Comparative Study on the Effect of Various Implant-Abutment Connections on Microbial Leakage

ABSTRACT

Background:

Microbial leakage at the implant-abutment interface can lead to peri-implantitis, jeopardizing the long-term success of dental implants. The design and type of implant-abutment connection play a significant role in minimizing this leakage.

Materials and Methods:

Thirty dental implants were divided into three groups (n = 10): group I – internal hex connection, group II – external hex connection, and group III – Morse taper connection. Each implant was inoculated with Escherichia coli bacteria and assembled under standardized torque. The assemblies were incubated for 7 days at 37°C. Microbial leakage was assessed by culturing samples from the external surfaces of each implant system on MacConkey agar. The bacterial growth was quantified by colony-forming units (CFU) analysis.

Results:

The microbial leakage was significantly different among the three groups (P < 0.05). Group II (external hex) exhibited the highest microbial leakage with an average CFU of 1.25 × 10⁶ followed by group I (internal hex) with 6.5 × 10⁵ CFU. Group III (Morse taper) demonstrated the least microbial leakage, with an average CFU of 1.8 × 10⁴ The Morse taper connection showed superior sealing ability compared to the other two connections.

Conclusion:

The type of implant-abutment connection significantly affects microbial leakage. Morse taper connections exhibit the least leakage and may be preferred to improve the long-term success of dental implants. Further clinical studies are required to corroborate these findings.

INTRODUCTION

Dental implants have become the gold standard for replacing missing teeth due to their high success rates and ability to restore function and aesthetics. However, long-term success depends on maintaining peri-implant tissue health, which can be compromised by microbial leakage at the implant-abutment interface.[1] Microbial colonization in this interface may lead to peri-implantitis, bone loss, and implant failure.[2,3]

The implant-abutment connection plays a pivotal role in preventing microbial leakage. Various connection designs, such as internal hex, external hex, and Morse taper, have been developed to improve the stability and seal of the implant-abutment interface.[4] The external hex connection, while historically popular, has been associated with a higher risk of micro-movement and bacterial infiltration due to its flat interface.[5] Conversely, internal hex connections provide improved mechanical stability but still exhibit some degree of microbial penetration.[6] Morse taper connections, known for their conical design and friction-fit mechanism, have been reported to minimize bacterial ingress due to a tighter seal.[7,8]

Understanding the relationship between connection types and microbial leakage is crucial for improving implant longevity. This study compares the microbial leakage in three widely used implant-abutment connections, namely internal hex, external hex, and Morse taper, under standardized in vitro conditions.

MATERIALS AND METHODS

Study design

This in vitro study was conducted to evaluate microbial leakage in three different implant-abutment connection types: internal hex, external hex, and Morse taper.

Sample preparation

Thirty dental implants (n = 10 per group) with abutments were selected and divided into three groups:

• Group I: Internal hex connection

• Group II: External hex connection

• Group III: Morse taper connection

All implants and abutments were of uniform dimensions (4.0 mm diameter and 10 mm length) and made from grade V titanium alloy.

Bacterial inoculation

• The bacterial strain Escherichia coli (ATCC 25922) was cultured in Luria-Bertani (LB) broth for 24 hours.

• Each implant fixture was filled with 10 μL of bacterial suspension (1 × 10⁶ CFU/mL) using a sterile micropipette.

• The abutments were assembled to the implants using a torque wrench with standardized torque (35 Ncm) as per the manufacturer’s recommendation.

Incubation

The assembled implant-abutment complexes were incubated for 7 days at 37°C in a sterile environment to allow microbial penetration. The assemblies were kept in microcentrifuge tubes with 2 mL of sterile LB broth covering the abutment.

Microbial leakage assessment

After 7 days, microbial leakage was evaluated using the following steps:

1. Sampling: 10 μL of the LB broth surrounding the abutment was collected and cultured on MacConkey agar plates.

2. Incubation: The plates were incubated at 37°C for 24 hours.

3. Colony Counting: The bacterial growth was quantified by counting colony-forming units (CFUs) using a digital colony counter.

Statistical analysis

The CFU values for each group were recorded and analyzed using SPSS software (version 26.0).

RESULTS

The microbial leakage was assessed by CFU analysis across the three implant-abutment connection groups: internal hex, external hex, and Morse taper. The results demonstrated significant differences in bacterial leakage among the groups [Table 1].

Table 1.

Microbial leakage (CFU/mL) across different implant-abutment connections

Group	Mean CFU/mL (±SD)	Range (CFU/mL)
Internal Hex	6.5×105±0.5×105	5.8×105–7.2×105
External Hex	1.25×106±0.6×106	1.1×106–1.4×106
Morse Taper	1.8×104±0.2×104	1.6×104–2.1×104

DESCRIPTION OF RESULTS

1. External Hex Group: The external hex group (group II) exhibited the highest microbial leakage, with a mean CFU of 1.25 × 10⁶ ± 0.6 × 10⁶. This group showed a wide range of bacterial leakage (1.1 × 10⁶–1.4 × 10⁶ CFU/mL).

2. Internal Hex Group: The internal hex group (group I) demonstrated lower microbial leakage compared to the external hex group, with a mean CFU of 6.5 × 10⁵ ± 0.5 × 10⁵. The range of bacterial leakage was narrower (5.8 × 10⁵–7.2 × 10⁵ CFU/mL).

3. Morse Taper Group: The Morse taper group (group III) exhibited the least microbial leakage, with a mean CFU of 1.8 × 10⁴ ± 0.2 × 10⁴ The bacterial leakage in this group ranged between 1.6 × 10⁴ and 2.1 × 10⁴ CFU/mL, indicating a significantly tighter seal.

DISCUSSION

Microbial leakage at the implant-abutment interface is a major concern in implant dentistry as it can lead to peri-implantitis and implant failure.[1] The implant-abutment interface acts as a reservoir for bacteria, which may cause inflammation in peri-implant tissues, compromising long-term stability.[2] The results of this study are consistent with previous studies highlighting that connection geometry plays a crucial role in minimizing bacterial penetration.[3]

The external hex connection demonstrated the highest microbial leakage in this study, with a mean CFU of 1.25 × 10⁶. This finding can be attributed to the flat mating surface and limited sealing ability of the external hex design, which increases micro-movements under functional loading and allows bacterial ingress.[4,5] Jansen et al.[6] similarly reported significant bacterial leakage in external hex connections, emphasizing their vulnerability to micro-gaps and leakage.

In contrast, the internal hex connection showed a moderate reduction in microbial leakage, with a mean CFU of 6.5 × 10⁵. The internal hex design offers better mechanical engagement and stability compared to the external hex, resulting in a reduced micro-gap.[7] However, studies have shown that despite improvements, internal hex connections may still permit bacterial infiltration due to micromotion and incomplete sealing under torque loads.[8]

The Morse taper connection exhibited the least microbial leakage, with a mean CFU of 1.8 × 10⁴ This superior performance can be attributed to the conical design and friction-fit mechanism of Morse taper connections, which create a tighter seal and significantly reduce micro-gaps.[9] Zipprich et al.[10] reported similar results, demonstrating that Morse taper connections exhibit minimal bacterial penetration due to their excellent sealing ability. Additionally, the absence of micromotion in Morse taper designs contributes to their superior performance, reducing the risk of bacterial ingress.[11]

CONCLUSION

This in vitro study provides valuable insights; however, its results may not fully replicate clinical conditions, where factors such as mastication forces and patient hygiene influence microbial leakage. Future studies should involve long-term clinical evaluations and explore the impact of dynamic loading on different implant-abutment connections.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.