Douglas N. Dederich

Scanning electron microscopic analysis of canal wall dentin following neodymium-yttrium-aluminum-garnet laser irradiation

Five maxillary canines were split labiolingually and the canal concavities were debrided. At a series of evenly spaced locations along the canal wall, the concavity was flattened by an inverted cone bur to form small circular areas to be utilized as target locations. The specimens were stored in a thymolwater solution and subsequently rinsed in a 5.25% NaOCl solution for 1 min before lasing. The specimens were dried and lased from 10 to 90 W and 0.1 to 0.9 with a neodymium-yttrium-aluminum-garnet laser. Scanning electron microscopic analysis showed the effects of lasing to vary from no effects to disruption of the smeared layer to actual melting and recrystallization of the dentin, depending on such factors as power level, duration of exposure, and color of the dentin. The recrystallized canal wall dentin appeared to be nonporous and continuous in nature and could conceivably demonstrate reduced permeability to fluids.

Anabolic effects of low-intensity pulsed ultrasound on human gingival fibroblasts §

OBJECTIVE Low-intensity pulsed ultrasound (LIPUS) demonstrated anabolic effects on cementoblasts, odontoblasts, and periodontal ligament cells. However, LIPUS effect on human gingival fibroblasts (HGF) remains to be investigated. Therefore, we evaluated the in vitro effects of LIPUS on HGF proliferation and differentiation to test its feasibility for periodontal therapy. DESIGN LIPUS treatment (1.5MHz, 30mW/cm(2)) was applied to HGF in the experimental groups after 24-h of culture (5 or 10min/day for 28 days) and omitted in the control. Changes in HGF activities were evaluated in response to LIPUS treatment in dose-dependent (5 and 10min) and time-dependent (weeks 1-4) manner. The effects of LIPUS on HGF cell viability (MTT), proliferation (total DNA content and growth pattern), alkaline phosphatase (ALP) activity, and gene expression by reverse-transcriptase polymerase chain reaction (RT-PCR) were determined. RESULTS Cell viability remained unchanged after LIPUS treatment during the 4 weeks of treatment as compared to the untreated control group which ensured a safe biological response. Both LIPUS treatments (5-10min/day) did not yield any significant changes in the proliferation, and expression of proliferating cell nuclear antigen (PCNA) and collagen-I (COL-I). Conversely, LIPUS treatment enhanced osteogenic differentiation potential of HGF as determined by significant up-regulation of specific ALP activity and osteopontin (OPN) expression, with optimum effect following 3 weeks of 5min/day LIPUS treatment. CONCLUSION LIPUS treatment at 30mW/cm(2) selectively enhanced HGF differentiation but not proliferation. The ability of LIPUS to enhance HGF differentiation is promising for its application in cell-based periodontal therapy.

The effects of cyclical axial motion on rotary endodontic instrument fatigue

A potential problem with the use of rotary engine-driven files to flare canals is metal fatigue and subsequent breakage. This study analyzes the effects of cyclical axial motion on instrument failure by fatigue testing of endodontic files with and without cyclical axial motion. Eighteen new instruments, sizes 15 to 45, were mounted in a lathe and turned at 1650 rpm in the lubricated lumen of a curved Pyrex capillary tube until failure occurred. Nine instruments of each size were turned with cyclical axial motion and nine were turned without it. The results indicated that cyclical axial motion can significantly extend the life span of rotary engine files. Torsional forces were not considered in this study.

In Vitro Osteogenic Induction Of Human Gingival Fibroblasts For Bone Regeneration

Background And Objective: Periodontitis is an inflammatory disease causing bone loss, and is a primary cause of tooth loss. Gingival fibroblasts are readily available with minimal donor site morbidity and may be ideal for tissue engineering efforts in regenerating lost alveolar bone. Dexamethasone (Dex) is commonly employed for in vitro osteogenic induction of a variety of cells, but its effect on human gingival fibroblasts (HGF) is still controversial. Therefore, the aim of our study was to investigate the osteogenic differentiation of HGF following Dex treatment. Methods: Cultured HGFs were exposed to osteogenic medium containing a wide range of Dex concentrations (0.01-10 µM). The osteogenic phenotype was assessed based on changes in alkaline phosphatase (ALP) activity, the mRNA expression of selected extracellular matrix proteins critical for mineralization and the extent of extracellular mineralization (Von Kossa staining and Ca-content). Results: All assays showed a consistent and maximal osteogenic effect of Dex on HGF at 0.1 and 0.5 µM (weeks 3 and 4), as evidenced by significant osteopontin and osteocalcin expression and mineralization. Longer cultures (week 4) also yielded positive osteogenic effect of Dex at 0.01 µM. Moreover, ALP activity was significantly stimulated at 0.1 and 0.5 µM Dex initially after one week, but ALP was subsequently reduced under Dex. Higher Dex concentrations caused down regulation of osteogenic effects observed at the optimal (0.1-0.5 µM) concentrations. Conclusion: Under appropriate osteogenic conditioning, Dex treated HGFs could be a potential source of cells for cell-based therapy for periodontal bone regeneration.

Effect of Increasing Low-Intensity Pulsed Ultrasound and a Functional Appliance on the Mandibular Condyle in Growing Rats: Ultrasound and Functional Appliance Effect on the Mandibular Condyle

Functional appliances are used for treatment of lower‐jaw deficiencies in growing individuals; however, their effectiveness is debatable. Low‐intensity pulsed ultrasound (US) is a noninvasive method, which has been shown to stimulate cartilage and bone formation with 20 minutes of application. This study was designed to test the hypothesis that increasing low‐intensity pulsed US application from 20 to 40 min/d will enhance mandibular condylar growth in growing rats, especially when combined with a functional appliance.

Effect of CO2 laser on dentinal bonding

Previous studies have suggested that pulsed laser energy can enhance the bond strengths to dentin of certain dentinal bonding agents. The objective of this study was to investigate and compare the shear bond strength of Scotchbond 2 dentin adhesive (3M) to continuous-wave carbon dioxide laser-irradiated vs. unirradiated dentin. Forty extracted molars were mounted in an acrylic base with the crowns exposed. Dentin surfaces of diameters greater than 5mm were cut perpendicular to the base of the acrylic, treated for 60 seconds with dentin primer, air-dried, and randomly distributed into two groups. The experimental was exposed to CW-C02 laser irradiated at 13.5W for 0.10 sec., and a spot diameter of 5mm. The other group served as the nonirradiated control. A brass ring of 4mm internal diameter was placed on each surface and filled to a depth of 1.0mm with SB 2 and cured. P-50 (3M) composite was condensed and cured into the rings in three one-millimeter increments and then shear strength tested on an Instron machine using a crosshead speed of 0.005 in/mm. The mean shear strength and strain values for the irradiated and control group were 2. 193 MPa, 3.87 x i03, 1 .023 MPa, and 3.3 1 x iO, respectively. Pillais Criterion and the Univariate F-test indicated that the mean shear strengths were significantly different (p=O.Ol49). These results suggest that dentin bond shear strengths may be enhanced by CWCO2 laser pretreatment.

Reactive Oxygen Species Mediate Therapeutic Ultrasound-Induced, Mitogen-Activated Protein Kinase Activation in C28/I2 Chondrocytes

Low-intensity pulsed ultrasound (LIPUS) has been used for the treatment of non-healing fractures because of its therapeutic properties of stimulating enhancing endochondral bone formation. However, its mechanism of action remains unclear. In this study, we hypothesized that LIPUS activates mitogen-activated protein kinases through generation of reactive oxygen species. C28/I2 cells were stimulated with LIPUS for 10 and 20 min, while the control group was treated using a sham LIPUS transducer. Through quantitative reverse transcription polymerase chain reaction and immunoblot analyses, we determined that LIPUS application increased reactive oxygen species generation and cell viability in C28/I2 cells. There were increases in the phosphorylation level of ERK1/2 and in expression of SOX9, COL2 A1 and ACAN genes. These effects were reversed when cells were treated with diphenylene iodonium, which is known to inhibit NADPH oxidase. It was concluded that exposure of chondrocytes to LIPUS led to reactive oxygen species generation, which activated MAPK signaling and further increased chondrocyte-specific gene markers involved in chondrocyte differentiation and extracellular matrix formation.