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JADA Specialty Scan - Orthodontics
Orthodontics - A Quarterly Newsletter on Dental SpecialtiesJADA Specialty Scan

Study finds more anterior tooth exposure deemed more attractive

When it comes to visibility of the maxillary anterior teeth, orthodontists and laypeople have similar perceptions about what constitutes an attractive amount of exposure, according to a study published in the September 2015 issue of Journal of the World Federation of Orthodontists.

It is well recognized that the maxillary central incisors play a major role in appearance perception. Considering that their exposure at rest is an important aspect of overall esthetics, yet finding no evidence-based literature addressing the topic, scientists in Brazil had 2 questions: Do different levels of maxillary incisor exposure affect dentofacial esthetics? What level is considered most attractive?

To explore these questions, they designed a study to evaluate the perceptions of orthodontists and laypeople of dentolabial esthetics at repose, while assessing different levels of maxillary incisor exposure. Photographs of 1 woman and 1 man were altered to create 6 close-up and 6 full-face images with varying degrees of central incisor exposure in 0.5-millimeter increments—0, 0.5, 1, 1.5, 2, and 2.5.  The judges—54 orthodontists and 54 laypeople—rated attractiveness on a visual analog scale from “very unattractive” to “very attractive.”

Scientists found that both orthodontists and laypeople assigned the highest scores to images with the most tooth exposure (2.5 and 2.0 mm for the woman and 2.5, 2.0 and 1.5 mm for the man). The lowest score was assigned to the images with no tooth exposure for both the female and male images. There was no significant difference between full-face and close-up view assessments and no significant difference between opinions in the 2 groups of judges—orthodontists and laypeople.

“The key aspect found in this research was that minimal maxillary incisor exposure was extremely unattractive,” the authors said in the discussion. Furthermore, the clinician must proactively plan for “… situations that may lead to a decrease of maxillary incisor exposure, such as (a) increased anatomic upper lip length; (b) decreased maxillary skeletal length; (c) attrition of the maxillary central incisors without restoration of the incisal edges; (d) improper bracket positioning during orthodontic treatments; and (e) … flattening of the smile arc.” They called for more studies to clarify if even greater tooth exposure at repose (that is, 3.0, 3.5, or 4.0 mm) would be assessed as even more attractive.

Some previous research has found a difference between orthodontists and laypeople when evaluating several smile characteristics, whereas this study did not. “Our hypothesis is that the variable tested in this study—esthetic perception of the amount of maxillary incisor exposure at rest—is not as specific as several smile characteristics that require a technical background and, thus, the perceptions between orthodontists and laypeople appear to be similar,” stated the authors.

Read the original article.


Consulting Editor: Lee W. Graber, DDS, MS, PhD
Diplomate, American Board of Orthodontics

Environmental factors are primary cause of maxillary canine impaction

A review article published in the October 2015 issue of American Journal of Orthodontics and Dentofacial Orthopedics discusses the reasons maxillary permanent canines become impacted and proposes an alternative interpretation of the evidence.

With the exception of the third molars, maxillary permanent canines are the most frequently impacted teeth. While many researchers believe genetic etiology is exclusively to blame, the authors of the October 2015 article cited varied reasons in 4 categories to support a guidance theory based on environmental factors.

The scientists at Hebrew University-Hadassah School of Dental Medicine, in Jerusalem, Israel, describe evidence of phenomena in each category—local hard-tissue obstruction, local pathology, departure from or disturbance of the normal development of the incisors, and hereditary or genetic factors—to support their perspective. The authors suggested that clinicians monitoring permanent tooth eruption need to be aware of potential disturbances, often indicated by uneven or delayed canine emergence.

They said that the environmental guidance theory and the genetic theory share the belief that certain genetic features (including small, peg-shaped, and missing lateral incisors; spaced dentitions; and late developing dentitions) occur in association with the cause of palatal displacement of the maxillary canine. However, according to the genetic theory, palatal displacement of the canine is just another associated genetic characteristic, whereas the scientists’ findings show that such factors create a genetically determined environment in which the developing canine is deprived of its guidance, which influences it to adopt an abnormal eruption path.

“The evidence presented here endorses the assertion that eruption of the canine is strongly influenced by environmental factors,” they said among conclusions. Providing further direction, the authors suggest, “Alteration of the immediate environment of the unerupted maxillary canine by hard tissue bodies, soft tissue lesions, or developmental pathologic entities can cause the tooth to become impacted, whereas their elimination often results in partial or complete resolution. On the other hand, creating space, by anteroposterior or lateral expansion, by extraction of teeth, and by uprighting premolar or incisor roots, is effective in favorably redirecting the eruption path of an errant canine.”

Read the original article.


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Posterior crossbite: relationship to skeletal and muscle asymmetry

Although most studies report skeletal asymmetric growth in participants with unilateral posterior crossbite, no definitive conclusion can be drawn about the nature of the relationship between posterior crossbite and skeletal asymmetry, reported scientists in an article published online January 28 in The European Journal of Orthodontics.

“Very few studies on the topic report long-term data, limiting the evidence on the topic and making it impossible to understand whether the posterior crossbite is a cause, an effect, or unrelated to skeletal and muscular asymmetries,” they concluded.

To investigate the correlations between posterior crossbite, which occurs in 8% to 22% of orthodontic patients and 5% to 15% of the general population, and different asymmetric conditions of the stomatognathic system, scientists in Italy conducted a systematic review. They searched for relevant studies published over the past 20 years to investigate the association between posterior crossbite and morphologic or functional asymmetries (that is, skeletal, masticatory muscle electromyographic [EMG] performance, bite force, muscle thickness, and chewing cycle asymmetries).

From over 2,100 initial citations, they ultimately selected 45 studies, based on specific inclusion and exclusion criteria, and analyzed them. Some studies were included in more than 1 group of associations.

The key findings from most studies of unilateral posterior crossbite were associated asymmetrical skeletal growth, uneven EMG activity on the crossbite versus noncrossbite side, and potential for significantly smaller bite force when compared with patients who did not have crossbites. Within the conclusions, scientists stressed that even if a significant association between unilateral posterior crossbite and skeletal and functional asymmetries had been reported elsewhere, a certain amount of asymmetry had to be considered physiological and present in all participants. Scientists called for future research with long-term data and more rigorous scientific methodology to better define causal relationships.

Read the original article.

Editor’s note: This systematic review could not define a causal relationship, but many of the referenced articles support early correction of posterior crossbites that have associated functional jaw shift so as to reduce the risk of developing asymmetrical growth and development.

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Opportunity to help kids

Economically disadvantaged children who lack insurance coverage or who do not qualify for other assistance in their states of residence may qualify for pro bono orthodontic care through the American Association of Orthodontists Donated Orthodontic Services (DOS) program. DOS is available in all 50 U.S. states. Dental Lifeline Network administers the program.

Each patient is required to have an examination by a dentist to assess overall oral health. Applicants must be patients of record of a general or pediatric dentist or a dental clinic. Many patients who have been accepted by the program were referred by their dentists.

Download the application at the AAO website.

Read more about the DOS program from AAO and in ADA News.


ADA’s Braces Journal charts patients’ progress

For teens embarking on the journey to a better smile, the ADA offers The Braces Journal. Focusing on the benefits of braces, the booklet coaches younger patients on how to get the most from the orthodontic experience. Space for notes, sketches, and photos is included, as well as lists of websites, books, and magazines geared toward teens. The booklet reminds kids that wearing braces is “a partnership between you, your family and your doctor to create a new smile—your new smile!”

The Braces Journal is sold in boxes of 36 booklets. Sample pages can be viewed here. Call 1-800-947-4746 or go to adacatalog.org. Readers who use the code 16401E before June 30 can save 15 % on all ADA Catalog products.


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What is Specialty Scan?

This is one in a series of quarterly newsletters updating dentists on selected specialties in dentistry. Information presented is aggregated and summarized from previously published materials, each item attributed to its publication of origin. This issue of JADA Specialty Scan focuses on orthodontics, the second in the series on this topic for 2016. Other Specialty Scan issues are devoted to endodontics, oral and maxillofacial radiology, oral pathology, periodontics and prosthodontics. The ADA has engaged the specialty organizations in these areas as well as its own Science Institute and Division of Legal Affairs to assist with these newsletters. We welcome feedback on this and all Specialty Scan issues.

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