Jeryl D. English

Does Malocclusion Affect Masticatory Performance

This purpose of this study was to evaluate the largely untested assumption that malocclusion negatively affects masticatory performance. A sample of 185 untreated subjects (48% male and 52% female) from 7 to 37 years of age, representing subjects with normal occlusion (n = 38), Class I (n = 56), Class II (n = 45), and Class III (n = 46) malocclusion, were evaluated. Masticatory performance was evaluated objectively using artificial (CutterSil, median particle size and broadness of the distribution) and real foods (number of chews for jerky and almonds), and subjectively using a visual analog scale. The results showed no significant differences in age or the body mass index (Wt/Ht2) between the occlusion groups. Subjects with normal occlusion had significantly smaller particle sizes (P = .001) and broader particle distributions (P < .001) than subjects with malocclusion. Compared with the normal occlusion group, the median particle sizes for the Class I, II, and III malocclusion groups were approximately 9%, 15%, and 34% larger, respectively. There were also significant group differences in their subjective ability to chew fresh carrots or celery (P = .019) and firm meat (P = .003). Class III subjects reported the greatest difficulty, followed by Class II subjects, Class I subjects, and subjects with normal occlusion, respectively. We conclude that malocclusion negatively affects subjects ability to process and break down foods.

A cephalometric and tomographic evaluation of Herbst treatment in the mixed dentition

This study describes combined treatment and posttreatment effects for patients treated with the Herbst appliance in the mixed dentition followed by retention with a prefabricated positioner. The sample included 24 female and 16 male patients with Class II malocclusions. Posttreatment lateral cephalograms were taken an average of 17 months after Herbst removal, when the patients presented for phase II comprehensive orthodontics. The cumulative treatment and retention effects were compared with a sample of untreated Class II controls matched for age, sex, and mandibular plane angle. The overjet and molar relationship were corrected by 3. 4 and 3.3 mm, respectively. A headgear effect of Herbst therapy was observed, as anterior maxillary displacement was reduced by 1.2 mm. Condylar growth was redirected to produce 2.0 mm greater posterior growth in the treatment group. These effects produced significantly greater decreases in SNA (0.8 degrees ) and ANB (1.4 degrees ), and a tendency toward an increase in SNB (0.5 degrees ) Mandibular orthopedic effects resulted in an increase in anterior facial height (1.6 mm) and inferior displacement of the chin. Minimal changes in the displacement of condylion in relation to stable cranial base structures suggest that glenoid fossa displacement does not contribute in a clinically significant way to Class II correction. Pretreatment, immediate posttreatment, and postretention corrected temporomandibular joint tomograms demonstrated a tendency for the condyle to be slightly forward (0.2 mm) at the end of treatment and then to fall back after treatment. Statistically significant joint space changes were limited to the posttreatment period. We conclude that Herbst treatment in the mixed dentition, in combination with retention, produces significant long-term improvements in dental and skeletal relationships as a result of dentoalveolar changes and orthopedic effects in both jaws.

Effects of high-speed curing devices on shear bond strength and microleakage of orthodontic brackets

This study evaluated the shear-peel bond strength and mode of bond failure of 3 curing devices (plasma arc light, argon laser, and conventional halogen light) and 2 orthodontic bracket adhesives with different filler contents (Transbond XT and Adhesive Precoated [APC]). Observations of microleakage were also reported. Ninety human adolescent premolars were randomly divided into 6 groups, and standardized brackets were bonded according to the manufacturers recommendations. The plasma arc light produced significantly (P =.006) higher bond strength than did the halogen light or the argon laser when Transbond was used. When APC was used, the plasma arc light and the halogen light produced similar results, and they both produced significantly (P =.015) higher bond strengths than did the argon laser. Overall, the APC showed substantially less variation in bond strength than did the Transbond. Although all curing methods showed significant microleakage (P <.001), differences among the 3 curing lights occurred only when APC was used. Microscopic evaluations demonstrated that 95% of the specimens failed for adhesion at the bracket or tooth surface; the argon laser produced the highest adhesive remnant index scores. On the basis of bond strength and microleakage results, the plasma arc light was comparable with or superior to the other curing devices, depending on the adhesive used.

Enamel thickness of the posterior dentition: Its implications for nonextraction treatment

This study describes mesial and distal enamel thickness of the permanent posterior mandibular dentition. The sample comprised 98 Caucasian adults (59 males, 39 females) 20 to 35 years old. Bitewing radiographs of the right permanent mandibular premolars and first and second molars were illuminated and transferred to a computer at a fixed magnification via a video camera. Enamel and dentin thicknesses were identified and digitized on the plane representing the maximum mesiodistal diameter of each tooth. The results showed that there were no significant sex differences in either mesial or distal enamel thickness. Enamel on the second molars was significantly thicker (0.3 to 0.4 mm) than enamel on the premolars. Distal enamel was significantly thicker than mesial enamel. There was approximately 10 mm of total enamel on the four teeth combined. Assuming 50% enamel reduction, the premolars and molars should provide 9.8 mm of additional space for realignment of mandibular teeth.

Orthodontic treatment and masticatory muscle exercises to correct a Class I open bite in an adult patient.

Diagnosing and treating an open bite malocclusion in an adult is a challenge for the clinical orthodontist. Patients with skeletal vertical growth patterns, typical of open bite malocclusions, exhibit common morphological and functional characteristics, including long anterior face height, short posterior face height, large mandibular plane and gonial angles, increased dentoalveolar height, marked antegonial notching, downward tipping to the posterior maxilla, and anterior open bite. Functionally, hyperdivergent patients typically have weak bite forces, and smaller, less efficient muscles. Control of the vertical dimension by intruding both maxillary and mandibular molars and facilitating counterclockwise rotation of the mandible is key to managing open bite malocclusion. Some studies have shown morphological improvements in children with open bites who do chewing exercises, and others have demonstrated significant forward mandibular autorotation. In this case report, we discuss open bite treatment that included a combination of anterior vertical elastics to extrude the maxillary and mandibular incisors and clenching exercises to intrude the maxillary and mandibular molars.