Prosthetic considerations.

Implants have changed prosthodontics more than any other innovation in dentistry. Replacement of lost teeth by a fixed or removable prosthesis is considered to be a restitutio ad similem, while implants may provide a feeling of restitutio ad integrum. Implant prosthodontics means restoring function, aesthetics, and providing technology; biology and technology are combined. Placement of implants is a reconstructive, preprosthetic surgical intervention and is therefore different from most goals in oral surgery that consist of tooth extraction, treating infection and removing pathology from soft or hard tissues. Thus, implants are part of the final prosthetic treatment which encompasses functional, aesthetic and social rehabilitation. The patient's needs and functional status determine the goal of prosthetic treatment. Treatment outcomes in implant prosthodontics are survival of implants and prostheses, impact on physiological and psychological status, oral health-related impact on quality of life, and initial and maintenance costs. A variety of prosthetic solutions are available to restore the partially and completely edentulous jaw and more recently specific methods have been developed such as computer guided planning and CAD-CAM technologies. These should allow more uniform quality and passive fit of prostheses, and simultaneously enables processing of biologically well-accepted materials.

Forces on implants supporting overdentures: a preliminary study of morphologic and cephalometric considerations.

It is usually suggested that loading forces be transmitted to implants in the vertical direction. In 44 subjects treated with mandibular implants and overdentures, the inclination of the implant axis relative to the occlusal plane of the corresponding prostheses was measured by means of cephalometric radiographs. The degree of mandibular atrophy was also assessed. Peri-implant parameters such as plaque index, bleeding scores, and probing depths were registered on four implant sites. About 70% of the implants showed a buccal inclination, 11% showed a lingual inclination, and only 19% were found with an angle of 90 degrees. After an observation period of 5 years, no positive relationship between inclination of the implant axis, mandibular atrophy, and peri-implant findings could be established. Aspects of facial morphology and the interalveolar relationship of both jaws should be considered additional parameters and should be included in investigations concerning functional dynamics of removable dentures.

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.

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.

Clinical evaluation of overdenture restorations supported by osseointegrated titanium implants: a retrospective study.

This paper reports the results of using osseointegrated titanium implants as abutments for overdenture restorations in the mandibles of 62 edentulous patients. All of these patients were edentulous for several years and required complete dentures. Six months after prosthodontic treatment, two implants (ITI, Straumann) were placed with consideration of the denture base and morphologic aspects of the mandibular residual ridge. The retention devices consisted of a bar connector or single ball-shaped precision attachments. Three or four implants splinted with a bar were placed in a control group of 11 patients. Attached keratinized gingiva (greater than or equal to 2 mm) surrounded approximately 48% of the buccal and 55% of the lingual implant sites. Evaluation after periods of 6 to 66 months postoperatively revealed good clinical results with five patients lost to recall in 1989. Two implants were lost after overdenture insertion. The findings suggest that two implants may adequately serve as retention for a mandibular complete denture and that attached gingiva surrounding the implants does not seem to be prerequisite for healthy function.

Life table analysis and clinical evaluation of oral implants supporting prostheses after resection of malignant tumors.

Seventeen mostly elderly patients, 13 men and 4 women, were consecutively admitted for implant-prosthodontic treatment after they had undergone resection of malignant tumors in the oral cavity. A total of 53 dental implants (ITI-Straumann) was placed, 12 in the maxilla, 41 in the mandible. The prosthetic rehabilitation consisted of overdenture therapy in 15 patients, and 2 patients were treated with fixed partial prostheses. Thirty-three implants were prescribed for patients who received radiotherapy either before or after implant placement. The average dose varied between 50 and 74 Gy. Eighteen implants were located in grafted bone from the fibula, scapula, or hip. For 2 patients, hyperbaric oxygen therapy was also prescribed after osteoradionecrosis had developed. One implant was lost before prosthetic loading. During an observation period of up to 7 years after loading, 3 more implants were removed. All implant losses occurred in the mandibles of patients who had received radiotherapy. A life table analysis was performed, and the cumulative survival rates, calculated for 2, 3, and 5 years, were 93%, 90%, and 90% respectively. No failures or complications were observed with technical components of the implants or prostheses. All prostheses could be maintained during the entire observation time. Although in the present investigation the survival rate of implants was slightly lower than under standard conditions, the treatment with implant-supported prostheses seemed to be advantageous for patients who had undergone intraoral resections.

In vivo measurements of maximal occlusal force and minimal pressure threshold on overdentures supported by implants or natural roots: a comparative study, Part 1.

Numerous investigations give evidence of improvement of masticatory performance when edentulous patients have had implants placed. A comparative study was carried out to investigate the oral function and tactile sensibility of patients restored with implant-supported overdentures. Twenty-six patients with ITI implants and 18 patients with natural-tooth roots were selected. The minimal pressure threshold perceived in vertical and horizontal directions was registered with dynamometers. Maximal occlusal force was recorded with a miniature bite recorder placed between each pair of antagonistic teeth on both jaw sides separately. All measurements were repeated three times and the average was calculated. The records of minimal perceived pressure revealed a significantly higher threshold (factor 100) for the implant group. In both test groups, values registered in the vertical direction were slightly increased. A tendency for test subjects with implants to reach higher maximal occlusal force was observed, but not at a statistically significant level. In both test groups, the average maximum was found on the second premolar. The minimal pressure threshold seems to depend on the presence of receptors in the periodontal ligament. The records of maximal occlusal force, which were similar in both test groups, lead to the assumption that the limitation in maximal occlusal capacity of overdenture wearers is multifactorial and does not depend on the presence of a periodontal ligament.

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.

Three-dimensional force measurements on mandibular implants supporting overdentures.

The purpose of this study was to determine masticatory and functional forces in three axes on mandibular implants supporting overdentures. Five edentulous test subjects were selected, each having two mandibular implants. Three-dimensional piezoelectric force transducers were mounted on the two-part ITI Bonefit implants and rigidly connected to the denture. Forces in vertical, lateromedial, and anteroposterior directions were measured by means of electrostatic plotter records. The test modalities were light tapping, grinding, maximal occlusal force, and chewing test food. Results showed that the five subjects developed similar stress patterns but quantitatively different occlusal and chewing forces. In all but one subject, reduced maximal occlusal force was found compared to dentate subjects and edentulous subjects with fixed partial prostheses supported by implants. The recordings of chewing cycles when eating test food resulted in very regular rhythmic strokes, similar to those of dentate subjects but with slightly reduced speed. All stress patterns showed that occlusal and chewing forces were mainly directed in vertical, medial, and anterior dimensions. The dominating component was vertical.

[Testing dental implants with an in vivo finite element model]. / Zahnimplantattestung am In-vivo-Finite-Elemente-Modell.

The finite element method (FEM) makes it possible to simulate biomechanical situations on a computer. In the present study the so-called voxel method [9, 14, 17, 18, 19] was used for the construction of the mandible model. For this, the relationship between the biological tissue (e.g. bone) and the corresponding attenuation coefficient of CT data (Hounsfield units = HU) were utilized. The CT data were obtained from an edentulous patient provided with a prosthesis borne on two titanium implants. In a parallel study, the bite forces of the same individual were measured. These were recorded digitally in three dimensions (cranio-caudal, anterior-posterior and left-right) The forces determined by a special program were then transferred to the FEM model implants. We were able to show that a bar joining the implants had a far greater effect on maximum equivalent stress than was expected from the measuring data alone. The highest stress at maximum occlusive force was lowered by 704% on using the connecting bar. On chewing, a stress reduction of 59.9% was observed. The reduction in stress achieved by the bar could, we believe, prolong the life of the implant.

Overdenture abutments and reduced periodontium in elderly patients. A retrospective study.

Among elderly patients attending a private office, a large number was seen having only few remaining teeth with advanced reduction of periodontal support. The long-term effect of overdenture rehabilitation within a mean observation time of 5.9 years (2 to 10 years) could be assessed in 109 patients (average age 74.1 years) wearing a total of 125 overdentures. After completion of treatment, 76% had regularly followed the maintenance care program. The degree of bone loss of the selected abutment teeth was assessed by means of radiographs. 56% showed a highly reduced periodontal support with bone loss of more than 50% of the root length. No, or moderate loss of periodontal support was found in only 9.5%. The overdentures were initially retained by 359 cast gold copings. Biologic and technical failures were registered for 54 copings and examined with regard to the reduction of periodontal support of the abutment teeth. Repair and treatment were prescribed for 30 copings, including guided tissue regeneration for 6 abutments. Twenty-four abutment roots with copings were extracted. Although most biologic failures were encountered in abutment teeth with severe reduction of the periodontium, the failure rate was not statistically higher for these abutments.

[The elderly patient in private practice]. / Der alte Patient in der Privatpraxis.

The aim of this study was to get an overview on therapeutic measures and recall compliance of elderly patients treated in a private dental office. Data regarding the dental treatment und prosthodontic rehabilitation were collected from a total of 429 patients who were 65 years old and older (average: 75.8 years). 94 patients (23%) were edentulous and had dentures in both jaws, whereas 335 patients still had remaining teeth in one or both jaws. Only 8 patients had a full complement of teeth. 239 patients (55%) had complete oral rehabilitation. Few fixed partial prostheses and mainly removable partial und complete dentures were inserted. 190 patients did not get new reconstructions, because 1) they did not need it, or 2) they did not want it. In some cases, existing prostheses could be adapted or repaired. Almost all patients with remaining teeth were in need of periodontal treatment. 54% of them underwent periodontal therapy. Maintenance care was supported by regular recall. 65% of the patients appeared regularly according to their individual interval. A strong correlation could be established between regular recalls, the extent of rehabilitation and the number of remaining teeth.

[The aftercare findings and recall behavior of older patients with removable dentures]. / Nachsorgebefund und Recallverhalten von älteren Patienten mit abnehmbaren Prothesen.

Data were collected from 285 patients (average: 63.8, range: 23 to 87) who received prosthodontic treatment at the Clinic for Removable Prosthodontics of the University of Bern during the years of 1981 through 1987. 62 edentulous patients received two osseointegrated implants in the lower jaw. For the partially edentulous patients, removable partial dentures (RPD-89 patients) or overdentures (OD-134 patients) were prescribed. These two groups received recall care for a period of 2 to 3 years after insertion of the dentures. Due to limited capacity of the university clinics, a great part of these patients were then referred to private practitioners. All patients from the student course, however, were carefully checked during the year after insertion of the denture. Implant patients received a regular recall throughout the observation time. The patients' behaviour was not up to the dentists' expectations: less than 50% of the RPD and OD patients followed the recall appointment regularly. In contrast, the implant patients participated 100% in the recall. The plaque and bleeding indexes were much higher in the partially edentulous than in the implant patients. RPD and OD patients with regular recalls scored significantly better, but never reached the same level of results as the implant patients. Nevertheless, the probing depths on implants were a bit higher compared to those of the natural teeth, but not significantly.

Influence of platform switching on bone-level alterations: a three-year randomized clinical trial.

The concept of platform switching has been introduced to implant dentistry based on clinical observations of reduced peri-implant crestal bone loss. However, published data are controversial, and most studies are limited to 12 months. The aim of the present randomized clinical trial was to test the hypothesis that platform switching has a positive impact on crestal bone-level changes after 3 years. Two implants with a diameter of 4 mm were inserted crestally in the posterior mandible of 25 patients. The intraindividual allocation of platform switching (3.3-mm platform) and the standard implant (4-mm platform) was randomized. After 3 months of submerged healing, single-tooth crowns were cemented. Patients were followed up at short intervals for monitoring of healing and oral hygiene. Statistical analysis for the influence of time and platform type on bone levels employed the Brunner-Langer model. At 3 years, the mean radiographic peri-implant bone loss was 0.69 ± 0.43 mm (platform switching) and 0.74 ± 0.57 mm (standard platform). The mean intraindividual difference was 0.05 ± 0.58 mm (95% confidence interval: -0.19, 0.29). Crestal bone-level alteration depended on time (p < .001) but not on platform type (p = .363). The present randomized clinical trial could not confirm the hypothesis of a reduced peri-implant crestal bone loss, when implants had been restored according to the concept of platform switching.