RESUMEN
PURPOSE: To compare the three-dimensional (3D) accuracy of conventional impressions (CIs) with digital scans (DSs) using an intraoral scanner (IOS) with intraoral scan bodies (SBs) and varying buccolingual interimplant angulations. A secondary aim was to measure the SB machining tolerance and height with and without application of torque. MATERIALS AND METHODS: Three master models (MMs) with two implants simulating an implant-supported three-unit fixed partial denture for bone-level implants were used. The implants had buccolingual interimplant angulations of 0, 10, and 20 degrees. Test models for the CI test groups were made with impression copings and polyether impressions. SBs were attached to the MMs, tightened to 15-Ncm torque, and scanned by an IOS for the DS test groups (six test groups, n = 5). A coordinate measuring machine measured linear distortions (dx, dy, dz), 3D distortions (dR), angular distortions (dθx, dθy), and absolute angular distortions (Absdθx, Absdθy) of the physical CI test models and STL files of the DS virtual models relative to the MMs. Metrology software allowed both physical and virtual measurement of geometric targets that were comparable and allowed computation of relative displacements of implant centroids and axes. RESULTS: Mean dR ranged from 31 ± 14.2 to 45 ± 3.4 µm for DS and 18 ± 8.4 to 36 ± 6.5 µm for the CI test groups. Mean Absdθx ranged from 0.041 ± 0.0318 to 0.794 ± 0.2739 degrees for DS and 0.073 ± 0.0618 to 0.545 ± 0.0615 degrees for the CI test groups. Mean Absdθy ranged from 0.075 ± 0.0615 to 0.111 ± 0.0639 degrees for DS and 0.106 ± 0.0773 to 0.195 ± 0.1317 degrees for the CI test groups. Two-way analysis of variance showed that the impression technique (P = .012) and implant angulations (P = .007) had a significant effect on dR. Distortions were mostly in the negative direction for DS test groups. Perfect coaxiality of the SB with the implant was never achieved. For SB to implant machining tolerances, the mean absolute horizontal displacement ranged from 4 ± 1.2 to 7 ± 2.3 µm. The SB dz was -5 ± 3.2 µm, which increased in the negative direction to -11 ± 4.9 µm with torque application (P = .002). CONCLUSION: Distortions were found for both DS and CI test groups. The best accuracy was obtained with CIs for parallel implants. With angulated implants, conventional and DSs were not significantly different. Excessive torque application that causes negative dz for SB fit would position the virtual implant at a deeper location compared with reality, resulting in possible framework misfit.
RESUMEN
PURPOSE: To compare the three-dimensional (3D) accuracy of conventional direct implant impressions with digital implant impressions from three intraoral scanners, as well as different implant levels-bone level (BL) and tissue level (TL). MATERIALS AND METHODS: Two-implant master models were used to simulate a threeunit implant-supported fixed dental prosthesis. Conventional test models were made with direct impression copings and polyether impressions. Scan bodies were hand-tightened onto master models and scanned with the three scanners. This was done for the TL and BL test groups, for a total of eight test groups (n = 5 each). A coordinate measuring machine measured linear distortions (dx, dy, dz), global linear distortion (dR), angular distortions (dθy, dθx), and absolute angular distortions (Absdθy, Absdθx) between the master models, test models, and .stl files of the digital scans. RESULTS: The mean dR ranged from 35 to 66 µm; mean dθy angular distortions ranged from -0.186 to 0.315 degrees; and mean dθx angular distortions ranged from -0.206 to 0.164 degrees. Two-way analysis of variance showed that the impression type had a significant effect on dx, dz, and Absdθy, and the implant level had a significant effect on dx and Absdθx (P < .05). Among the BL groups, the mean dR of the conventional group was lower than and significantly different from the digital test groups (P = .010), while among the TL groups, there was no statistically significant difference (P = .572). CONCLUSION: The 3D accuracy of implant impressions varied according to the impression technique and implant level. For BL test groups, the conventional impression group had significantly lower distortion than the digital impression groups. Among the digital test groups, the TR system had comparable mean linear and absolute angular distortions to the other two systems but exhibited the smallest standard deviations.
RESUMEN
The custom gingival mask technique duplicates the tissue contours created by an implant-supported fixed interim prosthesis, which has been verified for satisfactory esthetics, phonetics, hygiene access, and patient comfort. This allows the dental laboratory technician to accurately duplicate the contours of the interim prosthesis in the definitive prosthesis. The technique described also incorporates a cast verification step to ensure the accurate, passive fit of the definitive prosthesis while eliminating the duplicate impression copings and implant replicas typically required for a verification cast.
Asunto(s)
Técnica de Impresión Dental , Encía , Máscaras , Implantes Dentales , Materiales de Impresión Dental , Diseño de Prótesis Dental , Prótesis Dental de Soporte Implantado , HumanosRESUMEN
OBJECTIVES: The aim is to investigate the effect of modifying the liquid phase of a conventional glass ionomer restorative material with different chitosan volume contents on the antibacterial properties and adhesion to dentin. METHODS: The liquids of commercially available restorative glass ionomer cements (GIC) were modified with chitosan (CH) solutions at different volume contents (5%, 10%, 25%, and 50%). The GIC powders were mixed with the unmodified and the CH-modified liquids at the desired powder/liquid (P/L) ratio. For the characterization of the antibacterial properties, Streptococcus mutans biofilms were formed on GIC discs and characterized by scanning electron microscope (SEM), confocal microscopy, colony forming unit (CFU) count, and cell viability assay (MTS). The unmodified and CH-modified GICs were bonded to dentin surfaces and the micro-tensile bond strength (µTBs) was evaluated and the interface was investigated by SEM. RESULTS: Modification with CH solutions enhanced the antibacterial properties against S. mutans in terms of resistance to biofilm formation, CFU count, and MTS assay. Generally, significant improvement in the antibacterial properties was found with the increase in the CH volume content. Modification with 25% and 50% CH adversely affected the µTBs with predominant cohesive failure in the GIC. However, no difference was found between the control and the 5% and 10% CH-modified specimens. CONCLUSION: Incorporation of acidic solutions of chitosan in the polyacrylic acid liquid of GIC at v/v ratios of 5-10% improved the antibacterial properties of conventional glass ionomer cement against S. mutans without adversely affecting its bonding to dentin surface.