Radiodensity evaluation of dental impression materials in comparison to tooth structures

Metal artifact reduction using common dental materials

OBJECTIVES

To determine the effect of different dental lab materials on cone beam computed tomography (CBCT) metal artifact at different resolutions.

METHODS

A total of seven common dental lab materials were molded to a dental sextant of four extracted, restored teeth. In addition to base alone (control), each material was scanned using the Carestream 9600 CBCT unit at three resolutions - 0.3 mm, 0.15 mm, and 0.075 mm - at manufacturer established exposure parameters. A single, representative axial view of each trial was evaluated for metal artifact both quantitatively by histogram analysis and qualitatively by profile plot analysis in ImageJ.

RESULTS

No statistically significant differences between the control and the dental materials were found; however, post-hoc tests showed significance between Blu-mousse^® and polyvinyl siloxane with dental materials and control, predominantly in lower resolutions.

CONCLUSIONS

The current study provides initial evidence on the influence of dental materials have on CBCT metal artifact as described by beam hardening, photon starvation, scatter, and noise, especially at lower resolutions. Blu-Mousse^® and polyvinyl siloxane reduced the perceived beam hardening and photon starvation artifact the greatest, relative to other materials, at all three resolutions and lower resolutions, respectively.

Comparison of the Accuracy of Image Registration Methods for Merging Optical Scan and Radiographic Data in Edentulous Jaws

PURPOSE

The image registration of optical scans to radiographic images is essential for performing computer-guided implant surgery. This study aimed to evaluate the effect of different image matching conditions on the accuracy of image registration for computer-guided implant surgery in completely edentulous jaws.

MATERIALS AND METHODS

The optical scan image of a completely edentulous study model was registered to the respective cone-beam computed tomography data using three different image matching conditions: small point (SP), large point (LP), and entire surface (ES). For the SP and LP groups, gutta-percha markers (1.0 and 3.0 mm in diameter) were attached to a base template, and a radiopaque impression material was relined on the intaglio surface of template in the ES group. Image registration was performed by 20 operators in the images obtained from each group at an interval of 2 weeks (n = 20 in each group), and the registration accuracy was assessed by calculating the aligned position of the edentulous arch image. One-way analysis of variance with Tukey post hoc tests was used to compare the results among the groups (α = 0.05).

RESULTS

The mean registration error was significantly larger in the SP group (0.52 ± 0.19 mm) than in the LP group (0.29 ± 0.08 mm) and ES group (0.27 ±0.06 mm) (F = 24.689, p < 0.001). No difference was found between the LP and ES groups. The image matching discrepancy was more homogeneously distributed on the arch in the ES group than in the other groups.

CONCLUSION

The accuracy of image registration is affected by the size of the congruent area shown in the optical scan and radiographic images. The entire surface-based matching method is more accurate as compared to the small point-based matching method in the image registration for implant planning in full edentulous jaws.

Accuracy of cone beam computed tomography in measuring thicknesses of hard-tissue-mimicking material adjacent to different implant thread surfaces

Background/purpose

To evaluate the measurement accuracy of hard-tissue thicknesses adjacent to dental implants with different thread designs on images obtained from cone beam computed tomography (CBCT) using an in vitro model.

Materials and methods

On 4 × 13-mm implant, the neck of the implant was designed with micro-threads, and the apical part was covered by macro-threads; these implants were placed in a vinyl polysiloxane block that mimicked hard-tissue. Models were prepared with various thicknesses of 2.0, 1.0, 0.5 and 0.3 mm adjacent to the dental implant. Each model was scanned using CBCT, and the thickness of the cortical bone from the outer surface of the micro-threads and macro-threads were recorded. Ground sections were prepared, and the thickness was measured with electronic calipers as the gold standard (GS) measurement.

Results

CBCT measurements of the micro-thread surface were consistently underestimated compared to the GS measurement when the thickness of the hard-tissue-mimicking material was ≤1.0 mm. In comparison, CBCT measurements of the macro-thread surface closely approximated the standard measurement, except when the thickness of the hard-tissue-mimicking material was 0.3 mm. The mean percentage errors from the standard measurement for the 2.0-, 1.0-, 0.5-, and 0.3-mm thickness groups were 4.8%, 16.4%, 37.8%, and 92.6%, respectively, for the micro-thread group, and were 0.6%, 2.9%, 9.5%, and 40.8%, respectively, for the macro-thread group.

Conclusion

Within the limitations of this study, we conclude that CBCT may not produce sufficient resolution for thin sections of hard tissue-mimicking materials adjacent to micro-thread surfaces.

Alginate Materials and Dental Impression Technique: A Current State of the Art and Application to Dental Practice

Hydrocolloids were the first elastic materials to be used in the dental field. Elastic impression materials include reversible (agar-agar), irreversible (alginate) hydrocolloids and synthetic elastomers (polysulfides, polyethers, silicones). They reproduce an imprint faithfully, providing details of a high definition despite the presence of undercuts. With the removal of the impression, being particularly rich in water, the imprints can deform but later adapt to the original shape due to the elastic properties they possess. The advantages of using alginate include the low cost, a better tolerability on the part of the patient, the ease of manipulation, the short time needed for execution, the instrumentation and the very simple execution technique and possibility of detecting a detailed impression (even in the presence of undercuts) in a single step. A comprehensive review of the current literature was conducted according to the PRISMA guidelines by accessing the NCBI PubMed database. Authors conducted a search of articles in written in English published from 2008 to 2018. All the relevant studies were included in the search with respect to the characteristics and evolution of new marine derived materials. Much progress has been made in the search for new marine derived materials. Conventional impression materials are different, and especially with the advent of digital technology, they have been suffering from a decline in research attention over the last few years. However, this type of impression material, alginates (derived from marine algae), have the advantage of being among the most used in the dental medical field.

Comparing the Accuracy of Three Different Impression Materials in Making Duplicate Dies

BACKGROUND

Marginal adaptation is very important in cast restorations. Maladaptation leads to plaque retention, reduction of mechanical and esthetic properties. The aim of this study was to evaluate the precision of three different impression materials (including: Additional silicone [AS] and condensational silicone [CS] and polyether [PE]) for duplicating master dies.

MATERIALS AND METHODS

Three master dies from an acrylic tooth model-with supragingival and shoulder finishing line was made by using PE: Impergum, CS: Speedex, and AS: Panasil separately. The Ni-Cr copings were prepared from master dies separately. They were placed on the acrylic model and the mean marginal difference was recorded by using a stereomicroscope. Then 30 duplicate test dies were made by using the same impression materials and the marginal gaps were recorded. The comparison was done by one-way ANOVA and SPSS software (Version 13) at a significant level of 0.05.

RESULTS

The mean marginal difference of four walls from Impergum (38.56 um) was the lowest than Speedex (38.92 um) and Panasil (38.24 um). The Impergum had the highest capability in making duplicate dies (P > 0.05).

CONCLUSION

The Impergum impression material manifested the highest capability in making a better marginal adaptation of duplicate dies but further studies are needed to make a precise decision.

Impression Material Mass Retained in the Mucobuccal Fold

Trapped foreign bodies and tissue reactions to foreign materials are commonly encountered in the oral cavity. Traumatically introduced dental materials, instruments, or needles are the most common materials referred to in the dental literature. This paper describes an iatrogenic foreign body encapsulation in the oral mucosa, clinically appearing as5×10 mm tumor-like swelling with an intact overlying epithelium and diagnosed as a polymeric impression material. Detailed case history and, clinical and radiographic examinations including CBCT and spectrometric analysis of the retrieved sample were necessary to determine accurately the nature, size, and location of the foreign body. It is suggested that the origin of the material relates to an impression made 2 years ago, leaving a mass trapped in a traumatized mucosal tissue.