Joke Duyck

Time dependent failure rate and marginal bone loss of implant supported prostheses: a 15-year follow-up study

Abstract This study deals with 4971 implants (Brånemark system) installed in 1315 patients, either fully or partially edentulous, and followed from implant installation up to the last control. A predominance of female patients (61%) and a nearly equal number of upper and lower jaws characterised the study group. Patients were scheduled each 6–12 months for recall. The observation time varied from 0.5 to 15 years (mean 5.1). The whole cohort was split up into compromised (n=59) and non-compromised (n=1256) patients. The former are defined as grafted (autologous bone) and patients irradiated in the head and neck area. In the compromised patients 24 out of 59 patients (40.6%) showed failures, in whom 59 out of 310 (19%) implants failed. In the non-compromised patients, implant failures were observed in 11.6% of the patients, which corresponds to 5.9% of the installed implants, excluding iatrogenic failures. Failures were further divided chronologically into early (up to 1 year after abutment connection) and late failures. There were early implant failures in 12.5% of the compromised patients and in 3.4% of the others. Late implant failures occurred in 7.4 and 2% of the two patients groups, respectively. While gender did not affect the failure rate, implant lengths, corresponding to the available bone height did, since a 21.5% failure rate for the 7-mm implants contrasts with 4.1 and 3.8% for 13- and 15-mm implants, respectively. Early as well as annual late failures are more frequently found in the maxilla. Implant fractures only occurred in the fixed (both partial and full) prosthesis group but never surpassed the 0.2% annual level. Marginal bone loss, exceeding the third screw thread occurred in 1.8% of the implants at the last control. It appears that this type of implant configuration offers a high long-term predictability. Failures occur before, at or during the first year after abutment connection and in very short implants. Marginal bone as a whole is very stable over the years.

Bone quality assessment based on cone beam computed tomography imaging

OBJECTIVES The aim of this in vitro study was to investigate the accuracy of fractal analysis and morphometry for bone quality assessment as measured with dual energy X-ray absorptiometry (DXA). MATERIAL AND METHODS Nineteen mandibular bone samples were used for the creation of artificial bone lesions (n=5) or decalcification (n=12) to simulate osteoporosis; two samples were used as controls. Cone beam computed tomography (CBCT) and DXA scans were made before and after processing the samples. The image data obtained from the CBCT scans were used to calculate the mean fractal dimension (FD), bone area and density (morphometric analysis) of the samples. Bone mineral density (BMD) was obtained from the DXA scans and set as a reference value for bone quality. The correlation between BMD and FD and between BMD and morphometric results were calculated. RESULTS A significant correlation between FD and BMD (rho=+0.71 to +0.75; P<0.05) was observed. Bone area and BMD of the specimens (rho=+0.69 to +0.85; P<0.05) were also significantly related, in contrast to the density analysis, for which no significant correlation to BMD was found. CONCLUSIONS The results of this study suggest that fractal analysis and bone area measurement have potential to evaluate bone quality on CBCT images, while density measurement does not seem to be valid.

Influence of Implant Connection Type on the Biomechanical Environment of Immediately Placed Implants – CT-Based Nonlinear, Three-Dimensional Finite Element Analysis

PURPOSE The purpose of the present study was to evaluate the biomechanical environment of immediately placed implants, before and after osseointegration, by comparing three different implant-abutment connection types. MATERIALS AND METHODS A computer tomography-based finite element model of an upper central incisor extraction socket was constructed containing implants with either external hex, internal hex, or Morse-taper connection. Frictional contact elements were used in the bone, implant, abutment, and abutment screw interfaces in the immediately placed simulations. In osseointegrated simulations, the repair of bone alveolar defect and a glued bone-to-implant interface were assumed. By analysis of variance, the influence was assessed of connection type, clinical situation, and loading magnitude on the peak equivalent strain in the bone, peak von Mises stress in the abutment screw, bone-to-implant relative displacement, and abutment gap. RESULTS The loading magnitudes had a significant contribution, regardless of the assessed variable. However, the critical clinical situation of an immediately placed implant itself was the main factor affecting the peak equivalent strain in the bone and bone-to-implant displacement. The largest influence of the connection type in this protocol was seen on the peak equivalent stress in the abutment screw. On the other hand, a higher influence of the various connection types on bone stress/strain could be noted in osseointegrated simulations. CONCLUSIONS The implant-abutment connection design did not significantly influence the biomechanical environment of immediately placed implants. Avoiding implant overloading and ensuring a sufficient initial intraosseous stability are the most relevant parameters for the promotion of a safe biomechanical environment in this protocol.

Failure of oral implants: aetiology, symptoms and influencing factors.

Abstract The use of oral implants opened a wide range of prosthetic treatment possibilities in edentulous patients. Although the reported success rates of oral implants are high, failures do occur. This paper reviews the current knowledge about the aetiology, the signs and symptoms and the possible influencing factors of implant failure. Possible causes of implant failure are thought to be infection of the periimplant tissues, occlusal overload, or a combination of both. Nevertheless, pinpointing one of these as the aetiological factor in a particular case is difficult and should be handled reluctantly. Although the cause might seem obvious, influencing factors could play a role as well. Gaining insight into these processes might stimulate the adoption of preventive action and therefore increase the predictability of the treatment outcome with oral implants.

Use of microfocus computerized tomography as a new technique for characterizing bone tissue around oral implants.

Qualitative and quantitative analysis of peri-implant tissues around retrieved oral implants is typically done by means of light microscopy on thin histological sections containing the metal surface and the undecalcified bone. It remains, however, a labor-intensive and thus time-consuming job. Moreover, it is a destructive technique that allows tissue quantification in only a limited number of two-dimensional sections. As an alternative, we evaluated the bone structure around screw-shaped titanium implants by means of microfocus computerized tomography (micro-CT) because it presents a number of advantages compared to conventional sectioning techniques: micro-CT is nondestructive, fast, and allows a fully three-dimensional characterization of the bone structure around the implant. Images can be reconstructed in an arbitrary plane, and three-dimensional reconstructions are also possible. Because of its high resolution, individual trabeculae can be visualized. The accuracy of micro-CT was qualitatively evaluated by comparing histological sections with the corresponding CT slices for the same specimen. The overall trabecular structure is very similar according to both techniques. Even very close to the interface, the titanium implant does not seem to produce significant artifacts. Furthermore, because the complete digital data on the trabecular bone structure around the implant is available, it is possible to create finite-element models of the bone-implant system that model the trabeculae in detail so that mechanical stress transfer at the interface can be studied at the level of individual trabeculae. Therefore, micro-CT seems to be very promising for the in vitro assessment of the three-dimensional bone structure around oral implants. Further research will be needed to evaluate its accuracy in a more quantitative way.

Peri‐implant bone tissue assessment by comparing the outcome of intra‐oral radiograph and cone beam computed tomography analyses to the histological standard

OBJECTIVES The present study aims to identify radiographic methods revealing data that are most representative for the true peri-implant bone as assessed by histology. MATERIALS AND METHODS Eighty implants were placed in 10 minipigs. To assess matching between different image modalities, measurements conducted on intra-oral digital radiographs (IO), cone beam computer tomography (CBCT) and histological images were correlated using Spearmans correlation. Paired tests (Wilcoxon test) were used to determine changes in the bone parameters after 2 and 3 months of healing. RESULTS Significant correlations between bone defect depth on IO and histological slices (r= + 0.7, P<0.01), as well as on CBCT images and histological slices (r= + 0.61, P<0.01), were found. CBCT and IO images deviate, respectively, 1.20 and 1.17 mm from the histology regarding bone defects. No significant correlations were detected between fractal analysis on CBCT, intra-oral radiography and histology. For bone density assessment, significant but weaker correlations (r= + 0.5, P<0.01) were found for intra-oral radiography vs. histology. Significant marginal bone-level changes could be observed after 3 months of healing using intra-oral radiography. CONCLUSIONS This study allowed linking radiographic bone defect depth to the histological observations of the peri-implant bone. Minute bone changes during a short-term period can be followed up using digital intra-oral radiography. Radiographic fractal analysis did not seem to match histological fractal analysis. CBCT was not found to be reliable for bone density measures, but might hold potential with regard to the structural analysis of the trabecular bone.

In vivo forces on oral implants supporting a mandibular overdenture: the influence of attachment system.

Abstract This study was designed to gain insight into the influence of the attachment system on the loading conditions of oral implants supporting a mandibular overdenture on two implants. Five patients were selected and were provided with two implants in the canine area of the mandible (Brånemark System). All patients received a new mandibular overdenture that could be mounted on an ovoid-shaped bar (Dolder, C&M): (a) with and (b) without bilateral extensions and (c) on ball-attachments (Nobel Biocare). Using three strain gauges attached to the outer surface of the 5.5-mm standard abutments, the axial forces and bending moments on both supporting implants could be quantified. Load registrations were made during application of 50 N on seven predetermined positions along the occlusal surface of the prosthesis and during maximal biting in maximal occlusion (clenching). The results revealed no differences in induced axial force for the various anchorage devices, unlike the differences in bending moment. Although there is a tendency for better axial load sharing with bars and better sharing of bending moments with ball attachments, these differences were not significant.

The effect of whole-body vibration on peri-implant bone healing in rats

PURPOSE The aim of this study was to evaluate the effect of low-magnitude, high-frequency (LMHF) loading, applied by means of whole-body vibration (WBV), on peri-implant bone healing and implant osseointegration in rat tibiae. MATERIALS AND METHODS A custom-made titanium implant was inserted into the proximal metaphysis of the tibiae of 42 rats and left to heal for 3, 7, 14 or 25 days. Half of the animals received LMHF mechanical vibration for 5 days per week (test), whereas the others served as unloaded controls. The WBV consisted of 15 consecutive frequency steps (12, 20, 30, … to 150 Hz). Each of the 15 frequencies was applied for 2000 cycles, at an acceleration of 0.3 g. In the group with a 25-day healing period, PET images were taken at -1 (day before surgery), 3, 5, 7, 10, 14 and 21 days of loading, after an injection of [(18)F]sodium fluoride, a positron-emitting tracer. The ratio of the metabolic activity around the implants to that of a reference site (uptake ratio) was calculated as a measure of bone metabolism. Bone-to-implant contact (BIC) and peri-implant bone fraction (BF) were analysed for histomorphometrical measurement. RESULTS The mean BIC and BF were significantly influenced by both the loading and the healing time (ANOVA, P<0.01). The PET images did not reveal any significant difference in uptake ratio between the test and the control implants. CONCLUSION LMHF loading increased BIC and BF significantly. The results confirm the bone-stimulating potential of LMHF loading, through WBV, on peri-implant bone healing and osseointegration.

The effect of loading on peri-implant bone: a critical review of the literature.

In the 90s, there was a general belief that mechanical overloading was one of the main reasons for late implant failure. This triggered research to assess the role of mechanical loading on the establishment and the maintenance of oral implant osseointegration. Animal experimental studies indeed suggested the potential detrimental effect of excessive mechanical load on peri-implant bone, although randomised or controlled clinical trials of treatment interventions of oral implants designed to study overload are lacking. The lack of quantification of so-called overload at the implant level in the intra-oral setting is one of the main shortcomings in the literature. The level of evidence of the studies on bone response to implant loading is weak and does not indicate that overload can lead to peri-implant bone loss, except in case of inflammation. Clinical and animal experimental studies on early and immediate implant loading, however, provide information on the impact of mechanical loading on the process of osseointegration. It is obvious that micromotion between the implant and host tissues compromises osseointegration. However, in case of an efficient force transfer between implant and surrounding tissues, mechanical loading might even stimulate peri-implant bone formation and therefore osseointegration.

Impact of implant number, distribution and prosthesis material on loading on implants supporting fixed prostheses

The purpose of this study is to evaluate axial forces and bending moments (BMs) on implants supporting a complete arch fixed implant supported prosthesis with respect to number and distribution of the implants and type of prosthesis material. Seven oral Brånemark implants with a diameter of 3.75 mm and a length of 13 and 7 mm (short distal implant) were placed in an edentulous composite mandible used as the experimental model. One all-acrylic, one fibre-reinforced acrylic, and one milled titanium framework prosthesis were made. A 50 N vertical load was applied on the extension 10 mm distal from the most posterior implant. Axial forces and BMs were measured by calculating signals from three strain gauges attached to each of the abutments. The load was measured using three different models with varying numbers of supporting implants (3, 4 and 5), three models with different implant distribution conditions (small, medium and large) and three models with different prosthesis materials (titanium, acrylic and fibre-reinforced acrylic). Maximum BMs were highest when prostheses were supported by three implants compared to four and five implants (P < 0.001). The BMs were significantly influenced by the implant distribution, in that the smallest distribution induced the highest BMs (P < 0.001). Maximum BMs were lowest with the titanium prosthesis (P < 0.01). The resultant forces on implants were significantly associated with the implant number and distribution and the prosthesis material.