Objective: Since the hydroxyapatite film of hydroxyapatite-coated implants fabricated using plasma spraying is thick and shows low crystallinity, its in vivo fracture or detachment due to factors such as occlusal force has been reported. Therefore, these implants are not widely used at present.
Methods: To improve this situation, our research group developed implants coated with a thin hydroxyapatite film (thickness ＜1 μm) employing a laser ablation method (pulse laser deposition technique: PLD). In this study, the bone-bonding strength of implants coated with a thin hydroxyapatite film produced using PLD was evaluated in dogs.
Results: A longitudinal increase both in the removal torque of implants coated with a thin hydroxyapatite layer and titanium implants was recognized by two-way analysis of variance (ANOVA)(p＜0.01). There were significant differences between the removal torque of implants coated with a thin hydroxyapatite layer and titanium implants, and the removal torque of implants coated with a thin hydroxyapatite layer 12 weeks after placement was significantly higher than that of titanium implants (p＜0.05) .
Conclusion: The results suggest that thin-layer hydroxyapatite can contribute to the fixation after implant placement, allowing early loading.
Metal injection molding (MIM) has attracted attention as a method to produce implant bodies. The mechanical properties of titanium alloy materials produced using MIM are comparable to those of implant rods which are already being used for implantation. However, since the fracture of implant bodies has become a problem in recent years, further improvement is desired. Heat treatment is a method to improve the material properties of titanium, and it has been reported that the fatigue strength of titanium increases with heating at 450℃. In this study, we performed heat treatment of titanium alloy materials produced using MIM, and evaluated whether the mechanical strength of the heat-treated titanium alloy was improved.
The tensile strength after heat treatment was significantly greater than that before heat treatment. The proof stress (yield strength) was improved by heat treatment, being within the range of Japanese Industrial Standards (JIS). The elongation and hardness after heat treatment showed no significant differences in comparison with those before treatment. Metallographic structure observation confirmed voids, which developed accompanying sintering. However, no apparent differences in the structure were noted between before and after heat treatment.
It was suggested that the tensile strength of test specimens produced using MIM was improved after heat treatment at 450℃.
Implants can not only be used in the definitive prosthetic solution but can also be of great benefit as stable anchors during orthodontic therapy. However, for ideal results, it is essential to establish orthodontically favorable positions for the implants and, more importantly, the best position for an adequate occlusal restoration prior to orthodontic teeth movement.
This report describes the utility of implants for bite raising and occlusal support prior to orthodontic teeth movement in patients with a reduced occlusal vertical dimension and resultant flaring.
The patient was a 57-year-old woman with chronic periodontitis including resultant flaring of the maxillary anterior teeth and posterior bite collapse. She first received periodontal treatment using a bilateral free-end-saddle removable partial denture, however, she complained of maxillary anterior flaring after placement of the denture and wanted orthodontic treatment and implant therapy. Therefore, the degree of potential bite raising and the stability of the mandibular position after bite raising were checked by an anterior jig and Gothic arch. Possible positions of implant placements and orthodontic tooth displacement were determined using a wax setup cast and lateral cephalograms with an anterior jig. Nine implants were placed in the planned positions using a surgical stent. Consideration of possible future orthodontic tooth displacements and the stability of the mandibular position before treatment is essential for determining the best placement positions for implants. Implant-supported occlusions in orthodontically favorable positions provide patient satisfaction, such as the reduction of periodontal pockets, esthetical restoration and stable occlusion.
It is suggested that the use of implants prior to orthodontic teeth movement is effective for stable bite raising and occlusal support in patients with a reduced occlusal vertical dimension and resultant flaring.
Three cases in whom dental implants had migrated into the maxillary sinus were admitted to our hospital. General dentists at another private clinic had previously performed dental implant placement in combination with socket lift procedures in the posterior maxillae. In case 1, an implant had migrated into the maxillary sinus 7 months after placement. In case 2, an implant had migrated three months after the first surgery. In case 3, three implants had migrated into the maxillary sinuses at or immediately after the first surgery. All implants were removed through the access window on the lateral maxillary sinus wall under local anesthesia. Waters radiographs of cases 1 and 2 revealed signs of inflammation of the maxillary sinus at the first visit. Additional surgical intervention for removal of bone substitute was needed in case 1, because pain and nasal symptoms did not improve after removal of the implant. Case 3 was admitted to our hospital 2 years after implant displacement; the delay was because his previous dentist had told him not to worry about the implants in the sinus cavities, and no signs of inflammation presented in the maxillofacial region.
Two migrated implants of these three cases had been placed in the non-submerged condition and these three patients had minimum residual bone height of the posterior maxillae. Therefore, non-submerged implant placement and minimum residual bone height are the main risk factors for migration of implants into the maxillary sinus, because of insufficient primary stability and occlusal load on the healing abutments of the implants postoperatively.
Background: Bone augmentation treatment with bone grafts or sinus lift may be indicated for implant therapy in patients with insufficient bone height of the posterior. However, these procedures require invasive surgery and long healing times. Although the insertion of short implants is sometimes recommended in such cases, there has been no detailed study on the placement and prospect of short implants in Japan. Therefore, the purpose of this study was to assess the survival rate of short implants placed in the posterior region.
Methods: From April 1997 to March 2006, a total of 86 short implants with a diameter of 4.1 or 5.0 mm and length of 7.0 mm were placed in 43 patients with insufficient bone height of the posterior after connecting the superstructure. The follow-up period ranged from April 1997 to March 2011 (mean: 89.4±35.9 months). To elucidate the difference between successful and failed implants, we investigated the effect of such factors as bone quality (TypeⅠ to Ⅳ), implant location (first premolar, second premolar, first molar and second molar region), implant diameter (4.1 or 5.0 mm), type of superstructure (splinting or non-splinting) and crown-to-implant ratio.
Results: The overall survival rate of the 86 implants was 95.3%. The 46 implants in the posterior maxilla exhibited a survival rate of 95.7%, while the survival rate for the 40 implants in the posterior mandible was 95.0%. A total of 4 out of 86 implants were lost during the observation period. The bone quality and type of superstructure might not affect the implant survival rate. However, implants inserted at the distal end and those with large crown-to-implant ratios might exhibit a decreased survival rate.
Conclusion: Short implants could be used in cases of insufficient bone height of the posterior maxilla and mandible. However, consideration should be given to the clinical outcomes associated with the implant location, crown-to-implant ratio and preservation of mucosa.
In this study, to clarify the present state of implant-supported prostheses produced in dental laboratories, we conducted a questionnaire survey to investigate dental technicians' establishment of occlusal contact in the intercuspal position.
We surveyed special dental technicians who had attended the educational lecture at the 30th Annual Meeting of the Kinki-Hokuriku Branch of the Japanese Society of Oral Implantology, and dental technicians who were in charge of laboratory work under dental implant specialists belonging to this society. Regarding 21 investigation items, we report the results obtained from 84 dental technicians, excluding the 9 cases who omitted some items of the questionnaire. This questionnaire investigation was performed after obtaining approval from the special dental technician committee of this society.
Regarding occlusal contact in crown-bridges and dentures, 36.9% of the dental technicians answered that the condition of occlusal contact is the same in both prostheses, i.e., occlusal contact is established in the same position, and 61.3% of these dental technicians answered that the size of the area of occlusal contact is also the same. On the other hand, 61.9% of them answered that the condition of occlusal contact is not the same in both prostheses, depending on the position, area, and timing of occlusal contact, and occlusal scheme and balance in each case.
Among the dental technicians, there were differences in the area in which they established occlusal contact in implant-supported prostheses. More than half of the dental technicians answered that the area in which occlusal contact was established was the inner incline of the functional cusp when the opposing teeth were implant-supported prostheses or natural teeth. There were 15 patterns of occlusal contact area when the opposing teeth were implant-supported prostheses, and 16 patterns when the opposing teeth were natural teeth. No frequent patterns exceeding the majority in number were present, and no fixed patterns were clearly noted.
It was revealed that dental technicians in charge of implant-supported prostheses devote a considerable amount of time in coping with many implant systems. On the other hand, they commonly described no items to which they pay attention regarding prosthetic appliances including implants, showing differences in their approaches toward prosthetic appliances. These results suggest there is an urgent need to establish common goals and criteria between dentists and dental technicians.
For the primary stabilities of implants, we examined the insertion torque of a straight implant (Straumann®SP Implant) and a tapered implant (Straumann®TE Implant) using the implant training cortical-cancellous bone model (Model-1) and cancellous bone model (Model-2), and obtained the following results:
1. The insertion torque of the straight implant significantly increased with implant body length and with total number of screw lines counted on the axial length of the implant in Model-1 and -2.
2. The insertion torque of the tapered implant was higher than that of the straight implant. The implant body length and total number of screw lines hardly affected the insertion torque of the tapered implant of Model-1. The insertion torque of the tapered implant of Model-2 increased significantly both with implant body length and with number of screw lines.
3. The insertion torque showed larger values in order of tapered implant (Model-1) ＞tapered implant (Model-2)＞straight implant (Model-1)＞straight implant (Model-2), but the insertion torque of the straight implant (Model-2) showed abnormally low values at 2 and 3 screw lines.
4. From the results, it can be summarized that the primary stability of the tapered implant is better than that of the straight implant and the insertion torque is influenced by quality of bone, implant body length, implant body form (straight or tapered type) and number of screw lines.