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ABSTRACT: Abstract Objective. The aim of the present study was to analyze the changes in the gonial angle, ramus height, condyle height and cortical bone thickness in relation to gender and dental status in elderly patients. Materials and methods. The study population comprised 240 patients (age ranged from 60-69 years) who had digital panoramic radiographs taken for various purposes. One group consisted of 120 patients, 60 men and 60 women, who had all natural teeth present except for third molars. The second group consisted of the remaining 120 patients (60 men and 60 women) who were in a completely edentulous state (maxilla and mandible). The gonial angle, ramus height, condylar height and cortical bone thickness of the mandible were measured by computer software on their panoramic radiographs. Results. Women showed larger gonial angles than men, while men had greater cortical bone thickness and ramus height (p < 0.05). However, no significant difference in condylar height was found between both genders (p > 0.05). Edentulous subjects had a larger gonial angle than dentate subjects, while dentate subjects had greater cortical bone thickness on both sides and left side of condylar height (p < 0.05). The gonial angle had statistically negative correlations with cortical bone thickness and ramus height, regardless of gender. Conclusions. The outcomes of the present study indicate that the edentulous women undergo morphological changes of the mandible influenced by the dental status more than men.
Acta odontologica Scandinavica 07/2012; · 1.41 Impact Factor
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ABSTRACT: The purpose of the present study was to investigate the stress distribution around the bone-implant interface and the effect of the length of an immediately loaded implant in the anterior maxilla using a finite element model with simulated loading stresses.
Four-mm-diameter external-hex implants with different lengths (8.5, 10.0, 11.5, 13.0, and 15.0 mm) were used in this study. The anterior maxilla was assumed to be D3 bone quality. All of the material was assumed to be homogenous, isotropic, and linearly elastic. Average bone deformation during implant placement was calculated through the simulation process, and using this, insertion stress was created. The bone-implant interface was constructed using a contact element to simulate a nonosseointegrated condition. Then, 176 N of static force was applied at the middle of the palatoincisal line angle of the abutment at a 120-degree angle to the long axis of the abutment. The von Mises stresses were measured at intervals of 0.25 mm along the bone-implant interface.
Prior to loading, the stresses were evenly distributed around the implant and highly concentrated in the cortical area. When the load was applied, von Mises stresses were concentrated in the cortical bone of the implant neck area. More favorable stress distribution was seen with increasing implant length. However, when the implant length reached 15.0 mm, the stresses increased.
In the maxilla, when immediate loading is applied after implant placement, 11.5- and 13.0-mm-long single implants showed more favorable stress patterns than the others analyzed. If implants longer than 15.0 mm are used in immediate loading, sufficient bone volume in the recipient site should be considered an important factor.
The International journal of oral & maxillofacial implants 03/2012; 27(2):295-302. · 1.78 Impact Factor
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ABSTRACT: The poly-ether-ether-ketone (PEEK) polymer is of great interest as an alternative to titanium in orthopedics because of its biocompatibility and low elastic modulus. This study evaluated the fatigue limits of PEEK and the effects of the low elastic modulus PEEK in relation to existing dental implants. Compressive loading tests were performed with glass fiber-reinforced PEEK (GFR-PEEK), carbon fiber-reinforced PEEK (CFR-PEEK), and titanium rods. Among these tests, GFR-PEEK fatigue tests were performed according to ISO 14801. For the finite element analysis, three-dimensional models of dental implants and bone were constructed. The implants in the test groups were coated with a 0.5-mm thick and 5-mm long PEEK layer on the upper intrabony area. The strain energy densities (SED) were calculated, and the bone resorption was predicted. The fatigue limits of GFR-PEEK were 310 N and were higher than the static compressive strength of GFR-PEEK. The bone around PEEK-coated implants showed higher levels of SED than the bone in direct contact with the implants, and the wider diameter and stiffer implants showed lower levels of SED. The compressive strength of the GFR-PEEK and CFR-PEEK implants ranged within the bite force of the anterior and posterior dentitions, respectively, and the PEEK implants showed adequate fatigue limits for replacing the anterior teeth. Dental implants with PEEK coatings and PEEK implants may reduce stress shielding effects. Dental implant application of PEEK polymer-fatigue limit and stress shielding.
Journal of Biomedical Materials Research Part B Applied Biomaterials 02/2012; 100(4):1044-52. · 2.15 Impact Factor
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ABSTRACT: AIM: The purposes of this study were (1) to investigate the bucco-lingual course of the mandibular canal in the bony structure and (2) to figure out the relationship between the position of mental foramen on panoramic radiographs and the horizontal course of the mandibular canal. MATERIALS AND METHODS: A database of panoramic radiography and spiral computed tomography (CT) scans was searched and 100 subjects were selected based on the criteria. Mental foramina were classified into four groups according to its antero-posterior position. Three measurements were made on each slice of coronal CT scans at three different points: (1) apex of second premolar; (2) median point of two root apexes of first molar; and (3) median point of two root apexes of second molar. The bucco-lingual ratios were calculated to access the relative bucco-lingual position of the mandibular canal. RESULTS: The distribution of subjects according to the type of mental foramen was: (1) type 3, 67%; (2) type 2, 26%; (3) type 4, 5%; and (4) type 1, 2%. The overall horizontal course of the mandibular canal was relatively constant from the second molar to first molar, whereas much significant directional change was found on the remaining course. Between types 2 and 3, no statistically significant differences were found at the level of the second molar and first molar (P = 0.461 and 0.965, respectively). Only below the second premolar, significant differences were found (P = 0.001). CONCLUSIONS: Based on the findings of our computed tomographic image analysis, the position of mental foramen on panoramic radiographs was affected by its horizontal course of inferior alveolar nerve. The significant horizontal direction change of the course was found after the canal passing below the mandibular first molar regardless of the antero-posterior position of mental foramen.
Clinical Oral Implants Research 01/2012; · 2.51 Impact Factor
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ABSTRACT: This study evaluated the initial stability of different implants placed above the bone level in different types of bone.
As described by Lekholm and Zarb, cortical layers of bovine bone specimens were trimmed to a thickness of 2 mm, 1 mm or totally removed to reproduce bone types II, III, and IV respectively. Three Implant system (Brånemark System® Mk III TiUnite™, Straumann Standard Implant SLA®, and Astra Tech Microthread™-OsseoSpeed™) were tested. Control group implants were placed in level with the bone, while test group implants were placed 1, 2, 3, and 4 mm above the bone level. Initial stability was evaluated by resonance frequency analysis. Data was statistically analyzed by one-way analysis of variance in confidence level of 95%. The effective implant length and the Implant Stability Quotient (ISQ) were compared using simple linear regression analysis.
In the control group, there was a significant difference in the ISQ values of the 3 implants in bone types III and IV (P<.05). The ISQ values of each implant decreased with increased effective implant length in all types of bone. In type II bone, the decrease in ISQ value per 1-mm increase in effective implant length of the Brånemark and Astra implants was less than that of the Straumann implant. In bone types III and IV, this value in the Astra implant was less than that in the other 2 implants.
The initial stability was much affected by the implant design in bone types III, IV and the implant design such as the short pitch interval was beneficial to the initial stability of implants placed above the bone level.
The journal of advanced prosthodontics 12/2011; 3(4):190-5.
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ABSTRACT: The aim of this clinical report was to present and discuss the clinical procedure and the treatment considerations of prosthetic rehabilitation for hemimaxillectomy patients.
A 61-year-old man was successfully treated with all the remaining teeth reconstruction including replacing the implant-supported anterior fixed prosthesis and maxillary obturator.
An appropriate obturator design, remaining teeth reconstruction, and establishment of a proper vertical dimension of occlusion are important for acceptable facial appearance and patient satisfaction.
The Journal of craniofacial surgery 11/2011; 22(6):2359-61. · 0.81 Impact Factor
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ABSTRACT: The aim of the study was to investigate the influence of cortical bone and increasing implant fixture length on primary stability. Further investigation considered the correlation between the presence of cortical bone at the marginal bone and implant stability measured by insertion torque (IT) and resonance frequency analysis (RFA), as well as implant length, were determined.
Two different types of polyurethane bone models were compared. (Group 1: with cortical and cancellous bone; Group 2: with cancellous bone only). A total of 60 external type implants (∅ 4.1, OSSTEM(®) , US II(®) ) with different lengths (7, 10, and 13 mm) were used. IT was recorded automatically by a computer which was connected to the Implant fixture installation device during the placement. RFA was conducted to quantify the primary implant stability quotient (ISQ). All two measurements were repeated 10 times for each group.
All these differences were statistically significant between the two groups (P < 0.001) and intragroups (P < 0.001). Upon comparing the IT, cortical bone appears to have a greater influence on implant stability than implant lengths, whereas the RFA value strongly affects implant length rather than the presence of the crestal cortical bone.
The quantitative biomechanical evaluations clearly demonstrated that primary implant stability seems to be influenced by the presence of a cortical plate and total surface area of the implant fixture appears to be the decisive determinant for ISQ value.
Clinical Oral Implants Research 09/2011; 23(10):1193-7. · 2.51 Impact Factor
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ABSTRACT: Periodic fluoride treatment may contribute to the ability of fresh orthodontic adhesives to provide long-term F(-) release. The effects of periodic fluoride treatment on the amount of F(-) release from fresh orthodontic adhesives was investigated.
F(-) release was measured from a nonfluoride-releasing composite, a fluoride-releasing composite, a polyacid-modified composite (compomer), and two resin-modified glass-ionomer cements (RMGICs) at 1, 2, and 5 days after one of the following treatments: 225 ppm F(-) solution, 900 ppm F(-) solution, acidulated phosphate fluoride gel (APF), fluoridated dentifrice, and deionised water (control). F(-) release was measured in a 5-day cycle, which was repeated 9 consecutive times. The amount of F(-) release for each group was analysed using the repeated measures analysis of variance. Statistical significance was set at a level of α=0.05.
Periodic fluoride treatment temporarily increased F(-) release in fresh fluoride-releasing orthodontic adhesives, but not in fresh nonfluoride-releasing composite. The order of effective fluoride-release was RMGICs>compomer>fluoride-releasing composite>nonfluoride-releasing composite. The application of APF or 900 ppm F(-) solution was the most effective way to maintain F(-) release from fresh orthodontic adhesives. However, the amount of F(-) release gradually decreased with increasing specimen age.
Given the difficulty of routine use of APF at home, the results of this study show that a combination of RMGICs and high-dose fluoride mouth rinse is the most effective protocol to maintain F(-) release from fresh orthodontic adhesives.
Most studies have investigated fluoride-uptake abilities using aged materials in which fluoride had been lost for at least 1 month. This study has found that periodic fluoride treatment altered the conventional F(-) release pattern of fresh fluoride-releasing materials and type of fluoride-containing medium plays a more critical role in fluoride recharging of the materials than fluoride concentration. This study will help clinicians to find the most effective fluoride treatment protocol of fresh materials.
Journal of dentistry 08/2011; 39(11):788-94. · 2.00 Impact Factor
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ABSTRACT: This study tested the hypothesis that there would be differences in primary stability due to the presence of self cutting blades. We investigated the effect of a self-cutting blade implant design on the primary stability of tapered dental implants in a simulated low-density bone model.
Implant fixtures with 2 different designs, one with self-cutting blades and the other without self-cutting blades, were fabricated in the same implant system. Insertion torque, resonance frequency analysis, reverse torque, and pull-out and push-in tests were evaluated in grade no. 10 solid rigid polyurethane foam.
All 5 assessments of the group without self-cutting blades were significantly higher than those of the self-cutting group (P < .001).
The implants without self-cutting blades create a lateral compression with increased contact surface area and consequently improve the primary stability in a simulated low-density bone model.
Oral surgery, oral medicine, oral pathology, oral radiology, and endodontics 03/2011; 112(5):573-80. · 1.50 Impact Factor
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ABSTRACT: The aim of this biomechanical study was to assess the influence of self-tapping blades in terms of primary implant stability between implants with self-tapping blades and implants without self-tapping blades using five different analytic methods, especially in medium-density bone.
Two different types of dental implants (4 × 10 mm) were tested: self-tapping and non-self-tapping. The fixture design including thread profiles was exactly the same between the two groups; the only difference was the presence of cutting blades on one half of the apical portion of the implant body. Solid rigid polyurethane blocks with corresponding densities were selected to simulate medium-density bone. Five mechanical assessments (insertion torque, resonance frequency analysis [RFA], reverse torque, pull-out and push in test) were performed for primary stability.
Implants without self-tapping blades showed significantly higher values (P<0.001) in four biomechanical assessments, except RFA (P=0.684). However, a statistically significant correlation could not be detected between insertion torque values with the four different outcome variables (P>0.05).
The outcomes of the present study indicate that the implant body design without self-tapping blades has a good primary stability compared with that with self-tapping blades in medium-density bone. Considering the RFA, a distinct layer of cortical bone on marginal bone will yield implant stability quotient values similar to those in medium-bone density when implants have the same diameter.
Clinical Oral Implants Research 02/2011; 22(10):1179-84. · 2.51 Impact Factor
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ABSTRACT: Settling (embedment relaxation), which is the main cause for screw loosening, is developed by microroughness between implant and abutment metal surface. The objective of this study was to evaluate and compare the relationship between the level of applied torque and the settling of abutments into implants in external and internal implant-abutment connection.
Five different implant-abutment connections were used (Ext, External butt joint + two-piece abutment; Int-H2, Internal hexagon + two-piece abutment; Int-H1, Internal hexagon + one-piece abutment; Int-O2, Internal octagon + two-piece abutment; Int-O1, Internal octagon + one-piece abutment). All abutments of each group were assembled and tightened with corresponding implants by a digital torque gauge. The total lengths of implant-abutment samples were measured at each torque (5, 10, 30 N cm and repeated 30 N cm with 10-min interval) by an electronic digital micrometer. The settling values were calculated by changes between the total lengths of implant-abutment samples.
All groups developed settling with repeated tightening. The Int-H2 group showed markedly higher settling for all instances of tightening torque and the Ext group was the lowest. Statistically significant differences were found in settling values between the groups and statistically significant increases were observed within each group at different tightening torques (P<0.05). After the second tightening of 30 N cm, repeated tightening showed almost constant settling values.
Results from the present study suggested that to minimize the settling effect, abutment screws should be retightened at least twice at 30 N cm torque at a 10-min interval in all laboratory and clinical procedures.
Clinical Oral Implants Research 12/2010; 22(8):834-9. · 2.51 Impact Factor
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ABSTRACT: This study compared the accuracy of an abutment-framework (A-F) taken with open tray impression technique combining cementon crown abutments, a metal framework and resin cement to closed tray and resin-splinted open tray impression techniques for the 3-implant definitive casts. The effect of angulation on the accuracy of these 3 techniques was also evaluated.
Three definitive casts, each with 3 linearly positioned implant analogs at relative angulations 0, 30, and 40 degrees, were fabricated with passively fitted corresponding reference frameworks. Ten impressions were made and poured, using each of the 3 techniques on each of the 3 definitive casts. To record the vertical gap between reference frameworks and analogs in duplicate casts, a light microscope with image processing was used. Data were analyzed by two-way analysis of variance and the Tukey test.
The open tray techniques showed significantly smaller vertical gaps compare to closed tray technique (P < .05). The closed tray and the resin-splinted open tray technique showed significantly different vertical gaps according to the angulation of implant (P < .05), but the A-F impression technique did not (P > .05).
The accuracy of the A-F impression technique was superior to that of conventional techniques, and was not affected by the angulation of the implants.
The journal of advanced prosthodontics 03/2010; 2(1):25-31.
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ABSTRACT: Primary stability at the time of implant placement is related to the level of primary bone contact. The level of bone contact with implant is affected by thread design, surgical procedure and bone quality, etc.
The aim of this study was to compare the initial stability of the various taper implants according to the thread designs, half of which were engaged to inferior cortical wall of type IV bone (Group 1) and the rest of which were not engaged to inferior cortical wall (Group 2) by measuring the implant stability quotient (ISQ) and the removal torque value (RTV).
In this study, 6 different implant fixtures with 10 mm length were installed. In order to simulate the sinus inferior wall of type IV bone, one side cortical bone of swine rib was removed. 6 different implants were installed in the same bone block following manufacturer's recommended procedures. Total 10 bone blocks were made for each group. The height of Group 1 bone block was 10 mm for engagement and that of group 2 was 13 mm. The initial stability was measured with ISQ value using Osstell mentor® and with removal torque using MGT50 torque gauge.
In this study, we found the following results. 1. In Group 1 with fixtures engaged to the inferior cortical wall, there was no significant difference in RTV and ISQ value among the 6 types of implants. 2. In Group 2 with fixtures not engaged to the inferior cortical wall, there was significant difference in RTV and ISQ value among the 6 types of implants (P < .05). 3. There was significant difference in RTV and ISQ value according to whether fixtures were engaged to the inferior cortical wall or not (P < .05). 4. Under-drilling made RTV and ISQ value increase significantly in the NT implants which had lower RTV and ISQ value in Group 2 (P < .05).
Without being engaged to the inferior cortical wall fixtures had initial stability affected by implant types. Also in poor quality bone, under-drilling improved initial stability.
The journal of advanced prosthodontics 03/2009; 1(1):19-25.
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ABSTRACT: The purpose of this study was to define the surface properties of prepared titanium (Ti) disks, which served as a model system, and to contrast the biologic response of MG63 cells exposed to Ti disks with different levels of surface roughness. The surface properties interact with each other, resulting in a change of other surface qualities in addition to roughness due to the surface roughening procedure. The machined Ti disks were roughened by sandblasting and electric glow discharging. The surface properties of the Ti specimens were inspected through a comprehensive surface analysis. MG63 cell behaviors were compared along with cell number, alkaline phosphatase (ALP) activity, Runx2 gene expression, and type I collagen production. Statistics were evaluated, using analysis of variance (ANOVA). The sandblasted Ti disks demonstrated well-controlled surface roughness features and meaningful average roughness ranges, including the surface roughness of the "modern" microrough implant, used clinically. With increasing Ti surface roughness, the cell number decreased, while the ALP activity, type I collagen production, and Runx2 gene expression increased significantly. The rougher the Ti surface was, the sooner the Runx2 gene was expressed. Based on these results, we suggest that the microrough Ti surfaces of the 1-3 mum range may contribute effectively to osteogenic differentiation and proliferation in MG63 cells.
Journal of Biomedical Materials Research Part A 01/2007; 79(4):1023-32. · 2.63 Impact Factor
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ABSTRACT: The objective of this study was to determine the changes in color and translucency of dental porcelain-repairing resin composites compared to dental porcelain after thermocycling. Color and spectral reflectance of three shades (A2, A3, and A3.5) of one brand of dental porcelain and three basic shades (A2, A3, and A3.5) and three combinations (A2/A3, A3/3.5, and A2/A3.5) of three brands of porcelain-repairing resin composites (ABT, FSP, and TCR) were measured, before and after thermocycling for 3000 cycles, relative to the illuminant D65. The specimen was 2 mm in thickness, and 1 mm of each shade was layered to make combined shades. Changes in color (DeltaE*ab) and translucency parameter (DeltaTP) were calculated. A general linear model by the material (porcelain or resin composite) and shade was used to compare differences (alpha = 0.05). The range of color changes was 0.68-1.67 in porcelain, 0.56-1.30 in ABT, 2.28-3.10 in FSP, and 0.36-1.15 in TCR. The range of DeltaTP was 0.45-0.96 in porcelain, -0.48 to 0.94 in ABT, -1.31 to 0.82 in FSP, and -0.51 to 1.91 in TCR. After thermocycling, changes in color and TP were correlated with the shade of the material, but not with the material. The discrepancy in the changes of color and translucency after thermocycling between porcelain and porcelain-repairing resin composites should be considered when selecting repairing materials.
Journal of Biomedical Materials Research Part B Applied Biomaterials 08/2006; 78(1):1-6. · 2.15 Impact Factor
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ABSTRACT: After staining a porcelain restoration, increasing the lightness (value) and decreasing the chroma of a restoration is not practically easy to accomplish.
The purpose of this study was to determine the color change of enamel porcelain after repeated external staining procedures over the enamel porcelain surface. Changes in translucency and differences in surface roughness were also measured.
Enamel porcelain (VITA OMEGA 900 Metal Ceramics) disks (1 x 12 mm) of 1 shade (EN2) were prepared, and 1 of 4 types of external stains (VITA Akzent stains) was applied over the specimens and fired. Firing was repeated 3 times after application of the same stains. Color of the specimens before and after stainings was measured with a reflection spectrophotometer. Two-factor repeated-measures analysis of variance with the fixed factors of the stain type and number of staining cycles for the changes in CIE L(*), CIE a(*), CIE b(*), color (DeltaE(*)(ab)), and chroma (DeltaC(*)(ab)) after repeated staining was performed (alpha=.05). Chroma change was calculated as DeltaC(*)(a)=(Deltaa *(2) +Deltab *(2))(1/2). Changes in translucency (translucency parameter and masking effect) and difference in surface roughness (Ra) after the third staining cycle were also determined.
Color change after the first staining cycle was perceptible (DeltaE(*)(ab) >2) for 2 of 4 types of stains and was perceptible for all 4 types of stains investigated after the third staining cycle (DeltaE(*)(ab) = 2.36-11.04). Lightness generally increased, and chroma also increased after staining but varied by the type of stains and number of staining cycles. Translucency generally decreased after repeated staining. Surface roughness varied by the type of stain (P < .001).
Color difference and lightness increased significantly after repeated staining cycles, but chroma change was small after repeated staining cycles. Therefore, repeated staining may be a method to increase the lightness of enamel porcelain.
Journal of Prosthetic Dentistry 07/2006; 95(6):437-43. · 1.32 Impact Factor
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ABSTRACT: This study evaluated the accuracy of 2 implant-level impression techniques (direct nonsplinted and splinted) for the fabrication of multi-unit internal-connection implant restorations in 2 simulated clinical settings (parallel and divergent) using a laboratory model.
A dental stone master model was fabricated with 2 pairs of implant replicas. One pair simulated a parallel clinical condition and the other an 8-degree-divergent condition. Ten stone casts were made from vinyl polysiloxane impressions of the master model for each impression technique. Half of the samples were created by a direct nonsplinted technique (square impression copings, custom tray), and the other half were made by a direct splinted technique (square impression copings splinted with autopolymerizing acrylic resin, custom tray). Four strain gauges were fixed on each metal framework to measure the degree of framework deformation for each stone cast in half-Wheatstone-bridge formations. Deformation readings were made twice in 4 directions (anterior, posterior, superior, and inferior). Deformation data were analyzed using repeated-measures analysis of variance at a .05 level of significance.
No significant difference in deformation was found between the direct nonsplinted and splinted samples in either simulated clinical condition (P > .05). No significant difference in deformation was found between the techniques regardless of condition (P > .05).
Within the limitations of this study, using a 2-implant model, the accuracy of implant-level impressions for internal-connection implant restorations was similar for the direct nonsplinted and splinted techniques in settings with divergence up to 8 degrees.
The International journal of oral & maxillofacial implants 22(5):761-8. · 1.78 Impact Factor
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ABSTRACT: Titanium dioxide (TiO2), a photocatalyst, is known to decompose various organic compounds under ultraviolet (UV) illumination by generating various radicals, which is useful for killing bacteria. The purpose of the present study was to evaluate the photocatalytic bactericidal effects of variously treated titanium surfaces on Streptococcus sanguinis SL1.
Specimens were fabricated from grade 4 commercially pure titanium, 10 mm in diameter and 2 mm in thickness. Three different surfaces were prepared: anodized (AO) at 270 V, heat-treated (HT), and machined (MA). Surface analysis was performed using confocal laser scanning microscope, scanning electron microscopy, and thin-film x-ray diffractometry. The antibacterial activities were assessed by comparing adhesion and survival rates of S sanguinis on various surfaces under UV illumination.
The AO surface was rougher than the HT and MA surfaces. The AO surface showed TiO2 peaks of anatase structure, while the HT surface showed TiO2 peaks of rutile structure in x-ray diffractometry. HT and AO surfaces showed significantly decreased bacterial adhesion under UV illumination (AO and HT > control, AO > MA). In addition, bacterial adhesion decreased more significantly with extended UV illumination time. With respect to survival rates of bacteria, AO and HT showed a significant reduction over time compared to MA. The photocatalytic bactericidal effect was maximal on the AO titanium, followed by HT and MA.
The photo-induced bactericidal efficacy of TiO2 films is dependent on their surface characteristics.
The International journal of oral & maxillofacial implants 26(1):39-44. · 1.78 Impact Factor
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ABSTRACT: This study evaluated the effect of different screw-tightening sequences, forces, and methods on the stresses generated on a well-fitting internal-connection implant (Astra Tech) superstructure.
A metal framework directly connected to four parallel implants was fabricated on a fully edentulous mandibular resin model. Six stone casts with four implant replicas were made from a pickup impression of the superstructure to represent a "well-fitting" situation. Stresses generated by four screw-tightening sequences (1-2-3-4, 4-3-2-1, 2-4-3-1, and 2-3-1-4), two forces (10 and 20 Ncm), and two methods (one-step and two-step) were evaluated. In the two-step method, screws were tightened to the initial torque (10 Ncm) in a predetermined screw-tightening sequence and then to the final torque (20 Ncm) in the same sequence. Stresses were recorded twice by three strain gauges attached to the framework (superior face midway between abutments). Deformation data were analyzed using multiple analysis of variance at a .05 level of statistical significance.
In all stone casts, stresses were produced by the superstructure connection, regardless of screw-tightening sequence, force, and method. No statistically significant differences for superstructure preload stresses were found based on screw-tightening sequences (-180.0 to -181.6 microm/m) or forces (-163.4 and -169.2 microm/m) (P > .05). However, different screw-tightening methods induced different stresses on the superstructure. The two-step screw-tightening method (-180.1 microm/m) produced significantly higher stress than the one-step method (-169.2 microm/m) (P = .0457).
Within the limitations of this in vitro study, screw-tightening sequence and force were not critical factors in the stress generated on a well-fitting internal-connection implant superstructure. The stress caused by the two-step method was greater than that produced using the one-step method. Further studies are needed to evaluate the effect of screw-tightening techniques on preload stress in various different clinical situations.
The International journal of oral & maxillofacial implants 24(6):1045-53. · 1.78 Impact Factor
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ABSTRACT: The purpose of this investigation was to measure the accuracy of digital impressions (DIs) compared to conventional impressions (CIs). Using the iTero system, a master cast was scanned to produce stereolithography dies. As a control group, silicone impressions were taken and poured using stone. The resulting stereolithography and stone dies were scanned and overlayed on the scanned reference image of the master cast. The mean (± standard deviation) dimensional difference to the master cast was 23.9 (± 17.6) ?m for DIs and 17.6 (± 45.6) μm for CIs. The results indicate that DIs also provides enough accuracy for clinical application.
The International journal of prosthodontics 26(2):161-3. · 1.38 Impact Factor
