Objectives: The aim of this study was to compare two techniques of measuring cuspal deformation under occlusal load: Direct Current Differential Transformers (DCDTs) and strain gauges. The study ...investigated the relative dependence of the two techniques on the vertical orientation of the tooth in relation to direction of loading and differences in the patterns of change in response to a cavity preparation sequence.
Methods: Strain gauges and DCDTs were attached to the buccal and lingual surfaces of extracted maxillary premolars and mandibular molars. Premolars were subjected to simulated occlusal loads at varying vertical angulations before and after MOD cavity preparation. Molars were tested at progressive stages of cavity preparation. Cuspal deformation was recorded as linear cusp displacement (in μm, using DCDTs) and as cuspal strains (using strain gauges) and relative stiffness.
Results: Strain gauges were much less sensitive than linear displacement devices to vertical orientation of teeth, and computation of relative stiffness further reduced the effect of angulation. Strain gauges are much easier to use experimentally. DCDTs required precise three-dimensional adjustments for the testing of cuspal deformation. Patterns of change in cuspal flexure following cavity preparation were very different using the two techniques.
Conclusions: Use of both devices simultaneously yielded much more information than when used alone, and showed that cusps do not deform as simple cantilever beams.
Noncarious cervical lesions have a multifactorial etiology. Mechanical stress has been identified as one of the factors, but little evidence exists for its cause-effect relationship. This study was ...conducted at three different pH levels to observe the surface loss on dentin beams under tension and compression. Bovine dentin beams (10 x 3.75 x 1.45 mm) were fixed at one end and immersed in 0.1 M lactic acid solution at pH levels 4.5 (n = 20), 7 (n = 20), and 10 (n = 20) for 5 days under a load of 6.5 N (663 g). The mean surface loss was more on the surface under compression than that under tension at pH 4.5 and pH 7 than at pH 10. Also, the surface loss on the beams decreased as the distance from the fixed end increased. It was concluded that stress and lower pH both increase surface loss at the fixed end of the beam, which in a tooth represents the cervical region.
Objectives: This study was designed to measure the dissolution of buccal enamel of extracted teeth exposed to acid with or without simultaneous cyclic occlusal loading.
Methods: Twenty mandibular ...premolars were mounted in pairs in a servohydraulic testing machine, and immersed in 1% lactic acid (pH 4.5) or water. One tooth of each pair was subjected to cyclic loading (100
N at 2
Hz for 200,000 cycles), with the load applied at 45° to the tooth axis on the buccal incline of the buccal cusp. The second tooth of each pair was immersed in acid but not subjected to load. Control teeth were immersed in water, with one tooth of each pair undergoing cyclic loading. Impressions of the teeth were taken before and after exposure to acid and occlusal loading, and a profiling system was used to measure the depth and volume loss of enamel on the buccal surface.
Results: The depth of enamel dissolved ranged from approximately 50–200
μm. In certain locations teeth undergoing cyclic loading during acid exposure showed greater volumetric loss than teeth not subjected to load. Loaded teeth showed a complex pattern of enamel dissolution; volumetric loss in the cervical third was greater than in the middle third, and was much greater in the mesiobuccal segment (under tension) than in the distobuccal segment (under compression). Unloaded teeth showed greater volumetric loss in the cervical third than in the middle third, with a uniform pattern of enamel dissolution from mesiobuccal to distobuccal aspects.
Significance: Enamel dissolution is increased significantly in sites subjected to cyclic tensile load.
Background: The marginal ridge is considered fundamental to the ability of the tooth to resist functional and parafunctional occlusal loads without damage. Despite this role, very little is known of ...patterns of stress and strain in marginal ridges under load. This study investigated strains in proximal enamel of mandibular premolars using finite element analysis (FEA) and strain gauge measurements.
Methods: A three‐dimensional FEA model of a human mandibular premolar was developed using commercial FEA software, and strains were computed in response to loads simulating clenching and chewing functions. Strains were measured in extracted premolars using strain gauges mounted on the proximal surfaces, under similar occlusal loading conditions.
Results: Strains in the vicinity of contact areas and marginal ridges were lower than near the cementoenamel junction and on buccal and lingual surfaces. The magnitude of proximal strains increased with oblique loading on cuspal inclines. Finite element analysis results correlated well with strain gauge measurements and can be used to predict strain directions and magnitudes.
Conclusions: At least for mandibular premolars, the marginal ridges are not highly stressed areas during simulated occlusal loading.
Aims This study investigated the effect of stainless steel bands on cuspal flexure and fracture resistance of extracted maxillary premolars.
Methodology Twenty extracted maxillary premolars (10 ...matched pairs) with mesio‐occluso‐distal (MOD) cavities and endodontic access were subjected to occlusal loading tests (100 N) using a servo‐hydraulic testing machine. Cuspal deflections were measured by an extensometer, with and without the band present. Ten teeth (one of each pair) then had the band removed, and all teeth were subjected to loading until fracture.
Results Mean cuspal flexure of teeth with bands was one‐half of flexure without bands (P < 0.001). Teeth with bands fractured at higher load than their matched pairs with the band removed (P < 0.001), with mean loads at fracture of 1282 N and 729 N, respectively.
Conclusions The study showed that stainless steel bands used in endodontics reduce the cuspal flexure of maxillary premolars and increase their fracture resistance.
Highlights • We tested hair samples from ecstasy users for novel psychoactive substances (NPS). • Almost half had hair test positive for butylone and 10% tested positive for methylone. • NPS were ...detected in 41.2% of those reporting no use. • Racial minorities were more likely to test positive for butylone or other NPS. • Drug testing is needed for those who reject abstinence and use ecstasy.
Castrisos T, Palamara JEA, Abbott PV. Measurement of strain on tooth roots during post removal with the Eggler post remover. International Endodontic Journal, 35, 337–344, 2002.
Aim The aim was to ...measure root surface strains in teeth when removing cast post/cores with the Eggler post remover.
Methodology Two groups of 10 teeth each were tested: group 1 had 1 mm thickness of dentine coronally, and group 2 had 2 mm thickness of dentine. After root filling, 10 mm long cast post/cores were constructed and cemented with zinc phosphate cement, and strain gauges were applied to the roots. The post/cores were removed with the Eggler post remover whilst strain measurements were being recorded. Posts were removed twice: initially along the long axis of the tooth and then at a 10° angle to the long axis. Comparisons between groups 1 and 2 were analysed statistically with the Mann–Whitney U‐test whilst strains within each group were analysed with the Wilcoxon Signed Rank test at the 95% level of confidence.
Results There was no significant difference in the strains measured between groups 1 and 2, and no significant difference within each group when removing posts along the long axis of the tooth and at a 10° angle. Three teeth in group 1 and one tooth in group 2 fractured when removing posts at the 10° angle. Three fractures were small slivers of dentine at the point where the Eggler’s repeller arms contacted the tooth mesially and distally, whilst one tooth (from group 1) fractured obliquely.
Conclusions Post removal with the Eggler device is a relatively safe procedure but care must be taken when there is a possibility of pulling the post out in a nonaxial direction or when less than 1 mm of dentine surrounds the apical end of the post.
The study aimed to determine fracture loads in tooth roots after canal preparation using different techniques. Mesiobuccal roots of 39 extracted mandibular molars were used. Three groups each of 13 ...roots were prepared by stainless steel hand files (K-files), and two rotary nickel-titanium techniques (Lightspeed and Greater Taper files). After obturation, a vertical load was applied by means of a spreader inserted into the canal until fracture occurred. The mean fracture load was 10.2 ± 4.4 kg for K-files, 15.7 ± 9.1 kg for Lightspeed and 13.2 ± 6.1 kg for Greater Taper files, but differences were not statistically significant (p > 0.05). Most fracture lines were incomplete fractures on the buccal surface, followed by proximal and compound fractures. Greater apical enlargement (Lightspeed) or increased canal taper (Greater Taper files) did not increase fracture susceptibility of tooth roots.
Milk caseins stabilize calcium and phosphate ions and make them available to the neonate. Tryptic digestion of the caseins yields phosphopeptides from their polar N-terminal regions that contain ...clusters of phosphorylated seryl residues. These phosphoseryl clusters have been hypothesized to be responsible for the interaction between the caseins and calcium phosphate that lead to the formation of casein micelles. The casein phosphopeptides stabilize calcium and phosphate ions through the formation of complexes. The calcium phosphate in these complexes is biologically available for intestinal absorption and remineralization of subsurface lesions in tooth enamel. We have studied the structure of the complexes formed by the casein phosphopeptides with calcium phosphate using a range of physicochemical techniques including x-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and equilibrium binding analyses. The amorphous nature of the calcium phosphate phase was confirmed by two independent methods: x-ray powder diffraction and selected area diffraction. In solution, the ion activity product of a basic amorphous calcium phosphate phase was the only ion product that was a function of bound phosphate independent of pH, consistent with basic amorphous calcium phosphate being the phase stabilized by the casein phosphopeptides. Detailed investigations of calcium and calcium phosphate binding using a library of synthetic homologues and analogues of the casein phosphopeptides have revealed that although the fully phosphorylated seryl-cluster motif is pivotal for the interaction with calcium and phosphate, other factors are also important. In particular, calcium binding and calcium phosphate stabilization by the peptides was influenced by peptide net charge, length, and sequence.
Vertical root fracture seems to result from stresses generated within the root canal and typically occurs in a buccolingual direction through the thickest part of dentin. Because stresses in the ...canal wall are difficult to measure experimentally, we have attempted to correlate stress patterns derived from finite element models of maxillary and mandibular incisors with strain measurements on the root surfaces of extracted teeth. Finite element analysis indicated that circumferential tensile stresses were concentrated on the buccal and lingual surfaces of the canal wall, corresponding to areas of greatest canal wall curvature. Surface stresses were much lower and were consistently tensile on the proximal root surfaces but variable on the buccal and lingual surfaces. The measurement of root surface stresses does not provide a reliable picture of internal stresses in the root. Canal wall curvature is a major factor in stress concentration and hence in the pattern of fracture.
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