Variable-thread Versus Standard Dental Implants for Replacing Missing Teeth

Introduction

Implant stability is a prerequisite for successful osseointegration and implant survival as implant micro-motion can compromise osseointegration and lead to implant failure. Maintenance of implant stability over time has been considered one of the implant success criteria that is identified at the primary or secondary level. Primary implant stability occurs as a result of bone compression and mechanical interlocking between implant surface and bone at the time of implant placement. Therefore, primary stability can be largely influenced by implant surface characteristics and implant design in terms of microstructure, thread design and geometry as well as bone quality and quantity. In contrast, secondary implant stability is a biologically mediated process by which bone matures and remodels at the bone-implant interface.

Primary and secondary implant stability remain the most relevant and reliable clinical indicator for long-term survival of dental implants. Hence modifications of surface characteristics and implant macro-designs were introduced over the last two decades to enhance osseointegration during the initial phase of healing. In this context, an implant design was recently introduced to improve primary stability particularly in areas of poor bone quality such as the posterior maxilla. The recently introduced implant has self-cutting self-drilling body with variable thread configurations that are designed to allow controlled compaction and condensation of bone during insertion thus enhancing the initial bone to implant contact. It is claimed that high primary stability is achieved by a controlled bone compaction and densification mechanism resulting from the double variable thread design and the apical sharp threads. In addition, the implant is made up of titanium-zirconium alloy that provide strength, high resistance to loading and biocompatibility. Its moderately rough hydrophilic sandblasted and acid-etched (SLActive) surface can also improve bone-implant contact during the early phase of osseointegration.

At present, there are limited number of studies that evaluated this variable-thread implant design. These studies were mostly experimental, of short duration and limited number of participants. Therefore, the aim of the present randomized controlled trial is to compare two implant designs (variable-thread versus standard) in terms of clinical, radiographic and patient-reported outcomes.

Objectives:

The aims of the present randomized controlled trial are:

• To evaluate implant stability.
• To evaluate the changes in peri-implant marginal bone level.
• To evaluate implant survival rates.
• To evaluate biological and technical complications during the follow-up period.

Inclusion criteria

• Aged more than 18 years.
• Good general health (ASA I or II, according to the American Academy of Anesthesiology).
• Require replacement of a posterior single missing tooth with a dental implant.
• Controlled oral hygiene (full-mouth plaque and bleeding scores ≤ 25% at baseline.
• Good compliance and commitment to attend follow-up review appointments.
• Willing to provide informed consent. Exclusion criteria
• A healing period of less than four months postextraction at implant site.
• Localized/generalized periodontitis.
• Bone metabolic disease and/or taking medications that affect bone metabolism.
• Long term use of non-steroidal anti-inflammatory medications.
• History of malignancy, radiotherapy or chemotherapy.
• Pregnant or lactating women.
• Severe bruxism or parafunctional habits.
• Large occlusal discrepancies.
• Smokers.