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Biomedical subjects

S J Chaconas

Publications and source records attributed to S J Chaconas.

At least 19 recordsLinked to original sources
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↗
PubMed1979

Soft-tissue change as a result of maxillary surgery. A preliminary study.

A retrospective investigation of soft-tissue changes following two types of maxillary surgical procedure (anterior alveolar segmental, LeForte I) in nineteen adult patients was undertaken. Several hard-tissue coordinates were correlated to each coordinate of eleven soft-tissue points by multivariate regression analysis. This new method was compared to a previously derived nonsurgical prediction method (Ricketts). The following results were observed: 1. For eight horizontal and vertical coordinates (Glh, Glv, Nah, Av, Nch, Ncv, Pnh, and Pnv), neither method was accurate. 2. For ten horizontal and vertical coordinates (Snh, Snv, Ah, Av, ULh, ULv, Stv, LLh, Bv, and Pogv), the mean prediction residuals for the multivariate method were significantly smaller than those for the modified nonsurgical method. 3. For three horizontal and vertical coordinates (LLv, Bh, and Pogh), there were no significant differences between the mean prediction residuals of both methods. Two additional cases were used to test the new method for general applicability. Visual examination reveals that the predictions for these cases are clinicallly acceptable. Only further testing can establish the true validity of the new method.

Adolescent↗
PubMed1979

Effects of orthodontic intermaxillary Class III mechanics on craniofacial structures. Part I - photoerlastic analysis.

The relation between active growth and induced anatomic changes was examined using photoelastic stress techniques. The following can be concluded from this investigation: 1. Utilization of Class III mechanics on the photoelastic skull affected the zygomaticotemporal, zygomaticofrontal and frontomaxillary sutures. 2. The stress trajectories observed in the mandible lead to the conclusion that Class III traction affects mandibular growth and opening, as well as condylar repositioning. 3. Evidence of stress was observed in a section of the condyle due to the external pterygoid muscle. 4. The stress concentrated at the outer surface of the pterygoid plate was due to the action of the external pterygoid muscle. 5. The effect of the simulated Class III traction created concentrations of stress mesial and distal of the second molars and at the apical and midroot areas of first molars.

Facial Bones↗
PubMed1979

Effects of orthodontic intermaxillary class III mechanics on craniofacial structures. Part II - computerized cephalometrics.

The relation between active growth and induced anatomic changes was examined using a computerized cephalometric analysis of ten Class III cases treated with intermaxillary traction. The following can be concluded from this investigation: 1. Mandibular growth was redirected and mandibular opening was observed due to maxillary molar extrusion and counterclockwise rotation of the maxilla. 2. Condylar repositioning was noted to occur in all cases due to the effect of the external pterygoid muscle and a possible translatory movement during mandibular rotation. 3. Counterclockwise palatal development occurred in most of the treated cases through vertical action of the Class III mechanism. 4. The effect of the Class III traction was also observed in the mandibular incisor and molar teeth. The incisors retruded and the molars either were located in the predicted position or farther distally. 5. The soft tissue profile was less concave than the predicted value due to less mandibular growth and more retruded incisors in the treated cases. 6. Evidence was shown that a positive relationship exists between computerized cephalometrics and photoelastic techniques in the analysis of ten treated cases. This relationship is based on the fact that specific changes which took place during treatment were found to be consistent with the results of the photoelastic analysis.

Cephalometry↗
PubMed1978

Orthodontic force production by closed coil springs.

The effects of wire size, lumen size, and wire type on the production of force by closed coil springs were determined. Force production was affected as follows: (1) Keeping the lumen size constant, an increase in wire size produced an increase in force. (2) Keeping the wire size constant, an increase in lumen size produced a decrease in force. (3) For a given wire size, force varied with different wire types. This study has shown that the current recommendations for the use of closed coil springs produce forces of greater magnitude than is necessary for orthodontic tooth movement. The clinician should take care to select the proper closed coil spring for specific clinical situations.

Orthodontic Appliances↗
PubMed1978

Orthodontic effects of loop design and heat treatment.

The effects of heat treatment on Blue Elgiloy wire and loops formed from this wire were determined. The optimum heat treatment temperature was established to be in a narrow range in the vicinity of 950 degrees F. This regimen increases the yield and ultimate strengths of this wire. Heat treatment also produced a modification of the load-deflection characteristics of the loop configuration tested. Overall, heat treatment of the wire is indicated by this study.

Chromium Alloys↗
PubMed1978

Effects of intermaxillary elastic traction on orthodontic tooth movement.

Intermaxillary elastics are commonly used in orthodontic treatment, yet the exact mechanism by which they effect tooth movement has been unclear. A photoelastic model was produced to stimulate this type of therapy in examples of Class II and III malocclusions. In the open situation, inter-arch activity precipitated occlusal plane rotation; counter clockwise in Class II malocclusion and clockwise in Class III. Comment is made on the force vectors involved when using intermaxillary elastics.

Dental Stress Analysis↗
PubMed1977

Force-extension characteristics of orthodontic elastics.

The force-extension characteristics for a wide range of elastics were determined. It was found that (1) selection of elastics were determined. It was found that (1) selection of elastics based on 3 x lumen size will probably result in more force being generated than was previously reported, (2) there is very little difference seen in force-extension characteristics when the two manufacturers' elastics are compared, and (3) for experimental purposes, elastic testing can be done in the dry state for force-extension characteristic studies. This investigation has shown that stretching an orthodontic elastic to twice its original lumen diameter produces a force which better represents the manufacturer's expected value. Keeping these principles in mind, a more effective tooth-moving force can be realized, enabling the clinician to properly select orthodontic elastics for intra- and intermaxillary biomechanical procedures.

Orthodontic Appliances↗
PubMed1976

Orthopedic effect of the extraoral chin cup appliance on the mandible.

An anatomic photoelastic model of a human skull was constructed with the use of individual simulants for teeth, bone, and periodontal ligaments. The following effects of extraoral chin cup traction were observed: 1. Stresses were noted in the area of the pterygoid plates of the sphenoid bone due to the insertion of the simulated external pterygoid muscle. 2. Because of direct contact of the condyle against the posterior surface of the glenoid fossa, forces were seen to be transmitted to this anatomic area. 3. Stress trajectories followed the trabecular pattern of the anatomic configuration of the mandible. 4. Beginning at the apices of the incisor teeth, the stresses emanated through the body, the angle and retromolar triangle of the mandible, radiating in a posterosuperior fashion and concentrating at the neck of the condyle. 5. Selected sectioning of the mandibular model showed evidence of stress concentration at the lingual aspect of the angle and retromolar area as well as at the condylar neck at the level of the external pterygoid muscle insertion. The effects of orthopedic forces produced by an extraoral chin cup in this study are correlated with the histologic and clinical observations during the utilization of this appliance in the treatment of Class III malocclusion.

Facial Bones↗
PubMed1976

The effects of orthopedic forces on the craniofacial complex utilizing cervical and headgear appliances.

1. A three-dimensional anatomic model of a human skull was produced with birefringent materials for photoelastic analysis. By means of photoelastic techniques during application of high-pull and cervical extraoral traction, stresses were visualized within the model. 2. Extraoral anchorage affected the position of the maxillary molar and its resulting alveolar development. Cervical headgear had a much greater tipping effect on the maxillary molar than did the high-pull headgear. Both appliances examined could produce stresses which may be transmitted to distant eraniofacial sutures. As opposed to high-pull traction, cervical pull in general stressed more areas and to a much greater degree. 4. The pterygoid plates of the sphenoid bone, the zygomatic arches, the junction of the maxilla with the lacrimal bone and the ethmoid, and the maxillary teeth were affected by both types of headgear. 5. Only cervical traction produced stresses at the frontal process of the maxilla and the Zygomaticofrontal suture. 6. There were two findings which had not been previously reported: First, cervical traction tended to open the palate in the posterior region. Second, high-pull traction produced compressive stresses at the junction of the right and left maxillae inferior to the anterior nasal spine.

Facial Bones↗