Objective: To evaluate early and late velopharyngeal changes in cleft lip and palate (CLP) patients after use of the Rigid External Distractor (RED) device and to correlate these changes to the amount of maxillary advancement.

Materials and Methods: Thirty Class III CLP patients were included in the study. Maxillary advancement was performed using the RED device in combination with titanium miniplates and screws for anchorage. Lateral cephalograms, nasometer, and nasopharyngoscope records were taken before distraction, immediately after distraction, and 1 year after distraction. A paired t-test was used to detect differences at P < .05.

Results: SNA angle and A point and ANS to Y axis were significantly increased after maxillary distraction (P  =  .0001). Statistically significant increases in nasopharyngeal and oropharyngeal depths, velar angle, and need ratio were also found (P  =  .0001). Nasalance scores showed a significant increase (P  =  .008 for nasal text and .044 for oral text). A significant positive correlation was observed between the amount of maxillary advancement and the increase in nasopharyngeal depth and hypernasality (P  =  .012 and .026, respectively).

Conclusions: Nasopharyngeal function was deteriorated after maxillary advancement in CLP patients. There was a significant positive correlation between the amount of maxillary advancement and the increase in nasopharyngeal depth and hypernasality.

Maxillary hypoplasia is a common deformity in repaired cleft lip and palate (CLP) patients. This hypoplasia is related to a combination of congenital reduction in midfacial growth and the surgical scar from the repair of the cleft palate.1,2  About 25% of these patients require orthognathic surgery for the correction of this deformity.2  Le Fort I maxillary advancement offers significant improvement in terms of esthetic, functional, and psychosocial benefits. However, this immediate surgical advancement can trigger or worsen velopharyngeal insufficiency (VPI),37  which is one of the most important problems affecting speech in CLP patients.8 

Recently, distraction osteogenesis (DO) has been recognized as a widely accepted method to correct maxillary hypoplasia in CLP patients, with predictable and stable results.912  DO aids in prevention of velopharyngeal deterioration after maxillary advancement, in addition to enhancing bone stability, where slow movement of the maxillary bone allows the surrounding soft tissues as the facial envelop, soft palate, and pharynx to adapt to the structural changes and reduce skeletal relapse.13  Changes in speech and velopharyngeal function (VPF) after maxillary distraction have been detailed in a few studies and have yielded different results. Some investigators1416  have reported VPF deterioration in 14% and 16.7% of their patients after maxillary distraction. They identified the degree of distraction at which VPF is compromised as 15 mm. Another study17  reported that the deterioration of hypernasality was not always proportional to the amount of advancement. It depended on the position of the posterior pharyngeal wall and the rotation of the palatal plane.

Therefore, the impact of DO on the status of the velopharynx remains unclear, and the question of a possible correlation between degree of maxillary advancement and velopharyngeal deterioration remains unanswered. The aim of this study was to evaluate early and late velopharyngeal changes in CLP patients after using of a Rigid External Distractor (RED) and to correlate these changes to the amount of maxillary advancement.

Patients

This study was approved by the Ethics Committee of Alexandria University. This retrospective study was conducted on 30 CLP patients who underwent maxillary DO at the Maxillofacial Surgery Department, Faculty of Dentistry, Alexandria University, Egypt. The patients had mean age of 17.13 ± 4.9 years. Among the 30 patients, 20 patients were females and 10 patients were males. Twenty-four patients had a diagnosis of unilateral cleft lip and palate; the other six patients had a diagnosis of bilateral cleft lip and palate. Eight patients exhibited predistraction pharyngeal flaps. All patients had severe maxillary hypoplasia and remarkable negative overjet.

Surgery

A complete high-level Le Fort I osteotomy was made, then the maxilla was downfractured softly to ensure its mobility. Maxillary advancement was performed using a RED device10  (KLS-Martin L.P., Tuttlingen, Germany) in combination with titanium miniplates and screws for anchorage. Two titanium miniplates were fixed with screws at both sides of the anterior maxillary wall to be used for traction. The RED device was applied immediately after surgery using scalp screws. After a latency period of 5 days, distraction was performed at a rate of 1 mm/day until a positive overjet was achieved. The distraction device was left in place for 4 weeks for rigid retention.

Lateral cephalograms, nasometer, and nasopharyngoscopy were used for evaluating the patients at three stages: preoperatively (T0), postdistraction (T1), and 1 year after distraction (T2).

Cephalometric Analysis

All lateral cephalograms were manually traced. Reference points were marked, yielding 22 linear and seven angular measurements (Figures 1 and 2).14,18 

Figure 1. 

Cephalometric parameters for the evaluation of skeletal changes. Landmarks: S: Sella; N: Nasion; A: point A; B: point B; ANS: anterior nasal spine; PNS: posterior nasal spine; Go: Gonion; Me: Menton; Po: Porion; Or: Orbitale; References planes: S-N plane; FH plane; palatal plane; mandibular plane; X-axis: 7° below the SN line; Y-axis: the perpendicular line on the SN passing through the ‘S’ point. Linear and angular parameters: SNA; SNB; ANB; palatal plane to SN angle; FMA; mandibular plane to SN angle; A, ANS and PNS points to X-and Y-axes.

Figure 1. 

Cephalometric parameters for the evaluation of skeletal changes. Landmarks: S: Sella; N: Nasion; A: point A; B: point B; ANS: anterior nasal spine; PNS: posterior nasal spine; Go: Gonion; Me: Menton; Po: Porion; Or: Orbitale; References planes: S-N plane; FH plane; palatal plane; mandibular plane; X-axis: 7° below the SN line; Y-axis: the perpendicular line on the SN passing through the ‘S’ point. Linear and angular parameters: SNA; SNB; ANB; palatal plane to SN angle; FMA; mandibular plane to SN angle; A, ANS and PNS points to X-and Y-axes.

Close modal
Figure 2. 

Cephalometric parameters for the pharyngeal airway passage and soft tissue. Landmarks: ad1: the intersection of the PNS-Ba line and the posterior pharyngeal wall; ad2: the intersection of a perpendicular line from PNS to Ba-S line with the posterior pharyngeal wall; H: the point of intersection of a perpendicular line from PNS to Ba-S with the cranial base; Ptm: pterygomaxillary fissure; UPW (upper pharyngeal wall): the intersection of the pp and posterior pharyngeal wall; MPW (middle pharyngeal wall): the intersection of the line from point U to the posterior pharyngeal wall; LPW (lower pharyngeal wall): the intersection of the line from ‘V’ with the posterior pharyngeal wall;. U: tip of uvula; T: the tip of the tongue; V: the intersection of the epiglottis and the base of the tongue. Linear and angular parameters. Lower airway thickness: PNS to ad1; lower adenoid thickness: ad1 to Ba; total lower sagittal depth of the bony nasopharynx: PNS to Ba; upper airway thickness: PNS to ad2; upper adenoid thickness: ad2 to H; total upper airway thickness: PNS to H; posterior sagittal depth of the bony nasopharynx: Ptm to Ba; vertical airway length: PNS-V; nasopharyngeal depth: PNS to UPW; oropharyngeal depth: U to MPW; the lower pharyngeal depth: V to LPW; velar length: distance from PNS to U; velar thickness: represents the maximal thickness of the soft palate measured perpendicular to the PNS-U line; tongue length: T to V; tongue height: the perpendicular distance from the most superior point of the tongue to the V-T line; velar angle: ANS-PNS-U; need ratio: nasopharyngeal depth/velar length.

Figure 2. 

Cephalometric parameters for the pharyngeal airway passage and soft tissue. Landmarks: ad1: the intersection of the PNS-Ba line and the posterior pharyngeal wall; ad2: the intersection of a perpendicular line from PNS to Ba-S line with the posterior pharyngeal wall; H: the point of intersection of a perpendicular line from PNS to Ba-S with the cranial base; Ptm: pterygomaxillary fissure; UPW (upper pharyngeal wall): the intersection of the pp and posterior pharyngeal wall; MPW (middle pharyngeal wall): the intersection of the line from point U to the posterior pharyngeal wall; LPW (lower pharyngeal wall): the intersection of the line from ‘V’ with the posterior pharyngeal wall;. U: tip of uvula; T: the tip of the tongue; V: the intersection of the epiglottis and the base of the tongue. Linear and angular parameters. Lower airway thickness: PNS to ad1; lower adenoid thickness: ad1 to Ba; total lower sagittal depth of the bony nasopharynx: PNS to Ba; upper airway thickness: PNS to ad2; upper adenoid thickness: ad2 to H; total upper airway thickness: PNS to H; posterior sagittal depth of the bony nasopharynx: Ptm to Ba; vertical airway length: PNS-V; nasopharyngeal depth: PNS to UPW; oropharyngeal depth: U to MPW; the lower pharyngeal depth: V to LPW; velar length: distance from PNS to U; velar thickness: represents the maximal thickness of the soft palate measured perpendicular to the PNS-U line; tongue length: T to V; tongue height: the perpendicular distance from the most superior point of the tongue to the V-T line; velar angle: ANS-PNS-U; need ratio: nasopharyngeal depth/velar length.

Close modal

To estimate the method error, 15 randomly selected radiographs were traced and measured twice within a week by the same person. The mean values from the first tracing together with the mean values of the second tracing were applied to the Dahlberg's formula,19  thus: . For linear measurements, 0.47 mm was set as the method error, and for angular measurements it was 0.5°.

Nasometric Analysis

A Nasometer 6200-2 IM (30-02 software, 1.7 version; Kay Elemetrics, Pinebrook, NJ), a microcomputer-based system manufactured by Kay Elemetrics, was used. Nasalance scores were recorded during the reading of two sets of sentences, one consisting of sentences containing predominantly nasal sounds (nasal text), such as “mama betnayem manal,” for the identification of reduced nasalance, the other consisting of sentences with no nasal sounds (oral text), such as as “؟ali rah jel؟b kura.” The resultant signal is a ratio of nasal to nasal plus oral acoustic energy. This ratio is multiplied by 100 and expressed as a nasalance score.20,21  Hypernasality and hyponasality were judged using separate five-point scales, where 0  =  normal, 1  =  mild, 2  =  moderate, 3  =  severe, and 4  =  very severe.17 

Nasopharyngoscope

The Karl Storz fibroptic naso-pharyngo-laryngoscopy model 11001 RP was used. Commenting on the video record reply of all assessment aspects was done with three judges.

Velopharyngeal valve movements were recorded while the patient repeating the word /؟ mbar/; vowels /a/, /e/, and /u/; and syllables /pa/, /ta/, and /ka/ for a repeated number of times. Movements of the velum and lateral and posterior pharyngeal walls were traced on the monitor. The movement of each component was given a score (0–4), where 0 is a resting (breathing) position, 2 is half the distance to the corresponding wall, and 4 is the maximum movement reaching and touching the opposite wall.22 

Statistics

Data were analyzed using the computer program SPSS, version 17.0. Descriptive statistics were calculated in the form of mean ± standard deviation (SD).The significance of difference was tested using the Student's t-test (paired) to compare between the means of two related groups of numerical (parametric) data. The Pearson correlation coefficient test was used to correlate different parameters. A P value of <.05 was considered statistically significant.

Cephalometric Measurements

The parameters pertaining to the sagittal maxillary changes were 9.67° at the SNA angle, 8.5 mm at A point, 11 mm at ANS, and 9.5 mm at PNS.

The vertical treatment changes in the maxilla, at the position of A, ANS, and PNS points relative to the X-axis, were increased significantly (P  =  .0001, .0001, and .017, respectively), whereas the mean increases in SNB angle, FMA, MP to SN, and PP to SN angles were not statistically significant (P  =  .900, .749, .538, and .493, respectively; Table 1). Significant increases were observed in the nasopharyngeal and oropharyngeal dimensions (P  =  .0001), while the hypopharynx (V-IPW) showed a nonsignificant change (P  =  .878). Statistically significant results were recorded for the velar angle and the need ratio (P  =  .0001). However, the soft palate revealed no significant changes (Table 2). Regarding the follow-up cephalometric changes from T1 to T2, there were no significant changes during this period except for the velar angle (P  =  .005).

Table 1. 

Changes in the Skeletal Measurements

Changes in the Skeletal Measurements
Changes in the Skeletal Measurements
Table 2. 

Changes in the Pharyngeal Airway Passage and Soft Tissue

Changes in the Pharyngeal Airway Passage and Soft Tissue
Changes in the Pharyngeal Airway Passage and Soft Tissue

Nasometer

During the reading of oral text, there was a significant increase in the mean nasalance score (P  =  .044; Table 3). In the analysis of the five-point scales of hypernasality, 14 patients exhibited deterioration in hypernasality. Twelve patients had the same scores, and four patients showed some improvement in the hypernasality (Table 4).

Table 3. 

Changes in the Nasometer Measurements Before Distraction (T0), After Distraction (T1), and After Retention (T2)

Changes in the Nasometer Measurements Before Distraction (T0), After Distraction (T1), and After Retention (T2)
Changes in the Nasometer Measurements Before Distraction (T0), After Distraction (T1), and After Retention (T2)
Table 4. 

Judgments of Nasal Resonance Using a 5-Point Scale (0  =  Normal; 1  =  Mild; 2  =  Moderate; 3  =  Severe; 4  =  Very Severe)

Judgments of Nasal Resonance Using a 5-Point Scale (0  =  Normal; 1  =  Mild; 2  =  Moderate; 3  =  Severe; 4  =  Very Severe)
Judgments of Nasal Resonance Using a 5-Point Scale (0  =  Normal; 1  =  Mild; 2  =  Moderate; 3  =  Severe; 4  =  Very Severe)

In the reading of the nasal text, a significant increase in mean nasalance score was observed (P  =  .008 and .787) at T1 and T2, respectively (Table 3). Four out of six patients showed a postoperative decrease in hyponasality. The other two patients with unchanged mild hyponasality had a pharyngeal flap (Table 4).

Nasopharyngoscope

The mean increases in the grade of motion of the palate and right and left pharyngeal walls between T0 and T1 time intervals were not statistically significant (P  =  .104, .272, and .671, respectively). In addition, no statistically significant changes were observed between T1 and T2 (Table 5).

Table 5. 

Changes in Nasopharyngoscopy Before Distraction (T0), After Distraction (T1), and After Retention (T2)

Changes in Nasopharyngoscopy Before Distraction (T0), After Distraction (T1), and After Retention (T2)
Changes in Nasopharyngoscopy Before Distraction (T0), After Distraction (T1), and After Retention (T2)

Lateral cephalometric films and computed tomography are used to assess velopharyngeal status, providing observation of soft and hard tissues, although the reliability of the two-dimensional image has been questioned as a valid representation of the actual nasopharyngeal anatomy. Some studies23  have shown that pharyngeal airway space measured by cephalograms offers good agreement with a three-dimensional computed tomography scan.

Cephalometric analysis of the sagittal and vertical positions of the maxilla showed significant changes, which were expected as a result of distraction. When the maxilla was brought forward by DO, the depth of the nasopharynx and oropharynx were increased significantly (13.75 mm and 3.5 mm, respectively). This is due to the forward movement of the posterior nasal spine and soft palate along with the maxilla during DO. Ko et al.14  observed an increase in the nasopharyngeal depth by a 1:1 ratio with the bone movement after maxillary distraction in cleft patients. The length of the soft palate remained unchanged. This is parallel to the increase in the need ratio (1.14), suggesting borderline VPI (the average need ratio in normal patients was reported to be 0.87). This finding is also reported in other studies.14,17  However, other studies24,25  reported 0.4 mm of lengthening of the soft palate per millimeter of maxillary advancement. This diversity among results might be due to different degrees of advancement, different types of patients (cleft vs noncleft and unilateral vs bilateral cleft), operation techniques, assessment methods, and observation periods.

One of the prominent findings was the change in the velar angle. We found 15.25° increases in the inclination of the soft palate following 8.5 mm of maxillary advancement. Schendel et al.25  found a velar angle change of 2° per millimeter of maxillary advancement in cleft patients and after conventional osteotomy for maxillary advancement. Ko et al.14  found an increase in the velar angle of 1.6° per millimeter of advancement.

In our study, before distraction, 87% (26/30) of the patients had nasalance values for the reading of the oral text above the normal limit. This finding is consistent with the high prevalence of VPI reported for subjects with palatal clefts.8 

Fourteen of 30 patients (46.6%) experienced deterioration in hypernasality after distraction, which indicated decreased speech intelligibility and subsequent speech worsening. This effect might be attributed to the greater increase in the pharyngeal depth than the velar length resulting in compromised VP closure and coupling between the oral and nasal cavities. An increase in hypernasality after maxillary distraction in cleft patients was reported in other studies as well.1416  In agreement with our results, previous studies4,6  also reported a similar deterioration of hypernasality in the patients who experienced abnormal preoperative hypernasality before advancement. This indicates that maxillary advancement as performed in this study may contribute to the worsening of a previously existing hypernasality in subjects with cleft.

It was very obvious that the presence of a predistraction pharyngeal flap decreased the degree of resultant postdistraction hypernasality, and these findings were found to coincide with the results of Ko et al.,14  Guyette et al.,15  and Harada et al.,16  in whose studies the flap is a soft tissue obturator of the pharyngeal space.

Twelve patients maintained the same degree of hypernasality, and four patients showed some improvement, from moderate to mild hypernasality; thus, compensation in the VF mechanism might be assumed in these patients. The small, consistent increase in velar length and the significant increase in velar angle achieved some form of muscular compensatory activity in these patients. The increase in the velar angle was the result of stretching of the soft palate, which is aided in maintaining the vertical position of the soft palate and is considered to be a part of the compensation occurring in the VP mechanism.14  Through a gradual bone distraction procedure, the surrounding soft tissues may have a better chance to adapt to the structural changes, in contradiction to the sudden changes elicited by the Le Fort I osteotomy.

Warren and Drake26  reported that 60% of their subjects with cleft had nasal airway obstruction. In our cases, 20% (6/30) of the patients analyzed presented nasalance values for the reading of the nasal text below the normal limit before distraction. Hyponasality was found to be improved in 67% (4/6) of the patients. No patient experienced an increase in hyponasality as a result of DO. This finding is partially supported by other studies27,28  whose authors suggested that maxillary advancement increases the nasopharyngeal space, widens the nasal valve (thus favoring nasal respiration), and reduces nasal resistance.

Regarding the nasopharyngoscopic results, all of the patients had VPI preoperatively. This is may be due to the cicatrization from previous palatal repair surgery. After DO, there was no significant increase in the soft palate or lateral pharyngeal wall movements. These findings were documented by Satoh et al.,17  who found a widening of the gap between the posterior pharyngeal wall and the velum after DO in the patients with borderline closure before distraction. It is likely that once a loss of contact between the posterior pharyngeal wall and the velum occurs, patients cannot adapt to the changes to maintain the VPC. On the other hand, some studies15  suggested that it is possible for the maxillary distraction to encourage velopharyngeal movement. As the palate is advanced in small increments (approximately 1 mm per day), the patient has time to adapt to the change before the maxilla is advanced another 1 mm. However, the authors did not image palatal movement before or after the distraction procedure. They mentioned this observation only as a suggestion after pre- and postdistraction oral examination. They realize that intraoral observation is not sufficient to make judgments of velar movement, and they mentioned this observation only as a hypothesis for further research using appropriate imaging procedures.15 

In agreement with our correlation results, another study14  has found a significant positive correlation between the amount of forward skeletal movement and postdistraction hypernasality and pharyngeal depth (Table 6).

Table 6. 

Correlation Between A-Y and Other Variables

Correlation Between A-Y and Other Variables
Correlation Between A-Y and Other Variables

A comprehensive speech evaluation is an important component of treatment planning for maxillary DO, especially if done in cleft patients. If VP closure cannot be compensated for, pharyngoplasty and pharyngeal flap procedures should be considered to correct the VPI.

  • The maxilla was moved forward by gradual distraction, causing an increase in nasopharyngeal depth and compromising VPF.

  • There was a positive correlation between the amount of maxillary advancement and the increase in hypernasality and pharyngeal depth.

  • No significant relapse was encountered in maxillary skeletal position, nasopharyngeal measurements, or function during the follow-up period.

1
Huddart
AG
.
Maxillary arch dimensions in normal and unilateral cleft lip and palate subjects
.
Cleft Palate Craniofac J
.
1969
;
6
:
471
487
.
2
Ross
RB
.
Treatment variables affecting facial growth in unilateral cleft lip and palate: part 5. Timing of palate repair
.
Cleft Palate J
.
1987
;
24
:
54
56
.
3
Witzel
MA
.
Orthognathic Defects and Surgical Correction: The Effect on Speech and Velopharyngeal Function [Doctoral dissertation]
.
Pittsburgh, Pa
:
University of Pittsburgh
;
1981
.
4
Haapanen
ML
,
Kalland
M
,
Heliovaara
A
.
Velopharyngeal function in cleft patients undergoing maxillary advancement
.
Folia Phoniatr Logop
.
1997
;
49
:
42
47
.
5
Epker
BN
,
Wolford
LM
.
Middle third facial osteotomies: their use in the correction of congenital dentofacial and craniofacial deformities
.
J Oral Surg
.
1976
;
34
:
324
342
.
6
Witzel
MA
,
Munro
IR
.
Velopharyngeal insufficiency after maxillary advancement
.
Cleft Palate J
.
1977
;
14
:
176
180
.
7
Trindade
IE
,
Yamashita
RP
,
Suguimoto
RM
,
Mazzottini
R
,
Trindade
IE
.
Effects of orthognathic surgery on speech and breathing of subjects with cleft lip and palate: acoustic and aerodynamic assessment
.
Cleft Palate Craniofac J
.
2003
;
40
:
54
64
.
8
Maegawa
J
,
Sells
RK
,
David
DJ
.
Pharyngoplasty in patients with cleft lip and palate after maxillary advancement
.
J Craniofac Surg
.
1998
;
9
:
330
335
.
9
Polley
J
,
Figueroa
A
.
Management of severe maxillary deficiency in childhood and adolescence through distraction osteogenesis with an external, adjustable, rigid distraction device
.
J Craniofac Surg
.
1997
;
8
:
181
185
.
10
Polley
J
,
Figueroa
A
.
Rigid external distraction: its application in cleft maxillary deformities
.
Plast Reconstr Surg
.
1998
;
102
:
1360
1372
.
11
Huang
CS
,
Harikrishnan
P
,
Liao
YF
,
Ko
EW
,
Lio
EJ
,
Chen
PK
.
Long term follow up after maxillary distraction osteogenesis in growing children with cleft lip and palate
.
Cleft Palate Craniofac J
.
2007
;
44
:
274
277
.
12
Tae
KC
,
Gong
SG
,
Min
SK
,
Oh
SW
.
Use of distraction osteogenesis in cleft palate patients
.
Angle Orthod
.
2003
;
73
:
602
607
.
13
Molina
F
,
Ortiz Monasterio
F
,
de la Paz Aguilar
M
,
Barrera
J
.
Maxillary distraction: aesthetic and functional benefits in cleft lip-palate and prognathic patients during mixed dentition
.
Plast Reconstr Surg
.
1998
;
101
:
951
963
.
14
Ko
EW
,
Figueroa
AA
,
Guyette
TW
,
Polley
JW
,
Law
WR
.
Velopharyngeal changes after maxillary advancement in cleft patients with distraction osteogenesis using a rigid external distraction device: a 1-year cephalometric follow-up
.
J Craniofac Surg
.
1999
;
10
:
312
320
.
15
Guyette
TW
,
Polley
JW
,
Figueroa
A
,
Smith
BE
.
Changes in speech following maxillary distraction osteogenesis
.
Cleft Palate Craniofac J
.
2001
;
38
:
199
205
.
16
Harada
K
,
Ishii
Y
,
Ishii
M
,
Imaizumi
H
,
Mibu
M
,
Omura
K
.
Effect of maxillary distraction osteogenesis on velopharyngeal function: a pilot study
.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod
.
2002
;
93
:
538
543
.
17
Satoh
K
,
Nagata
J
,
Shonura
K
,
Wada
T
,
Fukuda
J
,
Shiba
R
.
Morphological evaluation of changes in velopharyngeal function following maxillary distraction in patients with repaired cleft palate during mixed dentition
.
Cleft Palate Craniofac J
.
2004
;
41
:
355
363
.
18
Al Maaitah
E
,
El Said
N
,
Abu
AL
,
Haija
E
,
Häggd
U
.
First premolar extraction effects on upper airway dimension in bimaxillary proclination patients
.
Angle Orthod
.
2012
;
82
:
853
859
.
19
Dahlberg
G
.
Statistical Methods for Medical and Biological Students
.
London, UK
:
George Allen and Unwin
;
1940
.
20
Dalston
RM
,
Warren
DW
,
Dalston
ET
.
Use of nasometry as a diagnostic tool for identifying patients with velopharyngeal impairment
.
Cleft Palate Craniofac J
.
1991
;
28
:
184
188
.
21
Dalston
RM
,
Warren
DW
,
Dalston
ET
.
Use of nasometry as a diagnostic tool for identifying patients with velopharyngeal impairment
.
Cleft Palate J
.
1991
;
28
:
184
189
.
22
Johns
DF
,
Rohrich
RJ
,
Awada
M
.
Velopharyngeal incompetence: a guide for clinical evaluation
.
Plast Reconstr Surg J
.
2003
;
112
:
1890
1897
.
23
Yamamato
E
.
A comparative CT evaluation of pharyngeal air way changes in Class III patients receiving bimaxillary surgery or mandibular setback surgery
.
Oral Surg Oral Med Oral Pathol Oral Radiol Endod
.
2008
;
105
:
495
502
.
24
Kummer
AW
,
Strife
JL
,
Graw
WH
,
Creaghead
NA
,
Lee
L
.
The effects of LeFort I osteotomy with maxillary movement on articulation, resonance and velopharyngeal function
.
Cleft Palate J
.
1989
;
26
:
193
200
.
25
Schendel
SA
,
Oeschlager
M
,
Wolford
LM
,
Epker
BN
.
Velopharyngeal anatomy and maxillary advancement
.
J Maxillofac Surg
.
1979
;
7
:
116
124
.
26
Warren
DW
,
Drake
AF
.
Cleft nose: form and function
.
Clin Plast Surg
.
1993
;
20
:
769
779
.
27
Schendel
SA
,
Carlotti
AE Jr
.
Nasal considerations in orthognathic surgery
.
Am J Orthod Dentofacial Orthop
.
1991
;
100
:
197
208
.
28
Wetmore
RF
.
Importance of maintaining normal nasal function in the cleft palate patient
.
Cleft Palate Craniofac J
.
1992
;
29
:
498
506
.