Effects of cyclic loading on loss of abutment screw torque of angled screw channel single implant crowns on narrow diameter implants.

STATEMENT OF PROBLEM: Screw access channels that emerge on the facial aspect of anterior screw-retained implant crowns can compromise esthetics. Recently, angled screw channels (ASCs) have been developed that can alter screw access channel angulations to improve esthetics. While ASCs can be used on narrow-diameter implants, information is limited on the loss of abutment screw torque on narrow-diameter implants with ASCs. PURPOSE: The purpose of this in vitro study was to compare the loss of abutment screw torque after thermocycling and the cyclic loading of ASCs from 3 different companies connected to narrow-diameter implants. MATERIAL AND METHODS: A total of 40 narrow-diameter implants (NobelReplace Conical Connection 3.5×11.5 mm) were mounted individually in acrylic resin blocks and divided equally into 4 groups. The first group, NB-0 (Control), consisted of screw-retained zirconia crowns fabricated on ASCs at 0-degree angulation (n=10). The other 3 groups consisted of a total of 30 screw-retained zirconia crowns fabricated on ASCs at 20-degree angulation: NB-20 (Angulated Screw Channel Solutions), ATL-20 (Atlantis Custom Base Solution with angulated screw access), and DA-20 (Dynamic TiBase). Each crown was secured on the mounted implant with its corresponding titanium base insert and screw and then tightened to the manufacturer's recommended torque with a digital torque gauge. The initial reverse torque value (RTVI) was obtained and recorded at baseline. Subsequently, a new set of screws were tightened to recommended values, and each specimen underwent thermocycling and then cyclic loading at 0 to 100 N at 10 Hz for 1 million cycles to simulate 1year of functional loading. After cyclic loading, the final reverse torque values (RTVF) were recorded and compared with the RTVI to evaluate the percentage torque loss (PTLF). Statistical analysis was performed using the Kruskal-Wallis analysis, Rank base analysis of covariance (ANCOVA), and the Tukey HSD post hoc comparisons (α=.05). RESULTS: Significant differences were found for the PTLF among all groups after cyclic loading (P<.001). The PTLF in ATL-20 (51.4%) was significantly higher than in NB-0 (22.2%) (P<.001) and NB-20 (29.2%) (P=.010). No significant difference was found in the PTLF among other groups (P>.05). CONCLUSIONS: The abutment screw torque loss after cyclic loading of the ASCs on narrow diameter implants among the 4 groups did not perform comparably. The largest percentage torque loss was recorded for the ATL-20 group. The NB-20 group demonstrated the lowest percentage torque loss. DA-20 showed percentage torque loss less than ATL-20; however, its RTVF was the lowest.

Conversion of Digital Dentures for Immediate Loading of Complete Arch Implant Prostheses.

The development and expanded use of digital dentures has led to their use in the immediate loading of complete arch implant prostheses. This paper reviews the prosthetic complications that can occur with immediately loaded conversion prostheses along with the advantages afforded by digital dentures in minimizing or eliminating these complications. The process of using digital dentures in the fabrication of conversion dentures for immediate loading of complete arch implant prostheses is presented as well as the use of digital dentures for definitive prostheses. The described procedures include methods of obtaining clinical records, the fabrication of conversion dentures, the immediate loading procedure using a conversion prosthesis, and use of a conversion denture in the fabrication of a definitive prosthesis.

Abutment screw torque changes with straight and angled screw-access channels.

STATEMENT OF PROBLEM: Angle-correcting options allow the use of screw-retained implant prostheses in situations where an implant has been placed with a facial inclination. However, manufacturers have different recommended torque values, and it is unclear whether the performance of these designs is equivalent to that of the traditional screw-retained crowns (SRCs) when subjected to cyclic loading forces. PURPOSE: The purpose of this in vitro study was to compare torque differences between conventional straight-line screw access and angulated access SRCs before and after simulated functional loading. MATERIAL AND METHODS: Five groups consisting of 10 SRCs and implants were formed: Nobel Biocare zirconia crowns with 20-degree access channels (NB-20); Dynamic Abutment Solution zirconia crowns (DA-20) with 20-degree access channels; Core3dcentre angle correction zirconia crowns with 20-degree access channels (C3D-20); Nobel Biocare zirconia crowns with 0-degree access channels (NB-0); and gold alloy crowns cast to Nobel Biocare Gold-Adapt abutments (GA-0). Each specimen underwent thermocycling before cyclic loading. A preload torque based on the manufacturer's recommendation was applied to each crown placed on an implant. Reverse torque measurements were obtained for each specimen before cyclic loading. Each implant-abutment assembly was then cyclic loaded at 0 to 100 N at 10 Hz for 1 million cycles. Reverse torque measurements were obtained after cyclic loading and the percentage difference calculated. RESULTS: No significant percentage torque loss differences were observed between the 0-degree and 20-degree SRCs after cyclic loading. No significant differences were seen among the angulated access channel crowns. DA-20 and C3D-20 specimens had significantly higher torque loss compared with the NB-0 group. The C3D-20 group reported the largest percentage torque loss (34.5%) among the angulated access screw channel groups. The GA-0 group reported the largest percentage torque loss of all the groups (35.9%). No crown mobility or other complications were observed in any of the groups after cyclic loading. CONCLUSIONS: Angulated access channel crowns performed comparably with conventional straight-line screw access SRCs with regard to percentage torque values after cyclic loading. Angulated access channel crowns with lower manufacturer recommended torque values had higher percentage torque differences.

Accuracy of 3D Printed Models Created by Two Technologies of Printers with Different Designs of Model Base.

PURPOSE: To evaluate the accuracy of three-dimensional (3D) printed models manufactured using two different printer technologies with different model base designs. MATERIALS AND METHODS: A maxillary typodont was scanned using a desktop scanner to generate the Standard Tessellation Language (STL) file as a reference scan. After the scanning procedure, the STL file was exported to Model Builder™ for designing the following two types of the model bases: a solid base design and a hollow base design with a 2.0 mm thickness of the external shell. Each design was printed to produce 10 models using a Continuous Liquid Interface Production (CLIP) printer and a Digital Light Processing (DLP) printer. The following four groups were tested: CLIP with solid base (CS); CLIP with hollow base (CH); DLP with solid base (DS); and DLP with hollow base (DH). A total of 40 models were scanned using the same desktop scanner to generate the STL files for evaluation of the accuracy by evaluation of trueness and precision. All STL files were superimposed with the control STL file via surface matching software and a comparison was performed using the 3D color mapping function and a 2D comparison of 48 points selected on the tested model. The data were collected by measuring the deviation between the tested model and the reference scan. Trueness was calculated by using the comparison among four tested groups. The Kruskal-Wallis analysis was conducted to assess the overall statistical significance of differences among the tested groups (α = 0.05). For precision measurement, the evaluation was conducted using Intraclass Correlation Coefficient (ICC) value at 95% confident interval to determine the deviation within the same tested groups. RESULTS: The median values for the deviated distance of the four tested groups were 0.045 (CH), 0.035 (CS), 0.077 (DH), and 0.077 mm (DS). There were no statistically significant differences between the trueness of the two groups when using the same printers regardless of the designs of model base (p > 0.05). However, when comparing the two printers using the same model base design and the two different designs of model base, there were statistically significant differences in trueness (p < 0.05). The 3D printed models created using CLIP technology had higher trueness than the DLP technology printer. Precision of the 3D printed model was displayed in ICC value. The ICC values of four tested groups were 0.968 (CH), 0.981 (CS), 0.969 (DH), and 0.983 (DS). All tested groups were classified as exhibiting an excellent level of precision based on 95% confident interval of the ICC estimation. CONCLUSIONS: The accuracy of 3D printed models was affected by the printer technology regardless of whether the model base was solid or hollow. The CLIP technology printer produced significantly less variation from the reference model than the DLP printer. However, all of the 3D printed models were determined to exhibit a clinically acceptable level of accuracy based on the recorded dimensions being less than 100 µm different than the reference model.

Errors associated with digital preview of computer-engineered complete dentures and guidelines for reducing them: A technique article.

Patient reports, clinical studies, and systematic reviews reveal a rapid increase in interest in computer-engineered complete dentures (CECDs). The advantages of CECDs include a reduced number of visits, improved fit and retention, and electronic archiving. However, patient dissatisfaction has been reported with CECDs, which may be due to the lack of a trial placement appointment. This technique article identifies errors that occur when CECDs are previewed digitally and proposes guidelines and a checklist to reduce complications such as inadequate esthetics, poor tooth arrangement, misaligned occlusal plane, and inappropriate denture base characteristics.

A 3D-printed guide for lateral approach sinus grafting: A dental technique.

Lateral approach sinus grafting has become a routine and predictable surgical method of augmenting the pneumatized sinus for implant placement. Outlining the lateral window access can be a challenging task for the clinician to envision and execute. Improper extension and access to the maxillary sinus can prevent proper placement of graft materials and lead to complications. The purpose of this report was to demonstrate a technique that will allow the precise planning of the lateral approach using radiographic information and 3-dimensional (3D) software to 3D-print a surgical guide.