OHSU

Research: Class of 2005

Herion, T . "A laboratory investigation of three cements used for orthodontic banding of porcelain molars." Orthodontic Thesis for M.S. degree, Oregon Health & Science University, April 2005.

ABSTRACT: 

Retention of bands cemented to porcelain crowns is an important consideration for some orthodontic patients. Objectives of this study were to: 1) compare the mean shear-peel bond strength of microetched orthodontic bands cemented to porcelain molar denture teeth with either a conventional glass ionomer (GIC; Ketac-Cem, 3M ESPE, St. Paul, MN), a resin modified glass ionomer (RMGIC; 3M Multi-Cure, 3M Unitek, Monrovia, CA), or a compomer (Transbond Plus, 3M Unitek, Monrovia, CA), 2) assess the amount of cement remaining on teeth following debanding, and 3) determine the survival time of cemented bands subjected to mechanical fatigue. Ninety porcelain denture teeth (Dentsply, York, PA) were secured to composite blocks, assigned to three groups, and 30 bands were cemented with each cement. Sixty banded teeth (20/cement group) were used to determine shear-peel bond strength and the remaining 30 (10/cement group) were used to determine survival time. Shear-peel bond strength was determined using an Instron machine (Model TT-B Universal Testing Instrument, Instron Engineering Corporation, Canton, MA) and groups were compared using one-way ANOVA. The amount of cement remaining on the teeth following band removal was scored visually and groups were compared with a chi-square test. Fatigue testing was simulated by placing the teeth with cemented bands in a vessel with water and ceramic pellets and rotating in a ball mill. A log-rank test was used to compare differences in survival times in the ball mill. The level of significance for all comparisons was set at P<0.05. No differences were found in mean shear-peel bond strength between the three cement groups. Shear-peel bond strength values determined for each group were: 0.63 MPa, Ketac-Cem; 0.59 MPa, 3M Multi-Cure; and 0.76 MPa, Transbond Plus. The amount of cement remaining on the teeth varied between the compomer and GIC groups (P=0.011) with more cement remaining on the teeth when compomer was used; no differences were found between other groups. The mean survival times of bands cemented with compomer (4.6 hours) or RMGIC (5.4) were longer than for bands cemented with GIC (2.3; P<0.001); no difference was found between compomer versus RMGIC. The findings show that on porcelain teeth the three band cements have comparable mean shear-peel bond strengths, but the survival times of RMGIC and compomer cements are superior to GIC when subjected to simulated mechanical fatigue.   

McDonald, R."Effects of time and direction of light exposure on the initial bond strength of orthodontic brackets activated with a high intensity light-emitting diode (LED) source versus a halogen light source" Orthodontic Thesis for M.S. degree, Oregon Health & Science University, April 2005.

ABSTRACT: 

Commercially available high-intensity light-emitting diode (LED) light-curing units recently have been introduced to the dental products market.  Few studies have evaluated initial bond strength achieved using manufacturer's recommended cure directions and times.  The purpose of this study was to compare the effects of time and direction on the initial shear bond strength of orthodontic brackets cured with a conventional halogen light cure unit (Ortholux XT, 3M Unitek) with a commercially available high intensity LED curing unit (Ortholux LED, 3M Unitek). One hundred forty metal precoated brackets were bonded to extracted premolars.  Specimens were divided into 7 groups of 20 teeth each.  Groups 1-3 were cured with the conventional halogen light for 20 seconds (10 Mesial(M)/10 Distal(D) – recommended time and direction), 30 seconds (15M/15D), and 30 seconds (10M/10D/10Occlusal), respectively. Groups 4-7 were cured with the LED light for 10 seconds (5M/5D – recommended time and direction), 20 seconds (10M/10D), 20 seconds (5M/5D/10Occl), and 10 seconds (Occlusal only), respectively. All samples were debonded at 5 minutes and tested in a shear mode on an Instron universal testing machine at a crosshead speed of 1mm/min until the brackets debonded. Adhesive remnant index (ARI) scores were determined after failure of brackets. The data was analyzed by two-way analysis of variance and Tukey's multiple comparisons test (α=.05).  The LED unit produced similar bond strength at its 10 second total recommended time compared to the 20 second total recommended time for the conventional halogen unit (P=.516).  Bond strength increased using the halogen light as exposure time increased  (P=.003); however, for the LED there was no significant change in bond strength (P=.99) as its exposure time was increased.  Adding exposure time to the occlusal while keeping total time constant did not significantly affect bond strength for either light [P=.899(QTH), .995(LED)].  However, only applying light from the occlusal surface with the LED light significantly decreased bond strength (P=.038).  A Pearson's correlation analysis of the ARI showed a negative correlation (-.401), or an inverse relationship between ARI and bond strength (as bond strength increased, ARI scores decreased meaning less composite was left on the bonded enamel surface). Within the limits of this study and materials, the results suggest the high intensity Ortholux LED unit can achieve adequate early bond strength using the recommended 10 second exposure time (half the time relative to the QTH), and that additional exposure time does not achieve any subsequent increase in bond strength.  Adding exposure time beyond the manufacturer recommended time to the interproximal or occlusal surfaces also does not significantly affect bond strength results. For cases of bonding 2nd bicuspids, 1st and 2nd molars, only applying light to the occlusal surface may produce adequate bond strength, though this study showed that the values may be lower than interproximal light applications and additional light exposure from the mesial may be indicated.   

Willcox, B."The influence of blood and hemostatic agent contamination on bond strength of orthodontic attachments cemented with resin modified glass ionomer cement." Orthodontic Thesis for M.S. degree, Oregon Health & Science University, April 2005.

ABSTRACT: 

Effective use of traditional composite resins to attach orthodontic appliances to an impacted tooth requires isolation of the enamel surface during bonding, which can be difficult due to limited access and the presence of contaminates.  Resin-modified glass-ionomer cements (RMGIC) have been shown to have the ability to bond to contaminated enamel surfaces.  The purpose of this study was to evaluate the effect of two common contaminates experienced in this situation (blood and Hemodent) on the mean shear bond strength of an orthodontic button applied with light-cured RMGIC to an intact enamel surface.  The shear-peel forces required to create bond failure were compared to the forces reported during orthodontic treatment to determine suitability for clinical application when bonded under the tested conditions.   125 enamel surfaces from intact human third molars were divided into five Groups of 25 samples.  Groups of teeth were exposed to one of five treatments prior to the bonding of a flat button with light-cured RMGIC (Fuji Ortho LC):  Group 1-distilled water, Group 2-blood, Group 3-blood then wiped with water, Group 4-blood then wiped with Hemodent, Group 5-Hemodent then wiped with water.  Shear-peel debond force was measured with a materials testing instrument.  Results were analyzed using a one-way ANOVA and Pearsons and Tukeys tests with p set to ≤ 0.05. Results showed no significant differences between Groups 1, 3 & 5 or Groups 2 & 4.  Significant differences were noted between combined Groups 1, 3, & 5 compared to 2 & 4.  The tests showed high variability in bond strengths within each Group.  Mean debond forces were above the minimum forces required for orthodontic treatment (6-8 MPa) in Groups 1, 3 & 5.  The findings suggest when an intact enamel surface is contaminated with either blood or Hemodent, bond strength similar to that of moist enamel can be obtained by wiping the surface clean with water prior to bonding with RMGIC.