Controversies in

OrthodonticsPresented by :

DR MOHAMMED ASLAM VDEPARTMENT OF ORTHODONTICS

contents• Introduction• Growth predicition• etiology of malocclusion

– a] Genetic V/s environmental factors.– b] Role of nasal obstruction and tongue thrust

• Extraction vs non-extraction• Orthopedics in orthodontics• Pre-adjusted edgewise appliance• Tmd disorders• Root resorption after orthodontic treatment• Third molars• Adult orthodontics• Retention

introductionControversy – A prolonged argument/ dispute especially when

conducted publicly.

The orthodontic profession hs evolved its set of values with the tacit approval of most clinicians, teachers and researchers.

A considerable variety of opinion concerning what constitutes good orthodontics has characterized the profession since beginning. No consensus exists today, and some opinions are even mutually exclusive.

Even the science of orthodontics has been oriented toward seeking explanations and validation of therapeutic methods rather than toward establishing a basis for objectively assessing the quality or utility of our clinical performance. Thus its more “Opinion –based” rather than “evidence – based”. Such science can neither validate the superiority of a technique nor help to make rational choices among alternatives

In time, for most clinicians, practice becomes routine, standardized and decreasingly introspective. Hence clinical experience & common sense assume a more commanding role in decision making.

It is tempting to follow techniques advocated because “they work” or atleast are “claimed” to work and be the “latest and best”. Also it is alluring to adopt innovations simply because they are new and thus seem to represent the state of art.

Orthodontics is unique among dental specialities in that deals with normal biologic variations rather than pathologies

Orthodontic treatment predominantly selective in terms of needs and inevitably subjective in terms of criteria used to assess prevalence, severity, treatment success and what constitutes optimum care.

Hence controversies are common and similar to some analogous issues in medicine.

Growth prediction One of the hallmark of science is the reliability with which the

outcome of future can be predicted.

We find the idea of predicting treatment outcome psychologically comforting.

The ability to predict is useful only to the extend to which it enables us to either to understand and modify the general processes of development or to control our patients response to therapeutic inclination.

Different craniofacial phenomena are predictable with different levels of precision and different craniofacial phenomena must be known at different levels for predictions to be useful.

To a considerable degree we can predict:1. The head and face of a preadolescent children will continue to

change in size and shape until the age of 20 yrs.2. The growth of jaws and face from mixed dentition period to maturity

will be greater in inferior direction than in anterior direction.3. Prominence of dentition within the face will decrease during

maturation.4. Class II malocclusion identified after eruption of molars to occlusal

contact ill rarley,if ever,resolve spontaneosly.

5. Crossbites in permanent dentition will rarely, if ever resolve spontaneously.

6. Anterior crowding & rotations visible after the permanent incisors have erupted will rarely resolve spontaneously.

7. Permanent teeth tend to migrate mesially into extraction space due to premature loss of teeth.

8. Unopposed teeth tend to supraerupt.9. Angle of mandible tend to close with respect to cranium from

mixed dentition period to maturity.10. Therapeutic intervention that alter occlusal intercuspation will

tend to open mandibular plane angle.

11. Mandibular incisors that have been displaced or proclined anteriorly during treatment will tend to relapse in post retention period.

12. Arches in which buccal segments have been expanded will tend to relapse to pretreatment widths.

13. Intercanine widths that has been increased returns to their pretreatment widths.

14. Attempts to retract canine by anchoring them to posterior teeth tend to result in advancement of posterior teeth.

On the other hand we cannot predict:1. The magnitude and timing of spontaneous growth remodeling at

specific sites n head, face & jaws.2. The impact of therapeutic intervention upon the expression of

each individual inherent growth potential.3. Amt of correction that can be achieved at a specific anatomic

loci.4. The amt of post therapeutic relapse that can occur..

etiology of malocclusionGenetic V/s environmental factors The relative influence of genetics and environmental factors in

the etiology of malocclusion had been a matter of discussion, debate and controversy in Orthodontic literature.

Each malocclusion occupies its own distinctive slot in the genetic/environmental spectrum.

While the phenotype is inevitably the result of both factors, there is irrefutable evidence for a single genetic influence in many dental and occlusal variables

Malocclusion could be produced by inherited characteristics in two possible ways:

1] Inherited disproportion between the size of teeth and that of the jaws-producing crowding/spacing.

2] Inherited disproportion between size/shape of upper and lower jaws –producing improper occlusal relations.

There is considerable anthropological evidence that population groups that are genetically homogenous tend to have a normal occlusion e.g.: Melanesians of Philippine islands; this is the result of genetic isolation and uniformity.

Since everyone in the group carries the same genetic information for tooth and jaw size, there would be no possibility of a child inheriting discordant characteristics.

Edward Angle and his contemporaries concluded that malocclusion was the disease of civilization. They blamed this on the improper function of jaws under degenerate modern conditions.

The earlier part of the 20th century saw the development of classical Mendelian genetics. The new view was that malocclusion is primarily the result of inherited dento-facial disproportions.

The seventies and eighties saw a revival and a swing back to the earlier concept that jaw function is related to malocclusion.

A number of familial and twin studies in the latter part of the century by workers like Lundstrom (1984), Corrucini (1980), Potter (1986), Bolton and Brush, Harris and Johnson (1991) gave a more balanced view showing that there is no single explanation for malocclusion in terms of function, heredity or environment, but is a result of a complex interplay of these elements.

Respiratory pattern as an etiologic factor for malocclusions:

• Respiration - Primary determinant of jaw and tongue posture.

• Altered respiratory pattern change posture of head, jaw, and tongue alters equilibrium jaw growth and tooth position affected.

• Effects - Increased face height, supra-erupted posteriors, open bite, mandibular rotates downward and backward narrow maxillary arch.

Ballard and Gwynne-Evans (58)Lip incompetence not necessarily associated with mouth breathing.Nose breathers, who have a lip - apart posture, usually have post seal

with tongue against soft palate as an adaptive mechanism.

Harvold, Tomer and Vargevik (81):Total nasal obstruction in monkeys, for a prolonged time led to the

development of malocclusion.

Katherine & Vig • Primates do not have same naso respiratory mechanism as

humans.• Total nasal obstruction not seen in humans. “Relationship between mouth breathing, altered posture

and deviation of malocclusion is not so clear cut as the theoretical outcome of shifting to oral respiration might appear at first glance”.

Wood side, Linder-Aronson, Lundstrom (91):Maxillary and mandibular growth in 38 children, 5 years after

adenoidectomy for severe nasopharyngeal obstruction.20% did not show shift in breathing.

Concluded that change from mouth-open to mouth-closed breathing:Greater mandibular growth expressed at chin in both sexes:

3.8mm in males (P<0.001)2.5mm in girls (P<0.01)

Greater facial growth expressed at midface, only in males.No change in maxillary growth direction.

Contemporary view:2 opposing principles, leaving large gray area between them:

– Total nasal obstruction likely to alter pattern of growth and lead to malocclusion. – High percentage of oral respiratory is over-represented in long-face population.

– Majority of individuals with long-face deformity have no evidence of nasal obstruction because some other etiological factor as principal cause.

Mouth breathing – contribute to development of orthodontic problems but as frequent etiologic agent is questionable.

Tongue-thrust as etiologic factor:Definition: placement of tongue-tip forward between incisors during

swallowing.Profitt (72) –the term tongue-thrust is a misnomer, since it implies

that the tongue is forcefully thrust forward. Laboratory studies indicate that individuals who place the tongue tip forward when they swallow do not have more tongue force against teeth than those who keep tongue tip back- in fact, tongue force may be lower.

The mature/ adult swallow pattern appears in some normal children as early as age 3, but not present in majority until about age 6 & is never achieved in 10-15% of a typical population. Some times children & adults who place their tongue between anterior teeth are spoken of as having a retained infantile swallow- this is clearly incorrect, since only brain damaged children retain a truly infantile swallow in which posterior part of the tongue has little or no role. (Proffit)

This is not to say that tongue has no role in the etiology of open bite. From the “equilibrium theory” point of view: Light but sustained pressure by tongue against the teeth would be expected to have significant effect. Tongue-trust swallowing simply has too short a duration to have an impact on tooth position.

Current view point:Tongue –thrust is primarily seen in 2 circumstances:

– In young children with normal occlusion – transitional stage in normal physiologic maturation.

– In individuals of any age with displaced anterior teeth – adaptive.

Hence it is more a “Result” than a “cause”

However tongue posture is more important. Light pressure for more duration change in tooth position.

“If the position from which tongue movement starts is different from normal, so that pattern of resting pressure is different, it can have an effect on teeth, whereas if posture is normal, tongue-thrust swallow has no clinical significance”.

Extraction vs non-extraction“To extract or not to extract” was one of the early debates

that clouded orthodontic world ever since its beginning.

2 main reasons for extraction:• Provide space to align remaining teeth – crowding.• Allow teeth to move – skeletal Class II / skeletal Class

III camouflaged.

History:Late 1800 – early 1920’s:

Late 1800 saw a casual attitude towards extraction. 1902 Edward H. Angle gave his line of reasoning

towards development of his treatment philosophy based on the ideas of Rousseau &Wolff

These influenced Angle to propose 2 key concepts:• Skeletal growth Influenced readily by external

forces.• Proper function of dentition would be the key for

maintaining teeth in their correct position.

For him “relapse” meant – adequate occlusion not reached.

“If correct occlusion is produced result is stable, if result not stable it was the fault of orthodontist and not the theory”.

Angle’s dogma:• Every patient could be treatment with expansion of

dental arches and rubber bands.• Extraction not necessary for stability or esthetics.

Calvin Case argued that although the arches could always be expanded so that the teeth could be placed in alignment, neither esthetics nor stability would be satisfactory in the long term for many patients

The controversy culminated in a widely publicized debate between Angle’s student Dewey and Case in the dental literature of 1920’s.

Angle’s followers won – extraction disappeared between World War I & II.

From 1930’s – 1970’sCharles Tweed re-treated with extraction; the relapse cases

previously treated with non-extraction methodology, & found occlusion to be much more stable.

Extraction reintroduced widely late 1940’s

Raymond Begg popularized “Begg” appliance for extraction treatment.

Between 1970-1990’s:Saw the revival of non-extraction philosophy.Reasons?

Premolar extraction does not guarantee stability of tooth alignment. Little, Wallen and Riedel – 1981 AJO. MC Reynolds and Little – 1991 Angle Orthod.

Argument :“If result not stable either way, why sacrifice teeth at all”. v/s.“If extraction cases are unstable, non-extraction would be worse”.

– Changing views of esthetics – fuller and more prominent lips,than the orthodontic standards of 1950s & 1960s.

– Change from banding to bonding and introduction of functional appliances eliminated the need for band space,made it easier to expand arches – border line case generally treated better without extraction.

– Premolar extraction causes distalization of mandible posteriorly, displacement of condyle resulted in perforation of articular disc TMD. – Witzig and Spahl (1980)

– Both Tweed’s and Begg’s rational for extraction, lost some of their validity.

The contemporary respective: Majority of patients can be treated without extraction, but

by no means all.Extraction can be undertaken to compensate for:• Crowding.• Incisor protrusion.• Camouflage skeletal discrepancies.&• For surgery.

Treatment modalities converting borderline cases into non –extraction cases:

Early intervention:• Use of ‘E’ space.• Proximal stripping of primary teeth.• Space regainers with space maintainers.• Arch expansion.• Use of functional appliances.• Molar distalization.• Bonded attachments rather than banded ones.

Adult:• Molar distalization.• Inter-proximal reduction.• Arch expansion.• Surgery for skeletal discrepancies

Orthopedics in orthodontics‘Orthopedic effect’ in orthodontics can be defined as:“Change in the position of bones in the skull in relation to

each other induced by therapy”. – Daterloo.

This change in amount and direction and growth should be permanent in nature. According to Issacson, orthopedic appliance, provide a new muscular and functional environment for the facial bones that encourages growth changes of either the mandible or the maxilla.

In dentofacial orthopedics, orthodontists attempt to influence growth by applying an external force, generally for two or three years. Almost all orthopedic appliances act intermittently.

The growth of the jaws of growing child might be influenced if the therapy starts at very young age and if it continuous until growth has stopped.

However, we cannot expect patient to cooperate for such a long time. Hence the main question remains whether orthodontists are able to alter growth within a limited time period (2 or 3 years) in a complex craniofacial skeleton that is growing and remodelling.

Controversies started with some clinicians who believe that the basic bone biology is such that one cannot alter the bone growth beyond its genetic potential except by chemical or surgical intervention.

But this hypotheses was rejected as many clinicians found that functional appliances could alter the craniofacial skeleton in a positive direction.

If at all failures occurred the blame was put on poor patient co-operation, misdiagnosis, from the beginning or were not reported at all.

The effect on mandibular growth is the most controversial issue. Certainly remodelling of alveolar bone and basal bone occurs from excessive force.

The dominance of role of genetic pattern was seen in the long run.

It was seen that condylar growth is a compensatory filling in of bone in response to vertical growth at the dentoalveolar process complex & a stimulus was required for a considerable postnatal development if the mandible had to be elongated & had to be renewed to keep the increased growth rate present.

According to basic biology once cells are stimulated, their receptors can be overwhelmed & their ability to respond depends either on rest, an inhibitory signal, or entrance of a new cell population that can be stimulated.

Therefore an intermittent stimulus of short frequencies makes the most physiologic sense.

Whether it produces the best clinical response is subject to speculation and testing.

Contoversies in Pre-adjusted edgewise appliance

Torque in Base or Face: Straight wire appliance developed from the concept, described by

Andrews in 1972, that the attainment of ideal orthodontic goals could be related to certain relationships of naturally occuring good occlusions which were judged not to require any orthodontic intervention.

Using the mid-point of the long axis of the clinical crown(LA) as the reference, it was intended that the appliance design should allow a completely flat rectangular archwire, filling the slot, to be placed at the completion of the treatment.

In this way, all the LA point of the individual teeth in each arch would come to lie in the so called Andrews plane. this necessitated the incorporation of labiolingual, tip and torque adjustments within each bracket, specific to the particular tooth for which it was designed.

It is possible to incorporate torque either into the bracket base or on the bracket face, but to fulfill strict straight wire design the torque has to be in the base of bracket.

When torque is in base: The bracket stem is parallel to and is bisected by the Andrews plane

which thus passes through the base point & also through the centre of the bracket slot.

Here the tooth surface has been represented as flat surface at an angle to Andrews plane.

When torque is in face: The bracket stem is perpendicular to the tooth surface and inclined at

an angle to the Andrews plane.A slot cut into the bracket face will give the same value of torque,

will be parallel to the Andrews plane, but its long axis will be displaced vetrically and will not intercept the LA point

It is seen that brackets with torque in face do not fulfill the strict criteria laid down for the straight wire appliance, as the slot axis will no longer intercept the base point and LA point.

If all the base points & LA points do lie in the Andrews plane, there will be vertical discrepencies between the bracket slots.

The undesirable effects of having torque in face could be summarized as:

• In-buit error in final vertical tooth positioning• Interference with free archwire sliding.Despite all the limitations commercially available systems do not

incorporate torque in base.

Tmd disordersFunctional disturbances of the masticatory system have been

identified by a variety of terms.In 1934 James Costen described a group of symptoms that centered

on the ear &TMJ.In 1959 Shore introduced the term Temporomandibular joint

dysfunction syndrome.Later came the term Functional temporomandibular joint disorders

coined by Ash & Ramfjord.Since the symptoms are not always isolated to the TMJ, Bell

suggested the term temporomandibular diorders(TMD).

In an article written by Dr James Costen in 1934, he suggested that changes in the dental condition were responsible for various ear symptoms.

In late 1930s and through 1940s , common therapies like bite-raising appliances were used.

Later in the 1950s the use of such appliances were questioned.Scientific investigations suggested that the occlusal condition could

influence masticatory muscle function.Occlusion and later emotional stresses were accepted as major causes through the 1960-70.

It was not until the 1980s that the profession began to recognize fully and appreciate the complexity of TMDs.

This complexity now has the profession striving to find its proper role in the management of TMDs and orofacial pain.

Occlusion And Temporomandibular Disorders:

Occlusion is cited as one of the major etiological factors within the acknowledged multifactorial origin of TMD’s.

The assumed strong association between TMD and Occlusion has been a major reason that the diagnosis and treatment has remained within the purview of dentistry.

Despite agreement among TMD experts that occlusion actually only has relatively small role in the etiologically diverse and multifactorial origins of TMD, the influence of occlusion continuous to be greatly over rated in comparison by practicing dentists/ specialists.

Seligman and Pullinger reported 2 comprehensive reviews on relation of occlusion to TMD.- One considering morphologic occlusal relationships and other, functional occlusal relationships.

However, 4 occlusal factors were mainly seen in TMD patients and not in healthy population.

• Presence of anterior skeletal openbite.• RCP-ICP slides > 2mm.• Overjets > 4mm• 5 or more missing and unreplaced posterior teeth.

Pullinger and coworkers concluded that many occlusal parameters that traditionally were believed to be influential contribute only in minor amount to the change in risk in the multiple factor analysis used in their study. They reported that although the relative odds for disease were elevated with several occlusal variables, clear definition of disease groups were evident only in selective extreme ranges and involved only in few subjects. Thus, they concluded that occlussion cannot be considered the most important factor in definition of TMD.

Orthodontic treatment and TMJ disorders :

It had been suggested that patients who received orthodontic treatment have a higher ratio of TMD disorders than average.

However in a study by Rendell, Norton, and Gay 1992 a relationship between either the onset of TMJ pain and dysfunction and the course of orthodontic treatment or the change in TMJ pain and dysfunction and the course of orthodontic treatment could not be established.

The prevalence of temporomandibular (TM) disorders and the status of the functional occlusion in former orthodontic patients many years after treatment were evaluated in two independent clinical studies Sadowsky and Polson in 1984.

The findings for these two studies are similar and suggest that orthodontic treatment performed during adolescence does not generally increase or decrease the risk of developing TM disorders in later life.

Extraction causes TMD disorders: First premolar extractions are considered by many to be an

etiologic factor in TMJ disorders. It is believed that extraction of premolars permits the posterior teeth to move forward resulting in a decrease in the vertical dimension of occlusion. The mandible is then allowed to overclose, and the muscles of mastication become foreshortened. As a result, TMJ problems are likely to occur.

Another theory that has been proposed is that first premolar extractions lead to overretraction of the anterior teeth, particularly the maxillary anteriors . This overretraction of anterior teeth is thought to displace the mandible and the condyles posteriorly

Staggers 1994: Evaluation of the treatment results of the extraction and

nonextraction cases showed that the vertical changes occurring after the extraction of first premolars were not different than those occurring in the nonextraction cases. This study does not support the theory that first premolar extractions reduce the vertical dimension of occlusion, and thus predispose extraction patients to TMJ disorders.

Beattie, Paquette, and Johnston 1994 In long-term evaluation of the functional status of both the head

and the neck musculature and the temporomandibular joints of treated Class II malocclusions showed no significant differences between the extraction and nonextraction samples. The popular notion that "premolar extraction causes TMJ disorders does not hold true.

Orthodontic treatment and posterior condylar displacement:

View point articles variety of traditional ortho procedures (premolar extraction, extraoral traction, retraction of maxillary anterior teeth) cause TMD signs/symptoms by producing distal displacement of condyle.

Gianelly, Cozzani, and Boffa 1991 There is little or no risk of condylar retroposition resulting from

maxillary premolar extraction treatment

Luecke and Johnston 1992Condylar position with Xn of maxillary first premolars70% - forward mandibular displacement and slight opening rotation

of mandible.30% Remainder – distal movement of condyle. Also said incisal movement – essentially unrelated to condylar

displacement.

Parafunction: Bruxism and clenching – cited as etiological factors but

similarly like occlusal interferences, this is endemic in general population.

Seligman and Pullinger – increasing evidence – parafunction not associated with chronic occlusal factors.

Okerson – Reversible rather than non reversible treatment – prevent/minimize harmful effects of this activity.

Summary:• Signs and symptoms of TMD occur in healthy individuals.• Signs and symptoms of TMD increase with age,

particularly with adolescence. Thus, TMD that originates during treatment may not be related to treatment.

• Orthodontic treatment performed during adolescence generally does not increase or decrease the odds of developing TMD later in life.

• Extraction of teeth as a part of orthodontic treatment does not increase the risk of TMD.

• Although a stable occlusion is a reasonable orthodontic treatment goal, not achieving a specific ideal occlusion does not result in TMD signs/symptoms.

• No method of TMJ disorders prevention has been demonstrated.

• When more severe TMD signs and symptoms are present, simple treatment can alleviate them in most patients.

Root resorption after orthodontic treatment

• Bates 1856 – 1st to discuss root resorption of permanent teeth.• Ottolengui 1914 – related root resorption to orthodontic treatment.• 1927 Root resorption was subject of major concern to

orthodontic field.

Etiology:By Phillips, Reitan and Shafer et al• Physiologic tooth movement.• Adjacent impacted tooth pressure.• Periapical or periodontal inflammation.• Tooth implantation / replantation.• Continuous occlusal trauma.• Tumors/cysts.

• Metabolic / systemic disturbances.• Hyperparathyroidism.• Hypophosphatemia.• Paget’s disease.• Hypothyroidism.• Hypo/hyperpituitarism.

• Local functional / behavioral problems.• Nail –biting.• Tongue thrust with open bite.• Dilacerations.

• Orthodontic treatment – Fixed > Removable Edgewise > Begg• Individual susceptibility.

Andresen 3 types of root resorption:» Surface resorption – self-limiting process, usually involving

small outlining areas followed by spontaneous repair.» Inflammatory resorption – initial root resorption has reached

dentinal tubules.» Replacement resorption – bone replaces resorbed tooth

material ankylosis.

Controversies – factors influencing root resorption:

Nutrition:• Marshall – malnutrition causes root resorption.• Beck – root resorption in animals deprived of Ca and Vit. D.• Linge and Linge – nutritional imbalance not a major factor.

Gender: Massler – no correlation between gender and root resorption.Newman – more in femalesSpurrier et al (1990) – males more than females.

Alveolar bone density:Becks, Reitan, Tager-Root resorption > dense boneWainwright – Density affects tooth movement rate, but no relation to

extent of root resorption.

Specific tooth vulnerability:Ketcham,Steadman-Maxillary teeth more vulnerableReitan - Maxillary incisors most proneHemley,Sjolien-Mandibular incisors > maxillary incisorsMost frequently affected according to severity maxillary lateral >

maxillary central > mandibular incisors > distal root of 6 > mandibular 2nd premolar > maxillary 2nd premolar.

Fixed V/s Removable:Linge and Linge – fixed > removable.Stuteville – removable > fixed Jiggling forces more harmful

Begg V/s edgewise:Begg < Edge wiseMalmgren et al (82) – root resorption higher in traumatized tooth

(maxillary incisors) when intruded by Begg technique compared with E.W. technique (48%: 43%).

Continuous V/s intermittent forces:Reitan, Oppenheim,Dougherly-Intermittent forces allows resorbed

areas to heal and prevents further resorption.Hall – Intermittent forces causes jiggling hence more detrimental.

Extent of tooth movement:Dermaut, Hollender, Sharpe-Root resorption and extent of root

movement.Philips,Dermaut-No correlation

Occlusal trauma:Doughery – Occlusal forces on poorly aligned teeth can cause root

resorption.Newman – no correlation.

Third molars The role that mandibular third molars play in lower

anterior crowding has provoked much speculation in the dental literature.

The removal versus the preservation of third molars became the subject of contention in dental circles. The differing views ranged between extremes, and can be expressed in two different statements:

– Third molars should be removed even on a prophylactic basis, because they are frequently associated with future orthodontic and periodontal complications as well as other pathologic conditions.

– There is no scientific evidence of a cause and effect

relationship between the presence of third molars and orthodontic and periodontal problems

Justification for 3rd molar extraction.Evolutionary

Most often absent/ malformed.Little room for a full complement of teeth.

Prophylactic:Will become impacted (poorly angulated).In adulthood-operative and postoperative problems – hemorrhage,

pain, swelling, osteitis and trismus likelihood of nerve damage increases.

Pathologic: Cysts, tumors, resorption of 2nd molar roots, caries,

pericoronitis and other infectious processes.

Orthodontic:Post treatment crowding – relapse / late lower arch crowding.Mandibular orthognathism surgery.

Relationship between 3rd molars and incisor crowding:Untreated normals:Bishara et al (89 and 96):Evaluated changes in lower incisor between 12 and 25 years and

again at 45 years – findings indicated : • Increase in tooth size arch length discrepancy with age –

consistent decrease in arch length.• Average changes 2.7mm in males; 3.5mm in females. These

changes were attributed to a consistent decrease in arch length that occurred with age.

Similar findings by Lundstrom (68) and Sinclair and Little (83):

Orthodontic treatment patients:Fastlicht (70) found that in orthodontically treated subject-

11% had 3rd molars, but 86% had crowding.Little et al (81) observed that 90% of extraction cases that

were well treated orthodontically ended up with an unacceptable lower incisor crowding.

Studies relating 3rd molar to crowding of dentition:• Bergstrom and Jensen (61) concluded:

– More crowding in the quadrant with 3rd molar present than in the quadrant with the third molar missing.

– Mesial displacement of lateral dental segments on the side with 3rd molar present in the mandibular arch not in the maxillary arch.

– The unilateral presence of a third molar did not have an effect on the midline.

Schwarze (75): In his studies found significantly greater forward movement

of first molars associated with increased lower arch crowding in the non extraction of 3rd molars.

Lindquist and Thilander (82): Extracted third molar unilaterally in 52 patients and found

more stable space conditions (less increase in crowding) on the extraction side compared with the control side in 70% of cases.

Belfast third molar study – Richarson M.E. (82-87).Produce further evidence “Pressure from behind” theory: According this theory that late lower arch crowding is caused by

pressure from the back of the arch. Whether this pressure results from: • Dev. 3rd molar.• Physiologic mesial movement / drift.• Anterior component of force derived from forces of occlusion

on mesially inclined teeth.Is not clear.

Another school of thought is (Graber, Woodside, Selmer-Olsen):

“In absence of 3rd molar, the dentition has room to settle distally under anterior pressures caused by late growth or soft tissue changes”.

Retrospective studies: Kaplan (74): Presence of 3rd molar does not produce a greater

degree of lower anterior crowding or rotational relapse after cessation of retention.

Ades et al (90):Majority of cases have incisal crowding, but no correlation with 3rd molars.

Lifshitz (82) :In his studies concluded that there is a significant decrease in arch length and a significant increase in crowding, but there were no significant difference between the groups that did or did not have premolar extractions or whether third molars were present or missing.

Prospective studies: Lindquist and Thilander (82):Unable to predict which patients

benefit from prophylactic extraction. Southhard (91) et al measured proximal contact tightness between

the mandibular teeth in cases with bilaterally unerrupted third molars. Surgical removal of 3rd molar – no significant effect on contact tightness.

Pirttiniccni et al (94) evaluated the effect of removal of impacted third molars on 24 individuals. They found that extraction of 3rd molar allowed for slight distal drift of 2nd molar but no significant change in incisal area.

Morphologic factors that can influence space available for 3rd molar:

Bjork et al (56): examined 243 cases to estimate the relationship between various cephalometric parameters and the space available for mandibular third molars they identified three skeletal factors that may influence third molar impaction:

– Vertical direction of condylar growth as indicated by mandibular base – ramus angle.

– Decreased mandibular length – Cd-Pog.– Backward – directed eruption of mandibular dentition as

determined by degree of alveolar inclination.Capelli (91) added two more factors :

– Retarded maturation of 3rd molars.– Greater mesial crown inclinations of 3rd molars crowns

Current views on removal of 3rd molars: According to the National Institution of Dental Research (79) and

American Association of OMFS (93). When and what condition – extraction of 3rd molar advised.• Lower incisor crowding – multifactorial etiology.

– Tooth size, shape and relationships.– Decrease in intercanine width.– Retrusion of incisors.– Growth changes.

• If adequate room is available – donot extract.

• Orthodontic treatment – distalization of molars – if causes impaction extract.

• Post-operative pain, swelling, infection etc. decreased if patients are young and roots 2/3rd deviation.

• If extraction is indicated – early extraction beneficial.• Present predictive technique not completely accepted hence

enucleation at 7-9 years not valid.• Inform patients about possible complications of extraction pain,

swelling, trismus, nerve damage etc.

Adult orthodontics

During the last decade the number of adults seeking orthodontic treatment has increased significantly. In addition epidemiologic studies have shown that more than 75% of adults older than 40 years of age have periodontal disease.

Because of physiologic differences between adolescent and adult patients, there may well be differences in the way malocclusions are corrected . Since adults do not experience any substantive growth during treatment, combined with physiologic bone differences, this would be a reasonable hypothesis.

Bone remodeling in adulthood:

After skeletal maturity at approximately the age of 20 years, the amount of cortical bone in many different bones has been reported to decrease as a normal accompaniment of the aging process.

Epker et al have documented a progressive thinning of cortical bone after adulthood is attained, stemming from enlargement of the marrow cavity.

Liu et al had assessed alveolar bone & observed a significant decrease in pore volume with increasing age along with a decrease in lacunar-canalicular pore diameter and an increase in density.

Periodontal changes:

In the growing child, the tooth-supporting tissues are in a state of proliferation. Within the periodontal ligament and in marrow spaces surrounding the alveolus, large numbers of connective tissue cells are actively involved in alveolar growth and remodeling.

Reitan in his study concluded that there is a measurable delay in bone formation in the adult that is not observed in the child.

Graber points out that older persons are more prone to root resorption, apparently because of the penetration of the cementoid layer and the inability of the cells in this area, with their reduced vitality to deposit new cementoid and protect the resorbing root surface.

Chasens listed the following clinical situation where orthodontic treatment should be avoided:

• Uncontrolled infection & inflammation• Lack of retention for stabilization of teeth in their new position• Inadequate space into which teeth can be moved• Movement of teeth against occlusal trauma• Movement of teeth in which periodontal health, function or esthetics will

not improve.• Movement of teeth against inadequate anchorage• Movement of teeth into unfavorable environment• Lack of patient motivation & co-operation• Patients with systemic problems

Although clinical studies have documented slight but statistically significant periodontal connective tissue loss among adolescent patients who have undergone fixed orthodontic treatment, there have been few studies reporting periodontal status among periodontically healthy adults undergoing fixed orthodontic treatment and the effect on periodontal bone support in adults with advanced loss of periodontal support.

Boyd, Leggott, Qui 1989In their study have indicated that during the course of fixed

orthodontic treatment:• 1. Tooth movement in patients with a reduced but healthy

periodontium does not result in significant further loss of attachment.

• 2. Tooth loss for periodontal reasons may occur in adults with severely periodontally compromised teeth that have pocket depths > 6 mm and/or advanced furcation involvements.

Vast majority of limitations claimed to be related to the biomechanical systems used.

Biologic basis for tooth movement is the same in adults and in growing children, but special consideration need to be given to dental and periodontal status.

With regard to intrusion and extrusion of teeth in these pts, both can be done but should be at constant but low force levels and under absolute 3 dimensional control.

Retention Retention is one of the controversies of modern

orthodontics, with uncertainty being the only certainty. Angle stated that "the problem involved in retention is

so great as to test the utmost skill of the most competent orthodontist, often being greater than the difficulties being encountered in the treatment of the ease up to this point."

Reidel attempted to rationalize the problem and summarized his findings in three statements:

1. Teeth moved through bone by orthodontic appliances often have a tendency to return to their former positions;

2. Arch form, particularly mandibular arch form, cannot be permanently altered by appliance therapy;

3. Bone and adjacent tissues must be allowed time to reorganize after treatment.

Kaplan 1988 in his study of different retention procedures has noted that:

1. There are very few cases requiring minimum or no retaining appliances and these would include:

a. Blocked out canines in Class I extraction cases with no incisor crowding

b. Class I anterior and/or posterior crossbites with very steep cusps and no anterior crowding

c. Class II cases slightly over treated with headgear to restrict maxillary growth with sufficient arch length indicated by mandibular anterior spacing and absolutely no mandibular incisor rotations

d. The above-described cases should be seen on a scheduled basis during the post treatment adolescent period to check possible spacing or unfavorable growth changes or TMJ symptoms.

2. Routine cases, extraction or nonextraction, should have retaining appliances— fixed or removable.

a. At least until the destiny of the third molar teeth is determined [or]

b. Until the growth process has slowed in late teens and early twenties [and]

c. Afterward at the option of the patient

3. Cases that will need indefinite retention a. Class II, Division 2 Angle deep bite cases b. Arch expansion treatment for esthetic demands c. Patients with uncontrolled muscular or tongue habits d. Again the orthodontist should be most emphatic about this need.

4. Cases that require operative procedures with indefinite retention a. Treatment limitations such as tooth size discrepancies (that is,

larger maxillary teeth) may result in increased overbite or super Class I.

b. Reversely, larger mandibular teeth will result in end-to-end incisor relationships, maxillary spacing, or buccal end-on occlusion.

c. Stripping or reproximation of oversized teeth and esthetic bonding of malshaped or undersized teeth may help resolve this problem.

d. A very vertical incisal relationship, which for any reason cannot be corrected, will lead to deepening overbite unless retained.

5. Cases requiring special construction and/or renewal of removable retaining appliances or acrylic on the labial bows

a. Posttreatment adolescent palatal changes b. Late mandibular growth spurt and Tweed type C

growers c. To maintain torque and overbite correction

Researchers have concluded that those cases that will relapse cannot be predicted and that indefinite retention is necessary if the finished result of active orthodontic treatment is to be maintained.

Many appliance types have been used for the retention

of post treatment tooth position.

There is no agreement in the literature of a uniform system of retention, and the clinical orthodontist, in consultation with each patient, must determine the appropriate retention regime for each case.

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