Suitability of the triple-scan method with a dental laboratory scanner to assess the 3D adaptation of zirconia crowns

Implementation of triple-scan protocol to evaluate the fit of complete-arch implant-supported fixed prostheses

Passive fit is essential for multiple-unit implant-supported prostheses. Conventional methods to assess the passivity of complete-arch implant-supported prostheses do not allow 3-dimensional (3D) visualization and quantification of misfit. This report describes the marginal and internal fit evaluation of a complete-arch implant-supported prosthesis by using the triple-scan protocol involving a scanner and a 3D analysis freeware. This technique allows researchers, clinicians, or dental technicians to detect and quantify 3D prosthetic misfit, which may facilitate the preparation for dental appointments and objective measurement of misfit for research studies.

Accuracy of zirconia crowns manufactured by stereolithography with an occlusal full-supporting structure: An in vitro study

STATEMENT OF PROBLEM

Additive manufacturing is emerging as an alternative method of fabricating dental restorations, but the support design needs to be optimized.

PURPOSE

The purpose of this in vitro study was to evaluate the 3-dimensional trueness and adaptations of zirconia crowns manufactured by stereolithography (SLA) with an occlusal full-supporting structure, compared with those SLA-printed with pillar supports, and those made by milling.

MATERIAL AND METHODS

A zirconia abutment was prepared, and an anatomic contour crown was designed. The crowns were manufactured by SLA and milling (n=6). For SLA manufacturing, a full-supporting base and pillar supports were designed. The 3-dimensional (3D) trueness of the fabricated crowns was characterized by 3D deviation analysis. The adaptations of crowns in the SLA-base and milling groups were measured by using a triple-scan method. Color-difference maps and the root mean square (RMS) values were used to characterize the 3D trueness. One-way analysis of variance (ANOVA) and Tukey post hoc test were used to analyze the difference in RMS values among the 3 groups, and Student t test was used to analyze the difference in cement-gap width between the milling group and the SLA group with the full-supporting base (α=.05).

RESULTS

The 3D deviation analysis showed that in the external area, the RMS value of the SLA-pillar group was significantly higher than that of the SLA-base and the milling groups (P<.05). In the intaglio area, the milling group showed a lower RMS value than the 2 SLA groups (P<.05). The color-difference maps showed the SLA-base group had smaller positive errors at the cusp inclines than the SLA-pillar group. No statistically significant difference was found in adaptations between the SLA-base and milling groups (P>.05).

CONCLUSIONS

The occlusal full-supporting base provided improved support in fabricating the crowns, and no remnants were left after removal. The zirconia crowns manufactured by SLA with an occlusal full-supporting structure had good external 3D trueness and clinically acceptable adaptation.

Adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3-dimensional gel deposition

STATEMENT OF PROBLEM

A novel monolithic zirconia restoration fabricated by additive 3-dimensional (3D) gel deposition, named as self-glazed zirconia (SGZ), has recently been developed. SGZ crowns exhibit reliable mechanical properties and esthetic appearance, but their adaptation and uniformity are unclear.

PURPOSE

The purpose of this in vitro study was to compare the adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3D gel deposition with that of milled zirconia and lithium disilicate crowns.

MATERIAL AND METHODS

Ten identical resin abutments were made based on the scanning data of an extracted and prepared human mandibular first molar. Three types of monolithic crowns were then fabricated by using 2 different processes: 3D gel deposition zirconia (SGZ), milled zirconia (ZZ), and milled lithium disilicate (EMX) (n=10) through a completely digital workflow. The nondestructive direct-view technique and replica technique were used to measure the marginal and internal discrepancy values individually. The uniformity index was calculated to describe the uniformity of the internal space. The results were analyzed by using 1-way ANOVA and Kruskal-Wallis statistical tests (α=.05).

RESULTS

The marginal discrepancy of EMX exhibited the highest values among the 3 groups (P=.001). The 2 types of zirconia crowns had comparable marginal discrepancy values (P>.05). The internal discrepancy values of SGZ were significantly lower than those of EMX at the occlusal region and of ZZ at all measured locations (P<.05). All 3 types of monolithic crowns showed comparable good uniformity (P=.056).

CONCLUSIONS

The marginal and internal adaptations of novel monolithic zirconia crowns were within clinical requirements. Compared with the zirconia and lithium disilicate crowns fabricated by subtractive milling, monolithic zirconia crowns fabricated by additive 3D gel deposition had comparable uniformity and better internal adaptation.

Effect of industrial scanner and framework material interaction on the marginal gaps of CAD-CAM complete arch implant frameworks

STATEMENT OF PROBLEM

Structured-light and computed tomography industrial scanners have been used as reference scanners to measure marginal gaps between implants and superstructures. However, the effect of framework material on the scanners' ability to detect gaps and on precision has not yet been evaluated.

PURPOSE

The purpose of this in vitro study was to investigate the interaction between the industrial scanner and framework material on measured marginal gaps of implant-supported fixed complete arch frameworks made from titanium and polymethylmethacrylate and on the precision of scans.

MATERIAL AND METHODS

A completely edentulous maxillary model with 4 implants and multiunit abutments at the first molar and canine sites was digitized by using a laboratory scanner. Implant-supported frameworks were milled from titanium and polymethylmethacrylate (n=5). Each framework was secured on the left molar site abutment. The marginal gaps between the frameworks and abutment sites without a screw were measured by using an industrial structured-light scanner and an industrial computed tomography scanner. The effect of the scanner, the framework material, and their interaction on measured gaps was analyzed by applying linear regressions and weighted least square methods. The F-statistics was used with Bonferroni corrections for precision analysis (α=.05).

RESULTS

No significant effect of scanner, material, or their interaction was found on the marginal gaps at the canine sites. The titanium framework gaps detected by using the computed tomography scanner were greater than those detected by using the structured-light scanner at the right molar site (estimated difference in means=0.054 mm; P=.003) and overall (estimated difference in means=0.023 mm; P=.033). The structured-light scanner's precision was higher than that of the computed tomography scanner when titanium frameworks were scanned (P=.001). The computed tomography scanner's precision was higher when scanning polymethylmethacrylate frameworks than when scanning titanium frameworks (P=.03).

CONCLUSIONS

Framework material and industrial scanner interaction affected the measured gaps. The computed tomography scanner detected greater marginal gaps with low precision when scanning titanium frameworks than the structured-light scanner. The sample size, the use of only 2 types of materials, and a laboratory scanner to obtain the computer-aided design file should be considered when interpreting the results.

Accuracy and margin quality of advanced 3D-printed monolithic zirconia crowns

STATEMENT OF PROBLEM

Nanoparticle jetting (NPJ) is a novel ceramic 3D-printing technology with high printing accuracy. However, studies reporting the accuracy of zirconia crowns manufactured by NPJ and comparing them with conventional zirconia crowns are lacking.

PURPOSE

The purpose of this in vitro study was to evaluate and compare the trueness, crown fit, and margin quality of monolithic zirconia crowns manufactured by NPJ with those milled by a computer numerical control system.

MATERIAL AND METHODS

A gypsum left mandibular first molar was prepared and scanned with an intraoral scanner (TRIOS 4). Three types of monolithic crowns were manufactured through 3D printing and subtractive manufacturing (SM): NPJ (3D printing), VITA (milling), UPCERA (milling). The crowns were scanned, and the dimensional deviation (trueness) was evaluated and compared by using a software program. The triple scan method was used to measure crown fit and uniform index through precise alignment in the software program, and margin quality was also observed with an optical microscope. The data were analyzed with 1-way analysis of variance and the Tukey post hoc test (α=.05).

RESULTS

The NPJ group reported better trueness of all crown and axial surfaces compared with the other SM group (P<.001), but marginal trueness (P=.601), intaglio surface (P=.596), and occlusal surface (P=.641) were statistically similar compared with the Vita milled group. All 3 groups reported clinically acceptable crown fit and uniformity with statistically similar values (P>.05). The NPJ group had more crowns judged to have flawless margin quality compared with the milled groups.

CONCLUSIONS

All 3 manufacturing methods can fabricate zirconia crowns with a clinically acceptable crown fit. The NPJ system could be used to manufacture monolithic zirconia crowns with better margin quality and proximal surface trueness than milled crowns.

Marginal gap and internal fit of 3D printed versus milled monolithic zirconia crowns

BACKGROUND

This study aimed to evaluate and compare the marginal gap using two different methods and the internal fit of 3D printed and zirconia crowns.

METHODS

3Y-TZP zirconia crowns (n = 20) were manufactured using subtractive milling (group M) and 3D printed (group P). The marginal gap was measured at 60 points using vertical marginal gap technique (VMGT). On the other hand, the silicone replica technique (SRT) was used to evaluate the internal fit and was divided into 4 groups: marginal gap, cervical gap, axial gap, and occlusal gap where the thickness of light impression was measured at 16 references. The numerical data was tested for normality using Shapiro-Wilk's test. They were found to be normally distributed and were analyzed using an independent t-test.

RESULTS

Using VMGT, group P had significantly higher mean marginal gap values of 80 ± 30 µm compared to group M = 60 ± 20 µm (p < 0.001). Also, with the SRT, the marginal gap of group P (100 ± 10 µm) had significantly higher values compared to group M (60 ± 10 µm). The internal fit showed significant difference between the tested groups except for Axial Gap.

CONCLUSIONS

Although milled crowns showed better results. The 3D printed zirconia crowns offer clinically acceptable results in terms of marginal adaptation and internal fit. Both VMGT and SRT are reliable methods for the assessment of the marginal gap.

Digital evaluation of the effect of nanosilica-lithium spray coating on the internal and marginal fit of high translucent zirconia crowns

OBJECTIVES

To evaluate the effect of a nanosilica-lithium spray coating on the internal and marginal fit of high translucent zirconia crowns using a digital evaluation method.

METHODS

A three-dimensional analysis model of a zirconia abutment was digitally scanned using a dental scanner, and 30 monolithic high translucent zirconia crowns were designed and fabricated. They were divided into groups (n = 10) according to the surface treatment method: (1) no treatment: as-sintered zirconia; (2) airborne-particle abrasion with 50 μm Al₂O₃ particles; and (3) nanosilica-lithium spray coating. Three-dimensional data for the abutment, crown, and crown seated on the abutment were obtained using a dental scanner. The three-dimensional seated fit between the crown and abutment was reconstructed using registration technology, and a three-dimensional (3D) deviation analysis was used to evaluate the effect of different modification methods on the internal and marginal fit of the crowns using root mean square (RMS) values.

RESULTS

The 3D deviation analysis of all groups conformed to a normal distribution (P > 0.05), and the variance was homogeneous (P > 0.05). The different surface treatments had no significant effect on the RMS values in the occlusal, axial, and marginal regions of the high translucent zirconia crowns (P > 0.05).

CONCLUSIONS

Nanosilica-lithium spray coating for the modification of as-sintered zirconia is clinically feasible and does not affect the internal or marginal fit of high translucent zirconia crowns.

CLINICAL SIGNIFICANCE

Nanosilica-lithium spray coating does not affect the adaptation of zirconia crowns and is a clinically feasible surface treatment method for zirconia. It is unnecessary to add the setting values of the internal and marginal fit when fabricating nanosilica-lithium-sprayed zirconia crowns.

In vitro comparison of five desktop scanners and an industrial scanner in the evaluation of an intraoral scanner accuracy

OBJECTIVES

The study aimed to compare the precision of ATOS industrial, 3ShapeE4, MeditT710, CeramillMap400, CSNeo, PlanScanLab desktop, and Mediti700 intraoral scanners. The second aim was to compare the trueness of Mediti700 assessed by ATOS and desktop scanners.

METHODS

Four plastic dentate models with 7-12 abutments prepared for complete arch fixed dentures were scanned by all scanners three times. Scans were segmented to retain only the abutments. The precision and trueness were calculated by superimposing scans with the best-fit algorithm. The mean absolute distance was calculated between the scan surfaces. The precision was calculated based on the 12 repeats. Trueness was evaluated by superimposing the desktop and IOS scans to the industrial scans. IOS was also aligned with the two most accurate desktop scanners.

RESULTS

The precision of 3ShapeE4 and MeditT710 (3-4μm) was only slightly lower than that of ATOS (1.7μm, p<0.001) and significantly higher than CeramillMap400, CSNeo, and PlanScanLab (6-10 μm, p<0.001). The trueness was the highest for the 3Shape E4 (12-13 μm) and Medit T710 (13-16 μm) without significant difference. They were significantly better than CeramillMap400, CSNeo, and PlanScanLab (22-31μm, p<0.001). Accordingly, the Mediti700 trueness was evaluated by ATOS, 3ShapeE4, and MeditT710. The three trueness was not significantly different; ATOS (23-26 μm), 3Shape E4 (22-25 μm), and Medit T710 (20-23 μm).

CONCLUSIONS

All desktop scanners had the acceptable accuracy required for a complete arch-fixed prosthesis. The 3Shape E4 and the Medit T710 might be used as reference scanners for studying IOS accuracy.

CLINICAL SIGNIFICANCE

3ShapeE4, MeditT710, CeramillMap400, CSNeo, PlanScanLab laboratory, and Mediti700 intraoral scanners can be used for the prosthetic workflow in a complete arch. 3ShapeE4 and the MeditT710 could be used to test the accuracy of various phases of a laboratory workflow, replacing the industrial scanners.

Triple scan evaluation of internal and marginal adaptation of overlays using different restorative materials

OBJECTIVE

Problems in the confection of indirect restorations may increase the marginal and internal gap. This study aimed to quantify the marginal and the internal fit of overlays fabricated with three different materials.

MATERIALS AND METHODS

Standardized cavities were prepared on endodontically treated human third molars and digital impressions were done using an intraoral camera (Trios 3). Restorations were designed (n = 15) and fabricated with three materials: Hybrid ceramic (Cerasmart; GC Corp, EUROPE), high-strength lithium disilicate (GC Initial® LiSi Press; GC Corp, Tokyo, Japan), and zirconia reinforced Lithium Silicate Glass Ceramic (Vita Suprinity; Vita, Germany). Axial, marginal, pulpal, and gingival gaps were calculated by measuring the distance between the restoration and the tooth at several reference points. Two-Way analysis of variance was used for statistical analysis. The significance level was set at α = 0.05.

RESULTS

Mean gap was significantly influenced by the material (p < 0.001), gap localization (p < 0.001), and interaction between the factors (p = 0.002). For all materials, the highest gap was observed at gingival and pulpal surfaces (p ≤ 0.015). LiSi Press achieved the overall lowest values at axial values measurements (p ≤ 0.003).

CONCLUSIONS

The performance of a CAD/CAM system relative to marginal adaptation is influenced by the restorative material used. High-strength lithium disilicate seems to be showed the best marginal adaptation.

CLINICAL SIGNIFICANCE

Marginal and internal adaptation of CAD/CAM restorations could be influenced by the type of material chosen.

[Independent innovation research, development and transformation of precise bionic repair technology for oral prosthesis]

According to the fourth national oral health epidemiological survey report (2018), billions of teeth are lost or missing in China, inducing chewing dysfunction, which is necessary to build physiological function using restorations. Digital technology improves the efficiency and accuracy of oral restoration, with the application of three-dimensional scans, computer-aided design (CAD), computer-aided manufacturing (CAM), bionic material design and so on. However, the basic research and product development of digital technology in China lack international competitiveness, with related products basically relying on imports, including denture 3D design software, 3D oral printers, and digitally processed materials. To overcome these difficulties, from 2001, Yuchun Sun's team, from Peking University School and Hospital of Stomatology, developed a series of studies in artificial intelligence design and precision bionics manufacturing of complex oral prostheses. The research included artificial intelligence design technology for complex oral prostheses, 3D printing systems for oral medicine, biomimetic laminated zirconia materials and innovative application of digital prosthetics in clinical practice. The research from 2001 to 2007 was completed under the guidance of Prof. Peijun Lv and Prof. Yong Wang. Under the support of the National Natural Science Foundation of China, the National Science and Technology Support Program, National High-Tech R & D Program (863 Program) and Beijing Training Project for the Leading Talents in S & T, Yuchun Sun's team published over 200 papers in the relevant field, authorized 49 national invention patents and 1 U.S. invention patent and issued 2 national standards. It also developed 8 kinds of core technology products in digital oral prostheses and 3 kinds of clinical diagnosis and treatment programs, which significantly improved the design efficiency of complex oral prostheses, the fabrication accuracy of metal prostheses and the bionic performance of ceramic materials. Compared with similar international technologies, the program doubled the efficiency of bionic design and manufacturing accuracy and reduced the difficulty of diagnosis and cost of treatment and application by 50%, with the key indicators of those products reaching the international leading level. This program not only helped to realize precision, intelligence and efficiency during prostheses but also provided functional and aesthetic matches for patients after prostheses. The program was rewarded with the First Technical Innovation Prize of the Beijing Science and Technology Awards (2020), Gold Medal of Medical Research Group in the First Medical Science and Technology Innovation Competition of National Health Commission of the People's Republic of China (2020) and Best Creative Award in the First Translational Medical Innovation Competition of Capital (2017). This paper is a review of the current situation of artificial intelligence design and precision bionics manufacturing of complex oral prosthesis.

The accuracy of single implant scans with a healing abutment-scanpeg system compared with the scans of a scanbody and conventional impressions: An in vitro study

PURPOSE

To compare the accuracy of polyvinylsiloxane (PVS) impressions and intraoral scans when a healing abutment-scanpeg system (HASP) or a conventional scanbody (CSB) was used on a single implant.

MATERIALS AND METHODS

A maxillary model with an implant (4.0 × 11 mm) (Neoss) and a CSB or an HASP (Neoss) was scanned by using a laboratory scanner (Ceramill Map 600; Amann Girrbach) (reference scans) and an intraoral scanner (Trios 3) (n = 10). PVS open-tray impressions were also made and stone casts of the model with a CSB were digitized with the laboratory scanner. Intraoral scanner and cast scans were superimposed to their reference scans. On superimposed scans, points were selected on HASP and CSB to calculate distance deviations (at points 1-4) and angular deviations (at points 5 and 6 on CSB and PVS, and 5-8 on HASP) between scans (trueness), and their variation (precision). The deviation data was analyzed with ANOVA and pairwise comparisons (trueness) with Tukey's adjustment, and F-tests (precision).

RESULTS

At point 1, PVS had lower trueness than CSB (difference in means (DIMs) = 0.184 mm, p = 0.006) and HASP (DIMs = 0.122 mm, p = 0.042). At point 3, CSB had higher trueness than HASP (DIMs = 0.134 mm, p = 0.001). Angular deviations with PVS were higher than with CSB (DIMs = 0.6°, p = 0.013) and HASP (DIMs = 0.7°, p = 0.005). CSB had higher precision than PVS (p < 0.05). HASP had higher precision than PVS for distance (Point 1)(p < 0.001) and angular deviations (p < 0.05). Deviation differences within the HASP parts were not significant.

CONCLUSION

The accuracy of intraoral scans and PVS impressions of an implant was similar.

CLINICAL RELEVANCE

The combined healing abutment-scanpeg system and the conventional scanbody can be recommended for scans of anterior single implants with the intraoral scanner used.