CLINICAL AND PRECLINICAL STUDIES OF IMPLANTS WITH A MORSE-TAPER IMPLANT-ABUTMENT CONNECTION
Creators: name: ALBERTI, ALICE
Publisher: name: Universit� degli Studi di Milano
Year: 2021

description: The project focused on the application of the Morse-taper connection in implant dentistry, which was investigated both through laboratory and through clinical examination. Mechanical laboratory study Among the complications that can occur at dental implants, the fracture of any implant component is a relatively infrequent but clinically significant problem. Small diameter implants are at higher risk of such complication. The aim of this laboratory study was to compare the mechanical behavior of a 2.9 mm and a 3.3 mm diameter implant with a conical connection under standard static and dynamic conditions, following the ISO 14801:2017. Finite element analysis was performed to compare the stress distribution on the tested implant systems under a 300 N, 30� inclined force. Static tests were performed with a load cell of 2 kN; force was applied on the experimental samples at 30� with respect to the implant-abutment axis, with an arm of 5.5 mm. Fatigue tests were performed with decreasing loads, at 2 Hz frequency, until three specimens survived without any damage after 2 million cycles. The emergence profile of the abutment resulted the most stressed area in finite element analysis, with a maximum stress of 5829 MPa and 5480 MPa for 2.9 mm and 3.3 mm diameter implant complex respectively. The mean maximum load resulted 360 N for 2.9 mm diameter and 370 N for 3.3 mm diameter implants. The fatigue limit was recorded to be 220 N and 240 N respectively. Despite the more favorable results of 3.3 mm diameter implants, the difference between the tested implants could be considered clinically negligible. This is probably due to the conical design of the connection, which has been reported to present low stress values in the implant neck region, thus increasing the fracture resistance. Microbiological in vitro test Tissue inflammation around implants could be due to microbial colonization of the implant-abutment interface (IAI). The aim of the present in vitro study was to evaluate bacterial microleakage at the IAI in Morse-taper implant-abutment connections. A bacterial suspension containing A. actinomycetemcomitans, F. nucleatum, and P. gingivalis was inoculated into the internal cavity of ten implant-abutment samples with a Morse-taper internal connection. The samples were assembled using a calibrated beater, totally immersed individually into culture tubes, and incubated at 37�C. Turbidity analysis, real-Time PCR, and horizontal electrophoresis were performed at 24, 48 and 72 h. Performed tests were negative for every specimen, except two of them because of contamination during the manipulation of the components. Morse-taper implants rely on a frictional connection, which results in a very narrow implant-abutment space. This can account for the sealing capability of conical connections against bacterial microleakage. Although in literature no connection type was able to provide a complete bacterial seal at the IAI, Morse-taper connection implants showed less microleakage in comparison with other connection types. The present in vitro evaluation confirmed the sealing capability of Morse-taper connections in static conditions. Clinical study The third part of the project is a clinical observational prospective single-arm study on Morse-taper connection implants. The main objective of the study was be to evaluate the survival rate and the clinical and radiographic success of Morse taper connection implants, used for single-tooth and partial rehabilitations, and to assess the incidence of technical and biological complications. The following data were collected: ? implant-related factors: implant type, length, and diameter ? patient-related factors: age, gender, smoking status, systemic diseases, medications, history of periodontal disease, bruxism ? cause of the initial tooth loss: aplasia, unerupted tooth, traumatic injuries, caries, periapical periodontitis, marginal periodontitis ? site-related factors: implant position, bone quantity / quality following the Lekholm and Zarb classification (Lekholm and Zarb 1985) ? prosthesis-related factors: prosthetic restoration extension (single crown, partial fixed denture), prosthetic restoration material (all-ceramic, metal-ceramic, resin). To evaluate the clinical and radiographic success of the implants used, the following parameters were recorded during follow-up visits, 3, 6, 18, 12 and 24 months after surgery: ? Full-mouth plaque score % (FMPS%) ? Full-mouth bleeding score % (FMBS%) ? probing depth (PD) on the mesial, distal, buccal and palatal/lingual surfaces of the implants. The higher PD and the mean PD, measured as the average of four measured values, was considered for each implant. ? Bleeding scores, assessed on the basis of this scale: 0) no bleeding; 1) bleeding on probing without redness and swallowing; 2) bleeding on probing with redness and swallowing; 3) spontaneous bleeding. ? Plaque scores, assessed on the basis of this scale: 0) no plaque accumulation; 1) plaque accumulation revealed using a probe; 2) moderate accumulation of visible plaque/calculus; 3) high accumulation of visible plaque/calculus. ? distance from the implant crown margin to the coronal border of the peri-implant mucosa (DIM) ? width of keratinized mucosa (KM) ? radiographic distance between the implant shoulder and the first crestal bone-implant contact (DIB), measured on intraoral peri-apical radiographs taken a Rinn alignment system ? radiographic presence of continuous peri-implant radiolucency, measured on intraoral peri-apical radiographs taken a Rinn alignment system ? Prosthesis function ? Technical complications: implant fracture; abutment fracture; screw fracture; veneer fracture or chipping; metal framework fracture; abutment loosening; screw loosening; loss of access hole restoration. A total of 13 patients were treated with 41 implants. At the time of the last evaluation no implants failed, and all were successful. As for complications, no technical complication occurred. None of the implants showed signs of peri-implantitis, but a diagnosis of peri-implant mucositis was formulated in 3 patients, for a total of 8 implants. Bone resorption was consistent with the phisiological bone remodelling that occurs in the first year after loading. The regression analysis did not reveal any significant effect of any of the parameters on bone resorption, except for the history of periodontitis, which had a small but significant negative effect (p=0.47).