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Canine Substitution

When lateral incisors are missing, there are 3 options:  canine substitution, tooth-supported restoration, and single-tooth implant (check out our previous blogs which explored these options in detail).  The primary consideration when choosing a treatment option is conservation and should be the least invasive option that satisfies the expected aesthetic and functional objectives. 

Criteria for canine substitution

Malocclusion & Amount of Crowding:  2 types of malocclusions permit canine substitution

1. Class 2 malocclusion with no lower crowding (end molar relationship class 2)
2. Class 1 malocclusion with lower arch crowding involving mandibular arch extractions (end molar relationship class 1)

Occlusal scheme: Lateral excursions should occur with group function, i.e. guidance with more than one tooth on the working side

Tooth size discrepancy: There is a likelihood of anterior maxillary excess through substitution, and may require reduction of the maxillary anterior to have normal overjet and overbite.  This should be assessed prior to treatment through a diagnostic set-up.

High Lip line: If patients have a high lip line the gingival level of the canine will appear level with the central incisor, giving a flat appearance to the gingival level. To resolve this the canine bracket position is placed gingival, extruding the canine tooth. Coupled with canine substitution is premolar substitution, where the inverse is required with the gingival margin needing to be apical to the usual premolar position, this can be managed through placing the bracket incisal, or crown lengthening.

Canine Shape and Colour

The ideal canine to substitute for a lateral incisor is one that is the same colour as the central, narrow at the CEJ (both bucco-lingual and mesio-distal, a relatively flat labial surface and narrow mid-crown width (bucco-lingual).

However ideals are infrequent occurrences, in life and orthodontics, so below are issues of non-ideal canine shape and colour (management of non-ideals in life however still illude the authors)

• Width: Wider the canine the greater the mesio-labial reduction and the more convex the labial surface the greater the labio-lingual. Issues which can form are dentin may show through (appearing darker), sensitivity through exposed dentine, and the possible need for more restorative treatment
• Width at CEJ: Crown width at CEJ should be evaluated on pre-treatment radiograph to determine final emergence profile.  Canine with a narrow mesio-distal width at the CEJ are more aesthetic than the emergence profile of a canine with a wide CEJ. 
• Cusp tip: Canines with a prominent cusp tip may need both tip reduction and composite restoration to the mesio-incisal and disto-incisal edges in order to achieve the appearance of a flat incisal edge
• Colour: Canines are typically 1-2 shades darker than central incisors, individual bleach the canine or a veneer can be used

Space opening for missing lateral incisor

Resin Bonded Bridges

The most common cause of failure is debonding.  Occlusal relationships and the amount of surface area bonded contribute to bridge failure.

Overbite: An increased overbite increases failure rate from increased lateral forces.  As the overbite increases, there is a decrease in the surface for bonding or requires greater preparation.  Ideally, there should be a slightly reduced overbite.  A patient with steep posterior cusps and deep anterior overbite is not an ideal candidate for a resin bonded bridges due to increased lateral forces anteriorly.

Overjet:  With an ideal overjet and complete overbite there will be with anterior tooth contacts in static occlusion, in this relationship ideal overbite is a reduced overbite, allowing the greater surface area coverage of the lingual aspect of the upper central or canine tooth by the metal framework

Inclination of the teeth: Resin bonded bridges can withstand 40% greater force when experienced as a shear force rather than tensile force prior to debonding. Proclined upper incisors create greater tensile occlusal forces at the bond interface when compared to shear forces. Upright teeth reduce tensile forces and direct forces vertically through the tooth rather than labially.

Mobility of the adjacent teeth is a contraindication to a resin bonded bridge.  Each abutment will independently move under occlusal forces and thus stress the bond.  Generally, it is the least mobile of the 2 abutments that debonds if a double abutment design is used

Shine-though. Incisal edges vary in translucency, if the metal wing is bonded to translucent surface, the appearance will be of a blue / grey shine through. If shine through is anticipated a metal winged bridge is contraindicated, the options for aesthetic wings through Zirconia or the use of opaque cement can be considered instead.

Anterior Conventional Bridges

No longer common as a design due to being the least conservative of all options, but consider if patients have endodontically treated teeth, previous restorations, or fractured incisors and canines that require restoration.  For this design two key occlusal parameters which aid the restoration: Increased overjet of 0.5-0.75mm on the abutment teeth, and achieving parallel long axis of the central and canine teeth when viewed from both the frontal and lateral aspect. Parallelism ensures an ideal path of insertion and avoids the need to over-prepare the teeth.

Single-Tooth Implants

Space requirement: Space requirements are determined by aesthetic need, occlusion and the size of the implant. For the aesthetic requirement golden proportions with used of 1:1.618. Most lateral incisors are between 5.5mm to 6.7mm, with the narrowest implant 2.9mm. Space between implant and adjacent tooth should be at least 1mm for proper healing and development of papilla, around 6mm of space achieves this. The narrower the space between implant and adjacent tooth, the more likely there will be bone loss over time. If the correct occlusion has been achieved but space for implant crown is too narrow, interproximal reduction from central incisors and canines can aid ideal space requirements. Root parallelism is a requirement which should be assessed through periapical radiographs. If orthodontic treatment was completed at a young age there can be relapse or convergence of the roots of the central and canine teeth, especially if there has been significant vertical facial growth. This can occur due to compensatory eruption and inadequate stabilization of edentulous space, the use of a bonded is recommended rather than removable retainer

In the absence of a calculator (or calculator app in its current incarnation) the table below displays the common sizes of central incisors and lateral incisors using the golden proportions.Timing of Implant Placement: Implants react similar to ankylosed teeth as adjacent teeth continue to erupt and a vertical discrepancy will be created between the incisal and gingival margins of the implant and adjacent teeth. Most orthodontic treatment is completed at 14-15 years of age, to assess vertical growth superimposition of serial cephalograms is ideal, with assessment of face height N-Me. Recent research recommends waiting until 30 as alveolar growth in males continues into their 20s.

Implant site development: After tooth extraction, maxillary anterior bucco-lingual width reduces by 23% in the first 6 months, and 11 % over the next 5 years, which is a total of 34% narrower over 5 years. If upper lateral is missing, and the canine has erupted in its position, with orthodontic treatment to re-open space results in bone loss of <1% over 4 years. Therefore the orthodontists should allow canines to erupt mesially if laterals are missing, then move canines distally to create an edentulous ridge that will not resorb as much as one following extraction.Surgical Ridge Augmentation: Is dependant on the width of bone remaining. Materials for augmentation include; non-resorbable membranes, resorbable membranes, autogenous bone, bone grafts and osteome splitting technique

• <4mm width: There is a need for surgical augmentation before implant placement. Following the graft a period of 9 months is needed for stabilization prior to implant placement. Therefore, planning for these cases should be such that 9-12 months prior to debonding of orthodontic appliance, the graft has been carried out
• 4-5mm width: Augmentation at time of implant placement is possible

Correcting Loss of Papilla During Space Opening

Formation of papilla in young patients more predictable, in adults, lack of eruption jeopardizes formation of papilla after orthodontic space opening. As space is opened between 2 teeth, papilla stays with the tooth that is not moving. If the canine erupts against the distal of the central, and is orthodontically moved distally, papilla stays on the distal of the central.  Sulcus on the mesial of the canine is stretched open and a red patch of non-keratinized sulcular epithelium develops (Atherton’s Patch). In growing patients this vertical defect gradually disappears and a sulcus redevelops.  But in adults with little or no tooth eruption, this does not occur, therefore surgical management is required at the time of implant placement, with the mesial aspect of the flap extended to the mesial of the adjacent central, therefore extending the flap coronally to recreate a papilla. 

Space Maintenance

During Orthodontics: Use plastic teeth in the anterior region.  Be careful not to impinge on the gingival tissue mesial and distal to the pontic because this area will become the papilla after implant placement

After Orthodontics: Removable retainer with prosthetic tooth is OK if implant will be done shortly after debonding  Permits implant placement and uncovering while retainer is being worn.  Again, avoid impingement on gingival tissue mesial and distal to the pontic because this area will become the papilla after implant placement.  If 4-5 years to go before placing implant, consider a resin bonded bridge as a temporary. 

We hope you have enjoyed part 3 of the blog, This blog started with a conversation between Farooq Ahmed and James Andrews, to follow more conversations, clinical tips and commentaries on orthodontics please check us out on Instagram:

James Andrews’ Instagram page @dr.jamesandrews

Farooq Ahmed’s Instagram page @farooqahmed_orthodontist

References

Artun J, Kokich VG, Osterberg.  Long-term effect of root proximity on periodontal health after orthodontic treatment.  Am J Orthod Dentofac Orthop 1987; 91:125-30.

Kinzer GA, Kokich VO.  Managing congenitally missing lateral incisors. Part II: Tooth-Supported Restorations. J Esthet Restor Dent 2005; 17:76-84.

Kokich VG, Mathews DP.  Impacted teeth: Orthodontic and surgical considerations.  Chapter 24, pg 1-27.

Kokich VG, Nappen DL, Shapiro PA. Gingival contour and clinical crown length: their effect on the esthetic appearance of maxillary anterior teeth. Am J Orthod 1984; 86(2): 89-94. 

Kokich VG, Spear FM.  Guidelines for managing the orthodontic-restorative patient. Semin Ortho 1997; 3:3-20.

Kokich VG.  Managing orthodontic-restorative treatment for the adolescent patient.  Chapter 25. pg 1-30.

Kokich VG. Esthetics: The orthodontic-periodontic restorative connection. Semin Orthod 1996; 2:21-30.

Kokich VG. Maxillary lateral incisor implants: planning with the aid of orthodontics.  J Oral Maxillofac Surg 2004; 62: 48-56.

Kokich VG. Surgical and orthodontic management of impacted maxillary canines. Am J Orthod Dentofacial Orthop 2004; 126:278-83.

Kokich VG. The role of orthodontics as an adjunct to periodontal therapy. Chapter 53, pg 704-718.

Kokich VO, Kinzer GA.  Managing congenitally missing lateral incisors. Part I: Canine substitution. J Esthet Restor Dent 2005; 17:5-10.

Kokich VO, Kiyak HA, Shapiro PA. Comparing the perception of dentists and pay people to altered dental esthetics.  J Esthet Dent 1999; 11:311-324.

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Mathews DP, Kokich VG.  Managing treatment for the orthodontic patient with periodontal problems.  Semin Orthod 1997; 3:21-38.

Ostler MS, Kokich VG.  Alveolar ridge changes in patients congenitally missing mandibular second premolars.  J Prosthet Dent 1994; 71(2):144-9.

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Spear, FM, Mathews DM, Kokich VG. Interdisciplinary management of single-tooth implants.  Semin Orthod 1997; 3:45-72.

Vermette ME, Kokich VG, Kennedy DB.  Uncovering labially impacted teeth: apically positioned flap and closed-eruption techniques. Angle Orthod 1995; 65(1):23-34.