Bone damage associated with orthodontic placement of miniscrew implants in an animal model.

INTRODUCTION: The purposes of this study were to quantify bone damage associated with insertion of 2 types of miniscrew implants and to relate the amount of bone damage to monocortical plate thickness. METHODS: Nondrilling (n = 28) and self-drilling (n = 28) miniscrew implants (6 × 1.6 mm, Dentaurum, Newtown, Pa), and pilot holes (n = 26) were placed bilaterally in the maxillae and the mandibles of 5 adult dogs immediately after death. Bone blocks were cut, bulk stained with 1% basic fuchsin, embedded in methyl methacrylate, sectioned, and mounted. Monocortical plate thickness was measured adjacent to the miniscrew implant insertion site. Damage amounts were quantified at distances of 0 to 0.5 mm (adjacent region) and 0.5 to 1 mm (distant region) from the bone-implant interface. Total fractional damaged area (%), fractional microcracked area (%), and fractional diffuse damaged area (%) were quantified by using standard histomorphometric methods. RESULTS: The mean monocortical plate thickness of the specimens from the mandible (2.2 mm) was significantly (P <0.001) greater than that of the maxillary specimens (0.9 mm). In the mandible, the 3 damage parameters were greater with self-drilling miniscrew implants than with nondrilling miniscrew implants; however, there were no differences in the damage parameters in the maxilla. CONCLUSIONS: Bone damage accumulation is related to the type of miniscrew implant and the thickness of the bone.

Effect of zoledronic acid on bone healing subsequent to mini-implant insertion.

OBJECTIVE: To examine remodeling in bone supporting mini-implants by comparing a no drug (ND) group with a group that received a potent intravenous bisphosphonate in a canine model. MATERIALS AND METHODS: Twelve skeletally mature (2- to 3-year-old) male dogs were divided into two groups. Seven dogs were administered 0.1 mg/kg/mo of zoledronic acid (ZA) for 16 weeks, while five age-matched dogs received no drug. Two mini-implants (Tomas, Dentaurum, Newton, Pa) were placed unilaterally in the maxilla and mandible (4 mini-implants per animal × 12  =  48). Serial fluorescent bone labels were administered in vivo. Postmortem, the bone blocks containing the mini-implants were harvested and used for histomorphometric analyses at two regions of interest (adjacent: within 1 mm of interface; distant: 1-4 mm from the interface) supporting the mini-implant. Data were analyzed using mixed models. RESULTS: In general, the ZA group had a significantly lower bone formation rate than the ND group (P < .05) for all jaws/regions except for the adjacent region in the maxilla, P  =  .12. Despite the reduction, mean intracortical remodeling in the ZA group ranged from 35%-42% per year in the implant adjacent bone. This rate is substantially higher than that reported for noninjured sites in the jaw. CONCLUSIONS: Bone remodeling is typically elevated in implant supporting bone. After ZA administration, the healing response represented by elevated turnover in implant supporting bone was diminished but was not abolished.

Effects of short-term zoledronic acid treatment on bone remodeling and healing at surgical sites in the maxilla and mandible of aged dogs.

PURPOSE: It is unknown whether zoledronic acid (ZA) interferes with initial bone healing at extraction and implant sites. The goal of this study was to examine the effect of short-duration ZA on bone remodeling and healing after surgical insult in an aged dog model. MATERIALS AND METHODS: Four 2- to 3-year-old male dogs were administered ZA (0.1 mg/kg per month for 4 months), and 3 age-matched untreated dogs received no drug. In both groups, after the ZA-treated group had completed receiving the drug, the third premolar was extracted unilaterally and 2 orthodontic mini-implants per jaw per dog were placed on the ipsilateral side. After a 6-week healing period, a pair of calcein bone labels were administered. Bone sections from the mandible, maxilla, rib, and femur were obtained. The percent necrosis in the alveolar and basal regions of tooth-supporting bone was assayed by lactate dehydrogenase, and dynamic histomorphometric parameters were quantified and analyzed by use of mixed models. RESULTS: All extraction sites healed uneventfully, and no lesions resembling osteonecrosis were detected. The total percent necrosis was limited to less than 1% for all the bone sites examined. The ZA reduced bone remodeling at both surgical sites (extraction sites and mini-implant site) and nonsurgical sites. Although there was a significant (P < .05) increase in bone formation rate at the surgical sites in the untreated group, this increase was not significant (P = .3) in the ZA-treated group. CONCLUSIONS: Bone remodeling occurs in ZA-treated animals at surgical sites. ZA dramatically reduced bone turnover, but no exposed lesions resembling osteonecrosis developed at extraction and mini-implant sites after the 4-month drug duration.

Short-term zoledronic acid reduces trabecular bone remodeling in dogs.

The effects of zoledronic acid, a bisphosphonate, on the trabecular bone remodeling (TBR) of the mandibular condyle are unknown. The objectives of this study were to quantify and compare TBR in the mandibular condyle and vertebrae of 2- to 3-yr-old dogs and to evaluate the effects of short-term zoledronic acid on TBR. Bone samples from two, age-matched groups of dogs [seven dogs were given no treatment (NT group) and seven dogs were treated with four total infusions of zoledronic acid administered monthly (ZOL group)] were analyzed using histomorphometry. Trabecular bone remodeling and microarchitecture were quantified and analyzed statistically. Physiologic TBR, quantified in the NT group, was significantly higher (more than sixfold) in the vertebrae than in the mandibular condyle. Trabecular bone remodeling in the vertebrae of dogs of the ZOL group was 96% lower than in dogs of the NT group. By contrast, TBR in the mandibular condyle of dogs in the ZOL group was statistically equivalent to that of dogs in the NT group. Our results demonstrate that the physiological TBR in aged dogs is vastly different in the mandibular condyle compared to that in the vertebra. A higher level of physiologic TBR in the vertebra than in the mandibular condyle results in greater reduction of TBR in response to short-term treatment with zoledronic acid.