Influence of soft tissues on mandibular gray scale levels

Soft tissue simulant materials in X-ray-based imaging in dentomaxillofacial radiology: a scoping review

INTRODUCTION

In in-vitro dental radiographic research, simulation of soft tissue is required to replicate the clinical condition as close as possible. This study aimed to find out which soft tissue simulation material have been studied to use in dentomaxillofacial radiology and showed similarity in radiodensity to the soft tissues of the maxillofacial region.

METHODS

In this scoping review, Web of Science, Embase, Scopus, Google scholar and PubMed databases were searched on April 9, 2023, considering the following PICOS: Population: soft tissue simulants, Intervention: X-ray-based imaging, Comparison: -, Outcome: properties of the soft tissue simulants, Study design: in-vitro studies. Screening, study selection, and data extraction were performed by two independent researchers. A third team member was consulted in the case of disagreement. Quality assessment of the included studies was made using Quality Assessment Tool For In-Vitro Studies (QUIN Tool).

RESULTS

Of the initial 1172 articles retrieved in the database search, 13 studies were included in the review. Seven studies had a low risk of bias. In 8 studies, computed tomography (CT) or cone beam computed tomography (CBCT), in 4 studies intraoral radiography, and in 2 studies panoramic radiography was used (one study has used CT/CBCT and panoramic radiography). The studies varied in the radiographic modality, acquisition parameters, selected outcomes, and gold standard. In the majority of the studies (n = 10, 77%), acrylic resin derivatives were used in the soft tissue simulant formula alone or as a major component. Wax was used in the simulant material in 8 studies (62%). In addition, in 3 studies (23%) ice/water was used as the main simulant.

CONCLUSION

Ballistic gelatin, expanded 2-cm thick polystyrene with or without 1-cm utility wax, and 0.5 cm of acrylic resin were shown to have a radiographic density similar to soft tissue in standardized studies employing CBCT scanning. For intraoral radiographs, using self-polymerizing acrylic resin, utility wax, and wood, as well as a polymethylmethacrylate box filled with water in thicknesses ranging from 4 to 45 mm, provides suitable radiographic contrast. However, for 4 and 8 mm of wax and 4 mm of water, the radiographic contrast is not appropriate. In addition, 13-17 mm wax and 14.5 mm acrylic resin showed acceptable soft tissue densities in intraoral radiography. Further studies using different imaging modalities with standardized conditions and objective metrics are required to confirm the most appropriate soft tissue simulant material for in-vitro dental radiographic research.

Convenient model of hard tissue simulation for dental radiographic research and instruction

BACKGROUND

The authors describe a technique for building an alternative jawbone phantom using dental gypsum and rice for research and dental radiology instruction.

AIM

To investigate the potential of an alternative phantom to simulate the trabecular bone aspect of the human maxilla in periapical radiographs.

METHODS

Half-maxillary phantoms built from gypsum-ground rice were exposed to X-rays, and the resulting images (experimental group) were compared to standardized radiographic images produced from dry human maxillary bone (control group) (n = 7). The images were blindly assessed according to strict criteria by three examiners for the usual trabecular aspects of the surrounding bone, and significant differences between groups and in assessment reliability were compared using Fisher's exact and kappa tests (α = 0.05).

RESULTS

The differences in the trabecular aspects between groups were not statistically significant. In addition, interobserver agreement among observers was 0.43 and 0.51 for the control and experimental groups, respectively, whereas intraobserver agreement was 0.71 and 0.73, respectively.

CONCLUSION

The tested phantom seemed to demonstrate potential for trabecular bone image simulation on maxillary periapical radiographs.

Ex-vivo imaging of buccal and oral periodontal bone with low-dose CBCT in porcine jaws

OBJECTIVES

New CBCT devices have been developed which can provide "low-dose CBCTs (LD-CBCT)". Aim of this study is to investigate the suitability of LD-CBCT for measurement of alveolar buccal/oral bone.

METHODS AND MATERIALS

Vestibular and oral bone loss of the teeth of seven porcine mandibles free of soft tissues were investigated by Micro-CT and three CBCT-modes: high-dose (HD), standard-dose (SD) and low-dose (LD). Radiographic measurements of bone loss (bl) and vestibular and oral bone thickness (bt) were made by two raters at 69 sites. Measurement means and differences, Intraclass correlation (ICC) and Bland-Altman plots were calculated.

RESULTS

ICCs between raters(r) concerning bl were 0.954 for HD, 0.949 for SD and 0.945 for LD; concerning bt they were 0.872 for HD, 0.845 for SD and 0.783 for LD. Means of differences of bt measurements were -0.01 mm(r1)/0.00 mm(r2) for HD, 0.04 mm(r1)/0.02 mm(r2) for SD and 0.02 mm(r1)/0.04 mm(r2) for LD; for bl measurements they were 0.06 mm(r1)/0.05 mm(r2) for HD, -0.01 mm(r1)/0.13 mm(r2) for SD and 0.07 mm(r1)/0.16 mm(r2) for LD.Linear regression indicates no noticeable differences between methods and the raters with respect to bl and bt.

CONCLUSIONS

Relating to the CBCT-device used in this study, LD-CBCT is a promising method to detect and describe buccal and oral periodontal bl and bt. Further studies with human anatomic structures must confirm these results.

Development of a model of soft tissue simulation using ballistic gelatin for CBCT acquisitions related to dentomaxillofacial radiology research

OBJECTIVES

To present the ballistic gelatin as a new material capable of simulating the soft tissues in cone-beam CT (CBCT) images.

METHODS

CBCT images of three piglet heads were acquired with their soft tissues intact (standard group). Subsequently, the piglet heads were fixed in a container using metallic pins and moulded with acrylic resin; the soft tissues were then removed and replaced by ballistic gelatin, with the same thickness of the original soft tissues. The images were evaluated by two oral radiologists, to check the adaptation on bone surfaces, thickness and density, penetration into large bone cavities and cancellous bone, and the presence of air bubbles using a 5-score scale. Additionally, an objective analysis was carried out by one oral radiologist. For each CBCT scan, three axial reconstructions were selected to represent the mandibular, occlusal, and maxillary levels. The mean and standard deviation (SD) of the grey values were calculated in four regions of interest determined on soft tissue areas and compared by two-way ANOVA.

RESULTS

The ballistic gelatin showed subjective scores ranging from good to excellent for all parameters evaluated. There was no significant difference in the mean and SD values of the grey values between ballistic gelatin and the gold standard groups for all levels (p > 0.05). Higher SD values were observed in the occlusal level for both groups (p < 0.05).

CONCLUSIONS

Ballistic gelatin has visual and objective similarity with the gold standard. Thus, the ballistic gelatin is a promising material capable of simulating soft tissues in CBCT images.

Evaluation of different soft tissue-simulating materials in pixel intensity values in cone beam computed tomography

OBJECTIVE

This study aimed to evaluate different materials as soft tissue simulators and the influence of soft tissues in cone beam computed tomography.

STUDY DESIGN

Images of 5 piglet heads were acquired with intact soft tissues, with the tissues stripped, and with the use of different soft tissue simulators, following the same acquisition protocol. Four different materials were tested, individually or in combination: acrylic, water, utility wax, and expanded polystyrene (EPS). Pixel intensity values of 8 quadrangular regions, that is, upper and lower teeth and alveolar bone, were obtained. The mean values were used for comparison by analysis of variance (ANOVA; α = 5%).

RESULTS

No differences were observed for the "No Material," "EPS," "Acrylic," and "EPS and Wax" groups for the lower anterior and posterior teeth, the upper posterior tooth, and the anterior and posterior bone, and for the "No Material," "EPS," and "EPS and Wax," groups for the lower posterior bone. All groups showed statistical differences for the lower anterior bone and the upper anterior tooth.

CONCLUSIONS

Expanded 2-cm thick polystyrene, with or without 1-cm thick utility wax, was effective for most regions, followed by acrylic 0.5 cm. Soft tissues were not of great influence in most regions. Water was not an effective material for any of the regions.

Evaluation of soft tissues simulant materials in cone beam computed tomography

OBJECTIVES

To evaluate different materials in simulating soft tissues and to analyze the influence of these materials on the mean (MPIV) and standard deviation of pixel intensity values comparing them to a gold-standard in CBCT images.

METHODS

Images of three piglet heads with their soft tissues intact (gold-standard) and different simulant materials were acquired: ice, modelling wax, and ballistic gelatin, with the same thickness of the original soft tissues. The pixel intensities were measured in dental, bone and soft tissues regions, in the mandible and maxilla, for all the groups. Analysis of variance, Dunnet's, Pearson's and linear regression tests were performed.

RESULTS

The simulators did not significantly change the MPIV of teeth in comparison with the gold-standard (p = 0.1017). Only ice (p = 0.0156) affected the MPIV of bone. Wax (p = 0.001) and ice (p = 0.0076), but not ballistic gelatin (p = 0.5814), altered the MPIV of soft tissue regions. When assessing the influence of the location (mandible or maxilla) among the simulants, the differences were significant only for the soft tissue regions. Standard deviation was not influenced by simulants (p > 0.05), but ballistic gelatin presented the lower variability.

CONCLUSIONS

The ballistic gelatin was the best soft tissue simulant since it had the lowest influence on the pixel intensity values for all regions.

Comparison of changes in dental and bone radiographic densities in the presence of different soft-tissue simulators using pixel intensity and digital subtraction analyses

OBJECTIVES

To evaluate the influence of soft-tissue simulation materials on dental and bone tissue radiographic densities using pixel intensity (PI) and digital subtraction radiography (DSR) analyses.

METHODS

15 dry human mandibles were divided into halves. Each half was radiographed using a charge-coupled device sensor without a soft-tissue simulation material (Wm) and with 5 types of materials: acrylic (Ac), wax (Wx), water (Wt), wood (Wd) and frozen bovine tissue (Bt). Three thicknesses were tested for each material: 10 mm, 15 mm and 20 mm. The material was positioned in front of the mandible and the sensor parallel to the molar region. The radiation beam was perpendicular to the sensor at 30 cm focal spot-to-object distance. The digital images of the bone and dental tissue were captured for PI analyses. The subtracted images were marked with 14 landmark magnifications, and 2 areas of analyses were defined, forming the regions of interest. Shapiro-Wilk and Kruskal-Wallis tests followed by Dunn's post-test were used (p < 0.05).

RESULTS

DSR showed that both the material type and the thickness tested influenced the gain of density in bone tissue (p < 0.05). PI analyses of the bone region did not show these differences, except for the lower density observed in the image without soft-tissue simulation material. In the dental region, both DSR and PI showed that soft-tissue simulators did not influence the density in these regions.

CONCLUSIONS

This study showed that the materials evaluated and their thicknesses significantly influenced the density-level gain in alveolar bone. In dental tissues, there was no density-level gain with any soft-tissue material tested.

Validity of wax and acrylic as soft-tissue simulation materials used in in vitro radiographic studies

OBJECTIVE

To determine the thickness of wax and acrylic that provides a radiographic density similar to that of the human cheek.

METHODS

An intraoral film radiograph of the human cheek including a 40×30×3 mm reference aluminium block was recorded under standardized conditions in 61 subjects. Radiographic density was measured by a densitometer in ten randomly selected sites of the film to serve as the gold standard for density values of the cheek soft tissues. Thereafter, the density of series of radiographs of two tissue-simulating materials-wax and acrylic-in systematically increasing thicknesses (wax, 1.5-30 mm; acrylic, 2-40 mm) plus the reference block were measured and compared with the gold-standard values.

RESULTS

The radiographic density of wax with a thickness of 13-17 mm or acrylic with a thickness of 14.5 mm corresponded to the average density of the human cheek.

CONCLUSION

The soft tissues of the average human cheek can be simulated with 13-17 mm wax or 14.5 mm acrylic in in vitro radiographic studies.