A composition comprising: a) 40 to 89 weight percent of at least one semi-aromatic polyester resin; b) 10 to 50 weight percent of at least one reinforcing agent; c) 0.5 to 5.0 weight percent hydroxyapatite; d) 0.5 to 4.0 weight percent of at least one epoxy component having two or more epoxy functional groups per molecule of the epoxy component; e) optionally, 0.5 to 15 weight percent of at least one toughener, wherein the at least one semi-aromatic polyester resin may be partially replaced by one or more styrenic-based copolymers, which, when present, may range up to 40 weight percent of the combined weight of the at least one semi-aromatic polyester resin plus the styrenic-based copolymers in these compositions, (d) and (e) having a combined epoxy functionality ranging from 40 and 500 milliequivalents per kilogram of the semi-aromatic polyester resin; and wherein: - when measured according to Test, each subsequent melt viscosity of the polyester composition is not greater than 160% of its initial melt viscosity and - when measured according to Test, the tensile strength of exposed test bars comprising the polyester composition is at least 60% of that of unexposed bars comprising the same polyester composition; whereby: Test comprises: - measuring initial melt viscosity of the polyester composition at five minutes after heating the polyester composition at a temperature between 30 and 45°C above the melting point of the semi-aromatic polyester, and - measuring at least one subsequent melt viscosity of the polyester composition during an interval between greater than 5 minutes and 48 minutes while the temperature of the polyester composition is maintained between 30 and 45°C above the melting point of the semi-aromatic polyester, wherein the measuring is done according to ISO 11443 at 1000 sec -1; and Test comprises: - measuring tensile strength of unexposed test bars comprising the polyester composition; - exposing test bars comprising the same polyester composition for a duration of at least 25 hours to steam at 100 percent relative humidity, pressure of 2 atmospheres, and temperature of 121 °C; and - measuring at the end of the duration tensile strength of the exposed test bars, wherein the measuring is done according to ISO527-1 and all test bars have been molded according to ISO527-2/1A. a) 40 to 89 weight percent of at least one semi-aromatic polyester resin; b) 10 to 50 weight percent of at least one reinforcing agent; c) 0.5 to 5.0 weight percent hydroxyapatite; d) 0.5 to 4.0 weight percent of at least one epoxy component having two or more epoxy functional groups per molecule of the epoxy component; e) optionally, 0.5 to 15 weight percent of at least one toughener, - when measured according to Test, each subsequent melt viscosity of the polyester composition is not greater than 160% of its initial melt viscosity and - when measured according to Test, the tensile strength of exposed test bars comprising the polyester composition is at least 60% of that of unexposed bars comprising the same polyester composition; Test comprises: - measuring initial melt viscosity of the polyester composition at five minutes after heating the polyester composition at a temperature between 30 and 45°C above the melting point of the semi-aromatic polyester, and - measuring at least one subsequent melt viscosity of the polyester composition during an interval between greater than 5 minutes and 48 minutes while the temperature of the polyester composition is maintained between 30 and 45°C above the melting point of the semi-aromatic polyester, wherein the measuring is done according to ISO 11443 at 1000 sec -1; and - measuring initial melt viscosity of the polyester composition at five minutes after heating the polyester composition at a temperature between 30 and 45°C above the melting point of the semi-aromatic polyester, and - measuring at least one subsequent melt viscosity of the polyester composition during an interval between greater than 5 minutes and 48 minutes while the temperature of the polyester composition is maintained between 30 and 45°C above the melting point of the semi-aromatic polyester, Test comprises: - measuring tensile strength of unexposed test bars comprising the polyester composition; - exposing test bars comprising the same polyester composition for a duration of at least 25 hours to steam at 100 percent relative humidity, pressure of 2 atmospheres, and temperature of 121 °C; and - measuring at the end of the duration tensile strength of the exposed test bars, wherein the measuring is done according to ISO527-1 and all test bars have been molded according to ISO527-2/1A. - measuring tensile strength of unexposed test bars comprising the polyester composition; - exposing test bars comprising the same polyester composition for a duration of at least 25 hours to steam at 100 percent relative humidity, pressure of 2 atmospheres, and temperature of 121 °C; and - measuring at the end of the duration tensile strength of the exposed test bars, wherein the measuring is done according to ISO527-1 and all test bars have been molded according to ISO527-2/1A.