Larger interface area at the human myotendinous junction in type 1 compared with type 2 muscle fibers

The myotendinous junction (MTJ) is structurally specialized to transmit force. The highly folded muscle membrane at the MTJ increases the contact area between muscle and tendon and potentially the load tolerance of the MTJ. Muscles with a high content of type II fibers are more often subject to strain injury compared with muscles with type I fibers. It is hypothesized that this is explained by a smaller interface area of MTJ in type II compared with type I muscle fibers. The aim was to investigate by confocal microscopy whether there is difference in the surface area at the MTJ between type I and II muscle fibers. Individual muscle fibers with an intact MTJ were isolated by microscopic dissection in samples from human semitendinosus, and they were labeled with antibodies against collagen XXII (indicating MTJ) and type I myosin (MHCI). Using a spinning disc confocal microscope, the MTJ from each fiber was scanned and subsequently reconstructed to a 3D-model. The interface area between muscle and tendon was calculated in type I and II fibers from these reconstructions. The MTJ was analyzed in 314 muscle fibers. Type I muscle fibers had a 22% larger MTJ interface area compared with type II fibers (p < 0.05), also when the area was normalized to fiber diameter. By the new method, it was possible to analyze the structure of the MTJ from a large number of human muscle fibers. The finding that the interface area between muscle and tendon is higher in type I compared with type II fibers suggests that type II fibers are less resistant to strain and therefore more susceptible to injury.

ZAKβ is activated by cellular compression and mediates contraction-induced MAP kinase signaling in skeletal muscle

Mechanical inputs give rise to p38 and JNK activation, which mediate adaptive physiological responses in various tissues. In skeletal muscle, contraction‐induced p38 and JNK signaling ensure adaptation to exercise, muscle repair, and hypertrophy. However, the mechanisms by which muscle fibers sense mechanical load to activate this signaling have remained elusive. Here, we show that the upstream MAP3K ZAKβ is activated by cellular compression induced by osmotic shock and cyclic compression in vitro, and muscle contraction in vivo. This function relies on ZAKβ's ability to recognize stress fibers in cells and Z‐discs in muscle fibers when mechanically perturbed. Consequently, ZAK‐deficient mice present with skeletal muscle defects characterized by fibers with centralized nuclei and progressive adaptation towards a slower myosin profile. Our results highlight how cells in general respond to mechanical compressive load and how mechanical forces generated during muscle contraction are translated into MAP kinase signaling.

The Myotendinous Junction-A Vulnerable Companion in Sports. A Narrative Review

The incidence of strain injuries continues to be high in many popular sports, especially hamstring strain injuries in football, despite a documented important effect of eccentric exercise to prevent strains. Studies investigating the anatomical properties of these injuries in humans are sparse. The majority of strains are seen at the interface between muscle fibers and tendon: the myotendinous junction (MTJ). It has a unique morphology with a highly folded muscle membrane filled with invaginations of collagen fibrils from the tendon, establishing an increased area of force transmission between muscle and tendon. There is a very high rate of remodeling of the muscle cells approaching the MTJ, but little is known about how the tissue adapts to exercise and which structural changes heavy eccentric exercise may introduce. This review summarizes the current knowledge about the anatomy, composition and adaptability of the MTJ, and discusses reasons why strain injuries can be prevented by eccentric exercise.

Remodeling of muscle fibers approaching the human myotendinous junction

The myotendinous junction (MTJ) is at high risk of strain injuries, due to high amounts of energy that is transferred through this structure. The risk of strain injury is significantly reduced by heavy resistance training (HRT), indicating a remodeling capacity of MTJ. We investigated the degree of remodeling of muscle fibers near the human MTJ. In 8 individuals, samples were taken from the semitendinosus and gracilis MTJ and they were stained immunohistochemically for myonuclei (DAPI), fibroblasts (TCF7L2), and satellite cells (CD56). A high portion of the muscle fibers adjacent to the MTJ contained a centrally located myonucleus (47 ± 8%, mean ± SD) and half of the muscle fibers were CD56 positive. The number of satellite cells and fibroblasts were not higher than what has previously been reported from muscle bellies. The immunohistochemical findings suggest that the rate of remodeling of muscle fibers near the MTJ is very high. The finding that there was no increased number of satellite cells and fibroblasts could be explained as a dynamic phenomenon. The effect of HRT should be evaluated in a randomized setting.

Composition and adaptation of human myotendinous junction and neighboring muscle fibers to heavy resistance training

The myotendinous junction (MTJ) is a common site of strain injury and yet understanding of its composition and ability to adapt to loading is poor. The main aims of this study were to determine the profile of selected collagens and macrophage density in human MTJ and adjoining muscle fibers, and to investigate whether heavy exercise loading would alter this profile. Fifteen individuals scheduled for anterior cruciate ligament repair surgery were randomized into three groups: control, acute or 4 weeks heavy resistance training. MTJ samples were collected from the semitendinosus and gracilis muscles and were sectioned and stained immunohistochemically for collagen types I, III, VI, XII, XIV, XXII, Tenascin-C and CD68. Macrophage density and distribution was evaluated and the amount of each collagen type in muscle and MTJ was graded. Collagen XXII was observed solely at the MTJ, while all other collagens were abundant at the MTJ and in muscle perimysium or endomysium. The endomysial content of collagen XIV, macrophages and Tenascin-C increased following 4 weeks of training. These findings illustrate the heterogeneity of collagen type composition of human MTJ. The increase in collagen XIV following 4 weeks of training may reflect a training-induced protection against strain injuries in this region.

A pilot study of dental students' esthetic perceptions of computer-generated mild dental fluorosis compared to other conditions

OBJECTIVES

Few studies have considered people's opinions about the esthetics of dental fluorosis. Assessments of fluorosis esthetics can be confounded by differences in a number of clinical factors, including tooth shape, color, contour, and gingival status. This pilot study compared esthetic perceptions of mild fluorosis and other conditions using computer-generated images made from a base set of normal appearing teeth.

METHODS

Entering dental students (n = 61) completed questionnaires about four sets of paired photographs. Three sets consisted of fluorotic teeth (very mild to mild) versus other conditions (diastema, isolated enamel opacity, "normal"/control) and the other pair compared two presentations of mild fluorosis (generalized versus limited to incisal one-third). Six questions, both qualitative and quantitative, were asked about each pair of photographs.

RESULTS

Mild fluorosis was assessed less favorably than normal/control, midline diastema was less favorable than mild fluorosis, and mild fluorosis was less favorable than isolated opacity.

CONCLUSIONS

This approach allows fluorosis to be better compared with other oral conditions because the images are standardized. Additional research with this method is warranted, including more variations in conditions, more comparisons, and other study populations.

The effect of preemptive and/or postoperative ibuprofen therapy for orthodontic pain

The control of pain during orthodontic treatment is of vital interest to both clinicians and patients. Surprisingly, there has been limited research into the control of orthodontic pain, and there is no standard of care for controlling this discomfort. The purpose of this study was to compare the effectiveness of preemptive ibuprofen therapy, postoperative ibuprofen therapy, and a combination of the 2 therapies. Forty-one orthodontic patients aged 9 years 3 months to 16 years 11 months who were to undergo separator placement were enrolled in this prospective study. Patients were randomly assigned to 1 of 3 experimental conditions: (1) 400 mg ibuprofen taken orally 1 hour before separator placement and 400 mg ibuprofen taken orally 6 hours after the initial dose, (2) 400 mg ibuprofen taken orally 1 hour before separator placement and a lactose capsule taken orally 6 hours after the initial dose, or (3) a lactose capsule taken orally 1 hour before separator placement and 400 mg ibuprofen taken 6 hours after the initial placebo. The results revealed that preemptive ibuprofen therapy significantly decreased pain that was experienced 2 hours after separator placement and at bedtime. Beginning on day 2, there was a trend for patients who had taken both preemptive and postoperative ibuprofen doses to have lower pain scores compared with the other 2 groups. In conclusion, these data indicate that ibuprofen taken 60 minutes before separator placement alleviates pain at 2 hours and at bedtime after treatment. Further study with the use of additional postoperative doses is warranted.

An evaluation of preoperative ibuprofen for treatment of pain associated with orthodontic separator placement

Patients undergoing orthodontic treatment can experience significant levels of pain. This study assessed the effectiveness of preoperative ibuprofen in reducing the incidence and the severity of pain after orthodontic separator placement. Sixty-three adolescent patients (mean age, 13 years) were included in this randomized, double-blind, placebo-controlled, prospective study. Patients were randomly assigned to 1 of 3 experimental conditions: (1) 400 mg of ibuprofen taken orally 1 hour before separator placement and a lactose placebo taken orally immediately after the appointment, (2) a lactose placebo taken orally 1 hour before separator placement and 400 mg of ibuprofen taken orally immediately after the appointment, or (3) a lactose placebo taken orally 1 hour before separator placement and again immediately after the appointment. The patient's level of discomfort was assessed with a visual analog scale at 2, 6, and 24 hours, as well as at 2, 3, and 7 days after placement of the orthodontic separators. An analysis of variance and Duncan's multiple range test revealed that 2 hours after their orthodontic appointment the patients who had taken ibuprofen 1 hour before separator placement had significantly less pain with chewing than did the patients who received either ibuprofen postoperatively or a placebo. Additional measures suggest a trend for less pain for this group of patients. These results support the use of pretreatment ibuprofen for patients requiring analgesics for orthodontic discomfort. Future study of the use of preemptive analgesics in orthodontics is warranted.

Effect of changing enamel conditioner concentration on the shear bond strength of a resin-modified glass ionomer adhesive

The purpose of this study was to determine the effects on shear bond strength of changing the concentration of the enamel conditioner used with resin-reinforced glass ionomer. Shear bond strength was measured within 30 minutes after bonding. Forty-six freshly extracted human molars were collected and stored in a solution of 0. 1% (weight/volume) thymol. The teeth were cleaned and polished, then randomly separated into 2 groups. In group I, enamel was conditioned with a 10% polyacrylic acid solution before bonding. In group II, the enamel was conditioned with a 20% polyacrylic acid solution. The results of t test comparisons of the 2 experimental groups (t = 4.9) indicate significant differences (P =.001). Shear bond strength was significantly greater in the group conditioned with the 20% polyacrylic acid concentration (X = 3.3 +/- 2.6 MPa) than in the group conditioned with the 10% concentration (X = 0.4 +/- 1.0 MPa). The present findings indicated that the lower initial shear bond strength of resin-reinforced glass ionomer adhesive can be improved more than 8-fold when the concentration of the polyacrylic acid enamel conditioner is increased from 10% to 20%. The clinician needs to take these properties into consideration when ligating the initial archwires.

Effect of altering the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer adhesive

The purpose of this study was to determine the effects of changing the type of enamel conditioner on the shear bond strength of a resin-reinforced glass ionomer within half an hour after bonding the bracket to the tooth. Freshly extracted human molars were collected and stored in a solution of 0.1% (weight/volume) thymol. The teeth were cleaned and polished. The teeth were randomly separated into 4 groups according to the enamel conditioner/etchant and adhesive used: group I, teeth were conditioned with 10% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group II, teeth were conditioned with 20% polyacrylic acid and brackets were bonded with a resin-reinforced glass ionomer adhesive; group III, teeth were etched with 37% phosphoric acid and the brackets were bonded with a resin-reinforced glass ionomer adhesive; group IV, teeth were etched with 37% phosphoric acid and the brackets were bonded with a composite adhesive. The results of the analysis of variance comparing the 4 experimental groups (F = 24.87) indicated the presence of significant differences between the groups (P =.0001). In general, the shear bond strengths were significantly greater in the 2 groups etched with 37% phosphoric acid. This was true for both the resin-reinforced glass ionomer (X = 6.1 +/- 2.7 MPa) and the composite (X = 5.2 +/- 2.9 MPa) adhesives. On the other hand, the shear bond strengths were significantly lower in the two groups conditioned with polyacrylic acid. The bond strength of the resin-reinforced glass ionomer adhesive conditioned with 10% polyacrylic acid (X = 0.4 +/- 1.0 MPa) was significantly lower than the group conditioned with 20% polyacrylic acid (&xmacr; = 3.3 +/- 2.6 MPa). The present findings indicated that the bond strength of the resin-reinforced glass ionomer adhesive can be significantly increased in the initial half hour after bonding if the enamel is etched with 37% phosphoric acid instead of being conditioned with either 10% or 20% polyacrylic acid. The clinician needs to take these properties into consideration when ligating the initial archwires.

Evaluation of profile esthetic change with mandibular advancement surgery

Our purpose was to investigate the impact of mandibular advancement surgery on profile esthetics and to attempt to define guidelines that could be of value to the clinician in predicting profile esthetic change. The sample consisted of 34 patients who had been treated with a combination of orthodontics and mandibular advancement surgery without genioplasty. Initial (pretreatment) and final (posttreatment) cephalometric radiographs of each patient were used to produce silhouette images and to quantify skeletal changes that occurred with surgery. The images were displayed randomly to lay persons and orthodontic residents who were asked to score the esthetics of each profile. On average, after mandibular advancement surgery, B point moved forward 5.0 mm (SD = 2.6 mm) and downward 4.7 mm (SD = 3.1 mm), and the ANB angle decreased 3.0 degrees (SD = 1.6 degrees ) Graphical analysis and results of paired t tests revealed that for patients with an initial ANB angle >/= 6 degrees, a consistent improvement in profile esthetics was seen following surgery (P </=.001). This represented, on average, about a 45% improvement in esthetics. For patients with an initial ANB angle < 6 degrees, an improvement in profile esthetics after surgery was seen about half the time but poorer esthetics were equally likely. These results underscore the importance of using the ANB angle as a skeletal guideline when deciding whether to treat patients with mandibular advancement surgery. If improved profile esthetics are a desired outcome, an initial ANB angle of at least 6 degrees is recommended.

Effect of light-cure time on the initial shear bond strength of a glass-ionomer adhesive

With the introduction of photosensitive (light-cured) restorative materials in dentistry, various methods were suggested to enhance the polymerization of these materials including layering and the use of more powerful light-curing devices. The purpose of this study was to determine the effects of increasing the light-cure time on the initial shear bond strength (in the first half hour) of a resin-modified glass-ionomer adhesive. Eighty-six teeth were divided into 4 groups according to either; (1) the adhesive system used, namely resin, reinforced glass ionomer, or composite, and (2) the light-cure time for the glass ionomer adhesive, namely 40, 45, and 50 seconds. The bonding approach followed the manufacturer's instructions unless otherwise specified. The results of the analysis of variance comparing the 4 experimental groups (F = 19.4) indicated the presence of significant differences between the groups (P =. 0001). In general, the shear bond strength was greater for the composite adhesive system (¿x(-) = 5.2 +/- 2.9 MPa), followed by the 2 groups bonded with the resin-reinforced glass-ionomer adhesive and light cured for 50 seconds (¿x(-) = 3.8 +/- 1.1 MPa) and 45 seconds (¿x(-) = 3.4 +/- 2.7 MPa). On the other hand, the shear bond strength was significantly lower for the group bonded with the glass ionomer adhesive and light cured for 40 seconds only (¿x(-) = 0.4 +/- 1.0 MPa). The present findings indicated the following: (1) the resin-reinforced glass-ionomer adhesive has a significantly lower shear bond strength in the first half hour after bonding when compared to a composite resin adhesive; (2) the initial bond strength of the glass-ionomer adhesive was significantly increased by increasing the light-cure time for an additional 5 to 10 seconds; (3) the mean increase in the shear bond strength between 5 and 10 seconds of additional light curing was not significant but the variability was less with the longer cure time.

Using standardized patients to assess presentation of a dental treatment plan

In this new era of relationship-based care, involvement in treatment planning and goal setting is a high priority for patient satisfaction. This study reports on the use of standardized patients (SPs) in training third-year dental students to gather dental, medical, and psychosocial information from patients and to involve the patient in the decision-making process leading to the dental treatment plan. Among the skill areas measured, students were most successful in gathering dental information, with 94 percent of the students obtaining the complete set. Students were least successful in identifying the patient's goals for treatment (81 percent of the students identified the patients' goals). Students were most challenged by discussing sensitive topics with patients such as grief-related depression (25 percent of the students recognized and discussed such topics). It is important that dental schools familiarize students with patient issues and teach them how to talk effectively to patients about personal issues and to incorporate those issues into a discussion of the treatment plan for the patient. Standardized patients can be used effectively toward this end.

Comparison of the debonding characteristics of two innovative ceramic bracket designs

Two new ceramic brackets-one designed with a metal-lined arch wire slot and the other with an epoxy resin base-have been recently introduced. The new brackets are thought to combine the esthetic advantages of ceramics and the functional advantages of debonding metal brackets. The purpose of this study was to compare the following: 1) the shear bond strength of the 2 brackets, and 2) the bond failure location when the brackets are debonded with pliers. Sixty-one Clarity (3M Unitek) collapsible ceramic brackets and 66 MXi (TP Orthodontics, Inc) brackets were bonded to the teeth with the same bonding system. The Zwick Universal Test Machine (Zwick Gm bH & Co) was used to determine the shear bond strength force levels needed to debond the brackets. The appropriate pliers also were used to debond both types of brackets to determine the mode of bond failure that will be encountered clinically. After debonding, all the teeth and brackets were examined with 10x magnification. Any adhesive that remained after the bracket removal was assessed according to the Adhesive Remnant Index. The findings indicated that the shear bond strength of the Clarity ceramic brackets was significantly greater than that of the MXi ceramic brackets. However, both brackets exhibited forces that were adequate for clinical use. The Adhesive Remnant Index scores for both the shear test and the plier debonding indicated a similar bond failure pattern when the 2 ceramic brackets were compared with each other. This suggests that, when these brackets are debonded with the Weingart (Ormco) and ETM (Ormco) pliers, there was a greater tendency for most of the adhesive to remain on the enamel surface. In conclusion, the most efficient method to debond the MXi ceramic bracket is by placing the blades of the ETM 346 pliers between the bracket base and the enamel surface. On the other hand, the most efficient method of debonding the Clarity bracket is by using the Weingart pliers and applying pressure to the tiewings. When the 2 ceramic brackets were debonded as recommended here, most of the residual adhesive remained on the enamel surface, a pattern similar to the one observed previously with metal brackets. The failure at the bracket-adhesive interface decreases the probability of enamel damage but necessitates the removal of more residual adhesive after debonding.

Changes in root length from early to mid-adulthood: resorption or apposition?

A significant number of adults are seeking orthodontic treatment, therefore, it is important to determine the normal changes in root length (resorption or apposition) that occur at this stage of maturation, specifically between early and mid-adulthood. The purpose of the study was to determine on a longitudinal basis the changes in root length between 25 and 45 years of age in a normative untreated population. Two sets of complete mouth surveys were available at early and mid-adulthood, on a total of 26 subjects (12 males and 14 females). Each set consisted of at least 18 periapical radiographs. On each set of radiographs, the roots of 28 teeth were measured including incisors, canines, premolars, and first and second molars, in both the maxillary and mandibular arches. Root length was measured as the perpendicular from the root apex to a line connecting the mesial and distal points of the cementoenamel junction of each tooth. A total of 1456 teeth (1664 roots) were measured; 672 teeth in males and 784 teeth in females. Allowable intraexaminer and interexaminer measurement variability was predetermined at 0.5 mm. Paired and Student t tests were used to determine: (1) whether significant changes occurred with age; (2) whether there were differences between males and females for the incisors, canines, premolars, and molars; and (3) whether there were differences between the right and left sides. Statistical significance was predetermined at P </=.05. The present findings indicated that there were no significant changes in root length for all tooth types evaluated between 25 and 45 years of age, in both males and females. These findings are important for the orthodontist to recognize because they provide some assurance that there is no systematic shortening of root length between early and mid-adulthood.

Geometric and densitometric standardization of intraoral radiography through use of a modified XCP system

OBJECTIVE

The purposes of this study were to examine the density correction afforded by curve-fitting algorithms and to investigate whether the device we developed significantly improves the reliability of longitudinal alveolar process bone radiographic density measurements.

STUDY DESIGN

Stepwedges were radiographed over a range of impulse settings, and curve-fitting algorithms were fitted to sets of step images on each digitized film. Differences between the actual thicknesses of an alternate set of steps and their corresponding thickness estimates were calculated. Next, clinicians made periapical radiographs from interproximal bony sites on a dry skull using our imaging device. Differences in bone densities between corresponding regions of interest taken 1 week apart were calculated.

RESULTS

Analysis of variance and Duncan's Multiple Range test demonstrated that piecewise linear, third-degree polynomial, and fourth-degree polynomial curves provided significantly better estimates of stepwedge thickness than did sigmoid or first degree polynomial-curves (P < .05) and that the differences between repeat bone density measurements made with density correction were significantly less than those made without density correction (P < .05).

CONCLUSIONS

Piecewise linear, third-degree polynomial, and fourth-degree polynomial curve-fitting algorithms provided the best densitometric correction. The use of our imaging device increased the reliability of longitudinal bone density measurements.

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 manufacturer's 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.

Soft tissue profile changes from 5 to 45 years of age

The purpose of this study was to describe the changes in five soft tissue parameters that are commonly used by orthodontic practitioners in their diagnosis and treatment planning as well as in their evaluation of profile changes that occur with growth and orthodontic treatment. The subjects in this study were 20 males and 15 females for whom lateral cephalograms were available between 5 and 45 years of age. The parameters evaluated were two angles of facial convexity, the Holdaway soft tissue angle, and the relationship of the upper and lower lips to Rickett's esthetic line. Descriptive statistics for the absolute and incremental changes were collected on a yearly basis between 5 and 17 years of age as well as at early (25 years) and middle (45 years) adulthood. Growth profile curves were constructed for each parameter to describe the age-related changes in the five parameters for both males and females. The analysis of variance was used to compare the absolute and incremental changes both longitudinally and cross-sectionally. Significance was predetermined at P </=.05. The present findings indicated that (1) in general, the changes in males and females were similar in both magnitude and direction. On the other hand, the timing of the greatest changes in the soft tissue profile occurred earlier in females (10 to 15 years) than in males (15 to 25 years); (2) the angle of soft tissue convexity that excludes the nose expressed little change between 5 and 45 years; (3) the upper and lower lips became significantly more retruded in relation to the esthetic line between 15 and 25 years of age in both males and females; the same trends continued between 25 and 45 years of age; (4) the Holdaway soft tissue angle progressively decreased between 5 and 45 years of age. It is important for clinicians to be aware of these changes when planning the orthodontic treatment of the still growing adolescent patients because the changes might influence the extraction/nonextraction decision.

Prediction of mandibular growth rotation: assessment of the Skieller, Björk, and Linde-Hansen method

The purpose of this investigation was to assess the method proposed by Skieller, Björk, and Linde-Hansen in 1984 to predict mandibular growth rotation. Our sample consisted of 40 randomly selected, untreated, adolescent subjects representative of the patient population generally encountered in orthodontic practice. The four independent variables identified in the Skieller study as having the highest predictive value (mandibular inclination, intermolar angle, shape of the lower border of the mandible, and inclination of the symphysis) were identified on initial lateral cephalograms. The proposed regression equations were applied and predicted mandibular rotations obtained. Final lateral cephalograms made 6 years after the initial profile radiographs were superimposed and actual mandibular rotation recorded. The observed and predicted rotations were compared and regression analyses performed to determine the amount of variability in observed values accounted for by the four variables individually and in combination. Only 5.6% of the variability in mandibular growth rotation could be accounted for using the four variables individually. Only 9% of the variability could be accounted for with a combination of the variables. In addition, we performed a Monte Carlo analysis, which mirrored the Skieller analysis but used random numbers instead of actual cephalometric data, to determine if the Skieller results may simply have capitalized on chance. Using the same forward stepwise selection procedure with a rejection level of P >.1, we found after 5000 simulations that a mean of 84% and a median of 94% of mandibular growth rotation variability could be accounted for using meaningless data in the Skieller analysis. This result was comparable to the Skieller value of 86%. In conclusion, information derived from pretreatment lateral cephalograms using the Skieller, Björk, and Linde-Hansen method does not permit clinically useful predictions to be made in a general population relative to the direction of future mandibular growth rotation.

Comparison of two nonradiographic methods of predicting permanent tooth size in the mixed dentition

The determination of the tooth size-arch length discrepancy in the mixed dentition requires an accurate prediction of the mesiodistal widths of the unerupted permanent teeth. Three approaches have been used to estimate the mesiodistal crown widths of unerupted canines and premolars: (1) measurements from erupted teeth, (2) measurements from radiographs, and (3) a combination of measurements from erupted teeth and from radiographs of unerupted teeth. The purpose of this study was to compare two mixed dentition prediction methods that do not require the use of periapical radiographs of the unerupted permanent teeth. The two methods compared were the Tanaka/Johnston and the Boston University Prediction approaches. Records on 33 male and 22 female subjects who were participants in the Iowa Longitudinal Growth Study were used in the present study. The findings indicated that on the average the Tanaka/Johnston approach slightly overestimated the tooth size of the unerupted teeth (mean = 1.1 +/- 0.9 mm). On the other hand, the Boston University approach slightly underestimated the tooth size of the unerupted teeth (mean = -0.1 +/- 1.2 mm). The findings further indicated that there were statistically significant correlations between the predicted and actual tooth size. In general the r values were higher for the Tanaka/Johnston method than with the Boston University approach. The error involved in the use of the predicted equations was expressed as the standard error of the estimate. The present findings indicated that the standard error of the estimate for Tanaka/Johnston prediction equations ranged between 0.67 and 0.92 mm and the corresponding values for the Boston University equations ranged between 0.92 and 1.02 mm. Depending on the stage of dental development, i.e., which deciduous and permanent teeth are present, the Tanaka/Johnston approach can be used when the four mandibular incisors have completely erupted, whereas the Boston University approach can be used when all the deciduous canines and first molars are still present.

The effect of microetching on the bond strength of metal brackets when bonded to previously bonded teeth: an in vitro study

The purpose of this in vitro study was to answer the following questions for three different metal brackets: (1) when rebonding a previously bonded tooth, how do shear bond strengths compare for new brackets, new microetched brackets, and debonded microetcher cleaned brackets? and (2) how do the different bracket types compare with respect to the time required to remove composite resin from their bonding pads with a microetcher? Ninety human premolars and canines previously debonded of metal brackets were randomly assigned to 9 groups of 10 teeth each. New, new etched, and debonded etched cleaned brackets of each type were bonded with composite resin onto teeth, and the bonds tested to failure for shear bond strength. An analysis of variance and Duncan's multiple range test were used to compare bracket/enamel bond strength. Within each bracket type no significant differences were found between mean bond strengths for new, new etched, and debonded etched conditions, a finding that supports the use of microetching to clean accidentally debonded brackets. Mean times for removal of resin from bonding pads with a microetcher varied from 9.3 seconds to 11.9 seconds, with bracket (M) requiring significantly less time for removal of resin.

A pilot study of esthetic perceptions of dental fluorosis vs. selected other dental conditions

The prevalence of fluorosis has increased over the past fifty years, and with this increase, esthetic concerns pertaining to fluorosis should also be taken into consideration. Canadian, Australian, and British studies have explored perceptions concerning enamel fluorosis, but no studies in this area have been published from the United States. In the previous studies, esthetic concerns resulting from fluorosis generally were not compared with the esthetic perceptions of other conditions such as isolated opacities, tetracycline staining, or various types of malocclusion. In the present investigation, respondents answered written questions about paired photographs, one of fluorotic teeth and the other with one of the other conditions. Results show that not only is fluorosis noticeable, but it may be more of an esthetic concern than the other conditions.

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.

In vitro study of 24-hour and 30-day shear bond strengths of three resin-glass ionomer cements used to bond orthodontic brackets

Interest in using composite resin-glass ionomer hybrid cements as orthodontic bracket adhesives has grown because of their potential for fluoride release. The purpose of this pilot study was to compare shear bond strengths of three resin-glass ionomer cements (Advance, Fuji Duet, Fuji Ortho LC) used as bracket adhesives with a composite resin 24 hours and 30 days after bonding. The amount of adhesive remaining on the debonded enamel surface was scored for each adhesive. Mesh-backed stainless-steel brackets were bonded to 100 extracted human premolars, which were stored in artificial saliva at 37 degrees C until being tested to failure in a testing machine. The hybrid cements, with one exception, had bond strengths similar to those of the composite resin at 24 hours and 30 days. Fuji Ortho LC had significantly lower bond strengths (ANOVA p < or = 0.05) than the other adhesives at 24 hours and 30 days when it was bonded to unetched, water-moistened enamel. Adhesive-remnant scores were similar for all cements, except for cement Fuji Ortho LC when it was bonded to unetched enamel. The resin-glass ionomer cements we tested appear to have bond strengths suitable for routine use as orthodontic bracket-bonding adhesives.

Changes in overbite and face height from 5 to 45 years of age in normal subjects

The purpose of this study was to evaluate changes in overbite over a 40-year span, and to relate these changes to those occurring in vertical skeletal facial relationships. Lateral cephalograms of 20 males and 15 females from the Iowa Facial Growth Study were evaluated at ages 5, 10, 15, 25, and 45 years. Correlation coefficients were computed to determine the relationship between overbite and various skeletal parameters. Analysis of variance and Duncan's multiple-range test were used to compare various periods of growth. Statistical significance was predetermined at the 0.05 level of confidence. No significant correlations were found between the absolute values of overbite and the vertical skeletal parameters in either males or females. Incremental changes in overbite during four growth periods were compared with changes in various vertical parameters and only a few significant correlations were found. In males, the change in overbite was significantly correlated with changes in N-Ans'/N-Me and MP:SN during the 10-to-15 year growth period. In females, the change in overbite was significantly correlated with changes in N-Ans'/N-Me% during the 5-to-10-year period and also with change in Ar'-Go/S-Go% during the 15-to-25-year period. In general, changes in overbite with age are difficult to predict from the initial overbite in the deciduous or mixed dentitions. On the other hand, evaluation of individual curves shows that males who initially had the least amount of overbite maintained that trend during the later stages of development. Although overbite changes were significantly associated with changes in some vertical parameters, the associations were not of clinical significance for predictive purposes, and overbite changes are probably dependent on concurrent changes in the growth of the alveolar processes.

Arch length changes from 6 weeks to 45 years

The purpose of this study was to evaluate, on a longitudinal basis, changes in maxillary and mandibular arch length over a 45-year period. Subjects were drawn from two pools of normal individuals. Twenty-eight male and 33 female infants were evaluated longitudinally at 6 weeks, 1 year, and 2 years (before the eruption of the deciduous dentition). Fifteen males and 15 females from the Iowa Facial Growth Study were evaluated at 3, 5, 8, 13, 26, and 45 years. Arch length measurements were obtained independently by two investigators. Intra- and interexaminer reliabilities were predetermined at 0.25 and 0.5 mm, respectively. The greatest incremental increases occurred during the first two years of life. Arch length continued to increase until 13 years in the maxillary arch, and until 8 in the mandibular. Then significant and consistent decreases occurred in both arches mesial to the permanent first molars.

Profile changes in patients treated with and without extractions: assessments by lay people

The purpose of this study was to assess the profile changes in subjects with Class II, Division 1 malocclusions who were treated either with or without the extraction of the four first premolars. The assessments were made by 39 lay persons. Profile silhouettes on 91 (44 extraction and 47 nonextraction) patients were evaluated at three stages: pretreatment, posttreatment, and approximately 2 years after treatment. Photographs matched for age and sex were also evaluated on 20 normal untreated subjects (10 males and 10 females). All rater assessments were analyzed statistically as to the effects of the following variables: (a) occlusion, i.e., normal or Class II, (b) treatment rendered, i.e., extraction or nonextraction, (c) gender, i.e., male or female, and (d) stage of observation, i.e., pretreatment, end of treatment or in retention. The current findings indicate that (1) before treatment, lay persons perceived the profile of normal patients more favorably than untreated patients with Class II, Division 1 malocclusions. (2) Immediately after treatment, raters perceived the changes in the profile of the extraction group more favorably than those in the nonextraction and normal groups. (3) At the end of the observation period (approximately 2 years posttreatment), raters did not evaluate the profile of any of the groups as being more favorable, but all groups were perceived more favorably than at the initial observation. (4) Raters perceived the profile changes with treatment more favorably in female subjects than in male subjects. In conclusion, orthodontic treatment seems to have a favorable effect on the profiles of both the extraction and nonextraction groups, both short- and long-term. Therefore, when based on proper diagnostic criteria, the posttreatment changes in the facial profile were perceived as favorable in both the extraction and nonextraction Class II, Division 1 groups when compared with the pretreatment profile.

An in vitro comparison of three fluoride regimens on enamel remineralization

The purpose of this study was to compare the enamel remineralization effectiveness of a fluoride rinse, fluoridated dentifrice, and fluoride-releasing restorative material. Forty extracted molars had 1 x 5 mm artificial carious lesions formed at the interproximal contact point. One-hundred-micrometer sections were obtained at the caries sites, and polarized light photomicrographs were obtained. The sections had varnish placed, leaving only the external section site exposed, and were situated back into the original tooth. Forty other molars were obtained; 10 had Class-II glass ionomer cement restorations placed. These 40 teeth were mounted to have interproximal contact with the adjacent teeth containing artificial carious lesions. Specimens were placed in closed environments of artificial saliva for 1 month, with saliva being changed every 48 h. Ten specimen pairs were brushed with a fluoridated dentifrice for 2 min, twice per day, 10 specimen pairs were rinsed with a 0.05% sodium fluoride rinse for 1 min twice per day, 10 specimen pairs had Class-II glass ionomer cement restorations positioned adjacent to 10 teeth with artificial carious lesions, and 10 specimen pairs acted as controls. After 30 days, the same sections were photographed again under polarized light, and areas of the lesions were digitized quantitatively. Results demonstrated the mean (+/- SD) remineralization (mu m2) in Thoulet's 1.41 imbibition media to be: lesions adjacent to glass ionomer cement restorations, 2.45 +/- 170; lesions exposed to a fluoridated dentifrice, 223 +/- 102; lesions exposed to 0.05% sodium fluoride rinse, 374 +/- 120, and control lesions only exposed to artificial saliva, 101 +/- 69. Duncan's analysis indicated the fluoridated rinse to have significantly greater remineralization effects on adjacent caries than the other groups (p < or = 0.05). The glass ionomer restorative material and fluoridated dentifrice also had significantly greater remineralization effects on adjacent caries than the control, yet significantly less than the fluoridated rinse (p < or = 0.05).

Comparison of shear bond strength and surface structure between conventional acid etching and air-abrasion of human enamel

Recently, air-abrasion technology has been examined for potential applications within dentistry, including the field of orthodontics. The purpose of this study was to compare the traditional acid-etch technique with an air-abrasion surface preparation technique, with two different sizes of abrading particles. The following parameters were evaluated: (a) shear bond strength, (b) bond failure location, and (c) enamel surface preparation, as viewed through a scanning electron microscope. Sixty extracted human third molars were pumiced and divided into three groups of 20. The first group was etched with a 37% phosphoric acid gel for 30 seconds, rinsed for 30 seconds, and dried for 20 seconds. The second and third groups were air-abraded with (a) a 50 microm particle and (b) a 90 microm particle of aluminum oxide, with the Micro-etcher microabrasion machine (Danville Engineering Inc.). All three groups had molar stainless steel orthodontic brackets bonded to the buccal surface of each tooth with Transbond XT bonding system (3M Unitek). A Zwick Universal Testing Machine (Calitek Corp.) was used to determine shear bond strengths. The analysis of variance was used to compare the three groups. The Adhesive Remnant Index (ARI) was used to evaluate the residual adhesive on the enamel after bracket removal. The chi square test was used to evaluate differences in the ARI scores among the groups. The significance for all tests was predetermined at p < or = 0.05. The results indicated that there was a significant difference in shear bond strength among the three groups (p = 0.0001). The Duncan Multiple Range test showed a significant decrease in shear bond strength in the air-abraded groups. The chi square test revealed significant differences among the ARI scores of the acid-etched group and the air-abraded groups (chi(2) = 0.0001), indicating no adhesive remained on the enamel surface after debonding when air-abrasion was used. In conclusion, the current findings indicate that enamel surface preparation using air-abrasion results in a significant lower bond strength and should not be advocated for routine clinical use as an enamel conditioner at this time.

A comparison of patient satisfaction and dentist evaluation of overdenture therapy

It has been argued that the retention of some teeth in the jaws as overdenture abutments prevents negative feelings about the loss of natural teeth. This study set out to evaluate how satisfied a group of patients were with wearing overdentures, and to compare their subjective evaluations with those of a dentist using objective criteria to examine the prostheses. A questionnaire was developed using questions adapted from several other studies. It was pretested, modified and used on all patients who were members of a longitudinal study of overdentures that started in 1974, and who returned on recall. At the end of 9 months, 101 subjects had completed the questionnaire and examination. The mean age of the patients was 65.9 years with an age range of 35 to 88 years. There were 68 men and 33 women in this study and 62 of them were satisfied with their dentures; 33 were satisfied, but felt they had some faults. Only 6 were unhappy about wearing the overdentures. The average length of time the dentures had been worn was 6.9 years, with a range of 1 to 15 years. The most frequent complaints were loss of retention (65.4%) and discomfort (62.2%) of the mandibular dentures. A number of correlations were evaluated and some significant relationships were found between dentist and patient evaluation of the dentures. The best predictor of patient satisfaction with denture wearing was the patient's perception of retention and appearance. In the maxilla the patient's ability to chew and the dentist's evaluation of occlusion were also significant predictors. In the mandible the only other factors apart from retention and appearance were patient comfort and age.

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.

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.

Fluoride release and shear bond strengths of three light-cured glass ionomer cements

Little is known about the release of fluoride from light-cured glass ionomer cements when used as orthodontic bonding agents. Fluoride release from three "hybrid" light-cured glass ionomer cements was measured during a 42-day period after initial curing in an in vitro test that simulated their use as orthodontic bonding agents. On day 48, the bonded teeth were exposed for 30 seconds to a stannous fluoride gel and checked for fluoride release during the following week. One cement (BL) released the most fluoride after initial cure and after an exposure to a stannous fluoride gel on day 48. The other two hybrid cements exhibited both significantly less fluoride release than material (BL) and resembled for most of the 55-day duration the composite resin control. After the 55-day duration, shear bond strengths of the composite resin control were significantly higher than the three light-cured glass ionomer cements. The light-cured glass ionomer cements in this study released fluoride after initial curing and after exposure to a topical fluoride gel. This property may help reduce or possibly even prevent enamel decalcifications seen around bracket bases. At present, the shear bond strengths of the light-cured glass ionomer cements tested appear to be too low for routine orthodontic bonding agents.

Bond strength following the application of chlorhexidine on etched enamel

The purpose of this study was to determine whether the application of chlorhexidine to etched enamel affects the shear bond strength and bracket/adhesive failure modes of orthodontic brackets. Forty recently extracted third molars were cleaned divided into two groups of twenty. The first group was etched with a 37% phosphoric acid gel, and a sealant was applied containing a chlorhexidine varnish. Stainless steel orthodontic brackets were bonded using the Transbond XT bonding system (3M/Unitek). Teeth in the second group were etched and bonded using the same bonding system but without chlorhexidine. A Zwick Universal Testing Machine was used to determine shear bond strengths. There were no significant differences in bond strengths between the chlorhexidine treated teeth (= 11.8 +/- 2.1 MPa) and the controls (= 12.4 +/- 3.1 MPa) (p = 0.129). The Chi Square test evaluating the residual adhesive on the enamel surfaces showed no significant differences (P = 0.136) between the two groups evaluated. The use of a primer containing chlorhexidine does not significantly affect shear bond strength nor the fracture site (bond failure location).

Changes in dentofacial structures in untreated Class II division 1 and normal subjects: a longitudinal study

The purpose of this study was to compare longitudinally the changes that occur in dentofacial structures from the deciduous to the permanent dentitions in untreated Class II division 1 and normal individuals. Complete records were assembled for 65 subjects at three stages of development: at the completion of the deciduous dentition, after the first permanent molars had erupted completely, and after the permanent dentition had erupted completely (third molars excluded). On a cross-sectional basis, only mandibular length (Ar-Pog) differed significantly in the two groups, and then only during the earlier stages of development; by the later stage, the difference was not significant, indicating that some "catch up" growth may occur in Class II individuals. Longitudinal comparisons of the curve profiles, i.e., growth trends between Class II division 1 and normal subjects, indicated that there were no significant differences between the two groups except in upper lip protrusion. Comparisons of the total change from the deciduous to the permanent dentition indicated the presence of a number of significant differences between Class II division 1 and normal subjects, including larger magnitude of maxillary and mandibular lengths in the normal group and greater skeletal and soft tissue convexities in the Class II group.

Evaluation of the shear bond strength of different ceramic bracket base designs

The purpose of this study was to compare the Ceramaflex bracket with a traditional ceramic orthodontic bracket with regard to shear bond strength and bond failure location. Forty newly extracted human premolars were randomly divided into two groups. Twenty Ceramaflex brackets (TP Orthodontics Inc, LaPorte, Ind) and 20 Transcend 6000 brackets (Unitek Corp, Monrovia, Calif) were bonded to the teeth using the same bonding system (Right On, TP Orthodontics Inc, LaPorte, Ind). A Zwick Universal Test machine (Zwick Gm bH & Co, Ulm, Germany) was used to determine the shear bond strength for each bracket. After debonding, the teeth and brackets were examined under 10x magnification. After debonding, the amount of resin material adhering to the enamel surface was assessed according to the Adhesive Remnant Index (ARI). The results of this study suggest that Ceramaflex brackets have a significantly lower bond strength than traditional ceramic brackets. On the other hand, the bond failure location of the Ceramaflex bracket was consistently more favorable, i.e., occurring at the ceramic bracket-polycarbonate base.

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.

Longitudinal comparisons of dental arch changes in normal and untreated Class II, Division 1 subjects and their clinical implications

The purpose of this study was to determine on a longitudinal basis whether the growth trends in maxillary and mandibular dental arch widths and lengths in persons with Class II, Division 1 malocclusions were different from those of normal subjects. Dental casts were available on a total of 37 subjects with Class II, Division 1 malocclusions (15 males and 22 females) and 55 normal subjects (28 males and 27 females). For each subject, three sets of casts were evaluated at the following developmental stages: (1) deciduous dentition (mean age = 5.0 years); (2) mixed dentition (mean age = 8.0 years); and (3) permanent dentition (mean age = 12.5 years). Eighteen dental arch lengths and widths parameters were measured on both the maxillary and the mandibular arches. Interexaminer and intraexaminer reliability were predetermined at 0.5 mm. The Analysis of Variance general linear models procedure was used to compare the various dental arch parameters on both a cross-sectional and a longitudinal basis. Curve parallelism and magnitude were evaluated. The results of the analysis of variance comparing the growth curves of the various dental arch parameters in the normal subjects and untreated subjects with Class II, Division 1 malocclusions indicated the absence of significant differences between the groups, i.e., the curves were parallel (p < 0.01). This finding indicates that the growth trends in the various dental arch parameters evaluated were similar in the normal and Class II, Division 1 malocclusion groups in both male and female subjects. In addition, the differences between the measurements of maxillary and mandibular intermolar arch widths were greater in the normal male subjects than in the male subjects with Class II, Division 1 malocclusions. Female subjects had similar trends but the differences were not statistically significant. In conclusion, the present findings indicate that the clinician should assume that the changes in arch lengths and widths in both the subjects with Class II, Division 1 malocclusions and the normal subjects follow the same general patterns. On the other hand, the relative constriction of the maxillary arch as related to the mandibular arch, In Class II malocclusions is expressed from the earlier stages of dental arch development. These trends continue in the mixed and early permanent dentitions and do not self correct without treatment. Therefore when such trends are diagnosed, early correction of transverse discrepancy should be attempted together with that of the anteroposterior discrepancy.

Fractal dimension in radiographic analysis of alveolar process bone

OBJECTIVES

This in vitro study examined radiographic fractal dimension changes in alveolar process bone during simulated osteoporosis.

STUDY DESIGN

Ten specimens of human maxillary alveolar process bone were progressively decalcified, and the percentage of calcium lost at each decalcification stage was quantified. Four radiographs of each specimen, together with an aluminum step-wedge, were exposed at 70 kVp at each stage. The test set of 560 radiographs was digitized, identical bony regions of interest were selected from the density-corrected images of each specimen, the regions were digitally filtered to reduce film-grain noise, and fractal dimension was computed on a line-to-line basis. Correlation analysis quantified the relationship between calcium loss and fractal dimension change. Analysis of variance and Duncan's multiple range test determined whether a difference existed in fractal dimension computed from images at x-ray beam angulations of -5, 0, and +5 degrees.

RESULTS

A strong correlation (average r = -0.94, p < or = 0.0037) was found between generalized demineralization and decreasing fractal dimension. In every bone sample fractal dimension changed significantly (p < or = 0.0189) with angular change.

CONCLUSIONS

Radiographic fractal dimension holds promise for detecting simulated osteoporosis in the maxilla under ideal conditions, but the sensitivity of fractal dimension to small x-ray beam angular change renders its clinical application questionable.

Effect of varying etching times on the bond strength of ceramic brackets

Damage to the enamel surface when debonding orthodontic ceramic brackets has been a clinical concern. Ideally, bond failure at the bracket-adhesive interface should occur without damaging the enamel surface. The purpose of this study was to determine the shear bond strength and debonding failure modes of ceramic brackets with varying etching times. Sixty freshly extracted human premolars were pumiced and divided into six groups of 10 teeth. Each group was assigned an etching time interval of either 30, 20, 15, 10, 5, or 0 seconds with 37% phosphoric acid. Ceramic orthodontic brackets were bonded to each etched tooth by using the same orthodontic bonding system. The teeth were mounted in phenolic rings and stored in deionized water at 37 degrees C for 48 hours. A Zwick universal testing machine (Zwick GmbH and Co., Ulm, Germany) was used to determine shear bond strengths. The residual adhesive on the enamel surface was evaluated with the Adhesive Remnant Index. The results of the analysis of variance indicated that there were significant differences in bond strengths between the various etching times (p=0.0001). The Duncan multiple range test revealed that the 5-second and no etch group exhibited significantly lower bond strengths. The results of the Chi square test evaluating the residual adhesives on the enamel surface also revealed significant differences (p=0.0001). However, when the 5- and 0-second groups were dropped from the test, the Chi square test revealed no significant differences between the 30-, 20-, 15-, and 10-second groups (p=0.211). In conclusion, decreasing etching time between 30 and 10 seconds does not significantly affect either bond strength or the site of bond failure.

Changes in tooth size-arch length relationships from the deciduous to the permanent dentition: a longitudinal study

The purpose of this investigation is to determine the changes in the maxillary and mandibular tooth size-arch length relationship (TSALD) after the complete eruption of the deciduous dentition (mean age = 4.0 years) to the time of eruption of the second molars (mean age = 13.3 years). In addition, an attempt was made to determine whether TSALD in the permanent dentition can be predicted in the deciduous dentition. Records on 35 male and 27 female subjects were evaluated. Each subject had a clinically acceptable occlusion--that is, a normal molar and canine relationship, at the time of eruption of the deciduous and permanent teeth. In addition, each subject had a complete set of data at the two stages of dental development. These selection criteria limited the number of subjects in this investigation to 62. The mesiodistal diameter of all deciduous teeth and their permanent successors, as well as various dental arch width and length parameters, were measured in the deciduous and permanent dentitions. A total of 68 parameters were measured or calculated. Student t tests were used to determine whether significant differences were present between the right and left sides for both male and female subjects. Correlation coefficients r were performed between the deciduous and the corresponding permanent teeth and also for the arch length parameters, as well as TSALD in the two dentitions. Significance was predetermined at the 0.05 level of confidence. Stepwise regression analysis (R2) was used to determine which of the variables in the deciduous dentition could be included in a regression model to determine associations between maxillary and mandibular TSALD in the permanent dentition.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in facial dimensions assessed from lateral and frontal photographs. Part I--Methodology

The purpose of this study was to evaluate the changes in facial dimensions between 4 and 13 years of age and to provide normative standards that can be used for comparative purposes. The measurements were obtained from serial frontal and lateral photographs available on 20 subjects; 10 boys and 10 girls. The photographs were digitized and displayed on a computer monitor. Thirty-two landmarks were identified and 29 linear dimensions were measured. Analysis of variance was used to compare boys and girls and the repeated measure analysis (ANOVA) was used to evaluate the changes with age. From the findings, the conclusions were made as follows: (1) Proportionately, the total length of the face increased at a rate about two times that of the width of the face. (2) The changes in the dimensions of the eyes were the most stable of all the parameters measured. (3) There was a greater degree of variability in parameters directly affected by variations in facial growth patterns, e.g., chin prominence. The standard deviation was several times greater than the average increment of change. (4) The rates of growth for the vertical length and sagittal depth of the nose were twice as much as the rate of increase for the lateral width of the nose. (5) The incremental changes in the size of the lips were the most variable, but the total change in the vermillion length was the smallest of all the parameters measured. The standardized photographs from which the present measurements were obtained provide a unique opportunity to study facial growth and provides an accurate description of facial changes.

A computer assisted photogrammetric analysis of soft tissue changes after orthodontic treatment. Part II: Results

The purpose of this study was to use standardized facial photographs to compare the soft tissue profile changes in persons with Class II, Division 1 malocclusions who were treated with either an extraction or a nonextraction treatment modalities. Ninety-one patients (44 extraction and 47 nonextraction) were evaluated using standardized facial photographs, available at pretreatment, posttreatment and 2-years in retention. The photographs were digitized and displayed on a computer monitor. Thirty-eight landmarks (18 frontal and 20 lateral) were located. From these landmarks, 29 angular and linear dimensions (8 frontal and 21 lateral) were constructed. Descriptive and analytical statistics were used to compare the absolute dimensions, as well as the incremental changes, between the extraction and nonextraction groups. The present findings indicate: (1) After treatment the upper and lower lips were retracted significantly more in the extraction group compared with the nonextraction group. These differences persisted into retention. (2) The upper lip length increased more among subjects who were treated without extractions. (3) The upper vermilion height in male subjects and the upper and lower vermilion heights in female subjects increased among subjects who were treated without extractions and decreased among subjects who were treated with four first premolar extractions. (4) The nasolabial angle became significantly more obtuse among the female subjects who were treated with four first premolar extractions.

A computer assisted photogrammetric analysis of soft tissue changes after orthodontic treatment. Part I: Methodology and reliability

The purpose of this study was to use standardized facial photographs to compare the soft tissue profile changes in persons with Class II, Division 1 malocclusions who were treated with either an extraction or a nonextraction treatment modality. Ninety-one patients (44 extraction and 47 nonextraction) were evaluated with standardized facial photographs, available at pretreatment, posttreatment, and 2 years in retention. The photographs were digitized and displayed on a computer monitor. Thirty-eight landmarks (18 frontal and 20 lateral) were located. From these landmarks, 29 angular and linear dimensions (8 frontal and 21 lateral) were constructed. Descriptive and analytical statistics were used to compare the absolute dimensions, as well as the incremental changes, between the extraction and nonextraction groups. The present findings indicate that (1) Photographs allow for measurement of structures from a profile, as well as frontal orientations. (2) Measurement of profile changes from facial photographs appear to be fairly reliable but also have significant limitations. (3) Certain landmarks tended to be less reliable than others, e.g., subnasale and gnathion. In general, measurements from frontal photographs were more reliable than those obtained from lateral photographs and linear measurements were more reliable than angular measurements. (4) Changes in head posture within the cephalostat have an impact on vertical facial dimensions measured from frontal photographs. Horizontal dimensions were effected to a lesser degree. (5) Facial structures that lie closer to the camera appeared to be relatively larger than structures located farther from the camera. (6) The overall process of evaluating facial changes from photographs is both technique and operator sensitive. (7) More research specifically testing the photogrammetric method in a clinical setting is needed.

The morphologic basis for the extraction decision in Class II, division 1 malocclusions: a comparative study

The purpose of this study was to compare the pretreatment dentofacial characteristics of persons with Class II, Division 1 malocclusions treated with either an extraction or a nonextraction approach. Such comparisons might help identify which parameters influence the extraction decision. Lateral cephalograms were available on 91 Class II, Division 1 cases, 44 were eventually treated with first premolar extractions and 47 were treated nonextraction. Twenty-four landmarks were located and digitized on each cephalogram. From these landmarks, 33 angular and linear dimensions were obtained. The Class II cases were also compared with normal subjects matched for age and sex. Comparisons between the Class II, Division 1 groups and normals indicated that, in general, the Class II, Division 1 malocclusion is associated with a larger overjet, deeper overbite, larger ANB angle, more retrusive mandible, and a convex soft tissue profile. Comparisons between subjects treated with and without extractions indicated that at pretreatment, the extraction groups had significantly larger tooth size-arch length discrepancies in both the maxillary and mandibular arches. In addition, the upper and lower lips in male subjects, and the lower lip in female subjects were significantly more protrusive in the subjects who were eventually treated with four first premolar extractions. These results indicate that in this group of patients, lip protrusion is one of the important parameters on which the extraction decision was based.

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.