Amount Of Resorption Research Articles

Horizontal Resorption of Fresh-Frozen Corticocancellous Bone Blocks in the Reconstruction of the Atrophic Maxilla at 5 Months.

BackgroundReliable implant-supported rehabilitation of an alveolar ridge needs sufficient volume of bone. In order to achieve a prosthetic-driven positioning, bone graft techniques may be required.PurposeThis prospective cohort study aims to clinically evaluate the amount of resorption of corticocancellous fresh-frozen allografts bone blocks used in the reconstruction of the severe atrophic maxilla.Materials and MethodsTwenty-two partial and totally edentulous patients underwent bone augmentation procedures with fresh-frozen allogenous blocks from the iliac crest under local anesthesia. Implants were inserted into the grafted sites after a healing period of 5 months. Final fixed prosthesis was delivered ± 4 months later. Ridge width analysis and measurements were performed with a caliper before and after grafting and at implant insertion. Bone biopsies were performed in 16 patients.ResultsA total of 98 onlay block allografts were used in 22 patients with an initial mean alveolar ridge width of 3.41 ± 1.36 mm. Early exposure of blocks was observed in four situations and one of these completely resorbed. Mean horizontal bone gain was 3.63 ± 1.28 mm (p < .01). Mean buccal bone resorption between allograph placement and the reopening stage was 0.49 ± 0.54 mm, meaning approximately 7.1% (95% confidence interval: [5.6%, 8.6%]) of total ridge width loss during the integration period. One hundred thirty dental implants were placed with good primary stability (≥ 30 Ncm). Four implants presented early failure before the prosthetic delivery (96.7% implant survival). All patients were successfully rehabilitated. Histomorphometric analysis revealed 20.9 ± 5.8% of vital bone in close contact to the remaining grafted bone. A positive strong correlation (adjusted R2 = 0.44, p = .003) was found between healing time and vital bone percentage.ConclusionsAugmentation procedures performed using fresh-frozen allografts from the iliac crest are a suitable alternative in the reconstruction of the atrophic maxilla with low resorption rate at 5 months, allowing proper stability of dental implants followed by fixed prosthetic rehabilitation.

Anin vitrostudy into the effect of zinc substituted hydroxyapatite on osteoclast number and activity

Zinc ions have been shown to inhibit osteoclast development and proliferation both in vitro and in vivo. The same inhibiting effect has been observed in vitro when zinc was substituted into tri-calcium phosphate (TCP). Because of the solubility of TCP it is not an ideal candidate for a material to inhibit osteoclast activity in the long term. Hydroxyapatite (HA) is less soluble and so potentially offers a more long-term, sustainable effect. Previous work has shown that zinc can successfully be substituted into HA and still retain phase purity after heat treatment. The study reported here presents the effects of zinc substituted HA on the development and activity of osteoclast-like cells. It was found that increasing zinc substitution levels led to a decrease in the number of these cells present after 21 days. When resorption activity was investigated it was found that an increase in the amount of zinc present in the discs led to a significant decrease in the amount of resorption taking place on the discs. These results provide evidence for the potential of zinc substituted HA as a material to reduce resorptive activity to provide long-term bonding of implant to bone.

Evaluation of apical root resorption in orthodontic patients with maxillary anterior intrusion using utility arches and mini screws: A comparative clinical trial

Objectives: The purpose of this study was to compare the amount of apical root resorption in orthodontic patients undergoing maxillary anterior intrusion using utility arches and mini screws; and to compare the efficacy of mini screws and utility arches in reducing over bite. Materials and Methods: The study sample consisted of 20 patients, divided in two groups. Group A consisted of ten patients in whom titanium mini-screws were used Group B consisted of 10 patients in whom utility arches made of 0.017 × 0.25 TMA were used. Diagnostic records (study models and radiovisiography [RVG]) were taken at 2 time intervals, T1 (just before implant/utility arch placement) and T2 (at the end of intrusion 6 months later). The pre and post radiographic images were measured from incisal tip to the root apex with the help of intrascan DC software. Root resorption was computed as the difference between the pre-treatment total tooth length and the post treatment total tooth length. These values were subjected to statistical analyses using SPSS 16.00 statistical software. (Statistical Package for the Social Sciences, IBM Corporation, December 2007) Results: The results showed that root resorption was seen in both groups. Amount of resorption seen was higher in mini implant group than utility arch group. Mini implants were more efficient in reducing the overbite when compared to utility arches. Conclusion: It was concluded from the study that intrusion using mini implant resulted in more root resorption than utility arch; and mini implant was more effective in intruding the incisors than utility arch.

Comparison of autogenous tooth bone graft and synthetic bone graft materials used for bone resorption around implants after crestal approach sinus lifting: a retrospective study.

This retrospective study compares the amount of bone resorption around implants between an autogenous tooth bone graft (AutoBT) and a synthetic bone graft after a bone-added crestally approached sinus lift with simultaneous implant placements. In all, 37 patients participated in this study. Seventeen patients were grouped as group I and underwent an AutoBT-added sinus lift using the crestal approach. The remaining 20 patients were grouped as group II and underwent synthetic bone grafting. Both groups received the implant placements simultaneously. Of the 37 participating patients, only 22 patients were included in the final results: Eleven patients of group I and 11 patients of group II. Before the surgery, the distance from the alveolar crest to the sinus floor was measured using panoramic radiography. After the surgery, the distance was measured again from the neck of the implant thread to the most superior border of the added graft materials. Then, the amount of sinus lift was calculated by comparing the two panoramic radiographs. After a year, a panoramic radiograph was taken to calculate the resorption of the bone graft material from the radiograph that was taken after the surgery. The significance of the resorption amount between the two types of graft materials was statistically analyzed. The bone height was increased to an average of 4.89 mm in group I and 6.22 mm in group II. The analysis of panoramic radiographs 1 year after the surgery showed an average bone resorption of 0.76 mm and 0.53 mm, respectively. However, the degree of lifting (P=0.460) and the amount of bone-grafted material resorption (P=0.570) showed no statistically significant difference. Based on this limited study, AutoBT can be considered a good alternative bone graft to a synthetic bone graft in a bone-added sinus lift, when extraction is necessary prior to the surgery.

Association of complete denture wearing with the rate of reduction of mandibular residual ridge using digital panoramic radiography

Background: Residual ridge reduction is one of the main causes of loss of stability and retention of mandibular complete dentures. The severity of bone loss is very important clinical condition facing the aging population. Objectives: To investigate the association of the mandibular ridge reduction with duration of complete denture wearing in relation to age and gender is using digital panoramic radiography. Methods: Seventy-five (40 men and 35 women) with a mean age 66.21±10.21 years, denture-wearing patients were included in this study. Resorption in the mandibular residual ridges was assessed by using the mental foramen and the inferior border of the mandible, as they appear in digital panoramic radiographs, using Wical and Swoope Analysis method. Measurements were performed digitally using Sidexis next Generation software. The amount of resorption was calculated and correlated to gender, age and duration of denture wearing. Statistical analysis was performed using SPSS (V17.0). Level of significance was set at 0.05. Results: The mean ridge resorption was 7.74±5.80 mm (20%), Women significantly (P<0.05).recoded more resorption than men (women: men ratio was 3:2). Men significantly (P<0.0001) had greater mandibular ridge and mental foramen heights than women. Ridge resorption significantly increased with increasing age (P<0.0001) and duration of denture wearing (P<0.001). Women significantly (P<0.05) had greater ridge resorption than men below 50 and above 80 years old; and in all denture wearing duration groups. Conclusion: Reduced mandibular height is directly related to age and duration of complete denture wearing. Women are at more risk to have ridge resorption compared to men.

Buccal Fat Pad Lifting: An Alternative Open Technique for Malar Augmentation

The purpose of the study was to introduce a novel technique for malar augmentation using buccal fat pad pedicle flaps and to evaluate the long-term results and complications of the technique. The investigators designed and conducted a prospective clinical trial. Patients underwent unilateral malar augmentation surgery using buccal fat pad pedicle flaps from June 2011 through June 2012. Patients underwent surgery for esthetic reasons or for trauma with severely comminuted or old zygomaticomaxillary complex fractures that could not be reduced precisely. The primary predictor variable was the buccal fat pad pedicle flap technique. The primary outcome variables included the amount of augmentation and resorption (which was estimated by comparing pre- with postsurgical photographic views), pain, edema, bruising, and nerve and parotid duct injuries. Thirteen patients (8 men and 5 women) underwent malar augmentation in the cheekbone area using the buccal fat pad pedicle flap technique. One year after surgery, the average amount of resorption was 0.376 mm. Other major complications, such as prolonged bruising, massive hematoma, intense pain, asymmetry, and parotid duct injury, were not observed. These results indicate that this new open-access technique should be considered an alternative method for the management of mild to moderate malar depression in patients undergoing esthetic and post-trauma surgery.

Gelatin powders accelerate the resorption of calcium phosphate cement and improve healing in the alveolar ridge

The aim of this study was to show the effectiveness of combining calcium phosphate cement and gelatin powders to promote bone regeneration in the canine mandible. We mixed gelatin powders with calcium phosphate cement to create a macroporous composite. In four beagle dogs, two saddle-type bone defects were created on each side of the mandible, and calcium phosphate cement alone or calcium phosphate cement containing composite gelatin powders was implanted in each of the defects. After a healing period of six months, mandibles were removed for µCT and histological analyses. The µCT and histological analyses showed that at experimental sites at which calcium phosphate cement alone had been placed new bone had formed only around the periphery of the residual calcium phosphate cement and that there had been little or no ingrowth into the calcium phosphate cement. On the other hand, at experimental sites at which calcium phosphate cement containing composite gelatin powders had been placed, we observed regenerated new bone in the interior of the residual calcium phosphate cement as well as around its periphery. The amount of resorption of calcium phosphate cement and bone regeneration depended on the mixing ratio of gelatin powders to calcium phosphate cement. New bone replacement was significantly better in the sites treated with calcium phosphate cement containing composite gelatin powders than in those treated with calcium phosphate cement alone.

Use of platelet rich fibrin and platelet rich plasma in combination with fat graft; which is more effective during facial lipostructure?

Purpose: Fat grafts have always represented a challenge in inducing the necessary neoangiogenesis, which results in significant resorption. This study was designed to compare the efficiency of firstand second-generation platelet-rich plasmas (PRPs) combined with a fat graft during facial lipostructure surgery. Methods and Materials: To address the research purpose, the investigators designed and implemented a double-blinded prospective clinical trial. The patients underwent bilateral facial lipostructure, a natural long-lasting method of filling and supporting the face using intricate layers of infiltrated autologous fat. The method involved the use of PRP on 1 side and platelet-rich fibrin (PRF) on the other side. The study population was composed of all patients presenting to the authors’ department for the evaluation and management of facial contouring in the cheek and cheekbone areas from June 2008 through December 2010. The primary predictor variable was the type of combination (PRP/fat or PRF/fat). The outcome variables were the amount of resorption, which was estimated by comparing preand postsurgical photographic views, pain, edema, and bruising. The statistical evaluation of the findings was performed using SPSS software. Parametric tests (t test and Levene test) were used to compare the treatment efficacy and complications between the groups. Results: Twenty-five patients (8 men and 17 women) underwent bilateral facial lipostructure surgery in the cheek and cheekbone areas using PRP and PRF. One year after the operation, a slight esthetic asymmetry was noticeable, with greater average resorption on the PRP/fat side. Conclusions: This first comparative clinical study highlights the value of using concentrated platelets for adipocyte grafts. The results suggest that the combination of fat and PRF is more effective than the combination of fat and PRP in the context of facial lipostructure surgery. © 2013 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 71:610-621, 2013

Comparative Humeral Microanatomy of Terrestrial, Semiaquatic, and Aquatic Carnivorans using Micro-Focus CT Scan

In order to investigate the relationship between limb bone internal structure and the aquatic adaptation, we examined humeri of multiple carnivoran species of various lifestyles (terrestrial, semiaquatic, and aquatic) using micro-focus CT scanner. The transverse section image passing through the inferred center of ossification is analyzed in order to estimate the structural remodeling in periosteal bone. Meanwhile, structural characteristics in sagittal section images of proximal end were described in order to assess the characteristics in endochondral bone. The degree of cancellousness around the center of ossification, which is interpreted as the amount of resorption in periosteal compact bone, is the lowest in the semiaquatic group and the highest in terrestrial groups. This suggests that the ratio of periosteal bone resorption in limb bones decreases in the first stage of the aquatic adaptation, possibly due to the less need for skeletal lightening in semiaquatic taxa than the terrestrial taxa, and then increases as the limb bones reduces their support function on land, presumably in relation to the deep diving. The bone trabecular architecture in humeral head is fine and well-oriented in terrestrial to semiaquatic carnivorans, while that of aquatic carnivorans is rather coarse and randomly oriented.

Treatment of class 2 division 1 malocclusion with severe short roots of upper central incisors

The average amount of resorption per root of examined maxillary incisors or anterior teeth is < 1.5 mm during comprehensive orthodontic treatment. About 5% of adults and 2% of adolescents are likely to have at least one tooth with resorption of more than 5 mm during active treatment. Although resorption stops once the active appliances are removed, fortunately, truly severe resorption that threatens the longevity of the tooth or forces a halt to treatment is rare. The fact is, however that orthodontic tooth movement does directly cause irreversible resorption of the root. As the movers of the teeth, it is incumbent for us to know as much as possible about the causes, effects and prevention of this phenomenon.

Effect of Angiotensin II Receptor Blocker on Experimental Periodontitis in a Mouse Model of Marfan Syndrome

Marfan syndrome is an autosomal dominant disease characterized by aneurysm and dilatation of the aortic root, tall stature, and ectopia lentis. These manifestations reflect excessive signaling of transforming growth factor beta (TGF-β). Moreover, cases are frequently associated with severe periodontitis, which is a chronic inflammation of the gingiva, periodontal ligament, and alveolar bone. Recently, angiotensin II receptor blockers (ARBs) were discovered to be an effective drug class that can prevent aortic aneurysm and dilation in Marfan syndrome by inhibiting TGF-β signaling. To investigate the effect of ARB on the progression of periodontitis, the application of a potent ARB, telmisartan, was examined in a mouse model of Marfan syndrome (MgΔ). Six-week-old male heterozygous MgΔ and wild-type mice were challenged with Porphyromonas gingivalis, which causes chronic periodontitis, with and without telmisartan application. After infection, alveolar bone resorption was measured by micro-computed tomography (μCT), and inflammatory cytokine levels were examined. Infection of Porphyromonas gingivalis induced alveolar bone resorption in both MgΔ and wild-type mice. The amount of resorption was significantly larger in the former than the latter. Immunoarray and enzyme-linked immunosorbent assay (ELISA) analyses demonstrated that interleukin-17 (IL-17) and tumor necrosis factor alpha (TNF-α) levels were significantly higher in infected MgΔ mice than infected wild-type mice. Telmisartan treatment significantly suppressed the alveolar bone resorption of infected MgΔ mice. Telmisartan also significantly decreased levels of TGF-β, IL-17, and TNF-α in infected MgΔ mice to levels seen in infected wild-type mice. This study suggests that ARB can prevent the severe periodontitis frequently seen in Marfan syndrome.

Use of Platelet-Rich Fibrin and Platelet-Rich Plasma in Combination With Fat Graft: Which Is More Effective During Facial Lipostructure?

Fat grafts have always represented a challenge in inducing the necessary neoangiogenesis, which results in significant resorption. This study was designed to compare the efficiency of first- and second-generation platelet-rich plasmas (PRPs) combined with a fat graft during facial lipostructure surgery. To address the research purpose, the investigators designed and implemented a double-blinded prospective clinical trial. The patients underwent bilateral facial lipostructure, a natural long-lasting method of filling and supporting the face using intricate layers of infiltrated autologous fat. The method involved the use of PRP on 1 side and platelet-rich fibrin (PRF) on the other side. The study population was composed of all patients presenting to the authors' department for the evaluation and management of facial contouring in the cheek and cheekbone areas from June 2008 through December 2010. The primary predictor variable was the type of combination (PRP/fat or PRF/fat). The outcome variables were the amount of resorption, which was estimated by comparing pre- and postsurgical photographic views, pain, edema, and bruising. The statistical evaluation of the findings was performed using SPSS software. Parametric tests (t test and Levene test) were used to compare the treatment efficacy and complications between the groups. Twenty-five patients (8 men and 17 women) underwent bilateral facial lipostructure surgery in the cheek and cheekbone areas using PRP and PRF. One year after the operation, a slight esthetic asymmetry was noticeable, with greater average resorption on the PRP/fat side. This first comparative clinical study highlights the value of using concentrated platelets for adipocyte grafts. The results suggest that the combination of fat and PRF is more effective than the combination of fat and PRP in the context of facial lipostructure surgery.

Evaluation of augmented alveolar bone and dental implant after autogenous onlay block bone graft

Introduction: The purpose of this study is to evaluate the clinical results of vertical alveolar ridge augmentation using autogenous block bone graft, especially resorption rate, and outcomes of dental implants placed in the grafted site. Patients and Methods: Medical records and radiographs were reviewed. Twenty-seven patients who have been received the autogenous block bone graft which harvested from chin, ramus, and ilium, and the implant installation on 31 areas(22 maxillas and 9 mandibles) were included. Eight implants were installed simultaneously at the time of bone graft in 4 patients, and 65 implants were installed after 4.9 months(range 2~18 months) of autogenous block bone graft in 23 patients. The resorption amount and rate of augmented bone, and the success and survival rates implants were evaluated. Results: Mean height of the augmented block bone was 5.9pm2.3mm(range from 2.5 to 13.0 mm). Mean follow-up period after block bone graft was 30.4 months(range from 16 to 55 months). Mean resorption of the augmented block bone was 2.0pm1.5mm (range from 0.5 to 7.24 mm). The success and survival rates of the implants were 78.1 % and 98.6%, respectively. Conclusion: This study indicates that the autogenous block bone graft is a useful and stable method for alveolar ridge augmentation for dental implant. And more augmentation is needed to compensate the resorption of the grafted bone.

A Semi-Empirical Cell Dynamics Model for Bone Turnover Under External Stimulus

The normal periodic turnover of bone is referred to as remodeling. In remodeling, old or damaged bone is removed during a 'resorption' phase and new bone is formed in its place during a 'formation' phase in a sequence of events known as coupling. Resorption is preceded by an 'activation' phase in which the signal to remodel is initiated and transmitted. Remodeling is known to involve the interaction of external stimuli, bone cells, calcium and phosphate ions, and several proteins, hormones, molecules, and factors. In this study, a semi-empirical cell dynamics model for bone remodeling under external stimulus that accounts for the interaction between bone mass, bone fluid calcium, bone calcium, and all three major bone cell types, is presented. The model is formulated to mimic biological coupling by solving separately and sequentially systems of ODEs for the activation, resorption, and formation phases of bone remodeling. The charateristic time for resorption (20 days) and the amount of resorption (~0.5%) are fixed for all simulations, but the formation time at turnover is an output of the model. The model was used to investigate the effects of different types of strain stimuli on bone turnover under bone fluid calcium balance and imbalance conditions. For bone fluid calcium balance, the model predicts complete turnover after 130 days of formation under constant 1000 microstrain stimulus; after 47 days of formation under constant 2000 microstrain stimulus; after 173 days of formation under strain-free conditions, and after 80 days of formation under monotonic increasing strain stimulus from 1000 to 2000 microstrain. For bone fluid calcium imbalance, the model predicts that complete turnover occurs after 261 days of formation under constant 1000 microstrain stimulus and that turnover never occurs under strain-free conditions. These predictions were not impacted by mean dynamic input strain stimuli of 1000 and 2000 microstrain at 1 Hz and 1000 microstrain amplitude. The formation phase of remodeling lasts longer than the resorption phase, increased strain stimulus accelerates bone turnover, while absence of strain significantly delays or prevents it, and formation time for turnover under monotonic increasing strain conditions is intermediate to those for constant strain stimuli at the minimum and maximum monotonic strain levels. These results are consistent with the biology, and with Frost's mechanostat theory.

Prevalence of Internal Inflammatory Root Resorption

Introduction Internal inflammatory root resorption is regarded as rare because it is only occasionally detected in clinical or radiographic examination of teeth. However, inflammation is supposedly an important etiologic factor of internal resorption. Therefore, we tested the hypothesis that there is no difference in the presence of internal resorption between teeth with vital, healthy pulp and teeth with a history of pulp inflammation. Methods Thirty teeth with no previous root canal treatment that were to be sequentially extracted from adult patients were diagnosed for their pulpal status (ie, healthy, pulpitis, or necrosis). After extraction, the teeth were split buccolingually, and both halves were exposed to 6% sodium hypochlorite for 10 minutes under constant shaking to remove all organic debris covering the root canal walls. The specimens were washed in water and prepared for scanning electron microscopy to examine the root canals for the presence of internal resorption. Results The null hypothesis of this study was rejected. None of the 9 teeth with healthy pulps revealed signs of internal resorption. Four of the 8 teeth with pulpitis (50%) and 10 of the 13 teeth with necrotic pulps (77%) had internal resorption ( P < .01). The average number of resorptive lesions in the affected necrotic teeth was 2.4, whereas in teeth with pulpitis and internal resorption, the average number of lesions was 1.25. The amount of resorption was always <100-μm deep; the length of the lesions varied from 200 μm to >1 mm. Most lesions (15) were detected in the middle third of the root, followed by the apical third (13). Only 1 internal resorptive lesion was detected in the coronal third of the root canal. Conclusions Internal resorption was a frequent finding in teeth with pulp inflammation or necrosis.

Predictive value of ridge dimensions on autologous bone graft resorption in staged maxillary sinus augmentation surgery using Cone‐Beam CT

No studies are available that provide predictive parameters regarding the expected amount of resorption after maxillary sinus augmentation surgery using autologous bone grafts. Therefore, the aim of this study was to determine parameters influencing the outcome of the bone graft resorption process. In 20 patients, three-dimensional analysis of alveolar ridge dimensions and bone graft volume change in the atrophic posterior maxilla was performed by Cone-Beam Computerized Tomography imaging. Ridge dimensions were assessed before maxillary sinus augmentation surgery. Bone graft volumes were compared after maxillary sinus floor augmentation surgery and a graft healing interval of several months. To analyze the relation between bone volume changes with the independent variables, patients' gender, age, alveolar crest height and width, and graft healing time interval, a multi-level extension of linear regression was applied. A residual bone height of 6.0mm (SD=3.6mm) and 6.2mm (SD=3.6mm) was found at the left and right sides, respectively. Moreover, alveolar bone widths of 6.5mm (SD=2.2mm) and 7.0mm (SD=2.3mm) at the premolars, and 8.8mm (SD=2.2mm) and 8.9mm (SD=2.5mm) at the molars regions were found at the left and right site, respectively. Bone graft volume decreased by 25.0% (SD=21.0%) after 4.7months (SD=2.7, median=4.0months) of healing time. The variables "age" (P=0.009) and mean alveolar crest "bone height" (P=0.043), showed a significant influence on bone graft resorption. A decrease of 1.0% (SE=0.3%) of bone graft resorption was found for each year the patient grew older, and an increase in bone graft resorption of 1.8% (SE=0.8%) was found for each mm of original bone height before sinus floor augmentation. Graft resorption occurs when using autologous bone grafts for maxillary sinus augmentation. Alveolar crest bone height and patient age have a significant effect on graft resorption, with increased resorption for higher alveolar crest bone height and decreased resorption for older patients. Consequently, patient characteristics that affect the process of bone graft resorption should be given full consideration, when performing sinus augmentation surgery.

Root resorption diagnosed with cone beam computed tomography after 6 months of orthodontic treatment with fixed appliance and the relation to risk factors

To investigate root resorption after 6 months of active orthodontic treatment and its relation to possible risk factors. Ninety-seven patients (10-18 years) with a Class I malocclusion and crowding treated with fixed appliance and premolar extractions were examined with cone beam computed tomography before and after 6 months of active treatment. The exposure covered all teeth from first molar to first molar in both jaws. The Malmgren index was used to evaluate the degree of root resorption. Irregular root contour (score 1) was seen in most teeth already before active treatment, and therefore resorptions were registered only as score 2 (<2 mm, minor resorption) or higher. Minor root resorption was noted in 10% of the patients and severe root resorption, >2 mm (score 3) was found in four patients. Root resorption was more frequently seen in the upper jaw, especially the incisors. There was no statistically significant correlation of root resorption with any of the selected risk factors. After 6 months of treatment, clinically significant resorption was diagnosed in 4% of the patients, ie, in 96% of the patients the radiographic examination did not reveal any significant information. The selected risk factors did not have any impact on the amount of resorption after 6 months of active treatment.

Apical Root Resorption: A Prospective Radiographic Study of Maxillary Incisors

The aim of this study was to determine the prevalence of apical root resorption in maxillary incisors during the initial stages of active orthodontic treatment and to test the hypothesis that root resorption increases with the progress of the treatment. The study sample consisted of 80 teeth of 20 patients (14 female, 6 male) with a mean age of 14.9±2.8 years. Root resorption was determined with standardized digitized periapical radiographs. All the periapical radiographs were obtained at the beginning of orthodontic treatment (T0) and 3 months (T1), 6 months (T2) and 9 months (T3) after the beginning of the treatment by a paralleling device. They were digitalized as 600 dpi with a flatbed scanner and analyzed by software for image analysis at 400x magnification utilizing a personal computer. All of the 4 maxillary incisors had an increasing amount of resorption during the 9-month period. The amount of root resorption between the time intervals was statistically significant (P<.05). Root resorption of maxillary incisors can be detected in the early stages of orthodontic treatment and appears to be related to treatment duration. According to 9-month evaluation period, apical root resorption is of limited clinical significance for the average orthodontic patient.

Effects of cobalt and chromium ions at clinically equivalent concentrations after metal-on-metal hip replacement on human osteoblasts and osteoclasts: Implications for skeletal health

Metal-on-metal hip replacement (MOMHR) using large diameter bearings has become a popular alternative to conventional total hip arthroplasty, but is associated with elevated local tissue and circulating levels of chromium (Cr) and cobalt (Co) ions that may affect bone health. We examined the effects of acute and chronic exposure to these metals on human osteoblast and osteoclast formation and function over a clinically relevant concentration range previously reported in serum and within hip synovial fluid in patients after MOMHR. SaOS-2 cells were cultured with Co(2+), Cr(3+) and Cr(6+) for 3 days after which an MTS assay was used to assess cell viability, for 13 days after which alkaline phosphatase and cell viability were assessed and for 21 days after which nodule formation was assessed. Monocytes were isolated from human peripheral blood and settled onto dentine disks then cultured with M-CSF and RANKL plus either Co(2+), Cr(3+) or Cr(6+) ions for 21 days from day 0 or between days 14 and 21. Cells were fixed and stained for TRAP and osteoclast number and amount of resorption per dentine disk determined. Co(2+) and Cr(3+) did not affect osteoblast survival or function over the clinically equivalent concentration range, whilst Cr(6+) reduced osteoblast survival and function at concentrations within the clinically equivalent serum range after MOMHR (IC(50) =2.2 μM). In contrast, osteoclasts were more sensitive to metal ions exposure. At serum levels a mild stimulatory effect on resorption in forming osteoclasts was found for Co(2+) and Cr(3+), whilst at higher serum and synovial equivalent concentrations, and with Cr(6+), a reduction in cell number and resorption was observed. Co(2+) and Cr(6+) within the clinical range reduced cell number and resorption in mature osteoclasts. Our data suggest that metal ions at equivalent concentrations to those found in MOMHR affect bone cell health and may contribute to the observed bone-related complications of these prostheses.

Implications of garnet resorption for the Lu-Hf garnet geochronometer: an example from the contact aureole of the Makhavinekh Lake Pluton, Labrador

In the contact aureole of the Makhavinekh Lake Pluton (MLP), Labrador, garnet resorption caused redistribution of Lu and loss of Hf, creating spuriously young Lu-Hf garnet ages. Garnet grew during granulite facies regional metamorphism at 1860-1850 Ma. At 1322 Ma, garnet rims were replaced by coronas of cordierite and orthopyroxene during contact metamorphism. Garnet-ilmenite Lu-Hf geochronology using bulk-garnet separates yields apparent ages that young from 1876 ± 21 Ma at 4025 m from the contact to 1396 ± 8 Ma at 450 m from the contact. Toward the contact, garnet crystals are progressively more resorbed. Concentrations of Lu measured by LA-ICP-MS along radial traverses on central sections through relict garnet decrease gently away from the cores but rise steeply within 50-200 lm of the edges of the relicts. Enrichments of Lu in rims of relict garnet demonstrates strong partitioning of Lu into garnet during resorption and modest intracrystalline diffusion. Hafnium distributions could not be measured, but considering the strong incompatibility of Hf with garnet, it is likely that nearly all Hf in resorbed portions of the garnet was lost from the crystals. Lu-Hf ages in the aureole are thus controlled predominantly by this retention of Lu and loss of Hf during garnet resorption. This deduction was tested with a simple numerical model in which the partial retention of Lu and loss of Hf is tracked as a population of garnet is resorbed. Assuming a spherical geometry for garnet porphyroblasts, Rayleigh fractionation is used to approximate initial Lu zoning profiles ranging from flat to steeply decreasing toward garnet rims. The model simulates: (i) Lu-Hf decay for a specified period before resorption; (ii) instantaneous resorption with retention of Lu and loss of Hf from the resorbed portion of the crystal and (iii) Lu-Hf decay during a specified period after resorption. Several parameters influence the modelled age, but garnet resorption and Lu retention are the primary factors. When all other parameters are held constant, larger amounts of resorption and higher degrees of Lu retention produce younger apparent ages (false ages). Similarly, flatter initial Lu profiles yield younger apparent ages as a consequence of the larger proportion of Lu and Hf that resides in the outer portions of the porphyroblast. The difference between the apparent and actual ages is greater if the duration of the pre-resorption decay period is large relative to the post-resorption decay period. Larger crystals in a Gaussian crystal-size distribution (CSD) generally dominate the Lu-Hf budget and produce an older apparent age relative to the age of the mean crystal size. Compared to a symmetrical Gaussian CSD, positively skewed CSDs result in reduced resorption of large crystals and produce an older apparent age. Application of the model to the MLP aureole, positing growth at 1850 Ma and resorption at 1320 Ma, yields model ages that young from 1850 to 1374 Ma toward the contact, in good agreement with the apparent ages determined from geochronology.