Class I malocclusion treatment: Influence of a missing mandibular incisor on anterior guidance

Class I malocclusion treatment: Influence of a missing mandibular incisor on anterior guidanceCASE REPORT
Class I malocclusion treatment: Influence of a missing mandibular incisor on anterior guidance
Sergio Estelita C. Barros,a Guilherme Janson,b Fernando Cesar Torres,a Marcos Roberto de Freitas,c
and Renato Rodrigues de Almeidad
Bauru, Brazil
This case report describes the orthodontic treatment of a patient with a deep-overbite Angle Class I malocclu- sion, agenesis of a mandibular central incisor, and 2 supernumerary teeth, which caused impaction of the mandibular first premolars. The 15-year-old patient also had a convex profile, maxillary dentoalveolar protru- sion, and deficiency of space for the correct alignment of teeth. Therefore, treatment consisted of fixed appli- ance therapy, cervical headgear, extraction of the supernumeraries and the mandibular and maxillary first premolars, and mesiodistal reduction of the maxillary incisors to solve the arch perimeter discrepancy as much as possible with interproximal stripping. This method of treatment significantly improved the patient’s facial and dental esthetics and provided a good functional occlusion, despite the absence of a mandibular incisor, which generally impairs achieving adequate incisal guidance. (Am J Orthod Dentofacial Orthop 2010;138:109-17)
A nomaly can be defined as something that devi- ates from the rule, type, or form. In dentistry, anomalies can involve the number of teeth,
such as supernumerary teeth or agenesis of a tooth.1
Ninety percent to 98% of all supernumerary teeth occur in the maxilla, most commonly in the premaxilla, with an incidence of only 2% to 10% in the mandible.2,3
Nevertheless, supernumerary premolars occur most often in the mandible (74%).4,5 Supernumerary premolars appear to be more common than previously estimated, occurring 3 times more often in males than in females, and with a greater frequency in the permanent dentition.4 The most widely accepted theory for the mechanism of supernumerary development is lo- calized hyperactivity of the dental lamina. The occur- rence of supernumeraries can create various clinical problems such as derangement of the occlusion, preven- tion of eruption of adjacent permanent teeth, damage to adjacent teeth, cystic degeneration, and root resorption.
From the Department of Orthodontics, Bauru Dental School, University of Sao
Paulo, Bauru, Brazil. aPostgraduate student. bProfessor and head. cProfessor. dAssociate professor.
The authors report no commercial, proprietary, or financial interest in the
products or companies described in this article.
Reprint requests to: Sergio Estelita C. Barros, Rua Pe. Joao, 14-68, Bauru, SP,
17012-020, Brazil; e-mail, [email protected].
0889-5406/$36.00
doi:10.1016/j.ajodo.2008.02.030
Hence, clinical and radiographic evaluation of patients should always be thorough to detect them.
The absence of teeth can also be a challenge to or- thodontists. Hypodontia is the congenital absence of at least 1 tooth. The most commonly missing teeth are the third molars, followed by the maxillary lateral inci- sors and second premolars. The etiology of agenesis might be related to nutritional, traumatic, infectious, he- reditary, or phylogenetic factors.6 Agenesis of canines, maxillary central incisors, and mandibular incisors is relatively rare.
The difficulty of achieving adequate functional oc- clusion in patients with congenital absence of a mandib- ular incisor is well known, particularly when the patient has an excessive overbite or overjet and a Bolton tooth- size discrepancy with excess in the mandibular anterior teeth.7,8 In these situations, anterior and lateral occlusal guidance will be impaired.
This article presents and discusses the treatment of a patient with Class I malocclusion, with agenesis of a mandibular incisor, deep anterior overbite, excessive overjet, and 2 supernumerary teeth that were blocking the eruption of the mandibular first premolars.
DIAGNOSIS AND ETIOLOGY
A girl, aged 15 years 1 month, had no significant medical history; her chief complaints were spaces be- tween her mandibular teeth and proclined maxillary an- terior teeth. Her mother reported no family history of similar malocclusions and mentioned that her daughter
Fig 1. Pretreatment facial and intraoral photographs at age 15 years 1 month.
110 Barros et al American Journal of Orthodontics and Dentofacial Orthopedics
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had regular dental care. No facial trauma or parafunc- tional habits were reported. The cause of her malocclu- sion was presumed to be a combination of genetic and developmental factors.
From a frontal view, her face was well balanced and symmetric (Fig 1). Her facial profile was convex, with an acute nasolabial angle, slight mandibular retrusion, strained lip seal, and normal vertical proportions. Intra- orally, she had Angle Class I molar and Class II canine relationships on both sides. The maxillary midline was coincident with the facial midline, and both arch forms were ovoid. Her oral hygiene was excellent, with good periodontal health, and all restorations were satisfac- tory. She was congenitally missing a mandibular central incisor and had 2 nonerupted mandibular first premo- lars, which were impacted by supernumerary teeth. Overbite was excessive (70%), overjet was 6 mm, and both mandibular and maxillary incisors were proclined (Fig 2).
The panoramic radiograph confirmed the presence of the 2 supernumeraries above the mandibular first premolars. The cephalometric analysis showed a skel- etal Class II anteroposterior discrepancy with man- dibular retrusion. The facial pattern had a slight vertical tendency. Both maxillary and mandibular incisors were tipped labially (Fig 3). The lateral ceph- alometric radiograph showed the impacted teeth in the mandible.
TREATMENT OBJECTIVES
The primary objectives in treating this malocclusion were to eliminate the mandibular spacing and correct the maxillary dentoalveolar protrusion. Additional ob- jectives were to maintain upper lip support for satisfac- tory facial harmony and the Class I molar relationship. Ideal overjet and overbite relationships were also desir- able to improve the esthetics of the occlusion and estab- lish immediate anterior guidance.
Fig 2. Pretreatment study models.
American Journal of Orthodontics and Dentofacial Orthopedics Barros et al 111 Volume 138, Number 1
TREATMENT ALTERNATIVES
It was obvious that both supernumeraries should be extracted because they were blocking the eruption of the first premolars, and their positions and shapes were un- favorable. Therefore, the main issues were the severity of the mandibular premolar impaction, the arch-length discrepancy and maxillary tooth-size excess, the lack of space for the mandibular premolars, and the proclina- tion of the mandibular and maxillary incisors.
According to these factors, 2 treatment options were presented to the patient. The first included the orthodon- tic eruption of the mandibular left premolar, after ex- traction of the supernumerary teeth and the right mandibular premolar. In this situation, the maxillary first premolars would be extracted to maintain a Class I molar relationship and reduce the maxillary incisor proclination. This option would involve placing the mandibular left canine in the position of the left lateral incisor, and the mandibular left first premolar would substitute as a canine. The main advantage of this treat- ment would be to eliminate the arch-length discrepancy, leaving only a small Bolton tooth-size discrepancy because of the greater mesiodistal canine width.
The second alternative involved extraction of the supernumeraries and the 4 first premolars to maintain a Class I molar relationship, achieve a Class I canine relationship, and reduce the incisor proclination. This treatment option would require anterosuperior stripping to reduce the arch-length discrepancy created by the
missing mandibular incisor. This could be achieved by removing approximately 5 mm of interproximal enamel on the maxillary anterior teeth.
TREATMENT PLAN
Considering the position of the impacted premolars, the negative space discrepancy, and the patient’s profile, we discussed the treatment options with the patient and her parents. We decided to reposition the mandibular left first premolar. A setup was made to simulate the eventual treatment outcome to ensure that the orthodon- tic treatment would produce successful results.
TREATMENT PROGRESS
The supernumeraries, the maxillary first premolars, and the mandibular right first premolar were extracted initially. Then surgical access and bonding of the man- dibular left premolar were accomplished. Treatment began with banding of the maxillary first molars and placing cervical headgear (GAC International, Central Islip, NY), with 450 g of force. This appliance was to be worn 12 hours a day during leveling and alignment and 16 hours a day during tooth retraction to maintain the Class I molar relationship and allow improvement of the excessive overjet and the incisor proclination.
Fixed 0.022 3 0.028-in preadjusted appliances were placed, and continuous 0.016-in nickel-titanium arch- wires were placed, with an open-coil spring to obtain
Fig 3. Pretreatment panoramic and cephalometric radiographs.
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space for the mandibular left premolar. When there was enough space, premolar traction was started. Initial align- ment was obtained, and the deep bite was corrected with an accentuated reverse curve of Spee. Continuous 0.018 3
0.025-in nickel-titanium archwires were placed to continue leveling and alignment, and elastic chains were used to encourage the premolar to erupt. However, the pre- molar did not respond to traction, possibly because of tooth ankylosis9 after the surgical procedure,10 or perhaps related to the patient’s other tooth anomalies.11
After 8 months of unsuccessful treatment, it was de- cided to extract the remaining mandibular first premo- lar. To obtain optimal overjet and immediate lateral and anterior guidance, careful stripping of the mesiodis- tal surfaces of the maxillary anterior teeth was planned. A wax setup was constructed to simulate the treatment effects and avoid increasing the risk of caries and tooth sensitivity.12
Continuous 0.019 3 0.025-in stainless steel arch- wires were then placed, to prepare the teeth for the an- terior retraction phase. The maxillary anterior teeth
were retracted with maximum anchorage, but no an- chorage was used in the mandibular arch. After closure of the extraction spaces, interproximal stripping of the anterior teeth was performed, and the open spaces were consecutively closed by using Class II elastics and 0.020-in and 0.019 3 0.025-in stainless steel arch- wires in the maxillary and mandibular arches, respec- tively. Vertical intermaxillary elastics (0.75 in, 2 oz) were used for about 6 weeks to obtain satisfactory tooth interdigitation. The appliances were removed, and a maxillary Hawley retainer and a mandibular fixed re- tainer were placed for retention. The Hawley retainer was worn full time for 18 months, followed by 6 months of nighttime wear, whereas the lingual retainer would be maintained permanently to enhance the long-term stability of the results. The total treatment time was 34 months.
TREATMENT RESULTS
The patient’s facial esthetics were improved signif- icantly by establishing a passive lip seal (Fig 4). The teeth were well aligned and leveled over the basal bone. Class I molar and canine relationships were estab- lished, with ideal overjet and overbite (Figs 4 and 5). The maxillary dental midline was coincident with the facial midline and with the center of the remaining mandibular central incisor. A mutually protected occlusion was achieved in centric relation, with group function in lateral excursion and anterior guidance in posterior disclusion. Excellent root parallelism was achieved, and root resorption was minimal (Fig 6). Fa- cial esthetics and balance were improved by correcting the maxillary incisor proclination (Figs 7-9). There was improvement of the maxillomandibular relationship (ANB angle and Wits appraisal), incisor inclination, and soft-tissue profile (H and S esthetic lines; naso- and mentolabial angles).
DISCUSSION
In some situations, the intentional extraction of a mandibular incisor can enable the orthodontist to pro- duce enhanced functional occlusal and esthetic results, with minimal orthodontic manipulation and, conse- quently, minimal profile modification.12 The extraction of a mandibular incisor is primarily indicated in 4 types of clinical situations: anomalies in the number of ante- rior teeth (supernumerary mandibular incisor), tooth- size anomalies (macrodontia of mandibular incisors or microdontia of the maxillary lateral incisors), ectopic eruption of incisors (severe malpositioning of the man- dibular incisors), and moderate Class III malocclusions
Fig 4. Posttreatment facial and intraoral photographs, age 18 years 6 months.
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(anterior crossbite or edge-to-edge relationship of the incisors, with a tendency toward anterior open bite).7
Nevertheless, in other situations, a mandibular inci- sor can be congenitally missing.12 Thus, one must be well aware of the unfavorable anterior tooth-size dis- crepancy in such situations and of the difficulties and limitations of this problem in achieving a satisfactory occlusal result.
In our situation, the anteroposterior skeletal discrep- ancy, accentuated overjet, and excessive ovebite were unfavorable characteristics associated with the absence of a mandibular incisor. This was the reason that the first treatment alternative consisted of extracting 3 premo- lars and substituting the mandibular left premolar for the mandibular left canine. This procedure would elim- inate the arch-length discrepancy. However, the tooth did not respond favorably to traction, causing unfavor-
able collateral effects on the anchorage teeth. This prob- ably occurred because of the relatively deep position of the impacted premolar, tooth ankylosis, or any of the other eruption disturbances mentioned previously.13
The patient’s age, lack of growth potential, and concern about an extensive treatment time were further compli- cating factors.14 So, it was decided to extract the im- pacted premolar. To overcome the resultant deficient maxillary to mandibular incisor relationship (immediate anterior guidance7), interproximal stripping of the max- illary anterior teeth was performed.
It is important to eliminate anterior arch-length dis- crepancies caused by congenital absence of a mandibu- lar incisor.15 This adjustment can be accomplished by reduction of tooth width. However, tooth anatomy and patient sensitivity might limit the amount of tooth strip- ping.16 Long-term evaluation of reshaped teeth has
Fig 5. Posttreatment study models.
114 Barros et al American Journal of Orthodontics and Dentofacial Orthopedics
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demonstrated that careful interdental enamel reduction does not result in iatrogenic damage, and interdental stripping is not correlated to increased sensitivity, caries susceptibility, and periodontal diseases.17 But for a safe stripping procedure, each interproximal surface should not be stripped more than 0.5 mm, because mean enamel thickness in this anatomic area is not greater than 1 mm.18 Excessive interproximal stripping can cause a transitory increase in tooth sensitivity to changes in temperature,12 especially if water or air cool- ing is not adequate.17 When too much enamel is removed and dentin is exposed, there is an increased risk for caries.12 This potential problem can be reduced if the prepared surfaces are carefully smoothed and fluo- ride mouthrinses are prescribed.17 Additionally, if the interproximal surface is indiscriminately flattened, the interproximal contact will be lengthened gingivally, fur- ther reducing the space for the gingival papillae and po- tentially compromising the cosmetic results.12 In other cases, this interproximal contact lengthening can pre- vent interdental gingival retraction and black-triangle development after anterior crowding resolution.19
Acording to Kokich and Shapiro,12 in clinical practice, these complications are a less common problem than achieving a satisfactory occlusal result after mandibular incisor extraction. Zachrisson et al17 did not find dental caries, gingival problems, alveolar bone loss, or reduced distances between the roots of anterior teeth with inter- proximal reduction after a period of 10 years.
Interdental stripping of the maxillary anterior teeth is a common clinical procedure when a mandibular
incisor is extracted or is congenitally missing.8,12
Several stripping techniques can be used, such as hand-held or motor-driven abrasive strips, hand piece- mounted diamond-coated disks, or tungsten carbide or diamond burs.20 To avoid plaque accumulation due to rough interdental surfaces, it is important to eliminate grooves and furrows, making the stripped interproximal surfaces as smooth as possible.21,22 The finer the grain size used for removing enamel, the easier and less time-consuming the subsequent polishing.21 Conse- quently, in our patient, mesiodistal enamel reduction was performed with a perforated diamond-coated disk with less than 30-mm grain size at medium speed (about 30,000 rpm) in a contra-angle hand piece.17 The inter- proximal corners were rounded by using a round or triangular diamond fissure bur (Komet #8833, Gebruder Brasseler, Lemgo, Germany) to reestablish the incisal crown shape.23 The subsequent polishing was done with fine and ultrafine Sof-Lex XT disks (3M Espe, St. Paul, Minn) at low speed (200-400 rpm) for approximately 40 seconds each, as recommended by Zhong et al.21,22 The Sof-Lex disks were changed of- ten because of significant deterioration with use. The patient was instructed to use a diluted (0.05%) sodium fluoride mouthrinse once daily for interproximal surface remineralization, and a topical fluoride agent was also applied immediately after polishing.
A careful and realistic diagnostic setup can be a significant aid in determining whether the occlusal result will be acceptable and consistent with the treat- ment objectives. It can also help to demonstrate the
Fig 6. Posttreatment panoramic and cephalometric radiographs.
Fig 7. Cephalometric tracings superimposed on the sella-nasion plane at sella. Pretreatment, solid lines; posttreatment, dashed lines.
American Journal of Orthodontics and Dentofacial Orthopedics Barros et al 115 Volume 138, Number 1
amount of enamel that can be removed from the max- illary incisors without impairing their natural shape.12
The diagnostic setup for this patient showed that ap- proximately 5 mm of interproximal enamel from the 6 maxillary anterior teeth should be removed to estab- lish immediate anterior guidance. However, even with careful water cooling during stripping, the patient’s sensitivity limited the intended amount of stripping to about 3 mm, distributed as equally as possible among the 12 maxillary anterior interproximal surfaces. Tooth sensitivity after stripping is not common,17 but it can be attributed to an individual condition regarding enamel thickness, which was not radiographically evaluated before enamel reduction, as suggested by Kokich and Shapiro.12 The individual variations in patients’ pain thresholds can also explain the early tooth sensitivity. In this case, air cooling during grinding, as suggested by Zachrisson et al17
for successful tooth sensitivity control, was not done. However, no studies have compared water and air cooling during the stripping procedure.
When the maxillary anterior tooth width cannot be reduced adequately, excessive overjet might remain. This overjet was avoided by changing the orthodontic mechanics during interproximal space closure. The Class II elastics were used with maxillary round arch- wires to allow significant maxillary incisor uprighting.8
The mandibular incisor positions were controlled as much as possible, because of their excessive initial labial proclinations. But even with these compensatory mechanics, anterior guidance was compromised be- cause of the tooth-size discrepancy.8 Therefore, group function was obtained in lateral excursions. During pro- trusion, the anterior teeth discluded the posterior teeth.
A significant improvement in facial and dental es- thetics was produced, despite the absence of a mandibu- lar incisor. The cephalometric superimposition shows the improved maxillomandibular relationship and com- pensated incisor position8 (Figs 7-9). The premolar extractions and the use of headgear, Class II elastics, and anterior stripping produced favorable uprighting of the maxillary incisors.
There were increases in the facial angles and facial height (FMA, SN.Occl, SN.GoGn, LAFH, and LPFH). The mandibular incisors showed slight labial tipping, probably from the Class II elastics when closing
Fig 9. Cephalometric tracings of the maxilla superim- posed on the palatal plane at ANS. Pretreatment, solid lines; posttreatment, dashed lines.
Fig 8. Cephalometric tracings of the mandible superim- posed on the mandibular plane at menton. Pretreatment, solid lines; posttreatment, dashed lines.
116 Barros et al American Journal of Orthodontics and Dentofacial Orthopedics
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the interproximal spaces. These small dentoalveolar changes also produced favorable soft-tissue changes (Fig 4).
Zachrisson et al17 showed that interproximal reduc- tion of enamel results in stability of alignment in the long term. The irregularity index in the experimental sample was small, even in patients whose retainers had been lost or removed. Their explanation for the ex- cellent stability was that neither canine-to-canine ex- pansion nor mandibular-incisor proclination had been performed. The interproximal enamel reduction in- creased the available space in the arch. Furthermore, the stripping procedure also provides broader contact areas and thereby results in greater contact stability.24
Because the maxillary anterior segment was not pro- clined or expanded, and initial crowding was slight, the expected long-term alignment stability for the max- illary anterior teeth in this patient is good and enhanced by broader contact point areas.24 A…