**Chapter 4** Alloplastic TMJ Reconstruction

*Sundaram Ravanasamudram Rajaram, Gauthami Sundar and Rajaram Ravanasamudram Sundaram*

### **Abstract**

Total Alloplastic Temporomandibular joint reconstruction has been the treatment of choice for extreme cases of Temporomandibular Joint Disease and Pathology. Some of the remarkable advantages that are enjoyed with this device are early functional restoration, long term stability and improved jaw function. The prosthesis can be custom made to the particular individual also. This chapter provides an insight of the basics of Total Alloplastic Temporomandibular joint reconstruction which is evidence based.

**Keywords:** temporomandibular joint, alloplastic TMJ reconstruction, TMJ anatomy, comparative anatomy TMJ, 3D reconstruction

## **1. Introduction**

The need for the joint prosthesis comes up with the severity of the joint pathology. Failure of conservative therapies and non-surgical management, and surgical procedures with limited success rates leading to recurrence of the disease form the background for the development of the total alloplastic device for Temporomandibular Joint (TMJ).

The main goal of the reconstruction is to restore the form and function [1] of the jaw. In the yesteryears, Autogenous bones were used in most cases of Temporpmandibular Joint Reconstruction (TMJR). Revision surgeries in cases of TMJR with costochondral grafts need to be considered keeping in mind its excessive growth potential. The autogenous bone in growing individuals pose significant risks that may impair the jaw anatomy and function on a long run frequently leading to readdressing the joint problem. Innumerable evidence now exists in favour of the total joint replacement procedure where the joint anatomy and function being restored focussing more on the Biomechanical aspects [2].

Emerging studies support TMJR in terms of improved quality of life, improved masticatory function, improved jaw movement, speech and anatomy [3–5].

The device is made up of Cobalt-Chrome-Molybdenum (Co-Cr-Mo) or Titanium (Ti) condylar components with ultrahigh molecular weight polyethylene (UHMWPE) owing to their inert and bio friendly nature. These implants are available as stock fit and custom made that are patient specific.

On reviewing the literature, in the field of alloplastic TMJR, is interesting in that in 1974, Kiehn et al. attempted to construct an alloplastic TMJR prosthesis which was based on the principle used for total hip replacement with vitallium fossa and condyle unit.

In 1982, the vitek- Kent proplast—Teflon (PT) containing process was created (Vitek, Inc., Houston, Texas). What was initially successful was found to be a failure in a long run. In 1989 custom fit total TMJR system based on CAD CAM data was introduced by Techmedia that continues to be successful as of now [6].

In any TMJR, to be successful, some of the biological and mechanical characteristics are to be considered [7–9].


#### **1.1 Comparative anatomy pertaining to TMJ**

The TMJ of mammals is different from other vertebrates, interestingly for functional modifications in that the articulating disc arose as a tendon which became pinched by the joint that is originated by intramembranous bones. Hence the growth depends on cartilaginous structures [10–12].

The TMJ anatomy size, shape, type of movements, and the load that it can take are species specific such as loss of synovial cavities in whales, loss of primary absence of disc in marsupials (sloths), variation in orientation of joint cavity in rodents, reversal of usual convex concave relationship to turn the mandibular condyle into a female element in sheeps and cattle, size variation and higher loading or lower loading depending on its pre requirement. Eg: crocodiles [13].

Sliding or side to side movement is also a variant. Considering all the animals, the human being's TMJ anatomy has the most evolved anatomical structures for efficient masticatory function for present day.

#### **1.2 Anatomy of TMJ**

The TMJ is a synovial joint of condylar variety [14]. It is also known as ginglimo arthrodial joint. It has two compartments namely the upper joint space and lower joint space lined by cartilaginous cells and divided by a fibrocartilaginous disc.

The upper bony component is formed by the temporal bone and the lower articulating joint is formed by the head of the condylar process of the mandible. The joint cavity is encapsulated by a fibrous capsule that is filled with the synovial fluid. The disc is held in position by the discal ligaments and the lateral pterygoid insertion.

This attachment leads to certain disorders like clicking joint and so on and so surgical anatomy of TMJ should be studied at length before analysing the pathology.

The ligaments supporting the TMJ can be classified into intracapsular and extracapsular.

The intracapsular ligaments are the capsule, the interdiscal ligaments.

The extracapsular ligaments are the ligament of TMJ, stylomandibular ligament and sphenomandibular ligament.

## **1.3 Freakishness of TMJ**

Anatomical considerations of freakishness of TMJ [15] pertaining to healing of alloplastic reconstruction are interesting in that these qualities are not met with in other joints of humankind.

Non weight bearing aspect of TMJ is peculiar. The function of TMJ on one side depends considerably on the health of other side TMJ and occlusal apparatus. This tripartiate relationship is very useful at times and also troublesome while treating TMJ pathologies with alloplastic TMJR.

Abundant vascular supply for the TMJ is any another unique feature. What triggers excellent tendency to heal in comparison with other joint procedures is yet not clearly understood so the whole focus in alloplastic grafting is to limit excessive post-surgical ankyloses to make it success.
