Current challenges in implant dentistry involve achieving predictable long-term results in any clinical situation, especially when there are high aesthetic requirements. Currently, treatment with implants offers predictable long-term results in replacing all types of dental deficiencies, single or multiple, becoming the most appropriate therapeutic alternative to removable dentures and fixed prostheses [1]. Over the years, continuous variations in implant design have been proposed, with modifications varying considerably to achieve the best possible results in terms of the degree of osseointegration. Nevertheless, all such innovations, which often lack solid evidence, complicate clinical decision making. The maintenance of stable bone levels over time remains the gold standard when evaluating success in implantology, but currently the final objective in implant treatment is based not only on achieving good results in bone integration, but also in reaching aesthetic and predictable contours of the soft tissues; thus, making the aesthetic component an inherent part of oral rehabilitation [2-5]. During the early years of implant science, the most commonly used implants were two-piece; these components were placed on the bone crest during the first phase of the surgical procedure, allowing submerged healing during the period of osseointegration with the aim of minimizing implant failure [6]. However, a second surgical procedure was necessary during the prosthodontic phase. Resorption of the bone crest after 1 year of prosthetic loading was a common occurrence in this type of implant, with a marginal bone loss of not more than 1.5 mm in the first year and 0.2 mm in each successive year [3]. Changes around the neck of the implant were assumed to be due to establishing biological width [7]. It has also been suggested that inflammation and micromotion in the gap between the implant and the abutment also play a role in marginal bone loss and the consequent soft tissue recession [8]. More recently, implants have been designed at the soft tissue level, requiring only one surgical stage. This has decreased morbidity and shortened the treatment period, with a similar success rate for the initial approach [9]. This type of implant has a rough surface designed to facilitate osseointegration and a polished coronal part that facilitates the adaptation of soft tissues. Multiple studies have established that the supracrestal position of the implant causes less marginal bone reaction compared with implants placed at the epicrestal level [10]. The main drawback of this type of implant is the possible exposure of the polished neck, especially in aesthetic areas with a fine biotype.  In recent decades, the concept of platform switching appeared serendipitously [11]. It was observed that, when restoring bone level implants with prosthetic attachments of smaller diameter, the loss of peri-implant crestal bone was minimized. In this way, with the advent of the switching platform concept, it was possible to place the shoulder of the implant at the level of the crestal bone with minimal and predictable marginal bone resorption. Thus, such an approach offers obvious aesthetic advantages by allowing the neck of the implant to be hidden [12-15]. Currently, most systems offer two types of implants: soft tissue level (STL) implants are typically placed transmucosally in a single surgical phase, while bone level (BL) implants are placed at the epicrestal level with a narrow platform abutment that aims to maintain levels of the peri-implant bone crest. Both types of implants promise good results in the medium and long term [16] and are versatile, allowing for immediate loading of any type of prosthetic restoration, screwed or cemented. Despite wide use of BL and STL implants during past decades, the results have not been evaluated with an evidence-based approach. There are few systematic reviews or meta-analyses in this regard, the most recent one finding no differences between the two approaches.⁸ Although most studies report no differences in marginal bone loss or survival rates between the two systems, and in fact, find the two to be interchangeable, other factors may identify superior performance for one system over the other. Currently there are specific indications for each type of implant, thus, STL would be indicated for the posterior sector and for prostheses, while BL would be the implant indicated for aesthetic requirements. However, this is an overly simplistic approach and other factors may be taken into account. The aim is to compare soft tissue level vs. bone level implants indications through a systematic review of the literature. Few studies have analyzed the advantages and disadvantages of each implant system depending on the different clinical situations. In this context, a clinical guide could be useful for making decisions for implant planning.

This systematic review was performed according to the PRISMA statement (Supplementary Table S1). Focused questions what is the difference between STL and BL implants depending on other clinical situations regardless of bone availability? The question to answer is in relation to the two implant systems: which type is more advantageous than the other in the different clinical situations mentioned? The PICO question is based on P: partially or totally edentulous patients who have received treatment with both types of implants; I: STL implant placed supracrestally in one-stage surgery receiving any type of fixed or removable restoration; C: BL implant placed epicrestally in two surgical stages that receive any type of fixed or removable restoration; O: beneficial effects in terms of promoting osseointegration, shortening treatment times, facilitating procedures, superior utility in some type of restoration, avoiding adverse effects (such as non-osseointegration and peri-implantitis), and desirable economic factors. Study design before beginning the systematic review, the authors developed a protocol designed along the general lines of the review for each of the study sections. In this way, an independent review was established comparing the favorable effects, advantages, and disadvantages of the STL and BL implants, depending on various aspects, such as dimensions of the edentulous space, aesthetics, connection-reconnection of the abutments, type of prosthetic restoration, and available prosthetic space. It also includes the search strategy of each section, inclusion and exclusion criteria, screening, and quality assessment technique. This paper focuses on BL and STL implant systems from the same manufacturer (Straumann AG, Basel, Switzerland); however, these findings are applicable to other commercial implants, in which the diameter and length vary slightly.

Search Strategy

An electronic search was performed in two databases (Medline via PubMed and Scopus), looking for studies published before July 2020, only in English, and using MESH terms and keywords. The MESH terms included dental implants and the following keywords/search terms and their combinations: STL transmucosal, submerged, nonsubmerged, one stage, one piece, one-part, single part, BL submucosal, submerged, two stage, two pieces, and two parts. These search terms were completed with specific keywords for each of the topics specifically:  Mesiodistal edentulous space: edentulous gap, edentulous space, implant diameter, mesiodistal size, interimplant distance, and jumping distance. Filters were for dental journals, clinical trials, and reviews were applied. Aesthetics: Implant aesthetic(s), failures, emergence profile. Filters for dental journals, clinical trial, and review were applied. Type of prosthetic restoration: Implant restoration, implant rehabilitation, overdenture, single tooth replacement, fixed partial denture, prosthetic planning. Filters for dental journals, clinical trial, and review were applied. Connection-reconnection: Abutment disconnection, connection, reconnection, disconnection. Filters for dental journals, clinical trial, and review were applied. Denture space; Vertical restorative space, interridge space, denture space, prosthetic space, restorative space, interarch space. Filters for dental journal.  In addition, a hand search and expert opinions were sought using articles and references retrieved from the electronic search and peer-reviewed journals.

Screening

Inclusion criteria: These included publication in the peer-reviewed literature of studies in partially or totally edentulous patients with fixed or removable implant restorations through STL or BL implants in the English language and animal or human clinical studies evaluating BL or STL implants about focused questions. Clinical studies: Randomized clinical trials, controlled trials, cohort studies/case series, and case control studies. Additionally, in vitro studies, review articles, and textbooks were included for review. Follow-up time: at least 6 months after functional loading.

Exclusion criteria: Studies in patients with medical conditions that may affect implant therapy (diabetes mellitus, cancer, and drugs). Studies using STL and BL implants for other nondental uses (orthodontic anchor, maxillofacial prosthesis). Studies with multiple interventions, i.e., ridge augmentations and/or sinus lift. Studies describing peri-implantitis treatments and those that report immediate loading.

Eligibility criteria: The number of studies published on each of the topics is variable. In all cases, a sequential screening process was performed independently and secondarily by two of the authors (L.L. and B.R.) to increase the relevance of the data obtained. In a first step based on the title and abstract, studies not focused on the topic and duplicate studies were eliminated. Then, eligibility for full-text assessment and, finally, selection of studies was performed according to the inclusion and exclusion criteria. The primary outcome was any advantage or disadvantage about STL or BL implants. The excluded articles, together with the reasons, are referenced in Supplementary Table S2.

Quality Assessment

The risk of bias was evaluated for the selected articles. The included systematic reviews were assessed for quality, using AMSTAR 2, whose checklist aims to assess the overall confidence in the results of a systematic review. AMSTAR 2 is composed of 16 items scored yes, partial yes, no, and meta-analysis. Of the 16 items, seven are considered critical domains:

• protocol registered before commencement of the review (Item 2);
• adequacy of the literature search (Item 4);
• justification for excluding individual studies (Item 7);
• risk of bias of included individual studies (Item 9);
• appropriateness of meta-analytical methods (Item 11);
• consideration of risk of bias when interpreting the results (Item 13);
• assessment of presence and likely impact of publication bias (Item 15) [17].

The overall confidence in the results of the systematic reviews proposed by the AMSTAR 2 tool was defined as:

1. High (no, or one noncritical weakness: the systematic review provides an accurate and comprehensive summary of the results);
2. Moderate (more than one noncritical weakness but no critical flaws: the systematic review provides an accurate summary of the results);
3. Low (one critical flaw, with or without noncritical weakness: the systematic review may not provide an accurate or comprehensive summary of the results);
4. Critically low (more than one critical flaw, with or without noncritical weakness: the review should not be relied on to provide an accurate nor comprehensive summary of the results).

A pair of reviewers (B.R., L.L.) performed the AMSTAR 2 assessment; disagreements were resolved by discussion or arbitration with a third reviewer (S.D.).

The Cochrane Collaboration's “Risk of Bias” was used to assess the included randomized controlled trials (RCTs) as recommended by the Cochrane Handbook for Systematic Reviews of Interventions. For each study, a cumulative score was estimated and the overall risk of bias was evaluated for the included RCTs. A low risk of bias was assigned to studies that fulfilled all criteria. A moderate risk of bias was assigned to studies in which at least one criterion was only partially fulfilled. A high risk of bias was assigned to studies in which one or more criteria were not fulfilled (Higgins JPT, Green S eds. Cochrane Handbook for Systematic Reviews of Interventions, Version 5.1.0. updated March 2011. The Cochrane Collaboration, 2011. www.handbook.cochrane.org). Finally, quality appraisal for nonrandomized studies (cohort and case series studies) was executed according to the Newcastle-Ottawa Scale (NOS) [18]. The NOS calculates the study quality based on three major components: selection, comparability, and outcome for cohort and case series studies. It assigns a maximum of four stars for selection, a maximum of three stars for outcome, and a maximum of two stars for comparability. According to that quality scale, a maximum of nine stars/points can be given to a study. In the analysis, the studies are defined as high quality: 7-9; medium quality: 4-6; low quality: 1-3.  Pooling of data in a meta-analysis was not possible due to heterogeneity and low number of RCTs. Therefore, a qualitative analysis was made.

Overall, 1098 articles were identified, of which 48 were selected for review (Figure 1). 7 of them were systematic reviews, 8 were randomized controlled trials (RCTs), and 33 were non-RCTs (5 case control studies, 4 cohort studies, and 24 other types of non-RCTs). Regarding the risk of bias and quality of studies, in the case of systematic reviews, the overall confidence was high for one, moderate for one, low for two, and critical for three systematic reviews (Table 1). For the eight RCTs analyzed, the risk of bias was low for four and high for the other four (Table 2). In the case of non-RCTs, the five case control studies were of medium quality and the four cohort studies showed a high quality (Table 3a, b). Mesiodistal edentulous space Regarding the mesiodistal distance, the size of the edentulous gap may be a factor in the choice of the type of implant [19,20]. In most implant systems, although the diameter of the intraosseous part is identical, the coronal part presents differences, including the widest STL implant. For a single implant, if the mesiodistal distance is close to 15 mm, the possibility of excessive embrasures is high. This also occurs with most standard implants having a diameter of 4.1 mm. STL implants always minimize this inconvenience and improve the possible food packing and interproximal hygiene. At a distance of 7–9 mm, a BL implant allows maintaining 1.5-mm bone walls on each side. Similarly, if the distance is around 20 mm, the placement of two implants can be subject to the same considerations. Regardless of bone availability, the size of the gap can be adapted to the different diameters of the implants. If the distance is around 15 mm, two BL implants would be indicated, whereas if it is greater than 15 mm, two STL implants would be more suitable [21]. A narrow implant with a shoulder diameter of 3.5 mm (STL) or 3.3 mm (BL) is generally used to replace the lateral incisor, particularly in areas between 5.0 and 5.5 mm, [22], but it can be useful in other areas with reduced dimensions [23,24].

Figure 1: Flow chart of the selection strategy used in the systematic review.

Table 1: Summary assessment of risk of bias for systematic reviews.

Table 2: Summary assessment of risk of bias for RCT’s using Cochrane Collaboration’s.

* Ebler et al. (2015) blinding participants/personnel was not reported

+ Gamper et al. (2017) blinding outcome assessment was not reported

**Barbisan de Souza et al. (2018) blinding outcome assessment was not possible

Table 3a: Summary assessment of case-control studies.

Table 3b: Summary assessment for cohort studies.

 Aesthetics

Although there seems to be no difference in marginal bone loss between STL and BL implants, [8] the use of platform switching in BL implants can improve the stability of soft tissues [15]. Regardless of the thickness of the mucosa, BL implants allow a more appropriate aesthetic management [24,25]. Since the transmucosal polished neck of the STL implants is at least 1.8 mm, higher mucosal thicknesses are required so that either the neck does not become visible or the subcrestal placement of the implant can be performed, with the risk of greater bone loss during the formation of biological width [26]. Placing the neck of the implant at the correct depth has important aesthetic implications²⁷ since it allows the use of healing caps with an adequate emergency profile and substitution of the prosthetic part in the event of marginal tissue recession [22,28-30].

Type of Prosthetic Restoration

In general, when the planned prosthetic restoration is an overdenture or a fixed detachable prosthesis, the most suitable implant appears to be an STL implant. Since, in this type of restoration, it is feasible that the mucosa could be subjected to loads by the prosthesis. However, in a bone level implant, due to the apical position of the microgap, an anaerobic environment exists that could favor a more pathogenic bacterial composition, leading to peri-implantitis [28] Another related aspect is the type of union between the abutment and the prosthetic restoration and whether it is cemented or screwed in. Retaining the restoration involves positioning the shoulder of the implant to facilitate an adequate emergence profile and adequate soft tissue architecture.²² The two-piece bone-level implant is placed at the level of the bone crest, which is usually restored by means of screw-retained crowns because the unseen coronal margin can hinder correct seating of the crown, resulting in excess cement being left to damage the tissue [31]. In contrast, the STL implant offers more favorable characteristics for a cemented restoration, the margin is far from the bone crest, removal of the cement is feasible, the cemented crown is technically simpler to manufacture, and it offers better occlusal aesthetics and less maintenance [32].  In this way, although both implant systems render similar outcomes [33-35], prosthetic management may vary depending on the anterior or posterior location of the implant and whether or not it is submerged [36,37].                                   

Connection-Reconnection

Abrahamsson [38]. reported on the influence of connecting and reconnecting implant abutments on the health of the peri-implant tissues, as well as on the apical migration of the connective tissue of the mucosal barrier; similar observations were reported by Canullo [39,40]. More recently, Becker [41]. suggested that repeatedly reconnecting the abutments may be associated with dimensional changes of the peri-implant tissues. Although there is no clear evidence on the effect of this repetition at the marginal peri-implant bone levels [42-46], the most recent meta-analysis suggests it is necessary to choose the implant type during the planification protocol phase [47]. Indeed, the need to repair overdentures over time is constant. In this situation, STL offers advantages since it outdistances implant abutment junction. Similarly, in the case of fixed detachable prostheses, it is customary to disconnect the prosthesis during routine check-ups to assess the soft tissues [48-50]. Thus, move implant abutment junction away from the bone will favor maintenance of the bone level.                                    

Denture space 

Evaluating available restorative space is necessary during the diagnostic phase. Regardless of the type of restoration, fixed, fixed detachable, or removable, failure to consider this factor before the placing the implants can lead to structurally weakened prosthesis, invasion of the resting space, aesthetic difficulties, and compromised retention and stability of the prosthesis [51-55]. In case of overdentures, this aspect is more dramatic. A minimum vertical space of 13 or 14 mm is recommended for an overdenture supported by bars and 10-12 mm for individual attachments [56]. In the case of locator attachments, a minimum vertical space of 8.5 mm is required, corresponding to 1.8 mm to the polished neck of the implant, 1.5 mm from the height of the shortest attachment, 3.2 mm for the patrix part, and 2 mm of acrylic resin on the attachment [57]. The limitation of minimal available space may involve such complications as alveoplasty, increasing the vertical dimension of the occlusion, altering the occlusal plane, or selecting inappropriate attachments [57-59]. In cases of partial edentulism, if the space between the arches is limited by extrusion of the antagonists, the BL implant allows more space for the abutment and the prosthetic restoration. In such cases, the low height of the abutment offers little retention and should be screw-mounted. In general, the implant at the level of the tissues offers 1.8 mm less space, which is the minimum height of the polished portion of the implant neck.                   

Historically, evaluation of an implant system was based mainly on maintaining stable bone levels over time. However, current systems are a great improvement over the initial losses of 1.5 mm for the first year [60]. A systematic review⁸ revealed that both implant systems sustain acceptable levels of bone loss. Also, the implant survival rates are similar. Another evaluation by Andreassi [61]. Found no differences in the parameters studied (survival rate, success rate, such as bone resorption around the implant neck) between the two implant systems. Although many studies that have found statistically significant differences in peri-implant marginal bone loss, this difference may not be clinically significant [27]. A recent example is the study by Hadzik [62], which found less marginal bone loss in the BL implant than in STL implants; however, this difference was less than 0.5 mm, which is not relevant clinically. At this point, it does not seem that bone loss is the key factor when choosing between one types of implant over the other. Each individual case has different characteristics, and the best implant for each situation must be determined on a case-by-case basis. A flow chart can be made to determine where an STL or BL implant offers advantages, or where either approach would be sufficient in specific clinical situations (Figure 2). In this way, the clinician should follow a train of thought that will lead him or her to analyze the factors that indicate the best approach. In conclusion, all current implant approaches offer excellent results in terms of marginal bone maintenance and survival and success rates. Thus, the choice of one approach over another is based on the particular characteristics of each case. It is necessary to point out the heterogeneity of the studies reviewed and that prospective randomized studies are scarce. Therefore, the possible external evidence has a high risk of bias that should be taken into account when considering the conclusions of this review.

Figure 2:  Clinical decision-making flow chart.

All current implant approaches offer good results in terms of marginal bone loss and survival and success rate. The choice between BL or STL must be based on the particular characteristics of each case.

The authors report no conflicts of interest.

1. Misch CE. Contemporary implant dentistry. ed 3. St. Louis: Mosby. 2000;130-146
2. Buser D, Weber HP, Lang NP. Tissue integration of nonsubmerged implants. 1-year results of a prospective study with 100 ITI hollow-cylinder and hollow-screw implants. Clin Oral Implant Res. 1990;1: 33-40
3. Albrektsson T, Zarb G, Worthington P, Eriksson AR. The long-term efficacy of currently used dental implants: a review and proposed criteria of success. Int J Oral Maxillofac Implants. 1986; 1: 11-25.
4. Smith DE, Zarb GA. Criteria for success of osseointegrated endosseous implants. J Prosthet Dent. 1989; 62: 567-572.
5. Meijindert L, Raghoebar GM, Meijer HJ, Vissink A. Clinical and radiographic characteristics of single-tooth replacement preceded by local ridge augmentation: a prospective randomized clinical trial. Clin Oral Implants Res. 2008; 19: 1295-1303.
6. Adell R, Lekholm U, Rockler B, Branemark PI. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int J Oral Surg. 1981; 10: 387-416.
7. Gardner DM: Platform switching as a means to achieving implant esthetics. N Y State Dent J. 2005; 71: 34-37.
8. Vouros ID, Kalpidis CD, Horvath A, Petrie A, et al. Systematic assessment of clinical outcomes in bone-level and tissue-level endosseous dental implants. Int J Oral Maxillofac Implants. 2012; 27: 1359-1374.
9. Esposito M, Gruvosin MG, Chew YS, Coulthard P, et al. One-stage versus two-stage implant placement. A Cochrane systematic review of randomised controlled clinical trials. Eur J Oral Implantol. 2009; 2: 91-99.
10. Al-Nawas B, Kammerer PW, Morbach T, Ophoven F, et al. Retrospective clinical evaluation of an internal tube-in-tube dental implant after 4 years, with special emphasis on peri-implant bone resorption. Int J Oral Maxillofac Implants. 2011; 26: 1309-1316.
11. Lazzara RJ, Porter SS. Platform switching: a new concept in implant dentistry for controlling postrestorative crestal bone levels. Int J Periodontics Restorative Dent. 2006; 26: 9-17.
12. Jung RE, Jones AA, Higginbottom FL, Wilson TG, et al. The influence of non-matching implant and abutment diameters on radiographic crestal bone levels in dogs. J Periodontol. 2008; 79: 260-270.
13. Enkling N, Johren P, Klimberg V, Bayer S, et al. Effect of platform switching on peri-implant bone levels: a randomized clinical trial. Clin Oral Implants Res. 2011; 22: 1185-1192.
14. Canullo L, Quaranta A, Teles RP. The microbiota associated with implants restored with platform switching: a preliminary report. J Periodontol. 2010; 81: 403-411.
15. Strietzel FP, Neumann K, Hertel M. Impact of platform switching on marginal peri-implant bone-level changes. A systematic review and meta-analysis. Clin Oral Implants Res. 2015; 26: 342-358.
16. Lago L, da Silva L, Martinez-Silva I, Rilo B. Crestal bone level around tissue-level implants restored with platform matching and bone-level implants restored with platform switching: a 5-year randomized controlled trial. Int J Oral Maxillofac Implants. 2018; 33: 448-456.
17. Shea BJ, Reeves BC, Wells G, Thuku M, et al. AMSTAR 2: a critical appraisal tool for systematic reviews that include randomized or non-randomised studies of healthcare interventions, or both. BMJ. 2017; 21: 358.
18. Wells GA, Shea B, O’Connell D, et al. The Newcastle-Ottawa Scale (NOS) for assessing the quality of nonrandomised studies in meta-analyses. Available at: http://www.ohri.ca/programs/clinical_epidemiology/oxford. asp. Accessed May 30, 2020.
19. Tarnow DP, Cho SC, Wallace SS. The effect of inter-implant distance on the height of inter-implant bone crest. J Periodontol. 2000; 1: 546-549.
20. Rodriguez-Ciurana X, Vela-Nebot X, Segala-Torres M, Calvo-Guirado JL, et al. The effect of interimplant distance on the height of the interimplant bone crest when using platform-switched implants. Int J Periodontics Restorative Dent. 2009; 29: 141-151.
21. Misch CE. Endosteal implants for posterior single tooth replacement: alternatives, indications, contraindications, and limitations. J Oral Implantol. 1999; 25: 80-94.
22. Buser D, Martin W, Belser U. Optimizing esthetics for implant restorations in the anterior maxilla: anatomic and surgical considerations. Int J Oral Maxillofac Implants. 2004; 19: 43-61.
23. de Souza AB, Sukekava F, Tolentino L, Cesar-Neto JB. Narrow- and regular-diameter implants in the posterior region of the jaws to support single crowns: A 3-year splint-mouth randomized clinical trial. Clin Oral Implants Res. 2018; 29: 100-107.
24. Leblebicioglu B, Rawal S, Mariotti A. A review of the functional and esthetic requeriments for dental implants. J Am Dent Assoc. 2007; 138: 321-329.
25. Meijndert CM, Raghoebar GM, Santing HJ, Vissink A. Performance of bone-level implants with conical connections in the anterior maxilla: A 5-year prospective cohort study. Clin Oral Impl Res. 2020; 31: 173-180.
26. Hermann JS, Buser D, Schenk RK, Higginbottom FL. Biological width around titanium implants. A physiologically formed and stable dimension over time. Clin Oral Implants Res. 2000; 11: 1-11.
27. Buser D, von Arx T. Surgical procedures in partially edentulous patients with ITI implants. Clin Oral Implants Res. 2000; 11: 83-100.
28. Kumar VV, Sagheb K, Kammerer PW, Al-Nawas B. Retrospective clinical study of marginal bone level changes with two different screw-implant types: comparison between tissue level (TE) and bone level (BL) implant. J Maxillofac Oral Surg. 2014; 13: 259-266.
29. Grossberg DE. Interimplant papilla reconstruction: assessment of soft tissue changes and results of 12 consecutive cases. J Periodontol 2001;72:958-962
30. Canullo L, Rasperini G. Preservation of peri-implant soft & hard tissues using platform switching of implants placed in immediate extraction sockets: a proof- of concept study with 12-to-36 months follow-up. Int J Oral Maxillofac Implants. 2007; 33: 995-1000.
31. Staubli N, Walter C, Schmidt JC, Weiger R. Excess cement and the risk of peri-implant disease- a systematic review. Clin Oral Implants. Res 2017; 28: 1278-1290.
32. Jones AA, Cochran DL. Consequences of implant design. Dent Clin North Am. 2006; 50: 339-360.
33. Sanz M, Ivanoff CJ, Weingart D, Wiltfang J. Clinical and radiologic outcomes after submerged and transmucosal implant placement with two-piece implants in the anterior maxilla and mandible: 3-year results of a randomized controlled clinical trial. Clin Implant Dent Relat Res. 2015; 17: 234-246.
34. Ebler S, Ioannidis A, Jung RE, Hammerle CH. Prospective randomized controlled clinical study comparing two types of two-piece dental implants supporting fixed reconstructions – results at 1 year of loading. Clin Oral Implant Res. 2016; 27: 1169-1177.
35. Gamper FB, Benic GI, Sanz-Martin I, Asgeirsson AG. Randomized controlled clinical trial comparing one-piece and two-piece dental implants supporting fixed and removable dental prostheses: 4- to 6-year observations. Clin Oral Implants Res. 2017; 28: 1553-1559.
36. Belser UC, Mericske-Stern R, Bernard JP, Taylor TD. Prosthetic management of the partially dentate patient with fixed implant restorations. Clin Oral Implant Res. 2000;11: 126-145.
37. Mahn DH. Implant abutment and restoration design and risk factors for peri-implant disease. Compend Contin Educ Dent. 2019; 40: 572-577.
38. Abrahamsson I, Berglundh T, Lindh J. The mucosal barrier following abutment dis/reconnection. An experimental study in dogs. J Clin Periodontol. 1997; 24: 568-572.
39. Canullo L, Bignozzi I, Cocchetto R, Cristalli MP. Immediate positioning of a definitive abutment versus repeated abutment replacements in post-extractive implants: 3-year follow-up of a randomised multicentre clinical trial. Eur J Oral Implantol. 2010; 3: 285-296.
40. Canullo L, Tallarico M, Gracis S, Vela X. Clinical considerations on strategies that avoid multiple connections and disconnections of implant abutments. Int J Periodontics Restorative Dent. 2020; 40: 9-17.
41. Becker K, Mihatovic I, Golubovic V, Schwarz F. Impact of abutment material and dis/re-connection on soft and hard tissue changes at implants with platform-switching. J Clin Periodontol. 2012; 39: 774-780.
42. Alves CC, Munoz F, Cantalapiedra A, Ramos I. Marginal bone and soft tissue behavior following platform switching abutment connection/disconnection- a dog model study. Clin Oral Impl Res. 2015; 26: 983-991.
43. Bressan E, Grusovin MG, D´Avenia F, Neumann K. The influence of repeated abutment changes on peri-implant tissue stability: 3-year post-loading results from a multicentre randomised controlled trial. Eur J Oral Implantol. 2017; 10: 373-390.
44. Grandi T, Guazzi P, Samarani R, Garuti G. Immediate positioning of definite abutments versus repeated abutment replacements in immediately loaded implants: effects on bone healing at the 1-year follow-up of a multicentre randomised controlled trial. Eur J Oral Implantol. 2012; 5: 9-16.
45. Esposito M, Bressan E, Grusovin MG, D´Avenia F. Do repeated changes of abutments have any influence on the stability of peri-implant tissues? One-year post-loading results from a multicentre randomised controlled trial. Eur J Oral Implantol. 2017; 10: 57-72.
46. Praca LDFG. Teixeira RC, Rego RO. Influence of abutment disconnection on peri-implant marginal bone loss: A randomized clinical trial. Clin Oral Impl Res. 2020; 31: 341-351.
47. Koutouzis T, Gholami F, Reynolds J, Lundgren T. Abutment disconnection/reconnection affects peri-implant marginal bone levels: a meta-analysis. Int J Oral Maxillofac Implants. 2017; 32: 575-581.
48. Assaf A, Daas M, Boittin A, Eid N. Prosthetic maintenance of different mandibular implant overdentures: A systematic review. J Prosthet Dent. 2017; 118: 144-152.
49. Saleh MHA, Ravida A, Suarez-Lopez Del Amo F, Lin GH et al. The effect of implant-abutment junction position on crestal bone loss: A systematic review and meta-analysis. Clin Implant Dent Relat Res. 2018; 20: 617-633.
50. Sasada Y, Cochran DL. Implant-abutment connections: a review of biologic consequences and peri-implantitis implications. Int J Oral Maxillofac Implants. 2017; 32: 1296-1307.
51. Abujamra NF, Stravridakis MM, Miller RB. Evaluation of interarch space for implant restorations in edentulous patients: a laboratory technique. J Prosthodont. 2000; 9: 102-105.
52. Ahuja S, Cagna DR. Defining available restorative space for implant overdentures. J Prosthet Dent. 2010;104:133-136.
53. Lago L, Rilo B, Fernandez-Formoso N, Da Silva L. Implant rehabilitation planning protocol for the edentulous patient according to denture space, lip support, and smile line. J Prosthodont. 2017; 26: 545-548.
54. Hsu YT. A technique to evaluate the space for retentive components under a removable prosthesis. J Prosthodont. 2016; 25: 252-255.
55. Carpentieri J, Greenstein G, Cavallaro J. Hierarchy of restorative space required for different types of dental implant prostheses. J Am Dent Assoc. 2019;150:695-706
56. Sadowsky SJ. Treatment considerations for maxillary implant overdentures: a systematic review. J Prosthet Dent. 2007; 97: 340-348.
57. Lee CK, Agar JR. Surgical and prosthetic planning for a two-implant-retained mandibular overdenture: a clinical report. J Prosthet Dent. 2006; 95: 102-105.
58. Ahuja S, Cagna DR. Classification and management of restorative space in edentulous implant overdenture patients. J Prosthet Dent. 2011; 105: 332-337.
59. Chaimattayompol N, Emtiaz S, Woloch MM. Assessing the space limitation inside a complete denture for implant attachments. J Prosthet Dent. 2003; 89: 82-88.
60. Lago L, Da Silva L, Gude F, Rilo B. Bone and soft tissue response in bone level implants restored with platform switching: a 5-year clinical prospective study. Int J Oral Maxillofac Implants. 2017; 32: 919-926.
61. Andreasi Bassi M, Lopez MA, Confalone L, Gaudio RM, et al. A prospective evaluation of outcomes of two tapered implant systems. J Biol Regul Homeost Agents. 2016; 30:1-6.
62. Hadzik J, Botzenhart U, Krawiec M, Gedrange T, et al. Comparative evaluation the effectiveness of the implantation in the lateral part of the mandible between short tissue level (TE) and bone level (BL) implant systems. Ann Anat. 2017; 213: 78-82.