Distraction osteogenesis: application to dentofacial orthopedics

Accelerated Bone Formation in Distracted Alveolar Bone After Injection of Recombinant Human Bone Morphogenetic Protein-2

BACKGROUND

This study evaluates the effect of recombinant human bone morphogenetic protein-2 (rhBMP-2) on the quality and quantity of regenerated bone when injected into distracted alveolar bone.

METHODS

Sixteen adult beagle dogs were assigned to either the control or rhBMP-2 group. After distraction was completed, an rhBMP-2 dose of 330 μg in 0.33 mL was injected slowly into the distracted alveolar crest of the mesial, middle, and distal parts of the alveolar bone in the experimental group. Histologic and microcomputed tomography analyses of regenerated bone were done after 2 and 6 weeks of consolidation.

RESULTS

After 6 weeks of consolidation, the vertical defect height in the middle of the regenerated bone was significantly lower in the rhBMP-2 group (2.2 mm) than in the control group (3.4 mm) (P <0.05). Additionally, the width of the regenerated bone was significantly greater in the rhBMP-2 group (4.3 mm) than in the control group (2.8 mm) (P <0.05). The bone density and volume of regenerated bone in the rhBMP-2 group were greater than in the control group after 6 weeks of consolidation (P <0.001).

CONCLUSION

Injection of rhBMP-2 into regenerated bone after a distraction osteogenesis procedure significantly increased bone volume in the dentoalveolar distraction site and improved both the width and height of the alveolar ridge and increased the bone density.

Quantitative histologic evidence of amifostine-induced cytoprotection in an irradiated murine model of mandibular distraction osteogenesis

BACKGROUND

Head and neck cancer management requires adjuvant radiotherapy. The authors have previously demonstrated the damaging effect of a human equivalent dose of radiation on a murine mandibular model of distraction osteogenesis. Using quantitative histomorphometry, the authors' specific aim was to objectively measure amifostine radioprotection of the cellular integrity and tissue quality of an irradiated and distracted regenerate.

METHODS

Sprague-Dawley rats were assigned randomly into two groups: radiotherapy/distraction osteogenesis and amifostine/radiotherapy/distraction osteogenesis, which received amifostine before radiotherapy. Both groups received a fractionated human equivalent dose of radiation prior to left mandibular osteotomy with fixator placement. Distraction to 5.1 mm was followed by a 28-day consolidation period. Quantitative histomorphometry was performed on left hemimandibles for osteocytes, empty lacunae, bone volume-to-tissue volume ratio, and osteoid volume-to-tissue volume ratio.

RESULTS

Amifostine/radiotherapy/distraction osteogenesis exhibited bony bridging as opposed to radiotherapy/distraction osteogenesis fibrous unions. Quantitative histomorphometry analysis revealed statistically significant higher osteocyte count and bone volume-to-tissue volume ratio in amifostine-treated mandibles compared with irradiated mandibles. There was a corresponding decrease in empty lacunae and the ratio of osteoid volume-to-tissue volume between both groups.

CONCLUSIONS

The authors have successfully established the significant osseous cytoprotective and histoprotective capacity of amifostine for distraction osteogenesis in the face of radiotherapy. The amifostine-sparing effect on bone cellularity correlated with increased bony unions and elimination of fibrous union. The authors posit that the demonstration of similar efficacy of amifostine in the clinic may allow the successful implementation of distraction osteogenesis as a viable reconstructive option for head and neck cancer in the future.

Cephalometric evaluation of airways after maxillary anterior advancement by distraction osteogenesis in cleft lip and palate patients: a systematic review

OBJECTIVE

This study was conducted to review the changes in airways after maxillary anterior advancement by distraction osteogenesis in patients with cleft lip and palate.

MATERIALS AND METHODS

Several electronic databases were searched. The selection criteria were set to include clinical trials and at least 1 year of postsurgical data. The original articles were then retrieved and evaluated by two investigators to ensure that they met the selection criteria. The references were also hand searched for possible missing articles.

RESULTS

Forty-three abstracts were found in the electronic searches. After the first set of selection criteria was applied to these abstracts, 14 articles were retrieved. After the final selection criteria, only four articles were finally selected. However, sample sizes of the selected articles were small, and the methodological quality of the studies was inadequate. All selected articles were consistent in that upper airway sizes increased and nasal resistance was reduced after distraction osteogenesis.

CONCLUSIONS

Despite the consistency of increasing the upper airway size and reducing nasal resistance in the only four found articles, limitations of the studies merit caution in interpreting these findings. We conclude that there are insufficient prospective randomized controlled clinical trials to confirm these results.

Clinical Applications of Orthodontic Microimplant Anchorage in Craniofacial Patients

Microimplant anchors, also known as temporary anchorage devices, mini- and micro-screws, have been used to enhance orthodontic anchorage for difficult tooth movements. Here, the authors describe how microimplants can be used to help treat craniofacial patients by supporting distraction osteogenesis procedures, maxillary protraction procedures, cleft segment expansion and stabilization, and tooth movement into narrow alveolar cleft sites. While most craniofacial patients are treated without microimplants, it would be worthwhile to identify which cases could benefit from microimplant anchorage. As an adjunct to orthodontic treatment, the microimplant offers a potential method for solving troublesome orthodontic and surgical problems such as guiding distraction procedures with orthodontics when primary teeth are exfoliating, addressing residual maxillary cants after vertical distraction osteogenesis of a ramus, stabilizing an edentulous premaxilla, and moving teeth into atrophic alveolar ridges. These cases are presented to open a dialogue on their possible uses in craniofacial patients.

Long-term stability after craniofacial distraction osteogenesis

PURPOSE

This study was conducted to systematically review long-term skeletal stability after craniofacial distraction osteogenesis.

MATERIALS AND METHODS

Several electronic databases (Old Medline, Medline, Medline In-Process and Other Non-Indexed Citations, Pubmed, Embase, Web of Science, and all EBM reviews [Cochrane Database of Systematic Reviews, ACP Journal Club, DARE, and CCTR]) were searched. Key words used in the search were "distraction," "osteogenesis," "craniofacial," "maxillofacial," "stability," "relapse," and "recurrence." MeSH terms and truncations of these terms were selected with the help of a health science librarian. Abstracts that appeared to contain at least 3 years of postsurgical data were selected. The original articles were then retrieved and evaluated to ensure that they actually had 3 years of data after craniofacial distraction osteogenesis. The references were also hand-searched for possible missing articles that were not indexed in the searched databases.

RESULTS

A total of 118 abstracts were found in the electronic searches. After the first set of selection criteria was applied on these abstracts, 22 articles were retrieved. After the final selection criteria were applied on these 22 articles, only 6 articles were finally selected. These 6 articles reported long-term stability after craniofacial distraction osteogenesis. Sample sizes were small, and the methodological quality of the studies was poor.

CONCLUSIONS

Although, based on the selected studies, craniofacial bone distraction osteogenesis appeared to show long-term stability; limitations of the studies merit caution in interpreting these findings. Some early relapse occurred in the first 3 years postdistraction, but stability was maintained thereafter. Some methodologically sounder studies are needed to confirm the present findings.

[Distraction osteogenesis in the treatment of facial and mandibular deformities]

<Zakljucak> Prikazani protokoli lecenja i kriterijumi uspesnosti svakako ce zahtevati dalje izmene i dopune, ali se mogu koristiti u buducim klinickim studijama u cilju obezbedjivanja objektivnih podataka. Buduci pravci razvoja kraniofacijalne OD ukljucuju: uticaj faktora rasta na OD, uticaj OD na kraniofacijalni skelet u procesu rasta, usavrsavanje tehnike osteotomije putem endoskopije, razvoj minijaturnih multidirekcionih distrakcionih uredjaja koji omogucavaju interceptivnu OD i modifikaciju i usavrsavanje protokola lecenja putem kraniofacijalne OD.

Mechanobiology of mandibular distraction osteogenesis: experimental analyses with a rat model

We analyzed mechanobiological influences on successful distraction osteogenesis (DO). Mandibular distraction surgeries were performed on 15 adult male Sprague-Dawley rats. Animals underwent gradual distraction (GD), progressive lengthening by small increments (5-day latency followed by 0.25 mm distractions twice daily for 8 days followed by 28-day maturation period). Distracted hemimandibles were harvested on postoperative days (POD) 5, 7, 10, 13, and 41. Load-displacement curves were then recorded for ex vivo distractions of 0.25 mm and stresses determined. Histologically, new bone formation appeared in GD specimens on distraction day 2 (POD 7), filling 50-60% of the gap by distraction day 8 (POD 13), with nearly complete bony bridging at end maturation (POD 41). Average tensile strains imposed by each incremental distraction ranged from approximately 10% to 12.5% during distraction days 2-8 and were associated with bone apposition rates of about 260 microm/day. Because this GD protocol was previously determined to be optimal for DO, we conclude that strains within this range provide an excellent environment for de novo bone apposition. Distraction caused tissue damage in distraction day 2, 5, and 8 specimens as evidenced by distinct drops in the load/displacement curves. Taken together, our interpretation of these data is that daily distractions cause daily tissue damage which triggers new mesenchymal tissue formation.

Orthodontic spring guidance of bilateral mandibular distraction in rabbits

Although distraction osteogenesis can lengthen congenitally small mandibles, the distraction procedure can be difficult to control. To study the efficacy and safety of orthodontic spring guidance on bilateral mandibular distraction, an 8-mm anterior open bite was experimentally produced and corrected during bilateral mandibular distraction in rabbits. Orthodontic springs were attached to the anterior maxilla and mandible to redirect an ongoing distraction procedure. Sixteen rabbits underwent mandibular distraction: 6 rabbits received heavy springs (8 oz), 6 rabbits received light force springs (2 oz), and 4 rabbits served as control animals with anterior open bites without spring guidance. Nickel-titanium springs were applied during the last week of osseous distraction and the first week of consolidation. Distractors were left in place throughout a 2-month consolidation period. None of the animals developed fibrous union as a result of spring guidance. The 8-mm open bite did not close in the control group or in the light spring group after 2 weeks of spring wear or during the consolidation period. Heavy springs completely closed the experimental open bites within 2 weeks (P <.01, analysis of variance). Bite corrections did not change during the consolidation period. This study indicated that the addition of an orthodontic spring to a mandibular distraction procedure did not impair bone healing. With the distraction device in place, heavy spring forces redirected an ongoing mandibular distraction procedure and corrected an open bite, distraction side effect. Direct measurements, radiographic measurements, and tissue histologic factors described changes in segment position and shape of the distraction site.

Bending of the distraction site during mandibular distraction osteogenesis in the rabbit: a model for studying segment control and side effects

PURPOSE

The purpose of this investigation was to develop an animal model for studying and correcting mandibular distraction side effects.

MATERIALS AND METHODS

Twenty-nine rabbits underwent bilateral mandibular distraction. Bending of the mandible was accomplished by offsetting a linear distraction by 35 degrees from the occlusal plane (4 screws per distractor), rotating the anterior segment inferiorly (2 screws per distractor), and removing a 3- or 6-mm wedge of the distraction site. The amount of bite opening varied according to the surgical design. Direct measurements, radiographs, and histology samples were compared.

RESULTS

Linear distraction produced a 4-mm anterior open bite and a Class III malocclusion after 2 weeks of distraction. Segmental rotation produced an 8-mm anterior open bite without complications. Removal of a wedge initiated rotation of the anterior segment. A large wedge (6 mm) produced fibrous union in the distraction site. The amount of bite opening or closure depended on the number of surgical screws and position of the distractor. Serial histologic sections showed bone formation at the rotated, triangular distraction site.

CONCLUSION

Bite opening or closure can occur from loss of segment control or by altering surgical design. This information is needed to counter unwanted side effects or to plan segment rotations.

Craniofacial distraction osteogenesis: a review of the literature: Part 1: clinical studies

A review of the literature dealing with distraction osteogenesis (DO) of the craniofacial skeleton, provided by a PUBMED search (National Library of Medicine, NCBI; revised 3 April 2000) from 1966 to December 1999 was conducted. Key words used in the search were distraction, lengthening, mandible, mandibular, maxilla, maxillary, midface, midfacial, monobloc, cranial, craniofacial and maxillofacial. This search revealed 285 articles. One hundred and nine articles were clinically orientated and were analysed in detail in this study. The type of distraction, indications, age, type of surgery, distraction rates and rhythms, latency and contention periods, amount of lengthening, follow-up period, relapse, complications and the nature of the distraction device were analysed. This review revealed that 828 patients underwent DO of the craniofacial skeleton; 579 underwent mandibular DO, 129 maxillary DO, 24 simultaneous mandibular and maxillary DO and 96 midfacial and/or cranial DO. Craniofacial DO has proven to be a major advance for the treatment of numerous congenital and acquired craniofacial deformities. Treatment protocols and success criteria for craniofacial DO are suggested on the basis of these results. There is still, however, a lack of sufficient data, especially on follow-up and relapse, so that treatment strategies have to be validated by long-term studies in the future.