Introduction

One of the most challenging aspects of orthodontic treatment is “Anchorage control”. As described by Archimedes (Greek philosopher), “give me a place to stand and I will move the earth”. He was a pioneer in the field of mathematics and mechanics and presented with anchorage problems much earlier than the clinicians faced it.1 Anchorage has been defined as “the resistance to the forces generated against the active component of an orthodontic appliance”. Simply, it means resistance to displacement. There are two elements of orthodontic appliance. One is the active tooth movement itself and another is the resistance elements.2 Anchorage abides by Newton’s third law which means every action (force) has an equal and opposite reaction. To sum up, all anchorage elements are relative, and all resistance forces are comparative. Various elements that provide orthodontic anchorage include the teeth, hard palate, head, neck, and implants.3

The Temporarily placed Miniscrew for orthodontic anchorage was mentioned for the first time in 1997 by Kanomi followed by the invention of more advanced screw designs.4 Temporary anchorage devices (TADs), like mini-plates, mini-screw, micro-screw, micro-implants were advantageous because of their smaller size that can be placed easily at various implant sites. Also, surgical placement of mini-implants was easy since it does not require full flap retraction and can be loaded immediately. Thus, these were more popular than endosseous implants as a means of anchorage device for orthodontic procedures.5 Though, miniscrews had several advantages yet they had some limitations.

Anchorage through miniscrew was limited by position and angulation of dental roots as well as inter-radicular space.

There were certain recommendations for the safe placement of miniscrews. To preserve periodontal health, a minimum of 1mm alveolar bone is recommended around the miniscrew. Therefore, a total of 3mm or larger inter radicular space is required for safe placement of miniscrew when the diameter of miniscrew and alveolar bone clearance is taken into consideration.6 6 The maxilla was a more suitable site for placement of mini-implants due to its sufficient bone quantity and tooth roots were more widely placed in it. Thus, Maxilla offered a higher success rate.7 Several studies determined the safe site in inter radicular bone for the placement of miniscrews. These sites were called “safe zones”. Moreover, the availability of inter radicular space was different for a different endoskeletal pattern. The inter radicular space was larger in the maxilla in patients with Class II Skeletal pattern as compared to Class III skeletal pattern and vice versa for mandibular jaw. 8 Also, inter-radicular bone availability also depends on gender and age. Studies show that Males and population older than 18 years of age have a larger buccal and lingual cortical bone thickness in both the jaws. 9 To plan miniscrew placement, Panoramic and periapical radiographs were not recommended as they provided two-dimensional images. Computed cone-beam tomography was preferred to obtain volumetric data to plan the mini-screw placement owing to its three-dimensional imaging, low cost, and relatively low radiation dose.10 Thus, our aim of this study was to measure the inter-radicular spaces in the anterior and posterior region on the right side of the maxillary and mandibular jaw and to determine the most reliable sites for miniscrew placement using Cone-beam computed tomography.

Material and Methods

The sample of 75 subjects was selected and divided into 3 groups with 25 subjects in each group. A signed informed consent form was taken in English or Marathi language. Initially, each subject was thoroughly examined clinically according to inclusion and exclusion criteria.

Results

In vertical growth pattern, in posterior maxilla highest mesiodistal width between 2nd premolar and 1st molar at 7mm. in mandible, it was between 1st and 2nd molar at 11mm. (Table 1, Table 2)

In horizontal growth pattern, in posterior maxilla highest mesiodistal width between 1st and 2nd premolar, and mandible it was between 1st and 2nd molar at 11mm. (Table 3, Table 4 )

In average growth pattern, in posterior maxilla highest mesiodistal width between 2nd premolar and 1st molar and 1st molar at 7mm., in mandible, it was between 1st and 2nd molar at 11mm. (Table 5, Table 6, Table 7)

Discussion

In this study, Interradicular distance between 1^st and 2^nd premolar, 2^nd premolar and 1^st molar as well as between 1^st and 2^nd molar was calculated in both the arches. The Cone beam computer tomography was used in this study. Both mesiodistal, as well as buccolingual distances, were measured. Significance difference between groups was found between the inter radicular bone values of maxillary 2^nd premolar and 1^st molar region and between 1^st and 2^nd maxillary molars. Thus, the null hypothesis for this study was rejected. In the posterior maxilla, the greatest amount of mesiodistal inter radicular bone was found between 1^st and 2^nd premolar at 11mm, 2^nd premolar and 1^st molar at 9mm,1^st molar and 2^nd molar at 3mm apically from the alveolar crest. Moreover, the highest buccolingual inter radicular bone was found between 1^st and 2^nd premolar at 11mm, 2^nd premolar and 1^st molar at 5mm, and between 1^st and 2^nd molar at 5 mm. In the posterior mandible, the greatest amount of mesiodistal inter radicular bone was found at 11mm and buccolingually at 9 mm between all the teeth. It can be said that the inter radicular bone is greater apically than towards the alveolar crest. The least amount of bone was between maxillary 1^st and 2^nd molar (1.8 mm at 3mm depth from alveolar crest) and between mandibular 2^nd premolar and molar (2.04 mm at 3mm depth for alveolar crest).

In the study conducted by Poggio, the greatest mesiodistal inter radicular bone was between the 2^nd premolar and 1^st molar (5.5 mm SD 1.3) at 5mm from the alveolar crest. Lesser mesiodistal space is available on the buccal side than the lingual aspect. Buccopalatally, the greatest amount of inter radicular bone was found between 1^st and 2^nd molars (14.1 mm SD 1.1) at 5 mm depth from the alveolar crest. Thus, it was concluded that the palatal aspect had more sites for mini-implant placement due to great bone availability.8

Mini implant size varies around 5-6 mm in length and 1-1.2 mm in diameter. Ideally, 1 mm of sound bone is needed to maintain periodontal health. Thus, a minimum of 3.2 mm of inter radicular bone is required for placement of the mini-implant for orthodontic anchorage.11 The insertion site for placement of the mini-implant depends on implant biomechanics as well as the patient’s oral anatomy like the location of maxillary sinus and course of mandibular nerve. 12, 13 Mental foramen lies between 1^st and 2^nd mandibular premolar.14 Buccal alveolar cortical depth becomes thinner in the posterior region. It is only about 1-1.5 mm at the distal aspect of the 2^nd molar. 15 These landmarks must be taken into consideration for safe placement of mini-implant for orthodontic anchorage.

Conclusion

The importance of the relationship between the growth pattern and the availability of inter radicular space may aid the clinician in planning appropriate surgical sites for miniscrew implant placement. This study helps in reducing dilemma about ideal insertion sites for implant placement, as it has given a more definite and accurate finding of insertion sites for implant placement in different growth patterns

Source of Funding

No financial support was received for the work within this manuscript.

Conflicts of Interest

There are no conflicts of interest.