Dentin tubule numerical density variations below the CEJ.

AIM: To evaluate dentin tubule numerical density variations below the CEJ. METHODOLOGY: Three human non-carious permanent canines were sectioned parallel to the CEJ to obtain dentin disks 1mm thick whose surfaces were 1mm and 2mm below the CEJ. Each disk was sectioned into quarters resulting in four segment locations: facial, lingual, mesial, and distal. The outer (PDL side) and inner (pulp side) surfaces of the specimens were shaped to expose dentin with SiC papers and polished. Numerical tubule density was determined from SEM images. All data were statistically analyzed using a three-way ANOVA. RESULTS: The dentin tubule density (number/mm(2)) ranged from 13,700 to 32,300. Dentin tubule density was relatively uniform at 1mm and 2mm below the CEJ and increased by a factor of about two from the outer to the inner surface, which was significantly different (P<0.0001). CONCLUSIONS: The tubule density variations at the cervical root did not present marked.

Dentin erosion simulation by cantilever beam fatigue and pH change.

Exposed root surfaces frequently exhibit non-carious notches representing material loss by abrasion, erosion, and/or abfraction. Although a contribution from mechanical stress is often mentioned, no definitive proof exists of a cause-effect relationship. To address this, we examined dimensional changes in dentin subjected to cyclic fatigue in two different pH environments. Human dentin cantilever-beams were fatigued under load control in pH = 6 (n = 13) or pH = 7 (n = 13) buffer, with a load ratio (R = minimum load/maximum load) of 0.1 and frequency of 2 Hz, and stresses between 5.5 and 55 MPa. Material loss was measured at high- and low-stress locations before and after cycling. Of the 23 beams, 7 withstood 1,000,000 cycles; others cracked earlier. Mean material loss in high-stress areas was greater than in low-stress areas, and losses were greater at pH = 6 than at pH = 7, suggesting that mechanical stress and lower pH both accelerate erosion of dentin surfaces.

Dentin shear strength: effect of distance from the pulp.

OBJECTIVE: Dentin structure varies with orientation and location. Ultimate shear strength (USS) has also been found in previous studies to vary with location. The present study further explores this relationship between USS and various locations in coronal dentin as well as distance from the pulp. METHODS: Stick specimens were prepared from coronal dentin located in the center or under cusps of human molar teeth. These were tested in the shear mode at various distances from the pulp. RESULTS: Median values ranged from 52.7 (range 29.0-73.1) MPa near the pulp to 76.7 (range 53.9-104.0) MPa near the dentino-enamel junction. No differences were found among the buccal, central or lingual locations, however, the USS near the pulp was found to be significantly lower. SIGNIFICANCE: The properties of coronal dentin vary with distance from the pulp, which may affect adhesion and other aspects of restorative dentistry.

Dentin shear bond strength of compomers and composites.

OBJECTIVE: The aim of this study was to compare the shear bond strengths and fracture characteristics of two compomers bonded with a single step bonding agent with two modern composites, a microfil and hybrid, bonded with a fourth generation bonding agent. METHODS: Freshly extracted human third molars were sectioned parallel to the occlusal surface to expose midcoronal dentin, prepared with 320-grit surface finish, and bonded (N = 11 samples/group) following manufacturer's directions with the compomers (Dyract, DeTrey Konstanz, Germany or Compoglass, Vivadent, Schaan Liechtenstein) or the dentin bonding agent SMP+ (Scotchbond Multi-Purpose Plus, 3M Dental Products, St. Paul MN) with Silux Plus or Z100 (3M Dental Products, St. Paul, MN). The samples were tested using a single plane lap shear bond strength test at 5 mm/min until failure. Statistical analysis was performed using ANOVA with Scheffe multiple comparison testing. Fracture surfaces of the debonded surfaces were examined using SEM to determine the failure mode of each specimen. RESULTS: Bond strengths for the compomers were 12.7 +/- 2.9 MPa for Dyract and 8.9 +/- 4.1 MPa for Compoglass and were not significantly different. Bond strengths for the dentin bonded composites were significantly stronger than the compomer Compoglass, but were not different from one another, despite the use of different composites. The averages values for SMP + /Silux Plus and SMP + /Z100 were 15.7 +/- 4.5 MPa and 15.2 +/- 5.6 MPa, respectively. SEM analysis showed that all materials exhibited mixed failure patterns. Compoglass specimens exhibited 5 of 11 failures classified as adhesive, while each of the other materials showed only 1 of 11 adhesive failures. SIGNIFICANCE: Compomers have undergone rapid development over the last several years, but their bond strengths have not yet reached the same level as modern dentin bonded composites. Difference in composite filler type and amount had little influence on the bond strength determined in this work.

Microhardness of carious deciduous dentin.

The purpose of this study was to measure the microhardness values of deciduous dentin and to compare the values as a function of position in the caries-affected layers of dentin including transparent, adjacent sound dentin, and dentin regions far from and not related to caries. Seven extracted or exfoliated deciduous anterior teeth that had dentin caries on a proximal surface were sectioned parallel to the long axis of the tooth. Ten sectioned and polished specimens were dehydrated and dried. Microhardness was measured with a Knoop indenter and correlated with wet-SEM micrographs. All data were statistically analyzed using a two-way ANOVA with subsequent Tukey-Kramer multiple comparison tests at p < 0.05. The hardness decreased from the dentinoenamel junction to the pulp chamber wall, except for the region under the caries. The hardness values of the region under the caries were significantly lower than those of other regions except for the inner region. For both the carious and sound sides, the hardness values of the inner region were significantly lower than those of the outer and middle regions. In comparing the hardness among regions in the carious and sound sides, the hardness of the outer, middle, and inner regions on the carious side was significantly lower than those in the sound side.

Acid-etching and hydration influence on dentin roughness and wettability.

Adhesion of restorative and protective materials to dentin is an important requirement for operative and preventive dentistry. Wettability and roughness are dentin substrate conditions that are critical to establishing good adhesion. This study examined superficial and deep dentin for variations in water contact angle measurements and roughness for polished, etched, dehydrated, and rehydrated states. Superficial and deep dentin disks from 6 non-carious third molars were prepared for AFM (Atomic Force Microscope) observation, roughness measurement, and contact angle measurements following specific treatments: hydrated and polished, etched (10% H3PO4), dehydrated (desiccator for 24 hrs); and rehydrated (in water for 24 hrs). Contact angles were measured by means of the ADSA (Axisymmetric Drop Shape Analysis) technique with filtered and purified water of surface tension 72.79 ergs/cm2. The AFM was used to quantify the intertubular roughness. Mean and SD of roughness and contact angle were calculated for each dentin state, and two-way Repeated Measures ANOVA with Tukey's HSD multiple comparisons were performed at p < 0.05. Wetting and roughness both increased after etching, with roughness tending to increase further while wettability dramatically decreased after desiccation. After rehydration, water contact angle values were equivalent to those of the etched condition. Although intertubular roughness did not depend on depth, lower water contact angles were found for deep dentin. Depth and dehydration resulted in altered dentin substrates with exposed hydrophobic moieties that could interfere with bonding to hydrophilic primer coats.

Adhesion between collagen depleted dentin and dentin adhesives.

PURPOSE: To determine the influence of sodium hypochlorite treatment of dentin on shear bond strength and morphology. MATERIALS AND METHODS: Shear bond strengths of several dentin bonding agents were compared following specific surface treatments that included manufacturer's directions, etching plus sodium hypochlorite, and sodium hypochlorite alone. The treated surfaces and interfaces between bonding materials and treated surfaces were observed using an FE-SEM. RESULTS: Acetone-containing systems yielded equivalent or higher shear bond strengths when sodium hypochlorite was used following etching, as compared with normal procedures. In these cases it is proposed that the adhesive interacts strongly with the treated surface, that contains a high mineral content.

Effect of citric acid concentration on dentin demineralization, dehydration, and rehydration: atomic force microscopy study.

Most current dentin bonding procedures use acid etchants to partially demineralize the dentin structure and provide pathways for resin infiltration. This study determined the recession rates of peritubular dentin and intertubular dentin as a function of pH during demineralization in citric acid solutions (0.0005-2.5M) and the effects of dehydration and rehydration on the partially demineralized dentin. Polished dentin disks were prepared with an internal reference layer and were studied at specific intervals for citric acid etching between pH 1 and 3.4 in an atomic force microscope. Peritubular dentin etched rapidly and linearly with time until it could no longer be measured. The intertubular surface began etching at nearly the same rate, but then recession slowed for all concentrations and stabilized after recession of less than 1 microm for all but the pH 1 solution. The decrease in recession was attributed to the limitation of contraction of the demineralized collagen scaffold as long as it remained hydrated. Dehydration following etching resulted in significant collapse of the surface, changes in roughness, and a slight decrease in tubule diameter for samples etched for 30 min. Measurements could not be made of the collapse for low pH samples, because shrinkage stresses disrupted the integrity of the reference layer. On rehydration, the dehydrated surfaces underwent an expansion up to the level seen after etching and tubule diameters returned to the etched values. These results indicate that the collapse of demineralized matrix is almost totally recoverable on rehydration.

Removal of intracanal smear by doxycycline in vitro.

UNLABELLED: Cleansing and shaping result in a smear layer on the instrumented canal wall surfaces. The smear layer may inhibit close contact between sealers and dentin, and inhibits diffusion of medicaments. OBJECTIVE: This study assessed the effect of doxycycline hydrochloride (DH) on smear layer on intracanal walls. STUDY DESIGN: Scanning electron microscopy was used to evaluate the remaining smear layer using different concentrations of DH. Single-canal palatal roots of extracted maxillary molars were irrigated with saline-15% EDTA; saline-25 mg/ml DH; saline-50 mg/ml DH; saline-100 mg/ml DH; NaOCl-15% EDTA; NaOCl-25 mg/ml DH; NaOCl-50 mg/ml DH; and NaOCl-100 mg/ml DH. The roots were fractured into halves and the amount of smear layer assessed in the middle and apical third. RESULTS: Doxycycline-HCl of 100 mg/ml was the most effective in removing smear layer. In the saline group, 100 mg/ml of DH was more effective than EDTA. In the hypochlorite group, 50 mg/ml and 100 mg/ml of DH were more effective than EDTA (p < 0.05). CONCLUSION: Doxycycline solution may be an effective irrigant.

The effect of endodontic medicaments on the sealing ability of provisional restorative materials.

The purpose of this study was to determine the effect of intracanal medicaments on the sealing ability of commonly used provisional filling materials. Ninety extracted, unrestored human molars were prepared. The contents of the pulp chamber were removed, and distal and mesial root canal systems were cleansed to a size 25 file. Group A received a cotton pellet with no medication, group B a cotton pellet with Cresatin, and group C a cotton pellet with 2% iodine potassium iodide (IKI). The prepared teeth from each category were divided into three subgroups of 10 to receive Cavit, IRM, or TERM. After the fillings were placed, the teeth were thermocycled, stained, and sectioned longitudinally. The average dye penetration was greater in the medicated groups (B and C) than in the control group (A) for each provisional material tested. Statistical analysis revealed that sealing ability of all three filling materials was significantly affected by Cresatin and 2% IKI.

Dentin shear strength: effects of tubule orientation and intratooth location.

OBJECTIVES: Dentin has a highly oriented tubule structure, and the tubule number density and area fraction of intertubular dentin vary with distance from the pulp. This investigation sought to determine the influence of tubule orientation on shear strength of dentin from samples derived at various intratooth locations. METHODS: Third molars were sectioned and prepared to provide samples from two locations (center and cusp) and with one of three specific tubule orientations. In series 1, matched pairs of midcoronal samples were tested using two tubule orientations. A paired t-test was used for statistical analysis. In series 2, three samples from central and cuspal areas were tested using three different tubule orientations. A two-day ANOVA was used for statistical analysis. Each sample had dimensions of approximately 1 x 1 x 5 mm and was tested in a hydrated state by a single plane lap shear method. RESULTS: The paired dentin samples of the midcoronal dentin in the two orientations had shear strengths of 72.4 +/- 15.6 MPa and 78.4 +/- 13.2 MPa, and were not significantly different (p > 0.05; paired t-test). In the second series, samples from the center location with tubules parallel to the shear plane with applied force in directions rotated by 90 degrees did not exhibit a significant difference (p > 0.05), with an average value of 53.5 +/- 9.5 MPa. Samples oriented with tubules along the long axis of the specimen and tested with shear force applied perpendicular to the tubule direction had significantly higher (p < 0.05; two-way ANOVA) shear strength (78.0 +/- 8.5 MPa). The specimens from the cusp area did not exhibit a statistically significant difference (p > 0.05; two-way ANOVA) with respect to the three orientations (83.6 +/- 8.4; +/- 13.8; 91.8 +/- 12.7 MPa). Cuspal areas were stronger than central areas in two of the three orientations tested. SIGNIFICANCE: Results indicated that the shear strength differs in central and cusp areas and is dependent on dentin tubule orientation in the central area. Shear strengths were much larger than values reported in shear bond strength tests. This suggests that dentin shear strength is far in excess of dentin bond strengths using shear tests, and that fractures through dentin in such result from flaws or stress concentration in the dentin.

The mandibular incisor: rethinking guidelines for post and core design.

In post and core research, little attention has been given to the tooth with minimal bulk and mesialdistal width. The purpose of this in vitro study was to investigate retention and fracture characteristics of lower incisors restored with variable dowel designs. Fifty freshly extracted mandibular incisors were endodontically treated. Four groups of 10 teeth, decoronalized and dowel- and core-restored, were tested for retention characteristics and fracture resistance. One group of 10 teeth restored with composite resin in intact natural crown acted as controls. Dowel variables included a prefabricated round cross-sectional design and a morphologic dowel that reproduced the canal space. A universal testing machine created tensile and transverse loads, and failure was measured and recorded. Results showed no difference in resistance to transverse loading between morphological and standardized dowels (p > 0.05). However, when analyzing modes of failure, ferruled morphological post and core design was less likely to result in a catastrophic root or post fracture. In addition, morphological dowels were significantly more retentive than standardized round dowels in teeth with narrow cross-sections (p = 0.007). This study also reaffirmed the findings of previous investigations, that the intact natural crown of an endodontically treated tooth provides maximum resistance to root fracture.

The effect of glass ionomer liners in lowering pulp temperatures during composite placement, in vitro.

New restorative systems allow for more esthetic restorations, but may cause adverse pulp tissue reactions due to either physical or chemical effects. This study evaluated the effect of glass ionomer liners in limiting temperature rise during composite placement with visible light-cure lamps. Neither chemical or light-cured glass ionomer liners limited the amount of pulp chamber temperature rise. Exposure time of the light-cure lamps played the greatest role in pulpal temperature rise regardless of glass ionomer liner of composite. Visible light-cure lamps varied in the amount of heat emitted.

Tensile adhesion evaluation in a new universal test.

A tensile testing jig was designed to test adhesion between various materials and tooth surfaces, and between materials of various consistencies, modes of setting and properties. This study examined the adhesion of both flowable and condensable, light cured and chemically cured, direct and indirect restorative materials to dentin. All materials were mixed and placed according to manufacturer's directions. The bonds were tested in tension after 24 hours. The substrate was dentin, except in group 1. Results in MPa +/- SD: 1. Photobond & Photoposterior to enamel 15.84 +/- 3.93; 2. Superbond C&B and metal inlay 6.20 +/- 3.00; 3. SuperBond C&B and amalgam 5.76 +/- 1.89; 4. All-Bond and metal inlay 4.46 +/- 1.16; 5. Mirage Bond and Newbond and amalgam 2.97 +/- 0.85; 6. Vitrebond 2.06 +/- 0.95; 7. Newbond and amalgam 1.70 +/- 0.61; 8. Ketac-Bond 0.73 +/- 0.40. The groups (2,3,4), (4,5), (5,6,7) and (6,7,8) were not significantly different at the 95% confidence level, calculated by the Student-Newman-Keuls test. The testing method was useful for all materials studied.

Load-deflection characteristics of nickel-titanium alloy wires after clinical recycling and dry heat sterilization.

The desirable mechanical properties of nickel-titanium alloy wires and their relatively high cost has prompted many clinicians to recycle these wires. Clinical recycling exposes the wires to several weeks or months of mechanical stresses and elements of the oral environment, as well as sterilization between uses. In a previous study it was noted that clinical recycling combined with cold sterilization alters the load-deflection characteristics and surface topography of nickel-titanium wires. Whether similar changes in mechanical properties occur in wires subjected to repeated clinical use and dry heat sterilization is not yet clear. The purpose of this investigation was to determine the effects of in vivo recycling interposed by dry heat sterilization (together referred to as clinical recycling, CR) on the load-deflection characteristics of nickel-titanium alloy wires. To differentiate the effects of dry heat sterilization (DHS) from those of CR on the behavior of these wires, a series of wires were also subjected to DHS only. Two types of nickel-titanium wires, namely Nitinol and NiTi were subjected to a three-point bending test in an as-received condition (T0), after one cycle (T1), and two cycles (T2) of DHS or CR. Ten wires comprised each subsample. Statistical analyses were done by one-factor repeated measures analysis of variance and Scheffe F test. Both DHS alone, as well as CR, produced significant changes in the loading and unloading characteristics of Nitinol and NiTi wires. However, the changes in the load-deflection characteristics of these wires after DHS only were relatively small, and the clinical significance of these changes is open to question.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of clinical recycling on mechanical properties of nickel-titanium alloy wires.

The purpose of this investigation was to determine the effects of clinical recycling on the load-deflection characteristics and the surface topography of nickel-titanium alloy wires. Thirty wires each of Nitinol and NiTi were subjected to a three-point bending test in an as-received condition (T0) and after clinical exposure of one cycle (T1) and two cycles (T2). Ten wires made up the sample at each of these time points. One cycle was defined as 8 weeks, plus or minus 1 week, of clinical use. Wires undergoing two recycles were cold sterilized after their first clinical exposure. Statistical analyses were done by one-factor repeated measures ANOVA and Scheffe F test. Recycling produced significant changes in both the loading and unloading characteristics of NiTi wires, but only with the loading forces associated with nitinol wires. Representative scanning electron micrographs demonstrated increased pitting of both nitinol and NiTi wires. Several areas were also observed to be smoothened on nitinol wires and scored on NiTi wires.

Application of a device to lower pulpal temperatures in vivo.

Heat generated by tooth reduction and restoration procedures may be harmful to the pulp. Water spray during those procedures aids in maintaining lowered pulpal temperatures. A device that lowers intrapulpal temperatures has been developed and tested in an animal model. The animal's pulp chamber temperatures were lowered to 15.5 degrees C and 12.4 degrees C and maintained at those temperatures for 20 min. Histological examinations disclosed no inflammatory reaction to the testing. Therefore, this device may aid in reducing the trauma of dental preparation procedures as well as other effects of lowered temperature on the biology of the dental pulp.

Shear bond strength of visible-light-cured resin relative to heat-cured resin.

One promising clinical application of visible-light-cured (VLC) denture resin is for relining complete and partial dentures. Typically, a VLC resin would be used to reline an existing prosthesis fabricated from heat-cured resin (HCR). This study measured the shear bond strength of a VLC resin bonded to HCR specimens by different bonding agents. For comparison, we measured the shear bond strengths of VLC resin bonded to VLC resin specimens and of autopolymerizing resin (APR) to HCR specimens. Cylindrical specimens of HCR (n = 126) and VLC (n = 24) were thermocycled to simulate aging, and the bonding surfaces were prepared by being sanded to approximate clinical roughness. The specimens were divided into seven groups of approximately 20 each, and test materials were bonded by different bonding agents. Statistical analysis by ANOVA and the Student-Newman-Keuls test showed significant differences (p less than 0.05) among all groups except APR to HCR/no bonding agent, VLC to HCR/VLC bonding agent, or VLC to HCR/VLC and HCR bonding agent. The traditional bond of APR to HCR with HCR bonding agent was significantly stronger (p less than 0.05) than the strongest bond of VLC to HCR with HCR and VLC bonding agents.

Adhesive monomers for porcelain repair.

The purpose of this investigation was to test the bond strengths of several adhesive systems intended for intraoral resin-to-porcelain and resin-to-metal bonding. All measurements were compared with resin bonding to etched bovine enamel. Based on these data and the authors' own clinical experiences, protocols for intraoral porcelain repair are presented for fractures in porcelain only, fractures with both porcelain and metal exposed, and fractures with all metal exposure.