Strategic use of obturator prostheses for the rehabilitation of oral cancer patients during the COVID-19 pandemic.

During the current pandemic scenario, maxillofacial rehabilitation specialists involved with supportive care in cancer must transform its practice to cope with COVID-19 and improve protocols that could quickly return the oral function of complex cancer patients who cannot wait for surgical complex rehabilitation. This includes the role of the maxillofacial prosthodontist for the rehabilitation of surgically treated patients with maxillary cancers by the means of filling obturator prostheses that are considered an optimal scientific-based strategy to reduce hospital stay with excellent pain control, oral function (speech, swallowing, mastication, and facial esthetics), psychologic and quality of life outcomes for the patients following intraoral cancer resection. Therefore, the aim of this commentary was to bring new lights to the strategic use of obturator prostheses for the rehabilitation of oral cancer patients during the COVID-19 pandemic as well as to present a protocol for managing such cases.

Comparison and evaluation of the morphology of crowns generated by biogeneric design technique with CEREC chairside system.

OBJECTIVES: To better guide clinicians to choose the appropriate chairside system, we compared and evaluated the morphology of crowns generated by three different biogeneric design modes (biogeneric copy (BC), biogeneric individual (BI), and biogeneric reference (BR)) of the CEREC software. METHODS: Maxillary and mandibular casts were obtained from twelve volunteers and digital impressions were acquired. All ceramic crown preparations of all right maxillary central incisors were prepared and digital impressions were taken. Then, crowns were automatically designed under BC, BI and BR modes separately and their morphologies were evaluated by six doctors. The "optimal fitting alignment" and "3D analysis" functions of the Geomagic Qualify software were carried out between original teeth and auto-generated full crowns. The auto-generated crowns were modified by a technician according to clinical criteria and the adjustment time was recorded. The discrepancies between technician modified crowns and the auto-generated full crowns were evaluated with the same functions in the Geomagic Qualify software. RESULTS: The subjective evaluation results of BC group were significantly better than those of BI and BR group (p < 0.05). Compared with the original teeth and modified crowns, auto-generated crowns in BC group all had the smallest differences, followed by BR and BI group (p < 0.05). BC group needed the shortest adjustment time than BI and BR group (p < 0.05). CONCLUSIONS: Using crowns generated by BC mode is more aesthetic and suitable in clinics use than those generated by BI and BR modes and can reduce clinic adjustment time.

Crestal module design optimization of dental implants: finite element analysis and in vivo studies.

The aim of this study was to evaluate the biomechanical behavior of Bone Level dental implants with four different neck designs in contact with cortical bone. Numerical simulations were performed using a Finite Element Method (FEM) based-model. In order to verify the FEM model, the in silico results were compared with the results obtained from histological analysis performed in an in vivo study with New Zealand rabbits. FEM was performed using a computerized 3D model of Bone Level dental implants inserted in the lower jaw bone with an applied axial load of 100 N. The analysis was performed using four different implant neck designs: even surfaced, screwed, three-ring design and four-ring design. Interface are of bone growth was evaluated by analyzing the Bone-Implant-Contact (BIC) parameter obtained from in vivo histological process and analyzed by Scanning Electron Microscopy (SEM). Bone Level implants were inserted in the rabbit tibia, placing two implants per tibia. The BIC was evaluated after three and six weeks of implantation. FEM studies showed that the three-ring design presented lower values of stress distribution compared to the other studied designs. The lower levels of mechanical stress were then correlated with the in vivo studies, showing that the three-ring design presented the highest BIC value after 3 and 6 weeks of implantation. In silico and in vivo results both concluded that the implants with three-ring neck design presented the best biomechanical and histological behavior in terms of new bone formation, enhanced mechanical stability and optimum osseointegration.

Influence of Intra-Oral Scanner (I.O.S.) on The Marginal Accuracy of CAD/CAM Single Crowns.

The aim of this in vitro study was to compare the quality of digital workflows generated by different scanners (Intra-oral digital scanners (I.O.S.s)) focusing on marginal fit analysis. A customized chrome-cobalt (Cr-Co) implant abutment simulating a maxillary right first molar was fixed in hemi-maxillary stone model and scanned by eight different I.O.S.s: Omnicam® (Denstply Sirona, Verona, Italy) CS3500®, CS3600®, (Carestream Dental, Atlanta, GA, USA), True Definition Scanner® (3M, St. Paul, MN, USA), DWIO® (Dental Wings, Montreal, Quebec, Canada), PlanScan® (Planmeca Oy, Helsinki, Finland), 3D PROGRESS Plus® (MHT, Verona, Italy), TRIOS 3® (3Shape, Copenhagen, Denmark). Nine scans were performed by each tested I.O.S. and 72 copings were designed using a dental computer-assisted-design/computer-assisted-manufacturing (CAD/CAM) software (exocad GmbH, Darmstadt, Germany). According to CAD data, zirconium dioxide (ZrO2) copings were digitally milled (Roland DWX-50, Irvine, CA, USA). Scanning electron microscope (SEM) direct vision allowed for marginal gap measurements in eight points for each specimen. Descriptive analysis was performed using mean, standard deviation, and median, while the Kruskal⁻Wallis test was performed to determine whether the marginal discrepancies were significantly different between each group (significance level p < 0.05). The overall mean marginal gap value and standard deviation were 53.45 ± 30.52 µm. The minimum mean value (40.04 ± 18.90 µm) was recorded by PlanScan®, then 3D PROGRESS Plus® (40.20 ± 21.91 µm), True Definition Scanner® (40.82 ± 26.19 µm), CS3500® (54.82 ± 28.86 µm) CS3600® (59,67 ± 28.72 µm), Omnicam® (61.57 ± 38.59 µm), DWIO® (62.49 ± 31.54 µm), while the maximum mean value (67.95 ± 30.41 µm) was recorded by TRIOS 3®. The Kruskal⁻Wallis tests revealed a statistically significant difference (p-value < 0.5) in the mean marginal gaps between copings produced by 3D PROGRESS Plus®, PlanScan, True Definition Scanner, and the other evaluated I.O.S.s. The use of an I.O.S. for digital impressions may be a viable alternative to analog techniques. Although in this in vitro study PlanScan®, 3D PROGRESS Plus® and True Definition Scanner® may have showed the best performances, all I.O.S.s tested could provide clinically encouraging results especially in terms of marginal accuracy, since mean marginal gap values were all within the clinically acceptable threshold of 120 µm.

Imaging Aspects of the Mandibular Incisive Canal: A PROSPERO-Registered Systematic Review and Meta-Analysis of Cone Beam Computed Tomography Studies

PURPOSE: This study aimed to perform a systematic review and meta-analysis of the literature on the mandibular incisive canal (MIC) studies using cone beam computed tomography (CBCT). MATERIALS AND METHODS: A PROSPERO-registered systematic review (#42017056619) was conducted following the PRISMA statements to summarize current knowledge on the CBCT aspects of the MIC. A search was performed in PubMed's Medline and Scopus databases, without date or language restrictions, using the algorithm {[(Interforaminal region) OR (mandibular incisive channel) OR (mandibular incisive nerve) OR (mental mandible) OR (anterior mandible) (cone beam computed tomography). Also, the references were crosschecked. The Meta-Analysis of Statistics Assessment and Review Instrument and meta-analysis was used to evaluate the selected studies. RESULTS: A total of 410 articles were found, and 25 studies were selected after a two-step selection process. The CBCT systems differed regarding field of view (FOV) (large, n = 3; medium, n = 2; small, n = 4; not informed, n = 16) and voxel size (0.15 to 0.4 mm). Geographically, the studies were distributed across four continents (South America, North America, Asia, and Europe), and there was a statistical significance of studies from the American and Asian continents (P < .0001). From 3,421 CBCT exams, the number of female patients was slightly higher than male, and the mean age ranged from 29.8 to 59.1 years. The overall mean prevalence of MIC was 89.6% ± 15.08%, and bilateral occurrence was statistically significant (P < .0001). The studies using a voxel size lower than 0.3 mm showed the highest mean prevalence (93.88%) in comparison with voxel size described as ≥ 0.3 mm (89.33%). Diameter (0.45 to 4.12 mm) and length (6.6 to 40.3 mm) showed great variability among the included studies. CONCLUSION: In summary, the results of this systematic review evidenced a high worldwide prevalence of MIC. There was no prevalence of MIC in relation to sex, and its presence was mainly related to adults between the fourth and sixth decades of life. In addition, great heterogeneity of methodologies was observed.

Clinical Outcomes of Monolithic Zirconia Crowns with CAD/CAM Technology. A 1-Year Follow-Up Prospective Clinical Study of 65 Patients.

Aim/Purpose: The primary aim of this study was to examine the clinical performance of posterior monolithic single crowns in terms of failure or complications and the secondary aim was to assess the quality of these restorations according to the United States Public Health Service (USPHS) criteria. Methods: Ιn a private dental clinic, 65 patients with need of posterior crowns were restored with monolithic zirconia crowns. All the restorations were evaluated 6 and 12 months after their cementation. The modified United States Public Health Service (USPHS) criteria and periodontal parameters were applied for the clinical evaluation of the crowns. Restorations with Alpha or Bravo rating were considered a success. Results: Descriptive statistics and nonparametric tests were used for statistical analysis. Sixty-five patients (mean age: 49.52) were restored with 65 monolithic zirconia crowns. No fracture of the restorations was recorded. The overall success rate was 98.5%. The clinical quality of all crowns was acceptable except for the marginal discoloration of one crown at the 6- and 12-month follow-up examination. Conclusions: In this study, no fracture of single-tooth monolithic crowns occurred and the success rate was high. Monolithic zirconia restorations fabricated is a viable option for the restoration of single posterior teeth.

Complete-arch accuracy of intraoral scanners.

STATEMENT OF PROBLEM: Intraoral scanners have shown varied results in complete-arch applications. PURPOSE: The purpose of this in vitro study was to evaluate the complete-arch accuracy of 4 intraoral scanners based on trueness and precision measurements compared with a known reference (trueness) and with each other (precision). MATERIAL AND METHODS: Four intraoral scanners were evaluated: CEREC Bluecam, CEREC Omnicam, TRIOS Color, and Carestream CS 3500. A complete-arch reference cast was created and printed using a 3-dimensional dental cast printer with photopolymer resin. The reference cast was digitized using a laboratory-based white light 3-dimensional scanner. The printed reference cast was scanned 10 times with each intraoral scanner. The digital standard tessellation language (STL) files from each scanner were then registered to the reference file and compared with differences in trueness and precision using a 3-dimensional modeling software. Additionally, scanning time was recorded for each scan performed. The Wilcoxon signed rank, Kruskal-Wallis, and Dunn tests were used to detect differences for trueness, precision, and scanning time (α=.05). RESULTS: Carestream CS 3500 had the lowest overall trueness and precision compared with Bluecam and TRIOS Color. The fourth scanner, Omnicam, had intermediate trueness and precision. All of the scanners tended to underestimate the size of the reference file, with exception of the Carestream CS 3500, which was more variable. Based on visual inspection of the color rendering of signed differences, the greatest amount of error tended to be in the posterior aspects of the arch, with local errors exceeding 100 µm for all scans. The single capture scanner Carestream CS 3500 had the overall longest scan times and was significantly slower than the continuous capture scanners TRIOS Color and Omnicam. CONCLUSIONS: Significant differences in both trueness and precision were found among the scanners. Scan times of the continuous capture scanners were faster than the single capture scanners.

Digital evaluation of absolute marginal discrepancy: A comparison of ceramic crowns fabricated with conventional and digital techniques.

STATEMENT OF PROBLEM: Marginal discrepancy is key to evaluating the accuracy of fixed dental prostheses. An improved method of evaluating marginal discrepancy is needed. PURPOSE: The purpose of this in vitro study was to evaluate the absolute marginal discrepancy of ceramic crowns fabricated using conventional and digital methods with a digital method for the quantitative evaluation of absolute marginal discrepancy. The novel method was based on 3-dimensional scanning, iterative closest point registration techniques, and reverse engineering theory. MATERIAL AND METHODS: Six standard tooth preparations for the right maxillary central incisor, right maxillary second premolar, right maxillary second molar, left mandibular lateral incisor, left mandibular first premolar, and left mandibular first molar were selected. Ten conventional ceramic crowns and 10 CEREC crowns were fabricated for each tooth preparation. A dental cast scanner was used to obtain 3-dimensional data of the preparations and ceramic crowns, and the data were compared with the "virtual seating" iterative closest point technique. Reverse engineering software used edge sharpening and other functional modules to extract the margins of the preparations and crowns. Finally, quantitative evaluation of the absolute marginal discrepancy of the ceramic crowns was obtained from the 2-dimensional cross-sectional straight-line distance between points on the margin of the ceramic crowns and the standard preparations based on the circumferential function module along the long axis. RESULTS: The absolute marginal discrepancy of the ceramic crowns fabricated using conventional methods was 115 ±15.2 µm, and 110 ±14.3 µm for those fabricated using the digital technique was. ANOVA showed no statistical difference between the 2 methods or among ceramic crowns for different teeth (P>.05). CONCLUSIONS: The digital quantitative evaluation method for the absolute marginal discrepancy of ceramic crowns was established. The evaluations determined that the absolute marginal discrepancies were within a clinically acceptable range. This method is acceptable for the digital evaluation of the accuracy of complete crowns.

Finish line distinctness and accuracy in 7 intraoral scanners versus conventional impression: an in vitro descriptive comparison.

BACKGROUND: Several studies have evaluated accuracy of intraoral scanners (IOS), but data is lacking regarding variations between IOS systems in the depiction of the critical finish line and the finish line accuracy. The aim of this study was to analyze the level of finish line distinctness (FLD), and finish line accuracy (FLA), in 7 intraoral scanners (IOS) and one conventional impression (IMPR). Furthermore, to assess parameters of resolution, tessellation, topography, and color. METHODS: A dental model with a crown preparation including supra and subgingival finish line was reference-scanned with an industrial scanner (ATOS), and scanned with seven IOS: 3M, CS3500 and CS3600, DWIO, Omnicam, Planscan and Trios. An IMPR was taken and poured, and the model was scanned with a laboratory scanner. The ATOS scan was cropped at finish line and best-fit aligned for 3D Compare Analysis (Geomagic). Accuracy was visualized, and descriptive analysis was performed. RESULTS: All IOS, except Planscan, had comparable overall accuracy, however, FLD and FLA varied substantially. Trios presented the highest FLD, and with CS3600, the highest FLA. 3M, and DWIO had low overall FLD and low FLA in subgingival areas, whilst Planscan had overall low FLD and FLA, as well as lower general accuracy. IMPR presented high FLD, except in subgingival areas, and high FLA. Trios had the highest resolution by factor 1.6 to 3.1 among IOS, followed by IMPR, DWIO, Omnicam, CS3500, 3M, CS3600 and Planscan. Tessellation was found to be non-uniform except in 3M and DWIO. Topographic variation was found for 3M and Trios, with deviations below +/- 25 µm for Trios. Inclusion of color enhanced the identification of the finish line in Trios, Omnicam and CS3600, but not in Planscan. CONCLUSIONS: There were sizeable variations between IOS with both higher and lower FLD and FLA than IMPR. High FLD was more related to high localized finish line resolution and non-uniform tessellation, than to high overall resolution. Topography variations were low. Color improved finish line identification in some IOS. It is imperative that clinicians critically evaluate the digital impression, being aware of varying technical limitations among IOS, in particular when challenging subgingival conditions apply.

Zirconia-based versus metal-based single crowns veneered with overpressing ceramic for restoration of posterior endodontically treated teeth: 5-year results of a randomized controlled clinical study.

OBJECTIVES: The aim of this 5-year randomized controlled trial was to compare the longevity and clinical behavior of single posterior crowns made with pressable ceramic on zirconia and on metal frameworks, and if failures occur, to delineate the contributing factors. METHODS: 72 patients, who needed the covering of at least a molar and/or premolar, were included in the study. All teeth were endodontically treated, with absence of periapical lesion or active periodontitis. Ninety single crowns were made with zirconia or metal framework and covered with pressable veneering ceramics. Two independent examiners assessed the survival of restorations at 6 months, 1-4 and 5 years after restoration placement including periapical radiographs, intraoral photographs, and USPHS modified criteria. The statistical analyses were performed with the Kaplan-Meier method. RESULTS: One core fracture occurred in Zircad/Zirpress crowns and one metal ceramic crown was lost for root fracture. Chipping fracture of the veneering ceramic was detected in 2 metal-ceramic crowns and in 3 zirconia-based crowns. The Estimate Cumulative Survival (ECS) and the Estimate Cumulative Success (ECSs) with standard deviation (SE) were respectively 97,73±2,19 and 92,64±4,14 for zirconia-based crowns whereas 97,44±2,39 and 91,11±4,27 for porcelain fused to metal crowns. CONCLUSIONS: The present randomized controlled trial shows that the survival of zirconia-based and metal-based single crowns is similar over a follow-up period of 5 years. No significant differences in esthetic, functional and biological outcomes were demonstrated between the two groups. The main failure mode was the chipping fracture of the veneering ceramic in both materials. Study number on ClinicalTrial.gov NCT02758457. CLINICAL SIGNIFICANCE: According to the results of this clinical study, zirconia-based rehabilitations with overpressing veneering technique represent a valid alternative to metal-based for posterior single crown restorations.

Consequences of experience and specialist training on the fabrication of implant-supported prostheses: A survey.

STATEMENT OF PROBLEM: Fabricating fixed restorations on implants requires that dentists stay up-to-date with the scientific publications. MATERIAL AND METHODS: A questionnaire containing 29 questions was sent to dentists, members of the Israeli Society of Prosthodontics, and university faculty members. Differences were evaluated using the chi-square and Fisher exact tests and Mann-Whitney U and Wilcoxon tests for questions enquiring into the frequency of use of certain methods (α=.05). RESULTS: A total of 155 questionnaires were completed by 84 general dental practitioners and 71 specialists and residents. Statistical differences (P<.05) were found in the course of the fabrication of the implant-supported prostheses in the diagnostic waxing, trial restoration, and impression-making processes. Trial restorations were often used by residents and specialists before starting an esthetic restoration. Diagnostic waxing was used when treating patients with complex esthetic needs, mainly by prosthodontists (P=.019). A custom tray for impression making was used more by residents and specialists than by general dental practitioners (P<.001). The open tray technique for impression making of single or up to 3 implants was performed mainly by residents, specialists, and general dental practitioners with professional experience of fewer than 15 years. General dental practitioners used primarily plastic or metal trays for impression making. CONCLUSIONS: Significantly, impression techniques and the use of custom open trays, diagnostic waxing, and trial restorations were performed by residents, specialists, and dentists with fewer than 15 years of experience.

Experimental investigation of commercial small diameter dental implants in porcine mandibular segments.

Small diameter (mini) dental implants have become more popular in recent years as alternatives to classical implant treatment in clinical cases with critical bony situations. However, an in-depth scientific analysis of the mechanical and biomechanical effects of small diameter implants has not yet been published. The aim of the present study was to investigate experimentally different commercial mini implants by measuring their displacements under immediate loading. Twelve commercially available mini implants were measured. Implants were inserted into porcine mandibular segments and loaded by means of a predefined displacement of 0.5 mm of the loading system. The implants were loaded at an angle of 30° to the implant long axis using the self-developed biomechanical hexapod measurement system. Implant displacements were registered. The experimental results were compared to the numerical ones from a previous study. Measured implant displacements were within the range of 39-194 µm. A large variation in the displacements was obtained among the different implant systems due to the different designs and thread profiles. Comparing experimental and numerical results, the displacements that were obtained numerically were within the range of 79-347 µm. The different commercial mini implants showed acceptable primary stability and could be loaded immediately after their insertion.

Quality Evaluation of Zirconium Dioxide Frameworks Produced in Five Dental Laboratories from Different Countries.

PURPOSE: The aim of this study was to assess and compare quality as well as economic aspects of CAD/CAM high strength ceramic three-unit FDP frameworks ordered from dental laboratories located in emerging countries and Switzerland. MATERIAL AND METHODS: The master casts of six cases were sent to five dental laboratories located in Thailand (Bangkok), China (Peking and Shenzhen), Turkey (Izmir), and Switzerland (Bern). Each laboratory was using a different CAD/CAM system. The clinical fit of the frameworks was qualitatively assessed, and the thickness of the framework material, the connector height, the width, and the diameter were evaluated using a measuring sensor. The analysis of the internal fit of the frameworks was performed by means of a replica technique, whereas the inner and outer surfaces of the frameworks were evaluated for traces of postprocessing and damage to the intaglio surface with light and electronic microscopes. Groups (dental laboratories and cases) were compared for statistically significant differences using Mann-Whitney U-tests after Bonferroni correction. RESULTS: An acceptable clinical fit was found at 97.9% of the margins produced in laboratory E, 87.5% in B, 93.7% in C, 79.2% in A, and 62.5% in D. The mean framework thicknesses were not statistically significantly different for the premolar regions; however, for the molar area 4/8 of the evaluated sites were statistically significantly different. Circumference, surface, and width of the connectors produced in the different laboratories were statistically significantly different but not the height. There were great differences in the designs for the pontic and connector regions, and some of the frameworks would not be recommended for clinical use. Traces of heavy postprocessing were found in frameworks from some of the laboratories. The prices per framework ranged from US$177 to US$896. CONCLUSIONS: By ordering laboratory work in developing countries, a considerable price reduction was obtained compared to the price level in Switzerland. Despite the use of the standardized CAD/CAM chains of production in all laboratories, a large variability in the quality aspects, such as clinical marginal fit, connector and pontic design, as well as postprocessing traces was noted. Recommended sound handling of postprocessing was not applied in all laboratories. Dentists should be aware of the true and factitious advantages of CAD/CAM production chains and not lose control over the process.

Understanding dental CAD/CAM for restorations--dental milling machines from a mechanical engineering viewpoint. Part B: labside milling machines.

Nowadays, dental numerical controlled (NC) milling machines are available for dental laboratories (labside solution) and dental production centers. This article provides a mechanical engineering approach to NC milling machines to help dental technicians understand the involvement of technology in digital dentistry practice. The technical and economic criteria are described for four labside and two production center dental NC milling machines available on the market. The technical criteria are focused on the capacities of the embedded technologies of milling machines to mill prosthetic materials and various restoration shapes. The economic criteria are focused on investment cost and interoperability with third-party software. The clinical relevance of the technology is discussed through the accuracy and integrity of the restoration. It can be asserted that dental production center milling machines offer a wider range of materials and types of restoration shapes than labside solutions, while labside solutions offer a wider range than chairside solutions. The accuracy and integrity of restorations may be improved as a function of the embedded technologies provided. However, the more complex the technical solutions available, the more skilled the user must be. Investment cost and interoperability with third-party software increase according to the quality of the embedded technologies implemented. Each private dental practice may decide which fabrication option to use depending on the scope of the practice.

Evaluation of a Reverse-Tapered Design on the Osseointegration of Narrow-Diameter Implants in Beagle Dogs: A Pilot Study.

PURPOSE: The purpose of this study was to evaluate a reverse-tapered design on the osseointegration of narrow-diameter implants in comparison with a conventional tapered design in beagle dogs. MATERIALS AND METHODS: All mandibular premolars and first molars were extracted bilaterally in four beagle dogs. Three months later, three kinds of implants were placed in both quadrants of the mandible: tapered narrow-diameter implants processed by cold working (TNC; n = 8), reverse-tapered narrow-diameter implants (RTN; n = 8), and reverse-tapered narrow-diameter implants processed by cold working (RTNC; n = 8). The animals were sacrificed at 4 weeks. Implant stability quotient (ISQ) values were measured at the time of implant placement and sacrifice. Histomorphometric analysis was performed. RESULTS: The baseline ISQ values were significantly lower in the RTN (56.0 ± 11.6) and RTNC (57.2 ± 9.8) than in the TNC (68.0 ± 5.4; P = .021). At 4 weeks, the TNC (69.9 ± 5.1) exhibited significantly higher ISQ values compared with the RTNC (61.6 ± 4.1; P = .024). Histologic analysis in the RTN and RTNC revealed osseointegration without any signs of inflammation; however, unresolved coronal gap or dehiscence was also observed. The total bone-to-implant contact ratios (BIC) in TNC, RTN, and RTNC were 55.1% ± 11.5%, 47.8% ± 19.1%, and 60.2% ± 15.3%, respectively, and no significant differences were shown among them. The BIC for the coronal part in each group was 51.1% ± 29.4%, 28.8% ± 33.8%, and 23.9% ± 23.3%, respectively, and the differences were not significant. In the threaded part, TNC, RTN, and RTNC showed a BIC of 56.3% ± 9.6%, 50.7% ± 18.3%, and 65.3% ± 15.6%, respectively. There was no significant difference among them. CONCLUSION: The reverse-tapered design on narrow-diameter implants showed a lower initial stability than the conventional tapered design; however, there was equivalent osseointegration in an early healing phase.

In vitro evaluation of marginal, axial, and occlusal discrepancies in metal ceramic restorations produced with new technologies.

STATEMENT OF PROBLEM: Marginal and axial discrepancies of metal ceramic restorations are key to their long-term success. Little information is available for metal ceramic restorations fabricated with soft metal milling and laser sintering technologies. PURPOSE: The purpose of this in vitro study was to compare the marginal, axial, and occlusal discrepancies in single-unit metal ceramic restorations fabricated with new production techniques with those in a single-unit restoration fabricated using a conventional technique. MATERIAL AND METHODS: After the artificial tooth was prepared, impressions were made, and 40 dies were obtained. Dies were randomly divided into 4 groups (n=10). Cobalt-chromium (Co-Cr) cast (C), hard metal milled (HM), laser sintered (LS), and soft metal milled (SM) copings were fabricated. Marginal, axial, and occlusal discrepancies of these copings were measured using the silicone replica technique before and after the application of veneering ceramic. Data were analyzed with repeated measurements 2-way ANOVAs and Bonferroni post hoc tests (α=.05). RESULTS: Significant differences were found in the increase of marginal discrepancy after the application of veneering ceramic in the LS group (P=.016). However, no significant differences in marginal discrepancy were found whether veneering ceramic was applied to copings before or after in the other groups (P>.05). With regard to marginal and occlusal discrepancies, significant differences were found among the production techniques (P<.001 and P<.05, respectively). No significant differences in axial discrepancies were found among the groups (P>.05). CONCLUSION: This in vitro study showed that metal ceramic restorations produced with HM and newly introduced SM techniques exhibited better marginal adaptations than those produced with the LS or C technique.

Evaluation of the marginal fit of single-unit, complete-coverage ceramic restorations fabricated after digital and conventional impressions: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: In existing published reports, some studies indicate the superiority of digital impression systems in terms of the marginal accuracy of ceramic restorations, whereas others show that the conventional method provides restorations with better marginal fit than fully digital fabrication. Which impression method provides the lowest mean values for marginal adaptation is inconclusive. The findings from those studies cannot be easily generalized, and in vivo studies that could provide valid and meaningful information are limited in the existing publications. PURPOSE: The purpose of this study was to systematically review existing reports and evaluate the marginal fit of ceramic single-tooth restorations after either digital or conventional impression methods by combining the available evidence in a meta-analysis. MATERIAL AND METHODS: The search strategy for this systematic review of the publications was based on a Population, Intervention, Comparison, and Outcome (PICO) framework. For the statistical analysis, the mean marginal fit values of each study were extracted and categorized according to the impression method to calculate the mean value, together with the 95% confidence intervals (CI) of each category, and to evaluate the impact of each impression method on the marginal adaptation by comparing digital and conventional techniques separately for in vitro and in vivo studies. RESULTS: Twelve studies were included in the meta-analysis from the 63 identified records after database searching. For the in vitro studies, where ceramic restorations were fabricated after conventional impressions, the mean value of the marginal fit was 58.9 µm (95% CI: 41.1-76.7 µm), whereas after digital impressions, it was 63.3 µm (95% CI: 50.5-76.0 µm). In the in vivo studies, the mean marginal discrepancy of the restorations after digital impressions was 56.1 µm (95% CI: 46.3-65.8 µm), whereas after conventional impressions, it was 79.2 µm (95% CI: 59.6-98.9 µm) CONCLUSION: No significant difference was observed regarding the marginal discrepancy of single-unit ceramic restorations fabricated after digital or conventional impressions.

Effects of Impression Coping Design, Impression Technique, and Dental Undercuts on the Accuracy of Implant Impressions Assessed by 3-Dimensional Optical Scanning: An In Vitro Study.

INTRODUCTION: The aim of this in vitro study was to evaluate the effect of the type and design of the impression copings on the accuracy of implant impressions in 2 different conditions. MATERIALS AND METHODS: A reference model with 2 implants inserted in bilateral mandibular canines was fabricated. The posterior teeth were inserted as tilted to simulate intra-oral undercuts. The teeth were eliminated to create an edentulous condition. Three different impression techniques were performed (open high retentive [OH], open low retentive [OL], closed [C]) for each condition. Total of 48 casts were made. Two scan-bodies were secured on each cast, scanned by an optical scanner. Then, they were compared to the scan of the reference model, and the calculated mean errors were analyzed with a 2-way ANOVA and Tukey test. RESULTS: There was no significant difference between the complete and partially edentulous groups (F = 3.252, P = 0.079). There was significant difference between the different designs of the impression copings (F = 31.789, P < 0.001) but the interaction between the dependent variables was not significant (F = 0.511, P = 0.603). CONCLUSIONS: The design of the impression copings was more important than the undercuts. The accuracy of the closed tray coping was greater than the low retentive coping and equal to the high retentive coping.

Influence of light source, polarization, education, and training on shade matching quality.

STATEMENT OF PROBLEM: Many factors influence the quality of shade selection, and isolating how significantly each of these factors influences results is difficult. PURPOSE: The purpose of this in vitro study was to compare results of shade matching using handheld lights with or without a polarizing filter with results obtained using a professional viewing booth and to analyze the influence of education and training on shade selection outcome. MATERIAL AND METHODS: A total of 96 third-year dental students (evaluators) were randomly separated into 4 groups. Each group was assigned 1 of 2 handheld shade-matching devices (lights) with or without a polarizing filter. Each group performed a shade matching exercise using the handheld light or a professional viewing booth. The exercise consisted of matching shade tabs placed in a typodont to a commercial shade guide. Each group repeated this procedure 4 times over a 9-week period. A lecture on shade matching was presented at the fifth week of the study, between "before" and "after" shade matching procedures. RESULTS: Shade matching scores with handheld lights (7.8) were higher than scores of shade matching with the viewing booth (7.2). The mean scores for before (7.2) and after (7.8) shade matching (with education and training in between) were significantly different. The combined effect of light and education and training improved the shade matching score by 1.2, from 6.8 in the before sessions using the viewing booth to 8.0 in the after sessions using handheld lights. A 21% increase in the number of evaluators who selected 1 of 4 best matches was recorded, 10% for handheld lights versus viewing booth after education and training versus before sessions and 11% between after sessions using handheld lights versus before sessions using viewing booth. CONCLUSIONS: Within the limits of the study, the shade matching scores with handheld lights were significantly better than the results obtained using a viewing booth (P<.01). Using a handheld light with or without a polarizing filter did not influence shade matching results. Mean shade matching scores were significantly better after education and training (P<.01). Light combined with education and training resulted in the greatest increase in shade matching quality.