Influence of crown shade, translucency, and scan powder application on the trueness of intraoral scanners.

OBJECTIVES: Natural teeth and dental restorations present with various shades and levels of translucency. This study aimed to determine whether these variations in ceramic crowns and scan powder application affect the trueness of intraoral scanners. METHODS: Eight identical premade resin typodonts, each prepared for a crown on the maxillary right second molar, were used. Eight lithium disilicate crowns, distinguished by two levels of translucency (high and low) and four shades (BL1, A2, A3, and A4), were fabricated to an identical design and cemented onto each typodont, providing eight distinct experimental groups (2 levels of translucency × 4 shades). Reference scans were acquired using a desktop scanner. Test scans were performed ten times for each experimental group using two different intraoral scanners (Medit i700 and CEREC Primescan AC), with and without the application of scan powder (n = 10). Three-dimensional metrology software was used to assess the trueness of the intraoral scan datasets. Statistical analysis involved the Kruskal-Wallis H test, Mann-Whitney U test, and independent t-test (α=0.05). RESULTS: For powder-free intraoral scan datasets, the crown shade did not significantly affect trueness within each translucency group (P = 1.000). For both intraoral scanners, compared with low translucency groups, higher marked deviations were exhibited by high translucency groups (P<.001). Scan powder use largely mitigated these differences (P>.05) and enhanced the trueness of the intraoral scan (P<.01). CONCLUSIONS: Shade did not significantly influence the trueness of intraoral scans. High-translucency crowns were scanned with less accuracy than were low-translucency crowns. CLINICAL SIGNIFICANCE: Unlike tooth shade, translucency significantly affected the accuracy of intraoral scans. Therefore, considering the use of scan powder when scanning objects with high translucency may be beneficial.

Retrieval of cement-retained zirconia implant-supported crowns with an Er,Cr:YSGG laser.

STATEMENT OF PROBLEM: Cement-retained implant-supported crowns can be challenging to retrieve from the abutment once technical or biological issues arise. Removal traditionally requires sectioning the crown with rotary instruments, which causes irreversible damage to the crown and potential damage to the periodontal apparatus stabilizing the implant. PURPOSE: The purpose of this in vitro study was to evaluate an erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG) laser as a minimally invasive alternative for the retrieval of zirconia implant-supported crowns from titanium abutments. Time, temperature, and structural changes to the crown after retrieval were assessed. Appropriate laser parameters were established for this method of crown retrieval. MATERIAL AND METHODS: Twenty zirconia crowns were milled for a maxillary left second premolar based on a CAD-CAM implant analog cast. Ten of these crowns were cemented with a noneugenol zinc oxide dental cement (group Temp) (n=10). The remaining 10 were cemented with a self-adhesive universal resin cement (group Resin) (n=10). Er,Cr:YSGG laser irradiation was performed with the Waterlase iPlus for 1-minute cycles. An attempt was made to remove the crown with a mechanical instrument after each cycle. A type K thermocouple continuously recorded temperature at the level of the abutment. For statistical comparison of decementation time and temperature, the Mann-Whitney test was used (α=.05). Scanning electron microscopy of the nonirradiated and the irradiated crowns was used for analysis of structural and dimensional changes. RESULTS: A significant difference (P<.001) was found in the time ±standard deviation required to retrieve the crowns between group Temp (02:40 ±00:18 minutes:seconds) and group Resin (05:26 ±00:36 minutes:seconds). A significant difference (P<.001) was found in the mean ±standard deviation temperature recorded between group Temp (24.0 ±1.19 °C) and group Resin (25.7 ±0.66 °C). No structural changes to crowns were observed after irradiation. CONCLUSIONS: Retrieval of cement-retained zirconia implant-supported crowns with an Er,Cr:YSGG laser is safe and efficient. Crowns luted with zinc oxide dental cement were retrieved significantly faster while maintaining a significantly lower average temperature than those luted with resin cement. Laser irradiation for decementation did not cause structural changes to zirconia implant-supported crowns.

Computer guided root tip extraction and implant placement: A clinical report.

Extraction of a residual root tip and implant placement can be challenging because of the complexity and invasiveness of the procedure. Improvised application of a guided implant surgery may avoid such challenges. This clinical report presents an innovative technique combining a 3-dimensionally printed surgical guide with conventional instrumentation for a residual root tip extraction in a minimally invasive and predictable way.

Accuracy of impression scan bodies for complete arch fixed implant-supported restorations.

STATEMENT OF PROBLEM: Despite the extensive studies on and comparisons of different implant impression techniques for completely edentulous patients, studies on novel techniques that combine conventional impression making with digital scanning are lacking. PURPOSE: The primary aim of this study was to compare the accuracy of the impression scan body technique with conventional impression making and digital scanning for a completely edentulous mandibular arch. The secondary aim was to assess the relationship between different implant angulations and interimplant distances in relation to the recording accuracy. MATERIAL AND METHODS: An edentulous mandibular definitive cast (control) was designed with 5 implants placed at different angles and interimplant distances. Three recording techniques were tested: a conventional impression with splinted copings (conventional) (n=15), an impression scan body technique where impression scan bodies were attached to the splinted impression copings in a conventional elastomeric impression and then digitally scanned with an extraoral scanner (n=15), and an intraoral digital scanning technique (digital) (n=15). For comparison, the definitive cast and the conventional impression stone casts were digitized into standard tessellation language (STL) datasets using the extraoral scanner. The 3-dimensional (3D) deviations between the 3 test groups and the control were calculated by superimposing the STL datasets. The 3D deviations from the control were compared by using the Kruskal-Wallis test followed by the Dunn post hoc test (α=.05). The Mann-Whitney test was used to investigate the effect of implant angulation and interimplant distance on impression accuracy (α=.05). RESULTS: The conventional splinted-coping impression technique showed a mean 3D deviation of 0.408 mm. The impression scan body and intraoral digital scan showed similar mean 3D deviations, 0.219 mm and 0.257 mm, respectively (P=.334). Both techniques showed significantly lower 3D deviations than the conventional technique (P<.001). Implants at an angle of 5 degrees and 10 degrees showed a statistically significant difference (P=.010) with mean 3D deviations of 0.340 mm and 0.396 mm, respectively. Implants with 5-mm and 10-mm interimplant distance showed a significant difference (P<.001) with mean 3D deviations of 0.301 mm and 0.423 mm, respectively. CONCLUSIONS: The impression scan body technique is comparable with intraoral digital scanning for a completely edentulous arch. Increased implant angulation and increased interimplant distance significantly reduced the accuracy of implant impression making or scanning.

A clinical comparison of sagittal condylar inclination and Bennett angle derived from a conventional electronic tracking device and an optical jaw tracking device.

STATEMENT OF PROBLEM: The challenges of conventional methods to measure the sagittal condylar inclination and the Bennett angle include patient discomfort and an output of averaged values calculated on the arc of mandibular movement. Programming these average values into a mechanical or mathematically simulated articulator may introduce occlusal errors. PURPOSE: The purpose of this clinical study was to compare the sagittal condylar inclination and Bennett angle measurements derived from a conventional electronic tracking device and an optical tracking device. MATERIAL AND METHODS: Fifteen dentate participants with at least 12 occluding units, 25 years old and above, participated in the study. Each participant's mandibular movements were recorded by the 2 systems for different condylar guidance values. A conventional tracking device, the Cadiax Compact 2, and an optical tracking device, the MODJAW, were used for this study. Sagittal condylar inclination was measured at 3 mm and 5 mm using protrusive records and the values of the Bennett angle at 3 mm were measured using excursive records along the path traced by mandibular condyles. The Wilcoxon signed-rank test was used to analyze the paired data from the 2 methods. RESULTS: A significant difference was found between right (P=.007) and left sagittal condylar inclinations (P=.010) measured at 3 mm with the conventional and optical tracking devices. A significant difference was found between right (P=.015) and left sagittal condylar inclinations (P=.004) measured at 5 mm with the conventional and optical tracking devices. The right and left Bennett angles measured at 3 mm with the conventional and optical tracking devices were statistically different (P=.043 and P=.035 respectively). CONCLUSIONS: The sagittal condylar inclination and Bennett angle measured at different positions along the path of movement exhibited significant differences. The sagittal condylar inclination and Bennett angle values obtained from the conventional tracking device were generally significantly less than those derived from the optical tracking device.

Effect of exposure energy dose on lateral resolution and flexural strength of three-dimensionally printed dental zirconia.

PURPOSE: This study aims to evaluate the effects of exposure energy on the lateral resolution and mechanical strength of dental zirconia manufactured using digital light processing (DLP). MATERIALS AND METHODS: A zirconia suspension and a custom top-down DLP printer were used for in-office manufacturing. The viscosity of the suspension and uniformity of the exposed light intensity were controlled. Based on the exposure energy dose delivered to each layer, the specimens were classified into three groups: low-energy (LE), medium-energy (ME), and high-energy (HE). For each energy group, a simplified molar cube was used to measure the widths of the outline (Xo and Yo) and isthmus (Xi and Yi), and a bar-shaped specimen of the sintered body was tested. A Kruskal-Wallis test for the lateral resolution and one-way analysis of variance for the mechanical strength were performed (α = .05). RESULTS: The zirconia green bodies of the ME group showed better lateral resolution than those of the LE and HE groups (both P < .001). Regarding the flexural strength of the sintered bodies, the ME group had the highest mean value, whereas the LE group had the lowest mean value (both P < .05). The ME group exhibited fewer agglomerates than the LE group, with no distinctive interlayer pores or surface defects. CONCLUSION: Based on these findings, the lateral resolution of the green body and flexural strength of the sintered body of dental zirconia could be affected by the exposure energy dose during DLP. The exposure energy should be optimized when fabricating DLP-based dental zirconia.

Milled PMMA, a Material for Long-Term Implant Supported Fixed Complete Dental Prostheses.

Traditionally, metal-ceramics, metal-reinforced acrylics, and more recently full-contour or layered zirconia have been the materials of choice for definitive fixed implant-supported rehabilitations. Polymethyl Methacrylate (PMMA) is commonly used in implant dentistry for the fabrication of implant-supported interim prostheses and as milled or 3D printed prototypes. This article describes a novel protocol to prosthetically restore a completely edentulous patient following a digital workflow, with fixed, screw-retained, implant-supported prostheses fabricated from CAD/CAM milled polymethyl methacrylate (PMMA), with no metal substructure. After two years follow up in terms of esthetics, phonetics, function and biological tissue response, the outcome remains functional and free of mechanical, biomechanical or biological complications. The aim of this article is to illustrate the feasibility of using milled PMMA as viable definitive prosthetic material for the fixed implant rehabilitation of edentulous patients.

Influence of varying titanium base abutment heights on retention of zirconia restorations: An in vitro study.

STATEMENT OF PROBLEM: Implant manufacturers have introduced titanium base (Ti-Base) abutments with increased abutment heights, ostensibly, to increase the retention of the bonded restoration and to improve overall strength. However, evidence regarding the effects of increasing Ti-Base height on improving retention is lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of different Ti-Base abutment heights on the retention of zirconia implant-supported crowns. MATERIAL AND METHODS: Thirty Ti-Base abutments of the same diameter and heights of 3.5 mm (n=10), 4.5 mm (n=10), and 5.5 mm (n=10), were used for testing. Zirconia restorations were cemented onto the Ti-Base abutments with a resin cement after treatment with a 10-methacryloyloxydecyl dihydrogen phosphate primer by a single operator using a positioning device. The zirconia-Ti-Base restorations were tightened to an implant analog embedded in an autopolymerizing resin block. The specimens were placed and tested in a universal testing machine for pull-out testing. Retention was measured by recording the force at load drop. Statistical analysis was performed using 1-way analysis of variance with the Tukey method for pairwise comparisons. RESULTS: The abutment height had a significant effect on retention (P=.010). Ti-Base abutments of 4.5 and 5.5 mm had significantly greater retention than Ti-Base abutments of 3.5 mm (P=.020, P=.040, respectively). However, Ti-Base abutments of 4.5 and 5.5 mm in height were statistically similar (P=.890). CONCLUSIONS: An increase in the height of Ti-Base abutments above the standard 3.5 mm height significantly improved the retention of the overlying restoration.

An analog-digital hybrid technique for immediate dentures with idealized border extensions.

In patients with severe tooth mobility, conventional impression making can be challenging because of the risk of accidental tooth extraction. Digital intraoral scanning avoids such a complication but does not capture optimal border extensions for a complete denture. This clinical report presents a combined digital and analog recording technique which allows the recording of optimal vestibular border extensions without the risk of tooth extraction.

Accuracy comparison of bilateral versus complete arch interocclusal registration scans for virtual articulation.

STATEMENT OF PROBLEM: Alternatives to the bilateral interocclusal registration scanning technique to improve virtual articulation have not been fully investigated. PURPOSE: The purpose of this in vitro study was to compare the accuracy of virtually articulating digital casts by using bilateral interocclusal registration scans versus a complete arch interocclusal scan. MATERIAL AND METHODS: A set of maxillary and mandibular reference casts were hand-articulated and mounted on an articulator. The mounted reference casts were scanned, and the maxillomandibular relationship record was scanned 15 times using 2 different scanning techniques, the bilateral interocclusal registration scan (BIRS) and complete arch interocclusal registration scan (CIRS), with an intraoral scanner. The generated files were transferred to a virtual articulator, and each set of scanned casts was articulated using BIRS and CIRS. The virtually articulated casts were saved as a set and transferred to a 3-dimensional (3D) analysis program. The scanned casts were set in the same coordinate system as the reference cast and overlaid on top of the reference cast for analysis. Two anterior and 2 posterior points were selected to determine points of comparison between the reference cast and test casts virtually articulated with BIRS and CIRS. The mean discrepancy between the 2 test groups and the anterior and posterior mean discrepancy within each group were tested for significance by using the Mann-Whitney U test (α=.05). RESULTS: A significant difference was found between the virtual articulation accuracy of BIRS and CIRS (P<.001). The mean deviation for BIRS was 0.053 ±0.051 mm and that for CIRS was 0.265 ±0.241 mm. Furthermore, significant differences were found between the anterior and posterior deviations in both BIRS (P=.020) and CIRS (P<.001). The mean deviation for BIRS was 0.034 ±0.026 mm in the anterior and 0.073 ±0.062 mm in the posterior. The mean deviation for CIRS was 0.146 ±0.108 mm anteriorly and 0.385 ±0.277 mm posteriorly. CONCLUSIONS: BIRS was more accurate than CIRS for virtual articulation. Moreover, the alignment accuracy of anterior and posterior sites for both BIRS and CIRS exhibited significant differences, with the anterior alignment exhibiting better accuracy in relation to the reference cast.

Occlusion as a predisposing factor for peri-implant disease: A review article.

BACKGROUND: The restoration of dental implants presents a unique challenge due to the intrinsic biomechanical differences between osseointegrated implants and natural teeth, and their subsequent responses to occlusal loading. However, controversy exists regarding the role that occlusion plays in the physiology of the peri-implant complex. PURPOSE: To provide an overview of the scientific literature regarding occlusion as it relates to implant dentistry and peri-implant disease. MATERIALS AND METHODS: This article presents a narrative review on occlusal loading and its potential effects on the peri-implant complex, as well as some generally accepted guidelines for occlusion in implant dentistry. RESULTS AND CONCLUSIONS: Although there is strong evidence linking occlusal factors to mechanical complications of dental implants, the same cannot be said regarding biological complications. There is no clear scientific evidence on the relationship between occlusal overload and peri-implant disease. However, occlusal overload may be an accelerating factor for peri-implant disease in the presence of inflammation. As the biomechanical properties of dental implants differ from that of the natural dentition, modifications to classic concepts of occlusion may be necessary when dental implants are involved. Thus, clinical recommendations are proposed which function to minimize unfavorable occlusal forces on implant restorations and reduce the associated biological and mechanical complications.

Materials and Applications of 3D Printing Technology in Dentistry: An Overview.

PURPOSE: This narrative review aims to provide an overview of the mechanisms of 3D printing, the dental materials relevant to each mechanism, and the possible applications of these materials within different areas of dentistry. METHODS: Subtopics within 3D printing technology in dentistry were identified and divided among five reviewers. Electronic searches of the Medline (PubMed) database were performed with the following search keywords: 3D printing, digital light processing, stereolithography, digital dentistry, dental materials, and a combination of the keywords. For this review, only studies or review papers investigating 3D printing technology for dental or medical applications were included. Due to the nature of this review, no formal evidence-based quality assessment was performed, and the search was limited to the English language without further restrictions. RESULTS: A total of 64 articles were included. The significant applications, applied materials, limitations, and future directions of 3D printing technology were reviewed. Subtopics include the chronological evolution of 3D printing technology, the mechanisms of 3D printing technologies along with different printable materials with unique biomechanical properties, and the wide range of applications for 3D printing in dentistry. CONCLUSIONS: This review article gives an overview of the history and evolution of 3D printing technology, as well as its associated advantages and disadvantages. Current 3D printing technologies include stereolithography, digital light processing, fused deposition modeling, selective laser sintering/melting, photopolymer jetting, powder binder, and 3D laser bioprinting. The main categories of 3D printing materials are polymers, metals, and ceramics. Despite limitations in printing accuracy and quality, 3D printing technology is now able to offer us a wide variety of potential applications in different fields of dentistry, including prosthodontics, implantology, oral and maxillofacial, orthodontics, endodontics, and periodontics. Understanding the existing spectrum of 3D printing applications in dentistry will serve to further expand its use in the dental field. Three-dimensional printing technology has brought about a paradigm shift in the delivery of clinical care in medicine and dentistry. The clinical use of 3D printing has created versatile applications which streamline our digital workflow. Technological advancements have also paved the way for the integration of new dental materials into dentistry.

Comparison of accuracy in digital and conventional cross-mounting.

STATEMENT OF PROBLEM: The use of digital interocclusal registration scans for virtual articulation and mounting has been studied extensively; however, the accuracy of the cross-mounting procedures in a digital workflow is not well understood. PURPOSE: The purpose of this in vitro study was to compare the accuracy of digital and conventional cross-mounting by measuring the 3-dimensional deviation at each step of sequential cross-mounting. MATERIAL AND METHODS: A set of reference casts and complete-arch interim restorations was prepared for complete-arch complete-coverage restorations, hand-articulated, and mounted in an articulator. The reference casts were then scanned with and without the interim restorations to generate 4 reference casts for cross-mounting. For the conventional group, 15 sets of the 4 casts were printed. Polyvinyl siloxane interocclusal registration records were made of the reference casts for each set, and casts were sequentially cross-mounted. For the digital workflow, 15 sets of bilateral interocclusal registration scans were made of the mounted reference casts and used to align the cast scans. Three-dimensional deviations at 2 anterior and 2 posterior points were recorded between the experimental mountings and the reference casts on each set of casts. Nonpaired t test and analysis of variance (ANOVA) were used to compare the average discrepancy between the 2 groups, and the pooled anterior versus posterior discrepancies were compared (α=.05). RESULTS: A significant difference was found between conventional and digital cross-mounting procedures (P<.001), but no significant difference was found in either group, conventional (P=.116) or digital (P=.987), at each step of the sequential mountings. The mean ±standard deviation at the final set of related casts in the conventional workflow was 201.6 ±137.0 µm and that in the digital group was 50.3 ±47.5 µm, with a significant difference between anterior and posterior deviations in the digital group (P=.028), but not in the conventional group (P=.143). The mean ±standard deviation anterior conventional deviation was 175.6 ±119.2 µm and that in the digital group was 36.9 ±30.9 µm. The mean ±standard deviation posterior conventional deviation was 227.6 ±50.2 µm and that in the digital group was 63.7 ±57.2 µm. CONCLUSIONS: Digital cross-mounting was more accurate than conventional cross-mounting, although increased deviation was found in the anterior region compared with the posterior region.

Assessment of Occlusal Vertical Dimension Change in Mechanical and Virtual Articulation: A Pilot Study.

The aim of this clinical study was to investigate the change in occlusal vertical dimension (OVD) with dental casts mounted on a mechanical articulator using an average axis facebow and on a virtual articulator mounted using the Bonwill triangle and the Balkwill angle and compare these groups with OVD change observed clinically in patients. Casts were obtained from each patient (n = 14) and mounted on a semi-adjustable articulator in the facebow preservation group (FPG) and on a virtual articulator using average anatomic values in the average mounting group (AMG). Customized mandibular anterior splints were virtually designed at an OVD increased by 3, 6, and 9 mm. Digital buccal scans were performed with the anterior devices in the participants' mouths in the intraoral group (IOG), AMG, and FPG at the different OVD increases accordingly. While no statistically significant differences (p > 0.05) were observed in the posterior interocclusal measurements with the incisal guide pin raised by 3 mm and 6 mm among all groups, a 9 mm increase resulted in a significant difference between AMG and IOG. The interocclusal posterior-to-anterior opening ratio observed clinically was 1:1.575. Increases in OVD up to 6 mm on dental casts mounted using average anatomic values performed similarly to the actual intraoral changes.

Diagnosis of Tooth Prognosis Using Artificial Intelligence.

The accurate diagnosis of individual tooth prognosis has to be determined comprehensively in consideration of the broader treatment plan. The objective of this study was to establish an effective artificial intelligence (AI)-based module for an accurate tooth prognosis decision based on the Harvard School of Dental Medicine (HSDM) comprehensive treatment planning curriculum (CTPC). The tooth prognosis of 2359 teeth from 94 cases was evaluated with 1 to 5 levels (1-Hopeless, 5-Good condition for long term) by two groups (Model-A with 16, and Model-B with 13 examiners) based on 17 clinical determining factors selected from the HSDM-CTPC. Three AI machine-learning methods including gradient boosting classifier, decision tree classifier, and random forest classifier were used to create an algorithm. These three methods were evaluated against the gold standard data determined by consensus of three experienced prosthodontists, and their accuracy was analyzed. The decision tree classifier indicated the highest accuracy at 0.8413 (Model-A) and 0.7523 (Model-B). Accuracy with the gradient boosting classifier and the random forest classifier was 0.6896, 0.6687, and 0.8413, 0.7523, respectively. Overall, the decision tree classifier had the best accuracy among the three methods. The study contributes to the implementation of AI in the decision-making process of tooth prognosis in consideration of the treatment plan.

Current Implementation of Digital Dentistry for Removable Prosthodontics in US Dental Schools.

Objectives: Although digital technology has been widely integrated into dental education, there is limited literature investigating the extent of the integration of computer-aided design and computer-aided manufacturing (CAD-CAM) for removable systems in the dental curriculum. The purpose of this study was to assess the current implementation of CAD-CAM complete and partial dentures in predoctoral (PP) and advanced graduate prosthodontic (AGP) education in US dental schools. The study also aimed to identify potential barriers to its implementation in the dental curriculum. Methods: An online survey with 15 questions was created using online survey software. The survey was distributed to the directors of predoctoral prosthodontics in 56 schools and advanced graduate programs of prosthodontics in 52 schools listed in the 2018-19 American Dental Education Association (ADEA) Directory. Results: The percentage of programs (PP and AGP) implementing CAD-CAM complete dentures (CAD-CAM CDs) and CAD-CAM removable partial dentures (CAD-CAM RPDs) in their didactic, preclinical, and clinical curricula was recorded. CAD-CAM CDs are taught in didactic courses in 54.2% of PP and 65.2% of AGP. However, CAD-CAM RPDs are only taught in 37.5% of PP and 47.8% of AGP. Programs are largely limited by a lack of funds, resources, time, and faculty members. Conclusion: While digital technologies have indeed become more prevalent in dental education, many institutions face barriers to implementation. More research must be conducted in order to support the continued incorporation of digital technologies into dental education.

A comparison of virtually mounted dental casts from traditional facebow records, average values, and 3D facial scans.

STATEMENT OF PROBLEM: Although average values and facebow records have been incorporated into prosthetic dentistry with much success, little is known about how using 3D facial scans for mounting compare with traditional mounting methods. PURPOSE: The purpose of this pilot clinical study was to determine differences in measurements among casts mounted virtually by using the average values of the Bonwill triangle and the Balkwill angle, casts mounted by using facebow records, and casts mounted from 3D facial scans. MATERIAL AND METHODS: Intraoral digital scans were obtained from each participant (n=10) and 3D printed in resin. For the facebow preservation group (FPG), a facebow record was used to mount the resin casts on a semiadjustable articulator. A desktop scanner was used to digitize this mounting while preserving the facebow record. The average mounting group (AMG) consisted of intraoral digital scans that were mounted virtually by using the concepts of the Bonwill triangle and the Balkwill angle. For the facial scan group (FSG), the participants' digitized casts were superimposed on the facial scans by using a target system. The Bergstrom point and the glabella were used to mount these casts and their associated facial scans in the digital environment. This study used the FPG as the group to compare with the other mounting techniques because of its wide acceptance in restorative dentistry. These virtual mountings were completed in a computer-aided design software program, and the distance from right and left condylar elements to the incisal embrasure between mandibular central incisors, distance from left mandibular first molar to left condylar element and from right mandibular first molar to right condylar element, and anterior and posterior recordings at 0 mm, 3 mm, and 5 mm of vertical dimension increase were recorded. A Kruskal-Wallis 1-way analysis of variance was performed (α=.05). The Mann-Whitney U test was performed to evaluate differences in measured values among groups, and multiple comparisons were adjusted by using Bonferroni correction. RESULTS: All anterior and posterior measurements to the condylar elements of the virtual articulator were found to be significantly different (P<.05). Both anterior and posterior condylar measurements between the FPG and the AMG were found to be significantly different (P<.05), while comparisons between the FPG and the FSG were found not to be significantly different (P>.05). All changes in vertical dimension were found not to be significantly different with respect to both anterior and posterior measurements (P>.05). CONCLUSIONS: When used to virtually mount dental casts, 3D facial scanners performed similarly to traditional facebow records.

Positional trueness of abutments by using a digital die-merging protocol compared with complete arch direct digital scans and conventional dental impressions.

STATEMENT OF PROBLEM: Complex prosthodontic treatments frequently require capturing an accurate impression of abutment teeth throughout the dental arch. Intraoral digital scanning has been reported to be accurate within single dental quadrants; however, the positional trueness of complete arch intraoral digital scans is not well understood. PURPOSE: The purpose of this in vitro study was to compare the positional trueness of a complete arch digital scan generated by digitally merging portions of a direct digital scan from an intraoral scanner (IOS) with a digitized polyvinyl siloxane (PVS) complete arch impression. MATERIAL AND METHODS: A 3D-printed reference cast was scanned with a desktop scanner, and reference standard tessellation language (STL) data sets were obtained. The reference cast was used to generate 4 nonmerged (NM) groups and 2 die-merged (DM) groups. In the NM groups (n=10), a direct digital scan of the reference cast was made with an IOS (NM-IOS), the PVS impression of the reference cast was digitized by using a cone beam computed tomography (CBCT) scanner (NM-PVS-CBCT) or a desktop scanner (NM-PVS-DESK), and the gypsum cast made from the PVS impression was digitized by using a desktop scanner (NM-STONE). In the DM groups (n=10), individual dies were cropped from the complete arch digital scan from the NM-IOS group and merged with the digital scans from the NM-PVS-DESK and NM-PVS-CBCT groups to generate the DM-PVS-DESK and DM-PVS-CBCT groups, respectively. Deviation was measured as the absolute value of the distance from a reference position on the reference cast. The Kruskal-Wallis and Dunn pairwise comparison tests were used to compare the difference in deviation between the groups (α=.05). RESULTS: The NM-STONE and NM-PVS-DESK groups demonstrated the highest positional trueness, with global deviations of 19.6 and 17.7 µm, respectively, with no statistically significant difference (P=1.00). However, both the NM-IOS and NM-PVS-CBCT groups differed significantly from the NM-STONE group (P<.001 and P=.003, respectively) and the NM-PVS-DESK group (P<.001 and P=.004, respectively). In the DM groups, the DM-PVS-CBCT group presented a higher deviation than the DM-PVS-DESK group. CONCLUSIONS: Complete arch digital scans of PVS impressions digitized with a desktop scanner exhibited less positional deviation than those digitized with a CBCT scanner or complete arch digital scans generated with an IOS. Complete arch digital scans generated with an IOS and CBCT scanner result in more deviations in the posterior regions, and their positional trueness may not be sufficient to construct an accurate digital scan. Generating a complete arch digital scan by digitally merging portions of a direct digital scan from an IOS with a digitized PVS complete arch impression is a suitable alternative to the contemporary workflow of digitizing a stone cast with a desktop scanner.

An In-Vitro Evaluation of Articulation Accuracy for Digitally Milled Models vs. Conventional Gypsum Casts.

With the advent of a digital workflow in dentistry, the inter-occlusal articulation of digital models is now possible through various means. The Cadent iTero intraoral scanner uses a buccal scan in maximum intercuspation to record the maxillomandibular relationship. This in-vitro study compares the occlusion derived from conventionally articulated stone casts versus that of digitally articulated quadrant milled models. Thirty sets of stone casts poured from full arch polyvinyl siloxane impressions (Group A) and thirty sets of polyurethane quadrant models milled from digital impressions (Group B) were used for this study. The full arch stone casts were hand-articulated and mounted on semi-adjustable articulators, while the digitally derived models were pre-mounted from the milling center based on the data obtained from the buccal scanning procedure. A T-scan sensor was used to obtain a bite registration from each set of models in both groups. The T-scan data derived from groups A and B were compared to that from the master model to evaluate the reproducibility of the occlusion in the two groups. A statistically significant difference of the contact region surface area was found on #11 of the digitally articulated models compared to the master. An analysis of the force distribution also showed a tendency for a heavier distribution on the more anterior #11 tooth for the digitally articulated models. Within the limitations of this study, the use of a digitally articulated quadrant model system may result in a loss of accuracy, in terms of occlusion, the further anteriorly the tooth to be restored is located. Care must be taken to consider the sources of inaccuracies in the digital workflow to minimize them for a more efficient and effective restorative process.

Photoprotective effects of sphingomyelin-containing milk phospholipids in ultraviolet B-irradiated hairless mice by suppressing nuclear factor-κB expression.

Ceramide-containing phospholipids improve skin hydration and barrier function and are ideal for use in skin care products. In this study, we evaluated the photoprotective effect of milk phospholipids on the skin condition of UVB-irradiated hairless mice. Skin parameters were assessed following oral administration of milk phospholipids. The UVB irradiation induced photoaging in mice. The animals were divided into 5 groups: a control group (oral administration of saline with no UBV irradiation), UVB group (oral administration of saline with UVB irradiation), and 3 UVB irradiation groups receiving the milk phospholipids at 3 different concentrations of oral administration, 50 mg/kg (ML group), 100 mg/kg (MM group), and 150 mg/kg (MH group), for 8 wk. An increase in skin hydration and transepidermal water loss were improved in the 150 mg/kg of milk phospholipid-administered group. Hematoxylin and eosin staining revealed a decrease in epidermal thickness in the milk phospholipid-administered groups (50, 100, and 150 mg/kg of body weight). In particular, the 100 and 150 mg/kg groups showed significant changes in the area, length, and depth of the wrinkles compared with the UVB group. Moreover, the gene expression of matrix metalloproteins was attenuated, and that of proinflammatory cytokines, especially tumor necrosis factor-α, was significantly reduced in the milk phospholipid-administered groups than in the UVB group. The reduced ceramide and increased sphingosine-1-phosphate levels in the skin tissue due to UVB exposure were restored to levels similar to those of the control group following milk phospholipid administration. These results were confirmed to be due to the downregulation of protein expression of nuclear factor kappa-B (NF-κB) and phosphorylated IκB-α (inhibitor of κB α). Collectively, oral administration of milk phospholipids improves skin health through a synergistic effect on photoprotective activity.