Soyeon Kim,Joo Won Lee,Jae-Heon Kim,Van Mai Truong,Young-Seok Park
Assessing Microleakage at 2 Different Implant-Healing Abutment Interfaces
Microleakage,Osseointegration,Implant-abutment interface,Peri-implantitis
Objectives This study aimed to evaluate implants from different manufacturers and determine whether implant-healing abutment interface has a significant impact on implant seal. Methods An air-injection pressure measurement test was performed on implants with either line-contact (modified TSIII [TSM] and Bone Level Tapered [BLT]) or partial face-contact (BlueDiamond [BD], SuperLine [SL], ISII, and UFII) interface design from 6 different manufacturers. Forty implants per implant type were analysed. Pressure data were evaluated with Kruskal–Wallis test and Dunn's post hoc analysis (statistical significance was set at P < .05). Results BLT implants leaked when the mean pressure was increased to 199.9 kPa. The following implants showed mean leakage pressures of 182.9 (TSM), 157.4 (BD), 112.9 (SL), 101.8 (ISII), and 30.6 (UFII). There was a significant difference between line-contact and partial face-contact implants (P < .001). Conclusions The implant interface design has a significant impact on implant microbial leakage. Implants with a line-contact interface exhibited a higher resistance to leakage than those with partial face-contact.
Assessing Microleakage at 2 Different Implant-Healing Abutment Interfaces

This study aimed to evaluate implants from different manufacturers and determine whether implant-healing abutment interface has a significant impact on implant seal.

An air-injection pressure measurement test was performed on implants with either line-contact (modified TSIII [TSM] and Bone Level Tapered [BLT]) or partial face-contact (BlueDiamond [BD], SuperLine [SL], ISII, and UFII) interface design from 6 different manufacturers. Forty implants per implant type were analysed. Pressure data were evaluated with Kruskal–Wallis test and Dunn's post hoc analysis (statistical significance was set at P < .05).

BLT implants leaked when the mean pressure was increased to 199.9 kPa. The following implants showed mean leakage pressures of 182.9 (TSM), 157.4 (BD), 112.9 (SL), 101.8 (ISII), and 30.6 (UFII). There was a significant difference between line-contact and partial face-contact implants (P < .001).

The implant interface design has a significant impact on implant microbial leakage. Implants with a line-contact interface exhibited a higher resistance to leakage than those with partial face-contact.

Although state-of-the-art implant manufacturing techniques are implemented using modern technology, challenges related to 2-piece implants still remain. The formation of microdefects on the surfaces of implant and abutment components during milling and manufacturing processes results in “microgaps” at the implant-abutment interface (IAI).1, 2, 3, 4 These microgaps could be a reservoir for bacterial accumulation, peri‑implant bone loss, and peri‑implantitis., The sealing performances of implants with different IAIs were investigated in numerous studies both in vivo and in vitro.6, 7, 8, 9, 10 A systematic review on the performance of internal conical (Morse taper) implants in vitro showed that less leakage was observed in conical implants compared to nonconical implants. Internal conical implants also had a better fit and stability, demonstrating their high resistance to abutment movement, torque loss, and microgap expansion under loading situations. Based on these findings, it is evident that IAI geometry is a major contributor to microleakage. Previous studies aimed to minimise microleakage using sealants and by increasing torque settings and modifying implant designs.12, 13, 14 However, microgaps are still unavoidable and contribute greatly to the initiation of peri‑implant disease.15, 16, 17 Although healing abutments are used temporarily, implant-healing abutment interfaces are still prone to bacterial colonisation., Healing abutments undergo several processes of loosening and tightening, stimulating the infiltration of microbes. In addition, 1-stage procedures require a longer healing abutment retention time than 2-stage procedures, suggesting the need for a robust seal at implant-healing abutment interfaces., Thus, microleakage during healing abutment placement can be as critical as during permanent abutment placement. Based on a previous study, the area of contact between healing abutments and fixtures has a significant impact on implant seal. The latter studay refers to the discrepancies in implants as “line-contact” and “partial face-contact” for convenience. In line-contact implants, the abutment is fixed to the implant fixture at only the most coronal region of the 2 components. In partial face-contact implants, the contact between the implant and abutment is much greater than that of line-contact implants. Along with selecting appropriate implant interface designs, using sealants may enhance the sealing performance of implants. Antibacterial or silicone sealant applications on IAIs demonstrated a significant reduction in bacterial leakage.,, Minocyclie, a tetracycline family antibiotic, active against both Gram positive and Gram negative bacteria is frequently used to manage oral infections. Due to its antibacterial and anti-inflammatory characteristics, previous studies implemented minocycline coatings on implant surfaces to reduce infection and biofilm formation., The consistency of minocycline also provides a potential for a physical seal when applied to IAIs. To assess the effects of minocycline as a potential temporary sealant, leakage tests were performed on minocycline-applied implants. This study aimed to determine whether the findings of the current study are consistent with those of previous studies, which demonstrated the superiority of line-contact interfaces over partial face-contact interfaces in seal maintenance. The present study tested additional partial face-contact implants from 4 different manufacturers to ascertain that line-contact interface is preferable for leakage prevention. The effects of minocycline as a potential temporary sealant were also determined. The null hypothesis states that no significant difference exists amongst implants with different interface designs.

Air-injection pressure measurement tests were performed on 6 different implant systems (Table 1). Forty implants from different manufacturers were evaluated. The modified TSIII (TSM) and Bone Level Tapered (BLT) implants represent line-contact designs, whilst the others were characterised by partial face-contact designs. Two implants underwent surface treatments; BLT implants were anodised, whilst BlueDiamond (BD) implants were SLA-treated (sandblasted, large grit, acid-etched). The sample preparation methods and testing processes followed the protocol of a recently published study. Healing abutments were tightened to 10 Ncm. Cross-sections showing the IAIs of different implants are shown in Fig. 1. Fig. 2 shows a simplified diagram of the air-injection mechanism. The effects of minocycline (Minoden Dental Ointment; Osstem Implant) as a potential sealant was tested through an accelerated aging approach. Minocycline was applied on the healing abutment along the Morse taper of TSO implants (TSIII–original; Osstem Implant). These implants were referred to as TSOM implants for convenience. TSO implants are the original TSIII implants characterised by partial face-contact. These implants were only used to compare it with minocycline-applied TSO implants. An air-injection test was first carried out on 10 TSO implants. An accelerated aging test was carried out on 10 TSOM implants in a 60 ± 1 °C chamber (Incubator; Visionbionex), and the results were compared to those of TSO implants. The external temperature was set at 30 ± 1 °C. The implants underwent the same pressure measurement test under 3 different conditions: immediately, 10 days after, and 20 days after their removal from the chamber. Ten days in an accelerated aging test are equivalent to 3.5 months in real time and 20 days are equivalent to 7 months (Q10 = 2.0). All implants were left to cool before performing the pressure measurement test at room temperature.

Shapiro–Wilk normality test was performed on comprehensive air-injection pressure measurement data. Kruskal–Wallis test was also used, followed by a Dunn's post hoc test. Mann–Whitney test was applied for line-contact and partial face-contact comparison. P < .05 was considered statistically significant.

The null hypothesis proposed in this study was rejected. The test results revealed that there was a significant difference amongst the implant systems (Fig. 3). BLT implants exhibited the highest mean leakage pressure of 199.9 kPa (Table 2). The following implants showed a mean leakage pressure of 182.9 (TSM), 157.4 (BD), 112.9 (SuperLine [SL]), and 101.8 (ISII). UFII implants had the lowest mean leakage pressure (30.6 kPa). According to the post hoc analyses, 6 implant groups showed a significant difference amongst each other (P < .001), except the comparisons between ISII and SL implants and TSM and BLT implants. Line-contact implants (BLT and TSM) showed higher mean leakage pressures than partial face-contact implants, and these implants showed no significant difference from each other. BD showed the highest resistance to leakage amongst partial face-contact implants, but it still deviated significantly from 2 line-contact implants. Mann–Whitney test revealed that the 2 groups, partial face-contact and line-contact implants, differed significantly from each other based on IAI type (P < .001).

The experimental implants (TSOM) did not leak even when the pressure was increased to 689.5 kPa despite having gone through accelerated aging test for up to 20 days (7 months in real time). This test was terminated when no change in pressure was observed at an injection pressure of 689.5 kPa. However, the control group (TSO) demonstrated leakage when the mean pressure reached 84.8 kPa. A significant difference was observed between TSO and TSOM implants (P < .001).

This study aimed to determine whether the tendency of line-contact implants to be superior to partial face-contact implants in terms of seal preservation is applicable to various commercial implants from different manufacturers. The previous study carried out the air-injection pressure measurement test and microbial test on 3 implant systems only: TSO, TSM, and BLT implants. The present study expanded the number of participants to assess whether this is a general tendency and not only limited to implants from certain manufacturers. The results from both studies have revealed that line-contact implants were better for seal maintenance at the implant-healing abutment interface. Understanding the morphology of implants and the current manufacturing technology is crucial to explain the impact of IAIs on microleakage. The present study used the term “partial face-contact” to broadly define implants with visible area of contact between the implant and abutment. Theoretically, a partial face-contact design would provide a secure seal at IAIs. However, the results from the previous and present study demonstrated otherwise. With the current commercial machining techniques, it seems practically impossible to achieve a perfect fit in partial face-contact implants. Moreover, microdefects resulting from limited manufacturing skills can cause abrasions along the intaglio or inner surfaces of implants and outer surfaces of abutment when loosening and tightening. Thus, a misfit of the 2 components occurs, and this increases every time the implant is tightened and loosened, leading to microgaps. Microgaps seem to occur more frequently in partial face-contact implants where the area of contact is greater. Since the tested partial face-contact implants vary in size and the area of contact, the differences between the sealing performances of these implants may be affected by the area of contact. According to this assumption, partial face-implants with greater area of contact at the IAI are less likely to have a smoother surface. Given the test outcomes and current manufacturing technology, a line-contact design is better for healing abutment connection, which is characterised by minimal contact between the implant and abutment. Şen et al, also pointed out the misfit of 2-piece implants caused by manufacturing flaws, concluding that connection designs and abutment materials affect the implant sealing performances. Numerous factors besides IAI geometry could influence implant sealing. Torque values, for example, are thought to be one of the most significant factors that influence implant leakage. A 10-Ncm torque was applied in this study, similar to previous studies testing with healing abutments., Whilst higher torque values tend to be preferred for permanent abutment placements, ideal torque values vary depending on the implant system., On the other hand, healing abutments undergo a series of loosening and tightening, creating microdefects. The inner surface of implants should be well preserved for a reliable fastening of a definitive abutment. In addition, the same torque value was applied across all tested implants in this study. Therefore, the torque value was disregarded in this study. Another potential factor that could affect the sealing performances of implants would be the implant material. The healing abutment of TSM implants was composed of titanium, as most implants are. As opposed to other implants, the healing abutment of BD implants was composed of stainless steel. Whilst the 2 implants differ in interface design, there is a possibility that the composition of the healing abutment could have had an impact on implant sealing as well. According to some studies comparing titanium and stainless steel, stainless steel is as equally durable or even harder than titanium., Although this may suggest that stainless steel might be advantageous in minimising leakage, this brings us back to the problem with the current manufacturing technology. Any defects on metal surfaces would cause gaps at IAIs; thus, stronger materials are likely to cause more damage to the opposing material than relatively softer materials. Although healing abutments are ultimately replaced with definitive abutments, damage along the surface of fixtures caused by misfits between the healing abutment and fixture will still remain, forming microgaps even after the placement of definitive abutments. Therefore, the selection of abutment materials will be crucial in minimising microleakage. Similar to the use of gold crowns to minimise wear on opposing dentitions, a less rigid material could be preferred to prevent abrasion along IAIs. Moreover, the authors have come across a unique finding where surface treatment might have an impact on sealing performance as well. BLT (anodised) and BD (SLA), which received surface treatment, demonstrated better seals than other implant systems. This is just an observation that was difficult to explain since the surface treatment was not applied to both areas of contact. The correlation between surface treatment and implant seal may be an interesting topic of investigation for a follow-up study. A mini pilot study was performed in addition to the pressure test to see whether applying an antibiotic with potential sealing abilities would have an impact on implant leakage. The local delivery of minocycline is an effective treatment against peri-implantitis. Moreover, its long-acting bacteriostatic property, along with its ability to stimulate osteoblasts, has proven its efficacy on periodontal diseases., When minocycline was applied onto the implants in this study, its viscous consistency created a tight seal at IAIs. Although minocycline is expected to serve only as a temporary sealant, the results demonstrated its potential in preventing initial microleakage. However, in future studies, the accelerated aging test conditions could be improved. Since humidity was disregarded in this case, an accelerated aging test under humid conditions that mimic the oral cavity would help further support the results of this study. In addition, the long-term effects of minocycline in vivo are also necessary. Although minocycline is long-acting, it will deteriorate over time, giving only a temporary effect. Therefore, the feasibility of minocycline as a permanent sealant is still questionable. Although consistent outcomes were observed across 2 studies, the manufacturing conditions and machining qualities of experimental implants were not standardised because they were different. However, the air-injection pressure measurement test could serve as a basis for the development of a standardised test. Considering the limitation of the current manufacturing technology, it is not guaranteed that line-contact implants would always perform better than partial face-contact implants. Thus, if manufacturing technology improves to a point where flawless surfaces of metals could be produced, the outcomes might be altered. Another factor which should be taken in to account is the condition in which the experiment was carried out. The tests were performed under static situations. If possible, experiments under loading conditions should also be performed and compared with the results of this study.

This study distinguishes implant-healing abutment interface design based on the area of contact between the 2 components—“partial face” for greater surface area contact and “line” for contact limited to the coronal region. Results have shown that implant interface design has a significant impact on implant microbial leakage. Implants with line-contact design are more resistant to leakage than partial face-contact implants, and 2 possible factors leading to this conclusion are the current manufacturing technology of implants and implant material. The results of the side project have shown that minocycline could be used as a temporary sealant, but its long-term efficacy should be assessed further.

None disclosed.