Abstract
Mandibular fractures at the level of the first molar tooth (M1) were assessed in twenty-nine dogs. Patients included in this study demonstrated fractures involving the M1 tooth, tooth bud, or alveolus (if tooth was absent). Diagnostic imaging evaluation included intraoral dental radiography and/or computed tomography (CT) with 3-dimensional reconstruction. The distal root was involved in 55.2% of cases, mesial root involvement in 34.5% of cases and the tooth was absent in 10.3% of cases. Fractures were described in the rostral-to-caudal direction. Fractures tended to occur in the caudoventral (CV) direction (p = 0.057). Cases with CT imaging were also evaluated in the buccolingual direction. Fractures were found to occur significantly more frequently in the caudolingual (CL) direction (p = 0.022). When classifying fracture patterns along M1 according to a previously published fracture classification system, it was noted that fractures occurred significantly more frequently in either the mesial (p<0.001) or distal (p<0.001) roots by coursing along the periodontal ligament space and communicating with the periapical region. Active or non-worsening periodontitis was described as radiographic or tomographic evidence of (>25%) bone loss in the vertical or horizontal direction. Periodontitis was associated with 7 cases (24.1%). These results help frame the challenges associated with fracture repair at the M1 location. Treatment planning considerations should include: limited structural support caudal to fractures involving the distal root, more frequent involvement of the distal root over the mesial root, risk for poor endodontic prognosis and the predilection for unfavorable fracture patterns to occur.
Keywords: mandible, mandible fracture, mandibular first molar, fracture, trauma
INTRODUCTION
Previous studies have reported that mandibular fractures represent 1.5–6% of all fractures in dogs (1–4). The dentulous regions are over represented, with one study showing the alveolus being involved in 85% of cases (1). This study also showed that the majority of open fractures (94%) occurred in tooth bearing regions and involved tooth roots. (1)
With most mandibular fractures occurring in tooth bearing regions of the mandible, it can be surmised that the presence of tooth structures potentially impacts fracture line orientation. Fracture line orientation has been shown to follow the route of least resistance, resulting in fractures tending to course along tooth roots, (5) likely directly associated with soft tissue structures encased within bone such as the periodonetal ligament. Previous studies show a high incidence of short oblique fractures in canine and premolar regions which supports this statement (4).
A recent retrospective study of 109 mandibular fractures reported the highest incidence of mandibular fractures occurring in the molar region, with the first molar (M1) being predominately involved in the fracture line (4). Another study reported the molar region was involved in 47.1% of cases, and the first molar involved in 85.9% of these cases (7). The commonly reported involvement of M1 in mandibular fractures was also seen in a retrospective study of mandibular fractures in dogs, where M1 was the predominant tooth in fracture lines (4). M1 is also the most frequently reported tooth to be involved in pathologic fractures. (6)
Due to the high rate of M1 involvement in mandibular fractures occurring in veterinary patients, further review of fracture characteristics is warranted. Better understanding and anticipation of mandibular fracture pattern at the level of M1 could allow for: further justification for the emphasis for prevention of periodontal disease in this area, help mitigate risks for iatrogenic fracture associated with extraction techniques in this area, and possibly create a better appreciation for the biomechanical circumstances necessary to facilitate successful stabilization and fixation for fractures at this location. The purpose of our study was to review and characterize fracture patterns occurring through mandibular M1 in dogs presenting to the University of Wisconsin - Veterinary Medical Teaching Hospital from August 2005 to December 2016.
METHODS & MATERIALS
Cases of canine mandibular fractures presenting to the University of Wisconsin–Madison, School of Veterinary Medicine between August 2005 and December 2016 were reviewed. For inclusion, cases included all patients that were anesthetized, received diagnostic imaging and potential repair/fixation of maxillofacial fractures involving the mandible in the location of M1. Patients were anesthetized for imaging and treatment planning with anesthetic protocols created for each individual patient by board certified anesthesiologists at the teaching hospital. Patient age, weight and fracture etiology were reviewed and collected from patient records.
Patient imaging included computed tomography (CT)a and/or intraoral dental radiography. When available, both imaging modalities were reviewed to assess fracture pattern in the rostral-to-caudal direction and in the buccal-to-lingual direction. Dental radiographs were viewed with image viewing softwareb or a comparable dental radiograph acquisition software used at the time of patient imaging. CT studies were evaluated with DICOM viewing softwarec. CT imaging was assessed in the axial and sagittal views, as well as with 3D reconstruction. Buccolingual fracture pattern was assessed with CT 3D reconstruction images.
Included cases involved fractures associated with the left or right M1 tooth, tooth bud, or alveolus (if tooth was absent). Fractures were evaluated and classified based on fracture propagation in the rostral-to-caudal direction. Fractures were classified along the length of the mandibular body in three ways. (Figure 1) Fractures coursing in the caudodorsal (CD) direction are commonly referred to as “favorable” fractures (8). Fractures coursing in the caudoventral (CV) direction have been previously referred to as “unfavorable” fractures (8). (Figure 2) Transverse fractures along the long axis of the mandible were defined as dorsoventral transverse (DVT). Fractures where further classified in a buccolingual direction. (Figure 3) Caudolingual (CL) fractures included fracture patterns where the buccal cortical plate fracture was mesial to the discontinuity in the lingual cortical plate. (Figure 4) Caudobuccal (CB) fractures included fracture patterns where the lingual cortical plate fracture was mesial relative to the buccal cortical plate discontinuity. Transverse fracture along the short axis of the mandible were defined as buccolingual transverse (BLT).
Figure 1:
Mandibular fractures were evaluated by both computed tomography and intraoral radiography to classify the nature of the fracture in the rostral-caudal direction through the first molar tooth. Dorsoventral transverse (DVT) fractures (solid line) were described as fractures occurring perpendicular to the long axis of the mandibular body. Fractures coursing in the caudodorsal (CD) direction are sometimes referred to as “favorable” fractures (dashed line). “Unfavorable” fractures course in the caudoventral (CV) direction (dotted line).
Figure 2:
A 3-D reconstruction of a clinical patient demonstrating a caudoventral fracture (CV).
Figure 3:
!! † Mandibular fractures were categorized by fracture direction when evaluated in the buccolingual direction of the first molar tooth and reported as the fractures occurred in the rostral-to-caudal direction. Only cases receiving computed tomographic evaluation were reported. Buccolingual transverse (BLT) fractures were fractures occurring perpendicular to the long axis of the mandibular body (solid green line). Fractures coursing through the buccal cortical plate mesially, and exiting through the lingual cortical plate caudally were denoted as caudolingual (CL) fractures (dashed line). Caudobuccal (CB) fractures course from the lingual plate through the buccal cortical plate in the caudal direction (dotted line).
Figure 4:
A ventrodorsal view of a 3-D reconstruction demonstrating a caudolingual (CL) fracture orientation.
The propagation of mandibular fractures along M1 were also classified on a system previously described by Schloss and Marretta (9). (Figure 5–7) If M1 was noted to be absent, the Schloss and Marretta classification to the fracture was not applied.
Figure 5:
Illustration reprinted with permission from: Schloss AJ and Marretta SM. Prognostic factors affecting teeth in the fracture line of mandibular fractures. JVD 1990;7(4):7–9.
A) Fracture propagation courses along the periodontal ligament space and communicates between the oral cavity and apex. B) Fracture is associated with the coronal third of the root only. C) Fracture compromises endodontic vascular supply at the location of the apex. D) Fracture line courses through alveolar bone sparing the root and apical vascular supply. E) The fracture courses through the coronal periodontal ligament space and continues through the alveolar bone sparing the apex. F) Fracture may originate at the alveolar margin by the tooth but does not course through the periodontal ligament space nor directly compromise the root.
Figure: 7.
Case example of the type B fracture pattern at the mesial root of M1 tooth. Note at the coronal third of the root, the fracture courses along the root surface and then changes direction and courses mesially, preserving the bony attachment around the apical third of the root.
Fracture involvement of the mesial and distal roots were evaluated and reported separately. Teeth were considered to have radiographic evidence of active or non-worsening periodontal disease if >25% of vertical or horizontal bone loss was evident on either CT or radiographically. Dental radiography and CT imaging were also evaluated for evidence of fracture comminution.
Statistical analysis consisted of summarizing the sample with mean (SD), median (range), or frequency (%) when appropriate based on distribution type. Testing for increase/decrease in rate of each fracture pattern by location was tested by tests of single proportions with null hypotheses that the rate of each possible fracture pattern was equally distributed across all patterns. Significance was set at p=0.05, and significant p-values allowed us to conclude that the increased or decreased rate since in this sample was significantly different than what we would expect to see by chance alone.
RESULTS
Twenty-nine cases matching the inclusion criteria were identified during the case selection period. The median age of the patients was 2 years (range: 3 months - 15 years). The median weight was 5.9 kg (range:1.65kg - 33.0kg). CT imaging studies were available for review for 20 of the 29 cases (69%) and dental radiographs were available for 26 of 29 (89.7%) cases. Nineteen cases (65.5%) received imaging with both CT and intraoral dental radiography. The distribution of fractures between mesial and distal roots was not significant (p=0.165). The mesial root was involved in 10 fractures (34.5%), and the distal root was involved in 16 fractures (55.2%). M1 was absent in three cases (10.3%) at the time of imaging, therefore those cases were not included in the Schloss and Marretta pattern classification, mesial versus distal root involvement, nor described as having significant periodontal disease. Other features evaluated showed comminuted fracture occurred in 5 cases (17.2%), and radiographic signs consistent with periodontal disease associated with >25% alveolar bone loss was present in 7 cases (24.1%). Six of 7 cases with radiographic evidence of radiographic evidence of periodontal disease demonstrated >50% alveolar bone loss associated with the root involved in the fracture site while 1/7 cases demonstrated 25–50% alveolar bone loss.
When evaluating the fracture patterns, fracture propagation was CV in 15 cases (51.7%), CD direction in 7 cases (24.1%), and DVT in 7 cases (24.1%). (Table 1) When CT imaging was available, the buccolingual orientation was assessed and demonstrated fractures occurring in the CL direction in 12 (60%) cases (p-value = 0.022), CB in 5 cases (25%), and BLT in 3 (15%) cases. (Table 2) CT was not available for 9 cases and review of the medical record description was inconclusive for reliable determination of the buccolingual fracture orientation.
Table 1:
Mesiodistal fracture orientation was described as being transverse, caudoventral or caudodorsal. The assumed frequency of distribution is how fractures are expected to occur if fracture orientation were purely random. A trend was noted (p = 0.057) for fractures to occur in a caudoventral orientation relative to fractures in the other orientations.
| Mesiodistal Fracture Orientation | N (%) | Assumed % | P-value^ |
|---|---|---|---|
| Caudoventral (CV) | 15 (51.7%) | 33.3% | 0.057 |
| Dorsoventral Transverse (DVT) | 7 (24.1%) | 33.3% | 0.394 |
| Caudodorsal (CD) | 7 (24.1%) | 33.3% | 0.394 |
Table 2:
Buccolingual fracture orientation was described as being buccolingual transverse, caudolingual or caudobuccal. The assumed frequency of distribution is how fractures are expected to occur if fracture orientation were purely random. Fractures occurred significantly more frequently (p = 0.022) in the caudolingual orientation.
| Buccolingual Fracture Orientation | N (%) | Assumed % | P-value^ |
|---|---|---|---|
| Caudolingual (CL) | 12 (60.0%) | 33.3% | 0.022 |
| Caudobuccal (CB) | 5 (25.0%) | 33.3% | 0.580 |
| Buccolingual transverse (BLT) | 3 (15.0%) | 33.3% | 0.133 |
When describing the fractures according to the Schloss and Marretta classification system, it was noted that Type A fracture patterns occurred significantly more often in either mesial (p<0.001) or distal roots (p<0.001) while no instances of Type C or E patterns occurred in either root, and a Type D pattern occurred in the distal root. (Tables 3 and 4) Figure 8 depicts the fracture pattern distribution between the mesial and distal roots as described by Schloss and Marretta. One fracture with M1 present did not receive Schloss and Marretta classification because the alveolus was not involved in the fracture line.
Table 3:
Fracture patterns affecting the mesial roots have been categorized according to the classification system described by Schloss AJ and Marretta SM. Number of cases is represented and the expected (assumed) calculated distribution if the fracture patterns occurred randomly across all 6 possible fracture patterns. Fracture pattern A occurred significantly more frequently (p<0.05) than by chance alone.
| Mesial Root Fracture Pattern | N (%) | Assumed % | P-value^ |
|---|---|---|---|
| A | 8 (80.0%) | 16.7% | < 0.001 |
| B | 1 (10.0%) | 16.7% | 0.888 |
| C | 0 (0%) | 16.7% | 0.322 |
| D | 0 (0%) | 16.7% | 0.322 |
| E | 0 (0%) | 16.7% | 0.322 |
| F | 1 (10.0%) | 16.7% | 0.888 |
Table 4:
Fracture distribution affecting the distal root have been categorized according to the classification system described by Schloss AJ and Marretta SM. Number of cases is represented and the expected (assumed) calculated distribution if fracture patterns were random across 6 possible fracture patterns. A non-random significant increase (p < 0.05) in pattern A is noted to have occurred.
| Distal Root Fracture Pattern | N (%) | Assumed % | P-value^ |
|---|---|---|---|
| A | 10 (62.5%) | 16.7% | < 0.001 |
| B | 1 (6.3%) | 16.7% | 0.434 |
| C | 0 (0%) | 16.7% | 0.146 |
| D | 2 (12.5%) | 16.7% | 0.911 |
| E | 0 (0%) | 16.7% | 0.146 |
| F | 3 (18.8%) | 16.7% | 1.000 |
Figure 8:
!! † A graphical presentation of the fracture pattern distribution involving the mesial or distal roots of the mandibular first molar tooth based upon the classification described by Schloss and Marretta.
When considering fracture etiology and root involvement, the distal root was involved in 16 total fractures with 10 due to animal on animal contact (62.5%), 2 fractures due to inanimate object (12.5%), 1 fracture due to motor vehicle accident (6.3%), 3 cases (18.8%) were categorized as pathologic fractures due to the radiographic presence of alveolar bone loss at the fracture site without a known reported injurious event resulting in fracture. When considering etiological causes for the 10 fractures involving the mesial root, animal-on-animal contact was related to 6 cases (60%), inanimate objects or falls were related to 4 fractures (40%).
DISCUSSION
Our results showed that when the tooth was present (26 cases), fractures involving the mesial root occurred in 38.5% of cases, while the distal root was involved 61.5% of the cases. Despite our results revealing a majority of fractures occurring through the distal root, there was no statistically significant difference in the occurrence of fractures in the mesial versus distal roots. The trend toward the distal root being more commonly involved in fractures through this location suggests that the previously reported decreased mandibular bone height is more significant to fracture development than decreased buccal cortical bone thickness involving the buccal alveolar aspect of the mesial root (10).
Of the 29 mandibular fractures reviewed in this study, only 5 (17.5%) demonstrated comminution. Other studies have reported comminution in mandibular fractures at a rate of 35% (1). The difference in occurrence of comminution could be secondary to several reasons. Firstly, the etiology for fractures in our study were predominantly resulting from animal-on-animal altercations. The previous veterinary study demonstrating 35% reported motor vehicle accidents as the most common fracture etiology (1). Comminuted fractures are thought to be more frequently associated with high velocity injuries. A study performed in humans assessing mandibular fracture etiology showed all comminuted mandibular fractures occurred secondary to missile injuries in the form of bullets or blasts (11). Injuries from other sources such as road traffic accidents, assaults and altercations, falls, industrial or work-related injuries, and sport-related injuries did not result in comminuted fractures in humans as referenced in this study. (11) Due to injuries sustained by these cases occurring from low velocity injuries, we believe that explains our lower results of comminuted fractures. Also, previous reports commenting on occurrence of comminution were reviewing all mandibular fractures, (1) while our study focused on fracture occurrence only at the level of M1. The structural anatomy at the level of M1 allows fractures to propagate with little resistance, as the fracture line will follow the route of least resistance, such as along the tooth root and the size of the M1 tooth roots likely predispose this to happen. (5)
Smaller dogs have previously been found to possess decreased mandibular bone height relative to M1 height. (12) This creates an anatomic circumstance where the PDL space extends from the alveolar margin to close to the ventral cortex. This soft tissue structure within the bone in smaller dogs provides the path of least resistance for fracture propagation, theoretically leading to less force required for fracture, and potentially fewer comminuted fractures. The presence of periodontal disease at the level of M1 can also lead to less bone that the fracture line must course through, therefore less opportunity for comminution to occur and greater compromise to the health of the bone. In our patient population, 7 cases (24.1%) exhibited active or non-worsening radiographic evidence of periodontal disease. Also, the average weight of our patients was 5.9 kg. The smaller size of our average patient, as well as the prevalence of periodontitis in our population could have contributed to low incidence of fracture comminution.
Periodontal disease is often thought to be a contributor to pathologic mandibular fracture, especially in older or small breed dogs and at the M1 region due to the prevalence of severe periodontitis found here. (6) Periodontitis can result in “weakening of the periodontal ligament and alveolus” in the region. (4) Of the 29 cases reviewed, 7 (24.1%) demonstrated evidence of periodontitis (as defined as greater than 25% bone loss) on imaging. Of the cases exhibiting bone loss, all but one patient was over 7 years of age (one patient was 4 years old), and all patients weighed ≤ 10.4kg. This supports previous reports of older or small breed dogs being overrepresented in cases of pathologic jaw fracture due to periodontitis (6) which is also consistent with epidemiologic reports that small breed dogs are overrepresented for the development of periodontal disease. (13) We suspect this value is under estimated in our report, as 3 cases did not have M1 present on imaging, therefore bone loss could not be assessed and periodontal disease could not be confirmed. Aside from radiographic or CT imaging of the fracture sites, the medical records of the included patients in this study did not include consistent or reliable assessment of the remainder of the mouth’s periodontal health. While it can be deduced that periodontal disease involvement impacts the occurrence of fracture at this location, influences fracture pattern development, or explains the absence of the M1 tooth in some patients, a definitive relationship requires further investigation with a larger population.
Small breed dogs are especially over represented in fractures involving M1. (1, 4, 7) A study by Kitschoff et al. assessing mandibular fractures reported the average weight of their patients to be 6.46 kg, with a median weight of 5.2 kg. (4) This trend was consistent with the signalment in the cases meeting our inclusion criteria resulting in mean weight and range for dogs in our study of 5.9 kg (range 1.65 – 33.0 kg). This small population is consistent with larger studies, though not statistically significant.
Young dogs have also been shown to be an overrepresented population for sustaining mandibular fractures. In previous studies, the average reported ages for fracture were approximately 3 years of age (1) with animals less than 2 years of age being over represented. (1,7) One study reported having 57% of their mandibular fractures occur in dogs under 12 months of age (4). These results are consistent with our study where the average of our 29 cases was 2 years (range: 3 months - 13 years).
A previous study by Kitschoff reported that of 135 fractures in the molar region, 54% were transverse, and 36% oblique (4). Of the 135 fractures within the molar region, M1 was involved in 54 cases (40%) (4). In the review of our cases, fractures through M1 resulted in 76% of fractures in an oblique direction, and 24% were oriented transversely. When reviewing mandibular fractures along the long axis of the mandible we found that fractures occur in the CV direction in 15 cases (51.7%), CD direction in 7 cases (24.1%), and DVT 7 cases (24.1%). While there was no significant difference between fracture pattern in this orientation, there was a trend for fractures to occur in the caudoventral direction (p=0.057). Specifics as to why the fracture distribution was predominately oblique in our population may be due to differences in fracture etiology or distinct region of interest (M1 specifically versus the molar region.) This case population demonstrates that fractures did not occur with a random pattern distribution. This fracture line propagation could be secondary to the presence of the tension surface lying along the dorsal aspect of the mandibular body and large coronal root circumference of the M1 roots.
The incidence of fractures in our patient population with M1 teeth occurred in the caudoventral direction (68%) demonstrating that most fractures were an unfavorable pattern. The ventromedial forces of the tongue and the dorsocaudal forces from the muscles of mastication result in the tendency for the fractures edges to be distracted. Recognizing the increased risk for unfavorable fractures to occur at this location can permit better anticipation of fracture morphology, drive investigation into improved repair techniques (load bearing techniques) at this location as well as to help communicate fracture healing prognosis and complication risk.
To the authors’ knowledge, this is the first study describing fracture propagation in the buccolingual direction in dogs. Our findings suggest fractures in the CL direction occur significantly more frequently (p-value = 0.022). We believe the tendency for fractures to occur in the CL direction may also associated with anatomic circumstances creating a path of least resistance for fracture propagation. The lingual cortical bone plate thickness has not been described in dogs to date. It is unknown whether thinning of the lingual cortical bone plate may play a role in fracture propagation in this direction. From the perspective of fracture repair, fractures occurring in the caudolingual direction may be somewhat considered “favorable” due to the adductive (mesial) pull by the digastricus muscle when closing the mouth. A force pull by muscles in this direction would generate compression of fracture fragments which would aid in fracture reduction. Conversely, pull by the intermandibular muscles would result in distraction of fracture fragments in the buccolingual direction regardless of the fracture orientation. Further investigation is necessary to discern the biomechanical advantage, if any, exist for reduction with fractures in either orientation.
One previous report stated that as much as 44.6% of the total M1 attachment surface lies within 5 mm apical to the furcation. (14) Especially, in relation to large size of M1 relative to the mandible, it is realistic for fractures to propagate from this location. When evaluating the fracture patterns at the mesial root we noted fracture Type A occurred in 8 cases (80%) (p < 0.001), and at distal root fractures, Type A occurred in 10 cases (62.5%) (p < 0.001), The occurrence of fracture pattern Type A was the only fracture pattern with statistical significance but occurred in both roots. Six fracture orientations have been described relative to tooth involvement (9). Application of these fracture patterns associated with the M1 tooth roots demonstrate that a non-random occurrence result for both roots. Therefore, some influence exists such as anatomic variabilities and/or trauma etiology. Variabilities could include: normal anatomical features such as PDL surface area, cortical bone thickness or height, M1 height: mandibular height ratio, stress riser formation, and normal bony composition and integrity. Other variabilities for cause of non-random fracture propagation also include changes in anatomy due to pathology such as periodontal or endodontic disease.
The authors believe that the use of the Schloss and Marretta fracture pattern classification is most appropriately designated for prognostic determination of endodontic health associated with teeth in the fracture line. The high propensity for Type A patterns to occur in both mesial or distal roots of M1 further emphasize the detrimental effect that fractures associated with this tooth likely have in endodontic non-vitality, however conclusively demonstrating this was beyond the scope of this study. Endodontic infection can negatively impact efforts in healing when reducing and stabilizing fractures at this location. Acute compromise of endodontic health also emphasizes the necessity for endodontic treatment considerations at the time of fracture repair. Considering the size of the M1 tooth and the valuable role it may play in reduction, stabilization and possible incorporation into non-invasive (intraoral) fracture repair methods, referral to a veterinarian comfortable in performing advanced endodontic procedures may be suggested. Procedures such as hemisection and root retention may result in useful stabilization of the fracture, and as an alternative to complete extraction. Hemisection and endodontic therapy will also reduce the negative impact that endodontic disease can have on fracture healing. (15)
In human studies, fracture propagation and relative risk can be affected by the presence of dentition and impacted teeth. (16, 22) Studies have shown that the presence of the mandibular third molar (M3) correlates with a higher risk of mandibular angle fracture. (18, 19, 20, 21) Patients with M3 were 2.16 times more likely to sustain an angle fracture when compared to those without M3. (23) It is proposed the biomechanics of impacted teeth are altered because teeth occupy space that would otherwise be occupied by bone, which reduces total bone mass. (17) This is further supported by studies in primates. Less force has been shown to be necessary to produce mandibular angle fractures in the presence of M3 as opposed to cases when M3 was not present. (16) Recognizing that in humans, the presence of teeth can influence fracture risk and propagation of fracture patterns, it is reasonable to assume the same applies to canine patients as demonstrated by this study’s results.
Limitations in this study included the retrospective nature which impacted the completeness of the overall oral health assessment of these dogs’ mouths, limited dental history and small case number. It is unknown whether sample size contributed to the limited number of fracture patterns reported here involving M1. Several patterns proposed by Schloss and Marretta were not demonstrated in our cases. Potentially a larger population may demonstrate instances of all patterns. The large propensity for Type A fractures to occur suggests that endodontic compromise must be suspected in mandibular fracture patients with M1 involvement. The retrospective nature of this study also limited the ability to comment on the buccolingual orientation of all patients since CT was not always performed. Further investigation is necessary to determine whether a relationship exists between the caudoventral and buccolingual fracture patterns.
In conclusion, mandibular fractures occurring at the level of M1 tend to occur in the CV direction, which has been described as unfavorable and require repair techniques to bear the load of the force to prevent distraction. The fractures in our population tended to occur more commonly at the distal root, with significantly more fractures coursing along the periodontal ligament space and involving the periapical area, representing a Type A fracture pattern. Type A fracture patterns can lead to endodontic compromise, therefore stressing the need of endodontic therapy for optimal fracture healing and prognosis. Fracture propagation in the orientation CL also occurred with statistical significance. These findings promote the need for fracture stabilization for adequate healing and need for long-term follow-up and monitoring for tooth vitality.
The frequency for fractures to occur at this location in dogs has been previously well reported. In our population, six of seven cases with radiographic evidence of periodontal disease demonstrated severe pathology with >50% alveolar bone loss and 3 fracture cases were categorized as spontaneous due to no reported injurious event. The importance of maintining periodontal health with homecare and routine dental cleanings should be stressed to clients in effort to maintain healthy attachment at this location in hopes of mitigating not only traumatic fracture but also spontaneous fracture or iatrogenic fracture associated with extraction, especially involving the distal root.
Figure: 6.
Case example of the type A fracture pattern along the distal root of M1 tooth. The fracture courses along the periodontal ligament space and exits at the root apex.
Acknowledgements:
The project described was supported by the Clinical and Translational Science Award (CTSA) program, through the NIH National Centre for Advancing Translational Sciences (NCATS), grant UL1TR000427. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.
Footnotes
GE HiSpeed LX/i CT, GE Medical Systems, Milwaukee, WI
Progeny, VetProR DC Digital Dental Radiography System, Midmark Corp, Dayton, OH
OsiriX Imaging Software version 5.4.2, http://www.osirix-viewer.com
Contributor Information
Ellen Scherer, Department of Surgical Sciences, University of Wisconsin-Madison, School of Veterinary Medicine, 2015 Linden Drive, Madison, WI 53706.
Scott Hetzel, Department of Biostatistics and Medical Informatics, University of Wisconsin-Madison, 600 Highland Ave, Madison, WI 53705.
Christopher J. Snyder, Department of Surgical Sciences, University of Wisconsin-Madison, School of Veterinary Medicine, 2015 Linden Drive, Madison, WI 53706.
REFERENCES
- 1.Umphlet RC, Johnson AL. Mandibular fractures in the dog. A retrospective study of 157 cases. Vet Surg. 1990;19(4):272–275. [DOI] [PubMed] [Google Scholar]
- 2.Wong WI. A survey of fractures in the dog and cat in Malaysia. Vet Rec. 1984;115(11):273–274. [DOI] [PubMed] [Google Scholar]
- 3.Phillips IR. A survey of bone fractures in the dog and cat. J Small Anim Pract. 1979; 20(11): 61–674. [DOI] [PubMed] [Google Scholar]
- 4.Kitshoff AM, de Rooster H, Ferreira SM, Steenkamp G. A retrospective study of 109 dogs with mandibular fractures. Vet Comp Orthop Traumatol. 2013;26(1):1–5. [DOI] [PubMed] [Google Scholar]
- 5.Scott HW. The skull and mandible In: Coughlan AR, Miller A, editors. BSAVA Manual of Small Animal Fracture Repair and Management. Cheltenham: British Small Animal Veterinary Association; 1998. 115–129. [Google Scholar]
- 6.Erikson T Physical orodental conditions In: Tutt C, Deeprose J, Crossley DA, editors. BSAVA Manual of Canine and Feline Dentistry 3rd ed Cheltenham: British Small Animal Veterinary Association; 2007:148–159. [Google Scholar]
- 7.Lopes FM, Gioso MA, Ferro DG, Leon-Roman MA, Venturini MA, Correa HL. Oral Fractures in dogs of Brazil - a retrospective study. J Vet Dent. 2005;2(2):86–90. [DOI] [PubMed] [Google Scholar]
- 8.Wiggs RB, Lobprise HB. Veterinary Dentistry Principles & Practice. Philadelphia, PA: Lippincott-Raven; 1997. 262–264. [Google Scholar]
- 9.Schloss AJ, Marretta SA. Prognostic factors affecting teeth in the line of mandibular fractures. J Vet Dent. 1990; 7(4):7–9.2369489 [Google Scholar]
- 10.Snyder CJ, Soukup JW, Drees R, Tabone TJ. Caudal mandibular bone height and buccal cortical bone thickness measured by computed tomography in healthy dogs. Vet Surg. 2016;45(1):21–29. [DOI] [PubMed] [Google Scholar]
- 11.Bede S Mandibular Fractures in Iraq: An Epidemiological Study. Craniomaxillofac Trauma Reconstr. 2014; 8(1):59–63. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 12.Gioso MA, Shofer F, Barros PSM, Harvey CE. Mandible and mandibular first molar tooth measurements in dogs: Relationship of radiographic height to body weight. J Vet. Dent 2001; 18(2):65–68. [DOI] [PubMed] [Google Scholar]
- 13.Harvey CE, Shofer FS, Laster L. Association of age and body weight with periodontal disease in North American Dogs. J Vet Dent. 1994;11:94–105. [PubMed] [Google Scholar]
- 14.Smith MM, Massoudi LM. Potential attachment area of the first mandibular molar in dogs. Am J Vet Res. 1992; 53:258–261. [PubMed] [Google Scholar]
- 15.Reiter AM, Lewis JR, Rawlinson JE, Gracis M. Hemisection and Partial Retention of Carnassial Teeth in Client-Owned Dogs. J Vet Dent. 2005;22(4):216–226. [DOI] [PubMed] [Google Scholar]
- 16.Fuselier JC, Ellis EE, Dodson TB. Do mandibular third molars alter the risk of angle fracture. J Oral Maxillofac Surg. 2002;60:514–418. [DOI] [PubMed] [Google Scholar]
- 17.Reitzik M, Lownie JF, Cleaton-Jones P et al. , Experimental fractures of monkey mandibles. Int J Oral Surg. 1978;7:100. [DOI] [PubMed] [Google Scholar]
- 18.Safdar N, Meechan JG. Relationship between fractures of the mandibular angle and the presence and state of eruption of the lower third molar. Oral Surg Oral Med Oral Pathol. 1995;79:680. [DOI] [PubMed] [Google Scholar]
- 19.Tevepaugh DB, Dodson TB. Are mandibular third molars a risk factor for angle fractures? A retrospective cohort study. J Oral Maxillofac Surg. 1995;53:646. [DOI] [PubMed] [Google Scholar]
- 20.Lee JT, Dodson TB. The effect of mandibular third molar presence and position on the risk of an angle fracture. J Oral Maxillofac Surg. 2000;58:394. [DOI] [PubMed] [Google Scholar]
- 21.Wolujewicz MA. Fractures of the mandible involving the impacted third molar tooth: An analysis of 47 cases. Br J Oral Surg. 1980;18:125–31. [DOI] [PubMed] [Google Scholar]
- 22.Banks P Killey’s fractures of the mandible. 4th ed London: Wright; 1991. p1. [Google Scholar]
- 23.Rajkumar K, Sinha R, Chowdhury R, Chattopadhyay PK. Mandibular third molars as a risk factor for angle fractures: a retrospective study. J Maxillofac Oral Surg. 2009;8(3):237–240. [DOI] [PMC free article] [PubMed] [Google Scholar]