Sutural deformation during bone-anchored maxillary protraction

Abstract

Introduction: Bone-anchored maxillary protraction (BAMP) is an emerging treatment option for orthopedic correction of maxillary deficiency in young patients. Compared to reverse pull headgear (RPHG), it is believed that forces generated during BAMP result in greater circum-maxillary sutural separation, mandibular retrusion, and improved maxillary protraction. Mechanical loading of the circum-maxillary sutures during BAMP is still poorly understood.

Methods: 20 ex-vivo pig heads were used. Miniplates and molar tubes were installed like clinical procedures. A series of five 200 ​g-force (gf) elastics were applied on the right and left side until 1000gf were reached. Strain gauges were installed across the zygomatico-maxillary (ZMS), zygomatico-temporal (ZTS), and nasofrontal suture (NFS). Differential variable reluctance transducers (DVRTs) were installed across the ZTS. Deformation of the sutures during BAMP and RPHG was measured and compared.

Results: Higher average sutural deformation of the ZTS and ZMS was seen in BAMP than RPHG: 36.6 ​± ​20.6με vs 18.0 ​± ​12.4με and 54.7 ​± ​28.5με vs 12.5 ​± ​14.8με, respectively. Similarly, higher NFS deformation was seen in BAMP (18.4 ​± ​12.9με vs. -0.8 ​± ​12.0με). DVRT data showed higher ZTS separation in BAMP than RPHG (6.3 ​± ​5.2 ​μm vs. 1.7 ​± ​2.1 ​μm). These differences were all statistically significant using the Wilcoxon-signed rank test.

Conclusion: Both RPHG and BAMP forces separate the ZTS and ZMS. BAMP resulted in higher levels of sutural separation at the ZTS and ZMS by 2- and 5-fold, respectively.

Keywords: Bone-anchored maxillary protraction; Class III; Maxillary deficiency; Maxillary protraction; Reverse-pull headgear.

Fig. 1

A: (Above) DVRT is comprised of a rod and a core. The attachment screws are placed in bones across the suture. When the suture is deformed, the rod will slide in and out of the core. The sliding movement will result in change of the core differential reluctance, enabling the calculation of the core movement at a high resolution of ±1 ​μm. (Below) Single-element strain gauge. Suture deformation causes flexing of the foil.This change is read by pre-calibrated software and the amount of deformation is calculated. B: Schematic image displaying location of strain gauges and DVRTs installed. Strain gauges were installed spanning the ZMS, ZTS, and NFS. DVRT was installed spanning the ZTS.

Fig. 2

Deformation observed at the ZTS (above) and ZMS (below) per each 200 ​g of protraction force from 200gf to 1000gf, along with the average deformation observed at each location.