A study to elucidate the pull out characteristics of microimplants .

1. Computed Tomographic
Characterization of
Mini-Implant Insertion
Pattern and
Maximum Anchorage
Force in Human
Cadavers
Dr Jean-Marc Retrouvey
Genevieve Lemieux

2. • For more complete information, please
read the article on the same topic in the
AJO-DO

3. History
Anchorage Devices
Osseointegrated Non Osteointegrated Implants
Implants
Mechanical Retention
Palatal Onplant Dental Implant Surgical Fixation
Screws
Retromolar Implant
Fixation Screws /
Mini Implants plates
Kanomi, 1997
(Sugawara)
Wehrbein, H. and Merz, B.R. 1998
Roberts, W.E. et als, 1990
Cope, J.B., Seminar Orthodontics 2005

4. Facts on Mini-Implants
1. Mini-implants are the most widely used
temporary orthodontic anchorage devices.
2. Principal indications: Melsen, B., Journal of Clinical Orthodontics, 2005
Insufficient teeth for the application of
conventional anchorage
Cases where forces on the reactive unit
would generate adverse side effects
Need for asymmetrical tooth
movements in all planes of spaces
As an alternative to orthognathic
surgery

5. 3.1. Length:
Varies approximately between 6 to 16 mm
The length chosen will depend on the bone
characteristics in the insertion location
Jiang, L et al (2009):
“The longest length in the safety range
is recommended”
Jiang, L et al, Advances in Engineering Software, 2009

6. 3.2. Diameter:
Varies between 1 to 2 mm
Smaller diameter 1.4 mm to 1.6 mm is preferred
•pros: fewer anatomical risks, hence more sites available for ease of
insertion between roots
•cons: potential for neck fracture upon retrieval for smaller
diameters
For intrusion, Park (AJO, 2003) advocated 2mm
implants
Park et al. (AJO 2006) reported that the smaller
implants were actually more successful than the
bigger ones
Melsen, B., Journal of Clinical Orthodontics, 2005

7. 3.2. Diameter:
Anatomical limitations
- Interradicular distance may
not allow the use of 2mm mini-
implants .
- Poggio, P.M. et al studied
interradicular width
» Several areas do not have
enough space for large
2mm screws….
Poggio, P.M. et al, Angle Orthodontist, 2006

8. 4. Failure rate
Schätzle et al, 2009, Systematic Review.
•Compared 17 studies accessing mini-implant failure rates
•Estimated an average failure rate of 16.4% by meta-analysis
Schätzle et al, Clinical Oral Implants Research, 2009

9. 5. Factors affecting stability
- One important factor is immediate loading
Immediate loading is suggested and may
improve screw stability
•Huja AJO 2005
Pull out forces are much higher than
orthodontic forces
•Salmoria, AJO 2008. Jacobson, AJO 2006
There does not seem to be a benefit in waiting
for loading mini implants

10. 6. Anatomical damage
Posterior area of the maxilla and mandible are
most suitable sites for micro implants insertion
•Hyo-Sun Park KJO 2002
Interradicular distance has to be carefully
monitored before placement
•Poggio, Angle 2008
Angulating the implants is recommended by
Park et al to lower root damage
•Park AJO 2006

11. Purpose of this investigation
• Despite the rapidly growing use of mini-
implants
– There is a lack of comprehensive and well
controlled studies examining all the potential
factors affecting initial stability simultaneously
– Few studies have examined primary stability in
human bone

12. Goals of this investigation
•to characterize the insertion
1 pattern of mini-implants using
CT imaging
•to determine and quantify the
factors affecting mini-implant
2
primary stability

13. Materials & Methods
A) Cadavers
- 5 unembalmed human cadavers
- Average age: 87 years old (SD of ± 5 years); 2
male, 3 female
B) Mini-implants placement
- 3M Imtec mini-implants used
- total of 12 mini-implants inserted per cadaver
- location of insertion:
- maxillary & mandibular buccal alveolar bone

14. Materials & Methods
3M Imtec 1.8 mm diameter mini-implant
(schematic representation)

15. Materials & Methods
B) Mini-implants placement
Location of insertion into alveolar bone on facial surface of maxilla and mandible

16. Materials & Methods
B) Mini-implants placement
Distribution of 60 mini-implants across 5 cadavers

17. Materials & Methods
C) Imaging
– High-resolution CT imaging (0.625mm slices)
– Imaging done before and after mini-implants
placement to assess bone characteristics at the
site of insertion

18. Materials & Methods
C) Imaging
- Data measured:
Bone
Bone type Density
thickness
surrounding the tip and parallel
sections of each mini-implants

19. Materials & Methods
C) Imaging
- assessment of position and bone characteristics
Example of measurements of bone thickness and density at site of insertion

20. Materials & Methods
C) Imaging
- assessment of anatomical damage
a) b) c)
Mini-implant insertion into:
(a) adjacent root structure
(b) lingual cortical bone
(c) maxillary sinus

21. Materials & Methods
D) Tensile strength apparatus
Slowly increasing tensile force applied to each mini-
implant until point of failure (10N/s)
•Point of failure: force at which the mini-implant pulled out of the
bone
Direction of the force applied
•Parallel to the occlusal plane

22. Materials & Methods
D) Tensile strength apparatus

23. Results
Part A) Analysis of the insertion pattern
Location of mini-implants as it relates to
bone architecture
Assessment of damage to neighboring
structure

24. Results
Part B) Maximum anchorage force (MAF)
Determination of:
•Initial maximum anchorage force
•Relation to implant length, insertion depth, bone
density

25. Results
Part A) Analysis of the insertion pattern
CT analysis of mini-implant
insertion into:
- soft tissue (A)
- buccal cortical bone (B)
- cancellous bone (C)
- lingual cortical bone (D)

26. Results
Part A) Analysis of the insertion pattern
The degree of implant
penetration strongly depends
on implant length
1. 15% of 6mm mini-implants
failed to anchor their parallel
sections into cortical bone
2. 95% of 10mm mini-implant
parallel sections penetrated
beyond the buccal cortical
bone
3. All 20 tips of 6mm mini-
implants reached cancellous
bone
4. 75% of 10mm penetrated both
corticals reaching the lingual
cortical bone

27. Part A) Analysis of the insertion pattern
- Assessment of damage to neighboring structure
6 mm 8 mm 10 mm
Implant Implant Implant
(n = 20) (n = 20) (n = 20)
Average distance to adjacent root structure 528 um 441 um 414 um
Incidence of penetration into root structure 5 (25%) 6 (30%) 3 (15%)
Incidence of bicortical insertion 0 (0%) 6 (30%) 15 (75%)
Incidence of sinus perforation 0 (0%) 2 (10%) 3 (15%)
Liou, AJO, 2004: 2mm minimum distance to
prevent root damage

28. Results
Part B) Maximum anchorage force (MAF)
MAF is defined as:
•Static tensile force at which each mini-implant
failed
Confounding factors:
• 7 mini-implant heads were damaged or broken
• 13 cord slippage encountered
• Therefore, 40 mini-implants were used in the
statistical model

29. Part B) Maximum anchorage force (MAF)
-Median forces:
128 N – 6mm
160 N – 8mm
211 N – 10mm
-Significant difference
between:
MAF of 6mm and 10 mm mini-
implants
(p<0.05)

30. Results
Part B) Maximum anchorage force (MAF)
Correlation between maximum anchorage force and various combinations of:
- insertion depth (ID)
- bone density (ρ)
- implant length (L)
Parallel Tapered
Correlation (0-1) P-Value
Section Section
Limplant x x 0.45 0.004
ρcortical n/a n/a 0.42 0.007
ρcancellous n/a n/a 0.36 0.02
IDcortical x 0.26 0.11
IDcancellous x 0.24 0.13
IDcortical + IDcancellous x 0.27 0.08
IDcortical x x 0.23 0.16
IDcancellous x x 0.21 0.18

31. Results
Part B) Maximum anchorage force (MAF)
Correlation between maximum anchorage force and various combinations of:
- insertion depth (ID)
- bone density (ρ)
- implant length (L)
Parallel
Parallel Tapered
Tapered Correlation (0-1)
Correlation (0-1) P-Value
P-Value
Section
Section Section
Section
IDcortical + IDcancellous x x 0.29 0.06
Limplant x x 0.45 0.004
(IDcortical • ρcortical) x 0.49 0.002
ρcortical n/a n/a 0.42 0.007
(IDcancellous •
ρcancellous n/a
x n/a 0.36
0.38 0.02
0.02
ρcancellous)
ID x 0.26 0.11
(IDcortical •cortical ) +
ρcortical
IDcancellous x
x 0.55
0.24 <0.001
0.13
(IDcancellous • ρcancellous)
(IDcortical+• IDcancellous
IDcortical ρcortical) x
x x 0.27
0.41 0.08
0.008
ID • ρ
(IDcancellous cortical x x 0.23 0.16
cancellous) x x 0.44 0.004
ID • ρ
(IDcortical cancellous ) + x x 0.21 0.18
cortical x x 0.65 <0.001
(IDcancellous • ρcancellous)

32. Discussion
Longer implants for more stability?
Pros Cons

33. Discussion
Root Damage
• In this study, the average distance of the mini-
implants, regardless of their length, was less
that 1 mm away from root structure
• Liou et al recommend of at least 2mm between
the roots and the surface of the implant
Liou EJW et al, AJODO, 2004

34. Discussion
• Maximum Anchorage Force
- Factors studied
Knowledge of the bone quality (density and thickness)
provides a stronger prediction for maximum anchorage
force than implant length
Clinically, the knowledge of bone thickness and density
may provide the strongest predictor of initial implant
stability for any given site.

35. Discussion
• Intra-Inter cadaver variability
Considerable
variation was
found within
and
between
cadavers
•Example: average
cortical bone density of
the 5 maxillas is 1084
HU . SD= 213 HU and
232 HU

36. Limitations of the study
– Recently unembalmed human cadavers were used
(realistic model)
Use of cadavers involves some important
restrictions when compared to the
placement of mini-implants in living bone:
• There is no bone remodeling
• The age of available cadavers is usually advanced
(average age in this study was 87 years) where bone
composition and other anatomical changes may be
important.

37. Conclusions
1) Shorter mini-implants (6 mm) tended to have
incomplete penetration of the buccal cortical
bone.
2) Longer mini-implants tended to penetrate
further into the bone (offering more mechanical
anchorage) but were also associated with a
greater incidence of sinus and bicortical
perforations.

38. Conclusions
3) The most important factors determining
maximum mechanical anchorage were found to
be (in decreasing order): bone density and
insertion depth combined, mini-implant length,
bone density, insertion depth.

39. Conclusions
4) Mechanical resistance to pull out force is much
higher than applied orthodontic force
5) Failure rate of mini-implants may not be related
to initial loading.
6) Large variability in bone density and quantity
between the sites

40. Conclusions
4) Mechanical resistance to pull out force is much
higher than applied orthodontic force
5) Failure rate of mini-implants may not be related
to initial loading.
6) Large variability in bone density and quantity
between the sites (intra and inter cadaver
variability)

41. Future Work
• Use of different brands of micro implants
• Dynamic pull out system to measure
potential bone fatigue
– Forces from mastication may be more important than we
currently think (large and intermittent)
• Animal studies to study inflammation in
relation to pull out force

42. Acknowledgement
McGill University
• Dr C. Cheretakis
• Adam Hart
• Professor Marc Mckee
Eastern Virginia Medical School
• Dr C. Goodmurphy
• Stephanie Trexler
• Christopher McGary