International Journal of Oral & Maxillofacial Surgery
Volume 39, Issue 3 , Pages 282-286, March 2010

The influence of expansion on intraoperative bone blood flow in multisegmental maxillary osteotomies: an experimental study

  • W.B. Kretschmer

      Affiliations

    • Department of Oral and Maxillofacial Surgery, Marienhospital Stuttgart, Germany
    • Corresponding Author InformationAddress: Winfried Bernhard Kretschmer, Department of Oral and Maxillofacial Surgery, Marienhospital Stuttgart, Boeheimstr. 37, 70199 Stuttgart, Germany. Tel: +49 711 6489 8261; Fax: +49 711 6489 8262.
    • ,
  • G. Baciut

      Affiliations

    • Clinic of Cranio-Maxillofacial Surgery, University of Medicine and Pharmacy “Iuliu Hatieganu” Cluj-Napoca, Romania
    • ,
  • C. Dinu

      Affiliations

    • Clinic of Cranio-Maxillofacial Surgery, University of Medicine and Pharmacy “Iuliu Hatieganu” Cluj-Napoca, Romania
    • ,
  • M. Baciut

      Affiliations

    • Clinic of Cranio-Maxillofacial Surgery, University of Medicine and Pharmacy “Iuliu Hatieganu” Cluj-Napoca, Romania
    • ,
  • I. Barbur

      Affiliations

    • Clinic of Cranio-Maxillofacial Surgery, University of Medicine and Pharmacy “Iuliu Hatieganu” Cluj-Napoca, Romania
    • ,
  • A. Muste

      Affiliations

    • University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Romania
    • ,
  • K. Dietz

      Affiliations

    • Department of Medical Biometry, University of Tübingen, Germany

Accepted 23 December 2009. published online 25 January 2010.

Article Outline

Abstract 

The aim of the presented study was to investigate the effect of maxillary expansion in multisegmental Le Fort I osteotomies on bone blood flow. Five sheep underwent a three-piece total maxillary osteotomy. Bone blood flow was measured intraoperatively by laser Doppler flowmetry in the premaxilla, the lateral segments and the mandible before osteotomy, after osteotomy and segmentation as well as after 4mm, 8mm and 12mm expansion with a Hyrax screw. A significant reduction in blood flow was seen after osteotomy and segmentation with a factor of 3.10 and between 4mm and 8mm expansion with a factor of 1.81. No significant differences could be found between 0mm and 4mm widening or between 8mm and 12mm widening. These results suggest that expansion of more than 4mm in multisegmental osteotomies enhances the risk of avascular sequelae. As greater maxillary widening has been carried out in many cases without avascular complications, further research on additional factors, influencing the recovery of perfusion, is needed.

Key words: multisegmental maxillary osteotomy, orthognathic surgery, bone blood flow, laser Doppler, animal study

 

Surgical correction of severe dentofacial deformities often requires segmental maxillary osteotomy. A possible sequela of this technique is aseptic necrosis due to compromised blood supply of the maxilla14. Expansion of the segmented maxilla seems to be the highest risk for this complication8, 14. Basic research into bone blood flow after different osteotomies of the maxilla was carried out by Nelson et al. and Bell et al. in animal studies1, 3, 16. In Nelson's study with radioactive microspheres on macaque monkeys the perfusion of the alveolar bone decreased by 57% in the animals with intact descending palatine artery and by 89% when the artery was cut16. Owing to early recovery, avascular sequelae were not seen. No study has been performed on the effect of expansion on the bone blood flow in osteotomized segments. In contrast to the technique with radioactive microspheres, measurement of perfusion with a laser Doppler allows continuous recording without immediate death of the animal. Studies using laser Doppler flowmetry have shown the effects of segmented maxillary osteotomies on pulpal blood flow 1–7 days postoperatively6, 7, 11. Expansion of the maxilla was not reported.

The current study was designed to evaluate the effect of intraoperative expansion on the bone blood flow of the premaxilla and lateral segments during multisegmental Le Fort I osteotomies.

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Material and methods 

Five healthy adult sheep were used. The surgical procedures were performed in the operating theatre of the University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca.

Anaesthesia 

All animals initially received 0.2mg atropine. Anaesthesia was introduced giving Xylazin Bio 2% 3mg/kg and ketamin 0.2mg/kg as an i.v. bolus. According to the depth of anaesthesia, the i.v. boluses were repeated. Local anaesthesia with articain 4% was administered above the trachea, the cheeks and the maxilla. Tracheostomy was performed with an 8.5 Charrière preshaped tube. Crystalloid solutions were used for fluid maintenance.

Surgical technique 

To facilitate the surgical approach, the cheeks were incised on both sides. After circumvestibular incision, a complete Le Fort I osteotomy was performed as described by Bell et al. for humans2. A 12mm hyrax screw (Dentaurum Maxi, Ispringen, Germany) was adapted individually to the palate (Fig. 1). Segmentation was done between the second and third premolar through the infraorbital foramen on both sides and paramedially to achieve a three-piece maxilla (Fig. 2, Fig. 3). For the measurement of blood flow, two small holes were drilled anteriorly and distally to the vertical osteotomy on both sides in the cortical bone next to the apex of the adjacent tooth. As a reference point, an additional hole was drilled after a small vestibular incision in the anterior mandible (Fig. 2). For intrasurgical widening of the maxilla the adapted hyrax screw was fixed with a custom-made splint to the teeth of each lateral segment.

Blood flow measurement 

A laser Doppler flowmeter (Periflux PF 5001, Perimed, Järfälla, Sweden) was used to assess the bone blood flow in the maxilla and the mandible. Light with a wavelength of 780nm is produced by a 1mW He–Ne laser. A straight probe (PF 407, Perimed, Järfällä, Sweden) was used to conduct the light to the measurement site in the cancellous bone and to return the backscattered light to the flowmeter. The probe has a diameter of 1mm. The optical fibre has a diameter of 125μm, the fiber-to-fiber distance is 500μm. According to the Doppler effect, the amount of backscattered light is recorded by the flowmeter. The voltage of the produced output signal has a linear relation to the flow of the red blood cells (number of cells×average velocity). The perfusion units (PU) shown by the laser Doppler are a relative measurement of the blood flow. The data were collected on a wide band setting. A computer was connected to the RS-232 port of the laser Doppler for storage of the date and later analysis with the specific software (PeriSoft for Windows, Perimed, Järfällä, Sweden). To ensure reproducibility of the measurements, a probeholder (Perimed, Järfällä, Sweden) for the specific demands of the bone blood flow measurement was used (Fig. 4). The probe was calibrated before surgery with a plastic bloc (Perimed, Järfällä, Sweden) for zero voltage and a motility standard (Perimed, Järfällä, Sweden) for 250PU.

Procedure 

After incision of the upper and lower vestibule, the first measurements were taken at all five sites (T1). The next blood flow recording was made after Le Fort I osteotomy and segmentation of the maxilla (T2). Having adapted the hyrax screw after the second measurement, perfusion data were collected with 4mm widening (T3), 8mm widening (T4) and 12mm widening (T5) of the lateral segments. For each site, the data were registered continuously until at least 2min of stable values were seen on the screen.

Data analysis 

The mean perfusion was calculated for each session during the phase of stable values. Peaks due to movement artefacts were excluded. As the circulation in sheep during general anaesthesia is not as stable as in humans24, 25, the perfusion values of the upper jaw were also calculated as percentage of the actual perfusion of the mandible for statistical analysis. The perfusion of the left and the right maxilla and of the premaxilla and the lateral segments were compared with an analysis of variance. The factors of reduction of the perfusion between recording sessions T1 to T5 are given together with their 95% confidence intervals (CI). A probability of P<0.05 was considered significant.

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Results 

All animals survived until the end of the surgical procedures. The descending palatine artery was preserved in all cases. Medians and ranges of all measurement sites and time points are given in Table 1. To reduce the effect of blood pressure and depth of anaesthesia all data were calculated as the ratio between the observed perfusion value of the maxilla and the respective value of the mandible. The ratio showed no significant differences between the left and right sides (F=1.61, P=0.2077) (Fig. 5). No significant difference could be found between premaxilla and lateral segments (F=2.06, P=0.1552) (Fig. 6). The geometric means of the overall perfusion of the maxilla as ratio to the respective mandibular perfusion were 0.508 at T1, 0.164 at T2, 0.169 at T3, 0.097 at T4 and 0.087 at T5 (Fig. 7). The reduction of perfusion from T1 to T2 had a factor of 3.10 and was highly significant (P=0.0012). Between T2 and T3 and between T4 and T5 no significant reduction of the perfusion could be found. Pooling the data of T2/T3 and T4/T5, this factor was 1.81 with a high level of significance (95% CI 1.22–2.70; P=0.0099).

Table 1. Bone blood flow (medians and ranges) in perfusion units (PU).
SiteT1T2T3T4T5
Mandible68.3 (52–105.5)46.4 (25.7–90)61.2 (29.9–72.1)78.4 (39.3–114.1)67.9 (39–129.9)
Left premaxilla23.8 (20.1–38.3)6.6 (4.2–21)9.6 (3.3–36.3)5.3 (3.4–12.5)5.6 (3.1–11.7)
Right premaxilla52.2 (18.9–87.1)6.5 (2.4–33)9.4 (3.3–24.4)3.1 (1.6–15.7)7.7 (2.3–14.1)
Left lateral segment23.7 (20.1–117.7)13.4 (12.7–15.4)12.1 (2.2–14.6)12.2 (5.3–14.5)8 (3.6–14.4)
Right lateral segment35.8 (13.9–106.8)6.9 (2.5–14.5)6.6 (6–17.4)6.2 (2.7–14.9)9.5 (1.3–16.3)

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Discussion 

Simultaneous expansion of the maxilla in multisegmental Le Fort I osteotomies seems to be a major risk for avascular sequelae8, 14. Epker mentioned a risk of avulsing portions of the palatal pedicle, on expanding the maxilla more than 3–5mm8. The authors’ experiences have led to a limit of expansion set at 6mm in the molar region. No research has been done to provide evidence-based guidelines for the planning of expansion in multisegmental maxillary osteotomies. To investigate the effect of expansion on blood flow in the maxilla, continuous monitoring of the same subject is indispensable. Therefore, it is not possible to use microangiograms1, 3, 18, 22, histological examinations of the dental pulp17, 22, 28 or radioactive microspheres15, 16 as in other studies. Laser Doppler flowmetry is a reliable method for blood flow measurements in orthognathic surgery. In most of these studies, research was carried out on pulpal or gingival blood flow4, 5, 6, 7, 9, 10, 11, 13, 20, 27. The reproducibility was confirmed in the studies of Hellem et al.12, Firestone et al.9 and Buckley et al4. Measurement of the pulpal blood flow (PBF) has some disadvantages: orthodontic treatment has an effect on PBF9, 10 as well as the distance of the subapical osteotomy to the apex27, 28. Direct injuries of the teeth also influence PBF. Bone blood flow (BBF) of the maxilla in orthognathic surgery has not been measured with laser Doppler. Animal studies with dogs21, rabbits23, pigs12 and sheep24, 25 have shown the reliability of laser Doppler flowmetry for the measurement of BBF in the femoral head, tibia and mandible.

Most of the basic research in blood flow in orthognathic surgery has been done on monkeys1, 3, 15, 16, 18, 27. It is difficult to carry out research on large animals, other than pigs or sheep. Pigs were not considered suitable for multisegmental Le Fort I osteotomies because of their long upper canines. Successful maxillary osteotomies in sheep were reported by Rachmiel et al.19.

Several authors have shown, that the highest reduction of maxillary blood supply can be found during the first hours after Le Fort I osteotomy1, 3, 10, 15, 16, 18, 22. Dodson et al. emphasized the importance of the intraoperative dynamics of maxillary blood flow5. In order to assess the effect of maxillary widening on BBF, intraoperative measurement with a laser Doppler seems to be reasonable.

Segmentation of the maxilla in Le Fort I osteotomies leads to a further reduction of its blood flow. Emshoff et al. reported an adverse outcome in 16% of cases (14 patients) 3–5 days after surgery, whereas only 8% of the single-piece maxillary osteotomies (12 patients) showed similar values7. Adverse outcome was defined as a 40% decrease of PBF measured by laser Doppler flowmetry in this study. In a previous study by the same authors with 12 multisegmental maxillary osteotomies, the PBF of lateral incisors, canines and first premolars was still significantly reduced 4 days after maxillary osteotomy6. Two of 14 patients in the study by Ramsay et al. had avascular complications20. One patient showed grey discoloration of a central incisor. The second patient exhibited loss of periodontal support around both central incisors. Both underwent a two-piece Le Fort I osteotomy with expansion and had one descending palatine artery severed. A significant difference in the drop of blood flow between Le Fort I horseshoe and Le Fort I osteotomy was found by Harada et al. one day after surgery11. In none of these studies was the amount of expansion mentioned. In the presented study a significant reduction of BBF with a factor of 3.10 could be found after Le Fort I osteotomy with segmentation. With an expansion of 4mm no further impairment of the blood supply was found. This confirms the good long-term results of the animal studies with 2mm repositioning of the segments or less1, 3, 18, 22, 26, 27. Poswillo did not find normal pulp, 6 months after segmental osteotomy of the premaxilla with 10mm advancement in a study with Old World monkeys17. As these monkeys have a severe open bite, the conditions were closer to the reality in human orthognathic surgery. Although anterior repositioning of the anterior segment cannot be completely transferred to maxillary expansion, it is obvious that the palatal pedicle should not be stretched by 10mm or more. The most extensive report of aseptic necrosis following maxillary osteotomies is by Lanigan & West14. Only 2 of 36 cases were single-piece Le Fort I osteotomies. The amount of expansion was mentioned in three cases: 6mm, 12mm and 15mm widening. In the 6mm case, the descending palatine arteries were severed during surgery. Nelson et al. demonstrated the impressive effect of this vascular injury on the reduction of bone blood flow16. As the descending palatine arteries were not transected in any subject in the present study, the significant reduction in bone blood flow between T2/T3 and T3/T4 by a factor of 1.81 can be attributed to the expansion of the maxilla. These results support the findings of Epker8, that expansion of more than 4mm in multisegmental osteotomies enhances the risk of avascular sequelae. As maxillary widening of greater magnitude has been carried out in many cases without avascular complications, further research is indicated to investigate the correlation between maxillary expansion and recovery of BBF within the first days after surgery and other, yet unknown factors.

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Funding 

None.

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Competing interests 

None declared.

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Ethical approval 

Ethical approval was given by University of Medicine and Pharmacy “Iuliu Hatieganu” Cluj-Napoca, Romania and University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Romania.

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PII: S0901-5027(09)01225-9

doi:10.1016/j.ijom.2009.12.018

International Journal of Oral & Maxillofacial Surgery
Volume 39, Issue 3 , Pages 282-286, March 2010

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