Grayson Marshall | University of California, San Francisco (original) (raw)

Papers by Grayson Marshall

Improving our knowledge of the morphology, composition and properties of the dentin, enamel, and ... more Improving our knowledge of the morphology, composition and properties of the dentin, enamel, and the dentin-enamel junction (DEJ) is vital for the development of improved restorative materials and clinical placement techniques. Most studies of dental tissues have used light microscopy for characterization. In our investigation, the spectroscopic properties of normal and non-carious transparent human root dentin, and the dentin-enamel junction

Journal of Dental Research, Jun 1, 2009

Quintessence International, May 1, 2004

Bonded amalgams were used as pit-and-fissure sealants without mechanical preparation. They were c... more Bonded amalgams were used as pit-and-fissure sealants without mechanical preparation. They were compared with resin-based pit-and-fissure sealants for retention over a 5-year period. Clinical examinations at 6 months, 1 year, 2 years, and 5 years revealed no difference between the two techniques. Although amalgam sealants may not be practical by themselves, they can be used to seal pits and fissures surrounding very conservative preparations, in the &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot;preventive amalgam restoration.&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;quot; Conventional amalgam retentive features and 90-degree cavosurface margins may not be necessary when bonding is used with amalgam.

Journal of Dental Research, Sep 1, 1994

American Journal of Dentistry, Dec 1, 2013

PURPOSE: To determine the bond strength, nanoleakage and interfacial morphology of four self-etch... more PURPOSE: To determine the bond strength, nanoleakage and interfacial morphology of four self-etch adhesives bonded to superficial dentin.METHODS: Microtensile (MT) (n= 15) and single plane shear (SP) (n= 8) bond tests were performed using human dentin polished through 320-grit SiC paper. Clearfil Protect Bond (PB), Clearfil S3 Bond (S3), Prompt L-Pop (PLP) and G-Bond (GB) were used according to their manufacturers' instructions. Composite was applied as cylinders with a thickness of 4 mm with a 1 mm diameter and stored in water at 370C for 24 hours. Specimens were debonded with a testing machine at a cross-head speed of 1 mm/minute. Means and standard deviations of bond strength were calculated. Data were analyzed using ANOVA. Fisher's PLSD intervals were calculated at the 0.05 level of significance. Failure modes were determined at x100. The hybrid layer was revealed by treatment with 5N HC1/5% NaOCl or fractured perpendicular to the interface and sputter coated with gold. Specimens were viewed at x1,000, x2,500, and x5,000 in a field emission SEM at 15 kV. Teeth (n=2) sectioned into 0.9 mm-thick slabs were immersed in ammoniacal silver nitrate solution for 24 hours, rinsed and immersed in photo-developing solution for 8 hours. Specimens were sectioned (90 nm-thick) and observed under TEM.RESULTS: Means ranged from 25.0 to 73.1 MPa for MT and from 15.5 to 56.4 MPa for SP. MT values were greater than SP, but were highly correlated (R2 = 0.99, P= 0.003) and provided the same order for the systems studied. Fisher's PLSD intervals (P< 0.05) for bond strength techniques and adhesives results were 1.7 and 2.3 MPa, respectively. Failures sites were mixed. TEM showed that hybrid layers were -0.5 pm for PB, GB and S3 and approximately 5 microm for PLP. SEM showed morphologic differences among adhesives. Silver nitrate deposits were observed within the interfaces for all adhesive systems.

Arch Oral Biol, 2007

Initiation of enamel formation requires reciprocal signaling between epithelially and mesenchymal... more Initiation of enamel formation requires reciprocal signaling between epithelially and mesenchymally derived cells.In this study, we used a transgenic mouse model which drives overexpression of an activated form of TGF-β2 under control of the osteocalcin promoter, to investigate the role of TGF-β2 in the dental mesenchyme, on enamel formation.Dentin and enamel were imaged by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Dentin mechanical properties were characterized for hardness and elasticity, following nanoindentation with a modified AFM. Pores found in enamel were quantified and compared using image analysis software (Scion Image™).The elastic modulus of dentin was significantly reduced in the male TGF-β2 overexpressor mice as compared to male wildtype mice, with no significant differences between female mice. Similarly, there were significantly more pores in enamel of the male transgenic mice as compared to male wildtype mice, with no significant differences between female mice. In situ hybridization of the continuously erupting incisor confirmed that osteocalcin expression was limited to the odontoblast cell layer at all stages of tooth formation.TGF-β2 overexpression in the dentin matrix, results in sex-linked differences in dentin and enamel formation.

Journal of Structural Biology, Jul 31, 2005

Glass coatings on metals including Ti, Ti6A14V and CrCo were prepared for use as implants. The co... more Glass coatings on metals including Ti, Ti6A14V and CrCo were prepared for use as implants. The composition of the glasses was tailored to match the thermal expansion of the substrate metal. By controlling the firing atmosphere, time, and temperature, it was possible to control the reactivity between the glass and the alloy and to fabricate coatings (25-150 .mu.m thick) with

Dental Materials, 2016

Dentin hypersensitivity often is treated by promotion of dentin tubule occlusion. In this in vitr... more Dentin hypersensitivity often is treated by promotion of dentin tubule occlusion. In this in vitro study we evaluated nanomechanical properties and degree of tubule occlusion conferred to sound and demineralized human root dentin following treatment with a 10% (w/w) strontium acetate solution and its relation to the treatment duration and delivery method. 24 human cervical root dentin disks (8 groups of 3) were polished through 0.25μm. 12 disks were subjected to an acid challenge (1% citric acid, pH3.8) for 2min. The specimens were incubated in artificial saliva, treated by soaking or brushing with deionized (DI) water or a solution of 10% strontium acetate for 2min twice a day for 28 days. The occlusion percent and nanomechanical properties were determined at the baseline, 5, 14 and 28 days. Cross-sectioned specimens were prepared to evaluate the depth affected by strontium acetate / dentin interaction by SEM. Statistical analysis was performed using linear mixed effects models. A 10% strontium acetate treatment over 5-28 days significantly increased tubule occlusion for normal root dentin and to a lesser extent for demineralized dentin and increased the AFM based nanomechanical properties of demineralized dentin. Brushing was more effective than soaking in recovery of properties of demineralized dentin when treated with strontium. No difference in tubuleocclusion was found between the two delivery methods. Strontium acetate itself proved to have the ability to occlude dentin tubules and result in small changes in the mechanical properties of dentin.

Archives of oral biology, 2016

Covalently bound functional GAGs orchestrate tissue mechanics through time-dependent characterist... more Covalently bound functional GAGs orchestrate tissue mechanics through time-dependent characteristics. The role of specific glycosaminoglycans (GAGs) at the ligament-cementum and cementum-dentin interfaces within a human periodontal complex were examined. Matrix swelling and resistance to compression under health and modeled diseased states was investigated. The presence of keratin sulfate (KS) and chondroitin sulfate (CS) GAGs at the ligament-cementum and cementum-dentin interfaces in human molars (N=5) was illustrated by using enzymes, atomic force microscopy (AFM), and AFM-based nanoindentation. The change in physical characteristics of modeled diseased states through sequential digestion of keratin sulfate (KS) and chondroitin sulfate (CS) GAGs was investigated. One-way ANOVA tests with P<0.05 were performed to determine significant differences between groups. Additionally, the presence of mineral within the seemingly hygroscopic interfaces was investigated using transmission ...

Proceedings of the National Academy of Sciences of the United States of America, 2005

This study was performed to determine variations in dentin microstructure from primary anterior t... more This study was performed to determine variations in dentin microstructure from primary anterior teeth at specific areas and depths in relation to the dentin enamel junction, (DEJ). Ten freshly extracted, non-carious primary maxillary anterior teeth were sectioned to provide two 1.0 mm x 1.0 mm matchsticks extending from the DEJ to the pulp chamber--one each from the central and distal regions of each tooth. Slices were prepared at distances of 0.15, 0.8, and 1.45 mm from the DEJ. Following polishing, each slice was examined in a wet scanning election microscope, (SEM) and tubule density, tubular diameter, and peritubular width were determined at nine grid locations. Statistical analyses were carried out using multi-factor ANOVA, Tukey's multiple comparisons, and linear regression to compare rates of change for each parameter. Tubule numerical density consistently decreased with distance from the DEJ. Decreases of 11,800 mm2/mm for canine distal matchsticks were significantly greater (P < 0.05) than the rate of 4,400 mm2/mm for canine central matchsticks. Rates for the lateral incisors were not significantly different. Tubule diameters increased with distance from the DEJ at rates of 0.28 micron/mm and 0.39 micron/mm for canines and lateral incisors, respectively, and there was a corresponding decrease in peritubular width. Microcanals or giant dentin tubules, 5-10 microns in diameter were incidently found in varying numbers in the midline of 4 of 20 teeth examined, including central and lateral incisors, but not in canines. The work shows substantial differences in the microstructure of primary dentin as compared to permanent dentin, substantial differences with location, and the relatively common occurrence of microcanals. Therefore, the area of solid dentin that is available for dentin bonding is significantly reduced, accounting for reported differences in bond strength. Such differences may be important factors in tooth sensitivity, susceptibility to trauma, and caries progression.

The Journal of the American Dental Association, Jan 31, 1980

The comparison of clinically retrieved conventional and copper-rich amalgam restorations demonstr... more The comparison of clinically retrieved conventional and copper-rich amalgam restorations demonstrated that there are at least two distinct types of compounds that form in vivo in amalgam restorations, tin-rich layers on the exposed surface of many amalgams and tin-chlorine and smaller amounts of stannous oxide products in the interior. In the systems rich in copper, corrosion was confined to the surface and a few isolated areas. The relatively small changes found in the systems rich in copper could account for the superior marginal integrity reported for copper-rich amalgams in clinical trials.

Journal of Structural Biology, Sep 1, 2001

Journal of Biomedical Materials Research, Mar 5, 2000

Atomic force microscopy (AFM) has been used to determine microstructural changes, etching rates o... more Atomic force microscopy (AFM) has been used to determine microstructural changes, etching rates of peritubular dentin, and intertubular dentin recession during demineralization in dilute acidic solutions. These studies have not included many forms of altered dentin, including noncarious sclerotic root dentin associated with Cl V (abfraction) lesions. We sought to determine microstructural changes and recession rates during demineralization in citric acid (pH 2.5, 0.018M) for the transparent/sclerotic zone. Highly polished dentin disks were prepared from teeth with noncarious C1 V lesions (n = 3) and compared with normal root dentin (n = 3). Samples were etched at 5-s intervals for 1 min and at longer intervals up to 30 min. The depth changes in various portions of the dentin with respect to the reference layer were measured and changes in microstructure observed in solution in the wet cell of the AFM. In sclerotic dentin, most tubule lumens were occluded with crystalline deposits that etched more slowly than the other dentin components, but etching rates could not be determined due to their irregular geometry. The intertubular dentin recession quickly reached a plateau after a depth change of <1 microm for all dentin types, in agreement with prior work. Mixed linear regression models indicated an important difference between the etching of sclerotic intertubular dentin and that of non-sclerotic root dentin that became apparent after 600 s (p = 0.037). The sclerotic intertubular dentin underwent less depth change at the plateau (558 nm) compared to normal root dentin (744 nm). In addition, normal root dentin underwent significantly greater recession than coronal dentin (p = 0.002). The results of this study indicate that intertubular sclerotic dentin from Cl V lesions etches differently than normal root dentin, and this may help explain the difficulties in restoring such lesions with current bonding procedures.

Dental Materials, 2015

A commercial restorative material, BondfillSB (BF), is a modification of 4-META/MMA-TBB resin cem... more A commercial restorative material, BondfillSB (BF), is a modification of 4-META/MMA-TBB resin cement. BF uses a self-etching primer and added pre-polymerized organic fillers. We compared BF with another self-etching system, EasyBond (EB), in shear bond strength, bonded interface characteristics to human dentin and contraction gap when used in bulk-filling. Shear bond strength of BF and EB+Z100 (Z), bonded by different experience-level operators, was evaluated. Bonded interfaces were characterized by SEM, AFM, and AFM based nano-indentation. Contraction gaps (CG) at 0h and 24h after polymerization were evaluated for BF or EB bulk filled class I cavities. To meet the clinical recommendation, BF&amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s powder was replaced by experimental radioopaque powder (BFO) for the CG study. EB was used with Z (EBZ) or with a resin marketed for bulk-fill base (SureFil-SDR-flow (EBSF)). Shear bond strengths (Mean±Standard Deviation (S.D.)) of BF (37.4±2.6MPa; n=36) were higher and less variable than EBZ (18.2±7.6MPa; n=36) (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.0001, One-way ANOVA). Weibull characteristic strength (η) differed significantly between materials (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.0001) but not between operators (p=0.90). EBZ often had non-uniform interfaces and a wider band of reduced elastic modulus (E) of greater than 20μm across the interface. BF had uniform interfaces and a smaller width of affected dentin under the interface (∼1μm). There was a difference in dentin-E between EBZ and BF up to 9μm from the interface (mixed-effects model; P=0.03). A stratified linear regression model used for CG. EBSF and BFO showed significantly smaller CG than EBZ at time 0. None of three combinations showed any significant change between 0h-CG and 24h-CG. BF possessed bonding characteristics required to serve as a restorative.

Objectives: To investigate biofilm formation of monoculture or co-culture of Streptococcus mutans... more Objectives: To investigate biofilm formation of monoculture or co-culture of Streptococcus mutans (MS) and lactobacilli (LB) on dentin and their ability to induce dentin caries in vitro. Methods: Biofilm formation and dentin caries induction were studied in 3 culture conditions: S. mutans UA159, lactobacilli rhamnosus 7469, and co-culture of the two bacteria. Midcoronal dentin blocks were gamma irradiated and rehydrated in 2 ml of Brain Heart Infusion broth with 1% sucrose. Mono-cultures of S. mutans, L. rhamnosus, or mixed cultures of the two bacteria in individual cell culture plates containing dentin blocks were incubated anaerobically for 7 days with half of the medium changed at day 3. The supernatants of the culture medium were collected at day 3 and day 7 for final pH measurements, bacteria counts by selective culture, cell density measurement by microplate spectrometer, and calcium evaluation using atomic absorption spectroscopy. The biofilm on dentin blocks were removed by ...