Implant bio-mechanics for successful implant therapy: A systematic review

Abstract

INTRODUCTION The use of dental implants is considered as the best treatment option for treating partial or complete edentulism and replacing single missing tooth in the anterior and posterior regions of the mouth.[1] High survival rates for dental implant supporting single crowns or fixed partial prothesis have been reported; however, systematic reviews of the literature have also identified a variety of the complications associated with dental implants and prothesis superstructures.[23] These complications are broadly classified into biologic, technical, and esthetic.[4] Biological complications affect the tissue supporting the dental implant while the mechanical complications affect the structural integrity of the implant and/or abutment of prosthetic superstructure. One of the most commonly reported biological complication is peri-implantitis and peri-mucositis. Common technical complications include veneering material or framework, loss of retention, and screw loosening. Despite the fact that majority of these complications does not threaten the survival of dental implants, management can be time consuming and requires additional financial resources for the patient and the clinician and may even affect the patient’s quality of life. To avoid or minimize the chance of occurrence of these complications, it is important to avoid known risk factors during the initial planning of the implant therapy.[5] The common approach of systematic reviews with a focus on risk factors associated with implant and implant-supported prosthetic compactions is the comparison of failure/complication rates to be expected with various types of implant characteristics and/or reconstructions.[67] There are, however, many variables that the clinician should consider such as implant connection system, torque applied, and abutment screw material that can be influenced in terms of the biomechanical yield of the implant prosthesis. This study will sytematically review primary research studies that have tested the bio-mechanical properties of dental implants. The aim was to address the role of bio- mechanical factors and which biomechanical factors are most advantageous for successful implant therapy in the restoration of missing teeth. The main outcome of this review is to determine what bio-mechanical factors are most critical for implant success. MATERIALS AND METHODS This systematic review is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline.[8] An electronic database search was performed for journal articles published in English, form database inception to December 2019, on MEDLINE (PubMed), Google Scholar, EMBASE, CAB Abstracts. A separate search strategy was prepared for each database using key words and Boolean operators. For the preparation of the search strategy, seven principal biomechanical factors were considered. Systematic reviews, editor letters, reviews, abstracts, short communications, books, and dissertations were not considered eligible. The type of studies considered eligible was: (1) Observational studies—prospective and retrospective. (2) Intervention studies (trials)—on humans and animals. (3) In vitro studies. These studies are a mix of laboratory experiments conducted on models, observational and intervention studies on animals, and partially or completely edentulous patients. Where human studies are being reviewed, the following eligibility criteria were followed. INCLUSION CRITERIA Completely or partially edentulous patients above 18 years of age Patients who received permanent restorations after implant surgery Patients who had been followed upfor at least 6 months after receiving permanent restoration EXCLUSION CRITERIA Patients who had any absolute contraindication to dental implants at the time of implant surgery Two independent reviewers screened titles and abstracts. After considering inclusion and exclusion criteria, full-text articles were selected. Studies were eliminated based on the eligibility criteria of study design and participants. After reading complete texts, studies were evaluated against eligibility criteria again and data were extracted from the final selected studies. Divergences between two reviewers were solved through discussion or through consensus with the intervention of third reviewer. The following data were extracted from the selected studies: authors, year of publication, study design, implant characteristics, prothesis characteristics, cantilevers extension and location, opposing dentition, type of abutment, screw type and material, main outcome measures, and values. After data extraction, considering the heterogeneity in terms of outcomes and measures proceeding with a meta-analysis was not considered appropriate. The results are presented using descriptive synthesis in the form of tables and text. Tools to assess the quality and risk of bias for in vitro studies could not be identified; so, this assessment was performed only for nonrandomized intervention studies in humans and animal models. The risk of bias of the included experimental in vivo studies was assessed using SYRCLE’s risk of bias tool.[9] Six types of bias (selection, performance, detection, attrition, reporting, and other biases). The score “yes” indicates a low risk of bias, “no” indicates a high risk of bias, and “?” indicates an unclear risk of bias. Following authors’ recommendations, we have not calculated a summary score for each individual study; however, a simple counting of all the domains that scored high for the risk of bias is provided. We initially planned to use the Cochrane Collaboration’s risk of bias assessment ROBII tool to assess risk of bias for randomized studies. However, none of the included studies fell into this category. The studies involving humans were observational studies; so, for quality assessments, Newcastle–Ottawa Scale (NOS) scale was used instead).[10] Assessment was performed independently by two reviewers, and eventual disagreements were solved through discussion or though consultation with a third author. RESULTS STUDY SELECTION AND DESCRIPTION Of the 234 titles resulting from the online search, 59 studies were selected for full-text review after abstract screening. In total, 28 full-text articles were included in the review for data extraction and analysis, 18 in vitro studies, 5 cohort clinical studies, 3 animal studies, and 2 nonrandomized studies of interventions. The results of the methodological quality and risk of bias for observational and animal studies are presented in [Supplementary Tables 1 and 2], respectively. Figure 1 displays details of the selection process used to identify the included publications.Supplementary Table 1: Evaluation of individual study quality with The Newcastle-Ottawa Scale (NOS) for assessing the quality of non-randomized studies in meta-analysesSupplementary Table 2: Risk of Bias of the included animal studies assessed using SYRCLEs RoB toolFigure 1: PRISMA flow diagram of literature search and selection process. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-AnalysesSix different outcomes were considered: loss of preload, fatigue/mode of failure, stress distribution, removal torque values, optimal torque generation, and biological/technical complications. On the basis of the outcome, six in vitro studies assessed the influence the loss of preload for screw abutment (four studies) and prosthetic screw (two studies) [Table 1]. The variable considered for the abutment screw was screw surface modification and dry lubrication while for the prosthetic screw the variable was loss of preload with time after clinical use or several hours after tightening of a new screw. In the majority of cases, the screws were exposed to a sequence of tightening and loosening, before measure performance. The laboratory specimens were not subject to loading test, only in one case the measures were performed in screws that have been subject to clinical masticatory functional load. Six in vitro studies considered the factors that might influence the reduction in removable torque after mechanical and technical stress application [Table 2]. Five in vitro studies were included that considered the influence of different factors on fatigue strength. Four studies assessed the influence of implant abutment connection design and one the implant diameter on fatigue and mode of failure under different loading conditions. Either static or cyclic loading was applied, consisting of different force values and the number of cycles [Table 3]. Two nonrandomized studies assessed the variability of optimal torque delivered based on the torqueing method [Table 4]. Six observational studies assessed the effect of cantilever presence and characteristics, loading conditions, and prothesis misfit on technical and biological complications [Table 5].Table 1: Summary of Data Extracted from Included In vitro Studies and variables that influence preload valuesTable 2: Summary of Data Extracted from Included In vitro Studies and variables that influence torque valuesTable 3: Summary of Data Extracted from Included In vitro Studies and variables that influence fatigue and mode of failure of IACTable 4: Summary of Data Extracted from Included Non-randomized Studies of Interventions and variables that influence generated torque valuesTable 5: Summary of Data Extracted from Included Non-randomized Studies of Interventions and the variables that influence implants clinical complicationsThe included studies were grouped according to six specific biomechanical factors: Abutment screw material/surface modification Prosthetic screw loss of preload Implant/abutment joint design Torque method Cantilever Prothesis misfit ABUTMENT SCREW MATERIAL/SURFACE MODIFICATION One in vitro study by Byrne et al.[11] determined that gold coating of the abutment screw produced higher preload values for a given torque application. Compared to uncoated analogue, the gold-coated screw resulted in twice the preload at 35N cm torque [Table 1]. The testing consisted of applying increasing torque values 10, 20, and 35N cm on each abutment-screw assembly. The preload values were measured after application of each of the above-described torque values, after which screws were loosened completely. This procedure of screw tightening and loosing was repeated for three consecutive times. There was a difference between coated and uncoated screws when the screws were tightened repeatedly. The gold-coated screw loss preload on the second and third tightening episodes, the gold alloy screw lost preload after the second tightening with values remaining constant thereafter while the titanium alloy screw remained unchanged for the three tightening episodes. Another variable considered in this in vitro study was the abutment type. Two types of abutments were considered the prefabricated abutment and the cast-on abutments, consisting of a machined gold alloy cylinder to fit the implant hex and a castable plastic sleeve. The type of abutment used during testing influenced the preload values regardless of the screw type with the latter consistently was associated with higher preloads values.[11] The preload generated by three different type of screws, gold alloy, titanium alloy, and gold-coated after appliaction of the same torque force were compared in another in vitro study. The difference in preload values was significant between the three groups and the gold alloy screw presented higher preload values followed by the gold-coated and the titanium alloy screw.[12] Moreover, statistically significant difference in the preload values was found for the gold and titanium alloy screws when these were torqued the values recommended by the manufacturer. However, at maximum torque, titanium screw-induced stress was below the titanium yield strength, meaning that even with higher torque values the screw might still function within the material’s elastic range.[13] Surface-treated titanium, and gold alloy, and non-treated titanium and gold alloy screws were compared in another study. Surface-enhanced screws, in particular gold-coated alloy screw, generated greater preload values when compared to conventional titanium and gold alloy screws.[14] PROSTHETIC SCREW LOSS OF PRELOAD Prosthetic screws were analyzed in two studies. After application of a defined torque, under standard, nonloading conditions a loss of preload was observed over time. The majority of preload loss occurred within 10s of tightening.[15] In another study, when screws have been in use for 18–120 months, the preload values decrease as a function of time during which the screw has been in use[16] [Table 1]. Other factors might, however, influence the preload values, such as troquing sequence, screw design abutment design, implant-abutment connection system. Considering the greatest loss of preload occurs during the initial period after torque application, torqueing and retorquing can affect preload loss recovery.[1718] Screw presents generally with a flat head, a long stem, and a variable number of threads. It has been observed that wider screws with a long stem provide less torque loss while there is controversy about the influence of the shape of the screw head on the loss of preload.[18] Despite abutment design has not been considered a crucial factor in the maintenance of the preload values, features such as abutment collar length has been found to influence the preload loss.[19] With regard to the type of connection, most authors have found that internal hexagon type exhibits greater preload than external hexagonal type.[19] IMPLANT/ABUTMENT JOINT DESIGN A comparison between 8- and 11-degree internal cone reveled that the 11-degree internal cone deformed before the cone joint, preventing screw fracture while the 8-degree cone fractured at the head of the screw.[20] Another study compared two commercial implant systems to address the effect of joint design on fracture strength under cyclic loading conditions with a force applied perpendicular to the long axis of the implant system assembly. The 8-degree internal conical implant/abutment interface performed better than the hex-mediated butt joint.[21] Six different implant systems with internal and external connection assessed for fracture strength after cyclic loading. Long internal connection and cam slott connection compared to short wither external or internal connections showed increased resistance to fracture strength.[2223] Cibirka et al.[23] examined the effect of three different implant/abutment joint configurations differing based on the vertical height of degree of fit tolerance of the implant abutment interface and found that after cyclic loading, no difference in the values between the three was compared to external hex connection to assess the effect on stress using three In the the stress in the at the implant was however, increasing stress in the abutment or abutment screw, compared to the The conical interface was compared to the flat interface to the interface design the stress at the of The conical interface type in the stress compared to the flat interface of the type Two observational studies assessed the and method on the variability on the torqueing force [Table 4]. were to a screw abutment with the maximum of force using a of torqueing were Considering the to an optimal and final torque for screw abutments, it is important to and the of force In a between delivered torque and torque was observed when using a and different mechanical In to torqueing should be observational studies examined the effect of cantilever on the implant and prothesis outcome [Table studies included were involving patients. Two studies examined the of posterior and of partial fixed and single implant prothesis in the and The of the period was and in the and second study, respectively. The study included a and compared the effect of cantilever presence on different were for and no difference in the loss was found between the cantilever and A higher of technical complications was observed in the cantilever and prothesis Another cohort study examined the factors that could influence the outcome of the presence of cantilever in implant-supported partial The prothesis was screw or and the length of the cantilever was for the and for the The cantilever length in was The primary outcome for this was A between the cantilever length and for the cantilever was of cantilever prothesis was higher than that of cantilever prothesis the difference was not statistically cantilever prosthetic reported a higher of prosthetic were observed on when the two were or on with implant-supported One cohort study assessed the influence of anterior cantilever on technical complications of implant prothesis by implants in the anterior cantilever length was to posterior cantilever length was and was to significant was observed between the length of anterior cantilever and screw however, the of posterior cantilever to was associated with screw The effect of implant on clinical outcomes was assessed in two observational clinical [Table The on clinical studies was 5 In one study, on and implants, supporting fixed partial prothesis were considered. The implant in the was and does not influence the implant loss under functional loading The other cohort study considered fixed partial or prothesis with implants for There was no influence of the implant on the survival after 5 years of functional loading of the The of and loading conditions on implants was assessed in two animal models. In a study, and loading conditions were by a partial or a prothesis by two implants. However, observed on loading during a loading conditions were by the restoration with abutments in another study. After 1 year of functional loading, no were observed between and abutments on The effect of prothesis misfit was considered in two in vitro studies, one clinical study and one animal et in an in vitro evaluated the effect of prothesis misfit on screw After vertical cyclic loading, significant prosthetic screw was observed compared with the One cohort was a study. One was followed for 1 year while the second has been a prothesis for the were implant-supported fixed of prothesis misfit was and none of to influence [Table et evaluated the influence of tightening and prothesis misfit after cyclic loading on torque The authors that the misfit the removal torque values and the application of tightening and removal torque independent of the of prothesis misfit [Table 2]. In an experimental animal study, vertical misfit of the had no influence on the process of In to the of the authors also evaluated the degree of preload on the between the implant and the the process of diameter One in vitro study compared and diameter implants. static and loading conditions, the diameter implant was as measured by fatigue Screw length The effect of screw length on screw after was assessed in one in vitro study. statistically significant difference was found between the groups with different abutment screw length and removal torque Torque implant abutment specimens and different tightening torque values and were evaluated under cyclic loading conditions. et that torque will to fatigue of dental and that abutment screws should be tightened to the torque recommended by the Torque application will in the of a force within the screw The screw is during torque application with and being into It is the elastic of the screw that the system a force that the joint system form by authors, a between the tightening torque and screw preload values will in a greater force to the screw. The application of an torque is of crucial for clinical success. Of the included studies, only one evaluated the effect of different torque on screw as measured by the removal The low tightened implant abutment resulted in mechanical failure after On the other that the yield strength of the screw may to loss of mechanical properties of the screw to plastic The torque may on several that were not in this However, it was reported in two of the included studies that variability when the torque force is delivered though a and that this will in consistently torque force compared to the The screw material the preload values. of the of the tightening force applied, gold screws higher preload values when compared to titanium screws or titanium an additional was gold the latter higher preload values. The the screw surface by a is to decrease the of increasing the preload results were reported for repeated tightening which is a common clinical In one study, this resulted in a of the preload for the gold-coated and in another study it was reported that when the same screw is fixed several preload values In screws, repeated tightening on which in the and of the results is not to the number of the included studies and the different measures of the outcome or variables that might influence the preload values such as application of different rates of torque force or torque that from optimal values as recommended by the opposing joint abutment design, and Six in vitro studies included in the review assessed the effect of implant abutment design on force strength and mode of failure, screw and and the of stress The systems were tested under or mechanical stress or conditions. There was a variability between the included studies with regard to the interface design and characteristics the to between studies. However, the type of connections that characteristics to the outcomes above were internal long and implant/abutment With the the stress at the of stress at the of abutment or abutment prothesis with cantilever are to provide or for and posterior cantilevers are in in vitro and clinical studies. In the three observational studies that posterior cantilever in partial fixed anterior cantilever in and the influence on implant were loss and implant was not by the presence of the cantilever this the of occurrence of technical such as cantilever type of cantilever and type of or tooth prothesis implant had no influence of prosthetic complications were reported for compared to anterior length to have no technical complications such as screw the presence or of a cantilever other factors such as the number of implants supporting the the type of and opposing dentition, implant connection and implant to might influence the and the of prosthetic of these factors were not considered in the included studies. on the results from two clinical observational studies, no effect was found between the and implant over a The type of implant and prothesis material which can influence the of implant loss were different in these two studies. the studies included in this review on loading conditions considering factors that can to an increased of results were reported based on animal However, in the study in loading conditions, were applied which are not with functional loading conditions in for the influence of prothesis misfit on different outcomes is based on different type of studies, in clinical and experimental animal studies. There is between studies that misfit between the implant abutment and the prothesis does not influence and screw However, the torqueing method and increased the removal torque and the of the abutment screw independent of the prothesis misfit For the other factors such as implant torqueing screw length and torque only one study factor was included in this review no could be on influence of implant therapy the of this study, the following can be The use of abutment screws can higher preload values conical implant/abutment interface performed better in strength under loading conditions. The in does not to be influenced by the presence of prothesis cantilever technical complications were found when a cantilever was The presence of prothesis misfit does not influence and connection screw loading conditions does not influence a torqueing should be used to optimal torque values. AND This research not any specific from in the or OF The no of financial or AND The research is a study to the of OF The data used to the of this study are included within the

Topics & Concepts