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Whitepaper - 2026 / Autumn

Maxillary expansion: what actually widens the maxilla?

The maxilla is built by force. We pulled 19 animal, suture and clinical studies to see which forces widen the palate: chewing, breathing, feeding, or a screw.

Wider sutures under pulsed load
+36%
Adult sutures that still split
92.5%
Odds of a bad bite if breastfed
0.34×
Model face with a narrow upper archNarrow tapered arch
Narrow maxilla
Model face with a wide upper archWide rounded arch
Wide maxilla
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Context

Bone follows load.

The upper jaw is two bones, the left and right maxilla, joined down the roof of the mouth by the midpalatal suture. That roof is also the floor of the nose. A narrow maxilla means a tighter arch, crowded teeth and a smaller nasal floor. Why it ends up narrow is in narrow maxilla vs wide maxilla, and a set-back one is in recessed maxilla vs forward maxilla.

A suture is not dead glue. It is a living joint full of stem cells that read force. Under tension, suture stem cells switch from a cartilage path onto a bone path [4], and distraction force makes Gli1⁺ cells in the facial sutures multiply and turn toward bone [10]. In adult mice, stretching a suture that had already closed still made its stem cells multiply [1].

So the real question is not whether the maxilla can widen. It is which forces it listens to, and which of those you control every day.

The question

Daily load or a screw?

Two kinds of force reach the palate. Daily load comes from your own body: the chewing muscles pulling on the bones they attach to, the tongue resting against the palate, air moving through the nose. Applied force comes from outside: a screw across the palate, or hands pressing on it.

Both act on the same seam. The difference is what carries the force in, and what it costs on the way.

Wide arch shaped by chewing, tongue and nasal breathing

Daily load (chewing, tongue, nose)

Expander screw banded to the teeth

Applied force (expander screw)

Same suture. One is loaded by muscle every day, the other by a screw through the teeth.

What we did

Two kinds of evidence, one suture.

We went through PubMed for studies that changed or measured a force on the growing face, or put force into a suture and measured what grew. That gave two groups. Cohort A changed a daily load: diet hardness, nasal breathing, feeding. Cohort B applied force directly, from rabbit and mouse loading experiments to clinical expanders.

Every number on this page is taken from the paper and linked below. Nothing is estimated or modelled. Animal results are labelled as animal results.

Cohort A · Daily loads
Allanimals changed face and bite
Harvold 1981Nose blocked in primates
8animals, 8 months
Ciochon 1997Hard vs soft diet, minipigs
Rats+ human ultrasound
Katsaros 2001Soft diet in rats, masseter in humans
18studies pooled
Zheng 2020Mouth vs nose breathers
27,023people, 41 studies
Peres 2015Breastfeeding and bite
Worldpopulation review
Corruccini 1984Bite across world populations
Cohort B · Applied force
12days, 10 min a day
Kopher 2003Static vs cyclic 5 N, rabbits
Micestem cell tracing
Jin 2024Distraction force, Gli1⁺ suture cells
Adultmice
Aldawood 2023Expanding a closed adult suture
8studies pooled
Kapetanović 2021Bone-anchored expansion, age 16+
314children, 17 studies
Camacho 2017Expansion and child sleep apnoea
8girls, 11–14
Garib 2006Tooth-anchored expanders on CT

Cohort A shows what daily life does to a growing maxilla. Cohort B shows how a suture answers when force goes straight into it, at any age, and what happens when that force is pushed through the teeth. One question runs through both:

The question

If force builds the maxilla, which forces does it actually listen to?

When it listens

Easiest young, never fully off.

The seam changes shape with age. Angelieri's group scanned 140 people and sorted it into five stages [2]. A straight or wavy line (A, B) showed up to about 13. Two parallel wavy lines (C) ran mostly from 11 to 17. Fusion at the back of the palate (D), then the front (E), appeared after 11. Persson and Thilander, looking at sutures from 15 to 35, found closure varies a lot between people [18].

Figure 1

The suture interlocks with age

Angelieri's five CBCT stages of the midpalatal suture, 140 people aged 5.6 to 58.4. Bars span the ages each stage was mostly seen at.

  • Stage A
    Straight line    5.6–13
  • Stage B
    Scalloped line    5.6–13
  • Stage C
    Two parallel lines    11–17
  • Stage D
    Palatine fused    11–58
  • Stage E
    Maxilla fused    11–58

Age (years)

Seam openFused
A to C are an open seam. D and E are fused at the back, then the front.

That is why growth is the window. Daily loads during childhood shape the arch with the least resistance. But an adult suture is not switched off. When force is put straight into the palate bone of people 16 and over, the seam opened in 92.5% of cases [11], and in 60 of 69 young adults in Choi's series [5].

Figure 2

Adult sutures still answer to force

Share of adults whose midpalatal suture opened when force was put straight into the palate bone.

  • Pooled review8 studies, age 16+92.5%
  • Choi 201669 young adults86.96%

Adults whose suture split under force

Pooled range shown as the thin line: 88.7 to 96.3%.

What we found

The suture wants rhythm, not a squeeze.

Pulsed load beats a still hold

The cleanest experiment is Kopher and Mao's. They put the same 5 N peak on the maxilla of growing rabbits for 10 minutes a day over 12 days, either as a still hold or pulsed at 1 Hz. The pulsed load widened the squeezed suture to 95.1 µm against 69.8 with no load, and the stretched one to 267.4 µm against 196.0. Both are 36% more. The still hold at the same peak did not beat no load at all (58.9 and 169.9) [13].

Pulsed 1 N loading at 8 Hz did the same in a second study, under both tension and compression [16], and Mao's review puts the effective dose as low as 600 cycles a day [14].

Chewing is a pulsed load. Every bite loads and releases the bones the chewing muscles attach to.

Figure 3

Rhythm beats a hold

Kopher and Mao put the same 5 N peak on the maxilla of growing rabbits for 10 minutes a day, either held still or pulsed at 1 Hz.

  • Pulsed (1 Hz)Premaxillomaxillary suture95.1
  • No loadsham69.8
  • Held stillstatic58.9

Suture width after 12 days (µm)

Pulsed load widened both sutures 36% over sham. The held load did not.

Soft food narrows the arch

Take that load away and the arch narrows. Rats raised on soft food grew less across the maxilla and the dental arch, with less bone laid down in the facial sutures, and in humans thicker masseters went with broader upper arches [12]. Minipigs on soft food with the same nutrients, with genetics and breathing controlled, ended up with markedly narrower arches, more crowding and a deep masseter 25% smaller than littermates on hard food [6].

Across world populations, bad bites rise as diets industrialise, at a speed that tracks how fast the change happens [7].

Breathing and feeding

Breathing and feeding leave the same kind of mark. Block a primate's nose and every animal ends up with a different face and bite [9]. In 18 studies of kids, mouth breathers had an SNA 1.33° lower than nose breathers, a maxilla sitting further back [19]; the full picture is in mouth breathing face.

Across 41 studies and 27,023 people, those ever breastfed had about a third of the odds of a bad bite [17].

Figure 4

Daily loads leave a mark

Two meta-analyses of growing faces: how the maxilla sits in mouth breathers, and how often breastfed children end up with a bad bite.

  • Mouth breathers18 studies, kids-1.33°
  • Nose breathersreference0°

Difference in SNA, mouth vs nose breathers

Square = pooled result. Line = 95% confidence interval.

What expanders show in adults

Applied force shows how far the adult seam can still go, and where the force leaks. With an expander anchored in the palate bone, adult bone width rose 2.33 mm while the molars moved 6.55 mm [11]. In Choi's young adults, bone was 1.92 of 4.43 mm, 43%, and it held through retention [5]. The rest of the width is teeth tipping out.

Figure 5

Bone versus teeth

Adults on a bone-anchored expander: width gained at the maxillary base (bone) against width across the first molars (teeth).

  • Pooled reviewadults2.33 / 6.55
  • Choi 2016young adults1.92 / 4.43

Width gained (mm)

TeethBone
The teeth travel further than the bone. The difference is tipping.

A wider palate, a wider airway

Widening the palate widens the nasal floor, and that shows up in sleep. In 17 studies of children with narrow, high palates and sleep apnoea, breathing events fell from 8.9 to 2.7 an hour, a 70% drop, and lowest overnight oxygen rose from 87% to 96%. The 52 kids followed past three years went from 7.1 to 1.5 [3].

Figure 6

A wider floor, a wider nose

Camacho's meta-analysis of 17 studies in children with narrow, high palates and sleep apnoea, before and after widening.

  • Up to 3 years after314 patients−70%
  • More than 3 years after52 patients−79%

Breathing events per hour of sleep

BeforeAfter
Small or removed tonsils: 73–95% drop. Large tonsils: 61%.

The cost of pushing through teeth

Pushing through the teeth has a price. With tooth-anchored expanders in girls aged 11 to 14, the outer bone wall over the anchor teeth thinned 0.6 to 0.9 mm, and roots were left exposed by 7.1 mm at the first premolars and 3.8 mm at the first molars, worst where the bone started thin [8]. Even bone-anchored expanders in adults tipped teeth and thinned outer bone [11]. Daily loads go in through muscle and bone, not through the roots.

Figure 7

Force through teeth costs bone

Garib's CT study of tooth-anchored expanders in girls aged 11 to 14, screw opened its full 7 mm.

  • Outer bone wallthinner-0.9 to -0.6
  • Inner bone wallthicker+0.8 to +1.3

Change in bone wall thickness (mm)

Thin outer bone going in meant more exposed root coming out.

Limitations

What the data leaves open.

Animals and growth

The loading and diet experiments were done in growing rabbits, rats, mice, minipigs and primates [13] [12] [6] [9]. The breathing and feeding data are associations in children [19] [17].

Adult evidence

The adult expander review pooled eight observational studies and rated the evidence very low quality [11]. Kids grow during treatment, and only 52 were followed past three years [3].

The faces

The two faces at the top of this page are illustrative models, not patients.

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Maxillary expansion questions

In growing faces, daily loads shape its width. Rats and minipigs raised on soft food grew narrower arches, mouth breathers have a maxilla sitting about 1.33° further back, and breastfed children had about a third of the odds of a bad bite. How many millimetres an adult gains from daily habits has not been measured in a trial.

Open data

Every number has a link.

Each figure comes from one of the papers below. Click a PMID to read the abstract on PubMed.

References

  1. 1
    Aldawood, Z. A., Mancinelli, L., Geng, X., Yeh, S. A., Di Carlo, R., C Leite, T., Gustafson, J., Wilk, K., Yozgatian, J., Garakani, S., Bassir, S. H., Cunningham, M. L., Lin, C. P., & Intini, G. (2023). Expansion of the sagittal suture induces proliferation of skeletal stem cells and sustains endogenous calvarial bone regeneration. Proceedings of the National Academy of Sciences, 120(16), e2120826120. PMID 37040407 · doi
  2. 2
    Angelieri, F., Cevidanes, L. H., Franchi, L., Gonçalves, J. R., Benavides, E., & McNamara, J. A. Jr. (2013). Midpalatal suture maturation: classification method for individual assessment before rapid maxillary expansion. American Journal of Orthodontics and Dentofacial Orthopedics, 144(5), 759–769. PMID 24182592 · doi
  3. 3
    Camacho, M., Chang, E. T., Song, S. A., Abdullatif, J., Zaghi, S., Pirelli, P., Certal, V., & Guilleminault, C. (2017). Rapid maxillary expansion for pediatric obstructive sleep apnea: a systematic review and meta-analysis. The Laryngoscope, 127(7), 1712–1719. PMID 27796040 · doi
  4. 4
    Chen, J., Zhao, Y., Zeng, C., Tian, G., Feng, Z., Cao, Y., et al. (2025). Mechanical tension-induced Dalrd3 elevation enhances osteogenic differentiation of bone suture stem cells by upregulating Id3 translation. Stem Cell Research & Therapy, 16(1), 309. PMID 40528244
  5. 5
    Choi, S. H., Shi, K. K., Cha, J. Y., Park, Y. C., & Lee, K. J. (2016). Nonsurgical miniscrew-assisted rapid maxillary expansion results in acceptable stability in young adults. The Angle Orthodontist, 86(5), 713–720. PMID 26938955 · doi
  6. 6
    Ciochon, R. L., Nisbett, R. A., & Corruccini, R. S. (1997). Dietary consistency and craniofacial development related to masticatory function in minipigs. Journal of Craniofacial Genetics and Developmental Biology, 17(2), 96–102. PMID 9224944
  7. 7
    Corruccini, R. S. (1984). An epidemiologic transition in dental occlusion in world populations. American Journal of Orthodontics, 86(5), 419–426. PMID 6594064
  8. 8
    Garib, D. G., Henriques, J. F., Janson, G., de Freitas, M. R., & Fernandes, A. Y. (2006). Periodontal effects of rapid maxillary expansion with tooth-tissue-borne and tooth-borne expanders: a computed tomography evaluation. American Journal of Orthodontics and Dentofacial Orthopedics, 129(6), 749–758. PMID 16769493 · doi
  9. 9
    Harvold, E. P., Tomer, B. S., Vargervik, K., & Chierici, G. (1981). Primate experiments on oral respiration. American Journal of Orthodontics, 79(4), 359–372. PMID 6939331
  10. 10
    Jin, M., An, Y., Wang, Z., Wang, G., Lin, Z., Ding, P., et al. (2024). Distraction force promotes the osteogenic differentiation of Gli1⁺ cells in facial sutures via primary cilia-mediated Hedgehog signaling pathway. Stem Cell Research & Therapy, 15(1), 198. PMID 38971766
  11. 11
    Kapetanović, A., Theodorou, C. I., Bergé, S. J., Schols, J. G. J. H., & Xi, T. (2021). Efficacy of Miniscrew-Assisted Rapid Palatal Expansion (MARPE) in late adolescents and adults: a systematic review and meta-analysis. European Journal of Orthodontics, 43(3), 313–323. PMID 33882127 · doi
  12. 12
    Katsaros, C. (2001). Masticatory muscle function and transverse dentofacial growth. Swedish Dental Journal Supplement, (151), 1–47. PMID 11803645
  13. 13
    Kopher, R. A., & Mao, J. J. (2003). Suture growth modulated by the oscillatory component of micromechanical strain. Journal of Bone and Mineral Research, 18(3), 521–528. PMID 12619937
  14. 14
    Mao, J. J. (2002). Mechanobiology of craniofacial sutures. Journal of Dental Research, 81(12), 810–816. PMID 12454093
  15. 15
    Park, S. Y., Hwang, H. J., & Park, K. N. (2022). Development of a cranial suture traction therapy program for facial asymmetry correction using the new Delphi technique. Medicina (Kaunas), 58(7). PMID 35888588
  16. 16
    Peptan, A. I., Lopez, A., Kopher, R. A., & Mao, J. J. (2008). Responses of intramembranous bone and sutures upon in vivo cyclic tensile and compressive loading. Bone, 42(2), 432–438. PMID 18032124
  17. 17
    Peres, K. G., Cascaes, A. M., Nascimento, G. G., & Victora, C. G. (2015). Effect of breastfeeding on malocclusions: a systematic review and meta-analysis. Acta Paediatrica, 104(467), 54–61. PMID 26140303
  18. 18
    Persson, M., & Thilander, B. (1977). Palatal suture closure in man from 15 to 35 years of age. American Journal of Orthodontics, 72(1), 42–52. PMID 267435 · doi
  19. 19
    Zheng, W., Zhang, X., Dong, J., & He, J. (2020). Facial morphological characteristics of mouth breathers vs. nasal breathers: a systematic review and meta-analysis of lateral cephalometric data. Experimental and Therapeutic Medicine, 19(6), 3738–3750. PMID 32346438

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