Immunolocalization of semicarbazide-sensitive amine oxidase in human dental pulp and its activity towards serotonin.

The semicarbazide-sensitive amine oxidase (EC 1.4.3.6; SSAO) from crude homogenates of human dental pulp was shown to catalyse the oxidative deamination of 5-hydroxytryptamine (serotonin; 5-HT) with a K(m) of 318+/-52 microM. In this respect the human enzyme resembles that in pig dental pulp, but differs from SSAO in all other tissues studied, which are inactive towards 5-HT. A method is described for obtaining intact dental pulp in which the anatomical details are preserved. Extracted teeth are frozen in dry ice and later defrosted rapidly before being fractured in a mechanical vice, facilitating pulp removal. Immunohistochemistry showed SSAO in the odontoblast layer, nerve fibres and blood vessels. The presence of SSAO in nerves in dental pulp appears to be unique. Tryptophan hydroxylase, a key enzyme in 5-HT synthesis, was also demonstrated in nerves and the odontoblast layer of human dental pulp.

Comparison of two heat-pressed all-ceramic dental materials.

OBJECTIVES: The processing route for two heat-pressed all-ceramic materials (Empress and OPC) is virtually identical. The purpose of this study was to determine the mechanical properties of both materials and determine if significant differences exist between them. METHODS: X-ray powder diffraction of the ceramics before and after processing was carried out to identify the crystal phases present. The mechanical properties of both materials were tested. Specimens were tested for hardness, fracture toughness (indentation method) and flexural strength (biaxial method). The results were statistically evaluated and tested for differences using a Mann-Whitney test. Secondary electron imaging of both materials was carried out before and after processing. RESULTS: X-ray powder diffraction revealed that OPC changes as a result of heat-pressing from being a complex mixture of crystalline oxides to a glass-ceramic. In contrast Empress is a glass-ceramic before and after processing. X-ray diffraction identified leucite as the main crystalline phase in both ceramics. The biaxial flexural strength of OPC was 153.6 (17.8) MPa and for Empress was 134.4 (11.5) MPa. The hardness of OPC was 7.28 (0.62) GPa and for Empress was 6.94 (0.79) GPa. Indentation fracture toughness of OPC was 1.36 (0.29) MPam0.5 and for Empress was 1.33 (0.08) MPam0.5. Secondary electron images show Empress to be the same before and after processing while OPC is clearly very different. Empress also appears to have a higher glass content compared with OPC. SIGNIFICANCE: The results of X-ray diffraction show that Empress is pre-cerammed whilst OPC is not. Statistical analysis revealed that no significant difference exists between the two materials for any of the mechanical properties tested at a 95% (p < 0.05) confidence level. It was concluded that no difference exists between the two materials on completion of processing.

Learning a clinical method to identify a mandibular reference position.

The teaching of clinical maxillomandibular relationships is an area of weakness in dental school curricula. Most difficulties arise when a reference position is required to adjust or reconstitute the maximum intercuspation of the dentition. The dentist-derived concept of the centric maxillomandibular relation position is used to solve this problem. There is no consensus on the definition of this term. In the descriptions of clinical technique for recording the centric maxillomandibular relation position, clinical criteria to judge whether or not the position required has been achieved usually are not given. The dorsal border paths of the envelope of movement were used to develop a clinical criterion to identify the centric maxillomandibular relation position. Force or "guidance" is not used in this method. Test-patients with normal masticatory systems were randomly selected and fitted with a mechanical tracking apparatus. 50 undergraduate dental students and dental nurses were randomly selected and given instruction in the clinical technique to identify the centric maxillomandibular relation position. The ability of these students to identify the reference position was assessed by having them perform the technique blindfolded on the test-patients on whom tracking apparatus was fitted. Sixty eight percent of the test-clinicians succeeded in using the method to identify the reference position. There was no significant difference in the abilities of subgroups to use the method successfully, e.g., women compared to men, 2nd year students to 3rd year students. It was concluded that the method was a satisfactory way of learning how to identify the centric maxillomandibular relation position in a gentle, non-invasive fashion.

Occlusal contacts in maximum intercuspation in normal dentitions.

A cross-sectional study of the contacts in maximum intercuspation was undertaken using a method to identify occlusal contacts, which is indicated as satisfactory by modern research. The aims were to describe in subjects with normal dentitions and normally functioning masticatory systems: (a) the general distribution of contacts; (b) the numbers in the various classes and types of occlusal contacts; (c) the numbers of teeth without contact. A randomized sample of 18 women and 20 men was used. Classical theoretical proposals for the numbers, distribution and nature of occlusal contacts were not supported. Wide variability was evident and asymmetry of distribution on the right and left sides of individual subjects was common. Contacts with stabilizing tendencies involved the mandibular supporting cusps in 79% of occurrences. Overall, the difference in the number of contacts with stabilizing effects was not significantly different from the number with unstabilizing tendencies. Contacts with mechanically unstabilizing effects did not produce clinically discernible, unfavourable sequelae in the dentitions. Because of the sparse number of stabilizing contacts, interventions involving the occlusal surfaces should maintain or improve on the number of such contacts in maximum intercuspation.

The effect of posture change on the position of the skin marks for the transverse horizontal axis.

Marks are placed on facial skin in clinical dentistry to indicate the position of more deeply placed landmarks or reference points. In this study the movement of the transverse horizontal axis skin points overlying the craniomandibular articulation were observed and quantified. The time taken for the skin displacement to occur when the posture changed between upright and supine was also studied. The extent of displacement of the skin point was approximately 3 mm in the sagittal plane and 2 mm in the frontal plane when the posture was changed from upright to supine and vice versa. The displacement was complete after 30 seconds in 95% of subjects. The direction of the displacement was primarily cephalad but with a dorsal component of more than 10 degrees in 87% of subjects. The extent of the movement in the sagittal and frontal planes was correlated. There was no gender difference for the skin displacement. Awareness by clinicians of the extent and direction of such facial skin movements can help to prevent errors.

A magnetic resonance imaging study of centric maxillomandibular relation.

The authors conducted research to determine the structural relationships of the craniomandibular articulation that resulted when a mandibular reference position was established. A noninvasive clinical method was used to identify and record centric maxillomandibular relation in normal subjects and a suitable reference position in subjects with derangements of the craniomandibular articulation. The reference positions were checked for repeatability. Magnetic resonance imaging was used to determine the intraarticular relationships resulting from application of the clinical techniques. The normal subjects conformed well to the 1987 "Glossary of Prosthodontic Terms" definition, with the mandible close to first-tooth contact. In subjects with deranged articulations, the condyle was always in an abnormal relationship on the affected side in the reference position, and there were many intersubject variations.