Journal of Pharmacy And Bioallied Sciences

: 2021  |  Volume : 13  |  Issue : 5  |  Page : 128--131

Comparative evaluation of primary stability of two different types of orthodontic mini-implants

Jyotirmay Singh1, Sanjay Kumar Singh2, Abhinav Raj Gupta3, Subhash Chandra Nayak4, Ritesh Vatsa5, Priyanka Priyadarshni6,  
1 Department of Orthodontics and Dentofacial Orthopaedics, Patna Dental College and Hospital, Patna, Bihar, India
2 Department of Orthodontics and Orthopedics, Patna Medical College and Hospital, Patna, Bihar, India
3 Consultant Orthodontist, G. S. Memorial Hospital and Trauma Center, Varanasi, Bihar, India
4 Department of Orthodontics and Dentofacial Orthopaedics, Hi-tech Dental College and Hospital, Bhbaneshwar, Odisha, India
5 Department of Dentistry, Sri Krishna Medical College and Hospital, Muzaffarpur, Bihar, India
6 Department of Prosthodontics, Patna Dental College and Hospital, Bihar, India

Correspondence Address:
Ritesh Vatsa
Department of Dentistry, Sri Krishna Medical College and Hospital, Muzaffarpur, Bihar


Background: The mini-implants introduced new possibilities of adequate anchorage in orthodontics. Furthermore, due to its small size, it can even be placed at relatively difficult sites with ease. Removal torque should be high to prevent implant unscrewing. Objective: This prospective clinical trial was aimed to evaluate the insertion torque and removal torque of single-threaded and double-threaded cylindrical orthodontic mini-implants. Materials and Methods: A total of 36 cases were randomly divided into two groups, with an equal number of patients in each group (n = 18). In Group 1 single-threaded cylindrical mini-implant was placed, and in the other group, cylindrical implants with double-threaded were placed. Maximum insertion torque (MIT) and maximum removal torques (MRTs) were recorded for both groups. Data collected were subjected to statistical analysis. Results: MIT was found to be significantly higher than MRT for both the groups and between the groups. Intergroup comparison in the present study showed significantly higher values for MIT than MRT. Intergroup comparison of MIT showed more values for Group 2 as compared to Group 1. Similar statistically significant values were seen in terms with MRT, where double-threaded cylindrical mini-implants had more torque value than the other group. Conclusions: Orthodontic mini screws represent effective temporary anchorage devices. Double-threaded cylindrical mini-implants have significantly higher insertion and removal torque than single-threaded mini-implants and hence better stability.

How to cite this article:
Singh J, Singh SK, Gupta AR, Nayak SC, Vatsa R, Priyadarshni P. Comparative evaluation of primary stability of two different types of orthodontic mini-implants.J Pharm Bioall Sci 2021;13:128-131

How to cite this URL:
Singh J, Singh SK, Gupta AR, Nayak SC, Vatsa R, Priyadarshni P. Comparative evaluation of primary stability of two different types of orthodontic mini-implants. J Pharm Bioall Sci [serial online] 2021 [cited 2023 Jan 27 ];13:128-131
Available from:

Full Text


Anchorage is the resistance to undesired movement of the teeth, and it is essential for the treatment of dental and skeletal malocclusions.[1] The term temporary anchorage devices (TAD) are any sort of implant, screw, pin, or implant that is placed to enhance skeletal anchorage and then removed after the completion of the treatment. Mini-implants proved to be effective in establishing absolute orthodontic anchorage.[2] The miniscrews belong to the (TAD) and the modern ones are usually made of bioinert titanium compounds (Ti6 Al4 V), their diameter range between 1.2 mm to 2.3 mm, and are between 4 mm and 15 mm in length.[3] Primary stability is necessary for the mini screws, because of immediate loading on them, and differs according to the various patient, the design of the mini screws, and clinical technique factors, also it is considered as the clinical condition of mini-implant immobility and ability to resist loads in different directions.[4] In the in vitro studies, using the double-layer artificial bone is mandatory to simulate the human cortical and cancellous bone with appropriate thickness and mechanical properties corresponding to the specific areas of the jaws.[5] The insertion of the orthodontic mini screws can be done either manually or motorized, and the manual insertion method is usually more straightforward, it can achieve better tactile sensation than the motorized one.[6] It is recommended that the mini-implant should be inserted at a slow speed, with low and continuous forces, and hence that the load on both the mini-implant and the surrounding bone is kept low.[7] Primary stability is achieved by mechanical retention between bone and mini-implant. Secondary stability for orthodontic mini-implants is achieved by osseointegration through continued bone remodeling.[8]

Periotest (device to measure the initial stability of dental implants) and resonance frequency analysis have all been used to measure primary stability.[5] Since the mini screws exist to improve the anchorage during the orthodontic treatment, and there are many commercially available brands of mini screws, so that there is a need for a method to assess the primary stability of various mini screws from different manufactures and compare among them, and there are no previous Iraqi studies presented to assess the primary stability.[6] All factors lead to an increase in the interlocking surface area between implant and bone. These modifications in implant design can lead to microfractures in the bone while placing implants and can cause discomfort to the patient.[7] Recently, to improve stability, different thread designs for mini-implants have been developed. However, only a few studies have compared different thread designs and their role in improving implant stability. The present study was designed to compare the stability of two different thread types of orthodontic mini-implants using torque test.

 Materials and Methods

This present prospective clinical trial was performed on the patients within the age group of 18–26 years and with sound mental and physical health, registered for orthodontic treatment in the department of orthodontics. Stratified randomization was done to prevent the allocation bias while enrolling the patients in the study. However, a sample of forty patients (females: 24 males: 16) was used for this study. The Frankfort-Mandibular Plane Angle of 24°–30° depicting growth patterns as average. All the included cases were Type-A anchorage cases with Angle's Class I bimaxillary protrusion with anterior crowding <2–3 mm. Patients with an underlying bony disease such as arthritis were excluded from the study. The informed consent was obtained from all the study patients individually.

Titanium (Ti-6Al-4V) alloy mini-implants, based on thread design and shape were divided into the following two groups: cylindrical single-threaded mini-implants, and cylindrical double-threaded mini-implants. The standard MBT technique was used in all the study participants with sliding mechanics. All the mini-implants were placed between the second premolar and first permanent molar in the maxilla with the help of the implant guide. Patients were divided into two groups having an equal number of patients (n = 18). In one group single-threaded cylindrical mini-implant was placed while the double-threaded cylindrical was placed in the other group. All the mini-implants (n =20) were inserted as well as removed using a contra-angle handpiece and surgical engine with a speed of 30 rpm. Maximum removal torque (MRT) and MIT were then measured. Postsurgery, the patients were prescribed 2% chlorhexidine mouth wash and antibiotics for 3 days.

The results were assembled and compared between the two groups using one-way ANOVA (analysis of variance). P < 0.05 was taken as statistically significant in the one-way analysis of variance. Means and standard deviations were reported.


The final study included 36 patients (females = 20, males = 16) as four patients did not comply with the treatment and backed out during the study period. The maximum insertion torque (MIT) was calculated in N cm for both study groups individually.

On comparing MIT for both the groups, the values showed a statistically significant difference between the groups [Table 1].{Table 1}

The statistical calculations suggested that MRT value for double-threaded cylindrical mini screws, i.e., Group 2 were statistically higher as compared to Group 1 with a mean value and standard deviation [Table 2].{Table 2}

While comparing MIT of Group 1, i.e, single-threaded cylindrical mini screws with MRT of Group 1 mini-implants, it was seen that MIT showed statistically significant higher values with the mean value and standard deviation [Table 3].{Table 3}

The intragroup comparison of Group 2 showed a statistically significant difference between the values of MIT and MRT, which is consistent with Group 1 results. The difference between the two values was statistically significant with a P ˂ 0.00001 [Table 4].{Table 4}

While comparing intergroup MIT value was significantly higher than MRT for both the groups, the values showed a statistically significant difference between the groups [Table 5].{Table 5}


Proper insertion and careful removal of orthodontic mini-implants is a necessary aspect for which torque plays an important role.

Attaining primary stability at the time of implant insertion depending upon the mini-implant characteristic, design, placement condition, and insertion site is crucial for success.[8] Few indirect measures for primary mini-implant stability are insertion torque,[9] and density of bone[10] are also necessary factors as inordinately low or high torque values can result in compromised implant stability.[11] Values of 5–10 Ncm for MIT are recommended by various authors for implant success.[12] A systematic review suggested a mean value of MIT as 13.28 Ncm with a standard deviation of 0.34 for self-tapering mandibular mini-implants.[13] Insertion torque is related to the length of implant and thickness of cortical bone positively,[14] in contrast, it relates to predrilling diameter negatively.[6] Thicker cortical bone, high thread angle, and large implant diameter are few factors that predict higher values of MIT in vitro with a value of 24.7%, 12.3%, and 10.7%, respectively.[15] Pull-out strength and MIT values were not affected by bone density, for a cortical bone thickness of 1 mm in an in vitro study.[16] These results were consistent with the present study.

A systematic review considered cadaver, animal, and clinical studies concluded that mini-implants placed near roots had higher values for insertion torque as compared to those without contact. Therefore, torque levels should be recorded during the entire process of mini-implant insertion.[17]

In cases where immediate implant loading is done, insertion torque is to be kept high. In cases with less insertion torque, delayed implant loading (6–8 weeks) should be attempted. Implants with a minimum insertion torque value of 15 Ncm survived immediate loading better.[10] Even in cases with longer treatment duration, the median survival time for implants was sufficient.[18] The risk of fracture during implant removal is a crucial factor. A systematic review reported a value of 10.01Ncm with a standard deviation of 0.17 for MRT in maxillary cylindrical mini-implants.[19] However, removal torque value is considerably lower than value for insertion torque for cylindrical as well as conical orthodontic mini-implants.20 This was in consent with present study where it had no significant correlation with insertion torque. Also, it did not relate significantly to placement period and thickness of cortical bone in vitro.[8],[20]


The success of mini-implants depends on the proper selection of implant length, tapering, diameter, and insertion site. Furthermore, adequate insertion is assessed in terms of predrilling angle, insertion site, primary stability, proper loading, lack of inflammation at the placement site, absence of mobility, and no injury. Furthermore, proper insertion and removal torque are necessary for achieving the primary stability of orthodontic mini-implants. However study with more patients, more extended monitoring periods, and different designs of mini screws are required to reach the definitive conclusion.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.


1Kim JS, Choi SH, Cha SK, Kim JH, Lee HJ, Yeom SS, et al. Comparison of success rates of orthodontic mini-screws by the insertion method. Korean J Orthod 2012;42:242-8.
2Cousley R. Mini-Implants in Orthodontics. Innovative Anchorage Concepts 2008; 2009. p. 215-16.
3Miyawaki S, Koyama I, Inoue M, Mishima K, Sugahara T, Takano-Yamamoto T. Factors associated with the stability of titanium screws placed in the posterior region for orthodontic anchorage. Am J Orthod Dentofacial Orthop 2003;124:373-8.
4Wilmes B, Rademacher C, Olthoff G, Drescher D. Parameters affecting primary stability of orthodontic mini-implants. J Orofac Orthop 2006;67:162-74.
5Huja SS, Rao J, Struckhoff JA, Beck FM, Litsky AS. Biomechanical and histomorphometric analyses of monocortical screws at placement and 6 weeks postinsertion. J Oral Implantol 2006;32:110-6.
6Wilmes B, Ottenstreuer S, Su YY, Drescher D. Impact of implant design on primary stability of orthodontic mini-implants. J Orofac Orthop 2008;69:42-50.
7Ueda M, Matsuki M, Jacobsson M, Tjellström A. Relationship between insertion torque and removal torque analyzed in fresh temporal bone. Int J Oral Maxillofac Implants 1991;6:442-7.
8Motoyoshi M, Uemura M, Ono A, Okazaki K, Shigeeda T, Shimizu N. Factors affecting the long-term stability of orthodontic mini-implants. Am J Orthod Dentofacial Orthop 2010;137:588.e1-5.
9Pithon MM, Nojima MG, Nojima LI. Primary stability of orthodontic mini-implants inserted into maxilla and mandible of swine. Oral Surg Oral Med Oral Pathol Oral Radiol 2012;113:748-54.
10Chaddad K, Ferreira AF, Geurs N, Reddy MS. Influence of surface characteristics on survival rates of mini-implants. Angle Orthod 2008;78:107-13.
11Motoyoshi M. Clinical indices for orthodontic mini-implants. J Oral Sci 2011;53:407-12.
12Meursinge Reynders RA, Ronchi L, Ladu L, van Etten-Jamaludin F, Bipat S. Insertion torque and success of orthodontic mini-implants: A systematic review. Am J Orthod Dentofacial Orthop 2012;142:596-614.
13Cunha AC, da Veiga AM, Masterson D, Mattos CT, Nojima LI, Nojima MC, et al. How do geometry-related parameters influence the clinical performance of orthodontic mini-implants? A systematic review and meta-analysis. Int J Oral Maxillofac Surg 2017;46:1539-51.
14Pithon MM, Figueiredo DS, Oliveira DD. Mechanical evaluation of orthodontic mini-implants of different lengths. J Oral Maxillofac Surg 2013;71:479-86.
15Katić V, Kamenar E, Blažević D, Spalj S. Geometrical design characteristics of orthodontic mini-implants predicting maximum insertion torque. Korean J Orthod 2014;44:177-83.
16Marquezan M, Souza MM, Araújo MT, Nojima LI, Nojima Mda C. Is miniscrew primary stability influenced by bone density? Braz Oral Res 2011;25:427-32.
17Meursinge Reynders R, Ladu L, Ronchi L, Di Girolamo N, de Lange J, Roberts N, et al. Insertion torque recordings for the diagnosis of contact between orthodontic mini-implants and dental roots: A systematic review. Syst Rev 2016;5:50.
18Lee SJ, Ahn SJ, Lee JW, Kim SH, Kim TW. Survival analysis of orthodontic mini-implants. Am J Orthod Dentofacial Orthop 2010;137:194-9.
19Cunha AC, da Veiga AM, Masterson D, Mattos CT, Nojima LI, Nojima MC, et al. How do geometry-related parameters influence the clinical performance of orthodontic mini-implants? A systematic review and meta-analysis. Int J Oral Maxillofac Surg 2017;46:1539-51.
20Pithon MM, Nojima MG, Nojima LI. In vitro evaluation of insertion and removal torques of orthodontic mini-implants. Int J Oral Maxillofac Surg 2011;40:80-5.