Biomedical subjects

J E A Palamara

Publications and source records attributed to J E A Palamara.

10 recordsLinked to original sources

PubMed2006

Effect of static loading of dentin beams at various pH levels.

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.

Animals↗

PubMed2006

An investigation of thermal stimulation in intact teeth.

OBJECTIVES: To investigate the response of extracted intact teeth to thermal stimulation in terms of fluid movement, in relation to temperature change within tooth structure. METHODS: Dentinal fluid movement was measured in response to thermal stimuli applied to enamel. Freshly extracted teeth with intact crowns were investigated for the effects of thermal stimulation; namely, hot water (80 degrees C), iced water (2 degrees C) and carbon dioxide dry ice (-72 degrees C) for 5s application. Two capillary-based methods were used to measure fluid flow. To measure temperature changes at the dentino-enamel junction (DEJ) and pulpal wall in response to the same stimuli, fine J type thermocouples were used. RESULTS: Thermal stimuli caused fluid movement, which occurred before the temperature changed at the pulp wall. Sealing the dentinal tubules resulted in a delayed response time. In general, fluid movement occurred coincident with the temperature change detected at the DEJ. However, many teeth showed a "bidirectional" response to thermal stimulation. The initial fluid movement in the bidirectional response was detected before the earliest temperature change observed at the DEJ, and was in the opposite direction to the main fluid movement. CONCLUSION: Our results imply that thermal contraction and expansion of dentinal fluid may not be the complete explanation for dentinal fluid movement in intact teeth. Enamel may serve not only as a temperature transfer medium but may also expand or contract when subjected to thermal stimulation.

Dental Enamel↗

PubMed2006

Effect of loading and pH on the subsurface demineralization of dentin beams.

It is important to understand subsurface dentin demineralization and caries from the clinical perspective as dentin properties are modified under acidic conditions and mechanical loading. This study was conducted to observe the subsurface demineralization of dentin beams at three different pH levels 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, 7, and 10 for 5 days under a load of 6.5 N (663 g), and the subsurface demineralization depth was measured using a polarized light microscope. The mean subsurface demineralization depth was more subjacent to the surface under compression than that under tension at pH 4.5 and decreased as the distance from the fixed end increased. No subsurface demineralization was observed at pH 7 or 10. It was concluded that both stress and low pH are associated with increased subsurface demineralization at the fixed end of the beam.

Animals↗

PubMed2006

Minimizing dentinal fluid flow associated with gap formation.

The relationship between gap formation and outward fluid flow and procedures to minimize both phenomena were investigated in extracted human premolars restored in vitro with MOD composite restorations. We hypothesized that either glass-ionomer cement (GIC) liners or low-shrinkage composite could reduce fluid flow related to gap formation. Two groups restored with bonding agents with either high- or low-shrinkage resin composites, and 2 groups restored by either conventional or light-cured GIC liner plus resin composite were compared (8 teeth/group). Fluid flow was measured with an automated apparatus. Baseline fluid flow was low and unchanged after bonding, but increased sharply (though transiently) after teeth were lined with GIC. Outward flow was significantly greater with conventional than with light-cured GIC. Inward fluid flow occurred during light-curing, followed by extensive, prolonged outward flow after curing. Low-shrinkage composite or GIC liners reduced gap formation and limited outward fluid flow. GIC liners promoted outward fluid flow during their setting reactions.

Analysis of Variance↗

PubMed2005

Tooth morphology and characteristics of non-carious cervical lesions.

OBJECTIVES: Two 3-dimensional models, one of a lower second premolar and one of a lower central incisor were used to investigate effects of load on the location and magnitude of cervical strains. METHODS: Point loads of 100 N were applied to the model premolar (at the cusp tip, parallel and 45 degrees to the long axis of the tooth) and incisor (at the mid-buccal point on incisal edge, parallel and 45 degrees to the long axis of the tooth). Outputs were presented in the form of tensile-strain contours and vector plots. RESULTS: Strains were concentrated near the cementoenamel junction (CEJ) regardless of load direction, and oblique loading showed higher tensile strains, opposite to the point of loading, than vertical loading for both models. For the premolar model, regardless of loading direction, strains were concentrated at the mid- buccal CEJ. In contrast, under vertical loading on the incisor model, tensile strains were concentrated at the line-angle of CEJ. From oblique loads, vector plots of both models showed tensile vectors in vertical directions while vertical loads showed tensile vectors in horizontal directions. CONCLUSION: Mechanisms of non-carious cervical lesions (NCCLs) may in part be due the changing orientation of tensile strains as well as their magnitude. Stress concentration at the CEJ related well to the common location of clinical NCCLs. The crown-root morphology may have an influence on the initial location of non-carious cervical lesions.

Bicuspid↗

PubMed2003

The effect of cleaning procedures on fracture properties and corrosion of NiTi files.

AIM: To evaluate the effect of repeated cleaning procedures on fracture properties and corrosion of nickel-titanium (NiTi) files. METHODOLOGY: New NiTi instruments were subjected to 2, 5 and 10 cleaning cycles with the use of either diluted bleach (1% NaOCl) or Milton's solution (1% NaOCl plus 19% NaCl) as disinfectant. Each cleaning cycle consisted of scrubbing, rinsing and immersing in NaOCl for 10 min followed by 5 min of ultrasonication. Files were then tested for torsional failure and flexural fatigue, and observed for evidence of corrosion using scanning electron microscope (SEM). Four brands of NiTi files were immersed in either Milton's solution or diluted bleach overnight and evaluated for corrosion. RESULTS: Up to 10 cleaning cycles did not significantly reduce the torque at fracture or number of revolutions to flexural fatigue (P > 0.05, two-way anova), although decreasing values were noted with increasing number of cleaning cycles using Milton's solution. No corrosion was detected on the surface of these files. Files immersed in 1% NaOCl overnight displayed a variety of corrosion patterns. The extent of corrosion was variable amongst different brands of files and amongst files in each brand. Overall, Milton's solution was much more corrosive than diluted bleach. Corrosion of file handles was often extreme. CONCLUSIONS: Files can be cleaned up to 10 times without affecting fracture susceptibility or corrosion, but should not be immersed in NaOCl overnight. Milton's solution is much more corrosive than bleach with the same NaOCl concentration.

Analysis of Variance↗

PubMed2002

Measurement of strain on tooth roots during post removal with the Eggler post remover.

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 degrees 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 degrees angle. Three teeth in group 1 and one tooth in group 2 fractured when removing posts at the 10 degrees 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.

Cementation↗

PubMed2002

Stainless steel bands in endodontics: effects on cuspal flexure and fracture resistance.

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.

Adolescent↗

PubMed2002

Strains in the marginal ridge during occlusal loading.

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 cemento-enamel 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.

Analysis of Variance↗

PubMedDate not supplied

Pulpal space pressure and temperature changes from Nd:YAG laser irradiation of dentin.

OBJECTIVES: To investigate pulpal space pressure and temperature after application of Nd:YAG laser, and high-speed diamond bur on dentin surface. METHODS: One and 3 W Nd:YAG laser and high-speed diamond bur were used to remove dentine from twenty extracted premolars. The pulp chambers were monitored for pressure and temperature changes with a pressure transducer and thermocouple, respectively. RESULTS: Regardless of the remaining dentin thickness (RDT), laser irradiation and high-speed diamond bur use generated an increase in pulpal space pressure and temperature (ANOVA and Fisher's LSD tests, P < 0.001). Pressure and temperature increased with an increase in laser power. Three-Watt laser irradiation caused greater changes than 1 W (1.75 kPa and 1.31 degrees C, 0.53 kPa and 0.34 degrees C, respectively). Both pulpal space pressure (P < 0.001) and temperature (P < 0.005) increased as the RDT decreased. CONCLUSIONS: Laser irradiation and the use of a high-speed diamond bur generated an increase in pulpal space pressure and temperature. Pulpal space pressure and temperature increased with an increase in energy density of laser and a decrease in RDT.

Adolescent↗