Esthetic solution for a missing lower central incisor

Daniel Ziskind, Dr. Med. Dent.

www.lingualcourse.com  Vol 1 No.4 Nov 2003

The mandibular incisors are the smallest teeth in the mouth and have labial angulation in the dental arch. They are the cornerstone for the occlusal concept of mutual protection, by playing an essential role in the idea of anterior guidance.
The frequency for the agenesis of the first and second lower Incisor is about 0.7% and 5.6% respectively. However, it is difficult to differentiate between the teeth which are morphologically similar.
Congenitally missing teeth presents a treatment challenge for the clinician in all disciplines. Most of the treatment options listed in Figure 1, requires a multidisciplinary treatment approach.

No treatment
During the smile, the exposure of the mandibular lower teeth is individual and age related. A survey, found a gradual increase in the mandibular teeth exposure with age. This is accompanied by a gradual reduction in the amount of maxillay incisor exposure. (1)
Patient desire and the Smile should be carefully evaluated.

Removable partial denture
An inexpensive alternative offers a good esthetic solution. The clasps in a single tooth replacement in this region are located in the posterior region. Guiding plane can be used for additional retention in the anterior region. However, this alternative is inconvenient for the patient and presents an oral hygiene hazard as well.

Three units Bridge
This is the most frequent solution for a single tooth replacement. However, preparation of the healthy neighboring teeth might present contra indication. The small dimension of lower incisors presents a special difficulty. Root canal treatment, post and core might be necessary to accomplish the restoration. In addition the lower embrasures may be difficult to maintain. A single implant might present better alternative.

Autotransplantation.
This treatment alternative is not a frequent procedure. However, it was concluded after an (average) observation period of eight years that, this method has a good prognosis
 
Implant
Implant presents a good alternative for this situation. Bone quality and quantity should be evaluated three dimensionally. In Figure 2, bone depression is evident. In some cases additional bone grafting procedures might be necessary. When choosing this treatment alternative, a small diameter implant is preferred. The distance between an implant and the tooth should be no less than two millimeters.

Fig. 2: A congenitally missing lower incisor; bone depression is evident.

Maryland Bridge: 
a) Metal
b) Ceramic
c) Composite resin

a) Metal
Resin bonded retainer offers the obvious advantage of conservative tooth preparation avoiding the contact with the gingival margin.
Replacing a single missing teeth in a conservative way was first introduced by Rochette (2) in 1973 and presented as the Maryland bridge using etching Casting by Livaditis in 1982 (3).
Hill et.al. (4) concluded that the most frequent cause of failure is faulty electro-chemical etching of the metal structure. Different materials may present better bonding surface for the resin luting cement.

b) Ceramic
Different processing methods of the ceramic material enable high strength and good marginal integrity. In the IPS Empress system for example, using the lost wax principle, Lucite-reinforced glass ceramic material is pressure injected. Pretreatment of the ceramic with sandblasting and / or silane coupling agent make it possible to bond the ceramic structure with composite resin luting cement to the teeth.
However, ceramic requires marginal thickness in the range of 1mm.
 
c) Composite resin
The composite resin structure may present a better interface for the adhesive procedure. In addition, the advantage of using composite material compared to metal or ceramic structure is in the ability of direct, intra-oral repairing.

1. Figure 3 presents a GRADIA® Maryland bridge. The GRADIA® (5) (GC, Japan) is a high strength micro-hybrid composite system. The bridge was fabricated in the laboratory* and cemented with composite resin luting cement Variolink II® (Ivoclar Vivadent, Lichtenstein)
GRADIA® is available in different shades. Dentin, enamel and translucent shades (6) differ in composition from the opaque shade (7). GRADIA-gum® (8) provides a solution for special cases.

2. Ribbond® (Ribbond, USA) (9), as a single visit bridge may provide a simple solution using the composite resin available in the practice. However, this chairside procedure is more time consuming and with less predictable esthetic results.

Discussion:
The demand for straight white teeth has never been more important to patients. Careful preoperative case assessment and multi disciplinary consultation in the planning phase will make the most of the knowledge available.
In general, uncommon clinical situations increase the uncertainty of the treatment prognosis.  For many clinicians an implant and three unit bridge may present the first choice of treatment. The space size and the size of the neighboring teeth make these alternatives difficult to perform. An implant and three units bridge are more invasive alternatives. An Implant also presents a special challenge in the esthetic management of the Dento-gingival Unit. The composite resin Maryland-bridge presents a conservative aesthetic solution for a single anterior edentulous space.

 
Fig. 3: A GRADIA® Maryland Bridge

* Mr. Avinoam Akabi, Eichut Dental laboratory, Jerusalem, Israel.

References:
1. Vig RG, Brundo GC, The kinetics of anterior tooth display, JPD, 39: 502-504, 1978
2. Rochette AL, Attachement of a splint to enamel of lower anterior teeth, JPD 1973, 30, 418-423
3. Livaditis GJ, Etched casting: An improved retentive mechanism for resin-bonded retainers. JPD, 47: 52-58, 1982
4. Hill GL, Ziddan O, Gomez martin O, Bond strength of etched base metals: effect of errors in surface area estimation JPD 1986, 56: 41-46
5. http://www.gcgradia.gceurope.com/en/index.php?f=intro&p=index#gradia
6. http://www.gcamerica.com/MSDS/001464.htm
7. http://www.gcamerica.com/MSDS/001420.htm
8. http://www.gcbelgium.be/docs/68/manual/en_Manual.pdf
9. http://www.ribbond.com/clintech/svbridge/index.htm

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Dr. Silvia Geron D.M.D., M.Sc
Dr. Rafi Romano D.M.D., M.Sc
Dr. Pablo Echarri D.M.D., M.Sc