Stepwise advancement using fixed functional appliances: Experimental perspective

Comparison of stepwise vs single-step advancement with the Functional Mandibular Advancer in Class II division 1 treatment

“…12,16 In particular, rat studies revealed that the amount of initial advancement is important. 9,23 Rabie and AlKalaly 23 demonstrated that a 4-mm advancement resulted in a significantly greater increase in type II collagen (the major component of condylar cartilage) and in total amount of new bone formation on the condyle compared with a 2-mm advancement group. The investigators stressed that a minimal threshold of strain must be exceeded to promote an ideal response.…”

“…The investigators stressed that a minimal threshold of strain must be exceeded to promote an ideal response. 9,23 Thus, the authors of the current study preferred an initial advancement of 4 mm, which could subject the condylar tissue to greater mechanical strain. Subsequent advancements were set at 2 mm every 2 months to repeatedly maximize the number of replicating cells in the condyle and glenoid fossa.…”

“…The experimental study of Rabie et al 9 demonstrated that bone formation at the condyle and glenoid fossa that reached the highest level during the first 30-day period with maximum ''jumping'' returned to the amount attained during natural growth from then on, while there was significantly more bone formation with stepwise advancement than with maximum jumping in the second 30-day period. Also, from the clinical standpoint, it has been stated that stepwise advancement could result in an increase of mandibular growth, less protrusion of the mandibular incisors, and better patient compliance.…”

“…Hence, in an effort to increase the orthopedic impact, attention has been drawn to the timing of treatment, 1,2 type of functional appliance, 2,3 rigidity of the fixed functional appliance, [4][5][6] and mode of mandibular advancement during treatment (single or gradual activation). [7][8][9] The consensus is that condylar growth can be stimulated efficiently if the functional treatment is performed during the adolescent growth spurt using rigid functional appliances. However, it is debatable whether the mode of mandibular advancement affects the amount of growth and position of the mandible.…”

Stepwise Advancement Herbst Appliance versus Mandibular Sagittal Split Osteotomy

“…8 Experiments that compared step-by-step and maximum jumping procedures in rats showed that stepwise advancement resulted in 100% and 50% more bone formation in the glenoid fossa and condyle, respectively. 20 Furthermore, a clinical study that compared stepwise and single-step advancement with the Herbst appliance in adult patients showed that the amount of correction resulting from skeletal changes was greater in the stepwise group. 10 The study in rats also showed that duration of advancement is a critical factor in the maturation of newly formed bone and in the stability of results.…”