A dental implant (Bone Level Tapered B2 4.1 x 10 mm, Biodenta) was embedded in a dentiform to simulate a single implant placed to restore a missing second premolar with ideal size and proportion. A scan body (DentaSwiss) was placed in the implant and scanned using a dental laboratory scanner (3Shape D2000, www.3shape.com). The scanned image was imported to the dental CAD software (DentaSwiss by 3Shape) and a custom abutment was designed. Ten custom titanium abutments were fabricated from PreFAB-4 abutment blanks (Figure 2) using the DS1300 (Figure 3). The occlusal surface sprue was manually cut and polished. Specimens were scanned using the same D2000 scanner and scanned images imported to the software (3Shape Convince Analyzer) for comparison.
First, scanned images were superimposed over the original design to evaluate trueness. Superimposed images were analyzed for discrepancy between two images. Overall analysis was performed; then each area (facial, lingual, mesial, distal, margin, supragingival, subgingival) was analyzed separately (Figure 4). Various statistics were calculated and one-way ANOVA repeated measurement and Bonferroni tests were used to compare root mean square displacement (RMSD) of each area. To evaluate precision, comparisons between each specimen were made and statistical analyses were performed in the same way.
For trueness, the average 90% interval of overall errors was 10.5±24.4 mm (Figure 5). The 90% intervals for various areas are listed in Table 1. One-way ANOVA repeated measurement and Bonferroni tests showed that the RMSD of subgingival area was greater than the other areas.
For precision, the average 90% interval of overall errors was 7.8±17.7 mm and 90% intervals for various surfaces listed in Table 2. One-way ANOVA repeated measurement showed that there was no statistically significant difference in RMSD between surfaces.
In summary, the average 90% interval overall errors for trueness was 10.5±24.4 mm and for precision was 7.8±17.7 mm. Within the limitations of this study, the PreFAB4 titanium blank that was tested using DentaSwiss 3Shape and the DS1300 milling system was fabricated with a high degree of accuracy that is equal to or exceeds conventional fabrication methods.
With the high precision of the milled custom abutments, laboratory* fabrication procedures can be simplified and made more efficient by milling the zirconia or lithium disilicate ceramic crowns simultaneously.
Clinical Demonstration of Completely Digital Workflow
A patient presented with a carious non-restorable endodontically treated root No. 4 (Figure 6). After clinical examination, an intraoral scan (TRIOS® Color, 3Shape) was performed. A CBCT radiograph was made of the maxillary arch and DICOM files imported into Implant Studio (3Shape). The design software was used to perform a 3D evaluation of available bone and plan surgical implant placement (Figure 7).
The radiographs showed a mesial bone defect and distally tilted root. To maintain at least 1.5 mm of bone between the distal of tooth No. 5 and bone at the anterior sinus wall, a 4.1x10 mm tapered implant (Biodenta, Bone Level B2) was selected.
With angulated root sockets, a common challenge during the initial osteotomy is that the twist drill wants to follow the path of least resistance. The surgical guide can ensure correct vertical implant placement. A tooth-supported surgical guide was designed and milled out of clear PMMA disk in a 5-axis milling machine (DentaSwiss DS2000).
With the predictability of surgically guided implant placement, a hybrid PMMA provisional crown was designed and milled out in advance of the surgery in the DS1300.
The root was atraumatically elevated with periotomes and the socket palpated with a periodontal probe confirming that the buccal wall was intact. The surgical guide was seated, the irrigated 2-mm twist drill aligned with the metal insert, and precisely seated to depth (Figure 8). The predetermined series of surgical drills was followed using the guide.
Because the insertion torque was only 15 Ncm, it was elected to cut off the clinical crown of the pre-surgically milled hybrid provisional crown and convert it to a custom healing abutment for soft tissue site development (Figure 9). The custom healing abutment also secured the grafting material and membrane. An intraoperative radiograph revealed sound implant positioning with ideal bone dimensions interproximally (Figure 10).