Cephalometric Assessment of Changes in Vertical Facial Height Following Extraction of Mandibular Second Premolars in Adult Long-face Patients with Skeletal Open Bite: A Case Series

INTRODUCTION

Open bite is among the most common dental anomalies. Anterior open bite is defined as absence of contact between the maxillary and mandibular anterior teeth while other teeth are in occlusion.¹ This anomaly is more common in the primary dentition period; however, it may continue to adulthood. Treatment of open bite, especially in the permanent dentition period, is highly challenging for orthodontists.²

The prevalence of anterior open bite ranges from 1.5 to 11% in different age groups.¹ Open bite is a multifactorial condition and finding its etiology plays an important role in its diagnosis and treatment. Researchers have mentioned several causes for this anomaly. Some have reported genetics as well as environmental and behavioral factors to be responsible for development of open bite.³ Many researchers believe that nonnutritive sucking habits are the main causes of anterior open bite.⁴ The following factors are the main local or environmental parameters responsible for the development of open bite at a young age:

• Nonnutritive sucking habits (such as thumbsucking or using a pacifier)^4,5
• Abnormal size, position, or function of the tongue
• Mouth breathing (which may be due to enlargement of lymph nodes)⁶

Correction of open bite is a complex procedure due to high risk of relapse (25–38%),⁷ particularly in adults since the skeletal growth and development of the jaws has terminated.⁸ In some cases, prevention of overgrowth of the maxilla and its rotation in the posterior area or prevention of overeruption of posterior teeth during the growth spurt fails due to the remaining growth.⁷

Most dentists believe that treatment of anterior open bite is more difficult and its course of treatment in long term is less predictable compared to treatment of other dentofacial deformities.⁹ The most important factor with regard to different modalities for treatment of anterior open bite is stability of treatment results in long term, which is challenging. At present, therapeutic procedures performed for treatment of this condition vary from using a simple removable orthodontic appliance to orthognathic surgery depending on the severity of open bite.¹⁰

Therapeutic interventions for treatment of anterior open bite also vary depending on the dentition stage. Therapeutic strategies are divided into three categories of treatment in the primary dentition period, the mixed dentition period, and the permanent dentition period. Simple orthodontic treatments are not effective in the permanent dentition period. Two treatment strategies are available for treatment of open bite in this period. In very severe cases, orthodontic treatment is not sufficient alone and the patient must undergo a surgical procedure as well. Maxillary surgeries are often performed to achieve adequate facial height in long-face patients, while mandibular surgeries are performed to correct the anterior–posterior dimension of the face.²

Several strategies have been suggested for treatment of open bite with moderate severity in the permanent dentition period. Several studies have reported orthodontic treatment with and without tooth extraction for correction of open bite with variable results in this respect. Some researchers prefer the correction of open bite with tooth extraction.⁸ However, some others believe that the effect of tooth extraction on closure of open bite is not significantly different from the outcome of nonextraction treatments.⁸ On the other hand, long-term stability of open bite treatments is a highly debated topic.

Selection of a suitable treatment modality is eventually done by taking into account the dental, skeletal, and functional factors.³

This study aimed to assess cephalometric changes in vertical facial height of patients with skeletal anterior open bite following extraction of mandibular second premolars.

MATERIALS AND METHODS

This study was conducted on 13 open bite patients with a mean age of 24.08 years (range 19–28 years), who were all in the permanent dentition period. According to a study by de Freitas et al.,¹⁰ the mean difference in the lower anterior facial height (LAFH) index before and after treatment was considered to be μ₁ − μ₂ = 69.08 − 71.39 = −2.31 and ²б = 5.35. Accordingly, we required a minimum of eight samples to find this difference by a test with 80% power and 5% error rate.

All patients underwent fixed orthodontic treatment and extraction of mandibular second premolars and maxillary first or second premolars. All patients were treated by the same orthodontist. Extractions in each jaw were performed before applying fixed orthodontic appliance of the respective jaw. The treatment was started by extraction of maxillary premolars (maxillary first premolars were extracted in 11 and maxillary second premolars were extracted in two patients) and after that, leveling and alignment of maxillary teeth were started. After a couple of months, mandibular second premolars were extracted before applying fixed orthodontic appliances.

The inclusion and exclusion criteria were as follows:

RESULTS

Cephalometric analyses and comparison of cephalograms after treatment with baseline cephalograms of patients revealed the following:

The sum of posterior angles, SN-MP, and LAFH decreased after treatment (T2) in all patients compared to baseline (T1). The Jarabak index increased after treatment in all patients compared to baseline. Also, ANB, U1-SN, and IMPA decreased after treatment in all patients. Overjet experienced a slight increase in five patients while it decreased in eight patients. Overbite increased in all patients and was positive enough to confirm open bite closure.

Cephalograms of patients taken at 24 months’ posttreatment (T3) were compared with those taken immediately after completion of treatment (T2) and showed no significant change in any parameter. With regard to overbite, six patients experienced a reduction and two patients experienced an increase in overbite; overbite remained unchanged in five patients. However, reduction in overbite in the mentioned six patients did not result in bite opening and all patients still had positive overbite.

Insignificant changes in cephalometric analysis of some variables such as SNA noted immediately after treatment and after 24 months (T3) were normal because cephalograms of patients had been taken by different X-ray units and at different times. Thus, insignificant changes at the two time points were inevitable and were considered normal.

Table 2 compares the mean and standard deviation of parameters measured on cephalograms of patients at baseline, immediately after treatment and at 24 months’ posttreatment. Also, Figures 1 to 3 show SN-MP, LAFH, and overbite at T1, T2, and T3.

According to the repeated measures ANOVA, the sum of posterior angles (p < 0.001), the Jarabak index (p < 0.001), SN-MP (p < 0.05), LAFH (p < 0.05), SNB (p < 0.05), ANB (p < 0.05), U1-SN (p < 0.001), IMPA (p < 0.001), and overbite (p < 0.001) showed significant changes during the period of T1–T2. Also, according to the repeated measures ANOVA, SNA, overjet, and molar extrusion did not show significant changes compared to their baseline values (p %3E; 0.05).

Statistical analysis of the data of patients at 24 months after treatment showed that none of the parameters evaluated in this study experienced any significant change compared to their value immediately after completion of treatment.

DISCUSSION

The effect of tooth extraction on vertical facial height and anterior open bite closure has been an interesting topic of research. The first challenging topic is to find out whether tooth extraction has any significant effect on open bite closure. The next question is that given that tooth extraction can significantly contribute to open bite closure, extraction of which teeth would have the greatest impact on bite closure. Stability of open bite treatment in long term is another important topic in this regard. Open bite treatment is among the most challenging orthodontic treatments due to the high risk of relapse in long term.

Some researchers believe that the results of nonextraction orthodontic treatment have optimal long-term stability.³ However, some others evaluated the success of extraction orthodontic treatment of open bite (in terms of relapse) and reported optimal stability of treatment results.³ Some other researchers believe that extraction of second premolars compared to first premolars results in greater mesial movement of the first molar tooth. This leads to the reduction of vertical facial height by the wedge effect.¹¹ In contrast, some studies showed that extraction of first or second premolars was not significantly different in terms of effect on vertical facial height; in other words, change in vertical facial height does not depend on the mesial movement of the first molar tooth.¹² Researchers have discussed that closure of space created by tooth extraction would be associated with extrusion of the first molar tooth, and the greater the mesial movement of this tooth, the greater its extrusion would be. Resultantly, vertical facial height would increase. Some clinicians prefer to extract first molar teeth in order to close the bite in open bite patients. They believe that movement of the second molar tooth to the first molar site would result in rotation of the mandible and open bite closure.¹²

In contrast, other researchers have discussed that extraction of second premolars and first molars would result in rotation of the mandible for the sake of open bite closure in skeletal open bite patients; however, extraction of first premolars does not cause significant changes in mandibular rotation.¹² Some others have mentioned that extraction of second premolars creates a wedge effect and results in greater mesial movement of the first molar compared to patients in whom first premolars are extracted, and can result in open bite closure and reduction in vertical facial height.^12,13

A few researchers have shown that tooth extraction does not change the vertical facial height.¹⁴ Staggers¹⁵ showed that changes in vertical facial height following extraction of first premolars were similar to changes in patients who underwent nonextraction treatment. Chua et al.¹⁶ demonstrated that nonextraction treatment resulted in an increase in LAFH; whereas, tooth extraction did not cause significant changes in LAFH.

Aras¹³ evaluated the effect of extraction of first premolars, second premolars, and first molars and concluded that extraction of first premolars had no significant effect on rotation of the mandible in patients with anterior open bite while extraction of second premolars and first molars affected the vertical facial height and resulted in mandibular rotation. Garlington and Logan¹⁷ showed that following extraction of mandibular second premolars, LAFH decreased in patients but no significant change was noted in facial height. Kim et al.¹² assessed the efficacy of the wedge-effect theory by extraction of first and second premolars for open bite closure. According to the wedge-effect concept, even small changes in mesial movement of molars would result in a pronounced effect on the mandibular plane angle and facial vertical dimension.¹² According to this theory, extraction of more posterior teeth results in greater mesial movement of molar teeth and better open bite closure. They concluded that extraction of first and second premolars has no significant effect on facial height of patients; thus, the wedge-effect theory for open bite closure via mesial movement of molars is inefficient.

In the current study, extraction of mandibular second premolars changed the cephalometric parameters such that the sum of posterior angles and SN-MP angle slightly decreased and the Jarabak index slightly increased. All these changes were statistically significant but not clinically perceivable. Also, the angle of maxillary and mandibular incisors relative to the palatal and mandibular planes significantly decreased. Significant increase in overbite was noted in all patients. Based on the results, it may be stated that despite reduction in facial height, open bite closure was mainly due to the retroclination of the maxillary and mandibular incisors. Thus, our study, similar to that of Kim et al.,¹² showed that extraction of mandibular second premolars and mesial movement of molars had no significant effect on open bite closure. Another important issue with regard to treatment of open bite is the stability of treatment in long term. Open bite treatment at a young age and the mixed dentition period would yield the best results with minimal rate of relapse. However, opinions on the outcome of treatment of open bite in adults are controversial.

Studies on the stability of results of extraction orthodontic treatment of open bite are not many and the available ones have not separately reported the outcomes of extraction and nonextraction treatments. Remmers et al.¹⁸ orthodontically treated 51 open bite patients; 71% of these patients had positive overbite upon completion of treatment, out of which 10% had relapse within 5 years after treatment and developed negative overbite. The authors concluded that orthodontic treatment of open bite has a long-term stability. However, they did not mention whether they performed extraction or nonextraction orthodontic treatment for correction of open bite.

de Freitas et al.¹⁰ evaluated the stability of extraction and nonextraction orthodontic treatments. The group that underwent extraction orthodontic treatment (n = 31) was followed up for a minimum of 5 years with a mean of 8.35 years. The nonextraction group (n = 21) was followed up for a minimum of 3 years with a mean of 5 years. The results of the aforementioned two retrospective studies showed that 38.1% of patients who underwent nonextraction orthodontic treatment and 25.8% of patients who underwent extraction orthodontic treatment relapsed during the follow-up period and developed open bite again. They concluded that stability of the results of open bite correction by extraction treatment is higher than that of nonextraction treatment. However, other studies that compared extraction and nonextraction orthodontic treatments for correction of open bite did not find a statistically significant difference between the two methods in long-term stability of treated open bite. Although a 24-month period is not sufficient to reach a definite conclusion with regard to long-term stability of treatment results, it should be noted that relapse often occurs during the first year following completion of treatment. Some researchers suggest that the stability of corrected anterior open bite malocclusion should be reported as a percentage of patients with a significant posttreatment change for the given treatment. The condition is considered “highly stable” if significant posttreatment changes are noticed in less than 10% of the patients and “stable” if it is less than 20% and almost none have major posttreatment changes.¹⁹ According to this definition, the closure of anterior open bite in our patients was “stable.”

CONCLUSION

• Extraction of mandibular second premolars in adult long-face patients results in slight counterclockwise rotation of the mandible but has no significant clinical effect on LAFH.
• In open bite patients who underwent orthodontic treatment along with extraction of mandibular second premolars, open bite was mainly closed by retraction and relative extrusion of anterior teeth in both jaws.
• Open bite closure in these patients during the first year after completion of treatment was stable and did not change significantly. Patients must be followed up for longer periods of time for more accurate assessment of the stability of treatment results.

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