Effect of Implant Thread Design on Implant Stability Quotient (ISQ) in Early Healing Period

The Effect of Implant Macro-Thread Design on Implant Stability in the Early Post-Operative Period: A Randomized, Controlled Pilot Study

The purpose of this study is to determine whether implant thread design impacts bone remodeling and/or dental implant stability in the early healing period.

The population of this study will consist of a group of subjects who are interested in replacing two or more missing teeth with dental implants. All implant sites will be healed and not require bone augmentation for the placement of a standard 4 mm diameter implant. Subjects first will undergo a brief screening exam. If accepted, comprehensive oral exam will be completed. Subsequently, enrolled subjects will be scheduled for dental surgery to place the implant(s). Subjects will return weekly for the first 8 weeks after placement for a brief post-operative appointment in order to conduct measurements for the study.

Study Design/Sample. This study will be a prospective cohort study. The study sample will be derived from patients presenting to the study site in need of at least two dental implants and who satisfy the criteria listed below. The study site for this project will be University of California, Los Angeles (UCLA) Postgraduate Periodontics and Implant Surgery Clinic. Implant surgeries will be performed by postgraduate periodontal residents of this program. Any resident involved in this study will have had previous experience in placing dental implants. Also, the residents will be, at all times, under the supervision of attending faculty with extensive experience in dental implant surgery.

The implants to be used in this study are Easy (EZ) Plus and AnyRidge. Both implants are manufactured by Megagen Implants United Kingdom (UK) and are currently on the market. The EZ Plus fixture features a "conventional" macroscopic thread design with self-tapping threads with four cutting edges. The AnyRidge fixture features a unique knife-edge thread design. The company claims this thread design results in "maximum bone to implant contact (BIC), maximized compressive force resistance and minimized shear force production," thereby preventing a drop in stability in the immediate post-placement healing period. Both fixtures are manufactured with the same material and surface (Super Resorbable Blast Media (RBM) Surface). Therefore, the only difference between the two implants is the macroscopic thread design.

Potential implant sites will be evaluated clinically and radiographically to determine the amount and location of available bone for the placement of dental implant(s). Implant sites are deemed appropriate when bone height (crest of ridge to vital anatomic structure such as the mandibular nerve canal) is equal to or greater than the length of the proposed implant plus 2+mm (margin of safety). In the case of locations without vital anatomic structures, the bone height may be equal to the length of the implant. The width of available bone should be at least 3mm greater in diameter than the proposed implant (i.e. at least 1.5mm of bone on all sides of the implant). Thus, a 4mm diameter implant requires a minimum of 7mm width of bone (anterior-posterior and mesial-distal). Finally, two implants may be placed next to one another when the available bone meets the above criteria for two implants (i.e. two 4mm implants require 14mm of bone with 3mm bone between the implants). As an example of the required minimum measurement for two 4mm implants: (1.5mm + 4mm + 1.5mm) + (1.5mm + 4mm + 1.5mm) = 14mm.

Following an appropriate medical evaluation and comprehensive clinical and radiographic examination, treatment for patients selected for this study will be executed according to the following standardized protocol:

1. Alginate or polyvinyl siloxane (PVS) impression of maxillary and/or mandibular arch

2. Fabrication of a radiographic stent using [materials]

3. Cone Beam Computed Tomography (CBCT) scan (J. Morita, 3D Accuitomo 170) of implant site

4. Fabrication of a computer generated guide using (Megagen or Anatomage InVivo 5 implant planning software)

5. Guided surgical placement of dental implant(s) using (Megagen or Anatomage Surgical Guide) with a one-stage approach. The implant size (diameter and length) will be determined individually based on usual parameters of implant selection.

6. Resonance frequency analysis measurements using (Osstell ISQ meter). These measurements are done by connecting a metal post to the top of the dental implant. This post is then connected to the ISQ meter which resonates at a certain frequency and provides the operator with a numerical value correlating to the stability of the implant. Taking these measurements does not harm the patient or the implant in any way. This technology is in widespread use among clinicians as a means of assessing implant stability.

   1. Immediately after placement
   2. Weekly for the first eight weeks

Measuring implant stability quotient (ISQ) using resonance frequency analysis (RFA) is not considered "standard of care" but as data from this technology is collected, analyzed and published, it is conceivable that it may become a standard of care procedure for dental implants (e.g. at the time of implant placement and after a period of healing just prior to placing an implant restoration in function).

Whenever it is clinically acceptable to do so, patients needing more than one implant will receive both the EZ Plus implant and the AnyRidge implant, thereby serving as internal controls. Implants may be placed adjacent to one another and/or adjacent to remaining natural teeth. No sites will receive any type of implant-supported provisional restoration. All implants will receive a short healing abutment that protrudes through the gingiva but remains out of occlusion.

For patients requiring two implants, the type of the implant placed in the first site will be determined by a coin flip. The second implant placed will automatically be the other type. For patients requiring three or more implants, an analogous process will occur (i.e. coin flip to decide the first, third, etc. implant type; the second, fourth, etc. will automatically be of the other type).

Data Collection. Data will be collected in a standardized, coded fashion. Data collection sheets will be stored in a locked file cabinet at the study site. Data will be entered into a password-protected database. At the completion of the study including analysis and publication, the data sheets will be destroyed.

Limitations. The limitations of this study include examining only two macroscopic implant designs. Conclusions drawn from this study may guide future research projects with the ultimate goal of minimizing or eliminating the transient drop in implant stability following implant placement and establishing protocols for immediately loaded prostheses based in resonance frequency analysis.

Inclusion Criteria:

• Missing two or more teeth with a desire to receive an implant-supported or implant-assisted tooth replacement
• Healed maxillary or mandibular edentulous site for implant placement
• Sufficient bone volume in the site to allow implant placement without the need for bone augmentation

Exclusion Criteria:

• Systemic disease, medication, or habit known to negatively influence bone healing and/or dental implant success

  • Poorly controlled diabetes (HbA1c > 8%)
  • History of bisphosphonate use
  • History of head & neck radiation therapy affecting the proposed implant site
  • History of smoking >10 cigarettes/day (within past 12 months)
  • Current use of medications that adversely affect healing (e.g. corticosteroids, chemotherapeutic drugs)
  • Immune compromised condition (resulting from disease or treatment)

• Insufficient bone volume for dental implant placement

• Otherwise contraindicated to undergo periodontal / oral / implant surgery