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Biomedical subjects

A E Phelps

Publications and source records attributed to A E Phelps.

6 recordsLinked to original sources
PubMed2000

Location of the apex of the lower central incisor.

Clinicians have always had difficulty finding the apex of the lower central incisor on a lateral cephalometric radiograph. This study was undertaken to define the radiographic anatomy surrounding the true apex. Standard cephalograms were taken of 38 skulls with metallic markers in the socket apex of 1 lower central incisor. Similar cephalograms were taken with the lower central incisor apex positioned in the central ray of the x-ray source. The comparison of the marked apices in the complete skulls and their separate mandibles showed that there was no distortion. Measurements from the markers to the lingual and labial symphyseal borders located the apices labial of center.

Adolescent↗
PubMed1993

Bond strength of aged composites found in brackets placed by an indirect technique.

The "Thomas" indirect technique for bracket attachment produces an interface not present in direct techniques, that is, an aged composite-sealant interface. Our primary goal was to determine if a weakened interface was produced by a modified (sealant was mixed prior to placement of brackets) Thomas indirect technique when the composite was aged for 7 days. The enamel-bracket system was investigated in vitro by comparison of shear bond strengths for metal and ceramic brackets bonded to bovine teeth by a direct and indirect method. Nearly all specimens failed at the bracket-composite interface and, subsequently, no difference was found between specimens placed by direct or indirect methods. No evidence was found to suggest that an aged composite would predispose the enamel-bracket system to fail at the sealant-composite interface. The ceramic brackets used in this investigation had lower bond strengths then metal ones, but the breaking loads were similar.

Adhesives↗
PubMed1993

Analysis of the "shear" bond strength of pretreated aged composites used in some indirect bonding techniques.

Investigations of the repair of composites have shown that bond strengths can be significantly reduced at an interface involving an aged composite. Brackets placed by some indirect bonding techniques also have an interface involving an aged composite. This study investigated some of the properties of sealant-composite interfaces and parameters affecting these properties independent of other regions and interfaces found in the total enamel-sealant-composite-bracket system using a shear bond-strength test and fractographic analysis. The effects of various pretreatments of 7-day-old composite surfaces on the bond strength and contact angle of a mixed sealant on these pretreated surfaces were determined. Fractured specimens with adhesive failure closest to the point of force application had low bond strengths (17.62 MPa), which could be correlated with surface pretreatment. Preliminary tests showed that acetone pretreatment produced the most consistently strong interfaces with the fewest adhesive failures of this type. Specimens with adhesive failure only in other regions had higher bond strengths (23.41 MPa), which showed no dependence on pretreatment. There was no statistical relationship between contact angle and bond strength. The data coupled with fracture path analysis suggest that: first, the critical region for fracture analysis is that part of the adhesive interface which is closest to the point of force application; second, failure during some dental shear bond strength tests probably occurs as a consequence of tensile stress induced by a bending moment rather than by shear stress; and third, specifying bond strength as breaking load/area may be incorrect.

Acetone↗
PubMed1978

A comparison of lower face changes.

A comparison has been made of cases treated with deliberate anchorage preparation (Class III elastic mechanics) prior to Class II elastic mechanics and cases treated with Class II elastic mechanics only. Treatment goals were the same. Extraoral traction was used as necessary to achieve those goals. Appliance quantity and size were the same. Age, sex, and severity of malocclusion were comparable. It remained that the anchorage-prepared cases demonstrated a flattening of the mandibular plane, greater retraction of the lower incisors, more retraction of midface, and more protraction of lower face. These changes of lower face are consistent with the normal growth changes of the human face.

Cephalometry↗