When studying clinical considerations of an existing dental condition, the two alternatives are that either the circumstances are preventive in nature, enhancing the ability of the oral tissues to protect themselves or they are potentially pathologic. Recognizing the difference is important. Not to recognizing a potentially pathologic situation is one thing, but being the cause of it because of ignorance in therapeutic treatment is even worse. Therefore a study of preventive clinical situations is important.
The teeth are encased in a hard, smooth outer covering (enamel) that offers protection from the accumulation of bacteria and debris (plaque). The smoothness of the enamel makes the adherence of plaque more difficult. This self-cleaning ability of the enamel therefore helps resist decay because decay is caused by bacterially produced acids that etch away the tooth surface. If the bacteria cannot accumulate and adhere to the tooth surface, decay cannot occur. Likewise, some prevention of periodontal disease is attributable to the very smoothness of this enamel because bacteria that destroy gum and bone tissue are also prevented from accumulating on the tooth.
However, not all periodontal disease is initially caused by bacteria. If the tooth has rough pits, grooves, or fissures, these areas allow debris to accumulate and provide a breeding ground for bacteria. The same is true if the tooth has rough margins on its restorations or if the tooth interproximally has an overhanging restoration—that is, a restoration that does not stay within the confines of the tooth form but protrudes into the gingival tissue. Bacteria can adhere around the margins of the excess material and lead to disease within the gum and tooth tissues. Restoration of any tooth must follow the normal anatomy of that tooth. A restoration must be polished smooth so that the tooth can resume normal function and the jaw its normal anatomy. Dental personnel provide a valuable service in preventive dentistry by polishing dental restorations. It is much more comfortable for patients to undergo the polishing of their restorations than a replacement (Fig. 9-1).
Rough surfaces on the roots of teeth and extra projections of cementum and calculus can also lead to decay and to the breakdown of periodontal tissues. It therefore becomes extremely important for dental professionals not only to remove calculus and stain from the roots of the teeth but also to smooth any rough areas on the root that may be formed from irregularities in the cementum or defects within the root formation.
This regular root cleaning, which can prevent disease by destroying any plaque-trapping areas that could harbor bacteria, is sometimes called root planing. The dental professional must always remember how thin the envelope of cementum is that wraps around the root. A painful situation occurs when bare dentin is exposed because the cementum is stripped away from part of the root of a tooth.
The hardness of enamel helps prevent occlusal wear or attrition, but this same hardness allows the full impact of trauma to be transferred from tooth to bone. If a tooth prematurely contacts another, only the two teeth will bear the initial brunt of forces when the jaws are closed. A more ideal situation is to have all the teeth hit equally on closure of the jaw, without any teeth hitting prematurely. This allows for the forces exerted to be dissipated over all the teeth. Should one tooth hit with a greater force than the rest of the teeth, it will be traumatized by this excess force. Such a situation is known as occlusal trauma and results in disease of the periodontal tissue, cracking of the enamel of the tooth, and possible fracture of the tooth (Fig. 9-2).
Occlusal trauma can also occur during eating. It is necessary to have spillways between the teeth to allow for the dissipation of forces. This dissipation of occlusal forces occurs because the spillways allow the food to escape from between the teeth.
The contours of the teeth, buccally and lingually, determine the angle at which food is deflected off the teeth and onto the gingiva. If the buccal or lingual contours are underdeveloped (undercontoured), food and debris are pushed into the gingival crevice. If the buccal and lingual contours are overdeveloped (overcontoured), the food and debris pass off the tooth and onto the gingiva at a poor angle. This results in gingival inflammation because the gum tissue is denied proper frictional massage (see Fig. 3-6).
An excess of contour, such as more than 1 mm of lingual contour on mandibular molars, creates an oral hygiene problem. If the tooth contour presents extreme undercuts, the natural cleaning action of the tongue and friction of the food and cheeks become ineffective. Special oral hygiene devices and instructions must be given to the patient.
Because it is very important in the restoration of teeth to reconstruct a tooth in its anatomic form, knowing the anatomic shape of each individual tooth is also important. Contact areas and buccal and lingual contours should also be learned. For instance, an overhanging restoration or an open interproximal contact is undesirable in restoring a tooth in the interproximal area. Measures should be taken to keep the filling material from impinging on the tissue. To prevent such overflow, a metal band is placed around the tooth and wedged into position (Fig. 9-3). This matrix band retains the ma/>