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Biomedical subjects

P Gjessing

Publications and source records attributed to P Gjessing.

6 recordsLinked to original sources
PubMed1992

Controlled retraction of maxillary incisors.

The force characteristics inherent in the prefabricated PG retraction spring have been shown to be efficient for controlled movement of canines. In the present investigation, this spring was analyzed with regard to its applicability for controlled retraction of the maxillary incisors. A description of the required system of moments and horizontal and vertical forces, acting at both the active (alpha) and reactive (beta) units, is presented. The three-dimensional force system generated by specific modifications of the spring was registered in a bench testing device mounted with strain gauges, and the resultant data presented in a graphic. It is concluded that the PG retraction spring can be used as a module for controlled retraction of both canines and incisors. The magnitude of horizontal and vertical forces is kept within the anticipated physiologic limits and can be identified by the shape of the activated spring. Variability of the distance between the anterior and the posterior points of force attack has no significant influence on the horizontal and vertical forces produced. Only minor clinical adjustments are needed to modify the retraction spring from canine-to-incisor retraction.

Calibration↗
PubMed1991

Location of centres of resistance for maxillary anterior teeth measured on human autopsy material.

The location of the centre of resistance (CR) of various consolidated units of maxillary anterior teeth was determined in this study using human autopsy material. The units studied consisted of two central incisors, four incisors, and six anterior teeth. When horizontal forces were applied the CR for the two- and six-tooth units was located approximately 6.5 mm apical to the bracket position. For the four-tooth unit, CR was placed slightly more occlusally, the distance being 5.0 mm. Applying vertical forces CR was located about 13.0 mm posterior to the bracket position for the two- and four-tooth unit. The incorporation of the canines into the incisor segment resulted in a distal shift of CR of 6 mm. CR for the six anterior teeth was, thus, located on a line 3 mm behind the distal surface of the canines. Increasing force levels had little effect on the location of CR for a given unit.

Adult↗
PubMed1985

Biomechanical design and clinical evaluation of a new canine-retraction spring.

Use of the sectional arch technique facilitates the creation of an optimal force system fulfilling the biomechanical requirements imperative for planned tooth movements. Controlled canine retraction, usually in extraction cases, requires the creation of a biomechanical system to deliver a predetermined force and a relatively constant moment-to-force ratio in order to avoid distal tipping and rotation. The responsive couple delivered to the anchorage unit should be adjusted in such a way that no single tooth is subjected to unwanted side effects and that undesirable changes in the occlusal plane are avoided. On the basis of a series of theoretical considerations described in the present report, a canine-retraction spring was constructed from 0.016 X 0.022 inch stainless steel wire, the principal element being a double ovoid loop 10 mm in height. A "sweep" bend was incorporated to avoid unwanted side effects at the second premolar. Load deflection and moment/force curves were derived experimentally and demonstrate the ability of the spring to generate and maintain biomechanical conditions necessary for optimal canine retraction (that is, load deflection = 45 gm per millimeter of activation, antitip moment/force ratio of approximately 11:1, and antirotation moment/force ratio of approximately 7:1). The clinical applicability of the spring is demonstrated in the present report by the presentation of two treated cases.

Biomechanical Phenomena↗