The Effect Of Implant Configurations On Osseointegration Under Early Loading

The implant-abutment system can replace the lost natural teeth as the support for crown, restorating the aesthetics and function of patients. Although the implants have been widely used in many countries currently, some patients choose to give up the implant therapy due to the long schedule. Thus, the conventional implant therapy should be improved immediately to shorten the course of treatment, so as to make more patients benefit from the implant treatment.Since the introduction of modern dental implant techanique by Branemark in1960s, the conventional delayed loading protocol has been widely used in clinical practice. Many researchers began to study the immediate and early loading protocol until the development of immediate loading by Babbush in1986. The immediate and early loading are still the the hot area of research until now.Typically, the delayed loading protocol was used to ensure successful and predictable placement of dental implants. However a number of clinical and experimental studies regarding early loading directly challenged this notion with convincing outcomes. The early loading protocol refers to load applied to implants between2days and3months post surgery (between immediate loading and conventional loading). Comparable or even better survival rates and less peri-implant bone loss for early loaded implants were achieved in a series of clinical trials.Although many studies were conducted to determine the outcomes of early loading applied to threaded implants, few experimental studies exist that investigate peri-implant bone reactions under early loading applied to plateaued implants. The cylinder plateaued implant has a series of separate circumferential fins existing along the intra-osseous portion of the implant, and a large space between the fins which have previously been described for blood clot formation and woven bone development. It has been suggested that a relatively rapid bone healing and thus biomechanical stabilization of the implant could result from the vascularization and woven bone filling in this space.The aim of this PhD thesis was to evaluate the effect of implant configuration on bone-implant osseointegration under early loading. Three parts were included:1. The effects of implant configurations on stress distribution:a3D finite element analysisMateriala and Methods:Three experimental groups were designed according to the implant configurations:cylindrical threaded (CT) implant, cylindrical plateaued (CP) implant and tapered plateaued (TP) implant. The CT dental implants used in this study were3.3mm in diameter. The CP dental implants were3mm in diameter with a1.0mm plateau pitch and0.2mm thickness of each plateau. The TP implants were of the same plateau pitch, thickness of plateau and diameter in the coronal part as the CP implants. The only difference between CP and TP implants was that the latter had a tapered implant body. The3D one-stage implants with various configurations and the peri-implant tissure were modeled by means of the PRO/E program. The100-N static axial, horizongtal and oblique (45°) load were applied to the top of one-stage implant. The3D finite element analysis (FEA) was run at the ANSYS Workbench program. The images showing the distribution of von Mises stresses were abtained to locate the stress concentration in implants and different tissues under load of different directions. In addition, the maximum von Mises stresses (MVMS) at implants of various configurations and different tissues under load of varous directions were quantitatively compared.Results:The images showing the distribution of von Mises stresses under axial load revealed that no stress concentration was observed within the implant, and high stress values were detected at the end of implants for CT and CP groups and at the cervical part of implant for TP group. The stress concentratons at cervical cortical bone and cancellous bone were lacated at the top regions arround the implants and the end of implants respectively for all groups. Under horizontal load, the stress concentrations within implant were located at the cervical region for CT group, while the stress distributed equally within CP and TP implants. The stress concentrations in the cortical bone were also located at the cervical region for all groups. The stress concentrations in the cancellous bone were located at the end of implant for CT group, while the stress distributed equally in cancellous bone adjacent to CP and TP implants. Under oblique load, the stress concentrations within the implant were lacated at the cervical region for CT group, while no stress concentration was observed within the CP and TP implants. The stress concentrations in cortical bone were still located in cervical regions for all groups. The stress concentrations in cancellous bone were lacated at the end of CT implants, while the stress distributed equally again in cancellous bone for CP and TP implants. In addition, the stress concentrations in mucosa existed at gingival margin for all groups under load of varous directions. The quantitative comparison of MVMS between implants of different configurations indicated that①The MVMS at the same tissue of the same group were compared: axial load> oblique load> horizontal load.②For MVMS at the same tissue under load of the same direction:The CT group had a higher MVMS within the implants and a lower MVMS at the cervical cortical bone than the CP and TP groups. The MVMS at cancellous bone adjacent to the CP implants was lower than others. The MVMS existed in mucosa adjacent to the CT implants was the highest of all groups, while the MVMS existed in the CP implants was the lowest.③The MVMS existed in different tissues for the same group under the load of the same direction were compared:implant> cortical bone> cancellous bone> mucosa.Conclusions:Higher stress existed within the implant and lower stress distributed in the cervical cortical bone for cylindrical threaded implant, which favours the resistance of cervical bone loss. Under non-axial load, the stress concentrations in cancellous bone were located at the end of implant for cylindrical threaded group, while the stress distributed equally in cancellous bone for both plateated implants. The configuration of implants did not affect the stress distribution in vertical cortical bone, as the stress concentration always existed in the top region of interface between implant and cortical bone.2. Bone formation adjacent to implants of various configurations under early functional loading in a dog modelMaterials and Methods:This study was designed to evaluate the effect of combining implant configuration and surgical technique on bone formation under early functional loading in a dog model. Bone formation adjacent to customized cylindrical threaded, cylindrical plateaued, and tapered plateaued dental implants were compared post-early loading. The Periotest values were monitored dynamically for6weeks. Peri-implant bone healing was evaluated by bone-to-implant contact, and bone volumes fraction analysis after3and6weeks of loading.Results:The cylindrical threaded implants showed the highest stability when load began, while both the cylindrical threaded and cylindrical plateaued implants had higher stability than tapered plateaued implants after6weeks of loading. No difference in stability was found between cylindrical threaded and cylindrical plateaued implants after6weeks of loading. The data from both micro-focus computed tomography and histomorphometric analysis showed that the cylindrical threaded implants had significantly higher bone-to-implant contact and bone volumes fraction compared to cylindrical plateaued and tapered plateaued implants after3weeks of loading, and the tapered plateaued implant had a lower bone-to-implant contact than the cylindrical threaded and cylindrical plateaued implants after6weeks. In addition, no significant difference was detected for bone volumes fraction between cylindrical threaded and cylindrical plateaued implants after6weeks of loading.Conclusions:Based on these results, we concluded that the cylindrical implant, whether threaded or plateaued, might be more suitable for early loading (1week) when compared to the tapered implant.3. Effect of decreased implant healing time on bone (re)modelling adjacent to plateaued implants under functional loading in a dog modelMaterials and Methods:The purpose of this study was to evaluate the effect of early functional loading to plateaued implants on bone formation and implant stability in a dog model. Early loading (EL), non-loading control and delayed loading (DL) groups were compared using6Beagle dogs under functional loading. The Periotest values (PTV) were measured dynamically for6weeks. Peri-implant bone architecture was evaluated qualitatively by micro-computed tomography (μCT) and analyzed quantitatively by mineral apposition rates (MAR), bone-to-implant contact (BIC) and bone volumes (BV/TV) after the euthanasia at3and6weeks after loading.Results:The EL implants showed poor stability at1week, but greater stability at2and4weeks after loading compared to DL implants. There was no significant difference between MAR of EL and unloaded implants at both time intervals. The EL implants displayed a significantly higher MAR when compared to DL implants at3-5weeks. A significantly higher BIC for the DL group was observed when compared to the EL group at3weeks following loading, however at6weeks, no significant difference between these groups was observed. The EL group gained a higher BIC than the no-treatment control group at6weeks.Conclusions:For plateaued implant, the decreased healing time (1week) displays a positive effect on peri-implant bone (re)modelling under functional loading during the early phase.Based on the three studies above, we concluded:Favourable osseointegration can be obtained for the cylindrical plateaued implants under early loading (1week after the implant installation) due to the positive effect of decreased healing time. The early application of functional loading on cylintrical plateaued implants could be used clinically to shorten the course of treatment and improve aesthetics.