Volume 9i Number 4

Reviews and abstracts

e patients reacted more or less distinctly to stress- ing. Some showed differences of angles and/or length of excursion. The results are discussed and it was found that gnathologic stressing limits the mandibular ex- cursions.

Alex Jacobson

Investigation of Bond ngths and Failure Locations Using

irect and Direct Bonding Techniques canard F. Vincent and Richard A. Hocevar Gainesville, Florida: University of Florida, 1986

Bond strengths and failure locations in direct and indirect bonding of orthodontic brackets with foil-mesh bonding pads were compared in an in vitro study using extracted human premolars. The direct technique com- prised bonding the attachments directly to the premolars with composite resin. The indirect technique comprised bonding the attachments to die-stone models of the teeth with composite resin, making silicone templates to transfer the attachments from the models to the teeth, and bonding to the teeth using two-part unfilled resin. One pa.rt of the unfilled resin was applied to the teeth and the other part to the composite resin that was already bonded to the attachments. Placing the templates on the teeth brought the two parts together to initiate setting.

Inspection after bonding disclosed marginal voids in two thirds of the indirect bonds. Of these, two thirds were then sealed with unfilled resin and one third were left defective.

There were no significant differences in strength among direct, void-free indirect, and sealed indirect bonds. Indirect bonds with voids were only half as strong.

Forty-four percent of the direct bonds fractured pre- dominantly at the bracket adhesive interface, whereas 72% of the indirect bonds failed mainly at the enamel- resin interface.

orphology Changes in Macaca

Farmington, Connecticut: Universily of Connecticut, 1986

The left mandibular canine of three Mucacafuscic- ularis monkeys was subjected to intrusion and root movement for 49 days. The contralateral tooth served

as a control. The force was calibrated to be within the clinical range for human root movement. Standa periapical radiographs were taken and viewed conven- tionally and with a subtraction technique.

The results of this study show that the force system used caused no apical root resorption as noted by blunt- ing or shortening of roots. However, surface root re- sorptions were noted at several sites on the roots of experimentally moved teeth. The resorption was limited to cementum in most areas but once it reached dentin, it tended to spread out. The changes observed histo- logically could not be conclusively correlated with the radiographic appearance because of the problems as- sociated with superimposition and the resolution of the radiographs.

Effects of Vasoactive lntestin and Nerve Growth Factor Osteosarcoma Ceils Monica Ann Fisher Farmington, Connecticut: University of Connecticut> 1986

Studies of limb regeneration have implicated the nervous system in the promotion of osteogenesis. The neurotrophic hypothesis states that neurons synthesize a substance called a neurotrophic factor, which is trans- ported to distant target organs or tissues.

The objective of this study was to investigate the direct neural involvement in osteogenesis. This study used in vitro cell culture techniques, focusing on two known neurotrophic substances-nerve growth factor (NGF) and vasoactive intestinal peptide (VIP). The ef- fect of these agents on the growth or ~he~otypic expres- sion of the permanent, clonal osteoblastic cell line, rat osteosarcoma (ROS 1712.8) cells, was assessed. Growth of the ROS X7/2.8 cells was determined by the cell number (measured by the coulter counter) and the osteobiastic differentiation was determined by the spe- cific biochemical assay of alkaline ~hosphatase (AP, a specific osteoblastic marker). The RGS 1712.8 cells were preincubated for 2 days in a culture medium con- sisting of modified Ham’s F- 12, 1% mycin sulfate, and 5% fetal bovine serum (FIB). ng the experi- mental period, the cells were maintained with Mam’s F-12, 2% PBS, 1% kanamycin, and the test agent. The

hypothesis was that the addition of VIP and NGF alters the AP-specific activity (Sp AC) or cell number of the ROS 17/2.8 cells.

NGF and VIP had the following direct effects c)n osteoblastic growth and differentiation:

1. VIP increased the Ap Sp AC and cell dumber when measured 60 hours following the initial addition of five doses of 0.165 p,glml at 12hour

Reviews and abstracts Am. J. Qrzhod. Dentofac. Orthop. April :9X7

intervals. This condition decreased the protein content. VIP had a similar effect when added in a single dose of 0.825 pg/ml.

2. VIP increased the AP Sp AC and cell number, and decreased the protein content when mea- sured 70 hours following the addition of a single dose (0.50 p,g/ml and 1.0 kg/ml).

3. GF inhibited the AP Sp AC and increased the cell number and protein content when measured 60 hours following the addition of a single dose (0.025 p,g/ml).

4. The phosphodiesterase inhibitor, isobutylmeth- ylxanthine (IBMX), either alone or in combi- nation with other agents, decreased AP Sp AC.

5. The effect of VIP in increasing AP Sp AC was more pronounced in the presence of IBMX and NGF.

These results are consistent with the hypothesis that the osteoblast responds directly to the neurotrophic sub- stances VIP and NGF.

Control of Vertical Dimension During cl Palatal Expansion Using a

Farmington, Connecticut: University of Connecticut, 1986

The effects of rapid palatal expansion upon vertical dimension were examined in 12 consecutively treated patients. Six patients had specific contraindications to increasing vertical dimension. These patients were treated with high-pull chin cup therapy during expan- sion and for 7 weeks postexpansion. Cephalometric analyses of preexpansion and postexpansion lateral head films were performed for each patient. Study mod- e1.s of each patient were analyzed before and after ex- pansion to determine any changes in buccolingual crown inclinations of the maxillary first molars.

Cranial base and separate maxillary superimposi- tions indicated increased extrusion of maxillary molars in patients receiving rapid palatal expansion without high-pull chin cup therapy. Analysis of study models indicated that patients expanded without chin cup ther-

y also experienced greater buccolingual tipping of maxillary first molars than patients wearing chin

cups during expansion. The results of this study led to the following conclusions.

1. Application of an extraoral force in the form of a high-pull chin cup results in a decrease in the extrusion and tipping of maxillary posterior teeth that occurs dur- ing rapid palatal expansion.

2. In addition to rigid appliance construction and ideal appliance placement, high-pull chin cup therapy can be used to minimize side effects of rapid palatal expansion that typically result in an increase in vertical dimension.

Mandibular Growth Durin Anterior Displacement i Ado!escent Monkeys Fred 0. Ziegler Farmington, Connecticut: University oj’ Connecticut, 1986

The effects on mandibular growth caused by dis- placing the mandible anteriorly during closure, as with a functional appliance, remain controversial. The pur- pose of this study was to evaluate changes in ma~dibul~ size and shape during use of a fixed func~iQ~a1 a~pli~ce in an animal model system.

Six adolescent Macaca ~ascicularis monkeys had metallic bite planes bonded to all first ~e~a~e~t molars and were observed over a 4-month period. Six age- matched animals served as controls. After placement of tantalum implants in the cra~iofacial region of all animals, serial cephalometric radiographs were taken at 28-day intervals. Angular and linear mea§nrements between landmarks were recorded and statistically analyzed.

Study animals showed a significantly increased mandibular length measurement (P < 0.001) over con- trol animals, which was mostly an increase in ramal length, after the first month of appliance wear. The vector of condylar growth in experimental animals be- came more vertical than that of unseated animals: the end of the observation period, animals wearing appliances nearly controls. These results suggest that anterior reposition- ing of the mandible may cause changes in rate and direction of mandibular growth.