The aim of this systematic review was to identify, evaluate, and provide a synthesis of the available literature on the effects of lip bumper (LB) therapy on the mandibular dental arch of children and adolescents.
MEDLINE, Scopus, Web of Science, Cochrane Library, and Lilacs were systematically searched without restrictions up to May 2019. Risk-of-bias assessment was performed using Cochrane’s tool for randomized controlled trials (RCTs) and the Risk of Bias in Nonrandomized Studies of Interventions tool for non-RCTs. The Grading of Recommendations, Assessment, Development and Evaluation tool was used to assess the quality of the evidence.
After examination of the full texts, 6 studies were included. One RCT presented unclear risk of bias, and 5 non-RCTs presented serious to moderate risk of bias. LB therapy resulted in a buccal inclination of the incisors, distalization of the permanent first molars, and distal inclination of the permanent first molars, which increased perimeter and arch length. An increase in the arch width with greater gain in the interpremolar and/or deciduous molar distance and less gain in intercanine and intermolar distances was also reported. LB therapy increased the risk of second molar impaction with inclination >30° and the risk of ectopic eruption when treatment time was >2 years. The level of the evidence was graded as very low for variable arch length and second molar eruption disturbances. All other outcomes were graded as having low level of evidence.
Owing to the low level of certainty identified, the conclusions should be considered cautiously. Increase in arch perimeter and width was attributed to the proclination of the incisors, buccalization of the deciduous molar and premolar areas, and distal inclination of the molars. However, there was an increased chance of impaction and ectopic eruption of permanent second molar after treatment with LB.
LB therapy may produce undesirable side effects.
There is a shortage of studies analyzing the quality of available evidence.
The potential adverse side effects can include increased chances of permanent second molar impaction or ectopic eruption.
Knowing the current stage of evidence may facilitate clinical decision-making by orthodontists.
Lip bumper (LB) therapy may represent a management alternative for the resolution of future space deficiency in the mandibular dental arch reducing the necessity for tooth extractions. The primary objective of LB therapy is to reduce anterior dental crowding by increasing the length and width of the mandibular dental arch. These alterations can be attributed to the removal of lip pressure on the anterior teeth and the concomitant distal forces exerted on the permanent first molars (M1). Hence, the therapeutic effect of the LB will occur by the labial displacement of the incisors and the distal inclination of the M1.
A few studies suggest that the LB can maintain the position of the M1 or distalize it, preserving or increasing the leeway space. However, if the LB distalizes the M1 crown while assisting in crowding resolution, it also reduces the available distal space, altering the physiological eruption of the permanent second molars (M2) and the available space for them. , This may leave many orthodontists reluctant to use this therapeutic approach.
To our knowledge, only 1 systematic review has evaluated the effects of LB therapy on mandibular dental arch dimensions under 3 aspects (ie, distalization and/or distoangulation of M1, labial inclination of the mandibular incisors, and arch width changes). However, that review did not consider the effect on the eruption of M2, and only 1 study was included at that time, possibly because of language restriction and exclusion of uncontrolled studies. No analysis of risk of bias and level of certainty supporting the conclusions were considered. Additional studies on LB therapy have been published in recent years.
For these reasons, the aim of this systematic review was to identify, evaluate, and provide a synthesis of the available literature on the effects of LB therapy on the mandibular dental arch of children and adolescents.
Material and methods
Protocol and registration
The report of this systematic review followed the guidelines of the Preferred Reporting Items for Systematic Review and Meta-Analyses statement. The study protocol was registered on the International Prospective Register of Systematic Reviews (CRD4201911937).
For this systematic review, a set of questions following the population, intervention, comparison, outcomes, and study design structure was established:
Population: children and adolescents (under the age of 18 years) with mixed or permanent dentition.
Intervention: orthodontic treatment with LB in the mandibular arch.
Comparison: control group of individuals who were not submitted to any treatment, a group of individuals submitted to orthodontic treatment with other appliances, or measurements before LB.
Primary outcome: arch perimeter, arch width, arch length, incisor angulation, distalization and tip of the M1 and stability or relapse of those changes; Secondary outcome: M2 eruption disturbances.
Study design: RCT or non-RCT.
The exclusion criteria were case reports, review articles, abstracts and discussions, animal studies, studies with orthodontic and/or orthopedic approaches performed concomitant with LB in the mandibular arch or maxillary arch, treatment with tooth extraction, or any other surgical procedure, studies evaluating individuals with craniofacial deformities, syndromes, cleft lip palates, and studies with a sample smaller than 10 individuals.
Electronic searches in MEDLINE (via PubMed and OVID), Web of Science, Cochrane Library, Scopus, and Lilacs were conducted up to May 2019. In addition, the Controlled-trials Database of clinical trials ( www.controlled-trials.com.easyaccess2.lib.cuhk.edu.hk ), the Clinical Trials-US National Institute of Health ( www.clinicaltrials.gov ), and the National Institute for Health and Clinical Excellence ( www.nice.org.uk ) were consulted to check for possible ongoing studies. There was no restriction of language or year or status of publication for inclusion.
The search strategy used was as follows: lip bumper OR lip-bumper OR lip bumpers OR buccal shield OR buccal shields. The search strategy was originally planned for PubMed and subsequently adapted for the other databases ( Supplementary Table ).
The selection of the studies consisted of 2 phases. During the first phase, 2 authors (LGS and ECF) independently examined the titles and/or abstracts. Those references that met the eligibility criteria were included. Full texts of references with insufficient information in the title and/or abstract for a decision on inclusion or exclusion were retrieved for evaluation in phase 2. During the second phase of article selection, the same authors independently evaluated the full texts. Those studies that met the eligibility criteria were included. In both phases, differences were resolved by consensus. If necessary, a third author decided whether or not to include the study (PAMJ). For the second phase, the reasons for exclusion of the studies were also recorded.
Data extraction and items extracted
The data extraction of the included articles was performed independently and in duplicate by 2 authors (LGS and ECF). A standardized table was used to extract the data. The following data were extracted: authors, year of publication, study setting, description of groups (sex and age of patients, control group, sample size, dentition at therapy onset), characteristics of the LB used, and outcomes. Data were compared for accuracy, and any discrepancy was resolved through the re-examination of the original study until a consensus was reached.
Assessment of bias risk within studies
The risk of bias in RCTs was assessed using the Cochrane tool. The following items were evaluated: (1) random sequence generation, (2) allocation concealment, (3) blinding of participants and personnel, (4) blinding of the outcome assessor, (5) incomplete outcome data, (6) selective outcome reporting, and (7) other sources of bias. To evaluate the last item of this tool, the authors considered the following characteristics as sources of bias: absence of sample size calculation; inclusion and exclusion criteria incompatible with the objectives of the study; inadequate statistical test; absence of standard deviation and confidence interval (CI); and observation period incompatible with the objectives of the study. For each item, the included study could be awarded with low risk of bias (plausible bias that would not seriously alter results), unclear risk of bias (plausible bias that raises some doubts about the results), or high risk of bias (plausible bias that seriously impacts the confidence in results).
The risk of bias of non-RCTs was assessed using the Risk of Bias in Nonrandomized Studies of Interventions tool. The following domains were evaluated: bias for confounding factors, selection bias, intervention bias, bias for lack of data, and bias in the measurement of outcomes and selective reporting. Bias in each domain and the risk of overall bias for the non-RCTs were judged as low, moderate, serious, critical, or no information.
Evaluation of the level evidence (risk of bias across studies)
The level of evidence was assessed using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) Pro software (GRADEpro Guideline Development Tool, available online at gradepro.org ). For each outcome examined, the GRADE assesses the number of studies included, the studies’ designs, risk of bias, inconsistency, indirectness, imprecision, and other considerations (such as publication bias). Depending on the seriousness of the limitation in each one of these domains, the evidence could be downgraded by 1 or 2 levels. Based on this assessment, the certainty of the evaluation of the outcome could be very low, low, moderate, or high quality. The level of evidence was assessed separately for clinical and observational studies, and the higher level of certainty was reported. When the level was the same for evidence from clinical trials and observational studies, the same outcome was presented in 2 different lines, summarizing the findings from the separate sets of evidence for each class of studies.
Measurements for the primary outcome were based on continuous data (millimeters or degrees from dental casts, tomography, or radiographies), but measurements for the secondary outcome were based on nominal or ordinal data (impaction or lack of space from dental casts or radiographies).
Synthesis of results
Data collected were synthetized in a descriptive table. A meta-analysis was planned if there was relative homogeneity among included studies.
The search strategy yielded a total of 553 studies from the electronic databases. After the removal of duplicates and application of the eligibility criteria, 63 articles were considered for full-text evaluation. The reasons for excluding studies after full-text assessment are provided in Table I . At the end of the final eligibility evaluation phase, only 6 articles were included in this systematic review. , , , A complete search flowchart is provided in Figure 1 .
|Reasons for exclusion||Number of studies|
|Description of clinical technique||4|
|Use of other appliances and/or techniques in conjunction with LB therapy||23|
|Abstract in conference proceedings||4|
|Case reports or case series||10|
|Investigation not relevant to the subject of this study||9|
|No appropriate data provided||1|
Table II provides the descriptive characteristics of the 6 studies included in this systematic review. Only 1 study was an RCT, whereas 5 studies were non-RCTs. , , A total of 34 individuals participated in the RCT. Regarding the non-RCTs, , 175 individuals participated in 4 studies in which a primary outcome of this systematic review was evaluated. A total of 395 individuals participated in the study in which a secondary outcome was evaluated.
|Authors, year||Study design, local setting||Age, dentition||Descriptions of groups (n)||LB characteristics and intervention protocol||Measurements investigated||Results, P value|
|Mandibular arch changes|
|Nevant et al (1991)||non-RCT, POC||G1: 11 y and G2: 12 y, NR||G1: patients with mandibular arch length deficiency (4-8 mm) were treated with LB (n = 20)
G2: patients with same characteristics as G1, were treated with another type of LB (n = 20)
|G1: LB with wire covered with a layer of plastic shrink tubing was activated at the adjustment loops to remain approximately 2-3 mm in front of the mandibular incisors at the level of the gingiva. It was set 4-5 mm away from the buccal segments and expanded approximately 2 mm at the M1. The mean treatment time was 1.4 y.
G2: LB with an acrylic from C to C was placed approximately 2 mm in front of the mandibular incisors; vertically, the top of the shield was positioned 7 mm from the incisal edge. The LB was placed, on average, 4 mm away from the 1PM and 4-5 mm away from the M1. The mean treatment time was 1 y.
|M1 apex movement (mm)
M1 cusp movement
M1-occlusal plane (°)
Total arch length (mm)
|1.2 ± 2.1
0.1 ± 1.0
−2.7 ± 4.9
2.6 ± 2.6
1.3 ± 0.7
2.0 ± 0.9
0.7 ± 1.5
|1.2 ± 2.1
−1.5 ± 1.9
−8.0 ± 8.3
7.4 ± 4.2
2.8 ± 2.9
4.7 ± 2.4
4.2 ± 0.8
|Davidovitch et al (1997)||RCT, NR||10.2 y, mixed||G1: white ethnicity patients, with 3-8 mm mandibular arch length deficiency, presence of the mandibular deciduous M2, and Class I malocclusion treated with LB (n = 16)
CG: same characteristics as G1, untreated (n = 18)
|LB with plastic shield from C to C was used and positioned approximately 1.5-2-mm labial to the gingival third of the mandibular incisors. The appliance was inserted in a passive state, and continuous wear was assured by ligating the LB to the mandibular M1 bands. The LB were used for 6 mo.||M1 angulation CT (°)
M1 angulation Cph (°)
M1 movement of Cres CT (mm)
M1 movement of Cres Cph (mm)
Incisor inclination (°)
Incisor apex movement (mm)
M2-M2 deciduous (mm)
Arch length (mm)
|−6.3 ± 1.2
−3.3 ± 3.6
−1.6 ± 0.5
−0.6 ± 1.1
3.1 ± 2.4
|2.1 ± 1.3
0.7 ± 1.7
0.6 ± 0.5
0.3 ± 0.7
0.1 ± 1.7
|Ingervall and Thüer (1998)||non-RCT, NR||G1:10.9 y and G2: 10.8 y,
|G1: patients were treated with a LB, which was covered with plastic tubing (n = 20)
G2: patients were treated with a LB, which had an acrylic shield in the labial fold below canine and incisors (n = 19)
|LB was anchored in buccal tubes on mandibular M1 and adjusted and positioned 6 mm below the edges of the mandibular incisors, and to lie 3 mm away from the labial surfaces of the incisors, C and from the buccal surfaces of the premolars. The LB were used for 8 mo.||Lower incisor:
Arch length (mm)
|Solomon et al (2006)||non-RCT, POC||11.6 y, mixed and permanent||G1: patients treated nonextractionwith a LB (n = 51)||Prefabricated LB was adjusted to rest in the vestibule at the level of the free gingival margins 1-2 mm facial to the teeth and tied in the buccal tube of the M1 to continuous wear. Average time of LB use was 16.40 (±4.99) mo.||C-C (mm)
Arch length (mm)
|Moin and Bishara (2007)||non-RCT, POC||NR, mixed||G1: consecutively patients treated with LB by the same orthodontist. Inclusion criteria were the presence of at least 4 mandibular incisors and 2 permanent M1 (n = 45)
CG: mean values obtained from untreated patients from another study (Moorrees, 1959)
|LB with acrylic in the region of canines and premolars, with welded hooks to tie the LB. A piece of plastic tubing was slipped onto the wire and placed at the anterior segment extending between the C. LB was adjusted 2 mm away from the incisor area and 4, 8, and 2 mm wider in the C, 2PM, and M1 areas, respectively. The mean treatment time was 15.7 (±7.6) mo.||C-C cusp tip (mm)
C-C cervical (mm)
M1 deciduous cusp (mm)
M1 deciduous cervical (mm)
M1 deciduous fossae (mm)
M2 deciduous cervical (mm)
M1-M1 permanent fossae (mm)
M1-M1 permanent cervical (mm)
Arch length (mm)
|2.4 ± 2.0
2.3 ± 1.8
5.0 ± 2.2
4.7 ± 2.6
3.4 ± 2.2
3.7 ± 2.0
2.4 ± 2.6
3.1 ± 2.4
1.6 ± 2.1
|0.6 ± 0.9
0.1 ± 0.7
0.4 ± 0.8
|Permanent M2 eruption disturbances|
|Ferro et al (2011)||non-RCT, POC||10.2 y, NR||G1 patients with 2 mm or more of anterior crowding treated with LB. Exclusion criteria were permanent M2 eruption and possible factors predisposing or impeding M2 impaction, such as agenesis, dental inclusions, destroying caries, and previous dental extractions (n = 260)
CG: same characteristics as G1, untreated (n = 135)
|LB was kept gingival in the vertical plane, and a distance of 1-2 mm from the incisor was kept in the sagittal plane. Patients could remove the LB by themselves but were asked to wear it 24 h/d, taking it out only for meals. The mean treatment time was 28 mo.||Impaction of M2:
Ectopic eruption of M2:
OR for M2 impaction
Inclination of M2 for ectopic