Sutural loading in bone- versus dental-borne rapid palatal expansion: An ex vivo study.

OBJECTIVES: To measure and compare the success rate and strains generated during bone- (BRPE) and dental-borne rapid palatal expansion (DRPE) at the alveolar bone, zygomaticomaxillary (ZMS) and internasal (INS) sutures. Additionally, the magnitude and the pattern of midpalatal suture (MPS) separation in the 2 groups was assessed. SETTING AND SAMPLE POPULATION: The study was performed ex vivo using 28 pig heads. MATERIALS AND METHODS: Heads were dissected, and the MPS, ZMS, INS and the alveolar bone were exposed. A differential-variable-reluctance-transducer (DVRT) was installed across the MPS, and single-element strain gauges were installed at the remaining sites. Expanders were placed and activated at one turn per minute for 30 turns. Strains at the alveolar bone and the sutures and the separation of the MPS were measured. RESULTS: Successful expansion of the MPS was achieved in 69% of the BRPE subjects compared to 27% in the DRPE group. The average separation of the MPS was higher (230 ± 109 µm per turn vs. 79 ± 61 µm) and the MPS opening happened at an earlier stage of expansion in the BRPE. Higher strains at the ZMS were seen in the BRPE group, while higher strain at the alveolar bone was found in the DRPE group. CONCLUSIONS: The BRPE group demonstrated more successful and effective expansion of the MPS. Higher strain was found at the alveolar bone in the DRPE. A tendency for higher strain at the ZMS was noticed in the BRPE.

Deformation of the zygomaticomaxillary and nasofrontal sutures during bone-anchored maxillary protraction and reverse-pull headgear treatments: An ex-vivo study.

INTRODUCTION: Bone-anchored maxillary protraction (BAMP) is an emerging treatment that involves applying a protraction load to the maxillary bone. Although it is believed that such an approach results in better sutural separation, this has not been investigated. This study aimed to assess and compare the deformation of 1 circumaxillary suture (zygomaticomaxillary suture [ZMS]) and 1 facial suture (nasofrontal suture [NFS]) during BAMP and reverse-pull headgear (RPHG) treatment. METHODS: The study was performed ex vivo on 15 pig heads. Miniplates were placed in the maxillary bone and the body of the mandible. A molar tube was bonded to the maxillary first molars. Six single-element strain gauges and 3 differential variable reluctance transducers were installed across the ZMS and NFS bilaterally. Each head underwent BAMP and RPHG unilaterally and bilaterally. RESULTS: In unilateral experiments, both BAMP and RPHG resulted in tension on the ipsilateral ZMS and NFS and compression on the contralateral side, with higher magnitude in the BAMP group. In bilateral experiments, both modalities resulted in tension at the ZMS, with higher magnitude in the BAMP group. Deformation of the NFS was different between the 2 groups: tension in majority of the BAMP and compression in most of the RPHG heads. CONCLUSIONS: Our study shows a higher magnitude of sutural separation in BAMP than in RPHG. The pattern of sutural deformation is consistent with a forward displacement of the midface in BAMP compared with an upward and backward rotation in the RPHG. Rotation of the maxilla was also present in some of the subjects who underwent BAMP.

Cellular proliferation in the nasal septal cartilage of juvenile minipigs.

The growth of the nasal septal cartilage is believed to be a driving force of midfacial growth. Cellular proliferation is an important contributor to growth of the cartilage, but this factor has been rarely investigated. The current study was undertaken to assess the proliferation and cellular density in the septal cartilage of fast-growing juvenile minipigs. Six minipigs averaging 4.4 ±â€…1 months old were injected with 5'-bromo-2'-deoxyuridine (BrdU), a thymidine analog, 24 h before death. The septal cartilage was sectioned in the coronal plane and reacted for BrdU. The proliferative index (number of BrdU-positive chondrocytes/total number of chondrocytes) and cellular density (number of cells mm(-2) ) of various locations of the septum were measured and compared in order to determine overall proliferation rate and whether regional variations in proliferative activity and cellular density are present. To provide a time perspective to the problem of midfacial growth, the lengths of the nasal bone and the palate were measured in a collection of 61 dry skulls of minipigs aged 1-8 months. Results showed that the septal chondrocytes were proliferating at a surprisingly high rate (~21%). The proliferative index was higher in the ventral and middle compared with the dorsal locations, and in the central cartilage compared with the perichondrium. No difference in proliferative index was found between the anterior and posterior parts of the septum. Cellular density was higher in the perichondrium than in the central cartilage. Within the central cartilage there was a trend for higher cellular density anteriorly. In conclusion, the rapidly growing midface of juvenile minipigs is associated with a high rate of septal proliferation, especially in the ventral half of the cartilage.

Compressive and tensile mechanical properties of the porcine nasal septum.

The expanding nasal septal cartilage is believed to create a force that powers midfacial growth. In addition, the nasal septum is postulated to act as a mechanical strut that prevents the structural collapse of the face under masticatory loads. Both roles imply that the septum is subject to complex biomechanical loads during growth and mastication. The purpose of this study was to measure the mechanical properties of the nasal septum to determine (1) whether the cartilage is mechanically capable of playing an active role in midfacial growth and in maintaining facial structural integrity and (2) if regional variation in mechanical properties is present that could support any of the postulated loading regimens. Porcine septal samples were loaded along the horizontal or vertical axes in compression and tension, using different loading rates that approximate the in vivo situation. Samples were loaded in random order to predefined strain points (2-10%) and strain was held for 30 or 120 seconds while relaxation stress was measured. Subsequently, samples were loaded until failure. Stiffness, relaxation stress and ultimate stress and strain were recorded. Results showed that the septum was stiffer, stronger and displayed a greater drop in relaxation stress in compression compared to tension. Under compression, the septum displayed non-linear behavior with greater stiffness and stress relaxation under faster loading rates and higher strain levels. Under tension, stiffness was not affected by strain level. Although regional variation was present, it did not strongly support any of the suggested loading patterns. Overall, results suggest that the septum might be mechanically capable of playing an active role in midfacial growth as evidenced by increased compressive residual stress with decreased loading rates. However, the low stiffness of the septum compared to surrounding bone does not support a strut role. The relatively low stiffness combined with high stress relaxation under fast loading rates suggests that the nasal septum is a stress dampener, helping to absorb and dissipate loads generated during mastication.

Real-time monitoring of the growth of the nasal septal cartilage and the nasofrontal suture.

INTRODUCTION: The nasal septum is thought to be a primary growth cartilage for the midface and, as such, has been implicated in syndromes involving midfacial hypoplasia. However, this internal structure is difficult to study directly. The aims of this study were to provide direct, continuous measurements of the growth of the nasal septal cartilage and to compare these with similar measurements of the nasofrontal suture to test whether the growth of the cartilage precedes the growth of the suture and whether the growth of the septal cartilage is constant or episodic. METHODS: Ten Hanford minipigs were used. Linear displacement transducers were implanted surgically in the septal cartilage and across the nasofrontal suture. Length measurements of the cartilage and suture were recorded telemetrically each minute for several days. RESULTS: The growth rate of the nasal septal cartilage (0.07% ± 0.03% length/h) was significantly higher than that of the suture (0.03% ± 0.02% length/h) (P = 0.004). The growth of both structures was episodic with alternating periods of growth (5-6 per day) and periods of stasis or shrinkage. No diurnal variation in growth of the cartilage was detected. CONCLUSIONS: These results are consistent with the notion that growth of the septal cartilage might drive growth of the nasofrontal suture. Growth of the midface is episodic rather than constant.

Deformation of nasal septal cartilage during mastication.

The cartilaginous nasal septum plays a major role in structural integrity and growth of the face, but its internal location has made physiologic study difficult. By surgically implanting transducers in 10 miniature pigs (Sus scrofa), we recorded in vivo strains generated in the nasal septum during mastication and masseter stimulation. The goals were (1) to determine whether the cartilage should be considered as a vertical strut supporting the nasal cavity and preventing its collapse, or as a damper of stresses generated during mastication and (2) to shed light on the overall pattern of snout deformation during mastication. Strains were recorded simultaneously at the septo-ethmoid junction and nasofrontal suture during mastication. A third location in the anterior part of the cartilage was added during masseter stimulation and manipulation. Contraction of jaw closing muscles during mastication was accompanied by anteroposterior compressive strains (around -1,000 muepsilon) in the septo-ethmoid junction. Both the orientation and the magnitude of the strain suggest that the septum does not act as a vertical strut but may act in absorbing loads generated during mastication. The results from masseter stimulation and manipulation further suggest that the masticatory strain pattern arises from a combination of dorsal bending and/or shearing and anteroposterior compression of the snout.