Drs. Zubad Newaz and Laurance Jerrold investigate whether providers’ own experiences correlate with their own treatment philosophies regarding extraction orthodontics
The issue of extraction therapy has been a historically contentious issue in orthodontics, but no study exists in the literature that investigates whether a provider’s own experience correlates with their own treatment philosophies regarding extraction orthodontics. A simple survey was distributed via various channels to orthodontists in North America. Seventy respondents completed the survey, of which 74% had orthodontic treatment. Among those treated, 24% had premolar extractions; 26% of providers who had extractions wished they did not have extractions, whereas only 6% of providers who did not have extractions wished that they did. Orthodontists who had extractions overall reported a greater number of perceived sequelae and were more skeptical about the role of extractions in temporo-mandibular disturbances and airway disturbances, although no statistically significant differences were found in any cross correlations between the extraction group and the others. A majority of both extraction and nonextraction groups reported no adverse sequelae.
No significant differences were noted between providers who had extractions and other providers for the parameters studied, but some tendencies were noted that characterize prior extraction subjects to be more averse to extraction therapy.
Orthodontists have been historically divided on the issue of extractions, dating back to the early 20th century when the practices of the father of modern orthodontics, Dr. Edward Angle, who was known not to subscribe to extraction therapy, were challenged by later leaders — namely, Dr. Charles Tweed, who retreated his allegedly failed nonextraction treatments with extractions and reported better outcomes.1 The wave of increase of extractions in the 1950s and 1960s that followed Tweed’s presentation in the 1940s represented the first shift of the “pendulum” we know today, with changes in thought regarding the appropriateness of extraction therapy in orthodontics, which many consider is currently back toward the nonextraction paradigm.
Some of the issues surrounding each pendulum shift include discussions about various topics, including stability, profile and facial esthetics, arch/smile width, periodontal health, TMJ disturbances, sleep disturbances and airway compromise, compatibility with holistic concepts (i.e., preservation of healthy tissues in the body), and changing perceptions of facial esthetics and beauty. Perhaps at the core of the debate is the nature versus nurture argument in jaw development. Some purport that we as a profession should adapt to the observational decrease in jaw size that has followed the evolution of mankind in modern history, and that accommodating to these discrepancies is possible by removing teeth. Others propose that reasonable interventions exist to guide jaw development that allow for even the modern human to be able to accommodate teeth predictably without extractions by emphasizing supportive therapies that better allow for this.
Brimm v. Malloy (1987) was a landmark legal case that precipitated a reawakening of the debate surrounding the appropriateness of extraction therapy, where the jury ruled against a Michigan orthodontist and awarded the plaintiff $850,000 who claimed she developed temporomandibular disorder (TMD) after upper premolar extraction and retraction, causing mandibular posteriorization and entrapment.2 Some authors have described the outcome of this ruling to be unfortunate and unfounded in scientific principles.2,3 Much of said scientific knowledge base stemmed from efforts from the orthodontic community following this ruling to prove that extraction orthodontics does not categorically cause TMD (nor has a detrimental effect on facial form). The publishing of many articles ensued, which contained a plethora of data and theories that essentially debunked the incidence of any detrimental effects of extraction orthodontics.4-12 These articles, which suggest that negativities in arch width, facial form, and temporomandibular balance do not occur following extraction therapy, are currently regarded as classical literature and required reading for every orthodontic resident in the United States, and are testable material for the American Board of Orthodontics’ certifying examination.
As modern trends toward nonextraction therapy progress in today’s orthodontic landscape, some providers continue to question the body of evidence that exists about the harmlessness of extraction therapy. Perhaps the most prominent limitation for these studies, and almost all clinical orthodontic literature, is that it is very difficult to design high-quality controlled studies that follow the patients for decades after their orthodontic treatment, especially when some of the alleged undesirable effects of extraction treatment typically arise at a much later age than the treatment.
It can also be contended that the effects of extraction can be classified based on their anticipated effects on the dentoalveolar complex, in that some extractions are not intended to result in any change in jaw size and morphology, and the teeth simply play “musical chairs” within the jaw in order to align, whereas other extractions are performed with the direct effect of reducing jaw size or dentoalveolar procumbency. It is likely that the effects of these treatments are fundamentally different from one another. This is not to say that the classical literature completely ignored this potential difference (by including headgear and maxillary incisor retraction groups in their studies), but the discrimination of these groups is considered by some to be inadequately addressed in a longitudinal period of sufficient duration to make conclusions.
This also leads to an area of recent heightened interest with airway and sleep-disordered breathing concerns, which was not an area of peak focus in the era of influx of extraction-supporting literature. As such, a lack of attention to airway resistance issues and effects of underdeveloped jaws with time is a limitation to many empirical demonstrations of the benign nature of extraction orthodontics. Understanding about this topic is evolving and is a work in progress, with conflicting reports in the literature demonstrating a mix of detrimental versus non-detrimental effects on the airway.13-23
The advent of CBCT has allowed for a better assessment tool to comprehensively evaluate some of the issues that relate to bone support, TMJ morphology and position, and airway characteristics in three dimensions. This serves to overcome limitations in the two-dimensional cephalometric support found in the extraction-supporting literature. It is empirically demonstrated that different orthognathic surgical movements and modifications to the jaws carry significant, predictable effects on airway morphology.24-29 This is regarded as support for those who suggest that changes from nonsurgical orthodontics may mimic such patterns as clearly demonstrated for corresponding surgical movements, albeit more minutely, but regarded as insignificant by others who deem these effects too minor to draw conclusions of clinical significance.
The need for longitudinal support to demonstrate adverse or non-adverse effects brings about another conundrum. If an extraction subject does develop problems later in life, the multifactorial etiologic possibilities of such conditions, known to have complex etiologies, will preclude identification of a primary etiology. This is a built-in obstacle to any provider or investigator who attempts to demonstrate that extractions have any detrimental effects and are challenged by the empiricists to produce proof that this is indeed what contributed to the rise of adverse effects after extraction treatment. This obstacle will, by its nature, be very difficult to ever overcome (empirically, that is).
The purpose of the preceding commentary is not to be, in itself, any support or detraction for either side of the argument. Rather, it serves to reinforce that great minds in our profession have failed to reach consensus about this topic after over 100 years of existence. The nature of the orthodontic profession is that a series of anecdotes and innovations have led to treatment modalities, and their effectiveness or ineffectiveness is eventually demonstrated through a combination of widespread provider experience and literature support. However, this process typically occurs significantly later than the time point where these principles are found to be effective by one or few individuals in practice and thereabout presented or proposed to the orthodontic community. In other words, one might argue that the orthodontic profession is largely founded and dependent on anecdotes as building blocks to regarding therapies as reliable and responsible. As such, the orthodontic professionals who ponder into the validity of anecdotal evidence and thereby defer to their colleagues to investigate how they perceive such issues, in order to build a case for or against a treatment modality, are valuable assets to the profession. This process has given rise to many proven therapies we rely on today to practice our profession.
With this, we sought to investigate how orthodontists’ own experiences with orthodontic treatment on themselves shape their views about the extraction issue. We were unable to locate any study in the accessible literature relating to this topic. Anecdotal reports on non-orthodontist patients are plentiful in support or opposition to extraction therapy, but those of orthodontists themselves may help qualify and validate some viewpoints given their own unique combination of expertise along with their experiences as orthodontic patients. Hence, our study serves as a pilot investigation via a simple survey that inquires about the provider’s own type of treatment and perception of it, how it might have influenced them, and whether certain thought processes regarding extractions might apply to them. We hope that this study will help precipitate more valuable investigations into this topic, so as to provide an alternate, supplemental dimension for the orthodontic practitioner to ponder over their treatment philosophies in addition to the clinical experience and body of evidence to which we conventionally refer.
An 11-item survey on pages 88 to 90 was sent to program directors or chair-persons of orthodontic residency programs in the United States and Canada with a request to distribute to all faculty and residents within their departments, as well as to other orthodontists for which the principal investigator had contact information.
The recruitment of subjects was made through an email welcome letter with a brief explanation of the topic being investigated, including an anonymous link to the survey supported by Qualtrics (Provo, Utah).
Complete responses were recorded. Incomplete surveys were excluded. Tallies were made and readily retrievable using the Qualtrics survey reporting tools. Proportions of respondents answering the questions were extracted. In addition to basic tallies and descriptive statistics, a cross-reference tool was utilized to weigh the responses of Questions No. 8 (about treatment sequelae) and No. 11 (about modes of thinking) against the provider’s extraction history, and a Chi-square analysis was used to determine significance of differences between responses of these categorical variables (alpha set to 0.05).
Seventy respondents completed the survey. The experience level of respondents was effectively bimodal, with 50.7% of respondents having 20-plus years of experience and 34.8% having 0-5 years; 74% of respondents underwent orthodontic treatment.
The following proportions are of those who had orthodontic treatment. A vast majority (72.6%) of the treated respondents had orthodontic treatment started early in life (childhood/adolescence), while 23.5% started later in life before practicing orthodontics and 11.8% during their practicing careers. The sum of these numbers exceeds 100% due to several respondents having undergone treatment more than once in their lifetime. A minority, 18%, had noteworthy dental anomalies of tooth size or number.
Nineteen respondents reported having extractions of some type. Twelve respondents (23.5 %) of treated respondents had premolar extractions without a major skeletal component, while one respondent reported having a skeletal component. Six (11.8%) reported having extractions of a different protocol, and 62.8% of respondents had no extractions. Of those who had extractions, five respondents (23%) replied that they wish they did not have them done, and seven (37%) responded that they are content with having had them done. Of those who did not have extractions, two respondents (6%) wish they had them done, while nine (28%) reported that they would not have wished to have them done. The remainder responded that their responses would depend on a review of their initial records or that the question did not apply to them.
A greater proportion of the extraction group reported narrow archforms, lack of smile fullness, flat profile, TMJ disturbances, premature anterior contact with posterior functional shift, and snoring/sleep apnea than nonextraction subjects. No respondent in any group indicated that their smile was either too broad or that their profile was too full. A greater proportion of the nonextraction group (77.4%) reported no negatives with treatment than the extraction groups (50% premolar group and 16.7% other extraction group). Cross tabulation showed that no significant differences were found between any of the answer choices and extraction history (p = 0.16).
A small majority of treated respondents (57%) replied that their own treatment experience has influenced the way they treat their patients. Among the extraction group respondents who were influenced by their treatment, five respondents reported that they recommend less extractions and four recommend more, showing almost equal distribution. Among the nonextraction group respondents who were influenced by their treatment, 13 reported that they recommend less extractions, and two recommend more, showing a noteworthy predilection toward nonextraction subjects recommending less extractions.
For Question No. 11, a greater proportion of premolar extraction subjects reported more skepticism about extractions correlating to TMJ disturbances (25%, versus 17% no tx and 9% non-extraction), and sleep/breathing disturbances (41%, versus 22% no tx and 16% non-extraction), and that anterior tooth retraction could have detrimental effects on the airway (25%, versus 5% no tx and 3% non-extraction). Cross tabulation showed that no significant differences were found between any of the answer choices and extraction history (p = 0.69).
Our study did not show any significant differences between provider treatment type and the items for questions No. 8 (sequelae) and No. 11 (attitudes). Despite this, the results of our pilot study suggest a tendency for orthodontists who have had extractions to a) be more wishful of the alternative (nonextraction) treatment, b) recommend proportionally less extractions than the converse of their nonextraction counterparts, c) be more skeptical of the role of extractions in temporomandibular disorder, sleep-disordered breathing, and anterior retraction effects on the airway, and d) report more adverse sequelae that they attribute to their treatment. It was interesting to note that no respondent thought that their smile was too broad or full, indicating, perhaps, a lesser risk of patient displeasure when employing such an approach in a borderline case.
This study had significant limitations. The sample was not at all random, having been distributed primarily to academic personnel (faculty, residents, etc.), and other orthodontists otherwise known or locally available to the investigators. With the cohort being mostly academic, it may have differed from general orthodontic populous if the survey was more far-reaching and did not grossly under-represent important sectors of orthodontic professionals (private practice, public service, internationals, etc.). The sample size was small, given the target population of at least 13,500 (and many more if distributed worldwide, as there was no reason to limit this survey to North Americans based on the objective).
There was substantial bias in survey distribution, which depended on many recipients of the email invitation to forward the survey to others, instead of acquiring proper lists of all personnel and sending the survey to individuals directly. There was bias built into question No. 11, which contained only statements of belief of those with a particular line of thought.
Another problem with this question was that the choice was simply to select or not select, whereas a better positioning of this question would be to offer a continuum or 5-point scale response. An example of such a modification would read “Extractions contribute to TMJ disturbances,” giving the respondent the ability to select on a scale of strongly disagree to strongly agree. Respondents might have answered the questions differently if presented in this way, and there may have been fewer empty data points as orthodontists harbor beliefs on a continuum.
A comments section was unavailable for the respondents to deliver feedback or personalized pertinent information, which, for a pilot study, would have been very useful in the shaping of future studies and to include as discussion points. Furthermore, this would have better captured the primary intent of this study, which was to collect thoughts about how providers truly feel about this issue given their experiences. There might have also been respondent-fatigue from question display, as questions No. 8 and 11 each had 12 answer choices, making for a less-than-ideal visual survey flow. It may have been better to pose these questions separately, and this may have further facilitated targeted statistical analysis.
This survey was potentially too inclusive of different variables and attitudes, as more meaningful data might have been acquired with a more selective focus of topic (e.g., extraction history effect on airway beliefs). However, it was chosen to include all variables as this pilot study sought to identify ways to refine future studies, and this, we believe, was better achieved by broadening the scope of this study.
Inadequate statistical testing and application of exclusion criteria are other potential criticisms of this study, as more extensive statistical comparisons could have been made, as well as cross references between variables other than extraction history.
Lastly, technical glitches seemed to contribute to some respondents not being displayed questions that should have otherwise been displayed, which reduced collectible data, and may have confused some respondents as to why the apparent objective of the study’s title was not at all explored, especially for those respondents who did not undergo orthodontic treatment and did not see the full spectrum of questions. Perhaps a medium where all questions are visible on a scroll-down page, so that respondents are more acquainted with the study, would be a better mode of visualization.
In addition to the immediately foreseeable improvements in this investigation as highlighted above, another potential supplement to the exploration of this topic in the future might include the formulation of an issue or collection of orthodontists’ detailed commentary on their own treatment and effects, with photographic and radiographic support. A chronicle or repository of sorts of orthodontists providing detailed documentation of their records, along with any supporting data such as health assessments, sleep studies, occlusal analyses, and other adjuncts could be a valuable resource for the profession.
Given the abundance of limitations and limited conclusiveness of this study, this body of work does not seek to be recognized as science and is absolutely not intended to guide clinical decision-making in any way for the target audiences. Rather, this study and its existence in the literature is intended to provoke thought among orthodontic professionals to consider personal experience in the professional milieu, and to gently challenge staunch views of evidence-based dogmatism in orthodontics — a field where the science is universally understood to be somewhat “soft” and very subjective in nature. This study proposes the orthodontist to value that anecdotal evidence that is akin to the essential professional act of listening to one’s own patient and considering all of their reported complaints and problems with an open ear, so as to deliver personalized, individualized care and understand the limits of a profession, especially of orthodontics, to produce hard evidence and then further apply it to the momentary clinical situation, especially when it involves an irreversible procedure.
This study also seeks to assign a different degree of anecdotal evidence — that which is observed by the practitioner in his/her own body in conjunction with his/her own expertise. Anecdotal evidence may take a new meaning when a person is himself/herself the anecdote in question. Additionally, it does not take much of a venture for the orthodontist to find reports in his/her own practice or on message blogs and websites to hear the valid concerns of patients and parents regarding this controversial aspect of our profession. There are few, if any, instances of a large percentage of professional practice in other disciplines of medicine and dentistry involving the removal of healthy organs to achieve a standard that the profession exclusively holds to be golden, with the exception of plastic surgery, perhaps.
No significant differences were noted between providers who had extractions and other providers for the parameters studied, but some tendencies were noted that characterize prior extraction subjects to be more averse to extraction therapy. Although both extraction and nonextraction treatment served many of the subjects well without problems, more perceived problems were reported by extraction subjects. Stronger, more focused studies are needed to build on the takeaways of this pilot study.
Survey: Orthodontic provider treatment experience and effects on treatment approaches and experience regarding extraction therapy
1. How long have you been practicing orthodontics?
- 0-5 yrs
- 5-10 yrs
- 10-15 yrs
- 15-20 yrs
- more than 20 yrs
2. Have you ever undergone orthodontic treatment?
- Yes (continue to Question #3)
- No (skip to Question #11)
3. When did you have the treatment started? (Select all that apply.)
- Early in life, childhood/adolescence
- Later in life, young adulthood or adulthood, but before my practicing career
- During my practicing career
4. Do/did you have any dental anomalies regarding tooth number (supernumerary/missing) or gross tooth size discrepancies?
5. Have you had extraction treatment performed?
- Yes, 4 premolars or 2 premolars in one jaw, and I do not remember having orthognathic surgery or a major skeletal discrepancy
- Yes, 4 premolars or 2 premolars in one jaw, and I know that I had orthognathic surgery or a major skeletal discrepancy
- Yes, some other protocol (lower incisor, substitution, atypical, second molars, etc.)
6. Having learned and practiced the profession as you have, do you wish that you did not have premolars extracted if you were treated with extraction mechanics?
- Not sure, it would depend on a comprehensive review of my initial records
- Does not apply to me
7. Having learned and practiced the profession as you have, do you wish that you did have premolars extracted if you were treated with expansion mechanics (which does not necessarily include all nonextraction cases, as spacing is not typically treated with expansion mechanics)?
- Not sure, it would depend on a comprehensive review of my initial records
- Does not apply to me
8. From a qualitative perspective (this question does not depend on whether you have had a definitive knowledge of your ortho-dontic workup or diagnoses), do you consider yourself to have any of the following characteristics, which you either know or question if they were related to your orthodontic treatment? [check all that apply]
- Narrow archform/excessive buccal corridors
- Smile too wide/arch too broad
- Lack of smile fullness/anterior teeth inclined too upright or far back
- Overly flat profile or other associated soft tissue characteristics such as inadequate lip support
- Unsightly dental protrusion in any arch
- Too much smile or profile fullness
- Gingival recession or periodontal compromise
- TMJ disturbances, not requiring intervention or impacting quality of life
- TMD or other orofacial pain that would benefit from intervention or that has adversely impacted quality of life
- Premature anterior occlusal contact with a posterior functional shift into centric occlusion
- Snoring/obstructive sleep apnea/airway resistance
- No perceived negatives secondary to my orthodontic treatment
9. Do you feel that your own treatment experience has influenced the way you treat your patients?
- Yes (continue to Question #10)
- No (skip to Question #11)
10. If yes, how so?
- I had extraction treatment, and it leads me to recommend fewer extractions than I otherwise would had I not been treated.
- I had extraction treatment, and it leads me to recommend more extractions than I otherwise would had I not been treated.
- I had nonextraction treatment, and it leads me to recommend fewer extractions than I otherwise would had I not been treated.
- I had nonextraction treatment, and it leads me to recommend more extractions than I otherwise would had I not been treated.
11. If any of the following thought processes apply to you, please select all that apply:
- A. “Despite a lack of evidence for extractions causing sleep/breathing disturbances, I am not convinced that there is no correlation.”
- B. “Despite a lack of evidence for extractions causing temporomandibular disturbances, I am not convinced that there is no correlation.”
- C. “I think there is some merit to archform broadening with slow, gentle mechanics as a means of creating space to accommodate all the teeth most or all of the time without compromising bone support”.
- D. “I do not believe that incisors get pushed off of the bone support when they are advanced or proclined as long as appropriate mechanics are used”.
- E. “I avoid retraction of the anterior teeth whenever possible because I am concerned about the effects on the airway, and/or I am not convinced that the tongue will necessarily adapt favorably to a smaller oral cavity.”
- F. “I am not so bothered with the bimaxillary protrusive profile and question (or refute) whether it is a condition that should be treated by removing otherwise healthy body parts (teeth).”
- G. “I do not believe that nonextraction treatment categorically increases the vertical dimension; i.e., there are non-cumbersome ways to offset adverse vertical effects of nonextraction treatment.”
- H. “I do not believe that nonextraction treatment increases the incidence of late incisor crowding.”
- I. “Proper myofunctional training and correct oral posture is essential to jaw development, treatment effectiveness, and for creating an environment for posttreatment stability.”
- J. “I do not think that mainstream orthodontic thought promotes the development of jaws to their full genetic capacity at a young age.”
- K. “I believe that full development of the jaws promotes health and good facial form and am willing to accept certain minor dental/orthodontic compromises to achieve such development.”
- L. “The airway is at least equally or more important to me than the dento-skeletal features of a malocclusion itself in the diagnostic process and is one of the most major considerations when determining appropriateness of a treatment plan
- Rinchuse DJ, Busch LS, DiBagno D, Cozzani M. Extraction treatment, part 1: the extraction vs. nonextraction debate. J Clin Orthod. 2014;48(12):753-760.
- Williams P, Roberts-Harry D, Sandy J. Orthodontics. Part 7: Fact and fantasy in orthodontics. Br Dent J. 2004;196(3):143-148.
- Rinchuse DJ, Kandasamy S. Temporomandibular Dysfunction: Controversies and Orthodontics (Chapter 24) in Integrated Clinical Orthodontics, 2012 – Wiley Online Library.
- Gianelly AA. Orthodontics, condylar position, and TMJ status. Am J Orthod Dentofacial Orthop. 1989;95(60:521-523.
- Gianelly AA, Hughes HM. Wohlgemuth P, Gildea C. Condylar position and extraction treatment. Am J Orthod Dentofacial Orthop. 1988;93(3):201-205.
- Gianelly AA, Petras JC, Boffa J. Condylar position and Class II deep bite, no-overjet malocclusion. Am J Orthod Dentofacial Orthop. 1989;96(5):428-432.
- Gianelly AA, Cozzani M, Boffa J. Condylar position and maxillary first premolar extraction. Am J Orthod Dentofacial Orthop. 1991;99:473-476.
- Gianelly, AA, Anderson CK, Boffa J. Longitudinal evaluation of condylar position in extraction and nonextraction treatment. Am J Orthod Dentofacial Orthop. 1991;100(5):416-420.
- Luppanapornlap S, Johnston LE Jr. The effects of premolar extraction: A long-term comparison of outcomes in “clear-cut” extraction and nonextraction Class II patients. Angle Orthod. 1993(4);63:257-272.
- Stephens CK, Boley JC, Behrents RG, Alexander RG, Buschang PH. Long-term profile changes in extraction and nonextraction patients. Am J Orthod Dentofacial Orthop. 2005;128(4):450-457.
- Erdinc AE, Nanda RS, Dandajena TC. Profile changes of patients treated with and without premolar extraction. Am J Orthod Dentofacial Orthop. 2007;132(3):324-331.
- Bishara SE, Cummins DM, Jakobsen JR, Zaher AR. Dentofacial and soft tissue changes in Class II Division 1 cases treated with and without extractions. Am J Orthod Dentofacial Orthop. 1995;107(1):28-37.
- Haddad S, Kerbrat JB, Schouman T, Goudot P. [Effect of dental arch length decrease during orthodontic treatment in the upper airway development. A review]. Orthod Fr. 2017;88(1):25-33.
- Bhatia S, Jayan B, Chopra SS. Effect of retraction of anterior teeth on pharyngeal airway and hyoid bone position in Class I bimaxillary dentoalveolar protrusion. Med J Armed Forces India. 2016;72(suppl 1):S17-S23.
- Pliska BT, Tam IT, Lowe AA, Madson AM, Almeida FR. Effect of orthodontic treatment on the upper airway volume in adults. Am J Orthod Dentofacial Orthop. 2016;150(6):937-944.
- Guilleminault C, Abad VC, Chiu HY, Peters B, Quo S. Missing teeth and pediatric obstructive sleep apnea. Sleep Breath. 2016;20(2):561-568.
- Hu Z, Yin X, Liao J, Zhou C, Yang Z, Zou S. The effect of teeth extraction for orthodontic treatment on the upper airway: a systematic review. Sleep Breath. 2015;19(2):441-451.
- Stefanovic N, El H, Chenin DL, Glisic B, Palomo JM. Three-dimensional pharyngeal airway changes in orthodontic patients treated with and without extractions. Orthod Craniofac Res. 2013;16(2):87-96.
- Zheng Z, Liu H, Xu Q, Wu W, Du L, Chen H, Zhang Y, Liu D. Computational fluid dynamics simulation of the upper airway response to large incisor retraction in adult class I bimaxillary protrusion patients. Sci Rep. 2017; 7;7:45706.
- Hang WM, Gelb M. Airway Centric® TMJ philosophy/Airway Centric® orthodontics ushers in the post-retraction world of orthodontics. Cranio. 2017;35(2):68-78.
- Buck LM, Dalci O, Darendeliler MA, Papageorgiou SN, Papadopoulou AK. Volumetric upper airway changes after rapid maxillary expansion: a systematic review and meta-analysis. Eur J Orthod. 2017; 1;39(5):463-473.
- Chen Y, Hong L, Wang CL, Zhang SJ, Cao C, Wei F, Lv T, Zhang F, Liu DX. Effect of large incisor retraction on upper airway morphology in adult bimaxillary protrusion patients. Angle Orthod. 2012;82(6):964-970.
- He J, Wang Y, Hu H, Liao Q, Zhang W, Xiang X, Fan X. Impact on the upper airway space of different types of orthognathic surgery for the correction of skeletal class III malocclusion: A systematic review and meta-analysis. Int J Surg. 2017;38:31-40.
- Gottsauner-Wolf S, Laimer J, Bruckmoser E. Posterior Airway Changes Following Orthognathic Surgery in Obstructive Sleep Apnea. J Oral Maxillofac Surg. 2018;76(5):1093.e1-1093.e21.
- Christovam IO, Lisboa CO, Ferreira DM, Cury-Saramago AA, Mattos CT. Upper airway dimensions in patients undergoing orthognathic surgery: a systematic review and meta-analysis. Int J Oral Maxillofac Surg. 2016;45(4):460-471.
- Al-Moraissi EA, Al-Magaleh SM, Iskandar RA, Al-Hendi EA. Impact on the pharyngeal airway space of different orthognathic procedures for the prognathic mandible. Int J Oral Maxillofac Surg. 2015;44(9):1110-1118.
- Marcussen L, Stokbro K, Aagaard E, Torkov P, Thygesen T. Changes in Upper Airway Volume Following Orthognathic Surgery. J Craniofac Surg. 2017;28(1):66-70.
- Jiang C, Yi Y, Jiang C, Fang S, Wang J. Pharyngeal Airway Space and Hyoid Bone Positioning After Different Orthognathic Surgeries in Skeletal Class II Patients. J Oral Maxillofac Surg. 2017;75(7):1482-1490.