Abnormalities in the development of the second molars and ... · PDF filesecond molars and...

DOI: 10.1051/odfen/2014021 J Dentofacial Anom Orthod 2014;17:406� RODF / EDP Sciences

1

Article received: 15-05-2014.Accepted for publication: 03-06-2014.

Abnormalities in the development of thesecond molars and orthodontic treatmentwithout extraction of premolars.Management of posterior crowding

H. Desnoes

Practice at the CMS in Nanterre

ABSTRACT

With the development of so-called ‘‘non-extraction’’10 treatments incontemporary orthodontics, complications in the eruption of the secondmolars are becoming noticeably more prevalent in our practices ranging froma simple delay of eruption, to ectopic eruption, up to retention of the secondmolars caused by a mechanical obstruction. Using a retrospective study ofsome cases and a review of the literature, we are seeking to find newdiagnostic approaches in order to choose the best treatment.

KEY WORDS

Premolar extraction, non-extraction, second molar impaction, mechanical retention/blockage of the second molars, molar distalization, preservation of the space formesial drift

INTRODUCTION

The consequences of non-extractiontreatment on impaction of the third molarshave been extensively studied, but there isstill little research concerning the subse-quent impact on the second molars oftreatment to prevent mesial drift12 of thefirst molars. Although low (0.2 to 2.3% ofthe general population according to thestudies27), it seems that the percentage ofretained second molars has increasedover the last few decades11. The various

studies do not always make a distinctionbetween the etiology of the delays or thefailure to erupt. The delays may be due toankylosis, a primary failure of eruption (oridiopathic failure to erupt) or because of amechanical obstacle9. Studies show thatwith environmental modifications, the den-to-maxillary discrepancies (DMD) tend toincrease8. But some authors are beginningto see a relationship between an increasein impactions of the second molars with

Address for correspondence:

Helene Desnoes27 rue du val d’Oise – 95620 [email protected]

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the reduction in the rate of extrac-tions of premolars in modern thera-peutics1,12,16,23,26,27.

After a brief statement on theeffects obtained by the different appli-ances for anchorage preservation andtheir consequences on the impactionof the second molars, the argumentsin favor of one or another treatmentare discussed. Thus, patients, particu-larly those who believe that orthodon-tics can always be done withoutextractions, will have the relevant factsto give informed consent.

The choice to extract premolars ornot in order to create the necessaryspace to align the anterior and mediansectors and to allow the dento-alveolarcompensations for the dysplasias isoften dictated by the latest trends.The current tendency is to ‘‘avoidextractions as much as possible,’’ aver-aging around 25% of cases treated withpremolar extractions compared to 73%observed in the 1960’s for all practi-tioners combined19.

It is sometimes difficult for thepractitioner to make an irreversible

decision in so-called borderline casesthat can be treated in a variety ofways. The reason is that it not asimple equation with one unknown.In addition to the concrete values ofcrowding, we contend with the phe-nomena of growth that are notalways predictable and that vary fromone individual to another.

There are numerous articles onthe esthetic, functional (occlusal,respiratory), periodontal, and psycho-logical repercussions of treatmentwithout the extraction of premolars.The management of the space in theposterior region, where crowding hasbeen reported, will therefore bestudied. Ideally, practitioners shouldhave all the required tools beforebeginning treatment that help themknow if the extraction of premolarsor the wisdom teeth alone will besufficient to provide the necessaryspace for placing all the teeth in thearch, or to predict if it is absolutelynecessary to sacrifice eight teeth,one quarter of the total number ofteeth.

EFFECTS ON THE MANDIBULAR SECOND MOLARS OF THERAPIES FORANCHORAGE PRESERVATION OR MOLAR DISTALIZATION

The available space provided bythe difference between the mesio-distal diameters of the primary man-dibular molars and the premolars isan average of 2.5 mm6,22 with strongindividual variations32.

According to Gianelly15, 85% ofClass I and II cases with crowdingconsisting of a maximum of between6 and 8 mm can be treated by molarretraction that does not exceed1 mm.

There were no articles on a ClassIII case treated by maintaining theposition of the mandibular molar.In these cases, perhaps the risk ofimpaction is significantly lower be-cause the mandibular molar wasmore mesial?

Four recent studies begin to ser-iously link impaction of the man-dibular second molars (M2) withtechniques to conserve space formesial movement.

H. DESNOES

2 Desnoes H. Abnormalities in the development of the second molars and orthodontic treatmentwithout extraction of premolars. Management of posterior crowding

Shinora et al.26, without presentingany particular study have noticed thatin their practice there is a netincrease in simultaneous impactionsof the second and third molars (M3)in adolescents.

For Sonis and Ackerman27, using alingual arch to keep the first molarsin their initial position multiplies byten to twenty times the risk ofimpaction of the second molars ascompared to the general population.In their study of two hundred cases,they observed a percentage ofimpaction of 8.5%.

For Ferro et al.12, the use of the lipbumper 31 studied in 260 cases wasfound to show an increase in the per-centage of impactions similar to thatof the Sonis study (7% against 1.4%in the control group) as well as astrong increase in ectopic eruptionsbetween 1.6 to 16.4%. It emphasizesas well that, if the duration of theapplication does not exceed 9 monthsto 1 year, and if the braces are adjustedproperly, a potential mechanical reten-tion seems avoidable.

Finally, the study of Rubin et al.22

compared the effects of treatmentwith a Schwartz Plate, lingual arch ora combination of the two in 301patients. The use of these two appli-ances, generated a higher rate ofanomalies of eruption (14.7%) asopposed to 7.8% with the Schwartzappliance and 4.7% with the lingualarch alone. Further, they showthat, the longer the appliances areworn the more the risk of impactionincreases.

In all these studies, no significantdifference has been shown betweenboys and girls.

Would the extraction of premolarsallow for the eruption of M3? Wouldthe removal of M3 at the start ofmulti-banded treatment allow for theeruption of M2 before removing theappliances? The repositioning of M2was impossible; the patient wasdiscouraged and unfortunately didn’tunderstand why it was necessary.

EFFECTS ON THE MAXILLARY SECOND MOLARS OF THERAPIES TOMAINTAIN ANCHORAGE OR TO DISTALIZE THE MOLARS (FIGS. 1 AND 2)

In the maxilla, there is considerablyless leeway space than in the mand-ible; this could explain why there arefewer impactions of maxillary secondmolars for the most part in studiesfollowing the application of thesetherapies. A recent Cochrane analy-sis17 gives an update on all the reli-able studies comparing the intra-oraland extra-oral appliances for molarretraction or for at least maintainingmolar position before the loss of the

primary second molars. It showsthat the intra-oral appliances allow forincreased molar retraction but thisincrease is associated with a loss ofanterior anchorage that is avoidedwith extra-oral forces (EOF). Thequantity of studies is small as well asthe level of proof. If these appliancesare truly effective one mightwonder if they have a significanteffect on the eruption of the secondmolars.

ABNORMALITIES IN THE DEVELOPMENT OF THE SECOND MOLARS AND ORTHODONTIC TREATMENT WITHOUT EXTRACTION OF PREMOLARS.MANAGEMENT OF POSTERIOR CROWDING

Rev Orthop Dento Faciale 2014;17:406 3

The pendulum appliances do nothave a skeletal effect20 or only an ef-fect limited to a greater opening ofthe mandibular compass (angle) if theapplication is late7 whereas theorthopedic effect of the EOF will notbe very controversial19.

With the arrival of absolute ancho-rage provided by miniscrews, it willbe truly possible to obtain even more

significant molar retraction, and onecan reasonably be apprehensiveabout an increase in the impaction ofthe second molars.

These appliances are currentlybeing used before the second molarshave yet erupted into the arch.Numerous authors20 have shownthat the presence of second molarsdoes not impede their action, the

Figure 1Marwann, without medical antecedents (ATCD). Mechanical retention of the four M2 follow-ing therapy with a lingual arch and straight wire (Roth). a) Radiograph at 12 years, dental agedelay. b) and c) After extraction of buds of the M3, late vestibular ectopic eruption of the M2in the maxilla and the mandible at 15 and one half years.

H. DESNOES


retraction of the first molar occursvery slowly with the help of heavyforces but with a significant transla-tional component. Perhaps it wouldbe preferable under certain condi-tions to delay the start of the ortho-dontic treatment plan until thecompletion of eruption of the youngadult dentition.

The application of distalizationappliances on two molars at thesame time leads to a greater loss ofanchorage (that could be resolved bythe use of miniscrews) as well as tobuccal displacement of the secondmolars.

For many authors, there would be acomplete relapse of tipping andmaintenance of the orthopedic effectsafter interruption of the distalizingforces. The action of the mechanismsof extra-oral forces have been amplydescribed in the literature, on the otherhand their influence on the spacefor the eruption of the second molarshas not been examined in detail.

According to Piva et al.24, maxillarymolar distalization treatment displacesthe pterygomaxillary fissure andappositional/resorption growth at themaxillary tuberosity thus compensatingthe absence of the mesialization of thefirst molars, and allowing the secondmolars to erupt without difficulty. It isnot certain if the wisdom teeth will beimpacted, the follow-up studies areongoing.

Nanda and Dandajena23 present acase with a significant delay of erup-tion. After 6 years of wearing an EOFdevice the treatment was discontin-ued at 13 years of age, the M2 at 16years had not yet erupted but werepresent in the arch at 21 years ofage. This eruption that took place allthe same but very late can beexplained simply by the relapse ofthe obtained dental effects. Only theorthopedic effects were maintainedover the long term.

There have been two recentstudies on preservation of molar

Figure 2Yacine without any medical ATCD. Mesio-lingual rotation following therapy for maintenance of the leeway space.a) Panoramic radiograph at 10 years. b) Mesio-lingual rotation of 46.



anchorage, or distalization of themaxillary molars and the effects onthe maxillary second molars. Thestudy of Abed1 involved 47 patientstreated by EOF shows that the appli-ance induces a delay of eruption butnot a mechanical retention (block-age). The study of Gour16 presents acase of retention (blockage) of 17 fol-lowing treatment by the DAC ofAknin, that was studied in 60 cases:30 treated with extraction of 14, 24,35, 45 and 30 treated by DAC. Butthe initial ALD is greater in the groupthat had extractions. The posteriorcrowding is judged statistically moresignificant (+3 mm) and the secondmolar is inclined more distally (+8.8�)in the group without extractions.

The different appliances that allowfor molar distalization generally cre-ate21 a distal inclination of the M1that occurs naturally and blocks thevertical eruption of the second molar(cf. Fig. 3).

Therefore, in almost all the pa-tients, a delay in the development ofthe second molars likewise hindersthe beginning of the second stage ofthe two phase treatment.

We might then question whetheror not a treatment started at the endof the mixed dentition treatment andnot ended until 13 years of age isactually effective, and whether or notit is accompanied by iatrogenic risks(caries, resorptions, loss of coopera-tion . . .).

INFLUENCE OF PREMOLAR EXTRACTIONS ON GROWTH

Do extractions, that eliminate acertain amount of osseous alveolarmaterial and that reduce the growthof the arches, have an impact on thesubjacent osseous structures? There

is scant scientific data in the litera-ture to back this hypothesis.

According to Kalwitzki18, extractiontreatment affects sagittal growthof the skeletal structures of the

Figure 3Mathieu: Unerupted 17 following molar de-rotation using a quad-helix.

H. DESNOES


orofacial complex with significant var-iations between individuals depend-ing upon the dysmorphosis. In Classskeletal Class III cases, the effectsare more pronounced in the mandiblethan in the maxilla. In either case,the alveolar effects are apparent.Moreover, in Class II cases, there are

also visible signs of these effects onthe basal bone.

A contrario, according to someauthors, the therapies used to retractthe molars also have orthopediceffects on the growth of the jaws6,30.The stability of these results is verycontroversial.

INFLUENCE OF PREMOLAR EXTRACTION ON THE DEVELOPMENTOF THE SECOND MOLARS

Many studies have been carriedout in order to demonstrate the im-pact of premolar extractons on thedevelopment of the third molarswhen there are no appliances for an-chorage support14. It seems logicalto think that the effects are the sameon the second molars. However, theconclusions of the studies are contra-dictory (since anterior and medianinitial crowding fluctuated), it wouldseem that it is particularly the

removal of the second premolars thatmight have beneficial effects on thedevelopment of the M2.

When mandibular second premo-lars are extracted, the potential forthe development of the wisdomteeth increased from 10 to 50%14.But, in one out of every two cases,the treatment led to the extraction of8 permanent teeth, in other words ¼of all the teeth.

CRITERIA OF DECISION

The ratio between space availableto mesio-distal diameter of the M2seems to be an excellent indicator,the risk of impaction is increased incases of posterior DDM but acci-dents of development of the M2 canalso be produced in cases of agen-esis of M3 if the angulation of thebuds is significant (cf. Fig.4).

Calculation of available space

Presently, we do not have anyspecific indicators for assessing howmuch space is required for the

development of the maxillary secondmolars16.

Contribution of radiographicdocuments

There is no possible way to mea-sure the necessary space on apanoramic radiograph but it does helpthe practitioner evaluate the positionof the tooth in relation to its neigh-bors and within the maxilla in thehorizontal and vertical dimensions, aswell as the degree of root develop-ment and the eruptive position.



It would seem that the evaluationof posterior space is more precise ona profile cephalometric radiographthan on a panoramic xray16, 6/PTV onthe maxilla, opposite the distal sur-face of M1 mandibular at Ricketts Xipoint25, 6-VLR24 (cf. Fig. 5).

There are significant individual var-iations in the available space pro-vided by the leeway space and itwould be better to calculate it pre-cisely32 (rule of three [tripoding] withperiapical films MOYERS15), beforechoosing this therapeutic pathway.

• Potential for residual growth

It is greater in boys than in girls.The works of Bjork have shown thatthe jaws continue to grow for at leasttwo years after the growth spurt thatis later in boys.

• Calculation of necessary space

Nguyen16 shows the cone beamcan be used to measure the diameter

of non-developed teeth with a marginof error of only 0.3 mm.

• Sexual dysmorphysm

Dental morphology and the size ofteeth25, is more prevalent in girls.

According to the Tweed-MerryfieldGuidelines those cases presentingwith 5-6 mm of crowding are consid-ered borderline29.

• Angulation of the tooth budsbefore treatment

The risk of impaction might be pre-dictable by measuring the angle be-tween the long axes of the first andsecond molars before treatment11,27.The practitioner should be careful inthe therapeutic choices if this angleis greater than 24� (30� according toFerro12), and it would be preferableto extract premolars than to maintainthe leeway space.

Figure 4Sana: syndromic patient, mother had rubella during pregnancy. a) Panoramic at 15 years of age. b) Panoramic at17 years of age.

H. DESNOES


However Lash Rubin, Baccetti andMcNamara22 do not think angulationis a predictable factor.

• Presence of the buds of the wisdomteeth

There is no study showing a linkbetween the presence of the buds of

M3 and the risk of impaction ofM227.

• Status of development of the toothbuds

The optimal time to wear EOF inorder to avoid mechanical retention isdetermined radiologically. It is best to

Figure 5Cephalometric evaluation of the available space. a) In the maxillaafter Piva24. Cephalometric lines = A: S-SE Line; B: S-N line; C: VRL

(vertical reference line); D: palatal line; E: vertical PTM line; F: MC-MR line (mesial cusp point of M1 – Mesial root apex of M1). Cepha-lometric parameters = 1: PTM-VRL distance; 2: 6-VRL; 3: MR-VRL;4: 6-PTMvert; 5: ENA-VRL; 6: S-N^S-SE angle; 7: ENA-ENP^S-SE;8: MC-MR^S-SE; 9: MC-MR^ENA-ENP. b) In the mandible afterSable25. 1: mandibular angle (FH^Go-Me). 2: facial axis (Ba-Na^Pt-Gn). 3: Condylion-Gnathion distance. 4: Articulare-Pogonion dis-tance. 5: Xi-opposite distal M1 mandibular (D6) measured thelength of the axis of the body (mm). 6: D6-symphysis (mm) (themost distal point of the lingual cortical bone). 7: Xi-symphysis (mm).b1) cephalometric measurements (1 to 4). b2) Cephalometricmeasurements 5 to 7.



begin treatment when the crown ofthe upper M2 has erupted beyond1/3 of the apices of the upper M13.

Posterior growth is much greaterin boys than in girls25.

• Distal root curvatures? (cf. Fig. 6)

There are no data found in the lit-erature on this subject but this caseas presented shows root curvaturesassociated with molar retention.

ALTERNATIVES TO EXTRACTION OF THE SECOND PREMOLARS

Early removal of the wisdomteeth

Recommended by Ricketts at 9-10years of age, the removal of the budsof the wisdom teeth is attractive. It isdone almost at the same time as theplacement of anchorage. It thereforeavoids mechanical retention of the sec-ond molars12. But there is no study

showing a relationship between im-

paction of M2 and the presence of

the bud of the M3. This solution hasbeen very controversial but someauthors4 show that this procedure in-cludes psychological risks to minorsand that, on the contrary, there is an in-crease in the technical difficulty of theprocedure in the mandible with rootdevelopment. Bjornland et al. have ob-served complications in 1.8% of casesin their study. From a surgical point ofview, enucleations of the wisdom teethwould be relatively uncomplicated pro-cedures, but the enucleations of themaxillary M3 are technically more diffi-cult to do26. The question arises as towhether the premature removal of theM3 deprives the retromolar region of asignificant potential for growth.

Extraction of the second molars

Anecdotally, some authors havecalled for the extraction of the sec-ond molar in cases of posterior

crowding in order to allow for thenatural development of the M3 witha satisfactory contact point13. Withthe new 3D imaging techniques, itwill be possible to predict more pre-cisely the shape of the third molarsand thus to more easily make thedecision to extract the M2.

Transplatation of the buds of theM3 with the M2

The transplantation of the buds ofthe M3 in place of the M2 can beplanned33.

After seeing the inclination of 38,would the extraction of 37 have

Figure 6

H. DESNOES


perhaps been better? (Fig. 7) Theperiodontal health of 37 that appearsto be less precarious would have

allowed for the application of ortho-dontic forces.

CONCLUSION

The point of this article is not topromote any particular technique. Butit does seem legitimate to ask ques-tions about the delay in the develop-ment or about the mechanicalretention of the second molars fol-lowing the utilization of techniquesfor anchorage maintenance or firstmolar retraction. The few studies onthe subject show an increase in risks.But if the indications are clearlyestablished and the appliances pre-cisely controlled with well adjustedbraces12, and above all if the durationof the application does not exceed9 months to 1 year, eventualmechanical retention seems to beavoidable. A good clinician does nothave to be an extractionist or non-extractionist, he must possess good

differential diagnostic skills as well asa certain artistic sensibility to makethe right diagnostic decision29. Takinginto account individual variation mustbe the rule and not the exception3.Let’s not forget that one of our treat-ment objectives must be the place-ment of the second molars in theplane of occlusion.

It is important to consider the treat-ment plan criteria for the M2 fromthe start of the placement of themechanics rather than two yearslater after multi-banded treatmenthas already been in progress.

We should not hesitate to reevaluatea case and to prescribe extractionsafter an unsuccessful interceptive firstphase29, without forgetting to informthe patient of this eventuality in the

Figure 7Yanis, without ATCD. a) panoramic at 15 years of age: impaction of 37 and 47 with strong mesial inclination.b) panoramic a 17 years of age: transplantation of M3 in place of M2, root development stopped. The 38 main-tained its mesial version, the apexification was stopped at the time of the transplantation, and orthodontic align-ment was judged too risky.



course of the establishment of thetreatment plan in borderline cases.We should not forget that extractionsare irreversible.

According to the majority ofauthors, the degree of the molar re-traction obtained with the distaliza-tion appliances of the maxillary M1does not seem to be affected by thepresence of the M27. Perhaps mightit be better to wait for the develop-ment of the M2 in borderline cases?Conversely, it would seem that theopening of the mandibular anglecould be greater in this option, wherea potential contra-indication exists inhyperdivergent patients.

According to Vaden29, it is neverdetrimental to make a choice ofextractions in borderline treatmentcases. According to Bradley5, thechoice of non-extraction treatmentcan be more problematic than withpremolar extractions, and the stabilitywould not be better. And further, theduration of active treatment in non-extraction of premolars is stronglyincreased25. Since it started in themixed dentition thus leading to aprobable delay in the development ofM2, the treatment will end later thanin cases with extractions, without for-getting what this implies in terms ofiatrogenic and psychological risks.

According to Richardson2,32, it israre for Europeans to have 32 teeth

well aligned at the end of growth.It logically follows that if the premo-lars have not been extracted, thenlater on the wisdom teeth will be ex-tracted19.

Treatment beginning in the youngadult dentition with newer techni-ques allowing for expansion usingself-ligating brackets have not beendiscussed, it would be interesting tostudy their effects on distal crowd-ing. Complimentary studies on thedevelopment on the second molarsfollowing the choice of treatmentwith or without premolar extractionswith a homogeneous group of bor-derline cases, similar in sufficientquantity or with absolute anchorageappliances (existing adult study16)could be rewarding. Similarly, per-haps a statistical study on the age ofthe prescription of the extractions ofthe wisdom teeth could provide as-sistance in making decisions in ourpractices?

Of course, the recovery of an im-pacted second molar is quite feasi-ble, after surgical exposure. Severalappliances have been described toaccomplish this. But it is advisable tonotice the impaction early enoughso that the patient does not refusethe procedure if and when coopera-tion changes over time.

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Conflicts of interest: The author declares noconflict of interest.

H. DESNOES


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H. DESNOES


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