DEFINITION OF MAXILLARY INCISO-LINGUAL: Where the inciso-facial restoration mates to a beveled enamel margin, forming a shoe that is within the occlusal envelope of the incisor
MAXILLARY LINGUAL SHOE
Unlike the lower incisor, over-contouring cannot be used to augment the strength of the restoration when treating linguo-incisal fracture in the maxillary teeth arch: we must conform to the occlusion. To offset this structural need, the preparation therefore requires deeper penetration into the incisal dentin, developing a deeper “mortise and tenon” interlock between the dentin and the resin, transferring loads from resin to dentin. However, normal function seats the restoration rather than dislodges it, so the penetration is usually less than a millimeter into dentin. In the image above, both central incisors present weak lingual enamel, which will be shoed.
First penetrate into the dentin with a 330 bur, to a suitable depth,usually 1.2 of a millimeter from the incisal edge to the floor of the preparation. This 2/3 the depth of a 330 bur, wqhose shaft is 1.8 mm in length. Remove all traces of dentin clinging to the facial enamel for the first 0.75mm to 1mm of depth. Bevel the lingual enamel with a 7406 bur to produce a shallow beveled margin – about ten degrees, as in the lower inciso-gingival restoration. The reasoning is the same: to engage enamel rod-ends and transfer the stress of the restoration to the DEJ. (Enamel Axioms #2,#3#4#5).
Intentionally establish a lingual enamel thickness of 1/2 to 3/4mm. re-exposing the dentin over time,leaving an island of composite surrounded by a trough of freshly ablating dentin. Have we not seen this clinically? This may include significant extension towards the gingival, In deep overbite cases,this increase in the footprint may be as much as several millimeters towards the gingival. It might even include the centric stop in the restoration. Because healthy tooth structure is being removed, this extension may intuitively seem destructive. On the contrary, this extension builds longevity in the result.
Centric occlusion is not placed on a margin; instead, the finish line is extended in a gingival direction until past the occlusal stop.
The schematics below illustrate the preparation in cross-section.
The pictures below illustrate a case of incisal breakdown, both facial and lingual, with accompanying discoloration of the incisal component. Both #11 and #21 require a lingual shoe, and Tooth #11 additionally requires a facial mini-shoe. In the following photo sequence, restoration of the incisal contour and elimination of discoloration has improved appearance markedly, despite there being no attempt to reconfigure other defects in the smile. This is limited, conformative dentistry, not aesthetic reconstruction.
A TYPICAL MAXILLARY INCISOR CASE
The photos below illustrate the preparation and typical outcome for two maxillary central incisors suffering from Linguo-incisal attrition and concomitant dentinal staining and some accompanying deterioration of the facial outline form. The goal was only to restore the weakened and deteriorating incisal edge within the confines of the existing bite. The resin used was 3M Espe Z-250, shade D3. Equally convincing outcomes have been achieved with Tokuyama Estelite, shade A3.5, which is warmer in hue. Experience has shown me that the best esthetics are obtained with a single shade of resin, closely matched in hue and value to the host tooth, with high “metamerism” or blending properties. The difficulty of layering and controlling placement in these small preparations precludes any esthetic improvement by layering.
Some practitioners want to place flowable resin for these defects. Why not?
Simply, flowable is higher in contraction and lower in physical properties and wears more rapidly than paste resin, despit3e manufacturers’ claims. So don’t shortchange the patient for operative convenience. A very satisfactory result can be obtained with this seemingly-too-simple single-shade paste resin approach, but all attempts at greater complexity have met with frustration.