Approaching modern materials

Perhaps the greatest challenge facing the restorative dentist is keeping up with the myriad of materials that are ever changing within the walls of a dental practice. How a dentist decides on what material will be used in any given situation varies tremendously from practice to practice. Many times the source of expertise for this decision may come from a dental laboratory or a supplier. While it is important for the doctor to collaborate with the dental laboratory and to have relationships with manufacturers, it is far better for the clinician to have a thorough understanding of the advantages of the specific materials, and align the best material with each clinical reality. This article is designed to establish a guide for restorative dentists to establish a programmed approach to restoration selection within their restorative practice.

The concept of risk assessment

Before a clinician can choose a material, a thorough clinical examination must be completed. Then and only then can the signs of occlusal instability as well as the patient’s esthetic demands be assessed.

Functional risk: While it is true that the proper management of the occlusion is the most important factor in increasing the lifespan of the restoration, aligning the best material for the patient also  is hugely important. Functional risk is directly related to occlusal disease. Thankfully if the patient in question has malocclusion or parafunctional issues, the evidence can be found in his or her mouth. Patients who present with worn teeth, mobile teeth (in the absence of periodontal disease), or have teeth that are actively migrating are all showing signs of instability. The greater the “sign,” the greater the functional risk, the greater the need to pay meticulous attention to detail with the occlusal design, and the greater the need to use the strongest materials possible.

Esthetic risk: While determining esthetic risk is more subjective than functional risk, it is equally important to consider when choosing a restorative material. Factors affecting esthetic risk are lip hypermobility, cosmetic motivation of the patient and the degree that the shade needs to be shifted while maintaining translucency. Patients who don’t show a lot of teeth and are motivated by disease-based needs are far different than patients with a high smile line. They are pursuing dental care based on a want to change their appearance. The key is to align the most appropriate material with each patient’s specific esthetic demands.

Quality and quantity of remaining enamel and dentin: If a restorative dentist chooses a restorative material that relies on a total-etch adhesive process, it is critical that the quality and quantity of remaining enamel and dentin be considered. While maximizing the bond to enamel is important, dentin that has eroded through bulimia or GERD should be avoided. Clinical situations that will comprise an ideal adhesive process should be avoided, and a restoration that allows for conventional cementation should be considered.

Need for 100% isolation: Certain porcelain materials require 100% isolation to perform a total-etch adhesive process. Prior to selecting a material for the patient, any clinical area should be evaluated for ease of rubber dam placement and optimum isolation. If isolation appears impossible, consider a material that can be conventionally cemented.

Restoration options

> Stacked Porcelain

Bonded stacked feldspathic porcelain veneers have been popular since 1983. This relatively fragile ceramic gains its fracture strength from the support of the underlying tooth structure through bonding. If strict attention to detail is paid during preparation and the adhesive process, the restorations will be equal in strength to enamel. It is an excellent choice in high esthetic risk, low functional risk situations.

• Fracture Strength -90 MPa (fracture strength of enamel is 50 MPa)

• The base (glass matrix) of most high-strength ceramics

• Cementation-must be bonded in place

• Unlimited shade selection, unlimited translucence

> Pressed Leucite Reinforced Ceramic

Ceramics reinforced with leucite have been popular since the early 1990s. The reinforcement of the ceramic resulted in a 60% increase in strength over the traditional feldspathic restoration. While initially fabricated through a “pressed” process, it is now possible to mill this material through a CAD/CAM process. It is an excellent choice in high esthetic risk, moderate-to-low functional risk situations.

• Fracture Strength -140 MPa-60% increase in strength over stacked porcelains.

• Excellent translucence and shade selection

• Cementation-must be bonded in place

> Milled or Pressed Lithium Disilicate (layering technique)

Lithium disilicate restorations were introduced in the late 1990s and are 2 to 3 times stronger than leucite reinforced porcelain (360-400 MPa). They can be fabricated with the pressed technique or CAD/CAM milling procedure. For optimum esthetics, the lithium disilicate core is pressed or milled, and then feldspathic porcelain is layered to finish the restoration. It is an excellent choice in high esthetic risk, moderate functional risk situations.

• Fabrication-press or milled (CAD)

• Fracture strength-360-400 MPa, 4 X stronger than feldspathic, 2 X stronger than leucite reinforced.

• Cementation-conventional cementation for crowns and bridgework, bonding adhesion for veneers

> Milled or Pressed Lithium Disilicate (monolithic technique)

Recent studies at New York University have shown a marked increase in strength when a lithium disilicate restoration is pressed or milled to full contour and then a stain and glaze technique is used to finish the restoration. This is an excellent choice in the moderate-high esthetic risk, moderate-high functional risk situation.

> Zirconia Based Restorations

These high-strength zirconia restorations are created via CAD software. Out of all the all-ceramic options, the restorative procedures of preparation and delivery most closely mimic the familiar porcelain-fused-to-metal restorations. Because of this, they are very attractive to the restorative dentist. To achieve maximum strength, the lab must design copings to appropriately support a uniform thickness of the layering porcelain. It is an excellent choice in moderate-high esthetic risk, moderate-high functional risk situations.

• The ability to be cemented with any type of adhesive or conventional cement

• Preparation design similar to porcelain fused to metal

• Fracture toughness greater than 900 MPa, which can support both single-unit and long-span restorations (bridgework)

> Porcelain Fused to Metal

While porcelain fused to metal has stood the test of time, it takes a lot of tooth reduction and a very talented ceramist to create an optimum esthetic result. While all-ceramic materials allow varying amounts of light to pass through the ceramic material, the metal coping and overlying opacious porcelains of the PFM kills light transmission. This material is ideal for patients with a moderate-to-high functional risk, and low-to-moderate esthetic risk.

> Cast Gold

It is not surprising that cast gold is the standard that all other materials are compared to when it comes to longevity. It is the restoration of choice in high functional risk situations when esthetics is not a concern.

Make the right choice?

Choosing the best material for each clinical situation is one of the greatest challenges the restorative team faces. As clinicians, it is imperative that we take the time to study the advantages and disadvantages of the materials that are available to us. By doing a proper risk assessment of the patient, combined with using the functional-esthetic grid, the restorative team should be able to choose an excellent restorative material in any clinical situation.