How_to_Treat_Deep_Overbites

DEEP OVERBITES: AETIOLOGY AND MANAGEMENT Definition The incisor overbite (OB) is the vertical relationship of anterior teeth, and it describes the degree of overlap of these teeth. Normal overbite = upper incisors cover between 1/3 to ½ of labial aspect of the lower incisors when viewed horizontally from the front. Deep overbite = Overlap of more than ½ of the lower incisor crowns Deep OB can be present in any of the main categories of malocclusion; but is one of the main features of Class II Division 2 malocclusion. Incisors erupt towards their full potential and they tend to do so until they meet some form of hard or soft tissue resistance. AETIOLOGY Deep overbites result from a combination of genetic, environmental and local factors. Although they may be considered separately, many of them are interdependent. SKELETAL FACTORS Vertical Relationship • Decreased lower facial height • Low maxillary-mandibular planes angle • Shape of the mandible • Forward growth rotation of the mandible (orientates lower incisors more lingually) • Downward rotation of the mandible Antero-posterior Relationship • Marked AP discrepancy = excessive overjet (could also be reverse OJ) • This may mean no contact between anterior teeth which continue to erupt Transverse • Where lower arch is very narrow (esp II Div 2s) a scissors bite situation may develop, thus producing a deepening of the bite anteriorly. SOFT TISSUE FACTORS • Any abnormal behaviour or posture of the lips which prevenys teeth from occluding in their normal relationship may allow teeth to erupt beyond their normal level. • Especially a high lower lip line, covering more than just the incisal 2-3 mm of the upper incisors. • High circum-oral muscle activity and taut tissues • These factors tend to retrocline incisors • In II Div 1s, lower lip trap may procline the uppers, but tends to retrocline the lowers, and may contribute to a deep OB DENTOALVEOLAR FACTORS Inter-incisal Angle • U & L incisor angles as they erupt will determine whether they occlude and achieve the ideal inter-incisal angle of around 130 degrees. Incisor Height • Incisors probably have a pre-determined limited potential for eruption. The direction of eruption (see above) is important; but also if nothing opposes this eruption, they continue to erupt until a deep OB develops. Dentoalveolar Compensation • In mild AP skeletal discrepancy cases, the upper incisors may compensate by becoming retroclined under the influence of soft tissues and function. Incisor Shape • The labio-lingual dimension (thickness) of upper incisors can be smaller than normal in many deep OB cases. • The diminution or absence of a cingulum plateau and a steep platal slope of the upper incisor crowns • Even if the roots are normal in inclination, sometimes a marked increased angle between the crown and the root of the upper incisors Lack of Posterior Support • Loss of deciduous teeth in children • Loss of permanent teeth due to excessive or wrong orthodontic extractions (extractions of more anterior teeth is more likely to deepen OB); or due to caries/periodontitis • Hypodontia Trauma • Lingual luxation of the upper labial segment during development MANAGEMENT Before any treatment you need to take a complete history and carry out thorough clinical and radiographic examinations. This will help diagnose the cause of the problem, and also assess the relative contribution of upper and lower incisors to it. The age of the patient must also be taken into consideration. INDICATIONS FOR TREATMENT • Poor appearance of teeth • Trauma or potential trauma to teeth and soft tissues • Poor function AIMS • Reduction of overbite itself • Correction (reduction) of inter-incisal angle to 130 or even less. This is important for stability. • Correction of the “edge-centroid relationship”. The lower incisor edges should ideally lie anterior to the centroids of the roots of the upper incisors. Thus further eruption is impeded and the OB stabilised WAYS OF REDUCING OVERBITE IN GENERAL • Intrusion of incisors • Prevention of further ncisor eruption • Extrusion of posterior teeth • Encouragement of posterior growth rotation of mandible • Proclination of incisor crowns/ palatal root torque • Surgical movement of the skeletal bases • Any combination of the above METHODS OF OVERBITE REDUCTION • Usually non-extraction or extractions as far back as possible aids OB reduction, as you get more extrusion of posterior teeth, and less retraction of labial segments. SIMPLE REMOVABLE APPLIANCES • Anterior biteplanes: prevention of eruption of lower incisors, possibly intrusion of lower incisors, encouragement of posterior eruption, encouragement of posterior growth rotation during growth • Z or T springs can procline upper incisors • Torquing springs can torque upper incisor roots palatally FUNCTIONAL APPLIANCES • Used in moderate to severe Class II skeletal growing patients • Separation of the posterior teeth and stretching of soft tissues promotes vertical/ posterior mandibular growth • Can incorporate proclining or torquing springs for incisors FIXED APPLIANCES • Various systems (Begg, Tip-Edge, Straight Wire, Bioprogressive, etc) have their own ways of reducing OB; but all rely on the same set of basic principles. • In most circumstances, it is desirable to over-correct the overbite reduction, and the reduction in the inter-incisal angle to ensure a more stable result. • In Begg treatment “anchor bends” of about 30 degrees are placed in front of the molar teeth; so that once the archwire is placed in molar tubes, the anterior part of the archwire lies close to the labial sulcus, and once brackets are engaged, there is an intrusive and bite opening force on the incisors. • When reducing overbites in Bioprogressive/Segmental mechanics the molars are connected using a trans-palatal arch, anterior and posterior segments are aligned separately separately (sectional archwires), and then an additional “utility arch” is used to intrude the incisor teeth. The utility arch is usually made of 016x016 or 016x022 Blue Elgiloy for 018 slot systems, or 019x019 Blue Elgiloy for 022 systems. Molar anchor bends provide the intrusive force, while engagement of the archwire into the anterior (pre-adjusted) brackets intudes the upper incisors and torques their roots palatally. The posterior anchorage unit (TPA) prevents extrusion and distal tipping of the molars. TMA wire is an alternative to Blue Elgiloy. Another alternative is to keep the last sectional rectangular wire in the anterior brackets, and then “lash” (tie) the utility arch to the anterior segmental wire. • With the Straightwire Appliance you tend to get an initial deepening of the overbite where distally-angulated canines are present. The incisors tend to extrude and tip forwards because the labial segment does not provide enough anchorage for the movement of the canine root. Canine lacebacks may help. • However, gradual progression through the sequence of AWs (from thins and flexible to thicker and stiffer) starts to reduce the overbite again. The incisors are proclined, their roots are torqued lingually/palatally, and there is also a combination of genuine and relative intrusion of the incisors too. • There is some extrsusion of the posterior teeth as the arches align, which is compensated by the vertical growth of the mandible and the alveolar processes (in the growing patient – posterior rotation and increase in lower face height) which further reduces the overbite. • Including the second molars in the bond-up reinforces vertical anchorage, and helps flatten the Curve of Spee (COS). • Placing a reverse COS in the lower rectangular SS AW, and an accentuated COS in the the same wire for the upper arch, helps further OB reduction. • The use of elastics may extrude the posterior teeth further, but must make sure upper labial segment torque in maintained. • Bracket positioning may also help with OB reduction. MINI/ MICRO IMPALNTS • Elastics or coils worn to anchor implants can help intrusion of incisors or extrusion of posterior teeth. ORTHOGNATHIC SURGERY • Used in a non-growing patient with a marked AP discrepancy. • Arches prepared by conventional orthodontics first • To allow proper anterior surgical movement of the mandible, decompensation may involve extractions to create an overjet before surgery. • Mandibular adnvancement corrects AP relationship. • A maxillary procedure may also be required to increase the vertical dimension and permit good interdigitation.. • Segmental surgery may also be considered. STABILITY • Over-correction • Appropriate mechanics • Permanent retention!