Elias G. Katsavrias

The Growth of Articular Eminence Height During Craniofacial Growth Period

ABSTRACT This study was done to study the growth of the articular eminence height during the postnatal craniofacial growth period. Ninety (90) skulls were divided into three equal groups, named A, B, and C. The A group belonged to individuals showing deciduous dentition, the B group showed mixed dentition, and the C group permanent dentition. The skulls were stabilized so that the FH plane was really horizontal. This was assured using a common facial bow, inserted into the acoustic meatuses and the infraorbital foramen, and a common water-level device. Using a silicone type impression material, impressions were taken of all temporal fossae. Special care was taken in order that the base of the materials was parallel to the FH plane. After setting, the impression was removed and a common eggslicer was used to cut the material into sections of 2.5mm each. The three middle sections were removed, photo copied with a common photocopy machine, enlarged to a 200% scale and the height of the eminentia were measured by using an electronic caliper. The mean of the three calculations was reduced to its normal value, and was tabulated for each eminence. The study concluded that the articular eminence height grows at a very high rate until the age of seven (the period of deciduous dentition, development, and function), almost stops until the age of eleven (the period of mixed dentition), and acquires the rest of its height by the age of 20. This growth plan more nearly approximates the somatic or the general growth curve.

Effect of loading rate on bond strength.

Abstract.The purpose of this study was to examine the effect of loading rate on the bond strength of brackets bonded to enamel. Forty premolars were used and brackets were bonded with a chemically cured or a light-cured adhesive, mounted on a testing machine, and debonded under shear stress at two loading velocities: a standard 1 mm/min, and a fast 200 mm/min which better approximates the actual jaw velocity during chewing. Bond strength results (N) were analyzed with two-way analysis of variance (loading rate, adhesive) (α = 0.05). An increased loading rate resulted in decreased bond strength, probably due to the induction of a stiff body response and elimination of the viscoelastic properties of the resin. The results indicated a similar effect on both chemically cured and light-cured adhesives, thus emphasizing the need for standardized test conditions in bond strength protocols. The implication of loads generated during chewing must be considered when estimating the long-term survival of the bond.Zusammenfassung.Ziel dieser Studie war es, den Einfluss der Vorschubgeschwindigkeit auf die Haftfestigkeit von Brackets zu Schmelz zu untersuchen. Dazu wurden 40 Prämolaren verwendet, wobei die Brackets mit einem chemisch- oder lichthärtenden Adhäsiv befestigt, in eine Materialprüfmaschine eingespannt und unter Scherbelastung bei zwei verschiedenen Vorschubgeschwindigkeiten abgelöst wurden: einer Standardgeschwindigkeit von 1 mm/min und einer höheren von 200 mm/min. Dabei entsprach Letztere eher der tatsächlichen Kieferbewegungsgeschwindigkeit beim Kauen. Die Haftfestigkeiten (N) wurden mithilfe einer zweifaktoriellen Varianzanalyse (Vorschubgeschwindigkeit, Adhäsiv) (α = 0,05) analysiert. Die zunehmende Belastung führte zu einer Abnahme der Haftfestigkeit. Dies lässt sich möglicherweise auf das Auftreten einer Festkörperreaktion und die Elimination der viskoelastischen Eigenschaften des Komposits zurückführen. Die Ergebnisse deuteten auf einen ähnlichen Effekt sowohl bei den chemischhärtenden als auch bei den lichthärtenden Adhäsiven, was die Notwendigkeit einer Standardisierung der Testbedingungen in beiden Haftfestigkeitsprotokollen unterstreicht. Zur Beurteilung der langfristigen Überlebensrate des Haftverbundes müssen die während des Kauens auftretenden Kräfte berücksichtigt werden.

Intermaxillary forces during activator treatment

The mode of action of the activator appliance is still unclear. Apart from a possible mandibular growth enhancing effect, some investigators believe that orthopedic forces may be applied to the maxilla, contributing to Class II correction by inhibition of maxillary growth. In addition, orthodontic forces may arise that produce dentoalveolar changes. The purpose of this study was to measure the magnitude of anteroposterior intermaxillary forces during wear of the activator appliance. Ten consecutive patients with Class II dental and skeletal relationships were treated with a modified activator appliance. The appliance had maxillary and mandibular segments that could be detached from each other during the measuring session. A force transducer was placed at the anterior part of the maxillary segment, and the anteroposterior force exerted by the mandibular segment was measured. Measurements were taken in the upright and reclined position at every patient visit for a period of 6 months. Results indicated that intermaxillary forces were generally in the orthodontic range (median values of 100 gf at the upright position and 123 gf at the reclined position). A wide variation in force levels was noted, both between patients and for the same patient during the experimental period. No statistically significant change in force levels was observed during the 6 month period and no difference was noted between upright and reclined posture.

The postglenoid tubercle: prevalence and growth

AIM To quantify the prevalence and growth of the postglenoid tubercle in a skull sample and in children. MATERIAL a) ninety skulls ranging in age from between 2 years and adulthood, b) sixtyfour corrected lateral tomograms of left and right temporomandibular joints of 32 boys and girls. Their age range was between 9 and 11 years. METHOD Impressions of the temporal fossae of the skull material were taken with a silicone type impression material, using a face-bow for leveling the base of the impression parallel to the FH plane. Each impression was divided into two halves along a paramedian plane from the tip of the postglenoid tubercle through the middle of the articular eminence and the surface was photocopied to a 200% scale. Height was measured with an electronic caliper. The presence or absence of a postglenoid tubercle was established on the corrected tomograms. FINDINGS Seventy-nine percent of the skulls had a postglenoid tubercle. It steadily enlarged and reached almost its final dimension by the age of 13 years. On corrected tomograms, 66% of the children showed a postglenoid tubercle. CONCLUSIONS a) the postglenoid tubercle exists in a high percentage of human temporomandibular joints b) growth is almost completed by the age of 13, and c) there exists a right-left symmetry.