Three-dimensional design of a geometric model for an ocular prosthesis in ex vivo anophthalmic socket models

PURPOSE

Fitting a customized ocular prosthesis for anophthalmic patients entails an artisanal labour-exhausting process and is standardly based on impression moulding of the socket, which may be anatomically inaccurate. The objective of the study was to design an impression-free socket mould with three-dimensional (3D) technology.

METHODS

The ex vivo anophthalmic socket models included one silicone, one fresh pig cadaver head and three fresh-frozen human cadaver heads. After intra-socket application with iodine substance, five observers obtained eighteen low-dose cone beam computed tomography (CBCT) scans and one observer one high-dose CBCT scan of each model. The observers designed non-impression 3D moulds of the socket with 3D software. For the human cadaver sockets 3D geometric models of the ocular prosthesis were rendered from the 3D mould of the socket and the mirrored cornea of the contralateral eye.

RESULTS

The posterior surface of the 3D mould was highly accurate, with a mean absolute deviation of 0.28 mm, 0.53 mm, 0.37 mm and mean upper deviation of 0.53 mm, 0.86 mm, 1.17 mm, respectively, for the phantom, pig and human model. The intra- and interobserver repeatability and reproducibility of the 3D moulds and designs was good (<0.35 mm). The largest variation in the 3D geometric model was found at the junction of the 3D mould and mirrored cornea.

CONCLUSION

3D design of an impression-free geometric model for an ocular prosthesis with low-dose CBCT is highly accurate in ex vivo anophthalmic socket models. This novel method is a critical step towards the manufacturing of 3D printed ocular prostheses and requires validation in anophthalmic patients.

Influence of CBCT-based volumetric distortion and beam hardening artefacts on the assessment of root canal filling quality in isthmus-containing molars

OBJECTIVES

To evaluate the influence of artefacts in cone beam CT (CBCT) images of filled root canals in isthmus-containing molars.

METHODS

10 teeth presenting canals with an isthmus were instrumented and filled with a thermoplasticised obturation technique. The teeth were scanned using a micro-CT device and two CBCT devices: 3D Accuitomo 170 (ACC) and NewTom VGi evo (NT), with different acquisition protocols: larger and smaller voxel size. Three examiners assessed the CBCT images for: (1) detection of filling voids; (2) assessment of under- or overestimation of the filling material and (3) resemblance of CBCT images to the reference standard. Analyses of Task 1 yielded accuracy, sensitivity and specificity for detection of filling voids. For tasks 2 and 3, statistical analysis was performed using Wilcoxon test. The level of significance was set at p < .05.

RESULTS

For Task 1, ACC showed higher sensitivity, whereas NT presented higher specificity. No significant difference was found between the protocols in ACC, however, for NT, differences between protocols were significant for all diagnostic values. In Task 2, visualisation of the filling was overestimated for NT, while for ACC, underestimation was observed. For Task 3, images with smaller voxel size were more similar to the reference image, for both CBCT devices.

CONCLUSIONS

Different artefacts compromise the detection of filling voids on CBCT images of canals in mandibular molars with isthmus. ACC and NT present rather similar diagnostic accuracy, even though artefact expression remains device-specific.

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.

Efficacy of lead foil for reducing doses in the head and neck: a simulation study using digital intraoral systems

OBJECTIVES

To assess the efficacy of lead foils in reducing the radiation dose received by different anatomical sites of the head and neck during periapical intraoral examinations performed with digital systems.

METHODS

Images were acquired through four different manners: phosphor plate (PSP; VistaScan(®) system; Dürr Dental GmbH, Bissingen, Germany) alone, PSP plus lead foil, complementary metal oxide semiconductor (CMOS; DIGORA(®) Toto, Soredex(®), Tuusula, Finland) alone and CMOS plus lead foil. Radiation dose was measured after a full-mouth periapical series (14 radiographs) using the long-cone paralleling technique. Lithium fluoride (LiF 100) thermoluminescent dosemeters were placed in an anthropomorphic phantom at points corresponding to the tongue, thyroid, crystalline lenses, parotid glands and maxillary sinuses.

RESULTS

Dosemeter readings demonstrated the efficacy of the addition of lead foil in the intraoral digital X-ray systems provided in reducing organ doses in the selected structures, approximately 32% in the PSP system and 59% in the CMOS system.

CONCLUSIONS

The use of lead foils associated with digital X-ray sensors is an effective alternative for the protection of different anatomical sites of the head and neck during full-mouth periapical series acquisition.

Mutations in Plasmodium falciparum dihydrofolate reductase and dihydropteroate synthase of isolates from the Amazon region of Brazil

Since the late 1970s pyrimethamine-sulfadoxine (PS; FansidarTM Hoffman-LaRoche, Basel) has been used as first line therapy for uncomplicated malaria in the Amazon basin. Unfortunately, resistance has developed over the last ten years in many regions of the Amazon and PS is no longer recommended for use in Brazil. In vitro resistance to pyrimethamine and cycloguanil (the active metabolite of proguanil) is caused by specific point mutations in Plasmodium falciparum dihydrofolate reductase (DHFR), and in vitro resistance to sulfadoxine has been associated with mutations in dihydropteroate synthase (DHPS). In association with a proguanil-sulfamethoxazole clinical trial in Brazil, we performed a nested mutation-specific polymerase chain reaction to measure the prevalence of DHFR mutations at codons 50, 51, 59, 108 and 164 and DHPS mutations at codons 436, 437, 540, 581 and 613 at three sites in the Brazilian Amazon. Samples from two isolated towns showed a high degree of homogeneity, with the DHFR Arg-50/Ile-51/Asn-108 and DHPS Gly-437/Glu-540/Gly-581 mutant genotype accounting for all infections in Peixoto de Azevedo (n = 15) and 60% of infections in Apiacás (n = 10), State of Mato Grosso. The remaining infections in Apiacás differed from this predominant genotype only by the addition of the Bolivia repeat at codon 30 and the Leu-164 mutation in DHFR. By contrast, 17 samples from Porto Velho, capital city of the State of Rondônia, with much in- and out-migration, showed a wide variety of DHFR and DHPS genotypes.