The assessment of periimplant soft tissue condition with morse taper abutment connection: a rapid review

Aim: This study aims to evaluate the clinical assessment results of periimplant soft tissue with morse taper (internal abutment connection). Methods: The study was conducted using a rapid review by searching the articles from PubMed NCBI and Cochrane by using keywords. All articles were selected by the year, duplication, title, abstract, full-text, and finally, all selected articles were processed for final review. Following clinical parameters were included; Periimplant Probing Pocket Depth (PPD), Plaque Score (PS), modified Plaque Index (mPI), Mucosal Thickness (MTh), Gingival Height (GH), periimplant mucosal zenith, Pink Esthetic Score (PES), Bleeding On Probing (BOP), Sulcus Bleeding Index (SBI), and modified Gingival Index (mGI). Results: 9 selected articles were obtained from the initial literature searching count of 70 articles. The overall samples included 326 morse taper implants. Based on the evaluation, 3 out of 4 articles reported pocket depth < 4 mm, no bleeding was reported in 2 out of 4 articles. 4 out of 4 articles reported low plaque accumulation, low soft tissue recession was reported in 3 out of 3 articles, and 4 out of 4 articles reported acceptable PES values. Conclusion: The evaluations indicate that the morse taper (internal abutment connection) has favorable assessment results based on various clinical parameters.


Introduction
Dental implants have been widely used for the replacement of missing teeth 1 . The survival rate of dental implant treatment for five years reached 96.3% 2 . However, this treatment still caused several complications such as; technical complications or screw loosening 8.8%; soft tissue complications 7.1%; marginal bone loss 5.2%; and aesthetic complications 7.1% 2 .
The implant system can be differentiated based on the material used in dental implants, surface topography, morphology, and geometry of the abutment connection 3 . The geometry of the abutment connection influences the incidence of screw loosening and may play a crucial role of the bacterial composition in the neck area of the implant 4 . The formation of microgap due to bacterial leakage on the abutment connection causes microleakage to occur 5 . Microleakage allows penetration and accumulation of bacteria through the microgap which leads the periimplant soft tissue inflammation 5 . Therefore, this can affect the stability of marginal bone, periimplant soft tissue, and aesthetics condition 5 .
Basically, the geometry of the abutment connection is divided into external connection and internal connection 1 . External connection was first implemented in the Branemark implant system and has a hexagonal structure 3,6 . Internal connection has several variants, including internal hexagon and morse taper 7 . Morse taper abutment connection that was placed in the anterior maxilla had the lowest global annual failure rate (0.2%) 8 . This design can reduce microgap and micromovement formation due to its ability to resist leakage 9 . Therefore, better load distribution on the abutment connection obtained and minimal marginal bone loss observed with morse taper 9 .
The stability of periimplant soft tissue is one of the key aspects of successful dental implant treatment because it provides sealing ability and stability of the marginal bone, prevents penetration of oral microorganisms, and enables good aesthetic results 10 . A considerable amount of literature from NCBI PubMed and Cochrane databases regarding morse taper internal abutment connection have been published. However, no previous study has been conducted using a rapid review method for evaluating the periimplant soft tissue. Based on the explanation that has been presented, this paper aims to systematically evaluate the clinical assesment results of periimplant soft tissue using morse taper (internal abutment connection) with the rapid review method.

Material and Methods
This rapid review was performed according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) statement ( Figure 1

Discussion
The examinations of PPD and BOP have been considered as the assessment to define a successful dental implant treatment [22][23][24]  This result might be explained by the concept of morse taper connection, which is a particular kind of internal abutment connection with a matching conical or taper shape and an equal angle (5-16° of conicity) between the wall of abutment and the implant 3 . This creates an intimate contact and a significant amount of mechanical friction locking. Hence, this design can stabilize under static load, eliminates microgap below dynamic load, and prevents micromovement 14 . Recent study reported that no type of abutment connection could 100% prevent microleakage 25 . However, the microgap formed in morse taper (2-3 μm) was smaller than in external connection (10 μm), which pointed out that morse taper had a better bacterial seal compared to the external connection 6,[26][27][28][29][30] . Bacterial contamination through microgap causes an inflamma-tory reaction in the periimplant soft tissue and triggers an osteoclastic process that may precipitate on marginal bone resorption around the implant 5,15,31 . Gingival recession due to bone resorption caused by the absence of supracrestal connective tissue as established in periodontal tissue leads the periimplant soft tissue to thoroughly rely on the supporting marginal bone 4 . This view is supported by the recent systematic review by Caricasulo et al. 9 (2018) who stated that the least marginal bone loss was found in the internal connection, especially in the morse taper.
Favourable periimplant soft tissue assessment results in this review are likely to be related to the optimal support from the marginal bone due to low bone resorption 13,15,17,20 . Consequently, a healthy periimplant soft tissue condition and a satisfactory aesthetic result will be obtained 15 . This is consistent with that of Kaminaka et al. 17 (2015) who concluded that morse taper was more effective in preserving the stability of the periimplant hard and soft tissue. Another factor that might influence this condition is the presence of platform switch, which is a concept of the placement of narrower diameter abutment. Therefore, if the bacterial contamination on the microgap persists; a certain distance between the microgap and the neck of the implant that attached to the marginal bone will be maintained 15 . Hence, minimal marginal bone resorption obtained and adequate biological width will be established 15 . This accords with another study by Macedo et al. 26 (2016), that reported low marginal bone resorption and wide biological width observed in apical and lateral directions with morse taper and platform switch abutment.
In this article, all types of abutment connections reported acceptable PES results 13,14,16,18 . However, only some appeared to be in healthy periimplant soft tissue conditions and some of the results showed the presence of bleeding on probing and pocket depth ≥ 4 mm which may lead to periimplant mucositis and periimplantitis 20,21 . According to some studies, there were several factors other than the variation of the implant abutment connection that may influence the PES results such as, the presence of implant thread, the surface roughness of the implant neck, tissue biotype, and the experience of the clinicians 15,16 . Dani et al. 32 (2018) found that higher soft tissue recession was observed with inexperienced clinicians after 3 years following implant placement. Time may also play as a contributing factor to this outcome. Cosyn et al. 18 (2016) stated that recession more than 1 mm was found in 3 out of 17 implants after 5 years following implant placement, which caused a significant change in PES results. This finding seems to be consistent with a study by Pozzi et al. 20 (2014) which stated that statistically significant results may be obtained by the longer research period.
High plaque accumulation within the study period may increase the risk of periimplant disease 33 . likewise, Dhir 34 (2013) and Prado et al. 25 (2016) stated that bacterial contamination might exist in the implant abutment connection causing fluid leakage into the microgap and reduce the mechanical friction between surfaces. Therefore, this could affect the periimplant soft and hard tissue condition 25,34 . Better sealing capability from morse taper can reduce microgap and prevent any leakage 6 . This view is supported by low plaque accumulation results around the periimplant soft tissue surfaces with morse taper in this review 14,18,35 . In contrast to earlier findings, recent study have failed to demonstrate significant changes of plaque index results between morse taper (0.64 ± 0.28) and internal connection (0.61 ± 0.36) 21 . Mishra et al. 6 (2017) stated that implant abutment connection plays an important role in preventing bacterial leakage. However, infiltration of inflammatory substances may occur regardless of the amount of plaque accumulation 6 . A possible factor that may increase the formation of biofilms other than the type of connection is the implant surface roughness ≥ 0.2 µm 34 .
A limitation of this study is that only a few articles have assessed the role of implant abutment connection towards periimplant soft tissue condition in 5 years follow-up period with comprehensive assessment and randomized control trial method. Another source of uncertainty is the varied specifications of morse taper that came from several implant systems. Therefore, it is difficult to determine which factors have a significant impact on the assessment results. Future researches on the current topic are therefore suggested.
In conclusion, the results of this evaluation indicate that the morse taper (internal abutment connection) has favorable assessment results based on various clinical parameters such as; PPD; PS; mPI; MTh; GH; periimplant mucosal zenith; and PES. The low percentage of bleeding around periimplant soft tissue surfaces were reported from the assessment of BOP, SBI, and mGI examinations.