Clinical application and complications of short implants (≤6 mm) / 口腔疾病防治

@#Short implants can be used as an alternative in cases of insufficient vertical bone volume after dentition defect or absence of dentition to simplify or avoid bone augmentation procedures. Short implants (≤ 6 mm) are reported to have a mean survival rate of 96% after a period of 1-5 years in function and have been widely used in cases of dentition defects or absence of dentition. Compared with conventional implants (≥ 10 mm) combined with bone augmentation procedures, short implants have fewer surgery-related complications, less marginal bone loss, shortened treatment times and reduced costs, and are preferred by patients. Due to a lack of evidence, a high crown-implant ratio should not be an obstacle for the use of short implants. In addition, most of the current literature has not enough follow-up time, the long-term implant survival data of short implants remain unclear. To improve the clinical outcomes of short implants, attention should be paid to the implant site, bone quality, and occlusal force as well as to the presence of oral health maintenance, periodontal diseases and habits through a careful intraoral and radiographic examination. The choices of wider implant use and splint restoration are recommended, occlusal force should be paid attention during implant maintenance. Inappropriate stress on restorations should be avoided. Future studies should be focused on the long-term clinical outcomes of short implants.

Evaluation of stress contours on a maxillary molar subjected to simulated tooth loads by finite element analysis technique

Forces applied by dental occlusion generate stresses which are transmitted to the surrounding bone via the periodontal ligament causing a tissue response. The purpose of this study was to evaluate the response of a maxillary molar under secondary trauma from occlusion by observing the changes in its stress patterns. In order to visualize the exact pattern of stress distribution, three dimensional finite element analysis models were developed. A force of 3 N, moment of 27 Nmm and a counter rotation moment of 15 Nmm were applied to simulate orthodontic forces. Stresses produced at the periodontal ligament-tooth interface on a maxillary molar model with normal bone height subjected to an orthodontic force were compared with molar models showing bone loss and analyzed using finite element analysis technique. As the bone loss increased, it was observed that, the concentration of stresses at the apical one-third of the tooth also increased and there was high tendency for tooth displacement. The results suggest that an alteration in the magnitude of forces applied may be necessary in teeth with an increased crown to root ratio to maintain a healthy periodontium.

The three dimensional finite element analysis of the stress distribution according to the thread designs and the marginal bone loss of the implants

A study about the change of locations of the center of resistance according to the decrease of alveolar bone heights and root lengths during anterior teeth retraction using the laser reflection technique / 대한치과교정학회지

Treatment mechanics should be individualized to be suitable for each patient`s personal teeth and anatomic environment to get a best treatment result with the least harmful effects to teeth and surrounding tissues. Especially, the change of biomechanical reaction associated with that of the centers of resistance of teeth should be considered when crown-to-root ratio changed due to problematic root resorption and/or periodontal disease during adult orthodontic treatment. At the present study in order to investigate patterns of initial displacements of anterior teeth under certain orthodontic force when crown-to-root ratio changed in not only normal periodontal condition but also abnormal periodontal and/or teeth condition, the changes of the centers of resistance for maxillary and mandibular 6 anterior teeth as a segment were studied using the laser reflection technique, the lever&pulley force applicator and the photodetector with these quantified variables reducing alveolar bone 2mm by 2mm for each of maxillary 6 anterior teeth until the total amount of 8mm and root 2mm for each of mandibular 6 anterior ones until the total amount of 6mm. The results were as follows: 1. Under unreduced condition, the center of resistance during initial displacement of maxillary 6 anterior teeth was located at the point of about 42.4% apically from cemento-enamel junction(CEJ) of the averaged tooth of them and kept shifting to about 76.7% with alveolar bone reduction. 2. The distance from the averaged alveolar crest level of maxillary 6 anterior teeth to the center of resistance for the averaged tooth of them kept decreasing with alveolar bone reduction, but the ratio to length of the averaged root embedded in the alveolar bone was stable at around 33% regardless of that. 3. Under unreduced condition, the center of resistance during initial displacement of mandibular 6 anterior teeth was located at the point of about 43% apically from CEJ of the averaged tooth of them and this ratio kept increasing tc about 54% with root reduction. Bur the distance from CEJ to the center of resistance decreased from around 5.3mm to around 3.3mm, that is to say, the center of resistance kept shifting toward CEJ with the shortening of root length. 4. A unit reduction of alveolar bone had greater effects on the change of the centers of resistance than that of root did during initial phase of each reduction. But both of them had similar effects at the middle region of whole length of the averaged root.