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PubMed2000

The fibrous structure of the cemento-dentinal junction in human molars shown by scanning electron microscopy combined with NaOH-maceration.

The cemento dentinal junction was studied in acellular and cellular cementum of human mandibular third molars by scanning electron microscopy combined with NaOH-maceration. Scanning electron microscopy with NaOH-maceration was applied to observe the fibrous structure in detail through long sections of the cemento-dentinal junction. In macerated specimens, the cemento dentinal junction was a fibril-poor groove. Some cemental fibrils or fibril bundles penetrated the groove and appeared to intermingle with dentinal fibrils. Prolonged maceration caused detachment of the cemento-dentinal junction irrespective of fibril intermingling allowing observation of the inner cementum surface facing the root dentin. Observations suggested that the fibril intermingling was point-like and present only in places at the cemento-dentinal junction. It was established that NaOH-maceration removes interfibrillar substances effectively in connective tissues and does no damage to the collagen fibril structure and architecture. This study showed the 3-dimensional fibrous structure of the cemento-dentinal junction in human mandibular third molars, and suggested that interfibrillar adhesive substances are more important than the fibril intermingling for the cemento-dentinal attachment.

Caustics↗

PubMed2002

The effects of dentine pretreatment on the adhesion of root-canal sealers.

AIM: The adhesion of five root-canal sealers to dentine and gutta-percha was studied. The effects of various dentine pretreatments on adhesion were also investigated. METHODOLOGY: Root dentine cylinders, 4 mm in diameter, were prepared from human teeth. The dentine surfaces were conditioned with either 37% H(3)PO(4) for 30 s, 25% citric acid for 30 s, 17% EDTA for 5 min or a rinse with 10 mL distilled water (control). Gutta-percha cylinders, 4 mm in diameter, were prepared and their end surfaces polished flat. The dentine and gutta-percha surfaces were coated with freshly mixed sealer: Grossman's sealer (GS), Apexit (AP), Ketac-Endo (KE), AH Plus (AH), RoekoSeal Automix (RS) or RoekoSeal Automix with an experimental primer (RP). The surfaces were pressed together and the sealers allowed to set. The test specimens were subjected to a tensile force in a universal testing machine. RESULTS: Mean tensile bond strengths (MPa +/- SD) ranged from 0.07 +/- 0.01 (AP) to 1.19 +/- 0.47 (AH). Pretreatment with EDTA showed no effect or produced weaker bonds than controls. Phosphoric and citric acid pretreatments increased adhesion of GS. A primer used with RoekoSeal significantly enhanced its adhesion to untreated dentine. Inspection of fractured surfaces indicated failure of adhesion to dentine for GS and RS and to gutta-percha for KE and RP. The failure appeared to be mainly cohesive within the sealer for AH and AP. CONCLUSIONS: Removal of the smear layer may impair sealer adhesion to dentine. Different sealer types require different dentine pretreatments for optimal adhesion.

Acid Etching, Dental↗

PubMed2002

A scanning electron microscopic study of dentinal erosion by final irrigation with EDTA and NaOCl solutions.

AIM: The purpose of this in vitro study was to examine dentinal erosion caused by final irrigation with EDTA and NaOCl. METHODOLOGY: Twenty-five single-rooted human teeth were instrumented with rotary nickel-titanium Series 29 Profile Instruments. The teeth were divided into five groups and subjected to final irrigation as follows: group A, irrigated with 6% NaOCl (3 mL) for 2 min; group B, 15% EDTA (3 mL) for 1 min; group C, 15% EDTA (3 mL) for 1 min, followed by 6% NaOCl (3 mL) for 2 min; group D, 15% EDTA (3 mL) for 3 min and group E, 15% EDTA (3 mL) for 3 min, followed by 6% NaOCl (3 mL) for 2 min. Photomicrographs of dentinal walls were produced using a scanning electron microscope (3000 x) at 1, 3 and 6 mm from the apex. The amount of debris and dentinal tubule diameter were evaluated, and values were statistically analysed using one-way ANOVA and Fisher's PLSD test. RESULTS: When the root canal was irrigated with 15% EDTA alone, the dentine had a smooth and plane appearance, and dentinal tubule orifices were regular and separated. When the root canal was irrigated with EDTA followed by NaOCL the dentine was eroded and the dentinal tubule orifices were irregular and rough. Dentinal tubule diameter increased to 3.43 +/- 0.23 microm in group C and to 3.93 +/- 0.44 microm in group E. Significant differences were observed between groups B and C, and between groups D and E (P < 0.05). However, more debris was removed by irrigation with EDTA followed by NaOCl than with EDTA alone (P < 0.05). CONCLUSIONS: Final irrigation with 6% NaOCl accelerates dentinal erosion following treatment with 15% EDTA.

Analysis of Variance↗

PubMed2003

Influence of dentinal regions on bond strengths of different adhesive systems.

This in vitro study assessed comparatively the shear bond strengths of three composite resins, 3M Valux Plus (3MVP), Herculite (H), Clearfil AP-X (CAP-X), a polyacid modified composite resin Dyract (D), and a resin modified glass-ionomer materials Vitremer (V), to cervical and buccal dentine regions of extracted human molar teeth. Four different bonding systems, 3M ScotchBond Multipurpose (SB), Clearfil Liner Bond 2 (LB2), Opti Bond (OB), and Prime & Bond 2.1 (PB 2.1) were used with the manufacturer's respective composite and compomer materials. One hundred freshly extracted mandibular molar teeth were selected for this study. Flat buccal dentine surfaces were created on 50 teeth and cylindrical rods of the five materials were bonded to the dentine surfaces. For assessment of cervical bond strengths, the materials were bonded to mesial and distal enamel bordered occlusal dentinal surfaces of the remaining 50 teeth. The five groups of restorative procedures were applied as follows; Group 1: SB + 3MVP, Group 2: LB2 + CAP-X, Group 3: OB + H, Group 4: PB2.1 + D, Group 5: Vitremer primer (VP) VP + V. Each restorative procedure thus had 20 specimens (10 buccal + 10 cervical). After 24 h of water storage (37 degrees C), the specimens were tested on a Universal Testing machine in shear with a cross head speed of 0.5 mm min-1. The bond strength values were calculated in MPa and the results were evaluated statistically using Kruskal-Wallis one-way/anova and Mann-Whitney U-tests. It was found that the bond strengths of SB + 3MVP, LB2 + CAP-X and VP + V to buccal dentine surfaces were significantly stronger (P < 0.05) than those to the occluso-cervical dentine floors. When the bond strengths to the occluso-cervical dentine and buccal dentine surface were compared, there was no significant difference between the materials (P > 0.05). Vitremer was found the least successful adhesive material in terms of shear bond strength on both buccal and occluso-cervical dentine surfaces.

Acrylic Resins↗

PubMed1999

A microradiographic and electron microscopic study of tertiary dentin in human deciduous teeth.

This study deals with the structure of the inorganic phase of tertiary dentin, and is limited to dentin formation caused by mild or moderate stimuli, e.g., attrition or initial or shallow carious lesions. Ground sections were prepared from 20 human deciduous teeth extracted mainly because of orthodontic treatment, and contact microradiographs were produced. Based on visual inspection of the ground sections in reflected and transmitted light and microradiographic findings, small areas were dissected out and processed for electron microscopy. In the tertiary dentin formed in the pulp horns the number of tubules was reduced, while in that on the side walls of the pulp there was often no marked reduction in the number of tubules. Several tubules could be followed from the physiological (primary and secondary) dentin into the tertiary dentin, and a change in the direction of the tubules was often noted. Interglobular dentin was frequently observed, and in some teeth incremental lines with alternating high and low mineral content were seen, indicating that tertiary dentin, like other mineralized tissues, is subject to biological rhythms during formation. When studied in the electron microscope, tubules with varying size and distribution as well as occluded tubules with a high mineral content were seen. The tubules often had an irregular circumference with projections of mineralized tissue protruding into the lumen. Highly mineralized peritubular dentin was rarely observed. The present results show that orthodentin is formed when dentin in primary human teeth is exposed to mild or moderate stimuli.

Dental Cavity Preparation↗

PubMed2002

Experimental dentin-based approaches to tissue regeneration in vital pulp therapy.

The potential direct induction of odontoblastlike cell differentiation at the surface of implanted dentin matrix has been tested in a series of capping experiments. Pieces of Teflon (control) or autogenous dentin matrix were placed in contact with the wound surface at a conventional capping situation, or at the dentinal base of the cavity at a distance from the exposed pulp periphery. Tissue responses were studied by light microscopy after periods of 2 and 4 weeks. Partial degradation of the dentin matrix implants was seen. Formation of a tubular calcified matrix, occasionally followed by tubular reparative dentin, was consistently detected in association with dentinal particles. The area between the traumatized dental pulp periphery and the capping material had been occupied by a well-vascularized tissue, regardless of the capping material and postoperative time period. Traces of calcified matrix were detected along the cut dentinal walls. The present data indicate that dentin matrix is limited in its ability to directly induce odontoblastlike cell differentiation and reparative dentin formation at the surface of mechanically exposed pulp of mature teeth. Furthermore, it seems that the traumatized mature pulp maintains the ability to grow, while a calcifying potential could be expressed by this growing part of the pulp core.

Animals↗

PubMed2005

Effects of laser irradiation on tensile strength of bovine dentin.

OBJECTIVE: The purpose of the present study was to investigate the tensile strengths of dentin after laser irradiation using three kinds of dental lasers to elucidate the laser-irradiation effect on dentin properties. BACKGROUND DATA: Different kinds of laser devices have been developed in dentistry. The characteristics of each laser are determined by its original wavelength; however, one common feature is to generate heat in irradiated tissues, and such heat possibly affects dentin collagen, which contributes to tensile strength of the tissues. MATERIALS AND METHODS: Er:YAG, CO2, and diode (GaAlAs) lasers were used to irradiate bovine dentin. Subsequently, tensile test specimens were made from the irradiated dentin and tensile tests were conducted. The tensile strengths were analyzed using the paired-t test and Weibull analysis. Irradiated dentin was also observed transversally using light microscopy. RESULTS: The tensile strengths of the lased dentin and the control group for the Er:YAG, CO2, and diode lasers were 73.1 and 78.5, 70.3 and 74.3, and 64.3 and 71.0 MPa, respectively. The tensile strength of the dentin had a tendency to decrease with laser irradiation. Weibull analysis indicated that the laser influence was different among the three kinds of laser apparatuses and seemed to correspond to the depths the laser beam reached, which were suggested by light microscopy observation. CONCLUSION: Laser irradiation could possibly decrease dentin tensile strength, which suggests the importance of careful use of laser for hard tissue treatment, considering its energy-transforming characteristics.

Animals↗

PubMed2000

Displacement of the contents of dentinal tubules and sensory transduction in intradental nerves of the cat.

Experiments were performed on anaesthetized cats to test the hypothesis that fluid flow through dentinal tubules is part of the mechanism involved in the transduction of pain-producing stimuli in teeth. In 11 animals, fluid flow through dentine and single- and multi-unit activity in intradental nerves were recorded simultaneously during the application of changes in hydrostatic pressure (-500 to +500 mm Hg) to exposed dentine. Seventeen A-fibres (conduction velocity (CV), 10.6-55.1 m s(-1)) were isolated that were pressure sensitive. The thresholds of these units in terms of dentinal fluid flow were in the range 0.3-2.1 nl s(-1) mm(-2) during outward flow from the pulp and 2.0-3.5 nl s(-1) mm(-2) during inward flow. All the units were more sensitive to outward than inward flow. Twenty-eight units (CV, 0.6-48.8 m s-1) were not pressure sensitive, and 12 of these had conduction velocities in the C-fibre range (< 2.5 m s(-1)). The velocities of the tubular contents were calculated by estimating the number and diameters of dentinal tubules exposed. At the threshold of single-fibre responses these velocities were in the range 31.7-222.9 microm s(-1) during outward flow 211.4-369.6 microm s-1 during inward flow. Repetitive pressure stimulation of dentine resulted in a progressive reduction in the evoked discharge, which was probably due to pulp damage. In seven animals, 10 single intradental nerve fibres were selected that responded to hydrostatic pressure stimuli and their responses to the application of hot, cold, osmotic, mechanical and drying stimuli to exposed dentine were investigated. With these stimuli dentinal fluid flow could not be recorded in vivo for technical reasons and was therefore recorded in vitro after completion of the electrophysiological recordings. With each form of stimulus, the discharge evoked in vivo was closely related to the flow predicted from the in vitro measurements. The results were therefore consistent with the hypothesis that the stimuli act through a common transduction mechanism that involves fluid flow through dentine.

Animals↗

PubMed1994

Hyperfibers and vesicles in dentin matrix in dentinogenesis imperfecta (DI) associated with osteogenesis imperfecta (OI).

Dentin matrix of deciduous teeth from two patients affected by dentinogenesis imperfecta (DI) associated with types IB and IVB osteogenesis imperfecta (OI) displayed previously undescribed structures in transmission electron microscopic examination. Vesicles were seen in dentin of both patients, and abnormally thick collagen fibers (hyperfibers) were found in dentin of the patient with the rare type IB OI. Both vesicles and hyperfibers were situated in abnormal, atubular areas of dentin. Matrix vesicles, which have normally been identified in mantle dentin only, were abundant in selected areas of the affected dentin, thereby supporting the concept that dentin matrix in OI is elaborated by successive cell generations. The hyperfibers, not previously described in either normal or abnormal human dentin, have possibly been formed by fusion of several collagen fibers. Further ultrastructural studies of dentin in DI with OI may help to clarify the marked clinical variation in teeth of patients affected by OI.

Child↗

PubMed1989

In vitro investigation of shear bond strength of a phosphate based dentinal bonding agent.

The objective with this study was to investigate how the shear bond strength of a phosphate based dentinal bonding agent is influenced by storage in saline at 37 degrees C up to 6 months. The effect of dentin bonding agent on the leachability of calcium from dentin was also determined. The results showed that the shear bond strength decreased after saline storage. After half a year, the strength was ca. 60% of the initial dry strength. The bonding agent also accelerated the leaching of calcium from the dentin discs, a finding which was explained as being a result of acidic reactions occurring at the dentin-bonding agent interface. In addition to the increased calcium leachability, the dentin bonding agent peeled off with time from the dentin discs. SEM investigation of the dentin surfaces after either shear strength determination or the film had peeled off due to water storage showed that a residual film was left on the dentin. This film, based on morphologic appearance, is most likely composed of the bonding agent but may also contain residuals of the smear layer.

Adhesives↗

PubMed1995

Effect of sucrose and xylitol diets on dentin formation and caries in rat molars.

To investigate the effects of a high sucrose diet and xylitol on secondary dentinogenesis and dentinal caries, a part of the sucrose in a high-cariogenic diet was replaced by xylitol. Fifty-four 3-wk-old Wistar rats were labeled with tetracycline and divided into groups. One group received a high sucrose diet (43% sucrose). In two other groups 5% and 20% of the sucrose was replaced by xylitol. A control group received non-cariogenic food. Six weeks later the mandibles were sectioned sagittally. Schiff staining was used to classify the caries, and the areas of dentin formed during the experiment and dentinal caries in first and second molars were measured planimetrically. The high sucrose diet reduced dentin formation of the molars, and this reduction was further increased by xylitol. Caries initiation and dentinal caries progression were significantly reduced by 20% xylitol, whereas only a slight reduction in caries progression was observed with 5% xylitol. Also, a negative correlation between the dentin formation and dentinal caries progression was observed in the high sucrose and 5% xylitol groups. In conclusion, xylitol together with high sucrose reduced dentin formation and dentinal caries progression, and the effect was dose-dependent.

Animals↗

PubMed1995

Autofluorescence of bulk sound and in vitro demineralized human root dentin.

The aim of this paper is to report on the demineralization-induced changes in dentin autofluorescence. Confocal laser scanning microscopy (CLSM) images and fluorescence excitation and emission spectra in vitro demineralized root surfaces and sound controls on the same tooth roots were compared. When observed in CLSM images, demineralized dentin, excited at 488 nm, gave an increased emission at 529 nm compared to sound dentin. The difference in fluorescence decreased deeper into the root, as the sound dentin underneath the lesion was reached. In contrast, when using fluorescence spectrophotometry, excitation around 460 and 488 nm yielded a lower emission around 520 nm for demineralized dentin than for sound dentin, but in a more pronounced peak. From excitation spectra for emission around 520 nm, it could be seen that in demineralized dentin the contribution of excitation between 480 and 520 nm was more important than in sound dentin. The recorded fluorescence in CLSM images was not affected by demineralization-caused changes in scattering and absorption properties, due to the small measurement volume. Thus, the increased fluorescence for demineralized dentin implies an increased quantum yield. In fluorescence spectrophotometry, where the measurement volume is large, changes in scattering and absorption do have an influence on the fluorescence signal. Then, increased absorption by non-fluorescing chromophores and increased re-absorption around the emission wavelength may compensate for the increase in quantum yield and absorption around the excitation wavelength by fluorophores.

Absorption↗

PubMed1999

The structure and function of the cemento-dentinal junction in human teeth.

The structure and function of the cemento-dentinal junction were studied in human molars by light and electron microscopy. The cemento-dentinal junction was an approximately 1-3-micron-thick layer full of proteoglycans with mucopolysaccharides but containing fewer collagen fibrils than the root dentin and cementum. In places, cemental fibrils crossed the cemento-dentinal junction. These fibrils appeared to intermingle with dentinal fibrils. By enzymatic treatment of decalcified specimen with hyaluronidase and trypsin, the cemento-dentinal junction decreased or lost staining affinity to toluidine blue. Prolonged treatment caused the separation of cementum from the root dentin during routine histological processes. These data suggest that the adhesion of proteoglycans is more important than the intermingling of dentinal and cemental fibrils for the cemento-dentinal attachment.

Adolescent↗

PubMed1990

Evidence for an inhibitor of osteoclast attachment in dentinal matrix.

The ability of osteoclasts to colonize in vitro different preparations of dentin extracted with guanidinium hydrochloride (GuHCl) was studied in order to establish morphological evidence for an extractable inhibitor of osteoclast spreading within dentin. Osteoclasts were isolated from neonatal rats and seeded onto pieces of fully mineralized dentin, demineralized dentin and predentin extracted with GuHCl. Osteoclasts were also seeded onto unextracted tissues. The results were evaluated with scanning electron microscopy. Osteoclasts colonized and resorbed fully mineralized dentin, whereas clastic cells were not observed on unextracted demineralized dentin and predentin. In contrast to this, osteoclasts attached and spread on demineralized dentin and predentin extracted with GuHCl. It was concluded that the non-collagenous organic component of dentin contains an extractable inhibitor of osteoclastic attachment and spreading. It is tempting to speculate that the inhibitor may be responsible for the naturally occurring resistance of dentin to resorption.

Animals↗

PubMedDate not supplied

Pronase digestion of carious dentin.

The aim of this study was to investigate the individual capabilities of the proteolytic enzyme preparation Pronase, the enzyme collagenase and sodium hypochlorite to disintegrate and solubilize carious dentin. Samples of carious dentin, and samples of sound dentin for comparison, were extracted 4 times in succession for 24 h with buffered solutions of Pronase. Separate carious dentin samples were extracted in the same manner with buffered solutions of collagenase or with aqueous sodium hypochlorite. The extracts, the solid residues left over after the extractions and untreated samples of carious and sound dentin were digested with sulfuric acid-H(2)O(2) and then analyzed for nitrogen content by a special adaptation of the Berthelot color reaction. Although Pronase did not attack sound dentin, it solubilized more than 90% of the nitrogen present in carious dentin. Collagenase solubilized approximately 66% of the nitrogen, whereas sodium hypochlorite released only 12-20% of the nitrogen of carious dentin. In clinical dentistry, chemical disintegration of carious dentin may reduce the need for mechanical removal of sound tooth structure.

Collagenases↗

PubMedDate not supplied

Caries progression and inhibition in human and bovine root dentine in situ.

Since the use of bovine instead of human dentine to evaluate cariogenic and anticariogenic substances is not well established, this in situ study was conducted. Eleven volunteers wore palatal acrylic devices containing 4 dentine slabs (2 human and 2 bovine). Sucrose solution (20%) was dripped over all slabs 4 times a day, simulating a cariogenic challenge. Dentifrice slurries, fluoridated or not, were dripped over specified dentine slabs 3 times a day to evaluate caries reduction. After 14 days, the biofilm formed on the dentine slabs was collected for microbiological analysis. In dentine, mineral loss (DeltaZ) and lesion depth (LD) were determined by cross-sectional microhardness and by polarized light microscopy, respectively. The total streptococci and mutans streptococci counts in the biofilm formed either on human or on bovine slabs, whether treated or not with fluoride dentifrice, were not statistically different. The DeltaZ and the LD values of dentine treated with fluoride dentifrice were significantly lower than the values of dentine treated with non-fluoride dentifrice. The differences in the DeltaZ and LD values between the human and bovine dentine were not statistically significant. The results suggest that bovine dentine can be used instead of human to evaluate caries development and inhibition.

Animals↗

PubMed2006

Microhardness as a predictor of sound and carious dentine removal using alumina air abrasion.

Clinical air abrasion is known to remove dental hard tissues effectively. The aim of this study was to quantify and compare the efficiency of alumina air abrasion in the removal of sound and carious dentine. Twelve non-cavitated carious lesions in freshly extracted molars were bisected mesiodistally. The Knoop hardness number (KHN) was measured on the cut sample surface at 250-microm intervals along a line running axially through the centre of the lesion, from the enamel-dentine junction to the pulp including both sound and carious tissue. The cut surface was then abraded over the same path using alumina particles (27 microm). Powder flow rates, pressure, distance and the angle of the nozzle to the tooth were kept constant throughout the experiment. Non-contact surface profilometry and surface analysis software were used to calculate the rate of dentine removal at the site of each KHN measurement. The results showed that dentine Knoop hardness can be used as a predictor of the rate of dentine removal, with a Somers' D value of 0.826. Carious dentine with a low KHN was removed less efficiently than the hard sound dentine with a higher KHN. Thus, dentists should be aware that air abrasion systems using alumina particles remove healthy dentine more efficiently than carious dentine, with the associated implications for clinical caries excavation and cavity preparation.

Air Abrasion, Dental↗

PubMed1995

Effect of air-drying on demineralized and on sound coronal human dentine: a study on density and on lesion shrinkage.

Recently, several papers investigated the linear dimensional changes in dentine after air-drying. This paper pertains to weight changes, volume changes, and density changes caused by air-drying of sound and demineralized intact dentine. The densities of sound and artificially demineralized human coronal dentine were measured in the wet state and after various drying periods of up to 24 h. The volume was assessed either by means of a pyknometer (wet samples) or by means of dimension measurements. The air-drying experiments were done using a Mettler thermobalance at room temperature. The density of wet sound coronal dentine was found to be 2.24 +/- 0.12 g.cm-3; the value of wet demineralized dentine was about 1.6 g.cm-3. The data show that previously published density values of powdered sound dentine may have been influenced by powdering effects, air-drying, and air inclusion. In whole demineralized air-dried dentine, air inclusion can be very severe: up to 30% by volume. The results show furthermore that in demineralized dentine we have two drying stages: during the first one (up to about 10 min of air-drying), the lesions shrink about 23%, while a main part of the water in the lesion evaporates, and air is incorporated into the tissue; during the second stage (drying longer than 10 min), the lesions hardly shrink anymore, but water is evaporated mainly from underlying sound dentine, followed by air incorporation.

Air↗