional stability of 3D-printed dies.