C. de Putter

The combined use of endosteal implants and iliac crest onlay grafts in the severely atrophic mandible: a longitudinal study

Thirteen patients, who received an onlay bone graft augmentation to their severely atrophic mandible in combination with a simultaneous implant insertion, were studied prospectively. A reproducible method that allowed for accurate assessment of graft resorption, consisting of lateral and oblique-lateral cephalometric radiographs in combination with an image analysis system, was used to assess the resorption rate in all patients and between subgroups of patients, according to selected patient and treatment characteristics. Thirty implants were placed, none of which were lost, and all patients expressed satisfaction after a mean observation period of 877 days. A mean resorption rate of 36% of the grafted bone height occurred, mainly during the first year and with some degree of individual variance. After three years the resorption had virtually stopped. No statistically significant differences between any of the subgroups of patients could be distinguished. Peri-implantitis was found around eight implants in seven patients. It is concluded that the described surgical technique should be used only if there are stringent indications.

Polyactive® as a bone-filler in a beagle dog model

Calcification is a crucial step in the bone-bonding mechanism of PEO/PBT hydrogel copolymers (Polyactive, a new generation of bone-fillers. A beagle dog study was conducted to determine whether the preoperative presence of a calcium phosphate layer (precalcification) on a PEO/PBT 80/20 copolymer would further increase the bone-bonding rate. Standard bone cavities were filled with either precalcified or nonprecalcified porous cylindric PEO/PBT 80/20 implants, or hydroxyapatite granules held together with PEO/PBT 70/30, or were left unfilled. A significantly higher percentage of mineralized component was present in the cavities filled with the precalcified PEO/PBT 80/20 copolymer than in the control defects. As a result of swelling by fluid-uptake, the press-fit inserted copolymer implants showed a significant reduction in pore size, thus preventing optimal bone ingrowth. Both precalcification of the copolymer and underfilling of the defect, to create space for the copolymer to increase in diameter, stimulate postoperative calcification and bone ingrowth in PEO/PBT 80/20 copolymers.

Flexible (Polyactive®) versus rigid (hydroxyapatite) dental implants

In a beagle dog study, the peri-implant bone changes around flexible (Polyactive) and rigid hydroxyapatite (HA) implants were investigated radiographically by quantitative digital subtraction analysis and by assessment of marginal bone height, with the aid of a computerized method. A loss of approximately 1 mm of marginal bone height was observed for both the dense Polyactive and the HA implants, after 6 months of loading. This value appeared to be stable from 12 weeks of loading onward. Along the total length of the implant during the first 6 weeks of loading, both the flexible (dense Polyactive) and the rigid (HA) implants showed a decrease in density. However, after this 6-week period, the bone density around the implants increased, and after 18 weeks the original bone density was reached. The flexible Polyactive implants provoked less decrease in density than the rigid HA implants, although not to a statistically significant level. This finding sustains the hypothesis that flexible implant materials may transfer stresses to the surrounding bone more favorably.

A nationwide evaluative study on implant-retained overdentures

OBJECTIVES In the Netherlands, dental implants have been included in the National Dental Insurance Scheme (NDIS) since 1989. Nowadays, out-of-pocket expenditure is low, making implant treatment financially feasible for a large group of edentulous, potential implant candidates. Treatment can be performed by both oral surgeons and general dentists. Results of implant treatment in the literature are usually obtained in academic and specialized centers. In contrast to this, the present study evaluates the quantitative and qualitative aspects of rehabilitation with oral implants in combination with an overdenture when applied on a nationwide scale. METHODS For this purpose all patients (n = 5410) treated between January 1989 and July 1992 were extensively documented pre-operatively, implant patients (n = 429) were clinically investigated by two independent observers and the effect of treatment on denture complaints was assessed by means of a questionnaire (n = 460). RESULTS Only a small proportion of the potential pool of implant candidates is actually being treated, to a constant number of approximately 2000 patients a year. The selected patients have major denture problems and have received relatively high levels of prosthetic care during the last decade. Clinical results are comparable to those reported in the literature, implant survival after 3 years for the lower jaw being 96.3% and for the upper jaw 70.4%. Oral hygiene was frequently considered suboptimal and seen in conjunction with marginal inflammation of the peri-implant mucosa. Subjective results were excellent, patients were quite satisfied with the improvements in the comfort and esthetics of their lower denture. CONCLUSIONS Implant-overdenture treatment, within the guidelines and regulations set by the Dutch NDIS, is a safe and effective treatment alternative, in particular for the rehabilitation of the lower jaw.

Augmented mandibular bone structurally adapts to functional loading

Long-term changes in trabecular bone structure during the 10 years following onlay grafting with simultaneous mandibular implant placement were studied. Extraoral radiographs of both mandibular sides in eight patients were taken regularly. Bone structure was analysed using a custom-written image analysis program. Parameters studied were trabecular area and perimeter and marrow cavity area and perimeter. After skeletonisation of the trabecular network, the number of end points and branching points, skeleton length, and branch angle were determined. The observed structural changes agree with the development of a more complex and more delicate or fine osseous structure. The bone shows more trabecular branching. All changes are most pronounced in the graft spongiosa, but are also found in the graft cortex and in the original mandible. The mean trabecular branch angle becomes more horizontal. The applied technique can be used to analyse long-term changes in the architecture of bone grafts. Changes found in the graft architecture correspond to changes expected after functional adaptation to loading.