Dental inlays and onlays

Introduction and basic concepts

The process of dental inlay prosthetics has its own specific features. It is important to note that the sequence of clinical and laboratory stages may vary. First of all, such changes depend on the chosen restorative material — this is especially relevant when porcelain or metal-ceramic inlays are planned.

The basis for creating a precise micro-prosthesis is the wax pattern. In dental practice, there are two fundamentally different ways to obtain such a wax reproduction:

1. Direct method — the dentist shapes the wax component directly in the patient's oral cavity, working on the natural tooth.
2. Indirect method (also known as the indirect or reverse method) — the modeling is transferred to the dental laboratory and performed on a working cast.

Advantages and disadvantages of the direct method

The main advantage of the direct method is the highest accuracy in recording functional occlusion. Since the dentist models the inlay directly on the natural tooth in the oral cavity, it can be perfectly adapted to the antagonistic teeth. The second important advantage is the ability to strictly control the margins of the future inlay. The dentist clearly sees the edges of the prepared cavity, especially in the critical gingival margin zone. Such control serves as reliable prevention of traumatic periodontitis.

Despite its advantages, the direct method has a considerable list of disadvantages:

• Patient discomfort. Prolonged stay in the dental chair with an open mouth causes severe fatigue.
• Risk of injury. There is a real danger of thermal burns to the oral mucosa. The dentist works with hot wax and a heated modeling instrument.
• Complexity of work. It is extremely difficult to model wax in interproximal spaces (especially in Black's class II–IV cavities).
• Loss of time. There is an inefficient waste of the dentist's clinical time on a procedure that could be performed by a dental technician.
• Qualification requirements. The method requires special training from the doctor, high manual skills, and their constant practice.
• Risk of remaking. If the wax deforms upon removal from the cavity or if the metal casting fails, the entire intraoral modeling process must be started over.
• Increased adjustment time. There is no possibility to pre-fit the finished inlay on the working plaster model, which significantly increases the time required for its adjustment in the patient's mouth.
• Technological limitations. With the direct method, it is impossible to apply methods to compensate for metal shrinkage. In particular, it is not possible to selectively coat the walls and bottom of the plaster model with a die spacer to provide the necessary clearance for the luting cement.
• Course duration. In case of multiple tooth preparations, the process is inevitably split into several visits.

Indications for method selection

The choice between the direct and indirect methods is strictly regulated by the clinical picture.

The direct method is considered appropriate in the following clinical situations:

• Restoration of teeth with defects exclusively on the occlusal surface.
• Restoration of teeth with cervical surface defects.
• Modeling of an artificial tooth crown core fitted with a post (fabrication of a cast post and core).

The indirect method is indicated in more complex cases requiring good visibility:

• For crown defects of molars and premolars involving multiple surfaces: MOD (mesio-occluso-distal), MO (mesio-occlusal), and OD (occluso-distal).
• For defects of contact surfaces of the anterior group of teeth (incisors and canines), regardless of whether the incisal edge is involved.
• When prosthetically treating several adjacent teeth with inlays simultaneously.
• When restoring the anterior group of teeth using combined inlays.

Important note: When modeling in interproximal spaces, preference is always given to the indirect method. The removable plaster cast provides the dentist and technician with better visual control over the process.

Initial stages of direct modeling

If the clinical situation requires the use of the direct method, the dentist proceeds to work directly in the oral cavity. The initial stages of the inlay modeling technique include a strict sequence of actions:

1. Medication treatment. The prepared tooth cavity undergoes thorough rinsing. A hydrogen peroxide solution is used for this purpose.
2. Material preparation. The dentist takes a stick of special modeling wax and carefully heats it to a plastic state.
3. Wax insertion. The warmed and softened wax is forcefully pressed into the prepared tooth cavity, filling all its areas.
4. Cooling. The inserted wax is cooled to set its shape (subsequent stages of the technique involve extracting and processing the resulting pattern).

Class and exam questions

What else to study on this topic

• Features of prosthetics with porcelain and metal-ceramic inlays.
• Technique for safely removing the wax pattern from the oral cavity without deformation.
• Methods for compensating metal shrinkage on plaster models.
• Continuation of the clinical stages of direct modeling (after wax cooling).
• Features of shaping MO, OD, and MOD cavities for dental inlays.

Other topics in the "Additional Topics" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.