The natural CAD/CAM anterior implant single tooth restoration: A novel digital workflow

OBJECTIVE

To report a novel digital workflow to replace an anterior maxillary tooth lost due to trauma with an implant multilayer restoration by using the patient's extracted tooth as a final crown restoration using computer-aided design/computer-aided manufacturing (CAD/CAM) technology.

CLINICAL CONSIDERATIONS

Instead of using the patient's natural tooth as an immediate provisional restoration to achieve predictable results in terms of esthetics and soft tissue structure, a novel digital strategy was performed to obtain a natural final crown restoration by using the patient's tooth associated with a lithium disilicate customized implant abutment.

CONCLUSIONS

The perspective of using this strategic approach for implant restorative dental treatments in patients with traumatic root fractures in the anterior region has great potential as it helps to maintain the emergence profile of the natural dentition and esthetics.

CLINICAL SIGNIFICANCE

Optimal esthetic outcomes are challenging in implant dentistry regarding soft tissue structure and morphology factors. Using natural teeth from surgery to deliver the final restoration might be beneficial when an anterior tooth is lost due to trauma.

Digital impressions' accuracy through "cut-out-rescan" and "data exchange by over scanning" techniques in complete arches of two intraoral scanners and CAD/CAM software

PURPOSE

This technical procedure describes the accuracy of "cut-out-rescan" and "data exchange by over scanning" on cast areas using computer-aided design and computer-aided manufacturing software and two intraoral scanners (IOSs).

METHODS

A customized cast was used as a reference standard and scanned using an ATOS Triple Scan digitizer. Two IOS setups were used in three scanning groups, namely, the control, cut-out-rescan, and data exchange by over scanning groups. Sixty digital files (n = 10 per group) were obtained and converted into the standard tessellation language format. A metrology program was used to evaluate the difference in accuracy between the control group and the other groups using Welch's unequal variances t-test.

CONCLUSION

For trueness and precision of complete arch scans, the present technique provides statistical evidence that using data exchange by over scanning and a Primescan IOS results in higher accuracy scans compared to using cut-outrescan and a Primescan IOS. The cut-out-rescan procedure provides scans with higher accuracy when using an Omnicam IOS. This technique is simple and saves time in workflows using a Primescan IOS.

Impact of different scanning strategies on the accuracy of two current intraoral scanning systems in complete-arch impressions: an in vitro study

AIM

To determine the scanning strategy that obtains the most accurate results for two intraoral scanners (IOS) in complete-arch digital impressions. Scan time was evaluated and correlated with scan strategies.

MATERIALS AND METHOD

A custom model used as the reference standard was fabricated with teeth having dentin- and enamel-identical refractive indices simulating natural dentition. A reference scan of the custom typodont was obtained using an ATOS III Triple Scan 3D optical scanner. Two IOS setups - Omnicam v 5.1.0 and Primescan v 5.0.2 - were used for complete-arch scanning, each using 13 scanning strategies, obtaining 260 digital files (n = 10 per group), recording each scan time, converting all experimental scans to standard tessellation language (STL) format, and using a comprehensive metrology program to compare the reference standard scan with the experimental scans. Statistical analyses utilized Welch's unequal variances t test.

RESULTS

Group M exhibited the lowest trueness and precision values (P < 0.05) for Primescan (47.5% of the average among all other groups) and the lowest trueness value (P < 0.05) for Omnicam (53.4% of the average among all other groups), where group B exhibited the lowest precision value (65.6% of the average among all other groups) with P < 0.05. Primescan featured a better trueness index (4.79 µm) than that of Omnicam (19.13 µm), with a statistically significant difference (P < 0.00001). Primescan, group M, also featured a better precision index (4.67 µm) than Omnicam, group B (16.75 µm), with a statistically significant difference (P < 0.00001).

CONCLUSION

For both IOS systems, group M provided the lowest scanning times. For trueness and precision of complete-arch scans, group M was the dominant scanning strategy in Primescan, while there was no dominant strategy in Omnicam. Group M had the best scanning time for both IOS systems.

Effect of thickness, translucency, and firing protocol on the masking ability of a CAD/CAM zirconia-reinforced lithium silicate for different backgrounds

PURPOSE

To evaluate the masking ability of computer-aided design/computer-aided manufacturing (CAD/CAM) zirconia-reinforced lithium silicate (ZLS) glass-ceramic under the different material configurations of thickness, translucency, and finishing protocol as well as significance of the color difference due to the manufacturer's one-firing protocol.

MATERIALS AND METHODS

Ninety high-translucency (HT) and low-translucency (LT) ZLS glass-ceramic discs of different thicknesses (1.0, 1.5, and 2.0 mm) were evaluated as a monolithic structure with and without the use of a one-firing protocol. Disc samples were placed onto the substrates for measurement; a spectrophotometer measured the L*, a*, and b* color attributes of each specimen. ∆E value was calculated for determining color differences in tooth-colored substrate specimens (shade B1) compared with three darker backgrounds (shade C2, and two metal substrates - gold and silver). ∆E values were then compared against clinically acceptable (∆E = 5.5) and ideal (∆E = 2.6) thresholds. Color differences between the control and test groups were evaluated under different effects using a series of one-sided paired t tests (P < 0.01). The 99% confidence interval (CI) for the true ∆E mean and P values are reported and discussed. A complementary regression analysis depicts the effect size of translucency and firing protocol.

RESULTS

Over C2, a 1-mm thickness demonstrated P < 0.01 for the clinically acceptable threshold, whereas the ideal threshold was ensured only with P < 0.01 under a 2-mm thickness. Over silver, only the clinically acceptable standard was met with P < 0.01 under a 2-mm thickness. Over gold, a 1-mm thickness was clinically acceptable with P < 0.01, and the ideal standard was met with P < 0.01 under a 1.5-mm thickness. These results remained valid regardless of the firing protocol or translucency; however, significant (P < 0.01) yet small-sized effects were found for translucency and firing protocol over gold, and for translucency over silver, through multiple regression analysis.

CONCLUSIONS

To achieve ideal masking, the minimum thickness of CAD/CAM ZLS glass-ceramic should be 1.5 mm over a gold background, and 2 mm over a C2 background. The silver background did not achieve ideal masking in any situation. The one-firing protocol did not affect the final color and can be used to increase restoration strength.

Fracture strength of CAD/CAM posterior ceramic crowns after manual enhancement of occlusal morphology

PURPOSE

The aim of this study was to investigate the fracture strength of computer-aided design/computer-aided manufacturing (CAD/CAM) posterior ceramic crowns with and without post-milling manual enhancement of occlusal morphology (MEOM), as indicated especially with early CAD/CAM restorations that have limited capacity to generate natural occlusal morphology.

MATERIALS AND METHODS

A mandibular molar of an acrylic tooth model was prepared to receive a CAD/CAM all-ceramic crown and was used as a master die to fabricate 80 prepared tooth replicas using an epoxy resin with an elastic modulus (E) of 18 GPa. The crown was designed using Cerec software's Biogeneric Copy Design mode (Sirona). Eighty identical monolithic crowns were fabricated by milling four types of ceramic blocks. Forty monolithic crowns (10 of each ceramic system) were randomly selected as the control group, and MEOM was performed for each of the other 40 crowns by a certified dental technician. Restorations were crystallized and glazed according to the manufacturers' instructions and firing protocols. All crowns were cemented to their respective die using resin cement, and loaded to fracture at a crosshead speed of 0.5 mm/min. The resultant fractures were classified into three modes. Data were statistically analyzed using the nonparametric Mann-Whitney U test at α = 0.05.

RESULTS

The MEOM treatment decreased the fracture load for all ceramic brands.

CONCLUSION

The MEOM procedure should be considered detrimental for monolithic CAD/CAM-generated crowns and should thus be avoided.

Fracture resistance of single-rooted pulpless teeth using hybrid CAD/CAM blocks for post and core restoration

PURPOSE

The purpose of this study was to determine whether there is a significant difference in the fracture strengths of hybrid computer-aided design/computer-aided manufacturing (CAD/CAM) blocks and fiber posts for post and core restorations in both ferrule and nonferrule pulpless mandibular canines.

MATERIALS AND METHOD

Forty extracted human mandibular canines were divided into ferrule and nonferrule groups and restored with hybrid CAD/CAM blocks using either the CAD/CAM system or fiber posts (control). Thus, there were four subgroups of ten specimens each. A 45-degree oblique load was applied with a crosshead of 0.5 mm/min, and the fracture loads were recorded. The mode of fracture was evaluated using an optical microscope at 3× magnification, and the data were tabulated and statistically analyzed using the Mann-Whitney U test and the t test, respectively, for the existence of significant difference at a 0.05 significance level.

RESULTS

No statistically significant difference was found between the fracture strength under oblique loading when using hybrid CAD/CAM blocks and fiber posts in both ferrule and nonferrule groups. The failure mode distribution of the nonferrule group presented no unfavorable failures, whereas failures in the ferrule groups were spread out between the Favorable and Unfavorable groups.

CONCLUSIONS

The results show that hybrid CAD/CAM blocks can be considered as an alternative restorative system in post and core restorations. Further basic and clinical research should be conducted to support the improvement of this system.