The effects of manufacturing technologies on the surface accuracy of CAD-CAM occlusal splints

Cameo and intaglio surface stability and variability of additively, subtractively, and conventionally manufactured occlusal devices after long-term storage

STATEMENT OF PROBLEM

Additive and subtractive manufacturing have become alternative technologies for fabricating occlusal devices. However, knowledge of the long-term stability of occlusal devices fabricated using these recent technologies is limited.

PURPOSE

The purpose of this in vitro study was to evaluate the cameo and intaglio surface stability and variability of additively, subtractively, and conventionally manufactured occlusal devices after 18 months of storage.

MATERIAL AND METHODS

A standard tessellation language (STL) file of a dentate maxillary typodont was used to design a master occlusal device. The STL file of this design was used to fabricate occlusal devices additively either with a digital light processing (AM-1) or a continuous liquid interface production (AM-2) printer, subtractively with 2 different 5-axis milling units (SM-1 and SM-2), and conventionally (TM-HP) (n=10). STL files of each device's cameo and intaglio surfaces were generated using a laboratory scanner after fabrication and after 18 months of storage in a moist environment. These generated files were imported into an analysis software program (Geomagic Control X) to analyze the dimensional stability of tested devices by using the root mean square method. The average deviation values defined the variability of measured changes over time. Cameo and intaglio surface deviations were analyzed using the Kruskal-Wallis and Dunn tests, while the variability of measured deviations was analyzed with 1-way analysis of variance and the Tukey HSD tests (α=.05).

RESULTS

Significant differences were observed among tested devices when the intaglio surface deviations and the cameo surface variability were considered (P<.001). SM-2 had significantly higher intaglio surface deviations than AM-1, SM-1, and AM-2 (P≤.036). Among the test groups, AM-1 had the greatest cameo surface variability (P≤.004).

CONCLUSIONS

SM-2 resulted in lower intaglio surface stability than the additive and the other subtractive manufacturing technologies, while AM-1 led to the highest cameo surface variability among the test groups.

The Effect of Build Angle and Artificial Aging on the Accuracy of SLA- and DLP-Printed Occlusal Devices

The aim of this study is to investigate the influence of printing material, build angle, and artificial aging on the accuracy of SLA- and DLP-printed occlusal devices in comparison to each other and to subtractively manufactured devices. A total of 192 occlusal devices were manufactured by one SLA-printing and two DLP-printing methods in 5 different build angles as well as milling. The specimens were scanned and superimposed to their initial CAD data and each other to obtain trueness and precision data values. A second series of scans were performed after the specimens underwent an artificial aging simulation by thermocycling. Again, trueness and precision were investigated, and pre- and post-aging values were compared. A statistically significant influence was found for all main effects: manufacturing method, build angle, and thermocycling, confirmed by two-way ANOVA. Regarding trueness, overall tendency indicated that subtractively manufactured splints were more accurate than the 3D-printed, with mean deviation values around ±0.15 mm, followed by the DLP1 group, with ±0.25 mm at 0 degree build angle. Within the additive manufacturing methods, DLP splints had significantly higher trueness for all build angles compared to SLA, which had the highest mean deviation values, with ±0.32 mm being the truest to the original CAD file. Regarding precision, subtractive manufacturing showed better accuracy than additive manufacturing. The artificial aging demonstrated a significant influence on the dimensional accuracy of only SLA-printed splints.

Evaluation of the clinical performance of different occlusal device materials

STATEMENT OF PROBLEM

Computer aided technologies have been used to fabricate occlusal devices. However, the clinical behavior of the newly developed materials developed for occlusal devices is unknown.

PURPOSE

The purpose of this prospective, double-blind study was to assess the clinical efficacy of recently introduced computer-aided design and computer-aided manufacturing (CAD-CAM) materials for the fabrication of occlusal devices.

MATERIAL AND METHODS

A total of 24 participants were divided randomly into 2 study groups; polyetheretherketone (PEEK) and polymethyl methacrylate (PMMA), and a control group (CG). Conventional impressions and gypsum casts were obtained from all participants. In the study groups, the casts were digitalized with an extraoral digital scanner, designed with a software program (Bite Occlusal Device Module; exocad GmbH) and milled from PEEK and PMMA blocks. Clear resin sheets were used for occlusal device fabrication in the CG. The baseline measurements were made during the initial appointments. After 6 months, the participants returned for follow-up evaluations. Clinical performance based on surface roughness, wear of the antagonist teeth, occlusal device fit and therapeutic effect, as well as participant satisfaction were compared using the 1-way ANOVA test between the main groups (α=.05). The post hoc and Kruskal Wallis-H tests were used to compare the nonparametric group.

RESULTS

The therapeutic effects of the occlusal devices did not differ. All participants showed improvement in palpation and mandibular movement scores, but no statistically significant differences were found among the groups (P>.05). PEEK and PMMA had statistically less surface wear than CG (P<.001) and led to less antagonist tooth wear. No significant participant satisfaction difference was seen among the groups (P>.05). The control group had the best fit (P<.001).

CONCLUSIONS

Recent CAD-CAM materials exhibit clinically acceptable outcomes, and their performance is comparable with that of traditional materials. CAD-CAM materials appear suitable in terms of accuracy, surface wear, and therapeutic efficacy.

Fully digital workflow of an occlusal device including digital facebow record: A clinical report

In many current digital workflows for the production of occlusal devices and dentures, the traditional facebow record for the individual determination of the hinge axis has been omitted. A novel digital facebow record procedure including a scannable occlusal fork is described as a straightforward to use, cost-effective, and less time-consuming alternative to close this gap in fully digital prosthetic workflows.

Marginal and internal discrepancies associated with carbon digital light synthesis additively manufactured interim crowns

STATEMENT OF PROBLEM

The carbon digital light synthesis (DLS) or continuous liquid interface production (CLIP) technology is an innovative additive manufacturing technology using oxygen-inhibited photopolymerization to create a continuous liquid interface of unpolymerized resin between the growing component and the exposure window. This interface eliminates the need for an incremental layer-by-layer approach, allowing for continuous creation and increased printing speed. However, the internal and marginal discrepancies associated with this new technology remain unclear.

PURPOSE

The purpose of this in vitro study was to evaluate the marginal and internal discrepancies by using the silicone replica technique of interim crowns fabricated by 3 different manufacturing technologies: direct light processing (DLP), DLS, and milling.

MATERIAL AND METHODS

A mandibular first molar was prepared, and a crown was designed with a computer-aided design (CAD) software program. The standard tessellation language (STL) file was used to create 30 crowns from the DLP, DLS, milling technologies (n=10). The gap discrepancy was determined using the silicone replica approach, with 50 measurements made with a ×70 microscope for each specimen for the marginal and internal gaps. The data were analyzed using 1-way ANOVA, followed by the Tukey HSD post hoc test (α=.05).

RESULTS

The DLS group had the least marginal discrepancy compared with the DLP and milling groups (P<.001). The DLP group showed the highest internal discrepancy followed by the DLS and milling groups (P=.038). No significant difference was found between DLS and milling in terms of internal discrepancy (P>.05).

CONCLUSIONS

The manufacturing technique had a significant effect on both internal and marginal discrepancies. The DLS technology showed the smallest marginal discrepancies.