Prosthetic abutment height and peri‐implant mucosal thickness are con‐ sidered factors that influence marginal bone remodeling during biological width es‐ tablishment around dental implants. However, no clinical studies have evaluated their simultaneous effect on marginal bone loss (MBL). This study analyzes the influence of abutment height on MBL around implants surrounded by both thin and thick mu‐ cosa up to 12 months after prosthetic loading.
Seventy platform‐switched implants with internal hex were placed equicrestally in two groups of patients with different vertical mucosal thick‐ ness: thin (≤2.0 mm) and thick mucosa (>2.0 mm). After three months of submerged healing, prosthetic abutments with a height of 1 mm (short) or 3 mm (long) were randomly assigned for single crown screwed restoration in both groups. MBL was evaluated on radiographs taken at implant placement (T0), restoration delivery (T1), and after 6 months (T2) and 12 months (T3) of loading.
After 12 months of loading, 66 implants were functioning (two dropouts, two failures), resulting in a 97% survival rate. Compared with T0, mean MBL at T3 ranged between 0.59 and 0.80 mm in short abutment groups and between 0.28 and 0.37 mm in long abutment groups. Differences resulted statistically significant, ir‐ respective of vertical peri‐implant mucosal thickness. The MBL pattern over time showed the greatest amount of bone resorption in the first 6 months after loading, particularly around implants with short abutments.
Platform‐switched implants restored with short abutments present greater marginal bone loss than identical implants with long abutments, without sig‐ nificant peri‐implant mucosal thickness effects.
abutment height, dental implants, marginal bone loss, platform switching, thick mucosa, thin mucosa
One of the main criteria for long‐term implant success has always been related to the limitation of marginal bone loss (MBL) around implant necks (Albrektsson, 1986). However, peri‐implant bone loss of 1.5–2.0 mm during the first year of loading and an annual bone loss thereafter of <0.2 mm has generally been considered acceptable for two‐piece implants. (Adell, Lekholm, Rockler, & Brånemark, 1981; Albrektsson et al., 1986). Despite numerous explanations, the multifactor etiology of MBL is not yet well understood (Oh, Yoon, Misch, & Wang, 2002; Tatarakis, Bashutski, Wang, & Oh, 2012).
Early marginal bone loss may be influenced by both surgical factors (overheating during site preparation, excessive cortical compression, insufficient crestal bone width and/or implant malpositioning, and implant crest module characteristics) and by prosthetic variables (type of implant/abutment connection, entity and location of implant/abutment microgap, multiple abutment disconnections, and cement remnants; Canullo, Bignozzi, Cocchetto, Cristalli, & Iannello, 2010; Oh et al., 2002; Qian, Wennerberg, & Albrektsson, 2012; Tatarakis et al., 2012). An important additional influence upon MBL around healthy implants is biologic width establishment following abutment connection (Broggini et al., 2006; Cochran, Hermann, Schenk, Higginbottom, & Buser, 1997; Eriksson, Nilner, Klinge, & Glantz, 1996; Hermann et al., 2001). More recent findings even suggest that early marginal bone resorption is influenced more by prosthetic rehabilitation characteristics than by the post‐surgical bone remodeling process, significantly increasing up to 6 months after functional loading before stabilizing (Galindo‐Moreno et al., 2015).
The influence of mucosal thickness upon MBL around implant necks was discussed by Cochran et al. (1997), suggesting that soft tissue creates a protective barrier against inflammatory infiltration toward the underlying alveolar bone. Later studies suggested that the vertical mucosal thickness necessary for biological width establishment around two‐piece dental implants should be at least 2 mm to avoid MBL (Linkevicius, Apse, Grybauskas, & Puisys, 2009; Suárez‐López Del Amo, Lin, Monje, Galindo‐Moreno, & Wang, 2016). Other studies suggested that a variable amount of MBL may occur to provide the necessary space for biological width establishment (Berglundh, Abrahamsson, & Lindhe, 2005; Hermann et al., 2001).
More recently, this concept has been re‐elaborated by Linkevicius, Apse, Grybauskas, and Puisys (2010), specifically stating that vertical keratinized mucosal thickness is a significant factor in limiting peri‐implant marginal bone loss around platform‐ switched implants placed at crestal level. One year after loading, implants with an initial vertical mucosal thickness greater than 2 mm maintained marginal bone levels more successfully than implants with an initial mucosal thickness ≤2 mm (Linkevicius, Puisys, Steigmann, Vindasiute, & Linkeviciene, 2015). Indirect confirmation of this concept was then provided by Vervaeke, Collaert, Cosyn, and Bruyn (2016), who concluded that initial peri‐implant bone remodeling was affected by mucosal thickness, even though initial mucosal thickness was not measured in their case series study. The authors postulated that abutment height was determined by mucosal thickness, as abutments were chosen at the time of implant insertion and their height was adapted to site‐specific mucosal thickness.
Furthermore, Galindo‐Moreno et al. (2014, 2016) demonstrated that abutment height may influence marginal bone level by showing that marginal bone is better preserved when abutments longer than 2 mm are used to restore multi‐unit screw‐retained implants. In these two radiographic retrospective studies, abutment height was not determined by mucosal thickness, which was neither recorded nor analyzed. In some cases, keratinized mucosa could be compressed apically by both short abutments and crown placement, reducing the distance from the prosthetic emergence profile to peri‐implant crestal bone (Collaert & De Bruyn, 2002).
In close agreement with these outcomes, a recent randomized clinical trial has shown that short abutments (1 mm) lead to greater MBL than long abutments (3 mm) around implants surrounded by thick mucosa (≥3 mm) after 6 months of prosthetic loading with screw‐retained rehabilitations (Blanco et al., 2018). This inverse correlation between MBL and abutment height has also recently been confirmed for implants restored with both single and multi‐unit cement‐retained prostheses (Spinato, Bernardello, Sassatelli, & Zaffe, 2017a,2017b; Spinato, Galindo‐Moreno, Bernardello, & Zaffe, 2018). Moreover, the use of long abutments seems to be more effective in preventing MBL when using platform‐switched implants than implants with a regular platform, probably due to a synergic action of the two aforementioned factors (Spinato et al., 2018).
However, to our knowledge, no studies are present in the literature considering the influence of abutment height on peri‐implant MBL, when abutment choice was not dictated by mucosal thickness. In other words, no evidence is available to discern if biological width establishment is actually influenced only by mucosal thickness, irrespective of prosthetic abutment characteristics.
Therefore, the primary aim of this present multicenter cluster randomized controlled study is to analyze the influence of abutment height on peri‐implant MBL around platform‐switched implants surrounded by thick or thin peri‐implant mucosa, up to 12 months after prosthetic loading. The null hypothesis of this study is that there are no differences in MBL around implants restored using short or long abutments, irrespective of vertical mucosal thickness and other clinical variables (sex, age, and oral hygiene).
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