Continuous forces are more effective than intermittent forces in expanding sutures

Abstract

While both intermittent and continuous forces are commonly used to expand sutures, it remains unclear which force is most effective. Using nickel-titanium (NiTi) open coil springs (50 g) and 3 mm long miniscrew implants (MSIs) for skeletal anchorage, intermittent and continuous forces were used to expand the midsagittal sutures in 18 New Zealand white juvenile male rabbits, 11 weeks of age, for 29 days. In the intermittent group, expansion forces of 50 g were delivered for 5 days (on) and paused for 1 day (off); the on/off cycles were repeated five times. Expansion forces of 50 g were delivered for 29 consecutive days in the continuous group. Longitudinal biometric and histomorphometric analyses were performed to evaluate sutural separation and bone formation using implanted tantalum bone markers and fluorescent bone labelling, respectively. Multilevel modelling procedures were undertaken to compare the groups and time intervals. Continuous forces produced significantly greater overall sutural separation (1.3 mm) than intermittent forces (0.8 mm). Although they were delivered over a period of time 86 per cent as long, intermittent forces produced only 61 per cent of the sutural separation of continuous forces. Between days 7 and 17, continuous forces resulted in significantly greater mineral apposition and bone formation rates than intermittent forces. Intermittent forces produced approximately 59 per cent as much mineral apposition and 61 per cent as much bone formation as continuous forces. Due to greater sutural separation and bone formation, continuous forces provide a more effective approach for separating sutures than intermittent forces.

Recombinant human bone morphogenetic protein-2 stimulates bone formation during interfrontal suture expansion in rabbits

“…After flap closure by 4-0 Vicryl sutures (Ethicon Inc, Somerville, NJ), the suture was expanded using 200 g of constant force applied by a nickel-titanium open-coil spring similar to the procedures in previous studies. 11,12 Penicillin (27216 IU/kg, intramuscularly) and buprenorphine (0.02 mg/kg, subcutaneously, as needed) were given immediately after surgery.…”

“…An increase in sutural width over time with 100 g indicates that the maximum rate of bone formation is slower that the maximum expansion rate. 11 Beyond this limit (100 g of continuous expansion force), greater amounts of force did not increase the bone formation rate, but only increased the sutural gap and subsequent relapse potential. 3 Therefore, an "ideal" mechanical force exists to expand the suture and generate maximal bone formation in a given circumstance.…”

“…Two possible mechanisms were proposed to control and enhance sutural bone formation. One was to apply an "ideal" mechanical force to expand the suture 3,11 ; the other was to use pharmaceutical agents to accelerate the bone formation rate during expansion. 12 Using miniscrew implants and controllable force in an animal model, 50 g of continuous force was shown to be more effective in generating sutural bone formation than the same magnitude of intermittent force.…”

“…12 Using miniscrew implants and controllable force in an animal model, 50 g of continuous force was shown to be more effective in generating sutural bone formation than the same magnitude of intermittent force. 11 The amount of bone formation was proportional to the magnitude of continuous expansion force and its consequent distance of suture expansion. However, the bone formation rate plateaued after exceeding a certain force limit (bone formation rate of 50 g \100 g 5 200 g).…”

Effects of Platelet-Rich Plasma and Recombinant Human Bone Morphogenetic Protein-2 on Suture Distraction Osteogenesis

“…In our previous study, we established a suture distraction osteogenesis model by rabbits. 12 The rabbit cranium is a membranous bone of a broadly similar thickness to pediatric bone, and it has many similarities to the human suture structure. Springs have been clearly demonstrated to have similar effects in expanding the cranial and maxillofacial bones of both rabbits and humans.…”