Material and methods

Seven skeletally mature male beagle dogs, weighing between 20 and 25 pounds, were used in this experiment. All animals had fully erupted dentitions and were healthy. Housing, care, and experimental protocols were approved by the Institutional Animal Care and Use Committee at Texas A&M University, Baylor College of Dentistry in Dallas. During the experiment, the dogs were fed a soft diet to minimize damage to the orthodontic appliances.

After a 10-day quarantine, the animals fasted for 12 hours and then were sedated with an intramuscular injection of ketamine (8-24 mg/kg) mixed with xylazine (0.22 mg/kg). Dental prophylaxis using an ultrasonic scalar irrigated with 0.12% chlorhexidine gluconate was performed, and bone markers (6-mm long Imtec miniscrew implants; 3M Unitek, Monrovia, Calif) were placed for radiographic reference. Four markers were placed in the mandible, 2 on each side. The heads of the screws were removed to the level of the gingival tissue for animal comfort.

Right and left periapical radiographs were taken before and after bone marker placement using size 4 film. A custom holder was designed to standardize film and x- ray tube angulations and distances. To standardize intraoral measurements, notches were cut into the cusp tips of the canines and third premolars and at the most gingival aspect of the mesiobuccal groove of the first molars. Digital calipers were used to measure the distance between the canines and third premolars, as well as the distance between the third premolars and first molars. Three replicate caliper measurements were made for each distance and averaged. Triad custom tray material (Dentsply, York, Pa) was used to make mandibular impression trays, and alginate impressions of the mandibles were taken. The impressions were poured in die stone, and the models were used for appliance fabrication.

Appliances were designed based on an established protocol. Orthodontic band material (Dentaurum, Ispringen, Germany) was custom pinched and welded to fit the mandibular canines and third premolars. Headgear tubes (diameter, 0.051 indiameter) (3M Unitek) were soldered to the orthodontic bands on the third premolars.

Orthodontic wire (diameter, 0.045 in) was soldered to the canine bands and inserted through the headgear tubes on the bands of the third premolars ( Fig 1 , A ). The wire was designed to have a loop at the distolingual aspect of the canine band to attach a spring at the time of appliance delivery. The third premolars were able to move freely along the wire. The interior aspect of each band was microabraded before cementation. For animal comfort, a ball of solder was placed on the distal end of the wire.

A, Orthodontic appliance on a model before insertion and activation; B, surgical site after second premolar extraction and flap elevation; C, appliance in place and activated.

After initial sedation with the ketamine and xylazine cocktail previously described, the dogs were intubated and administered 1% to 1.5% isoflurane in oxygen at a rate of 1 L per minute. Vital signs were monitored throughout. Local anesthetic (2% lidocaine with 1:100,000 epinephrine) was administered at the surgical sites via regional infiltration and an inferior alveolar block.

Both mandibular second premolars were sectioned, elevated, and extracted. On the experimental side, chosen using an electronically generated random number table, a full-thickness mucoperiosteal flap was elevated from the distal aspect of the third premolar to the mesial aspect of the first premolar. A vertical releasing incision was made at the mesial limit of the flap that went past the keratinized gingiva and into the level of the buccal mucosa ( Fig 1 , B ). The tissue was reapproximated with simple interrupted 4-0 vicryl resorbable sutures.

A 12-fluted carbide bur was used to remove calculus and debris from the teeth and to cut retention grooves around the canines and third premolars. The teeth were etched with 37% phosphoric acid gel for 15 seconds. After irrigating and drying the teeth, the appliance was cemented as 1 unit on each side of the arch with light-cured RelyX Unicem (3M ESPE, St Paul, Minn) resin cement. Excess cement was removed to prevent gingival irritation.

The appliances were activated by attaching a 9-mm heavy nickel-titanium coil spring (3M Unitek) from the third premolar headgear tube attachment to the soldered wire loop on the canine using 0.012-in stainless steel ligatures ( Fig 1 , C ). The springs were activated to 200 g, which was verified with a Correx force gauge (Haag-Streit, Bern, Switzerland). Postoperative periapical radiographs were taken.

Immediately after surgery, the dogs were given 1 dose of ketoprofen (1 mg/kg intramuscularly). For the next week, they were also given postoperative analgesic (nalbuphine, 2 mg/kg intramuscularly) and antibiotics (clindamycin, 11 mg/kg intramuscularly) twice daily. Intraoral caliper measurements and periapical radiographs were taken every 2 weeks for 8 weeks after surgery. At each of these occasions, the nickel-titanium spring was checked and retied to ensure that it was delivering 200 g of force.

After 9 weeks of third premolar protraction (day 56), the animals were again sedated with the previously described ketamine and xylazine cocktail, and final records were obtained, including periapical radiographs, caliper measurements, and impressions. Surgical plane anesthesia was then confirmed, and the common carotid arteries were both cannulated, and the external jugular veins severed. An intracardial injection of 2 cm ³ of beuthanasia-D was given. After cessation of heart function was confirmed, approximately 1.5 L of saline solution followed by 1 L of 70% ethanol was flushed through the cannulas. The mandible was then harvested and stored in 70% ethanol.

Periapical radiographs were imported into Viewbox 4.0 (DHAL Software, Kifissia, Greece). The mesial and distal alveolar crest of the fourth premolar, mesial and distal root apices of the third premolar, and furcation of the third premolar were digitized ( Fig 2 ). The long axis of the third premolar was defined by a line extending from the midpoint between the root apices to the furcation. The angle formed by the long axis of the third premolar and the alveolar crest landmark was used to assess tipping. The midpoint of the furcal bone of the third premolar was calculated and used to assess translation of the tooth’s center of resistance. This midpoint was projected perpendicularly onto the plane defined by the alveolar crest landmarks, and the distance to the mesial crest of the fourth premolar was measured.

Radiographic landmarks and measurements. θ , The angle formed by the long axis of the third premolar and the alveolar crest landmark; d , the distance to the mesial crest of the fourth premolar.

After the animals were killed, all specimens were stripped of soft tissue, sectioned to fit into 27-mm wide microcomputed tomography tubes, and scanned using a microcomputed tomography 35 scanner (Scanco Medical, Basserdorf, Switzerland). The specimens were stabilized so that the occlusal plane was approximately perpendicular to the long axis of the specimen tubes, which were filled with 70% ethanol and sealed with Parafilm (Pechiney Plastic Packaging, Chicago, Ill).

The specimens were imaged at 30 μm resolution, 55 kVp, 145 μA, and 600 ms integration time. The images were smoothed with a Gaussian filter of sigma equal to 0.9 and support equal to 1. With the operator blinded, a medullary bone volume (1.4 × 1 × 3 mm) mesial to the third premolar was segmented (using a minimum threshold of 270) and analyzed with the microcomputed tomography software (version 6.0; Scanco). The medullary bone segment was located within the area of the surgical flap. It was the bone into which the third premolar was being moved. The inferior limit of the volume was located 25 slices apical to the third premolar distal root apex; the superior limit was 50 slices coronal from the inferior limit. It was within the center of the medullary bone, parallel to the lingual cortex ( Fig 3 ). Bone volume/total volume, apparent bone density, and material bone density were measured on both the control and experimental sides.

Area of medullary bone mesial to the third premolar assessed by microcomputed tomography. The area measured was approximately 1 × 3 mm, represented by the green box .

The specimens were cut to include bone immediately mesial to the mandibular third premolar and distal to the first premolar, from the alveolar crest to the level of the mental foramina. The specimens were decalcified in ethylenediaminetetraacetic acid, dehydrated in graded alcohol, cleared with xylene, and then infiltrated and embedded in paraffin. Using a coronal orientation, the block was sectioned into slices 5 to 10 μm thick, starting with the section closest to the mesial root of the third premolar. Every sixth slice was mounted, producing a total of 6 sections. These sections were mounted on glass slides and stained with hematoxylin and eosin to evaluate osteoclast populations. The slides were visualized and photographed under a microscope (Eclipse 80i; Nikon, Tokyo, Japan).

Results

After surgery, healing proceeded normally with no signs of swelling or infection. Four dogs had damaged appliances during the experiment, due to either bond failure or spring detachment ( Table I ). All appliances were repaired within 48 hours of when the damage occurred. Tooth movements of dog F were not evaluated, because of the number of appliance breakages that occurred and the aberrant tipping of the third premolars.

Intraoral caliper measurements showed that the third premolar was protracted mesially. Tooth movements followed a quadratic pattern, with significant side differences in the amount ( P <0.01) and rate of tooth movement ( P <0.05), for both intraoral measurements ( Table II ). Relative to the first molars, the third premolars moved 4.6 and 5.6 mm on the control and experimental sides, respectively ( Fig 4 , A ). Relative to the canines, the third premolars moved 3.1 mm on the control side and 3.9 mm on the experimental side ( Fig 4 , B ). The differences amounted to approximately 21.7% and 25.8% when measured relative to the first molars and canines, respectively. The relative overall difference in tooth movement, based on the average of the 2 estimates, was 25.3%.

Table II

Multilevel comparisons of control-side tooth movement and differences to experimental-side tooth movement (mm) with linear and quadratic estimates, and their standard errors

	Experimental-side tooth movement						Differences between experimental and control side tooth movement
	Intercept	SE	Linear	SE	Quadratic	SE	Intercept	SE	Linear	SE	Quadratic	SE
Caliper measures
Third premolar to canine	5.58	3.40e-1	1.89	2.19e-1	1.22e-1	5.05e-2	−9.30e-1	2.93e-1	−2.36e-1	1.20e-1	NS	NS
Third premolar to first molar	3.83	2.28e-1	1.38	1.47e-1	9.65e-2	3.38e-2	−6.37e-1	1.96e-1	−1.97e-1	8.01e-2	NS	NS
Radiographic measures
Linear movement	1.66	1.54e-1	9.90e-1	1.21e-1	1.44e-1	2.79e-2	−4.13e-1	1.61e-1	−1.20e-1	6.59e-2	NS	NS
Tipping	9.97	0.89	2.34	0.25	–	–	NS	NS	NS	NS	–	–

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. Effects of short-term in-vivo studies on orthodontic root resorption paradigms
2. Harms and adverse events in clinical research
3. Compliance with removable orthodontic appliances and adjuncts: A systematic review and meta-analysis
4. Lateral open bite and crossbite correction in a Class III patient with missing maxillary first premolars
5. Introduction to incidence rates and time-changing variables for cohort studies
6. Correlation between buccolingual tooth inclination and alveolar bone thickness in subjects with Class III dentofacial deformities

Stay updated, free dental videos. Join our Telegram channel

Join