Q & A Case Study

A patient presents to comp care clinic at IUSD. The patient has an existing upper RPD, which is now showing radiographically signs of a caries lesion on distal of a posterior tooth. This posterior tooth also has a reciprocal clasp where the caries is. After removing decay, the lesion extended from the distal-occlusal to the lingual. After removing decay, a direct restoration on the current tooth structure would not retain the restoration so a pin needed to be placed. Resin was used, but would amalgam have been a better choice?

Fracture resistance, wear resistance, and polymerization shrinkage are all issues of concern when placing a resin.

Fracture toughness describes the ability of a material containing a crack to resist fracture.
When there is an increase from 3 walls to 4 walls that need to be restored, the percent of failure increases by 30-40% (1). Dentinal pins can be used with composite resin to retain the restoration and keep from failing. Using a pin is an alterative to increasing the prep design, which increases failure rate. Dentinal pins, when used with acid etching technique have a statistically significant increase in fracture toughness (2). This is opposite of amalgam, where a dentinal pin weakens the strength of amalgam. Another reason restorations fail is because of caries. If the patient is a high caries risk, there is a greater chance of failure for both amalgam and composite resin restorations. When comparing amalgam to resin in patients who are at high risk, amalgam showed a better performance with longer lifespan of 5-8 years, and more secondary caries occurred next to composite resin (3). However, resin does have a lower fracture rate because adhesive restorations strength the tooth (3). Composite restorations as opposed to amalgam have a longer life span in patients who are low caries risk (3). With the dentinal pin, acid etch technique, and 3-wall surface restorative need, resin seems to still be an adequate choice for this patient
Resin consists of 3 different materials: the organic matrix, inorganic matrix and filler or disperse phase. The disperse phase is what determines the mechanical properties of the restorative material (4). When increased filler is added, thermal coefficient of expansion and polymerization shrinkage reduce and the overall handling esthetic results are improved (4). Different resins have different wear results due to their filler particles. Macrofilled resins have a higher amount of monomers compared to hybrid and microfilled composites and this result in higher wear rate of composite because of the large diameter of the main filler (5). The majority of filler used today is silicon dioxide; quartz and boron silicates and lithium aluminum (4). There have also been studies that state, patients with severe tooth wear have a high risk of composite failure as compared to amalgam, but if using composite choose hybrid resin because it has a higher wear and fracture resistance (2). Conservative posterior caries preparations, after 3 years, that used composite with glass fillers had wear rates not significantly different from those of a high-copper amalgam (6). The mean occlusal wear contact for resins is 7 micrometers after 2 years use and for enamel in a premolar is about 29 micrometers (6). This means that a composite resin when produces occlusal forces is producing a strength less than that of