The selection of proper anchorage is an essential factor for successful orthodontic treatment. Every orthodontic device, which applies a force onto the tooth, generates an opposite force which then affects the anchorage. The implant in the bone remains stable, which ensures a secure anchorage when no teeth are used. The purpose of this article is to review and update current data on the use of implants for orthodontic anchorage. Following the successful use of conventional prosthodontic implants, osseointegrated and non-osseointegrated implants were used for intra oral orthodontic anchorage. In this research, Pubmed and Cochrane libraries were reviewed based on the key words. The results were confined by some limiting factors such as human clinical trials. Finally the research came up with 16 articles. In this set of material, the application of mini implants and orthodontic anchorage control has been reviewed, and in most cases mini implants have been found to be more successful and reliable in controlling the anchorage unit relative to other orthodontic appliances such as Headgear and Trans Palatal Arches.
Keywords
"Orthodontic Anchorage Procedures"[Majr], implants
Introduction
Anchorage control plays a pivotal role in the effective management of orthodontic mechanics. Anchorage is defined as the resistance to unwanted tooth movement 1. Depending on the requirement, it can be classified as minimum, medium, or maximum anchorage 2. Achieving maximum anchorage has always been difficult for orthodontic practitioners, which often has resulted in loss of anchorage. Anchorage loss is the reciprocal reaction of the anchor unit that can obstruct the success of orthodontic treatment by complicating antero-posterior correction 3. Maximum anchorage to prevent forward movement of the maxillary posterior teeth during anterior teeth retraction can be provided with different approaches. Although several methods have been described to close spaces without losing posterior anchorage, there is no strong scientific evidence of the effectiveness of various anchorage systems for retracting anterior teeth 4. In addition to distal tip-back of the posterior teeth and cortical anchorage via buccal root torque of the molars, orthodontic anchorage can also be prepared by using intra oral holding appliances such as a Nance holding arch or trans-palatal arch. Also, extra oral headgear appliances are commonly used to reinforce posterior anchorage during anterior tooth retraction or are directly applied to retract anterior teeth 5.
With the introduction of dental implants, mini-plates, and micro screws as anchorage units, it is now possible to obtain absolute anchorage of the posterior teeth and close the extraction spaces completely by anterior tooth retraction. However, there still seems to be little accurate scientific evidence pertaining to the treatment effects of skeletal anchorage in these patients. Most treatment assessments were based on anecdotal clinical observations.
In 1997, Kanomi 6 published a case report on the use of mini-implants for orthodontic anchorage. These devices held promise as a low-cost anchorage technique that would be well tolerated by patients, would be clinically and anatomically flexible, and could be loaded immediately. That report started intense clinical interest in and experimentation with orthodontic mini-implants (OMIs), a term that concisely communicates the function (orthodontic), the size (mini: diameter ≤2 mm), and the shape of the device implant.
Despite the growing number of positive case reports, animal studies and human studies, direct clinical interpretation of their results is often difficult. The designs and controlled variables of the few clinical human studies of OMIs vary greatly, and the studies neglected some key issues. Questions remain regarding ideal dimensions of the OMIs, optimal placement locations, best placement techniques, clinical indications, appropriate force levels, and possible need for latency periods.
Materials and Methods
For this set of material Pubmed and Cochrane library were reviewed. Mesh database was used to determine key words " Orthodontic anchorage procedures" and "implants". The search brought up 171 articles. The articles were limited by "English" "Clinical Trial", "Humans", "Randomized Controlled Trial", "Meta-Analysis". Research resulted in 16 articles. Next, those articles were reviewed and compared based on materials and methods and results.
Results
In a study published in 2008 by Upadhyay et al.7, thirty patients requiring maximum anchorage after extraction of the maxillary first premolars were selected. They were divided into 2 groups of 15 each. In the first group (G1), mini-implants were used for en-masse retraction; in the second group (G2), conventional methods of anchorage preservation were followed. Horizontal, vertical, and angular positions of central incisor and maxillary first molar were evaluated cephalometrically before and after orthodontic retraction. 3
Another randomized controlled trial study8 was performed to quantify the treatment effects of en-masse retraction of anterior teeth with mini-implants as anchor units in bi-alveolar dental protrusion patients who received the extraction of all four first premolars. In this study a total of 40 patients were randomly assigned either to group 1 (G1), anterior space closure with mini-implants, using titanium mini implants (1.3 mm in diameter and 8mmin length) as anchor units, or group 2 (G2), anterior space closure with conventional methods of anchorage (without mini-implants). Soft-tissue, skeletal and dental changes were analyzed in both groups on lateral cephalograms taken before retraction and after space closure. Results showing anchorage loss, in both the horizontal and vertical directions, was observed in G2, whereas G1 showed intrusion and distal movement (anchorage gain) of molars. Although the soft-tissue response was variable, lower lip protrusion, nasolabial angle and facial convexity angle had greater changes in G1. Significant reduction in facial convexity in G1, significant increase in nasolabial angle in G1 and a greater level of mandibular lip retraction in G1 compare to G2 were noted .
In a study done by Garfinkle JS et al. 9, thirteen patients were treated with 82 OMIs. By placing 6mm in length and 1.6 mm in diameter implants, they randomly selected left or right side of each arch to load immediately direct forces of up to 250g. The contra lateral side was loaded 3 - 5 weeks later. Serial impressions, Clinical observations and orthodontic adjustments were continued until space closure was adequately achieved. The OMI success rate was determined by comparing the odds of success in relation to clinical parameters such as application of force (loaded or unloaded), timing of force (early or delayed loading), anatomic location (tissue type; maxilla or mandible), and surgical procedure (direct placement or cortical notching). The overall success rate for OMI was calculated as 70.73%. Mixed-model analysis showed no statistically significant difference between the success rates of delayed loaded OMIs (80.95%) and immediately loaded OMIs (80.0%) .
In research conducted by Feldmann et al. 10, one hundred twenty patients were analysed and randomized into 4 anchorage systems: Orthosystem implant (Institute Straumann AG, Basel, Switzerland), Onplant (Nobel Biocare, Gothenburg, Sweden), headgear, and trans-palatal bar. The ultimate results were the measures of the cephalometric analysis of incisor movement, maxillary first molar and sagittal growth changes of the maxilla, and finally the treatment time. The results showed that the maxillary molars were stable during the levelling/aligning phase in the headgear groups and Onplant, Orthosystem implant, but the trans-palatal bar group had anchorage loss (mean, 1.0 mm; P <.001). In the Orthosystem groups and Onplant, during the space-closure phase, the molars were still stable, whereas the headgear and trans-palatal bar groups had lost the anchorage to some extent (means, 1.6 and 1.0 mm, respectively; P <.001).
In a randomized clinical trial conducted by Sandler et al.11, 51 patients with the age range of 12- 39 who actually required maximum anchorage in their treatment plan were randomly selected to receive either headgear or mid-palatal implant to support the anchorage unit. The result of the trial were the surgical and orthodontic success rate as determined by peer assessment rating (PAR), score reductions and the patient's attitudes to implant placement. As a result, headgear and implants proved to be equally effective for anchorage reinforcement. However, the total number of appointments in the implant group was greater than headgear group and there was no significant difference between two groups.
A retrospective study conducted by Yao CC et al. 12, designed to make a comparison between orthodontic outcomes in patients with maxillary dentoalveolar malocclusion, protrusion who were treated with extra oral headgear or mini-implants for maximum anchorage. In this study, 47 cases who had class II malocclusion or Angle class I bimaxillary dentoalveolar protrusion were treated by retraction maxillary incisors through utilizing the created space by the bilateral extraction of maxillary first premolars. They used two different anchorage systems. They used traditional anchorage system with a headgear and trans-palatal for Group 1and mini implants ( mini plates , mini screws or micro screws) for bony anchorage. Pre-treatment and post-treatment lateral cephalograms were considered in order to make comparison the following variables: 2- Movements of the maxillary first molar and central incisor in the vertical direction. 3- Reduction in maxillary central incisors' angulations 4- Loss of anchorage in maxillary first molar 5- Amount of maxillary central incisor retraction. The implant group had greater retraction in anterior teeth (8.17 vs. 6.73mm) and less maxillary molar mesial movement (0.88 vs. 2.07) compare to headgear group. Also, the treatment duration was shorter in implant group (29.81 vs. 32.29 months). In group 2 (mini implant) translation of the incisors was more commonly seen than tipping. Also, in maxillary dentition, intrusion was greater in group 2.
Discussion
Implants for orthodontic anchorage is a relatively new research area. Scientists hold different opinions on most of the questions, therefore more sophisticated and detailed analysis is needed in order to come to a unanimous truth. Firstly, prosthodontic implants were used for the orthodontic purpose. At the time they were the only type of implants used in dentistry. Their application in orthodontics dates back to the late 70s. However, the use of these implants is rather limited due to their size, and time consumption for osseo integration. For various clinical situations several treatment methods can be applied. It is possible to choose different implant systems and positions of screws. The latter fact led to the invention and increasing research of new implant systems, such as, palatal or mini screw implants. Due to simpler biomechanics, small size, non-invasive surgery they have become increasingly popular. The research on the subject is on the increase and the small implants are used more and more widely replacing the bigger ones. With the invention of new implant systems the implantation methods need to be improved and newly risen questions need to be answered. The smaller the implant the less surgical invasion is needed, the lighter swelling and pain and, thus, the discomfort.
Conclusion
Implants are excellent alternatives to traditional anchorage methods in orthodontic treatment, considering the fact that the patient should be an acceptable candidate to receive implants as part of the orthodontic treatment.
