In-vitro accuracy of a novel jaw-tracking technology.

OBJECTIVES: As jaw-tracking systems integrate into digital prosthetic workflows, their accuracy remains underexplored. This study aimed to evaluate the in vitro accuracy of a novel digital jaw-tracking system (Modjaw, Villeurbanne, France) by comparing its precision and trueness to that of an industrial scanner. METHODS: Upper and lower typodont models were scanned with an industrial-grade optical scanner (ATOS Q, Carl Zeiss GOM Metrology GmbH, Germany) to produce master scans. The models were placed in a phantom head with artificial joints to replicate five different intermaxillary relationships (IMRs). The 1, 2, 3, 4, and 5 mm IMR distances were stabilized by five silicone bites. The silicone bites were repositioned after each measurement. ATOS scanned the whole artificial joint with the models three times in each IMR to assess the precision of the repositioning (i.e., bite precision). The master scans were uploaded to Modjaw. Modjaw recorded the five IMR positions three times each to assess the precision of the Modjaw. Precision was calculated by aligning the scans within the same group, whereas Modjaw trueness was evaluated by aligning ATOS and Modjaw scans. The mean absolute distance (MAD) between aligned surfaces was calculated. The effect of IMR on the MAD was evaluated using a linear mixed model. RESULTS: The mean bite precision across the IMRs was 7.6 ± 0.53 µm. Modjaw precision over the IMRS was 9.7 ± 1.76 µm, and the trueness was 10.8 ± 1.40 µm. Increased IMRs up to 4 mm significantly increased the MAD from 6.5 to 8.5 µm for the bite precision, 4.8 to 15.7 µm Modjaw precision, and 7.1 to 14.9 µm for trueness. CONCLUSIONS: Modjaw excelled in accuracy, comparable to industrial scanners and superior to traditional methods. IMR elevation marginally deteriorates the accuracy. Future studies should extend to varied movements beyond centric relations and encompass the influence of intraoral scanners.

Reproducibility of the digital palate in forensic investigations: a two-year retrospective cohort study on twins.

OBJECTIVES: The palatal scans of the same individuals were compared after two years to assess forensic reproducibility. The effect of orthodontic treatment, the comparison area and the digitization approach were investigated. METHODS: The palate was scanned three times in 20 pairs of monozygotic twins with an intraoral scanner (IOS), to assess repeatability. The same subjects were re-scanned two years later, with two different IOSs. An elastic impression and a plaster model were also made and scanned with a laboratory scanner (indirect digitization). Mean absolute distance between scans was compared after best-fit alignment. Scans from the two sessions were compared to evaluate the combined effect of aging, orthodontic treatment and different digitization methods (forensic reproducibility). Additionally, the scans of different digitization methods from the second session were compared (technical reproducibility). The between-siblings difference was compared in the two sessions, to evaluate the effect of aging on palatal morphology. RESULTS: The anterior palatal area showed significantly better repeatability and forensic reproducibility than the whole palate (p < 0.001), but orthodontic treatment had no effect. Indirect digitization produced lower forensic and technical reproducibility than IOSs. For IOSs, repeatability (22 µm) was significantly (p < 0.001) better than either forensic (75-77 µm) or technical reproducibility (37 µm). No significant changes were observed from the first to the second session in the between-sibling comparison. The closest between-sibling value (239 µm) considerably exceeded the highest forensic reproducibility value (141 µm). CONCLUSIONS: Reproducibility is acceptable between the different IOSs, even after two years, but is poor between IOS and indirect digitization. The anterior palate is relatively stable in young adults. CLINICAL SIGNIFICANCE: Intraoral scanning of the anterior palatal area has superior reproducibility, regardless of the IOS brand. Therefore, the IOS method could be suitable for identifying humans through anterior palatal morphology. However, the digitization of elastic impressions or plaster models had low reproducibility, preventing their application for forensic purposes.

Marginal and internal fit of full ceramic crowns milled using CADCAM systems on cadaver full arch scans.

BACKGROUND: Chairside systems are becoming more popular for fabricating full-ceramic single restorations, but there is very little knowledge about the effect of the entire workflow process on restoration fit. Therefore, this study aimed to compare the absolute marginal discrepancy (AMD) and the full internal fit (FULL) of all-ceramic crowns made by two chairside systems, Planmeca FIT and CEREC, with detailed and standard mill settings. METHODS: One upper molar was prepared for an all-ceramic crown in human cadaver maxilla. Full-arch scans were made by Emerald or Omnicam four times each. Twenty-four e.max crowns were designed and milled by the Planmill 30s or 40s or CEREC MCXL mills with either detailed or standard settings. The cadaver tooth was extracted, and each crown was fixed on it and scanned by a high-resolution microCT scanner. The AMD and FULL were measured digitally in mesio-distal and bucco-lingual 2D slices. The actual and predicted times of the milling were also registered. RESULTS: No differences were observed between detailed or standard settings in either system. The AMD was significantly higher with CEREC (132 ± 12 µm) than with either Planmill 30s (71 ± 6.9 µm) or 40s (78 ± 7.7 µm). In standard mode, the FULL was significantly higher with CEREC (224 ± 9.6 µm) than with either Planmill 30s (169 ± 8.1 µm) or 40s (178 ± 8.5 µm). There was no difference between actual and predicted time with the two Planmeca models, but with CEREC, the actual time was significantly higher than the predicted time. The 30s had significantly higher actual and predicted times compared to all other models. Across all models, the average milling time was 7.2 min less in standard mode than in detailed mode. CONCLUSIONS: All fit parameters were in an acceptable range. No differences in fit between Planmeca models suggest no effect of spindle number on accuracy. The detailed setting has no improvement in the marginal or internal fit of the restoration, yet it increases milling time.

A novel method for complex three-dimensional evaluation of intraoral scanner accuracy.

AIMS: The aim of this study was to compare two existing methods and one novel method for measuring the distortion of three-dimensional (3D) models created with complete-arch digital impressions, and to assess the accuracy of different scan patterns using these methods. MATERIALS AND METHODS: Maxillary and mandibular models were imaged with the PlanScan intraoral scanner using four different scan patterns. Accuracy and distortion were assessed by comparing the master scans with the intraoral scans using the following three methods: 1) Mean surface deviation was measured after complete arch superimposition; 2) 28 points were selected identically on the experimental and on the master reference models, and the deviation between identical points was assessed after superimposition over the complete arch; 3) In the case of the novel technique, the superimposition was made only at the scanning origin, and after that the 28 points were compared. RESULTS: Significant differences were found between the three different methods, regardless of the arch and pattern. The overall mean deviation between identical points when the models were aligned at the scanning origin was the highest, and the mean deviation between the non-identical values was the lowest. The novel method revealed local tooth-wise differences between the scan patterns as well as a pattern of amplified model error extending away from the scan origin. CONCLUSIONS: The novel method better detects the cumulative deviation of stitching errors in complete arch intraoral scans and is suitable to investigate the effect of scanning pattern in a very sensitive manner.