3D printed implant surgical guides with internally routed irrigation for temperature reduction during osteotomy preparation: A pilot study.

OBJECTIVE: The purpose of this study was to test a novel through-the-guide means of irrigation in an in-vitro bovine bone model and to explore the method clinical applicability. MATERIALS AND METHODS: Surgical guides were designed to fit over five fresh bovine samples. Control osteotomy sites were compared to experimental sites irrigated through a 3D printed surgical guide with customized channels that direct the coolant toward the interface of the alveolar crest and drill. Temperature was measured during surgery with thermocouples located at 3 and 6 mm from the crestal height of the bone, and with an infrared thermal camera taking direct temperature readings from a window cut into axial wall at 9 mm from the crestal height of the ridge. RESULTS: Incorporation of routed irrigation significantly decreased heat generation, keeping temperature consistently below 47°C. A clinical case illustrates the method applicability using standard implant planning software, 3D printing technology, and regular implant armamentarium. CONCLUSIONS: The in-vitro analysis shows that this method mitigates temperature increase caused by static surgical guide irrigation blockade at the osteotomy site. This technique can be incorporated in the surgical guide design using commercially available software and 3D printing technology and has immediate applications in practice. CLINICAL SIGNIFICANCE: The in-vitro analysis shows that this method can significantly mitigate the temperature increase caused by static surgical guide irrigation blockade at the osteotomy site. This technique also has the advantage that it can be incorporated in the digital surgical guide design using commercially available software and 3D printing technology. The method has immediate applications in practice, and especially in the treatment of edentulism in esthetic zone where use of guided surgery for implant placement is crucial in obtaining consistent results.

Evaluation of complete-arch implant scanning with 5 different intraoral scanners in terms of trueness and operator experience.

STATEMENT OF PROBLEM: The intraoral scanning of the edentulous arch might be challenging for an inexperienced operator because of the large mucosal area and the use of scan bodies. PURPOSE: The purpose of this ex vivo study was to compare the trueness of 5 intraoral scanners in replicating implant scan bodies and soft tissues in an edentulous maxilla and to investigate the effects of operator experience. MATERIAL AND METHODS: The maxilla was resected from a fresh cadaver, 5 implants placed, and a reference scan made. Eight scans were made by experienced operators and 8 by an inexperienced operator with each scanner (iTero Element 2, Medit i500, Primescan, TRIOS 3, TRIOS 4). The implant platform deviation was measured after complete surface alignment and after scan body alignment. Deviation data were analyzed with a generalized linear mixed model (α=.05). RESULTS: After complete surface alignment, the mean ±standard deviation implant platform deviation was higher for the inexperienced operator (421 ±25 µm) than for experienced ones (191 ±12 µm, P<.001) for all scanners. After scan body alignment, no significant differences were found between operators for Element 2, Primescan, and TRIOS 3. The experienced operators produced a lower deviation for TRIOS 4 (35 ±3.3 µm versus 54 ±3.1 µm, P<.001), but higher deviation for i500 (68 ±4.1 µm versus 57 ±3.6 µm, P<.05). The scanner ranking was Element 2 (63 ±4.1 µm), i500 (57 ±3.6 µm, P=.443), TRIOS 4 (54 ±3.1 µm, P=.591), TRIOS 3 (40 ±3.1 µm, P<.01), Primescan (27 ±1.6 µm, P<.001) for the inexperienced operator and i500 (68 ±4.1 µm), Element 2 (58 ±4.0 µm, P=.141), TRIOS 3 (41 ±2.8 µm, P<.001), TRIOS 4 (35 ±3.3 µm, P=.205), Primescan (28 ±1.8 µm, P=.141) for the experienced operators. CONCLUSIONS: Mucosal alignment greatly overestimated the platform deviation. The intraoral scanners showed different trueness during the complete-arch implant scanning. The operator experience improved the trueness of the edentulous mucosa but not implant platform deviation.

Aerosol and spatter mitigation in dentistry: Analysis of the effectiveness of 13 setups.

OBJECTIVES: The current study aims to investigate the aerosol and spatter mitigation quality of 13 dry-field isolation methods in a simulated setup that replicates real-life work scenarios encountered in dental practices. METHODS: A crown preparation on a manikin was performed on tooth number 30 and repeated five times for each setup to simulate a patient under care. Aerosol, environmental, and operator face shield spatter, and sound intensity was measured. Generalized linear mixed models were used, and posthoc pairwise comparisons were performed to compare least-squares means when appropriate using a Tukey adjustment. RESULTS: All tested setups showed some environmental spatter formation; however, these were able to control most (and in some cases all) spatter on the operator face shield. All methods resulted in excellent aerosol mitigation when a second line of high-volume evacuation (HVE) was added to the device setup. However, in most setups, total sound levels exceeded 85 dB, posing a concern for prolonged noise exposure. CONCLUSIONS: The Prototype device and four other tested setups with secondary HVE addition completely eliminated aerosol creation as tested. Spatter of the Face Shield was best eliminated using the Prototype device. CLINICAL SIGNIFICANCE: Within the limitations of this study, it can be concluded that the dental community has at its disposal equipment that can effectively mitigate aerosol and spatter.

The effect different substrates have on the trueness and precision of eight different intraoral scanners.

OBJECTIVE: This in vitro study compares the newest generation of intraoral scanners to their older counterparts, and tests whether material substrates affect the trueness and precision of intraoral scanners (IOS). MATERIAL AND METHODS: A custom model, used as the reference standard, was fabricated with teeth composed of different dental materials. The reference standard scan was obtained using a three-dimensional (3D) optical scanner, the ATOS III. Experimental scans were obtained using eight different IOS, operated by experienced clinicians, using the manufacturer's recommended scanning strategy. A comprehensive metrology program, Geomagic Control X, was used to compare the reference standard scan with the experimental scans. RESULTS: For all scanners tested, except Trios3, the substrate does influence the trueness and precision of the scan. Furthermore, differences exist when comparing the same substrate across different scanners with some of the latest generation scanners clearly leaping ahead of the older generation regarding both trueness and precision. CONCLUSIONS: Substrate type affects the trueness and precision of a scan. Active Triangulation scanners are more sensitive to substrate differences than their parallel confocal counterparts. Some scanners scan certain substrates better, but in general the new generation of scanners outperforms the old, across all substrates. CLINICAL SIGNIFICANCE: The substrates being scanned play an import role in the trueness and precision of the 3D model. The new generation of scanners is remarkably accurate across all substrates and for complete-arch scanning.

Effect of scan pattern on complete-arch scans with 4 digital scanners.

STATEMENT OF PROBLEM: Complete-arch digital scans are becoming popular as digital dentistry is adopted for expanded clinical situations such as complete-arch prostheses, removable prostheses, extensive implant-supported treatment, and orthodontic aligners. Whether the scan pattern technique affects the trueness and precision of complete-arch scans and whether differences in accuracy exist among different scanners remain unclear. Furthermore, each manufacturer recommends a different scan pattern, but evidence of the superiority of the manufacturer's recommended pattern is lacking. PURPOSE: The purpose of this in vitro study was to determine whether the scan pattern affects the trueness, precision, and speed of complete-arch digital scans performed by using 4 different digital scanning systems. MATERIAL AND METHODS: A custom model used as the reference standard was fabricated with teeth having the same refractive index as dentin and enamel to simulate the natural dentition. The scan of the custom typodont was obtained by using an ATOS III Triple Scan 3D optical scanner. This study evaluated the CEREC Omnicam, Planmeca Emerald, Align iTero Element, and 3Shape TRIOS 3. Experimental scans were obtained from each of the 4 different digital scanning systems by using 4 unique scan patterns by experienced clinicians. Four experimental scans were acquired from each of the scanners by using 4 distinct scan patterns for a total of 16 scans for each scanner. Scan patterns 1 to 4 were based on the operator manuals for each different scanner. The scan time was recorded for each scan. All experimental scans were converted to standard tessellation language (STL) format, and a comprehensive metrology program, Geomagic Control X, was used to compare the reference standard scan with the experimental scans. RESULTS: For trueness, the scanner (P<.001), scan pattern (P=.001), and their interaction (P<.001) were found to be significant. Overall, scan pattern 2 showed the highest average trueness and precision. Likewise, for overall scan pattern precision, the scanner, scan pattern, and their interaction were found to be significant (P<.001). CONCLUSIONS: Scan pattern affected trueness and precision for some scanners, but not for others. Differences exist in the complete-arch scan speed, trueness, and precision of individual scanners. Scan pattern can play an important role in the success of digital scanning.

Comparing the trueness of seven intraoral scanners and a physical impression on dentate human maxilla by a novel method.

BACKGROUNDS: Intraoral scanner (IOS) accuracy is commonly evaluated using full-arch surface comparison, which fails to take into consideration the starting position of the scanning (scan origin). Previously a novel method was developed, which takes into account the scan origin and calculates the deviation of predefined identical points between references and test models. This method may reveal the error caused by stitching individual images during intraoral scan. This study aimed to validate the novel method by comparing the trueness of seven IOSs (Element 1, Element 2, Emerald, Omnicam, Planscan, Trios 3, CS 3600) to a physical impression digitized by laboratory scanner which lacks linear stitching problems. METHODS: Digital test models of a dentate human cadaver maxilla were made by IOSs and by laboratory scanner after polyvinylsiloxane impression. All scans started on the occlusal surface of the tooth #15 (universal notation, scan origin) and finished at tooth #2. The reference model and test models were superimposed at the scan origin in GOM Inspect software. Deviations were measured between identical points on three different axes, and the complex 3D deviation was calculated. The effect of scanners, tooth, and axis was statistically analyzed by the generalized linear mixed model. RESULTS: The deviation gradually increased as the distance from scan origin increased for the IOSs but not for the physical impression. The highest deviation occurred mostly at the apico-coronal axis for the IOSs. The mean deviation of the physical impression (53 ± 2 µm) was not significantly different from the Trios 3 (156 ± 8 µm) and CS 3600 (365 ± 29 µm), but it was significantly lower than the values of Element 1 (531 ± 26 µm), Element 2 (246 ± 11 µm), Emerald (317 ± 13 µm), Omnicam (174 ± 11 µm), Planscan (903 ± 49 µm). CONCLUSIONS: The physical impression was superior compared to the IOSs on dentate full-arch of human cadaver. The novel method could reveal the stitching error of IOSs, which may partly be caused by the difficulties in depth measurement.

Marginal and internal fit of full ceramic crowns milled using CADCAM systems on cadaver full arch scans.

BACKGROUND: Chairside systems are becoming more popular for fabricating full-ceramic single restorations, but there is very little knowledge about the effect of the entire workflow process on restoration fit. Therefore, this study aimed to compare the absolute marginal discrepancy (AMD) and the full internal fit (FULL) of all-ceramic crowns made by two chairside systems, Planmeca FIT and CEREC, with detailed and standard mill settings. METHODS: One upper molar was prepared for an all-ceramic crown in human cadaver maxilla. Full-arch scans were made by Emerald or Omnicam four times each. Twenty-four e.max crowns were designed and milled by the Planmill 30s or 40s or CEREC MCXL mills with either detailed or standard settings. The cadaver tooth was extracted, and each crown was fixed on it and scanned by a high-resolution microCT scanner. The AMD and FULL were measured digitally in mesio-distal and bucco-lingual 2D slices. The actual and predicted times of the milling were also registered. RESULTS: No differences were observed between detailed or standard settings in either system. The AMD was significantly higher with CEREC (132 ± 12 µm) than with either Planmill 30s (71 ± 6.9 µm) or 40s (78 ± 7.7 µm). In standard mode, the FULL was significantly higher with CEREC (224 ± 9.6 µm) than with either Planmill 30s (169 ± 8.1 µm) or 40s (178 ± 8.5 µm). There was no difference between actual and predicted time with the two Planmeca models, but with CEREC, the actual time was significantly higher than the predicted time. The 30s had significantly higher actual and predicted times compared to all other models. Across all models, the average milling time was 7.2 min less in standard mode than in detailed mode. CONCLUSIONS: All fit parameters were in an acceptable range. No differences in fit between Planmeca models suggest no effect of spindle number on accuracy. The detailed setting has no improvement in the marginal or internal fit of the restoration, yet it increases milling time.

Effect of scan substrates on accuracy of 7 intraoral digital impression systems using human maxilla model.

OBJECTIVE: This study aimed to determine how the accuracy of digital impressions was affected by four common dental substrates using seven prevalent IOS systems to scan the complete arch of a human maxilla. SETTING AND SAMPLE POPULATION: The Department of Oral Rehabilitation at the Medical University of South Carolina. A single cadaver maxilla. MATERIALS AND METHODS: Seven digital intraoral impression systems were used to scan a freshly harvested human maxilla. The maxilla contained several teeth restored with amalgam and composite, as well as unrestored teeth characterized by enamel. Also, three teeth were prepared for full coverage restorations to expose natural dentin. An industrial grade metrology software program that allowed 3D overlay and dimensional computation compared deviations of the complete arch and its substrates on the test model from the reference model. RESULTS: Substrates were significantly different from each other when considering scan data as a whole, as well as when comparing IOS devices individually. Only PlanScan failed to reveal trueness differences between the different substrates, while only Emerald revealed precision differences between the substrates. CONCLUSIONS: Substrate type does impact the overall accuracy of intraoral scans with dentin being the most accurate and enamel being the least accurate. The four substrates scanned impacted the trueness of all IOS devices.

Evaluation of the trueness and precision of complete arch digital impressions on a human maxilla using seven different intraoral digital impression systems and a laboratory scanner.

OBJECTIVES: An impression accuracy study using a cadaver maxilla was performed using both prepared and intact teeth as well as palatal tissue. MATERIALS AND METHODS: Three crown preparations were performed on a cadaver maxilla. Seven different digital impression systems along with polyvinylsiloxane impressions were used to create digital models of the maxilla. Three-dimensional (3D) files of the experimental models were compared to a master model. The 3D files were overlaid and analyzed using a comparison software to create color coded figures that were measured for deviations between the master and experimental models. RESULTS: For scanning tooth structure, only the Planscan was significantly less accurate than the rest of impression techniques. No significant differences in accuracy were found between models created using digital impressions and those created from traditional vinyl polysiloxane impressions with cross arch deviations ranging from 18 to 39 µm for each. CONCLUSIONS: Impressions taken using all digital impression systems, save for the Planscan, were able to accurately replicate the tissues of a complete arch human maxilla. CLINICAL SIGNIFICANCE: Studies examining accuracy of digital impression systems have generally been performed on materials other than dental tissues. Optically, materials such as plastic and metal have properties different from enamel and dentin. This study evaluates accuracy of digital impression systems on human dentin, enamel, and soft tissues.

Evaluation of removable partial denture frameworks fabricated using 3 different techniques.

STATEMENT OF PROBLEM: Rapid advancements in computer-aided design and computer-aided manufacturing (CAD-CAM) have opened new pathways in the fabrication of removable partial dentures (RPDs) through additive and subtractive processes. Questions remain whether the digital pathway is an acceptable one compared with conventional analog or combined analog and digital pathways. PURPOSE: The purpose of this clinical study was to determine the quality of RPD frameworks fabricated using 3 different fabrication methods: analog, combined analog-digital, and digital. MATERIAL AND METHODS: Three RPD frameworks were fabricated for each of the 9 participants using each of the 3 techniques. Of the 9 participants enrolled, 4 were of Kennedy class I, 3 were of Kennedy class II, and 2 were of Kennedy class III. The first technique was completely analog: a physical impression was made using polyvinyl siloxane, stone casts were made, a survey was performed, and a laboratory technician waxed and cast the RPD framework. The combined analog-digital workflow had the analog steps, but the stone cast was scanned with a laboratory scanner to generate a digital cast. The 3Shape CAD software was then used to design a digital RPD, which was fabricated from a cobalt-chroumum alloy by selective laser melting. The third technique was completely digital: an intraoral digital scanner was used to make a definitive scan, which was sent to the 3Shape software for digitally designing the RPD framework and subsequent selective laser melting for fabrication. For all frameworks in the same participant, the same design was used for consistency. The evaluation consisted of a yes/no survey with 7 framework-related parameters and was completed by 5 clinicians. For statistics, an overall P value was calculated using a chi-squared test to determine any difference among the groups (α=.05). RESULTS: Seven of the 9 participants received the framework fabricated using the digital pathway as their definitive prosthesis. The completely digital method was significantly better than the traditional method of analog fabrication (P<.001). Intraoral scanning was also significantly better than the combined method of fabrication (P<.001). The completely analog method was better than the combined method of framework fabrication (P=.008). CONCLUSIONS: Within the limitations of this clinical study, it was concluded that the combined analog-digital pathway of RPD fabrication was the least clinically acceptable one as determined by 5 calibrated clinicians using a yes/no questionnaire, whereas the completely digital method of fabrication was found to be the best.

A novel method for complex three-dimensional evaluation of intraoral scanner accuracy.

AIMS: The aim of this study was to compare two existing methods and one novel method for measuring the distortion of three-dimensional (3D) models created with complete-arch digital impressions, and to assess the accuracy of different scan patterns using these methods. MATERIALS AND METHODS: Maxillary and mandibular models were imaged with the PlanScan intraoral scanner using four different scan patterns. Accuracy and distortion were assessed by comparing the master scans with the intraoral scans using the following three methods: 1) Mean surface deviation was measured after complete arch superimposition; 2) 28 points were selected identically on the experimental and on the master reference models, and the deviation between identical points was assessed after superimposition over the complete arch; 3) In the case of the novel technique, the superimposition was made only at the scanning origin, and after that the 28 points were compared. RESULTS: Significant differences were found between the three different methods, regardless of the arch and pattern. The overall mean deviation between identical points when the models were aligned at the scanning origin was the highest, and the mean deviation between the non-identical values was the lowest. The novel method revealed local tooth-wise differences between the scan patterns as well as a pattern of amplified model error extending away from the scan origin. CONCLUSIONS: The novel method better detects the cumulative deviation of stitching errors in complete arch intraoral scans and is suitable to investigate the effect of scanning pattern in a very sensitive manner.

Evaluation of the effect scan pattern has on the trueness and precision of six intraoral digital impression systems.

OBJECTIVE: Clinicians have been slow to adopt digital impression technologies due possibly to perceived technique sensitivities involved in data acquisition. This research has two aims: determine whether scan pattern and sequence affects the accuracy of the three-dimensional (3D) model created from this digital impression and to compare the 5 imaging systems with regards to their scanning accuracy for sextant impressions. MATERIALS AND METHODS: Six digital intraoral impression systems were used to scan a typodont sextant with optical properties similar to natural teeth. The impressions were taken using five different scan patterns and the resulting digital models were overlayed on a master digital model to determine the accuracy of each scanner performing each scan pattern. Furthermore, regardless of scan pattern, each digital impression system was evaluated for accuracy to the other systems in this same manner. RESULTS: No differences of significance were noted in the accuracy of 3D models created using six distinct scan patterns with one exception involving the CEREC Omnicam. Planmeca Planscan was determined to be the truest scanner while 3Shape Trios was determined to be the most precise for sextant impression making. CONCLUSIONS: Scan pattern does not significantly affect the accuracy of the resulting digital model for sextant scanning. CLINICAL SIGNIFICANCE: Companies who make digital impression systems often recommend a scan pattern specific for their system. However, every clinical scanning scenario is different and may require a different approach. Knowing how important scan pattern is with regards to accuracy would be helpful for guiding a growing number of practitioners who are utilizing this technology.

Antibacterial properties of copper iodide-doped glass ionomer-based materials and effect of copper iodide nanoparticles on collagen degradation.

OBJECTIVES: This study investigated the antibacterial properties and micro-hardness of polyacrylic acid (PAA)-coated copper iodide (CuI) nanoparticles incorporated into glass ionomer-based materials, and the effect of PAA-CuI on collagen degradation. MATERIALS AND METHODS: PAA-CuI nanoparticles were incorporated into glass ionomer (GI), Ionofil Molar AC, and resin-modified glass ionomer (RMGI), Vitrebond, at 0.263 wt%. The antibacterial properties against Streptococcus mutans (n = 6/group) and surface micro-hardness (n = 5/group) were evaluated. Twenty dentin beams were completely demineralized in 10 wt% phosphoric acid and equally divided in two groups (n = 10/group) for incubation in simulated body fluid (SBF) or SBF containing 1 mg/ml PAA-CuI. The amount of dry mass loss and hydroxyproline (HYP) released were quantified. Kruskal-Wallis, Student's t test, two-way ANOVA, and Mann-Whitney were used to analyze the antibacterial, micro-hardness, dry mass, and HYP release data, respectively (p < 0.05). RESULTS: Addition of PAA-CuI nanoparticles into the glass ionomer matrix yielded significant reduction (99.999 %) in the concentration of bacteria relative to the control groups. While micro-hardness values of PAA-CuI-doped GI were no different from its control, PAA-CuI-doped RMGI demonstrated significantly higher values than its control. A significant decrease in dry mass weight was shown only for the control beams (10.53 %, p = 0.04). Significantly less HYP was released from beams incubated in PAA-CuI relative to the control beams (p < 0.001). CONCLUSIONS: PAA-CuI nanoparticles are an effective additive to glass ionomer-based materials as they greatly enhance their antibacterial properties and reduce collagen degradation without an adverse effect on their mechanical properties. CLINICAL RELEVANCE: The use of copper-doped glass ionomer-based materials under composite restorations may contribute to an increased longevity of adhesive restorations, because of their enhanced antibacterial properties and reduced collagen degradation.

A novel technique for reference point generation to aid in intraoral scan alignment.

OBJECTIVE: When using a completely digital workflow on larger prosthetic cases it is often difficult to communicate to the laboratory or chairside Computer Aided Design and Computer Aided Manufacturing system the provisional prosthetic information. The problem arises when common hard tissue data points are limited or non-existent such as in complete arch cases in which the 3D model of the complete arch provisional restorations must be aligned perfectly with the 3D model of the complete arch preparations. In these instances, soft tissue is not enough to ensure an accurate automatic or manual alignment due to a lack of well-defined reference points. A new technique is proposed for the proper digital alignment of the 3D virtual model of the provisional prosthetic to the 3D virtual model of the prepared teeth in cases where common and coincident hard tissue data points are limited. Clinical considerations: A technique is described in which fiducial composite resin dots are temporarily placed on the intraoral keratinized tissue in strategic locations prior to final impressions. These fiducial dots provide coincident and clear 3D data points that when scanned into a digital impression allow superimposition of the 3D models. CONCLUSIONS: Composite resin dots on keratinized tissue were successful at allowing accurate merging of provisional restoration and post-preparation 3D models for the purpose of using the provisional restorations as a guide for final CLINICAL SIGNIFICANCE: Composite resin dots placed temporarily on attached tissue were successful at allowing accurate merging of the provisional restoration 3D models to the preparation 3D models for the purposes of using the provisional restorations as a guide for final restoration design and manufacturing. In this case, they allowed precise superimposition of the 3D models made in the absence of any other hard tissue reference points, resulting in the fabrication of ideal final restorations.

Evaluation of the accuracy of 7 digital scanners: An in vitro analysis based on 3-dimensional comparisons.

STATEMENT OF PROBLEM: As digital impressions become more common and more digital impression systems are released onto the market, it is essential to systematically and objectively evaluate their accuracy. PURPOSE: The purpose of this in vitro study was to evaluate and compare the trueness and precision of 6 intraoral scanners and 1 laboratory scanner in both sextant and complete-arch scenarios. Furthermore, time of scanning was evaluated and correlated with trueness and precision. MATERIAL AND METHODS: A custom complete-arch model was fabricated with a refractive index similar to that of tooth structure. Seven digital impression systems were used to scan the custom model for both posterior sextant and complete arch scenarios. Analysis was performed using 3-dimensional metrology software to measure discrepancies between the master model and experimental casts. RESULTS: Of the intraoral scanners, the Planscan was found to have the best trueness and precision while the 3Shape Trios was found to have the poorest for sextant scanning (P<.001). The order of trueness for complete arch scanning was as follows: 3Shape D800 >iTero >3Shape TRIOS 3 >Carestream 3500 >Planscan >CEREC Omnicam >CEREC Bluecam. The order of precision for complete-arch scanning was as follows: CS3500 >iTero >3Shape D800 >3Shape TRIOS 3 >CEREC Omnicam >Planscan >CEREC Bluecam. For the secondary outcome evaluating the effect time has on trueness and precision, the complete- arch scan time was highly correlated with both trueness (r=0.771) and precision (r=0.771). CONCLUSIONS: For sextant scanning, the Planscan was found to be the most precise and true scanner. For complete-arch scanning, the 3Shape Trios was found to have the best balance of speed and accuracy.

Evaluation of the Marginal Fit of CAD/CAM Crowns Fabricated Using Two Different Chairside CAD/CAM Systems on Preparations of Varying Quality.

PURPOSE: This study evaluated the marginal gap of crowns fabricated using two new chairside computer-aided design/computer-aided manufacturing systems on preparations completed by clinicians with varying levels of expertise to identify whether common preparation errors affect marginal fit. The null hypothesis is that there is no difference in the mean marginal gaps of restorations of varying qualities and no difference in the mean marginal gap size between restorations fabricated using the PlanScan (D4D, Richardson, TX, USA) and the CEREC Omnicam (Sirona, Bensheim, Germany). MATERIAL AND METHODS: The fit of 80 lithium disilicate crowns fabricated with the E4D PlanScan or CEREC Omnicam systems on preparations of varying quality were examined for marginal fit by using the replica technique. These same preparations were then visually examined against common criteria for anterior all-ceramic restorations and placed in one of four categories: excellent, good, fair, and poor. Linear mixed modeling was used to evaluate associations between marginal gap, tooth preparation rating, and fabrication machine. RESULTS: The fit was not significantly different between both systems across all qualities of preparation. The average fit was 104 µm for poor-quality preparations, 87.6 µm for fair preparations, 67.2 µm for good preparations, and 36.6 µm for excellent preparations. CONCLUSION: The null hypothesis is rejected. It can be concluded that preparation quality has a significant impact on marginal gap regardless of which system is used. However, no significant difference was found when comparing the systems to each other. CLINICAL SIGNIFICANCE: Within the limitations of this in vitro study, it can be concluded that crown preparation quality has a significant effect on marginal gap of the restoration when the clinician uses either CEREC Omnicam or E4D PlansScan.

Translucency of chairside monolithic zirconias using different sintering ovens: An in vitro investigation.

OBJECTIVE: To evaluate the translucency of several monolithic zirconias (MZ) processed in various sintering ovens designed for single-visit, chairside use. METHODS: Discs (n = 40) from zirconia blocks were fabricated for each MZ at manufacturer-recommended minimal thicknesses, as provided in each material's instructions for use: IPS e.max ZirCAD LT (ZLT); CEREC Zirconia+ (CZ+); 3M Chairside (3M); KATANA Zirconia (KT). Groups (n = 10) were sintered following manufacturer instructions for each oven: CEREC SpeedFire, Ivoclar CS4, Ivoclar CS6, and Ivoclar S2 (laboratory furnace control). Specimens were highly polished on one side and glazed on the other. Each side was measured with a spectrophotometer against white and black backgrounds to determine translucency parameter (TP) and contrast ratio (CR) values. Results for TP and CR for each material and oven combination were compared with a linear mixed model. Oven precision was evaluated using the Kruskall-Wallis test. RESULTS: Glazed specimens were more translucent than polished ones (p < 0.001). ZLT and CZ+ were more translucent than 3M and KT regardless of the sintering oven (p < 0.01). Several oven/material combinations reached or exceeded the S2 oven TP: CS4 with CZ+ and 3M; CS6 with ZLT and KT (p < 0.01). SpeedFire was significantly less precise (p < 0.05) and produced lower TP values for ZLT, CZ+, and KT (p < 0.01). Results for TP and CR were highly correlated. CONCLUSIONS: MZ surface finish, material thickness, and oven used all had a significant effect on translucency. Some chairside-oriented solutions produced results with translucency equal to conventionally processed zirconia. CLINICAL SIGNIFICANCE: The translucency of a ceramic restoration is an important factor in determining its esthetics. Clinicians desiring the most esthetic outcomes with monolithic zirconia should be aware of the significant effects that surface finishing, material thickness, and the sintering oven used can have on restoration translucency.

Application of the virtual-fit method for fixed complete denture cases designed on intraoral scans: Effect of cement spacing.

OBJECTIVES: To validate the virtual-fit alignment, analyze the impact of cement spacing on internal/marginal gaps, and correlate results with conventional trueness measures. METHODS: Four dental abutment models were scanned using an industrial reference scanner (one time each), Emerald S (three times each), and Medit i700 (three times each) intraoral scanners (IOS). On each IOS scan (n = 24), three complete-arch fixed frameworks were designed with 70 or 140 µm cement space with no marginal space (groups 70 and 140) and 70 µm with an additional 20 µm space, including the margin (group 70+20). Two types of alignment were performed by GOM Inspect software. The reference and IOS scans were aligned through a conventional iterative closest point algorithm (ICP) where the penetration of the two scans was permitted into each other (conventional trueness method). Second, the computer-aided designs were superimposed with the reference scan also using an ICP, but preventing the design from virtual penetration into the model (virtual-fit method). The virtual-fit algorithm was validated by non-penetration alignment of the designs with the IOS scans. Internal and marginal gap was measured between the design and the abutments. The difference between spacing groups was compared by Friedman's test. A statistical correlation (Spearman's Rho Test) was computed between the measured gaps and the conventional trueness method. A significant difference was accepted at p<0.05 after the Bonferroni correction. RESULTS: The gaps deviated from the set cement space by 3-13 µm on IOS scans (validation of virtual-fit algorithm). The internal gap of the design on the reference scan was not affected by cement spacing (Emerald S, p = 0.779; Medit i700, p = 0.205). The marginal gap in groups 70 and 70+20 was significantly lower than in group 140 in Emerald S (p<0.05). In Medit i700, it was lower in the 70+20 group than in the group 70 (p<0.01) and in the group 140 (p<0.05). Some Medit i700 scans exhibited high marginal gaps within group 70 but not in groups 70 and 140. The measured gaps correlated significantly (r = 0.51-0.81, p<0.05-0.001) with the conventional trueness but were 2.6-4.6 times higher (p<0.001). CONCLUSION: Virtual-fit alignment can simulate restoration seating. A 20 µm marginal and 90 µm internal spacing could compensate for scan errors up to several hundred micrometers. However, 140 µm internal spacing is counterproductive. The conventional trueness method could only partially predict framework misfit. CLINICAL SIGNIFICANCE: The virtual-fit method can provide clinically interpretable data for intraoral scanners. Emerald S and Medit i700 intraoral scanners are suitable for fabricating complete-arch fixed tooth-supported prostheses. In addition, a slight elevation of spacing at the margin could compensate for moderate inaccuracies in a scan.

Complete-arch accuracy of seven intraoral scanners measured by the virtual-fit method.

OBJECTIVES: This study compared the accuracy of seven intraoral scanners (IOS) by the virtual-fit method. METHODS: Four maxillary arches with tooth abutments were scanned with an industrial reference scanner (n=1) and by Aoralscan3, EmeraldS, Helios600, Lumina, Mediti700, Primescan, and Trios5 IOSs (each n=12). Two complete-arch fixed frameworks were designed on each IOS scan with a 70 µm (group 70) and a 90 µm internal cement space (group 70+20, additional 20 µm at the margin). The virtual-fit method was comprised of superimposing the framework designs onto the reference scan using a non-penetrating algorithm simulating the clinical try-in. Internal and marginal gaps were measured. Precision was estimated by the mean absolute errors (MAE). RESULTS: In group 70, Mediti700 (43 µm), Primescan (42 µm), and EmeraldS were in the best homogenous subset for the marginal gap, followed by the Lumina (67 µm), Aoralscan3 (70 µm), and Trios5 (70 µm), whereas Helios600 (118 µm) was in the third subset. Based on the MAE at the margin, Mediti700, Trios5, and EmeraldS were in the first-best homogenous subset, followed by Primescan. Lumina and Helios600 were in the third subset, and Aoralscan3 was in the fourth subset. In group 70+20, the marginal gap was significantly decreased for Lumina and Aoralscan3, whereas MAE significantly decreased for EmeraldS and Aoralscan3. The rank of IOSs was similar for the internal gap. CONCLUSION: EmeraldS, Mediti700, Primescan, and Trios5 meet the marginal and internal fit criteria for fixed tooth-borne complete arch restorations. Increasing the cement space during design could enhance restoration fit. CLINICAL SIGNIFICANCE: The virtual-fit alignment method can effectively evaluate the accuracy of different intraoral scanners, offering valuable clinical guidance for distinguishing among them. Recent software and hardware versions of long-standing IOS manufacturers are suitable for fabricating complete arch restoration.

Differences in Volumetric Tooth Loss for Monolithic Ceramic Crowns, Occlusal Overlays and Partial Coverage Onlays.

PURPOSE: The purpose of this in vitro study was to compare the volumetric loss of clinical crown structure for commonly encountered clinical situations for monolithic ceramic crowns, occlusal overlays, and partial coverage onlays. MATERIALS AND METHODS: Typodont teeth made with pre-existing mesio-occluso-distal (MOD) preparations for mandibular first molars and maxillary first premolars were prepared with three different preparations: a full contour monolithic zirconia crown, a lithium disilicate occlusal overlay, and mesio-occluso-disto-buccal/mesio-occluso-disto-lingual (MODB/MODL) lithium disilicate onlays for premolars/molars. 3D metrological software was used to evaluate the volumetric loss of clinical crown structure for each preparation type. Subsequently, the mesiolingual cusps of mandibular molars and buccal cusps of maxillary premolars were excluded for a separate analysis, to simulate patient presentation with an existing restoration and sheared off cusp. RESULTS: Full coverage monolithic zirconia crowns removed 45.37 - 219.53 mm3 of remaining clinical tooth structure, depending on the clinical scenario and tooth position, while lithium disilicate overlays removed 27.48 - 105.13 mm3. MODB/MODL lithium disilicate onlays removed 5.48 - 47.45 mm3 . In each scenario tested, MODB/MODL onlays removed significantly less clinical crown structure than overlays (P<0.001); both MODB/MODL onlays and overlays removed significantly less structure than full coverage crowns (P<0.001). CONCLUSION: Monolithic zirconia crown restorations require significantly more removal of remaining tooth structure than lithium disilicate occlusal overlays and partial coverage onlays for commonly occurring clinical situations requiring indirect restorations. Int J Prosthodont 2023. doi: 10.11607/ijp.8011.