Interproximal wear versus incisors extraction to solve anterior lower crowding: A systematic review

OBJECTIVE: To determine by means of a systematic review the best treatment, whether interproximal wear or incisor extraction, to correct anterior lower crowding in Class I patients in permanent dentition. METHODS: A literature review was conducted using MEDLINE, Scopus and Web of Science to retrieve studies published between January 1950 and October 2013. In selecting the sample, the following inclusion criteria were applied: studies involving interproximal wear and/or extraction of mandibular incisors, as well as Class I cases with anterior lower crowding in permanent dentition. RESULTS: Out of a total of 943 articles found after excluding duplicates, 925 were excluded after abstract analysis. After full articles were read, 13 were excluded by the eligibility criteria and one due to methodological quality; therefore, only fours articles remained: two retrospective and two randomized prospective studies. Data were collected, analyzed and organized in tables. CONCLUSION: Both interproximal wear and mandibular incisor extraction are effective in treating Class I malocclusion in permanent dentition with moderate anterior lower crowding and pleasant facial profile. There is scant evidence to determine the best treatment option for each case. Clinical decision should be made on an individual basis by taking into account dental characteristics, crowding, dental and oral health, patient's expectations and the use of set-up models.

The aim of this study was to determine -in cases in which there is doubt as to the most appropriate procedure -the best treatment option between interproximal wear and incisor extraction to correct anterior lower crowding in Class I patients in permanent dentition and to achieve good facial esthetics.

MATERIAL AND METHODS
The guidelines and directives set by the Preferred Reporting Items for Systematic Reviews and Meta-Analysis, the PRISMA Statement, were adopted for this review. 35 The search, as well as the inclusion/exclusion criteria, were based on PICO format (Table 1).
For sample selection, the following inclusion criteria were applied: studies involving interproximal wear and/or extraction of mandibular incisors in cases of anterior lower crowding and Class I malocclusion in permanent dentition. The exclusion criteria were: case reports; case series; laboratory studies; epidemiological studies; narrative reviews; opinion articles; studies involving orthognathic surgery, distraction osteogenesis, extraction of premolars, syndromic and/or cleft patients, supernumerary teeth and/or abnormal shape of teeth, transverse deficiencies, anterior crossbite, use of auxiliary devices; primary or mixed dentition and/or Class II or III malocclusion.
The literature review was conducted using MED-LINE (via PubMed), Scopus and Web of Science to retrieve studies that met the eligibility criteria and had been published from January 1950 to October 2013, without language restrictions. The combinations of words or terms used are described in Table 2.
Duplicate articles were eliminated from the final search results. Titles and abstracts were read independently by two reviewers who analyzed the articles in light of the inclusion and exclusion criteria. All articles found to be compatible and somehow related to the question (Table 1) were reviewed. Disagreements between reviewers were settled in a consensus meeting held with a third investigator. The articles selected were fully read. The references of the articles included in the research were also analyzed in search of potential relevant articles that might not have been found in the selected databases.
The articles selected were assessed for methodological quality according to a list based on CON-SORT, 36 whenever applicable, and modified by the reviewers (Table 3). Disagreements were solved in consensus meetings, and articles were classified into high (≥13), moderate (<13 and ≥9) and low (<9) methodological quality.
Data were extracted from the articles by two reviewers.

P = Population
Angle Class I patients in permanent dentition presenting with lower anterior crowding.

I = Intervention
Subjected to orthodontic treatment involving interproximal wear or extraction of a lower incisor.

C = Comparison
Between the two types of treatment and the original characteristics of each malocclusion.

O = Outcome
The best solution for each malocclusion.

Question
What is the best treatment for lower anterior crowding in patients with Class I malocclusion in permanent dentition, interproximal wear or incisor extraction?

RESULTS
The search in the literature identified 1,094 studies, 706 from MEDLINE, 240 from Scopus and 148 from Web of Science, which are all presented in a "Prism Flow Diagram" 35 (Fig 1). After excluding 151 repeated articles, all titles and abstracts were read and those found to be unrelated to the review were eliminated. Eighteen preselected articles were read in full and the inclusion and exclusion criteria were applied. Five articles remained and were classified according to the methodological quality assessment.
One article was assigned as presenting low methodological quality 22 and was, therefore, not included in this study. Four articles showed moderate quality, [23][24][25][26] and none presented high quality (Table 4). Most articles offered insufficient sample description, both demographically and in terms of sample size calculation.
Of the four studies included, two were randomized prospective 23,24 and two were retrospective studies. 25,26 Only one article presented sample size calculation. 25 In the study by Ileri et al, 25 only the sample data for incisor extraction (IE) were considered, given that no wear was mentioned in the non extraction (NE) group, and although the authors were contacted by e-mail, no response was given. Only the data from groups of interest were extracted from the articles. [23][24][25][26] All information regarding the author, year, study type, sample, type of treatment, statistical analysis, data evaluated and total treatment time, was gleaned from the included articles and described in Table 5.   Table 4 -Methodological quality scores for the selected articles. Items A to L are described in Table 3.  Given that studies included different data, it was impossible to compare them directly and/or perform meta-analysis.

DISCUSSION
By the end of this research, only one systematic review 37  Excluded after the full text was read and the inclusion/exclusion criteria were applied (n = 13).
Reasons: These articles failed to describe the treatment performed in nonextraction cases; also, data from Class I, Class II and Class III groups were presented in combination.
Excluded after eligibility criteria were applied (n = 1) Interproximal wear versus incisors extraction to solve anterior lower crowding: A systematic review original article lower crowding in patients in permanent dentition and Class I malocclusion.

Articles included (n = 4) Included
Several clinical cases 1,2,5,9,12-15,17-21,30,31,38 reported interproximal wear or mandibular incisor extraction as potential therapies for mild or moderate anterior lower crowding in patients in permanent dentition, with Class I malocclusion and a pleasant facial profile. Nevertheless, there are yet few clinical trials or randomized controlled trials addressing this issue.
Of the 943 articles found after duplicates removal, only eighteen were selected for full reading. The articles excluded after title and abstract reading included case reports or epidemiological research. Either that or the sample had undergone treatment for crossbite, distal movement of molars, surgical treatment and extraction of other permanent teeth. Some articles addressed mixed and primary dentition, or only Class II or Class III malocclusion.
Of the eighteen 16,22-26,37,39-49 articles included for full reading, only five [22][23][24][25][26] were selected for methodological quality assessment. The reasons for exclusion were: no description of treatment used when referring to nonextraction; lack of clear information on whether or not interproximal wear had been performed; treatment including dental arch expansion or incisor protrusion; 39,40,[42][43][44][45][46][47][48][49] use of auxiliary appliances; 40 systematic review performed using some other approach; 37 description of clinical cases; 16 and whenever data from Class I, II and III groups were presented together, which precluded the use of data from Class I patients, only. 41 Only one 22 out of the five articles selected for methodological assessment was excluded due to low methodological quality and also because it failed to report the final results. Two out of the four articles included after qualifying addressed treatment with incisor extraction 25,26 while two reported using interproximal wear. 23,24 Mandibular wear performed in the study by Germeç et al 23 measured 5.1 ± 0.9 mm, with 2.0 ± 0.5 mm in anterior lower teeth, only. To solve crowding of 4 mm to 8 mm, Sheridan 50 advocates interproximal reduction carried out mostly, but not exclusively, in the anterior segment. Wear should be limited to about 0.5 mm on each side of anterior teeth, and 0.8 mm on posterior teeth. 9,28 It should not exceed original article Almeida NV, Silveira GS, Pereira DMT, Mattos CT, Mucha JN 50% of total enamel thickness. 7 The areas of mandibular teeth where enamel thickness is greater are the distal surfaces of lateral incisors 2,7 and the mesial and distal surfaces of canines. 2 Germec-Cakan et al 24 observed that cases in which interproximal wear was carried out had a decrease in intermolar width whereas intercanine width and arch perimeter remained unchanged. This treatment allows the creation of a contact area between teeth, which favors stability. 6 When performed carefully, interproximal wear yields a healthy dentition, which is not susceptible to periodontal disease and tooth decay. 29,51 There is a certain degree of concern, however, that a thin interdental alveolar septum might accelerate gingival attachment loss and the spread of periodontal disease. 52 According to Ileri et al, 25 a PAR index comparison showed that malocclusions were corrected by extracting mandibular incisors, which was indicated in cases with mandibular anterior Bolton 53 discrepancy whereby the anterior ratio equals to 81.7 ± 4.5,25, thereby corroborating other articles. 5,13,16,17,18,25,37,38,54 This seems to suggest that in cases in which mandibular dental volume excess is smaller, the best alternative may be interproximal wear. 15,16 The other groups compared by Ileri et al 25 (premolar extraction and treatment without extraction) were assigned better scores after treatment, perhaps due to difficult intercuspation and/or overjet remaining in cases involving mandibular incisor extraction. 25 Thus, in these cases, interproximal wear is indicated on maxillary anterior teeth to correct remaining overjet. 1,5 Priority should be given to extracting incisors in patients with decreased overjet and overbite. 13,16,18,20,37,38 Dacre 26 showed in a follow-up of 16 patients, after mandibular incisor extraction and retainer removal, that only five cases preserved good alignment, while seven had mild crowding relapse, one had moderate relapse, and three showed space opening. Intercanine width was slightly reduced, since extraction caused canines to move closer to the region where the dental arch is narrower. 26 Selection of the incisor to be extracted is usually based on malposition, periodontal involvement, color change, decay and/or fracture, 1,18 factors which are less likely to induce changes in profile, 5,12 and arch length. 13 Loss of interdental papilla or formation of Interproximal wear versus incisors extraction to solve anterior lower crowding: A systematic review original article triangular space are examples of common undesirable effects. 13,16,37 From an esthetic point of view, teeth with a triangular shape 2,31 may benefit from interproximal wear while those with a rectangular shape respond better to extraction.

CONCLUSIONS
» Both mandibular incisor extraction and interproximal wear are effective to treat patients with Class I malocclusion with moderate anterior lower crowding, in permanent dentition and with a pleasant facial profile. There is, however, scant evidence to determine the best treatment approach.
» Decreased overjet, overbite and Bolton's toothsize discrepancy were the most decisive parameters used to indicate mandibular incisor extraction.
» Clinical decision should be made on an individual basis by taking into account patient's dental anatomical characteristics, crowding, dental and oral health conditions, expectations and the use of set-up models.