Generalized Bézier-like model and its applications to curve and surface modeling.

The subject matter of surfaces in computer aided geometric design (CAGD) is the depiction and design of surfaces in the computer graphics arena. Due to their geometric features, modeling of Bézier curves and surfaces with their shape parameters is the most well-liked topic of research in CAGD/computer-aided manufacturing (CAM). The primary challenges in industries such as automotive, shipbuilding, and aerospace are the design of complex surfaces. In order to address this issue, the continuity constraints between surfaces are utilized to generate complex surfaces. The parametric and geometric continuities are the two metrics commonly used for establishing connections among surfaces. This paper proposes continuity constraints between two generalized Bézier-like surfaces (gBS) with different shape parameters to address the issue of modeling and designing surfaces. Initially, the generalized form of C3 and G3 of generalized Bézier-like curves (gBC) are developed. To check the validity of these constraints, some numerical examples are also analyzed with graphical representations. Furthermore, for a continuous connection among these gBS, the necessary and sufficient G1 and G2 continuity constraints are also developed. It is shown through the use of several geometric designs of gBS that the recommended basis can resolve the shape and position adjustment problems associated with Bézier surfaces more effectively than any other basis. As a result, the proposed scheme not only incorporates all of the geometric features of curve design schemes but also improves upon their faults, which are typically encountered in engineering. Mainly, by changing the values of shape parameters, we can alter the shape of the curve by our choice which is not present in the standard Bézier model. This is the main drawback of traditional Bézier model.

Effect of surface treatment strategies on bond strength of additively and subtractively manufactured hybrid materials for permanent crowns.

OBJECTIVES: The purpose of this study is to evaluate the bond strength of different computer-aided design / computer-aided manufacturing (CAD/CAM) hybrid ceramic materials following different pretreatments. METHODS: A total of 306 CAD/CAM hybrid material specimens were manufactured, n = 102 for each material (VarseoSmile Crownplus [VSCP] by 3D-printing; Vita Enamic [VE] and Grandio Blocs [GB] by milling). Each material was randomly divided into six groups regarding different pretreatment strategies: control, silane, sandblasting (50 µm aluminum oxide particles), sandblasting + silane, etching (9% hydrofluorics acid), etching + silane. Subsequently, surface roughness (Ra) values, surface free energy (SFE) were measured. Each specimen was bonded with a dual-cured adhesive composite. Half of the specimens were subjected to thermocycling (5000 cycles, 5-55 °C). The shear bond strength (SBS) test was performed. Data were analyzed by using a two-way analysis of variance, independent t-test, and Mann-Whitney-U-test (α = 0.05). RESULTS: Material type (p = 0.001), pretreatment strategy (p < 0.001), and the interaction (p < 0.001) all had significant effects on Ra value. However, only etching on VSCP and VE surface increased SFE value significantly. Regarding SBS value, no significant difference was found among the three materials (p = 0.937), while the pretreatment strategy significantly influenced SBS (p < 0.05). Etching on VSCP specimens showed the lowest mean value among all groups, while sandblasting and silane result in higher SBS for all test materials. CONCLUSIONS: The bond strength of CAD/CAM hybrid ceramic materials for milling and 3D-printing was comparable. Sandblasting and silane coupling were suitable for both millable and printable materials, while hydrofluoric etching should not be recommended for CAD/CAM hybrid ceramic materials. CLINICAL RELEVANCE: Since comparable evidence between 3D-printable and millable CAD/CAM dental hybrid materials is scarce, the present study gives clear guidance for pretreatment planning on different materials.

Computer-Aided Design and Biological Evaluation of Diazaspirocyclic D4R Antagonists.

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive loss of dopaminergic neurons in the substantia nigra, resulting in motor dysfunction. Current treatments are primarily centered around enhancing dopamine signaling or providing dopamine replacement therapy and face limitations such as reduced efficacy over time and adverse side effects. To address these challenges, we identified selective dopamine receptor subtype 4 (D4R) antagonists not previously reported as potential adjuvants for PD management. In this study, a library screening and artificial neural network quantitative structure-activity relationship (QSAR) modeling with experimentally driven library design resulted in a class of spirocyclic compounds to identify candidate D4R antagonists. However, developing selective D4R antagonists suitable for clinical translation remains a challenge.

Effect of different polishing methods on roughness and color stability of air-abraded restorative materials after artificial accelerated aging.

PURPOSE: To evaluate the effect of air abrasion and polishing procedures on roughness and color stability of ceramic and composite materials after artificial accelerated aging. METHODS: In this study, six restorative materials were tested: feldspathic ceramic (CEREC Blocks), glass ceramic (IPS e.max CAD), resin-based hybrid ceramic (Cerasmart), microhybrid composite (Charisma Classic), nanohybrid composite (Charisma Diamond) and nanoceramic composite (CeramXOne). Forty square-shaped composite specimens were fabricated from each composite and CAD-CAM ceramic material. Initial surface roughness measurements were performed using a profilometer and color measurements of each specimen with a spectrophotometer. Ten control specimens for each group did not receive air abrasion. The other specimens were treated by an air abrasion device and then were randomly divided into three subgroups of 10 specimens (n= 10). After air abrasion, 10 specimens of each group did not receive polishing (Air abrasion group) and others were repolished with Sof-Lex kit (Sof-Lex group) or a rubber kit (Rubber group). Surface roughness and color measurements were repeated before and after 300 hours of artificial accelerated aging (AAA). The univariate test and then three-way ANOVA and two-way ANOVA were performed for comparison of groups (α= 0.05). RESULTS: The univariate statistical analysis revealed that the restorative materials were differently affected after air abrasion, polishing methods and AAA (P< 0.001). Three-way ANOVA showed that the surface roughness of the restorative materials increased after air abrasion and AAA (P< 0.001). Two-way ANOVA showed statistically significant differences between color changes of ceramic (CEREC and IPS e.max CAD) and composite based restorative materials (P< 0.001). CLINICAL SIGNIFICANCE: Clinicians should be aware that air abrasion at a specified power and time significantly changes the surface roughness of the materials except for CEREC. Additionally, polishing procedures (Sof-Lex, Rubber) did not significantly reduce the surface roughness of the ceramic groups. After air abrasion, depending on the material type used clinically, restorations should be repolished to reduce roughness and ensure color stability.

The effect of different deep margin elevation methods on the fracture strength of CAD-CAM restorations.

PURPOSE: To evaluate the effect of two resin composites (with different viscosities) and the elevation amount on fracture strength and fracture behavior of molars with and without deep margin elevations (DME). METHODS: 70 extracted, caries-free human molars were selected. All teeth were prepared as MOD onlay cavities with a margin 2 mm below the cemento-enamel junction (CEJ) on the mesial and buccal sides and 2 mm above the CEJ on the distal side. The teeth were divided into two groups according to the type of resin composite used in margin elevation, elevated with flowable composite (Universal Flo) or condensable composite (G-Aenial Posterior). These two groups were further subdivided into subgroups in which the elevation was 2, 3, or 4 mm, and a control group in which the non-elevated indirect restoration was directly bonded to the subgingival margin, making a total of seven groups (n= 10). After elevations, the restorations were completed using a nanoceramic CAD-CAM block (Cerasmart A3 HT) and as adhesive cement, G-Cem Link Force. Static force was applied to the restored teeth using a universal testing machine at an angle of 15° until fracture occurred. Fracture strength values were recorded, and fracture types were examined under 6x magnification. One-way ANOVA was carried out to determine the effect of DME on the fracture strength. A two-way ANOVA was conducted to investigate main and interaction effects of the material type used in the elevation and the amount of elevation made on the fracture strength (P< 0.05). RESULTS: Using flowable or condensable composite as elevation material did not affect the fracture strength of CAD-CAM restorations. Flowable and condensable composites of 2, 3, or 4 mm did not significantly affect fracture strength values for either material. Specimen margins with and without elevation exhibited similar fracture strength values. The type of material used in the elevation and the amount did not affect the fracture strength of teeth. CLINICAL SIGNIFICANCE: The deep margin elevation technique for teeth with carious lesions extending subgingivally, may be useful in routine practice.

Effect of primer compositions on the bond strength of resin cement to ceramic materials.

PURPOSE: To investigate the effect of different chemical compositions of primers on the bond strength between nano-ceramic, polymer-infiltrated ceramic, and zirconia ceramic materials and dual-cure cement. METHODS: Fifty 2 mm-thick specimens were prepared from Vita Enamic, Cerasmart, and Katana Zirconia UTML. The specimens were embedded in acrylic blocks. To standardize the surfaces, 600 grit silicon carbide abrasives were applied underwater for 60 seconds. Then, each section underwent grit-blasting using Al2O3 with a particle size of 50 µm at 10 mm and a pressure of 2 bar for 10 seconds. Each prepared sample from the experimental groups received the appropriate primer (Z-PRIME Plus, G-Multi Primer, Alloy Primer, Clearfil Primer Plus) according to the manufacturers' instructions. Subsequently, the prepared CAD-CAM specimens underwent cementation using Duo-Link Universal Adhesive Resin Cement with a cylinder mold of 2.6 mm diameter and 3 mm height. The cement was light-cured for 20 seconds from both sides. The specimens obtained were stored in distilled water at 37°C for 24 hours. The shear bond strength test of the specimens was performed using a Bisco Shear Bond Tester device. The data were statistically analyzed using ANOVA and the Kruskal-Wallis test (P< 0.05). RESULTS: The highest bond strength was observed in Z-Prime Plus applied specimens, regardless of material differences (Cerasmart 11.60±4.61; Vita Enamic 12.93±3.86; Katana Zirconia 13.85±4.00). The lowest bond strength, showing differences according to materials (P< 0.05), was found for Clearfil Ceramic Primer Plus-Cerasmart (7.88±3.90), Alloy Primer-Vita Enamic (7.90±2.14), and G Multi Primer-Katana Zirconia UTML (4.98±3.67). CLINICAL SIGNIFICANCE: Failure of the restoration usually occurs at the weakest point in this three-element structure, thus correct primer selection according to material type is important. Additionally, for all CAD-CAM materials used in the study, Z-Prime Plus showed significantly greater adhesion strength than other systems so it may be more appropriate for use in clinics.

Intra-radicular retention with custom designed CAD-CAM fibRe-reinforced composite post-core: a dental technique.

A technique is outlined for utilising a polymeric composite reinforced with glass fibres in a three-dimensional mesh as a post-core in aesthetic cases. The clinical procedure involves obtaining an impression of the root canal space, scanning the definitive cast, and milling a fibre-reinforced composite post-core. Subsequently, the intra-radicular post-core is cemented using an adhesive resin cement. The use of custom-made computer-aided design-computer-aided manufacturing (CAD-CAM) fibre-reinforced composite post-core facilitates repairability, provides better adaptation to the root canal space, avoids uneven cement thickness, ensures chemical adhesion to resin cement, and promotes favourable aesthetics when combined with all-ceramic crowns.

Digital workflow feasibility for the fabrication of intraoral maxillofacial prosthetics after surgical resection: a systematic literature review.

OBJECTIVES: To evaluate the current evidence of digital workflow feasibility based on the data acquisition methods and the software tools used to fabricate intraoral prostheses for patients with partial or total maxillary and mandibular defects. MATERIALS AND METHODS: An electronic search was performed in PubMed, SCOPUS, and Web of Science using a combination of relevant keywords: digital workflow, digital designing, computer-assisted design-computer aided manufacturing, 3D printing, maxillectomy, and mandibulectomy. The Joanna Briggs Institute Critical Appraisal Tool was used to assess the quality of evidence in the studies reviewed. RESULTS: From a total of 542 references, 33 articles were selected, including 25 on maxillary prostheses and 8 on mandibular prostheses. The use of digital workflows was limited to one or two steps of the fabrication of the prostheses, and only four studies described a complete digital workflow. The most preferred method for data acquisition was intraoral scanning with or without a cone beam computed tomography combination. CONCLUSION: Currently, the fabrication process of maxillofacial prostheses requires combining digital and conventional methods. Simplifying the data acquisition methods and providing user-friendly and affordable software may encourage clinicians to use the digital workflow more frequently for patients requiring maxillofacial prostheses.

Intaglio surface trueness of dentures bases fabricated with 3D printing vs. conventional workflow: a clinical study.

The latest generation of intraoral scanners can record the prosthetic field with relative ease, high accuracy and comfort for the patient, and have enabled fully digital protocols for designing and manufacturing complete dentures. The present study aims to examine the intaglio surface trueness of 3D printed maxillary dentures produced by fully digital workflow in comparison with dentures produced by analogue clinical and laboratory prosthetic workflow. The edentulous maxillary arch of 15 patients was scanned with an intraoral scanner as well as the intaglio of the delivered conventional denture. The scan of the edentulous arch was imported into a dental design software to produce the denture base which was then 3D printed. The intaglio surface of the finished 3D printed denture bases was digitized and used to assess the trueness of the printed denture bases compared to the intaglio surface of the conventional dentures as well as performing a trueness comparison in relation to the scanned edentulous arches. The dataset (n = 30) was subjected to Kruskal-Wallis test analysis, the significance level being established at α = 0.05. The results of the study showed that the printed group displayed better trueness values with a median of 176.9 µm while the analogue group showed a median of 342 µm. Employing a fully digital workflow to produce 3D-printed denture bases yields a consistent and precise manufacturing method when accounting for the intaglio surface of the denture.

The effect of restorative material selection and cementation procedures on the durability of endocrowns in the anterior teeth: an in-vitro study.

OBJECTIVE: To investigate the fracture resistance and failure modalities of anterior endocrown restorations fabricated employing diverse ceramic materials, and bonded using various cementation methodologies. MATERIALS AND METHODS: Forty maxillary central incisors were divided into two main groups based on the ceramic materials used; GroupI (Zir): zirconia endocrwons (Zolid HT+, Ceramill, Amanngirrbach) and GroupII (E-Max): e-max endocrowns (IPS e.max CAD, Ivoclar Vivadent). Both groups were further split into two subgroups depending on the cementation protocols; subgroup IA "ZirMDP": endocowns cemented with MDP primer + MDP resin cement, subgroup IB (ZirNon-MDP): cemented with MDP primer + non-MDP resin cement, subgroup IIA (E-maxMDP): cemented with MDP primer + MDP resin cement, subgroup IIB (E-maxNon-MDP): cemented with MDP primer + non-MDP resin cement. (n = 10/subgroup). Endocrowns were manufactured using CAD/ CAM. Teeth were subjected to 10,000 thermal cycles. The fracture test was performed at 45o with a palatal force direction until the fracture occurred. Test results were recorded in Newton. The failure mode was examined using a stereomicroscope. A One-way ANOVA test was utilized to compare different groups regarding fracture strength values. Tukey`s Post Hoc was utilized for multiple comparisons. RESULTS: The comparative analysis of fracture strength across the diverse groups yielded non-significant differences, as indicated by a p-value exceeding 0.05. Nonetheless, an observable trend emerged regarding the mode of failure. Specifically, a statistically significant prevalence was noted in fractures localized within the endocrown/tooth complex below the cementoenamel junction (CEJ) across all groups, except for Group IIB, "E-max Non-MDP," where fractures within the endocrown/tooth complex occurred above the CEJ. CONCLUSIONS: Combining an MDP-based primer with an MDP-based resin cement did not result in a significant effect on the anterior endocrown fracture strength. CLINICAL RELEVANCE: Regardless of the presence of the MDP monomer in its composition, adhesive resin cement achieved highly successful fracture strength when used with MDP-based ceramic primers. Additionally, ceramic materials exhibiting elastic moduli surpassing those of dentin are discouraged due to their propensity to induce catastrophic fractures within the tooth structure.

Assessing the suitability of fused deposition modeling to produce acrylic removable denture bases.

OBJECTIVE: To study the feasibility of using poly methyl methacrylate (PMMA) filament and fused deposition modeling (FDM) to manufacture denture bases via the development of a study that considers both conventional and additive-based manufacturing techniques. MATERIALS AND METHODS: Five sample groups were compared: heat and cold cured acrylic resins, CAD/CAM milled PMMA, 3D-printed PMMA (via FDM), and 3D-printed methacrylate resin (via stereolithography, SLA). All groups were subjected to mechanical testing (flexural strength, impact strength, and hardness), water sorption and solubility tests, a tooth bonding test, microbiological assessment, and accuracy of fit measurements. The performance of sample groups was referred to ISO 20795-1 and ISO/TS 19736. The data was analyzed using one-way ANOVA. RESULTS: Samples manufactured using FDM performed within ISO specifications for mechanical testing, water sorption, and solubility tests. However, the FDM group failed to achieve the ISO requirements for the tooth bonding test. FDM samples presented a rough surface finish which could ultimately encourage an undesirable high level of microbial adhesion. For accuracy of fit, FDM samples showed a lower degree of accuracy than existing materials. CONCLUSIONS: Although FDM samples were a cost-effective option and were able to be quickly manufactured in a reproducible manner, the results demonstrated that current recommended testing regimes for conventionally manufactured denture-based polymers are not directly applicable to additive-manufactured denture base polymers. Therefore, new standards should be developed to ensure the correct implementation of additive manufacturing techniques within denture-based fabrication workflow.

Accuracy of semi-occlusive CAD/CAM titanium mesh using the reverse guided bone regeneration digital protocol: A preliminary clinical study.

PURPOSE: The reverse guided bone regeneration protocol is a digital workflow that has been introduced to reduce the complexity of guided bone regeneration and promote prosthetically guided bone reconstruction with a view to achieving optimal implant placement and prosthetic finalisation. The aim of the present study was to investigate the accuracy of this digital protocol. MATERIALS AND METHODS: Sixteen patients with partial edentulism in the maxilla or mandible and with vertical or horizontal bone defects were treated using the reverse guided bone regeneration protocol to achieve fixed implant rehabilitations. For each patient, a digital wax-up of the future rehabilitation was created and implant planning was carried out, then the necessary bone reconstruction was simulated virtually and the CAD/CAM titanium mesh was designed and used to perform guided bone regeneration. The computed tomography datasets from before and after guided bone regeneration were converted into 3D models and aligned digitally. The actual position of the mesh was compared to the virtual position to assess the accuracy of the digital project. Surgical and healing complications were also recorded. A descriptive analysis was conducted and a one-sample t test and Wilcoxon test were utilised to assess the statistical significance of the accuracy. The level of significance was set at 0.05. RESULTS: A total of 16 patients with 16 treated sites were enrolled. Comparing the virtually planned mesh position with the actual position, an overall mean discrepancy between the two of 0.487 ± 0.218 mm was achieved. No statistically significant difference was observed when comparing this to a predefined minimum tolerance (P = 0.06). No surgical complications occurred, but two healing complications were recorded (12.5%). CONCLUSION: Within the limitations of the present study, the reverse guided bone regeneration digital protocol seems to be able to achieve good accuracy in reproducing the content of the virtual plan. Nevertheless, further clinical comparative studies are required to confirm these results.

Assessment of CAD/CAM Fabrication Technologies for Post and Core Restorations-A Narrative Review.

The primary objective of this study is to conduct a comprehensive review of the existing literature that discusses research on post and core restorations, covering aspects such as their composition, manufacturing methods, and clinical effectiveness. The methodology employed in this review encompasses the implementation of a well-defined search strategy, the establishment of criteria for inclusion and exclusion, and the selection of relevant studies to summarize their findings. To gather relevant literature published between 1993 and 2023, the research team conducted separate searches on PubMed, Web of Science, and Embase databases. In total, 168 titles were initially retrieved from these electronic databases. By applying the predefined exclusion criteria, the researchers identified 73 articles that specifically address the conventional and computer-aided design/computer-aided manufacturing (CAD/CAM) technologies employed in post and core restorations. These treatments are commonly employed to restore teeth that have received endodontic therapy and subsequently experienced loss of dental structure. The development of computerized technology for the creation of customized posts and cores has emerged as a straightforward and efficient alternative to traditional methods. The review synthesizes papers discussing the techniques and materials involved in CAD/CAM-based construction of post and cores. It explores strategies for restoring endodontically treated teeth, highlighting both direct and indirect approaches. Commonly mentioned materials include zirconia, composite resin, and hybrid ceramics. Despite the limited literature on CAD/CAM post and core procedures, the review emphasizes the necessity of further research to assess long-term outcomes and efficacy. Additionally, it suggests including implications for future research and clinical recommendations to enhance the depth and practical relevance of the review.

Influence of the Manufacturing Trinomial (Technology, Printer, and Material) on the Marginal and Internal Discrepancies of Printed Metal Frameworks for the Fabrication of Tooth-Supported Prostheses: A Systematic Review and Meta-analysis.

PURPOSE: The purpose of this systematic review and meta-analysis was to compare the influence of fabrication method (conventional, subtractive, and additive procedures) and manufacturing trinomial (technology, printer, and material combination) on the marginal and internal fit of cobaltchromium (Co-Cr) tooth-supported frameworks. MATERIALS AND METHODS: An electronic systematic review was performed in five data bases: MEDLINE/PubMed, Embase, World of Science, Cochrane, and Scopus. Studies that reported the marginal and internal discrepancies of tooth-supported Co-Cr additive manufacturing (AM) frameworks were included. Two authors independently completed the quality assessment of the studies by applying the Joanna Briggs Institute Critical Appraisal Checklist for Quasi-Experimental Studies. A third examiner was consulted to resolve lack of consensus. RESULTS: A total of 31 articles were included and classified based on the evaluation method: manufacturing accuracy, the dual- or triple-scan method, stereomicroscope, optical coordinate measurement machine, microCT, profilometer, and silicone replica. Six subgroups were created: 3D Systems, Bego, Concept Laser, EOS, Kulzer, and Sisma. Due to the heterogeneity and limited data available, only the silicone replica group was considered for meta-analysis. The metaanalysis showed a mean marginal discrepancy of 91.09 µm (I2 = 95%, P < .001) in the conventional group, 77.48 µm (I2 = 99%, P < .001) in the milling group, and 82.92 µm (I2 = 98%, P < .001) in the printing group. Additionally, a mean internal discrepancy of 111.29 µm (I2 = 94%, P < .001) was obtained in the conventional casting group, 121.96 µm (I2 = 100%, P < .001) in the milling group, and 121.25 µm (I2 = 99%, P < .001) in the printing group. CONCLUSIONS: Manufacturing method and selective laser melting (SLM) metal manufacturing trinomial did not impact the marginal and internal discrepancies of Co-Cr frameworks for the fabrication of tooth-supported restorations.

DIGITAL FABRICATION OF COMPLETE DENTURES, COMPARED TO CONVENTIONAL METHODS, MAY OFFER A MORE COST-EFFECTIVE APPROACH WITH IMPROVED PATIENT OUTCOMES.

ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION: Digitally versus conventionally fabricated complete dentures: A systematic review on cost-efficiency analysis and patient-reported outcome measures (PROMs). Tew, In Meei, Suet Yeo Soo, and Edmond Ho Nang Pow.The Journal of Prosthetic Dentistry (2023). SOURCE OF FUNDING: No fund was received. TYPE OF STUDY/DESIGN: Systematic review.

DIGITAL SCANS, COMPARED TO CONVENTIONAL IMPRESSIONS, MAY EXPEDITE FABRICATION TIME FOR FULL-ARCH IMPLANT-SUPPORTED PROSTHESES WHILE MAINTAINING A COMPARABLE LEVEL OF MARGINAL BONE LOSS.

ARTICLE TITLE AND BIBLIOGRAPHIC INFORMATION: Clinical outcomes of digital scans versus conventional impressions for implant-supported fixed complete arch prostheses: A systematic review and meta-analysis. I. A., Spin-Neto, R., Sesma, N., & da Silva, E. V. F. The Journal of Prosthetic Dentistry (2023). SOURCE OF FUNDING: Not reported. TYPE OF STUDY/DESIGN: Systematic review with network meta-analysis of data.

Computer-simulated TOUCH prosthesis cup malposition and solutions.

INTRODUCTION: Total joint replacement has become significantly more common as a treatment for advanced trapeziometacarpal joint osteoarthritis in recent years. The latest generation of prostheses with dual-mobility designs leads to very good functional results and low rates of loosening and dislocation in the short and medium term. Biomechanical studies showed that central placement and parallel alignment of the cup with respect to the proximal articular surface of the trapezium are crucial for both cup stability and prevention of dislocation. Despite correct positioning of the guidewire, incorrect placement or tilting of the inserted cup may occur, requiring immediate intraoperative revision. METHODS: The existing spherical and conical cup models in sizes 9 mm and 10 mm were transferred to a computer-aided design dataset. Depending on the intraoperative complication (tilting or incorrect placement), the revision options resulting from the various combinations of cup type and size were simulated and analyzed according to the resulting defect area and bony contact area. RESULTS: In well centered cups, a size 9 conical cup could be replaced by a size 9 spherical cup and still be fixed by press-fit. Conversely, a size 9 spherical cup could not be replaced by a size 9 conical cup, but only by a size 10 cup, of whatever shape. When a size 9 conical cup was tilted up to 20°, the best revision option was to resect the sclerotic margin and insert a size 10 conical cup deeper into the cancellous bone, to achieve the largest contact area with the surrounding bone. When a size 9 cup of whatever shape was poorly centered (misplaced with respect to the dorsopalmar or radioulnar line of the trapezium), placement should be corrected using a size 10 cup, combined with autologous bone grafting of the defect. Again, the size 10 conical cup showed the largest bony contact area. CONCLUSION: Our computer-based measurements suggested options for intraoperative cup revision depending on cup shape and size and on type of misalignment with resulting bone defects. These suggestions, however, need to be confirmed in anatomic specimens before introducing them into clinical practice.

Positional accuracy of a single implant analog in additively manufactured casts in biobased model resin.

OBJECTIVES: To evaluate the positional accuracy of implant analogs in biobased model resin by comparing them to that of implant analogs in model resin casts and conventional analogs in dental stone casts. METHODS: Polyvinylsiloxane impressions of a partially edentulous mandibular model with a single implant were made and poured in type IV dental stone. The same model was also digitized with an intraoral scanner and additively manufactured implant casts were fabricated in biobased model resin (FotoDent biobased model) and model resin (FotoDent model 2 beige-opaque) (n = 8). All casts and the model were digitized with a laboratory scanner, and the scan files were imported into a 3-dimensional analysis software (Geomagic Control X). The linear deviations of 2 standardized points on the scan body used during digitization were automatically calculated on x-, y-, and z-axes. Average deviations were used to define precision, and 1-way analysis of variance and Tukey HSD tests were used for statistical analyses (α = 0.05). RESULTS: Biobased model resin led to higher deviations than dental stone (all axes, P ≤ 0.031) and model resin (y-axis, P = 0.015). Biobased model resin resulted in the lowest precision of implant analog position (P ≤ 0.049). The difference in the positional accuracy of implant analogs of model resin and stone casts was nonsignificant (P ≥ 0.196). CONCLUSIONS: Implant analogs in biobased model resin casts mostly had lower positional accuracy, whereas those in model resin and stone casts had similar positional accuracy. Regardless of the material, analogs deviated more towards mesial, while buccal deviations in additively manufactured casts and lingual deviations in stone casts were more prominent.

Effect of different impression coping and scan body designs on the accuracy of conventional versus digital implant impressions: An in vitro study.

OBJECTIVES: This in vitro study compared the accuracy of conventional versus digital impression techniques for angulated and straight implants using two different impression coping and scan body designs. METHODS: Two implant systems were used: Straumann and Dentegris. Two implants were placed for each system, straight and angulated at 15 degrees mesiodistally. Conventional impressions were made using the splinted open-tray technique using narrow impression coping (NIC) and wide impression coping (WIC). The stone casts produced from the conventional impression were digitized with a lab scanner (3Shape D2000). Digital impressions were made using four intraoral scanners (IOS): 3Shape Trios 3, Medit i700, Cerec Omnicam, and Emerald Planmeca using short scanbodies (SSB) and long scanbodies (LSB). The scanning was repeated ten times to generate the Standard Tessellation Language (STL) files. The distance and angle deviations between impression copings and scanbodies were measured in reference to the master model. RESULTS: The trueness and precision of SSB and WIC were significantly better than LSB and NIC (p<0.001). The range trueness of the platform deviation was better with SSB (37.1 to 51.9) than LSB (89.6 to 127.9 µm) and for WIC than NIC in conventional impressions (58.2 and 75.1 µm, respectively). The trueness of the angle deviation of digital scans with SSB (0.11 to 0.25 degrees) was significantly better than scans with LSB (0.31 to 0.57 degrees) and for WIC than NIC (0.21 and 0.52 degrees, respectively). The precision of the platform deviation of digital scans with SSB (12.4 to 34.5 µm) was higher than other scans and conventional impressions (42.9 to 71.4 µm). The precision of the angle deviation of Medit i700 and Trios 3 with SSB (0.17 and 0.20 degrees, respectively) was higher than other scans with SSB and conventional impressions (0.54 to 1.63 degrees). CONCLUSIONS: Digital scans with SSB were more accurate than conventional splinted open-tray impressions. The type of impression coping and scanbody significantly affected the impression accuracy. CLINICAL SIGNIFICANCE: The use of a short scanbody can increase the accuracy of digital impressions, and wide impression coping can increase the accuracy of conventional impressions, resulting in improved clinical outcomes.

Effect of milling procedures in CAD-CAM systems on the color changes of CAD-CAM polymethyl methacrylate resin material as interim material.

PURPOSE: This study aimed to investigate the effects of new and used burs on CAD-CAM PMMA resin color changes following thermocycling. MATERIALS AND METHODS: Twenty disk-shaped specimens (10 × 2 mm) were made using a single brand of CAD-CAM polymethyl methacrylate resin (Polident) for the color test. Group N consisted of half of the specimens that were machined using the new tungsten carbide bur set, and Group U consisted of the specimens that were milled using the used bur set (500 machining time). A color test was performed on the specimens both before and after thermocycling. For the statistical analysis, the Kruskal-Wallis and Dunn Pairwise Comparison tests were employed. RESULTS: The ∆E* value of specimens (2.057) milled with the used bur was higher than those of specimens milled with the new bur (0.340), but this value is within clinically acceptable limits. After thermocycling, specimens milled with the utilized burs had the greatest L* (93.850) and b* (5.000) values. After thermocycling, statistically significant differences were discovered between Group N and Group U as well as between specimens milled with the utilized bur before and after thermocycling. CONCLUSION: Thermocycling process have an effect on the mean ∆E values of specimens milled with the used carbide bur, but these ∆E* values were not statistically significant. CLINICAL SIGNIFICANCE: The color and clinical performance of CAD-CAM restorations may be affected by variations in CAD-CAM milling bur properties, particularly those related to their frequent use.