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Permanent First Molars (permanent + first_molar)

Distribution by Scientific Domains

Medical Sciences	85%

Selected Abstracts

Variations in the mechanical properties of Alouatta palliata molar enamel

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2010
Laura A. Darnell
Abstract Teeth have provided insights into many topics including primate diet, paleobiology, and evolution, due to the fact that they are largely composed of inorganic materials and may remain intact long after an animal is deceased. Previous studies have reported that the mechanical properties, chemistry, and microstructure of human enamel vary with location. This study uses nanoindentation to map out the mechanical properties of Alouatta palliata molar enamel on an axial cross-section of an unworn permanent third molar, a worn permanent first molar, and a worn deciduous first molar. Variations were then correlated with changes in microstructure and chemistry using scanning electron microscopy and electron microprobe techniques. The hardness and Young's modulus varied with location throughout the cross-sections from the occlusal surface to the dentin-enamel junction (DEJ), from the buccal to lingual sides, and also from one tooth to another. These changes in mechanical properties correlated with changes in the organic content of the tooth, which was shown to increase from ,6% near the occlusal surface to ,20% just before the DEJ. Compared to human enamel, the Alouatta enamel showed similar microstructures, chemical constituents, and magnitudes of mechanical properties, but showed less variation in hardness and Young's modulus, despite the very different diet of this species. Am J Phys Anthropol 2010. © 2009 Wiley-Liss, Inc. [source]

Caries incidence in permanent first molars after discontinuation of a school-based chlorhexidine-thymol varnish program

COMMUNITY DENTISTRY AND ORAL EPIDEMIOLOGY, Issue 3 2003
Pilar Baca
Abstract , Objectives: To determine whether the cessation for 3 years of a 24-month program of chlorhexidine-thymol varnish applications would affect caries incidence in the first permanent molars of a population of schoolchildren of middle and lower-middle socioeconomic level. Methods: Two groups of 6,7-year-old schoolchildren, randomized by school-class, were followed up in a clinical trial. One group received applications of chlorhexidine-thymol varnish every 3 months and the other group acted as controls. The program ended after 24 months and its effects were evaluated. Three years later, 55.5% of the schoolchildren were re-examined and the caries increments were documented. Results: At the end of the 24-month program, the treated children had significantly fewer decayed and filled surfaces in permanent molars (lower DFS index) versus the controls. At 3 years after the discontinuation of the program, this difference had disappeared; there were no differences in the incidence of decayed, missing and filled surfaces (DMFS) index in permanent molars between the treated children and the controls. Conclusion: The cessation for 3 years of a 3-month program of chlorhexidine-thymol varnish applications resulted in a nonsignificant increase in the prevalence of dental caries in the permanent first molar. [source]

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

INTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 5 2008
TOBIAS G. FAGRELL
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 µm. 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. [source]

Evaluation of spontaneous space closure and development of permanent dentition after extraction of hypomineralized permanent first molars

INTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 5 2007
BIRGITTA JÄLEVIK
Aim., ,The aim of this study was to evaluate spontaneous space closure, development of the permanent dentition, and need for orthodontic treatment after extraction of permanent first molars due to severe molar,incisor hypomineralization (MIH). Subjects., ,Twenty-seven children aged 5.6,12.7 (median 8.2) years had one to four permanent first molars extracted due to severe MIH. Each case was followed up on individual indications 3.8,8.3 (median 5.7) years after extractions. The eruption of the permanent dentition, and space closure were documented by orthopantomograms, casts, photographs, and/or bitewings. Results. ,Fifteen children were judged to have a favourable spontaneous development of their permanent dentition without any orthodontic intervention. Seven children were or should be subjected to orthodontic treatment for other reasons registered prior to the extraction. Five children were judged to have a treatment at least caused by the extractions, but three of them abstained because of no subjective treatment need. Conclusion. Extraction of permanent first molars severely affected by MIH is a good treatment alternative. Favourable spontaneous space reduction and development of the permanent dentition positioning can be expected without any intervention in the majority of cases extracted prior to the eruption of the second molar. [source]

Scanning electron micrograph analysis of hypomineralized enamel in permanent first molars

INTERNATIONAL JOURNAL OF PAEDIATRIC DENTISTRY, Issue 4 2005
B. JÄLEVIK
Summary. First molars with cream- to yellow-coloured demarcated opacities of the enamel, often in combination with severe loss of substance, are common in many child populations. The aetiology is obscure. Aim and Method., The aim of this study was to study the ultrastructure of the enamel of 10 affected teeth by means of scanning electron microscopy (SEM) in order to gain a better understanding of the clinical appearance and treatment problems of this condition, and to find some clues to its aetiology. Results., The basic enamel structure with enamel rods and interrod zones was found in porous parts of the enamel, as well as in normal parts, but the packing of the hydroxylapatite crystals seemed to be looser and less well organized in the porous parts. The border between normal and hypomineralized enamel was usually distinct, and followed the direction of the rods. The preserved basic structure indicates normal function of the ameloblasts during their secretion phase, but impaired function during their maturation stage. Conclusion., Considering the poor etch profile, it seems reasonable to recommend removal of all affected enamel surrounding the cavity, if possible, and to use a glass ionomer filling with its chemical bonding to tooth substrate, when restoring first molars with remaining affected enamel. [source]