Conventional and digital complete-arch implant impression techniques: An in vitro study comparing accuracy.

STATEMENT OF PROBLEM: Varying complete-arch digital-implant-scanning techniques have been described, but their accuracy remains uncertain. PURPOSE: The purpose of this in vitro investigation was to assess the effect of the implant angulation and impression method (conventional, intraoral digital scan, intraoral scan with a splinting framework, and combining cone beam computed tomography [CBCT] and intraoral scan) on the accuracy of complete arch implant recording. MATERIAL AND METHODS: The following 2 casts were obtained: one with 4 parallel (P group) and the other with 4 angled (up to 30 degrees) implant abutment analogs (NP group). Both the casts were digitized (7Series Scanner) (control file). The following 4 subgroups were created: conventional polyether impression with a splinted framework (CNV subgroup), intraoral scan (IOS subgroup), intraoral scan with a splinting framework (S-IOS subgroup), and intraoral scan combined with CBCT scan (CBCT-IOS subgroup) (n=10). For each file, an implant-supported bar was designed and imported into a program (Netfabb) to perform linear and angular interimplant abutment measurements. Two-way ANOVA (Analysis of Variance) and Tukey tests were selected to examine the data (α=.05). RESULTS: Implant angulation (P=.010) and impression method (P=.003) significantly influenced the linear trueness. The P group (112 µm) obtained better linear trueness than the NP group (144 µm). The CNV subgroup obtained the best linear trueness, while the IOS and CBCT-IOS showed the worst trueness. Group (P<.001) significantly influenced angular trueness. Group (P=.009) and subgroup (P<.001) influenced the linear precision. The P group (72 µm) obtained better linear precision than the NP group (91 µm). The IOS subgroup obtained the best linear precision. Group (P=.034) significantly influenced the angular precision. The P group (0.46 degrees) had higher angular precision compared with the NP group (0.60 degrees). CONCLUSIONS: Implant angulation and the impression methods tested, impacted the accuracy of the complete-arch implant recording. Parallel implants had better trueness and precision values than nonparallel implants. The conventional impression method showed the best trueness and precision. Among the digital implant scan methods assessed, the S-IOS and CBCT-IOS subgroups acquired significantly better trueness and precision than the IOS subgroup.

Influence of the surface humidity, implant angulation, and interimplant distance on the accuracy and scanning time of complete-arch implant scans.

OBJECTIVES: To assess the influence of implant angulation, humidity, and interimplant distance on the accuracy and scanning time of complete-arch implant scans. METHODS: A definitive cast with 4 parallel implant abutment analogs (P group), and another cast with 4 angulated (up to 30 degrees) implant abutment analogs (NP group) were digitized by using a scanner (7Series) (reference scans). Two subgroups were created: dry (D subgroup) and wet (W subgroup). For the D subgroup, the casts were digitized without altering the surface humidity by using an intraoral scanner (IOS) (TRIOS 3). For the W subgroup, the cast surface was humidified with artificial saliva and digitized by using the same IOS. The interimplant distance discrepancies were assessed by computing linear and angular measurements. Trueness data was analyzed using 3-way ANOVA followed by the pairwise comparison Tukey tests. The Bartlett test, followed by the pairwise comparison tests, was used to assess the precision (α=.05). RESULTS: Regarding the trueness, implant angulation (P<.001) and inter-implant distance measurement (P<.001) influenced the linear discrepancies. Implant angulation (P=.002), humidity conditions (P<.001), and inter-implant distance (P=.001) influenced the angular discrepancies. Regarding the precision, significant differences in the variance of linear and angular measurements and inter-implant distances were found. Humidity conditions (P<.001) influenced the scanning time. CONCLUSIONS: Implant angulation, humidity, and interimplant distance influenced the accuracy and scanning time of complete-arch implant scans. Parallel implants resulted in higher trueness and precision values. Dry conditions resulted in slightly higher scanning trueness and precision and shorter scanning time. CLINICAL SIGNIFICANCE: Drying the surface being scanned increases intraoral scanning accuracy and decreases intraoral scanning time.

Influence of implant angulation and clinical implant scan body height on the accuracy of complete arch intraoral digital scans.

STATEMENT OF PROBLEM: The accuracy of digital implant scans can be affected by the implant angulation, implant depth, or interimplant distance. However, studies analyzing intraoral scanning accuracy with different implant angulations and different scan body heights are scarce. PURPOSE: The purpose of this in vitro study was to determine the influence of the implant angulation and clinical implant scan body height on the accuracy of complete arch scans. MATERIAL AND METHODS: Two definitive implant casts with 6 implant analogs (Zimmer Biomet) were obtained: 1 cast had all the implant analogs parallel (GP group), and 1 cast had the implant analogs with divergence of up to 30 degrees (GD group). A coordinate measurement machine (Global Evo 09.15.08) was used to measure the positions of the implant analogs. Each group was divided into 3 subgroups depending on the clinical implant scan body height: 10, 6, and 3 mm. An implant scan body (Elos Accurate Scan Body Brånemark system) was positioned on each implant analog. A total of 10 scans of each subgroup were recorded by using an intraoral scanner (TRIOS 3). Each STL file obtained was imported into a reverse engineering software program (Geomagic), and linear and angular Euclidean measurements were obtained. The Euclidean calculations between the implant analog positions of the definitive implant casts were used as a reference to calculate the discrepancies among the corresponding subgroups. The Kolmogorov-Smirnov test revealed that the lineal measurements were not normally distributed, so the Kruskal-Wallis and pairwise comparison Dunn tests were used (α=.05). The Kolmogorov-Smirnov test revealed that the angular measurements were normally distributed. Therefore, the 2-way ANOVA and pairwise comparison Tukey tests were used (α=.05). RESULTS: The Kruskal-Wallis test revealed significant differences in the linear Euclidean medians between the GP and GD groups with different clinical implant scan body heights (H(5)=23.18, P<.001). Significant differences in the linear Euclidean medians were computed between the GP-6 and GD-10 subgroups (P=.009), GD-3 and GD-6 subgroups (P=.029), and GD-3 and GD-10 subgroups (P=.001). Two-way ANOVA revealed that the implant angulation (F(1, 3.3437)=28.93, P<.001) and clinical implant scan body height (F(2, 0.4358)=3.77, P=.029) were significant predictors of discrepancies in the angular measurement. CONCLUSIONS: Implant angulation and clinical scan body height influenced scanning accuracy. The lowest clinical implant scan body height tested had the lowest accuracy in both parallel and angulated implants, but statistically significant differences were found only in the angulated group.

Fracture resistance of additive manufactured and milled implant-supported interim crowns.

STATEMENT OF PROBLEM: Interim dental prostheses can be fabricated by using subtractive or additive manufacturing technologies. However, the fracture resistance of implant-supported interim crowns fabricated by using vat-polymerization additive manufacturing methods remains unclear. PURPOSE: The purpose of this in vitro study was to evaluate the fracture resistance of anterior and posterior screw-retained implant-supported interim crowns fabricated by using subtractive and vat-polymerization direct light processing (DLP) additive manufacturing procedures. MATERIAL AND METHODS: An implant (Zinic Implant RP ∅4.0×10 mm) was placed in a 15×15-mm polymethylmethacrylate block. An implant abutment (ZiaCam, nonrotatory RP) was positioned on each implant. The virtual implant abutment standard tessellation language (STL) file provided by the manufacturer was imported into a software program (exocad v2.2 Valletta) to design 2 anatomic contour crowns, a maxillary right central incisor (anterior group) and a maxillary right premolar (posterior group). Each group was subdivided into 2 subgroups depending on the manufacturing method: milled (milled subgroup) and additive manufacturing (additive manufacturing subgroup). For the milled subgroup, an interim material (Vivodent CAD Multi) and a milling machine were used to fabricate all the specimens (N=40, n=10). For the additive manufacturing subgroup, a polymer interim material (SHERAprint-cb) and a DLP printer (SHERAprint 30) were used to manufacture all the specimens at a 50-µm layer thickness and 45-degree build orientation as per the manufacturer's instructions. Then, each specimen was cemented to an implant abutment by using composite resin cement (Multilink Hybrid Abutment HO) as per the manufacturer's instructions. A universal testing machine was used for fracture resistance analysis, and the failure mode was recorded. The Shapiro-Wilk test revealed that data were normally distributed. One-way ANOVA and Tukey multiple comparison were selected (α=.05). RESULTS: One-way ANOVA revealed significant differences among the groups (P<.05). The anterior milled subgroup obtained a significantly higher fracture resistance mean ±standard deviation value of 988.4 ±54.8 N compared with the anterior additive manufacturing subgroup of 636.5 ±277.1 N (P<.001), and the posterior milled subgroup obtained significantly higher mean ±standard deviation of 423.8 ±68 N than the additive manufacturing subgroup of 321.3 ±128.6 N (P=.048). All groups presented crown fracture without abutment fracture. CONCLUSIONS: Manufacturing procedures and tooth type influenced the fracture resistance of screw-retained implant-supported interim crowns. Milled specimens obtained higher fracture resistance compared with the DLP additive manufacturing groups. The anterior group was higher than the posterior group.

Comparative study of the accuracy of an implant intraoral scanner and that of a conventional intraoral scanner for complete-arch fixed dental prostheses.

STATEMENT OF PROBLEM: Most of the available digital systems are designed to image teeth and soft tissue rather than dental implants. However, although some are marketed specifically to record implant position, whether these products are better for implant scanning is unclear. PURPOSE: The purpose of this in vitro study was to compare the accuracy of an implant intraoral scanner (PiC camera) with that of an intraoral scanner (TRIOS 3) for 6 implants placed in completely edentulous arches. MATERIAL AND METHODS: Two maxillary master models with 6 external hexagonal Ø5.1-mm implants were used, one with parallel and the other with angled implants. The reference values were obtained with a coordinate measuring machine. Ten scans were made per model (parallel and angled) and system (intraoral and implant) (n=10), after which the 3-dimensional coordinates for each implant were determined with a computer-aided design software program and compared with the linear and angular reference values. Statistical significance was determined with the Student t test (α=.05). RESULTS: Statistically significant differences (P<.001) were found in both precision and trueness. The overall errors relative to the reference in the parallel implant-supported casts based on the implant scanner were 20 µm (P=.031) and 0.354 degrees (P=.087) compared with 100 µm (P<.001) and 1.177 degrees (P<.001) in the cast based on conventional digital scans. The global errors in the angled implant casts were 10 µm (P=.055) and 0.084 degrees (P=.045) for the implant digital scans and 23 µm (P=.179) and 0.529 degrees (P<.001) for the conventional digital scans. CONCLUSIONS: The implant intraoral scanner delivered greater precision and trueness than the conventional instrument for imaging complete-arch implant-supported prostheses.