Teeth take the brunt of force in normal activities such as playing, working, and even normal mastication. Due to their relative inelasticity, in many cases, teeth are fractured or otherwise traumatized. The extent of the fracture can vary in every instance and from a clinical standpoint, may be as minor as requiring no treatment to needing endodontic therapy or extraction. The American Veterinary Dental College Nomenclature Committee has created examples of each type of fracture and has listed them on its website for public reference. These examples can be found at www.avdc.org.
Tooth Fracture Classification
Teeth are usually strong, but in cases of trauma or developmental defects, lesions can occur. Important clinical considerations include the source of trauma or wear, the amount of remaining crown and tooth structure, the overall health of the tooth, the importance of the tooth for function or esthetics, and the likelihood of continued trauma. We will investigate a clinically based review of dental lesions including:
- Worn Teeth
- Uncomplicated Crown Fractures
- Uncomplicated Crown and Root Fractures
- Complicated Crown Fractures
- Root Fractures
- Carious Lesions
- Enamel Hypoplasia
- Discolored Crowns
- Sub-luxated, Luxated or Avulsed Teeth
Worn Teeth
Due to aggressive chewing of abrasive materials, wear of the teeth may occur. Technically speaking, attrition is the normal wearing of the cusps or occlusal surfaces of teeth during mastication, or tooth-on-tooth contact. Abrasion is the abnormal wear of teeth when chewing on objects not intended for ingestion. Either condition may result in loss of tooth structure and is treated similarly. Clinically, what is important is whether the pulp canal has been exposed or is close enough to exposure to allow bacterial contamination of the endodontic canal.
Dental radiographs with comparison of the same contralateral tooth may be helpful. Transillumination and careful exploration of the fracture surface for pulp exposure can assist in trying to determine if the pulp is indeed still vital. Worn teeth without pulp exposure, with no radiographic evidence of pulp necrosis and that transilluminate normally, may be vital, but these teeth need to be reevaluated radiographically on a periodic basis.
The tooth itself is composed of three major components: pulp, dentin and enamel. The pulp is the innermost layer of the tooth and is made up of vessels and nerves that provide nutrition and sensation. The major cell type found is the fibroblast, but the cell of notoriety is the odontoblast. The odontoblast’s function is to make dentin throughout the life of the tooth. As such, the pulp cavity starts out very wide in an immature tooth, and as the tooth, and patient mature, the pulp canal becomes narrower and the dentin around the pulp thickens.
The part of the pulp cavity within the crown of the tooth is called the pulp chamber, and the part within the root is called the root canal. It is important to note that the nerve fibers within the pulp detect only one sensation: pain. There are two types of pain receptors in the pulp—one for sharp, acute pain and one for dull, throbbing pain. Clinically, this becomes very important in a tooth with pulp exposure. The dentin is the middle layer of the tooth and may be thin or thick, depending on the age of the tooth and patient.
Dentin is mostly inorganic and contains small tubules that normally contain fluid. At the interface with the pulp, odontoblastic processes extend into these tubules. Any stimulus that causes an abnormal movement of fluid within the tubules—either in or out—can result in sensitivity in a vital tooth. Areas near pulp exposures can be sensitive and, theoretically, could allow for bacterial penetration through the dentin to the pulp.
Clinically, this is especially important in younger patients where the pulp is closer to the outer edges of the tooth. These tubules can be sealed with a dentin bonding agent to help prevent and reduce sensitivity. The dentin extends to the root surface and is covered by a cellular layer called cementum. The outermost extent of the dentin within the crown of the tooth meets the enamel which is the outermost covering of the tooth normally exposed through the gingiva. Enamel is 97% inorganic and is the hardest substance in the body. As such, it is also brittle, like porcelain, and does not have the capacity to regenerate itself.
In contrast, if the enamel, dentin or root surface is damaged, resulting in sensitivity or irritation to the underlying pulp, the odontoblasts have the capacity to lay down more dentin in response, provided the irritation does not result in the overall death of the pulp. This dentin laid down in response to irritation is also known as reparative dentin, also known as tertiary dentin. It can be seen in teeth that have slow progressive wear. The result is a dark-stained center with no observable pulp exposure. Clinically, if these teeth have no pulp exposure, and are radiographically normal, dentin bonding may help reduce the irritation to the pulp. If the source of wear can be removed, then these teeth may continue to remain vital. Follow-up radiographs and visual evaluation are recommended six to 12 months following treatment. Worn teeth may present with a smooth surface and a dark stain. Careful exploration should reveal whether the pulp canal has been entered. If so, either extraction or root canal therapy is indicated. If not, If the tooth appears nonvital, root canal therapy or extraction is appropriate. If the tooth appears vital, dentin bonding or crown placement may help protect the tooth.
Uncomplicated crown fractures
For crown fractures that do not involve the pulp or root structure, several options may be available based on the extent of the tooth damage. Enamel infractions are generally of no clinical significance and typically require no treatment. However, dental radiographs and transillumination with comparison of the same tooth on the opposite side of the arcade can be helpful to determine if the tooth is vital.
For enamel fractures, without invasion into the dentin, smoothing with an Arkansas white stone, followed by etching and placement of a bonding agent can help restore enamel smoothness and prevent plaque and calculus deposition. Uncomplicated crown fractures are likely to be sensitive due to dentin exposure.
Treatment involves cleaning and smoothing any rough enamel edges, followed by clinical and radiographic evaluation to confirm the pulp is not exposed. Non-fluoride pumice polishing, acid etching, and the application of a dentin bonding agent should follow. This seals any exposed dentinal tubules and prevents and reduces sensitivity.
The materials used for restorations include non-fluoride pumice, 37% phosphoric acid etch, a bonding agent, and possibly glass ionomer, composite, amalgam, metal crowns, and other restorative materials. The non-fluoride pumice is used to help clean the surface of the tooth without adding waxes or fluoride which may inhibit the overall bonding of materials to the tooth. The 37% phosphoric acid is used primarily to etch the prisms of the enamel demineralizes intratubular dentin and expose collagen fibrils, and open the dentinal tubules to allow micromechanical attachment of the bonding agent to a hybrid layer of collagen and water within the dentinal tubules.
Bonding the hybrid collagen layer greatly enhances adhesion. Over the years, bonding agents have improved bond strength, ease of use and application time. Each new upgrade is called a new generation. Within the past 20 years, bonding agents have improved from fourth-generation bonding agents, which required a dentin conditioner layer and two separate liquids mixed together and then applied to an acid-etched surface, to eighth-generation bonding agents. Currently, seventh and eighth generation bonding agents. Which have the acid-etch within one package, are applied with the bonding agent and allowed to dry before light curing.
Some bonding agents are light-cured, hardening in response to a specific wavelength of light, and some are chemically cured by mixing two materials together. Dual-cure bonding agents combine both methods, allowing for faster setting when a light is used, along with a complete cure in areas the light cannot reach. The bonding agent is sometimes referred to as an “unfilled resin.” In contrast, “filled resins,” also known as composites, are bonding agents that have been filled with particles of glass, plastic, or fibers that impart some special characteristic, such as color, added resistance to wear, or resistance to fracture. Composites also are categorized based on their viscosity, with some being relatively liquid called flowable composites and others that are firm called compactible composites.
Some composites contain large filler particles, called “macrofilled” composites, which make them more wear-resistant. Others have small particles called “microfilled” composites, which are easier to polish. A combination of small and large filler particles, designed to provide both wear resistance and a smooth, polishable surface, is often called a “hybrid composite.” All of these materials can be shaded to match the tooth being restored. Glass ionomers are cements made of glass particles that create a weak ionic bond to the dentin surface. These are good for sealing the tooth between the vital pulp and final composite restorations in vital pulpotomy procedures or underneath final fillings of complete pulpectomy and standard root canal procedures.
These materials were once used extensively for fillings in resorptive lesions in cats because they have the added advantage of releasing small amounts of fluoride. However, it was later discovered that many of the fillings failed due to continued resorption of the tooth by odontoclasts. Amalgam was once the mainstay of all cavity fillings. A mixture of silver mercury and tin, this material had the advantages of being easily molded into cavity defects and became extremely hard once set in place, something especially beneficial for the occlusal surface of teeth.
The disadvantages include its relatively technique-sensitive nature, its inability to directly bond to the tooth (although there are now amalgam bonding agents available), the release of trace amounts of mercury, and the potential for expansion during setting, if placed in the presence of moisture, which could result in further damage such as splitting of the crown.
There are many clinical instances where dentin bonding agents and composite restorations may be indicated. Worn teeth with near pulp exposures, enamel chip fractures, enamel developmental defects, carious lesions, early resorptive lesions, cosmetic restorations, and endodontic access sites are all indications where restorations may be needed. As such, a basic understanding of the importance of exposed dentin and the benefits of sealing a damaged tooth along with the knowledge of what restorations can do in managing damaged teeth, will help the practitioner, patient and client make better decisions regarding overall dental health.
Uncomplicated (or Complicated) crown-root fractures:
Some fractures of the crown, while not involving pulp, may extend subgingivally along the root. While it is difficult to find references with hard and fast rules to guide treatment decisions; ultimately, the practitioner needs to use his or her clinical judgment to decide if the overall periodontal health of the tooth has been jeopardized. If the fracture extends below the gingival margin, the extent must be explored. In some cases, gingival flap surgery will be indicated to fully evaluate the extent of the fracture.
If the fracture extends further apical than the mucogingival line beneath the gingiva, the attached gingiva may need to be repositioned more apically, with recontouring of the alveolar bone to allow for normal biologic attachment of the gingiva in its new location. If this cannot be performed, such as in an area where adequate tissue repositioning is not possible, and periodontal pocketing will remain alongside the treated tooth, the owner should be made aware that this tooth may develop periodontal disease and become a source of chronic infection in the future, which may need to be extracted at a later date. Some clients are willing to take that risk in an effort to save the tooth, while others may opt for extraction.
Complicated Crown Fracture:
If the pulp canal is involved, or if there are signs of pulp necrosis, endodontic or exodontic therapy is indicated. If the tooth has been fractured less than 48 hours, a partial coronal pulpectomy and vital pulp therapy (vital pulpotomy) may be an option. Based on human studies, the success rate of this procedure is approximately 85%, which means the tooth stays vital. Most veterinary dentists are performing this treatment less frequently, especially in mature teeth, as standard root canal therapy tend to have a higher success rate. However, if the tooth has an open apex or a very wide pulp canal, then vital pulp therapy may allow the tooth to mature to a level where standard root canal therapy is easier and would carry a higher success rate.
If the tooth is immature with an open apex and the pulp exposure is is older than 48 hours apexification should be considered. This involves removing the pulp contents and replacing them with either calcium hydroxide paste or mineral trioxide aggregate (MTA) to give the body a chance to form firm osteoid around the apex of the tooth, creating a root terminus for eventual standard root canal therapy. Most “complicated” crown fractures involve mature teeth and most are greater than 48 hours old, leaving the two basic options: standard root canal therapy, if the tooth is periodontally sound and if the roots are not undergoing inflammatory root resorption, or extraction.
Root Fractures:
It is possible for the root to fracture without traumatizing the crown. As a general rule, the closer the root fracture is to the apex, and the more stable the coronal segment of the tooth is, the better the prognosis. If the tooth is vital and the coronal segment is stable, then no treatment may be needed, other than clinical and radiographic monitoring.
If the crown is not stable and the tooth is or was recently vital, stabilizing the tooth with an interdental splint is indicated, regardless of the location of the root fracture. In some cases, osteoid can fill in the fracture site, stabilizing the tooth and preserving its vitality. If the tooth is or becomes nonvital there are procedures to maintain the tooth, but the prognosis decreases. Options for nonvital teeth with root fractures include:
- Standard root canal procedure on both the coronal and apical segment
- Root canal therapy for the coronal segment and no treatment for the apical segment
- Coronal segment apexification followed by standard root canal therapy of the coronal segment with no treatment of the apical segment
- Intraradicular splint with root canal therapy and a post placed into both the coronal and apical segment
- Endodontic implant in which the apical part of the implant replaces the surgically removed apical segment of root
- Removal of the coronal segment and root extrusion followed by root canal therapy of the remaining root segment and post/core build-up for restoration.
(From: Principles and Practice of Endodontics by Walton & Torebinejad, Saunders, 2002)
Carious lesions:
True carious lesions (sometimes called “cavities”) are not as common in dogs and cats as they are in humans. It is theorized that this is due to the difference in shape of the crown, material ingested, natural oral flora bacteria and pH of the saliva, among other things. True carious lesions are caused by certain bacteria (Steptococcus mutans is the primary culprit in humans) that digest carbohydrates (CHOs) and produce acid. This acid demineralizes the enamel, allowing destruction to progress into the dentin and possibly the pulp.
For this reason, small enamel carious lesions may be larger than expected once the diseased enamel is removed and the full extent of dentin destruction is revealed. The occlusal surfaces of the molar teeth are the most common location, but these can occur in the developmental grooves of premolar teeth, interproximal areas between teeth and along the root surfaces. Treatment involves removal of the diseased or demineralized tooth structure and replacement with a restorative material. See the information listed above for placement of a composite restoration.
Enamel hypoplasia:
Disruption of ameloblasts during tooth development can result in a loss of enamel or a defect in the mineralization of the enamel (hypomineralization). Enamel hypoplasia is a focal or generalized complete loss of enamel structure, revealing the underlying dentin. Enamel hypomineralization is a focal or generalized deficiency in enamel hardness, clinically seen as a soft, rough, irregular surface of enamel that can be scaled away easily with an ultrasonic scaler. The end result of either condition is a loss of the protective nonporous layer of smooth enamel over the tooth’s crown. Exposure of the dentin can allow for dentin sensitivity.
See the discussion in item No. 1 above“ Worn Teeth”. Another important clinical consideration is that when the enamel is formed by the ameloblasts, the roots are also being formed by another epithelial tissue, Hertwig’s epithelial root sheath, which acts as a template for root formation. Some epitheliotropic viruses not only disrupt enamel formation, but also the root formation. The clinical result is shortened, blunted roots. Full mouth dental radiographs are indicated in these cases to help detect root hypoplasia.
Even if root hypoplasia is found, there is no known treatment to stimulate root development.. This finding is informational only and should prompt the practitioner to inform the owner that even a small amount of periodontal disease or less-than-normal crown stress may cause otherwise normal-appearing teeth to become prematurely dislodged. Treatment of these teeth focuses on preventing dentin sensitivity and creating a plaque-retardant surface to mimic the lost enamel.
Treatment involves general anesthesia, full-mouth dental radiographs, thorough cleaning of the teeth, non-fluoride pumice polishing, acid etching, dentin bonding and composite restoration of all teeth—or select teeth—depending on the wishes of the client.
Discolored Teeth:
Discolored crowns may clinically appear harmless, however, more than 92% are actually non-vital or are in the process of becoming non-vital. The teeth can become necrotic and can even begin to form an abscess. Imaging can reveal a non-vital tooth 40% of the time.
If the pulp canal was wider on the affected tooth, we could conclude this tooth was no longer maturing and was considered non-vital. In some instances, periapical changes might indicate infection or abscess as well. Transillumination is the process of passing a bright light source behind a tooth, like candling an egg, to check for vitality. A vital tooth will be translucent, and a non-vital tooth will have a “shadow” within the tooth. While this test is subjective, it can be used as an aid in questionable teeth.
Nonvital pulps eventually necrose, setting the stage for infection and abscessation. My current recommendation for significantly discolored teeth is either endodontic or exodontic therapy. For those cases where only a small part of the crown is discolored, I still recommend regular periodic radiographs and evaluation to hopefully diagnose a nonvital tooth before it causes the patient any problems.
Sub-luxated, Luxated, or Avulsed Teeth:
These are teeth that have been dislodged from their alveolar socket to varying degrees. A subluxated tooth is one that has had trauma to create tooth mobility but has not been displaced from the alveolar socket. This tooth should be stabilized if necessary, with an interdental splint and monitored periodically (every six months) for vitality or any signs the tooth is not vital, then further treatment is indicated. A luxated tooth is one that remains within the alveolar socket but has been partially displaced.
These teeth should either be extracted or treated through replantation and endodontic therapy. Replantation involves gently flushing any clot or debris out of the alveolus with sterile saline, followed by replacement of the tooth into the alveolus. Any soft tissue torn should be securely sutured and the tooth stabilized with a semi-rigid interdental splint. Since the apical neurovascular bundle was likely disrupted at the time of the trauma this tooth should have standard or retrograde endodontic therapy. An avulsed tooth is one that has been completely displaced out of its alveolar socket.
The neurovascular bundle is damaged, and if the tooth is to be saved, it should be replanted as soon as reasonably and safely possible for the patient. In any case, if the tooth is completely avulsed from the mouth, it should be immediately placed in either Hank’s balanced salt solution (HBSS) or in whole milk in a plastic bag until replantation. HBSS can be found at many pharmacies. The tooth should be gently rinsed with sterile saline, and the protocol for luxated teeth should be followed. An alternative is to perform standard root canal therapy on the avulsed tooth prior to replantation, but this must be done with gentle care, holding the root with saline-soaked gauze.
The goal is to avoid disrupting any viable periodontal ligament or cementum left on the root surface. Eventually external replacement root resorption is a possible consequence of tooth replantation. Some studies have recommended the calcium hydroxide as either an intermediate obturation or use of a calcium hydroxide endodontic sealer cement in the obturation process (CRCS-Hygenic/Coltene Whaledent).
About the Author
Michael Peak | DVM, DAVDC
Dr. Peak graduated with honors from Auburn University’s College of Veterinary Medicine. He completed a veterinary dentistry residency at the Dallas Dental Service Animal Clinic in 2000 and became Board Certified by the American Veterinary Dental College in 2001. He has served as President of the American Veterinary Dental College, chair of the Examination Committee, the Fiscal and Audit Committee, and the Board of Directors. He has been the Program Chair for the Veterinary Dental Forum, and chair for the Veterinary Dental Oversight Group, a committee that oversees the operations of the Veterinary Dental Forum. Dr. Peak has published several articles relating to veterinary dentistry and believes strongly that the education of other veterinarians and the public about dental disease in pets is the key to providing optimal oral health. He has lectured and performed wet labs in many locations and veterinary practices across the country from California to Maine.