Insertion Torque and Pull-Out Strength of Orthodontic Mini-implants Comparing Manual and Motor Insertion Methods.

The Journal of Craniofacial Surgery

Volume 26, Number 3, May 2015

Hyun Ju Lee, MD, PhD Department of Pathology College of Medicine Soonchunhyang University Cheonan, Korea

ACKNOWLEDGEMENT This work was supported by the Soonchunhyang University Research Fund.

REFERENCES

Correspondence

The mechanical imbrication of the mini-implant body to the bone, that is, its primary stability, is critical to the success of the technique.5 The primary stability of mini-implants can be affected by the screw and the host. Therefore, mini-implant design, bone quality, and insertion technique and angle must be carefully analyzed before installation.6,7 Moreover, factors that help maintain primary stability such as oral hygiene, the patient’s health condition, bone response to the injury inflicted, insertion site selection, and choice of the proper mini-implant system8 are responsible for mini-implant retention (secondary stability) during the time required for treatment.6,9 Measurements of insertion torque and pull-out strength of the screw are indicators of primary stability, but they do not always respond similarly depending on the type of experiment. Overly high torque insertion values can cause microfractures and bone injury that may lead to necrosis of the area. In vivo studies have reported a negative correlation between insertion and removal torques of miniimplants after weeks under orthodontic forces.9 –11 Conversely, in ex vivo or in vitro12 studies, where there is no inflammatory reaction of the host, a positive correlation between insertion torque and removal torques or pull-out strength has been observed. It should be noted that the ideal mini-implant should have an insertion torque high enough to provide good primary stability, without causing major bone damage, and high pull-out strength.7 Because mini-implant design is of great importance in achieving stability and subsequent success in the technique, and given the great diversity of commercial brands available in the market, this study aimed to evaluate in vitro the insertion torque and pull-out strength of orthodontic mini-implants from 5 commercial brands, comparing between manual and motor insertion methods.

1. Jung SN, Shin JW, Kwon H, et al. Fibrolipoma of the tip of the nose. J Craniofac Surg 2009;20:555–556 2. Lee SY, Jung SN, Sohn WI, et al. Submuscular fibrolipoma of the forehead. J Craniofac Surg 2010;21:1993–1994 3. Kim YT, Kim WS, Park YL, et al. A case of fibrolipoma. Korean J Dermatol 2003;41:939–941 4. Baharloo F, Corhay JL, Hotermans G, et al. A case of tracheal fibrolipoma. Acta Clin Belg 1994;49:23–25 5. Kajihara M, Sugawara Y, Sakayama K, et al. Subcutaneous fibrolipoma in the back. Radiat Med 2006;24:520–524 6. Shin SJ. Subcutaneous fibrolipoma on the back. J Craniofac Surg 2013;24:1051–1053 7. Janas A, Grzesiak-Janas G. The rare occurrence of fibrolipomas. Otolaryngol Pol 2005;59:895–898 8. Furlong MA, Fanburg-Smith JC, Childers EL. Lipoma of the oral and maxillofacial region: site and subclassification of 125 cases. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2004;98:441–450 9. Ragidale BD. Tumors with fatty, muscular, osseous, or cartilaginous differentiation. In: Lever WF, Schaumburg-Lever G, eds. Histopathology of the Skin. 9th ed. Philadelphia, PA: JB Lippincott; MATERIALS AND METHODS 1990:1065–1066 Fifty self-drilling mini-implants were used, 10 each from the following 10. Riebel JF, Greene WM. Liposarcoma arising in the pharynx nine years after fibrolipoma excision. Otolarygol Head Neck Surg commercial brands with respective surgical kits: SIN (Sistema de 1995;112:599–602 Implantes Nacional, Saõ Paulo, Saõ Paulo, Brazil), Neodent (NEO, 11. Mazzocchi M, Onesti MG, Pasquini P, et al. Giant fibrolipoma in the Curitiba, Parana´, Brazil), Conexaõ (CON [Conexaõ Sistemas de leg-a case report. Anticancer Res 2006;26:3649–3654 Pro´tese Ltda, Aruja´], Saõ Paulo, Brazil), Rocky Mountain (RMO, 12. Gundes H, Alici T, Sahin M. Neural fibrolipoma of the digital nerve: a Seoul, South Korea), and Morelli (MOR, Sorocaba, Brazil). case report. J Orthop Surg (Hong Kong) 2011;19:123–125 All mini-implants had similar design and size to facilitate 13. Brooke RI, MacGregor AJ. Traumatic pseudolipoma of the buccal comparisons and statistical analysis (Table 1). mucosa. Oral Surg Oral Med Oral Pathol 1969;28:223–225 To standardize the bone surface evaluated, we opted for using 14. Rozner L, Isaacs GW. The traumatic pseudolipoma. synthetic polyurethane bone (Sawbones; Pacific Research LaboraAust N Z J Surg 1977;47:779–782 tories Inc, Vashon, WA). Biomechanical test blocks were chosen 15. Signorini M, Cushman-Vokoun AM. Molecular diagnostics of over a cadaver model because they offer uniform and consistent soft tissue tumors. Arch Pathol Lab Med 2011;135:588–601 physical properties that eliminate the variability encountered when 16. Copcu E, Sivrioglu NS. Posttraumatic lipoma: analysis of 10 cases and testing with human cadaver bone. Two 120 170 41.5-mm explanation of possible mechanisms. Dermatol Surg 2003;29:215–220

Insertion Torque and Pull-Out Strength of Orthodontic Miniimplants Comparing Manual and Motor Insertion Methods To the Editor: Mini-implants appeared on the market to provide absolute anchorage for orthodontics. The possibility to control movement without patient compliance, their versatility, ease of installation and removal, and low cost have attracted the attention of orthodontists and researchers in an attempt to reduce flaws in this anchorage procedure.1,2 These features enable orthodontic treatment, especially in rehabilitation of partially edentulous patients.3,4 #

2015 Mutaz B. Habal, MD

(length width height) synthetic bone plates were used, with 1.5 mm in height simulating the cortical bone (40-pounds per cubic foot density) and the remaining 40 mm simulating the medullary bone (15-pounds per cubic foot density). A 20 20-mm area was demarcated in the 2 bone blocks for testing. In each block, 5 areas were demarcated for each implant brand, totaling 25 areas per block. Each block was used for testing 1 insertion method only. The 50 mini-implants were installed by a single, previously calibrated operator, 25 by the manual insertion method using the hand driver provided in the surgical kit of each brand and 25 by the motor insertion method using an implant motor with torque control (SIN MSIN1 motor, 20-N/cm torque; Figs. 1A, B). After installation of all mini-implants, the final thread and insertion torque readings were performed using a Lutron TQ8800 digital hand torque wrench (Lutron Electronic Enterprise Co, Ltd, Taipei, Taiwan) until the transmucosal profile reached the cortical bone. Maximum insertion torque was recorded in N/cm. After the insertion torque of mini-implants was recorded in the 2 methods, the bone blocks were sectioned for specimen preparation

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Copyright © 2015 Mutaz B. Habal, MD. Unauthorized reproduction of this article is prohibited.


Correspondence


TABLE 1. Mini-implant Features According to Manufacturer’s Specifications Group

Manufacturer

NEO MOR RMO CON SIN

NEO MOR RMO CON SIN

Origin

ND, mm

NL, mm

Profile, mm

Shape

Lead Thread

Curitiba, Parana´, Brazil Sorocaba, Saõ Paulo, Brazil Seoul, South Korea Aruja´, Saõ Paulo, Brazil Saõ Paulo, Saõ Paulo, Brazil

1.60 1.60 1.60 1.50 1.60

7.00 6.00 6.00 6.00 6.00

1.00 2.00 0.00 1.00 0.00

Cylindrical Cylindrical Cylindrical Conical Cylindrical

Single Single Single Double Single

ND, indicates nominal diameter; NL, nominal length. Source: Manufacturer’s catalogs.

for use in pull-out strength tests. Bone blocks were cut using a Dhpro diamond disc (REF DRT 45; Dhpro Tecnologia Profissional, distributed by Rhadartrade Comercial Importadora de Peças Ltda, Paranagua´, Parana´, Brazil), and bone segments were individualized and resized to 20 20 41.5-mm blocks. The bone segments were then subjected to pull-out tests using an MTS 810 Material Testing System (MTS Corporation, Minneapolis, MN). The specimens were placed in a vise, and the mini-implant was connected to an orthodontic wire coupled to the testing machine. Tests were conducted with a load cell of 10 kN at a speed of 0.5 mm/min. Peak load force to fail was recorded for each miniimplant in newtons (Fig. 1C). Differences in insertion torque and pull-out strength between implant brands and insertion methods were determined using 2-way analysis of variance followed by Tukey post hoc test where appropriate. Significance level was set at P < 0.05. The Pearson correlation test (rP) was used to determine the relationship between pull-out strength and insertion torque in the different implant brands and insertion methods. The correlation is weak with rP values between 0 and 0.3, satisfactory between 0.3 and 0.6, and strong between 0.6 and 0.9, and at greater than 0.9, the correlation is very strong or perfect (rP ¼ 1.0). Negative rP values indicate a negative correlation between the 2 variables, and the correlation is statistically significant when P < 0.05.

CON implants (Table 3). Insertion torque values and pull-out strength were weakly correlated (Table 4).

DISCUSSION The results of our study show that the manual insertion method provided greater primary stability than the motor insertion method regardless of mini-implant design. The use of synthetic bone as a replacement for human bone in pull-out strength and insertion torque tests enabled us to standardize cortical and medullary bone thickness and density and remove the variable bone type from the experiment. Thus, retention results are a function of mini-implant design and insertion method only. Synthetic bone has been widely used in in vitro studies,6,7,13–16 and although these studies do not precisely reproduce clinical settings, they can provide standardized information on the receptor bone. It should be noted that because this is an in vitro study, it only addresses mechanical questions regarding mini-implant/bone imbrication, which closely approximates the primary stability achieved in vivo soon after mini-implant insertion. Because secondary stability, that is, the stable retention of the mini-implant in the TABLE 2. Insertion Torque Values (Mean SD) of Orthodontic Mini-implants From Different Commercial Brands Using Manual and Motor Insertion Methods Insertion, N/cm

RESULTS Insertion torque was significantly lower in the motor insertion method than in the manual method (Table 2). In addition, insertion torque values differed significantly between SIN and MOR/CON, SIN and RMO/NEO, and between RMO/NEO and CON/MOR brands in the 2 insertion methods (Table 2). Similarly to insertion torque values, pull-out strength was significantly lower in the motor insertion method than in the manual method (Table 3). Pull-out strength values differed significantly between SIN/RMO and NEO/CON/MOR brands in the 2 insertion methods. In addition, MOR implants had the lowest pull-out strength values and also differed significantly from NEO and

Implant MOR CON NEO RMO SIN

Motor 5.1 1.1 4.4 1.1 8.0 0.7 8.5 0.6 10.3 2.2

Manual 5.5 0.6 5.8 1.0 8.5 0.6 9.5 1.8 11.0 1.2

cB cB bB bB aB

cA cA bA bA aA

Means followed by different lowercase letters in the same column and uppercase letters in the same row differ significantly (P < 0.05).

TABLE 3. Pull-Out Strength Values (Mean SD) of Orthodontic Mini-implants From Different Commercial Brands Using Manual and Motor Insertion Methods Torque, N Implant MOR CON NEO RMO SIN FIGURE 1. A, Mini-implant installation by the manual insertion method; (B) mini-implant installation by the motor insertion method; (C) mini-implant subjected to pull-out strength test.

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Motor 53.1 6.9 75.9 10.5 79.5 8.2 99.6 8.8 99.8 15.8

Manual 65.7 7.1 91.8 7.5 84.7 5.8 113.6 6.7 115.5 15.7

cB bB bB aB aB

cA bA bA aA aA

Means followed by different lowercase letters in the same column and uppercase letters in the same row differ significantly (P < 0.05).

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TABLE 4. Pearson Correlation Coefficients (rP) Between Pull-Out Strength and Insertion Torque Values of Orthodontic Mini-implants From Different Commercial Brands Using Manual and Motor Insertion Methods Insertion Method Implant SIN NEO RMO CON MOR

Manual

Motor

0.053 P ¼ 0.93 0.873 P ¼ 0.05 0.115 P ¼ 0.854 0.086 P ¼ 0.89 0.023 P ¼ 0.97

0.238 P ¼ 0.70 0.446 P ¼ 0.45 0.153 P ¼ 0.80 0.200 P ¼ 0.74 0.168 P ¼ 0.78

bone, is greatly influenced by the biological response of the host, our results should not be extrapolated to secondary stability without conducting an in vivo test. Nevertheless, our results were contrary to those of Shin et al,17 who found no significant differences between manual insertion and motor insertion with a hand piece in surfacetreated mini-implants. The results showed that the 5 mini-implant brands had clinically acceptable values compatible with those reported in studies using synthetic bone.9,13 Moreover, SIN implants had the greatest retention, shown by the highest insertion torque and pull-out strength values, followed by RMO and NEO brands, whereas CON and MOR implants provided lower mechanical retention. The screw body from all brands had similar features (ie, cylindrical shape, equal diameter, and single thread), except CON implants, which had a conical, double-thread design. Among the cylindrical implants, RMO, SIN, and NEO had sharper, morespaced-out threads than the MOR screw body. In fact, brands with sharper threads exhibited higher insertion torque values. Conversely, implants with a cylindrical double-thread design had lower torque insertion values, contrary to the studies of Chen et al,9 Suzuki and Suzuki and Suzuki,11 Kim et al,18 Heo et al,13 and Song et al.19 A possible explanation for the conflicting results is that even though the commercial brands evaluated differed among the studies, miniimplants used in this study had threads that were less sharp. Pull-out strength values observed in this study ranged from 65.7 to 155.5 N, and while clinically acceptable, they are lower than those reported in other studies using synthetic bone (133.75–175.01 N).14,16 This difference in pull-out strength values between studies is likely due to differences in bone density and thickness used in each experiment.14–16,20– 23 Axial pull-out strength is the result of bone failure and reflects the magnitude of the pull-out strength that the screw bears before bone rupture.20 There was a weak correlation between insertion torque and pullout strength values. This result is in agreement with the study of Pfeiffer et al24 and contrary to several studies that found a positive correlation between insertion torque and pull-out strength.25 Despite the weak statistical correlation, SIN, RMO, and NEO brands had higher pull-out strength values than MOR and CON, similarly to what was observed in insertion torque values. Even though insertion torque and pull-out strength are direct indicators of primary stability, overly high values may cause microfractures and bone injuries that result in ischemic necrosis in the area.9,11,18 Thus, in vivo studies that determine the response of bone tissue to the forces generated by imbrication would be needed to rank the commercial brands evaluated in this study as to their secondary stability. #


Correspondence

The results of this in vitro study showed that primary stability of mini-implants was influenced by the design of each commercial brand and that primary stability was greater in the manual insertion method than in the motor insertion method regardless of miniimplant brand. Viviane A. Assunçaõ, MD Nadia Lunardi, MD Eloisa M. Boeck, MD Department of Orthodontics School of Dentistry Araraquara University Center (UNIARA) Araraquara Saõ Paulo, Brazil [email protected] Luis Geraldo-Vaz, MD Department of Dental Materials and Prosthodontics School of Dentistry Saõ Paulo State University (UNESP) Araraquara Saõ Paulo, Brazil Rodolfo J. Boeck-Neto, MD Department of Surgery School of Dentistry Araraquara University Center (UNIARA) Araraquara Saõ Paulo, Brazil Eloa´ R. Luvizuto, MD Department of Surgery and Integrated Clinic UNESP–Univ Estadual Paulista Araçatuba Dental School Saõ Paulo, Brazil

REFERENCES 1. Berens A, Wiechmann D, Dempf R. Mini- and micro-screws for temporary skeletal anchorage in orthodontic therapy. J Orofac Orthop 2006;67:450–458 2. Wilmes B, Drescher D. Impact of insertion depth and predrilling diameter on primary stability of orthodontic mini-implants. Angle Orthod 2009;79:609–614 3. Kanomi R. Mini-implant for orthodontic anchorage. J Clin Orthod 1997;31:763–764 4. Costa A, Raffainl M, Melsen B. Miniscrews as orthodontic anchorage: a preliminary report. Int J Adult Orthodon Orthognath Surg 1998;13:201–219 5. Consolaro A, Sant’ana E, Francischone CE Jr, et al. Mini-implantes: pontos consensuais e questionamentos sobre o seu uso clıńico. R Dental Press Ortodon Ortop Facial 2008;13:20–27 6. Holm L, Cunningham SJ, Petrie A, et al. An in vitro study of factors affecting the primary stability of orthodontic mini-implants. Angle Orthod 2012;82:1022–1028 7. Shah AH, Behrents RG, Kim KB, et al. Effects of screw and host factors on insertion torque and pullout strength. Angle Orthod 2012;82:603–610 8. Kyung HM, Park HS, Bae SM, et al. Development of orthodontic micro-implants for intraoral anchorage. J Clin Orthod 2003;37: 321–328 quiz 314 9. Chen Y, Kyung HM, Gao L, et al. Mechanical properties of self-drilling orthodontic micro-implants with different diameters. Angle Orthod 2010;80:821–827 10. Kim JW, Baek SH, Kim TW, et al. Comparison of stability between cylindrical and conical type mini-implants. Mechanical and histological properties. Angle Orthod 2008;78:692–698

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11. Suzuki EY, Suzuki B. Placement and removal torque values of orthodontic miniscrew implants. Am J Orthod Dentofacial Orthop 2011;139:669–678 12. McManus MM, Qian F, Grosland NM, et al. Effect of miniscrew placement torque on resistance to miniscrew movement under load. Am J Orthod Dentofacial Orthop 2011;140:93–98 13. Heo YY, Cho KC, Baek SH. Angled-predrilling depth and mini-implant shape effects on the mechanical properties of self-drilling orthodontic mini-implants during the angled insertion procedure. Angle Orthod 2012;82:881–888 14. Meira TM. Biomechanical behavior of orthodontic mini-implants at different angles. Dissertaçaõ [mestrado]—Pontifıćia Universidade Cato´lica do Parana´, Curitiba 2010:1–59 15. Petrey JS, Saunders MM, Kluemper GT, et al. Temporary anchorage device insertion variables: effects on retention. Angle Orthod 2010;80:446–453 16. Wang CH, Wu JH, Lee KT, et al. Mechanical strength of orthodontic infrazygomatic mini-implants. Odontology 2011;99:98–100 17. Shin YS, Ahn HW, Park YG, et al. Effects of predrilling on the osseointegration potential of mini-implants. Angle Orthod 2012;82:1008–1013 18. Kim YK, Kim YJ, Yun PY, et al. Effects of the taper shape, dual-thread, and length on the mechanical properties of mini-implants. Angle Orthod 2009;79:908–914 19. Song YY, Cha JY, Hwang CJ. Mechanical characteristics of various orthodontic mini-screws in relation to artificial cortical bone thickness. Angle Orthod 2007;77:979–985 20. Salmo´ria KK, Tanaka OM, Guariza-Filho O, et al. Insertional torque and axial pull-out strength of mini-implants in mandibles of dogs. Am J Orthod Dentofacial Orthop 2008;133:790.e15–790.e22 21. Berzins A, Shah B, Weinans H, et al. Nondestructive measurements of implant-bone interface shear modulus and effects of implant geometry in pull-out tests. J Biomed Mater Res 1997;34:337–340 22. Huja SS, Litsky AS, Beck FM, et al. Pull-out strength of monocortical screws placed in the maxillae and mandibles of dogs. Am J Orthod Dentofacial Orthop 2005;127:307–313 23. Leung MT, Rabie AB, Wong RW. Stability of connected mini-implants and miniplates for skeletal anchorage in orthodontics. Eur J Orthod 2008;30:483–489 24. Pfeiffer M, Gilbertson LG, Goel VK, et al. Effect of specimen fixation method on pullout tests of pedicle screws. Spine (Phila Pa 1976) 1996;21:1037–1044 25. Roe SC, Pijanowski GJ, Johnson AL. Biomechanical properties of canine cortical bone allografts: effects of preparation and storage. Am J Vet Res 1988;49:873–877

Implantoprosthesis Treatment in Subject Suffering From Osteogenesis Imperfecta With New Multifactorial Rehabilitation Protocol To the Editor: The patient, T.L., a 40-year-old woman, not smoking, suffers from type III osteogenesis imperfecta and has been treated with the administration of bisphosphonates intramuscularly for at least 10 years (neridronate 100 mg every 3 months). The problem of this bad bone mineralization is traced back to a mutation of the N-terminal end of the collagen; she was diagnosed with congenital hip dysplasia. At the dental anamnesis, the patient reported having defective dentinogenesis that has caused fracture of the deciduous dentition. She also reported that both upper and lower permanent incisor elements have been splinted to avoid an early loss.

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FIGURE 1. Initial radiographic OPT examination.

The drug therapy with bisphosphonates she was given for at least 10 years has been discontinued for 6 months before the surgery, in accordance with her doctor. During the presurgical phase, study of the preliminary hematochemical and radiological examinations specific for the bone were performed (computerized bone mineralometry, C-terminal telopeptide, computed tomography dentascan, ortopanthomografy). The orthopantomograph examination highlighted the pathological state of many compromised dental elements and the previously applied fixtures (Fig. 1). The objective examination has confirmed the impossibility of treatment of the compromised dental elements 11, 21, 22, 23, and 24. Therefore, it has been agreed with the patient a clearance of the oral cavity. For the surgery, the patient has been premedicated with amoxicillin/clavulanic acid (Augmentin) 1 g (2 tablets) (GlaxoSmithKline, Brentford, UK), to be taken every 12 hours for 5 days. During the intraoperative phase, before any surgical maneuver, the patient’s mucosa has been treated with ozone in order to reduce the bacterial concentration. The preparation of the implant sites and the placement of the prosthetic roots have been carried out following the rules laid down by primary bone reparation.1 –6 To define the depth of work, the True Max Implant probe (TMI, Rome, Italy) has been used at a speed lower than 40 revolutions/min without irrigation, so as to not traumatize the alveolar bone. Subsequently, the site has been completed with UNICA osteotome (TMI) at a speed lower than 60 revolutions/min. The implant sites have been treated with ozone for 30 seconds to decrease the bacterial load, and then the surgical site has been biostimulated using a 532-nm LBO laser at a power of 1 to 1.5 W for a time between 20 and 60 seconds. Then, 4 prosthetic fixtures (TMI) have been inserted to replace 11, 21, 23, and 26 elements (Fig. 2). The prosthetic roots have been inserted in the implant sites using the ‘‘fibrin buffy coat technique,’’7– 13 where the prostheses are screwed into a block of fibrin that is interposed between the implant surface and the bone surface. The autologous bone needed to fill the bone defects that took place has been gotten during the preparation of the implant sites, thanks to the cutting action of UNICA (TMI). The regeneration

FIGURE 2. Postextractive prosthetic roots in the maxillary arch in zones 21 and 23.

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or microarchitecture?

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