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Biomedical subjects

R S Nanda

Publications and source records attributed to R S Nanda.

At least 91 records · Page 5Linked to original sources
PubMed1990

Evaluation of friction between ceramic brackets and orthodontic wires of four alloys.

The purpose of this investigation was to determine the frictional resistance offered by ceramic brackets used in combination with wires of different alloys and sizes during in vitro translatory displacement of brackets. Findings with ceramic brackets were also compared with outcomes of treatment with stainless steel brackets. Stainless steel, cobalt-chromium, beta-titanium, and nickel-titanium wires of different cross-sectional sizes were tested in medium-twin monocrystalline ceramic brackets with both 0.018-inch and 0.022-inch slot sizes. The wires were ligated into the brackets with elastomeric modules. Brackets were moved along the wire by means of an Instron universal testing machine, and frictional force was measured by a compression cell and recorded graphically on an xy recorder. Wire friction in the ceramic brackets increased as wire size increased, and rectangular wires produced greater friction than round wires. Beta-titanium and nickel-titanium wires were associated with higher frictional forces than stainless steel or cobalt-chromium wires. These findings follow the same general trends as those found with stainless steel brackets; however, wires in ceramic brackets generated significantly stronger frictional force than did wires in stainless steel brackets.

Analysis of Variance↗
PubMed1990

An evaluation of the shape-memory phenomenon of nickel-titanium orthodontic wires.

This investigation was undertaken to quantitatively analyze the shape-memory phenomenon of wires made of seven commercially available nickel-titanium alloys. The shape memory was determined by calculation of the percent shape recovery that occurred when the wire of each alloy was first plastically deformed below its TTR and then heated to a temperature above its TTR. The findings indicate that: 1. The mean percent recovery ranged from 89% to 94% for Ni-Ti, nitinol, Orthonol, Titanol, Sentinol Light, and Sentinol Medium alloys. The Sentinol Heavy alloy showed a mean recovery of 41.3%, which was significantly less than that of the other alloys. 2. It appears that Sentinol Heavy wire showed relatively less percent recovery because its TTR was close to room temperature. This resulted in minimal plastic deformation, because the alloy recovered its original length almost immediately, and this also indicates the importance of a proper TTR. It was concluded that the TTR should be reasonably higher than the oral temperature for clinical application of the shape-memory phenomenon of nickel-titanium alloys. 3. The heat-recovery temperature was kept to 300 degrees F in this study for maximum possible recovery. Although the results indicate that the recovery was around 90% for most alloys tested, future studies are required to determine the shape recovery at or just above oral temperature.

Dental Alloys↗
PubMed1990

An in vitro evaluation of bond strength of three glass ionomer cements.

The purpose of this study was to determine the bond strength of three commercially available glass ionomer cements when used to bond mesh-backed medium twin (0.130 inch) brackets to enamel surface. Three different enamel surface conditions, which included use of pumice, pumice and polyacrylic acid, and pumice followed by acidulated phosphate fluoride, were also tested to determine their effect on the bond strength. In addition, bond strength of one composite resin was compared with those of glass ionomer cements. The teeth were bonded with all the materials according to manufacturers' instructions. Each specimen was embedded in Super-Die with the bonded facial surface exposed. A surveyor was used to align the teeth in the stone uniformly for all specimens. A special bracket holder was used to hold the brackets precisely under the wings during debonding. An Instron universal testing machine was used to measure the force required for bond failure. To stimulate oral conditions, the direction of pull was so designed that it included an element of torsional stress along with tensile force. The findings indicate that a large variation existed between the bond strengths of all materials tested. The bond strength of glass ionomer cements was significantly less than that composite resin. However, the bond strength of at least one glass ionomer cement appears to be adequate for clinical use. The different surface preparation before bonding did not significantly affect the bond strengths of glass ionomer cements. Further investigation is required to test the bond strengths of glass ionomer cements clinically.

Acidulated Phosphate Fluoride↗
PubMed1990

A 3-year evaluation of skeletal stability of mandibular advancement with rigid fixation.

The postsurgical changes associated with mandibular advancements using the sagittal ramus osteotomy and rigid fixation were evaluated. This retrospective study was based on examination of lateral cephalometric radiographs of 19 individuals (16 females and 3 males) with a mean age of 26.6 years. These radiographs were evaluated presurgically, immediately postsurgery, and 3 years postsurgically (2 years, 9 months to 4 years, 5 months). The mean amount of sagittal surgical advancement was 6.7 +/- 2.3 mm, and the mean amount of postsurgical relapse was 1.3 +/- 2.0 mm, representing a 14% relapse of the original surgical advancement. However, individual variation in the amount and direction of movement of the mandible was found during the follow-up period. Postsurgical relapse was found to be related to the amount of surgical advancement. Linear-regression analysis between these two variables resulted in an R2 value of 0.448. Fourteen of the subjects relapsed in the posterior direction, with 2 relapsing more than 50% of the surgical advancement. Five of the subjects moved further anteriorly, with 1 advancing as much as 50% more than the original advancement. The findings of this study suggest that mandibular advancement with the sagittal ramus osteotomy and rigid fixation does not provide consistently stable postsurgical results. However, when compared with previously reported relapse studies using nonrigid fixation techniques, rigid fixation yielded superior results.

Adolescent↗
PubMed1990

Arch perimeter changes on rapid palatal expansion.

Relationships between changes in arch perimeter and arch width resulting from rapid palatal expansion with the Hyrax appliance were analyzed with the use of dental study casts of 21 adolescent patients. Photographs and measurements from the dental casts obtained before treatment and approximately 3 months after stabilization were used. Regression analysis indicated that changes in premolar width were highly predictive of changes in arch perimeter (r2 = 0.69) at approximately 0.7 times the premolar expansion. Without any orthodontic appliances attached to the mandibular teeth in 16 of the 21 patients, buccal uprighting of the posterior teeth was observed because of the redirection of occlusal forces. In addition, posterior movement of the maxillary incisors and buccal tipping of the anchor teeth were quantified. The prediction of arch perimeter change for a given amount of expansion is helpful in the treatment planning of rapid palatal expansion cases and may facilitate nonextraction orthodontic treatment.

Adolescent↗
PubMed1990

Load-deflection rate measurements of activated open and closed coil springs.

The purpose of this investigation was to provide load-deflection rate data for a variety of open and closed coil springs. Ten millimeter lengths of open and closed coil stainless steel and Cobalt-Chromium-Nickel (Co-Cr-Ni) alloys in combinations of 0.008, 0.009 and 0.010 inch wire sizes, and 0.030 and 0.032 inch lumen sizes were tested. Other groups included heat treated Co-Cr-Ni springs and springs of 15 and 20 millimeter lengths. Forces and activations were measured by a tension load cell with an Instron universal testing instrument. Stiffness increased dramatically with wire size and pitch angle of the coils. Stiffness decreased slightly with increased lumen size. Co-Cr-Ni closed coil springs were slightly stiffer than stainless steel, whereas stainless steel open coil springs were much stiffer than Co-Cr-Ni. Heat treatment increased the stiffness of Co-Cr-Ni coil springs. The length of the spring had a great effect on the load-deflection rate. A shorter spring is stiffer than a longer spring by an amount directly proportional to the ratio of the length of the longer spring to that of the shorter spring.

Chromium Alloys↗
PubMed1990

Growth changes in the soft tissue facial profile.

Longitudinal growth changes in the soft tissue profile of 40 caucasians between the ages of 7 and 18 were studied. The sample consisted of 17 males and 23 females who had Class I dentitions and balanced faces at age 7 and 18 years. None of the subjects received any orthodontic treatment. Cephalometric radiographs were available, as a rule, on a yearly basis. Soft tissue thickness, measured at the nose, upper lip, lower lip and chin, as well as the length of the upper and lower lip, all increased by varying amounts over the period of the study. Females acquired more growth as a percentage of their adult size (at age 18) than males in all variables except the angle of inclination of the skeletal chin which increased more in males. The largest increase in relative size was noted in the nose measurements. In males, the nose had not attained adult size even at age 18. Upper lip length growth, on the other hand, in both males and females was complete by the 15th year. The difference between male and female lip length growth was clinically significant; the average aggregate increase in upper and lower lips combined in males was 6.9 millimeters compared to 2.65 millimeters in females. The total gain in thickness at laberale superius was over four times as much in males as in females and continued to increase in males even at age 18. The change in thickness of the soft tissue at pogonion was not large, an average of 2.4 millimeters in males and 1.5 millimeters in females. The major contribution to the anterior growth of the chin was translatory, contributed largely by growth in the skeletal length from pogonion to pterygomaxillary plane.

Adolescent↗
PubMed1989

The skeletal stability of Le Fort I downfracture osteotomies with rigid fixation.

Twenty subjects receiving Le Fort I downfracture osteotomies stabilized with rigid fixation were studied for relapse. The analysis was based on longitudinal cephalometric radiographs taken within 2 weeks presurgically, 1 week postsurgically, and after a minimum period of 6 months postsurgically. Vertical and sagittal changes in the maxilla were evaluated in reference to the Frankfort horizontal plane. It was found that the mean postsurgical relapse was minimal and not significant. It was smaller than that reported for patients who had received stabilization of the maxilla with intraosseous and maxillomandibular wiring. It was concluded that the rigid fixation technique is dependable and yields stable postsurgical results in the maxilla.

Adolescent↗
PubMed1988

Growth changes in the nasal profile from 7 to 18 years of age.

Lateral head cephalograms of 17 male and 23 female subjects, aged 7 to 18 years, were evaluated for age changes in morphology and position of the nose with reference to the pterygomaxillary vertical plane. The study was confined to persons with normal facial profiles, normal overjets, and Class I molar relationships. Four linear and two angular dimensions were measured. Statistical analysis included the calculation of medians, Q ranges, proportion of growth completed at each age expressed as a percentage of the size of the variable at 18 years, and a pairwise correlation matrix. The results indicated that (1) increments in nose height, depth, and inclination are essentially complete in girls by 16 years of age, while continuing to increase in males up to and beyond 18 years; (2) the ratio of upper to lower nose heights remains at approximately 3:1 from 7 to 18 years in both sexes; (3) the ratio of nose depth to sagittal depth of the underlying skeleton changed from 1:2 at 7 years in both sexes to 1:1.5 in male subjects and 1:1.6 in female subjects at 18 years; (4) although upper nose inclination was similar for the two sexes, lower nose inclination was slightly larger in female subjects, especially after the age of 10 years; (5) persons with greater increments in nose depth than in nose height, or in nose depth than in the sagittal depth of the underlying skeleton, develop larger upper nose inclinations. The impact of nasal growth changes on orthodontic diagnosis and treatment planning was emphasized.

Adolescent↗
PubMed1988

The longitudinal effects of growth on the Wits appraisal.

The longitudinal changes occurring between the ages of 4 and 24 years in the Wits appraisal and its component parts were evaluated in 40 persons. Contrary to what may have been believed previously, the Wits appraisal was not found to remain stable throughout the growth period. When the findings of the Wits appraisal were studied in individual subjects, there was a wide range of variation. Real changes in the Wits appraisal were found to be disguised clinically by the differential sagittal growth of pogonion in relation to B point, especially in male subjects. Furthermore, the appraisal was found to be affected profoundly by changes occurring in the angulation of the occlusal plane. It was concluded that if the Wits appraisal is to be used, it should be used in conjunction with other methods of assessment of apical base discrepancies and with due regard for the likely effects of changes in its component parts.

Adolescent↗
PubMed1988

The effect of a modified functional appliance on obstructive sleep apnea.

This study combined the use of cephalometrics and overnight polysomnographic monitoring to analyze the effects of a modified functional appliance on airway, sleep, and respiratory variables in patients with obstructive sleep apnea (OSA). Twelve patients without overt anatomic or pathologic evidence of obstruction were selected on the basis of an initial single night of polysomnographic monitoring, which confirmed the diagnosis of obstructive sleep apnea syndrome. The patients subsequently were fitted with a modified functional appliance designed to securely hold the mandible in an anterior-inferior position. A subsequent overnight polysomnographic study was obtained with each patient wearing the appliance. Lateral cephalometric radiographs with and without the appliance in place were also obtained. The mean vertical and horizontal changes in mandibular position while wearing the appliance were 8.49 mm and 2.28 mm, respectively. The findings indicate that 10 of the 12 patients had decreases in the rate of complete airway obstructions from a mean of 28.86 to 18.69 events per hour, and in the total apnea index from a mean of 53.81 to 35.99 events per hour. A reduction in the rate of obstructive events is attributed to the effect of the appliance on the oropharyngeal structures. Six cephalometric measurements are presented to provide a means of assessing effects of the appliance on the oropharynx and associated structures. The modified functional appliance is a conservative, successful treatment alternative that could benefit patients with obstructive sleep apnea syndrome.

Activator Appliances↗
PubMed1987

Professional prophylaxis and its effect on the periodontium of full-banded orthodontic patients.

The effect of professional prophylaxis on the periodontium was studied in 14 adolescent orthodontic patients while under active treatment using a split-mouth experimental design. A full-banded appliance was used on all of the patients. The following variables were examined: plaque registration, gingival index, gingival migration, and width of the attached gingiva. Professional rubber-cup prophylaxis was performed on the test side of all patients together with reinforced oral hygiene instruction on a monthly basis. Measurements for the plaque registration, gingival index, gingival migration, and the width of the attached gingiva were recorded at the initial visit (baseline records), the 6-month evaluation, and the 10-month evaluation. Monthly registrations were completed for the plaque deposits and gingival inflammation at each of the 11 visits. All measurements were taken at the midfacial surface of the selected teeth. Four conclusions can be drawn from the findings of this study: the presence of an orthodontic appliance did not result in an increase of plaque accumulation or gingival inflammation for the full-banded orthodontic patient; monthly oral hygiene instruction was effective in significantly reducing the amount of visible plaque and gingival inflammation; monthly rubber-cup prophylaxis had a significant effect in reducing the gingival enlargement routinely associated with a fixed orthodontic appliance; and the width of attached gingiva showed no significant change throughout the course of the study.

Adolescent↗
PubMed1987

Clinical application of a method to correct angle ANB for geometric effects.

Angle ANB does not provide an adequate assessment of the skeletal discrepancy between the jaws in the sagittal plane. Attempts have been made to avoid the fallacies with the introduction of quadrilateral and Wits analyses. Based on the Wits appraisal of zero, Hussels and Nanda (1984) were able to evaluate and eliminate four geometric factors that affect angle ANB. These four factors are (1) anteroposterior position of point N in relation to points A and B, (2) inclination of the occlusal plane, (3) dental height (a linear measurement between point A and B), and (4) distance between points N and B. The authors derived a mathematic formula to evaluate the influence of all four parameters in terms of angle ANB. This formula reflects the skeletal relationship of a patient when points A and B are on a perpendicular plane in relation to the occlusal plane (Wits = 0 mm). The authors define this to be a Class I skeletal relationship. A comparison of the measured ANB angle with the calculated angle ANB gives a better perspective of the skeletal discrepancy. If the measured angle ANB is larger than the calculated angle, the discrepancy is Class II. On the other hand, if the measured angle ANB is smaller than the calculated angle, the skeletal relation is Class III. This method of assessing the skeletal sagittal position of the jaws in relation to each other was applied to 508 patients. The authors showed that the geometric influence of the four factors indeed conceals the true skeletal relations when angle ANB is used without any correction.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗