Jörgen G. Norén

The prevalence of demarcated opacities in permanent first molars in a group of Swedish children

The permanent teeth of 516 7- and 8-year-old Swedish children from a low-fluoride area were examined for developmental enamel defects. Special attention was paid to demarcated opacities in permanent first molars and permanent incisors (MIH). The examination was done in their schools, using a portable light, a mirror, and a probe. The modified DDE index of 1992 was used for recording the enamel defects, supplemented with a further classification into severe, moderate, and mild defects. Demarcated opacities in permanent first molars were present in 18.4% of the children. The mean number of hypomineralized teeth of the affected children was 3.2 (standard deviation, 1.8), of which 2.4 were first molars. Of the children 6.5% had severe defects, 5% had moderate defects, whereas 7% had only mildly hypomineralized teeth. In conclusion, hypomineralized first molars appeared to be common and require considerable treatment in the Swedish child population.

Incidence of pulp necrosis subsequent to pulp canal obliteration from trauma of permanent incisors.

Little long-term data are available on the frequency by which pulp canal obliteration (PCO) subsequent to trauma leads to pulp necrosis (PN). In this study, 82 concussed, subluxated, extruded, laterally luxated, and intruded permanent incisors presenting with PCO were followed for a period of 7 to 22 yr (mean 16 yr). At final clinical examination, 51% of the observed teeth responded normally to electric pulp testing (EPT). An additional 40% of the teeth although not responding to EPT were clinically and radiographically within normal limits. Yellow discoloration was a frequent finding. During the observation period, periapical bone lesions suggesting PN developed in seven teeth (8.5%). Twenty-yr pulp survival rate was 84%, as determined from life-table calculations. There was no higher frequency of PN in obliterated teeth subjected to caries, new trauma, orthodontic treatment, or complete crown coverage than intact teeth. Although the incidence of PN in teeth displaying PCO seems to increase over the course of time, prophylactic endodontic intervention on a routine basis does not seem justified.

Bacterial invasion of dentinal tubules beneath apparently intact but hypomineralized enamel in molar teeth with molar incisor hypomineralization

BACKGROUND The most common problems for a patient with molar incisor hypomineralization (MIH) are the collapse of enamel and cavitations, loss of fillings, and secondary caries, but most of all, severe hypersensitivity. OBJECTIVE The aim of this paper was therefore to histologically study possible bacterial invasion of dentinal tubules beneath apparently intact, but hypomineralized enamel in permanent molars with MIH. MATERIAL AND METHODS Five extracted permanent first molars diagnosed with MIH were fixated, demineralized, and sagittally serially sectioned in a bucco-lingual direction in a microtome with a thickness of 4-5 microm. Sections were stained with a modified Brown and Benn staining for bacteria, unstained sections were analysed in field emission SEM. RESULTS Stained sections from the cuspal areas, below the hypomineralized enamel, the staining indicated the presence of bacteria in the dentinal tubules. The HTX staining showed that the pulp in sections without any findings was normal and free from bacteria or infiltrates from inflammatory cells. In sections where bacteria were found in the cuspal areas or deeper in the dentin, a zone of reparative dentin was found, and in sections from one tooth, the coronal pulp showed an inflammatory reaction with inflammatory cells. In sections adjacent to those without any bacterial staining, the SEM analyses revealed empty dentinal tubules without any odontoblast processes or signs of bacteria. When odontoblast processes were found, the dentinal tubules were filled with bacteria located on the surface of the odontoblast processes. In some areas, a large number of tubules were found with bacteria. No bacteria were found close to the pulp. The odontoblast processes appeared larger in areas where bacteria were found. CONCLUSIONS The presence of bacteria in the dentinal tubules and inflammatory reactions in the pulp indicate that oral bacteria may penetrate through the hypomineralized enamel into the dentin, thus possibly contribute to hypersensitivity of teeth with MIH.

Chemical, mechanical and morphological properties of hypomineralized enamel of permanent first molars

Abstract Objective. The microstructure of hypomineralized enamel in permanent teeth has been described in several studies as less distinct prism sheaths and disorganized enamel with lack of organization of the enamel crystals. The mechanical properties, hardness and modulus of elasticity of the hypomineralized enamel have lower values compared with normal. The aim of this study was to examine normal and hypomineralized enamel using scanning electron microscopy (SEM), hardness measurements and X-ray microanalysis (XRMA). Material and methods. Four extracted hypomineralized permanent first molars, sectioned and cut in half, were analyzed with SEM, XRMA and hardness measurements. Results. An inverse relation was found between the micro hardness and the Ca:C ratio in hypomineralized and normal enamel. The acid-etched hypomineralized enamel appeared on SEM to be covered with a structureless layer and the prisms appeared disorganized, with thick prism sheaths and loosely packed crystallites. Furthermore, bacteria were found deep in porous hypomineralized enamel close to the enamel–dentin junction. Conclusions. Teeth diagnosed with molar incisor hypomineralization have significantly lower hardness values in the hypomineralized enamel compared with normal enamel. The hardness values vary according to the morphological and chemical properties.

Enamel Structure in Deciduous Teeth from Low-Birth-Weight Infants

Ground sections of deciduous teeth from 64 infants with birth weights below 2000 g and from 43 healthy full-term infants were examined in polarized light and by microradiography. The deciduous enamel displayed various changes, which were more frequent and pronounced in the low-birth-weight group. The main findings were diffuse areas of increased porosity and distinct subsurface lesions in the postnatal enamel. Five teeth with enamel hypoplasia from the low-birth-weight group were also examined. The hypoplasias were all located along the neonatal line. The postnatal enamel seemed to be more susceptible to disturbances in the mineralization than the prenatal enamel. The subsurface lesions showed an arrest in the very late stages of enamel maturation, which frequently occurred in the cervical deciduous enamel. Enamel hypoplasia is considered to be a result of severe neonatal hypocalcemia.

Neonatal lines in the enamel of primary teeth—A morphological and scanning electron microscopic investigation

OBJECTIVE The neonatal line (NNL) is in principle found in all primary teeth and the line represents the time of birth. Earlier findings of the appearance of the NNL in light microscope and in microradiographs have shown not only changes in the prism direction of the enamel, but that the NNL has a hypomineralized character. METHODS The neonatal line was analyzed in un-decalcified sections of primary lower and central incisors, collected from individuals of different ages utilizing polarized light microscopy, microradiography, scanning electron microscopy (SEM) and X-ray analysis (XRMA). RESULTS In polarized light the NNL appeared to have a more porous structure than the enamel in general. The appearance of the NNL as a dark line in microradiographs is interpreted as the NNL being less mineralized than neighbouring enamel. Analysis with ImageJ visualized the reduction of the amount of grey value, indicating that the NNL is less mineralized. Analysis of the NNL in SEM showed a reduction of the diameter of enamel prisms, the more narrow diameters continued through the postnatal enamel. A change of the growth direction of the prisms was also observed at the NNL. In a three-dimensional image the NNL appeared as a grove, however, in non-etched enamel no grove was seen. The elemental analyses with XRMA showed no marked changes in the content of C, Ca, P, N, O or S in the area around the NNL. CONCLUSIONS The NNL is an optical phenomenon due to alterations in height, and degree of mineralization of the enamel prisms.

Microorganisms on toothbrushes at day-care centers

The microflora on 44 toothbrushes at 4 day-care centers in the city of Göteborg have been investigated as a presumptive risk factor for transmission of microorganisms by children. Non-supervised toothbrushing without the use of toothpaste was performed at the day-care centers twice a day. Streptococci, predominantly S. salivarius, S. sanguis, and S. mitis, were the most frequently recorded group of microorganisms and generally constituted the greatest part of the flora (on average, 50%). Beta-hemolytic streptococci were not found in any sample. Haemophilus species were noted in 82% of the samples. H. parainfluenzae being the most frequent, and H. influenzae being identified in only one sample. Anaerobes constituted on average a third of the microflora. Staphylococci were identified in 86% of the samples, S. epidermidis dominating. Fungi including molds were found in 50% of the samples, and from one day-care center large numbers of enteric organisms were identified. Thus this study shows that unsupervised toothbrushing at day-care centers can be questioned, more from a general hygienic point of view than from the risk of transmitting serious pathogens.

Microscopic study of enamel defects in deciduous teeth of infants of diabetic mothers

Ground sections of deciduous teeth from infants of diabetic mothers were examined in polarized light and by microradiography. Widened neonatal lines and subsurface lesions were the main findings in the enamel. Three teeth showed enamel hypoplasia in connection with the neonatal line. The widening of the neonatal line and the hypoplasias are related to the more frequent and more pronounced neonatal hypocalcemia occurring among infants of diabetic mothers.

Intubation and mineralization disturbances in the enamel of primary teeth

This study was undertaken to examine the effects of intubation on the enamel development of primary teeth in children intubated during the first 3 months of life. The teeth of 35 children were examined clinically for signs of defects. Dental enamel defects were seen in 26 (74%) patients; enamel hypoplasia was seen in 15 and enamel hypomineralization in 19 cases. In eight patients both enamel hypoplasia and hypomineralization were found. There was a preponderance of enamel defects in the right maxilla, which supports the hypothesis that an early trauma to mineralizing primary teeth caused by laryngoscope may lead to dental enamel hypoplasia.

Secondary ion mass spectrometry in the study of biomineralizations and biomaterials

Abstract Secondary ion mass spectrometry (SIMS) has developed into a powerful tool for the combined microanalytical and microstructural characterization of biomineralized tissues. The technique now routinely permits quantitative sub-μg g −1 analysis of more than 40 elements in bone and tooth tissues at sub-micrometer morphological resolution in three dimensions. Two recent applications of modern SIMS are presented: element distributions in recovering tissue at implanted titanium-base screws in rabbit tibia bone and high-resolution topography and elemental imaging of human dental enamel and dentine. By step-scan and quantitative profiling, the composition of the interface layer between the screw and the bone tissue was studied, and upper concentration limits of element leakage were determined. By high-resolution SIMS imaging new microstructures were detected in the recovery layer. The element distributions and morphologies of the dental tissues are presented in micrographs at very high lateral resolution (ca. 20 nm). For the first time SIMS imaging of individual apatite crystallites and their arrays is demonstrated.