Volume 9 I Number 6

Reviews and nbstrncls 517

their dentition-that is, the protruding teeth and everted lips. Evidently, this is also true for those races in whom this dentofacial pattern is predominant. The purpose of this study was an endeavor to settle the debate as to whether these persons can be treated to effect either a successful or stable result. The sample comprised 30 bimaxillary protrusion cases who had four premolars extracted; they were compared with 30 Class I mal- occlusion cases who likewise had similar extractions in treatment.

During treatment the interincisal angle was in- creased by 20” but relapsed by 4” posttreatment. The overbite appeared quite stable in both groups and stayed within normal limits throughout. The overjet was in- creased prior to treatment and, though it showed some reduction in treatment, it remained slightly high but was still within normal limits. Given the final interin- cisal angle, the overjet was normal. The author con- cludes that worthwhile treatment objectives can be achieved in these cases.

Alex Jacobson

ein Orthopadisches thodontisches Gerat?

e Experimentelle und Klinische Studie J. ~t~~~~~~~ and A. Petrovic Eortschr. Kieferorthop. 1986;47:254-80

The question raised is whether a Bionator is an orthopedic and/or orthodontic appliance. Earlier re- search by the investigators (1367) showed that it was possible to stimulate condylar growth in rats using dif- ferent types of “activators,” and minimize growth using chin-cups. Some investigators believe that Bionators move only the teeth, whereas others contend that con- dylar growth can be influenced during treatment.

Two different tests were conducted; one was de- signed to analyze the effect of the “Bionator” on the lengthening of the mandible in rats, the other to analyze the turnover rate of alveolar bone by organ culture in 1 I - to 13-year-old boys before and during treatment.

Twenty-day-old male rats were treated for 4 weeks (that is, during the prepubertal and pubertal periods) with a Bionator-type appliance. Whatever the variety of Bionator (either Balters Bionator with an edge-to- edge construction bite or the Bionator with a 1 mm forward construction bite), this appliance stimulates the growth rate of the condylar cartilage and causes more posterior growth of the condyle: this results in a sup- plementary lengthening of the mandible.

The Bionator “I mm forward” has a greater stim- ulating effect than the Balters Bionator.

When the rats were treated (inclndi~g ~rep~be~al, pubertal, and postpubertal periods), treatment with the Bionator produced an increase in growth, which caused the mandible to lengthen more than in untreated rats. The hypothesis stating that the length of the man- dible is genetically predetermined is thus once more refuted.

It is indeed the growth of the mandible that is influenced because no such effects were detected af- ter the growth was completed-that is: in the adult subject.

To determine the effect of the Bionator on tooth movement, the turnover rate of the alveolar bone of 1 I- to 13-year-old boys was analyzed by organ culture be- fore and during treatment. From this study it was shown that the Bionator induces only a mild increase in turn- over rate of alveolar bone mesially and distally in the region of the extracted teeth in cases exhibiting anterior growth rotation. On the other hand, there is sig~i~cant bone deposition on the distal side and significant re- sorption on the mesial side in cases of posterior growth rotations. These results can be interpreted as follows: (1) in the anterior “growth rotating” mandible, the Bio- nator acts primarily by inducing supplementary growth of the condylar cartilage and of the posterior border of the ramus with resultant lengthening of the lower jaw; (2) in the posterior “growth rotating” mandible, the biologic response of the condylar cartilage to the nator being weak, the appliance, by its construe provokes a mesially directed bodily movement or tip- ping movement.

So the Bionator appears to be not only an ortho- dontic appliance but also a functional appliance. The Bionator’s effectiveness depends primarily on supple- mentary lengthening of the mandible, which is greater in anterior than posterior “growth rotation” cases. These results are equivalent to Class II elastics, the Frlnkel appliance, and the LSU activator.

In a given growing individual (both the rat and the human), there is a parallelism among the alveolar bone turnover rate, the subperiosteal ossification rate, and the condylar cartilage growth and responsiveness rate. The variations in the growth direction of the con as well as the type of rotation, appear to be a conse- quence of mandibular tissue growth potential. Com- parative investigations relative to the human alveolar bone turnover rate and its o~hodo~t~cal~y induced vari- ations, to the ramus subperiosteal ossification rate, and to the clinical effectiveness of the Bionator clearly dem- onstrate that the biologic features of mandibular tissues are essential for the selection of the most a~pro~~at~ treatment of skeletal malrelations.

Alex Jacobson