On tissue reactions to and resorption of bone substitutes

Sammanfattning: Background: The increasing need for bone grafting procedures in implant dentistry and the introduction of a variety of bone substitutes require a deeper understanding of the biological response and shortand long-term behaviour of these materials to choose the adequate graft and surgical procedure for the intended clinical application. Aims: The overall aim was to clinically and histologically study the short- and long-term tissue reactions to and resorption of bone substitutes after bone augmentation. Material and methods: In paper I, dentin blocks with different demineralization times were placed subperiostally in 40 rat skulls. After a healing period of 4 weeks the rats were sacrificed and the healing of the dentin blocks were evaluated. In paper II, eleven patients were treated with bilateral sinus floor augmentation using biphasic calcium phosphate (BCP) on one side and deproteinized bovine bone (DPBB) on the contralateral side, acting as control. After 3 years, biopsies were retrieved from the grafted area for histological evaluation and histomorphometry and 62 dental implants, placed 8 months after graft healing, were clinically evaluated. In paper III and IV, fourteen (22 sinuses) of the included 20 patients (30 sinuses) treated with sinus floor augmentation with a mixture of 80% DPBB and 20% autogenous bone (AB) from the chin were followed throughout the 10 years study period. These patients had 53 implants placed in grafted sites and 15 implants placed in non-grafted bone. Clinical and radiographic examinations were performed. Biopsies were retrieved from the grafted sinuses after 11 years of graft healing for 16 histological evaluation and histomorphometry. The particle sizes were compared with samples retrieved after 6 months from the same patients and pristine particles from the manufacturer. In paper V, 13 patients (14 jaws) were treated with lateral ridge augmentation using 2 different mixtures of DPBB:AB (90:10 and 60:40) in a randomized and controlled trial, designed as a split mouth study. The width and volume changes were evaluated after 7.5 months by means of cone beam computed tomography. After 8 months of graft healing, at the time of implant placement, biopsies were retrieved for histological evaluation and histomorphometry. Results: Resorption increased with increasing degree of demineralization of dentin blocks while bone formation increased with increasing degree of demineralization, in the latter case provided inflammation was compensated for (paper I). After 3 years of healing the BCP particles showed different levels of dissolution, in contrast to DPBB particles that showed no signs of resorption. The overall implant survival rate was 96.8% and the success rate for implants placed in BCP and DPBB was 91.7% and 95.7% respectively (paper II). The cumulative survival rate of the implants after 10 years was 86% and the marginal bone loss was 1.6 mm. There was only a reduction in graft height between 3 months and 2 years but no further reduction up to 10 years (paper III). There was no difference between the size of DPBB particles after 11 years compared to those measured after 6 months or to particles from the manufacturer (paper IV). The gain in width of the alveolar crest was 3.5 mm and 2.9 mm and the reduction of the grafts were 37% and 47% for the 60:40 mixture and 90:10 mixture respectively (significant differences). There were no histomorphometrical differences between the groups (paper V). Conclusions: Partial demineralization may provide a method for optimizing the integration of dentin onlays. A similar degree of bone formation and bone-to-graft contact for BCP and DBB was found 3 years after maxillary sinus augmentation with similar success rates for implants placed in both grafting materials. At 10 years follow-up after sinus floor augmentation with 80:20 (DPBB:AB) graft, the remaining implants presented good clinical and radiological results and there seems to be no further graft resorption after 2 years of 17 graft healing. DPBB particles were found to be well integrated in lamellar bone, showing no apparent signs of resorption after 11 years in humans. Despite a small difference in width changes after lateral ridge augmentation, the amount of AB added to DPBB did not seem to have a major impact on the graft healing and graft reduction, thus making it possible to install implants in all grafted sites.