Accuracy and resolution of conventional and additively manufactured silicone elastomers as applied in maxillofacial therapies.

STATEMENT OF PROBLEM: Silicone elastomers are becoming more readily available for additive manufacturing, which may be advantageous for fabricating maxillofacial prostheses. However, the properties of three-dimensionally (3D) printed silicone as compared with conventionally processed silicone have not been well studied. PURPOSE: The purpose of this in vitro study was to compare the dimensional accuracy and surface resolution of additively manufactured with conventional room-temperature vulcanized (RTV) silicones. MATERIAL AND METHODS: A custom aluminum mold was used to generate hand-spatulated specimens (A103 and VerSilTal-50F, n=20). A computer-aided design and computer-aided manufacturing workflow was used to generate additively manufactured specimens (Sil30 and TrueSil, n=20). Digital surface scans of each specimen were recorded; a scan of the mold served as the control. Surface dimensions were measured with a digital metrology software program, while digital overlays were made using a 3D processing software program. The surface resolution of the specimens was assessed by analyzing 4 topographical landmarks (flat surfaces, raised lines, domes, and scribed lines) with a visual qualitative grading scale. The data were analyzed with 1-way analysis of variance, followed by a Student-Newman-Keuls post hoc test (α=.05). RESULTS: The specimens demonstrated statistical differences in trueness and precision (P<.001). The TrueSil specimens showed the largest deviation in measurements of trueness and precision (up to -1.374%). The other specimens yielded percentage mean differences that were more consistently within the range of the American Dental Association International Organization for Standardization standard for elastomers. The manually fabricated specimens yielded more consistently ideal ratings for resolution than did the additively manufactured ones, with the Sil30 specimens receiving the most Charlie (not clinically acceptable) ratings. CONCLUSIONS: Numerical differences between each specimen and the control were considered negligible for maxillofacial applications. Notable discrepancies related to the quality of resolution, wherein the benchtop-manufactured specimens consistently generated better results compared with additively manufactured ones. Other factors, such as resiliency, odor, and cost, posed limitations in justifying the use of silicones in a direct-to-print workflow.

Technique to Fabricate Custom Nasal Pillows and Monoblock Mandibular Advancement Device Using A Digital Workflow for Combination Therapy of Obstructive Sleep Apnea.

Combination therapy using continuous positive airway pressure and oral appliance therapy is an effective non-surgical treatment for obstructive sleep apnea. However, the laboratory expense and additional chairside time prevent it from being a preferred option. This article describes a technique for fabricating custom nasal pillows and monoblock mandibular advancement device with potential lower cost and accelerated timeline using a digital workflow.

An Investigation of the Effect of Modifying and Reusing Impression Copings on Transfer of Implant Analog Position and Angulation.

AIM: The aim of this research was to determine whether sterilization and reutilization of impression copings had an impact on the accuracy of casts made for multiimplant restorations. MATERIALS AND METHODS: Four master casts embedded with five implant analogs were fabricated. Polyvinyl siloxane (PVS) impressions of the master cast with copings attached to the analogs were made and poured in dental stone. The impression copings were subjected to cleaning and sterilization. These processes were repeated 30 cycles for each of the two groups of five impression copings: one without modification and one with modification that included air abrasion and PVS adhesive. A coordinate measuring machine (CMM) was used to measure relative angles and distances between the reference analog and analogs. The relative angles and distances measured on the stone casts were compared to the master resin cast to obtain positional and angular displacements. RESULTS: For impression copings that were not modified, a significant difference was detected for both positional and angular displacements. For impression copings that were modified, a significant change was observed only for positional displacement. The maximum discrepancies measured for positional and angular displacements after 30 cycles of reuse were only 81 µm and 0.46°, respectively, regardless of the modification. CONCLUSION: Within the limitations of this study, unmodified impression copings that have undergone 30 cycles of cleaning and sterilization appeared to incur more impression inaccuracy than those impression copings that were modified by airborne-particle abrasion and PVS adhesive. CLINICAL SIGNIFICANCE: Impression copings used in this study can likely be recycled up to 30 times without reducing the accuracy of the impression to a level that may be considered clinically significant.

Targeted Endodontic Microsurgery: Digital Workflow Options.

Targeted endodontic microsurgery (TEMS) combines a precisely designed 3-dimensional (3D)-printed surgical guide with a trephine bur for safe and efficient osteotomy and root-end resection. The TEMS digital workflow converts the patient's anatomy into digital data in 4 steps. First, bone, teeth, and neurovascular spaces are rendered with cone-beam computed tomographic imaging. Next, crowns and soft tissues are rendered with an intraoral optical scan, a benchtop optical scan of an impression or cast, or a cone-beam computed tomographic scan of an impression or cast. Third, these renderings are merged within design software to create a 3D construction containing a virtual model. Finally, guide design is performed on the virtual model for 3D printing. A significant gap in knowledge exists in that digital workflow principles and considerations are not documented in the endodontic literature. The aim of this article is to describe TEMS digital workflow guiding principles.

Effect of Split-File Digital Workflow on Crown Margin Adaptation.

PURPOSE: Computer-aided design/computer-aided manufacturing (CAD/CAM) is becoming increasingly integrated into dental practice workflow at a pace that exceeds scientific validation. The aim of this study is to evaluate a complete digital split-file protocol relative to segmental digital and analog techniques for restoring a single maxillary anterior edentulous space with custom abutment and crown. MATERIALS AND METHODS: Four treatment workflows were assessed: complete digital (CD), segmental digital (SD), milled wax (AM), and heat pressed and hand waxed (AH) and heat pressed. The CD workflow "split" an abutment and crown into separate files to fabricate a zirconia abutment and both zirconia/lithium disilicate crown restorations. The SD workflow scanned the existing abutment for design of segmental restorations in zirconia, lithium disilicate, and milled wax (AM). The AH specimens were conventionally hand waxed. Both the AM and AH specimens were heat pressed with lithium disilicate. All restorations were evaluated with standardized measurements using scanning electron microscopy (SEM) as manufactured without internal adjustments and after manual adjustment. The number of adjustments, adjustment time, and location of adjustments were recorded. One-way ANOVA with repeated measures was used to report geometric means with 95% confidence intervals. RESULTS: The mean marginal gap after adjustment of the CD group was 69 µm, with an upper bound (UB) of 79 µm and a lower bound (LB) of 60 µm. SD group mean was 26 µm with an UB of 31 µm and LB of 22 µm. The AM group mean was 32 µm, with an UB of 49 µm and a LB of 20 µm; AH group mean of 26 µm with an UB of 34 µm and a LB of 20 µm. The SD, AM, and AH workflows were statistically similar (p = 1.000), and the CD workflow was statistically greater than the other three (p < 0.001). CONCLUSIONS: The split-file (CD) protocol results in marginal gap size within clinical standards after adjustment; however, 52 of the 60 digitally produced restorations showed a horizontal marginal offset that required adjustment for proper contours.