Safe Zones for Miniscrew Placement: What Every Orthodontist Should Know

In one of the most cited studies in orthodontics, Poggio et al. (2006) published “Safe Zones: A Guide for Miniscrew Positioning in the Maxillary and Mandibular Arch” . This landmark paper used cone-beam CT to identify precise locations in the upper and lower jaw where miniscrews can be safely inserted without harming roots or comprimising miniscrew stability.

Here’s a breakdown of the paper!

How was the study conducted?

• Sample: 25 maxillae and 25 mandibles from healthy adults (20–40 years old).

• Tool: NewTom DVT9000 CBCT scanner (cone-beam CT).

• Measurements: Bone thickness was recorded at 2, 5, 8, and 11 mm from the alveolar crest in both mesiodistal and buccolingual directions.

What are the ideal dimensions and characteristics of a miniscrew based on this study?

• Diameter: 1.2–1.5 mm (1.2 mm safest in tighter spaces)

• Length: 6–8 mm

• Shape: Conic design (reduces risk of root contact)

• Angle of insertion: 30–40° to the tooth axis (allows deeper placement without contacting roots)

Where are the safest sites for miniscrew placement in the maxilla?

Palatal side (maxillary first molar and second premolar)Interradicular space 2 - 8 mm from alveolar crest

Palatal side (maxillary second and first molars)Interradicular space 2 - 5 mm from alveolar crest

Buccal or Palatal side (second and first premolars)Interradicular space 5 - 11 mm from alveolar crest

Buccal or Palatal side (first premolar and canine)Interradicular space 5 - 11 mm from alveolar crest

Buccal side (first molar and second premolar)Interradicular space 5 - 8 mm from alveolar crest

• "In the maxilla, the more anterior and the more apical, the safer the location becomes."

Which places to avoid ?

• Avoid insertions above 8 - 11 mm in the maxillary molar region to stay clear of the maxillary sinus.

• Avoid the tuberosity area due to minimal bone

What about the mandible?

"•Interradicular spaces between the second and first molar.

• Interradicular spaces between the second and first premolar.

• Interradicular spaces between the first molar and second premolar at 11 mm from alveolar crest.

• Interradicular spaces between the first premolar and canine at 11 mm from the alveolar crest."

The author also mentioned that ,the findings are evaluations of data from a group of nontreated patients. They serve as a guide for clinicians but do not eliminate the need for radiographic evaluation in each individual case before miniscrew insertion!

Safe Zones Map according to Poggio et al:

Reference:

‘‘Safe Zones’’: A Guide for Miniscrew Positioning in the Maxillary and Mandibular Arch (Paola Maria Poggio; Cristina Incorvatib; Stefano Velob; Aldo Carano)

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