Impact of facial form on the relationship between conventional or implant-assisted mandibular dentures and masticatory function

Impact of facial form on the relationship between conventional or implantassisted mandibular dentures and masticatory function Kent T. Ochiai, DDS, PhD,a Satoru Hojo, DDS, PhD,b Camille Nakamura, DDS,c Hideki Ikeda, DDS, MS,d and Neal R. Garrett, PhDe Herman Ostrow School of Dentistry, University of Southern California, Los Angeles, Calif; Kanagawa Dental College, Kanagawa, Japan; School of Dentistry, University of California, at Los Angeles, Los Angeles, Calif Statement of problem. It is not clear if the interaction of craniofacial form with type of prosthetic restoration (conventional or implant-assisted) is related to masticatory function in complete denture patients. Purpose. The purpose of this study was to investigate the relationships among facial form, skeletal class, alveolar residual ridge heights and masticatory function in subjects treated with implant-assisted or conventional mandibular dentures with lateral cephalometric evaluation. Material and methods. Data from a previously reported randomized controlled clinical trial were accessed to compare treatment success rates, functional and perceptual outcomes, dietary intake, and craniofacial relationships between mandibular complete dentures and implant overdentures in edentulous diabetic subjects. Evaluation of the digitized post-insertion lateral cephalometric radiographs provided measures of facial form (mesocephalic “medium”, brachycephalic “broad and square”, dolichocephalic “vertical and long”), skeletal class (Class I, Class II, Class III), and alveolar ridge height (mm), which were compared to results of standardized masticatory tests as evaluated using MANOVA and REGW post-hoc evaluation (α=.05). Results. Masticatory performance on the preferred side was slightly reduced in the dolichocephalic group, compared to brachycephalic and mesocephalic groups (P=.085). Swallowing threshold performance was significantly less in skeletal Class II subjects compared to Class I (P=.034). Maxillary residual alveolar ridge height was significantly less in the brachycephalic group compared to the dolichocephalic group (P<.001). No differences in mandibular ridge height were seen associated with facial form or skeletal class groups. Conclusions. Facial form may be related to masticatory function with conventional and implant-assisted mandibular dentures, but larger controlled studies are needed to confirm this relationship. Alveolar ridge height is reduced in edentulous subjects with a brachycephalic facial form. (J Prosthet Dent 2011;105:256-265)

Clinical Implications

Pre- and post- treatment clinical cephalometric evaluations of facial form and skeletal class may quantitatively separate differences in mechanical influence or impact of different patient profiles upon treatment prognosis or outcome. Facial form assessment is a clinically valuable parameter for prosthodontic treatment evaluations involving dental implants, alveolar resorptions and masticatory function. Clinical Associate Professor, Restorative Dentistry, Herman Ostrow School of Dentistry, University of Southern California. Associate Professor, Department of Prosthetics and Maxillofacial Prosthetics, Kanagawa Dental College. c Research Assistant, Weintraub Center for Reconstructive Biotechnology, School of Dentistry, University of California, at Los Angeles. d Clinical Assistant Professor, Orthodontics, Advanced Education in Periodontics, Herman Ostrow School of Dentistry, University of Southern California. e Professor, Advanced Prosthodontics, Biomaterials, and Hospital Dentistry, Weintraub Center for Reconstructive Biotechnology, School of Dentistry, University of California at Los Angeles. a

b

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April 2011 The lateral cephalometric film has proved to be an effective tool for the diagnosis of craniofacial form for use in the planning of treatment mechanics and the understanding of individual patient function.1-4 Malocclusions evaluated and based on dental relationships have been used to rank the masticatory performance of differing occlusal profiles.5,6 The method of dentally-based estimation of skeletal relationships has been used to rank relative classifications of malocclusion for the purposes of planning dental care.5 The skeletal class evaluation may be independent of the facial profile evaluation. Previous functional evaluation of skeletal class, without the benefit of lateral cephalometric radiographs, demonstrated higher levels of masticatory function for Class I skeletal relation subjects.6 The determination of edentulous arch relationships using a dentally-based evaluative description may be a partial representation of observed craniofacial clinical relationships, especially following tooth loss or reconstruction. The origins of the cephalic index for comparative craniofacial evaluation have been attributed to Retzius.7 The advent of a standardized radiographic evaluation technique broadened the scope and extent of craniometric study.1 However, there are only limited reports of the use of cephalometric analysis for the mechanical evaluation of prosthodontic therapies or the assessment of functional treatment outcomes.8-13 The assessment of the functional outcomes of prosthetic treatment with conventional and implant dentures using craniometric measurements of facial form and skeletal class has not been previously reported. Prior craniometric studies of the facial form and prosthetic treatment used evaluations based upon complete denture prosthodontics.8-10 The differential expectations and predictions of relative function levels, differences in support, or changes in oral function relative to treatment with or without osseointegrated implants have not been reported in rela-

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tion to different facial form types and skeletal classes of evaluation. It has been suggested that correction of malocclusion and craniofacial relationships or the restoration of the dentition with conventional or implant-supported prostheses results in an improvement of masticatory function.14-21 The relative impact of these various treatment factors upon masticatory function outcomes is not clear. Improvements in masticatory function and increased occlusal force have been demonstrated after surgical craniofacial correction of the skeletal profile based on different pre- and post-operative functional assessments.15,16,19 Shiratsuchi et al,17 demonstrated gradual improvements in masticatory function from 6 to 24 months following surgery, with the Class II corrected group approaching the level of Class I subjects. Retrognathic patients with poor initial masticatory capacity have also demonstrated improvement in masticatory performance following orthognathic surgery.18 Additional factors to be considered when assessing the effects of facial form on masticatory function in edentulous patients are residual alveolar ridge support quality and type of prosthetic rehabilitation.22-24 The rate of edentulous ridge resorption has been shown to vary between different patients and for anatomic locations.25 However, the relationship between the level of resorption and cephalic index or skeletal class has not been evaluated. Masticatory function in patients with severe mandibular alveolar ridge resorption has also been shown to functionally benefit from the support provided by osseointegrated implants.14,15,26,27 The effects of skeletal facial form on the edentulous alveolar ridge have not been directly evaluated. Reduced levels of relative alveolar ridge height resorption are well known parameters of treatment difficulty and patient adaptation for conventional denture.22-24,28 Both Fontijn-Tekamp et al,21 and Kimoto and Garrett,26 found mandibular ridge height to have a

significant interaction with the type of denture (conventional or implantsupported) on masticatory function. Overall, patients with severely reduced alveolar ridge height undergoing prosthetic restoration with implant overdentures should have reasonable expectations for improvement in masticatory function. Facial form has not been suggested to affect the functional results for patients restored with complete or implantsupported dentures. In addition, the relationships between alveolar ridge heights, facial form and masticatory function have not been evaluated. Assessment of the skeletal profile and assignment to a cephalic facial form index was recommended based upon observed relationships for occlusal force and muscle function.8,10 The effect of dental implant support and implant overdentures with subjects of differing skeletal facial profiles has not been determined. Masticatory efficiency and occlusal force have been reported related to different Frankfort mandibular plane angles of skeletal relationships.9 The Frankfort mandibular plane angle is a single measurement in the determination of a facial form and cephalic facial index.8,10 Conventional cephalometric evaluations of dentate subjects uses skeletal, dental, and facial landmarks obtained from lateral cephalometric radiographs and may include posterior-anterior and coronal cephalometric radiographic evaluations of the hard and soft tissues.1,8,10 These comparative radiographic findings of hard and soft tissues have been previously documented to provide prognostic information for treatment planning purposes.2,8 The lateral cephalometric radiograph has been previously used as a primary assessment of completely edentulous subjects to determine basic independent measurements for differential determination and profile assessment.10,11,13,26 Few reports have discussed the use of craniometric assessment and osseointegrated dental implant treatment on treatment out-

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A

B

C

1 Radiographic examples: A, Brachycephaly, B, Mesocephaly, and C, Dolichocephaly. comes or patient prognosis.9,10,13, 26 The purpose of this study was to investigate the relationships among facial form, skeletal class, alveolar residual ridge height and masticatory function in subjects treated with conventional or implant-assisted mandibular dentures. Two primary null-hypotheses were evaluated: (1) masticatory performance does not differ between categories of facial form and (2) masticatory performance does not differ between categories of skeletal class. Additional aims included evaluation of the relationships between alveolar ridge height, facial form and skeletal class for subjects restored with conventional or implantassisted prostheses.

MATERIAL AND METHODS Sixty-nine subjects (25 with complete dentures (CDs) and 44 with implant overdentures (IODs), who received post-insertion lateral cephalometric radiographs, were evaluated for outcome-related functional and craniofacial characteristics following their participation in a completed randomized clinical trial. The clinical trial evaluated the outcomes related to treatment success, function, psychological perceptions and craniofacial characteristics following treatment with mandibular complete dentures (CD group) and implant overdentures (IOD group) of diabetic complete denture wearers. The initial trial and subsequent review and analysis of radiographic records

were approved by institutional review boards at the University of California, Los Angeles and the Department of Veterans Affairs Greater Los Angeles Healthcare System. The initial study subjects provided informed consent for the protocol. Results of outcomes related to treatment success, masticatory function, patient satisfaction, dietary intake, and food preferences have been previously reported.26,29-34 Subjects were evaluated at entry with their original dentures and again after treatment completion with either a conventional mandibular denture or implant overdenture of a uniform monoplane occlusal tooth form prosthetic design.35, 36 A total of 78 subjects completed functional evaluations at a 6 month period post prosthesis completion, 69 of which had cephalometric radiographs. Radiographs were not completed for 9 subjects due to scheduling conflicts or non-compliance with study protocol. Thus, radiographs were evaluated for 69 subjects who received post-insertion lateral cephalometric radiographs that were digitized for evaluation. Using a de-identified dataset, the digitized cephalometric radiographs were assessed by 2 dentists trained and calibrated in the use of imaging software (version 10.1; Dolphin Imaging, Chatsworth, Calif ) for evaluation of facial form, skeletal class and alveolar ridge height. Facial form categorization was based on craniofacial measurements from the digitized radiographs according to software guidelines (version 10.1;

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Dolphin Imaging), which used measurement values adjusted for age, gender and ethnic background to reference each subject to determining population group norms (normalized data). Subjects were classified into facial form categories (mesocephalic (M), brachycephalic (B) and dolichocephalic (D); Fig. 1) based on the following 5 cephalometric measures: (1) Frankfort-mandibular angle (FMA), the angle between the Frankfort horizontal and the mandibular plane; (2) lower facial height (LFH), the angle from the anterior nasal spine (ANS) to center of the mandibular ramus (Xi) to protuberance menti (PM); (3) facial axis (FA), the angle between facial axis and basion-nasion line; (4) facial angle (FD), the angle between the facial plane line and the Frankfort horizontal line; and (5) mandibular arc (MA), the angle between mandibular corpus line and condylar axis line. (Fig. 2) In addition, the non-normalized facial form category was determined according to methods described by Chaconas and Gonidis10 without reference to any population norms. While normalized data adjust determining measurement values for variations in gender, age and ethnicity, non-normalized facial form designations were determined based upon measurements obtained and their comparative relation to the mean designated mesocephalic facial profile. Comparison of these 2 different facial form classification methods was statistically evaluated using Fisher’s exact

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April 2011 tions of these methods have been previously reported.29-34,37-39 Comparison of mean scores for PS and SWT performances were evaluated with multivariate analysis of variance (MANOVA) for main effects of treatment (CD/IOD) and facial form (brachycephalic, mesocephalic and dolichocephalic) with a separate analysis for treatment by skeletal class (I, II, and III) (α=.05). MANOVA was used to separately compare the ridge height measurements between the 3 main facial form 2 Facial form cephalometric measures (in red) and basic anatomic landmarks. categories and 3 types of skeletal Angle 1- Frankfort – mandibular angle (FMA); angle 2- Lower facial height (LFH); angle 3- Facial axis (FA); angle 4- Facial angle (FD); angle 5 - Mandibular arc (MA). class. Additional univariate analyses and Ryan-Einot-Gabriel-Welsch Table I. Facial form classification: cephalometric measurements and diag- (REGW) post hoc tests were pernostic parameters, in degrees with landmarks formed following a significant omnibus test result (α=.05). Mesofacial ± 1SD The original study was not deMeasure (Standard Deviation) Dolichofacial Brachyfacial signed to specifically make comparisons of masticatory performance FMA 25 ± 6 > 1 SD < 1 SD between facial form categories. For LFH 47 ± 4 > 1 SD < 1 SD this study, a mean difference of 20 in masticatory performance (PS with FA 90 ± 3 < 1 SD > 1 SD peanuts) between the three facial form categories (normalized data) FD 87± 3 < 1 SD > 1 SD could be detected with a power of MA 26 ± 4 < 1 SD > 1 SD 0.70. For comparisons of the mesocephalic form group (n=34) with the FMA - Frankfort-mandibular angle; LFH - lower facial height; FA - facial axis; brachycephalic form group (n=27) FD - facial angle; MA - mandibular arc. FMA and LFH weighted more heavily compared only, a difference of 10 in masticatory to FD, FA, and MA respectively. performance could be detected with a power of 0.7. test. The specified skeletal landmark alveolar ridge above the symphysis. The values for 3 facial form designations ratio of maxillary to mandibular height RESULTS are shown in Table I and diagrammed was calculated. in Figure 2. Masticatory performance was evalu- Facial Form Characterization Using the same software (version ated with standardized tests of masti10.1; Dolphin Imaging), the skeletal cation for each study subject on the Comparisons of the frequency disClass relationship (I, II, III) based preferred side (PS) of mastication tributions resulting from the 2 methupon the measured facial landmarks with 2 foods. Subjects masticated 3 ods (normalized vs. non-normalized was obtained for all subjects. Maxil- standardized specimens for a speci- for age, gender and ethnicity) of claslary and mandibular alveolar ridge fied number of masticatory strokes sifications of facial form are presentheights were determined using radio- (20-peanuts; 40-carrots). The ratio ed in Table II. The mean age of the 69 graphic landmark boundaries. Maxil- of the volume of fine particles to the subjects was 66.0 ± 6.8 years. More lary ridge height was determined from total volume of food recovered and than 88% of subjects were identified a perpendicular bisection of the pala- expressed as a percent defined mas- as having either brachycephalic or metal plane (ANS-PNS) to the most in- ticatory performance. Similar tests socephalic facial forms. Greater repreferior point on the maxillary anterior of swallowing threshold performance sentation of dolichocephalic form patridge. Mandibular alveolar ridge height (SWT) were made, the subject being terns were found with the normalized was determined by the perpendicular instructed to masticate freely without method (12%) compared to the nonbisection of the mandibular plane (Go- regard to side of mastication, until normalized method (3%). The comGn) with the uppermost point of the ready to swallow. Detailed descrip- parison of the facial form categoriza-

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Table II. Distribution and facial form assignment by normalized and non-normalized referenced evaluation Classification Method

Classification Method

Category

Normalized

Age (Years)

Non-normalized

Age (Years)

Brachyfacial

27

68.5 ± 6.8

30

68.2 ± 6.4

Mesofacial

34

64.7 ± 6.6

37

64.4 ± 6.7

Dolichofacial

8

63.1 ± 6.2

2

62.5 ± 12.0

Total

69

66.0 ± 6.8

69

66.0 ± 6.8

70

Table III. Skeletal class distribution of subjects and age Number of Subjects

Age (Years)

Class I

28

66.3 ± 6.3

Class II

3

72.7 ± 4.2

Class III

38

65.3 ± 7.2

Total

69

66.0 ± 6.8

Category

Conventional Implant-supported

60 50 40 30 20 10 0

Brachycephalic

Mesocephalic

Dolichocephalic

3 Conventional vs. implant-supported denture function (peanut preferred side performance) and facial form in percent.

Table IV. Comparison of preferred side masticatory performance by facial type (normalized data) Brachycephalic (n=27)

Mesocephalic (n=34)

Dolichocephalic (n=8)

Mean

SD

Mean

SD

Mean

SD

F

P

Peanut

40.0

(14.17)

41.15

(14.16)

35.4

(14.41)

2.56

.085

Carrot

73.9

(21.98)

78.89

(19.00)

71.6

(22.60)

1.56

.218

Test Food

tion methods revealed a significant difference (Fisher exact test; P<.001) in the distributions of subjects among facial form categories (Table II). Distribution of the subjects by skeletal class is reported in Table III. The majority of the subjects were Class III (55.0 %), with 40% identified as skeletal Class I. There was only limited representation of skeletal Class II

for this sample (n=3). Masticatory Performance and Swallowing Threshold Comparisons among Facial Forms Preferred side of mastication performance (PS) and swallowing threshold (SWT) performances did not show statistical separation for CD

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and IOD in the 3 facial form categories (normalized and non-normalized determination of facial form). Since there were no differences in performance outcomes between the facial categories defined using the normalized or non-normalized methods, only evaluations based on the normalized facial categories are presented. Preferred side mean masticatory

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Table V. Comparison of swallowing threshold performance by facial type (normalized data) Brachycephalic (n=27)

Dolichocephalic (n=8)

Mesocephalic (n=34)

Mean

SD

Mean

SD

Mean

SD

F

P

Peanut

66.8

(18.93)

58.90

(15.14)

59.1

(18.95)

0.54

.585

Carrot

82.5

(17.64)

74.67

(18.42)

75.4

(15.42)

0.66

.522

Test Food

70

Conventional Implant-supported

60 50 40 30 20 10 0

Class I

Class II

Class III

4 Conventional vs. implant-supported denture function (peanut preferred side performance) and skeletal class as percent.

Table VI. Comparison of preferred side masticatory performance by skeletal class Class 1 (n=28)

Class II (n=3)

Class III (n=38)

Test Food

Mean

SD

Mean

SD

Mean

SD

F

P

Peanut

43.15

(14.58)

36.85

(13.51)

37.98

(13.70)

1.17

.317

Carrot

78.19

(20.59)

63.46

(19.49)

75.57

(20.54)

0.73

.488

performances with both peanuts and carrots were not significantly different (MANOVA P=.967) between CD and IOD, between facial categories, or the interaction between the 2 main factors (Fig. 3, comparison for preferred side peanuts). For the total sample, the dolichocephalic facial form group demonstrated the lowest and the mesocephalic group the highest mean masticatory function for both test foods (Table IV). Similarly, no significant differences (P=.967) were found between CD and IOD for swallowing threshold performance. However, mean perfor-

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mance for both test foods were lowest for the mesocephalic group and highest for the brachycephalic group for the combined sample (Table V). There was no significant difference between the facial categories for either food (peanuts, P=.585; carrots, P=.522). Masticatory Performance and Swallowing Threshold Comparisons among Skeletal Class Although the MANOVA comparison of masticatory performance showed a significant difference (P=.037) between CD and IOD, post–hoc comparisons

did not indicate a difference (REGW, P>.05) for either test food with the standardized performance and swallowing threshold tests. (Fig. 4, comparison for preferred side peanuts). The low mean performance seen in Figure 3 for the CD with Class II is only based on 1 subject in this category. Masticatory performance with both test foods was found to be lowest for Class II subjects and highest for the Class I group (Table VI), although these differences were not statistically significant (peanuts, P=.317; carrots, P=.488). A similar pattern was seen among the 3 skeletal classes for the

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Table VII. Comparison of swallowing threshold performance by skeletal class Class 1 (n=28)

Class II (n=3)

Class III (n=38)

Test Food

Mean

SD

Mean

SD

Mean

SD

F

P

Peanut

63.36

(17.07)

51.99

(14.91)

60.00

(18.13)

0.71

.497

Carrot

*83.82

(12.43)

*61.90

(30.03)

74.68

(19.32)

3.57

.034

*Groups are significantly different (REGW, P<.05), Class I > Class II.

Table VIII. Comparison of alveolar ridge heights (millimeters) by facial type Brachycephalic (n=27)

Mesocephalic (n=34)

Dolichocephalic (n=8)

Mean

SD

Mean

SD

Mean

SD

F

P

Maxillary

*14.4

(2.75)

17.6

(2.96)

19.6

(2.19)

15.01

.001

Mandibular

20.9

(7.21)

21.9

(6.95)

23.58

(3.55)

0.55

.581

Mx/Md ratio

0.76

(0.26)

0.87

(0.16)

0.84

(0.25)

1.54

.223

* Statistically significant (Brachycephalic < Mesocephalic, Dolichocephalic; REGW: P<.05).

Table IX. Comparison of alveolar ridge heights (millimeters) by skeletal class Class I (n=38)

Class II (n=3)

Class III (n=28)

Mean

SD

Mean

SD

Mean

SD

F

P

Maxillary

16.93

(2.95)

20.07

(5.62)

16.09

(3.33)

2.28

.110

Mandibular

21.60

(5.50)

29.10

(7.89)

21.0

(7.28)

2.14

.126

Mx/Md ratio

0.81

(0.25)

0.69

(0.09)

0.84

(0.27)

0.49

.613

swallowing threshold performances. However, there was a significant difference among skeletal classes for the carrot SWT performance (P=.034). (Table VII) The Class I mean SWT performance with carrots of 83.8 was significantly higher (REGW; P<.05) than the 61.9 mean performance for the Class II group. Relationships between Facial Form and Alveolar Ridge Height Significant differences in maxillary alveolar ridge height were found

between the 3 facial form groups (MANOVA F=15.01; P<.001) (Table VIII). Post-hoc analysis demonstrated that all 3 groups differed significantly (REGW; P<.05), with the brachycephalic group having the lowest maxillary ridge height of 14.4 mm, followed by the mesocephalic group at 17.6 mm and the dolichocephalic group at 19.6mm. Mandibular residual ridge heights, despite a similar pattern of low to high ridge height for the 3 groups (brachycephalic less than mesocephalic less than dolichocephalic) did

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not differ significantly (P=.581). No significant differences among the 3 facial groups were seen for the ratio of maxillary to mandibular ridge height (brachyfacial, 0.76 ± 0.26; mesofacial, 0.87 ± 0.16; dolichofacial 0.84 ±0.25) (P=.223). Relationships between Skeletal Class and Alveolar Ridge Height Both maxillary and mandibular residual ridge heights were found to be greater in the skeletal Class II group compared to the Class I and Class

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April 2011 III groups (Table IX). Class I ridge heights were also slightly greater than those for Class III for both the maxilla and mandible. However, none of these differences were significant. The mean ratio of maxillary to mandibular ridge height of 0.69 for the Class II group was considerably lower than those for the Class I (0.81) and the Class III (0.84), but this difference was not significant.

DISCUSSION The null hypothesis that masticatory performance does not differ among facial form categories was not rejected. The functional evaluations of the facial form indicated a slight trend of poorer masticatory function for dolichocephalic subjects compared to mesocephalic and brachycephalic facial form subjects. However, the use of the lateral cephalometric radiograph for functional and anatomic clinical evaluations of subjects treated with conventional or implant prosthodontics remains of significant interest. Prior craniometric assessments of prosthodontic treatments did not use information on age, gender or ethnicity as normative references for facial form assessment. The classification of facial form group distributions by matching of population norms for age, gender, and ethnicity was found to be significantly different from non-normalized classifications, particularly for the dolicofacial form. Normalized values resulted in a larger number of subjects being classified as having the dolichofacial form. The use of references to population norms for facial form categories may be difficult in routine clinical treatment situations or informal examinations. Although significant differences in the distributions of facial form categories were seen in this study, the relationships between facial form and function were similar, whether using the normalized or non-normalized facial form category assessments. Chaconas and Gonidis11 suggested that cephalometric assessment

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may be useful for prosthodontic treatment, and the dolichocephalic forms would be the most difficult facial form to treat. The PS performance shown within the dolichocephalic subject groups was found to be not significantly lower. The small sample of dolichocephalic subjects in the present study may indicate the need for a more extensive study to determine a relationship. Although functional evaluation did not demonstrate distinct statistical difference among facial form groups, anatomic support evaluations of alveolar ridge height demonstrated significantly reduced maxillary alveolar ridge heights for brachycephalic subjects. In contrast to the low maxillary alveolar ridge heights for brachycephalic subjects, slightly higher mean values for alveolar ridge height of the mandible were found, but not statistically confirmed, for dolicocephalic and Class II skeletal class subjects. These alveolar height findings are consistent with reports of mandibular alveolar bone loss and a flat mandibular plane associated with the brachycephalic facial form.9,11,25 The alternative hypothesis that masticatory performance differs among skeletal class categories was partially accepted. Swallowing threshold performance with a fibrous test food (carrots) was significantly reduced in Class II compared to Class I subjects. While a similar trend was seen in swallowing threshold performance with a brittle test food (peanuts) and standardized masticatory performance tests with both test foods, these differences were not statistically significant. The greater range of expected jaw movements required with a fibrous test food may affect masticatory force and jaw excursion with restored skeletal Class II subjects. These functional differences, together with the findings of differences in alveolar ridge height among facial form groups, demonstrate the potential utility of the lateral cephalometric evaluation methods used to determine comparative differences between

differing facial form profiles and their specific patient characteristics. Several factors may be considered as limitations in the design and interpretation of this study. The functional evaluation of subjects by skeletal class would be expected to favor the skeletal class dental relationships to be prosthetically improved by a restored Class I dental relationship of reduced vertical overlap. Lower numbers of Class II and dolichocephalic subjects were found in this sample relative to the other class and facial form groups evaluated. The small sample size for the dolichocephalic group severely limits the statistical comparisons of these facial forms. It was not possible in this study to uniformly determine the original dental relationship in subjects prior to tooth loss and prosthetic treatment. Alveolar resorption toward the corpus of both the mandible and maxilla has been reported to result in a progressive Class III arch relationship.23,25 Although 3 different skeletal class groups were represented within the subject pool, the skeletal class evaluation was performed after the subjects were treated with implant-supported or conventional dentures. Evaluation of this similarly restored subject population using the monoplane occlusal design demonstrates denture prosthodontics of similar vertical and horizontal overlaps, reduces dental differences and focuses evaluations to the relationships of the skeletal form and cranial landmarks of these study subjects The monoplane denture design is a readily reproducible denture occlusion that reduces the permutations of different dental relationships of horizontal overlap, and vertical overlap that ordinarily exist within a larger study population.31,32 The remaining standardizations for occlusion, food type, implant connection and attachment were incorporated into this study. Alveolar ridge height remains a critical parameter for complete denture patient function. The evaluation of the facial form with concomitant

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Volume 105 Issue 4 evaluation of skeletal class relationships may better define patient preand post-treatment functional capacities and classifications in the area of predicted alveolar ridge height, thus permitting improved estimations of functional ability, capacity or change. Previous studies of implant overdenture outcomes with cephalometric documentation related anatomic measurement of mandibular alveolar ridge height for limited correlational comparison to masticatory performance and patient satisfaction reports.14,15,26 The evaluation of facial form and skeletal type is complementary to these prior evaluations and may assist in the development of future studies. Prior investigations of facial form assessment and prosthodontics evaluated prosthodontic treatment with conventional complete dentures.8,9,10 The findings of this study demonstrate that an assessment of a patient’s facial form may anticipate a relative level of alveolar resorption using the diagnosed facial profile and skeletal class. Tallgren25 demonstrated the effect of a flat mandibular plane angle and expected resorption patterns. The differential effect of facial type and alveolar bone height are likely related to alveolar resorption rate and occlusal masticatory functional forces. Further evaluation regarding resorption rate and facial form is recommended. Two contrasts exist within the findings of this study. While masticatory function evaluations indicated the possibility of lower masticatory performance levels for dolichocephalic facial form patients, the brachycephalic facial form groups demonstrated reduced maxillary alveolar bone heights. The placement of osseointegrated dental implants has been suggested to reduce the occurrence of alveolar resorption for an edentulous patient. 21 Recommendations for implant placement for alveolar ridge stability in various facial form treatment situations may be appropriately indicated. These skeletal or occlusal dental support considerations may include rela-

tive positioning, location, number and dimensional size modifications to restorative implant treatment planning. A 4:1 resorptive pattern for an edentulous maxilla compared to the edentulous mandible has been suggested by Tallgren.25 In this study, the ratio of maxillary to mandibular alveolar bone height for the 3 facial and skeletal profiles demonstrated a slightly higher overall relationship compared to the 4:1 (.75) ratio. Although the brachycephalic maxillary ridge heights were significantly lower than mesocephalic and dolichocephalic facial types, these findings did not significantly affect the reported maxillary to mandibular alveolar ridge height ratio findings. The effect of study population size on this ratio is unknown. The resorption ridge height ratio findings for this study do not permit any corroboration with reports of relative alveolar bone resorption rates as reported by Tallgren25 or Hickey et al.23 Evaluations for prognostic inference require large study populations for statistical comparisons and recommendations, and this is a limitation of the current study. Newer methods in radiographic imaging technology may provide greater access and improved craniofacial assessment for pre- and post-treatment evaluations using specifically designed software for these analyses. The use of a limited radiographic study with lateral cephalometric evaluation of prosthetically restored implant- and non implant-supported complete denture occlusions remains of interest. Facial form assessment is a clinically valuable parameter for prosthodontic assessment involving dental implants, alveolar resorption and masticatory function. Further evaluation of these interactions between facial form, skeletal class, prosthodontic treatment and functional outcome is indicated. The further evaluation of these relationships would facilitate estimations of clinical impact or modifications to treatment recommendations. Longer term and larger comparative studies

The Journal of Prosthetic Dentistry

of the relationships of facial form and treatment success are recommended for future evaluation.

CONCLUSIONS Facial form classification and diagnosis may be related to different levels of masticatory function with conventional or implant-assisted mandibular dentures, but larger controlled studies are needed to confirm these relationships. Regardless of the classification method (normalized vs. nonnormalized), mean masticatory performance was slightly less in persons with a dolichocephalic form, compared to persons with mesofacial and brachyfacial forms. In contrast to the functional outcomes, physical measurements of alveolar ridge height of brachycephalic edentulous subjects demonstrated alveolar ridge heights related to the facial form. Maxillary alveolar ridge height was found to be significantly reduced in vertical height for edentulous patients with a diagnosed brachyfacial facial profile as compared to patients with a mesofacial or dolichocephalic facial form. Classification by skeletal class demonstrated higher masticatory function for Class I compared to Class III then Class II patient categories. Ridge height distributions based upon skeletal class suggest higher alveolar ridge heights for subjects exhibiting a skeletal Class II arch relationship.

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