PubMed · 1622572
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C E Misch. 1992. Single tooth implants: difficult, yet overused.. https://pubmed.ncbi.nlm.nih.gov/1622572/
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The purpose of this study was to propose a systematic approach to validate a finite element model (FEM) of the human mandible and to investigate the effects of changing the geometry and orthotropic material properties on the FEM predictions. Thirty-eight variables affecting the material properties, boundary conditions, and the geometry of a FEM of a human mandible, including two dental implants, were systematically changed, creating a number of FEMs of the mandible. The effects of the variations were quantified as differences in the principal strain magnitudes modeled by the original FEM (gold standard), prior to the sensitivity analyses, and those generated by the changed FEMs. The material properties that had the biggest impact on the predicted cortical principal strain were the shear moduli (up to 31% in difference from the unchanged state), and the absence of cancellous bone (up to 34%). Alterations to the geometry of the mandibular cross section, such as an increase in corpus dimensions, had the greatest effect on principal strain magnitudes (up to 16%). Changes in the cortical thickness in relation to the width of the corpus section modified strain more than alterations to the corpus depth (14% and 5%, respectively). The relatively small difference (up to 13.5%) between the predicted and measured interimplant distances indicates the accuracy of the FEM. Changes in geometry and orthotropic material properties could induce significant changes in strain patterns. These values must therefore be chosen with care when using finite element techniques for predicting stresses, strains, and displacements.
Osseointegrated implants have proven to have a high degree of success in the edentulous arches. This success has been replicated in partially edentulous arches. When natural teeth are present, it can be tempting to fabricate restorations using support from both implants and natural teeth. The mechanism of attachment and the perceived problem of the differential support provided by the implant and the tooth have been discussed by many authors.
BACKGROUND: Dental implants can be placed in fresh sockets just after tooth extraction. These are called 'immediate' implants. 'Immediate-delayed' implants are those implants inserted after weeks up to about a couple of months to allow for soft tissue healing. 'Delayed' implants are those placed thereafter in partially or completely healed bone. The advantages of immediate implants are that treatment time can be shortened and that bone height might be maintained thus possibly improving the aesthetic results. The potential disadvantages are an increased risk of infection and failures of the immediately placed implants. OBJECTIVES: To evaluate success, function, complications and patient satisfaction between 'immediate', 'immediate-delayed' and 'delayed' implants. SEARCH STRATEGY: The Cochrane Oral Health Group's Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE and EMBASE were searched. Several dental journals were handsearched. The bibliographies of review articles were checked, and personal references were searched. More than 55 implant manufacturing companies were also contacted. Last electronic search was conducted on 7 August 2006. SELECTION CRITERIA: Randomised controlled trials (RCTs) and preference RCT evaluating immediate, immediate-delayed, and delayed implants, reporting the outcome of the interventions to at least 1 year after functional loading. DATA COLLECTION AND ANALYSIS: Screening of eligible studies, assessment of the methodological quality of the trials and data extraction were conducted independently and in duplicate. Authors were contacted for any missing information. Results were expressed as random-effects models using mean differences for continuous outcomes and risk ratios for dichotomous outcomes with 95% confidence intervals (CIs). The statistical unit of the analysis was the patient. MAIN RESULTS: Two RCTs were included. One RCT compared immediate implants placed in periapical infected sites versus delayed implants in 50 patients and after 1 year found no statistically significant differences. The second RCT compared immediate-delayed versus immediate implants in 46 patients. After 1 year and a half there were no statistically significant differences for prosthesis and implant failures, complications, aesthetics assessed by the patient and the papilla height assessed by the dentist. However, patients in the delayed group perceiving the period between tooth extraction and insertion of the crown significantly longer than patients in the immediate-delayed group, mean difference of VAS -20.30 (95% CI -33.36 to -7.24). There was also statistically significantly higher patient satisfaction in the immediate-delayed group, mean difference (VAS) -6.51 (95% CI -12.63 to -0.39). An independent blinded assessor judged the level of the perimplant marginal mucosa in relation to that of the adjacent teeth as more appropriate in the immediate-delayed group, with risk ratio (RR) 1.68 (95% CI 1.04 to 2.72). AUTHORS' CONCLUSIONS: Despite that the evidence is derived from only two RCTs with a limited number of patients, it is possible to suggest that immediate implants and immediate-delayed implants may offer some advantages over conventional implants in healed sites in terms of patient satisfaction and aesthetics possibly by preserving alveolar bone. Immediate implants can work and are able to shorten treatment periods, however properly designed RCTs are still needed to fully evaluate the potential advantages and risks of this treatment modality since more complications and failures may occur.