Browsing by Author "Andres, Carl J."

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    A Frictional Evaluation of a New Surface-Modified Titanium Orthodontic Bracket
    (2000) Olsen, Marc E.; Oshida, Yoshiki; Andres, Carl J.; Katona, Thomas R.; Moore, B. Keith; Roberts, W. Eugene; Shanks, James C.
    Sliding mechanics is a popular method of moving teeth orthodontically. Sliding mechanics refers to the guiding of a tooth by means of the bracket slot along an archwire in response to some applied force. This concept of tooth movement is subject to both static and kinetic friction. An accurate evaluation of an appliance's frictional properties enables a clinician to identify applications where the utilization of a new appliance may be advantageous. The aim of this study was to evaluate the frictional properties of this new surface-modified titanium orthodontic bracket compared with a traditional stainless steel orthodontic bracket and a currently available non-surface modified titanium bracket. Fifteen brackets (5 Stainless steel, 5 Titanium, 5 Coated Titanium) were combined with five archwires from each material type (SS, NiTi, βTi). Frictional evaluation was completed on each bracket material utilizing .021" x .028" size archwire materials in a specially designed apparatus under wet conditions. The frictional resistance was measured on an Instron Universal Testing machine (Instron Corp, Canton, Mass). The brackets/archwire samples were tested one at a time individually. In addition, a single bracket/ archwire sample from each group was repeatedly tested five times. Measurements were made at every 0.1mm for 30mm via a computer attached to the testing machine. An ANOV A was used to determine differences between groups. The results indicate that stainless steel brackets exhibited significantly better static and kinetic frictional properties than the titanium brackets. Stainless steel wires possessed superior frictional properties to NiTi and β-Ti wires. NiTi wires were generally superior than β-Ti wires. As brackets and archwires were reused, the overall frictional values showed a distinct trend to increase.
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    The effect of using variable curing light types and intensities on the parameters of a mathematical model that predicts the depth of cure of light- activated dental composites
    (2009) Ridha, Hashem; Levon, John A.; Andres, Carl J.; Chu, Tien-Min Gabriel; Brown, David; Hovijitra, Suteera
    The purpose of this study is to further investigate the effect of using six different light source types with different light output intensities on the parameters of a mathematical model that predicts the DOC in VLDC’s. In this equation: D = Dp In(E0/Ec), D is the depth of cure in millimeters, E is the curing energy in J/cm2, Ec is the critical curing energy for the composite to reach a gel layer, and Dp is a characteristic coefficient. Three LED and three halogen dental curing units with different light output intensities were used to cure three shades (B1, A3, D3) of a hybrid resin composite. The exposure duration was at the intervals of 10, 20, 30, and 40 seconds for each sample setting. ISO scraping technique was performed to measure the depth of cure of each sample. Regression analysis was used to assess the fit of the proposed mathematical model D = Dp In(E0/Ec) to the experimental data obtained in this study. 72 For all the shade-light combinations; A3, B1, and D3 had significantly different regression lines (P < 0.05) with significantly higher Dp and Ec for B1 than A3 and D3. The only exceptions were for the Ec values between B1 and D3 in Allegro, Astralis 5, and Visilux 2 groups; and the Ec between A3 and B1 in Allegro group. The Dp and Ec parameters didn’t show significant differences between A3 and D3 shades in all the groups. Also, most of the significant differences for Dp values occurred in the B1 shade-light combinations; however, none of the D3 shade-light combinations showed significant differences for Dp. Several factors play combined influential effects on the kinetics of polymerization and depth of cure in VLDC’s. The shade has a more dominant effect on both parameters Dp and Ec than the curing light type or source output intensity. As we cure lighter shades “B1,” the effect of using different lights with different output intensities on the two parameters Dp and Ec will be greater and more significant than for darker shades “A3 or D3.” The clinical significance drawn from this study is that clinicians should recognize that using curing lights w/ increased output intensities doesn’t absolutely increase the DOC of VLDC’s especially with the darker shades.
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    The influence of delayed light curing on the degree of conversion and polymerization contraction stress in dual-cured resin luting agents
    (Taylor & Francis, 2018) Labban, Nawaf; Iskander, Mounir; Platt, Jeffrey A.; Andres, Carl J.; Levon, John A.; Hovijitra, Suteera; Brown, David T.; Biomedical and Applied Sciences, School of Dentistry
    The aim of the study was to assess the effect of delayed photo-initiation on the polymerization contraction stress (PCS) and degree of conversion (DC) of a dual-cure resin-luting agent. Thirty-five disk (6 mm × 1 mm) samples (n = 10 each group) of dual cure resin luting agent for PCS assessment were fabricated and polymerized using two illuminated quartz rods. Based on the delay in photo-initiation, 30 disks were divided among six groups [group A-0 min (min) delay, group B-2 min, group C-4 min, group D-6 min, group E-8 min and group F-10 min]. A non-photoinitiated group (group G – chemical cure – n = 5) was included as control. The PCS for all specimens was assessed using a Tensometer. For DC evaluation thirty-five specimens were divided into seven groups with delays in photo-initiation (group H-0 min, group I-2 min, group J-4 min, group K-6 min, group L-8 min and group M-10 min, group N-chemical cure). DC was assessed using attenuated total reflectance spectroscopic technique. Statistical comparison among groups was performed using analysis of variance (α = 0.05). The maximum and minimum PCS and DC values with delayed photo-initiation was observed in group-C (3.34 MPa) & group-F (2.44 MPa); and group-M (0.78 MPa) and group-H (0.55 MPa) respectively. Chemically cured samples showed the least PCS (group-G, 1.94) and DC (group-N, 0.53) values in their respective categories. PCS significantly decreased with delayed photo-initiation. A significant increase in DC was noticed when photo-initiation was delayed in the dual cure resin luting agent.