Clinical Oral Implants Research

Abstract: A new X‐ray microtomographic technique for non‐invasive assessment of the structure of bone surrounding implants was tested. Three titanium microimplants retrieved directly (n=2) or 6 months (n=1) after insertion in 3 patients were used as test samples. Two samples were used dry and one was embedded in plastic resin prior to microtomography. The technique provided high‐resolution consecutive cross‐sectional X‐ray images of the specimens with a slice‐to‐slice distance of 4.4 to 11.0 μm. The pictures could be imported into an image analysing software with which semiautomatic quantitative measurement of the bone area and three‐dimensional images of the specimens could be made. It is suggested that the technique may be used for non‐invasive assessment of the bone structure around implants. Further studies are needed to evaluate the accuracy of the technique, for instance by comparing tomographic sections with histologic ones.

Abstract: Occlusal forces affect an oral implant and the surrounding bone. According to bone physiology theories, bones carrying mechanical loads adapt their strength to the load applied on it by bone modeling/remodeling. This also applies to bone surrounding an oral implant. The response to an increased mechanical stress below a certain threshold will be a strengthening of the bone by increasing the bone density or apposition of bone. On the other hand, fatigue micro‐damage resulting in bone resorption may be the result of mechanical stress beyond this threshold. In the present paper literature dealing with the relationship between forces on oral implants and the surrounding bone is reviewed. Randomized controlled as well as prospective cohorts studies were not found. Although the results are conflicting, animal experimental studies have shown that occlusal load might result in marginal bone loss around oral implants or complete loss of osseointegration. In clinical studies an association between the loading conditions and marginal bone loss around oral implants or complete loss of osseointegration has been stated, but a causative relationship has not been shown.

Abstract: It could be hypothesised that attachments, which provide more retention against vertical and horizontal dislodgement, will be associated with more favourable parameters of oral function. This in vivo study is designed to provide data regarding initial retention force, loss of retention force after 3 months of function and postinsertion maintenance and complications associated with the use of magnet, bar‐clip and ball attachments in mandibular overdenture treatment. Eighteen edentulous subjects received two permucosal implants in the inter‐foramina region of the mandible, a new denture and three successive suprastructure modalities (magnet‐, bar‐clip and ball attachments). The retention force of the attachments at baseline and after 3 months was measured in a standardised way. The amount and type of postinsertion maintenance that was related to the attachment were evaluated. No differences in retention force at baseline and after 3 months of loading were observed for all three attachment types. The mean retention forces of magnet attachments, bar‐clip attachments and ball attachments were 8.1, 31.3 and 29.7 N respectively. Functional maintenance complications related to the attachments were predominantly observed in 11/36 magnet attachments. Functional problems in the ball attachment group were relatively rare, easily manageable and seen in 4/36 attachments. The bar‐clip attachments exhibited no maintenance problems at all.

Objective: The aim of this 5‐year prospective comparative study was to evaluate treatment outcome (survival rate, condition of hard and soft peri‐implant tissues, patient satisfaction, prosthetic and surgical aftercare) of mandibular overdentures supported by two or four implants.

Material and methods: Sixty edentulous patients with a mandibular height between 12 and 18 mm participated. Thirty patients were treated with an overdenture supported by two IMZ implants (group A) and 30 patients were treated with an overdenture supported by four IMZ implants (group B). Standardised clinical and radiographic parameters were evaluated 6 weeks after completion of the prosthetic treatment and after 1, 2, 3, 4 and 5 years of functional loading. Prosthetic and surgical aftercare was scored during the evaluation period.

Results: One implant was lost (group A) during the healing period. There were no significant differences with regard to any of the studied clinical or radiographic parameters of the peri‐implant tissues between the groups. None of the patients reported sensory disturbances in the lip or chin region. No differences in satisfaction were observed between the groups. With regard to aftercare, there was a tendency of a greater need of prosthetic interventions in group A, while correction of soft‐tissue problems was restricted to patients of group B.

Conclusion: There is no difference in clinical and radiographical state of patients treated with an overdenture on two or four implants during a 5‐year evaluation period. Patients of both groups were as satisfied with their overdentures.

Abstract: In general, an implant is loaded via axial and horizontal forces. Besides this, moment loading can also occur. The aim of this study was to investigate how different prosthetic connectors with overdentures develop force transfer to implant and bone as well as to the denture‐bearing alveolar ridge. Five connectors were investigated on a stereolithographic model fabricated according to a real patient situation. The model was fitted with strain gauges on the “bone” distal and medial to the implants and with vertical force transducers in the alveolar “bone” under the denture‐bearing area. The parallel‐sided rigid telescopic connector developed the highest moment loading of the implant (P<0.001), which would suggest restraint in the use of this connector. The bar construction also showed somewhat high moments but these may have been at least partly exaggerated by the individual patient situation. Loading results through the non‐rigid telescopic copings, single spherical attachments and magnet overdentures demonstrated a low level of implant moment loading which would in part result from horizontal forces caused by denture forward shift during force application. The denture‐bearing area loading was different with all attachments (P<0.001) and was related to the rigidity of the connector and reached the highest values with the non‐rigid telescopic coping. The clinical implications of the various findings are discussed.

The aim of this prospective comparative study was to evaluate the condition of the peri‐implant tissues of three different implant systems supporting a mandibular overdenture. Ninety edentulous patients (Cawood class V–VI) participated in this study. After randomization, 30 patients were treated with 2 Brånemark implants, 30 patients with 2 IMZ implants and 30 patients with 2 ITI implants. The implants were inserted in the canine region of the mandible. After 3 months overdentures were fabricated supported by a round bar and clip attachment. A standardized clinical and radiographic evaluation was performed 0,6 and 12 months after insertion of the denture. The intra‐oral radiographs were made, using the long‐cone technique with an aiming device. Two implants were lost (1 Brånemark, 1 IMZ) during the healing period. None of the patients showed any sensory change in lip or chin region. The pocket depth in the Brinemark group decreased significantly whereas the mucosa recession increased significantly in both the Brånemark as well as in the IMZ group. After 12 months, there was significantly less bone loss in the ITI group. From our study it was concluded that 2 (Brånemark, IMZ or ITI) implants placed in the interforaminal region connected with a bar supply a proper base for the support of a mandibular overdenture in the (Cawood V–VI) edentulous patient. The ITI implant appears to be the implant of choice for mandibular overdenture therapy. because only one operation is required for a comparable result.

Abstract: The aim of the present experiment was to study the effect of a long‐standing lateral static load on the peri‐implant bone. Three beagle dogs were used. The mandibular premolars were extracted and 12 weeks later 3 titanium implants (ITI^® Dental Implant System) were installed in each quadrant. Crowns were fitted to all implants 12 weeks after the installation procedure. The anterior and central crowns were fused and connected to the posterior crown by an expansion screw. In the right side of the mandible, the expansion screws were activated every 2 weeks during a 46‐week period. During the last 10 weeks of this period, an expansion force similar to that of the right side was applied in the left. The animals were sacrificed and block biopsies of each implant site harvested and prepared for histological analysis. Sites subjected to 10 weeks or 46 weeks of lateral load had a similar (i) distribution of bone markers (ii) proportion of bone density and (iii) degree of bone‐to‐implant contact. The proportion of fluorochromes was higher at sites subjected to 10 weeks of loading than at sites subjected to 46 weeks of loading.

Force transmission onto implants supporting overdentures was measured in viva by means of piezoelectric transducers that allow for simultaneous force registrations in 3 dimensions. The transducers are directly mounted onto the implants, beneath the anchorage device. The force registrations were analyzed with regard to the anchorage device and retention mechanism of overdenture support. The 3 types of denture anchorage were a U‐shaped bar, a round clip‐bar and single telescopes. Forces were measured in the following test situations: maximum force when biting in centric occlusion, maximum bite force during biting on a bite plate, grinding and chewing bread. Multiple regression showed that the vertical component of maximum forces was dependent on the anchorage device and test situation. The transverse components reached 10 to 50% of the vertical force magnitude. With the bite plate in situ maximum forces measured in vertical direction were significantly higher on the ipsilateral implant with telescopes than with bars (p<0.01 and p<0.001). Chewing and grinding resulted in lower vertical forces compared to maximum biting. In transverse dimensions, mainly in the anterior‐posterior direction, registered forces reached magnitudes that resembled the vertical component (50 to 100%). Force magnitudes of chewing and grinding were similar for all three anchorage devices. However, differences were observed between bars and telescopes with regard to the direction of transverse force components. The results of this study do not suggest the preference of one specific anchorage system or retention mechanism for overdenture support. However, rigid bars contribute to load sharing and stress distribution onto the implants.

Objective: To evaluate the biological effects of three calcium phosphate (CaP) coatings with nanostructures on relatively smooth implant surfaces.

Material and methods: Stable CaP nanoparticle suspensions of different particle sizes and structures were coated onto implants by immersion and subsequent heat treatment. An uncoated implant was used as the control. After topographical and chemical characterizations, implants were randomly inserted into rabbit tibiae for removal torque (RTQ) testing. To confirm the biological reaction, implants were placed in the bilateral femurs of three rabbits.

Results: The topographical characterization showed that each surface had different nanostructural characteristics and X‐ray photon spectroscopy showed various CaP compositions. The control and test groups had different nanotopographies; however, the differences among the test groups were only significant for Surfaces B and C and the rest were insignificant. The RTQ tests showed significantly higher values in two test groups (Surface A and Surface C). Histologically, no adverse effects were seen in any group. Histomorphometrical evaluation showed comparable or better osseointegration along the implant threads in the test groups.

Conclusion: The three different CaP coatings with nanostructures on the implant surfaces had enhancing effects on osseointegration. Along with the surface nanotopography, the CaP chemistry might have influenced the biological outcomes.