ABSTRACT
To investigate the effectiveness and periodontal side effects of laser circumferential supracrestal fiberotomy (CSF) and low-level laser therapy (LLLT) on orthodontically rotated teeth in beagles.
Eighteen mandibular incisors from nine dogs were divided into three groups by treatment (n = 6/group): A, orthodontic couple force application only (control); B, laser CSF following orthodontic couple force application; and C, LLLT following orthodontic couple force application. Both mandibular lateral incisors were rotated for 4 weeks, and the relapse tendency was observed for 4 weeks more without any retainers. The amount of relapse, sulcus depth, and gingival recession were measured at weeks 4 and 8. One-way analysis of variance (ANOVA) and Scheffé's post hoc test were used for data analysis. Tissue specimens were examined at week 8 under light microscopy after hematoxylin-eosin (H&E) and Masson's trichrome staining.
The mean percentage of relapse was 41.29% in group A, 14.52% in group B, and 56.80% in group C (P < .001). Four weeks after laser CSF, the sulcus depth increased by 0.67 mm, but no gingival recession was observed. There was no significant difference between groups A and C in terms of sulcus depth and gingival recession.
Laser CSF is an effective procedure to decrease relapse after tooth rotation, causing no apparent damage to the supporting periodontal structures, whereas LLLT on orthodontically rotated teeth without retainers appears to increase the relapse tendency.
INTRODUCTION
Stability of rotated teeth is a concern in orthodontic treatment. A significant cause of relapse is thought to be the gingival and transseptal fibers of the periodontium, which are stretched and twisted as the tooth is rotated.1–3
To relieve the rotated tooth from forces exerted by the stretched fibers, circumferential supracrestal fiberotomy (CSF) was introduced.4,5 In simple CSF using a scalpel blade, intergingival, transgingival, transseptal, and semicircular fibers are transected. CSF appears to help the tissue remodel and decrease relapse of orthodontically rotated teeth. The literature indicates that periodontal problems such as pocket formation, loss of attached gingiva, and gingival recession do not occur after CSF.6
However, conventional CSF has some clinical drawbacks: poor patient acceptability as an invasive procedure, and it is feasible only on teeth with a healthy periodontium. This lack of patient acceptance despite its demonstrated advantage suggests that an alternative technique needs to be considered. In 1990, Frick and Rankine7 demonstrated that electrosurgery is as effective as the conventional procedure for CSF, yet causes less bleeding and infection.
Laser offers numerous advantages compared with surgery. It offers biostimulatory effects, coagulates blood vessels, seals lymphatics, and sterilizes the wound during ablation while maintaining a clear, clean, surgical field.8,9 There is markedly less bleeding, minimal swelling, and less postoperative infection.10 Laser CSF is expected to prevent relapse of orthodontically rotated teeth in addition to the advantages offered by the properties of laser.
Low-level laser therapy (LLLT) has biostimulatory effects such as stimulation of wound healing, collagen synthesis, and acceleration of bone remodeling during tooth movement.11–13 However, its effects on the relapse tendency of orthodontically rotated teeth have not been fully characterized.
Therefore, this study was conducted to evaluate the effectiveness and periodontal side effects of laser CSF and LLLT on orthodontically rotated tooth. The specific aims were to compare the (1) amount of relapse, (2) sulcus depth, (3) gingival recession, and (4) connective tissue rearrangement.
MATERIALS AND METHODS
Nine domestic male beagles, each weighing about 10–13 kg and aged 12–18 months were used. Eighteen mandibular lateral incisors were divided into three groups (n = 6/group), as follows: A, orthodontic couple force only (control); B, orthodontic couple force with laser CSF; and C, orthodontic couple force with LLLT. This project was approved by the Kyung Hee Medical Center Institutional Animal Care and Use Committee.
Experimental Tooth Movement
Both mandibular lateral incisors were selected as the experimental teeth. Each dog was sedated with Zoletil 50 (Virbac Lab, France; 0.25 mg/kg, IM). A shallow groove was made on the facial enamel at the crest of the marginal gingiva as reference for measurement of the amount of gingival recession. Another groove was made on the incisal edge, and shallow pits were made on both second premolar cusp tips to measure the amount of rotation.
Orthodontic buttons (Ormco Corp, Orange, CA) were bonded to the labial and lingual surfaces of the experimental teeth and the labial surfaces of the mandibular canines with Superbond C&BR (Sun Medical Co, Moriyama, Japan). Elastic chains were engaged between buttons to create rotational couple forces (Figure 1). Each of these elastic chains exerted forces of around 50 gm. By grinding the incisal surfaces of the maxillary incisors, the experimental teeth were maintained out of occlusion. Rotational movement was accomplished within 4 weeks. The appliances were checked once a week to change the elastics.
Photographs of orthodontic buttons with elastic chains. (A) Occlusal view. (B) Frontal view.
Photographs of orthodontic buttons with elastic chains. (A) Occlusal view. (B) Frontal view.
After 4 weeks, the orthodontic couple forces were removed. No surgery was performed in group A, laser CSF was performed immediately after removing the orthodontic appliances in group B, and LLLT was carried out every 3 days for 4 weeks on group C. No retainer was used in any group. Rotational relapse of the experimental teeth were evaluated over a short observation period (4 weeks).
Laser Supracrestal Fiberotomy
A gallium-aluminum-arsenide (Ga-Al-As) diode laser (SoftLase Pro; Zap Lasers, LLC, Pleasant Hill, Calif) with an 808-nm wavelength and 0.4-mm fiber diameter was used. Infiltration of 2% lidocaine (YuHan Co, Seoul, Korea) with 1:100,000 epinephrine provided local anesthesia during the procedure. Immediately before laser CSF was performed, the sulcus depth of each tooth was measured. The maximum depth of insertion of the fiber tip was determined to be the sum of the sulcus depth and biologic width (∼2 mm).14,15 The laser tip was inserted into the gingival sulcus to the level of the alveolar bone crest, and the incision was extended around the tooth circumference with the system configured to the soft tissue cutting mode (continuous wave; 1.2 W). Postoperative care included gentamicin (Daesung Co, Seoul, Korea; 0.1 ml/kg) injection for one day.
Low-Level Laser Therapy
The biostimulation mode (pulsed wave, 10 Hz, 763 mW, 4.63–6.47 J/cm2) was used for irradiation, with the fiber tip held 2–3 mm away from the gingiva. The coronal and apical thirds of the mesiobuccal, distobuccal, mesiolingual, and distolingual sides of the roots (totaling 8 regions) were irradiated every 3 days for 30 seconds each for 4 weeks.
Amount of Relapse
We took alginate (GC Co, Tokyo, Japan) impressions on day 1, and at weeks 4 and 8. On the original, rotational, and relapse casts, a sharp pencil line was drawn on the groove of the incisal edge of the experimental tooth, and dots were marked in the shallow pits of the mandibular second premolar cusp tips. The line linking both these cusp tips was used as the reference line.
Each cast was placed on a prosthetic surveyor (the posterior occlusal plane and the incisal plane were positioned parallel to the floor) and photographed with constant magnification on a Kaiser copy stand (Kaiser Fototechnik, Boston, Mass) (Figure 2). From the photographs, the original, rotational, and relapse angles were measured by using lines superimposed on the reference line and incisal edge line (Figure 3). Double-determination measurements were performed by two investigators independently.
The cast was placed on a prosthetic surveyor and photographed on a Kaiser copy stand. (A) Kaiser copy stand. (B) Prosthetic surveyor with dental cast.
The cast was placed on a prosthetic surveyor and photographed on a Kaiser copy stand. (A) Kaiser copy stand. (B) Prosthetic surveyor with dental cast.
Pocket Depth and Gingival Recession
A periodontal probe was used to measure the pocket depth and gingival height on day 1, and at weeks 4 and 8. The pocket depths were recorded on the mesiolingual, lingual, distolingual, mesiolabial, labial, and distolabial surfaces of the experimental teeth. The amount of gingival recession was measured from the shallow horizontal groove in the facial enamel, corresponding to the preoperative level of the free gingival margin.
Histologic Examination
All experimental animals were euthanized by direct injection of Zoletil 50 (50 mg/kg) (Virbac Laboratories, Carros France) into the heart at week 8. Tissue blocks were fixed in 10% neutral buffered formalin and decalcified in 10% ethylenediaminetetraacetic acid (EDTA) solution. Paraffin blocks were sectioned perpendicular to the long axis of the experimental teeth, and the specimens were examined under light microscopy following hematoxylin-eosin (H&E) and Masson's trichrome staining.
Statistical Analysis
Data analysis was conducted using one-way analysis of variance (ANOVA) and Scheffé's post hoc test. A P value less than 0.05 was considered statistically significant.
RESULTS
The degree of initial rotation and relapse, and rate of relapse are shown in Table 1. The mean (± SD) degree of rotation after 4 weeks was 15.42° ± 2.60° in group A, 18° ± 4.98° in group B, and 17.25° ± 3.37° in group C, without statistically significant differences (P < .05). The mean degree of relapse was 6.42° ± 1.72° in group A, 2.58° ± 0.86° in group B, and 9.75° ± 2.44° in group C. The mean percentages of relapse were 41.29° ± 5.65%, 14.52° ± 3.59%, and 56.80° ± 10.98% in groups A, B, and C, respectively (Figure 4). The mean degree and mean percentage of relapse were statistically different (P < .001).
Percentage of relapse in the control, laser CSF, and LLLT groups. Asterisk indicates a significant difference between groups (P < .001). Values are mean ± SD.
Percentage of relapse in the control, laser CSF, and LLLT groups. Asterisk indicates a significant difference between groups (P < .001). Values are mean ± SD.
The Means of Rotational Movement of Teeth in Each Group Tested by One-Way ANOVA and Scheffé's Post Hoc Comparison

Figure 5 shows the average sulcus depth. All groups showed increased sulcus depth at week 4, which tended to decrease at week 8. In group B, the initial mean sulcus depth of 1.97 mm increased, reaching 3.14 mm at week 4, subsequently decreasing to 2.64 mm at week 8. Only in group B, pocket depth increased by 0.67 mm at week 8 compared with the initial level. No gingival recession was observed in any group (Figure 6). All groups showed gingival swelling due to wearing the orthodontic appliances for 4 weeks. However, after debonding, gingivitis subsided and the gingival height returned to its original level by week 8.
Histologic Findings
Supracrestal fibers of the experimental teeth in group A had a fiber pattern similar in density and arrangement to comparable areas of the nonrotated central incisors (Figure 7), showing mild waviness and then constant thickness.
Group A. Supracrestal fibers disclosed a fiber pattern with the nonrotated central incisors. (A) H&E staining, 100×, (B) Masson's Trichrome staining, 40×, (C) 200×; R, experimental tooth root; S, supracrestal fiber; N, nonrotated tooth.
Group A. Supracrestal fibers disclosed a fiber pattern with the nonrotated central incisors. (A) H&E staining, 100×, (B) Masson's Trichrome staining, 40×, (C) 200×; R, experimental tooth root; S, supracrestal fiber; N, nonrotated tooth.
Slight infiltration of inflammatory cells was observed in group B. Histological studies failed to show bone necrosis, sequestration, or destruction. Rearrangement of the fibrous structures was observed: the organizational pattern resembled that of the nonrotated teeth, in which large fiber bundles were seen interconnected with thin fibers (Figure 8).
Group B. Rearrangement of fibrous structures had taken place. (A) H&E staining, 100×, (B) Masson's Trichrome staining, 40×, (C) 200×; R, experimental tooth root; S, supracrestal fiber.
Group B. Rearrangement of fibrous structures had taken place. (A) H&E staining, 100×, (B) Masson's Trichrome staining, 40×, (C) 200×; R, experimental tooth root; S, supracrestal fiber.
Group C specimens showed no differences from group A specimens (Figure 9). As tooth relapse is a progressive condition, the diurnal changes and thickness of the fiber bundles, as well as the phase of the blood vessels, were similar to those of the control group.
Group C. Thickness of the fiber bundle and the phase of blood vessels are arranged similarly to the control group. (A) H&E staining, 100×, (B) Masson's Trichrome staining, 40×, (C) 200×; R, experimental tooth root; S, supracrestal fiber.
Group C. Thickness of the fiber bundle and the phase of blood vessels are arranged similarly to the control group. (A) H&E staining, 100×, (B) Masson's Trichrome staining, 40×, (C) 200×; R, experimental tooth root; S, supracrestal fiber.
DISCUSSION
The results of this study indicate that laser CSF alleviates the relapse of orthodontically rotated teeth. Four weeks after surgery, the supracrestal fibers had already healed and were rearranged regularly. There was no sign of gingival recession, although the periodontal pocket depth increased by about 0.67 mm. The approximate 1-mm increase in periodontal pocket depth at week 4 could have been caused by temporary hyperplastic gingivitis.
A short-wavelength laser (500 nm–1000 nm) is absorbed by pigmented tissue or blood elements but less absorbed by water or hydroxyapatite. Because light energy from the diode laser (810–830 nm) is highly absorbed by the soft tissues and poorly absorbed by teeth and bone, hard tissue damage is avoided.16 In this study, we were able to confirm the safety of the diode laser CSF procedure because there was no particular injury to teeth or bone.
Basically, by stimulating thrombocyte activation and blood vessel congealment, a laser can provide a sense of relief to both doctor and patient, as there is less blood loss during and after surgery. It can also reduce tissue swelling by sealing the lymphatic vessels.9 For example, laser gingivectomy has advantages such as minimal bleeding and postoperative pain and no swelling.17 Surgical lasers typically have (1) a central zone of carbonization surrounded by, (2) a zone of vaporization, coagulation, and protein denaturation, and (3) a stimulating zone. This may be one reason for the improved healing with laser surgery compared with traditional scalpel surgery. During laser curettage, sufficient hemostasis and significant reduction of the initial levels of periodontal pathogens are achieved.17 Although the procedures mentioned in the preceding are not identical to laser CSF, the treated part is composed of the same gingival fibers. In this experiment, gingival bleeding was sufficiently insignificant to be controlled with sterile gauze during laser CSF. It certainly seems that the bactericidal effect transferred by the laser within the periodontal pocket can reduce the risk of infection. However, for confirmation, further histologic or cytologic studies are needed.
Because a laser beam is irradiated from the end of a 0.4-mm-diameter laser tip, the sides of the tip cannot be used for transection; therefore, an up-and-down stroking movement was initially required. As the diode laser tip is made of relatively low-strength fiber, the tip can occasionally break.
LLLT of orthodontically rotated teeth without retainers increased the rotational relapse of the teeth in group C compared with those in the control group. There was no significant difference between groups A and C in terms of the orientation and extent of stretching of the supracrestal fibers and the distribution of blood vessels.
The coherence of electromagnetic laser energy plays a role in biostimulation efficacy. The coherent character of diode laser light is not lost after tissue penetration but is split into small, coherent and polarized islands called speckles. With these features, the energy can penetrate deep into the tissues, resulting in advantageous biostimulation effects.18 Published data indicate that low-level irradiation can enhance collagen production,19 as well as increase the proliferation rate20 and alter locomotor characteristics in connective tissue cells.21 These findings are true for skin and embryonic fibroblasts, but little is known about the effects on oral fibroblasts and particularly on human gingival fibroblasts.
The reason for orthodontic relapse of rotated teeth is poorly understood, but it is often related to the presence of the supragingival fiber group. Based on the results obtained from light microscopic studies by Edwards,2 we assume that rotational movements are brought about by stretching of collagen fibers. Hitherto, relapse was considered to be the effect of orthodontically stretched gingival collagen fibers, which pull the tooth toward its pretreatment position. However, using scanning and transmission electron microscopy, Redlich et al22 reported that the stretched gingival fibers were torn, ripped, disorganized, and laterally spaced; an increased number of elastic fibers were also seen near the torn collagen fibers. This study suggests that relapse may not be due to the stretched collagen fibers but rather it originates in changed elastic properties.
The fact that prolonged orthodontic retention or surgical excision of supracrestal fibers is required suggests that these fibers have low collagen-turnover activity and may be remodeled very slowly. Minkoff and Engstrom23 and Rippin24 stated that fibroblast activity is lower in dentogingival regions than in dentoalveolar regions. However, Deporter et al25 and Proye and Polson26 have suggested that collagen turnover in the transseptal region is at least as high as, and possibly higher than, that in the periodontal ligament.
As the histological and cytological causes of relapse are unclear, it is difficult to analyze the role of LLLT in the increased rate of relapse found in this study. We focused on the amount of relapse occurring on orthodontically rotated teeth, and could not observe the histological and cytological changes in more detail during laser irradiation. To find a more plausible explanation for the effect of LLLT on relapse tendency, further studies at the molecular level are needed.
CONCLUSIONS
Laser CSF is an effective procedure to decrease relapse following tooth rotation, causing no apparent damage to the supporting periodontal structures.
LLLT of orthodontically rotated teeth without retainers appears to increase the relapse tendency.
Acknowledgments
This study was supported by the Kyung-Hee University Research fund in 2007 (20071630), Seoul, Korea.