D. Ortho

Impacted maxillary canines: A review

An overview of the incidence and sequelae, as well as the surgical, periodontal, and orthodontic considerations in the management, of impacted canines is presented. The clinician needs to be familiar with the differences in the surgical management of the labially and palatally impacted canines, the best method of attachment to the canine for orthodontic force application, the advantages of one-arch versus two-arch treatment, and the implications of canine extraction. The various factors that influence all these decisions are discussed.

Arch width changes from 6 weeks to 45 years of age

The purpose of this study was to evaluate on a longitudinal basis, the changes in intercanine and intermolar widths over a 45-year span. The subjects in this study were from two pools of normal persons: (1) 28 male and 33 female infants evaluated longitudinally at approximately 6 weeks, 1 year, and 2 years of age (before the complete eruption of the deciduous dentition); and (2) 15 male and 15 female subjects from the Iowa facial growth study evaluated at ages 3, 5, 8, 13, 26, and 45. Arch width measurements on maxillary and mandibular dental casts were obtained independently by two investigators. Intraexaminer and interexaminer reliability were predetermined at 0.5 mm. From the findings in the current study, the following conclusions can be made: (1) Between 6 weeks and 2 years of age, i.e., before the complete eruption of the deciduous dentition, there were significant increases in the maxillary and mandibular anterior and posterior arch widths in both male and female infants. (2) Intercanine and intermolar widths significantly increased between 3 and 13 years of age in both the maxillary and mandibular arches. After the complete eruption of the permanent dentition, there was a slight decrease in the dental arch widths, more in the intercanine than in the intermolar widths. (3) Mandibular intercanine width, on the average, was established by 8 years of age, i.e., after the eruption of the four incisors. After the eruption of the permanent dentition, the clinician should either expect no changes or a slight decrease in arch widths. In conclusion, although the dental arch widths undergo changes from birth until midadulthood, the magnitude as well as the direction of these changes do not provide a scientific basis for expanding the arches, in the average patient, beyond its established dimensions at the time of the complete eruption of the canines and molars. Both patients and clinicians should be aware of these limitations.

Longitudinal changes in three normal facial types

The purpose of this study was to describe and compare the dentofacial relationships of three normal facial types (long, average, and short). Comparisons of the absolute and incremental changes between 5 years and 25.5 years of age were made both longitudinally and cross-sectionally. The subjects consisted of 20 males and 15 females for whom complete sets of data were available for the period of this study. All subjects had clinically acceptable occlusion and had not undergone previous orthodontic treatment. Descriptive statistics summarized the changes in 48 parameters, including that of height for males and females at 5, 10, 15, and 25.5 years of age. Longitudinal comparisons of the growth curves evaluated the curve profiles and curve magnitudes for the three facial types for both males and females. The analysis of variance was also used to compare the absolute and incremental changes at ages 5, 10, 15, and 25.5 years. The investigation resulted in the following findings. (1) Most persons (77%) have been categorized as having the same facial type at 5 and at 25.5 years of age. There is a strong tendency to maintain the original facial type with age. (2) Comparisons of the growth curves of the different parameters--with the exception of the incremental curves for MP:SN and Pog:NB in males--consistently demonstrated parallelism of the curves, regardless of the facial type. On the other hand, comparisons of curve magnitude indicated significant differences among the three facial types. (3) The persons within each facial type expressed a relatively large variation in the size and relationships of the various dentofacial structures. (4) Significant differences in the dentofacial parameters were present between males and females with the same facial type. The differences among facial types were not identical in males and females. (5) Longitudinal analysis of the data lends more consistent and, therefore, more meaningful results than cross-sectional comparisons when facial growth trends need to be evaluated. This is because growth changes are often subtle and of magnitudes not readily observed when the data are evaluated cross-sectionally. Standards that are age-, sex- and facial type-specific are presented.

Comparisons of different debonding techniques for ceramic brackets: An in vitro study: Part I. Background and methods

Techniques for removing metal orthodontic attachments are, for the most part, not as effective with ceramic brackets because the properties of ceramic brackets differ greatly from those of the conventional metal orthodontic brackets. Currently available ceramic brackets are composed of aluminum oxide crystals in either a polycrystalline or monocrystalline form that has a low fracture toughness compared with that of stainless steel. Metal brackets will deform 20% under stress before fracturing, whereas ceramic brackets will deform less than 1% before failing. The purpose of this study was (1) to evaluate the debonding characteristics of three different types of ceramic brackets when removed by techniques recommended by the manufacturers; (2) to evaluate and compare the conventional, ultrasonic, and electrothermal bracket-removal techniques, and (3) to evaluate and compare the mean enamel loss from removal by high-speed bur, by slow-speed bur, and by the ultrasonic method. In the first phase of the investigation, 140 teeth (70 maxillary central incisors and 70 third molars) were bonded with one of three types of ceramic brackets. Three different debonding methods were tested--(1) the conventional method recommended by the manufacturer (either pliers or wrench), (2) an ultrasonic method that employed specially designed tips, and (3) an electrothermal method involving an apparatus that transmits heat to the bracket. In each of the test groups, five variables were evaluated during and after bracket removal: (1) the incidence of bracket failure, (2) the amount of adhesive remaining after bracket removal, (3) the site of bond failure, (4) the debonding time for each technique, and (5) enamel damage resulting from bracket removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Stability of the LeFort I one-piece maxillary osteotomy.

The purpose of this study was to determine retrospectively the stability of the LeFort I osteotomy after one-piece maxillary impaction and wire fixation. Cephalograms of 31 patients were evaluated before surgery, immediately after surgery, in fixation, and postfixation. All subjects had characteristics of excessive vertical maxillary growth. Descriptive statistics for the absolute and relative changes of the various linear and angular parameters were calculated for the different stages. The analysis of variance general linear models procedure was used to compare the repeated measures of the total sample. From the present findings, it was concluded that (1) after the initial surgical superior repositioning, the maxilla continued to move superiorly and most of the upward movement occurred during fixation, (2) the anterior part of the maxilla moved superiorly more than twice that of the posterior part of the maxilla, (3) maxillary superior dental movement exceeded maxillary superior skeletal movement, and (4) maxillary horizontal skeletal movement exceeded maxillary horizontal dental movement. The clinical significance of the findings are discussed.

The effect on the bonding strength of orthodontic brackets of fluoride application after etching

Etching of the enamel surface in preparation for bonding orthodontic brackets is an essential part of the bonding procedure. In an attempt to alleviate concerns regarding the decalcified enamel, it has been suggested that a fluoride solution be applied to the etched surface before placing the bonding material. The purpose of this study is to test the tensile bonding strength of the composite to fluoride-treated enamel. Four groups of 10 teeth each were compared. Group I received a solution of 2% NaF in 0.1 M H3PO4 after etching; groups II and III received a solution of 4% NaF in 0.1 M H3PO4 after etching; and group IV served as the control--that is, no fluoride solution was applied to the enamel after etching. The orthodontic brackets were bonded to the teeth in the four groups with the same procedure. The 40 teeth were then placed in synthetic saliva. Groups I, II, and IV were debonded after 24 hours; group III was debonded after 7 days. The Instron Universal testing machine was used to determine the tensile bonding strength of the adhesive to the teeth. The basic statistics for the tensile strength were calculated and the analysis of variance, general linear models procedure, was used to determine whether significant differences were present among the groups. The findings indicate that the application of either 2% or 4% NaF in a 0.1 M H3PO4 solution does not significantly influence the tensile bonding strength of the adhesive material to the enamel surface.

Comparisons of the effectiveness of pliers with narrow and wide blades in debonding ceramic brackets

The removal of most ceramic brackets is accomplished by specially designed pliers that apply some form of tensile or shear force to the tooth surface. While the shear and tensile bond strengths for ceramic brackets in vitro have been reported, a simulation of the actual force application when using sharp-edged debonding pliers to debond a bracket has not. The purpose of this study is to determine the effectiveness and the force levels generated by the use of both the wide and the narrow blades in the debonding of ceramic brackets. The present findings indicate that the narrow blades effectively debonded ceramic brackets with a significantly lower mean debonding force (120 kg/cm2) than the wider blades (150 kg/cm2). The surface area of the blade in contact with the bracket-adhesive interface is less for the narrow blade (2.0 mm) than for the wide blade (3.2 mm). This relatively smaller contact area is sufficient to debond a bracket at a significantly lower debonding force.

Patient discomfort levels at the time of debonding: A pilot study

Several investigations have evaluated the degree of discomfort that patients experience during orthodontic treatment, but most of the research centered on tactile sensory (touch) threshold, reaction to spacers used to separate the teeth or reaction to the initial leveling wires, and the periodic adjustment of the appliances. The purpose of this investigation is to determine the discomfort threshold for patients undergoing orthodontic treatment at the time immediately before appliance removal. Such information will be useful in determining the force levels that patients can tolerate during debonding. From the findings in this study the following can be concluded: (1) The threshold of patient discomfort, at the time of debonding, is significantly influenced by two factors: the mobility of the tooth and the direction of force application. Sex and tooth type differences also influence the discomfort threshold but to a lesser degree. (2) At the time of debonding, patients can withstand intrusive forces significantly more than forces applied in a mesial, distal, facial, lingual, or an extrusive direction. The clinical implications of these findings are discussed.

Posttreatment changes in male and female patients: A comparative study

The purpose of this study was to determine whether the posttreatment changes in patients with Class II, Division 1 malocclusions who were treated with either extraction or nonextraction express similar trends in the male and female patients. The material for this investigation was obtained from the records available in the Graduate Orthodontic Clinic at the University of Iowa. Ninety-one patients were treated for their Class II, Division 1 malocclusions, 44 subjects (21 males and 23 females) had four first premolar extractions and 47 subjects (20 males and 27 females) were treated with nonextraction. Matched normal subjects included 20 male and 15 female subjects for whom complete sets of data were available for the period of this study. None of these subjects had undergone orthodontic therapy. Thirty-nine cephalometric anteroposterior and vertical skeletal, dental, and soft tissue linear and angular measurements were derived. Twenty-four dental arch parameters were evaluated and included: overbite, overjet, maxillary and mandibular arch lengths, and arch widths, as well as tooth size-arch length discrepancies. Student t tests were used to compare male and female subjects for the following parameters: (1) absolute dimensions recorded before treatment, after treatment, and at retention; (2) the incremental changes between the various stages; (3) the relative posttreatment changes. The level of significance was predetermined at p < 0.05. From the current findings the following can be concluded: (1) There were significant differences in the size as well as the incremental changes of the various cephalometric dentofacial parameters between normal male and female subjects. (2) There were significant differences in the absolute posttreatment cephalometric changes between male and female subjects, particularly in linear dimensions. Similar, but less frequent, findings were observed in the relative posttreatment changes. (3) Significant differences in the posttreatment dental arch changes between male and female subjects were the least frequent. (4) Male and female subjects expressed similar statistical trends in the direction of posttreatment changes. Therefore clinicians should not expect to observe significant differences in the posttreatment trends on the basis of the gender of the patient. On the other hand, the changes in linear dimensions are larger in male than female subjects. Therefore, for a more accurate interpretation of growth and/or treatment changes, it is advisable to independently analyze data on male and female subjects.