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S J Chaconas

Publications and source records attributed to S J Chaconas.

At least 19 recordsLinked to original sources
PubMed2000

Center of resistance of anterior arch segment.

It is important to know the location of the center of resistance (CR) to control tooth movement. In this study, photoelastic techniques were used to determine the center of resistance. The photoelastic model included the anterior 4 maxillary teeth, which were interconnected firmly with 6 mm of space between lateral incisors and canines. Determination of the CR for the anterior arch segment was based on considerations of a wide variety of load conditions that generated the more uniform stresses in the supporting alveolar bone simulant. For the arch having the anterior 4 teeth connected, the CR was located within the mid-sagittal plane, 6-mm apical and 4-mm posterior to a line perpendicular to the occlusal plane from the labial alveolar crest of the central incisor.

Birefringence↗
PubMed1994

Biomechanical rationale for surgical-orthodontic expansion of the adult maxilla.

OBJECTIVE: To develop a biomechanical rationale for surgical-orthodontic correction of transverse maxillary deficiencies in adults by clarifying the internal stress responses to rapid palatal expansion in a photoelastic model. MATERIALS AND METHODS: A three-dimensional photoelastic analog of an adult human skull was constructed by fabricating the individual facial bones from a photoelastic material and fixing them along their anatomic sutural areas. After determining the force-activation characteristics of a Hyrax expansion appliance in a straining frame, the appliance was applied to the analog and incrementally activated. The stresses developing at the different craniofacial areas were visualized and photographed in the field of a circular polariscope. Sequential cuts were performed to simulate midpalatal, zygomatic buttress, and pterygomaxillary osteotomies, and the alterations in the internal stress responses were recorded after each individual cut. RESULTS: The force-activation characteristics of the Hyrax appliance are in the orthopedic range (500 g). The magnitude and distribution of the stresses induced by appliance activation differed notably between the simulated osteotomies. Analysis of fringe patterns showed that the midpalatal and pterygomaxillary articulations were the primary anatomic sites of resistance to expansion forces. The patterns of distribution and the increase in the magnitude of the stresses at superior sutural location were particularly pronounced after the pterygomaxillary cuts. The forces produced by the Hyrax appliance had deep anatomic effects, with internal stresses also manifesting at regions distant from the site of force application. CONCLUSIONS: Based on photoelastic observation, it may be concluded that complete midpalatal and pterygomaxillary osteotomies are essential for predictable skeletal expansion in adults. Exclusive use of bilateral zygomatic buttress osteotomies appears to be inadequate. The expansion forces exerted by the Hyrax appliance are orthopedic in nature and produce deep anatomic effects. Clinicians should be aware that the craniofacial stresses produced by appliance activation may be experienced by the patient as pain or discomfort.

Adult↗
PubMed1993

Photoelastic evaluation of the standard bionator appliance.

A study was undertaken to demonstrate the forces in the craniofacial complex generated by the activation of the standard bionator appliance. A three-dimensional skull replica of an orthodontic patient with a Class II Division 1 malocclusion in the mixed dentition was fabricated using a urethane based photoelastic material to simulate bone. Four muscles of mastication were simulated on the photoelastic model. Various anatomical areas of the skull were viewed in a circular polariscope and recorded photographically before and after inserting the bionator. The downward and forward repositioning of the lower jaw by the bionator appliance caused various stresses on the craniofacial complex. The photoelastic stresses visualized in this investigation would most likely cause: an increase in the gonial angle; downward repositioning of the midface; and a posterior displacement and expansion of the maxilla.

Activator Appliances↗
PubMed1991

Bond strength of ceramic brackets with various bonding systems.

The purpose of this investigation was to determine the shear and tensile bond strengths of various ceramic and ceramic-filled brackets in combination with commonly used bonding systems. One monocrystalline, two polycrystalline and one ceramic-filled plastic bracket types were tested in combination with one light-cured and two chemically-cured bonding systems. Bonding procedures were performed on properly prepared human teeth. Shear and tensile tests were performed on an Instron test machine. The shear bond strength of the mono- and polycrystalline ceramic brackets was not affected by the bonding system. There was a difference among bonding systems used with the ceramic-filled plastic bracket. Ceramic-filled plastic and polycrystalline ceramic brackets exhibited the greatest resistance to tensile force, while monocrystalline brackets showed the highest propensity for tensile fracture of the wings.

Acid Etching, Dental↗
PubMed1991

Orthognathic diagnosis and treatment planning: a cephalometric approach.

Cephalometric analyses have long been important diagnostic tools for the orthodontic specialist. Such analyses, as they pertain to adult skeletal problems and their consequent therapy, should also be a valuable adjunct for various dental specialties, e.g. the oral surgical clinician. However, because of the complexity of most analyses, it is difficult to glean the important values needed for most orthognathic cases. In this article an analysis is presented to aid the clinician in surgical diagnosis and treatment planning.

Adult↗
PubMed1987

Biomechanical effects of maxillary protraction on the craniofacial complex.

The deformational effects on the human skull resulting from maxillary protraction were examined by means of strain gauges and displacement transducers. A maxillary protraction appliance was used that included a reverse headgear attached to the maxillary first molars. The protraction forces that were applied to this appliance were parallel to the occlusal plane at the following locations: the height of the maxillary arch, 5 mm above the palatal plane, and 10 mm above the Frankfort horizontal plane. The results indicated that protraction forces at the level of the maxillary arch produced an anterior rotation and forward movement of the maxilla, protraction forces 10 mm above the Frankfort horizontal plane produced a posterior rotation of the maxilla with a forward movement of nasion, and protraction forces 5 mm above the palatal plane produced a combination of parallel forward movement and a very slight anterior rotation of the maxilla. Moreover, constriction of the anterior part of the palate occurred in all cases.

Biomechanical Phenomena↗
PubMed1985

Photoelastic effects of maxillary protraction on the craniofacial complex.

The conventional treatment of anterior crossbites has been the application of orthopedic force to the mandible to redirect its growth. However, in the patient with an underdeveloped maxilla, this treatment alone is not sufficient. Therefore, the purpose of this investigation was to study the orthopedic effects of maxillary protraction appliances in the treatment of anterior crossbites. A three-dimensional anatomic model of a human skull was fabricated with birefringent materials for photoelastic analysis. Three maxillary protraction appliances that utilized different anchorage units were used. The protraction forces placed on these appliances were parallel to the occlusal plane, a downward vector 20 degrees to the occlusal plane, and a combination of these two vectors. The resulting stress patterns were observed. The effects of the forces produced by the three appliances were transmitted to the maxilla and distant craniofacial structures. Both a parallel traction and a 20 degrees downward pull to the occlusal plane caused a constriction of the anterior portion of the maxilla. The parallel traction caused a counterclockwise (opening) rotation of the molar tooth and palatal plane. A 20 degrees downward force to the occlusal plane decreased this effect.

Bicuspid↗
PubMed1984

Orthodontic force characteristics of open coil springs.

Applications of open coil springs in orthodontic tooth movement are many and varied. Current descriptions of force production by open coil springs are based upon force values produced in series of discrete compression tests. It was the purpose of this study to analyze and compare open-coil-spring force production from continuous load-deflection curves, thereby assisting the clinician in the selection of the ideal spring for a given application. Load-deflection curves were generated for open coil springs of various wire diameters and lumen sizes, as well as four wire alloys from three manufactures. Testing was performed on an Instron test machine using 0.016 inch round and 0.018 by 0.022 inch rectangular arch wires. With a constant lumen size, an increase in wire size produced an increase in force at a given activation. With a constant wire size, an increase in lumen size produced a decrease in force at a given activation. The effect of the arch wire size and shape was not significantly different for the coil springs with the smaller lumen sizes. For the larger lumen sizes, the springs used with the rectangular arch wire manifested a greater linear range than those used with the smaller arch wire. The difference between the load-deflection characteristics of the coil springs from different manufacturers was attributed to the difference in the pitch of the coils.

Equipment Design↗