Title Root Proximity is a Major Surgical Factor of Orthodontic Mini-Implant Failure.
Clinical Question In orthodontic patients needing a temporary anchorage device, will the mini-implants placed distant to adjacent teeth as compared to those placed in contact or close proximity to the adjacent teeth have lower failure rate?
Clinical Bottom Line Location of mini-implant placement, specifically root proximity, plays a significant role in the stability of skeletal anchorage. This is supported by numerous prospective observational studies that demonstrated orthodontic mini-implants have a statistically significant lower failure rate if they are placed distant from the roots of teeth as compared to when they are in contact or in close proximity to the roots. Other surgery-related, orthodontic-related, and patient-related factors may simultaneously impact the success rate of mini-implants as well. Careful investigation of surgical-related factors, especially the path of insertion, may significantly improve the stability of orthodontic mini-implant, leading to patient satisfaction, shortened overall chair time, and efficient orthodontic treatment.
Best Evidence  
PubMed ID Author / Year Patient Group Study type
(level of evidence)
29243679 Gintautaite/ 20171205 patients in 13 included studies Systematic Review
Key resultsA “successful” mini-implant is defined as a temporal skeletal anchorage device that is able to perform its anchorage function for a certain period of time in absence of any mobility, soft tissue inflammation, or pathologies. In this study, eight observational studies consistently showed a much higher success rate for mini-implants (MI) placed away from adjacent teeth roots. While overall MI success rate ranged from 87.7% to 97%, root contact contributed to 9% to 26.7% failure rate. According to the CBCT radiograph analysis in Watanabe et al., the success rate of MI was highest (94.5%) when all three designated points (apex, middle, and neck of MI) were >0.7mm away from root surface. When only the apex point, the middle point, or any two points were ≤0.7mm from root surface, the success rate dropped to 62.5%, 50.0%, and 14.29% respectively. A similar study done by Shigeeda analyzed the MI failure rates in groups A-C (A – no contact between the mini-implant and roots, B – one point of contact between the root and apex or body of the mini-implant, C – two or more contacts between the roots and mini-implant). The results were 1.5%, 9%, and 26.7% respectively, thereby demonstrating that multiple MI and root surface contacts increase the MI failure rate.
17448389Kuroda/ 2007110 patients with sum of 216 titanium screws placedProspective Cohort Study
Key resultsThis study used CBCT to examine 216 titanium screws in 110 patients classified into Category I, II, and III according to root proximity of the screws. Category I had screws completely separate from the root; Category II had apex of the screw touching the lamina dura; Category III had body of the screw overlaying on the lamina dura. Overall result showed that screws in category I had a higher success rate over 90%, whereas screws in category III showed a low success rate of 62.5%. When the screws placed in maxilla and mandible were compared, those placed in maxilla had significantly higher success rate (category I- 96.3%, category II- 91.4%, category III- 74.4%) than those placed in mandible (category I- 83.9%, category II- 75%, category III-35.3%) especially when placed overlaying the lamina dura of adjacent root (P<.001). In conclusion, the proximity of a miniscrew to the root is a major factor for the success or failure of screw anchorage. In addition, screws placed in the maxilla had higher success rates than those in the mandible.
Evidence Search (Orthodontic Mini-implant) AND (Stability) AND (Success rate)
Comments on
The Evidence
Gintautaite’s Systematic review contains a total of 13 studies with a sample size large enough to provide reliable evidence. The study consisted of a combined total of 1205 patients and 2652 mini-implants, with a majority of the studies each having a sample size of more than 100 mini-implants. The consistencies among the 13 studies include general site of insertion (between roots of 1st molar and 2nd premolar), dimension of mini-implant and the duration of load (at least 3 months). The inconsistencies that may weaken the validity of evidence include variations in bone quality, method of insertion, mini-implant manufacturer, practitioner’s experience, insertion torque and angle. Although using randomized samples with more strictly defined criterion would be helpful, the large sample size of Gintautaite’s review compensates for any possible bias in the data. Kuroda’s study consists of 216 titanium screws placed in 110 patients with consistent dimension of screws, clinician’s experience, insertion technique (flapless, self-tapping), insertion torque, and loading period. The author mentions that the lower success rate of mini-screws placed in the mandible may be related to surgical difficulty by the anatomic structure of the mandible. The placement of mini-screws in the alveolar mucosa significantly increases the risk of infection and failure; however, because the posterior mandible has narrow attached gingiva and small oral vestibule, the access and the location of miniscrew placement is more limited.
Applicability The temporary anchorage device (TAD), also known as an orthodontic mini-implant or miniscrew, is an innovative technique rising in popularity among orthodontists due to its ability to provide absolute anchorage for various types of tooth movement such as molar uprighting, correcting midline deviation, and closure of open bites. The failure rate of orthodontic mini-implants is on average approximately 10%, which is higher than that of dental implants (3%). Investigation of the etiologic factors related to success and failure of orthodontic mini-implants, especially in regards to path of insertion, is important to maximizing their stability when under load. This evidence may also help clinicians to decide whether to use a flap or flapless technique for mini-implant placement and will hopefully encourage the use of CBCT to obtain 3-dimensional images that aid in ideal positioning during placement. It is important to keep in mind that there are other contributing factors to mini-implant failure, such as bone thickness and density, type of soft tissue, insertion angle, torque, dimension of implant, insertion technique, and practitioner’s experience.
Specialty (Orthodontics)
Keywords Miniscrews, Mini-Implants, TADs, skeletal anchorage, location of placement, success rate, stability
ID# 3490
Date of submission 06/09/2022
E-mail kims23@livemail.uthscsa.edu
Author Susan Kim
Co-author(s) Kelly Lemke DDS MS
Co-author(s) e-mail lemkek@uthscsa.edu
Faculty mentor Brent Callegari DDS MS
Faculty mentor e-mail callegari@uthscsa.edu
Basic Science Rationale
(Mechanisms that may account for and/or explain the clinical question, i.e. is the answer to the clinical question consistent with basic biological, physical and/or behavioral science principles, laws and research?)
None available
Comments and Evidence-Based Updates on the CAT
None available