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Predictive value of radiographic analysis of menton, hyoid bone, and the third cervical vertebra angle
Volume 91 Number 2
Reviews and abstracts 1
esistance of Orthodontic st, Cold Worked, and
Loma
Linda
University,
1985
Corrosion rates were measured on three types of stainless steel (316-L) brackets: (1) cast, (2) cold worked, and (3) powdered metal. Interest in corrosion resistance of orthodontic brackets is increasing because of tooth enamel staining thought to be associated with corrosion of the metal bracket. Five brackets from each group were immersed in aerated normal saline solution as the corrosive agent. Voltage differences (potentiodynamic anodic polarization) between samples and a reference electrode were measured to determine the corrosion rate of a sample. Current flow is affected by corrosion layers; by plotting how the current responds to an applied voltage, the sample’s corrosion rate is determined. Results indicate that the powdered metal samples had the least relative corrosion rate-O.2256 milli. inches per year (mpy); cast metal was next with 0.4639 mpy, and cold worked had the greatest corrosion rate with 2.8 13.5 mpy. Pitting corrosion, or highly localized corrosion, was least in the cast metal group, although not significantly different from the other groups. Powdered metal brackets manufactured by an injection molding process have been shown in this study to be most resistant to normal saline corrosion.
The purpose of this study was to determine if the hyoid bone could be used as a reliable and stable reference landmark. Previous researchers have used cranial landmarks to determine the hyoid bone position. The results of these studies have shown a large variability in hyoid position. To determine the hyoid bone position, R. E. Bibby’s hyoid triangle analysis was used. The hyoid triangle is formed by joining the cephalometric points retrognathion (the most inferior posterior point on the mandibular symphysis), hyoidale (the most superior anterior point on the body of the hyoid bone), and C3 (the most anterior inferior point on the third cervical vertebra). The hyoid triangle was conS cted using landmarks that are closer to the axis of rotation of the head than the cranium. This decreases the effect of head movement on hyoid position. Thirty
pretreatment orthodontic patients ranging in age from 9 to 15 years were used. The sample was selected randomly, included males and females, and was not limited to any particular malocclusion type. Each patient had two lateral cephalometric films taken with a mechanical holding device to stabilize head position. Hyoid bone position was compared between the two radiographs. Results indicate that hyoid bone position is not reproducible with the methods used in this study. Greater measured differences in hyoid position might be expected with growth changes and o~hodont~c treatment, Thus, there is no evidence that the hyoid triangle analysis can be used to locate hyoid bone position.
Evaluation of the Modulus Stainless Steel Orthodontic Acoustic Pulse-Propagation
of plasticity
John Rick Neilson Loma Linda
University,
1985
Confusion exists in the orthodontic literature when the modulus of elasticity of standard orthodontic wire is reported to increase, decrease, or remain constant when that wire is heat treated or work hardened. The objectives of this work were (1) to introduce the acoustic pulse-propagation technique as a test for determining the modulus of elasticity in orthodontic wire, and (2) to determine whether the modulus of elasticity of stainless steel orthodontic wire changes when a wire is subjected to heat treatment and work hardening. Five sizes of stainless steel wire were evaluated: 0.014, 0.016, and 0.018 inch round, 0.016 x 0.016 inch square, and 0.016 X 0.022 inch rectangular. Two groups were tested to determine the sonic rno~~l~s. The first group was tested “as-received,” and then retested after the wires were tensile loaded. The second group was tested after annealing (1700” F for 20 minutes). Retesting was done when the annealed wires were tensile loaded as in the first group. Each wire was mechanically excited by a piezoelectric element. The piezo-element received its amplified signal from a square-wave pulse generator. The time-of-flight between two points on the wire was recorded and measured on a dual trace oscilloscope. The impulse time-of-flight range, from high to low, varied only 0.025 micro seconds. When converted to giga pascals, the measured elastic modulus varied 3.3% from the predicted value. It was concluded that (1) the acoustic pulse-propagation technique is a valid, reliable method for determining the modulus of elasticity of orthodontic wire
Reviews and abstracts 1
esistance of Orthodontic st, Cold Worked, and
Loma
Linda
University,
1985
Corrosion rates were measured on three types of stainless steel (316-L) brackets: (1) cast, (2) cold worked, and (3) powdered metal. Interest in corrosion resistance of orthodontic brackets is increasing because of tooth enamel staining thought to be associated with corrosion of the metal bracket. Five brackets from each group were immersed in aerated normal saline solution as the corrosive agent. Voltage differences (potentiodynamic anodic polarization) between samples and a reference electrode were measured to determine the corrosion rate of a sample. Current flow is affected by corrosion layers; by plotting how the current responds to an applied voltage, the sample’s corrosion rate is determined. Results indicate that the powdered metal samples had the least relative corrosion rate-O.2256 milli. inches per year (mpy); cast metal was next with 0.4639 mpy, and cold worked had the greatest corrosion rate with 2.8 13.5 mpy. Pitting corrosion, or highly localized corrosion, was least in the cast metal group, although not significantly different from the other groups. Powdered metal brackets manufactured by an injection molding process have been shown in this study to be most resistant to normal saline corrosion.
The purpose of this study was to determine if the hyoid bone could be used as a reliable and stable reference landmark. Previous researchers have used cranial landmarks to determine the hyoid bone position. The results of these studies have shown a large variability in hyoid position. To determine the hyoid bone position, R. E. Bibby’s hyoid triangle analysis was used. The hyoid triangle is formed by joining the cephalometric points retrognathion (the most inferior posterior point on the mandibular symphysis), hyoidale (the most superior anterior point on the body of the hyoid bone), and C3 (the most anterior inferior point on the third cervical vertebra). The hyoid triangle was conS cted using landmarks that are closer to the axis of rotation of the head than the cranium. This decreases the effect of head movement on hyoid position. Thirty
pretreatment orthodontic patients ranging in age from 9 to 15 years were used. The sample was selected randomly, included males and females, and was not limited to any particular malocclusion type. Each patient had two lateral cephalometric films taken with a mechanical holding device to stabilize head position. Hyoid bone position was compared between the two radiographs. Results indicate that hyoid bone position is not reproducible with the methods used in this study. Greater measured differences in hyoid position might be expected with growth changes and o~hodont~c treatment, Thus, there is no evidence that the hyoid triangle analysis can be used to locate hyoid bone position.
Evaluation of the Modulus Stainless Steel Orthodontic Acoustic Pulse-Propagation
of plasticity
John Rick Neilson Loma Linda
University,
1985
Confusion exists in the orthodontic literature when the modulus of elasticity of standard orthodontic wire is reported to increase, decrease, or remain constant when that wire is heat treated or work hardened. The objectives of this work were (1) to introduce the acoustic pulse-propagation technique as a test for determining the modulus of elasticity in orthodontic wire, and (2) to determine whether the modulus of elasticity of stainless steel orthodontic wire changes when a wire is subjected to heat treatment and work hardening. Five sizes of stainless steel wire were evaluated: 0.014, 0.016, and 0.018 inch round, 0.016 x 0.016 inch square, and 0.016 X 0.022 inch rectangular. Two groups were tested to determine the sonic rno~~l~s. The first group was tested “as-received,” and then retested after the wires were tensile loaded. The second group was tested after annealing (1700” F for 20 minutes). Retesting was done when the annealed wires were tensile loaded as in the first group. Each wire was mechanically excited by a piezoelectric element. The piezo-element received its amplified signal from a square-wave pulse generator. The time-of-flight between two points on the wire was recorded and measured on a dual trace oscilloscope. The impulse time-of-flight range, from high to low, varied only 0.025 micro seconds. When converted to giga pascals, the measured elastic modulus varied 3.3% from the predicted value. It was concluded that (1) the acoustic pulse-propagation technique is a valid, reliable method for determining the modulus of elasticity of orthodontic wire