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

Methods of evaluating mechanical properties of 3D printed occlusal device materials: Flexural strength, fracture toughness, and impact strength

STATEMENT OF PROBLEM

The best method of characterizing the strength of 3-dimensionally (3D) printed occlusal devices is unknown.

PURPOSE

The purpose of this in vitro study was to compare the flexural strength, flexural modulus, fracture toughness, and impact strength of flexible and stiff 3D printed occlusal device materials with those of milled and conventionally processed materials under wet and dry conditions.

MATERIAL AND METHODS

Specimens were fabricated from flexible (KeySplint Soft, NightGuard Flex 2) and stiff (KeySplint Hard, NightGuard Firm) 3D printed resins using a Digital Light Processing (DLP) printer and milled (ProArt CAD) and heat-polymerized (Excel Formula) materials. Specimen dimensions varied based on testing: flexural strength and flexural modulus (65×10×3.3 mm), toughness (4×8×39 mm, 3-mm cut with a 100- to 400-µm notch), and impact strength (63.5×12.7×4 mm, 1.2 mm, 45-degree notch). Specimens were stored wet (37 °C, 48 h) or dry (37 °C in water and then air dried for 24 h). Flexural strength and flexural modulus and fracture toughness were tested on a universal testing machine until fracture or 15-mm deflection, while impact strength was assessed with an Izod impact machine (7.5 J, 150 degrees). Data were analyzed using 2-way ANOVA and Tukey tests (α=.05).

RESULTS

Milled and heat-polymerized materials demonstrated higher flexural strength and flexural modulus than stiff 3D printed materials, which outperformed flexible 3D printed materials. Fracture toughness was better in milled and heat-polymerized materials under dry conditions, but one flexible 3D printed material outperformed all others under wet conditions. Flexible 3D printed materials exhibited significantly higher impact strength under both conditions.

CONCLUSIONS

Flexible 3D printed occlusal device materials excel in impact strength and show variable performance in other mechanical properties depending on material type and testing conditions.

Accuracy of occlusal splints printed in different orientations by liquid crystal display technology: an in vitro study

OBJECTIVES

To evaluate the accuracy of occlusal splints printed in different orientations by liquid crystal display technology.

METHODS

An occlusal splint was digitally designed, and additively manufactured using an LCD printer (Phrozen Sonic 4k, Phrozen) at three orientations relative to the printer building plate: 0, 45, and 70 degrees (n=10). The 3D-printed occlusal splints were digitised using a desktop scanner, resulting in experimental meshes. The meshes were analysed in a metrology software program, comparing the experimental ones with the initially designed occlusal splint (trueness) and each other within the same group (precision). The discrepancies were shown in a colour map and the root mean square indicated the magnitude of the total discrepancy between the meshes. Kruskal-Wallis test was used (α=0.05) followed by post-hoc Dunn's test.

RESULTS

There was no statistical difference in trueness among the groups (P=0.086); however, splints printed at 70 degrees showed better precision compared to those printed at 0 (P<0.001) and 45 degrees (P<0.001). The splints printed at 0 and 45 degrees exhibited a similar discrepancy pattern, with highest values concentrated in the posterior segment-positive on the buccal surface and negative on the lingual surface of molars. In contrast, splints printed at 70 degrees had highest discrepancy values in both anterior and posterior segments, with an inverted pattern on molars.

CONCLUSION

The accuracy of occlusal splints was affected by the different orientation in terms of precision, with 70 degrees resulted in highest precision compared to 0 and 45 degrees. No difference was found in terms of trueness. Higher discrepancies were found located in molars and incisal edge of anterior teeth.

CLINICAL SIGNIFICANCE

3D-printing using LCD technology stands out for its affordability and good resolution, however the optimal printing angle remains unclear. Vertical positioning allows more objects to fit on the printer building plate, while horizontal positioning reduces print time. According to literature, for DLP printers, a 0-degree angle provides good accuracy for occlusal splints, whereas a 90-degree angle results in lower accuracy. This study found that for LCD printers, 0, 45, and 70 degrees had similar trueness, with 70 degrees offering the highest precision. Thus, vertical positioning at 70 degrees can be a safe choice for the accuracy of occlusal splints printed on LCD technology.

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.

[Analysis of changes in the position of the temporomandibular joint articular disc during positioning splint therapy according to magnetic resonance imaging data]

THE AIM OF THE STUDY

Was to assess an impact of positioning occlusal splints made by various methods on the position of the articular disc of the temporomandibular joint according to MRI data.

MATERIALS AND METHODS

40 patients (8 men and 32 women) aged from 18 to 60 years with temporomandibular joint pain dysfunction syndrome were examined (ICD-10 code K07.60). Patients were treated with splint therapy using traditional splints made with combined method (20 patients) and subtractive occlusal splints made by CAD/CAM technology (20 patients). All patients had MRI of the temporomandibular joints before splint therapy and at the final stage of treatment to determine the position of the articular disc in the habitual occlusion and at maximum mouth opening.

RESULTS

After splint therapy, patients in both groups showed an improvement in the position of the articular disc in the usual occlusion: the rate of patients with bilateral dislocation of the articular disc decreased from 85% to 67.5%, and with unilateral articular disc dislocation decreased from 15% to 10%. With maximum mouth opening, complete reposition of the articular disc in both joints were recorded in 22.5%; the rate of patients with bilateral disorder of articular disc repositioning decreased from 85% to 67.5%, and with unilateral disorder of articular disc repositioning decreased from 15% to 10%.

CONCLUSIONS

Splint therapy had a pronounced positive clinical effect in patients with pain dysfunction syndrome in the temporomandibular joints. Splint therapy is more effective in correcting sagittal dislocation of the articular disc than transversal dislocation. The study showed comparable treatment results when using traditional and digital occlusal splints.

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.