Maxillary constriction causes nasal septum deviation and deformity of the nasal floor

This study on growing rats demonstrates that transverse maxillary constriction induces nasal floor slanting and mandibular shifts, which subsequently cause nasal septal deviation, whereas maxillary expansion does not produce similar deformities.

The Gist

The Big Idea: A Tug-of-War in Your Face

Imagine your face is a house. The upper jaw (maxilla) is the foundation and the floor of the attic (the nose). The nasal septum is the central wall that divides the attic into two rooms (your nostrils).

For a long time, doctors knew that if the attic floor was crooked, the central wall might get pushed out of shape. But they weren't sure why the floor got crooked in the first place, or if fixing the floor could straighten the wall.

This study used baby rats to prove a surprising connection: If you squeeze the upper jaw from the sides, it doesn't just get narrower; it tilts. And when the floor tilts, the central wall (the septum) gets bent, causing a deviated septum.

---

The Experiment: The "Squeeze" and the "Stretch"

The researchers took 60 growing baby rats and put them into four groups:

1. The Squeeze Group: They put a tiny spring on the rats' teeth that pushed their upper jaw inward (constriction).
2. The Stretch Group: They put a spring that pulled the upper jaw outward (expansion).
3. The Fake Group: They put a spring on the teeth, but it wasn't tight enough to do anything.
4. The Control Group: They did nothing.

They waited 28 days (which is a long time for a growing rat) and then took 3D X-rays (micro-CT scans) of their skulls.

What Happened? (The Results)

1. The "Squeeze" Created a Slanted Floor

When the researchers squeezed the rats' upper jaws, two things happened:

• The Jaw Narrowed: The teeth and the bone got closer together.
• The Floor Tilted: The floor of the nose didn't just get smaller; it started to slope like a ramp. One side went up, and the other went down.

The Analogy: Imagine a trampoline. If you pull the edges of the trampoline inward from both sides, the fabric doesn't just shrink; it can get distorted and tilt if the tension isn't perfectly even. In the rats, the "floor" of the nose tilted because the jaw was being squeezed.

2. The "Wall" Followed the Floor

Because the floor of the nose tilted, the nasal septum (the central wall) had to follow. Since the bottom of the wall was sitting on a slanted floor, the wall itself bent into a "C" shape.

• Result: The rats in the "Squeeze" group developed a deviated septum.
• The "Stretch" Group: The rats whose jaws were pulled outward did not get a deviated septum. Their floors stayed flat.

3. The "Chin Shift" Made it Worse

Here is the clever part of the discovery. When the rats' upper jaws got squeezed, their lower jaws (chins) couldn't fit properly anymore. To bite down comfortably, the rats had to shift their chins to one side.

The Analogy: Think of a sliding glass door. If the top track gets pinched, the door gets stuck. To open it, you have to push the whole door frame to the side.

• When the rat shifted its chin to the side to bite, it created extra pressure on the nose floor.
• This extra pressure made the "floor tilt" even more severe.
• Key Finding: The direction the rat shifted its chin was always the same direction the nose floor tilted.

Why Does This Matter for Humans?

This study suggests that maxillary constriction (a narrow upper jaw) is a major, often overlooked cause of nasal septal deviation (a crooked nose wall).

• The Cycle of Doom:
  1. A child has a narrow upper jaw (maybe due to mouth breathing, allergies, or diet).
  2. The narrow jaw forces the jaw to shift sideways to bite.
  3. This shift tilts the floor of the nose.
  4. The tilted floor bends the septum.
  5. A bent septum blocks the nose, forcing the child to mouth-breathe more.
  6. Mouth breathing makes the upper jaw narrower, restarting the cycle.

The Takeaway: Fix the Foundation, Fix the Wall

The most exciting part of this paper is the solution. It suggests that instead of just cutting out the crooked wall (septal surgery), we should fix the foundation first.

If you use orthodontic tools (like expanders) to widen a child's upper jaw:

1. The jaw widens.
2. The jaw stops shifting sideways.
3. The "floor" of the nose levels out.
4. The "wall" (septum) straightens itself out naturally because it's no longer being pushed by a tilted floor.

In short: Don't just fix the crooked wall; fix the slanted floor underneath it. By widening the upper jaw early in life, we might be able to prevent or even cure a deviated septum without major surgery.

Technical Summary

1. Problem Statement

Nasal septal deviation (NSD) is a leading cause of nasal obstruction and mouth breathing, yet its developmental etiology remains unclear. While trauma and congenital factors are known contributors, they do not fully explain the high incidence of NSD.

• The Gap: Previous studies have suggested a correlation between maxillary transverse deficiency (constriction) and NSD, but direct causal evidence and the underlying biomechanical mechanisms were lacking.
• The Hypothesis: The authors propose that maxillary constriction induces mechanical forces that alter the growth of the nasal floor and vomer, subsequently forcing the nasal septum to deviate. This creates a reciprocal negative feedback loop where constriction worsens NSD, and NSD (via mouth breathing) further constricts the maxilla.

2. Methodology

The study utilized a controlled animal model to isolate the effects of transverse maxillary forces on craniofacial development.

• Subjects: 60 growing Wistar rats (21 days old, ~47g).
• Experimental Groups (n=15 each):
  1. Constriction Group: Received a calibrated spring applying 100cN of compressive transverse force to the maxillary molars.
  2. Expansion Group: Received a spring applying 100cN of tensile (expansion) transverse force.
  3. Sham Group: Received an inactive spring (no force).
  4. Control Group: No appliance.
• Duration: 28 days.
• Force Application: Springs were cemented to molars using composite resin. Force was verified at 100cN (50cN per side), a level known to stimulate suture activity without being excessive compared to normal masticatory forces.
• Data Acquisition:
  • Micro-CT (µCT): Scans were performed at 13.55µm voxel resolution.
  • Measurements:
    • Intra-oral: Palatal width, interdental width, molar angulation.
    • Extra-oral: Mandibular plane angle, anterior/posterior facial height, condylar width.
    • Nasal: Nasal floor slant angle, nasal septum deviation angle, vomer tilt, and nasal cavity width.
• Statistical Analysis: ANOVA with Tukey's post hoc test (p < 0.05 considered significant).

3. Key Results

A. Effects of Maxillary Constriction (Experimental Group 1)

• Dental/Skeletal Changes: Significant narrowing of the dental arch and palate. Molars uprighted (decreased angulation).
• Mandibular Response: The constriction forced a mandibular shift (mostly to the left) to find a comfortable occlusion, resulting in a posterior crossbite.
• Vertical Changes: The mandible underwent clockwise rotation, increasing the mandibular plane angle, anterior facial height, and overjet, while decreasing posterior facial height (creating a Class II skeletal appearance).
• Nasal Floor Deformity:
  • Slanting: A significant average slant of 26° in the nasal floor was observed, starting at the molar region and extending posteriorly.
  • Direction: The direction of the slant always matched the direction of the mandibular shift.
• Septal Deviation:
  • Deviation: A C-shaped nasal septum deviation with an average angle of 11° (p < 0.03 vs. Sham).
  • Vomer Tilt: The vomer bone (which houses the septum) tilted in the same direction as the nasal floor slant.
  • Asymmetry: The nasal cavity on the side opposite the deviation was significantly wider (16% difference).

B. Effects of Maxillary Expansion (Experimental Group 2)

• Expansion alone did not cause significant nasal floor slanting or septal deviation.
• However, if expansion caused a mandibular shift (to correct occlusion), mild-to-moderate nasal floor slanting occurred in the direction of the shift.
• Conclusion from Expansion: Mandibular shift alone can induce slanting, but maxillary constriction exacerbates the effect significantly.

4. Key Contributions & Mechanisms

The study identifies three distinct pathways by which maxillary constriction leads to NSD:

1. Growth Mismatch: Constriction reduces the available space for the growing nasal septum, causing it to bulge away from the midline.
2. Mechanical Moments (Bulging): Constricting forces applied to the molars create large moments that push the palatal shelves upward toward the nasal cavity, reducing space for the septum and causing bulging.
3. Occlusal Force & Cortical Drift (Slanting):
   • Constriction forces a mandibular shift to establish occlusion.
   • This shift creates asymmetric horizontal forces and moments on the maxilla.
   • These forces induce cortical drifting (resorption on one side, apposition on the other), causing the nasal floor to slant.
   • Since the nasal septum rests in the vomerine groove of the vomer bone, the slanting of the nasal floor/vomer mechanically forces the septum to deviate (C-shape).

5. Significance and Clinical Implications

• Causal Link Established: This is the first study to directly demonstrate that maxillary constriction causes nasal septal deviation and floor slanting in a growing model.
• Public Health Impact: With the rising incidence of maxillary constriction in humans (linked to diet, mouth breathing, and environmental factors), this study suggests that early orthopedic intervention is critical.
• Treatment Paradigm:
  • Early Intervention: Treating maxillary constriction in children/pre-pubertal individuals via expansion can prevent or correct NSD by restoring the nasal floor geometry.
  • Reciprocal Relationship: The study highlights a "negative feedback loop" where mouth breathing constricts the maxilla, which deviates the septum, worsening obstruction. Breaking this cycle early is essential.
• Diagnostic Shift: Clinicians should screen for maxillary constriction in patients with NSD and nasal obstruction, as the root cause may be skeletal rather than purely cartilaginous.

Conclusion

Maxillary constriction acts as a primary developmental driver for nasal septal deviation. The mechanism involves a combination of space restriction, upward bulging of the nasal floor due to mechanical moments, and, most critically, the slanting of the nasal floor caused by mandibular shifts and altered occlusal forces. Early diagnosis and orthopedic expansion of the maxilla are recommended to prevent permanent nasal deformities and associated airway obstructions.