Anders Thylstrup

A clinical and microbiological study of deep carious lesions during stepwise excavation using long treatment intervals.

Concern about the survival of microorganisms in deep carious lesions may often lead to unnecessary exposure of the pulp during final excavation. There are reasons, therefore, to initiate systematic studies on the alternative procedure known as stepwise excavation. Clinical evaluation of stepwise excavation was performed on 31 deep carious lesions considered to result in pulp perforation by traditional excavation. This study examines the clinical and microbiological alterations during the final excavation performed during long intervals (6-12 months) after the initial treatment that included peripheral dentine excavation and removal of the central cariogenic biomass and the superficial necrotic dentine. The dentine colour and consistency were assessed by means of standardized scales before application of a Ca(OH)2 compound and a temporary sealing for 6-12 months. Reassessments were performed before the after final excavation. Microbiological dentine samples were obtained in 19 randomly selected lesions by a sterile bur, transferred to and diluted in reduced transport fluid, and plated on tryptic soy agar. After anaerobic incubation at 37 degrees C for 7 days, total colony-forming units per millilitre were counted from (1) peripheral excavated and hard dentine (control), (2) central demineralized dentine before and final excavation, and (3) central dentine after the final excavation. Six samples of central demineralized dentine were without any cultivable flora increasing to 9 samples after the final excavation. The clinical dentine changes occurring during stepwise excavation were characterized by enhanced hardness of the dentine which was associated with a marked reduction in bacterial growth after the final excavation. Despite the presence of bacteria in the excavated dentine none of the carious lesions resulted in pulp perforation, suggesting that the initial removal of the cariogenic biomass appears to be essential for control of caries progression. Stepwise excavation is not only an appropriate treatment of deep carious lesions but is also considered a suitable model for microbiological studies to determine the bacteria persisting in clinically excavated lesions.

Light microscope study of the effect of probing in occlusal surfaces.

This study aimed at examining whether tactile examination with an explorer may produce traumatic defects in occlusal fissures. The study was carried out in 10 young male adults each of whom was due to

A Quantitative Light Microscopic Study of the Odontoblast and Subodontoblastic Reactions to Active and Arrested Enamel Caries without Cavitation

This study describes cellular and microradiographic findings in thin undemineralized enamel-dentine sections from 36 enamel caries lesions from freshly extracted third molars. Lesions activity was determined by clinical examination and the estimated age of the lesion at extraction time. The cellular reactions to the enamel/dentine lesion complex were measured using computerized histomorphometry under the following conditions: (a) the cytoplasm:nucleus ratio of the odontoblast cell; (b) the odontoblast cell:dentinal tubule ratio, and (c) the adjacent predentine area (μm2). The first cellular reactions were observed beneath superficial enamel lesions before visible alterations in dentine mineralization. The cytoplasm:nucleus ratio of the odontoblast cells was markedly reduced, and only active lesions showed evidence of cellular proliferation into the cell-free zone. In more advanced active lesions the affected odontoblast cells had a significantly lower cytoplasm:nucleus ratio compared with the controls. Similar changes were not seen in arrested or slow-progressing lesions. Before onset of tertiary dentine formation there was a positive correlation between odontoblast cell size and predentine formation. Primary odontoblast cells were involved in early tertiary or reactionary dentine formation without odontoblast cell replacement. Reactionary dentine was only seen in active lesions, suggesting that reactions in the dentine/pulp complex are closely associated with the external environment.

Development and control of caries lesions on the occlusal surface using a new in vivo caries model.

The aim of this study was to develop a new in vivo caries model for the occlusal surface and to describe the enamel features observed before and after dental plaque control (DPC). Four volunteers (12-15 years old) participated in the experiment, each of which was due to have 2 homologous first premolars extracted for orthodontic reasons. Test surfaces did not present visible signs of demineralization, opacities or fillings. A wire mesh was used to promote dental plaque accumulation on the occlusal surface. After 4 weeks, the wire mesh was removed and DPC was performed. In Groups 1 and 2, DPC was performed by the subjects daily and, in Groups 3 and 4, DPC was performed by the subjects daily and by the professional weekly. One tooth/pair of Groups 1 and 3 was extracted after 2 weeks. One tooth/pair of Groups 2 and 4 was extracted after 4 weeks. All test surfaces showed demineralization after the wire mesh was removed. The observed re-establishment of the enamel brightness was directly related to the increase of the DPC duration. In polarized light microscopy, interindividual differences varying from pseudoisotropic areas to enamel lesions were noted in specimens submitted to 2 weeks of DPC. Specimens submitted to 4 weeks of DPC showed less tissue porosity. It was concluded that the new in vivo caries model was effective since all occlusal surfaces presented clinical and microscopic signs of mineral loss in different stages after 4 weeks of cariogenic challenge. After DPC on the test surfaces, there was a reduction of mineral loss suggesting control of demineralization on these surfaces.

A comparative histologic study of the pulp-dentinal interface in undemineralized and demineralized tooth sections

This study examines cellular differences between undemineralized and demineralized tooth sections. The material comprised unerupted and partly erupted third molars. After fixation for 24 h, 10- to 15-microns ground sections were prepared from half of the tooth, using a cutting-grinding system. The sections were compared with demineralized routine sections from the other half of the tooth. Undemineralized sections showed a better capacity for preserving the tissue integration. Especially between the odontoblast layer and the predentin a low frequency of disjunctions or tears were noted. At this level of examination fixation quality and vacuole frequency (intra-cellular spaces) did not show any differences between the two methods.

A method for light microscopy examination of cellular and structural interrelations in undemineralized tooth specimens

This study examines ameloblasts and odontoblasts in relation to mineralizing enamel and dentin in thin undemineralized tooth sections from unerupted and partly erupted human third molars. The material comprised 12 freshly removed third molars. After fixation for 24 h the specimens were dehydrated and embedded in hydroxyethylmethacrylate. Undemineralized sections 10-15 microns thick were prepared with a cutting-grinding system, and radiomicrographs were taken. Postsecretory ameloblasts were seen in different morphologic stages ranging from ruffle- and smooth-ended ameloblasts to cuboidal and squamous cells adhering to incomplete and fully mineralized enamel. The former occurred in the most coronal tooth part, whereas the latter were seen cervically. It was not possible to identify systematic modulation cycles as seen in postsecretory rat incisor ameloblasts. The well-defined subodontoblastic region with cell-free and cell-rich layers was established before tooth eruption. The function of the subodontoblastic region is not fully understood, but our findings suggest that the establishment of the region plays a role in maintaining the specific odontoblast phenotype in the coronal region possibly linked to progressive dentin mineralization.

Automated image analysis applied to the odontoblast-predentine region in undemineralized sections of human permanent third molars

A computerized histomorphometric analysis was made by Karnovsky-fixed, hydroxethylmethacrylate embedded and toluidine blue/pyronin-stained sections to determine: (1) the two-dimensional size of the coronal odontoblasts given by their cytoplasm:nucleus ratio; (2) the ratio between the number of coronal odontoblasts and dentinal tubules; and (3) the relation between odontoblast size and adjacent predentine. All conditions were measured in relation to three well-defined sectioning profiles of the dentinal tubules. The sections were randomly taken from 10 unerupted and erupted third-molar crowns. Sixty-three photomicrographs (x100), equally distributed among the three sectioning profiles, were scanned in a high-resolution scanner to produce images for the analysis. After initial user interaction for the description of training classes on one image, an automatic segmentation of the images with respect to odontoblast cell nuclei, cytoplasm and background was computed by statistical discriminant analysis. In longitudinal profiles of the dentinal tubules the cytoplasm:nucleus ratio in erupted teeth was 3.1 +/- 0.54, and the mean of the odontoblast cell:dentinal tubule ration was 1.19 +/- 0.20. Analysis of cytoplasm:nucleus ratio and the adjacent predentine in relation to the chosen sectioning profiles disclosed that there was less variation in the predentine measurements in the longitudinal sections. Thus, in future two-dimensional studies of the odontoblast-predentine region only longitudinal sectioning profiles should be analysed. The use of advanced image processing on undemineralized tooth sections provides a rational foundation for further work on the reactions of the odontoblasts to external injuries including dental caries.