The present study assessed the influence of tightening strength of abutment on the occurrence of cracking on the screw part of abutment. When the abutment (Platon Japan) was tightened at 15 N in a titanium implant (Platon Japan) inclined vertically by 50 degrees, the maximum load at which cracking occurred in the screw of abutment was 434.4±2.9 N (n=5). On the other hand, the maximum loads of the screw part of abutment, which inclined by 14 degrees and 12 degrees, were 1,624.0±100.0 N and 2,288.9±59.8 N, respectively. When the abutment was tightened at 30 N in an implant inclined vertically by 50 degrees, the maximum load at which cracking occurred in the screw part of abutment was 424.6±13.7 N (n=5). On the other hand, the maximum loads of the screw part of abutment, which inclined by 14 degrees and 12 degrees, were 1,548.5±54.9 N and 2,315.4±51.0 N, respectively. There was no statistical significance between the results obtained from tightening of 15 N and 30 N. These results suggest that the Platon titanium implant and abutment possess sufficient mechanical strength when tightened at a minimum of 15 N, and thus provide favorable clinical results.
A system designed to accurately measure the surface temperature of oral mucous membranes has been developed by bio-medical engineering techniques.
For the inflammation period right after implant placement, the surface temperature of oral mucous membranes, where implants were placed, was successively measured. As inflammation declined, the surface temperature of the affected side became closer to that of the opposite side. In a case of five implants simultaneously placed in a maxillary anterior tooth through a molar, the surface temperature of mucous membranes was the highest on the day following the surgery. Temperature transitions were different from part to part. It took six days after surgery for a molar, and twelve days for a canine, for the surface temperature of mucous membrane to return to the normal value. The body temperature, as well as respiratory and circulatory parameters, fluctuated within an allowable physiological range. It follows, from this, that the inflammatory response to surgical stress can objectively be assessed through local fever by measuring the temperature of the affected part, and that some suggestions will be obtained for post-surgerical management of implant placement.
In order to investigate, quantitatively, the adverse effect of electrolytic acid water (EAW) on human gingival mucoperiosteal flap tissue, the relative outgrowth value (ROV) was measured by tissue culture testing with MEM十10%FBS and a CO2 incubator. The tissue fragments were rinsed with and stored in the following nine different conditions:①MEM(Cont.), ②EAW, ③Aqua dest., ④Hanks solution, and ⑤KN solution, and also double treatment of ⑥EAW-Hanks, ⑦EAWKN, ⑧Aqua dest.-Hanks, and ⑨Aqua dest.-KN. After that, ROVs from the explants of mucoperiosteal flap tissue fragments were measured after 14 days of cultivation. In this tissue culture test, it was clearly demonstrated that EAW and Aqua dest. have severe cytotoxicity and an adverse effect on mucoperiosteal flap tissue, while KN solution and Hanks solution have no cytotoxic and adverse effects.
Use of KN solution or Hanks solution is highly recommended as a rinsing solution during mucoperiosteal flap operation in implant surgery. Water-irrigation or EAW desinfection should be avoided, without fail, during implant surgery.
However, post-rinsing with KN solution or Hanks solution may be effective to reduce the adverse effect of EAW or Aqua dest.
Numerous studies have indicated that the osseointegrated implant is appreciated as a highly reliable method to recover occlusal capability in the prosthetic treatment of missing teeth. However, such osseointegration may be broken if an excess of occlusal force is applied. Clinically, incongruity between superstructure length and fixture length is considered a pivotal factor that may cause osseointegration breakage. But no studies have looked at the effects of the ratio of superstructure length to fixture length (superstructure-fixture ratio) on perimaxillary distortion under an actual load. Therefore, to clarify this issue, fixtures were embedded in a human air-dried mandible. The experiments were carried out under static loading, and the distribution of strains on the bone surfaces surrounding the implant was measured.
1. When a composite of superstructure and fixture was placed at its central loading point, it was found that the strain of the bony tissue surrounding the fixture was only slightly affected by the superstructure-fixture ratio.
2. When the loading point was shifted eccentrically to the buccolingual side, it was found that the superstructure length was increased, resulting in an increase in the strain located at the cortical portion surrounding the junction of fixture and abutment.
3. Similarly, with eccentric loading, regarding the strain of the cortical portion surrounding the junction of fixture and abutment, it was found that a superstructure-fixture ratio of 1:1 was near the verge of osseointegration breakage.
4. Finally, it was found that equality of height of the superstructure and fixture length gave rise to an even distribution of occlusal force on the jaw bone, and resulted in no adverse effects.
It is widely known that hydroxyapatite coated implants show a better bone response than titanium implants. However, some shortcomings of hydroxyapatite coated implants, produced by plasma spraying, were reported. A thin physical vapor deposition technique was introduced to overcome such shortcomings. It was reported that thin-hydroxyapatite coated implants showed good biological behaviors in animal experiments or cell culture experiments. But there have been a few reports related to the mechanical behavior of thin coated implants, for example stress distribution around the implants under oral functioning conditions.
The finite element method (FEM) is a powerful tool to analyze the stress distribution on an implant. The purpose of this study was to investigate the influence of thickness and Young's modulus of a hydroxyapatite coated layer on the stress distribution around the implant by the finite element method.
Two finite element models were proposed to simulate the mechanical behavior of implant. One finite element model is called a macro-model. The macro-model is composed of a titanium implant, a hydroxyapatite coating, a cortical bond, and trabecular bone. The goal of the calculation of the macro-model is to simulate the whole stress distribution of the coated implant, including the surrounding bone. The other finite element model is called a micro-model. The micro-model is composed of a titanium implant, a hydroxyapatite coated layer, and cortical bone. The thickness of the coating layer was 5 or 100 μm. The micro-model is calculated in order to obtain the details of the stress distribution on the implant. Using these models, the influences of thickness and Young's modulus of the hydroxyapatite coated layer on stress distribution around implant, were discussed. The results were as follows
1. A vertical load of 100 N was applied on the top of the implants. Stress analysis of the macromodel showed that the maximum stress existed in cortical bone near the implant. Moreover, it was clear that the vertical load corresponded to three-point bending force to the surrounding cortical bone.
2. The micro-model showed that the stress level in the surrounded bone caused by a 5-μm coating, is greater than that of a 100-μm coating. On the other hand, the stress level in the coating layer of a 5-μm coating is less than that of a 100-μm coating. A greater Young's modulus of the hydroxyapatite coated layer gave a higher stress level in the surrounding cortical bone.
3. The results obtained in this study demonstrated that a functionally graded hydroxyapatite coated layer will be suitable for the optimal design of hydroxyapatite coated implants.
Presurgical imaging diagnosis is important to obtain a more accurate prediction of the outcome of implant treatment.
Cross-sectional jaw images in the bucco-lingual direction can usually be obtained by computed tomography (CT), or conventional X-ray tomography. However, it is considered that the measurement accuracy of conventional tomograms is affected by the angle of the tomographic objective plane and the mandibular shape. This study was performed to clarify the change in mandibular shape by shifting the angles of tomographic objective planes.
Cross-sectional tomographic images were obtained on the bilateral central incisor, first premolar, and first molar regions of 10 dried mandibles, using a panoramic machine with a tomographic function (AZ 3000 DLP, Asahi Roentgen Ind. Co., Japan). The angles of tomographic objective planes were shifted horizontally within a range of ±20 degrees, at intervals of 5 degrees, from the tomographic objective plane which was automatically determined. We measured the width between the surface of the buccal and lingual cortical bone.
The optimal tomographic objective plane was defined as the plane representing the thinnest buccolingual width.
The results were as follows.
The means of bucco-lingual widths in the optimal planes were 9.3 mm, 9.7 mm, and 11.2 mm, in the incisor, premolar, and molar regions, respectively. The angle from the optimal plane, which permitted magnification within 0.5 mm in bucco-lingual width, was from -12.3 degrees to＋11.4 degrees in the incisor region. In the molar region, it was from -12.1 degrees to＋9.8 degrees, while it could not be determined, because of the limit of the machine's movement, in the premolar region.
In conclusion, the change in mandibular shape by shifting the angles of tomographic objective planes was clarified.
The adherence of dental plaque to a dental implant plays an important role in the inflammation around a dental implant. It is known that silver ions have antibacterial activity and low toxicity. Therefore, we examined the antibacterial activity of dental implant material (IMZ implant) gotten or not by ion implantation and arc-plasmas coating. Under anesthesia, the tested materials were implanted into submaxillary of 6 beagle dogs. The dogs were given softened food, without carrying out brushing, for 2 weeks after inserting abutments. Oral photographs were taken after 2 weeks. There was an obviously difference in plaque adherence between the abutment with and without silver coating. These results indicate that the anti-plaque effect found in this study was due to the silver ions released by silver coated abutment of dental implants, and that it may be useful for protection against inflammation around a dental implant.
Implant mobility and bone formation surrounding implants under occlusal functioning were investigated using 3 different stress-absorbing mechanisms: an Intramobile Element (IME), an Intramobile connector (IMC), and a Ti Element (Ti), and 2 conditions of occlusal contact. Occlusal contact was set at either a uniform contact position, so that the implants evenly contacted the remaining teeth, or in a slightly elevated (by approximately 60 μm) position.
Two adult Japanese monkeys were used. They received 3 single-implant crowns, and, each stress absorbing element (IME, IMC, or Ti) was connected to an implant. In one, the occlusion was set at a uniform contact position, while the other had the occlusion adjusted to a slightly elevated position.
Implant mobility was judged weekly, from the second surgery until 4 weeks after connecting the implant crowns, for a total of 7 times. Four weeks after connecting the implant crowns, bone formation around the implant fixtures, and changes in microvasculature, were observed, using a plastic injection method with a scanning electron microscope.
The results were:
1. After connecting the implant crowns, mobility reduced over time as occlusal function increased. The reduction in mobility index (MI) scores showed a significant difference between the level at 1 week after connecting and that at 4 weeks, after adjusting for both the uniform and slightly elevated contact positions. However, no significant differences were found among the 3 stress-absorbing elements.
2. For both uniform and slightly elevated contact, and with each of the stress-absorbing elements, osseointegration was maintained. There were no differences in the implantal alveolar proper between the uniform and slightly elevated occlusions around the upper portion of implants, for any of the 3 stress-absorbing elements. However, around the middle portion and the bottom portion of the implants, the implantal alveolar proper, as well as the trabecula supporting it, was thicker with IMC and Ti, than with IME.
Hydroxyapatite (HA)-coated implants have been a subject of great interest since the mid-1980 s. Various clinical studies have shown that HA-coatings lead to good clinical results over a 15-year period. Statistics with a success rate of 95% were reported over a 5-year period. More recently, however, an increased number of failures with HA-coated implants have been reported.
One case of an HA-coated implant, which had to be removed due to implant mobility, marginal swelling and redness, and marginal bone loss (funnel-shaped resorption) around the implant, at 4 years after the implant had been placed, in a 48-year-old male patient, was reported. An explanted HA-coated titanium cylinder-form implant was examined, using scanning electron microscopy (SEM) and an electron probe X-ray microanalyzer (EPMA) to analize the main constructive elements. Also, soft tissue removed from the implant socket was microscopically examined.
The results were as follows
1. The removed implant demonstrated, macroscopically and microscopically, a dental calculus-like deposit on the plasma-sprayed surface, and loss of the HA-coating, with the presence of a smooth titanium substrate.
2. The loss of HA-coating was seen within the hole of the apical end of the implant.
3. For the EPMA data, the implant material mainly consisted of titanium, with a loss of the HA-coated layer. The dental calculus-like deposit chiefly consisted of calcium and phosphate, and showed no bone structure.
4. Microscopic examination revealed that granulation tissue replaced the resorbed bone and was separated from the implant itself by proliferating squamous epithelium. Epithelium proliferated apically to the encapsulated granulation tissue. The granulation tissue that resulted from the inflammatory process began marginally and followed the bacterial movement; the process proceeded rapidly with the loss of an implant.
From the above results, marginal bone loss may be induced by etiologic factors known to be causative, such as bacterial infection and mechanical overload. The most important factors for preventing late complications with implant-prosthetic treatment are the peri-implant osseous and soft tissue conditions. A check of the implant-borne suprastructure is essential. A thorough cleaning of the implant, as well as any remaining natural teeth of the patient who receives implant-prosthetic treatment, is necessary.
In the present study, we worked out the implant extraction rate, and looked into the relationships between jaws and local dental factors that might contribute toward implant extraction. In addition,we investigated clinical problems and treatment procedures after extraction.
Extracted implants used in this study were from among 5,092 implants (2,201 implants in men, and 2,891 implants in women), which had been placed one month to 22 years previously, in 2,969 cases (1,245 for men, and 1,724 for women) of 2,261 patients (957 men and 1,304 women; age,10～ 88 yrs). The clinical examination was accomplished by a total of 74 dentists.
The percentage of extracted implants was in the range of 5～6% of the total number of patients, cases, and implants, respectively. A significant gender difference was noted in the number of implants. The patients in their 40s had the lowest extraction rate. The patients under 40 years of age, or those of 50 and over, showed a higher extraction rate. One dentist extracted 3.3 implants from 1.9 patients and 2.4 cases, on average. The number of implants placed during the 1994s was larger than that placed before any preceding decade, and the extraction rate was on the decline. A check of dentists' experience in implant extraction showed that 48.6% of the dentists had extracted one to four implants, and that 32.4% had no previous experience.
When the relationships between jaws and local dental factors were examined by category, it was found that maxillae had a higher extraction rate than mandibles, in many cases. There were diverse reasons for implant extraction: inadequate bone quality, bone thickness and alveolar bone height, unfavorable occlusal relationships, osseointegration failure, and poor oral hygiene. After implant extraction, implant treatment was redone in a significant 55.2% of the cases.
The above-mentioned findings will serve as evidence that can contribute to the progress of implant therapy with high long-term predictability.
To observe details in postoperative endosseous implants in the maxillary molar region, a three-dimensional computed tomography (3 DCT) imaging technique was designed. CT examinations were performed on 4 patients in the follow-up stage. Oblique sagittal and oblique coronal imaging planes, which parallel the direction of implant fixtures, were measured using a multiplanar reformatting (MPR) technique. Cross-sectional reformatting slice images, and volume rendering crosscut images using the above imaging planes, were created in 9 implant fixtures, respectively. Sufficient 3 D images were obtained to evaluate the relationship between implant fixtures and the maxillary sinus cavity, three-dimensionally.3 DCT was a practical imaging technique to evaluate postoperative endosseous implants.
We experienced a case of osseointegrated implants (ITI Bonefit®) with an autogenous bone graft and a free gingival graft for occlusal reconstruction.
The patient was a 50-year-old male who was referred to our clinic for treatment of a fracture of the mandible, on April 14, 1997.
Surgery for the mandible fracture was performed under general anesthesia on May 2,1997. At the same time, his teeth(1-6, 1-6) were extracted,because they were all broken and their alveolar bone was missing due to the injury.
Autogenous bone grafting was performed in the region of 2-4, November 28, 1997. A free gingival graft and implantation were performed in the region of 1-6 1-6, and superstructures were fixed on the implants, on October 31, 1998.
We have observed this patient for 2 years since the implantation. The results were satisfactory in the esthetic aspect, as well as in speech and masticatory functions. All periodontal parameters have no signs of peri-implantitis.
Osseointegrated implants are useful for dental reconstruction of partial and complete edentulism. The use of implants is also advantageous for fixation of a prosthesis in patients following tumor surgery. Maxillectomy for tumor treatment decreases masticatory function and speech function. We used vascularized bone grafts and osseointegrated implants for masticatory rehabilitation after maxillectomy, and evaluated the masticatory function, by means of a questionnaire on masticatory efficiency, and by occlusal force measurement. As a result, the patient showed high points in the questionnaire and high magnitude of occlusal force.
In an implant prosthesis, the junction between the implant neck and the superstructure has often been placed subgingivally. The aim of this study was to examine the effect of the position of the implant-superstructure junction relative to the marginal gingiva on the surrounding tissue, using periodontal paramaters.
Sixty-seven ITI Bonefit® implants in 22 patients were selected for this study. The superstructures of implants were all fabricated using an octa system, and they were fixed to implant fixture with screws. The average observation period was 25 months. Four sites (mesial, distal, buccal, and libial sites) of each implant were checked using periodontal parameters (Plaque Index, Bleeding on Probing, Periotron Score, Probing Pocket Depth,and Probing Attachment Level). And these sites were divided into 3 groups (supragingival, equigingival, and subgingival groups) according to the position of the implant-superstructure junction relative to the gingival margin.
Result: There was no significant difference between the 3 groups in plaque index, but the subgingival group showed a significantly higher score of bleeding on probing, and in periotron score, compared with the other groups. This result suggested that the subgingival position could cause an inflammatory reaction in the surrounding tissue.
In anterior maxilla edentulous cases, sufficient bone is important to succeed both in consolidation of a fixture and aesthetic form. Therefore, alveolar ridge augmentation is performed to obtain sufficient bone for implant treatment. However, the augmentation, performed in the vertical dimension, has been difficult compared with other augmentations, because of frequent complications, such as infection, bone resorption, etc. Distraction osteogenesis has been produced for jaw bone lengthening. Continuously, alveolar bone lengthening which was used distraction osetogenesis was reported with good results. This method is able to obtain any direction and volume as bone augmentation. As such, we performed vertical augmentation in an anterior maxilla edentulous case using this method. Osteotomy and placement of distraction device were performed to the patient who was contracted vertical bone resorption. After 10 days, the device was activated once or twice daily for 8 days (total lengthening was 7.0 mm). After 8 weeks, the device was removed, and after 4 weeks, implant fixtures were inserted. Local infection occurred during lengthening, but a sufficient bone volume was obtained. Our result suggested that distraction osteogenesis was useful for alveolar bone augmentation in the anterior maxilla.