Restorative Dentistry

17
Restorative Dentistry


Anthony Caiafa1 and Louis Visser2


1 School of Veterinary and Biomedical Sciences, James Cook University, Townsville, Queensland, Australia


2 Arizona Veterinary Dental Specialists, Scottsdale, AZ, USA


17.1 Introduction


Operative dentistry is that field of dentistry concerned with restoring defective areas of vital and non‐vital teeth back to normal masticatory function, periodontal health, and esthetics. Defects can be due to disease, infection, trauma, or abnormal development. Operative dentistry includes the application of material and instrument science in the treatment planning and restoration of the teeth.


17.2 Restorative Terminology


Many areas and concepts of restorative and prosthodontic therapy overlap (see Chapter 18 – Crowns and Prosthodontics), with other basic terminology covered in Chapter 1 (Oral Anatomy and Physiology). Specific terms relevant to restoration are covered here:



  • Enamel prisms. Basic keyhole‐shaped enamel units running from the dentinoenamel junction to the surface of the tooth.
  • Contact point. The point or area of contact between the proximal surface of one tooth to the proximal surface of the neighboring tooth. For incisor teeth, the contact point tends to be closer to the incisal margin, whereas in caudal teeth, the contact point is more apical.
  • Embrasures. V‐shaped spaces located between the proximal surfaces of adjacent teeth and located both incisally/occlusally and apical to the contact point of two teeth. Applicable to incisors and caudal teeth.
  • Biologic width [1]. The combined width of the connective tissue and the epithelial attachment to the tooth above the crestal alveolar bone.
  • Undercut. A designed feature of a restorative preparation created by removing a portion of the dentin within the preparation for the intention of providing retentive qualities to a restoration. Often used for retention of amalgam restorations.
  • Overhang. An excess of restoration projecting beyond the parameters of a preparation margin resulting in a projection or shoulder. Overhangs can lead to accelerated periodontal disease.
  • Flashing. Restorative that extends beyond the preparation outline, but when initially placed does not cause an overhang.
  • Sealer. A cavity sealer is a material that seals the dentinal tubules and provides a protective coating for the freshly cut tooth structure of the prepared cavity.
  • Liner. A cavity liner is an aqueous or volatile organic suspension or dispersion of zinc oxide or calcium hydroxide that can be applied to a cavity surface in a relatively thin film. Glass‐ionomer cement (GIC) and resin‐modified glass ionomer cement (RMGIC) are also suitable for use as lining materials.
  • Base. A cavity base is a material, usually a type of cement, used to base a prepared cavity before the insertion of a permanent restoration, to protect the pulp and act as a dentine replacement. RMGICs are popular choices here.
  • Pin. A metal pin or wire cemented or threaded into the dentin at a preparation site to aid in retention of a restoration.
  • Post. A cylindrical metal or fiber rod cemented or threaded into the root canal system as a retentive device for a core or post and crown. Posts are used to support the crown core.
  • Core. A direct or indirectly made substructure for a crown, which may be part of a post and core system.

17.2.1 Surfaces of Teeth [2]


When describing a cavity or restoration, the location can be described by the surfaces of the tooth that are involved. These are as follows:



  • Mesial. Nearest to the midline of dental arch
  • Distal. Further from the midline of dental arch
  • Labial. Next to lips (anterior teeth)
  • Buccal. Next to cheeks (posterior teeth)
  • Lingual. Next to tongue (lower teeth)
  • Palatal. Next to palate (upper teeth)
  • Incisal. Cutting edge of anterior teeth
  • Occlusal. Chewing surface of posterior teeth.

17.2.2 Classifications of Cavities and Restorations


In order to properly treat lesions, they are best classified as to the tooth involved, type, and extent of lesion. Individual tooth identification systems can be found in the chapter on oral examination (see Chapter 2 – Oral Examination and Diagnosis). The following are some of the more common tooth pathology classifications dealing with type and extent. Classification by location includes the G.V. Black Modified Cavity Preparation Classification system (Table 17.1 and Figure 17.1), the Elementary Cavity Class, and the Practical Cavity Classifications.


Table 17.1 G.V. Black modified cavity preparation classification system.



























Class I I, PM, M Beginning in structural defects, such as pit or fissure, commonly found on occlusal surfaces (occlusal lesions)
Class II PM, M Proximal surfaces; when a tooth with a class 2 lesion includes a class 1, it is still considered as class 2 (proximal surfaces posterior/caudal teeth)
Class III I, C Proximal surfaces, incisal angle not included (proximal surfaces anterior/rostral teeth)
Class IV I, C Proximal surfaces, incisal angle included (proximal surfaces anterior/rostral teeth involving the incisal angle)
Class V I, C, PM, M Facial or lingual, gingival third; excluding pit or fissure lesions (cervical surfaces)
Class VI I, C, PM, M Defect of incisal edge or cusp; not included in Black’s original classification.

Note: There may also be two separate lesions present on the same tooth (i.e., Class II, Class V) or a combination lesion where two locations are present and contiguous (i.e., Class II/V).

Image described by caption.

Figure 17.1 (a) The modified G.V. Black lesion and cavity preparation classification system (illustration by Anthony Caiafa adapted from the First Edition). A: Class I – lesions beginning in pits, fissures, or developmental grooves of teeth (from left to right): developmental groove on the lingual surface of an incisor; pits and fissures on occlusal surfaces of premolar and molars; buccal surface developmental groove of maxillary fourth premolar. B: Class II – lesions of the proximal surfaces of premolars and molars. C: Class III – lesions of the proximal surface of an incisor or canine tooth. D: Class IV – lesions at the proximal surface of an incisor or canine tooth that involves an incisal edge. (b) E: Lesions on labial, buccal, or lingual surfaces of an incisor, cuspid, premolar, or molar. F: Lesions of the incisal edge or cusp tip (illustration by Anthony Caiafa adapted from the First Edition).


17.2.2.1 Elementary Cavity Class [3]



  • Simple. Involving only one tooth surface.
  • Compound. Involving two tooth surfaces, when prepared.
  • Complex. Involving three or more tooth surfaces, when prepared.

Practical Cavity Classification [3] (Note that descriptions with “facial” are more appropriate for human dentistry):



  • O – Occlusal
  • MO – Mesio‐occlusal, or the mesial and occlusal surfaces
  • DO – Disto‐occlusal
  • MOD – Mesio‐occluso‐distal
  • B – Buccal
  • L – Lingual
  • F – Facial (labial or buccal)
  • I – Incisal
  • DI – Distoincisal
  • MI – Mesioincisal
  • MID – Mesioincisodistal
  • DL – Distolingual
  • ML – Mesiolingual
  • MLD – Mesiolingodistal
  • MF – Mesiofacial
  • DF – Distofacial
  • MFD – Mesiofaciodistal.

17.2.3 Dental Fracture Class


The American Veterinary Dental College (AVDC) Nomenclature classification of dental fractures can be found in Chapter 6 (Traumatic Dentoalveolar InjuriesTDI), along with discussion of expanding these descriptions to include root fractures, luxation, and alveolar injuries [4]. A previously used staging classification is listed below, but it is recognized that a more complete nomenclature listing may be needed. This more inclusive system would identify fractures into the enamel (Stages 1 and 8 below), enamel–dentin fracture (Stages 2 and 8), enamel‐dentin‐pulp fracture (Stages 3, 4, and 9), root fractured and displacement/avulsion (see Chapter 6 – TDI). Additional classification of tooth resorption (TR) can be found in Chapter 20 – Domestic Feline Oral and Dental Diseases. Generally, these TR lesions are not restored.


17.2.4 Staging of Tooth Injuries [5, 6]


These are generally referred to as stages and are used in combination with Black’s Modified Classification of tooth lesion locations (classification by extent of pathology).


Stage:



  1. Simple fracture of the enamel.
  2. Fracture extends into the dentin.
  3. Fracture extends into the pulp chamber; pulp vital.
  4. Fracture extends into the pulp chamber; pulp non‐vital.
  5. Tooth displaced.
  6. Tooth avulsed.
  7. Root fracture; no coronal involvement; tooth stable.
  8. Root fracture; combined with stages 1–2 coronal fracture; tooth stable.
  9. Root fracture; combined with stage 3 coronal fracture; tooth stable.
  10. Root fracture; in combination with stages 1–4; unstable tooth.

17.2.5 AVDC Dental Abbreviations – Restorative AVDC Nomenclature


See Table 17.2.


Table 17.2 AVDC abbreviations – restorative (www.avdc.org/traineeinfo.html; accessed 25 October 2017).






















































































AB Abrasion
AT Attrition
C Caries
DP Defect preparation (prior to filling a dental defect)
E Enamel
E/D Enamel defect
E/H Enamel hypoplasia
E/HM Enamel hypomineralization
PCB Post‐and‐core buildup
PCD Direct pulp capping
PCI Indirect pulp capping
R Restoration (filling of a dental defect)
R/A Filling made of amalgam
R/C Filling made of composite
R/CP Filling made of compomer
R/I Filling made of glass ionomer
T/FX Tooth fracture
T/NE Tooth near pulp exposure
T/PE Tooth/pulp exposure
Other abbreviations that may be found:
DB Dentin bonding agent
P&F Pit and fissure
P&FS Pit and fissure sealer
SI Staining, intrinsic (blood, tetracycline, etc.)
SE Staining, extrinsic (metal, food etc.)
VBL Vital bleaching
NVBL Non‐vital bleaching
VER Veneer

17.3 Dental Defense Mechanisms


In human dentistry, dentinal and pulpal inflammation and pain responses are considered to be some of the first diagnostic indicators of pathology and initiators of the dentinal defense mechanism [7]. In animal patients the pain response is not as useful due to the fact that responses may be challenging to elicit.


17.3.1 Successful Dental Defense Mechanism Sequence



  1. Pain (sensible dentin).
  2. Pulpitis (reversible).
  3. Blockage of tubule with material from dentinal fluid or odontoblast.
  4. Mineralization of material at exposed dentinal tubule surface and apertures.
  5. Formation of sclerotic or tertiary (reparative) dentin at the site.

17.3.1.1 Pain


In order to understand the pain response of the tooth and its defense mechanism, a fundamental knowledge of the dentinal tubules and pulp is required. There are approximately 30 000–40 000 dentinal tubules per square millimeter of surface dentin [7]. In most domestic animals the odontoblastic process extends 0.2–1.5 mm into the dentinal tubule. In addition, there may be an afferent nerve fiber extending into the tubule 0.1–0.4 mm from the pulp. These fibers are sensory nociceptors, either A‐delta or C‐type fibers. A‐delta fibers are larger in diameter, are myelinated, and conduct nerve impulses more rapidly. They typically cause a rapid, sharp type of pain, often associated with a level of pulpitis that is still reversible. C‐type fibers are myelinated, have a smaller diameter, conduct impulses more slowly and elicit dull aches, as found in late pulpitis. As the response to thermal stimuli intensifies, the pain lasts well after the stimulus is removed. This inflamed pulp undergoes an irreversible change (irreversible pulpitis leading eventually to pulp necrosis). The tooth then will respond markedly to hot stimuli with cold stimuli potentially having a soothing effect on the tooth (an ice pack now relieves the pain).


If a tooth responds to pain, it is said to have sensible dentin, which can provoke pulpal inflammation or pulpitis. While the presence of sensible dentin implies that a tooth is still vital, it does not necessarily indicate if the pulpitis is reversible or irreversible. Insensible dentin is generally indicative of a non‐vital tooth [8] , though there can be areas of dentin in which there are no neural fibers in the tubules to elicit a pain response [9]. This can result in an insensible dentin response in a healthy vital tooth. It is interesting to note that while the afferent nerve endings respond to a variety of stimuli (temperature, pressure, etc.), the perceived sense is one of pain.


In addition to the fibers, a dentinal tubule is filled with dentinal fluid, making it a hydrodynamic organ. Capillary permeability and blood pressure in the pulp results in intrapulpal pressures of 15–30 mmHg. The outwardly directed pressure gradient of the pulpal fluid gently drives it into the dentinal tubules, around the odontoblasts and nerve fibers, to become dentinal fluid. A slow outward flow of water and small molecules occurs through the dentinal tubules, even in areas covered with intact enamel or cementum, as these structures are permeable. If a dentinal tubule’s surface is exposed, the flowrate could be around 1 mm per hour [9].


A series of studies described by Brannstrom provided evidence that the main cause of dentinal pain is a rapid outward flow of fluid in the dentinal tubules that is initiated by strong capillary forces [10]. Cold stimulus caused a rapid outward flow of fluid at the pulpal end of the dentinal tubule, whereas heat stimulus caused a rapid inward flow of fluid. Rapid capillary action can also be caused by surface dehydration, friction (venturi effect), or fluid contraction. This fluid flow, although being insufficient to displace odontoblastic processes within the dentinal tubules, was sufficient enough to stimulate the sensory nerve endings in the underlying pulp dentin border zone [10].


Within the pulp are distinct cell zones, each with a specific function in healing. The cell layer closest to the tubules is the odontoblastic cell layer or primary cell layer. Next, there is a cell free zone, followed by a subodontoblastic cell‐rich zone or secondary cell zone (layer of Höhl) [7].


The primary layer of odontoblasts is a highly differentiated group of sensitive cells. These cells can be easily killed by toxins defusing through open tubules or from aspiration during rapid capillary action. A new generation of odontoblasts can come from the subodontoblastic cells, fibroblasts, undifferentiated mesenchymal cells from the pulp core, and vascular‐derived pericytes. These cells are more tolerant of toxins and can traverse the cell‐free zone to differentiate into odontoblasts. These newly differentiated cells can lay down new layers of reparative (tertiary) dentin to block the apertures of the dentinal tubules [11].


17.3.1.2 Pulpitis


Pulpal inflammation, in association with sensible dentin, is the early defense mechanism for the tooth’s endodontic system [12]. In slight pulpitis, symptoms may not be apparent, but as the reactions increase, the healing sequence may be stimulated. Severe pulpitis may develop when profuse amounts of toxic products reach the pulp, accompanied by an excessive immunologic reaction, ultimately leading to pulpal necrosis [7]. Additionally, if the inflammatory or immune response is too weak or absent, the subsequent infection may result in liquefaction necrosis and pulpal death [12]. In mature teeth the pulp cavity is more narrow with a limited blood supply, with few, if any, undifferentiated mesenchymal cells left in a depleted cell‐rich zone of the pulp. These can limit the pulp’s ability to respond to disease [7].


17.3.1.3 Reparative Dentin


When tubules are exposed on the surface due to injury, disease, abrasion, attrition, scaling, or root planing, material may accumulate at the surface aperture and eventually mineralize [8]. Materials such as dentinal fluid, salivary substances, fluorides, some lithotropic bacteria, and other substances accumulate at the aperture and then mineralize in a fashion similar to that of plaque mineralizing into calculus [7, 13]. However, in some cases, continued attrition or abrasion may prevent the tubules from being protectively sealed in this fashion. In these cases, removal of the continued source of wear and some form of dentinal sealer can be used to rectify the problem, or more advanced restorative procedures performed (inlays, onlays, crowns, etc.).


Sclerotic dentin is more highly mineralized, with tubules being obliterated as they are filled with additional mineralization [7]. This process is similar to the surface mineralization, but extends well down into the tubule. For this to occur the odontoblast must have been lost, leaving a dead tract (unoccupied tubule). Tertiary (reparative or irregular secondary) dentin then forms at the tubule access, after which the sclerotic dentin can form [12]. Sclerotic dentin can also form in pulpless non‐vital teeth, although it may take more time [7]. It is seen in many older patients on exposed root surfaces as a highly translucent root dentin. Clinically, it is more difficult to bond a composite resin restoration to this type of dentin.


Tertiary dentin is of two types, either reactionary, where dentin is formed from a pre‐existing odontoblast, or reparative, where newly differentiated odontoblast‐like cells are formed due to the death of the original odontoblasts, from a pulpal progenitor cell [11]. Tertiary dentin is deposited rapidly, often with a sparse and irregular tubular pattern. It sometimes contains cellular inclusions within its structure (osteodentin). This provides a positive effect to seal the pulp cavity from invasion by toxins and microbes. However, it should also be realized that reparative dentin can also have negative effects [14]. To begin with, it can result in a response that causes no pain, therefore not stimulating the endodontic immune system to mount a response to impending disease. Second, it can result in a reduced pulp canal, which can cause problems when accessing, or in instrumentation of the pulp chamber and canal when performing endodontic procedures.


17.4 Basic Concepts of Restorative Procedures


When a defect occurs in the hard tissues of the tooth (enamel, dentin), optimally it is best to preserve the function and structure of the object by restorative means. It is essential to know basic components of restorative efforts before undertaking therapy, including knowledge of cavity preparation, from skills involved to the final preparation that is required. These rules include conservation, esthetics, contours and contacts, cavity preparation, and identification with resolution of the cause.


17.4.1 Conservation of Natural Tooth Structure


The conservation of natural tooth structure is the first rule of operative dentistry [3]. Conservation of tooth structure is essential for protection of the vital pulp. However, not only must the depth of preparationbe considered but also the size of the area. There are 30 000–40 000 odontoblasts per millimeter of dentinal surface area [7]. Therefore, a one‐centimeter squared preparation into the dentin will injure between three and four million odontoblasts in the pulp cavity, by severing off some degree of their processes or Tomes fibers. The degree of injury determines whether the individual odontoblasts become non‐vital. Crown preparation for a full coverage on a vital tooth will injure and irritate all of the odontoblasts in the crown pulp chamber. The more odontoblasts irritated, the more the pulp will be irritated.


17.4.2 Esthetics


Natural, healthy, unmarred enamel that is supported by health dentin, pulp, and periodontium is the most esthetically pleasing. Therefore, the conservation of these healthy tissues is the best esthetic outcome possible. However, when tooth structure fails, esthetic restorative procedures come into play. The functional and esthetic outcome desired by the owner will then dictate the design of the operative preparation.


17.4.3 Contours and Contacts


A good general knowledge of dental anatomy is required to understand the physiology and function of tooth crown contours (see Chapter 1 – Oral Anatomy and Physiology). Contact areas, marginal form, and the buccal and lingual contours must be properly designed to reduce food impaction during mastication. Typically, contact areas should be restored to the condition that was present when the tooth was young and healthy. Restoration of the axial contours (buccal bulge, etc.) should be performed to protect periodontal health.


17.4.4 Cavity Preparation


See later in the chapter.


17.4.5 Identification and Resolution of Cause


If the cause of the disease can be ascertained, steps should be taken to relieve it and prevent it from recurring. Long‐term success of any restoration will be in doubt if the cause cannot be identified and resolved. This is important when dealing with pets that have habits such as chewing on cages, rocks, or sticks. In police, military, and protection trained dogs the source of the trauma can usually be identified, but not removed. In the required continuing bite training, the reinforced bite sleeve can sometimes cause damage, as well as actual on‐duty activity. If the bite sleeve caused an injury, it should be examined to determine if it can be modified or improved to reduce the probability of a recurrence of the injury. Dogs with a strong grip and rotational apprehension methods can break the teeth subgingivally.


Abrasion patterns of incisors can be seen with atopic dogs, so dermatologic interventions may be needed. Any object that is non‐compressive or non‐bendable can cause tooth fractures with heavy chewing, especially of the carnassial teeth. Items with cloth or fibrous coverings can be extremely abrasive, especially if allowed to collect dirt or sand on surfaces. Play (or serious) fighting with other dogs or games of tug‐of‐war can also cause injuries to incisors and canine teeth


17.5 Treatment Planning


Treatment planning requires a systematic approach to assess the structures and associated problems that may challenge treatment success. A close study of existing conditions that have led to the problem is required. It should be determined if modification in behavior, environment, or a combination of both is required. Additionally, the patient’s occlusion and periodontal health must be taken into consideration to optimize success [3]. The tooth structure must be evaluated for the ability to sustain a load, its relative retentive qualities, and esthetic requirements.


17.5.1 Components of Prepared Cavities


Various walls, lines, and angles are created during cavity preparation. The following terms are used to identify the various components of a cavity prepared for restoration.


An enclosing side of a prepared cavity is termed a wall. The wall is named in relation to the tooth surface of which it is formed. There are two internal walls possible, the axial and pulpal walls. The axial wall is the internal wall formed by the surface of the long axis (axial or vertical plane) of the tooth. The pulpal wall is the internal wall in the horizontal plane (Figure 17.2).

Class II cavity prep walls with lines indicating the external walls with consists of the distal, facial, lingual, and gingival walls; pulpal and axial on the internal walls; and cementoenamel junction (CEJ).

Figure 17.2 Class II cavity prep walls – the external and internal walls (floors) for an amalgam tooth preparation. From: pocketdentistry.com/5‐fundamentals‐of‐tooth‐preparation‐and‐pulp‐protection. Reproduced with permission.


There are numerous non‐internal wall surface potentials in a cavity preparation. Some of these are:



  • Distal wall
  • Mesial wall
  • Buccal or labial wall
  • Lingual wall
  • Incisal wall
  • Occlusal wall
  • Gingival or apical wall
  • Facial (buccal or labial) proximal (mesial or distal) wall
  • Lingual proximal (mesial or distal) wall

Additionally, there are a few subdivisions of the walls, such as the enamel and dentinal walls. The enamel wall is that portion of the preparation wall that consists of enamel. The dentinal wall is that portion of the wall that consists of dentin. The dentinoenamel junction is that juncture in the wall where the dentinal and enamel walls meet.


Where two walls meet a line angle is formed. At the point where three walls meet a point angle is produced (Figure 17.3). The cavosurface angle is the line angle formed between a wall of the prepared surface and the unprepared tooth surface. The cavosurface angle is also sometimes termed the preparation margin, especially once the preparation is restored. The combined peripheral extent of all of the cavosurfaces or preparation margins is termed the cavity or preparation outline. In dealing with restoratives, the restorative margin is the restorative surface that abuts the cavosurface angle or preparation margin.

Diagram illustrating common line and point angles in a prepared cavity. Left: Lines indicate mesioaxial line angle, distoaxial line angle, etc. Right: Lines indicate cusp point angle, mesiogingivoaxial point angle, etc.

Figure 17.3 Common line and point angles in a prepared cavity (illustration by Anthony Caiafa adapted from the First Edition).


17.5.2 Preparation of Cavosurface Angles or Marginal Finish Lines


Design of the cavosurface angle requires special consideration in its preparation. The preparation marginal restoration greatly affects retentive qualities of the restoration, resistance to marginal leakage, physiologic contour reactions, gingival health, and resistance to attrition, abrasion, and fracture of the restoration and restored tooth. Selection of the specific cavosurface angle treatment is dependent upon the type of restoration selected, restorative materials to be used, degree of anticipated stress demand upon the restoration, and the length and direction of the enamel prisms (Figure 17.4).

Image described by caption.

Figure 17.4 Basic types of marginal finish lines used on gingival cavosurfaces: (a) short bevel; (b) long bevel; (c) full bevel or chisel; (d) slight bevel or shoulder; (e) occult or reverse feather finish line; (f) knife or feathered edge; (g) chamfer; (h) deep chamfer; (i) butt joint (illustration by Anthony Caiafa adapted from the First Edition).


17.5.3 Modern Cavity Preparation


The mechanical cavity preparation involves the removal of defective, injured, or infected enamel and/or dentin. Affected (not infected) dentin is preserved. The cavity is then filled with a suitable restorative material that will reestablish the health, function, and often the esthetics of the tooth as well as its contour and shape. Minimal intervention dentistry has taken over from G.V. Black’s old philosophy of extension for prevention. However, G.V. Black’s other ideas on cavity design and tooth preparation are still relevant today [15]. Today, minimal intervention dentistry or conservative cavity preparation is designed to preserve as much healthy tooth structure as possible, only limited by access to diseased tissues and dental material requirements. This philosophy is the goal of restorative clinicians around the world.



Modern cavity preparation and design and the evolution thereof cannot, or perhaps should not, be considered without reference to G.V. Black. Black’s text A Work on Operative Dentistry in 1908 was the first to prescribe a systematic method of cavity preparation and the ‘ideal’ cavity form [15].


Multiple factors must be taken into consideration prior to the design of the preparation outline being implemented upon the tooth, including location, extent, stresses, tooth condition, and esthetics. First, the classification by location by G.V. Black or similar classification is required. This classification will then direct certain biological mechanical principles to be applied. Next, classification by extent is a necessity. This usually does not overtly affect the cavity outline, but more the depth of preparation. This in turn determines whether cavity liners, indirect pulp capping, direct pulp capping, or root canal procedures will be required. Third, the occlusal and leverage stresses that must be encountered must be carefully studied. This impacts the types of restorative materials used and whether occlusal height of the crown should be reduced to diminish occlusal and leverage stresses. Four, the general condition of the tooth, including the presence of other restoratives currently in place or to be placed, must be contemplated. Finally, the esthetic demands by the client will need assessment. For example, the use of porcelain fused to metal (PFM) for the crown will require greater tooth reduction than the use for a typical metal crown.


A more recent classification of lesions and general principles are determined by the nature and extent of the lesion, the quantity and quality of the tooth tissue remaining following preparation, functional load, and the nature and properties of the restorative system to be used [16]. In general terms, the minimal tooth substance is removed to allow access to the diseased tissues as well as allowing space for the requirements of the restorative material. For the removal of dental caries, an understanding of caries progression, tooth anatomy, including the position of the pulp (often based on an intraoral radiograph) and dental material science, is essential before starting.


17.6 Steps of Cavity Preparation


Preparation of a tooth to accept any form of restorative material requires specific steps, requiring planning, instrumentation skills, and an attention to detail. Dr. G.V. Black, almost a 100 years ago, set forth the basic sequence of tooth preparation for restoration [17]. This sequence included: outline form, resistance form, retention form, convenience form, pathology removal form, wall form, and preparation cleansing form. In addition to these, marginal placement and pulpal protection are also closely observed.


17.6.1 Outline Form


Outline form consists of the external and internal pattern boundaries of the preparation. This includes consideration of the area of pathology, all undermined enamel, and adjacent pathology, tooth contours, and anomalous anatomy. The preparation margins are placed in areas least susceptible to pathology, where visualization and finishing are suitable for the operator, and where access for warranted hygiene by the client is adequate. In addition, the outline form must take into consideration access to the pathology, type of restorative material used, functional needs of the patient, and esthetic requirements. It is generally necessary to gain access using a friction‐retained, water‐cooled, diamond bur held in an air turbine handpiece. Diamond burs cut enamel very efficiently and would be the bur of choice for accessing caries through the enamel. The original tooth contour should be reestablished where possible and the reproduction of the contact point, if present, is important in preventing food impaction problems, which can lead to periodontal disease.


17.6.2 Resistance Form


Resistance form is the shape formulated for the preparation to resist fracture of the tooth and restoration, both during insertion and function. This would encompass the functional needs of the restorative material selected, by adequate reduction preparation for the volume of restorative material required and the correct angulation form of the walls to withstand the functional forces of occlusion. Any preparation will weaken a tooth and predispose it to fracture. To minimize this effect, all internal line angles should be rounded.


Any increase in cavity depth can lead to flexure of cusp walls, which may predispose them to fracture. Rounding or curving the floor of the preparation can assist in minimizing this flexure. If a cusp has been totally undermined with no supporting dentin, then the operator should consider cusp reduction and a cusp overlay with a restorative material to minimize cusp fracture.


17.6.3 Retention Form


Retention form is the shaping of the internal aspects of the preparation to assist in the prevention of the displacement of the restoration. This includes retentive undercuts, groove cuts to prevent rotation, dovetails, pins, posts, and the internal wall angle form. Today, with the use of adhesive materials, the need for pins, grooves etc. are less warranted. However, if a substantial amount of tooth structure has been lost, then an indirect type of restoration may need to be considered. In summary, the choice of material will influence the final form of the preparation, especially with the need for undercuts for non‐adhesive restorations such as amalgam.


17.6.4 Convenience Form


Convenience form is the shaping of the preparation in order to provide adequate visualization, suitable accessibility, and reasonable ease in placement of the restoration and its finishing.


17.6.5 Pathology Removal Form


Pathology removal form is the shaping of the preparation that is necessary to remove or compensate for diseased, injured, or esthetically unpleasing dental tissue. The extent of pathology removal many times determines the need for the use of materials or agents to protect vital pulps. This may also result in the need for specific endodontic procedures.


In the case of caries removal, caries should be initially removed from around the amelodentinal junction and then, working apically, toward the areas overlying the pulp. If caries extends down to the pulp, the operator will need to make a decision on whether to leave affected dentin or slightly soft dentin behind, so as not to enter the pulp. The use of caries detecting solutions may or may not assist the operator in identifying infected versus affected dentin. Affected dentin can be remineralized with the use of a therapeutic liner. The area of the amelodentinal junction must always be made completely caries‐free.


17.6.6 Wall Form


Wall form is the refinement in the shaping of the preparation. This is typically required to eliminate unsupported enamel rods at the margin, or the smoothing of an irregular or rough outline form.


17.6.7 Preparation Cleansing Form


Cleansing form is typically the final shaping of the preparation prior to restoration placement. It is generally accomplished with explorers, air, water, spray, cotton pellets, and other agents to remove debris from the preparation.


17.6.8 Margin Placement


G.V. Black originally proposed that margins should be placed well into the embrasures in cleansable areas and sometimes subgingivally. It is now accepted that margins should be kept free of the gingivae where possible to avoid periodontal problems and that incidence of overhangs and marginal gaps must be avoided. Any encroachment of the biologic width (approximately 2.5 mm from the margin of restoration to the crestal bone) will lead to periodontal inflammation. If the margin does violate biologic width, then a crown lengthening procedure will need to be performed prior to placing the restoration.


17.6.9 Pulpal Protection


As younger patients tend to have larger pulp chambers than older patients, inadvertent pulp exposure during the restorative procedure is a risk in the younger patient. A diagnostic radiograph showing the size and position of the pulp is mandatory. Where the operator gets within 0.5 mm of the pulp, pulpal protection is required in the form of a pulp capping material such as calcium hydroxide or mineral trioxide aggregate (MTA). Deep cavities may also require the need for a liner or base prior to restorative placement (see Chapter 16 – Advanced Endodontic Therapy).


17.7 Operating Fields


During operative procedures, various isolation schemes are used to enhance visualization, instrumentation, control moisture contamination from instruments, reduce salivary interference, and protect the patient from instrument or chemical injury. The isolation may be either for single teeth or entire arches. There are many methods for isolation, but the type and extent of isolation selected is determined by the type of procedure, length of procedure, area anatomy, and operator requirements. Moisture contamination including blood or saliva can interfere with the bonding of unfilled resins (bonding agent) to tooth structure as well as the cohesive bond between the composite resin and the unfilled resin. Blood contamination can also stain or discolor the restoration. Saliva may also contaminate the site with bacteria, especially when performing endodontic therapy on a tooth.


17.7.1 Mouth Mirror and Suction


The mouth mirror in combination with suction can be a highly expedient tool for isolation of an area. The mirror can be used as a lip or soft tissue retractor, an indirect visual aid, and to redirect light to an area to improve visualization. Suction can provide moisture and debris control for a clear field of view.


17.7.2 Cotton Rolls


Cotton rolls are tubes of absorbent material used to help control moisture at a site. They may improve or hinder visualization and access when in place and come in an assortment of diameters and lengths. Cotton rolls and hybrid cotton can be used to help isolate teeth, absorb excess moisture, occlude salivary duct openings, to aid in cheek retraction, or to apply medicaments. Rolls are used for tooth isolation for restorations and topical treatments, such as fluoride. They are placed in the buccal or lingual vestibule to aid in the control of moisture, being replaced as they become saturated. In the lower arch, cotton rolls and holders are sometimes used to provide retraction for access and improved visualization.


17.7.3 Retractors and Shields


Lip retractors are useful when working on the maxillary teeth to help prevent moisture contamination when placing a restoration. An atraumatic retractor can lift the upper lip out of the way, especially when working on rostral teeth. Cheek retractors can be made of metal or plastic and be single or double ended. They are used primarily to displace the cheeks away from the caudal teeth, either for dental visualization or shielding of soft tissues in dental procedures or for visualization during photography. Most tongue retractors are made of metal with rubberized tongue grips, and tongue shields are typically made of plastic or metal. Tongue retractors are used to move the tongue out of the way for procedures, while shields or guards generally partially cover the tongue for its protection.


17.7.4 Rubber Dam


A rubber dam is a thin sheet of rubber or latex used to isolate an operating field in the oral cavity. The rubber dam is by far the most effective method of tooth isolation and moisture control (Figure 17.5). However, it may be difficult to place in dogs and cats due to a lack of customized rubber dam clamps. It can provide an area that is easier to maintain asepsis, a dry field, retraction of soft and hard tissues during oral treatments, and also allows for better visualization of the operative field. Latex gloves with holes punched into them can be used as rubber dams in animals, as they can be easily slipped over the muzzle and hold their position more naturally, particularly when working on canine teeth. True rubber dams come in various thicknesses and sizes for use according to the size of the oral cavity and teeth. The heaviest thickness that can be managed for an area is generally best. Some form of stabilization is needed to maintain the placement, with rubber dam holders, clamps, ligatures, interproximal devices, and tooth attachments. Care should be taken to avoid damage to surrounding gingiva.

Close-up view displaying the use of a rubber dental dam and clamp to isolate the surgical site on the teeth of the dog.

Figure 17.5 Use of a rubber dental dam and clamp to isolate the surgical site.


17.7.5 Astringents and Retraction Cord


These may be applied to control gingival hemorrhage. A retraction cord can be placed, especially when restoring Class V lesions at the gingival margin. The retraction cord comes in various thicknesses. It can be soaked in astringent such as ferric sulfate to assist in the control of bleeding. The retraction cord also slows down the flow of gingival crevicular fluid from the gingival sulcus. The infiltration of a local anesthetic agent with adrenaline may also aid in the control of bleeding.


17.7.6 Lesion and Caries Detection


Detection of lesions, such as caries, TR, and enamel defects is commonly performed with a sharp explorer, mouth mirror, good lighting, air syringe, and intraoral radiographs. Early detection of enamel disease is most reliant upon visualization and tactile inspection of the teeth. Incipient carious lesions of enamel may appear as rough or chalky white in good light, when air is blown across it. Sharp explorers, when pressed into a dental disease lesion, will ordinarily stick or catch on withdrawal. In moderate to advanced carious lesions of enamel, a brown to black appearance may develop in the pit, fissure, or developmental grooves, but must be differentiated from staining. In moderate to advanced resorptive and carious lesions, lucent areas may be detected radiographically. Laser caries detectors using laser fluorescence are now being used in human dentistry to detect early occlusal caries where radiographs and probing are equivocal.


Once lesions have been detected, both the extent of involvement must be ascertained, as well as the relationship to the pulp cavity and pulp vitality. Near‐pulpal exposures can typically be visually detected by the pink hue of the dentin. This will usually be an indication for an indirect pulp capping procedure (see Chapter 16 – Advanced Endodontic Therapy). If the pulp has been exposed, but is still vital, a direct pulp capping or possibly a complete root canal procedure may be warranted. If the canal is exposed and the pulp is non‐vital, or is expected to become so, then a complete root canal procedure prior to restoration would be the treatment of choice.


17.8 Restorative Materials


Operative chairside restorations generally involve the use of one, or more, of three basic restorative materials: composite resins, GIC, and amalgam. These products are held in place by micromechanical retention, chemical crystal formations, or macromechanical retention. Micromechanical retention is obtained by the use of bonding agents that microscopically interlock in enamel porosities, dentinal tubules, or other microscopic anatomy. This is used primarily with light cured composites and bonded amalgam restorations. Chemical crystal formations occur with glass ionomers as they form a crystal between the ionomer and the minerals within the enamel and dentin. Macromechanical retention are undercuts in the dentin and are used with non‐bonded amalgams and self‐ or autocure composites.


17.8.1 Composites


The potential for the use of acrylic resins for permanent restorations in dentistry first began to be realized in 1955, when Buonocore reported upon the use of phosphoric acid on the tooth surface. He found that etching enamel dramatically enhanced the bonding of acrylic to the surface [18]. In 1962, Bowen introduced the new resin we today call composite, a reaction product of bis‐phenol A and a glycidyl methacrylate, commonly abbreviated to bis‐GMA [19]. The original formula was marketed as a powder–liquid system and a paste–paste form, both of which were self‐ or chemical‐cured products. In 1972, the first light‐cured composite resins were developed, which used an ultraviolet 365 nm curing light source [20]. This resulted in a controlled working and setting time. Most clinically used composites today use the visible light range of 460–480 nm, which provides a more controlled curing in a clinical setting. Today’s composites can be bonded to enamel, dentin, cementum, metals, porcelain, glass ionomers, and of course to other composites [20].


The composite resins on the market today come as a chemical cure, visible light cure, and ultraviolet light cured. The ultraviolet light cured resins are used mostly for indirect techniques using dental laboratories, while the chemical and visible light cured products are used predominately in clinics. The chemically activated resins normally use benzoyl peroxide as an activator. With the light cured products, most ultraviolet systems use benzoin methyl ether, while visible light systems use camphoroquinone [20].

Only gold members can continue reading. Log In or Register to continue

Aug 15, 2020 | Posted by in GENERAL | Comments Off on Restorative Dentistry
Premium Wordpress Themes by UFO Themes