Objectives

The long history of the Academy of Dental Materials (ADM) is documented with its strategies (a) to rapidly communicate science among its members, (b) to establish special awards to stimulate new science, and (c) to develop new dental materials scientists.

Methods

We searched the history of the last 35 years of the ADM newsletters, transactions, journals, and officer notes. We document the (a) presidents, (b) meeting history, (c) membership growth, and (d) development of special awards through 2019 with the recent creation of the ADM Marshall Post-Doctoral Award.

Results

There are 36 years of recent ADM history, 42 international meetings, membership growth to 400 individuals from 15 countries, service of 19 presidents, Paffenbarger annual Awardees since 1989, induction of >200 fellows, and recognition of the first winner of Marshall Post-Doctoral Award in 2018. New directions for recruiting members are suggested. Three potential new thrusts for the organization are presented: artificial intelligence, genetic engineering, and intensive member mentoring.

Significance

These suggestions for the ADM provide a path for the ADM to continue to adapt to the ever changing scientific landscape.

To determine the characteristics associated with having a mentor, the association of mentoring with self-efficacy, and the content of mentor-mentee interactions at the University of California, San Francisco (UCSF), we conducted a baseline assessment prior to implementing a comprehensive faculty mentoring program. We surveyed all prospective junior faculty mentees at UCSF. Mentees completed a web-based, 38-item survey including an assessment of self-efficacy and a needs assessment. We used descriptive and inferential statistics to determine the association between having a mentor and gender, ethnicity, faculty series, and self-efficacy. Our respondents (n=464, 56%) were 53% female, 62% white, and 7% from underrepresented minority groups. More than half of respondents (n=319) reported having a mentor. There were no differences in having a mentor based on gender or ethnicity (p>or=0.05). Clinician educator faculty with more teaching and patient care responsibilities were statistically significantly less likely to have a mentor compared with faculty in research intensive series (p<0.001). Having a mentor was associated with greater satisfaction with time allocation at work (p<0.05) and with higher academic self-efficacy scores, 6.07 (sd = 1.36) compared with those without a mentor, 5.33 (sd = 1.35, p<0.001). Mentees reported that they most often discussed funding with the mentors, but rated highest requiring mentoring assistance with issues of promotion and tenure. Findings from the UCSF faculty mentoring program may assist other health science institutions plan similar programs. Mentoring needs for junior faculty with greater teaching and patient care responsibilities must be addressed.

Objectives

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.

Methods

24 human cervical root dentin disks (8 groups of 3) were polished through 0.25 μm. 12 disks were subjected to an acid challenge (1% citric acid, pH 3.8) for 2 min. The specimens were incubated in artificial saliva, treated by soaking or brushing with deionized (DI) water or a solution of 10% strontium acetate for 2 min 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.

Results

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.

Significance

Strontium acetate itself proved to have the ability to occlude dentin tubules and result in small changes in the mechanical properties of dentin.

Amelogenins are a unique group of alternatively spliced proteins. While the full-length amelogenin is known to assemble into nanospheres and alter apatite crystal growth and alignment, the function of the leucine-rich amelogenin peptide (LRAP) in biomineralization is not understood. This study tested the hypothesis that LRAP self-assembles into a supramolecular structure and guides crystal growth similarly to the full-length protein. Synthetic LRAP and recombinant full-length amelogenin (rH175) were used at different concentrations and either immobilized onto fluoroapatite substrates (FAP) or immersed into saturated calcium-phosphate solutions. The structure of the assembled protein and the height of apatite crystals formed on the FAP template were determined using atomic force microscopy. Both LRAP and rH175 assembled into nanospheres. LRAP self-assembly, however, was only observed at concentrations of >0.5 mg ml-1 and limited to sizes between 5 and 30 nm. Apatite crystal growth was not significantly affected by LRAP, while rH175 accelerated crystal growth by up to 50-fold. The increased growth rate was only observed when rH175 precipitated at concentrations of >0.8 mg ml-1. It was concluded that the ability of amelogenins to self-assemble into nanospheres and to bind to apatite in vitro is not inevitably an indication for the ability to control apatite crystal growth.

The soft zone in dentine beneath the dentino-enamel junction is thought to play an important role in tooth function, strain distribution and fracture resistance during mastication. Recently reported asymmetry in mechanical properties with tooth side may point at a basic property of tooth function. The aim of our study was to test if this asymmetry was reflected in the nano- and micromechanical properties of dentine. We investigated the mechanical properties of dentine on the buccal and lingual side of nine extracted human teeth using nano- and microindentation. Properties were analysed on the natural log scale, using maximum likelihood to estimate the parameters. Two-sided 0.05-level likelihood ratio tests were used to assess the influences of surface (buccal versus lingual) and dentine depth, measured from the DEJ in crown dentine and from the CDJ in root dentine. Results showed the well known gradual increase in mechanical properties with increasing distance from the DEJ. Coronal dentine showed higher elastic modulus and hardness on the lingual side of teeth for all measurements, while root dentine was harder on the buccal side. Due to the subtlety of these effects and the small number of teeth studied, results failed to reach statistical significance. Results suggest that dentine nano- and micromechanical properties vary with tooth side in agreement with recent literature using macroscopic methods. They also reveal that buccal-lingual ratios of hardness are in opposite directions in crown and root dentine, suggesting compensatory functions.

Objectives

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.

Methods

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'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)).

Results

Shear bond strengths (Mean ± Standard Deviation (S.D.)) of BF (37.4 ± 2.6 MPa; n=36) were higher and less variable than EBZ (18.2 ± 7.6 MPa; n=36) (p<0.0001, One-way ANOVA). Weibull characteristic strength (η) differed significantly between materials (p<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 20 μm across the interface. BF had uniform interfaces and a smaller width of affected dentin under the interface (∼1 μm). There was a difference in dentin-E between EBZ and BF up to 9 μm 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.

Significance

BF possessed bonding characteristics required to serve as a restorative.

Mineralized and sound dentin matrices contain inactive preforms of proteolytic enzymes that may be activated during the demineralization cycle. In this study, we tested the hypothesis that protease inhibitors (PI) preserve demineralized collagen fibrils and other constituents of the dentin matrix and thereby affect the potential for remineralization. Artificial carious lesions with lesion depths of 140 μm were created with acetate buffer (pH = 5.0, 66 hours), and remineralized using a polymer-induced-liquid-precursor (PILP) process (pH = 7.4, 14 days) containing poly(aspartic acid) (pAsp) as the process-directing agent. De- and remineralizing procedures were performed in the presence or absence of PI. Ultrastructure and mechanical recovery of demineralized dentin following PILP remineralization were examined and measured in water with atomic force microscopy (AFM) and nanoindentation. Nanomechanical properties of hydrated artificial lesions had a low elastic modulus (ER <0.4 GPa) extending about 100 μm into the lesion, followed by a sloped region of about 140 μm depth where values reached those of normal dentin (18.0-20.0 GPa). Mapping of mineral content by both micro-FTIR and micro x-ray computed tomography correlated well with modulus profiles obtained by nanoindentation. Tissue demineralized in the presence of PI exhibited higher elastic moduli (average 2.8 GPa) across the lesion and comprised a narrow zone in the outer lesion with strongly increased modulus (up to 8 GPa; p < 0.05), which might be related to the preservation of non-collagenous proteins that appear to induce calcium phosphate mineral formation even under demineralizing physical-chemical conditions. However, mechanical aspects of remineralization through the elastic modulus change, and the micromorphological aspects with SEM and TEM observation were almost identical with PILP treatments being conducted in the presence or absence of PI. Thus, the application of the protease inhibitors (PI) seemed to be less effective in promoting the remineralization of demineralized dentin.

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.