Search PubMed⌕ Search

Biomedical subjects

R S Nanda

Publications and source records attributed to R S Nanda.

At least 55 records · Page 3Linked to original sources
PubMed1996

Fracture strength of ceramic brackets during arch wire torsion.

This study evaluated the fracture strengths of eight new vintage ceramic brackets with application of torsional forces. Palatal root torque was applied at the distal side of right maxillary central incisor brackets with 0.022-inch slots by means of a 0.0215 x 0.027-inch rounded edge stainless steel arch wire. A specially designed apparatus that attached to an Instron machine was used to test the ceramic brackets. The amount of torque, degrees of torsion at failure, and fracture locations were measured. The monocrystalline bracket did not break when the torquing test was applied; the portion of the wire outside the slot of the bracket twisted on itself. The mean torquing forces at failure ranged from 5755.2 gm-mm to 9316.5 gm-mm and could be separated into three statistically different groups. The mean torsional rotation at fracture ranged from 32.7 degrees to 68.1 degrees for the polycrystalline brackets. The results suggested that all the brackets studied were sufficiently strong to withstand the commonly accepted magnitudes of arch wire torquing forces. The present investigation showed higher angulation values for all the brackets than those reported by Holt who used the same apparatus with older style brackets.

Analysis of Variance↗
PubMed1995

Ceramic bracket design: an analysis using the finite element method.

This investigation was designed to generate finite element models for selected ceramic brackets and graphically display the stress distribution in the brackets when subjected to arch wire torsion and tipping forces. Six commercially available ceramic brackets, one monocrystalline and five polycrystalline alumina, of twin bracket design for the permanent maxillary left central incisor were studied. Three-dimensional computer models of the brackets were constructed and loading forces, similar to those applied by a full-size (0.0215 x 0.028 inch) stainless steel arch wire in torsion and tipping necessary to fracture ceramic brackets, were applied to the models. Stress levels were recorded at relevant points common among the various brackets. High stress levels were observed at areas of abrupt change in geometry and shape. The design of the wire slot and wings for the Contour bracket (Class One Orthodontic Products, Lubbock, Texas) and of the outer edges of the wire slot for the Allure bracket (GAC, Central Islip, N.Y.) were found to be good in terms of even stress distribution. The brackets with an isthmus connecting the wings seemed to resist stresses better than the one bracket that did not have this feature. The design of the isthmus for the Transcend (Unitek/3M, Monrovia, Calif.) and Lumina (Ormco, Glendora, Calif.) brackets were found to be acceptable as well. The Starfire bracket ("A" Company, San Diego, Calif.) showed high stresses and irregular stress distribution, because it had sharp angles, no rounded corners, and no isthmus. The finite element method proved to be a useful tool in the stress analysis of ceramic orthodontic brackets subjected to various forces.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Oxide↗
PubMed1995

Bond strengths and remnant adhesive resin on debonding for orthodontic bonding techniques.

Bond strengths and remnant adhesive resin on the tooth surface after debonding for three bonding techniques used to attach foil mesh orthodontic brackets to 315 freshly extracted bovine incisor teeth were compared in an in vitro study. Each method of bonding used 105 teeth in groups of 15, bonded with seven different (bis-GMA type) two-paste chemically cured resins. The direct method comprised bonding the attachments directly to the incisors with the composite resin. The indirect-1 method comprised securing attachments to die-stone models of the teeth with a water soluble glue, making silicone positioners to transfer the brackets from the models to the teeth, and bonding to the teeth with the use of the two-paste composite resin system. The indirect-2 method comprised bonding the attachments to die-stone models of the teeth with composite resin, making silicone positioners to transfer the brackets from the models to the teeth, and bonding to the teeth with the use of unfilled sealant resin. Significant differences in bond strength existed among the groups evaluated. The direct technique had statistically significant (p < 0.05) higher bond strength as compared with the indirect-1 and indirect-2 techniques in four of the seven groups evaluated. The indirect-1 and indirect-2 techniques were not significantly different (p < 0.05) in bond strength in six of seven groups tested. The indirect-2 technique had significantly lower adhesive remnant index scores (ARI) compared with the direct and indirect-1 techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Acid Etching, Dental↗
PubMed1995

The effects of exogenous prostaglandins on orthodontic tooth movement in rats.

The long-term effects of varying concentrations and frequencies of injectable, exogenous prostaglandin E2 (PGE2) on the rate of tooth movement and the amount of root resorption were evaluated. There were 132 male Sprague-Dawley rats 8 weeks old that initially weighed 225 to 250 gm. Five animals were in a pilot study, while seven were baseline controls and eight were appliance controls. The remaining 112 animals were divided into two experimental time periods of 2 and 4 weeks. Then, each experimental time period was divided into four subgroups of 14 animals based on concentration levels of PGE2 injections, i.e., 0.1, 1.0, 5.0 and 10.0 micrograms. Half of these animals in the dosage subgroup received a single injection at appliance placement and the other half received weekly injections. A fixed orthodontic appliance consisting of closed-coil nickel-titanium springs were ligated between the maxillary incisors and maxillary first molars. The initial activating force was 60 gm. The results showed that injections of exogenous PGE2 over an extended period of time in rats did enhance the amount of orthodontic tooth movement. However, there was no statistically significant difference in tooth movement between the single and multiple injection groups or among the four concentration levels of PGE2 used in either the 2- or 4-week time periods. The amount of root resorption as seen from scanning electron micrographs did increase with the use of prostaglandin injections, specifically with increased numbers of injections and with increased concentrations of PGE2.

Anesthetics, Local↗
PubMed1995

Interlayer formation and its effect on debonding polycrystalline alumina orthodontic brackets.

During the debonding of ceramic orthodontic brackets, there is a risk of causing fractures, cracks, or flaking of enamel or of the bracket itself. Preliminary work on the resin-enamel interface under bonded brackets with the indirect (modified Thomas) or the thermal-cured indirect bonding techniques revealed an interlayer of unfilled resin formed between the filled resin and the enamel surface. The direct bonding technique, on the other hand, showed no such layer. This study was designed to determine the effect of the interlayer on conventional debonding techniques for polycrystalline ceramic orthodontic brackets. Variables examined were bracket failure or fracture (BF), amount of remnant adhesive (ARI), and enamel damage. Brackets were bonded to 90 fresh bovine teeth. These were divided into three groups of 30 each, based on three methods of bonding, i.e., direct, indirect (modified Thomas), and an indirect technique that used a thermal-cured resin. Each bonding group was further divided into three groups of 10 each, based on the type of debonding technique used, i.e., lift off, delamination, and twisting. Brackets bonded by the indirect (modified Thomas, BF mean = 0.27, ARI mean = 0.93) and the indirect technique that used a thermal-cured resin (BF mean = 0.03, ARI mean = 0.43) resulted in an overall significantly lower failure (p < 0.01) and ARI score on debonding (p < 0.0001) compared with those bonded by the direct technique (BF mean = 1.03, ARI mean = 1.97). Specimens evaluated under the stereomicroscope revealed that the brackets bonded with the indirect techniques debonded at the filled-unfilled resin interface or within the interlayer of unfilled resin.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum Oxide↗
PubMed1995

Skeletal and dental changes associated with the treatment of deep bite malocclusion.

A retrospective study of 132 treated orthodontic cases presenting at least 70% overbite was conducted using dental casts and lateral cephalometric radiographs from before and after treatment. These were 61 Class I, 27 Class II, Division 1, and 44 Class II, Division 2 malocclusion patients. Six different treatment modalities for the correction of the deep bite were compared. On the basis of the analysis of cephalometric measurements, no statistically significant differences were observed between the various treatment mechanics in the correction of the deep bite. Only in the Class II, Division 2 sample, total anterior face height increased significantly (p < 0.01) with all treatment modalities. The data were then grouped according to Angle classification regardless of the type of mechanics used. Within each Angle class, the changes from before to after treatment were statistically significant for almost all of the cephalometric measurements. These significant changes were due to both anticipated growth and orthodontic treatment. The treatment of overbite primarily affected the proclination of incisors and the extrusion of molars. Within each Angle classification, the patients were also separated according to whether the permanent teeth had been extracted. The nonextraction group was compared with the extraction group for the changes in each cephalometric measurement. It was found that the extraction of teeth did have a significant effect on the changes observed with treatment in all the Angle classes but was more pronounced in the Class I sample. The proclination of incisors was less and the mesial movement of molars was more in patients who were treated with the extraction of premolar teeth than those who were treated with the nonextraction procedures.

Adolescent↗
PubMed1995

Lateral cephalometric analysis of skeletal patterns in patients with and without internal derangement of the temporomandibular joint.

Twenty-three female volunteers with normal temporomandibular joints (TMJ) were compared with 24 female patients with documented TMJ internal derangements. Magnetic resonance imaging and lateral cephalometric radiographs were used to investigate the relationship between TMJ disk displacement and skeletal facial form. Results indicated that the patients with internal derangements have significantly smaller mandibles and maxillae. However, these sagittal measurements of jaw length were not associated with disproportionate changes in other cephalometric variables. In general, no district relationship was found between the morphologic features of the face and the internal derangements of the temporomandibular joint.

Adolescent↗
PubMed1995

Relative kinetic frictional forces between sintered stainless steel brackets and orthodontic wires.

The level of kinetic frictional forces generated during in vitro translation at the bracket-wire interface were measured for two sintered stainless steel brackets as a function of two slot sizes, four wire alloys, and five to eight wire sizes. The two types of sintered stainless steel brackets were tested in both 0.018-inch and 0.022-inch slots. Wires of four different alloy types, stainless steel (SS), cobalt chromium (Co-Cr), nickel-titanium (Ni-Ti), and beta-titanium (beta-Ti), were tested. There were five wire sizes for the 0.018-inch slot and eight wire sizes for the 0.022-inch slot. The wires were ligated into the brackets with elastomeric ligatures. Bracket movement along the wire was implemented by means of a mechanical testing instrument, and time dependent frictional forces were measured by a load cell and plotted on an X-Y recorder. For most wire sizes, lower frictional forces were generated with the SS of Co-Cr wires than with the beta-Ti or Ni-Ti wires. Increase in wire size generally resulted in increased bracket-wire friction. There were no significant differences between manufacturer for the sintered stainless steel brackets. The levels of frictional force in 0.018-inch brackets ranged from a low of 46 gm with 0.016-inch Co-Cr wire to a high of 157 gm with 0.016 x 0.025-inch beta-Ti wire. In comparing the data from a previous study by Kapila et al. 1990 performed at OUHSC with the same apparatus, the friction of sintered stainless steel brackets was approximately 40% to 45% less than the friction of the conventional stainless steel brackets.

Analysis of Variance↗
PubMed1995

Longitudinal growth changes in the sagittal relationship of maxilla and mandible.

This is a longitudinal study of the growth pattern in sagittal linear measurements at points A, B, and pogonion relative to the pterygoid vertical plane in a Class I sample. Serial cephalometric radiographs were traced and digitized at ages 6, 12, 18, and 24 years. The results indicated that between the ages of 6 and 24 years there was a total growth increment of 6.07, 7.53, and 11.17 mm at points A, B, and pogonion, respectively, in the female Class I sample and 9.49, 11.65, and 16.21 mm at points A, B, and pogonion, respectively, in the male sample. Although the actual change in length of these measurements was larger in the male subjects than in the female subjects, in terms of percentage of growth increment in each of these three measurements from age 6 to 24 years, the anterior movement at point B relative to point A, and at pogonion relative to points B and A was approximately the same for both male and female subjects. When each of the subjects in both male and female samples was rank-ordered according to the size at age 6 years, considerable individual variation was noticeable for most persons within the group. The individual variation in growth pattern in each of the different measurements continues to raise questions about growth prediction and its application in visual treatment objectives.

Adolescent↗
PubMed1995

Facial soft tissue harmony and growth in orthodontic treatment.

The introduction of cephalometric radiography in orthodontic diagnosis inadvertently shifted the specialty's attention from the facial soft tissues to the skeletal structures. It has been shown that rigid adherence to the hard tissue norms results in neither facial balance and harmony nor long-term retention. The purpose of this article is to refocus the attention of the orthodontist on the consideration of harmonized facial structures as a primary goal of treatment. Balancing the position of the lips in relation to the nose and chin has a direct relationship with esthetic preference. Growth studies have clearly shown that dynamic changes in dental, skeletal, and facial integument occur over the entire period of active growth and even into the decades past the age of 20 years. Esthetic standards, therefore, must be different for children and for adults. Treatment results should be projected to when the patient is well into adulthood. Facial types also need to be considered because long-face and short-face individuals have different growth and maturational patterns. The compensatory nature of soft-tissue growth in these individuals should be noted. Caution must be exercised in using mean data from growth studies and applying them to all individuals at all ages, because of the wide variation among individuals in all races and both sexes.

Adolescent↗
PubMed1994

Longitudinal changes in the adult facial profile.

Longitudinal growth changes in the adult craniofacial complex were studied for 24 white male and 23 white female subjects between the ages of 18 and 42 years who had Class I or end-to-end molar relationships and no excessive protrusions or retrusions. The male profile straightened with age, and both lips became more retrusive. The males increased in all nose dimensions and in soft tissue thickness at pogonion, but decreased in upper lip thickness at labrale superius with a slight decrease in lower lip thickness at labrale inferius. The female profile did not become straighter with age, and the lips did not become more retrusive as with males. The females also increased in nose dimensions but decreased in soft tissue thickness at pogonion, decreased in upper lip thickness at labrale superius, and slightly increased in lower lip thickness at labrale inferius. For males most changes in hard tissue measurements had been accomplished by age 25 years, whereas soft tissue changes in the nose, lips, and chin occurred as much after age 25 years as from age 18 to 25 years. For females, both hard and soft tissue measurements had more changes after age 25 years than before. Those males who had high relative sagittal mandibular growth also experienced larger sagittal maxillary growth, and those who showed greater skeletal growth also had more soft tissue growth at the nose. The females also had good correlation between sagittal growth in the mandible and the maxilla. Later maturing males had greater adult craniofacial skeletal growth in several dimensions.

Adolescent↗
PubMed1994

Assessment of symphysis morphology as a predictor of the direction of mandibular growth.

The purpose of this study was to determine whether symphysis morphology could be used as a predictor of the direction of mandibular growth and to assess growth changes of the symphysis. Cross-sectional data included lateral cephalometric radiographs of 115 adults (58 women, 57 men) with the longitudinal sample a subset of 62 subjects (30 females, 32 males) at four age groups. The direction of mandibular growth was evaluated with seven cephalometric measurements that included Y-axis, SN to mandibular plane, palatal plane to mandibular plane, gonial angle, sum of saddle, articulare and gonial angles, percentage lower facial height, and posterior/anterior face height. The mandibular symphyseal dimensions studied were height, depth, ratio (height/depth), and angle. Symphysis morphology was found to be associated with the direction of mandibular growth, especially in male subjects with symphysis ratio having the strongest relationship. A mandible with an anterior growth direction was associated with a small height, large depth, small ratio, and large angle of the symphysis. Conversely, a posterior growth direction was associated with a large height, small depth, large ratio, and small angle of the symphysis. Symphysis dimensions continued to change until adulthood with male subjects having a greater and later occurring change compared with female subjects.

Adolescent↗
PubMed1994

Elastic energy/stiffness ratios for selected orthodontic wires.

This investigation determined the ratio of the energy available for orthodontic tooth movement to the stiffness and flexibility of a given wire. Twenty-five specimens each of five brands of orthodontic wire were tested in tension in the as-received condition. Force versus elongation diagrams were obtained and then converted into stress-strain data. Mean values were determined for the yield strength and yield strain for each brand of wire. The modulus of elasticity (E), modulus of resilience (R), and elastic compliance (C) were then calculated. Two ratios were established by using the three mechanical properties: (1) the modulus of resilience/modulus of elasticity (R/E) ratio and (2) the modulus of resilience/elastic compliance (R/C) ratio. The results confirmed that the use of these two ratios in combination permitted one to differentiate among the various types of orthodontic wires, with respect to stored energy and its relationship to the stiffness or flexibility of the wire.

Analysis of Variance↗
PubMed1994

Cephalometric assessment of sagittal relationship between maxilla and mandible.

This investigation was undertaken to evaluate if palatal plane could be used as a skeletal plane of reference in lateral cephalometric radiographs to evaluate sagittal maxillomandibular relationship. Various cephalometric landmarks in the maxilla and the mandible were projected to the palatal plane, and the linear distances between them were measured. In this three-part study, the first part evaluated changes in the inclination of palatal plane and in the linear distances from the age of 6 to 24 years in longitudinal records of 86 patients (46 male, 40 female). The second part established acceptable adult norms by evaluating 111 white dental students (89 men, 22 women) with Class I molar relationships, no history of orthodontic treatment, and good facial balance. The third part evaluated the proposed measures in pretreatment radiographs of 445 patients (171 men, 274 women) with a variety of malocclusions to compare the results of various diagnostic criteria for assessment of sagittal jaw relationships. The first part indicated the inclination of the palatal plane was stable throughout the growth period studied. The distance between projections from points A and B on the palatal plane (App-Bpp) was found to be the best indicator of sagittal jaw relationship. This was the least variable of the four measures considered in part two of the study. When compared with the angle ANB, the Wits appraisal and measurement of landmarks to a perpendicular from nasion in 50 patients, it was a more reliable diagnostic criterion than the other measures. Among the patients whose malocclusions were incorrectly diagnosed. Wits appraisal was consistently biased in the Class III direction. The methods using the ANB angle and the nasion perpendicular plane did not indicate any definitive trend.

Adolescent↗
PubMed1994

A cephalometric evaluation of nonextraction cervical headgear treatment in Class II malocclusions.

The effects of orthodontic treatment with the use of the cervical pull facebow headgear in patients with Class II malocclusions were evaluated with special reference to the dentition, the maxillary complex, the mandible, and the facial profile. The records of 85 patients, with a mean age of 11.3 +/- 1.7 years, were selected from a sample of 125 patient records requested from the office of John S. Kloehn in Appleton, Wisconsin. Dr. Kloehn has used traditional cervical pull facebow therapy in his practice. Over 100 linear and angular cephalometric measurements were made from the pretreatment and posttreatment records. These measurements were used to evaluate growth and/or treatment changes. The treatment sample was divided by size of the pretreatment FMA, sex, and the age range in which treatment was started, i.e., prepubertal, circumpubertal, and postpubertal. Overall, the results showed that the changes were very close to what would occur as a result of normal growth in Class I individuals. The maxillary permanent first molars continued to progress forward, the maxilla continued to grow forward, and the cranial base showed very little change, if any. The mandibular plane angle did not increase appreciably with treatment, regardless of the size of the pretreatment mandibular plane angle. Very few significant differences were found between sexes, pretreatment age groups, or between groups based on pretreatment Frankfort mandibular plane angle.

Adolescent↗