The success rate of microimplants used for orthodontic anchorage varies between studies but is typically around 90%. Initial stability is important for success, and microimplants are unlikely to succeed if they touch a root during placement. Factors like surgical technique, implant design, placement location, and patient characteristics can influence success rates. Several studies found high success rates (80-95%) when microimplants were left undisturbed for 2-3 weeks before loading and when placed by experienced clinicians. Younger patient age and immediate loading may increase failure risk slightly. Microimplants are a powerful tool for orthodontic anchorage when used properly.

1. Success and failure rates of
miniscrews and microimplants
Dr Maher Fouda
Professor of orthodontics
Mansoura Egypt

2. The failure of an orthodontic microimplant usually means that the
microimplant has become loose during treatment
This usually occurs within the first three months following placement
Initial mechanical stability is important to the success of
microimplant anchorage as if it’s not achieved immediately upon
insertion, the microimplant is not expected to be successful
The microimplant almost always fails if it touches a root during
placement and this is prevented by understanding:
a) The morphology of the roots and interradicular space into which
the microimplant is to be placed
b) Location of microimplant, its size and path of insertion and
quality of overlying soft tissue

3. The success rate of microimplants used for temporary
anchorage during orthodontic treatment varies from study
to study in the literature
Individual skill of the clinician affects the success rate of
microimplant placement. Moreover, some patients reject
any type of foreign material placed in their body (in these
patients, a gradual automatic rejection of microimplants
occurs) and patients should always be warned of this
possibility
Currently, a 100% success rate for microimplant placement is
not attainable

4. Factors contributing to failure of
microimplants
A) Iatrogenic factors
1-Excessive heat generation when drilling, resulting in bone
tissue necrosis
2-Root injury or approximation
3-Inadequate initial mechanical stability
4-Implant contamination
5-Inflammation due to negligence of oral hygiene
6-Inflammation by gingival impingement by elastic materials
7-Injury to anatomical structures e.g.: nerve, artery, sinus
8-Microimplant fracture

5. B) Host factors:
1- Systemic diseases
2- Bone quality and quantity
3- Amount of attached gingiva vs movable soft tissue available
4- Age and physical condition
5- Oral microflora, salivation, mouth-breathing, etc
C) Implant factors:
1- Choice of implant material
2- Implant surface type
3- Shape of implant screw

6. Data on success and failure rates
Data on the success and failure of miniscrews and
microimplants can be found in several studies
carried out during the last 5 years. The following
are examples;
[I] Park:
Park (2003) evaluated the clinical success rate of
microimplants used for intraoral anchorage on 73
patients (26 males, 47 females)

7. a) Microimplants used:
- 174 titanium microscrews 1.2mm diameter and 5-12mm length (152
from Osteomed Co. USA, 20 from Leibinger Co. Germany, 2 from Avana
Co. Korea
- 6 titanium miniscrews 2mm diameter and 12 mm length ( Martin Co.
Germany)
b) Incision:
A 3-5mm vertical stab incision was made through facial alveolar mucosa
when necessary. No incision was required in palatal mucosa
c) Location: based on their location they were divided into 4 categories:
- UB: maxillary buccal and labial alveolar bone and infrazygomatic crest
-LB: mandibular buccal and labial alveolar bone
-UP: maxillary palatal alveolar bone and maxillary tuberosity
-LR: mandibular retromolar area and edentolous ridge mesial to external
oblique ridge

8. d) Observation period :
15.8 ± 6.2 months
e) Insertion angle:
- UB,UP: angle of 30-40 relative to long axis of maxillary teeth
- LB: 10-20 relative to long axis of mandibular teeth
- LR: perpendicular to bone surface
f) Insertion methods:
Buccal: Self-tapping after 3-5mm vertical incision
Palatal: Self tapping with no incision
g) Force application: 2-3 weeks after placement
h) Overall success rate: 93% (168 out of 180)

9. [II] Kim and Choi
Kim and Choi (2001) evaluated the clinical success rate of miniscrews and microscrews
on 33 patients (5 males, 28 females)
a) Microimplants used:
- Osteomed Co. USA
b) size:
1.2, 1.6 and 2 mm diameter and 6-14mm long
c) Observation period:
3 months
d) Insertion methods:
- 79 (1.2 and 1.6mm diameter) by self tapping
- 27 (1.6 and 2mm diameter) by self drilling
e) Force application:
immediate force of 200-300gm

10. Failure relative to drilling method
Total (106)Self drilling
(27)
Self tapping
(79)
Time of
failure
26(25%)5 (19%)21 (27%)Immediate
18 (16%)12 (44%)6 (7%)Within 3
months
44 (41%)17 (63%)27 (34%)Totals

11. [III] Orthodontic residents of Kyungpook
National University Hospital
9 orthodontic residents in Department of Orthodontics KPNU Hospital evaluated their
success with microimplants on 25 patients ( 6 males, 19 females)
a) Microimplants used:
Osteomed Co. USA
b) size:
1.2mm diameter and 5-12mm long
c) Observation period:
24 months
d) Insertion methods:
- Buccal: Attached gingiva: self tapping without incision
Movable mucosa: self tapping after 3-5 mm
vertical incision
- Palatal: self tapping without incision
e) Force application: immediate and delayed

12. Failure of implanted screws relative to
dental arch and patient’s age
TotalFailureSuccess
448 (18%)36Maxilla
182 (11%)16Mandible
6210 (16%)52Total
Totalfailuresuccess
245 (21%)1910-18 years
385 (13%)3319-58 years
6210 (16%)52Total

13. [IV] Woo and colleagues
Woo and co-workers (2003) evaluated clinical success of microscrews and miniscrews
placed in 51 patients
a) Microimplants used:
- OSAS Epoch Medical, Korea
- Martin Co. Germany
b) size:
- 1.6 mm and 8 mm long in maxillary buccal area ( OSAS Epoch Medical )
- 1.6mm and 6mm long in mandible (OSAS)
- 2mm diameter and 6 mm long in maxilla and mandible (Martin Co.)
c) Observation period:
24 months
d) Insertion methods: self drilling and self tapping
e) Force application: immediate and 7 days after placement

14. N.B: there were no stastically significant differences between
men and women, maxilla and mandible or between self
tapping and self drilling methods of insertion
However, differences depended on:
- Age of patients where failure was approximately 10%
higher in group of patients less than 20 years age
- Failure rate of immediately loaded screws was 11% higher
than in screws loaded after 7 days
- The failure rate was 17% higher after an engine-driver was
used than after an hand driver was used

15. Failure rates based on age and dental
arch
TotalFailureSuccess
5611 (20%)45 (80%)<20 years
919 (10%)82 (90%)≥ 20 years
TotalFailureSuccess
8113 (16%)68 (84%)Maxilla
667 (11%)59 (89%)Mandible

16. Failure rates based on drilling protocol
TotalFailureSuccess
263(12%)23(88%)Self-tapping
12117 (14%)104 (86%)Self-drilling

17. Failure based on time of loading and
driving method
TotalFailureSuccess
6012(20%)48 (80%)Immediate
878(9%)79(91%)Delayed
TotalFailureSuccess
12213(11%)109(89%)Hand driven
257(28%)18(72%)Engine

18. [V] Kyung and colleagues (part 1 )
Kyung and 9 orthodontic residents from department of orthodontics KPNU
Hospital evaluated the newly developed microimplants made of grade 2
titanium (Dentos Inc. Korea) on 65 patients (13 males, 52 females)
a) Microimplants used:
Dentos Inc. Korea
b) size:
1.2 and 1.3 mm diameter and 6-12mm long
c) Observation period:
24 months
d) Insertion methods :
Buccal: self tapping with 3-5mm incision in movable mucosa
Palatal: self tapping without incision
e)Force application:
immediate and delayed

19. Rate of failure based on dental arch and
patient’s age
TotalFailureSuccess
9613(14%)83Maxilla
399(23%)30Mandible
13522(16%)113Total
TotalFailureSuccess
248(33%)1610-18 years
11114(13%)9719 years and over
13522(16%)113Total

20. [VI] Jang
Jang (2005) evaluated the clinical success rate of orthodontic microimplants
(Dentos Inc.) on 60 patients (53 females, 7 males)
a) Microimplants used:
Dentos Inc. Korea
b) size:
1.3 mm diameter 7mm long cylindrical and tapered
c) Observation period:
12-30 months
d) Insertion methods:
self tapping
e) Force:
150-200 gm delayed loading( 2 weeks )

21. Success rates of cylindrical vs tapered
microimplants
TotalTaperedCylindrical
110(92%)57(95%)53 (88%)Success
1037Failure
1206060Total

22. [VII] Kuroda and colleagues
Kuroda and colleagues (2004) evaluated clinical usefulness of miniscrews as
temporary anchorage devices on 75 patients (12 males and 63 females)
a) Microimplants used:
Type A: Keisei Medical Ind. Japan
Type B: Dentos Inc. Korea
Type C: Dentsply Japan
b) size:
Type A: 2mm, 2.3mm
Type B: 1.3mm
Type C: 2mm miniplate
c) Observation period: 40 months
d) Insertion methods:
Type B: self tapping without incision
Type A, C: self tapping with incision

23. e) Force:
50-200 gm
Type B: immediate and delayed
Type A,C: delayed 4-12 weeks
** The succcess rates of three kinds of microimplants**
Screw CScrew BScrew A
87%89%81%Succes rate
2 mm1.3 mm2, 2.3mmDiameter
5 mm6-12mm10-14mmlength
224018Subjects
387937Implants

24. [VIII] Kyung and colleagues (part2)
a) Microimplants used:
Dentos Inc. Korea
b) Diameter:
1.3mm tapered
c) Observation period:
12-24 months
d) Insertion methods:
Buccal: self tapping with 3-5mm incision in movable mucosa
Palatal: self tapping with no incision
e) Force application:
Immediate and delayed

25. Failure based on dental arch
TotalFailureSuccess
26119 (7%)242 (93%)Maxilla
16521 (13%)144 (87%)Mandible

26. Summary
A 100% success rate cannot be achieved when microimplants are
used for temporary skeletal anchorage. However, they do have a
high success rate of approximately 90% ( similar to that of
miniplates and titanium screws)
Microimplants can be used as temporary anchorage immediately
after placement for any type of orthodontic tooth movement
When they are placed without making an incision, the pain and
discomfort occurring after implantation is reduced significantly
They are small enough to be placed in any area of the mouth and if
one fails, another one can be placed immediately in an adjacent
area
The ability to replace a failed microimplant instantaneously results in
almost 99% success rate

27. Conclusion
Microimplants have become one of the most effective and
powerful tools for achieving absolute anchorage which are
causing paradigm shift in orthodontic treatment planning
At present, he smallest diameter microimplants (1.2-1.3mm)
are used widely due to the fact that they can be placed
between roots of adjacent teeth
Many successful treatment outcomes have been reported in
which microimplants placed between roots have provided
absolute anchorage enabling en masse retraction, molar
intrusion, molar distalization, molar protraction and molar
uprighting
It is possible to use microimplants for anchorage with
immediate loading after insertion .