Age dependence of the maturation of the midpalatal suture in the stability of orthodontic anchoring screws.

INTRODUCTION: Orthodontic anchoring screws (OASs) have been placed around midpalatal sutures in patients of various ages. Our previous study found that OAS placement more than 1.5 mm from midpalatal suture was more successful than placement directly at the suture. This study aimed to investigate the relationship between age and midpalatal suture maturation, considering factors affecting the failure of OASs using cone-beam computed tomography. METHODS: In total, 150 patients who underwent cone-beam computed tomography were selected. The total depth and sutured depth of the midpalatal suture corresponding area to anterior (interpremolar zone) and posterior region (mesial and distal borders of the first molar) were measured, and the ratio of sutured depth to total depth (sutured ratio) was calculated. RESULTS: The mean sutured ratios at interpremolar zone and mesial and distal borders of the first molar according to age were 40%, 60%, and 63% in the younger group (≤17 years), 46%, 76%, and 76% in the middle group (18-25 years), and 47%, 74%, and 76% in the older group (≥26 years), respectively. The sutured ratio of the anterior region was significantly lower than that of the posterior region (P <0.01). Each mean sutured ratio of the middle and older group was significantly higher than that of the younger group on both sides (P <0.01). According to the cervical vertebral maturation, the mean sutured ratio of cervical vertebral stages 5-6 was significantly higher than cervical vertebral stages 1-3 on the distal side (P <0.05). CONCLUSIONS: Incomplete closure of the midpalatal suture was observed frequently, even in the older group. This might be caused by insufficient calcification of the midpalatal suture, including in elder patients. To prevent OAS placement to the unsutured area, the midpalatal suture should be avoided regardless of age.

Influence of masticating cycles and chewing patterns on inadvertent enamel wear caused by zirconia brackets.

Little information is available about enamel wear caused by zirconia brackets, an inadvertent side effect of orthodontic treatment. The purpose of this study was to examine potential enamel damage induced by contact with zirconia brackets. Sliding and impact wear simulations were performed using bovine enamel specimens positioned at a 25° slant to a zirconium ball to determine wear behaviour. Different chewing patterns, tapping and grinding, were simulated. Specimens were profiled using confocal laser scanning microscopy, and the mean maximum depth and surface roughness were measured. Scanning electron microscopy was also performed. The mean maximum depth of wear values differed according to the number of mastication cycles, with a higher number of cycles producing higher depths of wear. The facet wear depth was significantly greater with the tapping pattern than with the grinding pattern. Scanning electron microscopic observation of the wear facets revealed that surface textures at the edges were rougher than those at the centre of all facets. The results of this study indicated that enamel wear was induced by contact with zirconia brackets during the early period of mastication, and that the patterns and number of cycles of mastication affected the wear progression of enamel.

Influence of pre-drilling diameter on the stability of orthodontic anchoring screws in the mid-palatal area.

PURPOSE: The aim of this study was to investigate the stability of orthodontic anchor screws (OASs) in the mid-palatal area according to pre-drilling diameter. METHODS: The success rate of 161 OASs (83 patients, φ2.0 mm, 6.0 mm in length) placed in a corresponding area to the mesial and distal borders of the first molar (mesial zone and distal zone) was assessed according to placement location and pre-drilling diameter (1.2 and 1.5 mm). Placement torque values from 73 OASs with a pre-drilling diameter of 1.2 mm were compared between success and failure groups. RESULTS: The success rates of OASs pre-drilled with φ1.2 and 1.5 mm were 94.5% and 83.0%, respectively (P < 0.05); corresponding rates in the mesial zone were 100.0% and 77.3% (P < 0.005), and those in the distal zone were 89.2% and 88.6%, respectively. Placement torques of OASs predrilled with φ1.2 mm in the success and failure groups were 25.9 and 19.2 N·cm, respectively (P < 0.05). CONCLUSION: A smaller pre-drilling diameter was associated with a higher success rate of OASs in the mid-palatal area, especially in the mesial zone. When pre-drilling diameter of 1.2 mm was used for φ2.0 mm OAS, greater placement torque was indicative of greater OAS stability.

Pain and removal force associated with bracket debonding: a clinical study.

OBJECTIVE: Pain is a problem during bracket removal, and more comfortable treatment is needed. This study examined the association of pain with the removal force required for ceramic brackets, compared with metal and plastic brackets, to determine which removal method resulted in less pain and discomfort. METHODOLOGY: 81 subjects (mean age, 25.1 years; 25 males and 56 females) were enrolled, from whom 1,235 brackets (407 ceramic, 432 plastic, and 396 metal) were removed. Measured teeth were distinguished at six segments. Pain was measured with a visual analogue scale (VAS) during the removal of each bracket. An additional grip was placed on the grips of debonding pliers with right-angled beaks; a mini loading cell sensor pinched by the grips was used to measure removal force during debonding. VAS and force values were statistically analyzed. The Kruskal-Wallis test followed by the Mann-Whitney U test with Bonferroni correction were performed for multiple comparisons; multiple regression analysis was also performed. RESULTS: Forces in the upper and lower anterior segments were significantly smaller (p<0.05) than those in the other segments. Pain tended to be greater in the upper and lower anterior segments than in the posterior segments. In all segments, the removal force was greater for metal brackets than for plastic or ceramic brackets. Ceramic brackets caused significantly greater pain than plastic brackets for the upper and lower anterior segments. Debonding force was involved in the brackets, following adjustments for pain, upper left segment, age, and sex. CONCLUSIONS: Pain and discomfort are likely to occur during bracket debonding.

Pain and removal force associated with bracket debonding: a clinical study

Abstract Objective: Pain is a problem during bracket removal, and more comfortable treatment is needed. This study examined the association of pain with the removal force required for ceramic brackets, compared with metal and plastic brackets, to determine which removal method resulted in less pain and discomfort. Methodology: 81 subjects (mean age, 25.1 years; 25 males and 56 females) were enrolled, from whom 1,235 brackets (407 ceramic, 432 plastic, and 396 metal) were removed. Measured teeth were distinguished at six segments. Pain was measured with a visual analogue scale (VAS) during the removal of each bracket. An additional grip was placed on the grips of debonding pliers with right-angled beaks; a mini loading cell sensor pinched by the grips was used to measure removal force during debonding. VAS and force values were statistically analyzed. The Kruskal-Wallis test followed by the Mann-Whitney U test with Bonferroni correction were performed for multiple comparisons; multiple regression analysis was also performed. Results: Forces in the upper and lower anterior segments were significantly smaller (p<0.05) than those in the other segments. Pain tended to be greater in the upper and lower anterior segments than in the posterior segments. In all segments, the removal force was greater for metal brackets than for plastic or ceramic brackets. Ceramic brackets caused significantly greater pain than plastic brackets for the upper and lower anterior segments. Debonding force was involved in the brackets, following adjustments for pain, upper left segment, age, and sex. Conclusions Pain and discomfort are likely to occur during bracket debonding.

Finite element analysis of stress caused by palatal orthodontic anchor screws.

This study used finite element (FE) analysis to investigate the stability of miniscrews (screws) placed at the median palate. FE models with variable suture maturity and screw-suture distances were used to examine the relationship with screw stability. Four groups were classified by extent of maturation of the midpalatal suture (0%, 60%, 75%, and 100%). The placement position was set at the center of the suture (0.0 mm), or 0.5, 1.0, and 1.5 mm to the side of the suture, and von Mises stress values in bone and screw displacement were compared among models. The stress value for the unsutured model, in which the screw was placed at the center of the suture, was greater than 30 MPa. Stress values for models in which screws were placed to the side (0.5-1.5 mm) were less than 28 MPa. Maximum screw displacement was greater in the 0.0-mm incomplete suture model than at other placement positions. Because bone conditions vary among patients, placement position and suture maturation should be examined on cone beam-computed tomography images, to ensure screw stability.

Effects of composition on the hardness of orthodontic adhesives.

Although there have been improvements in bracket systems precoated with adhesive, removal of adhesive remnants continues to be problematic. This study compared the hardness and maintainability of precoated adhesive with other commercial adhesives. Knoop hardness values were measured after light- or chemical-induced initial curing, immersion in distilled water at 37°C for 24 h and 1,000 and 10,000 thermal cycles after 24 h. Additionally, the forces required to move brackets by 0.5 mm were measured during bracket positioning, and brackets bonded to bovine enamel were examined by field-emission scanning electron microscopy. The Knoop hardness values of the precoated adhesives were lower than those of commercial resin composite adhesives, and hardness was dependent on the amount of filler in the resin matrix. The ability to maintain the device position may depend on the resin matrix composition. Precoated adhesives with less filler and more matrix material are light curable, and remnant resin may be easily removed.

Risk factors for failure of orthodontic mini-screws placed in the median palate.

This study investigated the stability of mini-screws placed in the median palate. The study included 25 patients (7 males, 18 females; mean age, 23.4 ± 5.6 years; age range, 15.0-34.5 years) who had mini-screws placed during orthodontic treatment at Nihon University School of Dentistry Dental Hospital. Mini-screws (diameter, 2.0 mm; length, 9.0 mm) were placed in the median palatal region; the first screw was inserted mesiodistally at the distal contact of the maxillary first molar, and the second screw was placed 6-9 mm mesial to the first screw. Immediately after placement, the placement sites were carefully examined with cone-beam computed tomography and a Periotest device. Screw stability was not related to perforation of the nasal cavity, patient age, or patient sex. The success rate was significantly higher in patients with screw-suture distances of 1.5-2.7 mm than in those with distances of 0-1.4 mm. Moreover, mini-screws could be stabilized when palatal cortical bone thickness was ≥1.5 mm. The success rate was significantly higher in the group with insertion depths of ≥4.5 mm. These results indicate that primary stability of mini-screws requires sufficient cortical bone thickness, insertion depth, and screw-suture distance.

A preliminary study of effects of low-intensity pulsed ultrasound (LIPUS) irradiation on dentoalveolar ankylosis.

The purpose of this experiment was to investigate whether low-intensity pulsed ultrasound (LIPUS) irradiation can inhibit dentoalveolar ankylosis in transplanted rat teeth. LIPUS irradiation (the pulsed ultrasound signal had a frequency of 3.0 MHz, a spatial average intensity of 30 mW/cm2, and a pulse ratio of 1:4) was performed on the face over the re-planted teeth of rats for 4 weeks. After the rats were euthanized, we measured mobility (Periotest value [PTV]) of the transplanted and control teeth using a Periotest. Finally, we performed histological evaluation to detect ankylosis. PTVs tended to be significantly lower for re-planted teeth than for control teeth. Histological evaluation revealed that the roots of all re-planted teeth were coalescent with alveolar bone. Furthermore, no ankylosis was observed in three-fifths of the re-planted teeth following LIPUS irradiation. These results indicate the potential efficacy of LIPUS to inhibit dentoalveolar ankylosis.

Enhancement of Orthodontic Anchor Screw Stability Under Immediate Loading by Ultraviolet Photofunctionalization Technology.

PURPOSE: Ultraviolet (UV)-mediated photofunctionalization technology is intended to enhance the osseointegration capability of titanium implants. There are concerns about orthodontic anchor screws loosening under immediate loading protocols in adolescent orthodontic treatment. The purpose of this in vivo study was to evaluate the effects of photofunctionalization on the intrabony stability of orthodontic titanium anchor screws and bone-anchor screw contact under immediate loading in growing rats. MATERIALS AND METHODS: Custom-made titanium anchor screws (1.4 mm in diameter and 4.0 mm in length) with or without photofunctionalization pretreatment were placed on the proximal epiphysis of the tibial bone in 6-week-old male Sprague-Dawley rats and were loaded immediately after placement. After 2 weeks of loading, the stability of the anchor screws was evaluated using a Periotest device, and the bone-anchor screw contact ratio (BSC) was assessed by a histomorphometric analysis using field-emission scanning electron microscopy. RESULTS: In the unloaded group, Periotest values (PTVs) were ~25 for UV-untreated screws and 13 for UVtreated screws (P < .01), while in the immediate-loading group, PTVs were 28 for UV-untreated screws and 16 for UV-treated screws (P < .05). Significantly less screw mobility was observed in both UV-treated groups regardless of the loading protocol. The BSC was increased ~1.8 fold for UV-treated screws, compared with UV-untreated screws, regardless of the loading protocol. CONCLUSION: Photofunctionalization enhanced the intrabony stability of orthodontic anchor screws under immediate loading in growing rats by increasing bone-anchor screw contact.

Are assessments of damping capacity and placement torque useful in estimating root proximity of orthodontic anchor screws?

INTRODUCTION: Placement torque and damping capacity may increase when the orthodontic anchor screws make contact with an adjacent root. If this is the case, root contact can be inferred from the placement torque and damping capacity. The purpose of this study was to verify the detectability of root proximity of the screws by placement torque and damping capacity. For this purpose, we investigated the relationship among placement torque, damping capacity, and screw-root proximity. METHODS: The placement torque, damping capacity, and root proximity of 202 screws (diameter, 1.6 mm; length, 8.0 mm) were evaluated in 110 patients (31 male, 79 female; mean age, 21.3 ± 6.9 years). Placement torque was measured using a digital torque tester, damping capacity was measured with a Periotest device (Medizintechnik Gulden, Modautal, Germany), and root contact was judged using cone-beam computed tomography images. RESULTS: The rate of root contact was 18.3%. Placement torque and damping capacity were 7.8 N·cm and 3.8, respectively. The placement torque of screws with root contact was greater than that of screws with no root contact (P <0.05; effect size, 0.44; power, <0.8). Damping capacity of screws with root contact was significantly greater than that of screws with no root contact (P <0.01; effect size, >0.5; power, >0.95). CONCLUSIONS: It was suggested that the damping capacity is related to root contact.

Measuring bone density at orthodontic miniscrew implantation sites using microcomputed tomography.

PURPOSE: This study was performed to determine the accuracy of measurements of bone mineral density (BMD) and cortical bone thickness (CBT) at miniscrew implantation sites in small animals and to verify the usefulness of in vivo microcomputed tomography (micro-CT). MATERIALS AND METHODS: Rat femurs were scanned before and after placing miniscrews using in vivo micro-CT. The images were superimposed using a subtraction method with bone volume measurement software. At each screw site, the total BMD was calculated as the average BMD of a cylinder 1.6 mm in diameter and 2.0 mm in depth, while the cortical BMD was the average BMD of a cylinder 1.6 mm in diameter and 1.0 mm in depth. CBT was measured three times on transaxial images of the rat femurs, and the average value was used. All miniscrews were placed using the maximum torque, verified with a digital torque tester. To verify the usefulness and accuracy of in vivo micro-CT, CBT on micro-CT images was compared with that measured on histologic sections. RESULTS: Significant correlations were observed between placement torque and cortical BMD (R = 0.572), total BMD (R = 0.732), and CBT (R = 0.788). There was a significant correlation between CBT measured via field-emission scanning electron microscopy images and CBT measured with in vivo micro-CT (R = 0.974). CONCLUSIONS: The BMD over a narrow range can be measured accurately in small animals with high reproducibility of the trabecular structure using a combination of high-resolution in vivo micro-CT and image superimposition using a three-dimensional subtraction method.

A healing period increases mini-implant stability in growing rats.

We assessed the stability of orthodontic mini-implants in young rats. Male rats with mean ages of 6 weeks (n = 16) and 20 weeks (n = 16) were divided into four groups (n = 8 each). In the 6- and 20-week immediate-loading groups, immediately after placement, mini-implants were exposed to an experimental traction force for 2 weeks. In the 6- and 20-week healing groups, the force was applied for 2 weeks after a 6-week healing period. Right tibiae served as the test limbs and the left tibiae as controls. A Periotest device was used to measure mini-implant mobility after traction, and Tukey's test was used to compare Periotest values among groups. The results showed significantly greater mobility in the 6-week immediate-loading group than in the 20-week immediate-loading and 6- and 20-week healing groups, and significantly less mobility in the 6-week healing group than in the 20-week immediate-loading group (P < 0.05). Mini-implants were stable during the healing period. The results indicate that mini-implants can be used for orthodontic anchorage in juvenile patients if the duration of healing is sufficient.

A preliminary study of the effects of low-intensity pulsed ultrasound exposure on the stability of orthodontic miniscrews in growing rats.

BACKGROUND: Orthodontic miniscrews placed in growing subjects often loosen during orthodontic treatment. The ability to place miniscrews, regardless of age, would be clinically beneficial. OBJECTIVES: To assess the effects of low-intensity pulsed ultrasound (LIPUS) on the stability of orthodontic miniscrews in growing rats. MATERIALS/METHODS: The mobility of miniscrews after placement was recorded and the miniscrew-bone interface was examined histomorphometrically using tibiae of seven male Sprague-Dawley rats (aged 6 weeks). Field-emission scanning electron microscopic images were used to evaluate the bone-miniscrew interface, and a mobility test device was used to assess the stiffness of miniscrew placement. Fourteen custom-made miniscrews with 1.4mm diameters and 4.0mm lengths were placed in the right and left tibiae. LIPUS was used to stimulate right tibiae at the sites of miniscrew placement, and left tibiae were left untreated as controls. RESULTS: Significantly lower mobility was observed in the LIPUS-treated group compared with the control group (P < 0.05). Histomorphometric evaluation indicated that bone-miniscrew adhesion was significantly better in the LIPUS-treated group than in the control group (P < 0.05). LIMITATIONS: This in vivo study used tibiae rather than jaw bones because the jaw bones of 6-week-old rats were too small to allow miniscrew placement. CONCLUSIONS: LIPUS was able to increase the bone-miniscrew contact and reduce the mobility of miniscrews in growing subjects. IMPLICATIONS: LIPUS may accelerate the bone healing process after miniscrew placement in growing subjects and can reduce the latent period.

Assessment of damping capacity as an index of root proximity in self-drilling orthodontic mini-implants.

OBJECTIVES: This study aims to investigate orthodontic mini-implant root proximity, placement torque, and damping capacity and to determine whether placement torque and damping capacity (Periotest value (PTV)) are useful indices for the estimation of mini-implant root proximity. MATERIALS AND METHODS: The root proximity of 143 orthodontic mini-implants (1.6 mm diameter, 8 mm screw thread length) was evaluated in 79 patients (24 males, 55 females; mean age, 22.5 ± 8 years) using cone-beam computed tomography. The placement torque and PTV of each implant were determined using a torque tester and the Periotest, respectively. Variability in these values according to root proximity was evaluated. RESULTS: PTVs of mini-implants with multiple (two or more) points of contact between the root and implant were significantly larger than those of mini-implants with no root contact in the self-drilling group. Placement torque did not differ significantly according to root proximity. In the self-drilling group, the odds ratio for root contact was 20.82 (P = 0.000) for a PTV >6. CONCLUSIONS: Placement torque could not be used to estimate root proximity. The PTV was significantly affected by root proximity in the self-drilling group. CLINICAL RELEVANCE: A threshold of PTV >6 could be applied clinically for the estimation of self-drilling mini-implant root proximity.

Evaluation of primary stability of inclined orthodontic mini-implants.

The aim of this study was to investigate the initial stability of mini-implants when placed slanting or perpendicular to the bone surface, and to examine the effects of differences in tractional direction. Titanium mini-implants were inserted into rabbit nasal bones, slanting (60 degrees , 120 degrees ) or perpendicular (90 degrees ) to the bone surface. These implants were then loaded with a force of approximately 2 N, using a NiTi coil spring. The mobilities on the traction and non-traction sides were assessed using the Periotest device immediately after placement and after traction for two weeks. Then, the tissues with the mini-implants were resected, and the contact between the bone and the implant was examined by electron microscopy. There was a tendency for the mobilities of the mini-implants at 60 degrees and 120 degrees to be smaller than those at 90 degrees when measured before and after traction. The bone-implant contact lengths at 60 degrees were significantly longer than those at 90 degrees . There was no significant difference in the bone-implant contact ratio among the different angles. Correlations were evident between implant mobility and contact length or contact ratio. It is concluded that in clinical practice, implants inclined to the bone surface tend to have better primary stability.