Influence of tooth position on wind instrumentalists’ performance and embouchure comfort

The recommendations for strengthening the reporting were followed in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement [1]. The protocol of this systematic review detailing the review method was developed a priori following initial discussions between members of the research team.

In observational studies and (randomized) controlled clinical trials, what is the difference in performance (primary outcome) and embouchure comfort (secondary outcome) between wind musicians with a normal tooth position and those with an abnormal tooth position?

The following criteria were imposed for inclusion in the systematic review:

The exclusion criteria were as follows:

The PubMed, Cochrane and Embase databases were searched from initiation up to November 2017 (Table 1; F.N.W. and D.E.S.). Furthermore, the main orthodontic journals (European Journal of Orthodontics [Volume 1, Issue 1, January 1979–Volume 39, Issue 5, October 2017]; American Journal of Orthodontics and Dentofacial Orthopedics [Volume 1, Issue 1, January 1915–Volume 152, Issue 5, November 2017]; Angle Orthodontist [Volume 1, Issue 1, January 1931–Volume 87, Issue 6, November 2017]) were searched for papers older than the inception date of PubMed using the search engine as provided by these journals (R.B.K and F.N.W.). Also grey literature was sought via Google Scholar (using various combinations of the following keywords: tooth position, malocclusion, wind instrument, musical instrument, performance). In addition, the reference lists of all selected studies were hand searched for additional relevant articles (F.N.W. and G.A.W.).

Titles and abstracts of the studies obtained from the searches were screened independently by two reviewers (F.N.W. and G.A.W.) and were categorized as definitely eligible, definitely not eligible, or questionable. No language restrictions were imposed. No attempt was made to blind the reviewers to the names of authors, institutions, or journals while making the assessment. If eligible aspects were present in the title, the paper was selected for further reading. If none of the eligible aspects were mentioned in the title, the abstract was read in detail to screen for suitability. Papers that could potentially meet the inclusion criteria were obtained and read in detail by the two reviewers (F.N.W. and G.A.W.). Disagreements in the screening and selection process concerning eligibility were resolved by consensus or, if disagreement persisted, by arbitration through a third reviewer (R.B.K.). The papers that fulfilled all of the inclusion criteria were processed for data extraction.

Two reviewers (F.N.W. and G.A.W.) scored the individual methodological qualities and potential risk of bias of the included studies using a comprehensive combination of the Critical Appraisal Checklist for Analytical Cross Sectional Studies, developed by the Joanna Briggs Institute [11], the Newcastle Ottawa scale adapted for cross-sectional studies [8] and the ROBINS-I tool [4].

Factors used to evaluate the clinical heterogeneity of the characteristics of the different studies were as follows: study design, participants, variables used to measure performance and embouchure comfort, variables used to assess tooth position.

The Grading of Recommendations Assessment, Development and Evaluation (GRADE) system was used, as proposed by the GRADE working group, to appraise the evidence emerging from this review. Two reviewers (F.N.W. and G.A.W) rated the strength of the evidence according to the following aspects: risk of bias, consistency of results, directness of evidence, precision, publication bias and magnitude of the effect [9, 10]. Any disagreement between the two reviewers was resolved after additional discussion.

The searches in PubMed, Cochrane and Embase resulted in 54 unique papers (Fig. 1). The screening of the titles and abstracts resulted in 14 potentially eligible papers. The full text of five papers was not retrievable. For nine papers the full texts were obtained and read in full. Of these, three [12, 15] met the eligibility criteria. However, two of these papers reported on the same experiment. Searching the main orthodontic journals revealed four potentially eligible papers of which one was selected [3]. Google scholar also yielded one suitable paper [13]. Screening the reference lists of the four selected full-text papers resulted in no additional paper. Subsequently, a total of four papers (Table 2) were included in this systematic review.

All four eligible papers had a cross-sectional study design. Three originated from the USA and one from the UK. The sample sizes ranged from 20–100 participants. The population characteristics varied from children to professional musicians.

To estimate the potential risk of bias, the methodological qualities of the included studies were assessed (Table 3). Lip form, lip thickness and lip closure as potential confounding factors were defined and assessed in three of the four studies [3, 13, 15], but were analysed in only one [13]. In three of the four studies [3, 12, 15] the sample was clearly defined and representative. Measurement of the tooth position was valid and reliable in three of the four studies [3, 12, 15]. In two of the four studies [3, 12] assessment of performance or embouchure comfort was measured in a valid and reliable way. Overall, the potential risk of bias of the included studies was estimated to be “serious” for one study [13] and “moderate” for the other three [3, 12, 15]. Because only four papers were identified, which provided heterogeneous outcome parameters, reporting bias could not be assessed nor was a sensitivity analysis feasible.

Table 7 presents a summary of the various factors used to rate strength of the evidence according to GRADE [9, 10]. Although most studies examined advanced or professional wind instrumentalists, the generalizability is limited because most studies have looked at woodwind musicians as one group. Although the outcomes of the included studies are rather consistent, the measurement of these outcomes was inexact. Furthermore, the potential risk of bias is estimated to be moderate to serious. Reporting bias cannot be assessed but can also not be ruled out. In the absence of distinct end points the magnitude of the effect is undeterminable. Therefore, the strength of the evidence emerging from this systematic review was estimated to be “very weak”.

This is the first systematic review that maps the influence of tooth position on wind instrumentalists’ performance and embouchure comfort. Little research appears to have been carried out in this field most of which is in the form of narrative reviews with the risk of being neither objective nor robust.

Most included studies regarded woodwinds as one group, although single reed-, double reed instrumentalists and flutists have a different embouchure (Table 8). In order to better comprehend the following paragraphs, it is useful to have knowledge of how different types of wind instruments are held in or against the mouth.

A Class I relationship without malocclusion is appropriate for every type of wind instrument [3]. Mainly the extreme malocclusion results in embouchure difficulties [3]. Observation among professional orchestra members suggest that a Class I relationship does not seem to be a prerequisite in order to reach a professional level of performance on the wind instrument [15]. Furthermore, it might be concluded that as long as the malocclusion is mild it does not negatively influence wind instrumentalists’ performance to an extent that it interferes with a professional career.

Based on the outcomes of the included studies, limited evidence is available to provide a conclusive answer regarding positive or negative influences of specific tooth positions on the performance and embouchure comfort of musicians of different types of wind instruments.

In the literature it has been suggested that a Class I relationship is suitable to any type of wind instrument. For single-reed musicians, a Class II relationship supposedly is least troublesome [2, 5]. Berkhout [2] suggests that a Class II-1 is less ideal for brass and flute musicians and a Class II-2 is relatively unfavourable for most wind instruments. Because the instrument must be kept uncomfortably high with a Class III relationship this is suggested to be especially unfavourable for single reed instruments [2]. Also a protruding lower jaw is presumably a distinct disadvantage to brass instrument playing because the upper and lower lips should be in a straight vertical line with the mouthpiece applied to them perpendicularly [20].

From the evidence emerging of the selected studies, it indeed appears that a Class I relationship without malocclusion seems appropriate for every type of wind instrument [3]. According to the same study, extreme disto-occlusion (large overjet) clearly disturbs the embouchure of brass musicians, whereas a disto-occlusion does not interfere with woodwind embouchure [3]. Among individuals with Class III malocclusion (reversed overjet) embouchure difficulties are distributed evenly among woodwind, small and large brass musicians [3].

It has been suggested that a deep anterior overbite is troublesome for playing a single reed instrument [16, 22]. It is presumed that it would be easier to play a single reed instrument with an anterior open bite because of its large intraoral mouthpiece [5]. But an open bite can also prevent lip support in musicians of certain instruments [18].

From the selected studies it appears that an extreme open bite seriously interferes with the embouchure of brass musicians [3]. No effect of overbite on trumpet player performance was found [12]. But among musicians with a Class II malocclusion it appears that the larger the overbite, the greater the tendency for embouchure difficulties [3].

In a narrative review the need of arch width between brass instruments and flute are compared [2]. The author suggests that for good tongue function and thus articulation and tone production on a brass instrument the internal width and shape of the upper dental arch is very important, whereas on the flute the contour and lingual width of the lower arch is more important.

One of the included studies [12] showed that trumpet players with a wider maxillary and mandibular molar arch and wider maxillary canine arch performed better on exercises such as triple tongue movement and flexibility.

The literature suggests that for brass instrument players it is important that the vestibular surface of both lower and upper incisors are regular and flat because they support the lips and the mouthpiece. The same would apply to double-reed instruments because the incisal ridges of the teeth are covered by the lips and the mouthpiece rests between the lips. If the arch is irregular, large forces are exerted on the lips at the site of ectostematic teeth, which can lead to pain or irritation. For single reed instrument players the lower anterior teeth are of special importance because they support the instrument and determine the pressure on the reed. Irregularities and sharp edges can be very painful [2, 5, 6, 18‐20, 22]. Flute playing may be disturbed by excessively irregular anterior teeth in the lower jaw [19, 22]. Also maxillary incisor irregularity is supposedly a handicap to flute playing [2].

One of the included studies [13] did not find evidence for a relationship between tooth evenness and successful performance on the brass and woodwind musical instruments. Two other authors [3, 12], however, did find a negative effect of anterior crowding on performance and embouchure comfort. Wind instrument players with anterior crowding complain that the sharp corners of the rotated crowns irritated the lips as they supported the instrumental mouthpiece [3].

In the literature it has been suggested that protruded teeth can cause pain, like irregular teeth [5, 18, 22]. There is disagreement whether protrusion of maxillary incisors is disturbing to single-reed musicians [5, 22]. Whereas retrusion of mandibular incisors is presumably troublesome to single-reed musicians, retrusion of maxillary incisors would be troublesome to brass instrument playing [22].

From two of the included studies [3, 12] it appears that maxillary protrusion has a negative effect on trumpet player performance and may impede the embouchure of brass musicians. Retrusion of all upper incisors does not present embouchure difficulties. Rather, when a Class II arch relationship exists, it is likely of advantage to the brass player [3]. Woodwind musicians experience no embouchure difficulties with maxillary protrusion but do experience difficulties with retrusion of lower incisors [3].

In the literature it has been suggested that diastemas between anterior teeth can be disturbing to double reed instrument players because the free corners of the incisors exposed by such space tend to irritate the lips. Where a space is substantially wider, such as between the upper central incisors, the upper lip could get stuck between the teeth during playing [5, 18, 19]. For brass musicians this can result in disturbance of lip vibration. Any eccentric position of the embouchure to avoid these problems may cause rapid tiring [2, 6, 22]. In single reed instruments diastemas between the lower anterior teeth can cause pain, whereas diastemas between the maxillary incisors result in “false air” and adversely affect the sound of flute playing [2].

One of the included studies [3] shows that all musicians with extreme anterior spacing experience embouchure difficulties. For all these individuals, the adaptation problems centred around discomfort and pain of the teeth and supporting bone and/or early fatigue and pain of the muscles of the floor of the mouth and lip. Another included study [12], however, did not find an effect of mid diastemas on trumpet player performance.

Quantz [21] was the flute teacher of Frederick the Great of Prussia and as far as is known the first who formulated requirements that the dentition and lips had to meet in order to play well:

Straight teeth, which are neither too long nor too short; Not thick, but thin, smooth, and fine lips, which have neither too much nor too little flesh, and can close the mouth without compulsion.

The role of the upper lip is relatively more important in flute playing than with other wind instruments because it directs the airflow [2]. A short upper lip or long (or protruding) upper incisors are a great handicap to flute musicians [2, 5, 6]. In brass instrument playing lip length has been suggested as a possible cause of disturbance in lip vibration. With relatively short lips higher tones will be more difficult to produce than the lower tones because the higher tones require an air column of smaller diameter to pass through the lips than the lower tones [20]. In double reed instrument playing, the lips also play an important role because they should be long enough to be stretched over the incisal edges [2, 18, 19].

In this systematic review the role of the lips in playing wind instruments can be regarded as a confounding factor. Only one of the included studies [3] investigated lip length and lip thickness. Thick lips were observed in a majority of Class II brass musicians with embouchure difficulties. Thin lip form appeared among many Class III brass musicians with embouchure difficulties. In addition, a tendency for a short upper lip or longer lip form was noticed among the Class I brass musicians with embouchure difficulties. The author [3] concludes that the emerging evidence is not clear-cut and that it is difficult to estimate the role of lip size in adjustment to embouchure.

The potential risk of bias of the included studies is estimated to be moderate to serious. Except for Kula et al. [12], all studies have been written four to seven decades ago during which period the criteria for reporting were not as strict as in the current guidelines. This may be one of the reasons that has an impact on the estimated risk of bias. Whereas the study of Kula et al. [12] is quantitative with objective measurements, the study of Cheney [3] can be classified as qualitative. Across studies the evidence emerging from this systematic review is graded to be “very weak”.

A limitation of this systematic review is that only four eligible studies could be included. Although no language filter was used, the possibility exists that some non-English papers were not added to the databases used. Also four potentially interesting non-English paper titles were identified by the search, of which the abstract and full text were not retrievable.

All the included studies have their own limitations. While the objective and reliable assessment parameters of Kula et al. [12] are a strength, the validity of the measurements can be questioned. Flexibility, which was measured as the quickest tempo while playing three exercises, also depends on finger dexterity, articulation also depends on tongue speed and endurance also depends on lung capacity. This is supported by the fact that a few students could not perform all tests. The variable “adjustment to embouchure” used by Cheney [3] is valid, but the reliability can be questioned because it is based on the subjective experience of wind musicians. It is an original idea of Lamp and Epley [13] to examine children during their first contact with a wind instrument on their aptitude for brass or woodwind and determine if there might be an association with tooth irregularities. After a certain instruction and period of practice an aptitude test was taken, but the test criteria were not described. Lovius and Huggins [15] measured and described the prevalence of a number of dental variables among a group of professional wind musicians. However, they did not measure any outcome variable. They just assumed that musicians of Liverpool Philharmonic Orchestra had a high standard of musical performance. Although this assumption is reasonable, professional musicians can also experience difficulties with their embouchure.

Most included studies have looked at woodwind musicians as one group. Kula et al. [12] only looked at trumpet musicians, Lamp and Epley [13] distinguished between brass and woodwind instruments, Cheney [3] further divided brass instruments into those with a small or large mouthpiece, and Lovius and Huggins [15] regarded all wind instruments as a single group. This is a shortcoming of all studies because brass, single reed, double reed instrumentalists and flutists have a different embouchure (Table 8).

Instead of cross-sectional studies, studies comparing predefined groups with respect to wind instrumentalists’ performance or tooth position would contribute to a better understanding of the impact of tooth position on the tone production. Malocclusion, up to a certain extent, might be compensated with an adaptation of the peri-oral musculature. Therefore, it would be interesting to investigate the role of the lips and other facial muscles in wind instrumentalists’ performance. Perhaps electromyography can be used. In addition it would be interesting to know if wind instrument players can perform better or with less difficulty after orthodontic correction. Finally, considering the various forms of embouchure (Table 8), it is important for future research to investigate the various types of wind instruments separately.

Conversely it would be of interest to systematically synthesize the available literature on the influence of playing wind instrument on tooth position.

Dental care professionals should be able to advise their patients who play a wind instrument about the effect of a correction of malocclusion on performance and comfort. Scientific evidence about the relationship of each type of instrumental mouthpiece to different malocclusions may aid in their recommendation.

Based on the outcomes of the included studies no firm answer can be given as to what specific tooth positions have a positive or negative influence on the embouchure comfort and performance of musicians of different types of wind instruments. A Class I relationship without malocclusion seems appropriate for every type of wind instrument. When a wind instrumentalist has a mild malocclusion it does not appear to impede a professional career. The more extreme the extent of malocclusion, the greater the interference with a wind instrumentalists’ performance and embouchure comfort.

(Semi-)professional wind instrument players may benefit from orthodontic therapy in case of a more extreme malocclusion. A young musician may experience problems wearing braces but the end result may help to improve the musical performance and embouchure comfort.