Introduction
Orthodontic space closure after premolar extraction commonly results in the formation of a gingival cleft, which may contribute to orthodontic relapse and poor periodontal health. The purpose of this study was to examine clinical parameters that may predispose patients to gingival clefts.
Methods
Twenty-nine patients planned for treatment with premolar extractions (n = 87) and orthodontic space closure were evaluated in this prospective study. The clinical measures included width of keratinized buccal gingiva, thickness of buccal gingiva, thickness of buccal bone, time of space closure, and the occurrence (presence or absence) and severity (volume) of cleft formation. The association of the clinical measures with gingival cleft formation and severity was assessed separately for patients according to age group: young adolescent (≤13 years of age), adolescent (14-18 years of age), and adult (≥19 years of age).
Results
The overall incidence of gingival cleft formation was 73.2%, with a trend toward greater cleft formation in the young adolescents (79.4%) than in the adolescent and adult groups (69.2% and 68.2%, respectively). The mean severity of clefts exhibited a significant positive association with age group—young adolescent (26.6 mm 2 ), adolescent (27.9 mm 2 ), and adult (41.5 mm 2 ). Buccal bone thickness was significantly correlated with gingival phenotype in the adolescent and adult groups ( r = 0.42 and r = 0.52, respectively; both, P <0.05). Rate of space closure was significantly correlated with cleft formation ( r = 0.71; P <0.001) in the adult group.
Conclusions
The formation of gingival clefts is common after premolar extraction and space closure. Adults with a thinner gingival phenotype were more likely to develop gingival clefts of greater severity. The rate of space closure was significantly and inversely correlated with cleft formation in adults, reflecting a greater likelihood of cleft formation with slower space closure. Although various clinical parameters show a correlation to both severity and incidence of clefts, all patients undergoing postextraction space closure appear to be at risk and should be monitored.
Highlights
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Gingival clefts are common side effects after orthodontic space closure of extraction sites.
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The severity of gingival clefts is significantly greater in adults than adolescents.
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The rate of space closure was significantly and inversely correlated with cleft formation in adults, reflecting a greater likelihood of cleft formation with slower space closure.
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Available clinical reports indicate that gingival clefts can be successfully corrected using bone grafts or GBR.
Premolar extractions are commonly indicated during orthodontic therapy to treat tooth size-arch length discrepancies. Practice surveys have shown that tooth extractions are performed in about 10% to 15% of orthodontic patients. Orthodontic space closure, most notably at premolar extraction sites, is commonly associated with the formation of gingival clefts, or invaginations, that may contribute to orthodontic relapse and poor periodontal health. The incidence of gingival cleft formation appears to be relatively high, with reported rates ranging from 35% to 100% of patients undergoing extractions and orthodontic space closure. Nevertheless, clinical factors that predispose patients to gingival cleft formation remain unclear.
Two current theories attempt to explain the etiology of gingival clefts. The first relates cleft formation to the underlying bony architecture of the extraction site. Loss of alveolar bone due to trauma, resorption, or both is thought to predispose to gingival invagination. Araújo and Lindhe, for example, documented a reduction in the volume of the dental alveolar ridge, particularly the buccal aspect, after extraction of mandibular premolars. The second explanation attributes gingival cleft formation to the transseptal fiber system, which may be displaced rather than remodeled during tooth movement, resulting in bunching, pressure on the subjacent bone, and concomitant invagination of the gingival tissues. This hypothesis is based, in part, on the clinical occurrence of reopening of previously closed extraction spaces. As space closure occurs, tissues on the tension side are stretched, whereas tissues on the pressure side are compressed. The pressure side is presumably responsible for gingival invagination, but the tension side contributes to the relapse.
Gingival clefts may delay or prevent complete space closure, and it has been shown that there is decreased interdental bone in sites with gingival invaginations. Incomplete space closure, with open contacts, is associated with an increased likelihood of food impaction and gingival trauma. Many studies have shown reduced interproximal bone height relative to original alveolar dimensions.
An important clinical question is whether it is possible to predict extraction sites at risk for gingival cleft formation after orthodontic space closure. Gingival phenotype can be characterized using several soft and hard tissue anatomic parameters, including gingival thickness, width of keratinized gingiva, alveolar bone thickness, and osseous architecture. Although there are different classifications of gingival phenotype, most classifications are based on several common clinical and anatomic features. A thick gingival phenotype is characterized by a flat gingival margin, a broad zone of keratinized gingiva, and a thick underlying bony architecture. A thin gingival phenotype is characterized by a scalloped gingival contour, a thin band of keratinized gingival, and a thin underlying bony architecture. Importantly, different gingival phenotypes have been shown to respond differently to inflammation and injury. When there is chronic inflammation, the gingival phenotype appears to be predisposed to distinctly different clinical outcomes—a thick gingival phenotype tends to develop periodontal pockets, whereas a thin gingival phenotype tends to undergo recession.
The purpose of this prospective cohort study was to examine the association between clinical measures of cleft formation and severity after orthodontic space closure of premolar extraction sites related to gingival phenotype.
Material and methods
Thirty-six participants were recruited from patients requiring premolar extractions as part of comprehensive orthodontic care at the University of Maryland, School of Dentistry, in Baltimore. All participants had complete orthodontic records (models, lateral cephalometric and panoramic radiographs, intraoral and extraoral photos, and examinations) and screening before enrollment in the study. Inclusion criteria included a full permanent dentition and a comprehensive orthodontic treatment plan that included 2 or 4 premolar extractions and space closure with fixed orthodontic appliances. Exclusion criteria included periodontitis and systemic conditions. Consent or assent and HIPAA authorization forms were reviewed with each participant or guardian. All participants provided verbal and written consent. Subjects contributed either 2 or 4 premolar extraction sites, and all measurements were performed on the study sites in triplicate. Measurements were averaged to create a mean score for analysis. This study was approved by the Institutional Review Board at the University of Maryland.
Initial gingival measurements were taken immediately before and after each tooth extraction. The width of the keratinized gingiva was measured with a Maryland/Moffitt color-coded periodontal probe (Hu-Friedy, Chicago, Ill) (millimeters) from the gingival margin to the mucogingival junction at the midfacial surface. After topical anesthesia with 20% benzocaine, local infiltration (2% xylocaine and epinephrine, 1:100,000) was administered on the buccal and lingual or palatal surfaces. After anesthesia, measurements of gingival thickness were obtained by transgingival probing using an endodontic probe with a stopper. Measurements were taken with bone sounding on the direct facial surface before extraction ( Fig 1 ).
Extractions were completed as atraumatically as possible to preserve the bony architecture, followed by gentle debridement and irrigation of the extraction socket with sterile saline solution. After extraction, the thickness of the buccal bone was determined using a bone caliper. Buccal bone thickness was measured at the midfacial surface at the crest of the bone.
Patients needing orthodontic treatment with premolar extraction were consecutively recruited until enrollment ended. Each subject was treated by 1 assigned orthodontist, ensuring consistency of care. All orthodontic care was delivered by 4 practitioners. When space closure was at or near (<2 mm) completion, the incidence and severity of clefting was measured using the coding system of Reichert et al. Soft tissue measurements were taken in 3 planes: mesiodistal (x-axis dimension), buccolingual (y-axis dimension), and incisal-gingival (z-axis dimension); the degree of clefting was determined by volumetric measurement ( Fig 2 ).
The following variables were categorized for analysis: age—young adolescent (≤13 years), adolescent (14-18 years), and adult (≥19 years); and gingival phenotype (thickness)—thin (≤2.5 mm) and thick (>2.5 mm).
Statistical analysis
The association of clinical parameters with the formation and severity (volume) of clefts was assessed separately in the age groups using the nonparametric Spearman rank correlation. Statistical significance was set at P ≤0.05.
Results
Twenty-nine of the 36 subjects completed the study. Two patientts underwent extractions under sedation, which precluded clinical evaluation; 5 subjects failed to complete treatment or did not come for the follow-up evaluation. Four subjects were planned for treatment with extraction of 3 premolars; consequently, data on the third premolar were not included in the analysis. A total of 82 premolar extraction sites were evaluated for cleft formation and cleft severity.
The overall incidence of gingival cleft formation was 73.2% (n = 60), with a similar frequency of cleft formation in the maxillary and mandibular extraction sites (72.9% vs 73.5%, respectively). Soft tissue measurements ranged from 0 to 1 mm in the mesiodistal dimension, 0 to 9 mm in the buccolingual dimension, and 0 to 7 mm in the incisal-gingival dimension. Clefts developing at maxillary and mandibular extraction sites were similar in average severity (31.4 and 29.8 mm 2 , respectively). The number of extraction sites (2 vs 4) contributed by subjects had no association with the occurrence and severity of clefts (r = −0.06 and r = −0.08, respectively).
Clefts formed in 79.4%, 69.2%, and 68.2% of subjects in the young adolescent, adolescent, and adult groups, respectively. Although the percentage of subjects with clefts had a modest inverse relationship with age group, this association was not significant. The mean severity of clefts, however, exhibited a significant positive association with age group. The mean severity values of clefts were 26.6, 27.9, and 41.5 mm 2 in the young adolescent, adolescent, and adult groups, respectively ( Table ).
| Young adolescent (≤13 y) | Adolescent (14-18 y) | Adult (≥19 y) | |
|---|---|---|---|
| Cleft formation (%) | 79.4 | 69.2 | 68.2 |
| Cleft severity (mm 2 ) | 26.6 | 27.9 | 41.5 |
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