ORTHODONTICS - an introduction

Dr. Prabhuraj Sabarad
                                 MDS

Email: mail2prabhuraj@gmail.com

"When facial deformity  has been corrected & mental anguish eliminated, a dull & unhappy facial expression becomes bright & happy. What greater reward could any orthodontist want or except"- Charles. H. Tweed

Orthodontic treatment goals: The mandibular condyles in a seated position in centic relation of jaws, structural balance- relaxed healthy musculature, Andrews 6 keys class I occlusion, Functional stability -a mutually protected occlusion, good periodontal health, , Esthetic harmony.

The  first orthodontic objective of tooth  leveling and aligning is defined as- The tooth movements needed to achieve passive engagement of a steel rectangular wire of 0.019/.025 dimension and of suitable  arch form, into a correctly placed preadjusted 0.022 bracket system.

Unwanted tooth movements in the initial stages of treatment should be avoided and need to be controlled , or the  underlying malocclusion is severed and will increase treatment time and efforts.

Anchorage control: The methods used to restrict   undesirable changes during the opening phase of treatment, so that leveling and aligning are achieved without key features of the malocclusion becoming worse.

Principles of anchorage control:

1.       Reduction of anchorage needs during leveling and aligning. There is a need to minimize the factors which threaten anchorage and which produce unwanted tooth movements. This reduces the demands on anchorage.

2.       Anchorage support during tooth leveling and aligning. Eg. Use of palatal and lingual bars.  
       Orthodontic miniscrews/microimplants (1.3mm to  1.8mm in diameter at neck & 1.2 to 1.7 mm at the apex; 5  to  12mm in length) & miniplates have been used as osseous anchorage  (temporary anchorage devices) for the treatment of various  malocclusions.

Mechanics of non extraction cases are more complex compared to extraction cases.

Orthodontic treatment mechanics are determined by four elements: Bracket selection, Archwire selection, Bracket positioning, Force levels. Appliance design and treatment mechanics are closely inter-related. In Straight Wire Appliance (SWA) for extraction cases, canine brackets with anti-tip, anti-rotation and power arms are available, incisor brackets with varying degrees of torque for different clinical situation are available. { Wagon wheel effect- a situation where tip was lost as torque was added. Hence additional tip to the anterior brackets was given to avoid wagon wheel effect. Roller coaster effect- excess  force  along with the use of elastic traction mechanics in an early treatment stage caused deepening of overbite and creation of lateral open bite.}  

Andrews SWA (1972)-the ‘translation’ series,  was followed by Roth’s minimum extraction series brackets (the second generation bracket  system). Roth emphasized use of articulators for diagnostic records, for early splint construction, and for the construction of gnathological positioners at the end of the treatment, to establish correct condyle position. Using wider arch forms avoid damage to canine tips & helps in obtaining good protrusive function. MBT bracket  system developed by McLaughlin, Bennett and Trevisi is the third generation bracket system.  

Disadvantages of  additional anterior  tip: puts more load drain on antero-posterior anchorage, tendency for increased overbite during aligning, close proximity of upper canine root apex to the first premolar root in some cases. When the original research values for tip are used  for anteriors, atotal  of 10 deg less distal root tip in the upper anterior segment and 12 deg less distal root tip in the lower anterior segment  is needed as compared  with the original SWA. 

Anterior tip values in MBT bracket system are based on the original research values. For example in upper canine SWA uses 11 degrees tip,  Roth  system uses 13 degrees tip, as compared to the research finding of 8 degrees tip in upper canine. With MBT bracket system there is a use of light continuous forces, lacebacks and bendbacks, and is designed to work ideally with sliding mechanics. Rhomboidal form brackets with laser numbering is used.

Recommended Tip  and Torque (in degrees)in MBT bracket  system:

Upper: I^st & II^nd molars 5,5 &-14, -14; PM 0,0 & -7,-7; Canine 8 &  -7,0,+7; lat. Incisor 8 &+10; C.I  4&+17

Lower: Ist & IInd Molars 2,2 &-20,-10; PM 2,2 & -17,-12; Canine 3 & -6,0,+6;lat.incisor 0 &-6; Cent.I 0&-6

{The original SWA I^st molar torque(-30degree)  &  II^nd molar torque (-35degree) specifications allowed ‘rolling-in’ of  lower molars.]

 Treatment timing guidelinies with orthopedic appliances:

Class I malocclusion: If there is crowding without severe overjet  or TMJ symptoms, initiation  of treatment can wait until 10.5 to 12 years of age. Starting earlier may prolong the treatment time. A three-way expansion  appliance will aid in uncrowding the maxillary dentition. A mandibular sagittal appliance will aid uncrowding of the mandibular arch.

Class II division 1 malocclusion: should be treated  early if the following conditions apply:

1.      There is a overjet of 5mm or more with labially inclined incisors.

2.      TMJ symptoms are present.

3.      Patient is keen to receive the treatment.

Treatment can begin early (between ages 8 and 10 years). When there is severe maxillary incisor proclination, the flared incisors have increased chances of traumatic fracture, particularly in boys.

 Class  II Division  2 malocclusion patient  can wait for treatment until age 10 to 12 years, unless there are symptoms of TMJ disorder. Usually the young patients  with TMJ disorder symptoms are not mature enough to wear a mandibular repositioning appliance until the age of 8 years.

Class III malocclusion is treated as early as patient co-operation permits. Some investigations suggest chin-cap therapy as early as  5 to 6 years.  A saggital appliance can help in the treatment of maxillary deficiency & anterior crossbite.

Treating the patient during a growth spurt is beneficial.

Treatment  of skeletal discrepancies (eg. Class II), is more advantageous if carried out in the  mixed dentition growth spurt period.(boys 8-11 yrs; girls 7-9 yrs). Pre-pubertal growth spurt for boys is at 14-16 yrs & in girls is 11-13 yrs (eg. arch expansion).

Orthognathic surgery should be carried out after growth ceases.

Neurotrophism: It is defined as a ‘non-impulse transmitting neural function that involves axoplasmic transport and provides for long term interactions between neurons & innervated tissues that homeostatically regulate the morphologic, compositional, and functional integrity of soft tissues.’ (Melvin Moss in his research had concluded that the nerve influences the gene expression of the cell, and suggested that the genetic control lies not  in the functional matrix alone, but reflects constant neurotrophic regulation stemming from a higher neural source.)