Orthodontics Flashcards
How is hard stainless steel wire made?
By drawing the metal in a cold state through a series of dies of successively smaller diameter. This process also causes work hardening, which gives the wire its spring properties.
Describe the Bauschinger Effect
When a coil is bent in a wire, it is differentially stretched so that the other surface becomes more work hardened and thus has better spring properties than the inner surface. If the coil is activated in the same direction as the previous bending, its elastic recovery is greater than if it is deflected in the opposite direction
What are the four causes of fracture of a stainless steel wire?
*overworking *mechanical abraision *fatigue *weld decay
What causes a stainless steel wire to become overworked?
The wire has been excessively overworked by bending and then straightening the wire at the same point creating extreme stresses within the immediate area which can result in fracture
What causes mechanical abraision of a stainless steel wire?
This can occur if the wire has been damaged by burs or stones in the finishing process of removable appliances or if the wire has been marked or crushed during the fabrication of components.
What are the causes of fatigue in a stainless steel wire?
This can be caused by a repeated straining action eg continually strained to engage a deep undercut with an Adams clasp
What causes weld decay in a stainless steel wire?
This is an intergranular corrosion created by overheating the alloy. This causes the chromium carbides to precipitate at the grain boundaries. The oral fluids can now access the surface of the other metals resulting in a galvanic action which weakens the area sufficiently to result in fracture
What type of stainless steel wire is commonly used in orthodontics, and what is it composed of?
18/8 austenitic stainless steel wire. *72% iron *18% chromium *8% Nickel *1.7% titanium 0.3% carbon
What is the difference between austenite and martensite?
In austenite the average unit cell is a perfect cube. The transformation to martensite sees this cube distorted by interstitial carbon atoms that do not have time to diffuse out during displacive transformation (quenching), so that it is a tiny bit longer than before in one dimension and a little shorter in the other two. A microscopic crystallite of steel is millions of unit cells long. Since all these units face the same direction, distortions of even a fraction percent become magnified into a major mismatch between neighbouring materials. This creates crystal defects within the material similar to work hardening; these defects prevent atoms from sliding past one another in an organised fasion, causing the material to become harder.
When writing a lab prescription for an orthodontic appliance, in what order should you make your requests?
*Aim *Active components *Retention *Anchorage *Baseplate
Define retention
Retention is the resistance to displacement forces. ie the tongue, mastication, gravity, talking, active components (applied forces can cause displacement)
Define anchorage
resistance to unwanted tooth movement
List four signs of a digit sucking habit
*proclined upper incisors *retroclined lower incisors *anterior open bite or incomplete open bite *narrow upper arch *unilateral posterior cross bite
what causes signs of a digit sucking habit?
the patients thumb/digits are postitioned in the mouth in such a way that they result in the mandible to drop open. This causes the patients tongue to occupy an area that is not deemed normal. The sucking action initiated by the muscular forces in the cheeks narrows the maxillary arch, causing a unilateral posterior cross bite
List four ways in which a digit sucking habit can be prevented or stopped
*URA *behavioural management therapy *sock/gloves on hands *plaster on thumb *foul tasting nail polish/hand cream *the use of a dummy
Describe the local causes of malocclusion
Localised problem within either arch, usually confined to 1, 2 or several teeth. Can be due to number, size/form, position, soft tissue or a pathology
Name four conditions of tooth number that can result in malocclusion
*supernumery *hypodontia *retained primary tooth/teeth *early loss of primary tooth/teeth (extraction or exfoliation)
List four supernumary teeth
*conical *tuberculate *supplimental *odontome
How can a crossbite be corrected?
A URA with a palatal midline screw
how often should a palatal midline screw be activated?
one per month
How can a URA be modified for a thumb sucker?
a deterant rake to stop the active habit and prevent relapse after treatment
what does the acronym ARAB stand for?
*Active component; induces a force by introducing displacement forces *Retention; resistance to displacement forces *Anchorage; resistance to unwanted tooth movement. Newtons 3rd law (for every action there is an equal and opposite reaction) *Baseplate; to provide anchorage, connector for the retentive components, cohesion, adhesion and stability
how would you write a prescription to correct a anterior crossbite?
Aim; please construct a URA to correct an anterior crossbite on tooth 12 A; z-spring on 12 0.5mm HSSW R; 16, 14, 24, 26 Adams clasps 0.7mm HSSW A; yes B; self cure PMMA, posterior bite plane
how would you write a prescription to correct a posterior crossbite?
Aim; please construct a URA to expand the upper arch A; midline palatal screw R; 16, 14, 24, 26 Adams clasps 0.7mm HSSW A; reciprocal anchorage B; self cured PMMA, posterior bite plane (most incorporate all posterior teeth to prevent unwanted tooth eruption)
list 6 things that can go wrong with the growth and development of teeth
*increased over jet *anterior/posterior cross bite *retained deciduous teeth *ectopic teeth *crowding *trauma *anterior/lateral open bites *ankylosis of deciduous teeth *diastema *dental asymmetries *deep overbit *early loss of deciduous teeth *impacted first molars *spacing *habits *cysts *supernummaries
Name five potential risks of orthodontic treatment
*decalcification *relapse *root resorption *pain/discomfort *soft tissue trauma *failure to complete treatment *loss of tooth vitality *inhale or swallow small components *candidal infections
When should an orthodontic exam be carried out?
*brief exam at around aged 9 *comprehensive exam when premolars and canines erupt (11-12 years) *when older patients first present *if a malocclusion develops later in life
What are Andrews 6 keys?
i) Molar relationship; the distal surface of the disto-buccal cusp of the upper first permanent molar occludes with the mesial surface of the mesio-buccal cusp of the lower second permanent molar ii) crown angulation iii) crown inclination iv) no rotations v) no spaces vi) flat occlusal planes (no curve of spee)
Describe FMPA
Frankfort mandibular plane angle; and angle created between teh frankfort horizontal plane and the lower border of the mandible. An increased FMPA if theres a premature meeting point A decreased FMPA if theres a delayed meeting point (should be at the back of the head)
Give the Britisd standards institute classification of incisor relationships
*Class I - the lower incisor edges occlude with or lie immediately below the cingulum plateau of the upper central incisors *Class II - the lower incisor edges lie posterior to the cingulum plateau of the upper incisors - Division I; the upper incisors are proclined or are of average inclination and there is an INCREASE IN OVERJET - Division II; the UPPER CENTRAL INCISORS ARE RETROCLINED. The OJ is usually minimal or may be increased *Class III - lower incisor edges lie anterior to the cingulum plateau of the upper incisors. The OJ is reduced or reversed
What special investigations should be carried out as part of an orthodontic assessment?
*radiographs (OPT, maxillary anterior occlusal, lateral cephalogram) *vitality tests *study models *photographs
When should you refer patient for orthodontic assessment?
deciduous dentition - CLP, craniofacial abnormalities (if not under MDT care) early mixed dentition - delayed eruption of perm incisors, impaction/FOE of 6s, poor prognosis of 6s, severe class 3, AXB, ectopic canines, pathology late mixed dentition - growth mod in class 2, hypodontia, other routine problems
What is ideal occlusion?
anatomically perfect arrangement of teeth
what is normal occlusion?
acceptable variation from the ideal
what are competent lips?
lips meet with minimal or no muscle activity
what are incompetent lips?
evident muscle activity is needed to make lips meet
Class I incisor relationship
lower incisors occlude with or lie immediately below cingulum of upper incisors
Class II incisor relationship
lower incisor edges lie posterior to cingulum of upper incisors div 1 - max centrals are upright or proclined, OJ increased div 2 - max centrals retroclined, OJ usually decreased, may be increased
Class III incisor relationship
lower incisors lie anterior to cingulum of upper incisors, OJ is decreased or reversed
OJ and OB
OJ - distance between max and mand incisors in horizontal plane OB - overlap of incisors in vertical plane
Complete vs incomplete OB
Complete - lower incisors contact upper incisors or palatal mucosa incomplete - they dont
Anterior Open bite
no vertical overlap of incisors when the buccal segments are in contact
Dento-alveolar compensation
inclination of the teeth to compensate for underlying skeletal abnormalities
Why are study models taken?
clinical records, legal documents, show what could be achievable, show what has changed, show the final treatment position
What indices are used for assessing orthodontic need
IOTN - grade 1 - minor malocclusions grade 2 - minimal need grade 3 - moderate need - use the aesthetic component grade 4 - great need grade 5 - very great grade 4/5 get NHS treatment grade 3 needs aesthetic component of 6+
How do you assess the dental health component?
MOCDOO Missing teeth overjet crossbite displacement overbite other
What are balancing extractions and compensating extractions?
balancing - extraction of same/adjacent tooth on the opposite side of the same arch - preserves symmetry compensating - extract of occluding tooth on the opposing arch. stops over eruption
When do you extract FPM?
poor prognosis, need calcification of the furcation of the 7s as optimal. if late - little space closure and 7 tilts mesially if early - get crowding
What is a median diastema, what causes it and how to treat
Diastema - gap between central incisors. 6yo = 98%, 12yo = 7% caused by small teeth, absent/peg laterals, midline discrepancy, proclination of ULS, physiological from pressure of developing teeth on roots, fraenum treatment - wait. before 3s erupt and <3mm after 3s - ortho Tx and retention.
Anchorage options for distal movement
temporary anchorage devices are preferred to headgear
How to treat buccally displaced max 3s
if crowded - XLA 4s and fixed applicances ortho Tx - buccal canine retractor
How to treat impacted canines
- do nothing and monitor for pathology 2. XLA 3s, restorative to close space (possible trauma from XLA, fixed treatment) 3. open exposure of 3s, ortho Tx to pull down (only if in favourable position, takes a while, fixed Tx and requires good cooperation) 4. autotransplantation - not always successful, can cause ankylosis/necrosis
Causes of increased OJ
Skeletal pattern, soft tissues, lip trap, habits, crowding
management of increased OJ
fixed appliances for class I and II to retract ULA, +/- XLA. functional appliance in class II to tilt teeth/growth mod ortho camouflage surgical correction if severe
Causes of increased OB
normal is 1/2-1/3 overlap. increased is associated with class II/2 only treat if traumatic. decreased LFH, high lower lip, retroclined incisors, increased inter incisal angle
how to treat increased OB
FABP to allow molars to erupt procline lower incisors
Cause of AOB
vertical growth > horizontal growth habits, tongue thrust, iatrogenic, CLP
Treatment of AOB
cease habit, FPBP
Treatment of reverse OJ
- Do nothing and accept 2. camouflage 3. surgery if ANB below -4 lower incisal angle to mand plan <80
How do you treat XB?
AXB - z spring and FPBP to disclude teeth PXB - quad helix, RME, midline palatal screw and FPBP
what are indications for removable appliances?
Require movement of blocs of teeth (PXB) interceptive treatment in mixed dentition (AXB) overbite reduction elimination of occlusal interferences spacemaintainer when passive retention when passive habit deterrent
What are the active components of removable appliances and what are they made out of
Z springs - 0.5mm HSSW buccal canine retractor roberts retractor midline palatal screw
What are the retentive components of removable appliances and what are they made out of?
Adams cribs - 0.7mm HSSW (0.6mm on deciduous) southend clasp labial bow
What are the components of fixed orthodontic appliances?
Bands - on molars Brackets - on each teeth, usually labial surfaces Archwire - active component. NiTi or steel. ligatures - elastic bands or wire to hold archwire in bracket can have class II or class III inter arch bands
What is the mode of action of functional appliances? and give an example of one
25% skeletal change, 75% dental tooth tipping twin block appliance
What information would you give a patient who has jsut been given their removable appliance?
- non compliance with significantly increase your treatment time 2. it will feel big, you will salivate more and you will find it hard to talk. practice and these will aleviate 3. wear is 24/7 except contact sports and swimming. clean after meals with toothbrush over filled sink 4. if it breaks, come back 5. some discomfort initially is to be expected - it means it is working. this will reduce 6. emergency contact details
How does a twin block appliance work?
retroclination of upper anteriors proclination of lower anteriors mid line palatal screw frequently incorportated to tip posterior teeth to correct PCB re-positions mandible forward reduces muscle action on jaws some skeletal grown from secondary growth centres correcting AOB with posterior bite planes and allows further eruption of anteriors
What is dento-alveolar compensation?
a system which attempts to maintain normal inter arch relationships can maintain occlusal relationship even though there are variations in growth and facial pattern
What is a supernumerary tooth?
a tooth that is in addition to the regular dentition
list the steps involved in class III malocclusion treatment
tooth alignment, eliminating crowding/spaces and XB coordination of the arches decompensate incisors flatten occlusal plane surgical fixatoin port surgery ortho
What are the risk/benefits you need to discuss with a patient who has carious 6s but wants ortho Tx?
- removal of 6s, tipping of 7s, loss of bone, spaces - long term prognosis of 6s - LA/GA for Xn, risk of death if GA - risks of ortho Tx
What are some risks of orthodontic treatment?
- root resorption - relapse - failure to complete treatment - treatment failure - devitalising of tooth - pain - trauma from components - decalcification of tooth
when would you treat an anterior over bite?
if mand displacement on closing if traumatic aesthetics
What characteristics of a malocclusion would make it ideal for treatment with a URA
- palatally tipped teeth - 1 or 2 teeth needing movement - class 1 molar relationship - space
What are causes of ectopic canines?
- ectopic crypt position - absent laterals - crowding - retention of deciduous canine - genetics
How do you monitor the eruption of canines?
palpation from 9/10 look at inclination of 2s mobility of cs colour of cs
What are the signs of impacted canines?
- delayed eruption - retained Cs - unable to palpate - distal tipping of 2s loss of vitality or mobility of 1s/2s
What are functions of a URA other than tipping teeth?
- space maintainer - habit breaker - retainer - correct OB
What warnings do you give someone on provision of a URA?
- big and bulky - non compliance increases duration - will feel uncomfortable, saliva, speech - will settle - beware of hot drinks
What do you use in a URA to correct an ACB and a PCB?
ACB - Z spring PCB - midline palatal screw
What are risks of bonded and pressure formed retainers?
bonded: can debond, caries, gingivitis, poor OH, fracture of wire pressure: lost/chewed by dog compliance and no longer fitting, keeping clean
How would you assess vertical skeletal relationship?
LAFH vs TFH - should be 50% ish FMPA - should meet at the back of the head
What are some causes of AOB?
digit sucking tongue thrust fracture of mandible skeletal discrepancy
How would you monitor canine movement?
measure, can use a definite point to compare against
A patient with fixed ortho presents with white areas around the brackets, what could be the cause?
- demineralisation - excess cements - plaque
How does a URA affect the anterio-posterior skeletal relationship?
it doesnt
How does a URA affect the vertical skeletal relationship?
FABP would decrease overbite and increased LAFH
design a URA for proclining anterior teeth
• Active: Roberts retractor 0.5mm in tubing • Retention: Adams cribs 6/6 0.7mm HSSW • ?Anchorage: Stops mesial to 3/3? • Baseplate: Flat anterior biteplane
What special tests are required for an orthodontic diagnosis?
*study models
*Radiographs (OPT, lateral cephalogram)
*Photos
*Sensibility tests
*cone beam CT scan
What are the three aims of orthodontic treatment?
To achieve;
Stable occlusion
Functional occlusion
Aesthetic occlusion
What are the three main risks of orthodontic treatment?
*Decalcification
*Relapse
*Root resorption
When should an orthodontic exam be carried out?
*Brief exam at around age 9
*Comprehensive exam when premolars and canines erupt
*When older patients first present
*if a malocclusion develops later in life
What is ideal occlusion?
It is a hypothetical rarely found in nature. It is the gold standard by which occlusal irregularities and treatment may be judged
Describe the AP class I relationship
maxilla 2-3mm in front of mandible
Describe the AP class II relationship
maxilla >3mm in front of mandible
Describe the AP class III relationship
mandible in front of maxilla
What is an increased FMPA?
Frankfort mandibular plane angle
increased if premature meeting point
What is a decreased FMPA?
Frankfort mandibular plane angle
decreased if delayed meeting point
Where is the ideal meeting point of the FMPA?
external occipital protuberance
What are the occlusal features of a sucking habit?
*Proclination of upper anteriors
*Retroclination of the lower anteriors
*Localised AOB or incomplete over bite
*Narrow upper arch
What are the average values in class I cephalometrics?
*SNA relates maxilla to anterior cranial base
Average value 81o +/- 3o
*SNB relates mandible to anterior cranial base
Average value 78o +/- 3o
*ANB relates mandible to maxilla
Average value 3o +/- 2o
Clinically speaking, what is the upper anterior face height and lower anterior face height?
Upper; glabella to base of nose
*Lower; base of nose to inferior aspect of chin
*Average ratio of LAFH to TAFH 50%
What is the average value of FMPA
27o +/- 4o
In terms of cephalometrics, what is the upper and lower anterior face height?
*Upper; nasion to anterior nasal spine
*Lower; anterior nasal spine to menton
*average value of LAFH to TAFH 55%
What is a dental cause of facial asymmetry?
displacement of normal mandible due to unilateral crossbite
What is a true mandibular cause of facial asymmetry?
*Hemi mandibular hypoplasia
*condylar hypoplasia
What are the four aetiologies of malocclusion?
*skeletal (ie class III)
*dental (missing teeth)
*soft tissue (lip trap)
*habit (thumb sucking)
What are five local causes of malocclusion?
*variation in tooth number
*variation in tooth size or form
*abnormalities of tooth position
*local abnormalities of soft tissues
*local pathology
What are the four types of supernumerary teeth?
*conical
*tuberculate
*supplemental
*odontome
Describe balancing extraction
by extraction of a tooth from the opposite side of the same arch. Designed to minimise midline shift.
Describe compensating extraction
by extraction of a tooth from the opposing arch of the same side. Designed to maintain occlusal relationship
What methods are there of clinically assessing ectopic canines?
*visualisation, palpation of any obvious bumps
*Inclination of 2(s)
*Mobility of c(s) or 2(s)
*colour of c(s) or 2(s)
*radiographic assessment (usually OPT and anterior occlusal (parallax technique))
*3p’s; presence, position, pathology
What is the physiological basis of orthodontics?
If an external force is applied to a tooth, the tooth will move as the bone around it remodels. This bony remodelling is mediated by the PDL.
What are the six types of tooth movement and their ideal force?
*Tipping (35-60g)
*Bodily movement (150-200g)
*Intrusion (10-20g)
*extrusion (35-60g)
*rotation (35-60g)
*torgue (50-100g)
What is interceptive orthodontics?
Any procedure that will reduce or eliminate the severity of developing malocclusion
What are the eruption dates for the
6’s
1’s
2’s
6’s - 6 yo
1’s - 7 yo
2’s - 8 yo
What are the eruption dates for
4’s
3’s + 5’s
7’s
4’s - 10yo
3’s + 5’s - 11-12 yo
7’s - 12-13 yo
What are the causes of unerupted central incisors?
Supernumeraries preventing eruption. Trauma/dilaceration
What are the treatement options for an unerupted central incisor due to a supernumerary?
Remove deciduous and supernumerary. Expose unerupted tooth (potentially bond gold chain). Create space. Monitor for up to 18 months
what is the term given to a tooth that sits below the occlusal plane?
Infraoccluded
According to Andrews six keys; what is the correct molar relationship?
The mesio-buccal cusp of the upper first molar occludes with the groove between the mesio-buccal and middle buccal cusp of the lower first molar. The disto-buccal cusp of the upper first molar contacts with mesio-buccal cusp of the lower second molar
According to Andrews six keys, what is correct crown angulation?
All tooth crowns are angulated mesially
According to Andrews six keys, what is correct crown inclination?
incisors are inclined towards the labial surfce. Buccal segment teeth are inclined lingually
What are the stages of treatment planning in orthodontics?
- Plan around the lower arch (angularion of lower labial segment is stable)
- Decide on treatment in lower (ext or no ext)
- Build upper arch around lower. Aim for class i incisor and canine relationship
- Decide on molar relationship. Class i or full unit class ii
What is the overlap technique?
A method of measuring space available and space required. Measure how much the teeth overlap to guage how much space is required
What are the general principles of space required in the lower arch?
- Mild (0-4mm) stripping or ext of 5s
- Moderated 5-8mm - extract 5s or 4s
- Severe >8mm - extract 4s
How should an orthodontic treatment plan be written?
- Diagnosis
- Problem list
- Treatment plan;
*list successive stages stating tooth movements to be carried out and appliances to be used
*Estimate length of treatment
*If it is not possible to give a detailed plan, indicate when it will be reviewed (ie following eruption of teeth)
What are the six options of treatment in orthodontics?
1) Accept malocclusions
2) Extractions only
3) URA
4) Functional appliances
5) Fixed appliances
6) complex treatment involving orthodontics and restorative treatment or orthodontics and orthognatic surgery
