J Oral Maxillofac 48:1283-1287,
Surg
1990
Evaluation of Anterior Maxillary Alveolar Ridge Resorption When Opposed by the Transmandibular Implant H. DEXTER BARBER, DDS,* RICHARD F. SCOTT, DDS, MS,t BARBARA B. MAXSON, DDS, MS,+ AND RAYMOND J. FONSECA, DMD§ Fifteen edentulous patients with complaints regarding denture comfort and/or function were treated with the transmandibular implant. All patients were restored with conventional maxillary dentures opposed by implantsupported removable prostheses. Two to 4 years after surgery, these patients were evaluated for vertical and horizontal maxillary bone loss with a radiographic analysis developed by the authors. With this technique, attention was focused on vertical alveolar ridge resorption in the anterior maxilla. Although the sample size was small, the findings from this study indicate that vertical bone loss in the anterior maxilla does occur when a maxillary denture is opposed by an implant-supported overdenture. Comparison of these results with a previous study that evaluated anterior maxillary resorption when a complete maxillary denture opposed natural mandibular anterior teeth and a distal extension removable partial denture demonstrated no statistically significant difference.
as the “combination syndrome.” This milieu of oral changes can occur when a maxillary complete denture is opposed by mandibular natural anterior teeth and a removable distal extension partial denture.3 When mandibular implants are substituted for the natural anterior teeth, a similar set of biomechanical relationships may exist. In a previous study, the signs of combination syndrome have been identified in a sample of edentulous patients restored with the transmandibular implant.’ Though mandibular implant therapy will improve both comfort and function for the edentulous patient, the long-term effects on maxillary bone resorption is unknown. Therefore, the purpose of this study was to evaluate anterior maxillary bone loss in patients wearing a complete maxillary denture opposed by an implant-supported overdenture using a cephalometric analysis. The findings were compared to those of Kelly,3 who, using a similar technique, evaluated maxillary bone loss associated with conventional prosthetic techniques.
Resorption of bone following tooth loss is observed by the clinician and is documented in the literature. ‘J Such bone resorp tion often results in compromised denture comfort and function.3 One method for successfully restoring masticatory comfort and function in patients with severe mandibular atrophy is reconstruction with the transmandibular implant system.46 Although atrophy of the mandibular ridge is generally more pronounced and problematic for the edentulous patient, preservation of maxillary bone is also of concern. Resorption of the anterior maxillary alveolar ridge is one of several signs identified Received from the University of Michigan, Ann Arbor. * Lecturer, Department of Oral and Maxillofacial Surgery. t Assistant Professor, Department of Oral and Maxillofacial Surgery. $ Assistant Professor, Department of Prosthodontics. 5 Dean, School of Dentistry, University of Pennsylvania, Philadelphia; formerly, Chairman, Department of Oral and Maxillofacial Surgery, University of Michigan. Address correspondence and reprint requests to Dr Barber: Department of Oral and Maxillofacial Surgery, The University of Michigan, School of Dentistry, Ann Arbor, MI 48109-1078. 0 1990 American Association geons 0278-2391/90/4812-0007$3.00/O
of Oral and Maxillofacial
Review of Literature
Sur-
Bone resorption that occurs in the jaws after tooth loss has been a phenomenon of longstanding 1283
1284 interest to the dentist. Atwood’ compared presurgical and postsurgical cephalometric radiographs of 32 patients following dental extraction. He found that the amount and rate of bone resorption varied between individuals. Using similar techniques, Atwood’ later examined 18 complete denture patients following dental extraction. He found that the rate of bone resorption was based on factors such as size, shape, and density of the alveolar ridges; cellular activity of osteoblasts and osteoclasts; frequency, duration, and direction of previous occlusal forces applied to the bone; the patient’s resistance to these previously applied occlusal forces and forces generated from prosthetic appliances. Individual differences in facial morphology may also be related to alveolar ridge height. Bell and Proffit’ found that people with long faces tend to have more alveolar bone height than those with short faces. They also found that persons with low mandibular plane angles and low gonial angles are capable of greater biting forces in both the molar and incisor region. These predisposing anatomic differences may affect the amount of bone resorption that occurs after tooth loss. The effect of prosthodontic treatment on oral anatomy, including bone resorption, also has been reported in the literature. Kelly3 originally described combination syndrome in a sample of patients with complete maxillary dentures opposing natural mandibular anterior teeth and a distal extension removable partial denture. He described five signs or symptoms that commonly occured in this situation. They include 1) loss of bone from the anterior maxillary ridge, 2) overgrowth of the tuberosities, 3) papillary hyperplasia of the hard palate, 4) extrusion of the lower anterior teeth, and 5) the loss of mandibular bone under the partial denture. Saunders” later described six additional signs associated with combination syndrome. They include 1) loss of the vertical dimension of occlusion, 2) occlusal plane discrepancy, 3) anterior spatial repositioning of the mandible, 4) poor adaptation of the prosthesis, 5) epulis lissuratum, and 6) periodontal changes. Recently, Shen and Gongloff” examined 150 patients with maxillary complete dentures. Evidence of alveolar ridge changes associated with combination syndrome was found in 24% of patients with natural mandibular anterior teeth opposing complete maxillary dentures. Maxson et al7 prospectively examined 13 edentulous patients restored with maxillary complete dentures opposed by an overdenture supported by the transmandibular implant. They reported findings consistent with the signs associated with combination syndrome.
MAXILLARY
RESORPTION
DUE TO MANDIBULAR
IMPACT
The transmandibular implant is a transosteal implant of gold alloy.6 Four posts penetrate the mandibular ridge crest between the mental foramina. These posts support a bar construction that accepts the occlusal load and retains the mandibular denture. The assembled implant has a rigid box-frame form that increases the bearing capacity and is intended to accept the masticatory forces. The overdenture reconstruction is implant-borne anteriorly and tissue-borne posteriorly and, therefore, behaves similarly to the distal extension partial denture. Materials and Methods Fifteen edentulous patients with mandibular atrophy and a history of considerable difficulty wearing a conventional mandibular denture were treated with the transmandibular implant system. Implant surgery was performed by the same two surgeons, and a single prosthodontist was responsible for prosthetic reconstruction and follow-up care. The implants were placed over a 2-year period. The length of time from denture delivery to the followup radiographs ranged from 22 to 46 months. The mean length of time was 33.9 months with a standard deviation of 9.4 months (Table 1). The 15 patients in this study included 2 males and 13 females who were between the ages of 45 and 80 (mean, 62.6 + 9.8 years) at the time of surgery (Table 1). All patients were healthy and without history of bone diseases such as osteoporosis and osteomalacia, or malnutrition. The day following surgery, a lateral cephalometric radiograph was made. For this radiograph, the patients were positioned in a relaxed head position with the lips at rest. Postoperatively, the patients were evaluated on a regular follow-up protocol. Dentures were fabricated for delivery 3 months after implant surgery according to the prosthodontic protocol for the transmandibular implant7 The prosthodontist evaluated each patient thereafter at 6 months, 1 year, and then annually. Denture occlusion was monitored at each follow-up visit and adjustments made to avoid premature anterior tooth contacts. Follow-up lateral cephalometric radiographs were made between 2 and 4 years after implant surgery. The postoperative radiographs were made with the same equipment and in the same head and lip position as the preoperative radiographs. A single technician made all of the radiographs. No patients reported any maxillary trauma or changes in their medical history, such as implant surgery, that might influence bone loss. Ail patients had been wearing a maxillary complete denture opposed by an overdenture supported by the transmandibular implant.
1285
BARBERETAL
Table 1.
Patient Data
Initials
Sex
Age at Surgery (yrl
AH HO LS wo JG LW BM PH PG EF AR LB MS ss cs
F F F F M M F F F F F F F F F
68 55 63 80 65 68 52 60 75 63 45 69 65 46 66
Initial Postoperative Radiograph Date
Denture Delivery Date
6181 9186 1l/85 3186 9186 9186 5i86 2186 9187 4187 10186 1l/86 9186 9186 5186
25 24 46 40 34 35 39 42 22 27 34 32 35 35 38
10189 12189 12189 1O/89 10189 11189 1l/89 1l/89 10189 1O/89 1l/89 lo/89 1l/89 1l/89 1O/89
9187 12186 2186 6186 12186 12186 8186 5186 12187 7187 l/87 2187 12186 12186 8/86
The immediate postoperative lateral cephalomettic radiographs and the follow-up radiographs were compared for vertical bone changes in the anterior maxilla using cephafometric landmarks. These landmarks are shown in Figure 1. Using these specific landmarks, vertical and horizontal changes in the anterior maxilla could be measured. The vertical
Months Prosthesis in Function
Follow-up Radiograph Date
measurements consisted of the distances between the cephalometric points C to C’ and E to E’ (Fig 1). Horizontal measurements consisted of the distances between the points ANS to PNS, ANS to C’, and C to D (Fig 1). All of the immediate postoperative and follow-up cephalometric radiographs were traced by a single
E-LINE
I
C-LME
I O-LINE
I
‘NS
C-O LINE
FIGURE 1. ANS, anterior nasal spine; c-point, the most anterior-inferior point on the maxilla; C-point, the point that represents the intersection of the palatal plane and c-line; o-line, the line passing through ANS perpendicular to the palatal plane; C-D line, the line passing through c-point parallel to the palatal plane; D-point, the point that represents the intersection of the D-tine and the C-D line; E'-point,the point 10 mm posterior to c’-point along the palatal plane; E-line, the line passing through E’point perpendicular to the palatal plane; E-point, the most inferior maxillary point along the E-line; PNS, posterior nasal spine. Vertical maxillary measurements: c to c’ and E to E’. Horizontal maxillary measurements: ANS to PNS, ANS to c’, and c to D.
1286
MAXILLARY
examiner. A two-dimensional computer-assisted digitizer (Dentofacial Planner, Dentofacial Software, Inc, Toronto, Canada) was used to map the cephalometric points from the tracings and provide appropriate calculations for linear measurements. The difference between the vertical and horizontal measurements between the immediately postoperative and follow-up tracings for each patient was calculated . Range, mean, and standard deviation were calculated for the vertical measurements, C to C’ and E to E’, and the horizontal measurements, ANS to PNS, ANS to C’, and C to D, for the immediate postoperative and follow-up tracings from the 15 patients. The differences between the postoperative measurements and the follow-up measurements (eg, C to C’ postoperative minus C to C’ follow-up, or ANS to C’ postoperative minus ANS to PNS follow-up) also were calculated. These differences defined the amount of vertical and horizontal bone loss in the anterior maxilla for each patient. Based on length of denture wear, the range, mean, and standard deviation for vertical and horizontal bone loss per month and per year were calculated for each patient. Student’s t tests (P < .05) were used to statistically evaluate vertical bone loss in our study group and also between our vertical bone loss results and those of Kelly,3 who reported anterior maxillary bone loss in six patients wearing a maxillary complete denture opposed by a distal extension partial denture (mean, 0.43 mm ? 1.36). Results We found statistically significant vertical bone loss as measured by postoperative to follow-up differences at landmarks C to C’ and E to E’ (P < .05) (Table 2). We also found no statistically significant difference when our results were compared with Kelly’s results (2’ < .05). There were minimal horizontal bony changes in the study group (Table 3). Discussion When Kelly3 originally studied combination syndrome, one area specifically evaluated was the loss of bone height in the anterior maxilla when a complete maxillary denture opposed natural mandibular anterior teeth and a class I removable partial denture. Over a 3-year period, cephalometric tracings at l-year intervals were made using the sellanasion line as a base. His sample of six patients showed a loss of 1 to 3 mm of anterior maxillary ridge height over this 3-year period. Statistical analysis of these
RESORPTION
Table 2.
DUE TO MANDIBULAR
IMPACT
Vertical Maxillary Measurements Minimum Maximum Mean
t Test
SD
C to C’ postoperative c to C’ follow-up C to C’ postoperative minus C to C’ follow-up Bone loss, C to C’ per month Bone loss, C to C’ per year
8 7
20 20
14.4 13.3
0
3
I
E to E’ postoperative E to E’ follow-up E to E’ postoperative minus E to E’ follow-up Bone loss, E to E’ per month Bone loss, E to E’ per year
I 6
19 18
12.5 12.8
3.3 3.2
0
1
.8
.7
4.43%
Measurements * P < 0.05.
3.1 3.4
.8
48.41*
0
.06
.03
.02
5.81*
0
.73
.36
.22
6.34*
0
.I
.02
.02
3.87*
0
.84
.24
.I6
5.81*
are in millimeters.
results showed a mean vertical bone loss in the anterior maxilla of 0.43 mm + 1.36 per year. In our sample of 15 edentulous patients restored with a maxillary complete denture opposed by an implant-supported overdenture, continuous maxillary anterior vertical bone loss also was found, as evidenced by the changes in anterior maxillary bone height from the postoperative baseline to the 2- to 4-year follow-up examination (Table 2). In comparison to Kelly’s findings, our results showed no statistically significant difference in the amount of horizontal maxillary bone loss identified Table 3.
Horizontal Maxillary Measurements Minimum
ANS to PNS postoperative ANS to PNS follow-up ANS to PNS postoperative minus ANS to PNS follow-up Bone loss, ANS to PNS per month Bone loss, ANS to PNS per year ANS to C’ postoperative ANS to C’ follow-up ANS to C’ postoperative minus ANS to PNS follow-up Bone loss, ANS to PNS per month Bone loss, ANS to PNS per year
45 45
Maximum 60 59
.04
0 0
SD
50
4.5 .36
49.5
0 0
Mean
.46
-2
8 8
-2
1
.36
.28
.Ol
.03
.12 4.4 3.9
.07 2.2 2.7
.07
.03
0
.04
.02
.03
0
.48
.19
.08
All measurements in millimeters. Measurements D-points were the same as ANS to C’-points.
for the C- to
1287
BARBERETAL
(P < .05) (Table 3). The difference in standard deviation may be related to the difference in sample size. Based on these findings, it can be inferred that the transmandibular implant caused no more maxillary bone loss than that expected when natural teeth are present in the anterior mandible. This information may be useful in counseling patients regarding the future sequelae of implant treatment. It should be mentioned that with a larger sample size a more definitive comparison with Kelly’s study could be made. However, some word of caution is necessary. The regular prosthetic follow-up may have been responsible for minimizing the amount of anterior maxillary resorption that can occur as a result of anterior occlusal prematurities that develop as a result of tooth wear or mandibular bone loss.’ Regular occlusal adjustments were made to eliminate these occlusal pressures. Therefore, in the absence of regular maintenance, there may be a potential for greater bone loss than reported in this study. Given this potential, the oral and maxillofacial surgeon and restorative dentist may wish to stress to their patients the importance of long-term follow-up care after denture delivery for conservation of maxillary bone. One assumption made in this study was that the transmandibular implant, when restored with an overdenture, creates a similar biomechanical situation to the distal extension removable partial denture. Several factors support this assumption. Maxson et al,’ in a 2-year prospective study of 13 edentulous patients who were restored with the transmandibular implant and overdenture, found clinical findings consistent with combination syndrome. These included evidence of lost posterior mandibular ridge height, epulis fissuratum, loss of vertical dimension of occlusion, and anterior occlusal prematurities. Fortunately, extrusion of the implant does not occur, and many of the sequelae associated with retained anterior mandibular teeth are avoided, The predominance of females in this sample also deserves mention. Bone loss identified in this study may not be representative for male denture wearers. Although the focus of the radiographic analysis in this study was vertical bone loss, mean horizontal bone loss along the palatal plane, ANS to PNS, was also measured and found to be negligible (0.12 mm per year). These findings compare with previous studies describing combination syndrome in which
natural anterior mandibular teeth were present instead of the transmandibular implant system. In the previous studies, maxillary horizontal bone loss was also identified as an insignificant finding. In fact, the mean difference found in this study for horizontal bone loss may be simply examiner error. It is unlikely that the -2 mm changes (ANS to C’) found for one subject represent true bone apposition. Differences in radiographic quality and tracing error may be greater for this measurement owing to the thin isthmus of bone that defines the differences between ANS and C’. Although the results for vertical bone loss demonstrate better consistency and less variability than those for the horizontal distances, the inherent problems associated with tracing cephalometric radiographs undoubtedly contributed to errors in this study. Larger sample size and repeated measures over more years would improve the power of statistical testing. However, it was not the intent of this preliminary study to determine absolute maxillary bone loss. Further studies with a larger sample size that considers gender differences and spans longer time periods are needed. References 1. Atwood DA: A cephalometric study of the clinical rest position of the mandible. The variability in the rate of bone loss following the removal of occlusal contacts. J Prosthet Dent 7544, 1957 2. Tallgren A: The continuing reduction of the residual alveolar ridges in complete denture wearers: A mixed-longitudinal study covering 25 years. J Prosthet Dent 27: 120, 1972 3. Kelly E: Changes caused by a mandibular removable partial denture opposing a maxillary complete denture. J Prosthet Dent 27:140, 1972 4. Bosker H: The transmandibular implant. Doctoral dissertation, The Netherlands, University of Utrecht, 1986 5. Bosker H, van Dijk L: The transmandibular implant: A 12year follow-up study. J Oral Maxillofac Surg 47:442, 1989 6. Powers MP, Maxson BB, Scott RF, et al: The transmandibular implant: A 2-year prospective study. J Oral Maxillofat Surg 47:679, 1989 7. Maxson BB, Powers MJ, Scott RF: Prosthodontic considerations for the transmandibular implant. J Prosthet Dent 63:554, 1990 8. Atwood DA: Some clinical factors related to rate of resorption of residual ridges. J Prostbet Dent 12:441, 1%2 9. Bell WH, Proffrt WR, White RP: Surgical Corrections of Dentofacial Deformities. Philadelphia, PA, Saunders, 1980, pp 234-441 10. Saunders TR, Gillis RE, Desjardins RP: Maxillary complete denture opposing mandibular bilateral distal extension partial denture: Treatment considerations. J Prosthet Dent 41: 124, 1979 11. Shen K, Gongloff R: Prevalence of the “combination among denture patients. J Prosthet Dent syndrome” 62642, 1989
Surg
1990
Evaluation of Anterior Maxillary Alveolar Ridge Resorption When Opposed by the Transmandibular Implant H. DEXTER BARBER, DDS,* RICHARD F. SCOTT, DDS, MS,t BARBARA B. MAXSON, DDS, MS,+ AND RAYMOND J. FONSECA, DMD§ Fifteen edentulous patients with complaints regarding denture comfort and/or function were treated with the transmandibular implant. All patients were restored with conventional maxillary dentures opposed by implantsupported removable prostheses. Two to 4 years after surgery, these patients were evaluated for vertical and horizontal maxillary bone loss with a radiographic analysis developed by the authors. With this technique, attention was focused on vertical alveolar ridge resorption in the anterior maxilla. Although the sample size was small, the findings from this study indicate that vertical bone loss in the anterior maxilla does occur when a maxillary denture is opposed by an implant-supported overdenture. Comparison of these results with a previous study that evaluated anterior maxillary resorption when a complete maxillary denture opposed natural mandibular anterior teeth and a distal extension removable partial denture demonstrated no statistically significant difference.
as the “combination syndrome.” This milieu of oral changes can occur when a maxillary complete denture is opposed by mandibular natural anterior teeth and a removable distal extension partial denture.3 When mandibular implants are substituted for the natural anterior teeth, a similar set of biomechanical relationships may exist. In a previous study, the signs of combination syndrome have been identified in a sample of edentulous patients restored with the transmandibular implant.’ Though mandibular implant therapy will improve both comfort and function for the edentulous patient, the long-term effects on maxillary bone resorption is unknown. Therefore, the purpose of this study was to evaluate anterior maxillary bone loss in patients wearing a complete maxillary denture opposed by an implant-supported overdenture using a cephalometric analysis. The findings were compared to those of Kelly,3 who, using a similar technique, evaluated maxillary bone loss associated with conventional prosthetic techniques.
Resorption of bone following tooth loss is observed by the clinician and is documented in the literature. ‘J Such bone resorp tion often results in compromised denture comfort and function.3 One method for successfully restoring masticatory comfort and function in patients with severe mandibular atrophy is reconstruction with the transmandibular implant system.46 Although atrophy of the mandibular ridge is generally more pronounced and problematic for the edentulous patient, preservation of maxillary bone is also of concern. Resorption of the anterior maxillary alveolar ridge is one of several signs identified Received from the University of Michigan, Ann Arbor. * Lecturer, Department of Oral and Maxillofacial Surgery. t Assistant Professor, Department of Oral and Maxillofacial Surgery. $ Assistant Professor, Department of Prosthodontics. 5 Dean, School of Dentistry, University of Pennsylvania, Philadelphia; formerly, Chairman, Department of Oral and Maxillofacial Surgery, University of Michigan. Address correspondence and reprint requests to Dr Barber: Department of Oral and Maxillofacial Surgery, The University of Michigan, School of Dentistry, Ann Arbor, MI 48109-1078. 0 1990 American Association geons 0278-2391/90/4812-0007$3.00/O
of Oral and Maxillofacial
Review of Literature
Sur-
Bone resorption that occurs in the jaws after tooth loss has been a phenomenon of longstanding 1283
1284 interest to the dentist. Atwood’ compared presurgical and postsurgical cephalometric radiographs of 32 patients following dental extraction. He found that the amount and rate of bone resorption varied between individuals. Using similar techniques, Atwood’ later examined 18 complete denture patients following dental extraction. He found that the rate of bone resorption was based on factors such as size, shape, and density of the alveolar ridges; cellular activity of osteoblasts and osteoclasts; frequency, duration, and direction of previous occlusal forces applied to the bone; the patient’s resistance to these previously applied occlusal forces and forces generated from prosthetic appliances. Individual differences in facial morphology may also be related to alveolar ridge height. Bell and Proffit’ found that people with long faces tend to have more alveolar bone height than those with short faces. They also found that persons with low mandibular plane angles and low gonial angles are capable of greater biting forces in both the molar and incisor region. These predisposing anatomic differences may affect the amount of bone resorption that occurs after tooth loss. The effect of prosthodontic treatment on oral anatomy, including bone resorption, also has been reported in the literature. Kelly3 originally described combination syndrome in a sample of patients with complete maxillary dentures opposing natural mandibular anterior teeth and a distal extension removable partial denture. He described five signs or symptoms that commonly occured in this situation. They include 1) loss of bone from the anterior maxillary ridge, 2) overgrowth of the tuberosities, 3) papillary hyperplasia of the hard palate, 4) extrusion of the lower anterior teeth, and 5) the loss of mandibular bone under the partial denture. Saunders” later described six additional signs associated with combination syndrome. They include 1) loss of the vertical dimension of occlusion, 2) occlusal plane discrepancy, 3) anterior spatial repositioning of the mandible, 4) poor adaptation of the prosthesis, 5) epulis lissuratum, and 6) periodontal changes. Recently, Shen and Gongloff” examined 150 patients with maxillary complete dentures. Evidence of alveolar ridge changes associated with combination syndrome was found in 24% of patients with natural mandibular anterior teeth opposing complete maxillary dentures. Maxson et al7 prospectively examined 13 edentulous patients restored with maxillary complete dentures opposed by an overdenture supported by the transmandibular implant. They reported findings consistent with the signs associated with combination syndrome.
MAXILLARY
RESORPTION
DUE TO MANDIBULAR
IMPACT
The transmandibular implant is a transosteal implant of gold alloy.6 Four posts penetrate the mandibular ridge crest between the mental foramina. These posts support a bar construction that accepts the occlusal load and retains the mandibular denture. The assembled implant has a rigid box-frame form that increases the bearing capacity and is intended to accept the masticatory forces. The overdenture reconstruction is implant-borne anteriorly and tissue-borne posteriorly and, therefore, behaves similarly to the distal extension partial denture. Materials and Methods Fifteen edentulous patients with mandibular atrophy and a history of considerable difficulty wearing a conventional mandibular denture were treated with the transmandibular implant system. Implant surgery was performed by the same two surgeons, and a single prosthodontist was responsible for prosthetic reconstruction and follow-up care. The implants were placed over a 2-year period. The length of time from denture delivery to the followup radiographs ranged from 22 to 46 months. The mean length of time was 33.9 months with a standard deviation of 9.4 months (Table 1). The 15 patients in this study included 2 males and 13 females who were between the ages of 45 and 80 (mean, 62.6 + 9.8 years) at the time of surgery (Table 1). All patients were healthy and without history of bone diseases such as osteoporosis and osteomalacia, or malnutrition. The day following surgery, a lateral cephalometric radiograph was made. For this radiograph, the patients were positioned in a relaxed head position with the lips at rest. Postoperatively, the patients were evaluated on a regular follow-up protocol. Dentures were fabricated for delivery 3 months after implant surgery according to the prosthodontic protocol for the transmandibular implant7 The prosthodontist evaluated each patient thereafter at 6 months, 1 year, and then annually. Denture occlusion was monitored at each follow-up visit and adjustments made to avoid premature anterior tooth contacts. Follow-up lateral cephalometric radiographs were made between 2 and 4 years after implant surgery. The postoperative radiographs were made with the same equipment and in the same head and lip position as the preoperative radiographs. A single technician made all of the radiographs. No patients reported any maxillary trauma or changes in their medical history, such as implant surgery, that might influence bone loss. Ail patients had been wearing a maxillary complete denture opposed by an overdenture supported by the transmandibular implant.
1285
BARBERETAL
Table 1.
Patient Data
Initials
Sex
Age at Surgery (yrl
AH HO LS wo JG LW BM PH PG EF AR LB MS ss cs
F F F F M M F F F F F F F F F
68 55 63 80 65 68 52 60 75 63 45 69 65 46 66
Initial Postoperative Radiograph Date
Denture Delivery Date
6181 9186 1l/85 3186 9186 9186 5i86 2186 9187 4187 10186 1l/86 9186 9186 5186
25 24 46 40 34 35 39 42 22 27 34 32 35 35 38
10189 12189 12189 1O/89 10189 11189 1l/89 1l/89 10189 1O/89 1l/89 lo/89 1l/89 1l/89 1O/89
9187 12186 2186 6186 12186 12186 8186 5186 12187 7187 l/87 2187 12186 12186 8/86
The immediate postoperative lateral cephalomettic radiographs and the follow-up radiographs were compared for vertical bone changes in the anterior maxilla using cephafometric landmarks. These landmarks are shown in Figure 1. Using these specific landmarks, vertical and horizontal changes in the anterior maxilla could be measured. The vertical
Months Prosthesis in Function
Follow-up Radiograph Date
measurements consisted of the distances between the cephalometric points C to C’ and E to E’ (Fig 1). Horizontal measurements consisted of the distances between the points ANS to PNS, ANS to C’, and C to D (Fig 1). All of the immediate postoperative and follow-up cephalometric radiographs were traced by a single
E-LINE
I
C-LME
I O-LINE
I
‘NS
C-O LINE
FIGURE 1. ANS, anterior nasal spine; c-point, the most anterior-inferior point on the maxilla; C-point, the point that represents the intersection of the palatal plane and c-line; o-line, the line passing through ANS perpendicular to the palatal plane; C-D line, the line passing through c-point parallel to the palatal plane; D-point, the point that represents the intersection of the D-tine and the C-D line; E'-point,the point 10 mm posterior to c’-point along the palatal plane; E-line, the line passing through E’point perpendicular to the palatal plane; E-point, the most inferior maxillary point along the E-line; PNS, posterior nasal spine. Vertical maxillary measurements: c to c’ and E to E’. Horizontal maxillary measurements: ANS to PNS, ANS to c’, and c to D.
1286
MAXILLARY
examiner. A two-dimensional computer-assisted digitizer (Dentofacial Planner, Dentofacial Software, Inc, Toronto, Canada) was used to map the cephalometric points from the tracings and provide appropriate calculations for linear measurements. The difference between the vertical and horizontal measurements between the immediately postoperative and follow-up tracings for each patient was calculated . Range, mean, and standard deviation were calculated for the vertical measurements, C to C’ and E to E’, and the horizontal measurements, ANS to PNS, ANS to C’, and C to D, for the immediate postoperative and follow-up tracings from the 15 patients. The differences between the postoperative measurements and the follow-up measurements (eg, C to C’ postoperative minus C to C’ follow-up, or ANS to C’ postoperative minus ANS to PNS follow-up) also were calculated. These differences defined the amount of vertical and horizontal bone loss in the anterior maxilla for each patient. Based on length of denture wear, the range, mean, and standard deviation for vertical and horizontal bone loss per month and per year were calculated for each patient. Student’s t tests (P < .05) were used to statistically evaluate vertical bone loss in our study group and also between our vertical bone loss results and those of Kelly,3 who reported anterior maxillary bone loss in six patients wearing a maxillary complete denture opposed by a distal extension partial denture (mean, 0.43 mm ? 1.36). Results We found statistically significant vertical bone loss as measured by postoperative to follow-up differences at landmarks C to C’ and E to E’ (P < .05) (Table 2). We also found no statistically significant difference when our results were compared with Kelly’s results (2’ < .05). There were minimal horizontal bony changes in the study group (Table 3). Discussion When Kelly3 originally studied combination syndrome, one area specifically evaluated was the loss of bone height in the anterior maxilla when a complete maxillary denture opposed natural mandibular anterior teeth and a class I removable partial denture. Over a 3-year period, cephalometric tracings at l-year intervals were made using the sellanasion line as a base. His sample of six patients showed a loss of 1 to 3 mm of anterior maxillary ridge height over this 3-year period. Statistical analysis of these
RESORPTION
Table 2.
DUE TO MANDIBULAR
IMPACT
Vertical Maxillary Measurements Minimum Maximum Mean
t Test
SD
C to C’ postoperative c to C’ follow-up C to C’ postoperative minus C to C’ follow-up Bone loss, C to C’ per month Bone loss, C to C’ per year
8 7
20 20
14.4 13.3
0
3
I
E to E’ postoperative E to E’ follow-up E to E’ postoperative minus E to E’ follow-up Bone loss, E to E’ per month Bone loss, E to E’ per year
I 6
19 18
12.5 12.8
3.3 3.2
0
1
.8
.7
4.43%
Measurements * P < 0.05.
3.1 3.4
.8
48.41*
0
.06
.03
.02
5.81*
0
.73
.36
.22
6.34*
0
.I
.02
.02
3.87*
0
.84
.24
.I6
5.81*
are in millimeters.
results showed a mean vertical bone loss in the anterior maxilla of 0.43 mm + 1.36 per year. In our sample of 15 edentulous patients restored with a maxillary complete denture opposed by an implant-supported overdenture, continuous maxillary anterior vertical bone loss also was found, as evidenced by the changes in anterior maxillary bone height from the postoperative baseline to the 2- to 4-year follow-up examination (Table 2). In comparison to Kelly’s findings, our results showed no statistically significant difference in the amount of horizontal maxillary bone loss identified Table 3.
Horizontal Maxillary Measurements Minimum
ANS to PNS postoperative ANS to PNS follow-up ANS to PNS postoperative minus ANS to PNS follow-up Bone loss, ANS to PNS per month Bone loss, ANS to PNS per year ANS to C’ postoperative ANS to C’ follow-up ANS to C’ postoperative minus ANS to PNS follow-up Bone loss, ANS to PNS per month Bone loss, ANS to PNS per year
45 45
Maximum 60 59
.04
0 0
SD
50
4.5 .36
49.5
0 0
Mean
.46
-2
8 8
-2
1
.36
.28
.Ol
.03
.12 4.4 3.9
.07 2.2 2.7
.07
.03
0
.04
.02
.03
0
.48
.19
.08
All measurements in millimeters. Measurements D-points were the same as ANS to C’-points.
for the C- to
1287
BARBERETAL
(P < .05) (Table 3). The difference in standard deviation may be related to the difference in sample size. Based on these findings, it can be inferred that the transmandibular implant caused no more maxillary bone loss than that expected when natural teeth are present in the anterior mandible. This information may be useful in counseling patients regarding the future sequelae of implant treatment. It should be mentioned that with a larger sample size a more definitive comparison with Kelly’s study could be made. However, some word of caution is necessary. The regular prosthetic follow-up may have been responsible for minimizing the amount of anterior maxillary resorption that can occur as a result of anterior occlusal prematurities that develop as a result of tooth wear or mandibular bone loss.’ Regular occlusal adjustments were made to eliminate these occlusal pressures. Therefore, in the absence of regular maintenance, there may be a potential for greater bone loss than reported in this study. Given this potential, the oral and maxillofacial surgeon and restorative dentist may wish to stress to their patients the importance of long-term follow-up care after denture delivery for conservation of maxillary bone. One assumption made in this study was that the transmandibular implant, when restored with an overdenture, creates a similar biomechanical situation to the distal extension removable partial denture. Several factors support this assumption. Maxson et al,’ in a 2-year prospective study of 13 edentulous patients who were restored with the transmandibular implant and overdenture, found clinical findings consistent with combination syndrome. These included evidence of lost posterior mandibular ridge height, epulis fissuratum, loss of vertical dimension of occlusion, and anterior occlusal prematurities. Fortunately, extrusion of the implant does not occur, and many of the sequelae associated with retained anterior mandibular teeth are avoided, The predominance of females in this sample also deserves mention. Bone loss identified in this study may not be representative for male denture wearers. Although the focus of the radiographic analysis in this study was vertical bone loss, mean horizontal bone loss along the palatal plane, ANS to PNS, was also measured and found to be negligible (0.12 mm per year). These findings compare with previous studies describing combination syndrome in which
natural anterior mandibular teeth were present instead of the transmandibular implant system. In the previous studies, maxillary horizontal bone loss was also identified as an insignificant finding. In fact, the mean difference found in this study for horizontal bone loss may be simply examiner error. It is unlikely that the -2 mm changes (ANS to C’) found for one subject represent true bone apposition. Differences in radiographic quality and tracing error may be greater for this measurement owing to the thin isthmus of bone that defines the differences between ANS and C’. Although the results for vertical bone loss demonstrate better consistency and less variability than those for the horizontal distances, the inherent problems associated with tracing cephalometric radiographs undoubtedly contributed to errors in this study. Larger sample size and repeated measures over more years would improve the power of statistical testing. However, it was not the intent of this preliminary study to determine absolute maxillary bone loss. Further studies with a larger sample size that considers gender differences and spans longer time periods are needed. References 1. Atwood DA: A cephalometric study of the clinical rest position of the mandible. The variability in the rate of bone loss following the removal of occlusal contacts. J Prosthet Dent 7544, 1957 2. Tallgren A: The continuing reduction of the residual alveolar ridges in complete denture wearers: A mixed-longitudinal study covering 25 years. J Prosthet Dent 27: 120, 1972 3. Kelly E: Changes caused by a mandibular removable partial denture opposing a maxillary complete denture. J Prosthet Dent 27:140, 1972 4. Bosker H: The transmandibular implant. Doctoral dissertation, The Netherlands, University of Utrecht, 1986 5. Bosker H, van Dijk L: The transmandibular implant: A 12year follow-up study. J Oral Maxillofac Surg 47:442, 1989 6. Powers MP, Maxson BB, Scott RF, et al: The transmandibular implant: A 2-year prospective study. J Oral Maxillofat Surg 47:679, 1989 7. Maxson BB, Powers MJ, Scott RF: Prosthodontic considerations for the transmandibular implant. J Prosthet Dent 63:554, 1990 8. Atwood DA: Some clinical factors related to rate of resorption of residual ridges. J Prostbet Dent 12:441, 1%2 9. Bell WH, Proffrt WR, White RP: Surgical Corrections of Dentofacial Deformities. Philadelphia, PA, Saunders, 1980, pp 234-441 10. Saunders TR, Gillis RE, Desjardins RP: Maxillary complete denture opposing mandibular bilateral distal extension partial denture: Treatment considerations. J Prosthet Dent 41: 124, 1979 11. Shen K, Gongloff R: Prevalence of the “combination among denture patients. J Prosthet Dent syndrome” 62642, 1989
