Intact Human Teeth Research Articles

In Vivo and In Vitro Expression of Connexin 43 in Human Teeth

Gap junctions are composed of transmembrane proteins belonging to the connexin family. These proteins permit the exchange of small regulatory molecules directly between cells for the control of growth, development and differentiation. Although the presence of gap junctions in teeth has been already evidenced, the involved connexins have not yet been identified in human species. Here, we examined the distribution of connexin 43 (Cx43) in embryonic and permanent intact and carious human teeth. During tooth development, Cx43 localized both in epithelial and mesenchymal dental cells, correlated with cytodifferentiation gradients. In adult intact teeth, Cx43 was distributed in odontoblast processes. While Cx43 expression was downregulated in mature intact teeth, Cx43 appeared to be upregulated in odontoblasts facing carious lesions. In cultured pulp cells, Cx43 expression was related to the formation of mineralized nodules. These results indicate that Cx43 expression is developmentally regulated in human dental tissues, and suggest that Cx43 may participate in the processes of dentin formation and pathology.

Cuspal deflection during polymerisation of composite lutes of ceramic inlays

Objective: The purpose of this study was to measure the cuspal deflection that occurs in teeth as a result of the dimensional changes of resin-based lutes during polymerisation. Methods: Standardised MOD cavities were cut in 15 intact human premolar teeth using a custom paralleling device. A ceramic inlay was machined by the CEREC 2 system for each tooth ensuring an interface width of 50 μm (SD=17.5) at the cavity margin. The 15 teeth were divided into three groups of five according to the cementation system employed: a microfilled hybrid posterior composite; a compomer restorative; a dual-cure luteing composite. The inter-cuspal tooth dimension was recorded continuously with a laser micrometer assembly during a 2 min photoactivation period and a further 30 min post-activation period. Results: A clear overall reduction in tooth dimension was detectable for the first 10 min of polymerisation. The mean changes ranged from −0.02% to −0.06% depending on the nature of the luting material. In addition, all samples exhibited a slight expansion of 0.03% during the time of light-activation. Conclusions: The dimensional changes that teeth experience during the polymerisation of resin-based lutes are clearly detectable. It can be postulated that an increase in the dimensions of the teeth during photoactivation occurs as a result of expansion of the lute due to the thermal energy delivered.

A scanning electron microscopic study of tooth surface changes induced by tannic acid

Statement of problem. Exposing the tooth structure to chemicals used in displacing the gingival tissue is inevitable. Purpose. This study was undertaken to microscopically examine the effect of tannic acid on the prepared dentin surface. Material and methods. Forty recently extracted intact human teeth were mounted for buccal surface preparation. Teeth were equally divided into 10 groups. One group was kept as a control and the other teeth received a topical application of 15%, 20%, and 25% aqueous tannic acid solutions each for 5, 10, and 15 minutes at room temperature. All samples were washed, air-dried, then prepared for scanning electron microscopic examination. Two different areas in the cervical region were randomly selected and examined under magnifications of ×1000 and ×2000, then photographed. The assessment of the changes was performed qualitatively. Results. The results showed an incomplete removal of the smear layer in all experimental samples. The astringent action of the tannic acid solution on both the smear layer and the surface peritubular dentin around the orifices of dentinal tubules had contributed to their constriction. The degree of constriction of the orifices of dentinal tubules increased as higher concentrations of tannic acid solutions were used and as the application time was further increased at each concentration. Conclusion. The tannic acid had an incomplete action on the removal of the smear layer. It also seemed to have an astringent action on both the smear layer and the peritubular dentin. (J Prosthet Dent 1998;79:169-74.)

The application of thermoelastic analysis to study stresses in human teeth

summary The aims of this investigation were to use a full‐field thermoelastic technique to study the stress distribution on human teeth subjected to dynamic loads and derive a value for the thermoelastic constant for human enamel. Surface stresses were observed on extracted intact human molar teeth subjected to a load of 200 N cycled at 20 Hz. Measurements were repeated for the same teeth following mesio‐occluso‐distal cavity preparation and restoration with amalgam and adhesively bonded composite restorations. A value for the thermoelastic constant for human enamel (Km) of 2.25 × 10−12 m2/N was calculated from physical coefficients in the literature. Unprepared specimens exhibited a comparable magnitude and distribution of stresses to those seen when teeth were restored with adhesively bonded composite restorations. Higher stresses were observed on prepared teeth and there was little change following restoration with amalgam. It can be concluded that a full‐field thermoelastic stress analysis technique can be successfully applied to study teeth subjected to axial dynamic loads in vitro and that the resultant stresses are greater in prepared teeth than those restored with bonded composite materials.

Effect of gutta-percha solvents on calcium and phosphorus levels of cut human dentin

Fresh intact human teeth were cut and treated with 3 commonly used gutta-percha solvents: chloroform, xylene, and Endosolv-E. Treatment consisted of embedding the specimens of each group for 15 or 30 min in the test solution. After each time interval, the specimens were rinsed, dried, and prepared for surface energy dispersive spectrometric analysis. The calcium and phosphorus levels in each specimen were recorded and the differences between the test groups were statistically analyzed. The changes in the calcium and phosphorus levels following treatment with the gutta-percha solvents were minimal and statistically nonsignificant.

In vitro peel/shear bond strength of orthodontic adhesives

Objectives: The purpose of this study was to evaluate the in vitro peel/shear bond strength of a selection of orthodontic bracket adhesives to human premolar teeth. Methods: Twenty-two commercially available bracket adhesives were used to bond the same bracket type (Miniature Twin, 3M Unitek, Monrovia, CA, USA) on 264 intact human premolar teeth and then adhesively tested to failure. Peel/shear bond strength values were calculated in newtons and megapascals. The site of bond failure was scored according to the Adhesive Remnant Index. Statistics included one-way analysis of variance and Tukey's Studentized Range test together with Weibull analysis. The latter is a survival analysis able to describe the performance of a material. Results: The mean bond strengths varied from 9.9 MPa for Concise to 4.1 MPa for Heliosit Orthodontic. The overall F-test showed a significant difference ( P < 0.0001). No significant differences in bond strength were found between Concise, AccuBond, Imperva Dual, Transbond XT, Kurasper and Spectrum. Conclusion: Concise and AccuBond are among the materials of choice for bonding fixed orthodontic appliances to teeth. These materials combine high bond strength with a reliable bond that is easily and quickly debonded.

Comparison of three instruments in the preparation of the curved root canal using the modified double-flared technique

Fifty-one extracted intact human first molar teeth with mature root apices were radiographed in a standardized way; their root curvature was determined and they were divided into three groups. One root canal in the mesial root of the mandibular molars, or the major mesiobuccal root in maxillary molars, was prepared with the modified double-flared technique, in one of three ways. The modified double-flared technique involves coronal flaring followed by working length determination and apical preparation. In group 1, unmodified tipped instruments (Flexofile) were manipulated with a balanced force technique. In groups 2 and 3, Flexogates files and Canal Master U files were operated in the manner recommended by the manufacturers. After preparation, the teeth were radiographed. The processed images of the root canals were traced using an image analysis computer software package. Comparisons were made between the preoperative and postoperative shapes of each root canal. A low viscosity polyvinyl siloxane was injected into the prepared root canals and the specimens were demineralized, dehydrated, and cleared. The preparation was evaluated subjectively according to desirable or undesirable criteria. The overall quality of preparation was rated. Statistical analysis showed that there was no significant difference in the overall change of area between the three groups (p = 0.994). There was a significant proportional increase in mesiodistal width in the coronal part of the canals in the Canal Master U group and more of the instruments in this group fractured.(ABSTRACT TRUNCATED AT 250 WORDS)

A morphometric analysis of the cross-sectional area of dentine occupied by dentinal tubules in human third molar teeth.

The number and the mean percentage tubular cross-sectional area of dentinal tubules per square millimetre were calculated in specimens of coronal dentine of 13 intact human third molar teeth from patients 18 to 28 years of age. The dentine was fractured at various known distances from the dentino-enamel junction. Near the dentino-enamel junction the number of tubules per square millimetre was 22,000 and the mean tubular cross-sectional area was 3.6%. Midway between the pulpal wall and the dentino-enamel junction the number of tubules was 37,000 mm-2 and the mean tubular cross-sectional area was 6.2%. Close to the pulp the number of dentinal tubules was 48,000 mm-2 and the mean cross sectional area of tubules was 10.2 percent. The number of tubules per square millimetre more than doubled and the area occupied by tubules increased threefold from the dentine close to the dentine-enamel junction, to that close to the pulp. These differences in tubular patterns at different depths in dentine are clinically significant in dentine permeability, the treatment of traumatized teeth, and pain transmission in dentine.

FT-IR photoacoustic depth profiling spectroscopy of enamel

Photoacoustic Fourier transform infrared (PA-FT-IR) depth profiling spectra of the enamel of an intact human tooth are obtained in a completely nondestructive fashion. The compositional and structural changes in the tissue are probed from the enamel surface to a depth of about 200 microns. These changes reflect the state of tissue development. The subsurface carbonate gradient in the enamel could be observed over the range of about 10-100 microns. The carbonate-to-phosphate ratio increases in the depth profile. The depth profile also reveals changes in the substitutional distribution of carbonate ions. Type A carbonates (hydroxyl substituted) increase relative to type B carbonates (phosphate substituted) with increasing thermal diffusion length. In addition to the changes in the carbonate ion distribution and content, the PA-FT-IR depth profile clearly indicates a dramatic increase in the protein content relative to the phosphate content with increased depth. The changes in the carbonate content and distribution, along with the changes in the protein content, may be responsible for the changes observed in the apatitic structure in the depth profile of the enamel.

FT-IR Step-Scan Photoacoustic Phase Analysis and Depth Profiling of Calcified Tissue

Rapid-scan- and step-scan-based Fourier transform infrared photoacoustic depth profiling results of an extracted but intact human tooth are compared. The effects of various data processing methods are examined. Analysis of the phase dispersion of the photothermal signal along with spectral linearization is used to access the extent of photoacoustic saturation in the photoacoustic spectra. Phase-modulated/phase-resolved depth profiling methods are less prone to photoacoustic saturation and provide superior localization of the surface and subsurface absorbers distributed in the tooth enamel. Mid-infrared depth profiling studies of calcified tissues can aid in the understanding of degenerative bone diseases, bone growth, and modeling, as well as tissue mineralization.

Alterations in human enamel surface morphology following vital bleaching

Extracted intact human teeth ( n = 4) were treated for 30 days by three protocols: Home 1 (Proxigel, n = 4) for 8 hours daily, Home 2 (White & Bright, n = 4) for 24 hours with 3 minutes of stannous fluoride gel, or an Office protocol ( n = 4) using 30% hydrogen peroxide (Superoxol) warmed by a high-intensity light while the controls remained untreated. “Home” bleaching agents contain approximately 10% carbamide peroxide. After treatment, the coronal surfaces were examined with a scanning electron microscope (SEM) at 2000 power magnification, and the surface topography was measured by a profilometer. The SEM photomicrographs of the controls and office-treated groups were similar to previously reported descriptions, while the home bleached surfaces appeared similar to each other. Profilometric analysis was used to examine surface roughness and surface waviness. Mean surface roughness in microns was: control, 1.9; Home 1, 0.6; Home 2, 0.9; and Office, 0.6. Surface waviness was ranked control > office > Home 1 = Home 2. Enamel surface alterations were evident after the three bleaching methods. The differences between the office and home-treated surfaces were unrelated to the pH of the bleaching agents.

Er:YAG laser ablation of enamel and dentin of human teeth: determination of ablation rates at various fluences and pulse repetition rates.

A pulsed Er:YAG laser (2.94 microns) was used to determine ablation depths per pulse of laser energy at 2 Hz and 5 Hz in human teeth cross sections of enamel and dentin. Ablation depths per pulse at 2 Hz in enamel of intact human teeth were measured and compared to ablation depths per pulse determined in enamel cross sections at 2 Hz. Close correlation was observed for ablation depths per pulse of laser energy between teeth cross sections and intact teeth for enamel. Photographs of lased holes at 2 Hz and 5 Hz indicated minimal thermal effects in enamel at fluences below 80 J/cm2. Minimal thermal effects in dentin were noted below 74 J/cm2. Scanning Electron Microscopy (SEM) pictures of lased dentin showed an irregular serrated surface. Results of this study suggest that the Er:YAG laser can effectively ablate enamel and dentin with minimal thermal effects at 2 Hz and 5 Hz.

Load fatigue of teeth restored by a dentin bonding agent and a posterior composite resin

A three-surface MOD preparation measuring one third of the isthmus cavity distance at the isthmus was prepared for five extracted, intact human maxillary premolar teeth. The teeth were restored with a posterior resin and a dentin bonding agent. Each tooth was tested under a cyclically varying load in a fatigue machine made at the University of Washington. The cyclic load rate was 75 cycles per minute. A strain gauge was applied to the buccal surface of each tooth. Under the load applied at an angle of 60 degrees to the long axis of the tooth, reinforcement of the tooth was established by the reduced deflection of the buccal surface of the restored tooth as compared with the unrestored tooth. The loss of this reinforcement due to the application of the cyclically varying load established the end point of the fatigue testing. Four different load values of 13, 16, 19, and 22 lb loads were applied separately to each tooth. The results of this testing were classic wherein the smallest load required the greatest number of load cycles before loss of adhesion was registered by the strain gauge. Failure always occurred within the adhesive joint.

Temperature change in the pulp chamber during complete crown preparation

This study observed the temperature changes in the pulp chamber during tooth preparation for a complete crown. Twelve extracted, morphologically intact human teeth were chosen: four canines, four premolars, and four molars. Six teeth, two of each, were cooled during preparation with an air-water spray; the remaining six were air-cooled. Minimal reduction of dentin using an air-water spray coolant resulted in a lowered temperature in the pulp chamber, mainly with the cross-grooved TDA diamond stones. The application of an air coolant resulted in a temperature rise in the pulp chamber.

Changes in heated and in laser-irradiated human tooth enamel and their probable effects on solubility.

Enamel of intact human teeth laser irradiated in vitro under certain conditions is known to have less subsurface demineralization than unirradiated enamel on exposure to acid; consequently, the potential use of laser irradiance to reduce caries is apparent. The laser-induced physical and/or chemical changes that cause this reduced subsurface demineralization are not known. A laser-irradiated tooth enamel surface will have a temperature gradient that decreases towards the dentin junction. Dependent on irradiant conditions, the temperature may range from greater than 1400 degrees C at the surface to near normal at the dentin-pulp junction. Along this steep temperature gradient, different compositional, structural, and phase changes in the tooth enamel are to be expected. Identification of changes occurring along this gradient has bearing on understanding the dissolution reduction mechanism and, in turn, optimizing its effect. Changes in laser-irradiated material from the highest temperature region have been characterized, but those occurring in sequential layers of decreasing temperatures have not. Since the laser-induced changes are expected to primarily arise from localized heating, previously reported thermally induced changes in tooth enamel on heating in conventional furnaces were utilized to infer corollary changes along the gradient in laser-irradiated tooth enamel. These thermally inferred changes which resulted in modifications in the tooth enamel apatite and/or newly formed phases were correlated with their probable effects on altering solubility. A temperature gradient range from 100-1600 degrees C was considered with subdivisions as follows: I, 100-650 degrees C; II, 650-1100 degrees C; and III, greater than 1100 degrees C. Two of the products formed in range III, alpha-Ca3(PO4)2 and Ca4(PO4)2O, and also identified in the fused-melted material from laser-irradiated tooth enamel, are expected to markedly increase solubility in those regions that contain considerable amounts of these compounds. Products and changes occurring in range II, separate phases of alpha- and/or beta-Ca3(PO4)2 and a modified phase of apatite, may increase or decrease the solubility depending on the Ca/P ratio and the resultant amounts of alpha-, beta-Ca3(PO4)2 formed. Modifications in tooth enamel apatite effected in range I are expected to decrease its solubility; the formation of pyrophosphate in this range may have a substantial effect on reducing the solubility rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Assessment of reliability of electrical and thermal pulp testing agents

The reliability of several pulp testing agents was compared in intact human premolar teeth. The electric pulp tester, CO2 snow and dichlorodifluoromethane were found to be more dependable than ethyl chloride and ice in producing a positive response. However, in young patients the electric pulp test was less reliable than CO2 snow and dichlorodifluoromethane but more reliable than ethyl chloride and ice. The thermal agents were also compared for their ability to decrease intrapulpal temperature in vitro. The rate of temperature decrease was greater when CO2 snow or dichlorodifluoromethane were applied to the tooth than in the case of either ethyl chloride or ice. The reliability of several pulp testing agents was compared in intact human premolar teeth. The electric pulp tester, CO2 snow and dichlorodifluoromethane were found to be more dependable than ethyl chloride and ice in producing a positive response. However, in young patients the electric pulp test was less reliable than CO2 snow and dichlorodifluoromethane but more reliable than ethyl chloride and ice. The thermal agents were also compared for their ability to decrease intrapulpal temperature in vitro. The rate of temperature decrease was greater when CO2 snow or dichlorodifluoromethane were applied to the tooth than in the case of either ethyl chloride or ice.

各種レーザー照射によるエナメル質耐酸性向上に関する研究 (第3報)

A peliminary experiments were carried out on the caries prevention with Nd-YAG laser using hamster molar teeth and intact human permanent teeth in vitro. Molar teeth of conventional hamsters were obtained from 9-14 weeks age.Human and hamster teeth were irradiated with AO Q-sw pulse and normal pulse of Nd-YAG laser at the various energy density.The results were as follows.1) There were the correlations between the value of energy density and the degree of the acquired acid-resistance of the dental enamel with AO Q-sw pulse and normal pulse of Nd-YAG laser. The pattern of acid-resistance with the two different kinds of pulses on the hamster teeth were similar to those of the human teeth.2) The lased enamel of hamster teeth indicated a grazing of surface enamel with scanning electron microscopic observation, and the morphological changes were also obtained from the human teeth. However, the degree of the morphological changes of the hamster teeth were harder than those of human teeth at the same energy density.3) The hamster teeth indicated the less variation in regard to the level of acquired acid-resistance with laser irradiatuin compared with the human teeth.These results suggested that the hamster is a good model for the experiment of acid-resistance with laser irradiation.

Spherical indentation of tooth enamel

Spherical indentation measurements were made on enamel surfaces of intact human teeth. From the load versus depth of indentation curve Young's modulus was found to be typically 8.3×1010 Pa and the yield stress to be 3.3×108 Pa. Young's modulus was observed to vary with moisture content and with the orientation of the enamel surface. Viscoelastic behaviour was evident, also depending on the moisture content of the enamel.

Variable ratios of lactate and malate dehydrogenase-like enzyme activities and LDH isoenzyme distribution in the odontoblast-predentine region of intact and carious human teeth.

Coronal odontoblast-predentine tissue was collected from intact teeth and from teeth with various types of occlusal caries. Lactate (LDH) and malate (MDH) dehydrogenase-like activities in the non-sedimentable (20,200 g), saline-soluble tissue extracts were measured. The calculated LDH/MDH ratio was higher (p < 0.050) in teeth with initial dentine caries (0.81) than in intact teeth (0.67). However, the ratios remained below 1.0 in all types of the tissues analyzed, suggesting a predominantly aerobic metabolism in the odontoblast-predentine region. In the enamel and in the initial dentine caries groups as well as in the group of teeth restored with amalgam, both the LDH and MDH values remained near to the level of intact teeth. The further development of the various lesion was associated with a gradual decrease in the dehydrogenase-like activities. This decrease became significant in recurrent carious lesions. The observation reassured the previously presented concept that a significant depression of several metabolic events occurs in the area of severe injury. Electrophoresis of odontoblast-predentine extracts revealed three anodally migrating LDH isoenzymes. Among these, LDH₂ and LDH₃ were the most prominent, both with intact and carious samples. This was thought to give further evidence of the aerobic pattern of metabolism suggested to predominate in the area.

The autoradiographic pattern of the in vitro uptake of proline by the coronal areas of intact and carious human teeth

Whole crowns of human teeth, both immediately after extraction and after preservation in liquid nitrogen, were incubated for 6 h in the presence of [ 14C]- or [ 3H]-proline. Autoradiographs were prepared from sections of intact teeth and teeth with carious lesions of varying depths and location. The number of silver grains per cm 2 in the predentine, odonto-blast layer and pulp were counted in selected fields magnified × 430 representing the deepest parts of the carious lesions. No differences in the labelling pattern were observed between the intact teeth incubated freshly after extraction and those preserved in liquid nitrogen. The densest labelling of intact teeth was seen in the predentine and odontoblast layer. The alterations under initial dentine caries appeared as increased labelling of the predentine and decreased labelling of the odontoblast layer; no alterations were observed in the underlying pulp. In advanced lesions, the predentine labelling decreased and that in the odontoblast layer and pulp increased. In the initial stages, caries seems to activate collagen synthesis in a relatively restricted area of the underlying structures, but in more advanced stages, caries seems to increase the odontoblastic cellular polypeptide chain formation but prevent further maturation of the collagen.