A novel post-processing strategy to improve the accuracy of complete-arch intraoral scanning for implants: an in vitro study.

OBJECTIVES: To develop a new post-processing strategy that utilizes an auxiliary device to adjust intraoral scans and improve the accuracy of 3D models of complete-arch dental implants. MATERIALS AND METHODS: An edentulous resin model with 6 dental implants was prepared. An auxiliary device, consisting of an opaque base and artificial landmarks, was fabricated and mounted onto the resin model. Twenty intraoral scans (raw scans) were taken using this setup. A new post-processing strategy was proposed to adjust the raw scans using reverse engineering software (verified group). Additionally, ten conventional gypsum casts were duplicated and digitized using a laboratory scanner. The linear and angular trueness and precision of the models were evaluated and compared. The effect of the proposed strategy on the accuracy of complete-arch intraoral scans was analyzed using one-way ANOVA. RESULTS: The linear trueness (29.7 µm) and precision (24.8 µm) of the verified group were significantly better than the raw scans (46.6 µm, 44.7 µm) and conventional casts (51.3 µm, 36.5 µm), particularly in cross-arch sites. However, the angular trueness (0.114°) and precision (0.085°) of the conventional casts were significantly better than both the verified models (0.298°, 0.168°) and the raw scans (0.288°, 0.202°). CONCLUSIONS: The novel post-processing strategy is effective in enhancing the linear accuracy of complete-arch implant IO scans, especially in cross-arch sites. However, further improvement is needed to eliminate the angular deviations. CLINICAL SIGNIFICANCE: Errors generated from intraoral scanning in complete edentulous arches exceed the clinical threshold. The elimination of stitching errors in the raw scans particularly in the cross-arch sites, through the proposed post-processing strategy would enhance the accuracy of complete-arch implant prostheses.

Comparison of the colour accuracy of a single-lens reflex camera and a smartphone camera in a clinical context.

OBJECTIVES: This study aimed to investigate the colour accuracy of digital photographs captured by a single-lens reflex (SLR) camera and a smartphone camera in a clinical setting. METHODS: Dentate subjects were recruited, and their maxillary anterior teeth were photographed along with a colour target and a dental shade guide. There were eight groups: Group 1: SLR camera with a 100 mm macro-lens and a ring-flash (SLRC); Group 2: SLRC with a polarizer; Group 3: SLRC with white-balance calibration; Group 4: SLRC with a polarizer and white-balance calibration. Groups 5 to 8 were similar to Groups 1 to 4, except a smartphone camera and an external light source (SC) were used. The CIE LAB coordinates of the colour target, shade guide, and centre of the maxillary right central incisor (tooth 11) in the digital photographs were retrieved. The colour difference ΔE=[(ΔL*)2+(Δa*)2+(Δb*)2]1/2 to the reference colour coordinates or the reading of the dental spectrophotometer was calculated. The results were analysed by the Kruskal-Wallis test at α=0.05 with Bonferroni correction. RESULTS: Thirty-nine subjects were photographed. SLRC with a polarizer showed the largest ΔE in this study (P<0.001). When capturing tooth 11, SLRC with calibrated white-balance resulted in the smallest ΔE in this study (P<0.001), and the use of a polarizer and/or calibrated white-balance did not result in a smaller ΔE than that of SC alone (P>0.001). CONCLUSION: Calibration for white-balance is recommended for the SLRC. The use of a polarizer does not show an improvement in colour accuracy. SC alone may be sufficient for intraoral photography. CLINICAL SIGNIFICANCE: When capturing intraoral photography using a single-lens reflex camera, it is recommended to calibrate the white-balance. The use of a polarizer does not significantly improve colour accuracy. However, a smartphone camera with an external light source can serve as a viable alternative.

Comparison of the virtual techniques in registering single implant position with a universal-coordinate system: An in vitro study.

OBJECTIVES: The aim of this in-vitro study was to compare the virtual techniques for registering single-implant position to the physical gold standard using a universal-coordinate system. MATERIALS AND METHODS: Thirty dentate maxillary resin models with a dental implant inserted in the incisor region were prepared. On each model, a tooth-supported acrylic stent with a 1 cm x 1 cm x 1 cm cubic-corner (CC) was prepared. The Cartesian x,y,z-coordinate of the implant neck and apex were measured physically by a coordinate-measuring machine (CMM) with reference to this CC and served as the gold-standard. The resin models were scanned by a benchtop scanner (Group BS), cone-beam computed tomography (Group CBCT), and intraoral scanner (Group IOS). Stone casts, poured from open-tray polyether impression of the resin models, were scanned by the benchtop scanner (Group BS-cast). The implant neck and apex coordinates with reference to the CC were measured and the differences in the coordinates (∆x, ∆y, ∆z) and distance r from the gold standard were calculated. The data were analyzed by one-sample t-test and one-way ANOVA/Kruskal-Wallis test with the level of significance set at 0.05. RESULTS: The implant neck and apex positions of Group BS were statistically different from that of the CMM, r>0 (p<0.001). Group IOS showed a significant less ∆z and r at the implant neck than Group BS-cast (p = 0.006). No significant difference was found in the coordinates and distance at implant apex among Groups BS, CBCT, IOS and BS-cast. CONCLUSIONS: The physical measurements could be adopted as the gold standard in assessing the single-implant positions. The IOS was more accurate in registering the single-implant neck positions than scanning of the cast. CLINICAL SIGNIFICANCE: A universal-coordinate system defined by the cubic-corner allows comparing the virtual techniques in registering single-implant positions to the physical gold standard.

Improving intraoral implant scanning with a novel auxiliary device: An in-vitro study.

OBJECTIVES: To develop a novel auxiliary device for improving the accuracy of intraoral implant scanning in the complete-edentulous arch. MATERIALS AND METHODS: A standard model of edentulous maxilla with six dummy implants was prepared. Scan bodies were attached to the model, which was scanned by a laboratory scanner. A simulated mucosa (Group 0), a resin base (Group 1), a resin base with a cuboidal reference block and 4 fiduciary spheres (Group 2) or artificial teeth (Group 3) in between the implants were mounted on the model, respectively. Each group were consecutively scanned using an intraoral scanner (n = 10). The scans were analysed for trueness and precision in inter-implant distances and angles by inspection software. Effects of the auxiliary device and different quadrants on the accuracy of complete-arch intraoral scanning were analysed by two-way ANOVA. RESULTS: Significant effects of the auxiliary device and quadrant were found on both linear and angular accuracies. The lowest linear accuracy was found in group 0. Group 1 and group 3 showed the best linear accuracy in quadrant 1 and quadrant 2, respectively. Group 2 showed the least angular precision among the three groups. CONCLUSIONS: The three designs of auxiliary devices significantly improved the accuracy of complete-arch intraoral implant scanning. The base-only design showed good scanning accuracy in a single quadrant, while the base with tooth-shaped landmarks design showed better accuracy in cross-arch. The fiduciary spheres might compromise the precision of scanning.

Evaluation of laboratory scanner accuracy by a novel calibration block for complete-arch implant rehabilitation.

OBJECTIVES: To compare the accuracies of 4 laboratory scanners using a new custom-made block for complete-arch implant rehabilitation. MATERIALS AND METHODS: A block comprised 4 cylinders, with 2 in the anterior (0° angulation) and 2 in the posterior region (45° distal angulation) (Experimental group) and a standard block with 2 parallel cones in 16° taper (ISO group), were fabricated. Both blocks were scanned consecutively for 15 times by 4 laboratory scanners: IScan, Zfx, 3Shape, and KaVo. Measurements were also made by a coordinate measuring machine (CMM) as the reference. Acquired digital models were inspected with a metrology software. Linear and angular distortions were computed evaluation of trueness, precision and expanded uncertainty of scanners. Effects of blocks and scanners on the scanning trueness and precision were analyzed by Two-way ANOVA (α = 0.05). RESULTS: The linear trueness and precision of scanners was significantly poorer when the Experimental block instead of ISO block was used. Significant greater distortions were noticed at the 45° sites than the 0° sites and no significant effect of inter-implant distance on the scanning accuracy was found. Zfx, IScan and 3Shape exhibited comparable expanded uncertainties (10.6∼11.8) but KaVo showed the greatest (19.3) in complete-arch implant scans. CONCLUSION: The ISO block might not be more suitable than the Experimental block for evaluating the accuracy of laboratory scanner for complete-arch implant scanning. All the scanners tested except one demonstrated acceptable accuracy for complete-arch implant digitization. Scanning accuracy was compromised by unfavourable angulation of implants. CLINICAL SIGNIFICANCE: It is questionable whether the laboratory scanners validated for tooth-borne cases could also perform well for implant cases. It might be necessary to develop a new calibration object specifically for complete-arch implant scenarios to verify the capability of laboratory scanners in the implant workflow.

Treatment Outcomes of Implant-Supported Maxillary Obturator Prostheses in Patients with Maxillary Defects: A Systematic Review.

PURPOSE: To systematically review the current evidence on clinical and patient-reported outcomes of implant-supported palatal obturator prostheses. MATERIALS AND METHODS: An electronic search of the PubMed, Web of Science, and Cochrane databases was carried out in June 2019. The titles and abstracts of all articles were screened by two independent reviewers. The references of the subsequently selected studies were further screened for potential articles. Assessment of the selected full texts was performed independently according to established inclusion and exclusion criteria. The quality of the selected studies was determined using the Newcastle-Ottawa scale. Interrater agreement on study selection was calculated using Cohen kappa statistic. RESULTS: The search yielded a total of 2,797 records. Ten studies were selected for data extraction, with a Cohen kappa value of 0.856. Five studies were prospective, and five were retrospective. The survival rates for conventional implants ranged from 21.42% to 100%, whereas for zygomatic implants, the survival rates varied from 30% to 100%. Four studies reported prosthodontic complications, with screw loosening being the most common. Patient quality of life (QoL) was analyzed in six studies. CONCLUSION: In spite of the limitations of the present review, it can be concluded that the clinical outcomes are acceptable in terms of survival rates, implant and prosthodontic complications, and QoL associated with implant-supported maxillary obturator prostheses. QoL of implant-supported prostheses in these patients are acceptable. The general study design was not homogenous between studies.