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Biomedical subjects

R Mericske-Stern

Publications and source records attributed to R Mericske-Stern.

44 records · Page 3Linked to original sources
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Effectiveness of maxillary overdentures supported by implants: maintenance and prosthetic complications.

PURPOSE: The aim of this study was to evaluate the prosthetic complications with implant-supported overdentures in the maxilla. MATERIALS AND METHODS: Forty-one patients (mean age 61 years) were consecutively admitted for treatment from 1991 to 1998. A total of 173 ITI implants were placed. Four to six implants either connected with a bar (34 overdentures) or with single anchors (seven overdentures) supported the denture, and only a few parties had fewer than four implants. The overdentures had a horseshoe design and were reinforced by a cast-metal framework. The mean observation time was 3.2 years. Oral hygiene and periimplant parameters were regularly assessed, and records were kept of prosthetic maintenance service. All prosthetic complications encountered were classified related to (1) implant components and anchorage devices, (2) mechanical and structural failures of dentures, or (3) denture-related adjustments. RESULTS: Three implants did not osseointegrate, and five implants were lost after loading. Thus, the overall survival rate of the implants was 95.5%. Altogether, 85 prosthetic complications were encountered. The most frequent finding was retightening of the bar screw and adjustments of the bar retainers. Repair of dentures was not frequent and was mostly related to broken teeth. No fracture of dentures was observed. Renewal of dentures occurred twice, once after loss of all implants in one patient. Thirty-nine overdentures had been continuously worn; thus, the overall denture stability was 95%. Mucosal irritation and need for occlusal adjustment were the most frequent findings in the first year. Over time, a decrease of complications was observed. CONCLUSION: Planned maxillary overdentures supported by implants are a successful treatment modality on a short-term basis.

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A longitudinal study on mandibular implants supporting an overdenture: the influence of retention mechanism and anatomic-prosthetic variables on periimplant parameters.

PURPOSE: The aim of this 5-year longitudinal study was to investigate the influence of the retention mechanism for overdenture fixation on the periimplant parameters of mandibular implants. MATERIALS AND METHODS: Ninety edentulous patients, each with two interforaminal implants supporting an overdenture, participated in the study. They had received either a straight or slightly bent round clip bar, a U-shaped rigid bar with or without distal extensions, or single-ball anchors. Anatomic-morphologic and prosthetic variables were assessed related to the implant position and the type of overdenture retention. The degree of mandibular atrophy was determined using cephalometric radiographs. The angle beta between the virtual axis connecting both implants and the mandibular hinge axis was measured on mounted casts. A supporting surface was identified between bent clip bars and U-shaped extension bars. Clinical periimplant parameters were recorded, and changes of the probing attachment level after 5 years were analyzed in 70 patients with respect to the retention device and anatomic-morphologic and prosthetic variables. RESULTS: A significant increase of the Plaque Index was observed after 5 years. The mean clinical attachment loss after 5 years was about 0.2 mm. In more than 50%, beta was small, i.e., < or = 5 degrees. For these implants, loss of clinical attachment was significantly lower. The correlation between attachment loss and beta was weak, while no significant correlation was found with regard to the degree of atrophy and surface. CONCLUSION: In view of the long observation period, it was concluded that the position and retention mechanism of mandibular implants supporting an overdenture have little influence on the long-term stability of the clinical parameters.

Adult↗
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Occlusal force and oral tactile sensibility measured in partially edentulous patients with ITI implants.

Maximal occlusal force and oral tactile sensibility were recorded in (1) a group of partially edentulous patients restored with ITI implants supporting fixed prostheses or single crowns and (2) a control group consisting of fully dentate subjects with healthy natural teeth. Maximal occlusal force was measured with a miniature force transducer placed between antagonistic implant/tooth pairs in the test group and antagonistic teeth in the control group. The detection threshold of minimal pressure (ie, passive tactile sensibility) was recorded with dynamometers, and minimal perceived thickness (active tactile sensibility) was assessed using steel foils with a thickness from 100 to 10 microns. Highest maximal occlusal force was measured in fully dentate subjects on second premolars (average 450 N). A significant reduction on the first premolars (300 N) was observed. With fixed prostheses supported by implants, the average value of maximal occlusal force was distinctly lower, about 200 N for first premolars and for molars, and 300 N for second molars. The maximum force was again found on second premolars. The detection threshold of minimal pressure was significantly higher on implants than on natural teeth. The average number of wrong assessments when testing steel foils was 3.2 for antagonistic implant/tooth pairs and 2.6 for natural teeth. The comparison of test sides (with implants) and control sides (without implants) in patients of the test group did not reveal significant differences of measurements. It seems that patterns of oral function depend primarily on the state of dentition, type of prosthodontic restorations, and on psychological aspects, and secondarily on the presence of implants.

Adult↗
PubMedDate not supplied

Oral tactile sensibility recorded in overdenture wearers with implants or natural roots: a comparative study. Part 2.

The capacity of dentate subjects to discriminate the thickness of objects placed between the teeth seems to depend on receptors in the periodontal ligament and muscles. The compensatory mechanism of ankylotic implants for the function of missing periodontal ligaments is not yet known. To investigate this question in overdenture wearers, 26 patients with ITI implants and 20 patients with natural roots were selected. According to the experimental protocol, the discriminatory ability was recorded with 10 steel foils (thickness ranging from 10 to 100 microns) placed between the premolars. Each thickness was tested 10 times and the test subjects were required to distinguish whether foil was positioned between the teeth. A maximum of 100 correct or 100 incorrect answers was possible. The average number of incorrect answers was significantly higher in test subjects with implants. The 50% limit (ie, the tested thickness recorded with at least 5 wrong answers) was established, but no statistically significant difference was found. In both groups, the critical tactile threshold of perceived thickness was 30 to 40 microns, with 2 being the average number of incorrect assessments. When comparing the minimal thickness, which was recorded without incorrect assessment, a significantly lower threshold was observed on patients with natural roots. Thus, active tactile sensibility appears to depend on the receptors in the periodontal ligament. However, wearing of removable prostheses is a modifying factor and may influence the oral tactile sensibility for both groups.

Aged↗
PubMedDate not supplied

Overdentures: an alternative implant methodology for edentulous patients.

Two groups of elderly edentulous patients with implant-supported mandibular overdentures were compared. There were 25 patients with an average age of 62.2 years and 34 patients with an average age of 68.9 years treated in Toronto and in Bern, respectively. A high incidence of compromised general health was found in both groups. All patients had been treated in the years 1984 through early 1987 and had worn their implant-supported overdentures for the previous 5 years. Regular monitoring of the patients was done by two investigators using periodontal and radiographic parameters. Two different implant systems were used: Brånemark fixtures in Toronto and ITI implants in Bern. Most overdentures were retained by only two implants in both groups. The 5-year longitudinal data show a similar high success rate (> 90%) for both patient groups.

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PubMedDate not supplied

Three-dimensional force measurements with mandibular overdentures connected to implants by ball-shaped retentive anchors. A clinical study.

The purpose of this in vivo study was to determine maximum and functional forces simultaneously in three dimensions on mandibular implants supporting overdentures. The anchorage system for overdenture connection was the ball-shaped retentive anchor. Five edentulous patients, each with two mandibular ITI implants, were selected as test subjects. A novel miniaturized piezo-electric force transducer was developed for specific use with ITI implants. Force magnitudes and directions were registered under various test conditions by means of electrostatic plotter records. The test modalities were maximum biting in centric occlusion, maximum biting on a bite plate, grinding, and chewing bread. Maximum forces measured in centric occlusion and on the ipsilateral implant when using a bite plate were slightly increased in vertical and backward-forward dimension (z-, y-axis) compared to the lateral-medial direction (x-axis). On the contralateral implant, equally low values were found in all three dimensions. This may be the effect of a nonsplinted anchorage device. With the use of a bite plate, force magnitudes on the ipsilateral implant were significantly higher on the z- and y-axis than mean maximum forces in centric occlusion (P < .001). Chewing and grinding resulted in lower forces compared to maximum biting, particularly in the vertical direction. The transverse force component in backward-forward direction, however, reached magnitudes that exceeded the vertical component by 100% to 300% during chewing function. This chewing pattern had not been observed in previous investigations with bars and telescopes, and therefore appears to be specific for retentive ball anchors. The prevalent or exclusive force direction registered on both implants in the vertical direction was downward under all test conditions. In the transverse direction during maximum biting the forward direction was more frequently registered, while no obvious prevalence of transverse force direction was observed during chewing and grinding.

Aged↗