Degradation of insoluble bovine collagen and human dentine collagen pretreated in vitro with lactic acid, pH 4.0 and 5.5

Dentin collagen denaturation status assessed by collagen hybridizing peptide and its effect on bio-stabilization of proanthocyanidins

OBJECTIVE

To assess dentin collagen denaturation from phosphoric acid and enzyme treatments using collagen hybridizing peptide (CHP) and to investigate the effect of collagen denaturation on bio-stabilization promoted by proanthocyanidins (PA).

METHODS

Human molars were sectioned into 7-µm-thick dentin films, demineralized, and assigned to six groups: control with/without PA modification, H₃PO₄-treated collagen with/without PA modification, enzyme-treated collagen with/without PA modification. PA modification involved immersing collagen films in 0.65% PA for 30 s. H₃PO₄ and enzyme treatments were used to experimentally induce collagen denaturation, which was quantitated by fluorescence intensity (FI) from the fluorescently-conjugated-CHP (F-CHP) staining (n = 4). FTIR was used to characterize collagen structures. All groups were subject to collagenase digestion to test the bio-stabilization effect of PA on denatured collagen using weight loss analysis and hydroxyproline assay (n = 6). Data were analyzed using two-factor ANOVA and Games-Howell post hoc tests (α = 0.05).

RESULTS

FTIR showed collagen secondary structural changes after denaturation treatments and confirmed the incorporation and cross-linking of PA in control and treated collagen. F-CHP staining indicated high-degree, medium-degree, and low-degree collagen denaturation from H₃PO₄-treatment (FI = 83.22), enzyme-treatment (FI = 36.54), and control (FI = 6.01) respectively. PA modification significantly reduced the weight loss and hydroxyproline release of all groups after digestion (p < 0.0001), with the results correlated with FI values at r = 0.96-0.98.

SIGNIFICANCE

A molecular method CHP is introduced as a sensitive technique to quantitate dentin collagen denaturation for the first time. PA modification is shown to effectively stabilize denatured collagen against collagenase digestion, with the stabilization effect negatively associated with the collagen denaturation degree.

Chemical Properties of Human Dentin Blocks and Vertical Augmentation by Ultrasonically Demineralized Dentin Matrix Blocks on Scratched Skull without Periosteum of Adult-Aged Rats

Vertical augmentation is one of the most challenging techniques in bone engineering. Several parameters, such mechano-chemical characteristics, are important to optimize vertical bone regeneration using biomaterials. The aims of this study were to chemically characterize human dentin blocks (calcified demineralized dentin matrix: CDM, partially demineralized dentin matrix: PDDM and completely demineralized dentin matrix: CDDM) (2 × 2 × 1 mm³) chemically and evaluate the behavior of PDDM blocks on non-scratched or scratched skulls without periosteum of adult rats (10–12 months old, female) as a vertical augmentation model. The dissolved efficiency of CDM showed 32.3% after ultrasonic demineralization in 1.0 L of 2% HNO₃ for 30 min. The 30 min-demineralized dentin was named PDDM. The SEM images of PDDM showed the opening of dentinal tubes, nano-microcracks and the smooth surface. In the collagenase digestion test, the weight-decreasing rates of CDM, PDDM and CDDM were 9.2%, 25.5% and 78.3% at 12 weeks, respectively. CDM inhibited the collagenase digestion, compared with PDDM and CDDM. In the PDDM onlay graft on an ultrasonically scratched skull, the bone marrow-space opening from original bone was found in the bony bridge formation between the human PDDM block and dense skull of adult senior rats at 4 and 8 weeks. On the other hand, in the cases of the marrow-space closing in both non-scratched skulls and scratched skulls, the bony bridge was not formed. The results indicated that the ultrasonic scratching into the compact parietal bone might contribute greatly to the marrow-space opening from skull and the supply of marrow cells, and then bony bridge formation could occur in the vertical augmentation model without a periosteum.

Influence of the digestive enzymes trypsin and pepsin in vitro on the progression of erosion in dentine

OBJECTIVES

In patients with eating disorders, gastric and pancreatic enzymes could possibly reach the oral cavity during vomiting and could perhaps degrade the organic matrix of eroded dentine. This in vitro study sought to investigate whether pepsin, trypsin or the combination of both, have an influence on erosive mineral loss in dentine and whether they are able to degrade the organic matrix.

METHODS

Sixty-four human dentine specimens were prepared and randomly divided into four groups. Specimens were cyclically de- and remineralised for six days. Demineralisation was performed with an HCl-solution (6x 5min daily, pH 1.6) in groups 1 and 3; in groups 2 and 4 the demineralisation solution additionally contained pepsin (750 microg/ml). After demineralisation, specimens of groups 3 and 4 were treated with a trypsin solution (6x 10min daily, 2000 BAEE/ml). After each day, mineral content (mum) was determined microradiographically, and the matrix degradation was determined by hydroxyproline analysis.

RESULTS

After six days, treatment with pepsin (group 2) or trypsin (group 3) had no significant influence on mineral loss. The combined impact of pepsin and trypsin led to significantly higher mineral loss (group 4: 202.5+/-37.4) compared to all other groups (group 1: 139.1+/-29.5, p<or=0.001; group 2: 108.8+/-34.7, p<or=0.001; group 3: 157.8+/-37.2, p<or=0.05). Hydroxyproline was found in all pepsin-solutions but in no trypsin- or HCl-solutions.

CONCLUSION

The combined impact of pepsin and trypsin intensified dentine erosion progression in vitro. This could be one reason for the fast proceeding of dental erosion in patients with chronic vomiting.

Effect of dentin hardness on ablation rate with Er:YAG laser

OBJECTIVE

This study used artificially demineralized bovine dentin to ascertain the effect of hardness of demineralized dentin on ablation rate with the Er:YAG laser.

BACKGROUND DATA

Before restoration of carious teeth, it is necessary to ablate any infected dentin that cannot be remineralized due to softening by the invading caries. A correlation has been suggested between the ablation efficiency of the Er:YAG laser and the progression of caries in dentin. To the best of our knowledge, no studies have investigated the relationship between degree of demineralization by dentinal caries and ablation rate with the Er:YAG laser.

MATERIALS AND METHODS

Bovine mandibular anterior tooth roots were used as dentin samples. Each sample was soaked in a demineralizing solution (2 M lactic acid, pH 4.0) for 3 d to obtain demineralized dentin (DD) samples. Another group of samples were prepared without demineralization as a sound dentin (SD) group for comparison. After determining the Knoop hardness number (KHN) of each sample, the dentin surface was ablated with an Er:YAG laser. Tip output and pulse rate were set at 50 mJ and 20 pulses per second (pps), respectively, and the water spray was set at 3.5 mL/min. Ablation width, depth, and volume were measured following irradiation.

RESULTS

In the DD group, dentin hardness was 10.4 +/- 1.6 KHN at 100 microm from the surface. In the sound dentin group, Knoop hardness was 51.0 +/- 1.6 KHN cross-sectionally throughout. No differences were observed from the surface to a depth of 2000 microm. In the DD group, dentin ablation volume at the superficial demineralized layer was 2888 +/- 272 x 10(4) microm. In the SD group, dentin ablation volume was 1298 +/- 219 microm(3). The relationship between ablation volume and Knoop hardness was defined as Y = -40.699x + 3350, revealing a marked negative correlation.

CONCLUSION

The results demonstrate that the ablation volume for demineralized dentin was greater than that for sound dentin. The results suggest that the Er:YAG laser is capable of ablating infected dentin without damaging sound dentin by adjustment of tip output and pulse rate.

Effect of bacterial collagenase on resin-dentin bonds degradation

The objective of this study is to evaluate the effect of a bacterial collagenase on the degradation of resin-dentin bonds. Human dentin surfaces were bonded with: an etch-&-rinse self-priming adhesive (SB), a two-step self-etching primer/adhesive (SEB), and a 1-step self-etching adhesive (OUB). Composite build-ups were constructed. The bonded teeth were stored (24 h, 3 months, 1 year) in distilled water or in a buffered bacterial collagenase solution. Half of the specimens were stored as intact bonded teeth (Indirect Exposure/IE). The other half were sectioned into beams prior to storage (Direct Exposure/DE). After storage the intact teeth were sectioned into beams and all specimens were tested for microtensile bond strengths (MTBS). ANOVA and multiple comparisons tests were performed. Fractographic analysis was performed by scanning electron microscopy. The inclusion of bacterial collagenase in the storing solution did not lower the MTBS values over those seen in specimens stored in water. SB and SEB bonds strength were equal, and were superior to OUB. After 3 months of DE, SB and OUB bonded specimens showed decreases in MTBS; similar reductions required 1 year for SEB/DE. MTBS did not decrease in IE specimens except for OUB. Resin and collagen dissolution were evident in DE groups after storing.

Effects of phosphoric acid and glutaraldehyde-HEMA on dentin collagen

The purpose of this study was to evaluate the effects of phosphoric acid (PA) and a proprietary glutaraldehyde-HEMA aqueous solution (Gluma Desensitizer; GD) on dentin collagen. Specimens of demineralized bovine dentin collagen were treated with either 37% or 50% PA for 1 or 5 min. An additional set of specimens was treated with 37% PA for 1 min followed by GD for 1 min. All specimens were washed with distilled water, lyophilized. reduced with standardized NaB3H4, hydrolyzed with 6 M HCl and subjected to amino acid and cross-link analyses. The results demonstrated that the treatment of demineralized dentin with PA under the conditions tested did not significantly alter the collagen cross-links. The GD-treated samples showed reduction of free lysine (Lys) and hydroxylysine (Hyl) residues, as well as a decrease in the levels of collagen reducible cross-links. In addition, unidentified reducible compounds were detected by high-performance liquid chromatography (HPLC) analysis. These compounds may be derived from cross-links formed between GD-derived aldehyde and Lys/Hyl of collagen. The findings indicate that PA treatment does not significantly affect dentin collagen amino acid and cross-link composition, and that GD treatment affects dentin collagen amino acid and cross-link composition.

H+-induced tension development in demineralized dentin matrix

Recent atomic force microscopy studies have shown that acid-etching dentin causes the surface to recede. The purpose of this work was to test the hypothesis that acidic solutions can cause contraction of demineralized dentin matrix. Small beams of dentin were cut from extracted human third molars. The central region of each specimen was completely demineralized in EDTA. Specimens held in a tester were immersed in acidic solutions, and the amount of tension was recorded. Test variables included gauge length, cross-sectional area, pre-strain, and pH. The results showed that immersion of demineralized dentin in acidic solutions caused tension that was directly related both to H+ concentration at pH < 2 and to pre-strain. The contractile stress development (ca. 0.2-0.4 MPa) was sufficient to cause a collapse of demineralized dentin matrix. The mechanism for this effect probably involves H+-induced conformation changes in the collagen matrix.

The effect of a re-wetting agent on dentin bonding

OBJECTIVES

Recently, a new generation of simplified one-bottle dentin bonding systems, sensitive to variations in the degree of substrate moisture, was introduced. This in vitro project compared the dentin bond strengths and interfacial ultra-morphology formed by three one-bottle bonding systems [OptiBond SOLO (ethanol-based), Prime&Bond 2.1 (acetone-based), and Single Bond (ethanol- and water-based)]. The null hypothesis tested was that re-wetting a dried dentin surface with a HEMA aqueous solution would not result in bond strengths, and resin impregnation into demineralized dentin, comparable to those obtained for moist dentin.

METHODS

Dentin specimens were assigned to the following three etched surface conditions: moist dentin-control group; dentin dried for 5 s; and dentin dried for 5 s and re-moistened with a commercial 35% HEMA aqueous solution. Mean shear bond strengths were calculated and analyzed with one- and two-way ANOVA. Dentin discs treated with the same combination of surface condition/adhesive were processed and observed under both transmission and scanning electron microscopes.

RESULTS

For moist dentin, the morphology of the resin-dentin interfaces showed penetration of the dentin adhesives to the depth of the transition between demineralized and unaffected dentin. Drying dentin for 5 s resulted in a significant decrease in mean bond strengths and an incompletely infiltrated collagen structure with areas of unveiled collagen fibers, regardless of the solvent. Re-wetting dentin with the aqueous HEMA solution re-established the level of bond strengths obtained to moist dentin and resulted in a raise of the fiber network with simultaneous increase in interfibrillar space dimensions.

SIGNIFICANCE

The results suggest that the use of an aqueous HEMA solution might compensate for the dryness induced on dentin surfaces by using air blasts from an air syringe, after rinsing off the etchant. As the behavior of the material that contained water was also affected by surface dryness, the percentage of water included in the composition of current ethanol- and water-based adhesives, such as Single Bond, may not be enough to compensate for the collapse of the collagen filigree upon drying.

Molecular pathogenesis of root dentin caries

Human dentin has a higher content of organic matrix and more non-ideal hydroxyapatite than human enamel. Ultrastructural studies indicate that root caries involves both mineral dissolution and breakdown of the organic matrix. Factors involved in the root caries process seem more complicated than those in enamel caries. Moreover, the distinct roles of acids and enzymes and the sequence of events in the root caries process are not well-understood. Although Streptococcus mutans and Actinomyces viscosus are considered to be major pathogenic micro-organisms of root caries, their roles in degradation of the organic matrix components of root dentin need clarification. The purpose of this paper is to review the basic composition of root dentin and the roles of acids and both endogenous and bacterial enzymes in the root caries process.

Involvement of V-ATPases in the digestion of soft connective tissue collagen

The contribution of vacuolar H+-ATPases (V-ATPases) to collagen degradation was investigated in soft connective tissue explants (periosteum). Immunolocalisation showed faint to intense staining of cells throughout the periosteum. The V-ATPase inhibitors, bafilomycin A1 and folimycin, decreased overall collagen degradation by 40 and 50% after 24 and 48 h, respectively. The participation of V-ATPases in intracellular degradation of collagen was demonstrated by the decrease of the amount of phagocytosed collagen in fibroblasts upon inhibition of pump activity. The inhibition of degradation was not due to a reduction in activity of gelatinase A, an enzyme previously found to mediate collagen degradation, as assessed by zymographic analysis of tissue and conditioned medium. Bafilomycin A1 even induced an increase of gelatinase A and B levels in both fractions. In conclusion, acidification by V-ATPases may represent an important mechanism in extracellular and intracellular collagen degradation in soft connective tissue.

Effects of acid-etching on the tensile properties of demineralized dentin matrix

OBJECTIVES

Little research has been done to evaluate the effects of acids commonly used in adhesive dentistry, on the tensile properties of the demineralized dentin matrix. The purpose of this study was to evaluate the effects of a number of acidic conditioners on the ultimate tensile strength (UTS) and modulus of elasticity (E) of human coronal dentin matrix.

METHODS

Small hour-glass shaped (for UTS) or l-beam shaped (for determination of E) were prepared from mid-coronal dentin of extracted human third molars. After protecting the ends with varnish, the middle of the specimens was completely demineralized in 0.5 M EDTA (pH 7). UTS was determined by tensile stressing to failure. Modulus of elasticity was calculated from stress strain curves. The results were analyzed by ANOVA and Student-Neuman-Keuls test at the 95% confidence level.

RESULTS

Brief (ca. 1-2 min) exposure of demineralized dentin matrix to acids had no measurable effects on its tensile properties. Ten-minute exposures to 2.5% and 17.5% nitric acid lowered (p < 0.05) the UTS compared to phosphate buffered saline (PBS)-exposed controls. Exposure of the decalcified dentin to 10% citric acid containing 3% ferric chloride, 10% citric acid, 37% phosphoric acid or 17.5% nitric acid containing 3% ferric chloride for 10 min had no effect on UTS. None of these acids consistently lowered stiffness.

SIGNIFICANCE

The results indicate that relatively long exposures to acids are required to alter the tensile properties of demineralized dentin. It is unlikely that the brief exposures to acids that are used in adhesive dentistry would acutely weaken the physical properties of demineralized dentin. However, long-term studies should be done to determine if such treatment increases the susceptibility of the matrix to hydrolysis.

Collagen--biomaterial for drug delivery

The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The biotechnological applications focus on the aspects of cellular growth or delivery of proteins capable of stimulating cellular response. However, basic knowledge about collagen biochemistry and the processing technology in combination with understanding of the physico-chemical properties is necessary for an adequate application of collagen for carrier systems. The purpose of this review article is to summarize information available on collagen dosage forms for drug delivery as well as to impart an overview of the chemical structures and the galenical properties including detailed description of the processing steps - extraction, purification, chemical crosslinking and sterilization. The most successful and stimulating applications are shields in ophthalmology, injectable dispersions for local tumor treatment, sponges carrying antibiotics and minipellets loaded with protein drugs. However, the scientific information about manipulating release properties or mechanistic studies is not as abundant as for some synthetic polymers.

Dentine permeability and dentine adhesion

OBJECTIVES

The objectives of this paper are to review the structure of dentine as it pertains to adhesive bonding and to describe the importance of resin permeation into dentinal tubules and into spaces created between collagen fibrils by acid-etching during resin bonding. The advantages and disadvantages of separate acid-etching, priming and adhesive applications are discussed.

DATA SOURCES

Although not an exhaustive review, the concepts included in the review were obtained from the dentine bonding literature.

STUDY SELECTION

Attempts were made to critically evaluate what is known about dentine permeability and adhesion and what remains to be discovered. Speculations were made on a number of controversial issues that are not yet resolved.

CONCLUSIONS

Acid-etching of dentine produces profound changes in the chemical composition and physical properties of the matrix which can influence the quality of resin-dentine bonds, their strength and perhaps their durability.

In vitro study on the dimensional changes of human dentine after demineralization

Dentine rods measuring approximately 0.7 x 0.7 x 5.0 mm were prepared from dentine of extracted human third molars stored in saline containing 0.5% sodium azide at 4 degrees C until used. Forty specimens were demineralized in 10% citric acid plus 3% ferric chloride (w/w) solution for 8 h, then assigned to four groups (A, B, C and D) of 10 specimens each. Groups A and B were used to investigate volumetric changes after air-drying and further immersion in either water, an aqueous solution of 50% 2-hydroxymethylmethacrylate (HEMA) or 100% HEMA, followed by air-drying. Groups C and D were used to investigate the ability of 100% HEMA or 100% ethylene glycol to prevent shrinkage of demineralized dentine during exposure to air. Demineralization caused a small, non-significant (1.9%) reduction in dentine volume. Air-drying further reduced the volume by 65.6%. When demineralized, shrunken specimens were immersed in water for 24 h, they recovered their original demineralized volume. Immersion in 100% HEMA did not re-expand demineralized shrunken dentine. Specimens immersed in 50% HEMA yielded a 50% volume shrinkage when exposed to air for 24 h. Both 100% HEMA and 100% ethylene glycol were effective in preventing shrinkage of demineralized dentine. The technique used provided useful information about maximal dimensional changes that may occur at a microscopic level during adhesive dental restorative procedures.