Stomatal density and responsiveness of banana fruit stomates

Determination of stomatal densities of the banana peel (Musa acuminata L. var Hort. Valery) by microscopic observations showed 30 times fewer stomates on fruit epidermis than found on the banana leaf. Observations also showed that peel stomates were not laid down in a linear pattern as on the leaf.It was demonstrated that stomatal responses occurred in banana fruit. Specific conditions of high humidity and light were necessary for stomatal opening: low humidity and darkness were necessary for closure. Responsiveness of the stomates continued for a considerable length of time after the fruit had been severed from the host.

A study of maximum bite force during growth and development

Bilateral bite force was measured in a sample of 457 subjects (231 males and 226 females) from 6 years through 20 years. The mean maximum bite force was found to increase from 78 Newtons at 6 to 8 years to 176 Newtons at 18 to 20 years. While earlier studies have shown adult males have a greater mean bite force than females, this difference is not evident during growth and development. Gender-related bite force difference likely develops during the postpubertal period in association with greater muscle mass development in males.

A study of bite force, part 2: Relationship to various cephalometric measurements

Maximum bilateral bite force, determined in 129 dental students, was evaluated with regard to six skeletal and eight dental measurements acquired from conventional lateral cephalometric radiographs. Statistically significant correlations for three of the skeletal measurements were found. Maximum bite force increased with regard to decreasing mandibular plane/palatal plane angle and to decreasing mandibular plane angles. Maximum bite force increased with an increasing ratio of posterior facial height to anterior facial height. Significant statistical correlation for only one of the eight dental measurements was found: maximum bite force related directly with increasing maxillary and/or mandibular dentoalveolar heights, and unexpected finding.

A study of bite force, part 1: Relationship to various physical characteristics

A new device for measuring and recording bilateral bite force in the molar/premolar region has been developed. Because this new device is elastic and conforms to the occlusal surfaces of the teeth, and because the sensing element is relatively comfortable, it is believed that experimental subjects are less reluctant to register true maximal forces than in earlier studies. Potential correlations of maximum bite force to gender, age, weight, body type, stature, previous history of orthodontic treatment, presence of TMJ symptoms (jaw motion limitation, clicking with pain, or joint pain), or missing teeth were studied in a sample of 142 dental students. The mean maximum bite force of the sample was found to be 738 N, with a standard deviation of 209 N. The mean maximum bite force as related to gender was found to be statistically significant, while the correlation coefficients for age, weight, stature, and body type were found to be low. Even so, all data scatterplots exhibited relatively positive relationships. Correlations of maximum bite force to an earlier history of orthodontic treatment or to the absence of teeth were not found. Subjects reporting TMJ symptoms did not exhibit a significantly different maximum bite force than subjects without symptoms.

Force generation by orthodontic coil springs

Nickel titanium (NiTi) coil springs are a new development in orthodontics, designed to produce light continuous forces. This study compares the force delivery by NiTi open and closed coil springs during unloading (de-activation) to that provided by comparable stainless steel (SS) springs. Open-coil springs (0.010 x 0.035 inch) were compressed from their initial length of 15 mm to 6 mm and the forces generated with spring recovery recorded. Closed-coil springs (0.009 x 0.035 inch) were distracted from their initial length of 3 mm to 9 mm and the force recorded as the spring recovered. The closed-coil NiTi springs produced light continuous forces of 75-90 g over the distraction range of 6 mm while the open-coil springs produced forces of 55-70 g within the 9 mm compression range. SS springs produced heavier forces, ca. 200 g, for an activation of 1 mm and the generated force increased rapidly as the activation was increased. The findings indicate that NiTi coil springs deliver optimal forces for orthodontic tooth movement over a longer activation range than comparable SS springs.

An analytical evaluation of a new spring design for segmented space closure

Contemporary segmented-arch space-closure springs require activation techniques that have the side effect of producing a significant amount of geometric nonlinearity. This nonlinearity makes these springs difficult to manipulate because it allows tipping during space closure which may be considered adverse. A new spring mechanism has been designed in response to these difficulties so that the advantages of the segmented-arch technique can be extended to those clinicians presently using simple sliding mechanics as a means of space closure. This spring mechanism has eliminated a significant portion of the geometric nonlinearity by using force-application devices (activators) such as elastics or coil springs as the means of activation. By selecting the right activator it may be possible to close an entire extraction site (approx. 7 mm) with one activation. The proposed mechanism essentially consists of two units: an anchorage unit (M/F = 18 mm), and a translational unit (M/F = 11 mm). These units are combined in order to achieve anterior retraction, posterior protraction, or a combination of the two, which is termed reciprocal-attraction. The finite-element method was used in place of bench studies to test the new spring design. The commonly used reciprocal-attraction spring tested with a nearly constant M/F ratio equal to 11 +/- 1 mm over an effective force range of 50 gm to 450 gm. The results from the other two tests also showed that precisely controlled couple-to-force (M/F) ratios can be maintained over a wide range of effective forces.