interproximal enamel reduction

Interproximal Enamel Reduction

Mohammed Almuzian

Table of Contents1 Introduction..............................................................................................................................................32 Definition...................................................................................................................................................33 What is IER used for?................................................................................................................................3

3.1 Improvement of microaesthetics and smile appearance................................................................33.2 Correction of dental midlines..........................................................................................................43.3 Retraction of upper anteriors where there is lack of overjet and overbite.....................................53.4 Providing additional space requirements........................................................................................53.5 Bolton’s discrepancies.....................................................................................................................53.6 As an adjunct to clear aligner treatment for space gain in non-extraction cases, minor crowding and rotations................................................................................................................................................63.7 IER & retainers for mild relapse or as adjunct to finishing..............................................................63.8 Reproximation to assist in post-treatment stability........................................................................73.9 IER in deciduous teeth.....................................................................................................................8

4 Methods of IER..........................................................................................................................................84.1 Enamel assessment.........................................................................................................................84.2 Air rotor stripping............................................................................................................................94.3 Diamond Coated Stripping Discs in Handpiece/Contra-angle.......................................................114.4 Handheld or motor-driven abrasive strips.....................................................................................12

4.4.1 Handheld...................................................................................................................................124.4.2 Reciprocating saws....................................................................................................................12

4.5 Post IER desensitising agents.........................................................................................................135 Long term effects of IER..........................................................................................................................14

5.1 IER & periodontal disease/caries...................................................................................................145.2 IER and pulp damage.....................................................................................................................15

6 References:.............................................................................................................................................16

1 Introduction.Interproximal enamel reduction (“IER” or “IPR”) is a useful tool for space creation, achieving ideal aesthetics for tooth size discrepancies (Bolton’s) for maxillary to mandibular dental arch compatibility in Class I occlusion and interdigitation of teeth during orthodontic finishing.

IER can be used as an option where extractions or overexpansion in non-extraction cases are unwanted. It can assist with increasing treatment efficiency, conservation of transverse arch widths and ideal incisor inclinations. IER is also useful in prevention of gingival papilla retraction commonly known as the “black triangles” of particular relevance to adult patients.2

2 DefinitionInterproximal enamel reduction has many aliases such as interdental “stripping”, proximal reduction, reproximation, enamoplasty, keystoning, enamel approximation and slenderising3-5_ENREF_3. IER is the reduction of MD width of teeth by removal of interproximal enamel in controlled increments5, 6. Peck & Peck3 use the term reproximation as it is “the act of ‘redoing’ the approximal surfaces”. They define tooth reproximation as involving the reduction, anatomic recontouring and protection of the mesial and or distal enamel surfaces of a permanent tooth (where protection refers to the post procedural topical cariostatic agents)3. IER however can be performed in deciduous and permanent teeth. Keystoning refers to oblique IER of the lower incisors to “lock” them together to prevent rotational relapse5.

3 What is IER used for?3.1 Improvement of microaesthetics and smile appearanceSarver (2011) describes the importance of including tooth shape and form assessment in the diagnosis and treatment of orthodontic problems and how enamoplasty is a key component to achieving ideal microaesthetic characteristics in orthodontic finishing1. Microaesthetics refers to tooth morphology, ideal ratios for dimensions, shape and contour, contacts, connectors embrasures, gingival margin form etc. Enamoplasty can be used to an advantage when one understands the principles of ideal tooth shape and morphology.

Figure 1: Tooth microaesthetics1, 7

Contact points are where the teeth touch and the connector is defined as the interdental contact area 8. ‘Black triangles’ or open gingival embrasures is a lack of interdental papilla 9. The papilla height is 49% of crown height and contact point to incisal edge is 51%. Prevalence in treated adolescents is 42% 10 and in treated adults approximately 38%11. Possible contributing factors include contact points located incisally, interdental papilla and alveolar bone height loss (e.g. related to periodontal disease), triangular crown shape, divergent roots and severely maligned incisors. However, rather than crowding it is more to do with undetected incisal attrition leading to incorrect bracket positioning11. The presence of interproximal papilla

is shown to be related to the distance from the contact point to the alveolar crest. A distance 5mm resulted in 98% presence of papilla, 6mm resulted in 56% papilla presence and >7mm resulted in 27% papilla presence12. Thus IER may be used to move incisal contact points to a better position for correct tooth proportions and improved interdental papilla.

Ensure that the teeth are well aligned prior to reshaping as rotations can conceal the true height:width ratio. Sarver lists the steps as follows1:

1. Establish ideal root divergence13

2. Establish HeightThe gingival margins should be corrected (with confirmation of periodontal probing) whether gingivectomy is required to correct the tooth height

3. Address WidthAfter gingival margin healing to final position, the width of the teeth can be reduced with a fine carbide bur (with rounded “safe tip” that avoids gouging a ledge) first recontouring the connectors in short vertical motion.

4. Check Connector LengthSqueeze the teeth together to show any interferences and contact length, adjust accordingly.

5. Round Line AnglesOnce the carbide bur has cleared from La-Pa/Li, use discs or hand held strips (better suited for interpoximal polishing) or cone-shaped diamond and follow the connector to round the line angles.

6. Close Space From IERPower chain over the fixed appliances can be used to close the space.

7. Create & Refine EmbrasuresUsing the cone shaped diamond as above refine emabrasures and line angles once spaces closed.

8. Polish A carbide long flame followed by rubber polishing tip is used to finish and polish the enamel.

It is this microaesthetic feature of IER that may initially not seem a significant complimentary orthodontic finishing tool, but in fact can transform a case that may look average to one with optimal aesthetic and finishing outcomes.

3.2 Correction of dental midlinesIER can assist in correction of midlines to establish symmetry of the anterior dentition and achievement of perfect Class I canine relationship.Achieving a coincident dental midline to the true vertical (facial midline) allows any deviation <4mm to be unnoticeable14. When midlines deviate from the true vertical, then dental midline discrepancies >2mm are noticed. Thus dental midline discrepancies of 2-4mm may be corrected with IER rather than having to resort to extraction (>4mm deviation).

Figure 2: Steps to correct microaesthetics1

3.3 Retraction of upper anteriors where there is lack of overjet

and overbiteIER can assist in more favourable overbite and overjet resulting in improved anterior function and a mutually protected occlusion15. IER can assist in retraction of upper incisors when there is not enough overjet for the retraction to occur, thus via lower incisor IER this can create the overjet required for further upper incisor retraction. There is a positive correlation between an increase in overbite with increase of IER16. Sometimes, the occlusion may provide “Class I” relationships but with the face the aesthetics don’t appear correct. Sarver mentions the importance of the ¾ profile smile photo as this can identify smile aesthetics and incisor proclination. If the incisors appear overproclined with no spaces remaining and retraction is required but there is no overjet for this i.e. the lower incisors are contacting the marginal ridges and cingulum of the upper incisors, IER in the upper and lower will assist in attaining ideal incisor angulations13. In addition during space closure after IER with powerchain, stainless steel round wire can be used to allow retroclination of the incisors with some extrusion for improved tooth display on smiling, increasing a minimal overbite and for consonance to the lower lip.

Figure 3: Space closure with power chain on round wire13

3.4 Providing additional space requirementsIER can also be used as an adjunctive tool to proclination, expansion, extraction, distallisation and use of Leeway space for space creation.

Sheridan uses 50% of interproximal enamel reduction as a guide from other references 16, 17 and quantifies this as18:Posterior segment IER available: 0.8mm/contact x 8 Buccal contacts = 6.4mm spaceAnterior segment IER available: 0.5mm/contact x 5 anterior contacts = 2.5mm spaceTotal space available from conservative IER = 8.9mm. More conservative amounts include recommendations of <4mm thus in cases with mild crowding where extractions are unwarranted IER can assist in correcting slight arch length discrepancies and reduce the need for extractions or canine expansion15, 19.

With large ranges of enamel reduction reported in the literature, Zachrisson et al 2 finds mm values useless clinically due to the wide variation in enamel morphology and thickness for each tooth. Clinically relevant judgements involve removing enamel conforming to the shape of the teeth 15. Thus those teeth that deviate from the norm may have more enamel available for removal compared to “screw-driver” shaped teeth, round premolars and incisors with parallel M-D surfaces which may be non-ideal candidates for IER.

3.5 Bolton’s discrepanciesIER is useful for achieving ideal aesthetics for tooth size (MD) discrepancies (Bolton’s) for maxillary to mandibular dental arch compatibility in Class I occlusion and interdigitation of teeth during orthodontic finishing. There may be a maxillary excess +/ mandibular deficiency, maxillary deficiency +/ mandibular excess. It is common for orthodontic patients to exhibit a Bolton’s tooth size discrepancy. A Bolton’s analysis (deviations from an ideal anterior ratio 77.2%; posterior ratio 91.3%) would identify this prior to starting treatment so that plans are in place for final modifications. Mandibular incisor IER will affect maxillary anterior tooth size relationships, however it is often required in cases with unfavourably large lower incisor MD/FL ratios with Bolton’s discrepancies involving anterior mandibular excess16. IER can correct Bolton’s discrepancies and allow for well aligned and ideally occluding teeth.4, 20

3.6 As an adjunct to clear aligner treatment for space gain in non-extraction cases, minor crowding and rotations

IER is used more frequently during clear aligner treatment than fixed appliances. In mild relapse cases where space is required, technicians would recommend IER to assist alignment as they were instructed to maintain lower intercanine width and not to flare the lower incisors6. “Virtual collisions” where the setup causes one tooth’s interproximal surface to virtually pass through the adjacent tooth’s interproximal surface was another reason for IER so that desired tooth movement could occur without physical interference. Collisions < 0.5mm are considered insignificant as the aligner “stretches” this amount, however if there are multiple collisions, although align would recognise this as insignificant this could be clinically significant as the tooth mass is greater than the space allowed for the aligner and teeth will be intruded to reduce arch length often at the last molar. 6 The clinician should choose the best IER option for the patient as the options available are “primarily”, “if needed” and “none”. “If needed” may not be the best as it gives the technician freedom to control the amount of IER, thus this should only be selected if the orthodontist gives specific instructions on the conditions IER is allowed. You can also request “no collisions” to ensure there are no insignificant collisions so that treatment imitates fixed appliance treatment6.

3.7 IER & retainers for mild relapse or as adjunct to finishingCustom-made positioners can correct minor corrections in tooth position and occlusal relationship. Positioners are made on articulated models where the teeth are sectioned, aligned and waxed into ideal and elastomeric or rubber material is contoured around the teeth and the coronal portion of the gingiva.When debanding, IER can be performed prior to taking an impression for a positioner (for minimal crowding), or document the precise amount of IER for the technician to complete on the set-up and clinically repeat when inserting positioner.21 Positioners are worn full time for the first 2 days, followed by 4hrs/day plus nightly. Patients should bite and clench cyclically for 20sec followed by 20sec rest intervals during the first 4hrs to enable desired tooth movement in 3wks, where its use becomes a passive rather than active appliance.

Figure 4: Positioner

The Essix appliance is a 0.5mm think removable plastic device that lock into position without needing adjustments intra-orally. A modified 3-3 Essix retainer (.015” thickness) to cover 3-5mm over the gingivae facially and buccally with cut outs for brackets at the 3’s was used in 10 patients with moderate 4-6mm lower incisor crowding by Ballard & Sheridan22 to provide anterior anchorage to

resist anterior forces resulting after ARS. Their appliance was worn full time except for eating and cleaning. The appliance boosted anterior anchorage via:

1) 6 anterior roots in bone2) Superior aspects of the lingual and facial cortical plate3) Anterior unit pitted against the distal movement of individual posterior teeth.

Their results found the Essix retainer reinforced anchorage, was aesthetic and treatment ranged from 3.5-4.5months.

Figure 5: Modified Essix retainer to provide anterior anchorage with ARS22

3.8 Reproximation to assist in post-treatment stability“Stripping” mesial +/ distal enamel along with orthodontic treatment to minimise postretention crowding has a long history. IER of the lower incisors is often the last resort at maintaining alignment and often used after other conventional methods have failed16. With reductions in intercanine width, arch length and depth continuously decreasing throughout life, crowding often ensues and IER can assist in long-term maintenance of lower incisor alignment4.

Peck and Peck (1972) proposed a method for evaluating tooth shape deviations contributing to mandibular incisor crowding from a study of 45 “perfect” lower incisor alignment cases compared to 70 control subjects. They use the MD/FL index as a numerical representation of lower incisor crown shape viewed incisally. Well aligned mandibular incisors are smaller MD & larger FL compared to controls. Their standards suggest ideally shaped lower centrals have MD/FL index = 88-92%, lower laterals = 90-95%. Concluding that well aligned mandibular incisors have siginificantly lower MD/FL indices compared to crowded incisors and reproximation recommended to correct unfavourable incisor shapes3.

Boese (1980) suggest serial reproximation to compensate for natural arch length reduction which appears to be common during increased horizontal mandibular growth. They state two main benefits of reproximation; first providing a broader contact point Fig. 6 harnessing greater contact stability and secondly increasing space available in the lower anterior region particularly useful seeing as the biological framework limits increases in arch length or arch form16. Three phases of IER are possible: 1) Early in treatment after initial alignment to provide good LI shape & OB correction (most IER is performed at this phase), 2) When no lower retention used, IER shortly after removal of fixed appliances, some IER performed serially over 4-6months post treatment recall checking if contact points tight or movement occurred then IER as required, 3) Depends on changes in mandibular anterior arch form and amount and direction of mandibular growth (particularly horizontal growth). Usually little IER required after 6months post treatment, however CCW growers exhibit lower incisor uprighting leading to secondary crowding16.

Figure 6: Interproximal contacts & stability in arch form15

Boese studied 40 patients with crowded mandibular arches orthodontically treated with premolar extractions without retention 4-9years post-treatment. Intercanine width was maintained as much possible and all cases had CSF and IER. The mean reproximation of lower incisors at the completion of treatment (phase I & II total 61.5% of cases IER, remainder in phase III) was 1.69mm SD 0.64mm. Conservative and precise IER increased long term stability of the mandibular anterior segment. The periodontium showed no

significant increases in probing depth, gingival recession or loss of alveolar crestal bone 4-9yrs post treatment.23

3.9 IER in deciduous teethIER can be used on occasions for interceptive guidance where no extractions of permanent teeth are planned and a local interference causes a shift leading to an anterior crossbite or rotation of a lateral incisor where the mesial of deciduous canine can be reduced6. Cases with prolonged retention of deciduous second molars can have their mesial and distal surfaces reduced, for example where the lower E forces the lower first premolar in a mesial position crowding out the canine, the mesial surface of the E can be reduced by the amount of the leeway space to allow space for the 1 st premolar to move distally and allow space for the canine to erupt into the arch6. A flush terminal plane can be converted to mesial step by IER on the distal of the lower E aiming for a Class I molar relationship 6. Congenitally missing lower 2nd premolar cases where the future plan is for implant replacement can have IER of the lower E’s (depending on pulp proximity) to simulate the space maintenance needed for a 2 nd premolar whilst holding bone until the child is of ideal age for implant replacement.

4 Methods of IERThe most common methods of IER reported by Zacchrisson2 include 1) the air-rotor stripping (ARS) technique with fine tungsten-carbide or diamond burs and diamond-coated strips (mostly posterior IER), 2) hand-piece or contra-angle handpiece with diamond-coated stripping discs and 3) handheld or motor-driven abrasive strips. The finer the grit, the more efficient and easier it is to complete polishing. Polishing is important to remove scratches, furrows and steps in enamel which promote plaque retention and increased risk to caries24.

4.1 Enamel assessmentIER is irreversible, so careful assessment and reduction amounts must be considered, once enamel is removed it cannot be replaced. Excessive IER must be avoided, Boese (1980) recommend less than 50% of interproximal enamel (per side of tooth), any greater increases the risk of caries, sensitivity, discolouration and possibly reduce transeptal bone between the lower incisors predisposing to periodontal disease16. [Refer to section 3.4 for IER recommended amounts]. IER should only be performed after alignment due to inability to be conservative and establish ideal broad contact areas if the teeth are malposed. Obviously select cases carefully, those with poor OH, high caries susceptibility, small teeth, severe crowding and tooth hypersensitivity, hypoplastic teeth with reduced enamel where IER could cause dentinal involvement should not be candidates for IER2, 25.

IER is limited to the enamel thickness at its contact point, this varies, thus bitewing films can be used to estimate this by projecting a line vertically from the cervical line of the tooth to the occlusal/incisal plane 18. Jarvis recommends 0.5mm per tooth surface as any greater IER will increase the risk of exposing dentine 25. Consider the extent of any prior stripping, amount of enamel remaining, colour of tooth, shape of lower incisor or tooth to be reduced, degree of overbite and predicted amount and direction of mandibular growth16. Remember to record tooth surfaces and amount of IER to prevent over IER at future appointments15.

4.2 Air rotor strippingThe use of tungsten carbide burs in an air-rotor handpiece (air-rotor stripping (ARS)) under water was introduced by Sheridan (1985)18 and updated by Chudasama & Sheridan

(2007)26. The IER is completed via a lateral approach. Guidelines for contemporary ARS in posterior segments26:

1) Remove only 1mm (0.5mm per proximal surface) of enamel from any buccal interproximal area, they do not recommend 50% reduction due to lack of scientific basis. Measure the IER performed with a gauge [Fig. 7] to within 1/10 thmm. The 1mm limit is conservative representing 1/3 rather than ½ enamel thickness. For upper laterals incisors and lower incisors remove only 0.5mm of enamel from any interproximal area retaining enamel morphology rather than leaving flat.

Figure 7: Gauges measure amount of IER & separator prior to IER

2) Use coil spring or separator prior to ARS to establish open contact to enhance visual and mechanical access.

3) Correct rotations prior to ARS thus level and align first to enable IER to position contact point in improved position.

4) Use .020-.030” brass or steel indicator wire gingival to contact to protect interdental tissue during ARS. Place the bur beneath the contact and begin IER with light and occlusally directed wiping motion moving bur from Bu-Li. The tapered bur results in good morphology to create parallel proximal surfaces.

Figure 8: Indicator wire for protection prior to ARS

5) Use safe-tipped ARS burs to prevent unwanted enamel ledging.

Figure 9: Safe-tipped ARS bur to prevent notching26 Figure 10: Sof-lex discs for finishing26

6) Use IntensivOrtho Strips as an alternative to a rotating bur in a handpiece. This can efficiently perform IER via hand-piece powered abrasive strips with reciprocating action 0.8mm. They are available in a range of grit sizes, for contouring and smoothing interproximally. Although more time consuming the result may be improved.

7) Finish surfaces to maintain morphology and texture using a 699L tapered fissure carbide bur and fine-medium grit diamond to contour proximal surfaces. Use Sof-Lex discs for smooth texture.

8) Complete final smoothing with a fine abrasive strip coated with 35% phosphoric acid gel4. Rinse with water spray.

9) IER sequentially from posterior to anterior in the posterior segments to maximise control, consolidate space and repeat at next visits until enough space is created as needed. I.e. move each posterior tooth distally one at a time like pearls on a string.

10) Establish anchorage when consolidating ARS space e.g. Li arch, Nance, headgear, miniscrews, stopped arch etc.

Figure 11: Fine abrasive strip coated in etch26

11) Avoid pre-emptive IER to balance tooth mass ratios between arches. Compensatory IER can be performed in the opposing arch during finishing for sound occlusal and incisal finish.

12) Use F gel/rinses to assist remineralisation.

13) Don’t use ARS as a stand-alone technique, it can be an adjunct to extraction treatment or for

Bolton’s discrepancies to adjust tooth widths for ideal occlusion.

Ideal orthodontic reproximation should result in proximal surfaces with continued interproximal morphology including marginal ridge height, contact points and embrasures; the only difference being reduced mesio-distal tooth dimension25. This allows for continued occlusal function with prevention of periodontal problems (e.g. food impaction from reducing the occlusal height of the contact area). Jarvis believed the lateral approach was disadvantageous as notching occurs, with lack of control for a smooth enamel finish. Jarvis describes an occlusal approach for IER in the posterior regions (distal canines to mesial 1st molars) using with an ultrafine 0.9mm diameter diamond bur [Fig. 12] used for his stepwise IER technique25:

1) Align posterior arch form – resolve rotations and correct marginal ridge heights

2) Separators plased 3-4 days prior3) IER with occlusal approach using bur (2.5mm or 4mm length) [Fig.

12] in a high speed air-rotor with water, with bur shoulder against marginal ridge to maintain its form thus contact is not relocated gingivally. Either complete one contact area per visit or all at once. Move bur from Bu to Li, recontour Bu and Pa surfaces. Use 4mm bur for Di canines and do not seat against marginal ridge, a straight diamond can be used for this. Refine enamel with soflex discs

4) Orthodontic space closure5) Further recontouring of Bu & Li surfaces at deband if required

Figure 12: IER bur occlusal approach25

Germec & Taner in their study of 26 Cl I borderline exo/non-exo patients with balanced facial profile and moderate dental crowding found that both extraction and non-exo with ARS produced effective treatment results with the latter group having an 8month shorter treatment duration. The main soft tissue profile differences was 1-1.5mm more retruded UL & LL positions in the exo group, however both groups finished within normal limits and had desirable facial aesthetics.27

The main disadvantage of the ARS approach is that the surfaces are rougher compared to fine grit diamond coated discs28.

4.3 Diamond Coated Stripping Discs in Handpiece/Contra-angle

Figure 13: Modified Tuverson Technique2

Zachrisson promotes the use of the modified Tuverson15 technique:2

1) Initial levelling 1-2months.2) Use Elliot anterior straight separator [Fig 13A]

tightened short of the amount of space required for the IER, 30-45s allows the PD membrane to compress providing adequate discing space starting at the least crowded teeth requiring less separation that subsequently provides more space for the crowded teeth.

Figure 14: Separation crucial for IER15

3) Extra-fine (8-10m) diamond-coated perforated stripping discs (Komet 8934A.220) in a contra-angle handpiece at medium speed (30,000 rpm) and reduce to amount calculated. Use 4 handed approach, assistant must provide air cooling with triplex and retraction of tongue with mouth mirror.

4) Round interproximal corners with friction-grip, cone-shaped triangular diamond burs (Komet 8833)5) Polish with sof-lex discs (3M)6) Close spaces

Figure 15: Example of disc stripping2

While the rotation of the discs can cause trauma to the patient, Zhong et al 29 used discs in an oscillating handpiece which eliminated the need for retractors and risk of damage to the lips, cheeks and tongue. Moreover the discs can be used in segments rather than full 360 and the addition of perforations increases visual access. They demonstrated in SEM studies on 32 patients that perforated diamond-coated (<30m grit) discs in an oscillating handpiece followed by two sof-lex discs (fine and ultra-fine) for polishing minimises scratches and furrows in the enamel with 90% of the surfaces smoother than untreated enamel and each surface was completed in 2.2minutes29.

4.4 Handheld or motor-driven abrasive strips4.4.1HandheldMetal strips can be manipulated with the fingers, however a pair of Matthiews forceps either side of an interproximal abrasive strip or custom “saw” like handle that allows insertion of sections of strips provide a means for control of hand stripping. These can be useful to gain initial patency interproximally as an adjunct to motor run strips or for minor reductions and refinement with finer grit strips.

Hand-pulled abrasive strips can be rather awkward and tedious thus air-turbine handpiece methods are more efficient26.

Figure 16: Metal strips for IER4

4.4.2Reciprocating saws

Various motor driven contra-angle handpieces which drive a reciprocating or oscillating abrasive strip are available. These are safer (don’t require extensive retraction like the rotating discs), user friendly, can provide IER to various thicknesses dependent on the size strip utilised and the strips are flexible to allow contouring the interproximal surfaces. They range from polyester strips coated with ultra-fine corundum abrasives to leave a polished finish to diamond coated strips and strips with regions or single sides without diamond abrasive to prevent unwanted enamel removal.

Figure 17: Example of commercially available reciprocating IER30

4.5 Post IER desensitising agentsTopical desensitising and remineralising agents most commonly used are casein phosphopeptide-amorphous calcium phosphate (CPP-ACP) e.g. Tooth Mousse and concentrated topical fluoride e.g.

Duraphat varnish. The new exposed enamel surface after IER will absorb topical agents and could penetrate undetected subsurface lesions unidentifiable on bitewings, this will enhance remineralisation and prevent demineralisation25.

The theory is IER results in removal of the outermost FA rich enamel layer, hence the recommendations for use of topical agents, however, recent findings by Zachrisson et al2 suggest this may be unnecessary in patients with good OH and regular use of F toothpastes and rinses. The key is the balance in the biofilm and the cariostatic mechanism of F on this rather than a high F content on the apatite lattice. Thus caries risk assessment and F exposure can determine the choice for F supplementation post IER.2 Jarjoura et al31 in their study on 40 patients 1-6yrs post IER with ARS and no topical F application immediately post IER support these findings suggesting patients exposed to F water and F toothpaste may not receive any additional benefit from topical F post IER.

5 Long term effects of IER5.1 IER & periodontal disease/cariesBoese analysed PA films to correlate fiberotomy and reproximation on the periodontium, he measured proportion of crown size to tooth length23:

And performed periodontal probing on the mandibular incisors with resulting pocket depths ranging 0.5-1.5mm and found IER did not influence any significant decrease in alveolar crest height or loss of interdental bone, with AI/TL ratios all very close. Not one of his 40 IER cases showed caries nor restorations on the post treatment radiographs23.

IER in posterior teeth must be controlled and result in contact areas 1mm above the gingival papilla otherwise if this space is encroached upon, the papilla is pushed from the embrasure area resulting in an oversized col resulting in a deep interproximal col (nonkeratinised plaque susceptible gingiva) and risk to pocket formation and periodontal disease.25

There was some thought that IER could reduce transeptal bone between teeth because the roots would finish in closer proximity and predispose them to periodontal disease, Artun et al in a study of 400 adult patients 16yrs post orthodontic treatment, found no significant differences in inflammation, level of attachment, and alveolar bone level between root proximity vs control sites and indicate anterior teeth aren’t predisposed to increased periodontal destruction with roots in close proximity32. Jarvis infers from studies such as this that thin alveolar bone between teeth that have had IER and closer root proximity doesn’t predispose to increased risk of periodontal disease25.

Zachrisson et al (2007)33 studied 61 patients 10yrs post IER with fine diamond discs under air cooling followed by polishging on the six lower anteriors and found no new carious lesions were present, no root pathology and only 3 adults had minor labial gingival recession. Interestingly the patients who had IER showed roots with greater separation distance than those that had not. 59/61 patients did not report sensitivity to thermal changes. They concluded that IER didn’t result in iatrogenic damage, dental caries, gingival problems, bone loss, nor reduced interradicular distances of the roots. Overall incisor irregularity was small.33

Zachrisson et al (2011)2 investigated the effects of careful IER with extrafine diamond discs with air cooling, followed by triangular diamonds for contouring and polishing on caries risk in premolars and molars on 43 patients 4-6yrs post IER. IER did not increase the risk of caries in posterior teeth and concluded that correct MD IER within limits and appropriate cases caused no harm to teeth and their periodontium. Overall patients had sound dentitions with good occlusion and only 2.5% new caries lesions (grade 1- outer half of enamel only), compared to the contralateral unground reference tooth surfaces where 2.4% of new caries lesions were found. No patients reported sensitivity to thermal changes.

Jarjoura et al (2006)31 in their study of 40 patients 1-6 years post IER with ARS and no topical F or sealant application found ARS does not increase the caries risk. IER in the anterior region could also assist in reduction of gingival recession as the teeth can be retracted over basal bone15.

5.2 IER and pulp damageZachrisson advises enamel IER does not result in pulp damage provided the IER doesn’t cause a notched surface inaccessible to cleaning which allows plaque retention, caries and damage to dentinal tubules leading to pulpal irritation34.

Sheridan states grinding enamel surface is not harmful, the amount of enamel needed for adequate protection of teeth against caries, thermal or chemical change is indeterminate and each tooth has various enamel thickness depending on the region, the thinner Bu and Li enamel compared to interproximal suggests there’s no advantage in having thicker enamel in this region so that careful IER with smooth cleanable surfaces is not harmful18.

Studies have demonstrated that marked grinding of teeth even into dentine, if done carefully with adequate water and air cooling with resultant smooth self cleansing surfaces can be performed without adverse effects, but if there is no cooling, extensive odontoblast aspiration into the dentinal tubules is a sign of irreversible damage2, 34_ENREF_1. Unintentional steps placed in enamel can lead to pulpal inflammatory cell infiltration34.

Cosmetic recontouring for example in cases of canine substitution for missing lateral incisors was studied 10-15yrs post treatment indicating favourable long term results with no significant colour differences, mobility, TTP, thermal sensitivity, or negative electric pulp testing results.35

6 References:1. Sarver DM. Enameloplasty and esthetic finishing in orthodontics-identification and treatment of

microesthetic features in orthodontics part 1. Journal of Esthetic & Restorative Dentistry: Official Publication of the American Academy of Esthetic Dentistry 2011;23(5):296-302.

2. Zachrisson BU, Minster L, Ogaard B, Birkhed D. Dental health assessed after interproximal enamel reduction: caries risk in posterior teeth. American Journal of Orthodontics & Dentofacial Orthopedics 2011;139(1):90-8.

3. Peck H, Peck S. An index for assessing tooth shape deviations as applied to the mandibular incisors. American Journal of Orthodontics 1972;61(4):384-401.

4. Rossouw PE, Tortorella A. Enamel reduction procedures in orthodontic treatment. Journal (Canadian Dental Association) 2003;69(6):378-83.

5. Daskalogiannakis J. Glossary of orthodontic terms. In: van der Linden F, Miethke RR, McNamara JAJ, editors. Berlin: Quintessence Publishing Co, Inc; 2000.

6. Graber LW, Vanarsdall RL, Vig KWL. Orthodontics Current Principles and Techniques. 5 ed. Philadelphia, PA: Mosby Elsevier; 2012.

7. Sarver DM. Principles of cosmetic dentistry in orthodontics: Part 1. Shape and proportionality of anterior teeth. American Journal of Orthodontics and Dentofacial Orthopedics 2004;126(6):749-53.

8. Saver D. Principles of cosmetic dentistry in orthodontis: Part 1. Shape and proportionality of anteiror teeth. Am J Orthod Dentofacial Orthop 2004;126:749-53.

9. Zachrisson B. Interdental papilla reconstruction in adult orthodontics. World Journal of Orthodontics 2004;5:67-73.

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