J Adv Prosthodont.  2016 Feb;8(1):62-69. 10.4047/jap.2016.8.1.62.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

• Mohammed H
• Lee JH
• Bae JM
• Cho HW

• KMID: 2393197
• DOI: http://doi.org/10.4047/jap.2016.8.1.62

Abstract

PURPOSE
The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants.
MATERIALS AND METHODS
Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests.
RESULTS
The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05).
CONCLUSION
Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.

Keyword

Dental implant-abutment connection; Abutment screw length; Removal torque value; Cyclic loading

MeSH Terms

Axis, Cervical Vertebra
Crowns
Dental Implant-Abutment Design
Molar
Titanium
Torque*
Titanium

Figure

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  Fig. 1 (A) Schematic illustrations of the components of the implant, abutment and abutment screw in external hex implants. (B) Schematic illustrations of the components of the implant, abutment and abutment screw in internal hex implants. (C) Cross-sectional view of abutment-implant assemblies for external hex implants. (D) Cross-sectional view of abutment-implant assemblies for internal hex implants.

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  Fig. 2 (A) The abutment screws prepared for 8 different length groups. (B) Abutment-implant assemblies positioned in the resin block.

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  Fig. 3 (A) Tightening the abutment screw with an insertion torque of 20 Ncm using a hand torque wrench. (B) Digital torque gauge used in this study. (C) Removal torque value measurement using the digital torque gauge.

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  Fig. 4 (A) Specimen fixed on a jig for cyclic loading. (B) Schematic diagram of loading conditions. (C) Cyclic loading machine used in this study.

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  Fig. 5 Removal torque values of 8 screw groups before and after cyclic loading. * Significant at P < .05.

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  Fig. 6 Scanning electron micrographs of abutment screw surfaces (200 × original magnification): (A) Abutment screw in EH implants before cyclic loading. (B) Abutment screw in EH implants after cyclic loading. (C) Abutment screw in IH implants before cyclic loading. (D) Abutment screw in IH implants after cyclic loading.

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