Application of Light-cured Dental Adhesive Resin for Mounting Electrodes or Microdialysis Probes in Chronic Experiments

Summary

In this report, we propose a new application of light-curing dental resins for mounting base of electrodes or microdialysis probes in chronic experiments. This material allows direct bonding to the cranium.

Abstract

In chronic recording experiments, self-curing dental acrylic resins have been used as a mounting base of electrodes or microdialysis-probes. Since these acrylics do not bond to the bone, screws have been used as anchors. However, in small experimental animals like finches or mouse, their craniums are very fragile and can not successfully hold the anchors. In this report, we propose a new application of light-curing dental resins for mounting base of electrodes or microdialysis probes in chronic experiments. This material allows direct bonding to the cranium. Therefore, anchor screws are not required and surgical field can be reduced considerably. Past experiences show that the bonding effect maintains more than 2 months. Conventional resin's window of time when the materials are pliable and workable is a few minutes. However, the window of working time for these dental adhesives is significantly wider and adjustable.

Protocol

Step 1. Preparation of probe implantation

1. Anesthesia (not shown in the video)
   
   Anesthetize each bird with an interperitoneal injection of a ketamine (12.5 mg/kg body weight) and xylazine (25 mg/kg) mixture to produce a steady level of surgical anesthesia.
   
   
2. Fix a head to a stereotaxic frame
   
   Use Xylocaine^(TM) jelly to reduce local pains of ear bars' pressure. The head of bird is fixed in a stereotaxic apparatus consisting of ear bars and a beak holder that holds the head at a 45° angle. During the stereotaxic surgery for implantation, warm the body of bird by surgical pad with thermal control (temperature = 34~36°C).
   
   
3. Disinfect surgical area
   
   Disinfect the surgical field with isodine^(TM) prior to the surgery.
   

Step 2. Stereotaxic positioning

1. Reference point alignment
   
   Align dummy probe (glass micropipette) to the Lambda (Y-point) and mark Y-point with the dye-filled pipette. Remaining Dextran-TMR of the last tracer study was used in the video.
   
   
2. Incision of the skin
   
   Remove skin and expose the surface of the cranium. Then, clean the surface of the cranium with cotton swabs.
   
   
3. Positioning of dummy cannula (in horizontal direction)
   
   Move the dummy cannula to the target site (A-P axis and Lateral coordination)
   
   
4. Small craniotomy and incision of dura mater.
   
   Use a fine forceps for craniotomy and a fine injection needle (30 G) for incisions of the dura mater. Then, clean the surface of cranium.
   
   
5. Final positioning (implantation) of dummy cannula
   
   Locate the tip of the guide cannula at 0.30 mm above the microdialysis probe-intended target region. Finally, clean the surface of cranium again, because a clean and dry surface is required for tough bonding.
   

Step 3. Pretreatment of the cranial surface

(The similar procedure for "direct filling restoration" of the dental product shall be employed.)

1. Primer treatment
   1. Mix PRIMAR liquid A with B on a dish.
   2. Apply the mixture on the surface of the cranium with a small brush.
   3. Leave for 30 seconds.
   4. Dry with mild air stream. (Do not wash.)
      
      
2. Application of bonding agent
   1. Apply the bonding agent on the surface of the cranium with a small brush.
   2. Apply a gentle air stream. (Do not wash.)
   3. Light-cure for 20 seconds.
      

Step 4. Mounting composite resin

1. Mount resin with plain plugger
   
   If a Plain plugger is not available, a micro-spatula can be used instead.
   
   
2. Light curing
3. Incremental mounting
   
   Incremental mounting is recommended to ensuring complete reaction of the resin.
   
   For incremental mounting, apply bonding agent before every mounting.
   
   
4. Mold the composite resin and light-curing for final hardening.
5. End of the surgery

Clean the surgical area, apply antibiotic (Gentamicin ointment), and remove the animal from the stereotaxic flame. Then, keep the animal in a thermo-controlled chamber (temperature = 33-35° C) for post-anesthetic recovery.

As shown in the video, no abnormal behavior was observed in any of the animals on the next day after the surgery.

Discussion

Compared to the application of conventional self curing acrylic resins, the introduced technique has several important advantages:

1. Direct bonding:
Self curing acrylic can be attached to the bone for a while but it does not adhere to the bone. Therefore, anchorage screws are required to fix a mounting base (See Figure 2A). In contrast, light curing resin can bond to the bone directly so screws are not required (Figure 2B). Therefore, size of mounting base can be reduced considerab...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Bengalese finches	Animal			Two adult male , Body weight: 14.2 g and 14.8 g
Microdialysis probe	Tool	EICOM		total weight of probe, guide cannula, cap nut and dental adhesive resin: 0.65 to 0.78 g.
Light-cured dental adhesive resin system		Kuraray Medical Inc		+Light cured composite resin (CLEARFIL AP-X). +Dual-cure dental adhesive system with the self-etching primer and bonding agent (CLEARFIL Liner Bond IIΣ).
Surgical instruments				Stereotaxic frame, surgical microscope, thermal controlled surgical pad and thermal controlled recovery chamber. Plain plugger for handling composite resin. Microspatula or sharp curette to ablate periosteum and muscles.Injection syringe and needle (30G) for inducing anesthesia.Small scissors. Fine forceps for making small craniotomy.
Light-unit		Rolence Enterprise Inc	Ultra-Lite 500E
Microscope		Konan Medical	KOM300	with C-mount adaptor
3- CCD camera	Tool	Hitachi	HV-D30