Jane R. Jakobsen

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 mesiodistal and bnccolingnal crown dimensions of the permanent teeth in three populations from Egypt, Mexico, and the United States

The purpose of this study is to examine the mesiodistal and buccolingual crown dimensions in three populations--57 subjects (35 boys and 22 girls) from Iowa City, Iowa; 54 subjects (30 boys and 24 girls) from Alexandria, Egypt; and 60 subjects (26 boys and 34 girls) from Chihuahua, Mexico. All subjects had normal Class I occlusion, with no history of orthodontic treatment. Comparisons of single teeth as well as sums of groups of teeth were performed between boys and girls within and between the two populations. The analysis of variance general linear models procedure was used for statistical comparisons. The findings from this investigation indicated that (1) differences between antimeres are of small magnitude and of no statistical significance; (2) all populations have significant differences in tooth dimensions between the sexes with boys having larger canines and first molars; (3) there is greater variation in the buccolingual than in the mesiodistal dimensions among the three populations; (4) there is a greater similarity in tooth dimensions among the boys from the three populations than among the girls, but the magnitude of these differences is considered to be of little clinical significance; and (5) standards for the buccolingual diameters were developed for the three populations. As a result, it was concluded that prediction equations used for space analysis in the mixed dentition to determine tooth size-arch length discrepancies in the Iowa population can also be used for persons from Egypt and from the northern part of the Mexican Republic, with some suggested modifications.

Changes in the maxillary and mandibular tooth size-arch length relationship from early adolescence to early adulthood. A longitudinal study.

The purpose of this study was to determine the association between the changes in maxillary and mandibular tooth size-arch length discrepancies (TSALD) and various dentofacial variables for 18 male and 14 female subjects with normal occlusion. All subjects were participants in the Iowa Longitudinal Growth Study and records were evaluated at two stages of dental development: stage I, when the permanent second molars initially erupted into occlusion (X age = 13.3 years); and stage II, at early adulthood (X age = 26.0 years). The following sets of variables were evaluated: mesiodistal crown diameters of single and groups of permanent teeth, dental arch widths and lengths, curve of Spee, maxillary and mandibular anterior and total crowding or spacing, anterior tooth rotations, and various cephalometric dentofacial parameters. Students t test were used to compare subjects with the most and least changes. Regression analyses also were used to assess the relationships between these parameters and the changes in the maxillary and mandibular tooth size-arch length relationship. The most consistent finding from the t test comparisons is the significantly greater reduction in the available arch length in the group with the most TSALD at early adulthood. No other variables were found to be consistently different in the comparisons between the two groups. The results of the regression analysis indicated that a number of dentofacial variables are associated with the changes in the maxillary and mandibular TSALD--for example, the mesiodistal diameter of different teeth and the changes in anterior and posterior facial heights. The clinical implications of the present findings are discussed.

Dentofacial and soft tissue changes in Class II, Division 1 cases treated with and without extractions

The purpose of this study was to compare the changes in subjects with Class II division 1 malocclusions treated with and without the extraction of four first premolars. Lateral cephalograms on 91 patients (44 extraction and 47 nonextraction) were evaluated at three stages: pretreatment, posttreatment, and approximately 2 years after treatment. The present findings indicate that before treatment, the upper and lower lips were more protrusive relative to the esthetic plane among the subjects treated with four first premolar extractions. After treatment the upper and lower lips were more retrusive in the extraction group, and more protrusive in the nonextraction groups. The extraction group tended to have straighter faces and slightly more upright maxillary and mandibular incisors, whereas the nonextraction group had the opposite tendencies. The average soft tissue and skeletal measurements for both groups were close to the corresponding averages derived from the Iowa normative standards. In general, differences between the groups after treatment were preserved into retention. The present findings indicate that the extraction or nonextraction decision, if based on sound diagnostic criteria, seem to have no deleterious effects on the facial profile.

Shear bond strength of composite, glass ionomer, and acidic primer adhesive systems

The purpose of this study was to determine the shear bond strengths of orthodontic brackets bonded with one of three methods: (1) a glass ionomer adhesive with a 20% polyacrylic acid enamel conditioner; (2) a composite resin adhesive used with 37% phosphoric acid etchant and a conventional primer; or (3) the same composite resin used with an acidic primer that combines the etchant with the primer in one application. The brackets were bonded to the teeth according to one of three protocols. Group I teeth were etched with 37% phosphoric acid and bonded with Transbond XT (3M Unitek, Monrovia, Calif) following the manufacturers instructions. Group I acted as the control group. Group II teeth were etched with an acidic primer (Clearfil Liner Bond 2. J.C. Moritta Kuraway, Japan) that contains both the acid (Phenyl-P) and the primer (HEMA and dimethacrylate) and was placed on the enamel for 30 seconds; the adhesive used to bond the brackets was Transbond XT as in Group I. Group III teeth were etched with 20% polyacrylic acid and the brackets were bonded with Fuji Bond LC (G.C. America, Chicago, Ill). A steel rod with one flattened end was attached to the crosshead of a Zwick test machine (Zwick GmbH & Co, Ulm, Germany). An occlusogingival load was applied to the bracket, producing a shear force at the bracket-tooth interface. The results indicated that the resin/phosphoric acid adhesive system (control group) provided the strongest shear bond strength x = 10.4 +/- 2.8 MPa). The glass ionomer adhesive system provided a significantly lower bond strength (x = 6.5 +/- 1.9 MPa). The least shear bond strength was present when the acidic primer was used with an orthodontic adhesive (x = 2.8 +/- 1.9 MPa). In the present study, the use of either a fluoride-releasing glass ionomer or an acidic primer in combination with an available orthodontic composite adhesive resulted in a significantly reduced shear bond strength when compared with that of the conventional composite resin adhesive system. At the present time, the orthodontist and the patient are better served by using phosphoric acid/composite resin adhesive system or other equivalent systems that provide a clinically reliable bond strength between the bracket, the adhesive, and the enamel surface.

Changes in the molar relationship between the deciduous and permanent dentitions: A longitudinal study

The purpose of this study was to describe the changes in the molar relationship from the deciduous dentition to the permanent dentition in 121 subjects from the Iowa Longitudinal Growth Study. In addition, an attempt was made to determine the association between the various dentofacial variables and the changes in the molar relationship in 55 persons (33 male and 22 female subjects) with normal occlusion. All subjects were evaluated at three stages of dental development: stage I, completion of the deciduous dentition (means age = 4.94 years); stage II, when permanent first molars initially erupt into occlusion (means age = 6.91 years); and stage III, at the completion of eruption of the permanent dentition excluding third molars (means age = 13.01 years). The following sets of variables were evaluated: molar relationship, mesiodistal crown diameters of single and groups of deciduous and permanent teeth, dental arch widths, arch lengths, and various cephalometric dentofacial variables. Correlation coefficients and regression analyses were used to assess the relationships between these measurements and the changes in the molar relationship from the deciduous to the permanent dentition. The findings indicate that of the 242 sides evaluated in the deciduous dentition, 61.6% developed into a Class I molar relationship, 34.3% into Class II, and 4.1% into Class III. Those sides that started with a distal step in the deciduous dentition proceeded to develop into a Class II molar relationship in the permanent dentition. Of the sides with a flush terminal plane relationship in the deciduous dentition, 56% progressed to a Class I molar relationship and 44% to Class II in the permanent dentition. The presence of a mesial step in the deciduous dentition indicates a greater probability for a Class I molar relationship and a lesser probability for a Class II molar relationship. In the 55 subjects who achieved normal occlusion, the magnitude of change in the molar relationship was 1.91 mm in male subjects and 1.64 mm in female subjects. On the average, these cases had a mesial step in the deciduous dentition of 0.8 mm in male subjects and 1.0 mm in female subjects. There was a favorable difference between the maxillary and mandibular leeway spaces of 1.3 mm in male subjects and 1.1 mm in female subjects. There was also a favorable decrease in the Wits appraisal of 1.2 mm in male subjects and 0.6 mm in female subjects.(ABSTRACT TRUNCATED AT 400 WORDS)

Evaluation of a new light-cured orthodontic bonding adhesive

The purpose of this study was to compare a new light-cured bonding system that used a hybrid adhesive containing a resin reinforced glass ionomer (Fuji Ortho LC, GC America, Inc.) with a more traditional light-cured bonding system (Transbond, 3M Unitek) that contained resin material only. Seventy-five recently extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were randomly separated into five groups of 15 molars each: Group I--using Transbond adhesive system with the enamel etched and dried before bonding. Group II--using Fuji Ortho LC (FOLC) adhesive system with no etch and the enamel wet with water before bonding. Group III--using FOLC adhesive system with the enamel etched and wet with water before bonding. Group IV--using FOLC adhesive system with no etch and the enamel wet with saliva before bonding. Group V--using FOLC adhesive system with the enamel etched and wet with saliva before bonding. The shear bond strength was performed after thermal cycling between 5 degrees +/- 2 degrees C and 50 degrees +/- 2 degrees C for a total of 2000 cycles with the Zwick test machine (Zwick Gm bH & Co.). After debonding, the teeth and brackets were examined under x10 magnification to evaluate the site of bond failure and the presence of residual adhesive. The analysis of variance was used to determine whether significant differences existed between the various groups. The findings indicated that there were no statistically significant differences among the three experimental groups I, III, and V that had the enamel surface etched before bonding, regardless of the adhesive used or the enamel surface contamination with water or saliva. On the other hand, the two experimental groups that did not have the enamel etched before bonding (II and IV) had significantly lower bond strengths. In conclusion, etching the enamel surface is a critical variable that affects shear bond strength as well as bond failure location when using the new adhesive system.

EVALUATION OF SCOTCHBOND MULTIPURPOSE AND MALEIC ACID AS ALTERNATIVE METHODS OF BONDING ORTHODONTIC BRACKETS

Damage to the enamel surface during bonding and debonding of orthodontic brackets is a clinical concern. Alternative bonding methods that minimize enamel surface damage while maintaining a clinically useful bond strength is an aim of current research. The purpose of this study was to compare the effects on bond strength and bracket failure location of two adhesives (System 1+ and Scotchbond Multipurpose, 3M Dental Products Division) and two enamel conditioners (37% phosphoric acid and 10% maleic acid). Forty-eight freshly extracted human premolars were pumiced and divided into four groups of 12 teeth, and metal orthodontic brackets were attached to the enamel surface by one of four protocols: (1) System 1+ and phosphoric acid, (2) Scotchbond and phosphoric acid, (3) System 1+ and maleic acid, and (4) Scotchbond and maleic acid. After bracket attachment, the teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 72 hours. A Zwick universal testing machine (Zwick GmbH & Co.) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The analysis of variance was used to compare the four groups. Significance was predetermined at p < or = 0.05. The results indicated that there were no significant differences in bond strength among the four groups (p = 0.386). The results of the Chi square test, evaluating the residual adhesives on the enamel surfaces, revealed significant differences among the four groups (mean 2 = 0.005). A Duncan multiple range test revealed the difference occurred between the phosphoric acid and maleic acid groups, with maleic acid having bond failures at the enamel-adhesive interface. In conclusion, the use of Scotchbond Multipurpose and/or maleic acid does not significantly effect bond strength, however, the use of maleic acid resulted in an unfavorable bond failure location.

A comparative study of the debonding strengths of different ceramic brackets, enamel conditioners, and adhesives

The purpose of this study is to evaluate the use of a sharp-edged debonding instrument on four different ceramic brackets with three different bonding materials and two different enamel conditioning techniques. The effectiveness of the debonding instrument was determined by evaluating the following variables: the amount of force required to debond the bracket, the amount of residual adhesive remaining on the enamel surface, the frequency of bracket failure, and the prevalence of any visible enamel damage. The results indicated that the bracket type, the adhesive, as well as the enamel conditioner, all have an effect on bond strengths when using a sharp-bladed debonding instrument. The following conclusions were derived from the present findings: (1) The mean debonding strength values for the different bracket, adhesive, and enamel conditioner combinations ranged between a low of 40 kg/cm2 and a high of 194 kg/cm2. Most debonding values were between 60 and 115 kg/cm2. (2) A number of bracket, adhesive, and conditioner combinations are considered to have clinically adequate bonding strength and are relatively safe (Table IX). (3) The use of polyacrylic crystal growth enamel conditioner resulted in significantly less adhesive being left on the tooth as compared with the phosphoric acid enamel conditioner.