Injuries to teeth are common in human dentistry. They are predominantly sports related injuries and frequently seen in children. In veterinary medicine, injuries to teeth most often present as fractures. However, avulsions and luxation injuries occur during trauma from fights and motor vehicle accidents. Clients should be made aware that salvage of these teeth is possible with prompt attention. Avulsion injuries often affect the canine teeth. The continued value of working dogs is related to the function of their dentition so preservation of the teeth is critical in these individuals.
In human dentistry, there are six classifications of injuries that result when the force applied to the tooth is greater than the physical limits of the periodontal ligament (PL), neurovascular supply and bone:
1. Concussion: no abnormal loosening, no radiographic changes are observed.
2. Subluxation: injury to the tooth support structure with hemorrhage and loosening-no radiographic changes
3. Extrusive luxation: partial displacement out of the socket with hemorrhage, complete disruption of the neurovascular and PL fibres. The tooth is elongated and there is a wider PL space on radiographs.
4. Lateral luxation: eccentric displacement with alveolus fracture and rupture of PL fibres. There is little mobility with the apex locked. An increased PL space is observed on radiographs.
5. Intrusive luxation: displacement deep to alveolar bone, fracture of the alveolus, a short tooth, no mobility and the apex in the nasal passages (canine teeth in the dog and cat).
6. Exarticulation (avulsion): complete loss of the tooth +/- alveolar fracture.(1)
Other factors that affect the type of displacement include force and direction of the impact, object shape and type, stage of root development, periodontal ligament health, and thickness of the surrounding soft tissue. The injury is invariably a complex one involving damage to gingiva, PL, bone, and cementum. Consequently, the pattern of repair is equally complex and dependent on a number of variables including extra-alveolar duration and storage, rate of pulpal necrosis and treatment, type of external support applied, and staging of treatment.(2) One study has reported less success for healing when multiple avulsions occur. In addition a higher success rate was noted in mandibular teeth when compared with maxillary teeth.(3)
There are several sequelae to avulsion and luxation injury in the tooth. The predominant and most consistent sequela is pulpal necrosis due to disruption of the blood supply to the tooth. In human dentistry pulp testing and frequent monitoring of pulp vitality is done in more minor injuries such as concussion. This is less feasible in our patients and the injuries most frequently presented are far more severe so there is little confusion as to whether blood supply is disrupted or not. One exception does occur where the apex is open and there has been a sub- luxation of the tooth. With the tremendous vascularity of these young teeth, there may be an opportunity for survival. However, these teeth must be monitored closely.
Surface resorption is a non-invasive process that occurs after avulsion injury. Small superficial resorption cavities occur within the cementum and the outer dentin. It is a repair process of the physical damage to calcified tissue by recruitment of cells following removal of damaged tissue by macrophages.
Replacement resorption occurs when large areas of PL are lost or damaged. Healing occurs from the alveolar side creating a union between tooth and bone. It is the incorporation of the root into the normal remodeling process of the alveolus with gradual replacement by bone.(4) The potential problem is the destruction of the root, infection via the gingival sulcus or crown fracture from loss of normal suspension provided by the PL. It is important to note that mechanical removal or curettage of the avulsed root will result in replacement resorption.
Inflammatory resorption is a rapidly progressive but treatable process. Bowl-shaped radiolucencies penetrating the dentin are evident on radiographs. It is a direct result of contact of dentinal tubules with necrotic pulp. Toxic products pass through the tubules to the PL.(2) The eventual outcome can be internal, external, or replacement resorption.
The healing pattern of the PL post avulsion has been examined in monkeys. At three days, there is a separation line in the middle of the PL mediated by the blood clot. At seven days, there is attachment of the junctional epithelium. The gingival collar fibres re-unite. The PL re-establishes continuity with connective tissue that contains disorganized fibroblasts. At one month, the PL has a normal appearance but the connective tissue is not mature. At 4 months, a functionally oriented PL was present.(4-7)
Treatment for concussive tooth injuries in human dentistry involves a soft diet for two weeks with close monitoring of pulp vitality for months to years. A splint is not considered necessary. The treatment for subluxation of a tooth is the same.(1)
Extrusive luxation injuries require gentle repositioning of the tooth with a slow extrusion of the clot. A functional (non-rigid) splint is applied for two to three weeks. Endodontics is performed by 20 days.(1) A soft diet is suggested.
Lateral luxation injuries require forceful repositioning of the tooth and compression of the alveolus. Gingival lacerations are repaired. A functional splint is applied for three weeks or longer (up to six weeks) if the alveolar fractures are more extensive. In human dentistry, endodontics may not be required, depending on the displacement and maturity of the tooth, but in veterinary dentistry, it is invariably required.
Intrusive injuries in an immature tooth, if not severe, may permit re-eruption. In a mature tooth, the pulp will necrose. Treatment requires surgical repositioning and splinting. Orthodontics may be required if the injury is older than 48 hours.(1)
Treatment of an exarticulated tooth requires immediate replantation within five minutes to gain a favorable result. Active ongoing research in human dentistry has yielded several treatment options but the one universal is to avoid drying of the PL cells on the root surface. Desiccation is the primary cause of PL cell death. Drying time of the root greater than five minutes is severely detrimental to PL cell survival.(4) Immediate replantation is not always possible in cases where the patient has sustained significant trauma. Patient survival often dictates a delay in replantation. In these cases, we extrapolate from human dentistry and do not use autologous saliva as an interim support but try to go directly to chilled low fat milk at 4° C until arrival at a veterinary hospital. It is important not to let the milk warm to room temperature during transit but to keep it chilled on ice.(4) Tap water will cause rapid cell death and if used it must be brief to lavage dirt from the root. Milk will prevent cell death and is only ideal in the short term as it cannot replenish cells but simply maintains osmotic pressure.(1) Transfer to Hanks Balanced Salt Solution (HBSS) until replantation. The goal is to preserve clonogenic potential of remaining PL cells. That is the ability of the PL to regenerate. PL will necrose after 20 minutes. The best support is tissue culture medium such as Eagle’s medium or Viaspan (8) but they are difficult to obtain and unlikely to be available at the required time.
During replantation, clot removal is controversial but gentle pressure should be used while not touching the root. The age of the socket is also critical in healing of the PL. In a recent study, teeth were supported in storage media but various ages of socket were used for replantation. As the socket aged, the degree of healing reduced.(9)
Various treatments are advocated depending on extra-oral time, dry time, and maturity of tooth. Some of the treatments for prolonged extraoral time include citric acid, doxycycline and fluoride. For prolonged dry time of greater than 120 minutes: curettage, citric acid doxycycline, fluoride, and extra-oral endodontics with CaOH.(1)
Once the tooth has been replanted, a functional splint must be applied. Requirements include: the splint is applied directly in the mouth, there is no trauma to the tooth during the application and removal process, no impingement on gingival tissues, the ability to permit oral hygiene is retained, and the split allows some movement for PL healing.(10, 11) Rigid splints promote ankylosis. The splint must permit access for endodontics. Usually wire and composite splints work well. They should be applied to at least two stable teeth on either side of the avulsion. The wire should have no memory to avoid orthodontic movement of the avulsed tooth. Light orthodontic arch wire 0.016–0.020 is used in human dentistry.(12) Additionally, a radiograph should be taken to verify replanted position after occlusion has been assessed. Depending on the degree of damage a splint may remain in place for two or more weeks.
Adjunct treatments include antibiotics, usually tetracycline in human patients. Tetracycline is used as it has antibacterial and anti-resorptive properties. It is anti-resorptive due to its direct inhibition on osteoclasts and collagenase.(13) Antibiotic therapy in veterinary patients is advised. Non-steroidal anti-inflammatories are also used after avulsion injuries. Chlorhexidine rinses are also advocated. Tetanus is also suggested in human patients.
A recent study examined the use of dexamethasone in periodontal healing. Better healing was noted with local dexamethasone (16 ug/ml in Viaspan) than with systemic dexamethasone use.(14) The steroid reduces and blocks expression of macrophage activation and reduces osteoclast numbers and function. Calcitonin receptors are also enhanced.(14)
The generally accepted time for pulp extirpaton and treatment with CaOH is seven to 14 days in human dentistry. One study suggests pulp extirpation is not critical if done at less than 20 days.(15) If pulpectomy is done at 7–10 days a creamy mixture of CaOH is used. If pulpectomy is done at 14 days or later a stiff CaOH is used.(11) The CaOH is replaced or repacked every three to six months until the lamina dura can be traced around the root apex on radiographs.(11)
Once the lamina dura is intact, final obturation with gutta percha and sealer cement is performed. Length of time for calcium hydroxide packing has been recently studied. Trop et al., concluded that when endodontics were initiated at 14 days, long- or short-term CaOH made no apparent difference to the healing pattern in replanted dog teeth.(16) In another study, it was concluded that long term CaOH therapy may be more effective than short term in the treatment of established inflammatory root resorption.(17)
Salvage of strategically important teeth is possible with prompt attention and thorough follow-up. The client needs to make an informed decision and financial and time commitment to multiple staged procedures in order to achieve success. According to Andreasen “if all avulsed teeth were replanted immediately, a PL healing rate of 85–97% could be expected.”
REFERENCES
1. Krasner, Paul “Management of sports related tooth displacements and avulsions” in Advances in sports dentistry Dental Clinics of N. Am 44(1): 111-135, 2000.
2. Layug ML, Barrett EJ, Kenny DJ Interim Storage of Avulsed Permanent Teeth. J Can Dent Assoc., 64(5) 357-63, 365-9, 1998.
3. Sheppard PR, Burich RL, Effects of extra-oral exposure and multiple avulsions or re-vascularization of re-implanted teeth in dogs. J Dent Res; 59(2) 140, 1980.
4. Barrett EJ, Kenny, DJ Avulsed permanent teeth: a review of the literature and treatment guidelines. Endod Dent Traumatol; 13: 153-163 1997.
5. Loe H, Waerhaug J, Experimental replantation of teeth in dogs and monkeys. Arch Oral Biol 3:176-84, 1961.
6. Nasjleti C, Caffesse R, Castelli, W, Replantation of mature teeth without endodontics in monkeys. J dent Res; 57: 650 1978.
7. Andreasen JO A time related study of periodontal healing and root resorption activity after replantation of mature permanent incisors in monkeys. Swed Dent J; 4:101-10, 1980.
8. Lekic PC, KennyDJ, BarrettEJ, The influence of storage conditions on the clonogenic capacity of periodontal ligament cells: implications for tooth replantation. International Endodontic Journal3(2): 137-40. 1998.
9. Trope M, Hupp JG, Mesaros SV, The role of the socket in the periodontal healing of replanted dogs teeth stored in Viaspan for extended periods. Endod Dent Traumatol; 13: 171-175. 1997.
10. AndreasenJO, Andreasen FM Luxation injuries. In Textbook and Color Atlas of Traumatic Injuries to Teeth, ed 3 St Louis, Mosby, 1994.
11. Trope M Protocol for treating the avulsed tooth. J of Calif Dent Assoc 24(3): 43-9, 1996.
12. Wong GB Non rigid splinting for avulsions and luxations Ontario Dentist 59(9) 12, 14, 16-7, 1982.
13. Sachim V, Wang CY, Choi GW, Trope M, The effect of systemic tetracycline on resorption of dried replanted dogs’ teeth. Endod Dent Traumatol 14(3): 127-132. 1998.
14. Sae-Lim V, Metzger Z, Trope M, Local dexamethasone improves periodontal healing of replanted dogs’ teeth. Endod Dent Traumatol 14:232-236. 1998.
15. Kinirons MJ, Boyd DH, Gregg TA, Inflammatory and replacement resorption in re-implanted permanent incisor teeth: a study of the characteristics of 84 teeth. Endod Dent Traumatol 15(6): 269-72, 1999.
16. Trope M et al Effect of different endodontic treatment protocols on periodontal repair and root resorption of replanted dog teeth. J Endod 18(10): 492-6. 1992.
17. Trope M et al Short vs long-term calcium hydroxide treatment of established inflammatory root resorption in replanted dog teeth. Endod Dent Traumatol 11(3): 124-8. 1995.