|Year : 2019 | Volume
| Issue : 1 | Page : 7
Do facial morphology, posture and function change following glossectomy? A systematic review
Tariq M Al Awadhi1, Eleftherios G Kaklamanos1, Athanasios E Athanasiou2
1 Department of Orthodontics, Hamdan Bin Mohammed College of Dental Medicine, Mohammed Bin Rashid University of Medicine and Health Sciences, Dubai, United Arab Emirates
2 Department of Dentistry, School of Medicine, European University Cyprus, Nicosia, Cyprus
|Date of Web Publication||23-May-2019|
Dr. Eleftherios G Kaklamanos
Hamdan Bin Mohammed College of Dental Medicine (HBMCDM), Mohammed Bin Rashid University of Medicine and Health Sciences (MBRU), Building 34, Dubai Healthcare City, Dubai
United Arab Emirates
Source of Support: None, Conflict of Interest: None
OBJECTIVES: To systematically investigate and critically appraise the quality of the currently available literature regarding the morphological, postural, and functional changes observed in individuals following glossectomy.
MATERIALS AND METHODS: A search without restrictions in eight databases (including grey literature) and hand searching from inception until March 2018 was performed. Data on morphological, postural, and functional changes after glossectomy were reviewed. Methodological quality was evaluated using the risk of bias in nonrandomized studies of intervention tool.
RESULTS: Out of 835 initially identified unique records, only three articles following patients for 1 year after glossectomy fulfilled the selection criteria. Overall, no significant morphological, postural, and functional changes were observed. Only the distance between the dorsum and the nasal line increased and the freeway space decreased significantly.
CONCLUSIONS: Overall, no significant differences were noted in the medium term, in terms of dentofacial structures adaptation and tongue function following glossectomy. Further research is warranted in order to elucidate the consequences of the altered oral environment.
Keywords: Craniofacial development, glossectomy, marcroglossia, tongue reduction surgery
|How to cite this article:|
Al Awadhi TM, Kaklamanos EG, Athanasiou AE. Do facial morphology, posture and function change following glossectomy? A systematic review. J Orthodont Sci 2019;8:7
|How to cite this URL:|
Al Awadhi TM, Kaklamanos EG, Athanasiou AE. Do facial morphology, posture and function change following glossectomy? A systematic review. J Orthodont Sci [serial online] 2019 [cited 2019 Jun 19];8:7. Available from: http://www.jorthodsci.org/text.asp?2019/8/1/7/258917
Tariq M. Al Awadhi
Present Address: Ministry of Health and Prevention, United Arab Emirates
| Introduction|| |
Tongue position and volume are considered important elements that influence dentofacial biomechanics and morphological characteristics.,, The classical equilibrium theory suggests that resting pressures from the tongue, lips, and cheeks are crucial in determining the position of the teeth. A very large tongue is thought to constitute an important etiologic factor for deformities like open bite, bimaxillary protrusion, or spacing by exerting an expansive resting pressure on the dental arches or by being interposed between them.,, Tamari et al. demonstrated a positive relationship between the size of the mandibular arch and the volume of the tongue. Other dentoalveolar findings in cases of an enlarged tongue include anterior or posterior cross-bite and protrusion of mandibular incisors.,,,
It has been suggested also that tongue volume affects the vertical dimension of the face and the location of the chin and the symphysis.,,, At the same time, a very large tongue may lead to disruption of physiologic functions including breathing, mastication, swallowing, and phonation. Consequently, the assessment of the size of the tongue has been held important in considering the etiology of the various types of malocclusion and the stability of orthodontic treatment outcomes.
Macroglossia is the term used to define tongue enlargement10 and might be classified into true, relative, and functional. True macroglossia is usually associated with a pronounced increase in tongue size due to a disease or syndrome,, whereas in relative macroglossia, the tongue size is only slightly larger when compared with normal. The functional type of macroglossia occurs when the tongue does not adapt to the oral cavity after osteotomies, for example, following mandibular setback surgery. The most frequently reported treatment for macroglossia is glossectomy, that is, surgery to decrease the volume of the tongue., However, the information on the effect of glossectomy on dentofacial growth and function is limited. Similarly, it is not known whether pressure on the teeth actually changes.
The aim of the present study is to investigate and critically appraise the quality of the currently available literature regarding the morphological, postural, and functional changes observed in individuals following glossectomy.
| Materials and Methods|| |
A specific protocol following the guidelines outlined in the PRISMA-P statement and registered in PROSPERO (CRD42017079878) formed the basis for the present review. The Cochrane Handbook for Systematic Reviews of Interventions and the PRISMA statement were followed during conduct and reporting.
The participants, intervention, comparison, and outcomes (PICO) acronym was used to define the eligibility criteria [Supplementary Table 1]. Studies evaluating facial morphology, posture, and function in individuals before and after any type of glossectomy, as a sole intervention or in combination with osteotomies, were reviewed. Subjects with tumors, clefts, syndromes, or congenital anomalies of the craniofacial region were excluded. Animal studies, noncomparative studies, systematic reviews, and meta-analyses were also not considered.
Information sources and search strategy
In total, eight databases (including grey literature) were searched since inception and up until March 2018. The first author developed detailed search strategies for each database. These were based on the strategy used for MEDLINE via PubMed but revised appropriately to consider the differences in controlled vocabulary and syntax rules [Supplementary Table 2].
No restrictions were placed on the language, date, or status of publication. In addition, efforts to obtain additional studies were made and the reference lists in reviews included or excluded studies, as well as other related articles were searched. The authors of studies were to be contacted in order to provide additional data if needed.
The first two authors assessed for eligibility, independently and in duplicate, the titles and the abstracts of the retrieved records. They were not blinded to the identity of the authors, their institution, or the results of the research. Subsequently, they obtained and assessed again the full text of the records considered by either reviewer to meet the inclusion criteria. Disagreements were resolved by discussion or consultation with the last author. A record of all decisions on study identification was kept. As recommended, kappa statistics were not calculated to describe the extent to which assessments by the two authors were the same.
Data collection and data items
The same two authors performed data extraction independently and in duplicate; any disagreements were resolved by discussion or consultation with the last author. Predetermined and prepiloted data collection forms were used to record the following information: bibliographic details of the study, details on study design and verification of study eligibility, characteristics of the subjects, details on the intervention, outcomes assessed, and results.
The retrieved data on the investigated outcomes was categorized as follows:
- Morphological and postural parameters
- Functional parameters.
Risk of bias in individual studies
The risk of bias in individual studies was assessed independently and in duplicate by the first two authors using the ROBINS-I tool. Any disagreements were resolved by discussion or consultation with the last author.
Summary measures and synthesis of results
If deemed possible, the random effects method for meta-analysis was to be used to combine data. However, quantitative data synthesis was not carried out as planned because of the lack of an adequate amount of data regarding each of the assessed variables.
Risk of bias across studies and additional analyses
If a sufficient number of studies were identified, analyses were planned for “small-study effects” and publication bias. If deemed possible, exploratory subgroup analyses were planned according to participant and intervention characteristics. Finally, the quality of evidence for the statistically significant differences at the longest follow-up was assessed based on the grades of recommendation, assessment, development, and evaluation (GRADE) approach.
| Results|| |
The flowchart of records through the reviewing process is shown in [Figure 1]. Initially, 835 records were identified, 346 were identified as duplicates, and 478 more were excluded on the basis of their title and abstract. From the 11 full-text records assessed, 8 were excluded because they included patients with tumors. Finally, three reports were included in the systematic review.,,
The characteristics of the studies included in the present systematic review are presented in [Table 1]. They were published between 1990 and 2013 and investigated the effect of glossectomy on (a) morphological and postural parameters: maxillomandibular relationships; position of the head, the cervical column, and the hyoid bone; rest position of the mandible and the tongue, and (b) functional parameters: tongue pressure on the teeth, oral motor ability, and ability to recognize forms. The mean age of the patients varied from 15 to 21 years, approximately. Ingervall and Schmoker and Fröhlich et al. assessed patients before and approximately 6 and 12 months after glossectomy. Kawakami et al. followed upto 1 year two different groups: one subjected to mandibular setback and glossectomy, and one to osteotomy alone.
|Table 1: Characteristics of the studies included in the systematic review|
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Risk of bias within studies
[Table 2] presents the summary of the risk bias assessment. All studies presented serious risk of bias regarding confounding, as important parameters were not always appropriately controlled. These included gender, age and growth status, type of malocclusion, presence of fixed appliances, tongue volume removed, glossectomy technique, etc., On the contrary, the risk of bias in the selection of participants and classification of interventions was found to be low. The risk of bias in the measurement of outcomes was considered serious as either the assessors were aware of the intervention, or there was no information on blinding or concerns existed regarding the reliability of the assessments. Finally, the risk of bias in the selection of the reported result was moderate for all the included studies.
Results of individual studies
(a) Effect on morphological and postural parameters
Following glossectomy, no significant spatial changes were shown in the position of the head, the cervical column, and the hyoid bone, as well as the craniocervical angulation. Evaluation of tongue at the rest position showed that the distance between the dorsum and the nasal line increased significantly (P < 0.01). However, no significant differences were observed on the distance between the posterior part of the tongue and the pharyngeal wall. The freeway space decreased significantly between the presurgical and the postsurgical evaluations (P < 0.01), but the anteroposterior position of the mandible in the rest position did not change.
In the study by Kawakami et al., no significant differences were noted between the glossectomy plus mandibular setback patients and the osteotomy only group regarding the ANB angle, the Frankfort mandibular plane angle, as well as the position of the hyoid bone and the tongue at 1 year after the operation. However, the researchers did not observe in the mandibular setback plus glossectomy group the narrowing of the airway width posterior to the tongue and the clockwise rotation of the mandible that occurred in the osteotomy-only patients.
(b) Effect on functional parameters
Fröhlich et al. tested the tongue pressure on the teeth (maxillary and mandibular incisors and molars) at rest, as well as during chewing and swallowing, following glossectomy. The pressures reported exhibited large variability. Even negative values were recorded at rest in many individuals, particularly in the maxillary incisors. In general, none of the measurements at 12 months differed significantly from the preoperative recordings. Moreover, glossectomy exerted a minor effect on patients' ability to recognize forms and overall oral motor ability.
Risk of bias across studies and additional analyses
As it was not possible to retrieve a sufficient number of trials, we were not able to conduct analyses for “small-study effects” and publication bias. Overall, the confidence in the observed estimates was not strong [Supplementary Table 3].
| Discussion|| |
Despite clinical reasoning that tongue volume influences not only the position of the maxillary and mandibular dentition, but also the posture of the mandible and the vertical height of the face, there is limited information about the effects of altering tongue volume on craniofacial growth and dental arch formation. Based on the data provided in the present systematic review, overall, no significant differences were observed in the medium term, in terms of dentofacial structures adaptation and tongue function following glossectomy. However, the quality of retrieved evidence gives an insight on the strength of the relevant estimates.
From the initially identified records, only three full-text studies evaluating the changes resulting from glossectomy were included in this systematic review, reflecting the scarcity of relevant research. No significant effects on morphological and postural parameters, like the spatial position of the head, the cervical column, and the hyoid bone, or the craniocervical angulation, were noted. However, it seems that the operation resulted in the tongue occupying less space in the oral cavity than before, this possibly being the reason for the observed decrease in the freeway space. Liu et al., employing a young animal model, reported that a surgical decrease in tongue volume slows craniofacial skeletal growth in the mandibular symphysis regions and anterior dental arch expansion during periods of accelerated growth. In addition, decreases in bone mineral density and content were noted, especially in the anterior mandibular region.
When glossectomy was applied as an adjunct to mandibular setback, no significant differences were noted between the glossectomy plus setback patients and the osteotomy-only group regarding the ANB angle, the Frankfort mandibular plane angle, as well as the position of the hyoid bone and the tongue, 1 year after the operation. It would seem logical that when the mandible is set back, the tongue would also move posteriorly and narrow the upper airway. However, the cervical hyperflexion that usually characterizes these patients postsurgically as well as subsequent alterations in hyoid bone position may compensate and prevent airway obstruction. The small effect of tongue reduction on mandibular relapse also supports the idea that large tongue volume is not inherent in patients with mandibular prognathism and that adjunctive tongue resection is rarely necessary in the mandibular prognathism patients without the existence of a disproportionate tongue size., The reported results could also be related to the methodology used. The use of lateral cephalometric radiography limits the accuracy of airway measurements. The two-dimensional images allow only assessments in the sagittal plane and fail to provide a full-scaled view of the upper airway. Cone beam-computed tomography (CBCT), by allowing a 3D registration of pre- and post-treatment data, and magnetic resonance imaging (MRI) appear to be superior to cephalometric radiography in estimating the size of the pharynx and the hypopharynx.
Regarding the recordings on functional parameters, such as tongue pressure on teeth, great variability was noted corroborating previous investigations in young adults., Twelve months after glossectomy, no measurement was significantly different from the preoperative assessment at rest, as well as during chewing and swallowing. Liu et al. showed in an animal study that immediately following glossectomy the overall strains from the tongue during mastication decreased and their orientation changed. However, this effect was less pronounced in the posterior mandible and palate. In the mandibular lingual symphysis, no strain change was observed. Four weeks after glossectomy, tongue strain during chewing increased again, particularly on the mandible. These findings are in contradiction to the hypothesis that lower loads would be exerted on the anterior oral cavity during function. The restructuring and healing processes in the tongue together with alterations in muscle contraction modes and kinematics during chewing could explain these observations.,, However, according to the classical equilibrium theory, functional pressures are not as critical in determining tooth position as resting pressures.
Finally, glossectomy exerted a minor effect on patients' oral motor ability and ability to recognize forms, possibly due to the fact that partial tongue reduction does not significantly affect overall oral proprioception. In general, individuals performing well before the operation continued to do so later, corroborating previous longitudinal observations in a young adult population. Learning effects have been reported in subjects non-subjected to glossectomy, that was not observed in the population under investigation. This finding could possibly be related to the fact that more patients wore fixed orthodontic appliances after surgery.
Strengths and limitations
The strengths of the present review include the use of a methodology which followed well-established guidelines. To our knowledge, there has been no other systematic review conducted on craniofacial changes after glossectomy. Moreover, the search strategy employed was both exhaustive, covering electronic, manual, and gray literature material up to March 2018, and comprehensive including every relevant study. Every effort to decrease bias in the methodology employed was made. Screening, verification of eligibility, abstraction of information, assessment of risk of bias, and of the quality of evidence were all performed in duplicate, and any disagreement was resolved by discussion or consultation until a final consensus was achieved.
There are also some limitations to the present review; these arise mainly from the nature and the characteristics of the data retrieved during the review process. The absence of contemporaneous control groups followed for similar time periods constitutes another significant methodological limitation. Furthermore, exploratory subgroup analyses for “small-study effects” and publication bias, could not be carried out, even though they were incorporated as possibilities according to the review protocol. Finally, the lack of appropriate tools to measure specific parameters following glossectomy, for example, Cone Beam CT for airway measurements may account for the observed results.
Recommendations for future research
Further research is warranted in order to elucidate the consequences of the altered oral environment following glossectomy on craniofacial growth, development, and function, especially in growing subjects.
It has been suggested that well-designed and properly executed randomized control trials provide the best evidence. Since random allocation of subjects might be unethical under certain situations, it would be advisable to conduct at least well-controlled prospective nonrandomized studies. Particular importance should be placed on possible ways to control bias due to confounding and bias in the measurement of outcomes. Moreover, long-term evaluation of outcomes would be valuable concerning a variety of malocclusions and clinical situations such as open-bite cases and tongue thrust. Also, using more advanced tools for assessment, like Cone Beam CT, could be beneficial to assess morphological adaptations and airway volume changes in three dimensions after glossectomy. Finally, it would be of great interest to further investigate the effect of the different surgical techniques, as well as the effect on other outcomes including speech, taste, and sensitivity.
| Conclusions|| |
Overall, no significant differences were noted in the medium term, in terms of dentofacial structures adaptation and tongue function following glossectomy. Further research is warranted in order to elucidate the consequences of the altered oral environment.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]