Segmentation Methods for Micro CT Images: A Comparative Study Using Human Bone Samples.

X-ray microtomography (microCT) is a nondestructive technique used to assess bone morphometry. For an accurate analysis, it is necessary to segment the bone tissue from the background images, avoiding under- or overestimation of the real bone volume. Thus, segmentation methods for microCT can influence the accuracy of bone morphometry analysis. The purpose of this study was to compare two different image segmentation methods available on microCT software (subjective and objective) regarding to the human bone morphometric analysis. Sixteen samples containing a fixation screws covered by 0.5-1mm of bone were scanned using the SkyScan 1173 scanner. Three examiners segmented the microCT images subjectively and recorded the threshold values. Subsequently, an objective segmentation was also done. The 3D analysis was performed for both images using the values​ previously determined in CTAn software. Five bone morphometric parameters were calculated (BV/TV, Tb.Th, Tb.N, Tb.Sp, Conn.Den) and used as dependent variables. ANOVA showed no significant differences between the methods concerning BV/TV (p=0.424), Tb.N (p=0.672), Tb.Th (p=0.183), Tb.Sp (p=0.973) and Conn.Den (p=0.204). Intra- and interobserver agreement ranged from satisfactory to excellent (0.55-1 and 0.546-0.991, respectively). Therefore, results obtained with subjective threshorlding were similar to those obtained with objective segmentation. Since objective segmentation does not have human input and it is a truly objective method, it should be the first choice in microCT studies that concern homogeneity and high resolution human bone sample.

Segmentation methods for micro ct images: a comparative study using human bone samples

Abstract X-ray microtomography (microCT) is a nondestructive technique used to assess bone morphometry. For an accurate analysis, it is necessary to segment the bone tissue from the background images, avoiding under- or overestimation of the real bone volume. Thus, segmentation methods for microCT can influence the accuracy of bone morphometry analysis. The purpose of this study was to compare two different image segmentation methods available on microCT software (subjective and objective) regarding to the human bone morphometric analysis. Sixteen samples containing a fixation screws covered by 0.5-1mm of bone were scanned using the SkyScan 1173 scanner. Three examiners segmented the microCT images subjectively and recorded the threshold values. Subsequently, an objective segmentation was also done. The 3D analysis was performed for both images using the values​ previously determined in CTAn software. Five bone morphometric parameters were calculated (BV/TV, Tb.Th, Tb.N, Tb.Sp, Conn.Den) and used as dependent variables. ANOVA showed no significant differences between the methods concerning BV/TV (p=0.424), Tb.N (p=0.672), Tb.Th (p=0.183), Tb.Sp (p=0.973) and Conn.Den (p=0.204). Intra- and interobserver agreement ranged from satisfactory to excellent (0.55-1 and 0.546-0.991, respectively). Therefore, results obtained with subjective threshorlding were similar to those obtained with objective segmentation. Since objective segmentation does not have human input and it is a truly objective method, it should be the first choice in microCT studies that concern homogeneity and high resolution human bone sample.

Resumo A microtomografia computadorizada (microTC) é uma modalidade de imagem não destrutiva utilizada para avaliar a morfometria óssea. Para análise acurada, faz-se necessário segmentar o tecido ósseo do fundo (background) da imagem, evitando assim, sub ou sobre estimação do volume ósseo real. Desta forma, fica evidente que os métodos de segmentação em análise de microTC podem influenciar a precisão dos cálculos da morfometria óssea. A realização do presente estudo teve como objetivo comparar o desempenho de dois diferentes métodos de segmentação de imagem de microTC, subjetivo e objetivo, através da avaliação dos resultados das análises morfométricas obtidas de ossos humanos. Dezesseis amostras contendo parafusos de fixação cobertos por 0,5- 1 mm de osso humano foram escaneados usando o microtomógrafo SkyScan1173. Três examinadores realizaram a segmentação das imagens de forma subjetiva (visualmente) obtendo seus respectivos valores de threshold. Em seguida, a segmentação objetiva (automática) foi realizada. As análises tridimensionais foram obtidas utilizando os valores determinados por ambos os métodos no software CTAn. Cinco parâmetros morfométricos do osso foram calculados (BV / TV, Tb.Th, Tb.N, Tb.Sp, Conn.Den) e usados ​​como variáveis ​​dependentes. O teste ANOVA não mostrou diferenças estatisticamente significantes entre os métodos comparados: BV / TV (p=0,424), Tb.N (p=0,672), Tb.Th (p=0,183), Tb.Sp (p=0 973) e Conn.den (p=0,204). A concordância intra e interobservardores variou entre satisfatória e excelente (0,55-1 e 0,546-0,991, respectivamente). Portanto, os resultados obtidos com a segmentação subjetiva foram semelhantes aos obtidos com a automática. Entretanto, a segmentação automática dispensa intervenção humana, sendo um método verdadeiramente objetivo e deve ser a primeira escolha em estudos microTC que objetivam avaliar a morfometria óssea humana.

MicroCT assessment of bone microarchitecture in implant sites reconstructed with autogenous and xenogenous grafts: a pilot study.

PURPOSE: To assess bone microarchitecture in maxillary sites grafted with autogenous or xenogenous grafts as well as to demonstrate the usefulness of microCT in dental implant research. MATERIALS AND METHODS: Samples (n = 12) consisting of titanium fixation screws covered by at least 0.5-1 mm of human bone were obtained from 17 sites grafted with autogenous or xenogenous materials and prepared for microCT scanning and conventional histology. Bone histomorphometric parameters were evaluated in three distinct regions (graft region, transitional region, and native bone region). Three-dimensional (3D) bone-to-implant contact (BIC) calculation was performed using microCT data. Histological sections were used to calculate two-dimensional (2D) BIC percentages, which were compared with values obtained from 2D microCT images. RESULTS: Histomorphometric parameters varied according to the type of graft used, but sites reconstructed with autogenous bone showed higher mean values in general. In autograft samples, indices for parameters such as Tb.Th and Tb.Sp were significantly different when the native bone region was compared to the graft region. While a higher mean 3D BIC was found in the native bone region for both graft materials, significant BIC differences were absent when graft types were compared. The 2D BIC percentages obtained from histological and microCT images were similar. CONCLUSIONS: Autografts outperformed the xenogenous material used in this study concerning the histomorphometric parameters assessed. While graft type did not seem to influence 3D BIC, the native bone region showed the highest BIC percentages when compared to the other regions in both graft groups. In addition, 2D BIC ratios were similar regardless of graft material or image source (histological sections x microCT slices). Taken together, our findings suggest that microCT is an effective tool for 2D and 3D histomorphometric and BIC assessments in dental implant research.

Dental wear estimation using a digital intra-oral optical scanner and an automated 3D computer vision method.

The objective of this work was to propose an automated and direct process to grade tooth wear intra-orally. Eight extracted teeth were etched with acid for different times to produce wear and scanned with an intra-oral optical scanner. Computer vision algorithms were used for alignment and comparison among models. Wear volume was estimated and visual scoring was achieved to determine reliability. Results demonstrated that it is possible to directly detect submillimeter differences in teeth surfaces with an automated method with results similar to those obtained by direct visual inspection. The investigated method proved to be reliable for comparison of measurements over time.

Peri-implant bone innervation: histological findings in humans.

PURPOSE: The aim of the present study was to describe nerve fibres around osseointegrated implants in humans. MATERIALS AND METHODS: Twelve mechanically failed implants, retrieved from 10 patients were collected from three dental centres over a period of 5 years. After implant removal, decalcified semi-thin sections (0.5 µm) were stained with thionic methylene blue for light microscopic analysis. In addition, an ultrastructural analysis was performed on serial ultra-thin sections (0.06 µm) using transmission electron microscopy. RESULTS: Both myelinated and unmyelinated nerve fibres could be identified inside the Haversian canals of the osteonal bone near the implant threads. Myelinated fibres were also located at the woven bone around the implant. However, no differentiated nerve endings could be observed around the implants. CONCLUSIONS: This study shows the presence of nerve fibres in human peri-implant bone. Previous studies in animals showed that those fibres participate in the process of bone modelling and remodelling. Yet, the role of peri-implant bone innervation in the osseoperception phenomenon cannot be ruled out since the mechanism of mechanoreception in bone is not fully understood.

Aplicabilidade dos enxertos em bloco de origem xenógena nas reconstruções ósseas: relato de caso clínico com avaliação tomográfica e histológica após seis meses / Applicability of xenogenous onlay grafts in bone reconstruction: case report with tomographic and histologic evaluation after six months

O osso autógeno é considerado padrão-ouro para reconstrução óssea em bloco e sustentação dos implantes dentários, mas limitações na disponibilidade e aumento na morbidade são associados a este material. Assim, o osso xenógeno em bloco vem sendo abordado como um substituto viável ao osso autógeno nos casos de recontorno vestibular do rebordo ósseo. Este caso clínico demonstrou a técnica de utilização deste material. Uma paciente de 52 anos de idade e com deficiência estética significativa na região anterior superior recebeu enxerto sintético em bloco fixado com parafusos apropriados. Após seis meses, quatro implantes foram instalados e permitida a osseointegração por mais seis meses. Tomografias computadorizadas foram realizadas antes (T0), após a cirurgia de enxertia do bloco (T1), e após o tempo de consolidação (T2), com as mudanças nos contornos volumétricos sendo comparadas em programa apropriado. Análises histológicas também foram realizadas ao redor do osso do parafuso removido. A estabilidade volumétrica do material foi considerada compatível com a literatura publicada após seis meses. Houve neoformação óssea ao redor do enxerto xenógeno com atividade de remodelação óssea.

Autogenous bone is considered the gold standard material for bone block reconstruction and dental implant supporting, but limited availability and morbidity are associated to this material. Thus, exogenous block substitutes have been studied for such bone augmentation. This case report describes the potential application of this material. A 52 years-old patient with significant deficit at the anterior region received a synthetic block secured with appropriate screws. Six months later, four dental implants were placed and osseointegration allowed for more six months. CBCT scans were performed at baseline (T0), after block grafting (T1), and after consolidation phase (T2). Volumetric changes were compared in the recommended software. Histological analyses were performed around the retrieved screws. The volumetric stability of this material after six months was considered compatible with the already published literature. Bone neoformation was seen around the xenograft with associated bone remodeling

Histomorphological study of myelinated nerve fibres in the periodontal ligament of human canine.

OBJECTIVE: This study aims to describe the human periodontal ligament (PDL) using serial sections, with a focus on mechanoreceptor distribution and morphology. MATERIALS AND METHODS: One permanent lower canine with surrounding PDL and alveolar bone tissues was retrieved from a human cadaver. After being embedded into paraffin block, the canine was horizontally cut in 6 µm thick serial sections. At root levels of 0.3, 1.5, 3, 4.5 and 6 mm from the apex, five slices each level were evaluated. Immunocytochemisty was performed on the same serial sections, enabling a more reliable description of neural structures. RESULTS: The distribution of myelinated fibres varied from apical to coronal level, with a total number of 38 at 0.3 mm from the apex, 25 at 1.5 mm, 25 at 3 mm, 31 at 4.5 mm and 32 at 6 mm. At all times, mesial and buccal regions were typically more densely innervated (p < 0.01) except at the 3 mm level. The average density of myelinated nerve fibres increased by arriving closer to the apex. However, the average diameter did not show any significant differences amongst quadrants or root levels (p > 0.05). The average diameter of myelinated fibres varied between 5.3-7.8 µm. Grouped myelinated axons were twice as common as isolated ones, with the innervation being rather close to the alveolar bone. Isolated myelinated axons showed a tendency to group around large blood vessels. CONCLUSION: The present results add to the understanding of human PDL innervation, indicating dense innervations by myelinated nerve fibres in close proximity to collagen fibres and alveolar bone. It also reveals that apical as well as mesial and buccal sites of the human canine are more densely innervated.

A comprehensive in vitro study of image accuracy and quality for periodontal diagnosis. Part 1: the influence of X-ray generator on periodontal measurements using conventional and digital receptors.

The aim of this study was the determination of image accuracy and quality for periodontal diagnosis using various X-ray generators with conventional and digital radiographs. Thirty-one in vitro periodontal defects were evaluated on intraoral conventional (E-, F/E-speed) and digital images (three indirect, two direct sensors). Standardised radiographs were made with an alternating current (AC), a high-frequency (HF) and a direct current (DC) X-ray unit at rising exposure times (20-160 ms with 20-ms interval) with a constant kV of 70. Three observers assessed bone levels for comparison to the gold standard. Lamina dura, contrast, trabecularisation, crater and furcation involvements were evaluated. Irrespective X-ray generator-type, measurement deviations increased at higher exposure times for solid-state, but decreased for photostimulable storage phosphor (PSP) systems. Accuracy for HF or DC was significantly higher than AC (p < 0.0001), especially at low exposure times. At 0.5- to 1-mm clinical deviation, 27-53% and 32-55% dose savings were demonstrated when using HF or DC generators compared to AC, but only for PSP. No savings were found for solid-state sensors, indicating their higher sensitivity. The use of digital sensors compared to film allowed 15-90% dose savings using the AC tube, whilst solid-state sensors allowed approximately 50% savings compared to PSP, depending on tube type and threshold level.. Accuracy of periodontal diagnosis increases when using HF or DC generators and/or digital receptors with adequate diagnostic information at lower exposure times.

Peri-implant bone tissue assessment by comparing the outcome of intra-oral radiograph and cone beam computed tomography analyses to the histological standard.

OBJECTIVES: The present study aims to identify radiographic methods revealing data that are most representative for the true peri-implant bone as assessed by histology. MATERIALS AND METHODS: Eighty implants were placed in 10 minipigs. To assess matching between different image modalities, measurements conducted on intra-oral digital radiographs (IO), cone beam computer tomography (CBCT) and histological images were correlated using Spearman's correlation. Paired tests (Wilcoxon test) were used to determine changes in the bone parameters after 2 and 3 months of healing. RESULTS: Significant correlations between bone defect depth on IO and histological slices (r= + 0.7, P<0.01), as well as on CBCT images and histological slices (r= + 0.61, P<0.01), were found. CBCT and IO images deviate, respectively, 1.20 and 1.17 mm from the histology regarding bone defects. No significant correlations were detected between fractal analysis on CBCT, intra-oral radiography and histology. For bone density assessment, significant but weaker correlations (r= + 0.5, P<0.01) were found for intra-oral radiography vs. histology. Significant marginal bone-level changes could be observed after 3 months of healing using intra-oral radiography. CONCLUSIONS: This study allowed linking radiographic bone defect depth to the histological observations of the peri-implant bone. Minute bone changes during a short-term period can be followed up using digital intra-oral radiography. Radiographic fractal analysis did not seem to match histological fractal analysis. CBCT was not found to be reliable for bone density measures, but might hold potential with regard to the structural analysis of the trabecular bone.

Proliferation of epithelial rests of Malassez following auto-transplantation of third molars: a case report.

INTRODUCTION: Auto-transplantation of third molars is frequently undertaken in order to restore a perfect occlusion and to improve mastication following a substantial loss of molars. However, little is known about the precise role of the periodontal membrane during this procedure. Therefore, we investigated if the epithelial rests of Malassez persist in the periodontal ligament of auto-transplanted teeth and, if so, whether these may show signs of a neuro-epithelial relationship. CASE PRESENTATION: We report a case of a 21-year-old Caucasian woman who underwent an auto-transplantation of two third molars. After two years, renewed progressive caries of the auto-transplanted teeth led to the removal of the auto-transplanted elements. The periodontal ligament was removed and studied with a light and transmission electron microscope. CONCLUSION: In this report we examined the ultrastructure of the periodontal ligament after auto-transplantation in order to see if the periodontal ligament recovers completely from this intervention. We observed fully developed blood vessels and a re-innervation of the epithelial rests of Malassez which were proliferating following auto-transplantation. This proliferation might be critical in the remodelling of the alveolar socket in order to provide a perfect fit for the transplanted tooth. In order to minimalise the damage to the epithelial rests of Malassez, the extraction of the tooth should be as atraumatic as possible in order to provide an optimal conservation of the periodontal ligament which will be beneficial to the healing-process.

Histological, histomorphometrical, and radiological evaluation of an experimental implant design with a high insertion torque.

OBJECTIVES: The aim of this study was to compare bone behaviour around an experimental implant design with a high insertion torque with the Astra-Tech implant (control). MATERIALS AND METHODS: In ten 18-month-old male minipigs, the last premolars and first molars were extracted to provide space for two implants in each quadrant. A first set of 40 implants were placed 3 months after the extraction and 40 additional implants were installed another 2 months later. The animals were sacrificed 3 months after the first implant installation so that half of the implants had healed for 1 month and the other half for 3 months. Radiological evaluation was performed at baseline, 1 month, 2 months, and 3 months after implant installation. Bone defect depth and area, bone level changes, bone-to-implant contact density, and peri-implant bone fraction were measured histomorphometrically. RESULTS: Radiological analyses revealed a significantly higher bone loss around the experimental implants. Histomorphometric analyses confirmed significantly more bone loss, larger marginal bone defects, and a lower overall peri-implant bone fraction around the experimental implants. CONCLUSION: The experimental implant design caused significantly more peri-implant bone loss compared with the control implant. As strain gauge measurements indicate excessive marginal strains around the experimental implants, osseocompression might have played a role in the observed marginal bone loss.

A comparative evaluation of Cone Beam Computed Tomography (CBCT) and Multi-Slice CT (MSCT) Part I. On subjective image quality.

AIMS: To compare image quality and visibility of anatomical structures in the mandible between five Cone Beam Computed Tomography (CBCT) scanners and one Multi-Slice CT (MSCT) system. MATERIALS AND METHODS: One dry mandible was scanned with five CBCT scanners (Accuitomo 3D, i-CAT, NewTom 3G, Galileos, Scanora 3D) and one MSCT system (Somatom Sensation 16) using 13 different scan protocols. Visibility of 11 anatomical structures and overall image noise were compared between CBCT and MSCT. Five independent observers reviewed the CBCT and the MSCT images in the three orthographic planes (axial, sagittal and coronal) and assessed image quality on a five-point scale. RESULTS: Significant differences were found in the visibility of the different anatomical structures and image noise level between MSCT and CBCT and among the five CBCT systems (p=0.0001). Delicate structures such as trabecular bone and periodontal ligament were significantly less visible and more variable among the systems in comparison with other anatomical structures (p=0.0001). Visibility of relatively large structures such as mandibular canal and mental foramen was satisfactory for all devices. The Accuitomo system was superior to MSCT and all other CBCT systems in depicting anatomical structures while MSCT was superior to all other CBCT systems in terms of reduced image noise. CONCLUSIONS: CBCT image quality is comparable or even superior to MSCT even though some variability exists among the different CBCT systems in depicting delicate structures. Considering the low radiation dose and high-resolution imaging, CBCT could be beneficial for dentomaxillofacial radiology.

The influence of gender and bruxism on human minimum interdental threshold ability

OBJECTIVE: To evaluate the influence of gender and bruxism on the ability to discriminate minimum interdental threshold. MATERIAL AND METHODS: One hundred and fifteen individuals, representing both genders, bruxers and non-bruxers, with a mean age of 23.64 years, were selected for this study. For group allocation, every individual was subjected to a specific physical examination to detect bruxism (performed by three different examiners). Evaluation of the ability to discriminate minimum interdental threshold was performed using industrialized 0.010 mm-, 0.024 mm-, 0.030 mm-, 0.050 mm-, 0.080 mm- and 0.094 mm-thick aluminum foils that were placed between upper and lower premolars. Data were analyzed statistically by multiple linear regression analysis at 5% significance level. RESULTS: Neither gender nor bruxism influenced the ability to discriminate minimum interdental threshold (p>0.05). CONCLUSIONS: Gender and the presence of bruxism do not play a role in the minimum interdental threshold.

The influence of gender and bruxism on human minimum interdental threshold ability.

OBJECTIVE: To evaluate the influence of gender and bruxism on the ability to discriminate minimum interdental threshold. MATERIAL AND METHODS: One hundred and fifteen individuals, representing both genders, bruxers and non-bruxers, with a mean age of 23.64 years, were selected for this study. For group allocation, every individual was subjected to a specific physical examination to detect bruxism (performed by three different examiners). Evaluation of the ability to discriminate minimum interdental threshold was performed using industrialized 0.010 mm-, 0.024 mm-, 0.030 mm-, 0.050 mm-, 0.080 mm- and 0.094 mm-thick aluminum foils that were placed between upper and lower premolars. Data were analyzed statistically by multiple linear regression analysis at 5% significance level. RESULTS: Neither gender nor bruxism influenced the ability to discriminate minimum interdental threshold (p>0.05). CONCLUSIONS: Gender and the presence of bruxism do not play a role in the minimum interdental threshold.

Apnéia e ronco tratados com placa oclusais / Apnoea and snoring trearted by using occlusal plates

Apnéia obstrutiva do sono é uma síndrome definida por paradas reptidas e temporárias da respiração durante o sono. Este distúrbio freqüentemente está associado a roncos. O ronco é simplismente a tradução sonora que indica diminuição ou estreitamento da via aérea durante a passagem do ar. Se o referido estreitamento torna-se severo acarreta o colapso da via aérea, resultando na apnéia obstrutiva do sono. O presente trabalho propõe um tratamento da Síndrome da Apnéia Obstrutiva do Sono (SAOS) com o uso de uma placa intra-oral que ajude o paciente a manter a dimensão vertical aumentada e a mandíbula protruída e, desta maneira, prevenir ou minimizar a obstrição das vias aéreas durante o sono, diminuindo assim o ronco. Os autores apresentam vários aspectos importantes para a confecção de uma placa para apnéia, sendo este dispositivo de baixo custo, fácil confecção, grande aceitabilidade e confortável para os pacientes