INTRODUCTION

The use of implants in dentistry began when Branemark et al1 published the success of osseointegrated titanium endosseous implants. Implants in dentistry are mostly used for prosthetic reasons,2 but in the past two decades, they have been incorporated into the orthodontic field for anchorage purposes.2–5

Extraoral headgear has been considered an effective form of orthodontic anchorage6 but depends on patient cooperation, and treatment results are limited without it.467 For this reason, other alternatives have been developed like intraoral appliances such as implants. Nevertheless, to use implants, good and sufficient bone structure is necessary for their placement.89 To overcome this disadvantage, smaller appliances such as mini-implants and screws are being developed.45

Although implants and screws seem to be effective alternatives for anchorage in orthodontics, there are some factors to consider before using them. All these appliances should be correctly osseointegrated or fixed to apply force on them.7 To obtain this osseointegration or fixation, a period of time has to be determined where no force would be applied on these devices and, thus, reducing the risk of failure.6 Nevertheless, some studies3710 have stated that forces can be applied immediately after the placement of such devices. This creates a controversy regarding the protocol on the use of implants and screws after their insertion in the mouth for orthodontic purposes.

The purpose of the present systematic review is to present the loading protocols applied when using implants or screws (or both) in orthodontic treatments on the basis of all available published scientific literature that met predetermined minimum criteria for study design.

MATERIALS AND METHODS

Terms used in the literature search consisted of implant, screw, temporary anchorage device, load, orthodontic, and their respective abbreviations according to the search engine used. The selection of these terms was made with the assistance from a senior librarian, specialized in Health Sciences databases. Inclusion criteria to apply on the initial selection of the appropriate articles from the published abstracts consisted of human clinical trials, implant/screw use for orthodontic purposes, nonsyndromic patients (ie, cleft patients), and no surgical or other simultaneous treatment, which could affect the implant/screw integrity during the evaluation period.

A computerized search was conducted using Medline (from 1966 to week 3 of May 2005), Medline In-Process & Other Non-Indexed Citations (from week 3 of May 2005 to week 4 of May 2005), Lilacs (from 1982 to May 2005), PubMed (from 1966 to week 3 of May 2005), Embase (from 1988 to week 22 2005), Web of Science (from 1945 to week 3 May 2005), and all EBM reviews (Cochrane Database of Systematic Reviews, ASP Journal Club, DARE, and CCTR) (to the second quarter of 2005) databases for implant/screw loading during orthodontic treatment.

Eligibility of the articles identified by each search engine was determined by reading their respective title and abstract. Two researchers selected the articles to be collected. An interexaminer agreement of 0.880 (interexaminer kappa) was obtained. Any discrepancies were settled through discussion. All the articles that appeared to meet the inclusion criteria on the basis of their abstracts were selected and collected. Articles from abstracts in which not enough relevant information was stated were also obtained.

The final selection was independently completed by the researchers reading the complete articles, and their results were compared. An interexaminer agreement of 0.920 (interexaminer kappa) was obtained. Reference lists of the selected articles were hand-searched for additional relevant publications that may have been missed by the search engines.

RESULTS

The search results and the initial number of abstracts selected according to the selection criteria from the various databases are shown in Table 1. From the 21 studies initially selected to be eligible on the basis of their title and abstract, only 14 studies actually fulfilled the selection criteria after reading the complete article. After hand-searching the reference lists of the 21 studies, no other study appeared that had not been shown in the electronic search.

TABLE 1.  Search Results from Different Databases

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Of the 14 remaining articles, two1112 were rejected because they reported prosthetic use of implants. Another study13 was rejected because treatment involved the usage of microplates (Table 2).

TABLE 2.  Flow Diagram of the Literature Search

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Finally, only 11 articles, which met all the inclusion criteria, remained. A methodological quality checklist was used to evaluate the selected articles, and the application of the methodological quality checklist is shown in Table 3. As shown in Table 4, all the selected articles received very low-quality scores and had definitive methodological failures.

TABLE 3.  Methodological Score for the Clinical Trials

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TABLE 4.  Methodological Score of Initial Selected Articles^a

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The scoring process was based on a version previously used in a systematic review by Lagravere et al14 No attempt was made to imply that this evaluation was validated. A summary of the sample size, type of appliances used, and protocols applied is shown in Table 5. A description of the manufacturer and appliance characteristics is shown in Table 6.

TABLE 5.  Description of Selected Articles

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TABLE 6.  Description of Appliances Used in Selected Articles

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DISCUSSION

Anchorage has been a concern among orthodontists and has created many problems in this field. This problem has arisen because appliances are in balance, meaning that two objects connected by active appliances are subject to equal and opposite forces. Intraoral and extraoral appliances have been used to fulfill the anchorage requirement, but because of side effects and compliance issues, new methods have been developed to obtain effective anchorage such as implants and screws.17

Although implants and screws do not present the side effects and compliance issues presented by other techniques, they have to be stable and capable of resisting forces that act on the teeth.9 To obtain these characteristics, these appliances have to be used following a correct protocol, ie, when to apply the force after their insertion.

No previous systematic review or meta-analysis has been published regarding loading protocols for implants and screws for orthodontic use. Although there are many studies published on these appliances, the majority are case reports and technical descriptions.

After reviewing all published material on implants and screws in orthodontics, only 11 articles satisfied the inclusion criteria of human clinical trials and reporting results in orthodontic treatments. When the methodological checklist was applied to them, the selected articles obtained very low-quality scores and had definitive methodological failures. From the final 11 articles, five2681516 evaluated implants use in orthodontics, and six3–571017 evaluated screw use in orthodontics.

When reviewing the implant studies, all presented a waiting period before loading for orthodontic reasons. These waiting periods varied from 2 months2 to a maximum of 12 months,2 presenting an average waiting time of 4 to 6 months.2681516

Although implants present a very rigid anchorage unit,5 they present some disadvantages. Among these are that their placement is limited by their size and design to edentulous and retromolar areas,57 laboratory work is required, they are difficult to remove (when necessary),517 it is a traumatic surgical procedure,467 and hygiene is difficult.47 Another factor is its high cost4517 as well as presence of symptoms during the healing process.7 This healing and osseointegration process is long (between 2 and 6 months),25–716 sometimes reaching a period between 915 and 12 months.2 Nevertheless, the implant success rate is 100%261516 in the majority of cases presented by the selected studies.

Regarding screws, four371017 studies applied forces immediately after insertion, whereas the other two45 presented a waiting period of a minimum of 2 weeks.

Screws present some advantages when compared with implants. For example, they do not present major anatomical limitations for insertion, no surgery is necessary, and the cost is low.3–5 Also, there are no symptoms after insertion,3 no laboratory work is necessary, they are easy to remove,5 and they only require a short waiting period before loading,45 if any.371017 This last advantage reduces the treatment period and, thus, increases patient acceptability.10

The short waiting period for healing and osseointegration after screw insertion is because of mechanical retention that is initially obtained. This gives the screws a sufficient primary stability to resist orthodontic loading forces,35 ranging between 30 and 250 g used in different orthodontic movements.9 Nevertheless, this short waiting period is sufficient for healing but not for osseointegration, which is an important factor in maintaining a rigid anchorage unit. Histologically, it has been demonstrated that the premature load generates the formation of fibrous tissue between the bone and the screw. This layer of tissue gives the mechanical retention for the screw to not displace in the direction of the applied force.5 In some cases, this layer of tissue can become granulation tissue because of the short time given for the formation of a correct osseointegration.18

Liou et al5 demonstrated that the screws are clinically stable but not absolutely stationary when forces are loaded on them, which, in the case of implants, would be because of the correct osseointegration. Although there is some displacement by the screws, they have enough stability to complete the treatment. These screws mostly move toward the direction of the applied force, ranging from −1 to 1.5 mm displacement. For this reason, it is recommended that they should be placed 2 mm away from any vital anatomical structure (roots, nerves).

When compared with implants, the screws present many advantages over implants, but in the success rate, the implants presented on average higher success rates than did screws on the selected studies.

Concerning the forces applied to implants or screws, these should be proportional to the amount of osseointegration, which at the same time depends on the surface contact between material and osseous tissue.919 Factors that are involved in this increase in surface are length, diameter, and shape of the appliance.9 According to Favero et al,9 there is an inverse relationship between length and diameter where if the length decreases, the diameter should increase. In this regard, studies on screws establish that the length of the screws have no relationship with their stability,34 whereas the diameter does.3

Success rates for implant and screw usage in orthodontics depend on many factors starting from the loading protocols to the dimensions and insertion sites of these appliances. Future research should involve randomized clinical trials to evaluate all these factors on implant and screw success rates in orthodontics and continued follow-up for possible relapse.

CONCLUSIONS

The following conclusions should be considered with caution because only a secondary level of evidence was found.

• Loading protocols for implants involve a waiting period of a minimum of 2 months before applying orthodontic forces.

• Loading protocols for screws involve immediate loading or a waiting period of 2 weeks to apply orthodontic forces.

• The success rates for implants were, on average, higher than for screws.