Synthetic octacalcium phosphate-enhanced reparative dentine formation via induction of odontoblast differentiation.

Synthetic octacalcium phosphate (OCP) has been suggested to be a useful biomaterial for the regeneration of hard tissues, including bone. However, it remains unknown whether OCP induces dentine formation by dental pulp. We investigated biomineralization of dental pulp exposed to synthetic OCP in vitro and in vivo. When dental pulp was exposed directly to OCP, rapid formation of reparative dentine (RD) was induced and expression of dentine sialoprotein synthesis was observed in dental pulp adjacent to newly synthesized RD. OCP inhibited the proliferation of rat pulp cells and also promoted their odontoblastic differentiation in vitro, as alkaline phosphatase activity, mineralization of pulp cells and the expression level of dentine sialophosphoprotein were enhanced. Direct contact between OCP and pulp cells is required for OCP to exhibit its effects in vitro. The expression level of Runx2, a transcription factor whose downregulation is closely related to odontoblast differentiation, was downregulated in pulp cells cultured with OCP. Structural changes of OCP during culture were determined by Fourier transform infrared spectroscopy. OCP tended to be converted to carbonate hydroxyapatite after incubation with or without pulp cells, which may be analogous to biological apatite crystals. Taken together, our data suggest that synthetic OCP supports RD formation by dental pulp and downregulation of Runx2 may be involved in that stimulatory activity. Furthermore, OCP-apatite conversion is involved in this stimulatory capacity of OCP.

A Fourier transform infrared spectroscopy analysis of carious dentin from transparent zone to normal zone.

It is well known that caries invasion leads to the differentiation of dentin into zones with altered composition, collagen integrity and mineral identity. However, understanding of these changes from the fundamental perspective of molecular structure has been lacking so far. In light of this, the present work aims to utilize Fourier transform infrared spectroscopy (FTIR) to directly extract molecular information regarding collagen's and hydroxyapatite's structural changes as dentin transitions from the transparent zone (TZ) into the normal zone (NZ). Unembedded ultrathin dentin films were sectioned from carious teeth, and an FTIR imaging system was used to obtain spatially resolved FTIR spectra. According to the mineral-to-matrix ratio image generated from large-area low-spectral-resolution scan, the TZ, the NZ and the intermediate subtransparent zone (STZ) were identified. High-spectral-resolution spectra were taken from each zone and subsequently examined with regard to mineral content, carbonate distribution, collagen denaturation and carbonate substitution patterns. The integrity of collagen's triple helical structure was also evaluated based on spectra collected from demineralized dentin films of selected teeth. The results support the argument that STZ is the real sclerotic layer, and they corroborate the established knowledge that collagen in TZ is hardly altered and therefore should be reserved for reparative purposes. Moreover, the close resemblance between the STZ and the NZ in terms of carbonate content, and that between the STZ and the TZ in terms of being A-type carbonate-rich, suggest that the mineral that initially occludes dentin tubules is hydroxyapatite newly generated from odontoblastic activities, which is then transformed into whitlockite in the demineralization/remineralization process as caries progresses.

Tenascin and fibronectin expression after pulp capping with different hemostatic agents: a preliminary study.

This study investigated the expression of extracellular matrix glycoproteins tenascin (TN) and fibronectin (FN) in pulp repair after capping with calcium hydroxide (CH), following different hemostasis protocols. Class I cavities with a pulp exposure were prepared in 42 human third molars scheduled for extraction. Different hemostatic agents (0.9% saline solution, 5.25% sodium hypochlorite and 2% chlorhexidine digluconate) were used and pulps were capped with CH cement. After 7, 30 or 90 days, teeth were extracted, formalin-fixed, and prepared for immunohistochemical technique. Hemostatic agents did not influence the expression of TN and FN. Both glycoproteins were found in the entire the pulp tissue and around collagen fibers, but were absent in the mineralized tissues. In the predentin, TN showed positive immunostaining and FN had a variable expression. Within 7 days post-treatment, a slightly more pronounced immunostaining on the pulp exposure site was observed. Within 30 days, TN and FN demonstrated a positive expression around the dentin barrier and at 90 days, a thin and linear expression of TN and FN was delimitating the reparative dentin. In conclusion, hemostatic agents did not influence TN and FN expression. Immunostaining for TN and FN was seen in different regions and periods, demonstrating their role in pulp repair.

Nuclear expression of p27(Kip1) is associated with in vivo differentiation of adult human odontoblasts.

INTRODUCTION: Odontoblasts are terminally differentiated cells of ectomesenchymal origin that produce the dentin. Differentiated odontoblasts cannot be identified yet by a single phenotypic marker protein; therefore, a combination of markers is currently used. Up-regulation of the cyclin-dependent kinase inhibitor p27(Kip1) has been associated with exit from the cell cycle and terminal differentiation of mammalian cells. Immunoreactivity for p27(Kip1) protein was shown in many adult mouse tissues, but no information is available on the expression of p27(Kip1) in mammalian dental pulp. METHODS: Healthy and carious adult human molars with reparative dentin formation were decalcified, cryoprotected, frozen embedded, and frozen sectioned. The expression of p27(Kip1) and nestin in cells of adult human dental pulp was analyzed by immunohistochemistry using free floating sections. RESULTS: p27(Kip1) showed strong nuclear expression in many differentiated human molar odontoblasts at the odontoblastic layer. Most cells of the cell-rich zone displayed low levels of p27(Kip1) despite the fact that preodontoblasts localized in the cell-rich zone of the subodontoblastic layer have been identified as quiescent cells. The nuclear expression of p27(Kip1) in stromal cells of the dental pulp was variable, indicating that subpopulations of these cells were in distinct states of differentiation. Odontoblasts generating reparative dentin showed comparable nuclear expression of p27(Kip1) in comparison with odontoblasts synthesizing primary/secondary dentin. This result indicates that odontoblasts synthesizing primary/secondary or reparative dentin exhibit a similar differentiation status. CONCLUSIONS: Our findings show that increased expression of nuclear p27(Kip1) occurred during differentiation from preodontoblasts to odontoblasts in adult healthy and carious molars. p27(Kip1) can be used as a novel nuclear marker protein for differentiated human odontoblasts in vivo.

Tenascin and Fibronectin Expression after Pulp Capping with Different Hemostatic Agents: A Preliminary Study

This study investigated the expression of extracellular matrix glycoproteins tenascin (TN) and fibronectin (FN) in pulp repair after capping with calcium hydroxide (CH), following different hemostasis protocols. Class I cavities with a pulp exposure were prepared in 42 human third molars scheduled for extraction. Different hemostatic agents (0.9% saline solution, 5.25% sodium hypochlorite and 2% chlorhexidine digluconate) were used and pulps were capped with CH cement. After 7, 30 or 90 days, teeth were extracted, formalin-fixed, and prepared for immunohistochemical technique. Hemostatic agents did not influence the expression of TN and FN. Both glycoproteins were found in the entire the pulp tissue and around collagen fibers, but were absent in the mineralized tissues. In the predentin, TN showed positive immunostaining and FN had a variable expression. Within 7 days post-treatment, a slightly more pronounced immunostaining on the pulp exposure site was observed. Within 30 days, TN and FN demonstrated a positive expression around the dentin barrier and at 90 days, a thin and linear expression of TN and FN was delimitating the reparative dentin. In conclusion, hemostatic agents did not influence TN and FN expression. Immunostaining for TN and FN was seen in different regions and periods, demonstrating their role in pulp repair.

Este estudo investigou a expressão das glicoproteínas Tenascina (TN) e Fibronectina (FN) da matriz extracelular no reparo pulpar após capeamento com hidróxido de cálcio (HC), seguindo diferentes protocolos de hemostasia. Cavidades de classe I com exposição pulpar foram preparadas em 42 terceiros molares humanos indicados para extração. Diferentes agentes hemostáticos (solução salina a 0,9%, hipoclorito de sódio a 5,25% e clorexidina a 2%) foram usados e as polpas foram capeadas com cimento de HC. Após 7, 30 ou 90 dias, os dentes foram extraídos, fixados em formalina e preparados para análise imunoistoquímica. Os agentes hemostáticos não influenciaram a expressão de TN e FN. Ambas glicoproteínas foram encontradas em todo tecido pulpar, ao redor das fibras colágenas e estiveram ausentes nos tecidos mineralizados. Na pré-dentina, a TN mostrou forte imunoexpressão e a FN teve uma expressão variável. Após 7 dias, foi observada uma expressão levemente mais pronunciada no lugar da exposição pulpar. Aos 30 dias, a TN e a FN demonstraram uma expressão mais forte sob a barreira dentinária e aos 90 dias, uma expressão fina e linear da TN e FN apresentava-se delimitando a dentina reparativa. Em conclusão, os agentes hemostáticos não influenciaram e expressão da TN e da FN. A imunoexpressão da TN e FN foi observada em diferentes regiões e períodos, demonstrando o seu papel no reparo pulpar.

Chemical characterization of etched dentin in non-carious cervical lesions.

PURPOSE: Bonding to non-carious cervical lesion (NCCL) sclerotic dentin that involves acid etching continues to be a challenging problem due to its altered chemical structure. In the present study, the objective was to investigate the chemical response of NCCL sclerotic dentin to the different acid etching times. MATERIALS AND METHODS: Extracted human premolars affected with NCCLs were selected, and a cavity matching the natural lesion with respect to size and location was prepared on the lingual surface of each tooth to serve as the control. The dentin surfaces were treated for 15 s and 30 s using 37% phosphoric acid and then analyzed by Raman microspectroscopic mapping/imaging. RESULTS: NCCL dentin substrates had dramatic effects on the chemical profile of dentin demineralization. The spectral comparison showed that the demineralized layer generated by the acid treatment was highly irregular in terms of depth and mineral component retained, especially when NCCL sclerotic dentin was etched for 15 s. When the etching time was increased to 30 s, the demineralization of NCCL sclerotic dentin was more effective and comparable to the nonsclerotic control that was treated for 15 s. Different etching times affected the depth, degree, and profile of the dentin demineralization. CONCLUSION: The shorter etching time (ie, 15 s) might not be adequate for NCCL sclerotic dentin. However, the longer etching time (ie, 30 s) would induce much deeper demineralized dentin for nonsclerotic substrates. Thus, although extended etching times can be used to remove the hypermineralized layer, further studies are required to analyze the impact this might have on the dentin bonding.

Dentin bonding-variables related to the clinical situation and the substrate treatment.

The wetness of dentin surfaces, the presence of pulpal pressure, and the thickness of dentin are extremely important variables during bonding procedures, especially when testing bond strength of adhesive materials in vitro with the intention of simulating in vivo conditions. The ultimate goal of a bonded restoration is to attain an intimate adaptation of the restorative material with the dental substrate. This task is difficult to achieve as the bonding process is different for enamel and for dentin-dentin is more humid and more organic than enamel. While enamel is predominantly mineral, dentin contains a significant amount of water and organic material, mainly type I collagen. This humid and organic nature of dentin makes this hard tissue very challenging to bond to. Several other substrate-related variables may affect the clinical outcome of bonded restorations. Bonding to caries-affected dentin is hampered by its lower hardness and presence of mineral deposits in the tubules. Non-carious cervical areas contain hypermineralized dentin and denatured collagen, which is not the ideal combination for a bonding substrate. Physiological transparent root dentin forms without trauma or caries lesion as a natural part of aging. Similar to the transparent dentin observed underneath caries lesions, the tubule lumina become filled with mineral from passive chemical precipitation, making resin hybridization difficult. An increase in number of tubules with depth and, consequently, increase in dentin wetness, make bonding to deeper dentin more difficult than to superficial dentin. While the application of acidic agents open the pathway for the diffusion of monomers into the collagen network, it also facilitates the outward seepage of tubular fluid from the pulp to the dentin surface, deteriorating the bonding for some of the current adhesives. Some dentin desensitizers have shown some promise as they can block dentinal tubules to treat and prevent sensitivity and simultaneously blocking the tubular fluid from flowing to the surface. A new approach to stop the degradation of dentin-resin interfaces is the use of MMP inhibitors. Although still in an early phase of in vitro and clinical research, this method is promising.

Dentin phosphophoryn promotes cellular migration of human dental pulp cells.

Dentin phosphophoryn (DPP) is a dentin sialophosphoprotein gene product that has an RGD motif and repeat sequences of aspartic acid and phosphoserine. To date, the function of DPP in the early stage of reparative dentin formation still remains unclear. The objective of this study was to evaluate the effects of DPP on pulp cell migration and proliferation. DPP promoted cell migration in a concentration-dependent manner, thus increasing it by about 3-fold at 1000 ng/mL compared with the control, but it had no effect on cell proliferation. Dephosphorylated DPP also promoted cell migration, similarly to DPP. However, cell migration was significantly suppressed by the addition of alphavbeta3 integrin antibody to the medium. Furthermore, porcine DPP-derived RGD peptide, but not its mutant RAD peptide, significantly promoted cell migration. These results indicated that the RGD motif of DPP plays an important role in the migration of human dental pulp cells.

SEM evaluation of neodentinal bridging after direct pulp protection with mineral trioxide aggregate.

The purpose of this study was to observe the basic morphology and determine the chemical composition of neodentinal bridges adjacent white mineral trioxide aggregate (WMTA) when used as a direct pulp capping material. The experimental procedures were performed on six intact dogs' teeth. The pulps were exposed and cavities were filled with WMTA. After 2 weeks, neodentinal bridge formation was evaluated by scanning electron microscope (SEM) of cross-sections of the specimens and electron probe microanalysis (EPMA) of the pulpal surfaces. Results of SEM observation showed that the most characteristic reaction of pulp cells was the intimate connection of cell processes and secreted extracellular fibres with the crystals of the pulp capping material. Results of EPMA indicated that the mineralisation of neodentinal bridge formation occurred progressively from the periphery to the central area. Based on these results, it appears that WMTA has the potential to be used as a direct pulp capping material during vital pulp therapy.

Reduced antigenicity of type I collagen and proteoglycans in sclerotic dentin.

Antigenic alterations to the dentin organic matrix may be detected by an immunohistochemical approach. We hypothesized that alterations in the antigenicity of type I collagen and proteoglycans occur in sclerotic dentin under caries lesions. Transverse sections were prepared from carious teeth in the sclerotic zone and normal hard dentin. A double-immunolabeling technique was performed on these sections, with anti-type I collagen and anti-chondroitin 4/6 sulfate monoclonal primary antibodies. We used gold-conjugated secondary antibodies to visualize the distribution of intact collagen fibrils and proteoglycans by high-resolution SEM. For sclerotic dentin, labeling densities were 19.57 +/- 3.01/microm2 for collagen and 9.84 +/- 2.62/microm2 for proteoglycans. For normal hard dentin, values were 35.20 +/- 2.73/microm2 and 17.03 +/- 1.98/microm2, respectively. Distribution of intact collagen fibrils and proteoglycans in sclerotic dentin was significantly lower than in normal hard dentin. Reductions in antigenicity from the organic matrix of sclerotic dentin under caries lesions raise concern about the potential of intrafibrillar remineralization.

Raman spectroscopic study of noncarious cervical lesions.

The surface of noncarious cervical lesions (NCCLs) consists of sclerosed dentin. This type of dentin may affect the ability of adhesive restorative materials to bond well to its surface, but little information exists on the chemical nature of this dentin surface and how it may be affected during acidic treatment. The inorganic part of normal dentin and dentin from NCCLs before and after acid conditioning with phosphoric acid or polyacrylic acid was investigated. Ten premolars with NCCLs and four human third molars (control) were used. Replicas of NCCLs were examined using scanning electron microscopy (SEM). Surfaces and longitudinal sections of four NCCLs and control dentin discs were analyzed using Raman spectroscopy. The discs and NCCLs were sectioned, and treated with 35% phosphoric acid or 20% polyacrylic acid/3% aluminum chloride, and Raman spectra obtained. The area under phosphate nu1 of the dentin spectrum was computed to obtain a ratio with the area under the second-order spectrum of a silicon phonon comparative standard. Mean phosphate nu1 and silicon phonon ratios from normal dentin and NCCLs were compared using a linear model with repeated measurements and Tukey's pairwise tests. Mean ratios from different locations of the NCCLs were compared using one-way analysis of variance (ANOVA) and Tukey's pairwise tests. SEM micrographs of NCCL surfaces showed variation from relatively smooth with no dentinal tubule openings to surfaces with occluded tubules. The mean phosphate nu1 and silicon phonon ratios for NCCLs were higher than those of normal dentin in all treatment groups (P < 0.05). Ratios from the untreated specimens were higher than those of the polyacrylic acid-treated specimens, and those for the phosphoric acid-treated group were the lowest (P < 0.05). The ratios obtained for the surfaces of NCCLs were higher than those halfway towards the pulp, and those adjacent to the pulp were the lowest (P < 0.05).

Resin bonding to sclerotic, noncarious, cervical lesions.

Noncarious, cervical, wedge-shaped, sclerotic lesions are commonly encountered in clinical practice. In such lesions, dentin has been pathologically altered, often resulting in partial or complete obliteration of the dentinal tubules. These lesions are known to respond to etching and bonding differently from normal dentin, leading to complications during clinical treatment. A search of the literature was performed to obtain background information on the most commonly cited etiologic factors, clinical diagnoses, and morphologic and chemical characterizations along with an extensive review of all potential obstacles to bonding the most recent adhesives to such a dentinal substrate. Recent progress in adaptive strategies to render dentin more receptive to resin bonding is emphasized in this article, and the major drawbacks of these strategies are discussed.

Resin bonding to cervical sclerotic dentin: a review.

Several reports have indicated that resin bond strengths to noncarious sclerotic cervical dentine are lower than bonds made to normal dentine. This is thought to be due to tubule occlusion by mineral salts, preventing resin tag formation. The purpose of this review was to critically examine what is known about the structure of this type of dentine. Recent transmission electron microscopy revealed that in addition to occlusion of the tubules by mineral crystals, many parts of wedge-shaped cervical lesions contain a hypermineralised surface that resists the etching action of both self-etching primers and phosphoric acid. This layer prevents hybridisation of the underlying sclerotic dentine. In addition, bacteria are often detected on top of the hypermineralised layer. Sometimes the bacteria were embedded in a partially mineralised matrix. Acidic conditioners and resins penetrate variable distances into these multilayered structures. Examination of both sides of the failed bonds revealed a wide variation in fracture patterns that involved all of these structures. Microtensile bond strengths to the occlusal, gingival and deepest portions of these wedge-shaped lesions were significantly lower than similar areas artificially prepared in normal teeth. When resin bonds to sclerotic dentine are extended to include peripheral sound dentine, their bond strengths are probably high enough to permit retention of class V restorations by adhesion, without additional retention.

Dentin bonding: effect of degree of mineralization and acid etching time.

This in vitro study verifies whether there are differences between bonding to hypermineralized dentin and normal dentin and if longer acid etching can improve the bond strength to this modified substrate without damaging the bond to normal dentin. Forty-two extracted human molars with chronic occlusal caries were transversally cut with a diamond saw under refrigeration. The occlusal surfaces were ground until the carious lesion was removed, exposing the sclerotic dentin in the center and polished to 600/grid. A 35% phosphoric acid (3M) was applied for 15 seconds in 15 specimens. SingleBond (3M) adhesive system was applied and a hybrid resin composite (Filtek Z250, 3M) was inserted in four 1-mm increments and light-cured. The remaining 15 molars were prepared in the same manner, but with an acid etching time of 30 seconds. After 24 hours in water, the specimens were cut in two perpendicular directions to obtain a cross section of approximately 0.7 mm2 (n=25). A visual examination was conducted to select sticks between the two groups: sclerotic dentin (G15S or G30S) and normal dentin (G15N or G30N). Sticks without 100% sclerotic dentin (translucent area) or those with normal areas were not tested. Two-way ANOVA computed the mu-TBS data taking into consideration dentin type and acid etching time. The dentin Knoop hardness number (KHN) of the sticks was verified. A t-test compared the KHN data between sclerotic and normal dentin. Twelve additional molars (n=6) were prepared to observe the interface under a SEM. The mean (+/- SD) microtensile bond strengths (mu-TBS) were: G15S=56.4(+/- 14.9), G15N=69.7(+/- 17.2), G30S=63.2(+/- 15.6) and G30N=67.7(+/- 13.3). Two-way ANOVA showed higher mu-TBS to normal dentin than sclerotic dentin. Duncan's Post Hoc showed G15N had higher mean mu-TBS than G15S. Other comparisons were not significantly different. The t-test showed statistically higher microhardness in sclerotic dentin than in normal dentin (p<0.0001). The hybrid layer (HL) formation was observed in all specimens without gap formation in any region. In sclerotic dentin (G15S), the HL was very thin, with minimal resin tags in the dentinal tubules and, when present, they were shorter. Doubling the etching time (G30S) resulted in more resin tags with an HL formation on peritubular dentin. The HL on normal dentin was thicker when it was acid etched for 30 seconds (G30N). Numerous resin tags were present with both etching times. The results suggest that the higher mineral amount in sclerotic dentin makes it difficult to bond to this substrate, resulting in a lower mu-TBS. However, doubling the etching time resulted in mu-TBS similar to normal dentin.

Histological and scanning electron microscopy assessment of various vital pulp-therapy materials.

Pulp capping and pulpotomy procedures were performed on 15 male mongrel dogs. Three materials were used: calcium hydroxide, acid-etched dentin bonding, and mineral trioxide aggregate. Six of the animals were killed at 50 days and nine were killed at 150 days. Samples from 11 dogs were used for histological evaluation, and the remaining dog samples were used for scanning electron microscopy evaluation. Each slide was graded histologically according to previously published criteria. Scanning electron microscopy analysis was performed, and the weight percentage of elements found in the dentin of a nontreated tooth versus the bridge formed in the exposed specimen was established. By evaluating pulp inflammation in vital pulp-therapy treatments, it was found that mineral trioxide aggregate was not significantly different from the untreated control group, both in pulp-capping procedures at 50 days (p = 0.357) or 150 days (p = 0.198) and pulpotomy procedures at 50 days (p = 0.357) or 150 days (p = 0.198). Moreover, histologically mineral trioxide aggregate was a considerably better material than calcium hydroxide or acid-etched dentin bonding in maintaining the integrity of the pulp.

Calcium salts deposition in rat connective tissue after the implantation of calcium hydroxide-containing sealers.

This study was conducted to observe the rat subcutaneous connective tissue reaction to implanted dentin tubes that were filled with mineral trioxide aggregate, Sealapex, Calciobiotic Root Canal Sealer (CRCS), Sealer 26, and the experimental material, Sealer Plus. The animals were sacrificed after 7 and 30 days, and the specimens were prepared for histological analysis after serial sections with a hard-tissue microtome. The undecalcified sections were examined with polarized light after staining according to the Von Kossa technique for calcium. At the tube openings, there were Von Kossa-positive granules that were birefringent to polarized light. Next to these granulations, there was irregular tissue, like a bridge, that was Von Kossa-positive. The dentin walls of the tubes exhibited a structure highly birefringent to polarized light, usually like a layer, in the tubules. These results were observed with all the studied materials, except the CRCS, which didn't exhibit any kind of mineralized structure. The results suggest that among the materials studied, the CRCS could have the least possibility of encouraging hard tissue deposition.

Thickness and morphology of resin-infiltrated dentin layer in young, old, and sclerotic dentin.

The purpose of the present study was to evaluate the morphology of the resin tags and the resin-infiltrated dentin layer (RIDL) of several bonding systems in superficial vs deep young, old, and sclerotic human dentin. Dentin was obtained after the removal of occlusal enamel from extracted molars. Phosphoric acid gels (35-37%) were used to etch dentin before the application of bonding systems (OptiBond FL; Prime & Bond 2.0; Scotchbond Multi-Purpose Plus and Scotchbond 1; One Step). Each bonded specimen was then sectioned into two halves. One half was polished using a standard procedure to evaluate RIDL thickness and morphology by SEM. The other half was demineralized and deproteinized to evaluate the presence and the morphology of resin tags. RIDL was thinner in superficial dentin than in deeper dentin for all the materials tested regardless of the type of dentin. Sclerotic and old dentin showed thinner RIDL, with short resin tags, and fewer lateral branches than normal dentin.

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.

Fibrinogen/fibrin and fibronectin in the dentin-pulp complex after cavity preparation in rat molars.

OBJECTIVE: The purpose of this study was to examine changes in distribution of fibrinogen/fibrin and fibronectin in the dentin-pulp complex after cavity preparation. STUDY DESIGN: Class V cavity preparations were prepared on maxillary first molars of 12 rats. The dentin and pulps were observed histologically and immunohistochemically for fibrinogen and fibronectin at 6 hours and 1, 2, and 3 days after the preparation. RESULTS: At 6 hours and 1 day after cavity preparation, positive staining for fibrinogen was noted in the exudative lesion and in the dentinal tubules under the cavity preparation. Fibronectin staining in the exudate showed a pattern with close similarity to the fibrinogen staining. At 3 days after cavity preparation, the irregularly shaped predentin under the cavity preparation showed strong positive staining for fibronectin. CONCLUSIONS: Fibrinogen/fibrin and fibronectin are present during the healing process of the dentin-pulp complex after cavity preparation.

The dentin substrate: structure and properties related to bonding.

OBJECTIVES: Dentin is a vital, hydrated composite material with structural components and properties that vary with location. These variations are reviewed along with alterations by physiological and pathological changes that allow classification into various forms of dentin. Structural characteristics and mechanical properties are reviewed and the limitations of our understanding of structure-property relationships for normal and modified forms of dentin are discussed with respect to their impact on dentin bonding. Recent progress in methods available to study dentin and its demineralization are emphasized with their promise to increase our understanding of dentin properties and structure. DATA SOURCES: Recent microstructural studies, focusing on scanning electron microscopy, atomic force microscopy and X-ray tomographic microscopy are included. A review of fundamental studies with emphasis on microstructurally sensitive methods, and prior reviews of basic mechanical properties are included with discussion of their correlation to composition and structure. STUDY SELECTION AND CONCLUSIONS: Emphasis in this work was placed on the major structural components of the tissue, including the collagen based organic matrix and its mineral reinforcement, the distribution of these components and their microstructural organization as related to mechanical properties and response to demineralization. Little information is included on biochemical and developmental studies or on non-collagenous proteins and other organic components for which limited understanding is available with respect to their role in structure-property relations and influence on bonding. In spite of the fact that the complexity of dentin precluded a comprehensive review, it is clear that local structural variations influence properties and impact nearly all preventive and restorative dental treatments. Much more work is needed in order to understand differences between vital and non-vital dentin, and dentin from extracted teeth. Although our knowledge is rudimentary in certain areas, increasingly sophisticated methods of studying dentin should provide the necessary information to model structure-property relations, optimize dentin bonding, and improve many aspects of preventive and restorative dentistry.