Needle Gauge, Rheology & Injection Depth Protocol - Lip Filler

1. Needle Gauge & Length

30 G × 4 mm needle optimal for vermillion border precision and minimal trauma.¹
33 G needles enhance control for micro-threading or fine vermillion definition.²
27 G cannula (≥ 25 mm) or 30 G needle suitable for mid-body or deep submucosal augmentation.³
Smaller gauge does not guarantee safety; risk depends on anatomical variation and injection plane.

2. Injection Depth & Plane

Labial artery position: typically 3.3 — 3.9 mm beneath the vermillion border.¹
Superficial safety plane: 1 — 2 mm dermal/subdermal placement avoids vascular compromise.⁴
Do not exceed 2.5 mm depth at the vermillion border to prevent arterial penetration.⁵
Stay above wet-dry junction; avoid muscular insertion zones.

3. Rheology & Product Selection

Rheologic parameters: Viscosity (η) determines flow; Elastic Modulus (G′) determines lift and projection.⁶
Superficial planes: low-viscosity, low-G′ HA for smooth contour and natural mobility.
Deeper planes: medium—high G′ fillers for structure and shape retention.²
Clinical translation: border → soft gels; body/submucosa → cohesive fillers.

4. Simplified Injection Protocol

Assess lip symmetry, vascular pattern, and prior filler presence.
Select filler rheology according to target plane and outcome.
Use 30—33 G for vermillion border; 27—30 G for lip body or cannula work.
Inject at 1—2 mm depth in superficial plane; avoid intramuscular plane.
Use linear threading or microbolus for even product distribution.⁷
Observe for blanching, pain, or resistance indicating vascular event.
Gently mould filler; avoid aggressive massage.
Reassess perfusion and symmetry post-injection.

5. Safety & Escalation Considerations

Up to 78% of labial arteries lie in submucosal tissue⁸ — depth misjudgement remains a key risk.
Needle gauge alone does not eliminate intravascular injection risk.
Hyaluronidase must be available on-site for emergency use.
Follow Vascular Occlusion Emergency Protocol (VOEP 2025).⁹
Document all adverse events, including dose, site, and management steps.
Post-procedure review at 2 weeks with photographic documentation.

6. Clinical Governance Notes

Injectors must demonstrate competency in vascular anatomy and hyaluronidase reconstitution.
Maintain a filler logbook with product, lot, and volume recorded.
Conduct annual audits of filler complications (infection, occlusion, granuloma) as per ACSQHC standards.

Sources

Walker L., et al. (2021), Lip augmentation using hyaluronic acid filler and a 4-mm cannula: A retrospective review of safety and outcomes, PMC Journal (PMC7869814), viewed 06 November 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC7869814/ ↩
Stéphane S., Maisse M., Dupont C., et al. (2022), “Bi-Bi” technique for lip augmentation: A retrospective study, Aesthetic Surgery Journal Open Forum, 2(3): ojac037, viewed 06 November 2025, https://pmc.ncbi.nlm.nih.gov/articles/PMC9796850/ ↩
Top Dermal — Needle Size for Lip Fillers, viewed 06 November 2025, https://en.topdermal.com/2022/11/04/what-needle-size-to-use-for-lip-fillers/ ↩
Dr Tim Pearce — 4 mm Needle Technique, viewed 06 November 2025, https://drtimpearce.com/2022/08/15/lip-augmentation-using-the-4mm-needle-technique/ ↩
Top Dermal — Depth Recommendations, viewed 06 November 2025, https://en.topdermal.com/2022/11/04/what-needle-size-to-use-for-lip-fillers/ ↩
OA Plastic Surgery Journal (2018) — HA Rheology Review, viewed 06 November 2025, https://www.oaepublish.com/articles/2347-9264.2018.10 ↩
Dr Tim Pearce — Lip Threading Techniques, viewed 06 November 2025, https://drtimpearce.com/2022/08/15/lip-augmentation-using-the-4mm-needle-technique/ ↩
JCAD Online — Arterial Variation in Lip Injection, viewed 06 November 2025, https://jcadonline.com/hyaluronic-acid-filler-4-mm-needle/ ↩
BINASSS — Hyaluronidase in Filler Complications (2022), viewed 06 November 2025, https://www.binasss.sa.cr/ago22/39.pdf ↩

Disclaimer for Newcastle Cosmetic Doctor Policies & Procedures

The policies and procedures contained within this document are the exclusive property of Newcastle Cosmetic Doctor and are provided for internal clinical governance and educational purposes only. These materials represent the internal operational framework, safety standards, and evidence-based protocols developed and implemented by Dr. Bart John Scanlon and the Newcastle Cosmetic Doctor team. They are designed specifically for use within Newcastle Cosmetic Doctor and reflect our clinic’s own professional standards, risk assessments, and compliance obligations under Australian law and regulatory authorities. External individuals, practitioners, or organisations must not copy, reproduce, distribute, or rely upon these materials, in whole or in part, for their own clinical, commercial, or educational use without prior written consent from Newcastle Cosmetic Doctor. These materials do not constitute medical, legal, or professional advice and are not intended to be adopted as official protocols or procedures by any other entity. Any external use or adaptation must be independently reviewed and modified to meet the relevant laws, guidelines, and standards applicable to the user’s own jurisdiction, scope of practice, and facility operations. Newcastle Cosmetic Doctor and Dr. Bart Scanlon accept no liability for any loss, injury, or damage arising from the unauthorised use, reliance upon, or misinterpretation of this material.