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.

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.

Enhancing scanning accuracy of digital implant scans: A systematic review on application methods of scan bodies.

STATEMENT OF PROBLEM: Scan bodies play a crucial role in the accuracy of digital implant scans by serving as implant-positioning transfer devices. Previous literature has demonstrated the effects of scan body characteristics on the accuracy of digital implant scans. However, the optimal application methods of scan bodies to enhance scanning accuracy remain unclear. PURPOSE: The purpose of this systematic review was to determine the optimal application methods of scan bodies to enhance the accuracy of digital implant scans. MATERIAL AND METHODS: An electronic search was conducted by using the PubMed (MEDLINE), Web of Science, Cochrane Library, and Embase databases from November 2018 to 2023. Relevant references from the included studies were further screened manually for eligibility. Following the population, intervention, comparison, and outcome (PICO) criteria, a research question focused on identifying the optimal application method for effectively using scan bodies to enhance scanning accuracy was developed. Specific inclusion criteria involved in vitro and in vivo studies. The Checklist for Reporting In Vitro Studies (CRIS) guidelines were followed and the assessment of the risk of bias in the included studies was conducted. RESULTS: Sixteen articles that met the eligibility criteria were included in this systematic review. Two studies investigated the effect of scan body bevel orientation on the accuracy of digital implant scans, and 3 examined the impact of tightening torque on scan bodies. Among the studies focusing on completely edentulous arches, 5 recommended the use of auxiliary geometric devices on the dental arch to enhance scanning accuracy. However, 2 studies reported no improvements in accuracy after splinting scan bodies with thread. CONCLUSIONS: Different techniques for applying scan bodies, such as configuring bevel orientation, adjusting tightening torque, and attaching auxiliary geometric devices, influence the accuracy of digital implant scans. For scanning completely edentulous arches, attaching auxiliary devices to scan bodies to cover the edentulous ridge effectively enhances scanning accuracy.

Analyzing the accuracy of a cross-mounting technique utilizing digitized interocclusal records.

PURPOSE: To compare the accuracy of a partially digital cross-mounting workflow of direct scans of interocclusal records to a conventional workflow by analyzing the deviations of sequentially cross-mounted casts. MATERIALS AND METHODS: A set of reference casts, comprising maxillary and mandibular full-arch prepared casts and interim prostheses, was articulated, mounted, and scanned to generate four reference casts for cross-mounting. In the conventional approach, 15 sets of these four casts were printed. Polyvinylsiloxane (PVS) records were made using the reference casts and utilized for sequential cross-mounting. In the partially digital group, the same PVS interocclusal records were scanned and used for digital cross-mounting via design software. The mean deviations of both groups from the reference cast were analyzed using a 3D inspection software program. Statistical tests, including paired t-test and analysis of variance (ANOVA), were conducted to compare the average discrepancies between the two groups and to evaluate discrepancies in the anterior and posterior regions (α = 0.05). RESULTS: The range of discrepancies was similar in both the conventional and partially digital groups. The final set of related casts had a mean deviation of 201.58 ± 136.98 mm in the conventional workflow and 248.69 ± 164.71 mm in the partially digital workflow. No statistically significant difference was found between conventional and partially digital groups (p = 0.091). Error propagation was examined by comparing discrepancies at each step within the cross-mounting process. In the conventional group, no significant difference was found (p = 0.148), but a significant difference was found among groups in the partially digital group at each step of sequential mounting (p < 0.001). A significant difference was observed between anterior and posterior deviations in the partially digital group (p < 0.001), but not in the conventional group (p = 0.143). CONCLUSIONS: The study reveals that there is no statistically significant difference between conventional and partially digital cross-mounting workflows. However, within the partially digital group, a significant difference in deviation emerges across cross-mounting steps, with increased deviation in the anterior region.

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.

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.

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 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.

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.

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.

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.

Quantitative analysis of the selective pressure impression technique using CAD-CAM technology: A pilot clinical study.

STATEMENT OF PROBLEM: Quantitative 3D clinical analysis of the selective pressure impression technique directly measuring tissue displacement during impression making for complete maxillary dentures is lacking. PURPOSE: The purpose of this clinical study was to digitally compare impressions made of the edentulous maxillary ridge by using the selective pressure impression technique with different amounts of relief incorporated into custom tray designs. MATERIAL AND METHODS: Nine participants receiving maxillary complete dentures were enrolled in the study. An initial custom tray was fabricated in urethane dimethacrylate by using the alternative border molding technique without relief and scanned to create a standard tessellation language (STL) file from which 3 groups of custom trays were designed and 3D printed with 0.0-mm (no relief), 1.0-mm, and 3.0-mm relief over the anterior ridge and median palatal suture. Definitive impressions using each of the 4 custom trays were made with a consistent volume of light-body polyvinyl siloxane impression material. The definitive impressions were scanned, and the STL files were superimposed to investigate the topographical differences among the groups, each with respect to the no relief, 3D-printed custom tray definitive impression. Mean volumetric differences for all 3 groups were measured in areas where relief was used and statistically analyzed with the Friedman test (α=.05). RESULTS: No significant difference was found among any of the 3 groups of superimposed impressions in areas of no relief, 1.0-mm, and 3.0-mm relief (P=.558). The mean difference ±standard deviation for each comparison in regions of the anterior ridge and median palatal suture were 0.07 ±0.06 mm for no relief, -0.03 ±0.07 mm for the 1.0-mm tray relief, and -0.04 ±0.09 mm for the 3.0-mm tray relief. The negative values in mean difference indicated less compression of underlying tissues compared with the reference border molded urethane dimethacrylate custom tray impression. CONCLUSIONS: Although results showed less compression when compared with that of the control group, custom tray relief of 1.0 mm and 3.0 mm over the anterior residual alveolar ridge and median palatal suture did not significantly impact the resulting impression topography when compared with no relief custom trays.

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.

A clinical study comparing digital scanning and conventional impression making for implant-supported prostheses: A crossover clinical trial.

STATEMENT OF PROBLEM: The impact of discrepancies between casts produced from digital scans and conventional impressions on the clinical performance of definitive restorations has not been fully investigated. PURPOSE: The purpose of this crossover clinical trial was to evaluate the clinical performance of single implant-supported restorations fabricated with the digital scanning technique and computer-aided design and computer-aided manufacturing (CAD-CAM) casts compared with the conventional impression technique and gypsum casts in terms of efficiency, accuracy, and participant preference. MATERIAL AND METHODS: Thirty participants underwent conventional impressions and digital scans of a single implant-supported restoration. Two crowns were fabricated for the same implant with each technique. The time taken for each procedure was recorded. After the accuracy and efficiency analysis of both crowns, the better crown was delivered. A questionnaire was used to assess participant preference and comfort with the techniques. The Wilcoxon signed-rank test was used to compare the time measurements, and multiple comparisons were performed using the Bonferroni method. The chi-square test was used to compare the implant locations of delivered crowns (α=.05). RESULTS: The total time for the conventional impression technique was 14.16 minutes, while that for the digital scanning technique was significantly less at 11.28 minutes (P<.001). Remake times were 0.56 minutes for conventional impressions and 2.27 for digital scans, also significantly different (P<.001). The adjustment time taken in delivering the crowns was 4.35 minutes for conventional impressions and 3.78 minutes for conventional impressions, which was not statistically significant (P=.940). Of the crowns chosen for delivery, 46.7% were from conventional impressions and 53.3% from digital scans. Participants preferred the digital scanning technique (89%) to the conventional impression technique (11%). CONCLUSIONS: The digital scanning technique was more efficient than the conventional impression technique for single implant-supported restorations. Digital scans and CAD-CAM implant casts had accuracy comparable with that of conventional impressions and gypsum casts. Most participants preferred digital scans to conventional impressions.

Effect of increasing occlusal vertical dimension on lower facial form and perceived facial esthetics: A digital evaluation.

STATEMENT OF PROBLEM: Increasing occlusal vertical dimension (OVD) is often indicated in complex prosthodontic rehabilitations to gain restorative space and improve the occlusal relationship and esthetics. The effect of increasing occlusal vertical dimension on lower facial height (distance from subnasale to soft-tissue menton) and perceived facial esthetics is not well understood. PURPOSE: The purpose of this clinical study was to investigate the effect of incremental increases in the occlusal vertical dimension on lower facial height and perceived facial esthetics by using a digital approach. MATERIAL AND METHODS: Twenty-five participants with Class I jaw relationship and no loss of OVD participated in the study. Custom mandibular devices were digitally designed and 3-dimensionally printed to increase the OVD by 3, 6, and 9 mm in each participant. Three-dimensional facial scans and frontal photographs were made with the participants wearing a specific device to achieve the desired OVD increase. The lower facial height, total facial height (distance between nasion to soft-tissue menton), nasolabial angle, lip width, and lip height were digitally measured on facial scans. All measurements were recorded in a computer-aided design (CAD) software program and were repeated 3 times. Subsequently, frontal photographs of 10 participants were randomly selected for survey. Three groups each of 10 prosthodontists, general dentists, or laypersons participated in the survey and were asked to detect OVD difference in 2 photographs of the same participant and to rank facial esthetics at varying OVDs. One-way repeated measures ANOVA (α=.05) for the facial measurements and descriptive statistics for the survey results were used. RESULTS: Lower facial height, the ratio of lower facial height to total facial height, lip height, and nasolabial angle increased with an OVD increase, whereas lip width decreased (P<.001). Bonferroni corrected paired t tests revealed all groups of OVD increase to be significantly different from each other (P<.001) except for an OVD increase to 6 mm versus 9 mm in lip height (P=.540) and lip width (P=.019), respectively. Prosthodontists, general dentists, and laypersons could detect a +3 mm OVD increase 63.9%, 62.5%, and 56.5% of the time, respectively. The participants' original OVD was considered the most esthetic (60.0%, 45.0%, and 68.0%) by prosthodontists, general dentists, and laypersons, respectively. CONCLUSIONS: Increased OVD increases lower facial height, the ratio of lower facial height to total facial height, lip height, and nasolabial angle but decreases lip width. Prosthodontists are more sensitive to a smaller increase in OVD, closely followed by general dentists and then laypersons. In case of no loss of OVD, a vertical increase as small as 3 mm can be detected by both dentists and the general public and perceived as less esthetic. The larger the increase in OVD, the more detectable the difference and the less the faces are perceived as esthetic.

Considerations in the replacement of over-retained primary teeth with implant restorations in the esthetic zone: A case report.

OBJECTIVE: There exist several treatment planning and clinical challenges when treating over-retained primary teeth with dental implants-especially in the esthetic zone where the existing hard and soft tissue positions are not in harmony with adjacent dentition and do not serve as reliable landmarks for implant placement and restoration. In this report, we highlight some of the key aspects for achieving predictable treatment outcomes for implant restorations replacing over-retained primary teeth in the esthetic zone. CLINICAL CONSIDERATIONS: This clinical report describes the treatment of a patient who presented with over-retained deciduous canines consequent to congenitally missing maxillary lateral incisors. The deciduous canines were deemed hopeless, and subsequently replaced with immediately placed implants following a computer-guided protocol. The optimal implant positions were determined through a diagnostic wax-up correcting the existing gingival discrepancies with the adjacent teeth. Existing periapical infections were addressed utilizing a vestibular approach to minimize the postoperative recession and scarring and achieve a more predictable esthetic outcome. Final restorations were fabricated with all ceramic materials for optimal esthetics. CONCLUSION: When planning for implants to replace over-retained primary teeth, it is essential to visualize the desired contours of the final restorations and correct the level of the existing gingival discrepancies by planning the proper implant position and angulation in relation to the adjacent teeth and gingival positions. CLINICAL SIGNIFICANCE: Careful treatment planning coupled with a guided implant workflow allows for a successful surgical and esthetic outcome for the replacement of over-retained primary teeth with implant restorations.

Morphological features of mucous secretory organ and mucous secretion of loach Misgurnus anguillicaudatus skin for friction drag reduction.

We examined the functional morphology of loach Misgurnus anguillicaudatus skin by using synchrotron X-ray micro-computed tomography (SR-µCT) and high-contrast staining using osmium tetroxide or phosphotungstic acid (PTA), which enhances the image contrast of soft tissues. The captured high-spatial resolution images revealed that the surface ornamentations were stuck in the basement membrane of the loach scales. The ornamentations consisting of grooves (radii) and ridges (circuli) that can move freely and bend flexibly. The cross-sectional lateral microstructures of flat, concave and convex loach skins were observed from a live image of loach skin obtained through dark-field optical coherence tomography (OCT) imaging. The thickness of loach skin was changed with varying empty space between the mucous-cell layer and the scales by bending motion of loach. In addition, through direct measurement of drag reduction of loach skin, the mucous layer was found to have a strong influence on the reduction of skin friction. The present results enhance the understanding of the functional morphologies of mucous layer of loach to secrete mucus for skin friction reduction.

Tissue surface adaptation of CAD-CAM maxillary and mandibular complete denture bases manufactured by digital light processing: A clinical study.

STATEMENT OF PROBLEM: Clinical studies evaluating the tissue surface adaptation of complete denture bases fabricated by digital light processing (DLP) are lacking. PURPOSE: The purpose of this clinical study was to assess the tissue surface adaptation of complete denture bases generated by the DLP technique and to compare the adaptation with that of denture bases manufactured by 5-axis milling (MIL) and pack-and-press (PAP) method. MATERIAL AND METHODS: A total of 9 participants with 12 edentulous arches (7 maxillary and 5 mandibular) were included in this study. For each edentulous arch, the complete denture bases with occlusion rims were prepared by 3 different techniques (PAP, MIL, and DLP). A virtual denture base with occlusion rim was designed by means of a digital subtraction tool and served to fabricate the DLP and MIL denture bases. The complete denture bases were placed intraorally with an indicator applied to the intaglio surfaces. The thickness of the indicator was measured within the denture-bearing areas and anatomic landmarks of the edentulous arch to obtain the absolute tissue surface adaptation (ATA) value. The relative tissue surface adaptation (RTA) value was calculated from the differences between the ATA values of DLP or MIL techniques and those of the PAP technique. The Kruskal-Wallis test and the McNemar test were used for statistical analysis (α=.05). RESULTS: No statistically significant differences were found among the 3 denture base fabrication techniques with respect to the ATA values of either arch (P>.05). In terms of the RTA values for the maxillary arch, the DLP base was significantly different from the MIL base in the RC and P areas (both P<.05). The DLP base exhibited a higher frequency of negative RTA values than the MIL base. Regarding the RTA values for the mandibular arch, no significant differences were detected between the DLP and MIL denture bases (P>.05). CONCLUSIONS: The DLP and MIL denture bases demonstrated clinically acceptable tissue surface adaptation to both edentulous the maxilla and mandible. The DLP denture base was likely to exhibit intimate tissue adaptation in the stress-bearing areas of maxillary arches compared with the PAP denture base. The maxillary MIL denture base was likely to exhibit small gaps between the supporting tissue and denture base. Both DLP and MIL mandibular denture bases were likely to show intimate adaptation on the lingual slope compared with the PAP base.

Assessment of the trueness and tissue surface adaptation of CAD-CAM maxillary denture bases manufactured using digital light processing.

STATEMENT OF PROBLEM: Limited information is available evaluating the trueness and tissue surface adaptation of computer-aided design and computer-aided manufacturing (CAD-CAM) maxillary denture bases fabricated using digital light processing (DLP). PURPOSE: The purpose of this in vitro study was to evaluate the trueness of DLP-fabricated denture bases and to compare the tissue surface adaptation of DLP with milling (MIL) and pack and press (PAP). MATERIAL AND METHODS: The maxillary denture bases were virtually designed on the reference cast and were fabricated using DLP and MIL. Their intaglio surfaces were scanned and superimposed on the reference computer-aided design denture base to evaluate the trueness. A total of 20 denture bases (10 per technique) were also fabricated on the duplicated master casts using DLP and MIL. Ten denture bases were additionally made using PAP. The intaglio surfaces of the dentures were scanned and superimposed on the corresponding casts to compare the degree of tissue surface adaptation among the 3 techniques. The Mann-Whitney test and Kruskal-Wallis ANOVA were used for statistical analyses (α=.05). RESULTS: The trueness of the DLP denture base was significantly better than that of the MIL denture base (P<.001). Statistically significant differences were detected with respect to tissue surface adaptation of the denture base among the groups (P<.001). The DLP denture base showed the best denture base fit among the 3 techniques with a small interquartile range. CONCLUSIONS: Within the limitations of this in vitro study, the DLP maxillary denture base showed better trueness and tissue surface adaptation of ≤100 µm of the 3-dimensional surface deviation than the MIL and PAP denture bases.