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S J Chaconas

Publications and source records attributed to S J Chaconas.

At least 37 records · Page 2Linked to original sources
PubMed1982

Experimental force analysis of the contraction utility arch wire.

An experimental apparatus consisting of a metal framework, a strain gauge, and a Wheatstone bridge was used to measure the retraction force delivered to the mandibular incisors by a contraction utility arch wire (0.016 by 0.016 inch blue Elgiloy). The contraction utility arch wire was activated 1 mm. and retraction forces were recorded as the deflection of a point image on an oscilloscope. The results indicated that the retraction forces at the incisor positions were reasonably within an optimal force range to move teeth quickly with minimal tissue damage and discomfort. However, the lateral incisor positions in both ovoid and narrow arch forms received significantly more force than the central incisor positions, and the narrow tapered arch form delivered more retraction force than the ovoid arch form.

Dental Stress Analysis↗
PubMed1982

Observation of orthopedic force distribution produced by maxillary orthodontic appliances.

A three-dimensional anatomic model was duplicated from a human skull, using different birefringent materials to simulate the various craniofacial structures. Individual bones of the midface were fabricated separately and then articulated in their correct sutural relation. One removable and four fixed maxillary appliances were used. The fixed appliances included the Haas, Minne-expander, Hyrax, and quad helix devices. The removable appliance incorporated an expansion screw in a full acrylic palate with appropriate retentive clasps. After the insertion of each appliance, intraoral forces were produced by incremental activation. The model was examined and photographed in the field of a transmission polariscope. Each appliance used produced a different range of load-activation characteristics. This was reflected by the differences in the stresses transmitted through the bones of the craniofacial complex and the effect on the various sutures. Stresses produced by the fixed appliances were concentrated in the anterior region of the palate, progressing posteriorly toward the palatine bone. The Haas, Minne-expander, and Hyrax appliances produced stresses that radiated superiorly along the perpendicular plates of the palatine bone to deeper anatomic structures, such as the lacrimal, nasal, and malar bones, as well as the pterygoid plates of the sphenoid. Similar stress characteristics were seen with the removable appliance. However, increased activation decreased retention of the appliance, thereby lessening the stress. The quad helix appliance proved to be the least effective orthopedic device. Although the effects of palate separation were seen with increased activation, this appliance primarily affected the posterior teeth.

Equipment Design↗
PubMed1982

Stress distribution under high-pull extraoral chin cup traction. A photoelastic study.

Birefringent materials were employed in the fabrication of a model of a human skull with distinct simulants for teeth, bone, and periodontal ligaments. The following observations were made subsequent to the application of force to this model with an extraoral high-pull chin cup: 1. Reciprocal stresses were observed in the posterior portion of the glenoid fossa and the contacting posterior part of the head of the condyle. 2. A tension coil spring representing the external pterygoid muscle applied reciprocal stresses at its insertions in the lateral pterygoid plate on the greater wing of the sphenoid and the anterior aspect of the head of the condyle. 3. Stresses were seen to radiate from the roots and apices of both the maxillary and mandibular posterior teeth. 4. A distinct concentration of stress was noted in the retromolar area of the mandible, away from the dentition, indicating a bending stress. 5. The posterior half of the sigmoid notch, below the anterior aspect of the head of the condyle, displayed a heavy band of stresses. 6. Selected sectioning of the mandible substantiated observations made from the intact hemimandible and also showed evidence of bending in the area corresponding to the head and neck of the condyle.

Dental Stress Analysis↗
PubMed1980

Canine retraction with J hook headgear.

Several methods have been described for accomplishing distal movement of canines without losing posterior anchorage. An accepted method in canine retraction is the use of headgear with J hooks. Since it incorporates extraoral anchorage, it is most effective in maximum-anchorage cases. It was the purpose of this study to analyze the distribution of force transmitted to the alveolus and surrounding structures by means of photoelastic visualization, utilizing J hook headgear for maxillary canine retraction. A three-dimensional model representing a human skull was used. This model was constructed with different birefringent materials to simulate bone, teeth, and periodontal membranes. Three different vectors of force were applied representing high-, medium-, and low-pull headgear, which were placed at angles of 40, 20, and 0 degrees to the occlusal plane. The photoelastic analysis was made by means of a circular-transmission polariscope arrangement, and the photoelastic data were recorded photographically. The stress areas created by the three different vectors of force were associated with various degrees of canine tipping. This effect was greater with the low-pull force component than with the medium-pull traction. The high-pull headgear produced the least tipping tendency, being closer to a bodily movemment effect. Further, stresses were transmitted to deeper structures of the simulated facial bones; these regions were the frontozygomatic, zygomaticomaxillary, and zygomaticotemporal sutures.

Alveolar Process↗
PubMed1980

Nasopharyngeal cephalometrics.

A sample of 104 patients, males and females between the ages of 6 and 16 years, was studied. The sample included patients with clinically diagnosed nasopharyngeal obstruction, patients with no obstruction, and random sample of patients for whom the presence or absence of obstruction was not known. More than 200 cephalometric measurements were used in an attempt to identify differences between the first two groups. Statistical t tests revealed four variables, all primarily related to adenoid size and nasopharyngeal dimensions, for which the mean values of the two groups were significantly different. Cephalometric norms for these four measurements were established, using the random sample patients, and these norms were calculated for various ages and both sexes. A method of identifying the degree of obstruction was then formulated on the basis of the four significant measurements. Preliminary results indicate that this method is highly correlated with observed clinical results.

Adenoidectomy↗
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↗