Implant Impression Making: Take-Off Guide for Beginners

Dental implants are fixtures that constitute for the replacements of the root of a missing natural tooth. Dental implant therapy has been widely used for the restoration of partially and fully edentulous patients. The implant literature emphasizes the importance of a passively fitting prosthesis to prevent prosthodontic complications or even loss of fixture integration. Failure to achieve a passively fitting prosthesis and force tightening of superstructure may result in complications such as abutment, framework, and gold screw loosening or fracture. Various materials that can be used for making an implant impression are polyether, polyvinylsiloxane, condensation silicone, polysulfide, irreversible hydrocolloid material, and various others. There are various studies in relation to the accuracy of these impression materials out of which various scientists concluded different results with most studies stating polyether with the maximum amount of dimensional accuracy in comparison to other materials. An accurate implant impression plays a significant role and serves as a starting point in the process of producing good working casts. Thus, the accuracy of impression techniques becomes a significant issue in consideration of passive fit. Reproduction of intraoral relationship of implants through impression procedures is the first step in achieving accurate fit prosthesis. This transference is still complicated by the number, angulation, depth, and position of implants. The advent of computer-aided design/computer-assisted manufacturing technology improved the framework fabrication procedures and has increased the precision of fit of implant prosthesis.

Evaluation of misfit and stress distribution in implant-retained prosthesis obtained by different methods

This study evaluated the vertical misfit, passivity, and stress distribution after tightening the screws of different prosthesis. Two implants were used to simulate the rehabilitation of partially edentulous mandible space from the second premolar to the second molar. 40 three-element screw-retained fixed dental prosthesis with distal cantilever were fabricated and divided into four groups according to the method of production of framework (n = 10): G1 = conventional casting one-piece framework, G2 = conventional casting sectioned and laser welding, G3 = conventional casting sectioned and tungsten inert gas (TIG) welding and G4 = framework obtained by CAD/CAM (computer-aided design/computer-aided manufacturing) system. The vertical misfits (both screws tightened) and the passive fit (one screw tightened) were measured under a comparator optical microscope. The data was submitted to Shapiro-Wilk test to enable comparison with ANOVA followed by Tukey with Bonferroni adjust (α = .05). The qualitative analysis of the stress distribution was performed by the photoelastic method. The vertical misfit (both screws tightened) of the G2 (24 μm) and G3 (27 μm) were significantly higher than G4 (10 μm) (p = 0,006). The passive fit (for the non-tightened) of the G1(64 μm) and G3 (61 μm) were significantly higher than the G4 (32 μm) (p=0,009). G1 showed high stress between the implants in the photoelastic analysis and G4 presented lower stress. In conclusion, CAD/CAM method results in less vertical misfit, more passivity, and consequently better stress distribution to the bone.

DIGITAL METHOD OF COMPARATIVE EVALUATION OF THE RIGIDITY BETWEEN THE CUSTOM MADE BY THE AUTHORS IMPLANT IMPRESSION TRAYS AND STOCK IMPLANT IMPRESSION TRAYS WITH REMOVABLE PARTS

Impression taking procedure from prosthetic area in case of constructing implant supported prostheses is one of the most important steps in the process of patient rehabilitation especially in producing long span structures. Quality of the impression could affect the precision and passive fit of the prosthesis to the implants therefore the overall quality of the work. Obtaining digital impressions of edentulous jaws with a different number of implants using intraoral devices is still an unresolved problem in full. The ergonomics of the process of obtaining an impression is not easy due to the need to place both scan abutments in the oral cavity and manipulate the working part of the intraoral scanner around them. The accuracy of digital impressions obtained from edentulous jaws for obtaining full-arch implant supported prostheses does not exceed that when obtaining a classic impression, and according to a number of researchers, it is even lower. The aim of this study was to construct implant impression convertible trays with increased to the optimum levels of rigidity, with simple disassemble process and having an easy access to the adapters, and also to digitally compare the rigidity of the author’s impression trays. The method of assessment was digital technology of analysing structural resistance and inherent stresses and deformations using SolidWorks software. We performed analysis of the resistance of the structure to external loads. We have developed and created the customised copyrighted versions of the upper and lower impression trays made of rigid titanium alloy by 3D printing using DMLM technology on a Concept Laser device made of titanium Ti6-Al4-V. Modeling was carried out in the Mimics Medical 21 program (Materialize, Germany) along the contours on the data of cone-beam computed tomography. Performed digital tests reveal the underlying advantages of the designed by authors impression trays.

Can transfer type and implant angulation affect impression accuracy? A 3D in vitro evaluation

Impression accuracy is fundamental to achieve a passive fit between implants and the superstructure. Three transfer types were tested to evaluate the differences in impression accuracy and their efficiency in case of different implant angles. A master model with four implant analogues placed at 0°, 15° and 35° was used. 27 impressions were taken with three different types of impression coping: closed tray technique coping (CT), open tray technique coping (COT) and telescopic open tray coping (TOT). The impressions were poured. Analogues were matched with scan bodies to be scanned and exported in STL. An implant bar was designed from each STL and another one from the master model. A comparison between these bars was obtained. Linear and angular measurements for every type of coping were calculated for different angulations. The collected data were analyzed with ANOVA test (95% of confidence). Student’s t test showed a significative discrepancy (p ≤ 0.001) on linear and angular measurements on Δx, Δy, Δz with different transfer types as well as diverse implant positioning angles (p ≤ 0.001). Within the limitations of this study, it can be concluded that the coping type and the implants divergence may be significant parameters influencing the impression accuracy.

The Passive Fit Concept- A Review of Methods to Achieve and Evaluate in Multiple Unit Implant Supported Screw Retained Prosthesis

Obtaining the most accurate 3-dimensional location of the implant positions, facilitates the fabrication of a prosthesis that, not only conforms to the biomechanics of the rehabilitation in relation to the TM joint and surrounding musculature but also lays minimal stresses imparted onto the implant-bone interface, maximizing the longevity of any prosthetic superstructure. The passive fit concept accentuates the need for this ‘minimal-stress’ interface in order to prevent any mechanical or, biological eventualities while the prosthesis is under masticatory load in the oro-facial environment. A wide horizon of techniques have been studied and devised upon, to achieve this ‘un-eventual fit’ and also methods developed, to assess and evaluate the misfit that the prosthetic superstructure bears in relation to the implants or, the abutments into which they are screwed. This article aims to define the concept, elaborate upon the need of the same and the methods to evaluate them in a clinical and laboratory set-up.

Pilot Study of Tooth Structure Removed in Primary Molar Zirconia Crown Preparations of Typodont Teeth

Prefabricated zirconia crowns (ZRCs) require a passive fit and more reduction than stainless steel crowns (SSC). To determine the mean and maximum reduction depths in the mesial-buccal and occlusal areas for three ZRC brands and one SSC in posterior primary typodont molars and to compare reduction depths to existing literature to determine the preparation’s proximity to pulpal tissue. Four primary maxillary and mandibular typodont teeth (J and S) were prepared according to the manufacturers’ guidelines for three ZRCs and an SSC. The teeth were scanned before and after preparation with an optical scanner, and the mean and maximum depths of reduction for each tooth were calculated in triplicate with custom software and statistically compared among the types of crown. The results were compared to existing data on primary tooth enamel and dentin thickness. Maximum mesial-buccal and occlusal depth respectively of preparation for any ZRC for tooth J was 1.19 mm and 1.58 mm while for tooth S it was 1.06 and 2.07mm Both EZ Crowns and Kinder Krowns required an additional 0.5mm occlusal reduction beyond the manufacturer’s recommendation for tooth S. Ideal preparations of ZRCs require more reduction than SSCs. Both EZ Crowns and Kinder Krowns require more reduction than the manufacturer’s recommendation for a mandibular first primary molar.

Realization of a Dental Framework by 3D Printing in Material Cobalt-Chromium with Superior Precision and Fitting Accuracy

We report on the generation of a cobalt-chromium dental framework with superior precision and fitting accuracy using selective laser melting. The objective of this study is the reduction of surface roughness and the possibility to manufacture a dental framework with high precision for passive fit with attachments, in particular a round tack. After selective laser melting, the dental framework is thermally post processed at 750 °C, shot-blasted with glass and highly polished. Nominal to actual 3D form deviation is analyzed by stripe light projection, revealing deviations being less than 250 μm, i.e., warpage is as low as to permit dental application and accurate passive fit. In particular, the critical area of the dental framework, the fixture to the implant (overdenture) shows negligible deviations. This superior fitting accuracy is confirmed by joining the bar with a testing stylus.