CORRESPONDENCE

Evaluation of Torsional Strength, Design, and Stress Distribution of Different Brands of Orthodontic Mini-Implants To the Editor: Treatment options in orthodontics have been expanded by skeletal anchorage through mini-implants over the last years. The stability of the orthodontic mini-implant is influenced by bone quality, especially by the amount of cortical bone in which it is inserted. Scientific evidence shows that stability is also affected by the design of mini-implants1; large-size mini-implants require deeper drilling which, consequently, results in greater damage to the bone microstructure, affecting the stability of these anchoring devices.2 Fracture and early loss of mini-implants during orthodontic treatment are still major concerns in using this type of anchorage system. The design of an orthodontic mini-implant is complex because of the need for reduced diameter to facilitate insertion between roots of adjacent teeth and in different bone regions with different bone qualities.3 – 6 To be effective, a mini-implant must have a reduced diameter associated with a resilient alloy to allow its insertion into bones of different qualities without fracturing the bone. Its design must allow proper bone resorption without causing injuries that could result in necrosis and subsequent screw loss.7,8 Given the great diversity of shapes and dimensions of orthodontic mini-implants, knowledge on the biomechanical performance of these anchorage devices can result in less failure and improved guidelines for clinical use. Therefore, this study aimed to evaluate the resistance to torsion, design, and stress distribution of mini-implants of 5 different manufactured brands.

Photoelastic Evaluation Araldite GY 279 and Aradur 2963 were used as photoelastic base resin and hardner, respectively, in the proportion of 100 g/42 g base/hardner, according to the manufacturer’s recommendations. Thus, 15  15  100 mm photoelastic resin sticks were prepared with the Araldite/Aradur mixture, and dried at room temperature for 72 hours until complete polymerization of the resin. Mini-implants (previously submitted to SEM) were inserted into each photoelastic resin stick. Each mini-implant/resin set was submitted to photoelastic analysis using a polariscope in the Mechanical Testing Laboratory (Faculty of Dentistry at Araraquara, UNESP, SP, Brazil) and photographed with digital equipment (Canon Rebel EOS 300D with Canon 100 mm macro Ultrasonic lens, 6.3 megapixels). Stress distribution was assessed from the photographic images. The analysis of the stress generated provided information on tension amounts and distribution. Format and location indicate distribution, and number of fringes refers to amounts of tension. The zero order fringes, the first to be counted, are black and facilitate the observation and determination of the tension gradient in the model. The first order fringes are violet, the second order fringes are in the red/blue/green transition, and the third and subsequent order fringes are in the red/green transition. The tension gradient increased with the number of fringes observed.

MATERIAL AND METHODS A total of 30 mini-implants were used in the study, 6 from each of the 5 different brands (Sin—SIN, Neodent—NEO, Rocky Mountain—RMO, Conexa˜o—CON, and Morelli—MOR) (Fig. 1A) along with their respective surgical kits for insertion. Araldite GY 279 and Aradur 2963 hardner (Araltec Produtos Quı´micos, SP, Brazil) were used as the photoelastic base resin for photoelastic evaluation.

Design Evaluation Mini-implants from each of the 5 brands were analyzed under scanning electron microscopy—SEM (LEO 435 VP, Cambridge, England) at 18 magnification. Measurements in the orthodontic mini-implants were taken from their body, head, and neck with the Image-Tool version 3.0 software (Health Science Center of the University of Texas, San Antonio, TX).

Torsional Strength Twenty-five self-drilling mini-implants (5 of each brand) were used to measure torsional strength. The same operator performed the mechanical testing using a digital torque meter. The device was mounted on a metallic apparatus that only allow rotation around its long axis and not lateral movements. Clockwise torsional movements were performed until the mini-implant was fractured. The results were statistically analyzed by one-way analysis of variance (ANOVA) and the Tukey’s test, with P < 0.05. The Journal of Craniofacial Surgery



FIGURE 1. (A) Characteristics of mini-implants according to their manufacturers’ specifications. (B) Average and standard deviation of fracture torque values for different mini-implant brands. (C) Measurements based on SEM photomicrographs (18 magnification) of mini-implants of different brands.

Volume 26, Number 5, July 2015

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

The Journal of Craniofacial Surgery

Correspondence

RESULTS Design Evaluation The presence of cutting threads in the NEO, RMO, and SIN mini-implants brands and double conical twin threads in the CON brand were the most relevant aspects observed when evaluating design (Fig. 1B).

Torsional Strength The results from fracture resistance showed statistically significant differences (P < 0.05) between the SIN and CON, NEO and CON, MOR and NEO, and CON and RMO brands (Fig. 1C). NEO and CON showed the highest and the lowest torsional strength values, respectively.



Volume 26, Number 5, July 2015

3. Arau´jo T, Nascimento M, Bezerra F, et al. Skeletal anchorage in orthodontics with mini-implants. Rev Dent Press Ortodon Ortop Facial 2006;11:126–156 4. Garfinkle JS, Cunningham LL Jr, Beeman CS, et al. Evaluation of orthodontic mini-implant anchorage in premolar extraction therapy in adolescents. Am J Orthod Dentofacial Orthop 2008;133:642–653 5. Lim SM, Hong RK. Distal movement of maxillary molars using a lever-arm and mini-implant system. Angle Orthod 2008;78:167–175 6. Carrillo R, Carillo RJ, Rossouw PE, et al. Closed-coil springs for intrusion mechanics with miniscrew anchorage. J Clin Orthod 2008;42:17–18 7. 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 8. Suzuki EY, Suzuki B. Placement and removal torque values of orthodontic miniscrew implants. Am J Orthod Dentofacial Orthop 2011;139:669–678

Photoelastic Evaluation The analysis of fringe patterns revealed that the CON brand was longer and presented a higher number of fringes below the apex than in the cervical and central regions, compared with the other brands. The MOR brand presented a balance in the distribution of fringes across the screw, giving the fringes a more rounded shape. The SIN, NEO, and RMO brands exhibited a higher number of fringes in the cervical and central regions than in the apex. Therefore, the SIN, NEO, and RMO brands showed higher stress in the cervical and central regions than in the apex. The MOR brand showed a balance of stress throughout the screw; the CON brand showed higher stress in the apical than in the cervical and central regions. The SIN and NEO brands presented higher differences in stress distribution between the apex and cervical region; the CON brand also presented greater stress difference between the apex and cervical region, however with inverted values compared with the SIN and NEO brands. The most homogeneous stress distribution was observed in the RMO and MOR brands. The authors conclude that the SIN, NEO, and RMO brands, which have cylindrical shape and sharp threads, showed the best results in torsional strength, and increased mechanical retention in the cervical region compared with MOR and CON brands. Dario F. Lopes-Neto, MD Leandro B. Rossi, MD Nadia Lunardi, MD Eloisa M. Boeck, MD Department of Orthodontics School of Dentistry Araraquara University Center (UNIARA) Araraquara, SP, Brazil Rodolfo J. Boeck-Neto, MD Department of Surgery, School of Dentistry, Araraquara University Center (UNIARA), Araraquara, SP, Brazil Eloa´ R. Luvizuto, DDS, MS Universidade Estadual Paulista, Arac¸atuba Dental School Department of Surgery and Integrated Clinic, Sa˜o Paulo, Brazil

REFERENCES 1. 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 2. Wawrzinek C, Sommer T, Fischer-Brandies H. Microdamage in cortical bone due to the overtightening of orthodontic microscrews. J Orofac Orthop 2008;69:121–134

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Cutaneous Metastasis on Scalp of Hepatocellular Carcinoma To the Editor: Hepatocelluar carcinoma (HCC) is one of the most common malignant tumors worldwide, and the sites of extrahepatic metastasis are the lung, adrenal gland, bone, and so on. In general, as skin metastasis of internal organ cancer is rarer than metastasis to other organs, skin metastasis of HCC is very rare.1 Skin metastasis of internal organs generally occurs in the late stage, and approximately 0.7% to 0.9% of the internal organ cancer patients have skin metastases and around 2.7% to 3.4% of patients with HCC have cutaneous metastasis.2,3 In addition, the cutaneous metastasis–free survival time is 3 months; hence, it is known as one of the bad prognostic factors.4 In general, metastatic carcinoma of the skin occurs after primary cancer has been detected; but, sometimes the first clinical sign is metastasis, based on which the internal organ cancer may also be tracked.5 The common sites for cutaneous metastasis of HCC are mainly the scalp, chest, and shoulders, and the like. A nodule appears first, and its appearance is similar to that of the true pyogenic granuloma; therefore, a biopsy is necessary to make the correct diagnosis.6 A 58-year-old man presented for admission with a mass on the scalp since the last 2 months. The mass was approximately 2  2 cm without ulceration, and there was no pain (Fig. 1A). It resembled soft tissue. Therefore, under local anesthesia, the whole mass was removed in the operating room. Tumor was located at the subcutaneous level, and it was hard. A wide excision was performed, and the surgical defect was covered by a local advancement flap. Stitches were removed after 1 week, and there were no problems. The patient had been diagnosed with HCC 6 months ago; hence, he underwent positron emission tomography-computed tomography (PET-CT) and bone metastasis to the right humerus was observed (Fig. 1B). In brain CT scan, brain metastasis was observed in the left centrum semiovale (Fig. 1C). There was no cutaneous lesion, except for that in the scalp. Complete blood count was performed, and biopsy undertaken in the operating room revealed that microscopically the tumor was located in the dermis/subcutaneous fat tissue and there was no connection with the overlying epidermis. The tumor showed a trabecular pattern, and it was composed of pleomorphic cells with increased N/C ratio, prominent nucleoli, and irregular nuclear membrane. Increased mitotic activity was also noted. Immunohistochemistry for hepatocyte antigen showed reactivity in focal tumor cells. Histologic and immunohistochemical findings were consistent with metastatic HCC, #

2015 Mutaz B. Habal, MD

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

Evaluation of Torsional Strength, Design, and Stress Distribution of Different Brands of Orthodontic Mini-Implants.

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