Influence of customized over-scan body rings on the intraoral scanning effectiveness of a multiple implant edentulous mandibular model.

OBJECTIVES: To evaluate the effectiveness of intraoral scanning with identical multiple implant scan bodies (ISB) using customized over scan body rings (COR) as an auxiliary system. METHODS: Six printed rings with different diameters and shapes were attached at different levels to each identical ISB of an edentulous mandibular master model. The master model was scanned using an intraoral scanner (Primescan CEREC) until valid digital models for the COR group (n=10) and for the unmodified ISB (UN) group (n=10) were obtained. The total scanning times and the number of rescans required was registered. To assess differences between scanning efficiency the Student T-test and Mann Whitney U-Test were applied. A Coordinate Measuring Machine (CMM) was used to register the reference model. To evaluate accuracy discrepancies between the test scans (n=20) and the reference model, Geomagic Control X was used. Mann Whitney U-test was applied to calculate statistically significant differences. RESULTS: To achieve a valid model, an average of 4.70 rescans / repetitions were required for the UN group, whereas for the COR group required an average of 1.40 rescans (p<.001). Mean total scanning time was 201.10 s and 542.40 s for the COR and UN group, respectively (p=.001). No statistically significant differences were found between the groups in terms of accuracy (p>.05) with respectively COR and UN values; mean linear trueness 34.38 µm and 31.14 µm, mean linear precision 22.94 µm and 18.51 µm, mean angular trueness 0.12° and 0.14°, mean angular precision 0.075° and 0.08°. CONCLUSION: The use of the COR system may increase the scanning efficiency of multiple implants with similar ISBs without impacting the accuracy.

Sensory innervation of the human palmar aponeurosis in healthy individuals and patients with palmar fibromatosis.

The human palmar aponeurosis is involved in hand proprioception, and it contains different sensory corpuscle morphotypes that serve this role. In palmar fibromatosis (classically referred to as Dupuytren's disease), the palmar aponeurosis undergoes fibrous structural changes that, presumably, also affect the nervous system, causing altered perception. We analysed the various sensory nerve formation morphotypes in the palmar aponeuroses of healthy subjects and patients with palmar fibromatosis. To do this, we used immunohistochemistry for corpuscular constituents and the putative mechanoproteins PIEZO2 and acid-sensing ion channel 2. Free nerve endings and Golgi-Mazzoni, Ruffini, paciniform and Pacinian corpuscles were identified in both the healthy and the pathological conditions. The densities of the free nerve endings and Golgi-Mazzoni corpuscles were slightly increased in the pathological tissues. Furthermore, the Pacinian corpuscles were enlarged and displayed an altered shape. Finally, there was also morphological and immunohistochemical evidence of occasional denervation of the Pacinian corpuscles, although no increase in their number was observed. Both PIEZO2 and acid-sensing ion channel 2 were absent from the altered corpuscles. These results indicate that the human palmar aponeurosis is richly innervated, and the free nerve endings and sensory corpuscles within the palmar aponeurosis undergo quantitative and qualitative changes in patients with palmar fibromatosis, which may explain the sensory alterations occasionally reported for this pathology.

Accuracy of digitization obtained from scannable and nonscannable elastomeric impression materials.

STATEMENT OF PROBLEM: Elastomeric impression materials have been marketed for optimizing direct digital acquisition without requiring a stone cast. The trueness and precision of the digitization of these new elastomeric impression materials are unclear. PURPOSE: The purpose of this in vitro study was to compare the trueness and precision of digital dental casts obtained from the direct digitization of 2 types of vinylsiloxanether (VSXE) impression materials by using a laboratory laser scanner. MATERIAL AND METHODS: Thirty-eight elastomeric impressions were made of a master die with a similar morphology to a premolar crown preparation. The impression materials were Identium (IDE) and Identium Scan (SCAN), designed for direct digitalization. Each impression was digitalized by using an optical scanner to create digital casts. A computer-aided design (CAD) reference model of trueness (CRM) was created and aligned to each digital cast for digital 3-dimensional discrepancy analysis. RESULTS: The mean ±standard deviation global trueness of IDE was 53 ±16 µm and that of SCAN was 46 ±3 µm. SCAN digital casts showed higher precision (58 ±5 µm) than IDE (69 ±18 µm) (P<.05). At the margin of the preparation and at the axial surfaces, SCAN models showed higher trueness (3 ±6 µm and 1 ±5 µm) than IDE (15 ±10 µm and 2 ±37 µm), respectively. CONCLUSIONS: Scannable impressions could be digitalized with higher global precision than conventional elastomeric materials. Higher trueness could be achieved in specific impression locations such as gingival areas or axial walls of preparations, where the light emitted by the scanner was not blocked.