The upper anterior bite plane built into the Kurz lingual orthodontic appliance has been a standard feature virtually since its original design over 20 years ago, and is one of its frequently cited advantages in the treatment of deep bite cases.1 To date, however, there has been relatively little published research to elucidate the precise bite opening effects of this appliance, although many clinical lingual operators may be subjectively familiar with the clinical effects of the technique. Some passing mention has been made of incisor intrusion, but results are either still unpublished,2 or lack statistical definition.3 It has been well documented elsewhere that bite opening with conventional labial appliances is typically accompanied by posterior dental eruption, often in conjunction with normal growth and/or undesirable backward mandibular rotation.4,5
Investigation of Specific Treatment Changes
Since many patients who undertake lingual orthodontic treatment are adults whose treatment would be unaffected significantly by growth, it was concluded at the outset that any changes during treatment could be ascribed essentially to the unique nature of the lingual appliance.
A sample of 44 adult patients was collated retrospectively, subject to the following criteria:
1. All patients had positive overbite prior to treatment.
2. All patients were treated non-surgically with Ormco Generation 7 lingual orthodontic appliances* on both upper and lower arches.
To assess changes in relation to bite opening, lateral cephalometric radiographs were traced before and after treatment, and digitised using a Numonics Model 2200 digitiser unit.** For all linear measurements, appropriate calculations were made to compensate for image magnification.
For each individual patient a set of radiographic superimpositions was performed according to the structural methods as described by Björk and Skieller,6-8 in order to measure vertical movement of central incisors and first molars relative to their skeletal bases. This approach was favoured over other commonly described superimposition methods (e.g. superimposition on ANS-PNS to quantify changes in the maxillary region, etc.) as it was the one most closely supported by longitudinal implant studies,9 and therefore possessed the greatest anatomical validity.10 A more authentic assessment of true intrusion and/or extrusion was therefore possible.
In addition to dental landmarks, various skeletal landmarks were examined to detect any vertical changes associated with mandibular rotation. A two-tailed paired t-test was performed to compare all measurements before and after treatment. |
Evidence of Incisor Intrusion
A summary of general changes during treatment (Table 1) revealed that there were no appreciable vertical skeletal alterations. Changes in interdental relationships were pronounced and variable, probably reflecting the individual nature of the patients, and the fact that the sample included a combination of Angle malocclusions. Of particular note were the highly variable responses with respect to incisor angulations, which may have influenced the minor changes detected in points A and B.
Examination of the vertical positions of incisors and molars (Table 2) indicated intrusion of the lower incisors and (to a lesser degree) vertical extrusion of the lower molars. No conclusive vertical intrusion/extrusion of the upper teeth was detectable, as the average upper incisor movement (0.3mm of extrusion) was within the likely range of measurement error.11,12 Individual patient responses were again highly variable in this respect, but with bite opening noted in virtually all cases treated. In a small minority of cases a very slight bite deepening was observed, and this effect was noted only in cases that were almost end-to-end before treatment (ie. in which slight bite closure may have been desirable).
It is possible that the bite plane effect of the lingual appliance may have prevented excessive bite closure in such cases, facilitating vertical control. This aspect of vertical control with lingual orthodontic mechanics is of particular importance during treatment of Class II division 2 malocclusions, which typically exhibit a tendency toward an excessively deep bite. In the present study, the greatest overbite reduction (7.4mm) was observed in such a case. Similar such responses have been noted routinely by the author during treatment with the Generation 7 lingual appliance. These findings are generally consistent with recent research by Suda, who noted similarly consistent lower incisor intrusion with lingual appliances, along with some possible suggestion of backward mandibular rotation.13
Conclusion
Despite the initial difficulties frequently encountered when integrating the lingual technique into clinical practice, one of the major advantages of lingual orthodontics over labial orthodontics is its capability to reduce excessive overbites without associated undesirable skeletal effects. It is suggested that combined lower molar extrusion and lower incisor intrusion would be especially efficacious in addressing the deep curve of Spee common to many deep bite cases.
Many patients in clinical practice appreciate the advantages of lingual orthodontic therapy, but for economical reasons may elect a combined approach involving maxillary lingual appliances and mandibular aesthetic brackets. Occasionally, objections have been raised to the use of lower ceramic brackets in deep-bite cases. The rapid bite-opening effects of the lingual bite plane have addressed this problem, since anterior bracket interference from the onset of treatment is limited to the lingual bite planes. Expanded treatment options such as this serve to open the door to a wider pool of patients.
Further study by the author is pending regarding similar skeletal and dental orthodontic changes with respect to other fixed lingual appliance systems, notably the Fujita method of “inside braces”, and the StealthTM bracket which was recently released on the market by American Orthodontics Corporation.
Acknowledgments
The author wishes to thank Dr. John Jenner, Postgraduate Orthodontic Tutor at The University of Adelaide, for his invaluable guidance during the author’s postgraduate training, and Professor Wayne Sampson, Head of Orthodontics at The University of Adelaide. With their support and encouragement, the author was permitted to lay the groundwork for the first Postgraduate Lingual Orthodontic Program in Australia. The author also expresses gratitude to Professor Ryoon-Ki Hong, Chairman of Orthodontics at Chong-A Dental Hospital in Seoul, Korea, for his mentorship and expert guidance
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References
1. Kurz, C.; and Romano R.: Lingual Orthodontics - Historical Perspective, in Lingual Orthodontics, ed. R. Romano, 1st ed., B.C. Decker Press, Hamilton, Canada, 1998: pp. 3-19.
2. Baker, R.W.: The lingual appliance - molar eruption versus incisor depression (Masters thesis), EastmanDentalCenter, Rochester, NY, 1987.
3. Ronchin, M.: Present clinical reality, in Lingual Orthodontics, ed. R.Romano, 1st ed., B.C. Decker Press, Hamilton, Canada, 1998: 22-24.
4. Burden, D.J.; McGuinnes, N.; Stevenson, M.; and McNamara, T.: Predictors of outcome among patients with Class II division 1 malocclusion treated with fixed appliances in the permanent dentition, Am.J.Orthod. Dentofac. Orthop. 116:452-459, 1999.
5. Luppanapornlarp, S.; and Johnston, L.E.: The effects of premolar extraction: a long-term comparison of outcomes in “clear-cut” extraction and non-extraction Class II patients, Angle Orthod. 63:257-272, 1993.
6. Björk, A.; and Skieller, V.: Postnatal growth and development of the maxillary complex, in Factors Affecting the Growth of the Midface, Monograph No. 6, Cranio-facial Growth Series, ed. J.A. McNamara, Center for Human Growth and Development, University of Michigan, Ann Arbor, MI, 1976.
7. Bjork, A.; and Skieller, V.: Growth of the maxilla in three dimensions as revealed radiographically by the implant method, Br. J.Orthod. 4: 53-64, 1977.
8. Bjork, A.; and Skieller, V.: Roentgencephalometric growth analysis of the maxilla, Trans.Eur.Orthod. Soc. 53rd Congress:51-55, 1973.
9. Björk, A.; and Skieller, V.: Normal and abnormal growth of the mandible: a synthesis of longitudinal cephalometric implant studies over a period of 25 years, Eur. J.Orthod. 5:1-46, 1983.
10. Houston, W.J.B.; and Lee, R.T.: Accuracy of different methods of radiographic superimposition on cranial base structures, Eur. J.Orthod. 7:127-135, 1985.
11. Houston, W.J.B.: Relationships between skeletal maturity estimated from hand-wrist radiographs and the timing of the adolescent growth spurt, Eur. J.Orthod. 2:81-93, 1983.
12. Houston, W.J.B.: The analysis of errors in orthodontic measurements, Am.J.Orthod. 83:382-390, 1986.
13. Suda, Y.: A clinical study on the anterior interferences of lingual brackets, 6th Eur. Lingual Orthod. Congress, Barcelona, 2004. |
