Faculty Bibliography

BACKGROUND: The design of periodontal curette handles may cause or aggravate arm pain in dental practitioners. The authors conducted a four-month randomized controlled trial to evaluate the effects of curette handle diameter and weight on arm pain among dental hygienists and dentists. METHODS: One hundred ten dental hygienists and dentists who performed scaling, root planing or dental prophylaxis procedures participated in this study. The authors assessed right wrist/hand, elbow/forearm and shoulder pain levels weekly. They randomized participants to receive either a set of light (14 grams) periodontal curettes with a large diameter (11 millimeters) or a set of heavy (34 g) periodontal curettes with a narrow diameter (8 mm). The authors compared changes in mean pain scores across the study period between intervention groups by using general linear models and controlling for covariates. RESULTS: The improvement in pain scores across the three body regions was greater for participants who used the lighter, wider-diameter curettes. In the final adjusted model, the differences were statistically significant only for the shoulder region (P = .02). CONCLUSIONS: The study results show that dental instrument design has an effect on upper-extremity pain in dental practitioners. Using a lighter instrument with a wider diameter may be an easy and cost-effective intervention to reduce or prevent upper-extremity pain associated with dental hygiene procedures. CLINICAL IMPLICATIONS: To prevent or reduce arm pain, practitioners should consider using lightweight instruments with large diameters when performing scaling and root planing procedures.

This study tests the hypothesis that silicon and calcium ions combinatorially target gene expression during osteoblast differentiation. MC3T3-E1 subclone 4 osteoblast progenitors (transformed mouse calvarial osteoblasts) were exposed to Si(4+) (from Na(2)SiO(3)) and Ca(2+) (from CaCl(2):H(2)O) ion treatments both individually (0.4 mM each + control treatment) and combinatorially (0.4 mM Si(4+) + 0.4 mM Ca(2+) + control treatment) and compared to control treated (alpha-minimum essential medium, 10% fetal bovine serum, and 1% penicillin-streptomycin) cells. Cell proliferation studies showed no significant increase in cell density between treatments over 5 days of culture. Cellular differentiation studies involved addition of ascorbic acid (50 mg/L) for all treatments. Relative gene expression was determined for collagen type 1 (Col(I)alpha1/Col(I)alpha2), core-binding factor a (cbfa1/Runx2), and osteocalcin (OCN), which indicated osteoblast progenitor differentiation into a mineralizing phenotype. Increased Si(4+) or Ca(2+) ion treatments enhanced Col(I)alpha1, Col(I)alpha2, Runx2, and OCN expression, while increased Si(4+) + Ca(2+) ion treatments enhanced OCN expression. Moreover, it was found that a Si(4+)/Ca(2+) ratio of unity was optimal for maximal expression of OCN. Collagen fiber bundles were dense, elongated, and thick within extracellular matrices (ECM) exposed to Si(4+) and Si(4+) + Ca(2+) treatments, while collagen fiber bundles were sparse, short, and thin within Ca(2+) and control treated ECM. These results indicated that individual ions enhance multiple osteogenic gene expression, while combined ion treatments enhance individual gene expression. In addition, these results indicated that Si(4+) enhanced osteoblast gene expression and ECM formation at higher levels than Ca(2+). These results support the larger concept that ions (possibly released from bioactive glasses) could control bone formation by targeting osteoblast marker expression.

Viruses are the most abundant known infectious agents on the planet and are significant drivers of diversity in a variety of ecosystems. Although there have been numerous studies of viral communities, few have focused on viruses within the indigenous human microbiota. We analyzed 2 267 695 virome reads from viral particles and compared them with 263 516 bacterial 16S rRNA gene sequences from the saliva of five healthy human subjects over a 2- to 3-month period, in order to improve our understanding of the role viruses have in the complex oral ecosystem. Our data reveal viral communities in human saliva dominated by bacteriophages whose constituents are temporally distinct. The preponderance of shared homologs between the salivary viral communities in two unrelated subjects in the same household suggests that environmental factors are determinants of community membership. When comparing salivary viromes to those from human stool and the respiratory tract, each group was distinct, further indicating that habitat is of substantial importance in shaping human viromes. Compared with coexisting bacteria, there was concordance among certain predicted host-virus pairings such as Veillonella and Streptococcus, whereas there was discordance among others such as Actinomyces. We identified 122 728 virulence factor homologs, suggesting that salivary viruses may serve as reservoirs for pathogenic gene function in the oral environment. That the vast majority of human oral viruses are bacteriophages whose putative gene function signifies some have a prominent role in lysogeny, suggests these viruses may have an important role in helping shape the microbial diversity in the human oral cavity.

From 2008 to 2011, the School of Dentistry at Muhimbili University of Health and Allied Sciences in Tanzania revised and then initiated implementation of a curriculum to improve the educational process for, and competence of, its graduates. As an increasing body of research demonstrates the detrimental effects of oral diseases on health and the interrelationships between oral and systemic diseases (including HIV and diabetes), the importance of dentistry education grows. We describe the population oral health problems in Tanzania, the need to enhance the dental workforce, and the process of curricular reform to meet these needs. This reform included transition to a competency-based curriculum featuring teaching methods that will enhance the effectiveness of the education and performance of graduates in traditional and new roles. We conclude with lessons for Tanzania and for health professions educational institutions elsewhere, as well as for public health-care planners concerned about linking health professions education to improving population health in resource-poor countries.

This study resulted in enhanced collagen type 1 and osteocalcin expression in human periodontal ligament fibroblasts (hPDLF) when exposed to bioactive glass conditioned media that subsequently may promote early mineralized tissue development. Commercial Bioglass (45S5) and experimental bioactive coating glass (6P53-b), were used to make a glass conditioned media (GCM) for comparison to control medium. ICP-MS analysis showed increased concentrations of Ca(2+), PO(4) (3-), Si(4+), and Na(+), for 45S5 GCM and Mg(2+), K(+), Ca(2+), PO(4)(3-), Si(4+), and Na(+) for 6P53-b GCM (relative to control medium). Differentiating hPDLF cultures exposed to 45S5 and 6P53-b GCM showed enhanced expression of collagen type 1 (Col1alpha1, Col1alpha2), osteocalcin, and alkaline phosphatase gene expression. These GCM also enhanced osteocalcin protein expression. After 16 d of culture, 45S5 and 6P53-b GCM treated cells showed regions of deep red Alizarin staining, indicating increased Ca within their respective extracellular matrices (ECM), while control-treated cells did not exhibit these features. SEM analysis showed more developed ECM in GCM treated cultures, indicated by multiple tissue layering and abundant collagen fiber bundle formation, while control treated cells did not exhibit these features. SEM analysis showed polygonal structures suggestive of CaP in 45S5 GCM treated cultures. These results indicate the osteogenic potential of bioactive coating glass in periodontal bone defect filling applications.

Viruses may play an important role in the evolution of human microbial communities. Clustered regularly interspaced short palindromic repeats (CRISPRs) provide bacteria and archaea with adaptive immunity to previously encountered viruses. Little is known about CRISPR composition in members of human microbial communities, the relative rate of CRISPR locus change, or how CRISPR loci differ between the microbiota of different individuals. We collected saliva from four periodontally healthy human subjects over an 11- to 17-mo time period and analyzed CRISPR sequences with corresponding streptococcal repeats in order to improve our understanding of the predominant features of oral streptococcal adaptive immune repertoires. We analyzed a total of 6859 CRISPR bearing reads and 427,917 bacterial 16S rRNA gene sequences. We found a core (ranging from 7% to 22%) of shared CRISPR spacers that remained stable over time within each subject, but nearly a third of CRISPR spacers varied between time points. We document high spacer diversity within each subject, suggesting constant addition of new CRISPR spacers. No greater than 2% of CRISPR spacers were shared between subjects, suggesting that each individual was exposed to different virus populations. We detect changes in CRISPR spacer sequence diversity over time that may be attributable to locus diversification or to changes in streptococcal population structure, yet the composition of the populations within subjects remained relatively stable. The individual-specific and traceable character of CRISPR spacer complements could potentially open the way for expansion of the domain of personalized medicine to the oral microbiome, where lineages may be tracked as a function of health and other factors.

The composition of the oral microbiota from 10 individuals with healthy oral tissues was determined using culture-independent techniques. From each individual, 26 specimens, each from different oral sites at a single point in time, were collected and pooled. An 11th pool was constructed using portions of the subgingival specimens from all 10 individuals. The 16S ribosomal RNA gene was amplified using broad-range bacterial primers, and clone libraries from the individual and subgingival pools were constructed. From a total of 11,368 high-quality, nonchimeric, near full-length sequences, 247 species-level phylotypes (using a 99% sequence identity threshold) and 9 bacterial phyla were identified. At least 15 bacterial genera were conserved among all 10 individuals, with significant interindividual differences at the species and strain level. Comparisons of these oral bacterial sequences with near full-length sequences found previously in the large intestines and feces of other healthy individuals suggest that the mouth and intestinal tract harbor distinct sets of bacteria. Co-occurrence analysis showed significant segregation of taxa when community membership was examined at the level of genus, but not at the level of species, suggesting that ecologically significant, competitive interactions are more apparent at a broader taxonomic level than species. This study is one of the more comprehensive, high-resolution analyses of bacterial diversity within the healthy human mouth to date, and highlights the value of tools from macroecology for enhancing our understanding of bacterial ecology in human health.

This study tested the hypothesis that bioactive coating glass (SiO(2)-CaO-P(2)O(5)-MgO-K(2)O-Na(2)O system), used for implant coatings, enhanced the induction of collagen type 1 synthesis and in turn enhanced the expression of downstream markers alkaline phosphatase, Runx2 and osteocalcin during osteoblast differentiation. The ions from experimental bioactive glass (6P53-b) and commercial Bioglass(TM) (45S5) were added to osteoblast-like MC3T3-E1 subclone 4 cultures as a supplemented ion extract (glass conditioned medium (GCM)). Ion extracts contained significantly higher concentrations of Si and Ca (Si, 47.9+/-10.4 ppm; Ca, 69.8+/-14.0 for 45S5; Si, 33.4+/-3.8 ppm; Ca, 57.1+/-2.8 ppm for 6P53-b) compared with the control extract (Si<0.1 ppm, Ca 49.0 ppm in alpha-MEM) (ANOVA, p<0.05). Cell proliferation rate was enhanced (1.5x control) within the first 3 days after adding 45S5 and 6P53-b GCM. MC3T3-E1 subclone 4 cultures were then studied for their response to the addition of test media (GCM and control medium along with ascorbic acid (AA; 50 ppm)). Each GCM+AA treatment enhanced collagen type 1 synthesis as observed in both gene expression results (day 1, Col1alpha1, 45S5 GCM+AA: 3x control+AA; 6P53-b GCM+AA: 4x control+AA; day 5, Col1alpha2, 45S5 GCM+AA: 3.15x control+AA; 6P53-b GCM+AA: 2.35x control+AA) and in histological studies (Picrosirius stain) throughout the time course of early differentiation. Continued addition of each GCM and AA treatment led to enhanced expression of alkaline phosphatase (1.4x control+AA after 5 days, 2x control+AA after 10 days), Runx2 (2x control+AA after 7 days) and osteocalcin gene (day 3, 45S5 GCM+AA: 14x control+AA; day 5, 6P53-b GCM+AA: 19x control+AA) and protein expression (40x-70x control+AA after 6 days). These results indicated the enhanced effect of bioactive glass ions on key osteogenic markers important for the bone healing process.

OBJECTIVE: To investigate the effect of hypoxia on isolated human periodontal ligament stem cells (hPDLSC) in vitro. METHODS: hPDLSC were exposed to normoxia (20% O(2)) and hypoxia (1.5% - 2% O(2)). Total cellular RNA and protein were collected on day 1, 2, 4 and 6 after culture. Western analysis and semi-quantitative RT-PCR were used to analyze osteogenic differentiation of hPDLSC, including alkaline phosphatase (ALP), osteocalcin (OCN), secreted protein acidic and rich in cysteine (SPARC) and bone morphogenetic protein-2 (BMP-2). RESULTS: In the first two days hypoxia slightly increased the growth of hPDLSC [A value was 0.697(hypoxia) vs 0.617 (nomoxia)] and after the third day hypoxia dramatically decreased the growth of the hPDLSC [A value was 0.870(hypoxia) vs 1.242 (nomoxia)]. Up to 90% reduction of ALP activity was observed in hPDLSC after 5 days of hypoxia [A value was 0.004(hypoxia) vs 0.049(nomoxia)]. Hypoxia decreased SPARC expression at protein level and down-regulated ALP, OCN and BMP-2 expression at mRNA level in comparison with nomoxia. CONCLUSIONS: Hypoxia inhibited proliferation of hPDLSC and down-regulated BMP-2 mRNA expression, then down-regulated their target genes such as ALP, OCN, and SPARC, thus inhibiting critical steps in osteogenic differentiation of hPDLSC.