Success of miniscrews used as anchorage for orthodontic treatment: analysis of different factors

ObjectivesTo examine factors involved in clinical success of miniscrew implants used for orthodontic anchorage in the upper jaw.Materials and methodsOne hundred and forty-four patients (93 females and 51 males) were fitted with a total of 324 miniscrew implants of two different morphologies (cylindrical and conical), and of different lengths and diameters. The clinical factors examined were screw length, side of insertion, miniscrew shape and diameter, bone quality, skeletal type, and relationship between bone quality and skeletal type and patient age.ResultsThe mean overall success rate of the implants was 91.4%. The length and shape of the miniscrews significantly influenced the success rate, whereas side of insertion (left or right), screw diameter and skeletal type showed no significant effects. Poor (soft) bone quality and good (hard) bone quality are risk factors for miniscrew failure, with the best results obtained when the screws are inserted into bone of medium quality (10-15 Ncm).ConclusionIn the posterior areas of the upper jaw, long, conical miniscrews showed a significantly greater success rate. An insertion torque of 10 Ncm to 15 Ncm is also a significant index of higher success rate.     

Mechanical characteristics of various orthodontic mini-screws in relation to artificial cortical bone thickness

OBJECTIVE: To evaluate the effect of cortical bone thickness on the maximum insertion and removal torque of different types of self-drilling mini-screws and to determine if torque depends on the screw design. MATERIALS AND METHODS: Three different types of self-drilling mini-screws (cylindrical type [Cl], taper type [Ta], taper type [Tb]) were inserted with the use of a driving torque tester at a constant speed of 3 rotations per minute. Experimental bone blocks with different cortical bone thicknesses were used as specimens. RESULTS: Differences in the cortical bone thickness had little effect on the maximum insertion and removal torque in Cl. However, with Ta and Tb, the maximum insertion torque increased as the cortical bone thickness increased. The maximum insertion torque of Tb was highest in all situations, followed by Ta and Tb, in that order. Cl showed less torque loss in all cortical bone thicknesses and a longer removal time compared to Ta or Tb. There were significant relationships between cortical bone thickness, maximum insertion and removal torque, and implantation time in each type of self-drilling mini-screw. CONCLUSION: Since different screw designs showed different insertion torques with increases in cortical bone thickness, the suitable screw design should be selected according to the cortical thickness at the implant site.     

Root contact during insertion of miniscrews for orthodontic anchorage increases the failure rate: an animal study

OBJECTIVES: Miniscrews and miniplates are increasingly being used for absolute anchorage during orthodontic treatment. However, potential problems of damaging adjacent roots and their consequences during mini-implant placement in the alveolar process have not been clearly described. MATERIALS AND METHODS: Animal experiments were used to evaluate the stability of miniscrews placed with intentional root contact. The root repair was evaluated after screw removal. Seventy-two miniscrews were surgically placed in the mandibular alveolar bone of six adult mongrel dogs with metabolic bone labeling at 3-week intervals. Miniscrews of the experimental group were placed so that they contacted the root of the adjacent teeth, were retained for different time durations, and were then removed. The insertion torque, clinical measurements, removal torque, and histological findings were analyzed. RESULTS: (1) miniscrews contacting the roots showed a significantly higher insertion torque than those without contact; (2) there was a significant difference in the removal torque measurements based on the mobility of miniscrews and the state of root contact; and (3) miniscrews contacting the root were at greater risk of failure. CONCLUSIONS: During placement of miniscrews in the aveolar process, increased failure rates were noticed among those contacting adjacent roots. Failed miniscrews appeared to be surrounded with a greater volume of soft tissue. When more inflammation was present, the adjacent roots seemed to experience more resorption. Nevertheless, the created lesion was repaired with a narrow zone of mineralized tissue deposited on the root surface, which was likely cellular cementum, and was mainly filled with alveolar bone, with the periodontal ligament space being maintained.     

Comparison of the primary stability of orthodontic miniscrews after repeated insertion cycles:: An in vitro study

ObjectivesTo compare the primary stability of miniscrews after repeated cycles of insertion through insertion torque (IT) measurements and resonance frequency analysis (RFA).Materials and MethodsSixty titanium miniscrews were divided into two groups according to the insertion protocol: one with predrilled sites and the other self-drilled into porcine iliac crest bone specimens. Each group had three cycles of reinsertion. After each insertion, the IT and RFA were measured. The IT was measured by using a torque meter, and the RFA was measured using the Osstell ISQ device. A total of five miniscrews of each group were selected for sequential assessment of the morphology of their tip and threads using scanning electron microscopy after each insertion cycle.ResultsNo statistically significant differences were found in the IT values of miniscrews reinserted up to three times in the group with predrilled surgical sites. The IT value increased significantly with the number of reinsertions in the self-drilled group. The RFA value decreased as the number of insertions increased in both groups.ConclusionsUnder the conditions of this in vitro study, reinserting miniscrews deteriorates the integrity of their tip and thread. Reinsertion should be discouraged particularly when insertion sites are not predrilled.     

Comparison of stability between cylindrical and conical type mini-implants. Mechanical and histological properties

OBJECTIVE: To investigate the mechanical and histologic properties of conical compared with cylindrical shaped mini-implants in terms of the success rate. MATERIALS AND METHODS: The samples consisted of cylindrical and conical groups, and commonly had 1.6 mm diameter and 6.0 mm length (Jeil Medical Corporation, Seoul, Korea) placed in beagle dogs. The mechanical study for analyzing maximum insertion torque (MIT), maximum removal torque (MRT), and torque ratio (TR; MRT/MIT) in Sawbones (Pacific Research Laboratories Inc, Vashon, Wash), and the animal study for resonance frequency analysis (RFA) and histomorphometric analysis (bone-to-implant contact and bone area) in two beagle dogs were done. All measurements were statistically evaluated using independent t-tests to determine any difference in MIT, MRT, TR, RFA, bone-to-implant contact (BIC), and bone area (BA) between the cylindrical group and conical group. A P value less than 0.05 was considered significant. RESULTS: The conical group showed significantly higher MIT and MRT than the cylindrical group in the mechanical study. However, there was no significant difference in RFA, BIC, and BA between the two groups in the animal and histomorphometric studies. CONCLUSIONS: Although the conical shaped mini-implant could induce tight contact to the adjacent bone tissue and might produce good primary stability, the conical shape may need modification of the thread structure and insertion technique to reduce the excessive insertion torque while maintaining the high resistance to removal.     

Influence of surface characteristics on survival rates of mini-implants

OBJECTIVE: To compare the clinical performance and the survival rate of two mini-implant systems with different surface characteristics under immediate orthodontic loading. MATERIALS AND METHODS: Seventeen machined titanium (MT) mini-implants and 15 sandblasted, large grit, acid-etched (SLA) mini-implants were placed in 10 patients. The mini-implants were immediately loaded and the patients seen at 7, 14, 30, 60, and 150 days. Clinical parameters such as anatomical location, character of the soft tissue at the screw head emergence, type of mini-implant system, diameter, and length were analyzed. In addition, the insertion torque recorded at the time of insertion was also assessed. Survival rate and clinical parameters were evaluated by the chi-square exact tests using the SAS version 9.1. RESULTS: The overall survival rate was 87.5%. Over the four failing mini-implants, three were MT and one SLA resulting in an individual survival rate of 82.4% and 93.4%, respectively. In the failure group, all the fixtures had their screw emergence at the oral mucosa and recorded a torque range of less than 15 Ncm. The insertion torque statistically influenced the survival rate of the mini-implants (P < .05). Surface treatment, anatomical location, as well as soft tissue emergence were not statistically significant. CONCLUSION: Surface characteristics did not appear to influence survival rates of immediately loaded mini-implants.     

Analysis of the osseous/metal interface of drill free screws and self-tapping screws.

Aim: A comparison of metal/osseous interface and bone remodelling after insertion of different types of titanium bone screws in vivo. Material: Samples of five of each of the following bone screw types were inserted into the anterior wall of the frontal sinus of five Göttingen minipigs: self-tapping micro- (1.5 mm) and miniscrews (2.0 mm) or drill free micro- (1.5 mm) and miniscrews (2.0 mm) (Martin Medizintechnik, Tuttlingen, Germany). Screw length was 7 mm. Methods: Sequential intraperitoneal injections of fluorochromes were performed between the second and ninth postoperative week. After 6 months the pigs were sacrificed, the screw-bone-blocks resected, and microradiographic, histological and fluorescence microscopical examinations were carried out. Results: Using drill free screws, mean screw/bone contact was 88.4% (miniscrews), or 93.8% (microscrews). With self-tapping miniscrews it was 54.9%, but in microscrews 81%; the differences were statistically significant (t -test: p<0.05). By fluorescence microscopy, the amount of bone remodelling (ratio of residual vs. newly formed bone) was measured. Significantly more of the residual bone was found in the region of the screw threads using drill free screws (miniscrews: mean 71.8%, microscrews: mean 67.9%) than in the region of screw threads with self-tapping screws (miniscrews: mean 33.1%, microscrews: mean 42.4%). Conclusion: The present data support the view that screw/bone contact with drill free screws was superior to that of self-tapping screws; the greater amount of original bone in the threads of drill free screws demonstrated that the insertion of drill free screws did not cause harm to the surrounding bone. Both results are important for osteosynthesis in regions where thin cortical bone is present, such as the central midface.     

Analysis of the osseous/metal interface of drill free screws and self-tapping screws

Aim: A comparison of metal/osseous interface and bone remodelling after insertion of different types of titanium bone screws in vivo. Material: Samples of five of each of the following bone screw types were inserted into the anterior wall of the frontal sinus of five G?ttingen minipigs: self-tapping micro- (1.5 mm) and miniscrews (2.0 mm) or drill free micro- (1.5 mm) and miniscrews (2.0 mm) (Martin Medizintechnik, Tuttlingen, Germany). Screw length was 7 mm. Methods: Sequential intraperitoneal injections of fluorochromes were performed between the second and ninth postoperative week. After 6 months the pigs were sacrificed, the screw-bone-blocks resected, and microradiographic, histological and fluorescence microscopical examinations were carried out. Results: Using drill free screws, mean screw/bone contact was 88.4% (miniscrews), or 93.8% (microscrews). With self-tapping miniscrews it was 54.9%, but in microscrews 81%; the differences were statistically significant (t -test: p<0.05). By fluorescence microscopy, the amount of bone remodelling (ratio of residual vs. newly formed bone) was measured. Significantly more of the residual bone was found in the region of the screw threads using drill free screws (miniscrews: mean 71.8%, microscrews: mean 67.9%) than in the region of screw threads with self-tapping screws (miniscrews: mean 33.1%, microscrews: mean 42.4%). Conclusion: The present data support the view that screw/bone contact with drill free screws was superior to that of self-tapping screws; the greater amount of original bone in the threads of drill free screws demonstrated that the insertion of drill free screws did not cause harm to the surrounding bone. Both results are important for osteosynthesis in regions where thin cortical bone is present, such as the central midface. Copyright 2001 European Association for Cranio-Maxillofacial Surgery.     

Do miniscrews remain stationary under orthodontic forces?

Miniscrews have been used in recent years for anchorage in orthodontic treatment. However, it is not clear whether the miniscrews are absolutely stationary or move when force is applied. Sixteen adult patients with miniscrews (diameter = 2 mm, length = 17 mm) as the maxillary anchorage were included in this study. Miniscrews were inserted on the maxillary zygomatic buttress as a direct anchorage for en masse anterior retraction. Nickel-titanium closed-coil springs were placed for the retraction 2 weeks after insertion of the miniscrews. Cephalometric radiographs were taken immediately before force application (T1) and 9 months later (T2). The cephalometric tracings at T1 and T2 were superimposed for the overall best fit on the structures of the maxilla, cranial base, and cranial vault to determine any movement of the miniscrews. The miniscrews were also evaluated clinically for their mobility (0: no movement, 1: < or =0.5 mm, 2: 0.5-1.0 mm, 3: >1.0 mm). The mobility of all miniscrews was 0 at T1 and T2. On average, the miniscrews tipped forward significantly, by 0.4 mm at the screw head. The miniscrews were extruded and tipped forward (-1.0 to 1.5 mm) in 7 of the 16 patients. Miniscrews are a stable anchorage but do not remain absolutely stationary throughout orthodontic loading. They might move according to the orthodontic loading in some patients. To prevent miniscrews hitting any vital organs because of displacement, it is recommended that they be placed in a non-tooth-bearing area that has no foramen, major nerves, or blood vessel pathways, or in a tooth-bearing area allowing 2 mm of safety clearance between the miniscrew and dental root.     

Biomechanical characteristics and reinsertion guidelines for retrieved orthodontic miniscrews

Objectives:To analyze morphological variations of retrieved orthodontic miniscrews and to evaluate the mechanical properties that may adversely affect relocation of miniscrews.Materials and Methods:Retrieved miniscrews were classified with scanning electron microscopy according to the degree of morphological deformation of the tip. To evaluate the differences in mechanical characteristics during reinsertion, changes in insertion torque, insertion time and differences in successful insertion load were compared between unused controls and retrieved miniscrews. In addition, surface composition analysis of retrieved miniscrews was performed using energy-dispersive x-ray spectroscopy.Results:Significant tip deformation was evident in the majority (>84.5%) of retrieved miniscrews. Initial conditions such as insertion site or duration of insertion were not associated with the presence of tip deformation. Insertion load for successful bone penetration increased in proportion to the degree of tip deformation; however, serial changes in insertion torque were similar to those of the controls. Deposited debris such as carbon, calcium, and phosphorus was noted on the retrieved miniscrews.Conclusion:Miniscrews retrieved after primary insertion exhibited decreased cutting ability due to deformation of the tip structure, as well as surface contamination.     

A new implant designed to maximize contact with trabecular bone: survival to 18 months

PROBLEM: A roughened, commercially pure titanium (CP-Ti) implant design has been developed that features a different length and pitch for each screw thread to direct functional stresses away from cortical bone and to the more resilient trabecular bone. Abutment-implant connection is made using a conical taper to provide a seal against invasion by microorganisms. PURPOSE: To assess short-term (18 months) clinical performance of this innovative implant design. METHODS: A total of 1,419 implants were placed in 313 patients to support 419 prostheses in a multidisciplinary, multicentered, prospective clinical study conducted by the Ankylos Implant Clinical Research Group (AICRG). More than 100 dentists at 32 centers in the United States, 1 in Korea, and 1 in Taiwan are involved in the study. Failure was defined as implant removal for any reason. The influence of mobility at placement, implant length and diameter, incision type, augmentation, crestal bone reduction, bone density, and the use of the operating room or dental clinic on survival were evaluated over 18 months. Crestal bone loss between placement and uncovering was also determined. RESULTS: Crestal bone loss ranged from 0.2 to 0.5 mm. The overall success rate from placement to 18 months was 96.6%. Implants mobile at placement failed more frequently (16.9%) compared with stable implants (3.1%). Wide-diameter implants and longer implants exhibited higher survival rates. Incision design and surgery location did not influence survival. Bone density was important to clinical survival.     

Holding power of bioabsorbable self-reinforced poly-L/DL-lactide 70/30 tacks and miniscrews in human cadaver bone

Several bioabsorbable internal fixation systems are currently in use in the field of bone surgery. To test the mechanical properties of recently developed amorphous self-reinforced poly-L/DL-lactide [SR-P(L/DL)LA] 70/30 tacks in comparison with commercially available SR-P(L/DL)LA 70/30 (BioSorbFX; Bionx Implants Ltd) miniscrews, SR-P(L/DL)LA miniscrews (length = 6.0 mm, core diameter = 1.5 mm, thread diameter = 2.0 mm) and tacks (length = 5.4 mm, core diameter = 1.5 mm, thread diameter = 2.0 mm) were applied to human cadaveric metatarsal (MT) bones (6 pairs of fourth MT bones and 6 pairs of fifth MT bones from donors who were from 29 to 56 years of age at the time of death). Pullout force was measured using a mechanical testing machine. Forty-eight pullout tests were carried out for each implant type. The Student test, Mann-Whitney test, and Spearman coefficient were used for statistical evaluation. The pullout force of tacks was 135.0 +/- 26.1 N, and that of the miniscrews was 119.3 +/- 26.1 N ( = 0.04, statistically significant difference). Accordingly novel SR-P(L/DL)LA 70/30 tacks have a statistically better pullout strength than the SR-P(L/DL)LA 70/30 miniscrews when tested in cadaver MT bones.     

Resonance frequency analysis of orthodontic miniscrews subjected to light-emitting diode photobiomodulation therapy

The aim of this prospective experimental study was to evaluate the effect of light-emitting diode (LED) photobiomodulation therapy (LPT) on the stability of immediately loaded miniscrews under different force levels, as assessed by resonance frequency analysis (RFA). Sixty titanium orthodontic miniscrews with a length of 8 mm and a diameter of 1.4 mm were implanted into cortical bone by closed flap technique in each proximal tibia of 15 New Zealand white adult male rabbits (n = 30). The animals were randomly divided into irradiated and control groups under different force levels (0, 150, and 300 cN). OsseoPulse? LED device (Biolux Research Ltd.) 618 nm wavelength and 20 mW/cm(2) output power irradiation (20 minutes/day) was applied to the miniscrews for 10 days. The RFA records were performed at miniscrew insertion session (T1) and 21 days after surgery (T2). Wilcoxon and Mann-Whitney U-tests were used for statistical evaluation at P < 0.005 level. It was found that initial primer stability of all miniscrews was similar in all groups at the start of the experimental procedure. Statistically significant differences were found for changes in implant stability quotient (ISQ) values between LED-photobiomodulated group and the control (0 cN, P = 0.001; 150 cN, P < 0.001; and 300 cN, P < 0.001). Significant increase was found in ISQ values of LPT applied miniscrews under 0 cN (+11.63 ISQ), 150 cN (+10.50 ISQ), and 300 cN (+7.00 ISQ) force during observation period. By the increase of force levels, it was determined that ISQ values decreased in non-irradiated control miniscrews. Within the limits of this in vivo study, the present RFA findings suggest that LPT might have a favourable effect on healing and attachment of titanium orthodontic miniscrews.     

一种微型自攻型支抗钉的设计与制造

目的 研制一种具有良好生物力学功能、可直接自攻到位的微型自攻型支抗钉。方法 选用高强度植入物用钛合金TC4，或316L植入物医用不锈钢，设计支抗钉螺杆尖端自攻、螺杆主体、非骨质埋入部(龈部)、支抗钉功能头部和周向稳定槽，并采用6轴数控加工中心、配专用夹具工艺制造微型自攻型支抗钉。结果 成功设计了一种支抗钉螺杆尖端、螺杆主体骨螺纹和轻锥度、力矩输入段及牵引悬挂结构的微型自攻型支抗钉，该支抗钉能满足多重牵拉结扎，无需通过黏膜切口手术，可直接从牙龈穿透自攻植入牙床骨质中。结论 支抗钉具有良好的植入稳定性、生物相容性，在自攻固位后即可牵拉结扎，有效地缩短了正畸周期，避免了牵引过程中出现植入部分松动或植入部分失效的现象。     

A retrospective analysis of the failure rate of three different orthodontic skeletal anchorage systems

OBJECTIVES: The aim of this retrospective study was to assess systematically the case distribution among three types of mini-implants and to evaluate the clinical factors that influence the failure rates of mini-implants used as an orthodontic anchorage. MATERIAL AND METHODS: Data for 359 mini-implants (miniplates, miniscrews, and microscrews) in 129 patients were collected. The factors related to mini-implant failure were evaluated using univariate analysis and multivariate stepwise logistic regression analysis. RESULTS: Among these three different types of skeletal anchorage, there was a significant difference between the failure rates of these mini-implants, with the miniscrews and microscrews showing much higher failure rates. There were no significant differences in failure rates among the mini-implants for the following variables: gender, type of malocclusion, local or full-arch treatment, whether on the buccal or lingual side, length of the screw, loading pattern, or the duration of the healing phase. Greater risks for failure were found in younger patients, when an implant was placed for retraction/protraction, when it was placed on the mandibular arch, when it was placed anterior to the second premolars, or when using the miniscrew/microscrew systems. After adjusting for potential confounding effects, only three factors (type of mini-implant, placement on the mandibular arch, and age) were found to be statistically significant in predicting mini-implant failures (P<0.05) with an R2 value of 85.2%. CONCLUSIONS: Mini-implants placed in younger patients or placed on the mandibular arch are at a greater risk of failing. The miniplate system has greater stability compared with miniscrews or microscrews. However, it requires flap surgery for insertion and removal, which usually causes swelling and discomfort. Therefore, selection of the proper type of skeletal anchorage should be based on the specific treatment needs of each individual patient.     

Holding power of bioabsorbable ciprofloxacin-containing self-reinforced poly-L/DL-lactide 70/30 bioactive glass 13 miniscrews in human cadaver bone

Antibiotics-plus bioactive glass-containing bioabsorbable self-reinforced (SR) polylactide screws have been developed for antibacterial osteoconductive bone fixation. The aim of the present study was to test the pullout properties of these recently developed miniscrews. Ciprofloxacin-plus bioactive glass-containing SR-polylactide miniscrews (BC) were compared with miniscrews made of neat SR-polylactide (A), SR-polylactide with bioactive glass (B), and ciprofloxacin-containing SR-polylactide (C). BC miniscrews and their controls (A, B, C) (all of length 6.0 mm, core diameter 1.45 mm, thread diameter 2.0 mm) were applied to one pair of cadaveric fibulae. Pullout force was measured using a materials testing machine. We carried out 49-50 pullout tests for each implant type. The Mann-Whitney test and Student's t-test were used for statistical evaluation. The pullout force for BC miniscrews was 114.9 +/- 34.0 (SD) N. Pullout forces for control miniscrews were 162.7 +/- 37.8 N (A), 99.1 +/- 16.2 N (B), and 142.9 +/- 26.9 N (C). Differences between the four groups were statistically significant (p < 0.001). Ciprofloxacin-plus bioactive glass-containing polylactide miniscrews have good holding power to human cadaver fibulae. However, adding bioactive glass and ciprofloxacin components to neat SR-polylactide results in lower pullout values.     

Factors influencing the stability of miniscrews. A retrospective study on 300 miniscrews

The aim of this study was to investigate, over a period of approximately 3 years, the reactions to orthodontic loading of a type V titanium miniscrew. In this retrospective study, conducted in a private practice, the records of 300 miniscrews inserted in 132 consecutive patients (80 females, 60.6 percent) by the same surgeon were evaluated. The mean age of the patients was 23.2 years. Three types of miniscrews (type A: diameter 1.5 mm, length 9 mm; type B: diameter 1.5 mm, length 11 mm; and type C: diameter 1.3 mm, length 11 mm) were used. The clinical variables evaluated included the loading time and location of the miniscrew in relation to the gingiva and root. The success rates with different variables were compared using chi-square or Fisher's exact test where appropriate. A cumulative survival rate of 81 percent (243/300) was found using Kaplan-Meier analysis, with an optimum success rate for the 1.3 mm wide miniscrew inserted in the attached gingiva, with immediate loading applied. Cox proportional hazard regression showed significant differences between success rate and the following parameters: gender, loading time, gingival or bone localization, and diameter of the miniscrews. Considering the clinically controllable parameters, and within the limits of this retrospective study, 1.3 mm diameter miniscrews inserted in attached gingiva and immediately loaded had the most favourable prognosis.     

转矩拮抗型微种植支抗钉的初期稳定性分析

目的：使用扭矩分析和共振频率分析比较一种转矩拮抗型微种植支抗钉与商用微种植支抗钉的初期稳定性差异。方法以猪肋骨为骨组织模型预成长为4.0 mm,直径为1.0 mm的植入孔,植入两种不同的微种植支抗钉。分别测量最大植入扭矩( maximum insertion torque,MIT)、最大旋出扭矩( maximum removal torque,MRT)、种植体稳定系数(implant stability quotient,ISQ)。使用SPSS 13.0软件对数据进行统计分析。结果转矩拮抗型微种植支抗钉的MIT、MRT、ISQ值分别为(11.86±1.58) N·cm、(8.45±2.24) N·cm、61.80±2.93,商用微种植支抗钉的MIT、MRT、ISQ值分别为(10.36±1.42) N·cm、(6.76±1.78) N·cm、58.15±2.98,转矩拮抗型微种植支抗钉的测量结果均大于商用微种植支抗钉,差异具有统计学意义(P<0.05)。结论转矩拮抗型微种植支抗钉的初期稳定性优于商用微种植支抗钉。     

Stability and success rate of dual-thread miniscrews:: A retrospective study using the buccal alveolar region as the insertion site

ObjectivesTo date, the clinical stability of dual-thread orthodontic miniscrews has not been studied. This study aimed to compare the primary stability and long-term clinical success rate of dual-thread and cylindrical orthodontic miniscrews and to examine the association between various clinical factors and the success rate of miniscrews.Materials and MethodsA total of 145 cylindrical and 135 dual-thread miniscrews were inserted in the maxillary and mandibular buccal alveolar areas of 142 patients. The torque and Periotest (Siemens, Bensheim, Germany) values were recorded during insertion and removal. The effect of clinical variables such as sex, age, screw design, jaw, side of placement, root proximity, and site of placement on the success rate was examined using logistic regression analysis.ResultsThere was no statistically significant difference (P = .595) in the overall clinical success rate between the two designs, with an overall success rate of 82.1% and 84.4% for the cylindrical and dual-thread miniscrews, respectively. Age and screw-root proximity were significantly associated with failure (P < .05).ConclusionsThe dual-thread miniscrews did not show superior long-term stability and clinical success rate as compared with the cylindrical miniscrews. The results of this study suggest that patient age and screw-root proximity influence the clinical success rate of miniscrews.     

Bioabsorbable ciprofloxacin-containing and plain self-reinforced polylactide-polyglycolide 80/20 screws: pullout strength properties in human cadaver parietal bones

The aim of this study was to compare the pullout forces of recently developed bioabsorbable ciprofloxacin-containing and plain self-reinforced polylactide/polyglycolide (SR-PLGA) miniscrews in human cadaver parietal bones. Parietal bone pieces (approximately 6 x 20 cm) were collected from five human male cadavers (44-75 years of age). Fifty plain SR-PLGA 80/20 miniscrews (diameter = 1.5 mm, length = 4.0 mm) and 50 ciprofloxacin-containing SR-PLGA 80/20 miniscrews (diameter = 1.5 mm, length = 4.0 mm) were used in this study. The force needed to pull the screws from human parietal cadaver bones was measured using a tensile strength-testing machine. The screw pullout speed was 10 mm/min. Means and SDs were calculated and analyzed using the Student t test (SPSS version 10.0 for Windows). The pullout forces of the ciprofloxacin-containing and plain miniscrews were 66.8 +/- 4.9 N and 96.3 +/- 9.3 N (significant difference, P < 0.001), respectively. The most common cause of failure was screw-shaft breakage (60% in the case of ciprofloxacin-containing screws and 52% in the case of plain SR-PLGA screws). Scanning electron microscopy showed that the fibrillar strip-like microstructure of plain SR-PLGA miniscrews turns into a coarse, uniaxial, platelet-like morphology in antibiotic SR-PLGA miniscrews as a result of the addition of ciprofloxacin. Ciprofloxacin-containing SR-PLGA screws consequently have a lower pullout strength than corresponding plain conventional SR-PLGA screws. Nevertheless, it is evident that the ciprofloxacin-containing screws can be applied in craniomaxillofacial surgery in nonload-bearing or slightly load-bearing applications.